Multiple lines of evidence have implicated that nicotinic acetylcholine receptor (nAChR)may bean important therapeutic target for the treatment of Alzheimer's disease (AD). Although thereare reports suggesting a link between alpha7 nAChR subtype and AD, there has been little reporton the mechanism. The present study investigates whether and how α7 nAChR activationaffects APP695 processing in SH-EP1 cell model. Cell line co-expressing α7 nAChR gene andhuman amyloid precursor protein 695 (hAPP695) gene were constructed by stable transfection.Expression of β-amyloid, α-form of secreted APP (αAPPs) and APP1695 was measured by ELISA,western blotting and real-time PCR respectively. Additionally, α, β, and γ-secretase activitieswere also analyzed in constructed SH-EP1-α7 nAChR-hAPP695 cell line. The results showed thatSH-EP1-α7 nAChR-hAPP695 cell line, expressing both hAPP695 gene and α7 nAChR subtype gene,was constructed successfully. The secreted Aβ was decreased and αAPPs was significantlyincreased by non-selective nAChR agonist nicotine (10μM) and specific α7 nAChR agonist GTS-21 (1μM), and APP expression was not affected. Furthermore, specific α7 nAChR antagonistmethyllycaconitine (MLA) reversed the alterations induced by activation of α7 nAChR. CTF-α wasincreased and CTF-γ was decreased when treated with nicotine (10μM). In addition, the resultsof enymatic activity analysis showed that nicotine (1μM) and GTS-21 (0.1, 1μM) decreased γ-secretase activity, but has no effects on α-secretase activity and β-secretase activity. Our findingsdemonstrate that, through regulating γ-secretase activity, α7 nAChR activation reduces APPprocessing in amyloidogenic pathway, and at the same time enhances APP processing in nonamyloidogenicpathway. The constructed SH-EP1-α7 nAChR-hAPP695 cell line might be usefulfor screening specific nAChR agonists against AD.

Panaxydol, a polyacetylenecompound isolated fromPanax ginseng, exerts anti-proliferative effects againstmalignant cells. No previous study, however, has been reported on its effects on hepatocellular carcinomacells. Here,we investigated the effects of panaxydol on the proliferation and differentiation of human hepatocarcinomacell line HepG2.We studied by electronic microscopy of morphological and ultrastructuralchanges induced by panaxydol. We also examined the cytotoxicities of panaxydol against HepG2 cellsusing the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and the effect of panaxydolon cell cycle distributions by flow cytometry. We investigated the production of liver proteins inpanaxydol-treated cells including alpha-fetoprotein and albumin and measured the specific activity ofalkaline phosphatase and gamma-glutamyl transferase.We further investigated the effects of panaxydolon the expression of Id-1, Id-2, p21 and pRb by RT-PCR or immunoblotting analysis.We found that panaxydolinhibited the proliferation of HepG2 cells and caused morphological and ultrastructural changes inHepG2 cells resembling more mature forms of hepatocytes. Moreover, panaxydol induced a cell cyclearrest at the G1 to S transition in HepG2 cells. It also significantly decreased the secretion of alphafetoproteinand the activity of gamma-glutamyl transferase. By contrast, panaxydol remarkably increasedthe secretion of albumin and the alkaline phosphatase activity. Furthermore, panaxydol increased themRNA content of p21 while reducing that of Id-1 and Id-2. Panaxydol also increased the protein levelsof p21, pRb and the hypophosphorylated pRb in a dose-dependent manner. These findings suggest thatpanaxydol is of value for further exploration as a potential anti-cancer agent.