[New hypotheses for the mechanisms of streptozotocin and alloxan inducing diabetes mellitus]

The Protective Effect of Marigold Hydroalcoholic Extract in STZ-Induced Diabetic Rats: Evaluation of Cardiac and Pancreatic Biomarkers in the Serum

Diabetes mellitus is the most common endocrine disorder worldwide and it is usually along with complications such as retinopathy, neuropathy, nephropathy, and cardiovascular disease. The prevalence of diabetes is increasing and its treatment has created concerns in society. The use of herbal medicine can be helpful in the management of diabetes mellitus. The aim of this study was to investigate the protective effect of marigold hydroalcoholic extract under diabetes condition. A total of 36 male Wistar rats were randomly divided into four groups: normal control group, diabetic control group, and groups treated with 250 or 500 mg/kg hydroalcoholic extract of marigold flower during four weeks. At the end of the study, the rats were anesthetized with ketamine/xylazine, and sampling was performed through cardiac puncture. The results showed that treatment with marigold improved body weight. In addition, we determined that marigold normalized the level of CK-MB, total CK, amylase, and lipase in a dose-dependent manner. Probably these effects resulted from antioxidant property of marigold; thus we suggest that marigold flower can be useful for reduction of diabetes complication.

Antioxidant effect of pomegranate against streptozotocin-nicotinamide generated oxidative stress induced diabetic rats

Oxidative stress attributes a crucial role in chronic complication of diabetes. The aim of this study was to determine the most effective part of pomegranate on oxidative stress markers and antioxidant enzyme activities against streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats. Male Sprague-Dawley rats were randomly divided into six groups. Experimental diabetes was induced by a single intraperitoneal injection (i.p), 15 min after the i.p administration of NA. Diabetic rats showed significant increase in plasma glucose level, and the significant decrease in plasma insulin level. The activities of antioxidant enzymes such as total antioxidant status (TAS), superoxide dismutase (SOD), and catalase (CAT) reduced while the levels of biomarkers of oxidative stress such as gamma-glutamyle transferase (GGT), and malondialdehyde (MDA) increased in diabetic control rats as compared to normal control rats. Oral treatment with pomegranate seed-juice for 21 days demonstrated significant protective effects on all the biochemical parameters studied. Besides, biochemical findings were supported by histopathological study. These results revealed that pomegranate has potential protective effect against oxidative stress induced diabetic rats.

Comparative study of the binding characteristics to and inhibitory potencies towards PARP and in vivo antidiabetogenic potencies of taurine, 3-aminobenzamide and nicotinamide

BACKGROUND

Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.

METHODS

PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.

RESULTS

3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.

CONCLUSIONS

At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.

Renal protective activity of Hsian-tsao extracts in diabetic rats

OBJECTIVE

To investigate the renal protective activity of Hsian-tsao Mesona procumbens Hemsl. water extracts in diabetic rats.

METHODS

Thirty Sprague-dawley female rats were randomly divided into three groups (n = 10 each), "control group" with intraperitoneal saline injection, "diabetic group" with 60 mg of intraperitoneal streptozotocin injection per kg of body weight and "Hsian-tsao group" with intragastric administration of Hsian-tsao extraction everyday for 4 weeks after intraperitoneal streptozotocin injection. The body weight and blood sugar were measured before and after model induction in the three groups. Thrombospondin-1 (TSP-1) expressions in the kidney were monitored by immunohistochemistry. Kidney ultrastructural changes were also analyzed by using transmission electron microscopy.

RESULTS

Before diabetic model induction, there were no significant differences among the three groups in body weight and blood sugar. Four weeks after the induction of diabetes, the differences became statistically significant. Electron microscopy also revealed disruption of the foot processes of the podocytes and other damages in diabetic group. These damages were significantly less severe in Hsian-tsao group when compared with the diabetic group. TSP-1 expressions in the kidney were significantly increased in both the diabetic group and Hsian-tsao group, but it was relatively lower in Hsian-tsao group than in diabetic group.

CONCLUSION

Our results showed that Hsian-tsao treatment in the diabetic rats effectively prevented the pathological alterations in the kidney and decreased the TSP-1 expression. It was suggested that Hsian-tsao had protective effect on the kidneys of the diabetic rats.

Evaluation of level of DNA damage in blood leukocytes of non-diabetic and diabetic rat exposed to cigarette smoke

The objective of the present study was to use the comet assay to evaluate the steady-state level of DNA damage in peripheral blood leukocytes from diabetic and non-diabetic female Wistar rats exposed to air or to cigarette smoke. A total of 20 rats were distributed into four experimental groups (n=5 rats/group): non-diabetic (control) and diabetic exposed to filtered air; non-diabetic and diabetic exposed to cigarette smoke. A pancreatic beta (beta)-cytotoxic agent, streptozotocin (40 mg/kg b.w.) was used to induce experimental diabetes in rats. Rats placed into whole-body exposure chambers were exposed for 30 min to filtered air (control) or to tobacco smoke generated from 10 cigarettes, twice a day, for 2 months. At the end of the 2-month exposure period, each rat was anesthetized and humanely killed to obtain blood samples for genotoxicity analysis using the alkaline comet assay. Blood leukocytes sampled from diabetic rats presented higher DNA damage values (tail moment=0.57+/-0.05; tail length=19.92+/-0.41, p<0.05) compared to control rats (tail moment=0.34+/-0.02; tail length=17.42+/-0.33). Non-diabetic (tail moment=0.43+/-0.04, p>0.05) and diabetic rats (tail moment=0.41+/-0.03, p>0.05) exposed to cigarette smoke presented non-significant increases in DNA damage levels compared to control group. In conclusion, our data show that the exposure of diabetic rats to cigarette smoke produced no additional genotoxicity in peripheral blood cells of female Wistar rats.

Oral administration of sodium tungstate improves cardiac performance in streptozotocin-induced diabetic rats

Normalization of hyperglycemia and hyperlipidemia is an important objective in preventing diabetes-induced cardiac dysfunction. Our study investigated the effects of sodium tungstate on cardiac performance in streptozotocin-induced (STZ) diabetic rats based on its potential antidiabetic and antioxidant activity. Male Wistar rats were made STZ-diabetic and then treated with tungstate in their drinking water for 9 weeks. Body mass, food and fluid intake, plasma glucose, insulin, triglyceride, and free fatty acids levels were measured. At the termination of the study period, an oral glucose tolerance test (OGTT) was performed, and cardiac performance was evaluated using an isolated working heart apparatus. Tungstate-treated STZ-diabetic rats showed a significant reduction in fluid and food intake, plasma glucose, triglycerides, and free fatty acid levels, and improved tolerance to glucose in OGTT, owing to tungstate-mediated enhancement of insulin activity rather than increased insulin levels. Left ventricular pressure development, the rate of contraction (+dP/dT), and the rate of relaxation (-dP/dT) were significantly improved in tungstate-treated diabetic rats. Apart from a decreased rate of body mass gain, no other signs of toxicity or hypoglycemic episodes were observed in tungstate-treated rats. This study extends previous observations on the antidiabetic activities of tungstate, and also reports for the first time the salutary effects in preventing diabetic cardiomyopathy.

Amelioration of diabetic nephropathy by dried Rehmanniae Radix (Di Huang) extract

The effects of dried Rehmanniae Radix (Di Huang) extract were investigated using a diabetic nephropathy model: rats given streptozotocin after nephrectomy. The results showed that this crude drug reduced the magnitudes of the increases in glucose, urea nitrogen, 5-hydroxymethylfurfural and thiobarbituric acid (TBA)-reactive substance levels, with the effects being most marked in the high blood glucose group. The renal histopathological lesions, which were conspicuous in rats not given dried Rehmanniae Radix extract, were ameliorated considerably in the high blood glucose group given this extract. It appears that dried Rehmanniae Radix extract may be useful as a therapeutic agent for inhibiting the progression of diabetic nephropathy. On the basis of these results, the possible mechanisms of action of this crude drug are discussed.

Genotoxicity of streptozotocin

Streptozotocin (Streptozocin, STZ, CAS No. 18883-66-4) is a monofunctional nitrosourea derivative isolated from Streptomyces achromogenes. It has broad spectrum antibiotic activity and antineoplastic properties and is often used to induce diabetes mellitus in experimental animals through its toxic effects on pancreatic beta cells. STZ is a potent alkylating agent known to directly methylate DNA and is highly genotoxic, producing DNA strand breaks, alkali-labile sites, unscheduled DNA synthesis, DNA adducts, chromosomal aberrations, micronuclei, sister chromatid exchanges, and cell death. This antibiotic was found to be mutagenic in bacterial assays and eukaryotic cells. STZ is also carcinogenic; a single administration induces tumors in rat kidney, liver, and pancreas. Several lines of evidence indicate that free radicals are involved in the production of DNA and chromosome damage by this compound. Because of the use of STZ as an antineoplastic agent, the study of its genotoxicity has considerable practical significance. The purpose of this review is to present our current knowledge regarding the genotoxicity of STZ.

Treatment of cultured pancreatic B-cells with streptozotocin induces cell death by apoptosis

Treatment of cultured pancreatic B-cells (HIT-T15 and RINm5F) with the diabetogenic drug streptozotocin resulted in a significant increase in the number of cells that became detached from the substrate during a subsequent culture period. Examination of the detached cells by fluorescence microscopy after staining with acridine orange or by electron microscopy revealed evidence of chromatin condensation and margination. Isolation and fractionation of DNA from these cells revealed a pattern of oligonucleosomal fragmentation that was not evident in untreated cells. All of these features are characteristic of entry of the cells into apoptosis and the results suggest that the diabetogenic action of streptozotocin involves induction of apoptosis in pancreatic B-cells.

Degradation products of streptozotocin do not induce hyperglycemia in rats

The present study was conducted to determine whether degradation products of streptozotocin formed under various conditions induce hyperglycemia in rats. Streptozotocin is completely degraded in pH 7.4 buffer in 4 hr and even more rapidly in plasma. Streptozotocin degradation products resulting from incubation in pH 7.4 phosphate buffer or in plasma were not diabetogenic in rats.