Pancreatic islet-cell toxicity

Diabetes fuels periodontal lesions via GLUT1-driven macrophage inflammaging

Hyperglycemia induces chronic low-grade inflammation (inflammaging), which is a newly identified contributor to diabetes-related tissue lesions, including the inflammatory bone loss in periodontitis. It is also a secondary senescent pattern mediated by an increased burden of senescent cells and senescence-associated secretory phenotype (SASP). Macrophage is a key SASP-spreading cell and may contribute to the maintenance of SASP response in the periodontal microenvironment. Using a transgenic diabetic model (BLKS/J-Lepr^db/lepr^db mice) we identified striking senescence of the periodontium in young (18-wk)-diabetic mice accompanied by amassed p16⁺-macrophages and enhanced early SASP response. Exposed to high glucose in vitro, bone marrow-derived macrophage (BMDM) revealed a strong GLUT1 mRNA response driving the elevated-glucose uptake. GLUT1 is a representative and facilitative glucose transporter in macrophages with potential roles in hyperglycemia-induced inflammation. In this study, both GLUT1 and the downstream GTPase Rheb expression upregulated in the gingiva of diabetic mice with impaired condition. Furthermore, SASP release and p16/p21 signaling were proven to be triggered by mTOR phosphorylation in BMDM and antagonized by restricting glucose uptake in GLUT1^-/- BMDM. Taken together, our findings suggest that elevated-GLUT1 sensor responded to high glucose is important for macrophage senescence and SASP response, generated as a result of hyperglycemia, and it is a potential molecular mechanism for the exacerbation of periodontitis in diabetes.

Functional and Morphological Characteristics of Pancreatic Islet Lesions Induced by Quinolone Antimicrobial Agent Gatifloxacin in Rats

We characterized pancreatic islet lesions induced by several quinolones using functional and morphological examinations of the pancreatic islets in male rats orally administered gatifloxacin, lomefloxacin, or levofloxacin at 300 mg/kg for 14 consecutive days. Consequently, in contrast to lomefloxacin or levofloxacin, gatifloxacin increased serum glucose and glycosylated albumin on day 14 and elevated serum glucose tended to decrease insulin in the intravenous glucose tolerance test. Microscopically, only gatifloxacin induced cytoplasmic vacuoles containing eosinophilic homogenous contents in islet cells. Immunohistochemical examination revealed that vacuolated islet cells were positively stained for insulin, demonstrating they were pancreatic β cells. Electron microscopy showed that the cytoplasmic vacuoles represented dilated cisterna of the rough endoplasmic reticulum filled with electron-lucent materials in pancreatic β cells. Moreover, insulin secretory granules were drastically decreased in vacuolated islet cells, suggesting impaired insulin synthesis and/or transport. This gatifloxacin-induced pancreatic toxicity in rats was considered to be associated with high pancreatic drug distribution. These results demonstrated that gatifloxacin provoked functional and morphological pancreatic β cell alteration associated with impaired insulin synthesis and/or transport, leading to hyperglycemia.

Salutary potential of ethanolic extract of avocado fruit on anomalous carbohydrate metabolic key enzymes in hepatic and renal tissues of hyperglycaemic albino rats

OBJECTIVE

To assess the beneficial potential of ethanolic extract of avocado fruit on abnormal carbohydrate metabolic key enzymes in hepatic and renal tissues in streptozotocin (STZ) induced hyperglycemic albino rats.

METHODS

Twenty-four male albino rats were randomly divided into four groups with six in each group by simple random sampling method. Group 1 as control rats; Group 2 as STZ induced diabetic rats; Group 3 as diabetic rats treated with avocado fruit extract (AFE), 300 mg/kg as aqueous suspension orally for 30 days; Group 4 as diabetic rats treated with gliclazide (5 mg/kg) in aqueous solution orally for 30 days. The rats were fasted overnight and sacrificed by cervical dislocation and the blood was collected for various biochemical analysis and excision of hepatic and kidney were done for histological analysis. Levels of fasting blood glucose, plasma insulin and glycosylated hemoglobin were estimated. The activities of key enzymes in carbohydrate metabolism such as hexokinase, pyruvate kinase, glucose-6- phosphatase, fructose-1, 6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase were assayed by standard methods described in the methodology.

RESULTS

Oral administration of AFE significantly improved the altered levels of blood glucose, plasma insulin, glycosylated hemoglobin, and modulated the activities of carbohydrate metabolizing enzymes (P<0.05, respectively). The glycogen content in hepatic tissues was significantly increased in diabetic rats treated with AFE (P<0.05, respectively).

CONCLUSION

AFE plays a pivotal role to maintain normoglycemia in diabetes by modulating the activities of carbohydrate metabolic enzymes.

Rosemary (Rosmarinus officinalis) essential oil components exhibit anti-hyperglycemic, anti-hyperlipidemic and antioxidant effects in experimental diabetes

INTRODUCTION

The present study aims to investigate the protective effects of Rosemary (Rosmarinus officinalis L.) essential oils (ROEO) against alloxan-induced diabetes and oxidative stress in rats.

METHODS

The animals were divided into four groups: Healthy Control (HC); Diabetic Control (DC); Healthy+ROEO (H+ROEO) and Diabetic+ROEO (D+ROEO).

RESULTS

The use of GC/MS technique has allowed us to identify fifteen compounds in ROEO. We have found that alloxan administration induced hyperglycaemia, lipid metabolic parameters deregulation as well as liver and kidney dysfunctions. Alloxan administration has also induced an oxidative stress status as assessed by malondialdehyde (MDA) content increase, thiol groups (-SH) level decrease and antioxidant enzyme activities depletion such as catalase (CAT), total superoxide dismutase (SOD), Cu/Zn-SOD, Mn-SOD and Fe-SOD in both liver and kidney tissues. More importantly subacute (15days) ROEO administration has significantly corrected all biochemical alterations induced by alloxan intoxication.

CONCLUSIONS

We propose that Rosmarinus officinalis essential oils exhibit protective effects in alloxan-induced hyperglycaemia as well as protecting against liver and kidney oxidative stress in rats, reflecting its antioxidant properties.

Fisetin improves glucose homeostasis through the inhibition of gluconeogenic enzymes in hepatic tissues of streptozotocin induced diabetic rats

Liver plays a vital role in blood glucose homeostasis. Recent studies have provided considerable evidence that hepatic glucose production (HGP) plays an important role in the development of fasting hyperglycemia in diabetes. From this perspective, diminution of HGP has certainly been considered for the treatment of diabetes. In the present study, we have analyzed the modulatory effects of fisetin, a flavonoid of strawberries, on the expression of key enzymes of carbohydrate metabolism in STZ induced experimental diabetic rats. The physiological criterions such as food and fluid intake were regularly monitored. The levels of blood glucose, plasma insulin, hemoglobin and glycosylated hemoglobin were analyzed. The mRNA and protein expression levels of gluconeogenic genes such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) were determined by immunoblot as well as PCR analysis. Diabetic group of rats showed significant increase in food and water intake when compared with control group of rats. Upon oral administration of fisetin as well as gliclazide to diabetic group of rats, the levels were found to be decreased. Oral administration of fisetin (10 mg/kg body weight) to diabetic rats for 30 days established a significant decline in blood glucose and glycosylated hemoglobin levels and a significant increase in plasma insulin level. The mRNA and protein expression levels of gluconeogenic genes, such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), were decreased in liver tissues upon treatment with fisetin. The results of the present study suggest that fisetin improves glucose homeostasis by direct inhibition of gluconeogenesis in liver.

Antihyperlipidemic effect of fisetin, a bioflavonoid of strawberries, studied in streptozotocin-induced diabetic rats

Chronic hyperglycemia in diabetes is associated with profound changes in lipid and lipoprotein metabolism, with resultant alterations in particle distribution within lipoprotein classes. In the present study, an attempt has been made to explore the antihyperlipidemic effect of fisetin in streptozotocin-induced experimental diabetes in rats. Upon fisetin treatment to diabetic rats, the levels of blood glucose were significantly reduced with an improvement in plasma insulin. The increased levels of lipid contents in serum, hepatic, and renal tissues observed in diabetic rats were normalized upon fisetin administration. Also, the decreased levels of high-density lipoprotein cholesterol, and increased levels of low-density lipoprotein (LDL) and very LDL (VLDL) cholesterol in serum of diabetic rats were normalized. Oil Red O staining established a large number of intracellular lipid droplets accumulation in the diabetic rats. Fisetin treatment exacerbated the degree of lipid accumulation. The results of the present study exemplify the antihyperlipidemic property of the fisetin.

Fisetin averts oxidative stress in pancreatic tissues of streptozotocin-induced diabetic rats

Persistent hyperglycemia is associated with chronic oxidative stress which contributes to the development and progression of diabetes-associated complications. The sensitivity of pancreatic β-cells to oxidative stress has been attributed to their low content of antioxidants compared with other tissues. Bioactive compounds with potent antidiabetic properties have been shown to ameliorate hyperglycemia mediated oxidative stress. Recently, we have reported that oral administration of fisetin (10 mg/Kg b.w.), a bioflavonoid found to be present in strawberries, persimmon, to STZ-induced experimental diabetic rats significantly improved normoglycemia. The present study was aimed to evaluate the antioxidant potential of fisetin in both in vitro and in vivo. Diabetes was induced by single intraperitoneal injection of streptozotocin (50 mg/kg body weight). Fisetin was administered orally for 30 days. At the end of the study, all animals were killed. Blood samples were collected for the biochemical estimations. The antioxidant status was evaluated. Histological examinations were performed on pancreatic tissues. Fisetin treatment showed a significant decline in the levels of blood glucose, glycosylated hemoglobin (HbA1c), NF-kB p65 unit (in pancreas) and IL-1β (plasma), serum nitric oxide (NO) with an elevation in plasma insulin. The treatment also improved the antioxidant status in pancreas as well as plasma of diabetic rats indicating the antioxidant potential of fisetin. In addition, the results of DPPH and ABTS assays substantiate the free radical scavenging activity of fisetin. Histological studies of the pancreas also evidenced the tissue protective nature of fisetin. It is concluded that, fisetin possesses antioxidant and anti-inflammatory property and may be considered as an adjunct for the treatment of diabetes.

Fisetin, a tetra hydroxy flavone recuperates antioxidant status and protects hepatocellular ultrastructure from hyperglycemia mediated oxidative stress in streptozotocin induced experimental diabetes in rats

Oxidative stress is a biological entity quoted as accountable for several pathological conditions including diabetes mellitus. Chronic hyperglycemia in diabetes is associated with oxidative stress mediated tissue damage. The present study is aimed to explore the role of fisetin, in ameliorating hyperglycemia-mediated oxidative damage to liver in streptozotocin induced diabetic rats. In addition to the levels of blood glucose, plasma insulin, glycosylated hemoglobin, the extent of oxidative stress was assessed by hepatic lipid peroxides and hydroperoxides. The levels of reduced glutathione and the activities of enzymatic antioxidants were determined in the liver tissues. The activities of serum aminotransferases and alkaline phosphatase were assayed. A portion of liver was processed for histological and ultrastructural studies. Oral administration of fisetin (10 mg/kg b. w.) to diabetic rats decreased the levels of blood glucose and glycosylated hemoglobin and increased the plasma insulin level. A reduction in lipid peroxides and hydroperoxides were observed. The diminished activities of antioxidant enzymes and reduced glutathione in diabetic rats were improved upon fisetin administration. Thus, the results of the present study indicate that fisetin treatment protects the hepatocytes by improving the antioxidant competence in hepatic tissues of diabetic rats which is further evidenced from histological and ultra structural observations.

Antioxidant potential of zinc-flavonol complex studied in streptozotocin-diabetic rats

BACKGROUND

Diabetic oxidative stress coexists with a reduction in the antioxidant status, which can further increase the deleterious effects of free radicals. Zinc is an essential trace element with significant antidiabetic activity. However, the acceptance of zinc compounds as promising therapeutic antidiabetic agents has been slowed due to concerns regarding chronic toxicity. Recently, we have designed, synthesized and characterized a novel zinc-flavonol complex and evaluated its antidiabetic efficacy in streptozotocin (STZ)-diabetic rats. The aim of the present study was to evaluate the role of the zinc-flavonol complex in the antioxidant status of diabetic rats.

METHODS

Diabetes was induced in rats by i.p. injection of STZ. Diabetic rats were then treated with the zinc-flavonol complex (5 mg/kg, p.o.) for 30 days. The extent of oxidative stress was assessed by determining lipid peroxide levels, pancreatic tissue antioxidant enzyme activities and plasma concentrations of non-enzymatic antioxidants. In addition, nuclear levels of nuclear factor (NF)-κB p65, pancreatic nitric oxide (NO), and plasma levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were determined. Pancreatic tissues were examined histologically.

RESULTS

Oral treatment with the zinc-flavonol complex significantly improved antioxidant levels and alleviated levels of oxidative stress markers. Furthermore, significant increases were seen in NF-κB p65, NO, TNF-α, IL-1β and IL-6 levels. Histological observations revealed that the zinc-flavonol complex effectively protects pancreatic β-cells against oxidative damage.

CONCLUSION

  The results of the present study indicate that the zinc-flavonol complex has an antioxidative and anti-inflammatory role in the diabetic milieu.

Evaluation of antioxidant efficacy of vanadium-3-hydroxyflavone complex in streptozotocin-diabetic rats

Since 1985, when Heyliger et al., first demonstrated that oral administration of sodium orthovanadate (0.8mg/ml) to STZ induced diabetic rats resulted in normoglycemia, numerous extensive studies have been reported on the antidiabetic actions of vanadium. The acceptance of vanadium compounds as promising therapeutic antidiabetic drugs has been slowed due to the concern for chronic toxicity associated with vanadium accumulation. In order to circumvent the toxic effects of vanadium, a combinational approach wherein a novel V3HF complex was synthesized, characterized and its toxic as well as antidiabetic potential were evaluated in STZ diabetic rats. Experimental and clinical studies suggest that hyperglycemia-induced oxidative stress primarily contributes to the pathogenesis and progression of both primary as well as secondary complications of diabetes. It is possible to reduce the risks caused by excessive generation of free radicals by either enhancing the body's natural antioxidant defenses or by supplementing with proven antioxidants. The present study was aimed to study the role of V3HF complex on hyperglycemia mediated oxidative stress in STZ-diabetic rats and the results indicate that the complex improves pancreatic beta cell function. Histological and ultrastructural studies also evidenced that the complex protect the beta cells from hyperglycemia-induced oxidative stress.

A novel insulin mimetic vanadium-flavonol complex: synthesis, characterization and in vivo evaluation in STZ-induced rats

Since 1985, when Heyliger et al., first demonstrated a serendipitous discovery that oral administration of 0.8 mg/ml of sodium orthovanadate in drinking water to streptozotocin-induced diabetic rats resulted in normoglycemia, numerous extensive studies have been pursued on the anti-diabetic and insulinomimetic actions of vanadium. The acceptance of vanadium compounds as promising therapeutic antidiabetic agents has been slowed due to the concern for chronic toxicity associated with vanadium accumulation. In order to circumvent the toxic effects of vanadium, we have taken up a combinational approach wherein a novel vanadium-flavonol complex was synthesized, characterized and its toxic as well as insulin mimetic potential was evaluated in STZ-induced experimental diabetes in rats. The results indicate that the complex is non-toxic and possess anti-diabetic activity.

Resveratrol protects diabetic kidney by attenuating hyperglycemia-mediated oxidative stress and renal inflammatory cytokines via Nrf2-Keap1 signaling

Hyperglycemia-mediated oxidative stress plays a crucial role in the progression of diabetic nephropathy. Hence, the present study was hypothesized to explore the renoprotective nature of resveratrol by assessing markers of oxidative stress, proinflammatory cytokines and antioxidant competence in streptozotocin-nicotinamide-induced diabetic rats. Oral administration of resveratrol to diabetic rats showed a significant normalization on the levels of creatinine clearance, plasma adiponectin, C-peptide and renal superoxide anion, hydroxyl radical, nitric oxide, TNF-α, IL-1β, IL-6 and NF-κB p65 subunit and activities of renal aspartate transaminase, alanine transaminase and alkaline phosphatase in comparison with diabetic rats. The altered activities of renal aldose reductase, sorbitol dehydrogenase and glyoxalase-I and elevated level of serum advanced glycation end products in diabetic rats were also reverted back to near normalcy. Further, resveratrol treatment revealed a significant improvement in superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase activities and vitamins C and E, and reduced glutathione levels, with a significant decline in lipid peroxides, hydroperoxides and protein carbonyls levels in diabetic kidneys. Similarly, mRNA and protein analyses substantiated that resveratrol treatment notably normalizes the renal expression of Nrf2/Keap1and its downstream regulatory proteins in the diabetic group of rats. Histological and ultrastructural observations also evidenced that resveratrol effectively protects the kidneys from hyperglycemia-mediated oxidative damage. These findings demonstrated the renoprotective nature of resveratrol by attenuating markers of oxidative stress in renal tissues of diabetic rats.

Resveratrol attenuates hyperglycemia-mediated oxidative stress, proinflammatory cytokines and protects hepatocytes ultrastructure in streptozotocin-nicotinamide-induced experimental diabetic rats

The present study was hypothesized to investigate the hepatoprotective nature of resveratrol in averting hyperglycemia-mediated oxidative stress by measuring extent of oxidant stress and levels of proinflammatory cytokines and antioxidant competence in the hepatic tissues of streptozotocin-nicotinamide-induced diabetic rats. After the experimental period of 30 days, the pathophysiological markers such as serum bilirubin and hepatic aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) were studied in addition to hepatic TNF-alpha, IL-1 beta, IL-6, NF-kappaB p65 and nitric oxide (NO) levels in control and experimental groups of rats. The levels of vitamin C, vitamin E and reduced glutathione (GSH) and activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) were determined in the liver tissues. Extent of oxidative stress was also assessed by hepatic lipid peroxides, hydroperoxides and protein carbonyls. A portion of liver was processed for histological and ultrastructural studies. Oral administration of resveratrol (5mg/kg b.w.) to diabetic rats showed a significant decline in hepatic proinflammatory cytokines and notable attenuation in hepatic lipid peroxides, hydroperoxides and protein carbonyls. The diminished activities of hepatic enzymic antioxidants as well as the decreased levels of hepatic non-enzymic antioxidants of diabetic rats were reverted to near normalcy by resveratrol administration. Moreover, the histological and ultrastructural observations evidenced that resveratrol effectively rescues the hepatocytes from hyperglycemia-mediated oxidative damage without affecting its cellular function and structural integrity. The findings of the present investigation demonstrated the hepatocyte protective nature of resveratrol by attenuating markers of hyperglycemia-mediated oxidative stress and antioxidant competence in hepatic tissues of diabetic rats.

Impact of D-pinitol on the attenuation of proinflammatory cytokines, hyperglycemia-mediated oxidative stress and protection of kidney tissue ultrastructure in streptozotocin-induced diabetic rats

Oxidative stress plays a crucial role in the progression and development of diabetes and its complications due to chronic hyperglycemia. The present study was aimed to investigate the kidney tissue protective nature of d-pinitol, a cyclitol present in soybean, by assessing the key markers of hyperglycemia-mediated oxidative stress, proinflammatory cytokines and ultrastructural alterations in streptozotocin-induced diabetic rats. Oral administration of d-pinitol (50mg/kg body weight/day) for 30 days to diabetic group of rats showed a significant elevation in the level of total protein and significant decline in the levels of blood urea, serum uric acid, creatinine and advanced glycation endproducts (AGEs) and kidney proinflammatory cytokines such as TNF-alpha, IL-1beta, IL-6, NF-kappaB p65 subunit and nitrite. Further, d-pinitol administration elicited a significant attenuation in the activities of kidney enzymatic antioxidants such as superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) and the levels of kidney non-enzymatic antioxidants such as vitamin E, vitamin C and reduced glutathione (GSH) in the diabetic group of rats, with a concomitant decline in the levels of kidney lipid peroxides, hydroperoxides and protein carbonyls. The histological and ultrastructural observations on the kidney tissues also confirmed the renoprotective nature of d-pinitol. Thus the present study demonstrated the renoprotective nature of d-pinitol by attenuating the hyperglycemia-mediated proinflammatory cytokines and antioxidant competence in kidney tissues of streptozotocin-induced diabetic rats.

EFFECT OF SULFUR DIOXIDE ON ACTIVE AND PASSIVE AVOIDANCE IN EXPERIMENTAL DIABETES MELLITUS: RELATION TO OXIDANT STRESS AND ANTIOXIDANT ENZYMES

The effect of sulfur dioxide (SO(2)) on hippocampus antioxidant status, lipid peroxidation and learning and memory was investigated in diabetic rats. A total of 40 rats were divided into four equal groups: Control (C), SO(2) + C (SO(2)), diabetic (DM) and SO(2) + D (DMSO(2)). Experimental diabetes mellitus (DM) was induced by i.v injection of alloxan with a dose of 50 mg/kg body weight. Ten ppm SO(2) was administered to the rats in the sulfur dioxide groups in an exposure chamber. Exposure occurred 1 h/d, 7 d/wk, for 6 wk; control rats were exposed to filtered air during the same time periods. SO(2) exposure, while markedly increasing Cu-Zn Superoxide dismutase activity, significantly decreased glutathione peroxidase activity in diabetic and non-diabetic groups compared with the C group; hippocampus catalase activity was unaltered. Hippocampus thiobarbituric acid reactive substances (TBARS) were found to be elevated in all experimental groups with respect to control group. The active avoidance training results indicated that diabetic condition has been associated with learning and memory impairment. SO(2) exposure caused deficits of learning and memory. Diabetes mellitus-induced impairment of learning and memory were potentiated by SO(2) exposure. These findings suggest that exposure to SO(2) by increasing lipid peroxidation, can change antioxidant enzyme activities and can elevated intensity of deficits of learning and memory in diabetic rats.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Lack of osteopontin improves cardiac function in streptozotocin-induced diabetic mice

The purpose of this study was to investigate the role of osteopontin (OPN) in diabetic hearts. Diabetes was induced in wild-type (WT) and OPN knockout (KO) mice by using streptozotocin (150 mg/kg) injection. Left ventricular (LV) structural and functional remodeling was studied 30 and 60 days after induction of diabetes. Induction of diabetes increased OPN expression in cardiac myocytes. Heart weight-to-body weight ratio was increased in both diabetic (D) groups. Lung wet weight-to-dry weight ratio was increased only in the WT-D group. Peak left ventricular (LV) developed pressures measured using Langendorff perfusion analyses were reduced to a greater extent in WT-D versus KO-D group. LV end-diastolic pressure-volume curve exhibited a significant leftward shift in WT-D but not in KO-D group. LV end-diastolic diameter, percent fractional shortening, and the ratio of peak velocity of early and late filling (E/A wave) were significantly reduced in WT-D mice as analyzed by echocardiography. The increase in cardiac myocyte apoptosis and fibrosis was significantly higher in the WT-D group. Expression of atrial natriuretic peptide and transforming growth factor-beta1 was significantly increased in the WT-D group. Induction of diabetes increased protein kinase C (PKC) phosphorylation in both groups. However, phosphorylation of PKC-betaII was significantly higher in the WT-D group, whereas phosphorylation of PKC-zeta was significantly higher in the KO-D group. Levels of peroxisome proliferator-activated receptor-gamma were significantly decreased in the WT-D group but not in the KO-D group. Thus increased expression of OPN may play a deleterious role during streptozotocin-induced diabetic cardiomyopathy with effects on cardiac fibrosis, hypertrophy, and myocyte apoptosis.

G-protein signaling participates in the development of diabetic cardiomyopathy

Diabetic patients develop a cardiomyopathy that consists of ventricular hypertrophy and diastolic dysfunction. Although the pathogenesis of this condition is poorly understood, previous studies implicated abnormal G-protein activation. In this work, mice with cardiac overexpression of the transcription factor peroxisome proliferator-activated receptor-alpha (PPAR-alpha) were examined as a model of diabetic cardiomyopathy. PPAR-alpha transgenic mice develop spontaneous cardiac hypertrophy, contractile dysfunction, and "fetal" gene induction. We examined the role of abnormal G-protein activation in the pathogenesis of cardiac dysfunction by crossing PPAR-alpha mice with transgenic mice with cardiac-specific overexpression of regulator of G-protein signaling subtype 4 (RGS4), a GTPase activating protein for Gq and Gi. Generation of compound transgenic mice demonstrated that cardiac RGS4 overexpression ameliorated the cardiomyopathic phenotype that occurred as a result of PPAR-alpha overexpression without affecting the metabolic abnormalities seen in these hearts. Next, transgenic mice with increased or decreased cardiac Gq signaling were made diabetic by injection with streptozotocin (STZ). RGS4 transgenic mice were resistant to STZ-induced cardiac fetal gene induction. Transgenic mice with cardiac-specific expression of mutant Galphaq, Galphaq-G188S, that is resistant to RGS protein action were sensitized to the development of STZ-induced cardiac fetal gene induction and bradycardia. These results establish that Gq-mediated signaling plays a critical role in the pathogenesis of diabetic cardiomyopathy.

Oxygen free radical scavengers protect rat islet cells from damage by cytokines

A possible role for oxygen free radicals in mediating the cytotoxic effects of cytokines in islets was sought by the use of agents that scavenge free radicals. Rat islet cell monolayer cultures were incubated for 6 days with t-butylhydroperoxide, alloxan, streptozotocin, or the cytokines, interleukin 1, tumour necrosis factor, and interferon gamma, without and together with the oxygen free radical scavenger combination of dimethylthiourea and citiolone, and islet cell lysis was measured in a 51chromium cytotoxicity assay. The free radical scavengers significantly inhibited the islet cell cytotoxic effects of t-butylhydroperoxide and alloxan, but not streptozotocin. Similarly, the cytotoxic effects of the cytokine combinations of interleukin 1 plus tumour necrosis factor, interferon gamma plus tumour necrosis factor, and interferon gamma plus interleukin 1 were significantly inhibited by the free radical scavenger combination of dimethylthiourea and citiolone. These results suggest that the cytokine products of macrophages and lymphocytes infiltrating islets in Type 1 (insulin-dependent) diabetes may contribute to B-cell damage by inducing the production of oxygen free radicals in the islet cells.

Cyproheptadine metabolites inhibit proinsulin and insulin biosynthesis and insulin release in isolated rat pancreatic islets

The contribution of drug metabolites to cyproheptadine (CPH)-induced alterations in endocrine pancreatic beta-cells was investigated by examining the inhibitory activity of CPH and its biotransformation products, desmethylcyproheptadine (DMCPH), CPH-epoxide and DMCPH-epoxide, on hormone biosynthesis and secretion in pancreatic islets isolated from 50-day-old rats. Measurement of (pro)insulin (proinsulin and insulin) synthesis using incorporation of 3H-leucine showed that DMCPH-epoxide, DMCPH and CPH-epoxide were 22, 10 and 4 times, respectively, more potent than CPH in inhibiting hormone synthesis. The biosynthesis of (pro)insulin was also inhibited by CPH and DMCPH-epoxide in islets isolated from 21-day-old rat fetuses. The inhibitory action of CPH and its metabolites was apparently specific for (pro)insulin, and the synthesis of other islet proteins was not affected. Other experiments showed the metabolites of CPH were active in inhibiting glucose-stimulated insulin secretion but were less potent than the parent drug in producing this effect. CPH and its structurally related metabolites, therefore, have differential inhibitory activities on insulin synthesis and release. The observation that CPH metabolites have higher potency than CPH to inhibit (pro)insulin synthesis, when considered with published reports on the disposition of the drug in rats, indicate that CPH metabolites, particularly DMCPH-epoxide, are primarily responsible for the insulin depletion observed when the parent compound is given to fetal and adult animals.

Somatostatin release from dispersed hypothalamic cells: effects of diabetes

We examined the release of growth hormone-release inhibiting factor (somatostatin) from dispersed hypothalamic cells obtained from mature diabetic rodents and normal age-matched controls, in an attempt to demonstrate a possible hypothalamic defect which might underlie some of the reported abnormalities in somatotrophic function in diabetes mellitus. Insulinopoenic diabetes was induced by either streptozotocin or alloxan. Somatostatin release from cells from diabetic rats was diminished both basally and after stimulation by membrane depolarisation. Stimulated release was calcium dependent in cells from both normal and diabetic animals. The defect was present in both streptozotocin and alloxan induced diabetes. We also compared hypothalamic somatostatin release from cells obtained from obese hyperinsulinaemic C57 BL/Ks db/db diabetic mice and non diabetic lean litter mates (db/-). Despite longstanding marked hyperglycaemia, no significant alteration in somatostatin release was apparent. Likewise, starvation of rats for 5 days did not result in significant diminution of somatostatin release. These observations document a defect in hypothalamic somatostatin release in experimentally induced insulinopoenic diabetes, which is not apparent in the db/db mouse, suggesting that glucose per se is not responsible. Rather than the anticipated increase in hypothalamic somatostatin release in insulinopoenic diabetes, a reduction in release was observed. These observations are compatible with the hypothesis that increased hypothalamic somatostatin release is not responsible for abnormal growth hormone secretion in this model.

Rapid in vitro formation of smooth endoplasmic reticulum aggregates within peptide-producing islet cells

We report here that heptanol (3.5 mM) induces in vitro a rapid formation of smooth endoplasmic reticulum aggregates (SERA) within isolated islets of Langerhans. SERA appeared after only 15 min of exposure to the alkanol and increased in number during the first 30 min of incubation. At that time, SERA represented 2% and 6% of the volume of B- and non-B-cells, respectively. Removal of heptanol resulted in the rapid disappearance of SERA, whereas reintroduction of the alkanol rapidly induced these structures again. SERA formation was seen in different types of endocrine and nonendocrine islet cells. In the insulin-producing B-cells, SERA formation was not modified by conditions known to alter the secretory activity and the microtubular-microfilament network or to inhibit protein synthesis. By contrast, SERA formation was inhibited by low temperature and by conditions depleting the energy sources of the cells. Similar observations were made in the presence of either octanol (1 mM) or nonanol (1 mM) but not of shorter chain alkanols, alkanes, oxidative derivates of either heptanol or octanol, and of other unrelated lipid-soluble compounds. Incubations in the presence of long-chain alkanols provide, therefore, a unique model to study in vitro the formation and disposal of smooth endoplasmic reticulum, as well as a system in which rapid membrane biogenesis is amenable to direct experimental testing.

Delayed brainstem auditory evoked responses in experimental diabetes mellitus

The brainstem auditory evoked responses (BAER) were utilized for the evaluation of central neural transmission in alloxan-induced diabetes in rats. The mean latencies of waves I, III, V and the interpeak latencies III-V and I-V were prolonged in diabetic rats as compared to the same rats before alloxan administration. The incidence of abnormal BAER was more frequent in the group of rats with severe diabetes (82 per cent) than in mildly diabetic animals (42 per cent). Our results may suggest the presence of a central neuropathy in experimental diabetes, which can be detected by the method of BAER.

Susceptibility of fetal rat endocrine pancreas to the diabetogenic action of cyproheptadine

The susceptibility of fetal endocrine pancreas to the diabetogenic action of cyproheptadine was investigated. Cyproheptadine (5 or 11 mg/kg) or water (control) was given orally once daily to pregnant rats on Days 13.5-20.5 or on Days 19.5-20.5 of gestation. Fetuses were obtained by cesarean section 24 hr after the last dose. Serum and pancreatic immunoreactive insulin and serum glucose from maternal and fetal animals were measured. Differences in maternal pancreatic insulin, serum insulin, and glucose between control and treated groups were not detected. In contrast, fetal pancreatic and serum insulin concentrations in animals exposed to 2 or 8 doses of cyproheptadine were less than 50% those of control. Drug treatment did not alter fetal pancreatic glucagon, pancreatic somatostatin, serum glucose, pancreas weight, or body weight. The drug-related depletion of fetal pancreatic insulin was reversible; the level returned to normal 3 days after cessation of the drug treatment. A similar depletion of fetal insulin was observed after 8 oral doses (11 mg/kg) of desmethylcyproheptadine, a metabolite which lacks the antiserotonin-antihistaminic properties of the parent compound. In vitro experiments showed that cyproheptadine inhibited the biosynthesis and release of insulin in fetal rat pancreas. These results indicate that cyproheptadine, when given to pregnant rats using a dose which produces no apparent effects in the maternal endocrine pancreas, causes abnormalities in the function of the insulin-secreting B cells in the fetal endocrine pancreas.

Alloxan-induced glucoprivic feeding deficits are blocked by D-glucose and amygdalin

Intracerebroventricular injection of alloxan, a pancreatic beta (B) cell cytotoxin, impairs glucoprivic feeding in rats. The goal of this experiment was to determine whether alloxan-induced impairment of glucoprivic feeding can be attenuated by agents which antagonize alloxan's toxicity in the B cell. Therefore, alloxan was co-administered into the fourth ventricle alone or in combination with D-glucose, L-glutamine, or amygdalin, all known antagonists of alloxan's B cell toxicity, or with L-glucose, which does not antagonize B cell toxicity. We found that alloxan produced deficits in glucoprivic feeding which were not attenuated by co-administration with L-glucose or L-glutamine. Alloxan/L-glucose treated rats ate 11% and 14% of control intake, respectively, after systemic administration of 2-deoxy-D-glucose (2DG, 250 mg/kg) and fourth ventricular 5-thioglucose (5TG, 120 micrograms/5 microliter). Alloxan/L-glutamine rats ate 20% and 22% of control intake after 2DG and 5TG, respectively. In contrast, D-glucose and amygdalin (15 mM) completely blocked alloxan-induced impairment of glucoprivic feeding and amygdalin (10 mM) exerted a partial protective effect. These behavioral results may indicate that in the brain, susceptibility to alloxan toxicity depends upon cellular characteristics shared with the B cell.

Pancreatic beta cell vacuolation in rats after oral administration of hexamethylmelamine

The effects of hexamethylmelamine (HMM) on morphology and function of the endocrine pancreas were investigated following the induction of a diabetic-like syndrome in a reproduction study in rats. Doses of 0, 20, 40, or 80 mg/kg/day were administered once daily, by gavage, to groups of 10 male and 10 female Sprague-Dawley rats for up to 77 days. Signs of toxicity were observed at all treatment levels and were of such severity at 80 mg/kg/day that this group was terminated after 8 days of treatment. Measurement of serum glucose levels revealed a dose- and time-related hyperglycemia in rats from the 20- and 40-mg/kg/day groups with levels exceeding 700 mg/dl in some rats after 77 days of treatment. Reversal of the hyperglycemia after discontinuing treatment with HMM occurred in some rats receiving 20 mg/kg/day, whereas the effects of higher doses were still present following a 2-month recovery period. Microscopically, there were hydropic degeneration of renal tubular epithelium and vacuolation of pancreatic beta cells. Ultrastructurally, vesiculation of the Golgi-smooth membrane reticular complex and a marked reduction in the number of insulin granules were observed. It appeared that HMM exerted a disruptive effect on the production of insulin at or prior to the level of the Golgi complex. The severity and time course of morphologic changes and hyperglycemia were dependent on dose and duration of treatment.

Ganglioside treatment of genetic and alloxan-induced diabetic neuropathy

Peripheral neuropathy is a common complication of diabetes. Using the mutant diabetic mouse C57BL/ks (db/db) and alloxan-treated rats, 30 days after intoxication, we investigated development and treatment with gangliosides of such a disease. The db/db mouse develops a neuropathy characterized by a loss in conduction velocity shown as early as 80-90 days after birth and maintained throughout life. At later stages (5-6 months of age) there is a drop in slow transport and myelin particle density. These changes are correlated by a lack of response to insulin treatment, which, prior to this stage, is capable of improving nerve conduction velocity (NCV). On the other hand gangliosides became effective, improving NCV, myelin particle density and sensory perception (auditory deficit) at 5 months of age in the db/db mouse. We presume that this differential neuronal response to insulin and gangliosides indicates a change of the neuropathy from a metabolic stage to neuronal. Alloxan induced diabetic neuropathy is treatable with gangliosides even 30 days after intoxication.

Effect of diabetogenic nitrosourea on the activity of the pentose phosphate hunt in isolated islets

The effect of streptozotocin (STZ) on the activity of the pentose phosphate shunt in islets was studied. Isolated rat islets were pre-incubated with glucose (1.7 mM) alone or with streptozotocin (STZ) or N-methyl-N-nitrosourea (MNU). The effects of these pretreatments on glucose metabolism and insulin secretion were assessed during subsequent incubation with either (1.14C), (6.14C). or (U.14C). glucose (16.7 mM) alone or plus phenazine methosulfate (PMS). Islets pretreated with STZ (1.5 mM) metabolized less (1.14C) and (U.14C). glucose. The order of inhibition by STZ of (14C)-glucose metabolism by islets was: (1.14C). greater than (U.14C). greater than (6.14C)-glucose. Whereas PMS (0.5 mM) increased the metabolism of both (U.14C). and (1.14C)-glucose, the metabolism of (6.14C)-glucose by STZ-pretreated islets was not increased by PMS. In a separate series of experiments, the total NADP+ + NADPH, but not the NAD content of the islets decreased after 2 min exposure of islets of STZ. At 30-min exposure, the levels of both pyridine coenzymes and that of 6-phosphogluconate were significantly decreased. The level of NADP+ + NADPH in islets was decreased more than the level of NAD. Insulin secretion was suppressed by the nitrosoureas. PMS (0.5 mM) increased the level of NADP+ + NADPH content of islets and augmented insulin secretion. It is concluded that the pentose phosphate pathway is inhibited on brief exposure of islets to STZ or MNU. Such inhibition may contribute to the suppression of insulin secretion caused by these nitrosoureas.

Animal models of diabetes

Spontaneous diabetes is a common occurrence in many animal species. In addition, animals can be rendered diabetic by a wide variety of experimental procedures. Diabetic animals may be regarded as models of the disease in man. However, such animals display a wide diversity of pathophysiology, and, in fact, no animal syndrome corresponds precisely to any type of diabetes in human subjects. The most common diabetes syndromes in animals occur in the context of obesity, hyperinsulinemia and insulin resistance. Many such syndromes remit spontaneously. Dietary restriction and weight reduction effectively reverse some of these syndromes, but in other cases only partial correction of the syndrome occurs. Diabetes in lean animals is less common. The diabetes of lean animals is more frequently characterized by hypoinsulinemia, ketosis and insulin dependence than is the case with obese animals. Diabetes may be produced experimentally by means of surgery, viral infection or the administration of various hormones and chemical agents. Both the spontaneous and experimental animal models have been used effectively to study the etiologies, complications, treatments and prevention of diabetes.

Alterations in islet cell ultrastructure following streptozotocin-induced diabetes in the rat

The response of islet cells to streptozotocin-induced diabetes was investigated by transmission electron microscopy. Rats were given streptozotocin i.p. (100 mg/kg followed by another dose of 25 mg/kg 24 h later) and sacrificed after 10 days. Pancreata from rats with high serum glucose values (381-553 mg/100 ml) were selected for ultrastructural examination. Islets in these animals were smaller and much less frequent than those of control animals. Cell types were not always easily identifiable in diabetic animals: distinction between A and B cells was often difficult. Cells of some islets displayed diminished electron density and less structured cytoplasm, yet nuclei were not pyknotic. Such cells were usually deficient in secretion granules. A cells were least affected. Cells in the centers of some islets possessed multivesicular bodies, prominent dilated Golgi cisternae and secretory granules which were often pleomorphic. Nuclear envelopes of some peripheral islet cells were swollen and distended; mitochondria were enlarged and the rough endoplasmic reticulum prominent. Some islet cells retained features of B cells in spite of marked ultrastructural alterations. This diversity of morphological findings contrasts with the homogeneity of the population of streptozotocin-diabetic rats with respect to metabolic responses.