Human vascular smooth muscle cell DNA synthesis stimulated by native low density lipoproteins involves redox-sensitive pathways. Inhibition by N-acetylcysteine and green tea constituents

R Locher
High plasma concentrations of LDL are an important cardiovascular risk factor. The mechanisms involved in DNA synthesis induced by native LDL in human vascular smooth muscle cells are unclear. We investigated the potential role of oxidative stress in human vascular smooth muscle cells (VSMC) DNA synthesis using the antioxidant N-acetylcysteine (NAC) and different green tea catechins, i. e. epigallocatechin (EGC), epigallocatechin gallate (EGCg) and green tea polyphenon, a mixture of green tea
more » ... ture of green tea catechins at physiological concentrations (0.01-1 g/mL). DNA synthesis was determined using radiolabeled thymidine incorporation, oxidative susceptibility of human serum was studied using 2,2'azobis(2-amidinopropane) (AAPH). Data are expressed as percent of control. LDL (100 g/mL LDL protein) increased DNA synthesis by 165% (from 100±3 to 265±6%, p<0.05), an effect that was completely blocked by pretreatment with the antioxidant N-acetylcysteine (98±22%, p<0.0001 vs. LDL). Similarly, epigallocatechin and epigallocatechin gallate concentration-dependently inhibited LDL-induced DNA synthesis to 122±4% and 117±4%, respectively (P<0.001 vs. LDL). Coincubation of both EGC and EGCg completely prevented LDL-induced DNA synthesis (92±2%, p<0.001 vs. LDL). Polyphenon alone reduced to DNA synthesis to 170±6%(p<0.05 vs. LDL), being less potent than the combination of EGC+EGCg, and also inhibited serum oxidation by 46±8% (p<0.05). However, combination of NAC and polyphenon markedly inhibited LDL synthesis below control levels (21±9%, p<0.0001 vs. LDL and control). Treatments had no effect on cell viability as determined by LDH release and Tryphan blue tests. These results demonstrate for the first time that LDL-induced DNA synthesis in human vascular smooth muscle cells involves redox-sensitive pathways that can be inhibited by physiological concentrations of green tea catechins and/or non-specific antioxidants. Antioxidant therapy may therefore be beneficial in inhibiting the growth-promoting effects of native LDL in human vascular smooth muscle cells
doi:10.5167/uzh-154278 fatcat:s7xky6vewfddfnrq6oc4iin7bq