Choice of tests in the biochemical assessment of nephrotoxicity in dogs and rats: A study with maleic acid

Abstract

Urinalysis represents a useful tool in the evaluation of new pharmaceutical agents acting on the kidney, during preclinical toxcological studies. In the present study, we studied the response of urinary creatinine, LDH, AAP, ALP, β-GAL, GGT, NAG and protein excretion to a single intravenous dose of maleic acid (25 mg/kg for dogs and 100 mg/kg for rats). Enzymes were selected based on their association with renal toxicity and their localisation within the renal tubule. They included lysosomal, brush border and cytosolic enzymes. In male dogs, increases in enzyme excretion occurred within 2 h of maleic acid administration, peaked 3 h after dosing, and returned towards, or to, predose value at 24 h. Marked increases in enzyme levels occurred only for LDH and GGT (10-fold or more). Additionally, there was a marked increase in total protein excretion whereas creatinine excretion decreased. In male rats, the only major difference from control was a higher 0–24 h protein excretion rate (approximately 2-fold). Moderate increases were also present for ALP, GGT and LDH (< 2-fold). In female rats, there was a marked increase in urinary excretion of proteins and LDH, GGT, NAG and ALP (8–13-fold when compared to controls). There were only moderate increases (2-fold or less) in β-GAL and AAP. Creatinine was unaffected by the treatment. Histopathological examination of the kidney revealed moderate to severe proximal tubular necrosis in dogs and minimal to moderate tubular necrosis in rats. Overall, urinary GGT, LDH, total protein and creatinine concentrations are the most sensitive biochemical indicators of maleic acid nephrotoxicity in dogs. For rats, in addition to LDH excretion, total proteins, NAG, GGT and ALP can be considered to be sensitive markers of renal injury. In the light of these results and those reported in literature, it was concluded that the response of urinary markers of nephrotoxicity is heavily dependent on the nephrotoxic agent, the dose, species, sex and study design. Consequently, a range of markers should be examined in order to identify the most useful.