Calcium-sensing receptor antagonist (calcilytic) NPS 2143 specifically blocks the increased secretion of endogenous A\u3b242 prompted by exogenous fibrillary or soluble A\u3b225-35 in human cortical astrocytes and neurons: therapeutic relevance to Alzheimer's disease

The "amyloid-\u3b2 (A\u3b2) hypothesis" posits that accumulating A\u3b2 peptides (A\u3b2s) produced by neurons cause Alzheimer's disease (AD). However, the A\u3b2s contribution by the more numerous astrocytes remains undetermined. Previously we showed that fibrillar (f)A\u3b225-35, an A\u3b242 proxy, evokes a surplus endogenous A\u3b242 production/accumulation in cortical adult human astrocytes. Here, by using immunocytochemistry, immunoblotting, enzymatic assays, and highly sensitive sandwich ELISA kits, we investigated the effects of fA\u3b225-35 and soluble (s)A\u3b225-35 on A\u3b242 and A\u3b240 accumulation/secretion by human cortical astrocytes and HCN-1A neurons and, since the calcium-sensing receptor (CaSR) binds A\u3b2s, their modulation by NPS 2143, a CaSR allosteric antagonist (calcilytic). The fA\u3b225-35-exposed astrocytes and surviving neurons produced, accumulated, and secreted increased amounts of A\u3b242, while A\u3b240 also accrued but its secretion was unchanged. Accordingly, secreted A\u3b242/A\u3b240 ratio values rose for astrocytes and neurons. While slightly enhancing A\u3b240 secretion by fA\u3b225-35-treated astrocytes, NPS 2143 specifically suppressed the fA\u3b225-35-elicited surges of endogenous A\u3b242 secretion by astrocytes and neurons. Therefore, NPS 2143 addition always kept A\u3b242/A\u3b240 values to baseline or lower levels. Mechanistically, NPS 2143 decreased total CaSR protein complement, transiently raised proteasomal chymotrypsin activity, and blocked excess NO production without affecting the ongoing increases in BACE1/\u3b2-secretase and \u3b3-secretase activity in fA\u3b225-35-treated astrocytes. Compared to fA\u3b225-35, sA\u3b225-35 also stimulated A\u3b242 secretion by astrocytes and neurons and NPS 2143 specifically and wholly suppressed this effect. Therefore, since NPS 2143 thwarts any A\u3b2/CaSR-induced surplus secretion of endogenous A\u3b242 and hence further vicious cycles of A\u3b2 self-induction/secretion/spreading, calcilytics might effectively prevent/stop the progression to full-blown AD.Peer reviewed: YesNRC publication: Ye