Thus, the change in membrane fluidity was observed at a concentration 10 times greater than that for hemolysis. This result could be explained by the fact that the spin probes are sparsely distributed in the membrane and, therefore, the spin probe spectroscopy only detects changes in fluidity when a widespread change occurs in the membrane. The molar ratio between spin probe and lipid present in the membranes used for the EPR

measurements was 1:200. Thus, to detect changes in membrane fluidity, the environment of most spin labels would have to be changed. This result also suggests that a highly localized change in the erythrocyte membrane is sufficient to provoke hemolysis. In cell cytotoxicity, the IC50 of nerolidol was 6 × 1011 molecules/fibroblast and the concentration this website that alters fibroblast membrane fluidity was approximately 10 times lower (6.3 × 1010 terpenes/cell). These calculations indicate that the concentrations that cause a general change in INK 128 molecular weight fibroblast membrane fluidity are smaller than those that inhibit the growth of fibroblasts. This result is indicative of the low toxicity of terpenes in cultured fibroblasts and suggests that, unlike in red blood cells, change in fibroblast membrane fluidity occurs without disruption of the membrane. In conclusion, we examined the hemolytic potential and cytotoxicity in fibroblasts treated with terpenes and showed that these reagents

cause cellular injury in a concentration-dependent manner. Nerolidol, α-terpineol and DL-menthol were the most hemolytic and limonene and 1,8-cineole were the least hemolytic, whereas in the cytotoxicity assay, nerolidol and α-terpineol were the most cytotoxic and 1,8-cineole

was the least cytotoxic; however, the correlation coefficient between the two tests was low (R = 0.61). This study demonstrated that monoterpenes are powerful membrane fluidizers in erythrocyte and fibroblast cells, and the observed effects were not significantly Oxalosuccinic acid different among them, suggesting that they possess the same potency in enhancing dermal permeation. However, less polar monoterpenes, such as limonene and cineole, showed low membrane aggressiveness and cytotoxicity. The sesquiterpene produced the greatest increase in membrane fluidity, but also a greater irritation potential. Although the mechanisms of cytotoxicity were not investigated, we suggest that terpenes could trigger various mechanisms, including interactions with the cellular membrane, which most likely occur during terpene-induced hemolysis. The antiproliferative effects of monoterpenes have been previously demonstrated through the modulation of gene expression associated with apoptosis ( Bardon et al., 1998, Bardon et al., 2002, Yang and Ping Dou, 2010 and Wu et al., 2012). Given that some monoterpenes show activity against Leishmania infantum promastigotes ( Morales et al., 2009) and the sesquiterpene nerolidol inhibits the growth of several species of Leishmania promastigotes and amostigotas ( Arruda et al.