HOP PROANTHOCYANIDINS PROTECT AGAINST SIN-1-INDUCED CYTOTOXICITY IN PC12 CELLS

The present work was conducted to determine if proanthocyanidins (PCys) from hops protect PC12, a rat pheochromocytoma derived cell line, from the toxic effects of SIN-1 (3-morpholinosydnonimime). Undifferentiated PC12 cells were pre-incubated with hop PCys for 3 h and then exposed to SIN-1 for 24 h at 37ºC. At 5 µg/ml, pooled PCy fractions of monomers, dimers, trimers and tetramers partially protected PC12 cells from the toxic effects of 1.0 mM SIN-1. Pentamers or higher oligomeric PCys were not cytoprotective. When the SIN-1 concentration was lowered to 0.75 mM, the PCy mixtures of monomers to tetramers were completely protective. Furthermore, the individual monomer, (-)-epicatechin, and the individual trimer, epicatechin-(4β→8)-catechin-(4α→8)-catechin, at 1 or 5 µg/ml, were effective in preventing the toxic effects of SIN-1 in PC12 cells. The protective effect of the PCys against SIN-1-induced cytotoxicity was confirmed by the LDH assay. In contrast, the major polyphenol in tea, epigallocatechin gallate (EGCG), at 1 or 5 µg/ml, enhanced the toxic effects of SIN-1 in PC12 cells. EGCG significantly increased the levels of H₂O₂ in the culture medium used in growing the cells. SIN-1, at 0.5 or 0.75 mM, also increased the levels of H2O2 in the culture medium. However, none of the pooled hop PCy fractions increased H2O2 levels in the PC12 culture medium; instead, the PCys prevented the SIN-1-induced increase in H₂O₂ levels. At 25 µg/ml, the hop PCy fractions, from monomers to tetramers, induced cell proliferation in PC12 cells in the presence and absence of SIN-1. It is proposed that SIN-1 impairs mitochondrial function and that hop oligomeric PCys protect PC12 cells against SIN-1-induced mitochondrial damage, possibly, by reducing H₂O₂ formation and by reacting with oxidizing/nitrating intermediate species arising from SIN-1.