Piperlonguminine attenuates renal fibrosis by inhibiting TRPC6

Liuwei Dihuang (LWDH) is a classic prescription that has been used to the treatment of "Kidney-Yin" deficiency syndrome for more than 1000 years in China. Recent studies have confirmed that LWDH can prevent the progression of renal fibrosis. Numerous studies have demonstrated the critical role that TRPC6 plays in the development of renal fibrosis. Due to the complex composition of LWDH and its remarkable therapeutic effect on renal fibrosis, it is possible to discover new active ingredients targeting TRPC6 for the treatment of renal fibrosis.

This study aimed to identify selective TRPC6 inhibitors from LWDH and evaluate their therapeutical effects on renal fibrosis.

Computer-aided drug design was used to screen the biologically active ingredients of LWDH, and their affinities to human TRPC6 protein were detected by microcalorimetry. TRPC6, TRPC3, and TRPC7 over-expressed HEK293 cells were constructed, and the selective activities of the compounds on TRPC6 were determined by measuring [Ca²⁺]_i in these cells. To establish an in vitro model of renal fibrosis, human renal proximal tubular epithelial HK-2 cells were stimulated with TGF-β1. The therapeutic effects of LWDH compounds on renal fibrosis were then tested by detecting the related proteins. TRPC6 was knocked-down in HK-2 cells to investigate the effects of LWDH active ingredients on TRPC6. Finally, a unilateral ureteral obstruction model of renal fibrosis was established to test the therapeutic effect.

From hundreds of LWDH ingredients, 64 active components with oral bioavailability ≥30% and drug-likeness index ≥0.18 were acquired. A total of 10 active components were obtained by molecular docking with TRPC6 protein. Among them, 4 components had an affinity with TRPC6. Piperlonguminine (PLG) had the most potent affinity with TRPC6 and blocking effect on TRPC6-mediated Ca²⁺ entry. A 100 μM of PLG showed no detectable inhibition on TRPC1, TRPC3, TRPC4, TRPC5, or TRPC7-mediated Ca²⁺ influx into cells. In vitro results indicated that PLG concentration-dependently inhibited the abnormally high expression of α-smooth muscle actin (α-SMA), collagen I, vimentin, and TRPC6 in TGF-β1-induced HK-2 cells. Consistently, PLG also could not further inhibit TGF-β1-induced expressions of these protein biomarkers in TRPC6 knocked-down HK-2 cells. In vivo, PLG dose-dependently reduced urinary protein, serum creatinine, and blood urea nitrogen levels in renal fibrosis mice and markedly alleviated fibrosis and the expressions of α-SMA, collagen I, vimentin, and TRPC6 in kidney tissues.

Our results showed that PLG had anti-renal fibrosis effects by selectively inhibiting TRPC6. PLG might be a promising therapeutic agent for the treatment of renal fibrosis.