A cholesterol switch controls phospholipid scrambling by G protein-coupled receptors.

Class A G protein-coupled receptors (GPCRs), a superfamily of cell membrane signaling receptors, moonlight as constitutively active phospholipid scramblases. The plasma membrane of metazoan cells is replete with GPCRs yet has a strong resting trans-bilayer phospholipid asymmetry, with the signaling lipid phosphatidylserine confined to the cytoplasmic leaflet. To account for the persistence of this lipid asymmetry in the presence of GPCR scramblases, we hypothesized that GPCR-mediated lipid scrambling is regulated by cholesterol, a major constituent of the plasma membrane. We now present a technique whereby synthetic vesicles reconstituted with GPCRs can be supplemented with cholesterol to a level similar to that of the plasma membrane and show that the scramblase activity of two prototypical GPCRs, opsin and the ß1-adrenergic receptor, is impaired upon cholesterol loading. Our data suggest that cholesterol acts as a switch, inhibiting scrambling above a receptor-specific threshold concentration to disable GPCR scramblases at the plasma membrane.

Comparative HPTLC fingerprinting profile and GC-MS analysis of raw and purified Guggulu (Commiphora wightii. Arn. Bhand) by Ayurvedic purification method.

BACKGROUND: Guggulu is an oleo gum resin obtained from the plant Commiphora wightii (Arn.) Bhand., used in Ayurved ic medicines for various ailments like anti-inflammatory conditions, hyperlipidemia, thyroid disorders etc. Guggulsterones E & Z are responsible for these broad ranges of pharmacological actions. It is recommended to do Shodhana (purification) before incorporating it into medicinal formulations. Sahasrayoga, an Ayurvedic text, emphasizes the purification of Guggulu in a particular media, which is a long run practice in Kerala. OBJECTIVES: To compare the physicochemical and phytochemical parameters, quantitative estimation of Guggulsterone E & Z using high performance thin layer chromatography (HPTLC) and qualitative gas chromatography-mass spectrometry (GC-MS) analysis of Guggulu before and after purification. METHODS: Shodhana of Guggulu was performed in Water boiled with crushed fresh leaves of Neem (Azadirachta indica) and fresh rhizome of turmeric (Curcuma longa) using a special equipment (Dolayantra). Preliminary physicochemical and phytochemical evaluation, quantification of Guggulsterones E & Z using HPTLC and GC-MS analysis of raw and purified Guggulu were performed. RESULTS: Phytochemical evaluation of metabolites revealed marked variations. The mean concentrations of Guggulsterone E & Z showed significant differences before and after purification (p<0.01). On GC-MS analysis, it was found that few new compounds were added in the purified Guggulu. CONCLUSIONS: Therapeutic efficacy of Guggulu might have enhanced after traditional purification.