Syzygium aromaticum-derived triterpenes modulate intestinal glucose handling in streptozotocin-induced diabetic rats.

Ph. D. University of KwaZulu-Natal, Durban 2014.Polyphagia in diabetes mellitus ascribed to elevated plasma ghrelin concentrations is associated with prolonged postprandial hyperglycaemia due to increased activities of intestinal carbohydrate hydrolyzing enzymes and glucose transporters. Postprandial hyperglycaemia is a major risk factor in the development of diabetic complications, and as such, should be managed to prevent chronic vascular complications. Previous studies in our laboratory have shown that Syzygium aromaticum-derived oleanolic acid (OA) and maslinic acid (MA) use various mechanisms to lower blood glucose concentrations in experimental diabetes. The effects of these triterpenes, however, on intestinal glucose handling remain unknown. Accordingly, this study was designed to investigate the effects of these triterpenes on intestinal glucose handling in STZ-induced diabetic rats. Materials and methods OA and MA were extracted from Syzygium aromaticum cloves using a previously validated protocol. Briefly, S. aromaticum-derived OA and MA were sequentially extracted with dichloromethane and ethyl acetate to obtain ethyl acetate solubles which contained mixtures of OA/ursolic acid (UA) and methyl maslinate/methyl corosolate. These solubles were purified by silica gel 60 column chromatography with hexane: ethyl acetate solvent systems to produce OA and MA. The structures of these triterpenes were confirmed by using 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy and were comparable with those previously reported in literature. The in vitro studies investigated the inhibitory effects of OA and MA against enzymes such as α-amylase, α-glucosidase and sucrase. Additionally, the effects of various concentrations of OA and MA (0.82 - 6.56 mmol/L) on intestinal glucose transport were investigated using the everted intestinal sacs protocol. The in vivo studies investigated the effects of OA and MA on intestinal carbohydrate handling in separate groups of non-diabetic and STZdiabetic male Sprague Dawley rats. These studies were subdivided into oral glucose tolerance (OGT) responses which were carried out over two hours following loading with various carbohydrates as well as sub-chronic studies that were carried out over 5-weeks where the rats were kept on standard rat chow. OGT responses were monitored in separate groups of nondiabetic and STZ-induced diabetic animals the rats treated with OA and MA (80 mg/kg, p.o.). The rats were loaded with monosaccharides, disaccharides and polysaccharides after an 18-hour fast. The sub-chronic studies investigated the effects of the triterpenes on blood glucose concentrations over 5-weeks in groups of non-diabetic and STZ-induced diabetic male Sprague- Dawley rats. In those animals in which the effects of OA/MA were investigated, the rats were administered with OA/MA (80 mg/kg, p.o.) twice daily. Blood glucose, body weights as well as food and water intake were assessed every third day for the duration of the experimental period. At the end of the experimental period, the rats were killed and blood was collected for plasma insulin and ghrelin measurements. Furthermore, mid portions of the small intestine were snap frozen in liquid nitrogen and stored in a BioUltra freezer at -70 °C for Western blot analysis of glucose transporters, carbohydrate hydrolyzing enzymes and ghrelin expression. Additionally, the effects of OA and MA on intestinal oxidative stress were evaluated through malondealhyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GPx) measurements.Results The in vitro studies revealed that OA and MA possess inhibitory effects on the activity of α- amylase, α-glucosidase and sucrase comparable with those of the standard drug acarbose. In addition, OA and MA significantly (p<0.05) inhibited intestinal glucose transport in the everted intestinal sacs in a dose-independent manner. The OGT studies showed that OA and MA had no significant effects on blood glucose concentrations in non-diabetic rats loaded with the various carbohydrates by comparison with the non-diabetic control. However, the triterpene-treated STZdiabetic rats loaded with the various carbohydrate showed significant (p<0.05) reductions in blood glucose concentrations by comparison with untreated STZ-diabetic rats. OA and MA progressively reduced blood glucose concentration as well as food and water intake over the 5- week study in STZ-induced diabetic rats by comparison with untreated STZ-diabetic rats. Treatment with OA and MA had no effects on plasma insulin concentration in STZ-induced diabetic rats. However, these triterpenes significantly (p<0.05) reduced plasma ghrelin concentrations by comparison with untreated STZ-induced diabetic rats. Furthermore, rats treated with OA and MA showed significant (p<0.05) decreases in ghrelin, SGLT1, GLUT2, α- amylase and α-glucosidase expression in the gastrointestinal tract by comparison with untreated STZ-diabetic rats. This was accompanied by improvements in their intestinal antioxidant status as there were significant (p<0.05) reductions in MDA concentrations with significant (p<0.05) increases in SOD and GPx by comparison with the STZ-diabetic control. Additionally, OA and MA-treated rats showed significant (p<0.05) increases in intestinal glycogen concentrations with concomitant significant (p<0.05) increases in the intestinal expression of glycogen synthase by comparison with untreated STZ-diabetic animals. Discussion The results of the present study indicate that the blood glucose lowering effects of OA and MA in STZ -induced diabetic rats are mediated, in part, via modulating postprandial hyperglycaemia. These findings suggest that this is achieved through the ghrelin-mediated reduction in food intake leading to decreased expression of intestinal carbohydrate hydrolyzing enzymes as well as intestinal glucose transporters. This was followed by significant improvements in the antioxidant status in the rats suggesting that these triterpenes could, by preventing chronic postprandial hyperglycaemia, prevent the onset of the development of diabetic complications. The results of this study are of considerable importance as they suggest another mechanism for the anti-diabetic properties of the triterpenes and further explain the role of the gastrointestinal tract in the management of diabetes mellitus. Conclusion The results of the present study suggest that the S. aromaticum-derived triterpenes possess antidiabetic properties that arise, in part, through the modulation of intestinal glucose handling

The effects of obesity on thyroid function in a metabolically healthy high-fat, high-carbohydrate diet-induced obese rat model

IntroductionObesity is a recognized exacerbator of thyroid dysfunction due to its detrimental effects on energy homeostasis, appetite regulation, basal metabolic rate, thermogenesis, and metabolism. However, almost all the reported findings on obesity-related thyroid dysfunction are based on models of metabolically unhealthy obesity (MUO) in the presence of insulin resistance. There are currently no reported studies using a metabolically healthy obesity (MHO) model characterized by the absence of insulin resistance to investigate thyroid dysfunction. Hence, this study aimed to investigate the association between thyroid dysfunction and obesity in a metabolically healthy high-fat high-carbohydrate diet-induced obese rat model.Materials and methodsMale Sprague Dawley rats were randomly divided into either the control diet or the high-fat high-carbohydrate diet group (HFHC) (n=9, per group). During the 5-month induction period, the control group did not develop obesity while consuming a standard diet with water. The HFHC diet group consumed the HFHC diet and water for the same duration and was diagnosed with obesity. Post-obesity confirmation, the animals continued with the respective diets for a further 7 months to maintain the obese state. Caloric intake, fasting blood glucose (FBG) and BMI were measured once a month for the duration of the experiment. Glucose homeostasis and thyroid functional parameters were assessed terminally, accompanied by satiety and pro-inflammatory markers.ResultsThe HFHC diet group presented with higher BMI, caloric intake and FBG, and elevated insulin, HOMA-IR, Hb1Ac, leptin and IL-6 levels compared to the control diet group. The HFHC diet group presented with significantly elevated levels of TSH, fT3 and fT4. These observations suggest that thyroid homeostasis is disturbed in the obese state. However, the reported elevated glycemic status indicators and IL-6 concentrations in the HFHC diet group did not satisfy the minimum criteria to be characterized as MUO.ConclusionThe HFHC diet has induced MHO in male Sprague Dawley rats. This warrants using this model to investigate the homeostatic changes that occur during the metabolically healthy obese state. This can open new avenues for developing preventative measures to avoid progressing to MUO

THE EFFECTS OF SYZYGIUM AROMATICUM-DERIVED TRITERPENES ON GASTROINTESTINAL GHRELIN EXPRESSION IN STREPTOZOTOCIN-INDUCED DIABETIC RATS

Background: Diabetic polyphagia has been associated with elevated plasma ghrelin levels in experimental type 1 diabetes. This increase in food consumption contributes to chronic hyperglycaemia in diabetes thus contributing to the development of micro- and macrovascular complications.We have reported that plant-derived oleanolic acid (OA) and maslinic acid (MA) reduce blood glucose levels, in part, through the inhibition of intestinal carbohydrate hydrolyzing enzymes and glucose transporters. However, their effects on food intake and plasma ghrelin concentrations are unclear. Accordingly, we investigated the effects of these triterpenes on food intake and ghrelin expression in streptozotocin-induced diabetic rats. Material: The effects of OA and MA on blood glucose concentration; food and water intake were monitored over five weeks after which plasma ghrelin concentrations were measured. Additionally, the expression of ghrelin in the various sections of the GIT was determined using Western blot analysis. Results: Ghrelin concentrations in untreated STZ-induced diabetic rats were significantly higher in comparison to the non-diabetic control. Interestingly, the administration of OA and MA reduced food intake, blood glucose levels and plasma ghrelin levels in STZinduced diabetic rats. This was further complemented by significant reductions in the gastrointestinal expression of ghrelin suggesting that the anti-diabetic properties of these triterpenes are mediated, in part, through the reduction of food intake and the modulation of ghrelin expression. Conclusion: The findings of the study suggest that the control of food intake through the reduction of ghrelin expression by plantderived OA and MA may constitute an avenue of glycaemic control in diabetes mellitus

Glycaemic abnormalities induced by small molecule tryosine kinase inhibitors: a review

In light of the expected increase in the prevalence of diabetes mellitus due to an aging population, sedentary lifestyles, an increase in obesity, and unhealthy diets, there is a need to identify potential pharmacological agents that can heighten the risk of developing diabetes. Similarly, it is equally important to also identify those agents that show blood glucose-lowering properties. Amongst these agents are tyrosine kinase inhibitors used to treat certain types of cancers. Over the last two decades, there has been an increase in the use of targeted chemotherapy for cancers such as renal cell carcinoma, chronic leukaemia, and gastrointestinal stromal tumours. Small molecule tyrosine kinase inhibitors have been at the forefront of targeted chemotherapy. Studies have shown that small molecule tyrosine kinase inhibitors can alter glycaemic control and glucose metabolism, with some demonstrating hypoglycaemic activities whilst others showing hyperglycaemic properties. The mechanism by which small molecule tyrosine kinase inhibitors cause glycaemic dysregulation is not well understood, therefore, the clinical significance of these chemotherapeutic agents on glucose handling is also poorly documented. In this review, the effort is directed at mapping mechanistic insights into the effect of various small molecule tyrosine kinase inhibitors on glycaemic dysregulation envisaged to provide a deeper understanding of these chemotherapeutic agents on glucose metabolism. Small molecule tyrosine kinase inhibitors may elicit these observed glycaemic effects through preservation of β-cell function, improving insulin sensitivity and insulin secretion. These compounds bind to a spectrum of receptors and proteins implicated in glucose regulation for example, non-receptor tyrosine kinase SRC and ABL. Then receptor tyrosine kinase EGFR, PDGFR, and FGFR

Investigating the Effects of Gossypetin on Liver Health in Diet-Induced Pre-Diabetic Male Sprague Dawley Rats

The rising prevalence of non-alcoholic fatty liver disease among patients with type 2 diabetes mellitus has emerged as a global health challenge. Gossypetin (GTIN) is a natural flavonoid which has recently demonstrated antihyperglycaemic, antioxidant, and anti-inflammatory effects. Despite these findings, no studies have investigated its effects on liver health in the pre-diabetic state. Hence, this study aimed to investigate the effects of GTIN on liver health in diet-induced pre-diabetic male rats in the presence and absence of dietary intervention and to compare these effects with those of metformin (MET). Following 20 weeks of pre-diabetes induction, the animals were divided into six groups (n = 6) as follows: non-pre-diabetic (NPD) control, pre-diabetic (PD) control, and PD groups treated with GTIN (15 mg/kg body weight (bw)) or metformin (500 mg/kg bw) on either a normal diet or a high-fat, high-carbohydrate diet for 12 weeks. The results showed that the PD group had significantly higher liver triglycerides (TAG), liver weights, sterol regulatory binding element regulatory protein-1c (SREBP-1c), malondialdehyde (MDA) levels, and liver injury enzyme levels, along with decreased liver superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, and plasma bilirubin levels in comparison to NPD. Histologically, there was an increased lipid droplet accumulation and structural disarray in the PD group. GTIN treatment significantly reduced liver TAGs, liver weights, and plasma SREBP-1c levels, as well as improved liver SOD and GPx activity while decreasing liver MDA levels and liver injury enzymes in comparison to the PD control. Notably, GTIN treatment increased plasma bilirubin levels. Liver histology in the GTIN-treated groups revealed decreased lipid droplet accumulation and improved tissue integrity. Similar results were observed for the liver parameters in the MET-treated groups. The findings of this study may suggest that GTIN and MET exhibit therapeutic effects on liver health in diet-induced pre-diabetes in both the presence and absence of diet intervention. Dietary intervention may confer beneficial effects on liver health, with the most favorable therapeutic outcomes observed through a combination of treatment with dietary intervention. Additionally, GTIN may exhibit greater hepatoprotective effects than MET in rats without dietary intervention

Prediabetes-Associated Changes in Skeletal Muscle Function and Their Possible Links with Diabetes: A Literature Review

The skeletal muscle plays a critical role in regulating systemic blood glucose homeostasis. Impaired skeletal muscle glucose homeostasis associated with type 2 diabetes mellitus (T2DM) has been observed to significantly affect the whole-body glucose homeostasis, thereby resulting in other diabetic complications. T2DM does not only affect skeletal muscle glucose homeostasis, but it also affects skeletal muscle structure and functional capacity. Given that T2DM is a global health burden, there is an urgent need to develop therapeutic medical therapies that will aid in the management of T2DM. Prediabetes (PreDM) is a prominent risk factor of T2DM that usually goes unnoticed in many individuals as it is an asymptomatic condition. Hence, research on PreDM is essential because establishing diabetic biomarkers during the prediabetic state would aid in preventing the development of T2DM, as PreDM is a reversible condition if it is detected in the early stages. The literature predominantly documents the changes in skeletal muscle during T2DM, but the changes in skeletal muscle during prediabetes are not well elucidated. In this review, we seek to review the existing literature on PreDM- and T2DM-associated changes in skeletal muscle function

Investigating the Effects of Diet-Induced Prediabetes on Skeletal Muscle Strength in Male Sprague Dawley Rats

Type 2 diabetes mellitus, a condition preceded by prediabetes, is documented to compromise skeletal muscle health, consequently affecting skeletal muscle structure, strength, and glucose homeostasis. A disturbance in skeletal muscle functional capacity has been demonstrated to induce insulin resistance and hyperglycemia. However, the modifications in skeletal muscle function in the prediabetic state are not well elucidated. Hence, this study investigated the effects of diet-induced prediabetes on skeletal muscle strength in a prediabetic model. Male Sprague Dawley rats were randomly assigned to one of the two groups (n = 6 per group; six prediabetic (PD) and six non-pre-diabetic (NPD)). The PD group (n = 6) was induced with prediabetes for 20 weeks. The diet that was used to induce prediabetes consisted of fats (30% Kcal/g), proteins (15% Kcal/g), and carbohydrates (55% Kcal/g). In addition to the diet, the experimental animals (n = 6) were supplied with drinking water that was supplemented with 15% fructose. The control group (n = 6) was allowed access to normal rat chow, consisting of 35% carbohydrates, 30% protein, 15% fats, and 20% other components, as well as ordinary tap water. At the end of week 20, the experimental animals were diagnosed with prediabetes using the American Diabetes Association (ADA) prediabetes impaired fasting blood glucose criteria (5.6&ndash;6.9 mmol/L). Upon prediabetes diagnosis, the animals were subjected to a four-limb grip strength test to assess skeletal muscle strength at week 20. After the grip strength test was conducted, the animals were euthanized for blood and tissue collection to analyze glycated hemoglobin (HbA1c), plasma insulin, and insulin resistance using the homeostatic model of insulin resistance (HOMA-IR) index and malondialdehyde (MDA) concentration. Correlation analysis was performed to examine the associations of skeletal muscle strength with HOMA-IR, plasma glucose, HbA1c, and MDA concentration. The results demonstrated increased HbA1c, FBG, insulin, HOMA-IR, and MDA concentrations in the PD group compared to the NPD group. Grip strength was reduced in the PD group compared to the NPD group. Grip strength was negatively correlated with HbA1c, plasma glucose, HOMA-IR, and MDA concentration in the PD group. These observations suggest that diet-induced prediabetes compromises muscle function, which may contribute to increased levels of sedentary behavior during prediabetes progression, and this may contribute to the development of hyperglycemia in T2DM

Investigating the Effects of Gossypetin on Cardiovascular Function in Diet-Induced Pre-Diabetic Male Sprague Dawley Rats

Gossypetin (GTIN) is a naturally occurring flavonoid recognised for its pharmacological properties. This study examined the effects of GTIN on cardiovascular function in a diet-induced pre-diabetic rat model, which has not been previously studied. Pre-diabetes was induced using a high-fat high-carbohydrate (HFHC) diet supplemented with 15% fructose water for 20 weeks. Thereafter, the pre-diabetic animals were sub-divided into five groups (n = 6), where they were either orally treated with GTIN (15 mg/kg) or metformin (MET) (500 mg/kg), both in the presence and absence of dietary intervention for 12 weeks. The results demonstrated that the pre-diabetic (PD) control group exhibited significantly higher plasma triglyceride, total cholesterol, low-density lipoprotein and very low-density lipoprotein levels, along with decreased high-density lipoprotein (HDL) levels in comparison to the non-pre-diabetic (NPD) group. This was accompanied by significantly higher mean arterial pressure (MAP), body mass index (BMI), waist circumference (WC) and plasma endothelial nitric oxide (eNOS) levels in PD control. Additionally, there were increased heart malondialdehyde levels, reduced heart superoxide dismutase and glutathione peroxidase activity as well as increased plasma interleukin-6, tumour necrosis factor alpha and c-reactive protein levels present in the PD control group. Notably, both GTIN-treated groups showed significantly reduced plasma lipid levels and increased HDL, as well as decreases in MAP, BMI, WC and eNOS levels in comparison to PD control. Additionally, GTIN significantly decreased heart lipid peroxidation, enhanced antioxidant activity and decreased plasma inflammation markers. These findings may suggest that GTIN administration in both the presence and absence of dietary intervention may offer therapeutic potential in ameliorating cardiovascular disturbances associated with the PD state. However, future studies are needed to determine the physiological mechanisms by which GTIN improves cardiovascular function in the PD state