Olfactory Receptors (ORs) are a large family of G protein coupled receptors predominantly expressed by the main olfactory epithelium at nasal level and are responsible for the generation of smelling sense. Microarray and deep sequencing analyses, however, have demonstrated that ORs are ectopically expressed in various human tissues including testis, kidneys, adipose tissue and liver and their biological functions become to be unrevealed. Molecular and pharmacological approaches have shown that some of these ORs modulate glucose and lipid metabolism at multiple interfaces, suggesting that ORs might be part of the large family of nutrient sensors. i.e. molecular/ cellular machines that respond to a specific nutrient component. By using nutrients- derived agonists it has been shown that ORs effectively modulates glucose and lipid metabolism raising interest on their possible therapeutic application in the treatment of metabolic disorders including dyslipidemia, obesity and metabolic syndrome.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is the key regulator of low-density lipoprotein cholesterol (LDL-C) plasma levels. We previously observed that treatment of dyslipidemic subjects with nutraceutical combination containing red yeast rice (monacolin K 3.3 mg), Berberis aristata cortex extract (Berberine 531.25 mg) and Morus alba leaves extract (1-deoxynojirimycin 4 mg) (LopiGLIK®) did not alter the plasma PCSK9 levels. Thus, the aim of the present study was to investigate the effect of these three components on PCSK9 expression in HepG2 cell line in relationship to their effects on LDL-C cellular uptake. HepG2 cell line were incubated with Berberis aristata cortex extract (BCE), red yeast rice (RYR) and Morus alba leaves extract (MLE) alone or in combination for 24 h. RYR (50 µg/mL) increased PCSK9 protein expression (WB and ELISA assays), PCSK9 mRNA and its promoter activity. BCE (40 µg/mL) reduced PCSK9 expression, mRNA levels and promoter activity. MLE determined a concentration-dependent inhibition of PCSK9 at mRNA and protein levels, with a maximal reduction at 1 mg/mL; no significant changes in PCSK9 promoter activity were found. MLE also downregulates the expression of fatty acid synthase and HMG-CoA reductase mRNA levels. The combination of RYR, BCE and MLE reduced PCSK9 at mRNA, protein, and promoter activity. Finally, this combination induced the LDL receptor and LDL-C uptake by HepG2 cells. In conclusion, the positive effect of MLE on PCSK9 supports the rational of using this nutraceutical combination to control hyperlipidemic conditions.