Allicin protects against myocardial apoptosis and fibrosis in streptozotocin-induced diabetic rats

To evaluate the cardioprotective effect of allicin (AL) on myocardial injury of streptozotocin (STZ)-induced diabetic rats and to further explore its underlying mechanisms. Hyperglycemia was induced in rats by single intraperitoneal injection of STZ (40 mg/kg). Three days after STZ induction, the hyperglycemic rats (plasma glucose levels ≥ 16.7 mmol/l) were treated with AL by intraperitoneal injection at the doses of 4 mg/kg, 8 mg/kg, and 16 mg/kg daily for 28 days. The fasting blood glucose levels were measured on every 7th day during the 28 days of treatment. The body weight, blood glucose, and parameter of cardiac function were detected after 4 weeks to study the cardioprotective effects of AL on diabetic rats in vivo. The apoptotic index of cardiomyocytes was estimated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. The expressions of Fas, Bcl-2, CTGF, and TGF-β(1) protein were studied by immunohistochemistry. Laser scanning confocal microscopy technique was utilized to observe the effects of AL on intracellular calcium concentration ([Ca(2+)](i)) in rat ventricular cardiomyocytes. AL at the doses of 4 mg/kg, 8 mg/kg, and 16 mg/kg significantly reduced blood glucose levels in a dose-dependent manner and increased body weight as well compared with the model group. Hemodynamic parameters including left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), and maximum rate of left ventricular pressure rise and fall (+dp/dtmax and -dp/dtmax) were significantly restored back to normal levels in AL-treated (8 mg/kg and 16 mg/kg) rats compared with diabetic model rats. AL markedly inhibited cardiomyocyte apoptosis induced by diabetic cardiac injury. Further investigation revealed that this inhibitory effect on cell apoptosis was mediated by increasing anti-apoptotic protein Bcl-2 and decreasing pro-apoptotic protein Fas. Additional experiments demonstrated AL abrogated myocardial fibrosis by blocking the expressions of CTGF and TGF-β(1) protein. AL shows protective action on myocardial injury in diabetic rats. The possible mechanisms were involved in reducing blood glucose, correcting hemodynamic impairment, reducing Fas expression, activating Bcl-2 expression, decreasing intracellular calcium overload, inhibiting the expressions of TGF-β(1) and CTGF, and further improving cardiac function.     

Visualisation studies and glomerular filtration in early diabetic rats

The purpose of this mini-review is to show that more modern multi-photon microscopy approaches allow quantitative glomerular filtration experiments. Modern science has now entered a transition period from light microscopy to multi-photon confocal microscopy. Since the late 20th century, multi-photon microscopy has been applied in the study of organ function. In keeping with observations made in renal physiology and other representative studies throughout this transition period, and in the context of advancing microscopy techniques, this review has been presented as a comment on the glomerular filtration barrier, with a focus on the early aetiopathogenesis of diabetes.     

Changes in the glomerular filtration barrier during aging in rats

In this work, we analysed histochemical, biochemical and functional modifications of the glomerular basement membrane (GBM), occurring for aging, in the Rat. The results suggest an increase of collagenous components and a decrease of sulfated glucosaminoglycans as a function of age. In other respects, fixed anionic sites of the GBM, disclosed by colloidal iron, are almost exclusively restricted to the laminae rarae in one month-old rats, whereas the marker appears randomly scattered among the lamina densa in 12 month-old animals. These changes could be the cause of increased permeability of the GBM during aging.     

Dietary nitrite inhibits early glomerular injury in streptozotocin-induced diabetic nephropathy in rats.

Increased production of reactive oxygen species (ROS) is a key event leading to microvascular complications, including nephropathy, in diabetes mellitus (DM). Excessive ROS and oxidative stress in DM have been reported to be associated with subsequent impaired nitric oxide (NO) bioavailability. The aim of this study is to examine the beneficial function of dietary nitrite supplementation as an interventional NO donor to attenuate early progression of diabetic nephropathy. To test this hypothesis, male Sprague-Dawley rats were randomly divided into four groups: non-diabetic rats given water with or without nitrite (nitrite-treated or untreated, respectively), and streptozotocin-induced diabetic rats given water with or without nitrite (nitrite-treated or untreated, respectively). After a 4 week experimental period, untreated diabetic rats exhibited significantly higher malondialdehyde (MDA) levels in the kidney compared with untreated non-diabetic rats, accompanied by a reduction in levels of endogenous NO synthase-derived nitrite. However, dietary nitrite supplementation to diabetic rats not only decreased MDA levels but also increased nitrite levels in the kidney to the same levels as in the non-diabetic kidney. These improvements accompanied an improvement in the parameters of glomerular injury, including urinary protein and albumin excretion, histopathological glomerular hypertrophy, and mesangial matrix accumulation. These results indicate that dietary nitrite is effective in the prevention of early diabetic glomerular injury in which NO bioavailability is impaired.     

Morin hydrate protects cultured rat glomerular mesangial cells against oxyradical damage

Cultured rat glomerular mesangial cells were damaged when exposed to oxyradicals generated either from xanthine oxidase plus hypoxanthine, or by superoxide radicals formed from menadione. Morin hydrate is an antioxidant extracted from yellow Brazil wood. When morin hydrate was added to cultured rat glomerular mesangial cells which were attacked by oxyradicals generated by xanthine oxidase plus hypoxanthine, the survival time of the cells was doubled. However, this protective effect of morin hydrate was less marked when the cells were attacked by menadione. Note that the protective effects of Trolox which is a polar analogue of vitamin E were miniscule relative to those of morin hydrate with both oxidants.     

Adrenomedullin improves cardiac function and prevents renal damage in streptozotocin-induced diabetic rats

Adrenomedullin (AM) is a potent vasodilating peptide and is involved in cardiovascular and renal disease. In the present study, we investigated the role of AM in cardiac and renal function in streptozotocin (STZ)-induced diabetic rats. A single tail-vein injection of adenoviral vectors harboring the human AM gene (Ad.CMV-AM) was administered to the rats 1-wk post-STZ treatment (65 mg/kg iv). Immunoreactive human AM was detected in the plasma and urine of STZ-diabetic rats treated with Ad.CMV-AM. Morphological and chemical examination showed that AM gene delivery significantly reduced glycogen accumulation within the hearts of STZ-diabetic rats. AM gene delivery improved cardiac function compared with STZ-diabetic rats injected with control virus, as observed by decreased left ventricular end-diastolic pressure, increased cardiac output, cardiac index, and heart rate. AM gene transfer significantly increased left ventricular long axis (11.69 +/- 0.46 vs. 10.31 +/- 0.70 mm, n = 10, P < 0.05) and rate of pressure rise and fall (+6,090.1 +/- 597.3 vs. +4,648.5 +/- 807.1 mmHg/s), (-4,902.6 +/- 644.2 vs. -3,915.5 +/- 805.8 mmHg/s, n = 11, P < 0.05). AM also significantly attenuated renal glycogen accumulation and tubular damage in STZ-diabetic rats as well as increased urinary cAMP and cGMP levels, along with increased cardiac cAMP and Akt phosphorylation. We also observed that delivery of the AM gene caused an increase in body weight along with phospho-Akt and membrane-bound GLUT4 levels in skeletal muscle. These results suggest that AM plays a protective role in hyperglycemia-induced glycogen accumulation and cardiac and renal dysfunction via Akt signal transduction pathways.     

Polymorphonuclear neutrophil dysfunctions in streptozotocin-induced type 1 diabetic rats

Since conflicting results have been reported on non-specific immune response in type 1 diabetes, this study evaluates polymorphonuclear neutrophil (PMN) functions in the infection free Long Evan diabetic rats (type 1) by using tests that include: polarization assay, phagocytosis of baker\'s yeasts (Saccharomyces cerevisiae) and nitroblue tetrazolium (NBT) dye reduction. Polarization assay showed that neutrophils from diabetic rats were significantly activated at the basal level compared to those from the controls (p < 0.001). After PMN activation with N-formylmethionyl-leucyl-phenylalanine (FMLP), control neutrophils were found to be more polarized than those of the diabetic neutrophils and the highest proportions of polarization were found to be 67 % and 57 % at 10(-7) M FMLP, respectively. In the resting state, neutrophils from the diabetic rats reduced significantly more NBT dye than that of the controls (p < 0.001). The percentages of phagocytosis of opsonized yeast cells by the neutrophils from control and diabetic rats were 87 % and 61 %, respectively and the difference was statistically significant (p < 0.001). Evaluation of the phagocytic efficiency of PMNs revealed that control neutrophils could phagocytose 381 +/- 17 whereas those from the diabetic rats phagocytosed 282 +/- 16 yeast cells, and the efficiency of phagocytosis varied significantly (p < 0.001). Further, both the percentages of phagocytosis and the efficiency of phagocytosis by the diabetic neutrophils were inversely related with the levels of their corresponding plasma glucose (p = 0.02; r = -0.498 and p < 0.05; r = -0.43, respectively), which indicated that increased plasma glucose reduced the phagocytic ability of neutrophils. Such relationship was not observed with the control neutrophils. These data clearly indicate that PMN functions are altered in the streptozotocin (STZ)-induced diabetic rats, and hyperglycemia may be the cause for the impairment of their functions leading to many infectious episodes.     

Aldosterone antagonists in monotherapy are protective against streptozotocin-induced diabetic nephropathy in rats

Angiotensin converting enzyme inhibitors (ACEi) and angiotensin II receptor blockers (ARB) are the standard clinical therapy of diabetic nephropathy (DN), while aldosterone antagonists are only used as adjuncts. Previously in experimental DN we showed that Na/K ATPase (NKA) is mislocated and angiotensin II leads to superimposed renal progression. Here we investigated the monotherapeutic effect of aldosterone blockers on the progression of DN and renal NKA alteration in comparison to ACEi and ARBs. Streptozotocin-diabetic rats developing DN were treated with aldosterone antagonists; ACEi and ARB. Renal function, morphology, protein level and tubular localization of NKA were analyzed. To evaluate the effect of high glucose per se; HK-2 proximal tubular cells were cultured in normal or high concentration of glucose and treated with the same agents. Aldosterone antagonists were the most effective in ameliorating functional and structural kidney damage and they normalized diabetes induced bradycardia and weight loss. Aldosterone blockers also prevented hyperglycemia and diabetes induced increase in NKA protein level and enzyme mislocation. A monotherapy with aldosterone antagonists might be as, or more effective than ACEi or ARBs in the prevention of STZ-induced DN. Furthermore the alteration of the NKA could represent a novel pathophysiological feature of DN and might serve as an additional target of aldosterone blockers.     

Protective effect of ginsenoside Rb1 against myocardial ischemia/reperfusion injury in streptozotocin-induced diabetic rats

The objective of the current study is to investigate whether ginsenoside Rb1, a major pharmacological extract of ginseng that could attenuate myocardial ischemia reperfusion (MI/R) injury in non-diabetic myocardium, can attenuate MI/R injury in diabetes that are more vulnerable to ischemic insult. Rats were divided into seven groups: (i) diabetic sham, (ii) diabetic, (iii) normal, (iv) diabetic + ginsenoside Rb1, (v) diabetic + wortmannin, (vi) diabetic + wortmannin + ginsenoside Rb1, (vii) diabetic sham + wortmannin. Ginsenoside Rb1 and/or wortmannin were administered prior to inducing MI/R (30 min of coronary artery occlusion followed by 120 min reperfusion). At the end of the experiment, postischemic myocardial infarct size was significantly higher in the diabetic untreated group as compared to normal (P < 0.05), accompanied with increased myocardial apoptosis, elevated plasma CK-MB and LDH release and reduced blood pressure. Ginsenoside Rb1 reduced infarct size, cardiomyocyte apoptosis and caspase-3 activity compared to the diabetic group. The cardioprotective effects of ginsenoside Rb1 were cancelled by wortmannin. Ginsenoside Rb1 significantly upregulated phosphorylated Akt expression, which was attenuated by wortmannin. Ginsenoside Rb1 exerts cardioprotective effects against MI/R injury in diabetic rats, which is partly through activation of phosphatidylinositol 3-kinase (PI3 K)/Akt pathway. Thus this study shows a novel pharmacological preconditioning with ginsenoside Rb1 in the diabetic myocardium.     

Hepatoprotective effects of melatonin against pronecrotic cellular events in streptozotocin-induced diabetic rats

Oxidative stress-mediated damage to liver tissue underlies the pathological alterations in liver morphology and function that are observed in diabetes. We examined the effects of the antioxidant action of melatonin against necrosis-inducing DNA damage in hepatocytes of streptozotocin (STZ)-induced diabetic rats. Daily administration of melatonin (0.2 mg/kg) was initiated 3 days before diabetes induction and maintained for 4 weeks. Melatonin-treated diabetic rats exhibited improved markers of liver injury (P?<?0.05), alkaline phosphatase, and alanine and aspartate aminotransferases. Melatonin prevented the diabetes-related morphological deterioration of hepatocytes, DNA damage (P?<?0.05), and hepatocellular necrosis. The improvement was due to containment of the pronecrotic oxygen radical load, observed as inhibition (P?<?0.05) of the diabetes-induced rise in lipid peroxidation and hydrogen peroxide increase in the liver. This was accompanied by improved necrotic markers of cellular damage: a significant reduction in cleavage of the DNA repair enzyme poly(ADP-ribose) polymerase 1 (PARP-1) into necrotic 55- and 62-kDa fragments, and inhibition of nucleus-to-cytoplasm translocation and accumulation in the serum of the high-mobility group box 1 (HMGB1) protein. We conclude that melatonin is hepatoprotective in diabetes. It reduces extensive DNA damage and resulting necrotic processes. Melatonin application could thus present a viable therapeutic option in the management of diabetes-induced liver injury.     

Lignin-derived lignophenols attenuate oxidative and inflammatory damage to the kidney in streptozotocin-induced diabetic rats

Abstract

This study investigated the effects of lignin-derived lignophenols (LPs) on the oxidative stress and infiltration of macrophages in the kidney of streptozotocin (STZ)-induced diabetic rats. The diabetic rats were divided into four groups with 0%, 0.11%, 0.33% and 1.0% LP diets. The vehicle-injected controls were given a commercial diet. At 5 weeks, superoxide (O₂^?) production, macrophage kinetics, the degree of fibrosis in glomeruli and mRNA expression for monocyte chemoattractant protein-1 (MCP-1) were examined. The NADPH-stimulated O₂^? levels in the kidney of the diabetic rats treated with 1.0% LP were significantly lower than those in untreated diabetic rats. The number of macrophages, levels of MCP-1 mRNA expression and degree of glomerular fibrosis increased in untreated LP and these levels were significantly lower in 1.0%LP-treated rats. The results suggested that LPs suppress the excess oxidative stress, the infiltration and activation of macrophages and the glomerular expansion in STZ-induced diabetic kidneys.     

Ovarian dysfunction in streptozotocin-induced diabetic rats

The effect of streptozotocin diabetes on some ovarian functions in adult rats was examined. Diabetic diestrus animals showed reduced ovary weight and lower circulating levels of progesterone. Scatchard plots of binding data derived from ovarian particulate fractions of normal and streptozotocin diabetic rats revealed the presence of one class of binding sites with high affinity for 125I-hCG. The apparent association constant of the hCG receptors of diabetic ovaries was comparable to that of normal gonads. However, a marked decrease (42%) in the number of hCG binding sites was found in diabetic animals. With isolated luteal cells similar results were obtained, and the administration of insulin to streptozotocin diabetic rats restored to normality the number of hCG binding sites. The maximal response of progesterone production by luteal cells from control ovaries was obtained with 10(-10) M hCG. A 100-fold higher concentration of hCG was required for the maximum stimulation of cAMP synthesis. The cAMP response of cells from diabetic rats was significantly higher than that of control cells. However, luteal cells from diabetic rats showed some loss of sensitivity in the synthesis of progesterone during incubation with hCG. Most of the alterations seen in diabetic female rats could be restored with insulin therapy, indicating that insulin plays an important role in the regulation and maintenance of normal reproductive functions. It is suggested that the diminution of the LH receptor population causes the disruption of normal luteal cell function. This fact could be responsible for some of the reproductive alterations in the diabetic female rat.     

Galangin,a natural flavonoid reduces mitochondrial oxidative damage in streptozotocin-induced diabetic rats

Objective: We designed this study to observe the effect of galangin on damaged mitochondria in the liver of diabetic rats.

Methods: Male albino Wistar rats were made diabetic by injecting streptozotocin (STZ) intraperitoneally (40?mg?kg^?1 body weight (BW)). Galangin (8?mg?kg^?1 BW) or glibenclamide (600?µg?kg^?1 BW) was given orally daily once for 45 days to both healthy and diabetic rats.

Results: Diabetic rats showed significant (P?P?P?P?P?Conclusion: From the results, we conclude that galangin could maintain liver mitochondrial function in diabetic rats.     

3,5-Diiodo-l-thyronine ameliorates diabetic nephropathy in streptozotocin-induced diabetic rats

3, 5-Diiodothyronine (T2), a natural metabolite of triiodothyronine (T3) from deiodination pathway, can mimic biologic effects of T3 without inducing thyrotoxic effects. Recent studies revealed T3 acted as a protective factor against diabetic nephropathy (DN). Nevertheless, little is known about the effect of T2 on DN. This study was designed to investigate whether and how T2 affects experimental models of DN in vivo and in vitro. Administration of T2 was found to prevent significant decrease in SIRT1 protein expression and activity as well as increases in blood glucose, urine albumin excretion, matrix expansion, transforming growth factor-β1 expression, fibronectin and type IV collagen deposition in the diabetic kidney. Concordantly, similar effects of T2 were exhibited in the cultured rat mesangial cells (RMC) exposed to high glucose and that could be abolished by a known SIRT1 inhibitor, sirtinol. Moreover, enhanced NF-κB acetylation and JNK phosphorylation present in both diabetic rats and high glucose-treated RMC were distinctly dampened by T2. Collectively, these results suggested that T2 was a protective agent against renal damage in diabetic nephropathy, whose action involved regulation of SIRT1.     

Interleukin 1 protects rats against oxygen toxicity

We studied the effect of interleukin 1 alpha (IL-1) in the protection against O2 toxicity. Tracheal insufflation of IL-1 resulted in a dose-dependent protection against O2 toxicity. All control rats died within 3 days of O2 exposure. In contrast, 84, 71, and 20% of rats insufflated with 5, 1, and 0.2 microgram(s) IL-1 (150, 30, and 6 x 10(4) U), respectively, survived 100% O2 exposure for greater than 11 days. At 2.3 days after O2 exposure, control rats showed severe pulmonary injury, which insufflation of 5 microgram(s) IL-1 markedly attenuated. The protection against O2 toxicity was associated with a selective enhancement of pulmonary Mn-superoxide dismutase (Mn-SOD) activity in IL-1-insufflated rats. In rats insufflated with IL-1 that survived exposure to 100% O2 for 7 days, the activities of pulmonary Mn-SOD, Cu,Zn-SOD, catalase, and glutathione peroxidase were all increased. The increased pulmonary Mn-SOD activity demonstrated in IL-1-insufflated rats at 2.3 days after O2 exposure may contribute to the protection against acute O2 toxicity, and the markedly increased activities of all pulmonary antioxidant enzymes shown in rats insufflated with IL-1 that survived O2 exposure for 7 days may in part be responsible for the chronic adaptation of these rats to a 100% O2 environment.     

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.     

Glial and neuronal dysfunction in streptozotocin-induced diabetic rats

Neuronal dysfunction has been noted very soon after the induction of diabetes by streptozotocin injection in rats. It is not clear from anatomical evidence whether glial cell dysfunction accompanies the well-documented neuronal deficit. Here, we isolate the Müller cell driven slow-P3 component of the full-field electroretinogram and show that it is attenuated at 4 weeks following the onset of streptozotocin-hyperglycaemia. We also found a concurrent reduction in the sensitivity of the phototransduction cascade, as well as in the components of the electroretinogram known to indicate retinal ganglion cell and amacrine cell integrity. Our data support the idea that neuronal and Müller cell dysfunction occurs at the same time in streptozotocin-induced hyperglycaemia.