[Aristolochic acid induces renal tubular injury and inhibits expression of bone morphogenetic protein-7 mRNA in renal tissue of rats].

OBJECTIVE

To investigate the pathogenic mechanism of aristolochic acid nephropathy (AAN) by observing the renal tubular injury and the change of the expression of bone morphogenetic protein-7 (BMP-7) mRNA in renal tissue of rats induced by aristolochic acid (AA), an active constituent in Caulis Aristolochiae Manshuriensis (CAM).

METHODS

Forty-six male Wistar rats were randomly divided into normal control group (n=20) and AA-treated group (n=26). Rats in AA-treated group were intragastrically administered with AA 20 mg/(kg.d), and rats in control group were treated with equal volume of potable water. At the end of the 4th, 8th and 12th week of administration, the 24 h-urine was collected by metabolic cage for detecting the activity of N-acetyl-beta-D-glucosaminidase (NAG) and the blood samples were obtained from abdominal aorta for detecting serum creatinine (SCr). Pathological change and the degree of injury of the kidneys were observed by microscopy. The expression of proliferative cell nuclear antigen (PCNA) was detected by immunohistochemical method, and mRNA expression of bone morphogenetic protein-7 (BMP-7) in the renal tissue was detected by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Compared with the normal control group, the activity of NAG and the ratio of SCr vs body weight were markedly increased in rats of the AA-treated group after treatment (P<0.05 and P<0.01). Pathological section of renal tissue showed that most renal tubules had cloudy swelling, and vacuolar degenerating in tubular epithelial cells, with brush border dropping off, and parts of tubular basement membrane were exposed. The degrees of injuries were aggravated depending on treating time. The tubulointerstitial injury (TI) parameter in rats of AA-treated group was higher than that of the normal control group. The positive expression of PCNA was observed in the damaged tubular cells. The proliferation index of PCNA was significantly increased after 4- and 8-week treatment (P<0.01), but was decreased after 12-week treatment (P<0.05). The mRNA expression of BMP-7 was markedly decreased in the AA-treated group compared with the normal control group after 4-week treatment (P<0.05), and decreased with the extension of treatment time.

CONCLUSIONS

AA can induce injury of the renal tubules, impair the cell regeneration, and inhibit the expression of BMP-7 mRNA in renal tissue. This may be one of the pathogenic mechanisms of AAN.