THE MUSCARINIC M1 AGONIST XANOMELINE INCREASES SOLUBLE AMYLOID PRECURSOR PROTEIN RELEASE FROM CHINESE-HAMSTER OVARY-M1 CELLS

The functionally selective M1 agonist xanomeline, which is currently undergoing clinical trials as a therapy for Alzheimer's disease, was compared to the muscarinic agonist carbachol for effects on secretion of soluble amyloid precursor protein (APPs) from Chinese hamster ovary cells transfected with the human mi receptor (CHO-m1). Release of APPs from CHO-m1 cells was increased maximally (4-10 fold) by 100 mu M carbachol (EC(50) = 11 mu M) and by 100 nM xanomeline (EC(50) = 10 nM) Stimulation of APPs secretion by xanomeline and carbachol was blocked by preincubation with 1 mu M atropine. Carbachol did not stimulate APPs secretion from non-transfected CHO cells. Pilocarpine at 1 mM also increased APPs release. The efficacy of carbachol, xanomeline and pilocarpine for stimulating APPs secretion did not differ significantly. Activation of protein kinase C (PKC) in mi transfected cell lines by 1 mu M phorbol dibutyrate (PDBu) increased APPs release, and this was inhibited 97% by the PKC inhibitor bisindolemalemide. The PKC inhibitor decreased xanomeline and carbachol - stimulated APPs secretion by only 25-30%. These results demonstrate that xanomeline increased APPs release by activation of mi muscarinic receptors and support the possibility that cholinergic replacement therapy for Alzheimer's Disease may reduce amyloid deposition.