Search

Introduction: Diabetes mellitus (DM) during pregnancy is associated with an increased risk for poor reproduction and a high rate of congenital malformations. The gerbil Psammomys obesus is a unique model for nutritionally induced Type 2 DM (T2DM) that enabled us to study the outcome of uncontrolled T2DM during pregnancy. Methods: Female Psammomys on low-energy (LE) or high energy (HE) diet were studied. The blood glucose levels and weights of pregnant animals were determined. The offspring from the different groups were followed-up to weaning. Results: Most of the HE-diet animals were diabetic (77%). There were no differences in the pregnancy rates in animals on both diets (32.7% in HE vs. 38.3% in LE). Pregnancy of the HE-diet group was longer than the LE-diet group (26.7 vs. 26.1 days), and litter average was reduced (2.7 vs. 3.0). At birth, the offspring of the HE-diet dams weighed less (5.2 vs. 7.2 g) and had smaller crown rump length (4.0 vs. 4.6 cm) These offspring also presented a 1–3 days delay in neuro-developmental parameters (first turn over, hair appearance, eye-opening and response to noise). However, from the fourth week of life they became diabetic, and from the third week they weighed more than the LE offspring. Conclusion: HE-diet caused diabetes, maternal complications and altered reproduction in Psammomys animals. The offspring of diabetic Psammomys presented birth weight and length changes as well as developmental delay.

G-protein-coupled receptor kinases (GRKs) play a key role in agonist-induced desensitisation of G-protein-coupled receptors (GPCRs) that are involved in metabolic regulation and glucose homeostasis. Our aim was to examine whether small peptides derived from the catalytic domain of GRK2 and -3 would ameliorate Type 2 diabetes in three separate animal models of diabetes.Synthetic peptides derived from a kinase-substrate interaction site in GRK2/3 were initially screened for their effect on in vitro melanogenesis, a GRK-mediated process. The most effective peptides were administered intraperitoneally, utilising a variety of dosing regimens, to Psammomys obesus gerbils, Zucker diabetic fatty (ZDF) rats, or db/db mice. The metabolic effects of these peptides were assessed by measuring fasting and fed blood glucose levels and glucose tolerance.Two peptides, KRX-683(107) and KRX-683(124), significantly reduced fed-state blood glucose levels in the diabetic Psammomys obesus. In animals treated with KRX-683(124) at a dose of 12.5 mg/kg weekly for 7 weeks, ten of eleven treated animals responded with mean blood glucose significantly lower than controls (4.7+/-0.4 vs 16.8+/-0.8 mmol/l, p/=0.0001). Significant reductions in blood glucose compared with controls were also seen in ZDF rats administered KRX-683(124) and in db/db mice, which had significantly reduced fasting and 2-hour postprandial glucose levels after the treatment.Sequence-based peptides derived from GRK2/3 have an antidiabetic effect demonstrated in three different animal models of Type 2 diabetes. By modulating GRK2/3 activity, these peptides enhance GPCR-initiated signal transduction, resulting in improved glucose homeostasis. Sequence-based peptide modulation of GRK could prove useful in the treatment of Type 2 diabetes.

Background Malonyl-CoA, an allosteric inhibitor of carnitine palmitoyl transferase, controls the oxidation of fatty acids in muscle and other tissues by regulating their entrance into mitochondria. The level of malonyl-CoA in muscle is influenced by the uptake of energy substrates such as glucose, the precursor of its synthesis. The desert gerbil, Psammomys obesus, develops a severe insulin resistance with hyperinsulinemia and hyperglycemia when transferred from its native nutrition to a relative high-energy (HE) rodent chow. In keeping with this it shows a low rate of glucose transport and a failure of insulin to suppress hepatic glucose production during a hyperinsulinemic-euglycemic clamp. Methods The concentration of malonyl-CoA has been determined by radio-enzymatic assay together with the levels of citrate and malate in the gastrocnemius muscle of diabetes-prone (DP) and diabetes-resistant (DR) P. obesus during the administration of exogenous insulin, during an hyperinsulinemic-euglycemic clamp and following a 48-h fast. Results Muscle GLUT4 protein was reduced by 44% in DP Psammomys on a HE diet, compared with normoglycemic-normoinsulinemic animals on a low-energy (LE) diet. Muscle levels of malonyl-CoA, its precursor citrate and the citrate counter-ion malate were not elevated in DP Psammomys on the HE diet despite the hyperinsulinemia. Likewise, the administration of external insulin in subcutaneous (sc) implants to DP Psammomys did not evoke hypoglycemia, decrease glucose production or increase the concentration of malonyl-CoA and citrate in muscle, as it did in both albino rats and a selected line of DR Psammomys. In contrast, fasting significantly reduced muscle malonyl-CoA and citrate levels in the DP and DR Psammomys and promoted the fat oxidative pathway. Conclusion Since non-diabetic Psammomys on a LE diet already show insulin resistance in the fed state, the sustained low malonyl-CoA levels in these animals imply a readiness for the oxidation of fatty acids. In a desert gerbil, adjusted to a food-scarce environment, such a continuing utilization of fatty acids as energy substrate by muscle would preserve the available glucose for glucose-dependent tissues and would diminish the need for gluconeogenesis. Copyright © 2002 John Wiley & Sons, Ltd.

The rats listed here have been extensively studied as animal models of diabetic complications and their pathogenesis. The results of studies with the SHROB, JCR:LAcp and OLETF rats are instructive in understanding macro vascular diseases. The Cohen, GK, SHROB and OLETF rats are model of diabetic kidney disease. The SHROB rat might also be useful for diabetic retinopathy study. The importance of mitochondrial inactivity in diabetes was demonstrated with the ZDF rat. The heterogeneous complication models may be useful to understand pathogenesis, prevention and treatment of complications of diabetes mellitus.

The sand rat (Psammomys obesus) is an animal model of nutritionally induced diabetes. We report here that several protein kinase C (PKC) isoforms (alpha, epsilon, and zeta, representing all three subclasses of PKC) are overexpressed in the skeletal muscle of diabetic animals of this species. This is most prominent for the epsilon isotype of PKC. Interestingly, increased expression of PKCepsilon could already be detected in normoinsulinemic, normoglycemic (prediabetic) animals of the diabetes-prone (DP) line when compared with a diabetes-resistant (DR) line. In addition, plasma membrane (PM)-associated fractions of PKCalpha and PKCepsilon were significantly increased in skeletal muscle of diabetic animals, suggesting chronic activation of these PKC isotypes in the diabetic state. The increased PM association of these PKC isotypes revealed a significant correlation with the diacylglycerol content in the muscle samples. Altered expression/activity of PKCepsilon, in particular, may thus contribute to the development of diabetes in these animals; along with other PKC isotypes, it may be involved in the progression of the disease. This may possibly occur through inhibition of insulin receptor (IR) tyrosine kinase activity mediated by serine/threonine phosphorylation of the IR or insulin receptor substrate 1 (IRS-1). However, overexpression of PKCepsilon also mediated down-regulation of IR numbers in a cell culture model (HEK293), resulting in attenuation of insulin downstream signaling (reduced protein kinase B [PKB]/Akt activity). In accordance with this, we detected decreased 125I-labeled insulin binding, probably reflecting a downregulation of IR numbers, in skeletal muscle of Psammomys animals from the DP line. The number of IRs was inversely correlated to both the expression and PM-associated levels of PKCepsilon. These data suggest that overexpression of PKCepsilon may be causally related to the development of insulin resistance in these animals, possibly by increasing the degradation of IRs.

Albert Renold strived to gain insight into the abnormalities of human diabetes by defining the pathophysiology of the disease peculiar to a given animal. He investigated the Israeli desert-derived spiny mice (Acomys cahirinus), which became obese on fat-rich seed diet. After a few months hyperplasia and hypertrophy ofβ-cells occurred leading to a sudden rupture, insulin loss and ketosis. Spiny mice were low insulin responders, which is probably a characteristic of certain desert animals, protecting against insulin oversecretion when placed on an abundant diet. We have compared the response to overstimulation of several mutant diabetic species and nutritionally induced nonmutant animals when placed on affluent diet. Some endowed with resilientβ-cells sustain long-lasting oversecretion, compensating for the insulin resistance, without lapsing into overt diabetes. Some with labile beta cells exhibit apoptosis and lose their capacity of coping with insulin resistance after a relatively short period. The wide spectrum of response to insulin resistance among different diabetes prone species seems to represent the varying response of human beta cells among the populations. In search for the molecular background of insulin resistance resulting from overnutrition we have studied the Israeli desert gerbil Psammomys obesus (sand rat), which progresses through hyperinsulinemia, followed by hyperglycemia and irreversible beta cell loss. Insulin resistance was found to be the outcome of reduced activation of muscle insulin receptor tyrosine kinase by insulin, in association with diminished GLUT4 protein and DNA content and overexpression of PKC isoenzymes, notably of PKCε. This overexpression and translocation to the membrane was discernible even prior to hyperinsulinemia and may reflect the propensity to diabetes in nondiabetic species and represent a marker for preventive action. By promoting the phosphorylation of serine/threonine residues on certain proteins of the insulin signaling pathway, PKCεexerts a negative feedback on insulin action. PKCεwas also found to attenuate the activity of PKB and to promote the degradation of insulin receptor, as determined by co-incubation in HEK 293 cells. PKCεoverexpression was related to the rise in muscle diacylglycerol and lipid content, which are prevalent on lascivious nutrition especially if fat-rich. Thus, Psammomys illustrates the probable antecedents of the development of worldwide diabetes epidemic in human populations emerging from food scarcity to nutritional affluence, inappriopriate to their metabolic capacity.

Previous studies The investigation of diabetes propensity in spiny mice, performed in Geneva and Jerusalem colonies, is reviewed. Spiny mice live in semi-desert regions of the eastern Mediterranean countries. Those transferred to Geneva in the 1950s were maintained on a rodent diet supplemented by fat-rich seeds. They became obese, exhibited pancreatic islet hyperplasia and hypertrophy. Low insulin secretion response was characteristic of this species, despite ample pancreatic content of insulin. After a few months, diabetes with ketosis occurred, often suddenly, in association with islet cell disintegration. In Jerusalem the spiny mice were collected from their native habitat and placed on diets containing 50% sucrose or fat-rich seed diets. On a sucrose-rich diet, spiny mice developed hepatomegaly, lipogenic enzyme hyperactivity, and elevation in very low density lipoproteins as a result of metabolism of the fructose component mainly in the liver. No overt diabetes or pancreatic islet disintegration were observed, although insulin content and β-cell hypertrophy and hyperplasia were apparent. On a fat-rich diet, spiny mice exhibited marked weight gain, adipose tissue growth and low hepatic lipogenesis. The obesity was accompanied by mild hyperglycemia and hyperinsulinemia with glucose intolerance leading to an occasional glucosuria after several months on the diet. Novel experiments The sucrose diet induced an extrathyroidal elevation of triiodothyronine (T3). Serum T3 level and hepatic T4–T3 conversion were increased, while serum T4 levels tended to decrease. The activity of the T3-inducible hepatic mitochondrial FAD-glycerophosphate oxidase and K+/Na+-ATPase, as well as body temperature were increased, indicating that the sucrose diet was associated with enhanced thermogenesis and energy-wasting metabolic cycling. The sucrose-rich diet might exert an adaptive thermogenesis-mediated defense mechanism, protecting against excessive weight gain and disruptive pancreatic islet lesion. After 18 months maintenance on sucrose-rich versus fat-rich diets the number of animals surviving was significantly higher on the sucrose diet whereas on the fat diet a significant number of animals succumbed to expansive islet cell disruption and diabetes. Copyright © 2000 John Wiley & Sons, Ltd.

TO THE EDITOR: over the years, we have had the opportunity to edit books and compendia that characterize diverse animal models of obesity and diabetes. Most of those animal models have been either selected through inbreeding or characterized following spontaneously arising mutations. It is now timely to provide, in a summary manner, a concise list of such models as an update and reference for future research. The major defects are described in the references cited. In some cases, insulin resistance has been linked to impaired insulin signaling at various levels, including negative feedback at the level of the insulin receptor substrate (IRS)-1 (5, 15, 24). However, in most cases the mechanism of the diabetogenic changes has not been exhaustively investigated. We hope that this list will guide studies geared at elucidating specific defects in the signal flow and how these studies may explain the metabolic failures leading to the diabetic proneness of the models as well as the mechanism of the ensuing complications. These animal models should also enable the discovery of therapeutic modalities with relevance to human diabetes and should continue to be a useful tool along with specific target-generated transgenic and knockout animals so amply used to understand metabolism and energy balance. Obesity and diabetes in mice with mutations in leptin or leptin receptor genes. Since the discovery that ob is a mutation in the leptin structural gene and db is a mutation in the leptin receptor gene, the nomenclature for these mutations has been changed to reflect their molecular basis. The Lep ob mutation on chromosome 6 was discovered in the Jackson Laboratory, Bar Harbor, ME, and recognized by marked obesity and hyperphagia. This mutation was subsequently transferred to the B6 inbred strain background. On this genetic background, the mutation produces juvenile-onset obesity, hyperinsulinemia, and insulin resistance with mild hyperglycemia and a sustained hyperplasia of the pancreatic -cells. The Lepr db mutation is a recessive mutation on chromosome 4 that occurred spontaneously in the C57BLKS/J inbred strain. The obesity/diabetes syndrome is associated with progressively severe hyperglycemia and correlated with pancreatic cell necrosis and islet atrophy at the end stage. The ob mutation is predominantly obese and exhibits only mild hyperglycemia. The current genetic nomenclature for these mice is as follows: Lep obJ , common name “obese” gene product; leptin or leptin mRNA and Lepr db-IJ , common name “diabetic” gene product leptin receptor or leptin receptor mRNA. Detailed information on these strains can be found in Chua et al. (2). Zucker diabetic fatty rat with a leptin receptor defect. The Zucker diabetic fatty (ZDF) rat exhibits leptin receptor defects. This type of obesity, although associated with insulin resistance, is unlike common forms of human obesity. The ZDF rat was developed into a reproducible type 2 diabetic model at Indiana University (16) from a Zucker rat colony (lepr fa )i n which certain individuals exhibited a propensity to diabetes. The male rat is characterized by hyperinsulinemia and hyperglycemia at 6‐7 wk of age, with glucose reaching levels of 500 mg/dl and insulin levels dropping successively. The female rat requires a high-fat diet for the expression of diabetes. The ZDF rat carries a genetic defect in -cell transcription that is independent of the leptin receptor mutation, causing obesity and insulin resistance likely to be inherited in the -cell gene. Goto-Kakizaki rat with impaired -cell mass and function due to polygenic inheritance. The Goto-Kakizaki rat is a nonobese substrain of Wistar rat origin with inherited chronic hyperglycemia. It was selected through a group of eight generation-inbreeding Wistar rats displaying high glucose levels during a glucose tolerance test. They present “starfish-shaped” islet abnormalities and pancreatic hormone deficiencies, resembling the polygenic basis of human type 2 diabetes (14). New Zealand obese mouse. This is a model of obesity, glucose intolerance, and metabolic syndrome of polygenic nature. This animal exhibits hepatic and peripheral leptin insensitivity, insulin resistance, impaired insulin secretion, hypercholesteremia, and hypertension (6). It displays classic features of obesity, including excessive body weight hyperphagia and reduced energy expenditure. Such obesity is responsible for its impaired glucose metabolism. JCR:LA-cp rat: exhibiting metabolic syndrome with microand macrovascular disease. The prediabetic state in the JCR: LA-cp rat is characterized by abdominal obesity, hypertriglyceridemia and insulin resistance, and a marked damage to the vascular system, which is associated with atherosclerosis, vasculopathy, and ischemic end-stage disease (19). It is a unique model of the obesity/insulin resistance syndrome with cardiovascular implications of polygenic derivation. SHROB rat: a model of metabolic syndrome. The spontaneously obese SHROB (Koletzky) rat is an overtly nondiabetic rat with the primary and secondary characteristics associated with the human metabolic syndrome, including insulin resistance. It exhibits a single recessive trait, a nonsense mutation causing loss of hypothalamic leptin receptors designated as fa k (12), and its insulin-signaling defects were initially reported by

Animals with genetically or nutritionally induced insulin resistance and Type 2 diabetes comprise two groups: those with resilient beta-cells, e.g., ob/ob mice or fa/fa rats, capable of longstanding compensatory insulin hypersecretion and those with labile beta-cells in which the secretion pressure leads to beta-cell degranulation and apoptosis, e.g., db/db mice and Psammomys gerbils (sand rats). Psammomys features low insulin receptor density; on a relatively high energy diet it becomes hyperinsulinemic and hyperglycemic. In hyperinsulinemic clamp the hepatic glucose production is only partially suppressed by insulin, even in the normoglycemic state. The capacity of insulin to activate muscle and liver receptor tyrosine kinase is nearly abolished. GLUT4 content and mRNA are markedly reduced. Hyperinsulinemia was also demonstrated to inhibit insulin signaling and glucose transport in several other species. Among the factors affecting the insulin signaling pathway, phosphorylation of serine/threonine appears to be the prominent cause of receptor malfunction as inferred from the finding of overexpression of PKC epsilon isoforms in the muscle and liver of Psammomys. The insulin resistance syndrome progressing in animals with labile beta-cells to overt diabetes and beta-cell failure is a "thrifty gene" characteristic. This is probably also true for human populations emerging from food scarcity into nutritional affluence, inappropriate for their metabolic capacity. Thus, the nutritionally induced hyperinsulinemia, associated with PKC epsilon activation may be looked upon from the molecular point of view as "PKC epsilon overexpression syndrome."

In liver, insulin and glucose acutely increase the concentration of malonyl-CoA by dephosphorylating and activating acetyl-CoA carboxylase (ACC). In contrast, in incubated rat skeletal muscle, they appear to act by increasing the cytosolic concentration of citrate, an allosteric activator of ACC, as reflected by increases in the whole cell concentrations of citrate and malate [Saha, A. K., D. Vavvas, T. G. Kurowski, A. Apazidis, L. A. Witters, E. Shafrir, and N. B. Ruderman. Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E641–E648, 1997]. We report here that sustained increases in plasma insulin and glucose may also increase the concentration of malonyl-CoA in rat skeletal muscle in vivo by this mechanism. Thus 70 and 125% increases in malonyl-CoA induced in skeletal muscle by infusions of glucose for 1 and 4 days, respectively, and a twofold increase in its concentration during a 90-min euglycemic-hyperinsulinemic clamp were all associated with significant increases in the sum of whole cell concentrations of citrate and/or malate. Similar correlations were observed in muscle of the hyperinsulinemic fa/fa rat, in denervated muscle, and in muscle of rats infused with insulin for 5 h. In muscle of 48-h-starved rats 3 and 24 h after refeeding, increases in malonyl-CoA were not accompanied by consistent increases in the concentrations of malate or citrate. However, they were associated with a decrease in the whole cell concentration of long-chain fatty acyl-CoA (LCFA-CoA), an allosteric inhibitor of ACC. The results suggest that increases in the concentration of malonyl-CoA, caused in rat muscle in vivo by sustained increases in plasma insulin and glucose or denervation, may be due to increases in the cytosolic concentration of citrate. In contrast, during refeeding after starvation, the increase in malonyl-CoA in muscle is probably due to another mechanism.

We investigated the possible relationship between islet amyloid polypeptide (IAPP) and the hyperinsulinemia and/or hyperglycemia that is seen in the desert-adapted gerbil Psammomys obesus, when the animal is transferred from a low-energy (LE) diet to a high-energy (HE) diet. The effects of vanadyl sulfate and transition from a HE to a LE diet on the diabetic state of the Psammomys were also studied. Psammomys maintained on a LE diet, showing normoinsulinemia and normoglycemia (group A), were used as controls. IAPP and insulin immunoreactivity in the islets of Langerhans was studied using the peroxidase-antiperoxidase technique and plasma levels of the two hormones were determined by radioimmunoassays. The islet immunoreactivity of both IAPP and insulin was significantly weaker in the hyperinsulinemic and hyperglycemic Psammomys (group C) compared to group A. Transfer to a LE diet resulted in complete recovery of the IAPP- and insulin-staining pattern to that seen in group A [group A--Rec (nutrition)]. The plasma IAPP levels of the group C animals were not significantly higher than in group A, while after vanadyl sulfate treatment the IAPP levels and IAPP/insulin ratios remained significantly higher [group A--Rec (vanadyl)]. At the same time the circulating levels of glucose and insulin were restored to normal. Conclusively, islet IAPP and insulin immunoreactivity disappeared and reappeared in parallel in Psammomys transferred to a HE diet and back to a LE diet. Furthermore, vanadyl sulfate treatment of the hyperinsulinemic and hyperglycemic animals normalized circulating glucose and insulin levels, but not IAPP levels, possibly due to a negative feedback effect of IAPP on insulin release.

METABOLISM AND HYPERTENSION Insulin Resistance Syndrome and Glycogen Synthesis, Roles of Muscle, Liver and Adipose Tissue, Hagit Eldar-Finkelman and Merav Yarkoni Hypertension and Insulin Resistance in the SJHR-Koletsky Rats, Jianhua Shao and Jacob Friedman Role of PTPase in Insulin Action and Insuln Resistance Recent Insights from Cellular and Animal Studies, Barry Goldstein Hypertension and Insulin Resistance in the Wistar Fatty Rat, M. Suzuki, H. Odaka and Y. Sugiyama Cardiovascular Disease in Insulin-Resistant, Atherosclerosis-Prone JCR:LA-cp Rat, J.C. Russell and S.E. Kelly The C57/BL6J Mouse as a Model of Insulin Resistance and Hypertension, Tonya Martin-Dixon, Sheila Collins and Richard Surwitt MOLECULAR AND GENETIC Molecular Features of Insulin Resistance, Obesity and Diabetes in Non-Human Primates, S.V. Angeloni and B.C. Hansen Altering Gene Expression to Study Insulin Sensitivity, Maureen J. Charron, et al. Access to Genes Involved in the Etiology of Insulin Resistance, G.R. Collier, et al. Insulin Signaling Pathway and GLUT4-Mediated Glucose Transport in Insulin Resistance Muscle, Amira Klip, et al. Leptin and Insulin Resistance, Kevin Stark Fat Feeding and Muscle Fat Disposition Eliciting Insulin Resistance, E.W. Kraegen, et al. D-chiro-inositol and Insulin Resistance: An Allosteric Point of View, Joseph Larner GPL-1 Exendin and Insulin Sensitivity, Andrew Young Insulin Resistance and the Autonomic Nervous System, L. Penicaud, et al. Hypothalmic Role in the Insulin Resistance Syndrome, Anthony Cincotta Insulin Resistance - Emerging Therapies for Affected Sites, Julie Moyers and Jose Caro AGING Effect of Age on the Emergence of Insulin Resistance, Nir Barzilai and Ilan Gabriely Postnatal and Adulthood Effects on the Metabolism and Sensitivity of Progeny of Perinatally Compromised Mothers, C.N. Hales, et al.

The desert gerbil Psammomys obesus (“sand rat”), a model of nutritionally induced insulin resistance and non-insulin-dependent diabetes mellitus, was treated after weaning with exogenous insulin implants in the normoglycaemic, normoinsulinaemic state. Albino rats matched for weight and age served as high energy diet adjusted reference animals. Insulin administration, elevating the serum insulin to 6000 pmol/l resulted in only a mild reduction in blood glucose levels in Psammomys, but caused a severe, often fatal hypoglycaemia in the albino rats. The hepatic response to insulin-induced hypoglycaemia in rats involved a significant loss in glycogen and suppression of phosphoenolpyruvate carboxykinase (PEPCK) activity. In Psammomys under similar hyperinsulinaemia no appreciable changes in liver glycogen and PEPCK activity were evident, indicating that blood glucose was replenished by continuing gluconeogenesis. Euglycaemic, hyperinsulinaemic clamp caused a complete shut-down of hepatic glucose production in albino rats. However, in both diabetes-prone and diabetes-resistant Psammomys lines, mean hepatic glucose production was reduced by only 62 to 53 % respectively, despite longer lasting and higher levels of hyperinsulinaemia. These results indicate that Psammomys is characterized by muscle and liver insulin resistance prior to diet-induced hyperglycaemia and hyperinsulinaemia. This is assumed to be a species feature of Psammomys, exemplifying a metabolic adjustment to survival in conditions of food scarcity of both animal and human populations. It may reflect a propensity to insulin resistance and hyperglycaemia in population groups exposed to affluent nutrition. [Diabetologia (1996) 39: 1269–1275]

Publisher Summary The focus of this chapter is to illustrate the use of a rodent other than the mouse or rat to serve as a model of an important human disease. This chapter provides limited information on basic species biology and husbandry, and instead concentrates on the research uses of sand rats. Psammomys, or the sand rat, is a rodent belonging to the subfamily Gerbillinae. Diabetes in sand rats ranges from mild hyperglycemia with hyperinsulinemia to hypoinsulinemia with ketoacidosis, which is a terminal stage with short survival. Psammomys are mainly important because it is found to be an intermediate host of the parasite Leishmania tropica, which is transmitted to humans by the sand fly. Psammomys attained additional interest when it was found to be an intermediate host of the parasite Leishmania tropica, which displays a range of phenotypic characteristics, as might be expected for noninbred progeny, when given free access to standard laboratory diet labeled as high-energy (HE) diet (Digestible energy—2.93 kcal/g).

The insulin receptor was evaluated at different disease stages in the sand rat (Psammomys obesus), a model for nutrition-induced diabetes. Nondiabetic sand rats showed markedly low receptor number in liver compared with albino rats. Their receptor had an intact tyrosine kinase activity but a higher Km for ATP in the phosphorylation reaction of exogenous substrates. The initial effects of overeating (i.e., development of hyperinsulinemia without hyperglycemia) were associated in the sand rat with a dramatic decrease in in vitro and in vivo insulin-induced receptor tyrosine kinase activity in both liver and muscle. In muscle, this coincided with a decrease in receptor number and an increase in basal tyrosine kinase activity. Similar changes were observed upon development of hyperinsulinemia with hyperglycemia. Upon recovery from the diabetic state by diet restriction, the impaired receptor kinase activation was corrected. Complete restoration occurred only in animals that fully recovered from the diabetic state and became normoinsulinemic. These observations indicate that loss and gain of receptor tyrosine kinase activity were dependent on insulin levels. Thus, overeating may lead to the development of hyperinsulinemia through ineffective extraction of excess insulin by the scarce liver receptors. Hyperinsulinemia, in turn, causes a reversible reduction in receptor kinase activity, leading to insulin resistance. This sequence of events may be relevant to diet-related changes in human non-insulin-dependent diabetes mellitus.

In most publications, animal models of diabetes have mainly been investigated for their multiple etiologies as well as for changes leading to diabetes and their genetic derivation. Aspects which seem important and need a special research endeavor are the mechanism of the causes of diabetes and the lapse into complications in different species, their molecular basis and possible arrest and prevention. A concise list and and short discussion of the intensively studied rodents is presented of spontaneous or nutritional background causing Type 2 diabetes but omitting diabetes evoked by transgenic manipulations or gene knockout techniques.

The existence of the enzyme glucose-6-phosphatase (G6Pase) in early and term human placenta was investigated by comparing the characteristics of placental microsomal glucose 6-phosphate (G6P) hydrolytic activity and liver G6Pase. Placental microsomes exhibited similar apparent Km values for G6 P and β-glycerophosphate in intact and deoxycholate-treated microsomes, heat stability at acidic pH, low latency of mannose 6-phosphate hydrolysis, very low activity of pyrophosphate:glucose phosphotransferase, and undetectable [U-14C]G6 P transport into the placental microsomes, all of which indicated that specific G6Pase activity does not exist in placenta. Immunological evidence of the absence of both 36.5 kDa and T2 proteins, which represent the G6Pase catalytic protein and the phosphate / pyrophosphate transporter protein, respectively, confirmed that early and term human placenta are devoid of the multicomponent G6Pase enzyme.

Objective Psammomys obesus gerbil exhibits PKCe over-expression on high-energy (HE) diet. Muscle insulin receptor (IR) signalling and tyrosine kinase activity are inhibited eliciting insulin resistance. We aimed at preventing diabetes by inhibiting PKCe-induced serine phosphorylation of IRS-1 with novel PKCe abrogating peptides. Research design PKCe abrogating peptides were copied from catalytic domain of PKC molecule (PCT patent IL2006/000755). Psammomys fed a diabetogenic HE diet received i.p. peptides KCe-12 and KCe-16 (18 mg/kg) on days 0, 7 and 14 controls received peptide solvent. Results Food consumption and animal weight remained unchanged. On day 16, non-fasting blood glucose levels returned to normal (90 ± 5 versus 347 ± 16 mg/dL in untreated controls). Hyperinsulinemia fell from 584 ± 55 to 180 ± 22 mU/L. Western blot analysis showed that the increased phosphoserine636, 639 content on IRS-1 in gastrocnemius muscle of diabetic animals was reduced three fold, the PKB/AKT activity increased two fold and muscle GLUT4 tended to increase, compared with controls. Likewise, administration of KCe-12 prior to placing the HE diet prevented the onset of diabetes. KCe-12 treatment did not reduce muscle PKCe level. Damage and loss of insulin in pancreatic beta cells on HE diet were prevented by KCe-12, as shown in micrographs of islet hematoxylin-eosin staining and insulin immunostaining. The preserved secretory function enabled Psammomys to normalize glucose homeostasis. Conclusions KCe-16 and KCe-12 peptides derived from PKCe substrate-binding region prevented the nutritional diabetes and protected muscle IRS-1 from PKCe-induced serine phosphorylation, abrogating the insulin-signalling impediment in the Psammomys model of type 2 diabetes. Anti-diabetic peptides may lead to novel modalities preventing human overnutrition-induced insulin resistance and diabetes. Copyright © 2008 John Wiley & Sons, Ltd.

Summary Since glycogen accumulates in the placenta in diabetes and does not appear to be susceptible, in general, to the effect of fasting, the capacity of catecholamines to elicit glycogenolysis was investigated in non-diabetic and diabetic rats. Injection of epinephrine or isoproterenol caused a decrease in placental glycogen within 20 min in non-diabetic, 20 day pregnant rats, in association with the rise in serum glucose and lactate. Incubation with isoproterenol induced glycogenolysis in placental slices from non-diabetic and diabetic rats, nearly commensurate with lactate production. This effect of isoproterenol was concentration dependent and of similar magnitude in non-diabetic and diabetic rat placentas. Glucagon was ineffective in inducing placental glycogenolysis in vivo or in vitro. Protracted stimulation of the catecholamine receptor by the administration of cholera toxin effected a pronounced decrease in placental glycogen, percentagewise higher in diabetic than non-diabetic rats. These results show that placental glycogen is amenable to mobilization by hormonal stimuli effecting phosphorylase activation.

Rat Models of Type 1 Diabetes, Genetics Environment, and Autoimmunity, J.P. Mordes, P. Poussier, A.A. Rossini, E.P. Blankenhorn, and D.L. Greiner The NOD Mouse and its Related Strains, H. Taniguchi, S. Makino, and H. Ikegami Obesity/Diabetes in Mice with Mutations in Leptin or Leptin Receptor Genes, S. Chua, Jr., L. Herberg, and E.H. Leiter The Zucker Diabetic Fatty (ZDF) Rat-Lessons from a Leptin Receptor Defect Diabetic Model, R.G. Peterson The Goto-Kakizaki Rat, C.-G. Ostenson The New Zealand Obese Mouse: Polygenic Model of Obesity, Glucose Intolerance, and the Metabolic Syndrome, B.C. Fam and S. Andrikopoulos The JCR:LA-cp Rat: Animal Model of the Metabolic Syndrome Exhibiting Micro- and Macrovascular Disease, J.C. Russell, S.E. Kelly, and S.D. Proctor The SHROB (Koletsky) Rat as a Model for Metabolic Syndrome, R.J. Koletsky, R.A. Velliquette, and P. Ernsberger OLETF Rats: Model for the Metabolic Syndrome and Diabetic Nephropathy in Humans, K. Kawano Neonatally Streptozotocin-Induced (n-STZ) Diabetic Rats: A Family of Type 2 Diabetes Models, B. Portha, J. Movassat, C. Cuzin-Tourrel, D. Bailbe, M. H. Giroix, P. Serradas, M. Dolz, and M. Kergoat The Rhesus Monkey (Macaca mulatta) Manifests all Features of Human Type 2 Diabetes, B.C. Hansen and X.T. Tigno Pigs in Diabetes Research, with Special Focus on Type 2 Diabetes Research, M.O. Larsen and B. Rolin Psammomys Obesus: Nutritionally Induced Insulin Resistance, Diabetes, and Beta Cell Loss, E. Ziv, R. Kalman, and E. Shafrir The Spontaneously Diabetic Torii (SDT) Rat with Retinopathy Lesions Resembling Those of Humans, M. Shinohara, T. Masuyama, and A. Kakehashi Cohen Diabetic Rat, S. Weksler-Zangen, E. Orlanski, and D.H. Zangen KK and KKA y Mice: Models of Type 2 Diabetes with Obesity, S. Taketomi Animal Models to Study Obesity and Type 2 Diabetes Induced by Diet, T. Coskun, Y. Chen, D. Sindelar, and M. Heiman Index

The dietary effects of hyperglycemia increasingly result in type 2 diabetes in humans. Two species, the spiny mice (Acomys cahirinus) and the desert gerbil (Psammomys obesus), which have different metabolic responses to such effects, are discussed. Spiny mice exemplify a pathway that leads to diabetes without marked insulin resistance due to low supply of insulin on abundant nutrition, possibly characteristic of a desert animal. They respond with obesity and glucose intolerance, beta-cell hyperplasia, and hypertrophy on a standard rodent diet supplemented with fat-rich seeds. The accompanying hyperglycemia and hyperinsulinemia are mild and intermittent but after a few months, the enlarged pancreatic islets suddenly collapse, resulting in loss of insulin and ketosis. Glucose and other secretagogues produce only limited insulin release in vivo and in vitro, pointing to the inherent disability of the beta-cells to respond with proper insulin secretion despite their ample insulin content. On a 50% sucrose diet there is marked lipogenesis with hyperlipidemia without obesity or diabetes, although beta-cell hypertrophy is evident. P.obesus is characterized by muscle insulin resistance and the inability of insulin to activate the insulin signaling on a high-energy (HE) diet. Insulin resistance imposes a vicious cycle of Hyperglycemia and compensatory hyperinsulinemia, leading to beta-cell failure and increased secretion of proinsulin. Ultrastructural studies reveal gradual disappearance of beta-cell glucokinase, GLUT 2 transporter, and insulin, followed by apoptosis of beta-cells. Studies using the non-insulin-resistant HE diet-fed animals maintained as a control group are discussed. The insulin resistance that is evident to date in the normoglycemic state on a low-energy diet indicates sparing of glucose fuel in muscles of a desert-adapted animal for the benefit of glucose obligatory tissues. Also discussed are the effect of Psammomys age on the disabetogenicity of the HE diet; the impaired function of several components of the insulin signal transduction pathway in muscles, which reduces the availability of GLUT4 transporter; the testing of several antidiabetic modalities for the prevention of nutritional diabetes in Psammomys; and various complications related to the diabetic condition.

Background Psammomys obesus is a desert gerbil developing hyperglycaemia, hyperinsulinaemia and insulin resistance when placed for 2 weeks on a high-energy (HE) diet. The mechanism underlying the antidiabetic effect of rosiglitazone (RG) treatment (20 mg/kg per day for 2 weeks) was studied. Methods The antidiabetogenic effect of RG treatment on serum insulin and metabolic parameters in serum and target tissues of insulin action was investigated in vivo and compared with the pancreatic beta cell protective effects of RG. Results Almost all RG-treated animals remained normoglycaemic compared to controls, but, at the same time, they were hyperinsulinaemic. RG had no effect on serum free fatty acid and serum and muscle triglyceride concentrations and did not appreciably affect body weight and fat depots. RG prevented a HE diet-induced reduction of GLUT 4 glucose transporter content in epididymal adipose tissue, but not in gastrocnemius muscle. The normoglycaemic effect was not associated with a suppression of liver PEPCK activity. Muscle PKCe expression, known to be elevated in diabetic Psammomys and to inhibit insulin signalling, was only marginally decreased. However, RG treatment prevented the marked decrease in insulin immunostaining as well as the vacuolization of the beta cells and accelerated beta cell proliferation. Conclusions These data indicate that the skeletal muscle is not the primary target of RG action, whereas the preservation of the insulin secretory capacity and the prevention of degenerative beta cell vacuolization in spite of persisting insulin resistance appear to be the basis for the anti-hyperglycaemic effect of RG in Psammomys. Copyright © 2005 John Wiley & Sons, Ltd.

Diabetes mellitus (DM) during pregnancy is associated with an increased risk for poor reproduction and a high rate of congenital malformations. The gerbil Psammomys obesus is a unique model for nutritionally induced Type 2 DM (T2DM) that enabled us to study the outcome of uncontrolled T2DM during pregnancy.Female Psammomys on low-energy (LE) or high energy (HE) diet were studied. The blood glucose levels and weights of pregnant animals were determined. The offspring from the different groups were followed-up to weaning.Most of the HE-diet animals were diabetic (77%). There were no differences in the pregnancy rates in animals on both diets (32.7% in HE vs. 38.3% in LE). Pregnancy of the HE-diet group was longer than the LE-diet group (26.7 vs. 26.1 days), and litter average was reduced (2.7 vs. 3.0). At birth, the offspring of the HE-diet dams weighed less (5.2 vs. 7.2 g) and had smaller crown rump length (4.0 vs. 4.6 cm) These offspring also presented a 1-3 days delay in neuro-developmental parameters (first turn over, hair appearance, eye-opening and response to noise). However, from the fourth week of life they became diabetic, and from the third week they weighed more than the LE offspring.HE-diet caused diabetes, maternal complications and altered reproduction in Psammomys animals. The offspring of diabetic Psammomys presented birth weight and length changes as well as developmental delay.

We present multiple findings on derangements in lipid metabolism in type 2 diabetes. The increase in the intracellular deposition of triglycerides (TG) in muscles, liver and pancreas in subjects prone to diabetes is well documented and demonstrated to attenuate glucose metabolism by interfering with insulin signaling and insulin secretion. The obesity often associated with type 2 diabetes is mainly central, resulting in the overload of abdominal adipocytes with TG and reducing fat depot capacity to protect other tissues from utilizing a large proportion of dietary fat. In contrast to subcutaneous adipocytes, the central adipocytes exhibit a high rate of basal lipolysis and are highly sensitive to fat mobilizing hormones, but respond poorly to lipolysis restraining insulin. The enlarged visceral adipocytes are flooding the portal circulation with free fatty acids (FFA) at metabolically inappropriate time, when FFA should be oxidized, thus exposing nonadipose tissues to fat excess. This leads to ectopic TG accumulation in muscles, liver and pancreatic beta-cells, resulting in insulin resistance and beta-cell dysfunction. This situation, based on a large number of observations in humans and experimental animals, confirms that peripheral adipose tissue is closely regulated, performing a vital role of buffering fluxes of FFA in the circulation. The central adipose tissues tend to upset this balance by releasing large amounts of FFA. To reduce the excessive fat outflow from the abdominal depots and prevent the ectopic fat deposition it is important to decrease the volume of central fat stores or increase the peripheral fat stores. One possibility is to downregulate the activity of lipoprotein lipase, which is overexpressed in abdominal relatively to subcutaneous fat stores. This can be achieved by gastrointestinal bypass or gastroplasty, which decrease dietary fat absorption, or by direct means that include surgical removal of mesenteric fat. Indirect treatment consists of the compliant application of drastic lifestyle change comprising both diet and exercise and pharmacotherapy that reduces mesenteric fat mass and activity. The first step should be an attempt to effectively induce a lifestyle change. Next comes pharmacotherapy including acarbose, metformin, PPARgamma, or PPARgammaalpha agonists, statins and orlistat, estrogens in postmenopausal women or testosterone in men. Among surgical procedures, gastric bypass has been proven to produce beneficial results in advance of other surgical techniques, the evidence basis of which still needs strengthening.

Phosphotyrosine phosphatase (PTPase) activity and its regulation by overnight food deprivation were studied inPsammomys obesus(sand rat), a gerbil model of insulin resistance and nutritionally induced diabetes mellitus. PTPase activity was measured using a phosphopeptide substrate containing a sequence identical to that of the major site of insulin receptor (IR) β-subunit autophosphorylation. The PTPase activity in membrane fractions was 3.5-, 8.3-, and 5.9-fold lower in liver, fat, and skeletal muscle, respectively, compared with corresponding tissues of albino rat.Western blotting of tissue membrane fractions inPsammomysshowed lower PTPase and IR than in albino rats. The density of PTPase transmembrane protein band was 5.5-fold lower in liver and 12-fold lower in adipose tissue. Leukocyte antigen receptor (LAR) and IR were determined by specific immunoblotting and protein bands densitometry and were also found to be 6.3-fold lower in the liver and 22-fold lower in the adipose tissue in the hepatic membrane fractions. Liver cytosolic PTPase activity after an overnight food deprivation in the nondiabeticPsammomysrose 3.7-fold compared with postprandial PTPase activity, but it did not change significantly in diabetic fasted animals. Similar fasting-related changes were detected in the activity of PTPase derived from membrane fraction. In conclusion, the above data demonstrate that despite the insulin resistance,Psammomysis characterized by low level of PTPase activities in membrane and cytosolic fractions in all 3 major insulin responsive tissues, as well as in liver. PTPase activity does not rise in activity as a result of insulin resistance and nutritionally induced diabetes.

The Psammomys obesus (sand rat) is a well-established model of nutritionally induced non-insulin-dependent type-2 diabetes. When fed a high-energy (HE) diet, the diabetes-prone animals develop hyperinsulinaemia and hyperglycaemia. Within 1 week, all animals become hyperinsulinaemic. However, a loss of immunostaining for insulin as well as for the GLUT2 glucose transporter in the plasma membrane and the glucokinase in the cytoplasm of the pancreatic beta cells became evident only when the animals subsequently developed hyperglycaemia. After 1 week of HE diet feeding, the pancreatic beta-cell volume was reduced by one-third in hyperglycaemic Psammomys. Insulin immunostaining as well as GLUT2 glucose transporter immunostaining in the plasma membrane and glucokinase immunostaining in the cytoplasm were reduced by more than 50%. After 3 weeks of HE diet feeding, all changes observed after 1 week were even more pronounced, with reductions in the range of 70–95%. The reduction of the total beta-cell volume of the pancreas due to beta-cell death and the diminution of insulin content of the remaining beta cells in the islets during the HE diet feeding was accompanied by a parallel fall of the pancreas insulin content. For all changes observed, there was a significant correlation with the increase of the blood glucose concentration (r>0.9) but not with the increase of the plasma insulin concentration (r>0.2). Thus, increasing glycaemia appears to be the factor responsible for the deterioration of the pancreatic beta-cell function and the resulting loss of the insulin secretory capacity in Psammomys. The final result of this development is an irreversible diabetic state due to the feeding of the HE diet.

Animal models for insulin resistance and type 2 diabetes are required for the study of the mechanism of these phenomena and for a better understanding of diabetes complications in human populations. Type 2 diabetes is a syndrome that affects 5-10% of the adult population. Hyperinsulinaemia, hypertriglyceridaemia, decreased high-density lipoprotein (HDL) cholesterol levels, obesity and hypertension, all form a cluster of risk factors that increase the risk of coronary artery disease, and are known as insulin resistance syndrome or syndrome X. The gerbil, Psammomys obesus is characterized by primary insulin resistance and is a well-defined model for dietary induced type 2 diabetes. Weanling Psammomys and Albino rats were held individually for several weeks on high energy (HE) and low energy (LE) diets in order to determine the development of metabolic changes leading to diabetes. Feeding Psammomys on HE diet resulted in hyperglycaemia (303 ± 40 mg/dl), hyperinsulinaemia (194 ± 31 µU/ml) and a moderate elevation in body weight, obesity and plasma triglycerides. Albino rats on HE diet demonstrated an elevation in plasma insulin (30 ± 4 µU/ml), hypertriglyceridaemia (170 µ 11 mg/dl), an elevation in body weight and obesity, but maintained normoglycaemia (98 µ 6 mg/dl). Psammomys represent a model that is similar to human populations, with primary insulin resistance expressed in young age, which leads to a high percentage of adult type 2 diabetes. Examples for such populations are the Pima Indians, Australian Aborigines and many other Third World populations. The results indicate that the metabolism of Psammomys is well adapted towards life in a low energy environment, where Psammomys takes advantage of its capacity for a constant accumulation of adipose tissue that will serve for maintenance and breeding in periods of scarcity. This metabolism known as 'thrifty metabolism', is compromised at a high nutrient intake.

Human and mammalian placenta is a glucose-dependent tissue although it may sparingly utilize other substrates, e.g. amino and fatty acids. Regulation of glucose uptake and metabolism is therefore of major interest, but until recently has been largely unclear (Illsley, 2000a). Placental glucose metabolism is not overtly controlled by maternal or fetal hormones, it responds mainly to substrate availability and is affected by substrate excess, e.g. in diabetes (Illsley, 2000b). Placenta is not permeable to insulin, but is endowed with high density of insulin receptors, which are activated by insulin without definite metabolic correlate to insulin action. The insulin action on the placenta began only lately to be elucidated. Therefore, our objective is to overview the novel knowledge of placental metabolism of glucose and fat, as well as the physiological significance of insulin action and insulin receptor in the placenta. Also, the role of leptin in the fetoplacental unit is slowly being unravelled with respect to fetal metabolism and obesity. The placenta constitutes maternal–fetal interface characterized by metabolic stability, shielding the fetus from the adverse effects of maternal metabolic fluctuations. Thus, while reviewing the various placental metabolic functions we intend to point out how they are affected by normal and metabolic alterations characteristic of the diabetic milieu. Alterations of placental functions have been described in type I diabetes but are less well understood in pregnancies complicated by type II and gestational diabetes (GDM). Most of the information on placental endocrine and metabolic functions has been derived from experimental models mainly from animals with streptozotocin diabetes or genetic mutation (Shafrir, 1996). The referral to these common models with short pregnancy duration may be an imperfect match for the

Background Numerous investigations have demonstrated the beneficial effect of vanadium salts on diabetes in streptozotocin (STZ)-diabetic rats, in rodents with genetically determined diabetes and in human subjects. The amelioration of diabetes included the abolition of hyperglycemia, preservation of insulin secretion, reduction in hepatic glucose production, enhanced glycolysis and lipogenesis and improved muscle glucose uptake through GLUT4 elevation and translocation. The molecular basis of vanadium salt action is not yet fully elucidated. Although evidence has been provided that the insulin receptor is activated, the possibility exists that cytosolic non-receptor tyrosine kinase, direct phosphorylation of IRS-1 and activation of PI3-K, leading to GLUT4 translocation, are involved. The raised phosphorylation of proteins in the insulin signaling pathway appears to be related to the inhibition of protein tyrosine phosphatase (PTPase) activity by vanadium salts. Novel experiments The model utilized in our study was Psammomys obesus (sand rat), a desert gerbil which becomes hyperglycemic and hyperinsulinemic on an ad libitum high energy (HE) diet. In contrast to the previously investigated insulin deficient models, vanadyl sulphate was used to correct insulin resistance and hyperinsulinemia, which led to β-cell loss. Administration of 5 mg/kg vanadyl sulfate for 5 days resulted in prolonged restoration of normoglycemia and normoinsulinemia in most animals, return of glucose tolerance to normal, and a reduction of hepatic phosphoenolpyruvate carboxykinase activity. There was no change in food consumption and in regular growth during or after the vanadyl treatment. Pretreatment with vanadyl sulfate, followed by transfer to a HE diet, significantly delayed the onset of hyperglycemia. Hyperinsulinemic-euglycemic clamp of vanadyl sulfate treated Psammomys demonstrated an improvement in glucose utilization. However, vanadyl sulfate was ineffective when administered to animals which lost their insulin secretion capacity on protracted HE diet, but substantially reduced the hyperglycemia when given together with exogenous insulin. The in vitro insulin activation of liver and muscle insulin receptors isolated from vanadyl treated Psammomys was ineffective. The in vivo vanadyl treatment restored muscle GLUT4 total protein and mRNA contents in addition to membrane GLUT4 protein, in accordance with the increased glucose utilization during the clamp study. These results indicate that short-term vanadyl sulfate treatment corrects the nutritionally induced, insulin resistant diabetes. This action requires the presence of insulin for its beneficial effect. Thus, vanadyl action in P. obesus appears to be the result of insulin potentiation rather than mimicking, with activation of the signaling pathway proteins leading to GLUT4 translocation, probably distal to the insulin receptor. Copyright © 2000 John Wiley & Sons, Ltd.