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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.11.003 Byline: Francesco Vacirca (a)(b), Thomas Ziegler (a), Eduard Hasenleithner (a) Keywords: TCP; Spurious timeout; UMTS; GPRS Abstract: This paper proposes an algorithm to identify TCP spurious retransmission timeouts by post processing of packet traces monitored in operational networks. The operational principles of the algorithm and the assumptions behind its design are explained in detail as well as the situations in which the algorithm is prone to inaccuracies. By extensive measurements in a lab testbed using realistic round trip time characteristics as observed in operational wireless networks and FTP-like as well as Web-like traffic generators, it is shown that the algorithm is accurate in detection of spurious retransmission timeouts. Subsequently, the algorithm is applied to real traffic traces captured at several interfaces of an operational UMTS and GPRS network to analyze the frequency of spurious retransmission timeouts as well as the spurious timeout probability dependent on the load situation in the network and the flow size. This investigation, to our best knowledge the first on large scale TCP traffic traces monitored in an operational UMTS network, shows that spurious timeouts are infrequent events in the considered UMTS as well as the GPRS network. Among other findings, it is additionally shown that the ratio between spurious timeouts and other congestion recovery events experienced by TCP flows is low, indicating a negligible impact of spurious timeouts on TCP performance. Author Affiliation: (a) ftw. Forschungszentrum Telekommunikation Wien, Donau-City-Strasse 1, A-1220 Vienna, Austria (b) Infocom Department, University of Roma "La Sapienza", Via Eudossiana 18, 00184 Roma, Italy Article History: Received 30 July 2005; Revised 17 November 2005; Accepted 21 November 2005 Article Note: (miscellaneous) Responsible Editor: S. Palazzo

Low molecular weight thiol/disulfide redox pools are dependent upon extracellular cysteine (Cys) availability. We determined whether dietary sulfur amino acid (SAA) deficiency induces oxidative stress in vivo, as determined by redox state of major thiol/disulfide couples in plasma [Cys/cystine (CySS)] and intestinal mucosa [glutathione (GSH)/glutathione disulfide (GSSG)]. Rats were fed isocaloric, isonitrogenous semipurified diets: either SAA-adequate (control), SAA-deficient, or SAA-supplemented, pair-fed to intake of the SAA-deficient group. Reference rats consumed standard rat food ad libitum. After 7 d, plasma and gut mucosal samples were analyzed for Cys, CySS, GSH and GSSG, and the redox potentials of Cys/CySS and GSH/GSSG were determined. Mean daily food intake in the pair-fed rats was similar (approximately one-half of reference-rat intake). Body weight decreased in all pair-fed groups, but rats fed the SAA-deficient diet lost significantly more body weight. Dietary SAA deficiency decreased GSH concentrations in both plasma and gut mucosa, increased plasma GSSG, and oxidized plasma and gut mucosal GSH/GSSG redox and plasma Cys/CySS redox. SAA supplementation resulted in a more reducing plasma Cys/CySS redox potential. Reference rats exhibited similar tissue and plasma GSH/GSSG redox as rats that ate semipurified SAA-adequate rat food, which provided similar net SAA intake. Our in vivo data show that inadequate dietary SAA intake oxidizes the thiol/disulfide redox status in rat-gut mucosa and plasma. Such oxidation of redox pools is associated with oxidative stress and the onset or progression of several pathological conditions. Thus, dietary SAA deficiency could contribute to the progression of disease by causing an oxidation of these components. KEY WORDS: * sulfur aminoacids * redox * intestine

Glutamine (Gln) prevents apoptosis in intestinal epithelial cells, but the mechanism(s) remain unknown. Gin-derived metabolites include ammonia, glutamate (Glu), glutathione (GSH), and nucleotides. We previously showed that Gln potently inhibited apoptosis in cytokine-treated human colonic HT-29 cells; this effect was specific to Gln, unaffected by Glu, and unrelated to intracellular GSH. The current research examines mechanism(s) for Gin-induced antiapoptotic effects in HT-29 cells treated with TNF-[alpha]-related apoptosis-inducing ligand (TRAIL). Proliferating cells were treated with Gln or selected Gln metabolites for 24 h. Cells were then treated with TRAIL and Gln or its downstream metabolites, and apoptosis was assessed at 8 h after treatment. The purine and pyrimidine precursors inosine and orotate inhibited TRAIL-induced apoptosis. However, inhibition of purine synthesis with azaserine did not alter the potent antiapoptotic effect of Gln. In contrast, the pyrimidine synthesis inhibitor, acivicin, completely prevented this response. Supplementation with the pyrimidine uracil or the pyrimidine precursor orotate rescued the acivicin-induced blockade of Gln antiapoptotic action. Removal of bicarbonate, a substrate for pyrimidine synthesis, also inhibited the antiapoptotic effects of Gln. Uracil and thymine alone also significantly decreased TRAIL-induced apoptosis. The antiapoptotic effects of Gln were independent of DNA/RNA synthesis as measured by flow cytometry and bromodeoxyuridine incorporation. In conclusion, Gln prevents TRAIL-induced apoptosis in HT-29 cells through a mechanism involving the pyrimidine pathway. Our data also demonstrate the novel antiapoptotic effects of pyrimidine bases and their precursor orotate in these human intestinal cells. apoptosis; glutamine; intestine; nucleotides; pyrimidines

Previous research shows that stimulation of proliferation of colon carcinoma (Caco-2) cells by a more reduced extracellular cysteine/cystine (Cys/CySS) redox state occurs with no apparent effect on intracellular glutathione and that this stimulation is lost on addition of epidermal growth factor. The purpose of the present study was to determine whether a more reduced extracellular Cys/CySS redox state activates the mitogenic p44/p42 mitogen-activated protein kinase (MAPK) pathway and whether this is signaled through the epidermal growth factor receptor (EGFR). Caco-2 cells were exposed to a range of physiological extracellular redox conditions from--150 to 0 mV. In the absence of added growth factors, the most reduced (-150 mV) redox state induced an 80% increase in EGFR phosphorylation, and this was followed by a marked increase in phosphorylation of p44/p42 MAPK. Inhibitors of EGFR (AG1478) and p44/p42 MAPK (U0126) phosphorylation blocked redox-dependent p44/p42 phosphorylation, indicating that signaling occurred by EGFR. These effects were inhibited by pretreatment with a nonpermeant alkylating agent, showing that signaling involved thiols accessible to the extracellular space. The EGFR ligand TGF-[alpha] was increased in culture medium at more reduced redox states. Redox-dependent phosphorylation of EGFR was completely prevented by a metalloproteinase inhibitor (GM6001), and an antibody to TGF-[alpha] partially inhibited the phosphorylation of p44/p42 MAPK by redox. Thus the data show that a redox-dependent activation of metalloproteinase can stimulate the mitogenic p44/p42 MAPK pathway by a TGF-[alpha]-dependent mechanism. Because Cys availability and Cys/CySS redox are dependent on nutrition, disease, and environmental exposures, the results suggest that cell proliferation could be influenced physiologically by Cys-dependent redox effects on growth factor signaling pathways. oxidation reduction; intestine; transforming growth factor-[alpha]; glutathione

Myopathies related to critical illness have received increasing recognition over the past decade and are common in patients even after a brief period in the intensive care unit. Recent studies have revealed that myopathies in the critically ill may in fact be more prevalent than neuropathies and that morbidity and mortality may be greater. Protein catabolism, an increase in urinary nitrogen loss, and muscle wasting are observed in critical illness myopathy. Muscle biopsies in critically ill patients demonstrate low glutamine levels, low protein/DNA levels, and high concentrations of extracellular water. The increased flux of glutamine in muscle in these patients is thought to be insufficient to meet the body's requirement for glutamine, and thus in critical illness this amino acid may be classified as 'conditionally essential.' Three subtypes of critical illness myopathy have been described that are often grouped together as acute quadriplegic myopathy: thick-filament myopathy, critical illness myopathy, and necrotizing myopathy. These can be differentiated based on clinical features and muscle biopsy. Treatments for critical illness myopathies range from primary prevention, i.e., avoiding myopathy-inducing drugs, to novel nutritional therapies, such as glutamine and glutathione supplementation. One should be particularly vigilant for the development of myopathies in critically ill alcoholic patients, who may have a chronic alcoholic myopathy at baseline. In the past decade, advances have been made in characterizing and identifying patients with myopathies due to critical illness. However, additional studies must be performed in order to develop appropriate therapies for this potentially devastating disorder. J. Nutr. 135: 1818S-1823S, 2005. KEY WORDS: * neuromuscular diseases * glutamine * arginine * alcohol abuse * glutathione

Two weeks after 70% enterectomy, glutamine (Gin) transport is downregulated in rabbit residual bowel due to a decrease in system [B.sup.0] activity. Providing epidermal growth factor (EGF) and growth hormone (GH) restores Gin transport by increasing systems A and [B.sup.0,+] activities. We hypothesized that changes in [Na.sup.+]-dependent broad-spectrum neutral amino acid transporter ([ATB.sup.0]/ASCT2) protein and mRNA expression correlate with system [B.sup.0] activity. New Zealand White rabbits underwent 70% jejunoileal resection or no resection. Resected rabbits immediately received parenteral EGF, GH, both, or neither agent for 2 wk. Tissues harvested from jejunum, ileum, and colon were subjected to Western and Northern blot analyses for [ATB.sup.0]/ASCT2 protein and mRNA. In all tissues, [ATB.sup.0]/ASCT2 mRNA was reduced by ~50% in resected rabbits compared with nonresected controls. Similar reductions in protein amount occurred in the ileum and cecum. None of the growth factor treatments restored [ATB.sup.0]/ASCT2 protein, but GH treatment increased [ATB.sup.0]/ASCT2 mRNA abundance 250% in the residual ileum. Because changes in the [ATB.sup.0]/ASCT2 protein amount paralleled those in the system [B.sup.0] activity in this model, it is likely that this is the protein responsible for this transport system. The increase in mRNA abundance in rabbits treated with GH for 2 wk may be a harbinger of subsequent increases in transporter protein and activity. Unlike reported upregulation of transporters in human colon after small bowel resection, [ATB.sup.0]/ASCT2 protein and mRNA expression in rabbit colon are decreased, suggesting different regulatory pathways. KEY WORDS: * small bowel resection * [ATB.sup.0]/ASCT2 * rabbits * epidermal growth factor * growth hormone

Glutamine (Gln) and keratinocyte growth factor (KGF) each stimulate intestinal epithelial cell growth, but regulatory mechanisms are not well understood. We determined whether Gln and KGF alter intra- and extracellular thiol/disulfide redox pools in Caco-2 cells cultured in oxidizing or reducing cell medium and whether such redox variations are a determinant of proliferative responses to these agents. Cells were cultured over a physiological range of oxidizing to reducing extracellular thiol/disulfide redox ([E.sub.h]) conditions, obtained by varying cysteine (Cys) and cystine (CySS) concentrations in cell medium. Cell proliferation was determined by 5-bromo-2-deoxyuridine (BrdU) incorporation. Gln (10 mmol/l) or KGF (10 [micro]g/]) did not alter BrdU incorporation at reducing [E.sub.h] (-131 to -150 mV), but significantly increased incorporation at more oxidizing [E.sub.h] (Gln at 0 to -109 mV; KGF at -46 to -80 mV). Cellular glutathione/glutathione disulfide (GSH/GSSG) [E.sub.h] was unaffected by Gln, KGF, or variations in extracellular Cys/CySS [E.sub.h]. Control cells largely maintained extracellular [E.sub.h] at initial values after 24 h (-36 to -136 mV). However, extracellular [E.sub.h] shifted toward a narrow physiological range with Gln and KGF treatment (Gln -56 to -88 mV and KGF -76 to -92 mV, respectively; P < 0.05 vs. control). The results indicate that thiol/disulfide redox state in the extracellular milieu is an important determinant of Caco-2 cell proliferation induced by Gln and KGF, that this control is independent of intracellular GSH redox status, and that both Gln and KGF enhance the capability of Caco-2 cells to modulate extremes of extracellular redox. cysteine; glutathione; intestine; oxidation-reduction; keratinocyte growth factor

Epithelial cell apoptosis is an important regulator of normal gut mucosal turnover; however, excessive apoptosis may inhibit mucosal restitution during pathophysiologic states. Apoptosis is induced by oxidative stress and cytokines, but regulation by specific nutrients has been infrequently studied under these conditions. Glutamine (Gin) is an important metabolic fuel for intestinal epithelial cells and a precursor to the antioxidative glutathione (GSH), which has antiapoptotic effects. In cultured intestinal epithelial cells, Gin depletion increases oxidant-induced apoptosis. This study examined whether Gin protects against apoptosis induced by the cytokine tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) in the human colon carcinoma cell line, HT-29. TRAIL-induced apoptosis in HT-29 cells was characterized by an increase in the percentage of cells in the sub-[G.sup.1] fraction by flow cytoimetry, nuclear condensation and the activation of caspase-8 and caspase-3. TRAIL-induced apoptosis was completely prevented by Gln, but not inhibited by other amino acids, including the GSH constituents, glutamate, cysteine and glycine. Similar antiapoptotic effects of Gin occurred when apoptosis was induced by a combination of tumor necrosis factor-alpha and interferon-gamma. Cellular GSH was oxidized during TRAIL-induced apoptosis. This effect was completely blocked by Gin, however, inhibition of GSH synthesis with buthionine sulfoximine did not alter Gin antiapoptotic effects. Furthermore, glutamate prevented GSH oxidation in response to TRAIL but did not protect against TRAIL-induced apoptosis. These results show that Gin specifically protects intestinal epithelial cells against cytokine-induced apoptosis, and that this occurs by a mechanism that is distinct from the protection against oxidative stress mediated by cellular GSH. J. Nutr. 133: 3065-3071, 2003. KEY WORDS: * apoptosis * cytokines * glutathione * intestine * TRAIL

The trefoil factor family peptides TFF1, TFF2, and TFF3 are important for gut mucosal protection and restitution. Keratinocyte growth factor (KGF) stimulates proliferation and differentiation of epithelial cells with potent effects on goblet cells. To investigate interactions between food intake and KGF, rats were fed ad libitum (control), fasted for 72 h, or fasted for 72 h and then refed for 72 h with or without KGF (3 mg * [kg.sup.-1] * [day.sup.-1]). With fasting, goblet cell number in duodenum increased, TFF3 mRNA in duodenum and jejunum decreased, and TFF3 protein did not change or increased. KGF during fasting stimulated colonic growth, normalized TFF3 mRNA in duodenum and jejunum, and broadly upregulated gut goblet cell number and TFF3 protein expression. With fasting-refeeding, KGF increased small bowel and colonic mucosal growth, goblet cell number, and TFF3 protein but had variable effects on TFF3 mRNA. KGF induced TFF2 mRNA and protein in duodenum and jejunum with both nutritional regimens. We conclude that nutrient availability modifies rat intestinal goblet cell number, TFF3 mRNA, and the gut-trophic effects of KGF in a region-specific manner. KGF enhances TFF2 expression in proximal small bowel and increases goblet cell number and TFF3 protein content throughout the intestine independent of food intake. colon; intestinal mucosa; keratinocyte growth factor

Background: Adiposity and mitochondrial dysfunction are related factors contributing to metabolic disease development. This pilot study examined whether in vivo and ex vivo indices of mitochondrial metabolism were differentially associated with body composition in males and females. Methods: Thirty-four participants including 19 females (mean 27 yr) and 15 males (mean 29 yr) had body composition assessed by dual energy x-ray absorptiometry and magnetic resonance (MR) imaging. Monocyte reserve capacity and maximal oxygen consumption rate (OCR) were determined ex vivo using extracellular flux analysis. In vivo quadriceps mitochondrial function was measured using 31P-MR spectroscopy based on post-exercise recovery kinetics (τPCr). The homeostatic model assessment of insulin resistance (HOMA-IR) was calculated from fasting glucose and insulin levels. Variables were log-transformed, and Pearson correlations and partial correlations were used for analyses. Results: Mitochondrial metabolism was similar between sexes (p > 0.05). In males only, higher fat mass percent (FM%) was correlated with lower reserve capacity (r = − 0.73; p = 0.002) and reduced muscle mitochondrial function (r = 0.58, p = 0.02). Thigh subcutaneous adipose tissue was inversely related to reserve capacity in males (r = − 0.75, p = 0.001), but in females was correlated to higher maximal OCR (r = 0.48, p = 0.046), independent of FM. In females, lean mass was related to greater reserve capacity (r = 0.47, p = 0.04). In all participants, insulin (r = 0.35; p = 0.04) and HOMA-IR (r = 0.34; p = 0.05) were associated with a higher τPCr. Conclusions: These novel findings demonstrate distinct sex-dependent associations between monocyte and skeletal muscle mitochondrial metabolism with body composition. With further study, increased understanding of these relationships may inform sex-specific interventions to improve mitochondrial function and metabolic health. [ABSTRACT FROM AUTHOR]

Madagascar's biota is characterized by an extraordinary species richness, with a high degree of endemism. The island's freshwater habitats harbor numerous micro‐endemic species, restricted to particular regions and thus particularly at risk of extinction, due to deforestation, overfishing, and introduction of exotic species. The present study investigates for which threatened Malagasy freshwater fish species ex situ populations have already been established, as a baseline to prioritize actions to develop an effective ex situ conservation breeding network. Populations in zoos and aquaria were primarily determined using the Zoological Information System. Of 173 fish species recorded from Malagasy freshwater habitats, 123 exclusively inhabit freshwater; 79 of these are endemic to Madagascar, and 50 are classified as threatened. Our survey found 21 Malagasy freshwater fish species kept in zoos worldwide, of which 19 are endemic and threatened (22 if counting species kept by private breeders). Nine of the 19 Malagasy freshwater fish species kept in zoos have successfully reproduced within the 12 months preceding our survey. The ex situ conservation activities for threatened Malagasy freshwater fishes thus have not improved significantly since the strong start in the early 2000s. More than half of the 50 threatened endemic Malagasy freshwater fish species (viz. 31 species) are not kept ex situ, including 11 species ranked as Critically Endangered. Based on these findings we call for a better distribution of offspring among institutions, including private breeders in the framework of citizen conservation initiatives; a closer connection of ichthyological field research in Madagascar with conservation breeding efforts to set up ex situ populations—both in Madagascar and abroad—of species not yet kept in captivity; and the development of effective, integrated in situ and ex situ conservation strategies. RESEARCH HIGHLIGHTS: Of the 79 endemic Malagasy freshwater fish species 50 are ranked as threatened and only 19 kept in zoos worldwide.We propose an ex situ conservation breeding network for threatened Malagasy freshwater fish species linked with in situ strategies. [ABSTRACT FROM AUTHOR]

Climate change is considered to negatively affect vertebrate biodiversity. Lizards in tropical regions are considered particularly vulnerable due to their narrow temperature tolerances. The crocodile lizard Shinisaurus crocodilurus , an ecologically specialized semiaquatic species, is under the risk of extinction due to habitat loss and overharvesting. It is only found in isolated relict populations in southern China and northern Vietnam. Data on the thermal niche of the species are crucial to assess its vulnerability to climatic changes. We developed a backpack system with temperature data loggers for S. crocodilurus in order to monitor the lizard's temperature preferences in its natural habitat in Vietnam. We found that S. crocodilurus vietnamensis preferred a mean ambient temperature range of 24 ± 1°C (min-max: 22-31°C) at natural habitat sites, a far lower temperature amplitude compared to the recorded ambient temperature range at habitat sites. In its natural habitat, S. crocodilurus vietnamensis avoided in particular high temperatures, indicating the importance of constantly cool streams and intact vegetation for the provision of shade and shelter. We further provide first insights into the seasonal variation in microhabitat use and activity of S. crocodilurus vietnamensis based on data from individuals kept in outdoor enclosures under natural climatic conditions in Vietnam, collected daily over a period of eight months. Our results aim to aid further conservation measures for the species, such as the identification and protection of core habitat sites and sites for restocking, as well as to adjust and improve conservation breeding programs for the species. [ABSTRACT FROM AUTHOR]

Cellular redox, maintained by the glutathione (GSH)- and thioredoxin (Trx)-dependent systems, has been implicated in the regulation of a variety of biological processes. The redox state of the GSH system becomes oxidized when cells are induced to differentiate by chemical agents. The aim of this study was to determine the redox state of cellular GSH/glutathione disulfide (GSH/GSSG) and Trx as a consequence of progression from proliferation to contact inhibition and spontaneous differentiation in colon carcinoma (Caco-2) cells. Results showed a significant decrease in GSH concentration, accompanied by a 40-mV oxidation of the cellular GSH/GSSG redox state and a 28-mV oxidation of the extracellular cysteine/cystine redox state in association with confluency and increase in differentiation markers. The redox state of Trx did not change. Thus the two central cellular antioxidant and redox-regulating systems (GSH and Trx) were independently controlled. According to the Nernst equation, a 30-mV oxidation is associated with a 10-fold change in the reduced/oxidized ratio of a redox-sensitive dithiol motif. Therefore, the measured 40-mV oxidation of the cellular GSH/GSSG couple or the 28-mV oxidation of the extracellular cysteine/ cystine couple should be sufficient to function in signaling or regulation of differentiation in Caco-2 cells. oxidation-reduction; cysteine; cystine; intestine; cell cycle

Glutathione (GSH) has a central role in the maintenance of the thiol-disulfide redox state in mammalian cells. GSH synthesis can be physiologically limited by the availability of cysteine (Cys), and Cys and its precursors are variable in the human diet. The purpose of this study was to determine the effect of severe Cys deficiency and readdition of Cys on the redox state of the GSH/glutathione disulfide (GSSG) pool in human colon carcinoma HT29 cells. Cells were cultured in Cys- (and cystine-)limiting medium for 48 h followed by culture in medium containing either Cys or cystine for 24 h. GSH and GSSG were measured by HPLC. Cys limitation decreased cellular GSH and GSSG concentrations with an associated >80 mV oxidation of the GSH/GSSG redox state. Upon addition of either Cys or its disulfide cystine (CySS), redox of GSH/GSSG recovered in 4 h, whereas GSH concentration continued to increase over 12 h. Maximal GSH concentrations attained were 200% of control cell values. These results show that severe Cys deficiency can have marked effects on cellular redox state but that redox recovers rapidly upon resupply. The magnitude of oxidation during Cys limitation in this cell model is sufficient to result in a >100-fold change in the reduced/oxidized ratio of redox-sensitive dithiol/disulfide motifs in proteins. If redox changes occur in vive in association with variations in dietary Cys and its precursors, these changes could have important physiologic effects through altered redox signaling and control of cell proliferation and apoptosis. KEY WORDS: * glutathione * cysteine deficiency * redox * colon * oxidative stress

There is an acute need for effective therapy for inflammatory bowel disease (IBD), particularly at the level of repair of the damaged epithelium. We evaluated the efficacy of recombinant human keratinocyte growth factor (rHuKGF) in both the dextran sodium sulfate (DSS) and the [CD4.sup.+]CD45R[B.sup.Hi] T cell transfer models of IBD. Disease was induced either by the ad libitum administration to normal mice of 4% DSS in the drinking water or by the injection of 4 x [10.sup.5] [CD4.sup.+]CD45R[B.sup.Hi] T cells into immunodeficient scid/scid mice. rHuKGF was administered by subcutaneous injection at doses of 1.0 or 3.0 mg/kg in both preventative and therapeutic regimens during both studies. rHuKGF significantly improved survival and body weight loss in the DSS model in both preventative and therapeutic dosing regimens. It also improved diarrhea, hematochezia, and hematological parameters, as well as large intestine histopathology. In the T cell transfer model, rHuKGF improved body weight loss, diarrhea, and levels of serum amyloid A, as well as large intestine histopathology. In both models of IBD, the colonic levels of intestinal trefoil factor (ITF) were elevated by the disease state and further elevated by treatment with rHuKGF. These data suggest that rHuKGF may prove useful in the clinical management of IBD and its effects are likely mediated by its ability to locally increase the levels of ITF. colitis; growth factor; epithelial repair; intestinal trefoil factor