Comment on Menke et al. Metals in Urine and Diabetes in U.S. Adults. Diabetes 2016;65:164-171

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 β-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.

Environmental pollution and diabetes mellitus

Diabetes mellitus (DM) is a chromic metabolic disease that affects a large segment of the population worldwide. Physical inactivity, poor nutrition, and genetic predisposition are main risk factors for disease development. In the last decade, it was clear to the scientific community that DM development is linked to a novel disease inducer that was later defined as diabetogenic factors of pollution and endocrine disrupting agents. Environmental pollution is exponentially increasing in uncontrolled manner in several countries. Environmental pollutants are of diverse nature and toxicities, including polyaromatic hydrocarbons (PAHs), pesticides, and heavy metals. In the current review, we shed light on the impact of each class of these pollutants and the underlined molecular mechanism of diabetes induction and biological toxicities. Finally, a brief overview about the connection between coronavirus disease 2019 and diabetes pandemics is presented.

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.

Salivary N1-Methyl-2-Pyridone-5-Carboxamide, a Biomarker for Uranium Uptake, in Kuwaiti Children Exhibiting Exceptional Weight Gain

In a longitudinal study of 6,158 Kuwaiti children, we selected 94 for salivary metabolomic analysis who were neither obese (by waist circumference) nor metabolic syndrome (MetS) positive (<3 diagnostic features). Half (43) remained healthy for 2 years. The other half (51) were selected because they became obese and MetS positive 2 years later. In the half becoming obese, metabolomic analysis revealed that the level of salivary N1-Methyl-2-pyridone-5-carboxamide (2PY) had the highest positive association with obesity (p = 0.0003, AUC = 0.72) of 441 salivary biochemicals detected. 2PY is a recognized uremic toxin. Also, 2PY has been identified as a biomarker for uranium uptake. Considering that a relatively recent military conflict with documented uranium contamination of the area suggests that this weight gain could be a toxicological effect of long-time, low-level uranium ingestion. Comparison of salivary 2PY in samples from the USA and Kuwait found that only Kuwait samples were significantly related to obesity. Also, the geographic distribution of both reported soil radioactivity from ²³⁸U and measured salivary 2PY was highest in the area where military activity was highest. The prevalence pattern of adult diabetes in Kuwait suggests that a transient diabetogenic factor has been introduced into the Kuwaiti population. Although we did not measure uranium in our study, the presence of a salivary biomarker for uranium consumption suggests potential toxicity related to obesity in children.