Irritable Bowel Syndrome

In the clinic. Constipation

This issue provides a clinical overview of constipation, focusing on prevention, diagnosis, treatment, and patient information. The content of In the Clinic is drawn from the clinical information and education resources of the American College of Physicians (ACP), including ACP Smart Medicine and MKSAP (Medical Knowledge and Self-Assessment Program). Annals of Internal Medicine editors develop In the Clinic from these primary sources in collaboration with the ACP's Medical Education and Publishing divisions and with the assistance of science writers and physician writers. Editorial consultants from ACP Smart Medicine and MKSAP provide expert review of the content. Readers who are interested in these primary resources for more detail can consult http://smartmedicine.acponline.org, http://mksap.acponline.org, and other resources referenced in each issue of In the Clinic.

Application of sequence-dependent electrophoresis fingerprinting in exploring biodiversity and population dynamics of human intestinal microbiota: what can be revealed?

Sequence-dependent electrophoresis (SDE) fingerprinting techniques such as denaturing gradient gel electrophoresis (DGGE) have become commonplace in the field of molecular microbial ecology. The success of the SDE technology lays in the fact that it allows visualization of the predominant members of complex microbial ecosystems independent of their culturability and without prior knowledge on the complexity and diversity of the ecosystem. Mainly using the prokaryotic 16S rRNA gene as PCR amplification target, SDE-based community fingerprinting turned into one of the leading molecular tools to unravel the diversity and population dynamics of human intestinal microbiota. The first part of this review covers the methodological concept of SDE fingerprinting and the technical hurdles for analyzing intestinal samples. Subsequently, the current state-of-the-art of DGGE and related techniques to analyze human intestinal microbiota from healthy individuals and from patients with intestinal disorders is surveyed. In addition, the applicability of SDE analysis to monitor intestinal population changes upon nutritional or therapeutic interventions is critically evaluated.

Paroxetine for somatic pain associated with physical illness: a review

OBJECTIVE

The purpose of this article is to review the prevalence of somatic pain with and without depression or anxiety and the pharmacologic effects of the selective serotonin reuptake inhibitor paroxetine on pain in physical conditions with and without comorbid depression or anxiety.

DATA SOURCES

MEDLINE and PsychLIT/PsycINFO database. Keywords included depression, anxiety, pain, somatic, antidepressants, and paroxetine. Only English-language publications and abstracts were considered.

STUDY SELECTION

More than 100 articles that reflected the prevalence of somatic pain in patients with physical illness with and without comorbid depression or anxiety and that evaluated the efficacy of antidepressants in this population were identified and reviewed.

DATA SYNTHESIS

Nearly two thirds of patients with major depressive disorder suffer from a physical illness, and about one fifth of patients with chronic physical illness are depressed. Both of these comorbidities pose diagnostic and therapeutic challenges. Therapeutic effects of antidepressants on pain improvement in patients with chronic physical illnesses and comorbid depression/anxiety have been attributed to the antidepressant or anxiolytic properties of these drugs. However, tricyclic antidepressants have demonstrated analgesic properties in patients with physical illness both with and without depression. The review looks at evidence for the efficacy of the selective serotonin reuptake inhibitor paroxetine on pain in physical illness with and without depression and the mechanisms for the relief of pain and depression.

CONCLUSIONS

The efficacy of paroxetine for depression and anxiety comorbid with physical illness looks promising. Studies also allude to evidence linking the analgesic properties of paroxetine with its serotonergic and noradrenergic activity. Large randomized controlled trials within specific antidepressant classes and also comparing dualaction antidepressants are warranted that could shed some light on the unique advantage of paroxetine over other antidepressants.

Composition and temporal stability of gastrointestinal microbiota in irritable bowel syndrome--a longitudinal study in IBS and control subjects

Irritable bowel syndrome (IBS) is a common intestinal disorder that includes continuous or recurrent intestinal pain and discomfort and altered bowel habits. The pathophysiology of IBS is incompletely understood, but it may involve an altered intestinal microbiota. The aim of the present study was to compare the composition and temporal stability of faecal microbiota of IBS patients and healthy controls by applying culture-based techniques and PCR-DGGE analysis. No difference in the prevalence or mean culturable manners of bacteroides, bifidobacteria, spore-forming bacteria, lactobacilli, enterococci or yeasts were observed between the IBS and the control groups, whereas slightly higher numbers of coliforms as well as an increased aerobe:anaerobe ratio was observed in the IBS group. PCR-DGGE revealed more temporal instability in the predominant bacterial population of IBS subjects than in controls. In 9 out of 21 IBS subjects and 5 out of 17 controls the PCR-DGGE profiles obtained from the samples of the same individual on different occasions (sampling points 0, 3 and 6 months) were clearly different. However, the instability in some of the IBS subjects could partly be explained by the antibiotic consumption during the study. The present study suggests that instability of intestinal microbiota may be involved in IBS. However, further studies are needed to associate the instability with specific IBS symptoms or with specific bacterial groups and species.

Identification of cytochrome P450 isoforms involved in the metabolism of loperamide in human liver microsomes

OBJECTIVE

The purpose of the present study was to elucidate the cytochrome P450 (P450) isoform(s) involved in the metabolism of loperamide (LOP) to N-demethylated LOP (DLOP) in human liver microsomes.

METHODS

Three established approaches were used to identify the P450 isoforms responsible for LOP N-demethylation using human liver microsomes and cDNA-expressed P450 isoforms: (1) correlation of LOP N-demethylation activity with marker P450 activities in a panel of human liver microsomes, (2) inhibition of enzyme activity by P450-selective inhibitors, and (3) measurement of DLOP formation by cDNA-expressed P450 isoforms. The relative contribution of P450 isoforms involved in LOP N-demethylation in human liver microsomes were estimated by applying relative activity factor (RAF) values.

RESULTS

The formation rate of DLOP showed biphasic kinetics, suggesting the involvement of multiple P450 isoforms. Apparent Km and Vmax values were 21.1 microM and 122.3 pmol/min per milligram of protein for the high-affinity component and 83.9 microM and 412.0 pmol/min per milligram of protein for the low-affinity component, respectively. Of the cDNA-expressed P450 s tested, CYP2B6, CYP2C8, CYP2D6, and CYP3A4 catalyzed LOP N-demethylation. LOP N-demethylation was significantly inhibited when coincubated with quercetin (a CYP2C8 inhibitor) and ketoconazole (a CYP3A4 inhibitor) by 40 and 90%, respectively, but other chemical inhibitors tested showed weak or no significant inhibition. DLOP formation was highly correlated with CYP3A4-catalyzed midazolam 1-hydroxylation (rs=0.829; P<0.01), CYP2B6-catalzyed 7-ethoxy-4-trifluoromethylcoumarin O-deethylation (rs=0.691; P<0.05), and CYP2C8-catalyzed paclitaxel 6alpha-hydroxylation (rs=0.797; P<0.05).

CONCLUSION

CYP2B6, CYP2C8, CYP2D6, and CYP3A4 catalyze LOP N-demethylation in human liver microsomes, and among them, CYP2C8 and CYP3A4 may play a crucial role in LOP metabolism at the therapeutic concentrations of LOP. Coadministration of these P450 inhibitors may cause drug interactions with LOP. However, the clinical significance of potential interaction of LOP metabolism by CYP2C8 and CYP3A4 inhibitors should be studied further.