Tobacco particulate matter is more potent than nicotine at upregulating nicotinic receptors on SH-SY5Y cells.

The effect of total particulate matter (TPM) from cigarette smoke on the expression and binding properties of nicotinic acetylcholine receptors (nAChRs) was investigated using a human neuroblastoma cell line (SH-SY5Y). TPM but not nicotine on its own inhibited cell growth at nicotine concentrations above 5 μM. To examine effects on nAChR expression, intact cells were incubated with 3 H-epibatidine, and a B max of 13 fmoles/10 5 cells (7.8 x 10 4 binding sites/cell) was measured in unexposed cells as well as in cells treated with 2 μM nicotine alone or with TPM containing 2μM nicotine. Using Scatchard analysis, we measured a Kd of 0.3nM for 3 H-epibatidine binding to nAChRs. This Kd was increased to 1.3nM by addition of nicotine or TPM extract, both at 2μM nicotine. B max , however, was unaffected, suggesting competitive binding of nicotine to its receptor. Short-term and prolonged 3-day exposures of SH-SY5Y cells to either TPM or nicotine at nicotine concentrations ranging from 0.2μM to 20μM increased specific binding, suggesting upregulation of nAChR expression. Most significant, binding was consistently greater in cells pretreated with TPM than in cells pretreated with nicotine. We conclude that TPM contains compounds that are toxic to cells at high concentrations (cell growth inhibition) but that do not compete with nicotine for binding to nAChRs (Scatchard analysis). These non-nicotinic compounds are capable of increasing the expression of one or more of the nAChR subunits. Furthermore, our cell culture assay provides a useful in vitro model for assessing the relative addictiveness of different tobacco products, including that of non-nicotine components.