TY - JOUR
T1 - Investigations on 5-HT4 receptor expression and effects of tegaserod on human platelet aggregation in vitro
AU - Serebruany, Victor L.
AU - Mouelhi, Mohamed El
AU - Pfannkuche, Hans Jürgen
AU - Rose, Kristine
AU - Marro, Martin
AU - Angiolillo, Dominick J.
PY - 2010/11
Y1 - 2010/11
N2 - A meta-analysis of 29 clinical studies on tegaserod revealed an imbalance of cardiovascular ischemic events in patients treated with drug versus placebo. Because increased platelet activity is known to attribute to cardiovascular events, we examined the presence of serotonin receptor type 4 (5-HT4) receptors and the effects of tegaserod on in vitro aggregation of human platelets. Blood samples were obtained from 20 healthy volunteers and 20 subjects with irritable bowel syndrome with constipation. Samples of whole blood-citrate mixtures were incubated with different tegaserod concentrations mimicking human Cmax values (10 nM), 3.3 times, and 10 times Cmax for at least 1 hour. Conventional plasma platelet aggregation was induced by adenosine diphosphate, collagen, thrombin receptor activating peptide, epinephrine, and serotonin plus adenosine diphosphate. Gene expression analyses targeting 5-HT4 and serotonin receptor type 2 receptors were carried out using human platelet RNA. The presence of 5-HT4 receptor protein was investigated by Western blot analysis using membrane fractions from human platelets. Preincubation with tegaserod resulted in mild but statistically significant increases in platelet aggregation induced by adenosine diphosphate, collagen, epinephrine, or serotonin, mostly at supratherapeutic concentrations of tegaserod. The effects were comparable using thrombocytes obtained from healthy volunteers and patients with irritable bowel syndrome with constipation. Expression analysis revealed that mRNA encoding both 5-HT4 and serotonin receptor type 2 receptors was present in human platelets. The expression of 5-HT4 receptor mRNA was approximately eightfold lower than serotonin receptor type 2 receptor mRNA. Results from Western blot analyses examining the presence of 5-HT4 receptor protein in human platelets were in agreement with the findings of the mRNA expression analysis. In platelets harvested from normal persons and patients with irritable bowel syndrome with constipation and exposed in vitro to tegaserod, we detected small but statistically significant concentration-dependent increases in induced platelet aggregation. The relationship of these in vitro effects to clinical cardiovascular ischemic events is presently unclear. Western blot analysis findings suggest the presence of 5-HT4 receptor protein on human platelets. Further investigations on the potential role of 5-HT4 receptors in human platelets may be warranted.
AB - A meta-analysis of 29 clinical studies on tegaserod revealed an imbalance of cardiovascular ischemic events in patients treated with drug versus placebo. Because increased platelet activity is known to attribute to cardiovascular events, we examined the presence of serotonin receptor type 4 (5-HT4) receptors and the effects of tegaserod on in vitro aggregation of human platelets. Blood samples were obtained from 20 healthy volunteers and 20 subjects with irritable bowel syndrome with constipation. Samples of whole blood-citrate mixtures were incubated with different tegaserod concentrations mimicking human Cmax values (10 nM), 3.3 times, and 10 times Cmax for at least 1 hour. Conventional plasma platelet aggregation was induced by adenosine diphosphate, collagen, thrombin receptor activating peptide, epinephrine, and serotonin plus adenosine diphosphate. Gene expression analyses targeting 5-HT4 and serotonin receptor type 2 receptors were carried out using human platelet RNA. The presence of 5-HT4 receptor protein was investigated by Western blot analysis using membrane fractions from human platelets. Preincubation with tegaserod resulted in mild but statistically significant increases in platelet aggregation induced by adenosine diphosphate, collagen, epinephrine, or serotonin, mostly at supratherapeutic concentrations of tegaserod. The effects were comparable using thrombocytes obtained from healthy volunteers and patients with irritable bowel syndrome with constipation. Expression analysis revealed that mRNA encoding both 5-HT4 and serotonin receptor type 2 receptors was present in human platelets. The expression of 5-HT4 receptor mRNA was approximately eightfold lower than serotonin receptor type 2 receptor mRNA. Results from Western blot analyses examining the presence of 5-HT4 receptor protein in human platelets were in agreement with the findings of the mRNA expression analysis. In platelets harvested from normal persons and patients with irritable bowel syndrome with constipation and exposed in vitro to tegaserod, we detected small but statistically significant concentration-dependent increases in induced platelet aggregation. The relationship of these in vitro effects to clinical cardiovascular ischemic events is presently unclear. Western blot analysis findings suggest the presence of 5-HT4 receptor protein on human platelets. Further investigations on the potential role of 5-HT4 receptors in human platelets may be warranted.
KW - constipation
KW - irritable bowel syndrome
KW - platelets
KW - tegaserod
KW - thrombocytes
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U2 - 10.1097/MJT.0b013e3181b63f21
DO - 10.1097/MJT.0b013e3181b63f21
M3 - Article
C2 - 19797939
AN - SCOPUS:78649673553
SN - 1075-2765
VL - 17
SP - 543
EP - 552
JO - American Journal of Therapeutics
JF - American Journal of Therapeutics
IS - 6
ER -