ABSTRACT
AIM: To explore the role of purinergic signaling mediated by ATP in the Alzheimer ’ s disease (AD)-related colon motility disorder and its related molecular mechanisms .METHODS:(1)Clinical trials:AD patients in our hospital were collected and studied .Radioimmunoassay was used for the determination of plasma motilin (MTL), cholecystokinin (CCK), vasoactive intestinal peptide (VIP) and nitric oxide (NO), and high-performance liquid chroma-tography ( HPLC) was applied to test the level of adenosine triphosphate ( ATP) .The patients were assessed by neuropsy-chology and scored accordingly .( 2 ) In animal experiments , AD mice received Morris water maze test , and the spatial learning and memory function were evaluated .The plasma levels of MTL , CCK, VIP and NO were examined by radioimmu-noassay , and the level of ATP was measured by HPLC .Choline acetyltransferase ( ChAT ) , VIP, nitric oxide synthase ( NOS) and ATP synthase were detected by immunohistochemistry .Western blot and immunohistochemistry were used to detect the expression of P2Y receptor.(3) In vitro, organ bath was applied to observe the effect of α,β-methylene ATP (α,β-MeATP), an agonist of P2Y receptor, on both spontaneous and electrically evoked contraction of colonic smooth muscle strip, and the technique of intracellular microelectrode was applied to observe the effect of α,β-MeATP on the membrane potential of colonic smooth muscle cells .RESULTS:Compared with control group , the levels of MTL and CCK were decreased (P<0.01), and the levels of NO and ATP were increased (P<0.05 or P<0.01), while the VIP level was not changed.Mini-Mental State Examination (MMSE) score was decreased (P<0.05), Alzheimer’s Disease Assess-ment Scale-Cognitive Subscale (ADAS-Cog) score, Neuropsychiatric Inventory (NPI) score and Alzheimer’s Disease Co-operative Study-Activities of Daily Living Scale ( ADCS-ADL ) were all increased as compared with control group ( P <0.01).The 4~6 d escape latency of APP/PS1 AD mice was significantly prolonged (P<0.05), and the space explora-tion ability distinctly reduced (P<0.05).In AD mice, the levels of MTL and CCK were decreased (P<0.01), and the levels of NO and ATP were increased (P<0.05 or P<0.01), while the VIP level was not changed .The protein expres-sion of colonic ATP synthase was significantly increased (P<0.05), but the expression of ChAT, VIP and NOS was not changed.The expression of P2Y receptor was increased (P<0.01).The results of in vitro experiment displayed that α,β-MeATP, from 20 μmol/L to 100 μmol/L, inhibited the spontaneous contraction of colonic smooth muscle strip in the nor-mal mice and AD mice ( P<0.05 or P<0.01 ) , and this inhibition was reversed by Na +channel inhibitor tetrodotoxin (TTX) (P<0.05 or P<0.01).In addition, the effect of α,β-MeATP at 100μmol/L on the AD mice was more obvious than that on the normal mice (P<0.05), and this inhibition was also antagonized by TTX (P<0.05 or P<0.01), pro-minent in AD group as compared with control group (P<0.05).In 10 Hz electrically evoked contraction of colonic smooth muscle strip,α,β-MeATP inhibited both the normal and AD mice (P<0.05 or P<0.01), while the inhibition was more obvious in the AD mice at the concentration of 40μmol/L or 100μmol/L (P<0.05 or P<0.01).CONCLUSION:AD patients and AD mice are accompanied by decreased MTL and CCK levels , and enhanced NO level , thus inducing colonic motor dysfunction along with AD .Meanwhile, ATP in plasma, purinergic neurons , and P2Y receptor expression are in-creased in the AD mice .Purinergic signaling mediated by ATP inhibits colonic smooth muscle strip contraction and further paralyzes the colonic movement function in AD .