Antihyperglycemic effect of extra virgin sacha inchi oil in type 2 diabetic rats: Mechanisms involved in pancreatic ß-cell function and apoptosis.

Background and aim: The purpose of the study was to investigate the anti-hyperglycemic effect of extra virgin sacha inchi oil (EVSIO) and its possible mechanisms and actions against pancreatic ß-cell death and dysfunction in type 2 diabetic (T2D) rats. Experimental procedure: T2D rats were induced with a high-fat diet and low-dose of streptozotocin. The rats were then treated for 5 weeks with EVSIO (0.5, 1, and 2 ml/kg), or pioglitazone. Biochemical and histopathological studies, oxidative and inflammatory markers, and expression of apoptotic-related proteins were then evaluated. Results: EVSIO treatment exhibited a dose-dependent reduction of fasting blood glucose, area under the curve of glucose, total cholesterol, and triglyceride levels in the diabetic rats, while improved pancreatic ß-function was demonstrated by increasing pancreatic and serum insulin levels. EVSIO treatment effectively lowered atrophic pancreatic islets and reduced the level of serum and pancreatic MDA in the diabetic rats. In addition to serum and pancreatic GPx activities in the diabetic rats, EVSIO also augmented serum SOD. Increased levels of NF-κB, TNF-α and IL-6 present in the diabetic rats were greatly reduced by EVSIO treatment. Furthermore, EVSIO revealed an anti-apoptotic effect on the diabetic rat pancreas by upregulating Bcl-2, and downregulating Bax and cleaved caspase-3 protein expression. Conclusion: The overall study results demonstrated the potential anti-hyperglycemic effect of EVSIO in the diabetic rats. The beneficial effects of EVSIO may be attributed to its ability to improve pancreatic ß-cell function and ameliorate ß-cell apoptosis by inhibiting oxidative stress and inflammatory cytokines.

Mango (Mangifera indica L.) seed kernel extract suppresses hyperglycemia by modulating pancreatic ß cell apoptosis and dysfunction and hepatic glucose metabolism in diabetic rats.

This study investigated the anti-hyperglycemic action of mango seed kernel extract (MKE) and various mechanisms involved in its actions to improve pancreatic ß cells and hepatic carbohydrate metabolism in diabetic rats. An intraperitoneal injection of 60 mg/kg of streptozotocin (STZ) followed by 30 consecutive days of treatment with MKE (250, 500, and 1000 mg/kg body weight) was used to establish a study group of diabetic rats. Using liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS) for identification, 26 chemical compounds were found in MKE and the high-performance liquid chromatography (HPLC) analysis of the MKE also revealed the existence of mangiferin, gallic acid, and quercetin. The results confirmed that in each diabetes-affected rat, MKE mitigated the heightened levels of fasting blood glucose, diabetic symptoms, glucose intolerance, total cholesterol (TC), and low-density lipoprotein-cholesterol (LDL-C). As demonstrated by a remarkable increment in serum and pancreatic insulin, the diabetic pancreatic ß cell function was potentiated by treating with MKE. The effect of MKE on diabetic pancreatic apoptosis clearly reduced the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells, which was related to diminished levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and Bax and an increase in Bcl-xL protein expression. Furthermore, diabetes-induced liver damage was clearly ameliorated along with a notable reduction in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and abnormal liver histology. By enhancing anti-oxidant superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, MKE alleviated diabetes-induced pancreatic and liver oxidative damage, as demonstrated by diminished levels of malondialdehyde. In minimizing the expression levels of glucose 6-phosphatase and phosphoenolpyruvate carboxykinase-1 proteins in the diabetic liver, MKE also enhanced glycogen content and hexokinase activity. Collectively, these findings indicate that by suppressing oxidative and inflammatory processes, MKE exerts a potent anti-hyperglycemic activity in diabetic rats which serve to protect pancreatic ß cell apoptosis, enhance their function, and improve hepatic glucose metabolism.

Sacha Inchi (Plukenetia volubilis L.) Oil Improves Hepatic Insulin Sensitivity and Glucose Metabolism through Insulin Signaling Pathway in a Rat Model of Type 2 Diabetes.

This study aimed to evaluate the role of sacha inchi oil (SI) in alleviating hepatic insulin resistance and improving glucose metabolism by inhibiting oxidative stress and inflammation in a rat model of type 2 diabetes. This model was established by providing a high-fat diet and streptozotocin to the rats, thereby inducing diabetes. The diabetic rats were treated orally with 0.5, 1, and 2 mL/kg body weight (b.w.) of SI or 30 mg/kg b.w. of pioglitazone daily for 5 weeks. Blood and hepatic tissues were used for insulin sensitivity, carbohydrate metabolism, oxidative stress, and inflammatory status assessment. Treatment with SI attenuated hyperglycemia and insulin resistance indices, and improved hepatic histopathological alterations in the diabetic rats in a dose-dependent manner, which is correlated with the decreased serum levels of the liver enzymes, alanine transaminase and aspartate transaminase. SI significantly diminished the hepatic oxidative status of the diabetic rats by inhibiting malondialdehyde and enhancing the antioxidant superoxide dismutase, catalase, and glutathione peroxidase activities. Moreover, pro-inflammatory cytokine levels, including tumor necrosis factor-α and interleukin-6, in the liver of the diabetic rats were significantly decreased by the SI. Furthermore, SI treatment enhanced the hepatic insulin sensitivity of the diabetic rats, as shown by the increased insulin receptor substrate-1 and p-Akt protein expression, decreased phosphoenolpyruvate carboxykinase-1 and glucose-6-phospatase protein expression, and increased hepatic glycogen content. Overall, these findings suggest that SI exerts a potential hepatic insulin-sensitizing effect and an improvement in glucose metabolism in the type 2 diabetic rats, at least in part through enhancing insulin signaling, antioxidant defense, and inhibiting inflammation.

Protective role of hesperidin against diabetes induced spleen damage: Mechanism associated with oxidative stress and inflammation.

Diabetes mellitus is a metabolic disease affecting various organs, including the spleen and is characterized by chronic hyperglycemia. Oxidative and inflammatory stress are key mediators in the development of spleen damage caused by diabetes. This study aimed to examine the splenoprotective effect of hesperidin and the mechanisms underlying its capacity to reduce oxidative stress and inflammation-mediated spleen damage in diabetes. The diabetic rats used in this study were induced with a 65 mg per kg body weight of streptozotocin. This was followed by 4 weeks of continuous daily dosage of hesperidin treatment at 100 mg/kg body weight. The results showed that hesperidin improved spleen weight and histopathological alterations in the diabetic rats. The hesperidin-treated diabetic group showed a marked induction of SOD and GPx enzymes and moderated malondialdehyde level. This was in addition to an obvious decrease in the levels of TNF-α and NF-ᴋB in the diabetic rat spleen. Through a remarkable upregulation in Bcl-xL and downregulation in Bax and cleaved caspase-3 proteins, hesperidin supplementation rescued splenic cell apoptosis in the diabetic rats. These findings demonstrate the effectiveness of hesperidin in helping regulate Bcl-2 family proteins and inhibiting the oxidative stress and inflammatory status of hyperglycemia-mediated spleen apoptosis. PRACTICAL APPLICATIONS: Diabetes-related spleen damage increases immune dysfunction, which often results in the heightened risks of infection, morbidity and mortality in diabetic patients. In this work, hesperidin was used in the treatment of rats with diabetes-induced splenic damage. The results were highly encouraging with hesperidin consistently presenting beneficial antioxidant and anti-inflammatory qualities and splenoprotective effect. Research outcomes support the notion that hesperidin treatment could be considered a good strategy for the prevention of diabetic complications in the spleen.

Effects of Cultured Cordycep militaris on Sexual Performance and Erectile Function in Streptozotocin-Induced Diabetic Male Rats.

Cordyceps militaris (CM), a valuable edible and medicinal fungus, has been used as traditional medicine to treat health conditions, as well as hyposexuality in Asian societies for over a century. Due to the high demand, several artificial cultivation methods have been developed for their biological activities. In this study, CM was cultured on medium that contained white rice and silkworm pupae, and the levels of cordycepin and adenosine, as well as its aphrodisiac effects in diabetes-induced erectile dysfunction (DIED), were evaluated. Diabetic rats were induced by streptozotocin (STZ) injection and administered orally with CM (0.1, 0.5, and 1.0 g/kg BW/day) for 3 weeks. Diabetic rats in negative and positive control groups received vehicle and sildenafil citrate (5 mg/kg), respectively. Results showed the changes in mating behaviour in which mount latency and intromission latency were significantly increased in diabetic rats, compared with the normal control group. Diabetic rats also showed a significant reduction in intracavernosal pressure (ICP) response to cavernous nerve stimulation, sperm count, testosterone level, penile nitric oxide synthase (NOS), and testicular superoxide dismutase (SOD) activities, when compared to the normal control group. Administration of CM (0.1, 0.5, and 1.0 g/kg BW/day) reversed the effects of diabetes on the mating behaviour, and the ICP responses to electrical stimulation. Moreover, the levels of penile NOS, testicular SOD activities, testosterone, and sperm count were significantly increased, and testicular malondialdehyde (MDA) levels were significantly decreased in these treated diabetic rats. Diabetic rats treated with sildenafil showed a significant induction in intromission frequency and NOS and SOD activities, as well as a marked increase in ICP responses. These results suggest that CCM exerts its aphrodisiac effect, possibly through activating testosterone production and suppressing oxidative stress to enhance erectile function in diabetic rats.

Hesperidin ameliorates pancreatic ß-cell dysfunction and apoptosis in streptozotocin-induced diabetic rat model.

AIMS: The current study was conducted to investigate the potential protective effects of hesperidin and its possible mechanisms of action on pancreatic ß-cells in diabetes. MAIN METHODS: Male Sprague Dawley rats were made diabetic using 65 mg/kg intraperitoneal injection of streptozotocin, and then administered daily with 100 mg/kg of hesperidin over 4 weeks. On conclusion of the experiment, blood and pancreatic tissue were collected to determine the function of ß-cells, apoptosis, oxidative stress, ER stress, and inflammation. KEY FINDINGS: Treatment of diabetic rats with hesperidin, significantly decreased fasting blood glucose and food intake, along with increased body weight, serum and pancreatic insulin levels, and pancreatic-duodenal homeobox-1 (PDX-1) protein expression. The beneficial roles of hesperidin on diabetic pancreatic ß-cells exhibited an increment in antioxidant SOD and GPx activities, and a decrement in nitrotyrosine as well as malondialdehyde (MDA) levels. Additionally, the elevated concentration of TNF-α and expressions of ER stress maker GRP78 and CHOP proteins in the pancreas of diabetic rats were significantly diminished by hesperidin treatment. Furthermore, hesperidin effectively modulated expressions of apoptosis-regulatory proteins in diabetic rat pancreas, as revealed by upregulating anti-apoptotic Bcl-xL; with a concomitant downregulating pro-apoptotic Bax, cleaved caspase-3, and inhibiting the activation of DNA repair protein poly (ADP-ribose) polymerase (PARP). SIGNIFICANCE: Collectively, these findings suggest that hesperidin may have the potential to protect pancreatic ß-cells and improve their function by suppressing oxidative and ER stress, along with activating its antioxidant, anti-inflammatory, and anti-apoptotic effects.

Protective effect of wax apple (Syzygium samarangense (Blume) Merr. & L.M. Perry) against streptozotocin-induced pancreatic ß-cell damage in diabetic rats.

The purpose of this study was to investigate the protective properties and mechanisms of wax apple (Syzygium samarangense (Blume)) against streptozotocin (STZ)-induced pancreatic ß-cell apoptosis in diabetic rats. Diabetes was induced by STZ (65 mg/kg; i.p.) injection and wax apple (100 mg/kg) was orally administered to diabetic rats for a period of 30 days. During this time, fasting blood glucose (FBG) and body weight were measured weekly. At the end of the experiment, serum insulin, HOMA-B, and pancreatic insulin expression were assessed. The expression of apoptosis-related proteins along with the nitrotyrosine level, antioxidant activities, and pro-inflammatory cytokine TNF-α in the pancreas were also determined. STZ-induced diabetic rats exhibited an increase in FBG, and a decrease in body weight, serum and pancreatic insulin, as well as HOMA-B. Pancreatic apoptosis was noted in diabetic rats and indicated by enhancing the expression of cleaved caspase-3 and Bax proteins and downregulating the expression of Bcl-2 and Bcl-xl proteins. The activities of antioxidant CAT and SOD in the pancreas of the diabetic rats was also reduced. Importantly, wax apple treatment resulted in a significant reduction of FBG and increased body weight in diabetic rats. Wax apple also improved pancreatic ß-cell function, this was clearly evidenced by increased HOMA-B and pancreatic and serum insulin levels in diabetic rats. Moreover, pancreatic ß-cell apoptosis was alleviated with significantly down-regulated cleaved caspase-3 and Bax protein expression, and upregulated Bcl-2 and Bcl-xl protein expression in wax apple treated diabetic rats. These were related to the induction of CAT and SOD activities, and reduction of nitrotyrosine and TNF-α levels in wax apple administration. Overall, these results provide evidence that wax apple protects against STZ-induced pancreatic ß-apoptosis and dysfunction in diabetic rats, possibly through inhibiting oxidative stress and pro-inflammatory cytokine, and activating anti-apoptotic proteins.

PAX4 R192H and P321H polymorphisms in type 2 diabetes and their functional defects.

We have previously identified PAX4 mutations causing MODY9 and a recent genome-wide association study reported a susceptibility locus of type 2 diabetes (T2D) near PAX4. In this study, we aim to investigate the association between PAX4 polymorphisms and T2D in Thai patients and examine functions of PAX4 variant proteins. PAX4 rs2233580 (R192H) and rs712701 (P321H) were genotyped in 746 patients with T2D and 562 healthy normal control subjects by PCR and restriction-fragment length polymorphism method. PAX4 variant proteins were investigated for repressor function on human insulin and glucagon promoters and for cell viability and apoptosis upon high glucose exposure. Genotype and allele frequencies of PAX4 rs2233580 were more frequent in patients with T2D than in control subjects (P=0.001 and 0.0006, respectively) with odds ratio of 1.66 (P=0.001; 95% confidence interval, 1.22-2.27). PAX4 rs712701 was not associated with T2D but it was in linkage disequilibrium with rs2233580. The 192H/321H (A/A) haplotype was more frequent in T2D patients than in controls (9.5% vs 6.6%; P=0.009). PAX4 R192H, but not PAX4 P321H, impaired repression activities on insulin and glucagon promoters and decreased transcript levels of genes required to maintain ß-cell function, proliferation and survival. Viability of ß-cell was reduced under glucotoxic stress condition for the cells overexpressing either PAX4 R192H or PAX4 P321H or both. Thus these PAX4 polymorphisms may increase T2D risk by defective transcription regulation of target genes and/or decreased ß-cell survival in high glucose condition.

Testosterone reduces AGTR1 expression to prevent ß-cell and islet apoptosis from glucotoxicity.

Hypogonadism in men is associated with an increased incidence of type 2 diabetes. Supplementation with testosterone has been shown to protect pancreatic ß-cell against apoptosis due to toxic substances including streptozotocin and high glucose. One of the pathological mechanisms of glucose-induced pancreatic ß-cell apoptosis is the induction of the local rennin-angiotensin-aldosterone system (RAAS). The role of testosterone in regulation of the pancreatic RAAS is still unknown. This study aims to investigate the protective action of testosterone against glucotoxicity-induced pancreatic ß-cell apoptosis via alteration of the pancreatic RAAS pathway. Rat insulinoma cell line (INS-1) cells or isolated male mouse islets were cultured in basal and high-glucose media in the presence or absence of testosterone, losartan, and angiotensin II (Ang II), then cell apoptosis, cleaved caspase 3 expression, oxidative stress, and expression of angiotensin II type 1 receptor (AGTR1) and p47(phox) mRNA and protein were measured. Testosterone and losartan showed similar effects in reducing pancreatic ß-cell apoptosis. Testosterone significantly reduced expression of AGTR1 protein in INS-1 cells cultured in high-glucose medium or high-glucose medium with Ang II. Testosterone decreased the expression of AGTR1 and p47(phox) mRNA and protein in comparison with levels in cells cultured in high-glucose medium alone. Furthermore, testosterone attenuated superoxide production when co-cultured with high-glucose medium. In contrast, when cultured in basal glucose, supplementation of testosterone did not have any effect on cell apoptosis, oxidative stress, and expression of AGT1R and p47(phox). In addition, high-glucose medium did not increase cleaved caspase 3 in AGTR1 knockdown experiments. Thus, our results indicated that testosterone prevents pancreatic ß-cell apoptosis due to glucotoxicity through reduction of the expression of ATGR1 and its signaling pathway.

Estrogen reduces endoplasmic reticulum stress to protect against glucotoxicity induced-pancreatic ß-cell death.

Estrogen can improve glucose homeostasis not only in diabetic rodents but also in humans. However, the molecular mechanism by which estrogen prevents pancreatic ß-cell death remains unclear. To investigate this issue, INS-1 cells, a rat insulinoma cell line, were cultured in medium with either 11.1mM or 40mM glucose in the presence or the absence of estrogen. Estrogen significantly reduced apoptotic ß-cell death by decreasing nitrogen-induced oxidative stress and the expression of the ER stress markers GRP 78, ATF6, P-PERK, PERK, uXBP1, sXBP1, and CHOP in INS-1 cells after prolonged culture in medium with 40mM glucose. In contrast, estrogen increased the expression of survival proteins, including sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA-2), Bcl-2, and P-p38, in INS-1 cells after prolonged culture in medium with 40mM glucose. The cytoprotective effect of estrogen was attenuated by addition of the estrogen receptor (ERα and ERß) antagonist ICI 182,780 and the estrogen membrane receptor inhibitor G15. We showed that estrogen decreases not only oxidative stress but also ER stress to protect against 40mM glucose-induced pancreatic ß-cell death.

Testosterone protects against glucotoxicity-induced apoptosis of pancreatic ß-cells (INS-1) and male mouse pancreatic islets.

Male hypogonadism associates with type 2 diabetes, and T can protect pancreatic ß-cells from glucotoxicity. However, the protective mechanism is still unclear. This study thus aims to examine the antiapoptotic mechanism of T in pancreatic ß cells cultured in high-glucose medium. T (0.0005-2 µg/mL) was added to INS-1 cells cultured in basal glucose or high-glucose media. Then cellular apoptosis, oxidative stress, and cell viability were measured. Endoplasmic reticulum (ER) stress markers and sensors and the antiapoptotic protein (B-cell lymphoma 2) were investigated by real-time PCR and Western blot analysis. ER stress markers were also measured in male mouse pancreatic islet cultured in similar conditions. T (0.05 and 0.5 µg/mL) did not have any effect on apoptosis and viability of INS-1 cells cultured in basal glucose medium, but it could reduce apoptosis and increase viability of INS-1 cells cultured in high-glucose medium. The protective effect of T is diminished by androgen receptor inhibitor. T (0.05 µg/mL) could significantly reduce nitrotyrosine levels, mRNA, and protein levels of the ER stress markers and sensor those that were induced when INS-1 cells were cultured in high-glucose medium. It could also significantly increase the survival proteins, sarco/endoplasmic reticulum Ca(2+) ATPase-2, and B-cell lymphoma 2 in INS-1 cells cultured in the same conditions. Similarly, it could reduce ER stress markers and increase sarco/endoplasmic reticulum Ca(2+) ATPase protein levels in male mouse pancreatic islets cultured in high-glucose medium. T can protect against male pancreatic ß-cell apoptosis from glucotoxicity via the reduction of both oxidative stress and ER stress.