Evidence for Involvement of GIP and GLP-1 Receptors and the Gut-Gonadal Axis in Regulating Female Reproductive Function in Mice.

Substantial evidence suggests crosstalk between reproductive and gut-axis but mechanisms linking metabolism and reproduction are still unclear. The present study evaluated the possible role of glucose-dependent-insulinotropic-polypeptide (GIP) and glucagon-like-peptide-1 (GLP-1) in reproductive function by examining receptor distribution and the effects of global GIPR and GLP-1R deletion on estrous cycling and reproductive outcomes in mice. GIPR and GLP-1R gene expression were readily detected by PCR in female reproductive tissues including pituitary, ovaries and uterine horn. Protein expression was confirmed with histological visualisation of incretin receptors using GIPR-Cre and GLP1R-Cre mice in which the incretin receptor expressing cells were fluorescently tagged. Functional studies revealed that female GIPR-/- and GLP-1R-/- null mice exhibited significantly (p < 0.05 and p < 0.01) deranged estrous cycling compared to wild-type controls, indicative of reduced fertility. Furthermore, only 50% and 16% of female GIPR-/- and GLP-1R-/- mice, respectively produced litters with wild-type males across three breeding cycles. Consistent with a physiological role of incretin receptors in pregnancy outcome, litter size was significantly (p < 0.001-p < 0.05) decreased in GIPR-/- and GLP-1R-/- mice. Treatment with oral metformin (300 mg/kg body-weight), an agent used clinically for treatment of PCOS, for a further two breeding periods showed no amelioration of pregnancy outcome except that litter size in the GIPR-/- group was approximately 2 times greater in the second breeding cycle. These data highlight the significance of incretin receptors in modulation of female reproductive function which may provide future targets for pharmacological intervention in reproductive disorders.

Beneficial actions of esculentin-2CHa(GA30) on high sucrose-induced oxidative stress in Drosophila melanogaster.

Hyperglycaemia-induced oxidative stress plays a critical role in the development of diabetes and its complications. This study investigated actions of esculentin-2CHa(GA30) on high sucrose-induced oxidative stress in adult Drosophila melanogaster. Adult flies were exposed to diets containing graded concentrations of sucrose in the presence or absence of esculentin-2CHa(GA30) (5.0-10 µmol/kg diet) for 7 days. Effects of high sucrose diet and/or esculentin-2CHa(GA30) on survival and longevity of flies, and markers of oxidative stress, antioxidant status and glucose were assessed. High-sucrose diet (15-30%) and esculentin-2CHa(GA30) (5-10 µmol/kg diet) enhanced the percentage of surviving flies by 33.5%-46.2% (P < 0.01) and 7.4%-26.9% (P < 0.01) respectively. Concentration-dependent reduction in total thiol (19.3-51.3%, P < 0.01), reduced glutathione (22.6-54.9%, P < 0.05-0.01), catalase activity (36.8-57.3%, P < 0.05-0.01) and elevated glucose concentration (1.8-2.9-fold, P < 0.001) were observed in high sucrose-fed flies. Esculentin-2CHa(GA30) alone did not affect levels of total thiol, reduced glutathione, glucose and catalase activity. Improved survival (1.2-1.3-fold, P < 0.05-0.01) and longevity (1.3-fold) were observed in flies treated with the peptide (5.0 and 7.5 µmol/kg diet). Feeding on sucrose and esculentin-2CHa(1-30) (5.0 and 7.0 µmol/kg diet) for 7 days increased total thiol (2 - 3-fold, P < 0.001) and reduced glutathione (1.6-1.8-fold, P < 0.05) levels. Reduced catalase activity (21.4-36.4%, P < 0.01) and reduced glucose level (38.6-49.4%, P < 0.01) were observed in peptide-treated flies. Esculentin-2CHa(1-30) inhibited sucrose-induced generation of hydrogen peroxide (7.5-13.7%, P < 0.05) and nitric oxide (22.3-42.9%, P < 0.01) in adult flies. Overall, findings from this study offered further insights into the anti-oxidative properties of esculentin-2CHa(GA30).

Antidiabetic activities of chloroform fraction of Anthocleista vogelii Planch root bark in rats with diet- and alloxan-induced obesity-diabetes.

ETHNOPHARMACOLOGICAL RELEVANCE: Anthocleista vogelii Planch is a medicinal plant traditionally used in West Africa for the management and treatment of diabetes mellitus. AIM OF THE STUDY: To determine the antidiabetic activities of chloroform fraction (CF) of Anthocleista vogelii Planch root bark in rats with diet- and alloxan-induced obesity-diabetes. MATERIALS AND METHODS: Inhibitory activities of CF against α-amylase and α-glucosidase activities were determined in vitro. Three weeks old rats were fed with high-fat diet for 9 weeks to induce obesity prior to further induction of diabetes using alloxan (150 mg/kg body weight, i.p.). Blood glucose levels and body weight were measured every 7 days throughout the experiment. Glucose tolerance was assessed in normal and CF-treated rats on day 21. Terminal blood samples were collected from sacrificed animals for the measurement of serum insulin levels. Pancreases were excised from treated and untreated animals for histopathological examination. RESULTS: LCMS/MS chromatographic profile of CF via positive and negative modes revealed 13 and 23 compounds respectively. Further analysis revealed quebrachitol (QCT), loganin, sweroside, oleoside 11-methyl ester and ferulic acid, which have been previously reported for their antidiabetic activities, as constituents of CF. CF inhibited activities of α-amylase (IC50 = 51.60 ±â€¯0.92 µg/ml) and α-glucosidase (IC50 = 5.86 ±â€¯0.97 µg/ml) in a dose-dependent manner. Treatment of animals with obesity-diabetes with 100 and 200 mg/kg CF significantly improved glucose tolerance (P < 0.001) and enhanced serum insulin levels (P < 0.05) compared to diabetic control rats. CONCLUSIONS: Antidiabetic activities of CF might be mediated via inhibition of α-amylase and α-glucosidase activities, elevation of serum insulin concentration, and enhancement of insulin and leptin sensitivity in obesity-diabetes rats. This study further substantiates the traditional use of A. vogelii in the management and treatment of diabetes in Africa and encourages further studies to investigate its mechanism of action.

Anti-diabetic actions of esculentin-2CHa(1-30) and its stable analogues in a diet-induced model of obesity-diabetes.

Actions of esculentin-2CHa(1-30) (GFSSIFRGVAKFASKGLGKDLAKLGVDLVA) and its analogues, ([D-Arg7, D-Lys15, D-Lys23]-esculentin-2CHa(1-30) and [Lys15-octanoate]-esculentin-2CHa(1-30), were evaluated in high-fat fed NIH Swiss mice with impaired glucose tolerance and insulin resistance. Twice-daily i.p. administration of the esculentin-2CHa(1-30) peptides (75 nmol/kg body weight) or exendin-4 (25 nmol/kg) for 28 days reduced body weight, without altering cumulative energy intake. All peptides reduced blood glucose levels by 6-12 mmol/l concomitant with lower plasma insulin levels, with significance evident from day 6. All peptides improved glucose tolerance, insulin sensitivity, blood glucose profile over 24 h and decreased HbA1c to a similar extent as exendin-4. The peptides also reduced high fat diet-induced increases in plasma GLP-1 and glucagon. None of the peptides altered bone mineral density/content or lean mass but decreased fat mass. Islets isolated from peptide-treated mice exhibited improved glucose-, alanine- and GLP-1-stimulated insulin secretion. Islet morphometric analyses revealed that exendin-4 and the esculentin-2CHa(1-30) peptides significantly reduced islet, beta and alpha cell areas compared to high-fat controls. Esculentin-2CHa(1-30) peptides markedly reduced high fat diet-induced increase in beta cell proliferation and apoptosis. Peptide treatments had beneficial effects on expression of islet genes (Ins1, Slc2a2, Pdx1) and skeletal muscle genes involved in insulin action (Slc2a4, Pdk1, Irs1, Akt1). High-fat diet significantly increased LDL cholesterol which was reduced by the acylated esculentin-2CHa(1-30) analogue. Peptide treatments did not alter circulating concentrations of amylase and marker enzymes of liver function, indicating a lack of toxicity. These data indicate that esculentin-2CHa(1-30) and its analogues may be useful for improvement of blood glucose control and weight loss in type 2 diabetes.

Actions of PGLa-AM1 and its [A14K] and [A20K] analogues and their therapeutic potential as anti-diabetic agents.

PGLa-AM1 (GMASKAGSVL10GKVAKVALKA20AL.NH2) was first identified in skin secretions of the frog Xenopus amieti (Pipidae) on the basis of its antimicrobial properties. PGLa-AM1 and its [A14K] and [A20K] analogues produced a concentration-dependent stimulation of insulin release from BRIN-BD11 rat clonal ß-cells without cytotoxicity at concentrations up to 3 µM. In contrast, the [A3K] analogue was cytotoxic at concentrations ≥ 30 nM. The potency and maximum rate of insulin release produced by the [A14K] and [A20K] peptides were significantly greater than produced by PGLa-AM1. [A14K]PGLa-AM1 also stimulated insulin release from mouse islets at concentrations ≥ 1 nM and from the 1.1B4 human-derived pancreatic ß-cell line at concentrations > 30 pM. PGLa-AM1 (1 µM) produced membrane depolarization in BRIN-BD11 cells with a small, but significant (P < 0.05), increase in intracellular Ca2+ concentrations but the peptide had no direct effect on KATP channels. The [A14K] analogue (1 µM) produced a significant increase in cAMP concentration in BRIN-BD11 cells and down-regulation of the protein kinase A pathway by overnight incubation with forskolin completely abolished the insulin-releasing effects of the peptide. [A14K]PGLa-AM1 (1 µM) protected against cytokine-induced apoptosis (p < 0.001) in BRIN-BD11 cells and augmented (p < 0.001) proliferation of the cells to a similar extent as GLP-1. Intraperitoneal administration of the [A14K] and [A20K] analogues (75 nmol/kg body weight) to both lean mice and high fat-fed mice with insulin resistance improved glucose tolerance with a concomitant increase in insulin secretion. The data provide further support for the assertion that host defense peptides from frogs belonging to the Pipidae family show potential for development into agents for the treatment of patients with Type 2 diabetes.

Glucoregulatory, endocrine and morphological effects of [P5K]hymenochirin-1B in mice with diet-induced glucose intolerance and insulin resistance.

The frog skin host-defence peptide hymenochirin-1B has been shown to stimulate insulin release in vitro from isolated pancreatic islets and BRIN-BD11 clonal ß-cells. This study examines the effects of 28-day administration of a more potent analogue [P5K]hymenochirin-1B ([P5K]hym-1B) (75 nmol·kg(-1) body weight) to high-fat-fed mice with obesity, glucose intolerance and insulin resistance. Treatment with [P5K]hym-1B significantly decreased plasma glucose concentrations and improved glucose tolerance, insulin secretion, insulin sensitivity and increased the magnitude of the incretin effect (difference in response to oral vs intraperitoneal glucose loads). Responses to established insulin secretagogues were greater in islets isolated from treated animals compared with saline-treated controls. [P5K]hym-1B administration significantly decreased total islet area and ß- and α-cell areas, and resulted in lower concentrations of circulating triglycerides and plasma and pancreatic glucagon. Peptide treatment had no effect on food intake, body weight, indirect calorimetry or circulating concentrations of amylase and marker enzymes of liver and kidney function. RT-PCR demonstrated that the Insr (insulin receptor) gene and genes involved in insulin signalling (Slc2a4, Irs1, Pik3ca, Akt1 and Pkd1) were significantly up-regulated in skeletal muscle from animals treated with [P5K]hym-1B. Expression of the Glp1r (GLP-1 receptor) and Gipr (GIP receptor) genes was significantly elevated in islets from peptide-treated mice. These data suggest that [P5K]hym-1B shows potential for development into an agent for treating patients with type 2 diabetes.

Molecular mechanisms mediating the beneficial metabolic effects of [Arg4]tigerinin-1R in mice with diet-induced obesity and insulin resistance.

The frog skin host-defense peptide tigerinin-1R stimulates insulin release in vitro and improves glucose tolerance and insulin sensitivity in animal models of type 2 diabetes. This study extends these observations by investigating the molecular mechanisms of action underlying the beneficial metabolic effects of the analogue [Arg4]tigerinin-1R in mice with diet-induced obesity, glucose intolerance and insulin resistance. The study also investigates the electrophysiological effects of the peptide on KATP and L-type Ca2+ channels in BRIN-BD11 clonal ß cells. Non-fasting plasma glucose and glucagon concentrations were significantly (p<0.05) decreased and plasma insulin increased by twice daily treatment with [Arg4]tigerinin-1R (75 nmol/kg body weight) for 28 days. Oral and intraperitoneal glucose tolerance were significantly (p<0.05) improved accompanied by enhanced secretion and action of insulin. The peptide blocked KATP channels and, consistent with this, improved beta cell responses of isolated islets to a range of secretagogues. Peptide administration resulted in up-regulation of key functional genes in islets involved insulin secretion (Abcc8, Kcnj11, Cacna1c and Slc2a2) and in skeletal muscle involved with insulin action (Insr, Irs1, Pdk1, Pik3ca, and Slc2a4). These observations encourage further development of tigerinin-1R analogues for the treatment of patients with type 2 diabetes.

In vitro and in vivo insulinotropic properties of the multifunctional frog skin peptide hymenochirin-1B: a structure-activity study.

Hymenochirin-1b (Hym-1B; IKLSPETKDNLKKVLKGAIKGAIAVAKMV.NH2) is a cationic, α-helical amphibian host-defense peptide with antimicrobial, anticancer, and immunomodulatory properties. This study investigates the abilities of the peptide and nine analogues containing substitutions of Pro(5), Glu(6), and Asp(9) by either L-lysine or D-lysine to stimulate insulin release in vitro using BRIN-BD11 clonal ß cells or isolated mouse islets and in vivo using mice fed a high-fat diet to produce obesity and insulin resistance. Hym-1B produced a significant and concentration-dependent increase in the rate of insulin release from BRIN-BD11 cells without cytotoxicity at concentrations up to 1 µM with a threshold concentration of 1 nM. The threshold concentrations for the analogues were: [P5K], [E6K], [D9K], [P5K, E6K] and [E6K, D9k] 0.003 nM, [E6K, D9K] and [D9k] 0.01 nM, [P5K, D9K] 0.1 nM and [E6k] 0.3 nM. All peptides displayed cytotoxicity at concentrations ≥1 µM except the [P5K] and [D9k] analogues which were non-toxic at 3 µM. The potency and maximum rate of insulin release from mouse islets produced by the [P5K] peptide were significantly greater than produced by Hym-1B. Neither Hym-1B nor the [P5K] analogue at 1 µM concentration had an effect on membrane depolarization or intracellular Ca(2+). The [P5K] analogue (1 µM) produced a significant increase in cAMP concentration in BRIN-BD11 cells and stimulated GLP-1 secretion from GLUTag cells. Down-regulation of the protein kinase A pathway by overnight incubation with forskolin completely abolished the insulin-releasing effects of [P5K]hym-1B. Intraperitoneal administration of the [P5K] and [D9k] analogues (75 nmol/kg body weight) to high-fat-fed mice with insulin resistance significantly enhanced glucose tolerance with a concomitant increase in insulin secretion. We conclude that [P5K]hym-1B and [D9k]hym-1B show potential for development into anti-diabetic agents.

[I10W]tigerinin-1R enhances both insulin sensitivity and pancreatic beta cell function and decreases adiposity and plasma triglycerides in high-fat mice.

AIMS: We have previously described the insulinotropic activities of [I10W]tigerinin-1R (RVCSAIPLPWCH.NH2) in vitro. In this study, we investigated the effects of the peptide on nutrient homoeostasis in mice with diet-induced obesity and insulin resistance. METHODS: Male NIH Swiss mice were maintained on a high-fat diet for 12 weeks prior to the study. Twice-daily intraperitoneal injections of [I10W]tigerinin-1R (75 nmol/kg body weight) were administered for 28 days. Body weight, energy intake, body fat content, and plasma concentrations of triglyceride, cholesterol, non-fasting glucose and insulin were monitored. Effects of the peptide on glycaemic control were measured by glucose tolerance and insulin sensitivity tests. Pancreatic hormone content and insulin secretory responses of islets isolated from treated and untreated mice were examined. Immunohistochemical analysis was performed to study possible changes in islet morphology. RESULTS: Administration of [I10W]tigerinin-1R to high-fat-fed mice produced significant (P < 0.05) decreases in plasma glucose, glucagon and triglyceride concentrations and an increase in plasma insulin compared to high-fat-fed controls. No changes in body weight or energy intake were observed with peptide treatment, but glycaemic control was significantly improved in response to oral or intraperitoneal glucose. Insulin sensitivity and secretory responses of islets to established insulin secretagogues were also significantly improved in peptide-treated mice. Total body fat, pancreatic insulin and glucagon contents, islet, beta and alpha cell areas were all significantly decreased in treated mice. CONCLUSIONS: This study shows that [I10W]tigerinin-1R improves insulin sensitivity, islet function and glycaemic control in high-fat-fed mice and has potential as a template for development of novel anti-diabetic agents.

Esculentin-2CHa-Related Peptides Modulate Islet Cell Function and Improve Glucose Tolerance in Mice with Diet-Induced Obesity and Insulin Resistance.

The frog skin host-defense peptide esculentin-2CHa (GFSSIFRGVA10KFASKGLGK D20LAKLGVDLVA30CKISKQC) displays antimicrobial, antitumor, and immunomodulatory properties. This study investigated the antidiabetic actions of the peptide and selected analogues. Esculentin-2CHa stimulated insulin secretion from rat BRIN-BD11 clonal pancreatic ß-cells at concentrations greater than 0.3 nM without cytotoxicity by a mechanism involving membrane depolarization and increase of intracellular Ca2+. Insulinotropic activity was attenuated by activation of KATP channels, inhibition of voltage-dependent Ca2+ channels and chelation of extracellular Ca2+. The [L21K], [L24K], [D20K, D27K] and [C31S,C37S] analogues were more potent but less effective than esculentin-2CHa whereas the [L28K] and [C31K] analogues were both more potent and produced a significantly (P < 0.001) greater maximum response. Acute administration of [L28K]esculentin-2CHa (75 nmol/kg body weight) to high fat fed mice with obesity and insulin resistance enhanced glucose tolerance and insulin secretion. Twice-daily administration of this dose of [L28K]esculentin-2CHa for 28 days had no significant effect on body weight, food intake, indirect calorimetry or body composition. However, mice exhibited decreased non-fasting plasma glucose (P < 0.05), increased non-fasting plasma insulin (P < 0.05) as well as improved glucose tolerance and insulin secretion (P < 0.01) following both oral and intraperitoneal glucose loads. Impaired responses of isolated islets from high fat fed mice to established insulin secretagogues were restored by [L28K]esculentin-2CHa treatment. Peptide treatment was accompanied by significantly lower plasma and pancreatic glucagon levels and normalization of α-cell mass. Circulating triglyceride concentrations were decreased but plasma cholesterol and LDL concentrations were not significantly affected. The data encourage further investigation of the potential of esculentin-2CHa related peptides for treatment of patients with type 2 diabetes.

The frog skin host-defense peptide CPF-SE1 improves glucose tolerance, insulin sensitivity and islet function and decreases plasma lipids in high-fat fed mice.

The frog skin host-defense peptide CPF-SE1 has previously been shown to stimulate the in vitro release of insulin from clonal BRIN-BD11 ß-cells. In this study, the in vivo effects of the peptide were investigated in male NIH Swiss mice maintained on a high-fat diet to induce obesity and insulin resistance. Insulin-secretory responses of islets isolated from treated and untreated mice and changes in islet morphology were also examined. Total body fat, plasma glucagon, triglyceride and cholesterol concentrations were measured at the end of the treatment period. Acute intraperitoneal administration of CPF-SE1 (75 nmol body weight) to high-fat fed mice together with glucose (18 mmol/kg body weight) improved glucose tolerance and insulin responses compared to high-fat fed controls. Long term administration of CPF-SE1 (twice-daily administration of 75 nmol/kg body weight for 28 days) did not affect body weight or energy intake but decreased circulating glucose and increased insulin concentrations. Insulin sensitivity and insulin-secretory responses of islets to secretagogues were also significantly improved at 28 days in peptide-treated mice. In addition, significant decreases in plasma glucagon concentrations, pancreatic insulin and glucagon content, islet and beta cell area, body fat and plasma triglyceride levels were observed in CPF-SE1 treated with mice. In conclusion, CPF-SE1 improves beta cell function, insulin sensitivity and glycaemic control whilst reducing total body fat and circulating triglyceride levels. The peptide shows potential for development into an agent for treatment of patients with metabolic syndrome and type 2 diabetes.

Methanolic extract of Moringa oleifera leaves improves glucose tolerance, glycogen synthesis and lipid metabolism in alloxan-induced diabetic rats.

BACKGROUND: Glucose-lowering effects of Moringa oleifera extracts have been reported. However, the mechanism for its hypoglycemic effects is not yet understood. This study investigated the effect of oral administration of methanolic extracts of M. oleifera (MOLE) on glucose tolerance, glycogen synthesis, and lipid metabolism in rats with alloxan-induced diabetes. METHODS: MOLE was screened for key phytochemicals and its total flavonoids and phenolic contents were quantified. Diabetes was induced by intraperitoneal injection of 120 mg/kg BW alloxan. Normal and diabetic control rats received saline, while rats in other groups received 300 or 600 mg/kg body weight of MOLE or metformin (100 mg/kg body weight of metformin) for 6 weeks. Food intake and body weight were monitored throughout the experiment. Intraperitoneal glucose tolerance was assessed and serum glucose, insulin, and lipids were measured at the end of the experiment. Liver and muscle glycogen synthase activities, glycogen content, and glucose uptake were determined. RESULTS: Administration of MOLE did not affect food intake but inhibited weight loss, significantly (p<0.01) improved glucose tolerance, and increased serum insulin levels by 1.3-1.7-fold (p<0.01). MOLE treatment significantly (p<0.001) reduced serum concentrations of triglyceride, total cholesterol, and low-density lipoprotein (LDL)-cholesterol and enhanced serum level of high-density lipoprotein (HDL) by 2.4- to 3.2-fold (p<0.001). Glycogen synthase activities and glycogen contents were higher in MOLE-treated rats compared with rats receiving metformin or saline and the extract improved glucose uptake by 49%-59% (p<0.01). CONCLUSIONS: These results showed that hypoglycemic effects of MOLE might be mediated through the stimulation of insulin release leading to enhanced glucose uptake and glycogen synthesis.

The impact of vitamin D deficiency on patients undergoing kidney transplantation: focus on cardiovascular, metabolic, and endocrine outcomes.

Vitamin D deficiency is common among kidney transplant (KT) recipients because of reduced sunlight exposure, low intake of vitamin D, the immunosuppressive drug regimen administered, and steroid therapy. Glucocorticoids regulate expression of genes coding for enzymes that catabolize vitamin D, further reducing its level in serum. Although vitamin D primarily regulates calcium homeostasis, vitamin D deficiency is associated with the risk of several diseases, such as diabetes mellitus and tuberculosis. Aim of this review is to highlight endocrine and metabolic alterations due to the vitamin D deficiency by evaluating the mechanisms involved in the development of KT-related disease (cardiovascular, bone mineral density, and new-onset diabetes after transplantation). Next, we review evidence to support a link between low vitamin D status and KT-related diseases. Finally, we briefly highlight strategies for restoring vitamin D status in KT patients.

Beneficial effects of tigerinin-1R on glucose homeostasis and beta cell function in mice with diet-induced obesity-diabetes.

AIMS: This paper investigates the anti-diabetic effects of tigerinin-1R (RVCSAIPLPICH.NH2), a previously described amphibian host defence peptide, in mice with diet-induced obesity-diabetes. METHODS: Proteolytic degradation of synthetic tigerinin-1R was investigated by reversed-phase HPLC and MALDI-TOF mass spectrometry. Changes in glycaemic responses and metabolic parameters were measured in mice with high fat diet-induced obesity-diabetes treated with twice-daily with of tigerinin-1R (75 nmol/kg bw) for 15 days. Indirect calorimetry and body composition were measured by CLAMS and DEXA whole body scanning. Insulin secretory responses of islets isolated from treated and untreated mice were examined. RESULTS: Tigerinin-1R was resistant to in vitro degradation by plasma enzymes. Twice-daily injection of tigerinin-1R for 15 days had no significant effect on food intake or body weight. Non-fasting glucose levels were significantly lowered, and insulin levels were elevated compared to saline treated controls. Glycaemic responses to both oral and intraperitoneal glucose administration were significantly improved by tigerinin-1R treatment. Plasma insulin was also significantly elevated. The peptide had no significant effect on insulin sensitivity but the beta cell responses of islets isolated from treated mice to a range of nutrients and peptidergic secretagogues were significantly improved. Oxygen consumption, CO2 production, respiratory exchange ratio, energy expenditure and body composition were not significantly altered by treatment with tigerinin-1R. CONCLUSION: Tigerinin-1R significantly improves glucose homeostasis and may have potential as a novel antidiabetic agent.

Computational biology and bioinformatics in Nigeria.

Over the past few decades, major advances in the field of molecular biology, coupled with advances in genomic technologies, have led to an explosive growth in the biological data generated by the scientific community. The critical need to process and analyze such a deluge of data and turn it into useful knowledge has caused bioinformatics to gain prominence and importance. Bioinformatics is an interdisciplinary research area that applies techniques, methodologies, and tools in computer and information science to solve biological problems. In Nigeria, bioinformatics has recently played a vital role in the advancement of biological sciences. As a developing country, the importance of bioinformatics is rapidly gaining acceptance, and bioinformatics groups comprised of biologists, computer scientists, and computer engineers are being constituted at Nigerian universities and research institutes. In this article, we present an overview of bioinformatics education and research in Nigeria. We also discuss professional societies and academic and research institutions that play central roles in advancing the discipline in Nigeria. Finally, we propose strategies that can bolster bioinformatics education and support from policy makers in Nigeria, with potential positive implications for other developing countries.

Insulin-releasing and cytotoxic properties of the frog skin peptide, tigerinin-1R: a structure-activity study.

The frog skin host-defense peptide tigerinin-1R (RVCSAIPLPICH.NH2) is insulinotropic both in vitro and in vivo. This study investigates the effects on insulin release and cytotoxicity of changes in cationicity and hydrophobicity produced by selected substitutions of amino acids by l-arginine, l-lysine and l-tryptophan. The [A5W], [L8W] and [I10W] analogs produced a significant (P<0.01) increase in the rate of insulin release from BRIN-BD11 rat clonal ß cells at concentration of 0.01 nM compared with 0.1 nM for tigerinin-1R. The increase in the rate of insulin release produced by a 3 µM concentration of the [S4R], [H12K], and [I10W] analogs from both BRIN-BD11 cells and mouse islets was significantly greater (P<0.05) than that produced by tigerinin-1R. No peptide stimulated the release of lactate dehydrogenase at concentrations up to 3 µM indicating that plasma membrane integrity had been preserved. [A5W] tigerinin-1R was the only analog tested that showed cytotoxic activity against human erythrocytes (LC50=265 ± 16 µM) and inhibited growth of Escherichia coli (MIC=500 µM) and Staphylococcus aureus (MIC=250 µM). The circular dichroism spectra of tigerinin-1R and [A5W] tigerinin-1R indicate that the peptides adopt a mixture of ß-sheet, random coil and reverse ß-turn conformations in 50% trifluoroethanol/water and methanol/water. Administration of [S4R] tigerinin-1R (75 nmol/kg body weight) to high-fat fed mice with insulin resistance significantly (P<0.05) enhanced insulin release and improved glucose tolerance over a 60 min period following an intraperitoneal glucose load. The study supports the claim that tigerinin-1R shows potential for development into novel therapeutic agents for treatment of type 2 diabetes mellitus.

Insulinotropic actions of the frog skin host-defense peptide alyteserin-2a: a structure-activity study.

Alyteserin-2a (ILGKLLSTAAGLLSNL.NH2 ) stimulated the rate of insulin release from BRIN-BD11 clonalß cells at a concentration of 30 nm (p < 0.05) with a response of 296 ± 26% of basal release at 3 µm (p < 0.001). The insulinotropic actions of analogs containing substitutions by l-lysine, d-lysine, or l-tryptophan at sites that maintain amphipathicity were evaluated. The [G11K], [S7k], [S7k,G11k], and [G11k,N15K] analogs were the most potent stimulating insulin release at 0.01 nm (p < 0.05). The [S7K], [G11K], [S14K], [N15K], [G11k], and [S7K,G11K] analogs were the most effective producing an approximately twofold greater (p < 0.001) release of insulin at 3 µm compared with alyteserin-2a. The [T8W] and [A9W] analogs were less active than alyteserin-2a. No peptide-stimulated release of lactate dehydrogenase at concentrations up to 3 µm, indicating that the integrity of the plasma membrane had been preserved. Membrane depolarization and an increase in intracellular Ca(2+) concentration are involved in the mechanism of action of the peptides. Administration of [G11k]alyteserin-2a (75 nmol/kg body weight) to high-fat-fed mice with obesity and insulin resistance significantly (p < 0.01) enhanced insulin release and improved glucose tolerance during the 60-min period following an intraperitoneal glucose load.

Caerulein-and xenopsin-related peptides with insulin-releasing activities from skin secretions of the clawed frogs, Xenopus borealis and Xenopus amieti (Pipidae).

Caerulein-related peptides were identified in norepinephrine-stimulated skin secretions of the tetraploid frog Xenopus borealis and the octoploid frog Xenopus amieti using negative ion electrospray mass spectrometry and their primary structures determined by positive ion tandem (MS/MS) mass spectrometry. X. borealis caerulein-B1 (pGlu-Gln-Asp-Tyr(SO(3))-Gly-Thr-Gly-Trp-Met-Asp-Phe.NH2) contains an additional Gly(5) residue compared with X. laevis caerulein and caerulein-B2 (pGlu-Asp-Tyr(SO(3))-Thr-Gly-Trp-Met-Asp-Phe.NH2) contains a Gln(2) deletion. X. amieti caerulein was identical to the X. laevis peptide. In addition, xenopsin, identical to the peptide from X. laevis, together with xenopsin-AM2 (pGlu-Gly-Arg-Arg-Pro-Trp-Ile- Leu) that contains the substitution Lys(3)→Arg were isolated from X. amieti secretions. X. borealis caerulein-B1, and X. amieti xenopsin and xenopsin-AM2 produced significant (P<0.05) and concentration-dependent stimulations of insulin release from the rat BRIN-BD11 clonal ß cell line at concentrations ⩾30nM. The peptides did not stimulate the release of lactate dehydrogenase at concentrations up to 3µM demonstrating that the integrity of the plasma membrane had been preserved. While their precise biological role is unclear, the caerulein- and xenopsin-related peptides may constitute a component of the animal's chemical defenses against predators.

Peptidomic analysis of skin secretions from the bullfrog Lithobates catesbeianus (Ranidae) identifies multiple peptides with potent insulin-releasing activity.

Using a combination of reversed-phase HPLC and electrospray mass spectrometry, peptidomic analysis of norepinephrine-stimulated skin secretions of the American bullfrog Lithobates catesbeianus Shaw, 1802 led to the identification and characterization of five newly described peptides (ranatuerin-1CBb, ranatuerin-2CBc, and -CBd, palustrin-2CBa, and temporin-CBf) together with seven peptides previously isolated on the basis of their antimicrobial activity (ranatuerin-1CBa, ranatuerin-2CBa, brevinin-1CBa, and -1CBb, temporin-CBa, -CBb, and -CBd). The abilities of the most abundant of the purified peptides to stimulate the release of insulin from the rat BRIN-BD11 clonal ß cell line were evaluated. Ranatuerin-2CBd (GFLDIIKNLGKTFAGHMLDKIRCTIGTCPPSP) was the most potent peptide producing a significant stimulation of insulin release (119% of basal rate, P<0.01) from BRIN-BD11 cells at a concentration of 30nM, with a maximum response (236% of basal rate, P<0.001) at a concentration of 3µM. Ranatuerin-2CBd did not stimulate release of the cytosolic enzyme, lactate dehydrogenase at concentrations up to 3µM, indicating that the integrity of the plasma membrane had been preserved. Brevinin-1CBb (FLPFIARLAAKVFPSIICSVTKKC) produced the maximum stimulation of insulin release (285% of basal rate, P<0.001 at 3µM) but the peptide was cytotoxic at this concentration.