Tamoxifen increases membrane fluidity at high concentrations

There are contradictory results in the literature relating to the effect of tamoxifen on membrane fluidity. The present work investigates the effect o f tamoxifen on membrane dynamics to find out whether the concentration of t amoxifen can be one of the factors in this discrepancy. Turbidity (absorban ce at 440 nm) and Fourier transform infrared spectroscopic studies reveal t hat tamoxifen causes opposite effects on membrane fluidity at low (1 mol.%) and high (30 mol.%) tamoxifen concentrations. Low tamoxifen concentrations increase the absorbance in the gel and liquid crystalline phase, whereas h igh tamoxifen concentrations decrease the absorbance in gel and liquid crys talline phase, whereas tamoxifen concentrations decrease the absorbance. Ob servations on both phases show that the bandwidth of the CH2 stretching ban ds decreases with 1 mol.% tamoxifen and increases with 30 mol.% tamoxifen p resent, indicating a decrease in membrane fluidity at low tamoxifen concent rations and an increase in fluidity at high tamoxifen concentrations. It is seen that the apparent discrepancy in the literature on the effect of tamo xifen on membrane fluidity mainly arises from the tamoxifen concentration u sed and the confusion on the concept of lipid fluidity and lipid order.