Effects of Cadmium and Diet on Metal Accumulation and Kidney Cell Death Pathways.

Cadmium (Cd) is a non-biodegradable environmental toxin and accumulates in the body with an estimated half-life of 30-45 years. Humans can be exposed to Cd through diet, drinking water, tobacco smoking, and industrial pollution. Cd can especially accumulate in the kidney due to the release of Cd from protein-metal complexes when filtering blood in the tubules causing oxidative stress and inducing kidney injury. Obesity is another risk factor for kidney disease therefore we examined the dual effects of Cd and obesity on the accumulation of essential metals in mouse kidneys. Starting in utero and continuing until 24 weeks postweaning, male/female mice were exposed to Cd (0, 0.5, or 5 ppm) and were fed on Normal Diet (ND)/High-Fat Diet (HFD) post-weaning. ICP-MS analysis was performed to evaluate Cd and essential metals accumulation in the aforementioned mouse kidneys. ICP-MS analysis demonstrated that female mouse kidneys accumulated significantly higher amounts of Cd than male mouse kidneys with increased iron absorption in 0.5 ppm Cd/ND treated female mouse kidneys compared to 5 ppm Cd/ND treated male mouse kidneys. To understand the mechanisms underlying increased Cd and iron accumulation in the female kidneys, we evaluated the expression of ABCD3 transporter and transferrin, which are known to transport Cd and iron, respectively. ABCD3 transporter expression was significantly higher in kidneys of female mice exposed to 0.5 ppm Cd/ND as compared to mice exposed to ND or HFD. ABCD3 expression was significantly induced in male mouse kidneys exposed to 5ppm Cd/ND and may play a role in transporting Cd in male and female mice. No significant changes in transferrin expression were seen in male and female mice. Ferroptosis is an iron-mediated cell death pathway that is closely linked with the autophagy and MAPK pathways. Therefore, we examined activation of these pathways and p38 MAPK. Western blotting was performed to evaluate levels of proteins in the pathways of interest. Western blotting results demonstrated activation of p38 MAPK only in female mouse kidneys while autophagy pathways were activated in both male and female mice. Expression of ferroptosis markers CD98, FTH-1, and GPX-4 are decreased during ferroptosis. Only CD98 expression was significantly decreased in male mice treated with 0.5 ppm/ND compared to 0 ppm/ND treated mice. However, 0.5 ppm and 5 ppm cadmium exposure with HFD induced ferroptosis in female mice as demonstrated by the decrease in FTH expression. No significant difference in GPX4 expression was detected in male mice while significant decrease in female mice treated with HFD+5 ppm Cd. The increase in p38 MAPK activation may contribute to enhanced Cd accumulation and/or activation of ferroptosis/autophagy pathways in female mouse kidneys.