Role of metallothionein in metal detoxification and metal tolerance in protein calorie malnutrition and calcium deficient monkeys (Macaca mulatta).

A monkey model has been set up for protein calorie malnutrition and calcium deficiency. Oral exposure of 5ppm Cd/kg body wt./day for 24 weeks led to increased excretion of Cd, metallothionein (MT) and zinc. Rehabilitation of PCM monkeys for one year resulted in gradual reduction and finally complete disappearance of urinary metallothionein. During Cd exposure, the accumulation of Cd and induction of MT was significantly higher in liver, kidney and intestine. MT was also induced in heart, lung and testis of Cd exposed PCM and calcium deficient monkeys. Metallothionein from liver has been resolved into three isoforms, viz MTa, MTb and MTc on DEAE-Sephadex A 25 ion exchange column. MTc is the major isoform in Cd-treated, normal and protein calorie malnourished monkeys whereas MTb is the major isoprotein in the cadmium treated calcium deficient monkeys. The iso-metallothioneins varied in their metal composition in the nutritional stress conditions and showed different capacities to reactivate apo-enzymes viz. alkaline phosphatase, ceruloplasmin, superoxide dismutase and glutathione peroxidase. Thus, metallothionein plays a key role in metal metabolism during cadmium toxicity under nutritional stress conditions.