Chronic contamination with 137Cesium affects Vitamin D3 metabolism in rats

Twenty years after Chernobyl disaster, many people are still chronically exposed to low dose of 137Cs, mainly through the food consumption. A large variety of diseases have been described in highly exposed people with 137Cs, which include bone disorders. The aim of this work was to investigate the biological effects of a chronic exposure to 137Cs on Vitamin D3 metabolism, a hormone essential in bone homeostasis. Rats were exposed to 137Cs in their drinking water for 3 months at a dose of 6500 Bq/l (approximately 150 Bq/rat/day), a similar concentration ingested by the population living in contaminated territories in the former USSR countries. Cytochromes P450 enzymes involved in Vitamin D3 metabolism, related nuclear receptors and Vitamin D3 target genes were assessed by real time PCR in liver, kidney and brain. Vitamin D, PTH, calcium and phosphate levels were measured in plasma. An increase in the expression level of cyp2r1 (40%, p < 0.05) was observed in the liver of 137Cs-exposed rats. However a significant decrease of Vitamin D (1,25(OH)D3) plasma level (53%, p = 0.02) was observed. In brain, cyp2r1 mRNA level was decreased by 20% (p < 0.05), while the expression level of cyp27b1 is increased (35%, p < 0.05) after 137Cs contamination.In conclusion, this study showed for the first time that chronic exposure with post-accidental doses of 137Cs affects Vitamin D3 active form level and induces molecular modifications of CYPs enzymes involved its metabolism in liver and brain, without leading to mineral homeostasis disorders.