Abnormal sterol-induced cell wall glucan deficiency in yeast is due to impaired glucan synthase transport to the plasma membrane.

Abnormal sterols disrupt cellular functions through yet unclear mechanisms. In Saccharomyces cerevisiae, accumulation of Δ8-sterols, the same type of sterols observed in patients of Conradi-Hünermann-Happle syndrome or in fungi after amine fungicide treatment, leads to cell wall weakness. We have studied the influence of Δ8-sterols on the activity of glucan synthase I, the protein synthetizing the main polymer in fungal cell walls, its regulation by the Cell Wall Integrity (CWI) pathway, and its transport from the endoplasmic reticulum to the plasma membrane. We ascertained that the catalytic characteristics were mostly unaffected by the presence of abnormal sterols but the enzyme was partially retained in the endoplasmic reticulum, leading to glucan deficit at the cell wall. Furthermore, we observed that glucan synthase I traveled through an unconventional exocytic route to the plasma membrane that is associated with low density intracellular membranes. Also, we found out that the CWI pathway remained inactive despite low glucan levels at the cell wall. Taken together, these data suggest that Δ8-sterols affect cell walls by inhibiting unconventional secretion of proteins leading to retention and degradation of glucan synthase I, while the compensatory CWI pathway is unable to activate. These results could be instrumental to understand defects of bone development in cholesterol biosynthesis disorders and fungicide mechanisms of action.

Quantification of nerolidol in mouse plasma using gas chromatography-mass spectrometry.

Nerolidol is a naturally occurring sesquiterpene found in the essential oils of many types of flowers and plants. It is frequently used in cosmetics, as a food flavoring agent, and in cleaning products. In addition, nerolidol is used as a skin penetration enhancer for transdermal delivery of therapeutic drugs. However, nerolidol is hemolytic at low concentrations. A simple and fast GC-MS method was developed for preliminary quantification and assessment of biological interferences of nerolidol in mouse plasma after oral dosing. Calibration curves were linear in the concentration range of 0.010-5 µg/mL nerolidol in mouse plasma with correlation coefficients (r) greater than 0.99. Limits of detection and quantification were 0.0017 and 0.0035 µg/mL, respectively. The optimized method was successfully applied to the quantification of nerolidol in mouse plasma.