Zinc supplementation alleviates the progression of diabetic nephropathy by inhibiting the overexpression of oxidative-stress-mediated molecular markers in streptozotocin-induced experimental rats

Zinc deficiency during diabetes projects a role for zinc nutrition in the management of diabetic nephropathy. The current study explored whether zinc supplementation protects against diabetic nephropathy through modulation of kidney oxidative stress and stress-induced expression related to the inflammatory process in streptozotocin-induced diabetic rats. Groups of hyperglycemic rats were exposed to dietary interventions for 6 weeks with zinc supplementation (5 times and 10 times the normal level). Supplemental-zinc-fed diabetic groups showed a significant reversal of increased kidney weight and creatinine clearance. There was a significant reduction in hyperlipidemic condition along with improved PUFA:SFA ratio in the renal tissue. Expression of the lipid oxidative marker and expression of inflammatory markers, cytokines, fibrosis factors and apoptotic regulatory proteins observed in diabetic kidney were beneficially modulated by zinc supplementation, the ameliorative effect being concomitant with elevated antiapoptosis. There was a significant reduction in advanced glycation, expression of the receptor of the glycated products and oxidative stress markers. Zinc supplementation countered the higher activity and expression of polyol pathway enzymes in the kidney. Overexpression of the glucose transporters, as an adaptation to the increased need for glucose transport in diabetic condition, was minimized by zinc treatment. The pathological abnormalities in the renal architecture of diabetic animals were corrected by zinc intervention. Thus, dietary zinc supplementation has a significant beneficial effect in the control of diabetic nephropathy. This was exerted through a protective influence on oxidative-stress-induced cytokines, inflammatory proliferation and consequent renal injury.     

Alterations in kidney tissue following zinc supplementation to STZ-induced diabetic rats

Diabetes mellitus is a chronic disease characterized by anomalies forming in carbohydrate, lipid, protein metabolisms and the incidence of this disease varies widely throughout the world. Zinc is an important element which is essential for life and is present in nature. In this study, the animals were divided into four groups. These groups were named as untreated; zinc sulfate; streptozotocin (STZ); STZ and zinc sulfate. STZ (65 mg/kg) was dissolved in a freshly prepared 0.01 M pH 4.5 citrate buffer and given with intraperitoneal injection in a single dose. Zinc sulfate (100 mg/kg) was dissolved in distilled water and given to the animals by gavage at a daily dose for 60 days. The rats were sacrificed under ether anesthesia. This study was aimed to investigate histological and biochemical changes of zinc supplementation on the kidney tissue in STZ-induced diabetic rats. In the current study, histological and histochemical observations showed that the occurred degenerative changes decreased after giving zinc in the kidney tissue of diabetic group. Kidney glutathione (GSH) levels decreased and lipid peroxidation (LPO), nonenzymatic glycosylation (NEG), urea and creatinine levels increased in diabetic rats. GSH levels increased, while LPO, NEG, urea and creatinine levels decreased in the kidney with administration of zinc to diabetic rats. As a result, we observed curative effects of zinc given to diabetic rats. We can say that zinc may be an important antioxidant for the treatment of secondary complications of diabetes in kidney tissue.     

Effects of oral zinc and magnesium supplementation on serum thyroid hormone and lipid levels in experimentally induced diabetic rats

This study was designed to investigate the effects of oral zinc and magnesium supplementation on serum thyroid hormone and lipid levels in alloxan-induced diabetic rats. Thirty-two albino male rats, weighing 234±34 g, were divided into four experimental groups (control, diabetic, diabetic+zinc supplemented and diabetic+ magnesium supplemented). The experiment lasted for 60 d. The first 45 d of the experiment was the supplementation and last 15 d was the supplementation and diabetes-inducing period. Diabetic+zinc-supplemented and diabetic+magnesium-supplemented groups were given orally (by adding in their drinking water) 227 mg/L of zinc and 100 mg/kg body weight (bw) of magnesium, respectively throughout the experiment. Control and diabetic groups served as controls and did not receive zinc or magnesium supplementation. Diabetic, diabetic+zinc-supplemented, and diabetic+magnesium-supplemented groups were given a daily injection (ip) of 100 mg/kg bw of alloxan for 15 d starting on d 46 of the experiment. The control group was only injected with the same volume of isotonic NaCl as the diabetic group received. At the end of the of the experiment, rats in all four groups were fasted for 12 h and blood samples were taken from the heart under ether anesthesia for the determination of thyroid hormone, glucose, total cholesterol, and triglyceride concentrations. It was found that serum glucose, total cholesterol, and triglyceride concentrations were higher and serum T3 and T4 concentrations were lower in diabetic rats than those in the control group. Zinc supplementation did not change any parameter in diabetic rats. However, magnesium supplementation decreased the elevated total cholesterol and triglyceride concentrations of the diabetic rats to the control level. It was concluded that oral magnesium supplementation might decrease the diabetes-induced disturbances of lipid metabolism.     

Zinc Supplementation Attenuates Metallothionein and Oxidative Stress Changes in Kidney of Streptozotocin-Induced Diabetic Rats

Zinc is an element that under physiological conditions preferentially binds to and is a potent inducer of metallothionein under physiological conditions. The present study was conducted to explore whether zinc supplementation morphologically and biochemically protects against diabetic nephropathy through modulation of kidney metallothionein induction and oxidative stress in streptozotocin-induced diabetic rats. Thirty-two Wistar albino male rats were equally divided into four groups. The first group was used as untreated controls and the second group was supplemented with 30?mg/kg/day zinc as zinc sulfate. The third group was treated with streptozotocin to induce diabetes and the fourth group was treated with streptozotocin and supplemented with zinc as described for group 2. The blood glucose and micro-albuminuria levels, body and kidney weights were measured during the 42-day experimental period. At the end of the experiment, the kidneys were removed from all animals from the four groups. Diabetes resulted in degenerative kidney morphological changes. The metallothionein immunoreactivity level was lower and the kidney lipid peroxidation levels were higher in the diabetes group than in the controls. The metallothionein immunoreactivity levels were higher in the tubules of the zinc-supplemented diabetic rats as compared to the non-supplemented diabetic group. The zinc and metallothionein concentrations in kidney tissue were higher in the supplemented diabetic group compared to the non-supplemented diabetes group. The activity of glutathione peroxidase did not change in any of the four groups. In conclusion, the present study shows that zinc has a protective effect against diabetic damage of kidney tissue through stimulation of metallothionein synthesis and regulation of the oxidative stress.     

Zinc and insulin sensitivity

Many studies have shown that zinc deficiency could decrease the response to insulin. In genetically diabetic animals, a low zinc status has been observed, contrary to induced diabetic animals. The zinc status of human patients depends on the type of diabetes and the age. Zinc supplementation seems to have beneficial effects on glucose homeostasis. However, the mechanism of insulin resistance secondary to zinc depletion is yet unclear. More studies are therefore necessary to document better zinc metabolism in diabetes mellitus, and the antioxidant activity of zinc on the insulin receptor and the glucose transporter.     

Effect of zinc supplementation on type 2 diabetes parameters and liver metallothionein expressions in Wistar rats

Zinc is a trace metal and acts as an active component of various enzymes. Zinc deficiency has been suggested to be associated with the development of diabetes. The present study investigated the role of zinc supplementation on prevention of diabetic conditions. A double-disease model mimicking hyperlipidemia and type 2 diabetes was created by applying high-fat diet and streptozotocin (STZ) to Wistar rats. We demonstrated that zinc supplementation improved symptoms of diabetes such as polydipsia and increased serum level of high-density lipoprotein cholesterol, indicating that zinc supplementation has a potential beneficial effect on diabetic conditions. The level of maldondialdehyde (MDA), an oxidative stress marker, was reduced in liver by zinc supplementation in high fat-fed rats with or without STZ injection. Meanwhile, we observed an increase in the expression of metallothioneins (MTs) in liver of rats treated with zinc. This suggests that the induction of MTs in liver, which has been shown to be important in scavenging free radicals, could be one of the underlying mechanisms of zinc supplementation on reducing MDA levels in liver. Finally, we found that zinc levels in liver were increased while there was no change in serum zinc levels, indicating that local zinc level might be a critical factor for the induction of MTs. Also, the level of MTs could potentially be an index of zinc bioavailability. Taken together, these results suggest that both zinc and MT could play an important role in balancing nutrition and metabolism to prevent diabetic development.     

A Preliminary and Qualitative Metallomics Study of Mercury in the Muscle of Fish from Amazonas, Brazil

In this study, we report the effect of zinc supplementation on the distribution of elements in kidney tissue of diabetic rats subjected to acute swimming exercise. Diabetes was induced by two subcutaneous injections of 40 mg/kg of streptozotocin within a 24-h period. Zinc was given intraperitoneally at a dose of 6 mg/kg per day for a period of 4 weeks. The rats (n = 80) were equally divided into eight study groups: controls, zinc-supplemented, swimming, diabetic, zinc-supplemented diabetic, zinc-supplemented swimming, diabetic swimming, and zinc-supplemented diabetic swimming. The levels of lead, cobalt, molybdenum, chromium, boron, magnesium, iron, copper, calcium, zinc, and selenium were determined in the kidney tissue samples by ICP-AES. Higher molybdenum, calcium, zinc, and selenium values were found in both swimming and nonswimming diabetic rats. Significantly higher iron values were found in swimming, diabetic, diabetic swimming, and zinc-supplemented diabetic swimming rats (p < 0.001). Diabetic, zinc-supplemented diabetic, diabetic swimming, and zinc-supplemented diabetic swimming rats had the highest copper values. These results show that zinc supplementation normalized the higher levels of molybdenum, calcium, selenium, and iron levels seen in diabetic rats, indicating that zinc may have a regulatory effect on element metabolism in kidney tissue.     

Effect of zinc supplementation on the distribution of various elements in the serum of diabetic rats subjected to an acute swimming exercise

The present study aims to examine the effect of supplementation of zinc on the distribution of various elements in the sera of diabetic rats subjected to an acute swimming exercise. A total of 80 Sprague–Dawley-type adult male rats were equally allocated to one of eight groups: Group 1, general; Group 2, zinc-supplemented; Group 3, zinc-supplemented diabetic; Group 4, swimming control; Group 5, zinc-supplemented swimming; Group 6, zinc-supplemented diabetic swimming; Group 7, diabetic swimming; and Group 8, diabetes. The rats were injected with 40 mg/kg/day subcutaneous streptozotocin (STZ) twice, with a 24-h interval between two injections. Zinc was supplemented at a dose of 6 mg/kg/day (ip) for 4 weeks. Blood samples were collected at the end of the 4-week study, and serum levels of lead, cobalt, molybdenum, chrome, sulfur, magnesium, manganese, sodium, potassium, phosphorus, copper, iron, calcium, zinc, and selenium (mg/L) were determined with atomic emission. The lowest molybdenum, chrome, copper, iron, potassium, magnesium, sodium, phosphorus, lead, selenium, and zinc values were obtained in Group 7 and 8. These same parameters were higher in the swimming exercise group (Group 4), relative to all other groups. The values in zinc-supplemented groups were found lower than the values in Group 4, but higher than those in Group 6 and 7. The results obtained from the study demonstrate that acute swimming exercise and diabetes affect the distribution of various elements in the serum, while zinc supplementation can prevent the negative conditions associated with both exercise and diabetes.     

Effects of dietary L-arginine supplementation on serum lipids and intestinal enzyme activities in diabetic rats

We investigated whether dietary supplementation with L-arginine, the endogenous precursor of nitric oxide, might affect serum lipid levels and activities of intestinal mucosa enzymes in animals, in which diabetes was induced by administration of streptozotocin. Control and diabetic rats were fed diets with or without 2% L-arginine supplementation for 4 weeks. Diabetic rats had significantly higher concentrations of serum triglycerides and LDL-cholesterol than control rats. These alterations were partially reduced by L-arginine supplementation. Experimental diabetes did not influence the lactase and leucine aminopeptidase activity in the intestine, but the activity of alkaline phosphatase was increased. Furthermore, activities of maltase and sucrase in the intestinal mucosa were elevated in streptozotocin-induced diabetic rats and were restored to control levels after dietary L-arginine supplementation. On the basis of the present experimental evidence, dietary L-arginine supplementation appears to affect the metabolism of lipoproteins and might alleviate some gastrointestinal dysfunctions, commonly seen in diabetes mellitus.     

Myocardial and metabolic dysfunction in type 2 diabetic rats: impact of ghrelin

Diabetes mellitus (DM) is commonly associated with metabolic and cardiac dysfunctions. The aim of this study was to examine the effect of ghrelin on metabolic and cardiac dysfunctions in a type-2 diabetes mellitus (T2DM) rat model. For this, 48 male adult Sprague-Dawley rats were divided equally into 4 groups: Group I, fed normal chow, served as normal control group; Groups II-IV, were fed a high-fat diet for 2?weeks followed by injection of streptozotocin (STZ) (35?mg/kg body mass) to create a model of T2DM; Group II, were not treated; Group III, were treated with the vehicle (saline); Group IV, were treated with ghrelin (40?μg/kg body mass) twice daily for 10 days. The untreated diabetic rats showed a significant increase in serum fasting blood glucose, insulin homeostasis model assessment (HOMA) index, triglycerides (TGs), low-density lipoprotein cholesterol (LDL-C), total serum cholesterol (TC), and body mass, with a decrease in high-density lipoprotein cholesterol (HDL-C) (p?< 0.05). Hearts isolated from diabetic rats showed a significant increase in myocardial fat content, a significant decrease in GLUT4, and an increase in acyl-CoA oxidase enzyme mRNA (p?< 0.05). Ghrelin administration for 10?days caused a significant improvement in lipid profile, HOMA index, and body mass, and significantly corrected the myocardial mass, significantly reduced the fat content of the myocardium, significantly increased GLUT4, and decreased acyl CoA oxidase mRNA (p?< 0.05). Thus, ghrelin improves both the metabolic functions and the disturbed energy metabolism in the cardiac muscle of obese diabetic rats.     

Supplementation of zinc mitigates the altered uptake and turnover of <Superscript>65</Superscript>Zn in liver and whole body of diabetic rats

Diabetes is a life threatening disease and its onset is linked with both environmental and genetic factors. Zinc metabolism gets altered during diabetes and results in many complications. The present study was designed to elucidate the effects of zinc supplementation on the biokinetics of ⁶⁵Zn in whole body, liver and its biodistribution in diabetic rats. The animals were divided into four groups viz; normal control; diabetic (single intraperitoneal injection of alloxan 150 mg/kg body weight); zinc treated (227 mg/l in drinking water); and diabetic + zinc treated. To carry out biokinetics study, each rat was injected intraperitoneally with 0.74 MBq radioactivity of ⁶⁵Zn following 4 weeks of different treatments and the radioactivity was determined by using a suitably shielded scintillation counter. Alloxan induced diabetic rats showed a significant decrease in both the fast (Tb₁) and slow (Tb₂) components of biological half-life of ⁶⁵Zn which, however, were normalized in whole body (P > 0.05) following zinc supplementation. In case of liver, Tb₂ component was brought back to the normal but Tb₁ component was not increased significantly. The present study indicates that the paucity of zinc in the tissues of the diabetic animals was due to decreased retention of tissue zinc as evidenced by increased serum Zn, hyperzincuria and increased rate of uptake of ⁶⁵Zn by the liver. Zinc supplementation caused a significant improvement in the retention of zinc in the tissues and is therefore likely to be of benefit in the treatment of diabetes.     

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.     

Soy lecithin supplementation alters macrophage phagocytosis and lymphocyte response to concanavalin A: a study in alloxan-induced diabetic rats

Dietary soy lecithin supplementation decreases hyperlipidemia and influences lipid metabolism. Although this product is used by diabetic patients, there are no data about the effect of soy lecithin supplementation on the immune system. The addition of phosphatidylcholine, the main component of lecithin, to a culture of lymphocytes has been reported to alter their function. If phosphatidylcholine changes lymphocyte functions in vitro as previously shown, then it could also affect immune cells in vivo. In the present study, the effect of dietary soy lecithin on macrophage phagocytic capacity and on lymphocyte number in response to concanavalin A (ConA) stimulation was investigated in non-diabetic and alloxan-induced diabetic rats. Supplementation was carried out daily with 2 g kg(-1) b.w. lecithin during 7 days. After that, blood was drawn from fasting rats and peritoneal macrophages and mesenteric lymph node lymphocytes were collected to determine the phospholipid content. Plasma triacylglycerol (TAG), total and HDL cholesterol and glucose levels were also determined. Lymphocytes were stimulated by ConA. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye reduction method and flow cytometry were employed to evaluate lymphocyte metabolism and cell number, respectively. Soy lecithin supplementation significantly increased both macrophage phagocytic capacity (+29%) in non-diabetic rats and the lymphocyte number in diabetic rats (+92%). It is unlikely that plasma lipid levels indirectly affect immune cells, since plasma cholesterol, TAG, or phospholipid content was not modified by lecithin supplementation. In conclusion, lymphocyte and macrophage function were altered by lecithin supplementation, indicating an immunomodulatory effect of phosphatidylcholine.     

Effects of cod liver oil on tissue antioxidant pathways in normal and streptozotocin-diabetic rats

Lipid disorders and increased oxidative stress may exacerbate some complications of diabetes mellitus. Previous studies have implicated the beneficial effects of some antioxidants, omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the protection of cells from the destructive effect of increased lipids and lipid peroxidation products. This study, therefore, was designed to investigate the effects of cod liver oil (CLO, Lysi Ltd. Island), which comprises mainly vitamin A, PUFAs, EPA and DHA. Effects were monitored on plasma lipids, lipid peroxidation products (MDA) and the activities of antioxidant enzymes, glutathione peroxidase (GSHPx) and catalase in heart, liver, kidney and lung of non-diabetic control and streptozotocin (STZ)-induced-diabetic rats. Two days after STZ-injection (55 mg kg(-1) i.p.), non-diabetic control and diabetic rats were divided randomly into two groups as untreated or treated with CLO (0.5 ml kg(-1) rat per day) for 12 weeks. Plasma glucose, triacylglycerol and cholesterol concentrations were significantly elevated in 12-week untreated-diabetic animals; CLO treatment almost completely prevented these abnormalities in triacylglycerol and cholesterol, but hyperglycaemia was partially controlled. CLO also provided better weight gain in diabetic animals. In untreated diabetic rats, MDA markedly increased in aorta, heart and liver but was not significantly changed in kidney and lung. This was accompanied by a significant increase in both GSHPx and catalase enzyme activities in aorta, heart, and liver of diabetic rats. In kidney and lung, diabetes resulted in reduced catalase while GSHPx was significantly activated. In aorta, heart, and liver, diabetes-induced changes in MDA were entirely prevented by CLO treatment. In the tissues of CLO-treated diabetic animals, GSHPx activity paralleled those of control animals. CLO treatment also caused significant improvements in catalase activities in every tissue of diabetic rats, but failed to affect MDA and antioxidant activity in control animals. The current study suggests that the treatment of diabetic rats with CLO provides better control of glucose and lipid metabolism, allows recovery of normal growth rate, prevents oxidative/peroxidative stress and ameliorates endogenous antioxidant enzyme activities in various tissues. Because CLO contains a plethora of beneficial compounds together, its use for the management of diabetes-induced complications may provide important advantages.     

Zinc supplementation ameliorates glycoprotein components and oxidative stress changes in the lung of streptozotocin diabetic rats

Zinc (Zn) is a component of numerous enzymes that function in a wide range of biological process, including growth, development, immunity and intermediary metabolism. Zn may play a role in chronic states such as cardiovascular disease and diabetes mellitus. Zn acts as cofactor and for many enzymes and proteins and has antioxidant, antiinflammatory and antiapoptotic effects. Taking into consideration that lung is a possible target organ for diabetic complications, the aim of this study was to investigate the protective role of zinc on the glycoprotein content and antioxidant enzyme activities of streptozotocin (STZ) induced diabetic rat tissues. Female Swiss albino rats were divided into four groups. Group I, control; Group II, control + zinc sulfate; Group III, STZ-diabetic; Group IV, diabetic + zinc sulfate. Diabetes was induced by intraperitoneal injection of STZ (65 mg/kg body weight). Zinc sulfate was given daily by gavage at a dose of 100 mg/kg body weight every day for 60 days to groups II and IV. At the last day of the experiment, rats were sacrificed, lung tissues were taken. Also, glycoprotein components, tissue factor (TF) activity, protein carbonyl (PC), advanced oxidative protein products (AOPP), hydroxyproline, and enzyme activities in lung tissues were determined. Glycoprotein components, TF activity, lipid peroxidation, non enzymatic glycation, PC, AOPP, hydroxyl proline, lactate dehydrogenase, catalase, superoxide dismutase, myeloperoxidase, xanthine oxidase, adenosine deaminase and prolidase significantly increased in lung tissues of diabetic rats. Also, glutathione levels, paraoxonase, arylesterase, carbonic anhydrase, and Na⁺/K⁺- ATPase activities were decreased. Administration of zinc significantly reversed these effects. Thus, the study indicates that zinc possesses a significantly beneficial effect on the glycoprotein components and oxidant/antioxidant enzyme activities.     

Zinc effects on hyperglycemia and hypoleptinemia in streptozotocin-induced diabetic mice.

Zinc has an antihyperglycemic effect. Zinc can also influence the production of leptin, a satiety factor that reduces appetite and blood sugar level. In this study, we investigated the effect of zinc supplementation on food intake and circulating leptin and glucose concentrations in streptozotocin-induced diabetic mice. Male diabetic mice received zinc supplementation (20 ppm) from drinking water for two weeks. The results showed that zinc treatment did not affect body weight gain, body fat content or food intake in these diabetic mice. However, zinc supplementation markedly ameliorated the hyperglycemia of diabetic mice. After zinc treatment, serum leptin concentrations tended to increase in the diabetic mice. This study suggests that zinc is a mediator of leptin production.     

Zinc and diabetes — clinical links and molecular mechanisms

Zinc is an essential trace element crucial for the function of more than 300 enzymes and it is important for cellular processes like cell division and apoptosis. Hence, the concentration of zinc in the human body is tightly regulated and disturbances of zinc homeostasis have been associated with several diseases including diabetes mellitus, a disease characterized by high blood glucose concentrations as a consequence of decreased secretion or action of insulin. Zinc supplementation of animals and humans has been shown to ameliorate glycemic control in type 1 and 2 diabetes, the two major forms of diabetes mellitus, but the underlying molecular mechanisms have only slowly been elucidated. Zinc seems to exert insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Furthermore, zinc might play a role in the development of diabetes, since genetic polymorphisms in the gene of zinc transporter 8 and in metallothionein (MT)-encoding genes could be demonstrated to be associated with type 2 diabetes mellitus. The fact that antibodies against this zinc transporter have been detected in type 1 diabetic patients offers new diagnostic possibilities. This article reviews the influence of zinc on the diabetic state including the molecular mechanisms, the role of the zinc transporter 8 and MT for diabetes development and the resulting diagnostic and therapeutic options.     

Changes in liver gangliosides in streptozotocin-induced diabetic rats

Diabetes mellitus is associated with various structural and functional liver abnormalities that affect the glycogen and lipid metabolisms. The effects of streptozotocin-induced diabetes and of insulin supplementation to Sprague-Dawley diabetic rats on ganglioside patterns in liver were determined. Diabetic livers showed a tendency to hepatomegaly 3 weeks after STZ-induction of diabetes. The concentration of total gangliosides in diabetic and non-diabetic livers was similar, but the concentration of total gangliosides in the liver of insulin-stabilized rats was slightly increased. Bidimensional TLC chromatographic analysis of gangliosides isolated from normal diabetic and insulin-stabilized diabetic livers showed quantitative and qualitative changes. In comparison with normal controls, the densitometric analyses of diabetic liver ganglioside patterns had increased amounts of GM3, GM1, GD1b, and GT1b gangliosides, while GM2 could not be detected. The hepatic ganglioside pattern of insulin-stabilized diabetic rats was partially restored, resembling the profile of normal rats. The activity of GalNAcT, GalT-2 and SialT-4 transferases was measured in liver microsomal fractions of the different groups of animals. Diabetic rats showed an increased activity of GalNAcT and a decrease in the activity of GalT-2 and SialT-4 compared with the controls. The enzymatic activities found in insulin-treated rats showed a tendency to return to the values observed in normal control animals. The results evidenced that streptozotocin-induced diabetes affects the liver ganglioside pattern and the ganglioside synthesis enzyme activity. The alterations found in ganglioside metabolism could represent one of the earliest changes associated with the diabetic pathology.     

Enriched protein diet-modified ghrelin expression and secretion in rats

Gastrointestinal (GI) integrity and function are regulated by nutrition and growth factors. The discovery of ghrelin, a natural growth hormone (GH) secretagogue produced by the gastrointestinal (GI) tract, is a potential link between diet and growth signals. The aim of this study was to evaluate macronutrient effect on ghrelin expression and secretion in addition to some possible function in intestinal trophic status. Wistar rats were fed a high-carbohydrate, high-protein (HP), high-fat or standard (St) diet. Animals received the same daily food volume and caloric intake. After 7 days, animals were fasted for 24 h and blood and tissue samples were obtained just before feeding or at 2 or 6 h after feeding. Fasting high-protein-fed rats had higher ghrelin plasma levels than with rats fed the high-carbohydrate, high-fat or standard diets. Two-hours after refeeding, ghrelin plasma levels had decreased in all groups with a slight recovery at 6 h after refeeding, except in the high-protein group. Ghrelin plasma levels in rats fed with the high-protein diet correlated negatively with their GH and insulin-like growth factor 1 (IGF-1) plasma concentrations which were also the lowest among the study groups. In conclusion, ghrelin secretion was nutritionally manipulated because a protein-enriched diet increased its levels.