Mitochondrial DNA deletion of proximal tubules is the result of itai-itai disease

Background. The pathogenesis of itai-itai disease continues to be controversial, although cadmium (Cd) poisoning which arises via polluted water and rice in Japan is likely involved. Until recently, however, a well-defined animal model for Cd intoxication was not available. An animal model for itai-itai disease was produced in rats by low-dose Cd treatment, intraperitoneally for a period of 70–80 weeks. Osteomalacia followed the renal damage. Results. A gene deletion in the mitochondrial DNA was found in the mitochondria of the proximal tubule cells of rats with chronic Cd intoxication, as was shown by the increased smaller PCR product seen by gel electrophoresis in one DNA region, where ATPase and cytochrome oxidase genes are located. However, the PCR product was different from that seen with a gene deletion associated with aging: del4834bp. Renal damage from Cd intoxication initially caused mitochondrial dysfunction indicated by the disturbance in reabsorption in the proximal tubules and decreased amounts of ATP, ATPase, and cytochrome oxidase with gradually progressing tubular proteinuria, and, finally, chronic renal failure with tubulointerstitial damage throughout the renal cortex. These gave rise to osteomalacia, subsequently. Conclusion. We concluded that in Cd poisoning, a mitochondrial gene deletion in the mitochondria of the proximal tubule cells was the primary event for the pathogenesis of osteomalacia in itai-itai disease.