#4598 ADMINISTRATION OF ASTRAGALUS MEMBRANACEUS IMPROVES RENAL CONDITIONS AND SERUM CARNOSINE LEVELS IN AN ACUTE KIDNEY INJURY MODEL

Abstract

Abstract Background and Aims Astragalus membranaceus (AM) exhibits various pharmacological effects against many diseases, including chronic kidney disease (CKD) (see http://nccih.nih.gov/health/astragalus). Acute kidney injury (AKI) is a sudden episode of kidney failure. AKI occurs frequently but is believed to heal completely and is likely an important factor causing CKD pathogenesis or progression. Previously, we demonstrated the lethal dose in old mice is 20 mg/kg cis-diamminedichloroplatinum (CDDP), and the dosage that will cause AKI in young mice is 14 mg/kg of CDDP. Low doses of CDDP caused AKI in old mice. However, the same dosage in young mice would manifest AKI that was subsequently completely reversible. On administration of AM, old mice (50 mg/kg) showed significantly improved AKI pathology, suggesting the therapeutic effect of AM is age-dependent with regard to AKI pathogenicity. Here, we further examined the possible effect of AM in preventing AKI and delaying CKD progression. Method Female C57BL/6 mice were separated into three groups based on age: young, 10 weeks; middle-aged, 35 weeks; and old, 52 weeks. The mice received oral administered of either AM powder mixed with sterilized 0.5% methylcellulose 400 (w/v) (AM group) or 0.5% methylcellulose 400 alone in the control group (CG). Four hours after most recent dose (twice a day at 20 mg/kg AM), 0.5 mg/ml CDDP (reduced dose: 14 mg/kg or 0.9% NaCl for the CG) was injected intraperitoneally. We measured blood serum urea nitrogen (BUN) and creatinine (CRE) levels, which are biomarkers of AKI. Additionally, we assessed histochemical changes in kidney sections stained with anti-CD3 and anti-CD68 antibodies after the mice were sacrificed on day x. Thereafter, serum carnosine levels in the samples collected 4 hours after AM administration (n = 6 per group) were determined using a carnosine ELISA kit (Novus, NBP2-75013). Data were analyzed statistically with PRISM software. Significance was considered P = 0.05. Results The 14 mg/kg CDDP dose in old mice significantly increased BUN and CRE levels and caused histological damage in renal tubule epithelial cells and glomeruli. However, these pathological changes were not observed in young and middle-aged mice receiving the same CDDP dose. Histochemical analysis of the old mice showed a significant increase in the number of CD3- and CD68-positive cells following AKI induction (Fig. 1). However, the increase of these inflammatory markers was clearly ameliorated by the AM pretreatment in the experimental group. Serum carnosine levels were markedly increased in young and middle-aged mice following AM administration (Fig. 2). Moreover, the serum carnosine concentration in old mice was upregulated at levels corresponding to those in young mice with AM administration. However, serum carnosine levels showed no additional increase after AM administration in old mice and remained stable. Our findings suggest that normal renal conditions show a simple upregulation of serum carnosine level after AM administration. Furthermore, AM administration improves renal conditions in old mice with high levels of CD-3 positive cells in particular (Fig. 1, arrow). Figure 2 shows the increased and then subsequent stabilizing of the serum carnosine levels (Fig. 2, arrow). Conclusion AM administration can upregulate serum carnosine in younger mice and shows at least some effectiveness in older mice, where serum carnosine is downregulated but concentrated. Serum carnosine might not be necessary for reducing the pathogenesis of AKI in younger mice, but it becomes important to prevent AKI in old mice. This indicates the effect of AM is probably age-dependent because AKI sequelae manifested spontaneously in all mice but were specifically ameliorated when administered to old mice as opposed to younger mice who recovered completely irrespective of AM administration.