Identification of renoprotective phytosterols from mulberry (Morus alba) fruit against cisplatin-induced cytotoxicity in LLC-PK1 kidney cells

The aim of this study was to explore the protective effects of bioactive compounds from the fruit of the mulberry tree (Morus alba L.) against cisplatin-induced apoptosis in LLC-PK1 pig kidney epithelial cells. Morus alba fruit is a well-known edible fruit commonly used in traditional folk medicine. Chemical investigation of M. alba fruit resulted in the isolation and identification of six phytosterols (1–6). Their structures were determined as 7-ketositosterol (1), stigmast-4-en-3β-ol-6-one (2), (3β,6α)-stigmast-4-ene-3,6-diol (3), stigmast-4-ene-3β,6β-diol (4), 7β-hydroxysitosterol 3-O-β-D-glucoside (5), and 7α-hydroxysitosterol 3-O-β-D-glucoside (6) by analyzing their physical and spectroscopic data as well as liquid chromatography/mass spectrometry data. All compounds displayed protective effects against cisplatin-induced LLC-PK1 cell damage, improving cisplatin-induced cytotoxicity to more than 80% of the control value. Compound 1 displayed the best effect at a relatively low concentration by inhibiting the percentage of apoptotic cells following cisplatin treatment. Its molecular mechanisms were identified using Western blot assays. Treatment of LLC-PK1 cells with compound 1 decreased the upregulated phosphorylation of p38 and c-Jun N-terminal kinase (JNK) following cisplatin treatment. In addition, compound 1 significantly suppressed cleaved caspase-3 in cisplatin-induced LLC-PK1 cells. Taken together, these findings indicated that cisplatin-induced apoptosis was significantly inhibited by compound 1 in LLC-PK1 cells, thereby supporting the potential of 7-ketositosterol (1) as an adjuvant candidate for treating cisplatin-induced nephrotoxicity.