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Liver X receptor (LXR) agonists exert potent antiatherosclerotic actions but simultaneously induce excessive triglyceride (TG) accumulation in the liver. To obtain a detailed insight into the underlying mechanism of hepatic TG accumulation, we used a novel computational modeling approach called analysis of dynamic adaptations in parameter trajectories (ADAPT).We revealed that both input and output fluxes to hepatic TG content are considerably induced on LXR activation and that in the early phase of LXR agonism, hepatic steatosis results from only a minor imbalance between the two. It is generally believed that LXR-induced hepatic steatosis results from increased de novo lipogenesis (DNL). In contrast, ADAPT predicted that the hepatic influx of free fatty acids is the major contributor to hepatic TG accumulation in the early phase of LXR activation. Qualitative validation of this prediction showed a 5-fold increase in the contribution of plasma palmitate to hepatic monounsaturated fatty acids on acute LXR activation, whereas DNL was not yet significantly increased. This study illustrates that complex effects of pharmacological intervention can be translated into distinct patterns of metabolic regulation through state-of-the-art mathematical modeling. [ABSTRACT FROM AUTHOR]

Acetate, propionate, and butyrate are the main short-chain fatty acids (SCFAs) that arise from the fermentation of fibers by the colonic microbiota. While many studies focus on the regulatory role of SCFAs, their quantitative role as a catabolic or anabolic substrate for the host has received relatively little attention. To investigate this aspect, we infused conscious mice with physiological quantities of stable isotopes [1-13C]acetate, [2-13C]propionate, or [2,4-13C2]butyrate directly in the cecum, which is the natural production site in mice, and analyzed their interconversion by the microbiota as well as their metabolism by the host. Cecal interconversion, pointing to microbial cross-feeding, was high between acetate and butyrate, low between butyrate and propionate, and almost absent between acetate and propionate. As much as 62% of infused propionate was used in whole body glucose production, in line with its role as gluconeogenic substrate. Conversely, glucose synthesis from propionate accounted for 69% of total glucose production. The synthesis of palmitate and cholesterol in the liver was high from cecal acetate (2.8 and 0.7%, respectively) and butyrate (2.7 and 0.9%, respectively) as substrates, but low or absent from propionate (0.6 and 0.0%, respectively). Label incorporation due to chain elongation of stearate was approximately eightfold higher than de novo synthesis of stearate. Microarray data suggested that SCFAs exert a mild regulatory effect on the expression of genes involved in hepatic metabolic pathways during the 6-h infusion period. Altogether, gut-derived acetate, propionate, and butyrate play important roles as substrates for glucose, cholesterol, and lipid metabolism. [ABSTRACT FROM AUTHOR]

The farnesoid X receptor (FXR) is involved in regulation of bile acid and lipid metabolism. Recently, a role for FXR in control of glucose metabolism became evident. Because FXR is expressed along the length of the small intestine, we evaluated the potential role of FXR in glucose absorption and processing. During intravenous infusion of a trace amount of D-[6,6-²H2]glucose, a D-[U-13C]glucose-enriched oral glucose bolus was given, and glucose kinetics were determined in wild-type and Fxr-/- mice. Compared with wild-type mice, Fxr-/- mice showed a delayed plasma appearance of orally administered glucose. Multicompartmental kinetic modeling revealed that this delay was caused by an increased flux through the glucose 6-phosphate pool in enterocytes. Thus, our results show involvement of FXR in intestinal glucose absorption, representing a novel physiological function for this nuclear receptor. [ABSTRACT FROM AUTHOR]

We previously reported that in high fat (HF, 24% w/w)-fed C57B16 mice, partial substitution of saturated fat diet for fish oil (FO) aggravated the impaired glucose disposal under hyperinsulinemic conditions. Surprisingly, hepatic insulin sensitivity was maintained under these conditions. However, the HF content of the diet and the degree of FO substitution might have been too low to affect hepatic insulin sensitivity. We therefore compared metabolic effects of chow (CTRL), HF (36% w/w) and HF/FO (21/15% w/w) diets fed to C57B16 mice for 6 weeks. Body weight and adipocyte size increased upon HF feeding compared to the CTRL group. These effects were even more pronounced in mice fed the HF/FO diet. Fasting blood glucose and plasma insulin levels were significantly elevated in the HF and HF/FO groups in comparison to controls. Gene expression levels of enzymes involved in hepatic de novo lipogenesis, in particular Scdl, were increased by HF feeding; this effect was reversed by feeding the HF/FO diet. Concomitantly, hepatic monounsaturated fatty acid (MUFA) content was significantly increased in the HF group and normalized in the HF/FO group (CTRL 24±5, HF 40± 12, HF/FO 22±3 mol%). Basal hepatic glucose production (HGP) was significantly reduced in the HF/FO group only (CTRL 131±18, HF 139±14, HF/FO 105±11 µmol/kg/min). Insulin sensitivity of HGP, however, was only marginally impaired in mice fed HF or HF/FO diets (insulin-mediated suppression of HGP: CTRL' -40, HF-27, HF/FO -28%). Insulin sensitivity of metabolic glucose clearance (MCR) was reduced in the HF group and even more reduced in mice fed the HF/FO diet (insulin-mediated stimulation of MCR: CTRL +304%, HF +286%, HF/FO +186%). Respiratory Exchange Ratio in mice fed the HF/FO diet was consistently lower compared to HF-fed animals, while oxygen consumption was similar. Moreover, expression levels of fatty acid oxidation genes in skeletal muscle were significantly higher in the HF/FO group compared to the HF group. Taken together, our data show that FO aggravates HF-induced peripheral insulin resistance in mice. Furthermore, it reduces basal hepatic glucose production in HF-fed animals, while lipogenic gene expression and MUFA content are decreased. Hepatic insulin sensitivity, on the other hand, is not affected by FO substitution of a HF diet. [ABSTRACT FROM AUTHOR]

Inappropriately elevated hepatic glucose production is considered a major contributor to hyperglycemia in type II diabetes. Increased long-chain fatty acid oxidation is held essential to drive glucose production during fasting. Complete inhibition of long-chain fatty acid oxidation has been explored as a therapeutic option but resulted in hypertrophic cardiomyopathy due to lipid storage. We assessed the effects of inhibition of fatty acid oxidation at the level of medium-chain acyl-CoA dehydrogenase (MCAD) by spiropentaneacetic acid (SPA) on hepatic glucose production in short-term fasted male C57BL/6J mice by infusing [U-13C]glucose, [2-13C]glycerol, [1-2H]galactose and paracetamol for 6 hours, which started immediately after injection of SPA, followed by mass isotopomer distribution analysis on blood glucose and urinary paracetamol-glucuronide. SPA-treatment caused mild hypoketotic hypoglycaemia. Under these conditions, the metabolic clearance rate of glucose was not affected (15.5 ± 0.8 vs. 16.1 ± 0.7 ml⋅kg-1⋅min-1, control vs. SPA). Compared to control mice, the rate of de novo synthesis of glucose-6-phosphate (G6P) was slightly, albeit significantly, decreased in SPA-treated mice (111 ± 8 vs. 84 ± 6 µmol⋅kg-1⋅min-1, control vs. SPA, p<0.05), associated with a corresponding decrease of endogenous glucose production (109 ± 7 vs. 82 ± 4 µmol⋅kg -1⋅min-1, control vs. SPA, p<0.05). Furthermore, only minor changes were observed in fluxes associated with glucose cycling or glycogen metabolism, which were not significant. As a consequence, partitioning of newly synthesised G6P to blood glucose was not changed (69 ± 2 vs. 67 ±. 2%, control vs. SPA, NS). Hepatic mRNA levels of genes encoding enzymes involved in de novo G6P synthesis (Pepck, Pc and Fop-1) were unaltered in SPA-treated mice, while G6P-hydrolase mRNA expressions were increased in SPA-treated mice. In conclusion, acute inhibition of MCAD using SPA only slightly suppressed gluconeogenesis, which resulted in decreased endogenous glucose production because partitioning of newly synthesised G6P to blood glucose did not change. [ABSTRACT FROM AUTHOR]

A correction to the article "Endocrinization of FGFI Produces a Neomorphic and Potent Insulin Sensitizer" by Jae Myoung Suh, Johan W. Jonker and Regina Goetz published in "Nature" Vol 513 2014 issue is presented.

Inappropriately high hepatic glucose production is a major contributor to hyperglycemia in type II diabetes,. Since long-chain fatty acid oxidation (1cFAO) is considered to be essential for driving gluconeogenesis, inhibition of 1cFAO has been explored as a therapeutic option to diminish glucose production. We assessed hepatic glucose metabolism in vivo after acute inhibition of 1cFAO by 2-tetradecylglycidic acid (TDGA) and subsequent short-term fasting in male C57BL/6J mice and control mice. We infused [U-13C]-glucose, [2-13C]glycerol, [1-2H]galactose and paracetamol for 6 hours, followed by mass isotopomer distribution analysis on blood glucose and urinary paracetamol-glucuronide. Under hypoketotic hypoglycaemic conditions induced by TDGA-treatment, endogenous glucose production was unaffected (127±10 vs. 118 ± 7 µmol⋅kg-1.⋅min-1, control vs. TDGA, NS), but metabolic clearance rate of glucose was enhanced (16 ± 1 vs. 26 ±1 ml⋅kg-l.⋅min-1, control vs. TDGA, p<0.05). Compared to control mice, the rate of de novo synthesis of glucose-6-phosphate (G6P) was only slightly decreased in TDGA-treated mice (108 ± 19 vs. 85 ± 6 µmol.⋅kg-1⋅min- 1, control vs. TDGA, p<0.05). Recycling of glucose was decreased upon TDGA-treatment (26 ±14 vs. 12 ±4 µmol.⋅kg -1⋅min-1, control vs. TDGA, p<0.05) due to decreased glucose phosphorylation (39 ± 8 vs. 16 ± 2 µmol⋅kg-1⋅min-1, control s. TDGA, p<0.05). Furthermore, glycogen synthesis decreased significantly (56 ± 5 vs. 33 ±1 µmol⋅kg-1⋅min-1, control vs. TDGA, p<0.05), resulting in an increased partitioning of newly synthesised G6P to blood glucose. Hepatic mRNA levels of genes encoding for enzymes involved in de novo G6P-synthesis were unaltered, while G6P-hydrolase mRNA expressions were increased in TDGA-treated mice. Glucokinase and pyruvate kinase mRNA levels were significantly decreased and Pdk-4 expression was increased 30-fold, suggesting decreased glycolytic activity. In conclusion, acute pharmacological inhibition of 1cFAO using TDGA in short-term fasted mice suppressed de novo G6P-synthesis only marginally, while endogenous glucose production remained unaffected. Hence, it appears that a fully active 1cFAO is not essential for maintenance of hepatic GNG in vivo, but affects predominantly metabolic handling of G6P. [ABSTRACT FROM AUTHOR]

LXR is a nuclear hormone receptor that coordinates lipid and cholesterol metabolism upon activation by oxysterols. Recently, it was proposed that LXR acts as a glucose sensor in the liver and that glucose and its metabolite glucose-6-phosphate are able to activate LXR in vitro at physiological concentrations. The aim of this study was to assess the functional relevance of the major hepatic LXR isoform in the control of hepatic and peripheral glucose metabolism in mice. Glucose metabolism was studied in fasted male LXR-alpha knockout (KO) mice and their wildtype (WT) littermates by infusing [U13C]glucose, [2-13C]glycerol, [1-2H]galactose and paracetamol for 6 hours, followed by mass isotopomer distribution analysis. Furthermore, hyperinsulinemic euglycemic clamps were performed using [U-13C]glucose. Blood glucose levels during steady state conditions were significantly reduced in LXRalpha KO mice (KO 7.3±0.5 WT 9.5±1.9 mmol/l, p<0.05). Whole body glucose turnover was significantly lower in LXRalpha null mice compared to wildtype littermates (KO 129.6±12.8 WT 159.1±26.2 µmol/kg/min, p<0.05). LXRalpha deficiency did not affect gluconeogenic flux (KO 97.9±9.5 WT 109.±17.1 µmol/kg/min, NS). However, all fluxes affecting the glucose-6-phosphate pool, i.e. through glycogen synthase (Gs), glycogen phosphorylase (Gp), glucose-6-phosphatase (G6pase) and glucokinase (Gk) were significantly lower in LXRalpha null mice compared to wildtype littermates. Expression levels of genes encoding Pyruvate Kinase (Pk), Gk and Gp were significantly reduced by LXRalpha deficiency. Glucose balance, i.e., the difference between G6pase and Gk fluxes was lower in LXRalpha null mice (KO 119.5±11.9 WT 142.8±27.1 µmol/kg/min, p<0.05). Glycogen balance, i.e., the difference between Gs and Gp fluxes was not altered in LXRalpha null mice (KO-14.4±8.1 WT -20.6±18.5 µmol/kg/min, NS). Metabolic clearance of glucose was not affected by LXRalpha deficiency (KO 18.2±2.7 WT 16.9±1.8 µmol/kg/min, NS). Under hyperinsulinemic conditions, LXRalpha null mice and wildtype littermates exhibited similar hepatic glucose production and metabolic glucose clearance rates, indicative for unaltered hepatic and peripheral insulin sensitivity. In summary, LXRalpha deficiency results in disturbed hepatic glucose-6-phosphate metabolism in mice. As a result, hepatic glucose output is impaired, leading to decreased blood glucose levels. [ABSTRACT FROM AUTHOR]

Hyperglycemia in type II diabetes is partly due to an inappropriately elevated hepatic glucose production. Long-chain fatty acid oxidation (1cFAO) is held essential to drive glucose production during fasting. Treatment of type II diabetes by inhibition of 1cFAO has been unsuccessful, because it is accompanied by hypertrophic cardiomyopathy due to lipid accumulation. Medium-chain acyl-CoA dehydrogenase (MCAD) is responsible for the first step in medium-chain fatty acid oxidation (mcFAO) essential for complete 1cFAO. As proof of principal to treat type II diabetes by MCAD inhibition, we assessed hepatic glucose metabolism in vivo in short-term fasted male MCAD-deficient (MCADD) mice and their WT littermates, by infusing [U-13C]glucose, [2-13C]glycerol, [1-2H]galactose, and paracetamol for 6 hours, followed by mass isotopomer distribution analysis on blood glucose and urinary paracetamol-glucuronide. Upon short-term fasting, glucose concentration in blood were comparable in both groups (6.2 ± 0.4 vs. 5.8 ± 0.6 mmol/L, control vs. MCADD mice, NS). Endogenous glucose production tended to be decreased in MCADD mice compared to controls (143 ± 14 vs. 113 ± 12 p-mol⋅kg-l⋅min-1, control vs. MCADD, NS). Metabolic clearance rate of glucose did not differ between the groups (18 ± 2 vs. 20 ± 3 ml⋅kg-1⋅min-1, control vs. MCADD, NS). De novo synthesis of glucose-6-phosphate (G6P) was not affected in MCADD mice (124 ± 23 vs. 124 ± 19 µmol⋅kg-1⋅min-1, control vs. MCADD, NS), as was glucose cycling (31 ± 10 vs. 27 ± 5 µmol⋅kg-1⋅min-1, control vs. MCADD, NS). In contrast, fluxes associated with glycogen metabolism were changed, with increased flux into glycogen (47 ± 10 vs. 70 ± 14 µmol⋅kg-1⋅min-1, control vs. MCADD, p<0.05) and decreased flux out of glycogen (59 ± 14 vs. 31 ± 15 µmol⋅kg-1⋅min-1, control vs. MCADD, p<0.05). Hepatic mRNA levels of genes encoding for enzymes involved in de novo G6P synthesis, glucose production, glucose phosphorylation and glycogen metabolism were unaltered in MCADD mice. In conclusion, short-term fasting did not affect gluconeogenesis in MCADD mice but surprisingly, changed fluxes associated with hepatic glycogen metabolism. Our data indicate that inhibition of mcFAO is not a therapeutic option in type II diabetes. [ABSTRACT FROM AUTHOR]

BACKGROUNDCytochrome P450 family 8 subfamily B member 1 (CYP8B1) generates 12α-hydroxylated bile acids (BAs) that are associated with insulin resistance in humans.METHODSTo determine whether reduced CYP8B1 activity improves insulin sensitivity, we sequenced CYP8B1 in individuals without diabetes and identified carriers of complete loss-of-function (CLOF) mutations utilizing functional assays.RESULTSMutation carriers had lower plasma 12α-hydroxylated/non-12α-hydroxylated BA and cholic acid (CA)/chenodeoxycholic acid (CDCA) ratios compared with age-, sex-, and BMI-matched controls. During insulin clamps, hepatic glucose production was suppressed to a similar magnitude by insulin, but glucose infusion rates to maintain euglycemia were higher in mutation carriers, indicating increased peripheral insulin sensitivity. Consistently, a polymorphic CLOF CYP8B1 mutation associated with lower fasting insulin in the AMP-T2D-GENES study. Exposure of primary human muscle cells to mutation-carrier CA/CDCA ratios demonstrated increased FOXO1 activity, and upregulation of both insulin signaling and glucose uptake, which were mediated by increased CDCA. Inhibition of FOXO1 attenuated the CDCA-mediated increase in muscle insulin signaling and glucose uptake. We found that reduced CYP8B1 activity associates with increased insulin sensitivity in humans.CONCLUSIONOur findings suggest that increased circulatory CDCA due to reduced CYP8B1 activity increases skeletal muscle insulin sensitivity, contributing to increased whole-body insulin sensitization.FUNDINGBiomedical Research Council/National Medical Research Council of Singapore. [ABSTRACT FROM AUTHOR]

Prevention of hypertriglyceridemia is one of the biomedical targets in Glycogen Storage Disease type Ia (GSD Ia) patients, yet it is unclear how hypoglycemia links to plasma triglyceride (TG) levels. We analyzed whole-body TG metabolism in normoglycemic (fed) and hypoglycemic (fasted) hepatocyte-specific glucose-6-phosphatase deficient (L-G6pc -/- ) mice. De novo fatty acid synthesis contributed substantially to hepatic TG accumulation in normoglycemic L-G6pc -/- mice. In hypoglycemic conditions, enhanced adipose tissue lipolysis was the main driver of liver steatosis, supported by elevated free fatty acid concentrations in GSD Ia mice and GSD Ia patients. Plasma very-low-density lipoprotein (VLDL) levels were increased in GSD Ia patients and in normoglycemic L-G6pc -/- mice, and further elevated in hypoglycemic L-G6pc -/- mice. VLDL-TG secretion rates were doubled in normo- and hypoglycemic L-G6pc -/- mice, while VLDL-TG catabolism was selectively inhibited in hypoglycemic L-G6pc -/- mice. In conclusion, fasting-induced hypoglycemia in L-G6pc -/- mice promotes adipose tissue lipolysis and arrests VLDL catabolism. This mechanism likely contributes to aggravated liver steatosis and dyslipidemia in GSD Ia patients with poor glycemic control and may explain clinical heterogeneity in hypertriglyceridemia between GSD Ia patients., (© 2021 The Authors. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.)

Background and Aims: Glycogen storage disease (GSD) type 1a is an inborn error of metabolism caused by defective glucose-6-phosphatase catalytic subunit (G6PC) activity. Patients with GSD 1a exhibit severe hepatomegaly due to glycogen and triglyceride (TG) accumulation in the liver. We have shown that the activity of carbohydrate response element binding protein (ChREBP), a key regulator of glycolysis and de novo lipogenesis, is increased in GSD 1a. In the current study, we assessed the contribution of ChREBP to nonalcoholic fatty liver disease (NAFLD) development in a mouse model for hepatic GSD 1a., Approach and Results: Liver-specific G6pc-knockout (L-G6pc -/- ) mice were treated with adeno-associated viruses (AAVs) 2 or 8 directed against short hairpin ChREBP to normalize hepatic ChREBP activity to levels observed in wild-type mice receiving AAV8-scrambled short hairpin RNA (shSCR). Hepatic ChREBP knockdown markedly increased liver weight and hepatocyte size in L-G6pc -/- mice. This was associated with hepatic accumulation of G6P, glycogen, and lipids, whereas the expression of glycolytic and lipogenic genes was reduced. Enzyme activities, flux measurements, hepatic metabolite analysis and very low density lipoprotein (VLDL)-TG secretion assays revealed that hepatic ChREBP knockdown reduced downstream glycolysis and de novo lipogenesis but also strongly suppressed hepatic VLDL lipidation, hence promoting the storage of "old fat." Interestingly, enhanced VLDL-TG secretion in shSCR-treated L-G6pc -/- mice associated with a ChREBP-dependent induction of the VLDL lipidation proteins microsomal TG transfer protein and transmembrane 6 superfamily member 2 (TM6SF2), the latter being confirmed by ChIP-qPCR., Conclusions: Attenuation of hepatic ChREBP induction in GSD 1a liver aggravates hepatomegaly because of further accumulation of glycogen and lipids as a result of reduced glycolysis and suppressed VLDL-TG secretion. TM6SF2, critical for VLDL formation, was identified as a ChREBP target in mouse liver. Altogether, our data show that enhanced ChREBP activity limits NAFLD development in GSD 1a by balancing hepatic TG production and secretion., (© 2020 The Authors. Hepatology published by Wiley Periodicals, LLC., on behalf of American Association for the Study of Liver Diseases.)

Long-term elevated plasma cholesterol levels put individuals at risk for developing atherosclerosis. Plasma cholesterol levels are determined by the balance between cholesterol input and output fluxes. Here we describe in detail the methodology to determine the different cholesterol fluxes in mice. The percentage of absorbed cholesterol is calculated from a stable isotope-based double-label method. Cholesterol synthesis is calculated from MIDA after 13 C-acetate enrichment. Cholesterol is removed from the body via the feces. The fecal excretion route is either biliary or non-biliary. The non-biliary route is dominated by trans-intestinal cholesterol efflux, or TICE. Biliary excretion of cholesterol is measured by collecting bile. Non-biliary excretion is calculated by computational modeling. In this article, we describe methods and procedures to measure and calculate dietary intake of cholesterol, fractional cholesterol absorption, fecal neutral sterol output, biliary cholesterol excretion, TICE, cholesterol synthesis, peripheral fluxes, and whole-body cholesterol balance. © 2016 by John Wiley & Sons, Inc., (Copyright © 2016 John Wiley & Sons, Inc.)

Severe malnutrition is a leading cause of global childhood mortality, and infection and hypoglycemia or hyperglycemia are commonly present. The etiology behind the changes in glucose homeostasis is poorly understood. Here, we generated an animal model of severe malnutrition with and without low-grade inflammation to investigate the effects on glucose homeostasis. Immediately after weaning, rats were fed diets containing 5 [low-protein diet (LP)] or 20% protein [control diet (CTRL)], with or without repeated low-dose intraperitoneal lipopolysaccharide (LPS; 2 mg/kg), to mimic inflammation resulting from infections. After 4 wk on the diets, hyperglycemic clamps or euglycemic hyperinsulinemic clamps were performed with infusion of [U-(13)C6]glucose and [2-(13)C]glycerol to assess insulin secretion, action, and hepatic glucose metabolism. In separate studies, pancreatic islets were isolated for further analyses of insulin secretion and islet morphometry. Glucose clearance was reduced significantly by LP feeding alone (16%) and by LP feeding with LPS administration (43.8%) compared with control during the hyperglycemic clamps. This was associated with a strongly reduced insulin secretion in LP-fed rats in vivo as well as ex vivo in islets but signficantly enhanced whole body insulin sensitivity. Gluconeogenesis rates were unaffected by LP feeding, but glycogenolysis was higher after LP feeding. A protein-deficient diet in young rats leads to a susceptibility to low-dose endotoxin-induced impairment in glucose clearance with a decrease in the islet insulin secretory pathway. A protein-deficient diet is associated with enhanced peripheral insulin sensitivity but impaired insulin-mediated suppression of hepatic glycogenolysis., (Copyright © 2015 the American Physiological Society.)

Acetate, propionate, and butyrate are the main short-chain fatty acids (SCFAs) that arise from the fermentation of fibers by the colonic microbiota. While many studies focus on the regulatory role of SCFAs, their quantitative role as a catabolic or anabolic substrate for the host has received relatively little attention. To investigate this aspect, we infused conscious mice with physiological quantities of stable isotopes [1-(13)C]acetate, [2-(13)C]propionate, or [2,4-(13)C2]butyrate directly in the cecum, which is the natural production site in mice, and analyzed their interconversion by the microbiota as well as their metabolism by the host. Cecal interconversion, pointing to microbial cross-feeding, was high between acetate and butyrate, low between butyrate and propionate, and almost absent between acetate and propionate. As much as 62% of infused propionate was used in whole body glucose production, in line with its role as gluconeogenic substrate. Conversely, glucose synthesis from propionate accounted for 69% of total glucose production. The synthesis of palmitate and cholesterol in the liver was high from cecal acetate (2.8 and 0.7%, respectively) and butyrate (2.7 and 0.9%, respectively) as substrates, but low or absent from propionate (0.6 and 0.0%, respectively). Label incorporation due to chain elongation of stearate was approximately eightfold higher than de novo synthesis of stearate. Microarray data suggested that SCFAs exert a mild regulatory effect on the expression of genes involved in hepatic metabolic pathways during the 6-h infusion period. Altogether, gut-derived acetate, propionate, and butyrate play important roles as substrates for glucose, cholesterol, and lipid metabolism.

Unlabelled: Diabetes is characterized by high blood glucose levels and dyslipidemia. Bile salt sequestration has been found to improve both plasma glycemic control and cholesterol profiles in diabetic patients. Yet bile salt sequestration is also known to affect triglyceride (TG) metabolism, possibly through signaling pathways involving farnesoid X receptor (FXR) and liver X receptor alpha (LXRalpha). We quantitatively assessed kinetic parameters of bile salt metabolism in lean C57Bl/6J and in obese, diabetic db/db mice upon bile salt sequestration using colesevelam HCl (2% wt/wt in diet) and related these to quantitative changes in hepatic lipid metabolism. As expected, bile salt sequestration reduced intestinal bile salt reabsorption. Importantly, bile salt pool size and biliary bile salt secretion remained unchanged upon sequestrant treatment due to compensation by de novo bile salt synthesis in both models. Nevertheless, lean and db/db mice showed increased, mainly periportally confined, hepatic TG contents, increased expression of lipogenic genes, and increased fractional contributions of newly synthesized fatty acids. Lipogenic gene expression was not induced in sequestrant-treated Fxr(-/-) and Lxralpha(-/-) mice compared with wild-type littermates, in line with reports indicating a regulatory role of FXR and LXRalpha in bile salt-mediated regulation of hepatic lipid metabolism., Conclusion: Bile salt sequestration by colesevelam induces the lipogenic pathway in an FXR- and LXRalpha-dependent manner without affecting the total pool size of bile salts in mice. We speculate that a shift from intestinal reabsorption to de novo synthesis as source of bile salts upon bile salt sequestration affects zonation of metabolic processes within the liver acinus.