The relationship of dietary protein to metallothionein and cadmium-induced renal damage.

The effect of dietary protein on the concentration of kidney metallothionein and cadmium in relationship to renal damage was investigated. Rats fed a low-protein diet accumulated significantly less cadmium in the kidney, liver, lung, and small intestine than rats fed a normal or high-protein diet. Metallothionein synthesis and/or storage was significantly reduced in rats fed the low-protein diet compared with rats fed the normal or high-protein diet. In rats fed the high-protein diet extensive proximal renal tubular necrosis was observed when kidney cadmium was below 200 microgram/g wet weight and metallothionein was above 740 microgram/g wet weight. Proximal tubular necrosis was slight to moderate in rats fed the normal or low-protein diet, which correlated with relatively low levels of cadmium and metallothionein in the kidney. These studies show that dietary protein affects the tissue level of both cadmium and metallothionein. The results also demonstrate that extensive renal damage can occur when the level of kidney cadmium is below the suggested critical concentration of 200 microgram/g wet weight. Based on studies which show the nephrotoxic effects of cadmium-metallothionein and results of the present experiments, we suggest that the concentration of this complex in the kidney is of greater pathological importance that the level of kidney cadmium.