Nitric oxide generation and poly(ADP ribose) polymerase activation precede beta-cell death in rats with a single high-dose injection of streptozotocin

Aloperine protects beta-cells against streptozocin-induced injury to attenuate diabetes by targeting NOS1

Type 1 diabetes (T1D) is a metabolic dysfunction characterized by the selective destruction of islet β-cells, with oxidative stress playing an essential role in the manifestation of this disease state. Aloperine (ALO) represents the main active alkaloid extracted from the traditional Chinese herbal Sophora alopecuroidesL. and features outstanding antioxidative properties. In this study, T1D was induced by a single high dose streptozotocin (STZ, 150 mg/kg, intraperitoneal) in mice. Diabetic animals were intragastrically administered ALO at a dose of 50 mg/kg/day. Notably, treatment of ALO (50 mg/kg/day) for seven consecutive days could observably reverse the onset of diabetes induced by STZ accompanied by weight gain, lower blood glucose levels, and relief of β-cells damage. Our in vitro study further demonstrated that ALO protected β-cells from STZ/hydrogen peroxide-induced oxidative damage as manifested by increased expression of MnSOD and CAT. Furthermore, a network pharmacology study revealed that NOS1 represented the main target of ALO. Mechanistic studies subsequently showed that treatment of ALO increased the expression of NOS1, whereas NOS2 was decreased. Moreover, a docking study carried out suggested that ALO could fit into the binding pocket of human NOS1 and molecular dynamics simulation further validated this docking event. Collectively, the administration of ALO prior to diabetes could be a viable approach to the prevention of β-cell injury. This study may offer a novel potential herbal medicine against T1D and may further help improve the understanding of the underlying molecular mechanisms of ALO-mediated protection against oxidative stress.

Protective effect of hypoxylonol C and 4,5,4',5'-tetrahydroxy-1,1'-binaphthyl isolated from Annulohypoxylon annulatum against streptozotocin-induced damage in INS-1 cells

We evaluated the protective effects of hypoxylonol C and 4,5,4',5'-tetrahydroxy-1,1'-binaphthyl (BNT) isolated from Annulohypoxylon annulatum on pancreatic β-cell apoptosis, using the β-cell toxin streptozotocin (STZ). Hypoxylonol C and BNT restored the STZ-induced decrease in INS-1 cell viability in a dose-dependent manner. In addition, treatment of INS-1 cells with 50 μM STZ resulted in an increase in apoptotic cell death, which was observed as annexin V fluorescence intensity. Apoptotic cell death was decreased by co-treatment with 100 μM hypoxylonol C and 100 μM BNT. Similarly, STZ caused a marked increase in the expression of cleaved caspase-8, caspase-3, Bax, and poly (ADP-ribose) polymerase (PARP), as well as a decrease in the expression of B-cell lymphoma 2 (Bcl-2), which was reversed by co-treatment with 100 μM hypoxylonol C and 100 μM BNT. These findings suggest that hypoxylonol C and BNT play an important role in protecting pancreatic β-cells against apoptotic damage.

Crocin attenuation of neurological deficits in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating subtype of stroke that is associated with high morbidity and mortality. However, up to now, there are no effective prevention methods or specific therapies to improve its clinical outcomes. Herein, we explore preliminarily the efficacy of crocin, a carotenoid extracted from the stigma of saffron known for its anti-oxidation and free radical scavenging activities, in a mouse ICH model induced with collagenase infusion. Crocin or saline was administrated 6 h after ICH and then every 12 h for up to 7 days. Neurological scores were examined on days 1, 3, and 7 after ICH. Mice were sacrificed after1, 3, and 7 days of crocin treatment for examination of histology and immunohistochemistry. The results showed that oral administration of crocin attenuated the neurological deficits and reduced the myelin loss, neuron degeneration, iron deposition, reactive oxygen species (ROS) production and heme oxygenase-1 (HO-1) expression in the early stage of ICH, making it potential to be an ideal candidate for medical therapy of ICH in clinic.

Rat brain glucose transporter-2, insulin receptor and glial expression are acute targets of intracerebroventricular streptozotocin: risk factors for sporadic Alzheimer's disease?

Accumulated evidence suggests that the insulin-resistant brain state and cerebral glucose hypometabolism might be the cause, rather than the consequence, of the neurodegeneration found in a sporadic Alzheimer's disease (sAD). We have explored whether the insulin receptor (IR) and the glucose transporter-2 (GLUT2), used here as their markers, are the early targets of intracerebroventricularly (icv) administered streptozotocin (STZ) in an STZ-icv rat model of sAD, and whether their changes are associated with the STZ-induced neuroinflammation. The expression of IR, GLUT2 and glial fibrillary acidic protein (GFAP) was measured by immunofluorescence and western blot analysis in the parietal (PC) and the temporal (TC) cortex, in the hippocampus (HPC) and the hypothalamus. One hour after the STZ-icv administration (1.5 mg/kg), the GFAP immunoreactivity was significantly increased in all four regions, thus indicating the wide spread neuroinflammation, pronounced in the PC and the HPC. Changes in the GLUT2 (increment) and the IR (decrement) expression were mild in the areas close to the site of the STZ injection/release but pronounced in the ependymal lining cells of the third ventricle, thus indicating the possible metabolic implications. These results, together with the finding of the GLUT2-IR co-expression, and also the neuronal IR expression in PC, TC and HPC, indicate that the cerebral GLUT2 and IR should be further explored as the possible sAD etiopathogenic factors. It should be further clarified whether their alterations are the effect of a direct STZ-icv toxicity or they are triggered in a response to STZ-icv induced neuroinflammation.

Peripheral Neuropathy in Mouse Models of Diabetes

Peripheral neuropathy is a frequent complication of chronic diabetes that most commonly presents as a distal degenerative polyneuropathy with sensory loss. Around 20% to 30% of such patients may also experience neuropathic pain. The underlying pathogenic mechanisms are uncertain, and therapeutic options are limited. Rodent models of diabetes have been used for more than 40 years to study neuropathy and evaluate potential therapies. For much of this period, streptozotocin-diabetic rats were the model of choice. The emergence of new technologies that allow relatively cheap and routine manipulations of the mouse genome has prompted increased use of mouse models of diabetes to study neuropathy. In this article, we describe the commonly used mouse models of type 1 and type 2 diabetes, and provide protocols to phenotype the structural, functional, and behavioral indices of peripheral neuropathy, with a particular emphasis on assays pertinent to the human condition. © 2016 by John Wiley & Sons, Inc.

D-Xylose as a sugar complement regulates blood glucose levels by suppressing phosphoenolpyruvate carboxylase (PEPCK) in streptozotocin-nicotinamide-induced diabetic rats and by enhancing glucose uptake in vitro

BACKGROUND/OBJECTIVES

Type 2 diabetes (T2D) is more frequently diagnosed and is characterized by hyperglycemia and insulin resistance. D-Xylose, a sucrase inhibitor, may be useful as a functional sugar complement to inhibit increases in blood glucose levels. The objective of this study was to investigate the anti-diabetic effects of D-xylose both in vitro and stretpozotocin (STZ)-nicotinamide (NA)-induced models in vivo.

MATERIALS/METHODS

Wistar rats were divided into the following groups: (i) normal control; (ii) diabetic control; (iii) diabetic rats supplemented with a diet where 5% of the total sucrose content in the diet was replaced with D-xylose; and (iv) diabetic rats supplemented with a diet where 10% of the total sucrose content in the diet was replaced with D-xylose. These groups were maintained for two weeks. The effects of D-xylose on blood glucose levels were examined using oral glucose tolerance test, insulin secretion assays, histology of liver and pancreas tissues, and analysis of phosphoenolpyruvate carboxylase (PEPCK) expression in liver tissues of a STZ-NA-induced experimental rat model. Levels of glucose uptake and insulin secretion by differentiated C2C12 muscle cells and INS-1 pancreatic β-cells were analyzed.

RESULTS

In vivo, D-xylose supplementation significantly reduced fasting serum glucose levels (P < 0.05), it slightly reduced the area under the glucose curve, and increased insulin levels compared to the diabetic controls. D-Xylose supplementation enhanced the regeneration of pancreas tissue and improved the arrangement of hepatocytes compared to the diabetic controls. Lower levels of PEPCK were detected in the liver tissues of D-xylose-supplemented rats (P < 0.05). In vitro, both 2-NBDG uptake by C2C12 cells and insulin secretion by INS-1 cells were increased with D-xylose supplementation in a dose-dependent manner compared to treatment with glucose alone.

CONCLUSIONS

In this study, D-xylose exerted anti-diabetic effects in vivo by regulating blood glucose levels via regeneration of damaged pancreas and liver tissues and regulation of PEPCK, a key rate-limiting enzyme in the process of gluconeogenesis. In vitro, D-xylose induced the uptake of glucose by muscle cells and the secretion of insulin cells by β-cells. These mechanistic insights will facilitate the development of highly effective strategy for T2D.

Streptozotocin-nicotinamide-induced diabetes in the rat. Characteristics of the experimental model

Administration of both streptozotocin (STZ) and nicotinamide (NA) has been proposed to induce experimental diabetes in the rat. STZ is well known to cause pancreatic B-cell damage, whereas NA is administered to rats to partially protect insulin-secreting cells against STZ. STZ is transported into B-cells via the glucose transporter GLUT2 and causes DNA damage leading to increased activity of poly(ADP-ribose) polymerase (PARP-1) to repair DNA. However, exaggerated activity of this enzyme results in depletion of intracellular NAD(+) and ATP, and the insulin-secreting cells undergo necrosis. The protective action of NA is due to the inhibition of PARP-1 activity. NA inhibits this enzyme, preventing depletion of NAD(+) and ATP in cells exposed to STZ. Moreover, NA serves as a precursor of NAD(+) and thereby additionally increases intracellular NAD(+) levels. The severity of diabetes in experimental rats strongly depends on the doses of STZ and NA given to these animals. Therefore, in diabetic rats, blood glucose may be changed in a broad range--from slight hyperglycemia to substantial hyperglycemia compared with control animals. Similarly, blood insulin may be only slightly decreased or substantial hypoinsulinemia may be induced. In vitro studies demonstrated that the insulin-secretory response to glucose is attenuated in STZ-NA-induced diabetic rats compared with control animals. This is due to reduced B-cell mass as well as metabolic defects in the insulin-secreting cells. Results of numerous experiments have demonstrated that this model of diabetes is useful in studies of different aspects of diabetes.

Resveratrol prevents streptozotocin-induced diabetes by inhibiting the apoptosis of pancreatic β-cell and the cleavage of poly (ADP-ribose) polymerase

Resveratrol (3,5,4'-trihydroxystilbene; RSV) is one kind of polyphenolic phytoalexin that has many effects on metabolic diseases. This study aimed to evaluate the protective effect of RSV pretreatment on β-cell. Male Sprague Dawley rats weighing 200-230 g were divided into 4 groups: (1) RSV; (2) streptozotocin (STZ, 70 mg/kg, intraperitoneally); (3) STZ after 7 days pretreatment with RSV; and (4) STZ pretreated with nicotinamide. Fasting glucose concentration was measured and an intraperitoneal glucose tolerance test was performed 72 h after STZ injection to determine the diabetic condition. The pancreas was removed 3, 6, 36, and 48 h after STZ injection. STZ induced diabetes in all rats not given RSV pretreatment, whereas none of the RSV-pretreated rats developed diabetes. Pretreatment with RSV inhibited apoptosis and reduced the activation of caspase-3 and poly(ADP-ribose) polymerase (PARP). However, expression of the total length PARP was not affected by pretreatment. Our findings suggest that RSV protects β-cells from STZ simultaneously with inhibiting the activation of PARP.

The potential role of combined antioxidant treatment on pancreas of STZ-diabetic mice

In diabetes, cells and tissues are damaged due to the imbalance between production of free radicals and removal of them. The effective biologic antioxidants for oxidative stress such as α-lipoic acid, vitamin E and selenium are effective in diminishing oxidative damage such as membrane lipid peroxidation. The experiment aimed to investigate the oxidative stress occurring in mitochondrial and cytoplasmic fraction of pancreatic tissues in streptozotocin-diabetic mice and the possible effects of α-lipoic acid + vitamin E + selenium combination on oxidative damage and antioxidative system by using microscopic and biochemical methods. The mice were divided into five groups. These groups were treated by citrate buffer, the solvents of the antioxidants, combined the antioxidants [α-lipoic acid (50 mg/kg), vitamin E (100 mg/kg), selenium (0.25 mg/kg)], streptozotocin (40 mg/kg × 5), combined the antioxidants and streptozotocin. The mice were sacrificed by cervical dislocation. In the experimental group given combined antioxidants following results were observed compared to diabetic group: increased percent insulin-positive cell area; decreased blood glucose levels; increased manganase superoxide dismutase activities and unsignificantly increased superoxide dismutase activities; unsignificantly decreased lipid peroxidase levels in both of fraction; unsignificantly decreased in mitochondrial fraction and unsignificantly increased in cytosolic fraction for catalase levels; not any alteration glutathione levels; not any activity in both of fraction for glutathione peroxidase. We can say that by taking the blood glucose levels and immunohistochemical results into account, the combination of triple antioxidants has a partly positive effect on diabetes. This positive effect could increase when trying different doses of combined antioxidant treatment.

Reg2 protects mouse insulinoma cells from streptozotocin-induced mitochondrial disruption and apoptosis

We reported previously that pancreas-specific ablation of IGF-I in mice induced an increased expression of regenerating family proteins Reg2 and Reg3&#x03B2; in the pancreas and protected them from streptozotocin (Stz)-induced &#x03B2;-cell damage. We, therefore, assessed the effect of ectopically introduced Reg2 on Stz-induced apoptosis in MIN6 mouse insulinoma cells and report here that Reg2 protects MIN6 cells from Stz-induced apoptosis by attenuating its ability to disrupt mitochondrial membrane integrity, activate caspase-3 and promote poly-ADP ribose polymerase cleavage, and induce apoptosis. These changes correlated with suppression of c-jun N-terminal kinase (JNK) phosphorylation by Stz. Reg2 inhibited Stz-induced proapoptotic events as well as the inactivation of JNK. Inclusion of chemical inhibitor of JNK to Reg2 expressing cells rendered them sensitive to Stz. These data demonstrate that Reg2 protects insulin-producing cells against Stz-induced apoptosis by interfering with its cytotoxic signaling upstream of the intrinsic proapoptotic events by preventing its ability to inactivate JNK.

Luminescence experiments involved in the mechanism of streptozotocin diabetes and cataract formation

Streptozotocin (STZ)-induced diabetes is linked to excessive nitric oxide (NO), and possibly peroxynitrite (OONO(-)) and/or other nitrogen oxides, e.g. nitrogen trioxide (N(2)O(3)), which damages DNA of pancreatic beta cells, causing death and loss of insulin. Simultaneous injection of carboxy-PTIO (CPTIO) and STZ prevents diabetes and cataract formation in rats, whereas 4-hydroxy-Tempo (4HT) does not. CPTIO oxidizes nitric oxide to nitrite, which prevents production of the diabetogenic toxin. Peroxynitrite may not be involved, since 4HT (converts O(2)(-) to H(2)O(2)) injected with STZ produces diabetes. All six of the control rats injected with STZ became diabetic and developed cataracts after 3 months. Eight rats injected with STZ and CPTIO were non-diabetic with no cataracts up to a year. This work establishes the idea that excessive nitric oxide is a primary initiator in STZ diabetes. Luminescence experiments using OONO(-) generation from SIN-1 with L-012 indicates that 4HT is an effective inhibitor, while CPTIO is ineffective. Experiments with dilute solutions of nitrogen trioxide added to ladder or plasmid DNA reveal extensive nicking of DNA, thereby raising the possibility that other oxides of nitrogen could be involved with the damage to DNA. It can be concluded that diabetes can be prevented by oxidizing excessive NO from STZ.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

Autophagy and VMP1 expression are early cellular events in experimental diabetes

BACKGROUND/AIMS

We have described VMP1 as a new protein which expression triggers autophagy in mammalian cells. Here we show that experimental diabetes activates VMP1 expression and autophagy in pancreas beta cells as a direct response to streptozotocin (STZ).

METHODS

Male Wistar rats were treated with 65 mg/kg STZ and pancreas islets from untreated rats were incubated with 1 mM STZ.

RESULTS

RT-PCR analysis shows early VMP1 induction after STZ treatment. In situ hybridization reveals VMP1 mRNA in islet beta cells. Electron microscopy shows chromatin aggregation and autophagy morphology that was confirmed by LC3 expression and LC3-VMP1 co-localization. Apoptotic cell death and the reduction of beta cell pool are evident after 24 h treatment, while VMP1 is still expressed in the remaining cells. VMP1-Beclin1 colocalization in pancreas tissue from STZ-treated rats suggests that VMP1-Beclin1 interaction is involved in the autophagic process activation during experimental diabetes. Results were confirmed using pancreas islets, showing VMP1 expression and autophagy in beta cells as a direct effect of STZ treatment.

CONCLUSION

Pancreas beta cells trigger VMP1 expression and autophagy during the early cellular events in response to experimental diabetes.

Alpha1-antitrypsin monotherapy prolongs islet allograft survival in mice

Islet transplantation for type 1 diabetic patients shows promising results with the use of nondiabetogenic immunosuppressive therapy. However, in addition to compromising the immune system of transplant recipients, long-term studies demonstrate that islet viability is impaired. Here, we demonstrate that, in the absence of immunosuppressive agents, monotherapy with clinical-grade human alpha1-antitrypsin (hAAT), the major serum serine-protease inhibitor, prolongs islet graft survival and normoglycemia in transplanted allogeneic diabetic mice, lasting until the development of anti-hAAT antibodies. Compared to untreated or albumin-control-treated graft recipients, which rejected islets at day 10, AAT-treated mice displayed diminished cellular infiltrates and intact intragraft insulin production throughout treatment. Using peritoneal infiltration models, we demonstrate that AAT decreases allogeneic fibroblast-elicited natural-killer-cell influx by 89%, CD3-positive cell influx by 44%, and thioglycolate-elicited neutrophil emigration by 66%. ATT also extended islet viability in mice after streptozotocin-induced beta cell toxicity. In vitro, several islet responses to IL-1beta/IFNgamma stimulation were examined. In the presence of AAT, islets displayed enhanced viability and inducible insulin secretion. Islets also released 36% less nitric oxide and 82% less macrophage inflammatory protein 1 alpha and expressed 63% fewer surface MHC class II molecules. TNFalpha release from IL-1beta/IFNgamma-stimulated islet cells was reduced by 99%, accompanied by an 8-fold increase in the accumulation of membrane TNFalpha on CD45-positive islet cells. In light of the established safety record and the nondiabetogenic potential of AAT, these data suggest that AAT may be beneficial as adjunctive therapy in patients undergoing islet transplantation.