Allicin inhibits tubular epithelial-myofibroblast transdifferentiation under high glucose conditions in vitro

Previous studies have suggested that tubular epithelial-mesenchymal transition (EMT) is an important event in renal tubulointerstitial fibrosis, which is a clinical characteristic of diabetic nephropathy. The present study aimed to investigate the effect of allicin, the major biological active component of garlic, on the EMT of a human renal proximal tubular epithelial cell line (HK-2) cultured under high glucose concentrations. HK-2 cells were exposed for 48 h to 5.5 or 25 mmol/l D-glucose, 25 mmol/l D-glucose plus allicin (2.5, 5, 10 or 20 mu g/ml) or 25 mmol/l D-glucose plus 20 mu m/mol/l PD98059, a selective inhibitor of the mitogen activated protein kinase/extracellular signal-regulated kinase (ERK) signaling pathway. The EMT of HK-2 cells was assessed by analyzing the protein expression of E-cadherin, a-smooth muscle actin (a-SMA), vimentin and collagen I via immunocytochemistry. In addition, reverse transcription-quantitative polymerase chain reaction and western blotting were used to detect the expression levels of transforming growth factor (TGF)-(31 and phosphorylated (p)-ERK1/2. Marked morphological changes were observed in HK-2 cells cultured under high glucose conditions, and these changes were abrogated by simultaneous incubation with allicin and PD98059. The expression levels of alpha-SMA, vimentin and collagen I were significantly increased in HK-2 cells cultured under high glucose conditions, as compared with those cultured under normal glucose conditions (P<0.01). Conversely, the expression levels of E-cadherin were significantly decreased upon stimulation with high glucose (P<0.01). Furthermore, the expression levels of TGF-beta 1 and p-ERK1/2 were significantly upregulated in HK-2 cells cultured under high glucose conditions, as compared with those cultured under normal glucose conditions (P<0.05). Allicin partially reversed the high-glucose-induced increase in alpha-SMA, vimentin and collagen I expression (P<0.01 at 20 mu g/ml), increased the expression of E-cadherin, and significantly downregulated the high glucose-induced expression of TGF-beta 1 and p-ERK1/2 in a dose-dependent manner (P<0.05). The results of the present study suggested that high glucose concentrations induced the EMT of HK-2 cells, and that allicin was able to inhibit the EMT, potentially via regulation of the ERK1/2-TGF-beta 1 signaling pathway.