A novel chronic in vivo oral cadmium exposure-washout mouse model for studying cadmium toxicity and complex diabetogenic effects.

Type II diabetes mellitus (T2DM) is characterized by insulin resistance, ß-cell dysfunction and hyperglycemia. In addition to well known risk factors such as lifestyle and genetic risk score, accumulation of environmental toxicants in organs relevant to glucose metabolism is increasingly recognized as additional risk factors for T2DM. Here, we describe the development of an in vivo oral cadmium (Cd) exposure model. It was shown that oral Cd exposure in drinking water followed by washout and high fat diet (HFD) in C57BL/6N mice results in islet Cd bioaccumulation comparable to that found in native human islets while mitigating the anorexic effects of Cd to achieve the same weight gain required to induce insulin resistance as in Cd naïve control mice. Inter individual variation in plasma glucose and insulin levels as well as islet Cd bioaccumulation was observed in both female and male mice. Regression analysis showed an inverse correlation between islet Cd level and plasma insulin following a glucose challenge in males but not in females. This finding highlights the need to account for inter individual target tissue Cd concentrations when interpreting results from in vivo Cd exposure models. No effect of Cd on insulin secretion was observed in islets ex vivo, highlighting differences between in vivo and ex vivo cadmium exposure models. In summary, our oral in vivo Cd exposure-washout with HFD model resulted in islet Cd bioaccumulation that is relevant in the context of environmental cadmium exposure in humans. Here, we showed that islet Cd bioaccumulation is associated with complex cadmium-mediated changes in glucose clearance and ß-cell function. The model described here will serve as a useful tool to further examine the relationship between Cd exposure, islet Cd bioaccumulation, dysglycemia and their underlying mechanisms.

Cadmium-mediated pancreatic islet transcriptome changes in mice and cultured mouse islets.

Type II diabetes mellitus (T2DM) is a multifactorial disease process that is characterized by insulin resistance and impairment of insulin-producing pancreatic islets. There is evidence that environmental exposure to cadmium contributes to the development of T2DM. The presence of cadmium in human islets from the general population and the uptake of cadmium in ß-cells have been reported. To identify cadmium-mediated changes in gene expression and molecular regulatory networks in pancreatic islets, we performed next-generation RNA-Sequencing (RNA-Seq) in islets following either in vivo (1 mM CdCl2 in drinking water) or ex-vivo (0.5 µM CdCl2) exposure. Both exposure regiments resulted in islet cadmium concentrations that are comparable to those found in human islets from the general population. 6-week in vivo cadmium exposure upregulates the expression of five genes: Synj2, Gjb1, Rbpjl, Try5 and 5430419D17Rik. Rbpjl is a known regulator of ctrb, a gene associated with diabetes susceptibility. With 18-week in vivo cadmium exposure, we found more comprehensive changes in gene expression profile. Pathway enrichment analysis showed that these secondary changes were clustered to molecular mechanisms related to intracellular protein trafficking to the plasma membrane. In islet culture, cadmium ex vivo significantly induces the expression of Mt1, Sphk1, Nrcam, L3mbtl2, Rnf216 and Itpr1. Mt1 and Itpr1 are known to be involved in glucose homeostasis. Collectively, findings reported here revealed a complex cadmium-mediated effect on pancreatic islet gene expression at environmentally relevant cadmium exposure conditions, providing the basis for further studies into the pathophysiological processes arising from cadmium accumulation in pancreatic islets.

Pancreatic Islets Accumulate Cadmium in a Rodent Model of Cadmium-Induced Hyperglycemia.

Cadmium (Cd) is an anthropogenic as well as a naturally occurring toxicant associated with prediabetes and T2DM in humans and experimental models of Cd exposure. However, relatively few studies have examined the mechanism(s) of Cd-induced hyperglycemia. The purpose of this study was to examine the role of pancreatic islets in Cd-induced hyperglycemia. Male Sprague-Dawley rats were given daily subcutaneous doses of Cd at 0.6 mg/kg over 12 weeks. There was a resulting time-dependent increase in fasting blood glucose and altered insulin release in vitro. Islets isolated from control (saline-treated) and Cd-treated animals were incubated in low (0.5 mg/mL) or high (3 mg/mL) glucose conditions. Islets from 12 week Cd-treated animals had significantly less glucose-stimulated insulin release compared to islets from saline-treated control animals. The actual Cd content of isolated islets was 5 fold higher than the whole pancreas (endocrine + exocrine) and roughly 70% of that present in the renal cortex. Interestingly, islets isolated from Cd-treated animals and incubated in high glucose conditions contained significantly less Cd and zinc than those incubated in low glucose. These results show that within whole pancreatic tissue, Cd selectively accumulates in pancreatic islets and causes altered islet function that likely contributes to dysglycemia.

Exploring the Association Between Demographics, SLC30A8 Genotype, and Human Islet Content of Zinc, Cadmium, Copper, Iron, Manganese and Nickel.

A widely prevalent single nucleotide polymorphism, rs13266634 in the SLC30A8 gene encoding the zinc transporter ZnT8, is associated with an increased risk for T2DM. ZnT8 is mostly expressed in pancreatic insulin-producing islets of Langerhans. The effect of this variant on the divalent metal profile in human islets is unknown. Additionally, essential and non-essential divalent metal content of human islets under normal environmental exposure conditions has not been described. We therefore examined the correlation of zinc and other divalent metals in human islets with rs13266634 genotype and demographic characteristics. We found that the diabetes risk genotype C/C at rs13266634 is associated with higher islet Zn concentration (C/C genotype: 16792 ± 1607, n = 22, C/T genotype: 11221 ± 1245, n = 18 T/T genotype: 11543 ± 6054, n = 3, all values expressed as mean nmol/g protein ± standard error of the mean, p = 0.040 by ANOVA). A positive correlation between islet cadmium content and both age (p = 0.048, R2 = 0.09) and female gender (women: 36.88 ± 4.11 vs men: 21.22 ± 3.65 nmol/g protein, p = 0.007) was observed. Our results suggest that the T2DM risk allele C is associated with higher islet zinc levels and support prior evidence of cadmium's higher bioavailability in women and its long tissue half-life.

Association between urinary cadmium levels and prediabetes in the NHANES 2005-2010 population.

Evidence suggests an association between exposure to cadmium and dysglycemia. To investigate this matter, we examined the relationship between urinary cadmium and prediabetes in the cross sectional National Health and Nutrition Examination Survey (NHANES). NHANES participants for the years 2005 through 2010 aged ≥ 40 years were included in the analysis. Participants with nephropathy, overt diabetes, or missing required data were excluded. To assess the non-linear relationship between cadmium and Prediabetes, non-parametric logistic regression with B spline expansion of urinary cadmium/creatinine ratio was performed. This analysis revealed a complex non-linear association between higher cadmium levels and prediabetes. This relationship persisted, though with varying magnitudes across smoking groups (never smokers, moderate smokers, heavy smokers). In a conventional logistic regression analysis, this relationship was less evident with significantly increased OR for prediabetes was found in the highest quintile of urine cadmium compared to the lowest quintile in the overall population and in moderate smokers. In an age stratified analysis, a significant linear association was found only in the age groups 60-69 and ≥ 70. We conclude that there is a significant non-linear, complex relationship between urinary Cd levels, age, smoking habits and odds of prediabetes.

Denosumab for management of parathyroid carcinoma-mediated hypercalcemia.

CONTEXT: Most of the morbidity and mortality from parathyroid cancer is due to PTH-mediated hypercalcemia. Classically, management mainly consists of surgical resection, chemotherapy, and alleviation of hypercalcemia using bisphosphonates and calcium receptor agonists. The use of denosumab in the treatment of parathyroid cancer-mediated hypercalcemia has not been reported. OBJECTIVE: The aim of this report is to describe the effect of denosumab on parathyroid cancer-induced hypercalcemia. SUBJECT, MEASURES, AND RESULT: The patient is a 39-year-old man with metastatic parathyroid cancer who presented at age 35. His calcium levels initially responded to surgery, bisphosphonates, calcium receptor agonist, and chemotherapy (dacarbazine). However, his disease progressed, and his hypercalcemia became refractory to these measures in the setting of rising PTH levels. The addition of denosumab, a humanized monoclonal antibody inhibiting receptor activator of nuclear factor κB ligand resulted in successful management of his hypercalcemia for an additional 16 months. CONCLUSIONS: Denosumab can be effective in the treatment of refractory hypercalcemia in parathyroid cancer. It may also be of potential use in settings of benign hyperparathyroid-related hypercalcemia such as parathyromatosis, where hypercalcemia is not amenable to surgery or medical therapy with bisphosphonates and calcium receptor agonists.

Accumulation of cadmium in insulin-producing ß cells.

Evidence suggests that chronic low level cadmium exposure impairs the function of insulin-producing ß cells and may be associated with type-2 diabetes mellitus. Herein, we describe the cadmium content in primary human islets and define the uptake kinetics and effects of environmentally relevant cadmium concentrations in cultured ß cells. The average cadmium content in islets from 10 non-diabetic human subjects was 29 ± 7 nmol/g protein (range 7 to 72 nmol/g protein). Exposure of the ß-cell line MIN6 to CdCl 2 concentrations between 0.1 and 1.0 µmol/L resulted in a dose- and time-dependent uptake of cadmium over 72 h. This uptake resulted in an induction of metallthionein expression, likely enhancing cellular cadmium accumulation. Furthermore, cadmium accumulation resulted in an inhibition of glucose stimulated insulin secretion in MIN6 cells and primary mouse islets. Our results indicate that this impairment in ß-cell function is not due to an increase in cell death or due to an increase in oxidative stress. We conclude that mouse ß cells accumulate cadmium in a dose- and time-dependent manner over a prolonged time course at environmentally relevant concentrations. This uptake leads to a functional impairment of ß-cell function without significant alterations in cell viability, expression of genes important for ß-cell function or increase in oxidative stress.

Acute cytokine-mediated downregulation of the zinc transporter ZnT8 alters pancreatic beta-cell function.

Genetic studies suggest that Zn transporters such as ZnT8 play a role in insulin secretion by pancreatic beta-cells; however, little is known about the dynamic roles of Zn trafficking pathways on beta-cell physiology. To test the acute effects of the inflammatory cytokines interleukin 1 beta (IL1 beta) and tumor necrosis factor alpha (TNFalpha) on Zn homeostasis, the mRNA expression profile of Zn transporters of the ZnT and ZIP families was examined. Exposure of MIN6 cells or primary murine islets to IL1 beta or TNFalpha altered the mRNA expression profile of Zn transporters; most notable was decreased ZnT8 mRNA levels. siRNA-mediated gene knockdown was used to examine the effects of decreased ZnT8 expression in primary dispersed murine islet cells from C57/BL6 mice and MIN6 cells. ZnT8 knockdown in these murine islets led to reduced glucose stimulated insulin secretion without altering the total cellular insulin content or cell viability at normal or supraphysiological Zn concentrations. The labile Zn content determined by flow cytometry after loading with the Zn-specific sensor FluoZin-3 AM was decreased in MIN6 cells following ZnT8 knockdown or IL1 beta treatment. These results suggest that an acute decrease in ZnT8 levels impairs beta-cell function and Zn homeostasis, and may contribute to inflammatory cytokine-induced alterations in beta-cell function.

1,25-Dihydroxyvitamin D-mediated hypercalcemia in oleogranulomatous mastitis (paraffinoma), ameliorated by glucocorticoid administration.

OBJECTIVE: To report a case of oleogranulomatous mastitis (paraffinoma) in which both the hypercalcemia and the inappropriately elevated 1,25-dihydroxyvitamin D [1,25(OH)2D] levels were successfully reduced by administration of prednisone. METHODS: We describe the clinical, imaging, and laboratory findings in the study patient. Furthermore, we review the relevant literature regarding hypercalcemia in oleogranulomatous mastitis. RESULTS: A 58-year-old man with oleogranulomatous mastitis (paraffinoma)-related hypercalcemia, renal failure, and inappropriately elevated levels of 1,25(OH)2D presented to our institution. Treatment with prednisone--0.5 mg/kg of body weight or 30 mg daily--for 10 days resulted in a reduction of his serum calcium and 1,25(OH)2D levels to near-normal or normal values and a substantial improvement of his renal function. Nevertheless, the patient ultimately died 11 months later of multiple paraffinoma-related complications. CONCLUSION: In selected cases, treatment with glucocorticoids may offer a temporary relief from paraffinoma-related hypercalcemia until definitive treatment options are feasible.