Protective effect of polyaspartic acid on apoptosis induced aminoglycoside nephrotoxicity in rats. an immunohistochemical study of cell regulatory proteins [p53 and proliferating cell nuclear antigen]

ABSTRACT

Aminoglycoside antibiotics as gentamicin can produce irreversible, cumulative nepbrotoxicity due to the toxic injury of the renal tubular epithelial cells resulting in acute or chronic renal failure due to the prolonged exposure to small amounts [Lieberthal and Levine, 1996]. The aim of the present study was to evaluate the possible protective effect of polyaspartic acid on apoptosis-induced gentamicin toxicity in albino rats. For this purpose 70 male albino rats were equally divided into seven groups control group, gentamicin groups [rats treated with geritamicin alone at daily doses of 10, 20 or 40mg/kg of body weight intraperitoneally] and protected groups [rats treated with polyaspartic acid [250 mg/kg/day subcutaneously] concurrently with gentamicin at the different studied doses. All rats were treated for seven consecutive days. Kidney cortex apoptosis was detected by the p53 antibodies. The cortical proliferative activity was determined by the proliferating cell nuclear antigen [PCNA] labeling index. The expression of p53 oncogene and the PCNA monoclonal antibodies were detected and quantitated using immunohistoehemical methods. The mean percentage of p53 positive cells in gentamicin treated rats at doses of 10, 20 and 40 mg/kg/day for seven days was 41.3 +/- 2.21,47 +/- 2.26 and 53.5 +/- 2.42 respectively, while that of PCNA positive cells was 21.5 +/- 1.96, 27.7 +/- 2.31 and 35.7 +/- 3.97 respectively. The apoptotic figures as well as the cell proliferative activity were used for assessing the efficacy of polyaspartic acid [PAA]. The mean percentage of p53 positive cells in protected rats at doses of 10, 20 and 40mg/kg/day for seven days was 22.4 +/- 2.07, 24.7 +/- 2.41 and 28.7 +/- 3.27 respectively, while that of PCNA positive cells was 2.8 +/- 0.98, 5.05 +/- 0.90 and 6.65 +/- 0.94 respectively. Rats treated with gentamicin alone developed an apoptotic process as part of the various cortical alterations induced by this antibiotic. Also a relation between gentamicin-induced tubular apoptosis and cortical proliferative response has been established. The marked apoptotic reaction induced by gentamicin in proximal tubules was dose dependent. In low doses it occurred in the absence of necrosis and it was correlated with the proliferative response. Coadministration of polyaspartic acid [PAA] with gentamicin proved to reduce significantly gentamicin-induced apoptosis. Although the underlying mechanism for this reduction remains uncertain, yet the molecular mechanism of the protective effect of PAA is most likely related to its biochemical mechanisms, which include antioxidative activities