Zinc supplementation aggravates body fat accumulation in genetically obese mice and dietary-obese mice

Association of Plasma Zinc and Copper with Body Composition, Lipids and Inflammation in a Cross-Sectional General Population Sample from Germany

We aimed to relate circulating plasma zinc and copper to a broad spectrum of adiposity-related traits in a cross-sectional Northern German study (n = 841, 42% female, age: 61 ± 12 years). Zinc and copper were measured by inductively coupled plasma-mass spectrometry. Subcutaneous (SAT) and visceral (VAT) adipose tissue and liver fat were derived from 534 and 538 participants, respectively, via magnet resonance imaging. Associations were assessed using multivariable-adjusted linear regression analysis. An increase per one standard deviation (SD) in zinc was associated with direct linear increases in body mass index (BMI) (1.17%; 95% confidence interval (95%CI) 0.15-2.20%), waist circumference (0.85%; 95%CI 0.04-1.67%) and waist-to-hip ratio (0.64%; 95%CI 0.18-1.09%). A 1-SD increment in copper was directly associated with BMI (1.64%; 0.41-2.88%) and waist circumference (1.22%; 95%CI 0.25-2.20%) but not waist-to-hip ratio. Independent of fat intake, zinc displayed associations with VAT (5.73%; 95%CI 2.04-9.56%) and with liver fat (3.84%; 95%CI 1.49-6.25%), the latter association being also independent of BMI. Copper was directly associated with SAT (4.64%; 95%CI 0.31-9.15%) before accounting for BMI, but showed no association with VAT or liver fat. Observed associations suggest a possible relevance of zinc and copper to adiposity. Particularly zinc displayed associations with traits of abdominal adiposity and liver fat.

Clinical Significance of Trace Element Zinc in Patients with Chronic Kidney Disease

The trace element zinc is essential for diverse physiological processes in humans. Zinc deficiency can impair growth, skin reproduction, immune function, maintenance of taste, glucose metabolism, and neurological function. Patients with chronic kidney disease (CKD) are susceptible to zinc deficiency, which is associated with erythropoiesis-stimulating agent (ESA) hypo-responsive anemia, nutritional problems, and cardiovascular diseases as well as non-specific symptoms such as dermatitis, prolonged wound healing, taste disturbance, appetite loss, or cognitive decline. Thus, zinc supplementation may be useful for the treatment of its deficiency, although it often causes copper deficiency, which is characterized by several severe disorders including cytopenia and myelopathy. In this review article, we mainly discuss the significant roles of zinc and the association between zinc deficiency and the pathogenesis of complications in patients with CKD.

Evaluation of visceral adiposity index with cardiovascular risk factors, biomarkers in postmenopausal women to predict cardiovascular disease: A 10 year study

BACKGROUND AND AIM

Visceral adiposity index (VAI) is reportedly beneficial in predicting cardiovascular disease (CVD) and metabolic syndrome (MetS). However, long-term studies analyzing the efficacy of VAI in the prediction of CVD risk are limited. The relationship between VAI and electrolytes is unclear. This study aimed to determine if VAI can be used as a predictor of CVD and provide early diagnosis possibility for future CVD patients. Moreover, the impact of biomarkers and electrolytes on VAI therefore indirect relation to CVD was analyzed.

METHODS

Postmenopausal women (aged >40 years) admitted to our hospital in 2011 were included and categorized into two groups according to their VAI scores: mild/moderate and severe. Groups were compared with insulin resistance, biochemical parameters, and anthropometric measurements. Patients have been reached out after 10 years and questioned for additional disease and cardiovascular risk. Statistical Package for Social Sciences (SPSSv22.0) was used for data analysis. The p < 0.05 value was considered significant.

RESULTS

Mean VAI score of patients with MetS (7.30 ± 4.75) was significantly higher than without MetS (2.95 ± 1.05) (p < 0.01). Serum magnesium level was found significantly lower in the severe group. Serum zinc (Zn) and hsCRP levels were higher in the severe group. Correlation analysis showed significant positive correlations between VAI scores and total cholesterol (r = 0.289, p < 0.05), Zn (r = 0.397, p < 0.01), fasting insulin (r = 0.455, p < 0.01) and no significant association with the 10-year CVD incidence (OR: 1.034 (0.888-1.203); p = 0.668).

CONCLUSION

Previous VAI results cannot assist in predicting the 10-year CVD risk. Additionally, including measurements of serum Zn, total cholesterol, fasting insulin, and FBG levels are reasonable approach for managing postmenopausal women with unfavorable CVD risk profiles.

Excess dietary zinc drives a Cushing's-like syndrome in ovariectomized mice - Implications for postmenopausal obesity

Postmenopausal women have an increased risk of obesity, but the underlying cause is not clear. We unexpectedly found that excess dietary zinc induced severe obesity and a Cushing's-like syndrome without increased food intake in ovariectomized (Ovx) but not in sham-operated mice. Zinc accumulated in the adrenal glands and inhibited adrenal 17,20-lyase activity and steroid synthesis. As adrenal steroids are the only source of estrogen in Ovx mice, estrogen deficiency induced adrenal hyperplasia, glucocorticoid overproduction, and consequent development of a Cushing's-like syndrome. Adrenal steroid supplementation prevented the effects of zinc. Plasma zinc was positively correlated with cortisol level and negatively correlated with the levels of adrenal steroids and estrogen in obese postmenopausal women. The finding of a link between dietary zinc, estrogen deficiency, and postmenopausal obesity, implies that postmenopausal obesity might be prevented by supplementation with a adrenal steroid and avoiding excess dietary zinc.

Association between zinc and body composition: An integrative review

BACKGROUND

Zinc deficiency is related to lean body mass reduction, fat deposition, and obesity. Zinc acts in catalytic, structural, and regulatory functions, being an essential micronutrient to humans. It is crucial for maintaining lean body mass, synthesizing nucleic acids and proteins, and forming new tissues. Pre-existing zinc deficiency may contribute to obesity due to its relationship with fat deposition associated with short stature. This integrative review aims to analyze the association between zinc and body composition, hitherto very poorly established in previous studies.

MATERIAL AND METHODS

The electronic databases utilized in this review were PubMed and Web of Science. We identified titles and abstracts from 1178 articles relating to zinc and body composition that were published in the last ten years. After duplicates were removed, the reference lists of relevant reviews were checked, and 47 articles were obtained by manual search.

MAIN FINDINGS AND CONCLUSIONS

The articles were transversal or longitudinal studies, clinical trials, randomized controlled trials, reviews, systematic reviews, and meta-analysis. Although there was heterogeneity among the methodologies, the existence of an association between zinc and body composition was predominant among the studies. All articles concluded that zinc had positive effects on proteogenesis. Moreover, zinc metabolism is dysregulated in obese individuals, whose mechanisms remain controversial.

The Impact of Serum Zinc Levels on Abdominal Fat Mass in Hemodialysis Patients

BACKGROUND

Zinc deficiency is highly prevalent and is caused by inadequate dietary intake, malabsorption and removal by treatment in hemodialysis patients. This study investigated the relationship between serum zinc levels and nutritional status in hemodialysis patients.

METHODS

A cross-sectional study examining 87 hemodialysis patients was performed. The serum concentrations of zinc were studied to evaluate their association with nutritional status, which was assessed by measuring abdominal muscle and fat areas with computed tomography.

RESULTS

Serum zinc levels were significantly and positively correlated with subcutaneous and visceral fat areas (r = 0.299, p < 0.01, and r = 0.298, p < 0.01, respectively), but not abdominal muscle areas. Multiple regression analyses demonstrated that serum zinc levels were a significant independent predictor of visceral fat areas (p < 0.01), but not subcutaneous fat areas (p = 0.631).

CONCLUSIONS

Our findings suggest that serum zinc levels could play a crucial role in determining abdominal fat mass in hemodialysis patients.

Effect of zinc and vitamin E supplementation on hormones and blood biochemicals in peri-partum Sahiwal cows

Thirty-two advanced pregnant multiparous Sahiwal cows were used to study the effect of additional zinc (Zn) and vitamin E (VE) supplementation on hormonal and biochemical changes. Cows were randomly assigned to four groups and fed a basal diet of compounded concentrate, berseem fodder, and wheat straw in a ratio of 60:20:20. The groups were: (1) the basal diet with no supplement (control treatment); (2) the basal diet supplemented with 60 mg/kg DM/cow daily of Zn (Zn treatment); (3) the basal diet supplemented with 1000 IU/cow daily of vitamin E (VE treatment); and (4) the basal diet supplemented with a combination of 60 mg Zn/kg DM/cow and 1000 IU vitamin E/cow/d (Zn + VE treatment). Blood samples were collected on -60, -45, -30, -15, -7, -3, 0, 3, 7, 15, 30, 45, 60, 90, and 120 d in relation to expected date of calving and were analyzed for endocrine variables and biochemical changes. Plasma concentrations of leptin, insulin, insulin like growth factor-1 (IGF-1), triidothyronine (T3), and tetraiodothyronine (T4) were decreased toward calving and observed lowest (P < 0.05) on 3 d post-partum. However, plasma levels of growth hormone (GH) and cortisol increased toward calving and were found highest (P < 0.05) on 3 d post-partum. Pre-partum concentrations of leptin and IGF-1 were higher (P < 0.05) than its respective concentration observed during post-partum. Post-partum concentrations of GH and cortisol were higher (P < 0.05) than its respective pre-partum concentration. Pre-partum concentrations of urea, triglycerides, Zn, and VE were higher (P < 0.05) and total cholesterol and HDL cholesterol were lower than its values observed in post-partum among all the groups. Treatments had significant (P < 0.05) effect on plasma hormonal levels and levels of Zn and VE but no effect on biochemical attributes. Cows fed on diet supplemented with Zn + VE had highest (P < 0.05) pre as well as post-calving concentrations of leptin (6.38 vs 5.01 ng/ml), insulin (1.39 vs 1.33 ng/ml), GH (9.29 vs 13.72 ng/ml), IGF-1 (14.55 vs 12.59 nmol/l), T3 (1.45 vs 1.40 ng/ml), T4 (32.44 vs 31.79 ng/ml) whereas as lowest concentration of cortisol hormone (3.05 vs 3.44 ng/ml). Cows supplemented with combination of Zn and VE showed minimum decline in plasma concentration of leptin, insulin, GH, IGF-1, T3, and T4, and minimum increase in cortisol concentration. In conclusion, dairy cows around parturition faces various endocrine and biochemical alterations and supplementation of Zn in combination with VE can ameliorate adverse effect of calving stress by maintaining circulatory concentration of hormone and biochemicals towards the basal levels.

Dietary Zinc Supplementation Attenuates Hyperglycemia in db/db Mice

Although zinc (Zn) deficiency has been associated with insulin resistance, and altered Zn metabolism (e.g., hyperzincuria, low-normal plasma Zn concentrations) may be present in diabetes, the potential effects of Zn on modulation of insulin action in Type II diabetes have not been established. The objective of this study was to compare the effects of dietary Zn deficiency and Zn supplementation on glycemic control in db/db mice. Weanling db/db mice and lean littermate controls were fed Zn-deficient (3 ppm Zn; dbZD and InZD groups), Zn-adequate control (30 ppm Zn; dbC and InC groups) or Zn-supplemented (300 ppm Zn; dbZS and InZS groups) diets for 6 weeks. Mice were assessed for Zn status, serum and urinary indices of diabetes, and gastrocnemius insulin receptor concentration and tyrosine kinase activity. Fasting serum glucose concentrations were significantly lower in the dbZS group compared with the dbZD group (19.3 ± 2.9 and 27.9 ± 4.1 mM, respectively), whereas the dbC mice had an intermediate value. There was a negative correlation between femur Zn and serum glucose concentrations (r = −0.59 for lean mice, P = 0.007). The dbZS group had higher pancreatic Zn and lower circulating insulin concentrations than dbZC mice. Insulin-stimulated tyrosine kinase activity in gastrocnemius muscle was higher in the db/db genotype, and insulin receptor concentration was not altered. In summary, dietary Zn supplementation attenuated hyperglycemia and hyperinsulinemia in db/db mice, suggesting that the roles of Zn in pancreatic function and peripheral tissue glucose uptake need to be further investigated.

Obesity and age-related alterations in the gene expression of zinc-transporter proteins in the human brain

The incidence of Alzheimer's disease (AD) is increasing. Major risk factors for AD are advancing age and diabetes. Lately, obesity has been associated with an increased risk of dementia. Obese and diabetic individuals are prone to decreased circulating levels of zinc, reducing the amount of zinc available for crucial intracellular processes. In the brain, zinc co-localizes with glutamate in synaptic vesicles, and modulates NMDA receptor activity. Intracellular zinc is involved in apoptosis and fluctuations in cytoplasmic Zn(2+) affect modulation of intracellular signaling. The ZNT and ZIP proteins participate in intracellular zinc homeostasis. Altered expression of zinc-regulatory proteins has been described in AD patients. Using microarray data from human frontal cortex (BrainCloud), this study investigates expression of the SCLA30A (ZNT) and SCLA39A (ZIP) families of genes in a Caucasian and African-American sample of 145 neurologically and psychiatrically normal individuals. Expression of ZNT3 and ZNT4 were significantly reduced with increasing age, whereas expression of ZIP1, ZIP9 and ZIP13 were significantly increased. Increasing body mass index (BMI) correlated with a significant reduction in ZNT1 expression similar to what is seen in the early stages of AD. Increasing BMI also correlated with reduced expression of ZNT6. In conclusion, we found that the expression of genes that regulate intracellular zinc homeostasis in the human frontal cortex is altered with increasing age and affected by increasing BMI. With the increasing rates of obesity throughout the world, these findings warrant continuous scrutiny of the long-term consequences of obesity on brain function and the development of neurodegenerative diseases.

Content of bioelements in the lungs and liver in rats with alimentary obesity

The synchrotron radiation X-ray fluorescence technique (SRXRF) was applied to the determination of K, Ca, Mn, Fe, Cu, Zn, Se, Br, Rb, and Sr concentrations in the liver and lungs in Wistar rats. The animals in the experiment included (1) healthy rats, (2) rats with alimentary obesity (AO), and (3) rats with alimentary obesity that were being given zinc sulphate with water for a long time (АО+Zn). Each group was divided into two subgroups. The experiment with the first subgroup was terminated with the animals in the state of physiological hunger and subsequent retrieval of liver and lung tissue, while the animals of the second subgroup were sacrificed two hours after ingestion of lard. The rats in physiological hunger manifested intergroup differences in the content of the bioelements (BEs) neither in the liver nor in the lungs. The rats with AO, as compared with the healthy animals, demonstrated in physiological hunger redistribution of inter-element correlations (IECs), which is an indirect reflection of sustained metabolic disorder. Additional zinc in the rats' ration did not affect their body weight and the concentration of the BEs (including zinc) in the liver and the lungs. However, the IECs in the tissues of these animals in physiological hunger also changed. This redistribution differed from that in the rats with AO. The IECs soon after ingestion of lard also changed, which also reflects sustained changes in the metabolism in the animals.

Association between serum zinc level and body composition: The Korean National Health and Nutrition Examination Survey

OBJECTIVE

The aim of this study was to examine the association between serum zinc levels and several body composition factors in Korean adults.

METHODS

We used data from the Korean National Health and Nutrition Examination Survey, a cross-sectional survey of Korean civilians. Data from 1896 adults were analyzed.

RESULTS

Serum zinc levels in men with elevated waist circumference were higher than in those with normal waist circumference (152.1 ± 3.7 μg/dL versus 137.8 ± 2.2 μg/dL; P < 0.001) and serum zinc levels increased with increasing tertiles of total body fat percentage (134.2 ± 2.8 μg/dL, 142 ± 2.9 μg/dL, and 148 ± 2.7 μg/dL; P = 0.001). Among men with a normal waist circumference, serum zinc levels of those with the highest total body fat percentage were higher than in those with the lowest or medium total body fat percentage values (145.4 μg/dL versus 135.2 μg/dL; P = 0.029). In contrast, in men with an elevated waist circumference, no difference in serum zinc levels according to total body fat percentage was detected. There was no relationship between serum zinc levels and body composition factors in women.

CONCLUSIONS

Body zinc status might be associated with the quantity and distribution of body fat in Korean men. Additional sex-specific studies are needed to determine whether the relationship of body zinc status with abdominal obesity and total body fat affects metabolic disorders and cardiovascular diseases.

Effect of zinc on the content of chemical elements in the lung tissue during obesity in the experiment

We found no deviations from normalcy in the content of chemical elements (K, Ca, Mn, Fe, Cu, Zn, Se, Br, Rb, and Sr) in the lungs of rats with mild alimentary obesity, but revealed redistribution of correlations between the elements indicating impaired metabolism in this organ. Zinc supplementation had no effect on the body weight and content of chemical elements (including zinc) in the lung tissue in rats fed high fat diet, but led to significant changes in the correlations between the elements. Bromine, rubidium, and strontium are actively involved in interelement interactions in the lung tissue. These elements should be given more attention in considering biological processes including alimentary obesity.

Zinc: The Metal of Life

The importance of zinc was 1st reported for Aspergillus niger. It took over 75 y to realize that zinc is also an essential trace element for rats, and an additional 30 y went by before it was recognized that this was also true for humans. The adult body contains about 2 to 3 g of zinc. Zinc is found in organs, tissues, bones, fluids, and cells. It is essential for many physiological functions and plays a significant role in a number of enzyme actions in the living systems. Bioinformatics estimates report that 10% of the human proteome contains zinc-binding sites. Based on its role in such a plethora of cellular components, zinc has diverse biological functions from enzymatic catalysis to playing a crucial role in cellular neuronal systems. Thus, based on the various published studies and reports, it is pertinent to state that zinc is one of the most important essential trace metals in human nutrition and lifestyle. Its deficiency may severely affect the homeostasis of a biological system. This review compiles the role of zinc in prophylaxis/therapeutics and provides current information about its effect on living beings.

Effects of zinc on the content of chemical elements in the liver of rats during early stages of obesity

In rats with slight alimentary obesity, the content of chemical elements in the liver did not differ from normal, but the correlations between these elements were changed, which attested to metabolic disorders. Additional zinc dose administered to rats receiving lipid-rich rations did not affect animal body weights and content of chemical elements (including zinc) in the liver, but corrected correlations between the elements. Active contribution of strontium, bromine, and rubidium to interactions between the elements in the liver necessitates studies of their role in biological processes, specifically, in initiation and development of obesity.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

GI functions of GPR39: novel biology

GPR39 is an orphan GPCR receptor belonging to the ghrelin/motilin receptor subfamily. The receptor is constitutively active and Zn(2+) is a physiological agonist of GPR39. The receptor is emerging as an important regulator of gastrointestinal motility and secretion. Although GPR39 does not seem to be involved in the regulation of food intake, contradictory results are available on the role of GPR39 in the regulation of body weight. A well-established stimulatory role for GPR39 has been defined in insulin secretion which makes the receptor an attractive target for the treatment of type 1 or 2 diabetes. GPR39 signaling also inhibits apoptosis and mediates neural synaptic signaling. Novel ligands of GPR39 are warranted to reveal the main physiological role of this receptor.

Short-term weight loss in overweight/obese low-income women improves plasma zinc and metabolic syndrome risk factors

Metabolic syndrome is a group of disorders involving obesity, insulin resistance, dyslipidemia and hypertension. Obesity is the most crucial risk factor of metabolic syndrome, because it is known to precede other risk factors. Obesity is also associated with disturbances in the metabolism of the trace mineral, zinc. The overall purpose of this study was to investigate the effects of short-term weight loss on plasma zinc and metabolic syndrome risk factors. An 8-week weight loss intervention study was conducted with 90 low-income overweight/obese mothers, whose youngest child was 1-3 years old. Plasma levels of zinc, glucose, insulin, leptin, triglycerides, total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol were measured and compared at weeks 0 and 8 of the weight loss program. At pre-study, plasma zinc was low in 39% and, within normal values in 46%, of obese/overweight mothers. By the end of intervention, plasma zinc rose by 22% and only 5% of the mothers continued to exhibit low plasma zinc. At post-study, the metabolic syndrome risk factors of waist circumference, HDL cholesterol, and diastolic blood pressure (p<0.05) showed significant improvements. Plasma zinc increased by a greater margin (67%) in women with low zinc, as compared to those with normal zinc (18%); weight reduction was similar in both the groups. Finally, changes in % body fat were related negatively with changes in plasma zinc (r=- 0.28, p<0.05). The circulating levels of zinc, as well as the metabolic syndrome components, showed significant improvements in overweight/obese low-income women after weight loss.

Impact of micronutrient deficiencies on obesity

Micronutrient deficiencies have been found in obese individuals across age groups worldwide. While the effects of micronutrient deficiencies on human functions have been studied widely in different populations, there is limited information on how these micronutrient deficiencies affect obese populations. An examination of the available literature suggests associations exist between micronutrient deficiencies and obesity in different populations. These associations and possible mechanisms of the deficiencies' metabolic effects, such as their influence on leptin and insulin metabolism, are discussed here. Further studies are needed to clarify the roles of the different micronutrient deficiencies with respect to obesity and its comorbid conditions.

Distinctive modulation of inflammatory and metabolic parameters in relation to zinc nutritional status in adult overweight/obese subjects

Overweight and obesity are associated with low grade of inflammation and chronic inflammatory response characterized by abnormal production and activation of some pro-inflammatory signalling pathways. Taking into account that obesity is the direct result of an imbalance between energy intake and energy expenditure, the nutritional factors in the diet, with particular focus on zinc, may play a pivotal role in the development of obesity-associated comorbidities. Considering the potential interactions among zinc nutritional status, inflammation, overweight/obesity and insulin secretion, the aim of the present work was to clarify the influence of zinc dietary intake on some metabolic, inflammatory and zinc status parameters in adult overweight/obese subjects. We found a close interrelationship between nutritional zinc and obesity. In particular, subjects with a lower zinc dietary intake display a deeper inflammatory status, general impairment of the zinc status, an altered lipid profile and increased insulin production with respect to obese subjects with normal zinc dietary intake. Moreover, in the presence of low dietary zinc intake, the obese subjects are less capable to respond to oxidative stress and to inflammation leading to the development of obesity or to a worsening of already preexisting obesity status. In conclusion, a possible zinc supplementation in obese subjects with a deeper inflammatory status and more altered zinc profile may be suggested in order to limit or reduce the inflammation, taking also into account that zinc supplementation normalizes "inflammaging" as well as zinc profile leading to a correct intra- and extracellular zinc homeostasis.

Role of zinc and zinc transporters in the molecular pathogenesis of diabetes mellitus

Diabetes is one of the most common chronic diseases in the United States. An estimated 18.2 million people in the US (6.3%) have diabetes; among them 2.8 million are African Americans (AAs). On average, AAs are twice as likely to have diabetes as European Americans (EAs) of similar age. AAs disproportionately suffer from various diseases in the US. Many of these diseases include hypertension, cardiovascular disease (CVD), diabetes mellitus (DM-beta predominantly Type II), and cancers of the prostate and pancreas. A number of risk factors such as smoking, a high fat diet, little physical activity, stress, and meager access to health care have been the subject of numerous investigations. However, the factor of the interaction between genetics and the environment has received very little attention in the scientific community. Of note, the content of zinc in pancreatic beta gells is among the highest in the body; however, very little is known about the uptake and storage of zinc inside these cells. We hypothesize that one of the major reason AAs disproportionally suffer from DM (as well as some other illnesses like prostate cancer, CVD and hypertension) is due to their inherent inability to transport appropriate amount of zinc in the crucial cell types that require relatively higher amount of zinc than the other cell types. In this article, we will explore in detail the possible genetic and environmental link between human zinc transporters (hZIPs) and their differential expressions in the islet beta cells from AAs as compared to other racial groups, particularly EAs, in both normal healthy individuals and diabetic patients. We hypothesize that the hZIPs play an important role in the development of diabetes, and the main reason AAs disproportionately suffer from DM (as well as other illnesses like prostate and pancreatic cancers, hypertension, and CVD) as compared to EAs may be due the low degree of expressions of the critical zinc transporters in the beta cells. Understanding the molecular events in the pathogenesis of DM with regards to regulation of zinc uptake would be critical to the evaluation of the natural history of diabetes in humans and especially in various racial groups. If a direct link between zinc transport and diabetes can be established, then a special nutritional formula, medication or other intervention might be especially designed to test the ability to decrease the incidence of this disease in DM susceptible groups, particularly in AAs.

Metallothionein as an adaptive protein prevents diabetes and its toxicity

Metallothioneins (MTs) are a group of intracellular metal-binding and cysteine-enriched proteins and are highly inducible in many tissues in response to various types of stress. Although it mainly acts as a regulator of metal homeostasis such as zinc and copper in tissues, MT also acts as a potent antioxidant and adaptive (or stress) protein to protect cells and tissues from oxidative stress. Diabetes affects many Americans and other populations, and its development and toxic effect on various organs have been attributed to increased oxidative stress. Studies showed that zinc-induced or genetically enhanced pancreatic MT synthesis prevented diabetes induced by chemicals such as streptozotocin and alloxan, and zinc pretreatment also prevented spontaneously developed diabetes. Since diabetic complications are the consequences of organ damage caused by diabetic hyperglycemia and hyperlipidemia through oxidative stress, whether MT in nonpancreatic organs also provides a preventive effect on diabetic toxicity has been recently investigated. We demonstrated that overexpression of cardiac MT significantly prevented diabetes-induced cardiomyopathy. Likewise, overexpression of renal MT also prevented diabetes-induced renal toxicity. In addition, we also found that MT as an adaptive protein is overexpressed in several organs in response to diabetes. Therefore, the biological importance of diabetes-induced MT in diabetic complications and subsequent other pathogenesis was further explored. We found that diabetes-induced hepatic and renal MT synthesis was accompanied by a significant prevention of endotoxin-induced hepatic toxicity and cisplatin-induced renal toxicity. These studies suggest that MT as an adaptive protein can prevent both diabetes development and its complications or subsequent suffered other pathogenic injury.

Effects of dietary fat and zinc on adiposity, serum leptin and adipose fatty acid composition in C57BL/6J mice

Zinc (Zn) has been implicated in altered adipose metabolism, insulin resistance and obesity. The objective of this study was to investigate the effects dietary Zn deficiency and supplementation on adiposity, serum leptin and fatty acid composition of adipose triglycerides and phospholipid in C57BL/6J mice fed low-fat (LF) or high-fat (HF) diets for a 16 week period. Weanling C57BL/6J mice were fed LF (16% kcal from soybean oil) or HF (39% kcal from lard and 16% kcal from soybean oil) diets containing 3, 30 or 150 mg Zn/kg diet (ZD = Zn-deficient, ZC = Zn control and ZS = Zn-supplemented, respectively). HF-fed mice had higher fat pad weights and lower adipose Zn concentrations than the LF-fed mice. The ZD and ZS groups had a reduced content of fatty acids in adipose triglycerides compared to the ZC group, suggesting that zinc status may influence fatty acid accumulation in adipose tissue. Serum leptin concentration was positively correlated with body weight and body fat, and negatively correlated with adipose Zn concentration. Dietary fat, but not dietary Zn, altered the fatty acid composition of adipose tissue phospholipid and triglyceride despite differences in Zn status assessed by femur Zn concentrations. The fatty acid profile of adipose triglycerides generally reflected the diets. HF-fed mice had a higher percentage of C20:4 n-6, elevated ratio of n-6/n-3, lower ratio of PUFA/SAT and reduced percentage of total n-3 fatty acids in adipose phospholipid, a fatty acid profile associated with obesity-induced risks for insulin resistance and impaired glucose transport. In summary, the reduced adipose Zn concentrations in HF-fed mice and the negative correlation between serum leptin and adipose Zn concentrations support an interrelationship among obesity, leptin and Zn metabolism.

Effects of arachidonic acid plus zinc on glucose disposal in genetically diabetic (ob/ob) mice

AIM

The present study is designed to determine whether arachidonic acid (AA) plus zinc improves clinical signs of diabetes in genetically diabetic ob/ob mice.

METHODS

In the first study, effects of acute administration of AA plus zinc on glucose disposal were determined in ob/ob and lean mice (n = 6 each). In the second study, ob/ob and lean mice were treated with increasing doses of AA plus zinc for 2 weeks (n = 5 each). Postprandial and fasting blood glucose concentrations, three-hour-area-average above fasting glucose concentration (TAFGC), water and food intake, body weight and plasma insulin concentrations were measured.

RESULTS

Acute administration of AA plus zinc significantly increased glucose disposal in ob/ob mice. In the second study, postprandial and fasting blood glucose concentrations, TAFGC, and water and food intake in ob/ob mice treated with AA plus zinc for 2 weeks were significantly decreased compared with those in mice given no AA. Plasma insulin concentrations in both lean and ob/ob mice were not changed by AA treatment in drinking water.

CONCLUSIONS

AA plus zinc in drinking water is effective in decreasing blood glucose levels in obese mice. These results indicate that use of these compounds should be considered as a dietary supplement to control hyperglycaemia in patients with type II diabetes.

Potential interactions of zinc in the neuroendocrine-endocrine disturbances of diabetes mellitus type 2

An accumulation of evidence implicates leptin, insulin, glucocorticoids, proopiomelanocortin (POMC), and neuropeptide Y (NPY) interactions as being integral to metabolic control associated with neuroendocrine-endocrine functioning. Dysfunction of neuroendocrine-endocrine interactions contributes to the metabolic disturbances of diabetes mellitus type 2 (DM-2). Since Zn has a direct impact on the healthy functioning of hormonal and neuropeptide balance, it is possible that altered Zn status and metabolism in DM-2 are involved in some of the metabolic dysfunctions of DM-2.Key words: zinc, insulin, leptin, neuropeptide Y, glucocorticoids, proopiomelanocortin (POMC), diabetes, obesity.

Effects of zinc supplementation on the plasma glucose level and insulin activity in genetically obese (ob/ob) mice

The effects of zinc supplementation (20 mM ZnCl2 from the drinking water for eight weeks) on plasma glucose and insulin levels, as well as its in vitro effect on lipogenesis and lipolysis in adipocytes were studied in genetically obese (ob/ob) mice and their lean controls (+/?). Zinc supplementation reduced the fasting plasma glucose levels in both obese and lean mice by 21 and 25%, respectively (p < 0.05). Fasting plasma insulin levels were significantly decreased by 42% in obese mice after zinc treatment. In obese mice, zinc supplementation also attenuated the glycemic response by 34% after the glucose load. The insulin-like effect of zinc on lipogenesis in adipocytes was significantly increased by 80% in lean mice. However, the increment of 74% on lipogenesis in obese mice was observed only when the zinc plus insulin treatment was given. This study reveals that zinc supplementation alleviated the hyperglycemia of ob/ob mice, which may be related to its effect on the enhancement of insulin activity.

Zinc supplementation on serum levels and hepatic conversion of thyroid hormones in obese (ob/ob) mice

The supplemental effects of zinc on thyroid status in obese (ob/ob) mice were studied. Four-week-old obese mice and their lean controls were fed either a basal diet or a zinc-supplemented diet (200 mg/kg diet) for 8 wk. Following the 8-wk basal diet, obese mice had lower serum T4 values, as well as hepatic T4 and T3 values, than lean mice (p < 0.05). A significant decrease in hepatic 5'-deiodinase activity was also observed in obese mice. Dietary zinc supplementation significantly reduced serum T4 levels in both the obese and lean mice. However, the zinc-supplemented effects on diminishing hepatic T4 and T3 values, as well as on 5'-deiodinase activities, were found only in obese mice (p < 0.05). Furthermore, the 5'-deiodinase activities in hepatic microsomal pellets after incubation with various zinc concentrations (0.5, 1.0, and 2.5 mM) were also examined. The 5'-deiodinase activities, in hepatic samples from all mice, were significantly attenuated by zinc treatments. However, this effect was more predominant in obese mice following the addition of 0.5 mM zinc. This study suggests that a lower hepatic 5'-deiodinase activity, resulting from a higher zinc level, might be related to abnormal energy metabolism in the ob/ob mice.

Zinc status in plasma of obese individuals during glucose administration

To know whether plasma zinc status is altered under acute hyperglycemic state, the interrelationships among plasma glucose, insulin, and zinc concentrations during oral glucose tolerance test (OGTT) in obese individuals and their lean controls were studied. Plasma glucose and insulin concentrations under fasting as well as those values in response to OGTT were significantly higher in obese individuals than those in lean controls. On the other hand, the obese had lower fasting plasma zinc concentrations compared to lean controls (13.5 vs 18.1 mumol/L, p < 0.005). Under fasting, plasma zinc concentrations in overall individuals inversely correlated to their body mass index (BMI) (r = -0.516), plasma glucose (r = -0.620), and plasma insulin (r = -0.510). However, there were no significant changes in plasma zinc and copper values during OGTT in both obese individuals and lean controls. This study showed that plasma zinc values had no changes during OGTT in obese individuals. The results also indicated that lower fasting plasma zinc concentrations in obese individuals were not the short-term metabolic result.

Zinc attenuation of GDP binding to brown adipocytes mitochondria in genetically obese (ob/ob) mice

In this study, we investigate the in vitro effect of zinc addition on guanosine diphosphate (GDP) binding to mitochondria in brown adipocytes of genetically obese (ob/ob) mice. Interscapular brown adipocytes of male mice (obese; lean) at 4 and 12 wk of age were incubated with 0, 50, 100, or 200 microM zinc sulfate. Mitochondria were then isolated and their GDP binding capacities were measured. The GDP-binding capacities of ob/ob mice were lower than lean mice, with or without zinc addition, in both age groups (p < 0.05). Zinc addition did not have any significant effect on GDP binding in lean mice. GDP binding decreased with increasing zinc addition in ob/ob mice, and this attenuation was more predominant in 12-wk old ob/ob mice. Moreover, we found that high magnesium addition (5 mM) increased GDP binding in lean mice, but this effect was not significant in ob/ob mice. This study reveals that brown adipose tissue thermogenesis in ob/ob mice could be greatly attenuated by zinc addition, suggesting that zinc may play a regulatory role in obesity.