Marginal Zinc Deficiency Promotes Pancreatic Islet Enlargement While Zinc Supplementation Improves the Pancreatic Insulin Response in Zucker Diabetic Fatty Rats.

Zinc deficiency has been associated with the worsening of diabetes while zinc supplementation has been proposed to ameliorate diabetes. This study examined the effects of marginal zinc deficiency (MZD) and zinc supplementation (ZS) on obesity, glycemic control, pancreatic islets, hepatic steatosis and renal function of Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed an MZD, zinc control (ZC) or ZS diet (4, 30 and 300 mg Zn/kg diet, respectively), and lean Zucker rats were fed a ZC diet for 8 weeks. MZD and ZS did not alter body weight or whole-body composition in ZDF rats. MZD ZDF rats had reduced zinc concentrations in the femur and pancreas, a greater number of enlarged pancreatic islets and a diminished response to an oral glucose load based on a 1.8-fold greater incremental area-under-the-curve (AUC) for glucose compared to ZC ZDF. ZS ZDF rats had elevated serum, femur and pancreatic zinc concentrations, unchanged pancreatic parameters and a 50% reduction in the AUC for insulin compared to ZC ZDF rats, suggesting greater insulin sensitivity. Dietary zinc intake did not alter hepatic steatosis, creatinine clearance, or levels of proteins that contribute to insulin signaling, inflammation or zinc transport in epididymal fat. Potential adverse effects of ZS were suggested by reduced hepatic copper concentrations and elevated serum urea compared to ZC ZDF rats. In summary, ZS improved the pancreatic insulin response but not the glucose handling. In contrast, reduced zinc status in ZDF rats led to impaired glucose tolerance and a compensatory increase in the number and size of pancreatic islets which could lead to ß-cell exhaustion.

Possible deleterious hormonal changes associated with low-sodium diets.

The average salt intake of people in Canada, the United States, and Europe is about 3,400 mg of sodium per day, which exceeds the recommended intake levels set by various health organizations. The World Health Organization recommends a worldwide reduction of sodium intake to less than 2,000 mg per day. Most research to date has focused on the negative effects of high-sodium intake; however, little information is available on the metabolic effects of low-sodium intakes. This review focuses on the hormonal changes associated with low-sodium diets, especially the hormones involved in metabolism and cardiovascular and renal function. Based largely on rodent studies, low-sodium diets have been associated with changes in glycemic control, energy metabolism, cardiovascular disease risk, cholesterol concentrations, inflammation, and functioning of the renin-angiotensin-aldosterone system. Overall, research has revealed mixed results regarding the impact of dietary sodium intake on various hormones. Further research is required to assess the effects of sodium reduction on hormones and their associated pathways in order to determine the likelihood of any unintended effects.

Effects of zinc deficiency and zinc supplementation on homocysteine levels and related enzyme expression in rats.

Methionine synthase (MS) and betaine-homocysteine methyltransferase (BHMT) are both zinc (Zn)-dependent methyltransferases and involved in the methylation of homocysteine. The objective of this study was to investigate the effects of dietary Zn supply on homocysteine levels and expression of the two enzymes in growing rats. Male weanling Sprague-Dawley rats were assigned randomly to four dietary groups (n=8/group) for 3 weeks: Zn deficient (ZD; <1mg Zn/kg); Zn control (ZC; 30mg Zn/kg); Zn supplemented (ZS; 300mg Zn/kg); pair fed (PF; 30mg Zn/kg) to the ZD group. Serum and femur Zn concentrations were 83% and 58% lower in ZD, and 49% and 62% higher in ZS compared to ZC (P<0.001), respectively. The ZD rats had lower feed intake (37%), body weight gains (45%), liver (43%) and kidney (31%) weights than those of ZC (P<0.001), but these parameters in ZD were not significantly different from the PF controls. Serum homocysteine concentrations were 65% higher in ZD compared to PF (P<0.05), and there was no significant difference in serum folate levels between ZD and PF groups. The mRNA expression of liver and kidney MS was 57% and 38% lower in ZD than PF (P<0.001), respectively. Hepatic and renal BHMT mRNA levels were not altered in ZD compared to controls. The aforementioned measurements were not significantly different between ZS and ZC groups, except Zn levels. These results demonstrated that homocysteine homeostasis appeared to be disturbed by Zn deficiency but not Zn supplementation, and elevated serum homocysteine might be due to reduced expression of MS during Zn deficiency.

The reduced proportion of New splenic T-cells in the zinc-deficient growing rat is not due to increased susceptibility to apoptosis.

Dietary zinc deficiency has been associated with an increased risk of infection. It has been reported that zinc-deficient rats have fewer New T-cells (TCRαß(+)CD90(+)) compared to diet-restricted and control rats, which over time could adversely affect the ability of the organism to fight off infections. We hypothesized that the lower proportion of New T-cells in zinc deficiency is due to an increased susceptibility to apoptosis. Weanling, Sprague Dawley rats were assigned to one of four dietary treatment groups for 3 weeks: zinc-deficient (ZD, <1mg zinc/kg, ad libitum), diet-restricted (DR, 30mg zinc/kg, limited to the amount of feed as consumed by ZD), marginally zinc-deficient (MZD, 10mg zinc/kg, ad libitum) or control (CTL, 30mg zinc/kg, ad libitum). Thymocytes and splenocytes were labeled for flow cytometric determination of cell surface markers and DNA staining (for simultaneous determination of the phenotype of apoptotic cells) and assessed by Western blotting for apoptotic markers. Cells were analyzed immediately, or after incubation for 7h with or without dexamethasone. There was no difference in the proportion of CD90(+) thymocytes; however ZD rats had a higher proportion of Cytotoxic (CD90(+)4(-)8(+)) thymocytes compared to MZD and CTL. ZD had a lower proportion of splenic New T-cells compared to DR, MZD and CTL. There was no effect of diet on the proportion of apoptotic thymocytes or splenocytes, except ZD splenoctyes had a lower Bax/Bcl-xl ratio compared to DR and CTL. We characterized the splenic New T-cells into Helper and Cytotoxic subsets and found that ZD had a higher ratio of Helper to Cytotoxic New T-cells compared to MZD and CTL. These results do not support the hypothesis of increased apoptotic removal of New T-cells in ZD in growing rats. The regulation of CD90 expression should be explored in future studies.