dc.description.abstract | Betel nut is one of the common substances consumed in Asia, and betel nut alkaloids (BNAs), especially arecoline, are found to be present in the saliva of areca nut chewers. Although arecoline has been shown to regulate glucose uptake and adipogenesis in 3T3-L1 adipocytes, little information is known about the action of arecoline on growth of preadipocytes. Using 3T3-L1 preadipocytes, we observed that arecoline, but not other structurally related alkaloids, such as arecaidine or guvacine, reduced cell viability of 3T3-L1 preadipocytes in dose- and time-dependent manners. Flow cytometric analysis of the cell cycle indicated that exposure to arecoline, but not arecaidine or guvacine, for 24 and 48 h decreased the cell population in G1 stage and increased the cell population in S stage and the G2/M stage of 3T3-L1 preadipocytes. Further Western blot analysis showed that arecoline at 24 h reduced levels of the G1 checkpoint-stimulating proteins, such as p21, p27 and AMP-activated protein kinase (AMPK), decreased levels of the G2 checkpoint-controlling protein, such as CDK1, increased cyclin B1 and p53 protein level, and unaltered CDK2 protein level. Interestingly, arecaidine and guvacine altered p21 and p53 protein levels and unaltered p27, CDK1, CDK2, and cyclin B1 protein levels. Pretreatment with N-acetyl-cysteine (NAC), a glutathione activator, suppressed the arecoline-induced decreases in levels of cell viability and G1 phase of the cell cycle. Moreover, NAC blocked the arecoline-increased percentages of S and G2/M stages of the cell cycle and levels of reactive oxygen species (ROS) production. In addition, NAC prevented the arecoline-decreased levels of p21, p27, CDK1 and AMPK proteins and the arecoline-increased levels of p53 and cyclin B1. However the muscarinic acetylcholine receptor (mAChR) antagonist, such as atropine, did not block the arecoline-reduced cell viability but enhanced further arecoline-stimulated ROS production. Neither GABA nor its type B receptor antagonist, such as saclofen, blocked arecoline-suppressed cell viability. In conclusion, arecoline is the selective ingredient from BNAs to inhibit 3T3-L1 preadipocyte growth through alterations of the cell cycle possibly in p53-, p21-, p27-, CDK1-, cyclin B1, AMPK- and ROS-dependent pathways and GABA B receptor- and mAChR-independent pathways. | en_US |