Supplementary Material for: Phosphorus restriction prevents rapamycin-induced kidney damage in rats

Introduction: There are conflicting reports about the effect or rapamycin on the kidneys. Rapamycin is known to promote phosphaturia that may be associated to renal injury. Methods: Detailed histopathological studies were performed on the kidneys of rats with normal (Control) and reduced (Nx) renal mass that were treated with rapamycin (1.3 mg/kg for 22 days) or placebo. The effect of rapamycin was also evaluated in Control and Nx rats fed different amounts of phosphorus: 0.6% P (NP), 1.2% P (HP) and 0.2% P (LP). Quantitative scores of kidney lesions were obtained for: interstitial nephritis (IN), tubular damage (TD), and nephrocalcinosis (NC). Results: When compared with placebo, rapamycin administration to Nx rats resulted in significant increases in IN (4.17±0.74 vs 1.51±0.53 %) and TD (14.45±1.51 vs 8.61±1.83 %). Rapamycin also increased NC both in Control (0.86±0.23 vs 0.14±0.06 %) and Nx (0.86±0.32 vs 0.15±0.14 %) rats. In Control rats receiving rapamycin, feeding HP aggravated IN (3.25±0.48 %), TD (22.47±4.56 %) and NC (3.66±0.75 %) while feeding LP prevented development of any renal lesions. In Nx rats treated with rapamycin, HP intake also increased IN (8.95±1.94 %), TD (26.86±3.95 %) and NC (2.77±0.60 %) whereas feeding LP reduced all lesions to lower levels than in rats fed NP. Rapamycin treatment increased fractional excretion of P (FEP) and an excellent correlation between scores for renal lesions and FEP was found. Conclusion: Rapamycin has deleterious effects on kidney pathology causing lesions that are located mainly at tubular and tubulo-interstitial level. Rapamycin-induced kidney damage is more evident in rats that already have decreased renal function and seems to be related to the phosphaturic effect of the drug. Dietary P restriction prevents kidney damage in rats treated with rapamycin.

引言：目前关于雷帕霉素对肾脏的影响存在相互矛盾的研究报道。已知雷帕霉素可诱导磷酸盐尿，这一作用可能与肾损伤相关。方法：本研究对肾质量正常（对照组，Control）与肾质量减少（肾切除模型，Nx）的大鼠肾脏开展详细的组织病理学研究，这些大鼠分别接受雷帕霉素（1.3 mg/kg，连续给药22天）或安慰剂（placebo）处理。此外，本研究还在饲喂不同磷含量饲料的对照组与肾切除模型大鼠中评估雷帕霉素的作用效果，饲料磷含量分别设置为0.6%P（正常磷组，NP）、1.2%P（高磷组，HP）与0.2%P（低磷组，LP）。研究对三类肾脏病变进行了量化评分：间质性肾炎（IN）、肾小管损伤（TD）与肾钙化症（NC）。结果：与安慰剂组相比，接受雷帕霉素给药的肾切除模型大鼠的间质性肾炎评分（4.17±0.74 vs 1.51±0.53%）与肾小管损伤评分（14.45±1.51 vs 8.61±1.83%）均显著升高。雷帕霉素还可同时升高对照组大鼠与肾切除模型大鼠的肾钙化症评分：对照组大鼠为0.86±0.23 vs 0.14±0.06%，肾切除模型大鼠为0.86±0.32 vs 0.15±0.14%。在接受雷帕霉素给药的对照组大鼠中，饲喂高磷饲料会加重间质性肾炎（3.25±0.48%）、肾小管损伤（22.47±4.56%）与肾钙化症（3.66±0.75%），而饲喂低磷饲料可完全阻断所有肾脏病变的发生。在接受雷帕霉素给药的肾切除模型大鼠中，高磷摄入同样会升高间质性肾炎（8.95±1.94%）、肾小管损伤（26.86±3.95%）与肾钙化症（2.77±0.60%）评分，而饲喂低磷饲料可使所有病变程度降至低于正常磷组大鼠的水平。雷帕霉素给药可升高磷排泄分数（FEP），且肾脏病变评分与磷排泄分数之间存在极佳的相关性。结论：雷帕霉素对肾脏病理存在有害作用，可诱发主要累及肾小管及肾小管间质的病变。雷帕霉素诱导的肾损伤在已存在肾功能减退的大鼠中表现更为显著，且似乎与该药的磷酸盐尿诱导作用相关。膳食磷限制可预防雷帕霉素给药大鼠的肾损伤。