Effect of dietary protein on glomerular proteinase activities.

Recent studies suggest that proteolytic enzymes are involved in the degradation of extracellular matrix components of the renal glomerulus. In the present study, the effects of feeding 3 different protein diets on glomerular cysteine proteinase and metalloproteinase activities to healthy rats for 6 weeks were examined. The diets contained 5, 20, or 60% casein and were made isocaloric by starch. On sacrifice, the glomeruli were isolated by differential sieving. Proteolytic activities were measured using fluorogenic substrates and were expressed per glomerular DNA content. Body weight was virtually unchanged by the amount of protein ingested, whereas kidney weight was closely correlated with dietary protein content (5%: 1,625 +/- 324; 20%: 2,110 +/- 326; 60%: 2,705 +/- 910 mg). Activity of cathepsin B, the most abundant cysteine proteinase in the glomerulus, decreased with protein loading (5%: 1,498 +/- 110; 20%: 1,321 +/- 82; 60%: 914 +/- 84 pmol/min/micrograms DNA). The same pattern emerged with cathepsin L (5%: 869 +/- 71; 20%: 846 +/- 70; 60%: 517 +/- 83 pmol/min/micrograms DNA) and cathepsin H (5%: 498 +/- 45; 20%: 478 +/- 55; 60%: 330 +/- 39 pmol/min/micrograms DNA). The differences between the 20 and 60% groups were statistically significant for all 3 cathepsins measured. The intraglomerular activity of the metalloproteinase collagenase declined significantly with the amount of protein ingested (5%: 233 +/- 14; 20%: 189 +/- 13; 60%: 137 +/- 11 microU/micrograms DNA). Gelatinase activity also fell as protein intake increased (5%: 183 +/- 18; 20%: 115 +/- 10; 60%: 94 +/- 11 F/micrograms DNA).(ABSTRACT TRUNCATED AT 250 WORDS)