Beneficial effect of all-trans retinoic acid (ATRA) on glomerulosclerosis rats via the down-regulation of the expression of α-smooth muscle actin: A comparative study between ATRA and benazepril

Although ATRA is a potent renoprotective agent, relatively little is known regarding the mechanisms of its action. The present study was designed to further elucidate the mechanisms of ATRA's action to GS rats and compare that with the beneficial effect of benazepril. Male SD rats weighting 160 to 200 g were used in this study. GS was induced by unilateral nephrectomy and intravenous injection of adriamycin (6 mg/kg). They were divided randomly 20 ones per group into GS group, GS treated with ATRA (20 mg/kg/day) group, and GS treated with benazepril (10 mg/kg/day) group. The other 20 ones were taken as sham-operation group, injected normal saline into caudal vein. 12 weeks later, all rats were subjected to sacrifice. As expected, the GS group exhibited significant lower serum TP and Alb, and higher BUN, Cr and proteinuria than those of the sham group. Administration of ATRA or benazepril did ameliorate these above disorders of biochemical parameters in GS rats. Extensive renal damage was observed in the GS group, such as mononuclear infiltration, mesangial proliferation, focal segment glomerular sclerosis, and tubulointerstitial fibrosis. The pathological changes in both ATRA and benazepril group were alleviated remarkably. Semiquantitative GSI was used to evaluate the degree of GS in all groups. GSI was significantly higher in the GS group than in sham group. GSI decreased from 21.9 ± 6.7 in the GS group to 6.9 ± 2.8 in the ATRA group and 7.0 ± 2.7 in benazepril group respectively. However, no significant difference in GSI between rats treated with ATRA and rats treated with benazepril was found. RT-PCR analysis revealed the renal expression of α-SMA mRNA was induced substantially in GS group as compared to sham group, which could be offset completely by ATRA or benazepril administration. However, expression level of α-SMA mRNA in GS rats treated with ATRA was identical to that in GS rats treated with benazepril. We also examined immunohistochemical staining for renal α-SMA, TGF-β1, Col IV, and FN in this model. Weak staining was observed in some glomerulus, mesangial cells, and tubular interstitium of sham rats. Staining was markedly enhanced in the majority of glomerulus, mesangial cells, and tubular interstitium of untreated GS rats. Compared with untreated GS animals, intensity and extent of staining for renal α-SMA, TGF-β1, Col IV, and FN were markedly reduced in glomerulus, mesangial cells, and tubular interstitium of GS rats treated with either ATRA or benazepril. However, no significant differences existed between ATRA and benazepril with respect to the glomerular and tubulointerstitial staining scores. Interestingly, our data documented some differences of therapeutic capacities between ATRA and benazepril. In comparison with benazepril, ATRA exerted no improvement in hypoproteinemia, but more significant decrease in serum Cr level in GS rats. The reasons leading to these variations are unclear. Whatever they are, the properties of down-regulate inflammatory/proliferative programs may make ATRA an attractive potential candidate for future therapeutic use in kidney disease.