Chronic cadmium exposure to minimal-risk doses causes dysfunction of epididymal adipose tissue and metabolic disorders.

Abstract

Cadmium (Cd) is among the top seven most hazardous environmental contaminants. Minimal risk levels for daily exposure have been established, such as no observable adverse effect level (NOAEL) and lowest observable adverse effect level (LOAEL). Chronic exposure to Cd, at both NOAEL and LOAEL doses, causes toxicity in diverse tissues. However, Cd toxicity in adipose tissue, an endocrine and metabolic organ, remains relatively understudied. We aimed to investigate the potentially toxic effects of chronic Cd exposure (at NOAEL and LOAEL doses) on epidydimal adipose tissue of adult male Wistar rats. Ninety male Wistar rats were divided into three groups (n = 30): Control Cd-free, NOAEL, and LOAEL that received CdCl₂ in drinking water for 15 days to 5 months. We evaluated over time zoometry, serum and adipose Cd concentration, redox balance, GLUT4 and Nrf2 expression, histology, leptin, adiponectin, adipose insulin resistance index, free fatty acids, and glucose tolerance. The higher dose group showed a more pronounced and sustained increase in serum and adipose tissue of Cd concentration. Zoometry was similarly affected in both Cd-exposed groups with adipocyte hypertrophy. The redox balance was maintained due to the augmenting of Nrf2 expression. Leptin concentration augmented, while adiponectin diminished. Adipose insulin resistance increased simultaneously to lipolysis and glucose intolerance despite high GLUT4 expression. In conclusion, this study provides strong evidence that chronic Cd exposure, even at minimal risk levels (LOAEL and NOAEL doses), has toxic effects, disrupting the function of epididymal adipose tissue and contributing to metabolic disorders.