Effect of high plant (cowpeas) and animal (casein) proteins on urinary –N-acetyl-beta-D- glucosaminidase (NAG) and micoalbuminuria in rats

Abstract

Background: Urinary NAG activity is one of the most frequently evaluated urinary enzymes used in the diagnosis of renal tubular toxicity in recent time. Urinary NAG activity has been reported to precede changes in serum creatinine and endogenous creatinine clearances while microalbumin is the excretion of albumin in urine; this is highly variable, ranging from non detectectable quantities to milligrams of albumin. The aim of this study is to determine the effect of the intake of high plant (Cowpeas) and animal (Casein) proteins on urinary NAG and microalbuminuria in rats.

Methods: One hundred and eighty wistar rats were used in this study. The rats were randomly distributed into 8 experimental groups (20 per group) and control (20). Blood and 24 hour urine samples were collected at baseline, 1 month, 3 months and 6 months intervals. Urinary NAG and microalbumin were determined spectrophotometrically.

Results: Urinary NAG concentration was observed to be significantly higher (P<0.01) in urine of rats on casein diets when compared to baseline values, increases of over tenfold were observed. When NAG values of cowpeas fed rats was compared to that of casein fed rats, there was a significant increase (P<0.01) in urinary NAG values of rats fed with casein diet and the increase seen was proportional to dosage and duration. However for urinary microalbumin concentration, there was a significant increase in urinary microalbumin concentration of 30% casein fed rats when compared to baseline at 1month (P<0.05), which dropped at 3 months and 6 months and for the 40% casein diet, there was a significant increase (P<0.01) at 1 and 3 months but dropped at 6 months. Values of 30% cowpeas fed rat were significantly higher (P<0.01) than baseline values at 1 month and at 3 months for 35% cowpeas fed rats. Others were not significant.

Conclusion: This study has clearly shown that the intake of a high plant protein, cowpeas leads to mild increase in NAG and microalbumin in urine. On the other hand, an intake of high casein diet, an animal protein, resulted in a marked increase in urinary NAG and mild increase in microalbumin. This study has also shown that the increase of urinary NAG precedes that of microalbumin.

Keywords: High-protein diet, Urinary NAG, Microalbumin