Irritable Bowel Syndrome
Chinwon Rim Department of Chemistry Southern Methodist University
What is Irritable Bowel Syndrome(IBS)?
A group of functional bowel disorders Chronic abdominal complaints without a structural or biochemical cause Constitutes a major health problem with gastrointestinal (GI) symptoms The cause of IBS is unknown. Affects up to ~20 % adults in the industrialized world The condition is more frequent in women. The direct medical costs of IBS are ~ $ US 8 billion in the US each year.
Symptoms of IBS
Abdominal discomfort and pain Bloating, mucous in stools, diarrhea, constipation, or alternating diarrhea and constipation Depression, anxiety or stress IBS can be subdivided into
Diarrhea-predominant (IBS-D) Constipation-predominant (IBS-C) Alternating diarrhea and constipation
Subclassification of patients
1.
Supportive symptoms of IBS
2.
3. 4. 5. 6. 7. 8.
Diarrhea-predominant IBS (IBS-D)
Fewer than 3 bowel movements a week More than 3 bowel movements a day Hard or lumpy stools Loose or watery stools Urgency Feeling of incomplete bowel movement Passing mucus during a bowel movement Abdominal fullness, bloating or swelling One or more of 2, 4 or 6 and none of 1, 3 or 5 One or more of 1, 3 or 5 and none of 2, 4 or 6
Constipation-predominant IBS (IBS-C)
Serotonin is important in gut function
GI disorders may be related to
an imbalance of serotonin in the gut an improper reaction of the digestive system to serotonin a faulty communication network between serotonin in the gut and the brain and spinal cord.
Serotonin plays a major role in modulating intestinal movement and perception of pain. Helps to soften stools by releasing water.
Serotonin (5-hydroxytryptamine, 5HT)
A monoamine neurotransmitter Found in cardiovascular tissue, the peripheral nervous system, blood cells, and the CNS HO 95 % resides in the GI tract Serotonergic neurons secrete 5HT The function of serotonin is exerted upon its interaction with specific receptors. 7 distinct families of 5HTreceptors; 5HT1, 5HT2, 5HT3, 5HT4, 5HT5, 5HT6, and 5HT7
NH2
N H
5HT3 receptors and its antagonists
5HT3 receptors A ligand-gated cation channel Present in the GI tract Control sensation, contraction of intestinal muscle Release of fluid into the intestines 5HT3 antagonists Slow intestinal transit Decrease intestinal secretions Decrease the water content of stool Diminish colonic pain
5HT4 receptors and its agonists
5HT4 receptors G-protein-coupled receptor Present in the GI tract Mediate both relaxation and contraction of circular smooth-muscle strips Induces small bowel and to a lesser extent colonic fluid secretion 5HT4 agonists Accelerate gastric emptying Accelerate small and large bowel transit Increase stool water content
Alosetron in IBS-D
The first drug is approved for female patients by FDA Brand name is Lotronex® by Glaxo Smith Kline A potent and selective antagonist of the 5HT3 receptors
Synthetic pathway of alosetron
Me N i NH O O NNa + Me N CPh3 Me N ClH2C N
Me N ii N O Alosetron Me N N H
(i) NaH, dimethoxyethane; (ii) HCl.
How does alosetron works?
The exact mechanism how alosetron relieves the symptoms of IBS-D is unknown. Serotonin in the intestines controls how pain is felt, contraction of intestinal muscle, and release of fluid into the intestines. An excessive release of or an excessive response to serotonin causes a pain and diarrhea. By blocking 5HT3 receptors, alosetron reduced pain and motor responses.
Alosetron-New Drug for IBS-D
Alosetron is rapidly absorbed and extensively metabolized. Effective in relieving pain, normalizing bowel frequency, and reducing urgency Constipation is the most common adverse effect Appears to provide a modest benefit to women Should be prescribed under the guidance of a specialist Serious side effects and high-cost maintenance problem
Tegaserod in IBS-C
The first selective serotonin 5HT4 receptor partial agonist approved by FDA for the treatment of abdominal pain and constipation predominent IBS patients Brand name is ZelnormTM by Novartis Pharmceu. Corp.
Synthetic pathway of tegaserod
OH O
i,ii
iii
N O O
HN
HN O O O NH N
H N
iv
HN
HN
Tegaserod
(i) K2CO3, RBr or ClCOX; (ii) t-BuOCH(NMe2)2 then H2, Pd/C; (iii) DMF, POCl3; and (v) N-pentyl-N’-aminoguanidine, MeOH/HCl.
How does tegaserod work?
The exact mechanism of tegaserod’s action is not yet understood completely. Tegaserod binds with high affinity at 5HT4 receptors. The activation of 5HT4 receptors in GI tract stimulates the peristaltic reflex and intestinal secretion. As a result, contractions increase and the increased contractions speed the transit of digesting food and reverse constipation. Reduces the sensitivity of the intestinal pain-sensing nerves and reduces pain by inhibiting visceral sensitivity
Tegaserod –a Promising Option
Tegaserod is rapidly absorbed and metabolized. Effective in increasing the frequency of stools, relieving abdominal pain and discomfort, and decreasing the sensations of bloating Diarrhea is an occasional side effect. Is approved only for women Should be prescribed under the guidance of a specialist
Conclusions
Alosetron, 5HT3 antagonists, appears to provide a modest benefit to women with IBS-D. Offers a new option for the treatment of IBS-D. Tegaserod, 5HT4 agonists, appears to be a promising options in women with IBS-C not responding to increased dietary fiber or laxative therapy. Both cases, need more researches on mechanism how drugs work and clinical studies for the treatment of men patients. Need to discover new drugs for alternating diarrhea and constipation
References
1. 2. 3. 4. 5. 6.
7. 8.
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