Travellers' diarrhoea

Design and characterization of a soluble fragment of the extracellular ligand-binding domain of the peptide hormone receptor guanylyl cyclase-C

The intestinal guanylyl cyclase-C (GC-C) was originally identified as an Escherichia coli heat-stable enterotoxin (STa) receptor. STa stimulates GC-C to much higher activity than the endogenous ligands guanylin and uroguanylin, causing severe diarrhea. To investigate the interactions of the endogenous and bacterial ligands with GC-C, we designed and characterized a soluble and properly folded fragment of the extracellular ligand-binding domain of GC-C. The membrane-bound guanylyl cyclases exhibit a single transmembrane spanning helix and a globularly folded extracellular ligand-binding domain that comprises about 410 of 1050 residues. Based on the crystal structure of the dimerized-binding domain of the guanylyl cyclase-coupled atrial natriuretic peptide receptor and a secondary structure-guided sequence alignment, we generated a model of the extracellular domain of GC-C comprised of two subdomains. Mapping of mutational and cross-link data onto this structural model restricts the ligand-binding region to the membrane proximal subdomain. We thus designed miniGC-C, a 197 amino acid fragment that mimics the ligand-binding membrane proximal subdomain. Cloning, expression and spectroscopic studies reveal miniGC-C to be a soluble and properly folded protein with a distinct secondary and tertiary structure. MiniGC-C binds STa with nanomolar affinity.

[Acute infectious diarrhea]

Acute infectious diarrhea has various causes: bacterial diarrhea with invasive or toxigenic mechanisms, especially frequent in hot regions and in travelers; viral diarrheas, frequent and cosmopolitan in children but also adults; and parasitic diarrhea, less frequent, and generally in subtropical areas. The major concerns involve the risk of complications, essentially dehydration and malnutrition, especially in vulnerable patients: young children, the elderly, and patients with immunosuppression, for whom rehydration is urgent. Diagnosis of diarrhea requires clinical assessment and history: underlying illnesses, severity of symptoms, presence and extent of dehydration and other clinical symptoms, travel history, known outbreaks, and pathogenic mechanism (invasive or toxigenic). Initial therapy should always include oral or parenteral rehydration; antimotility agents are generally not indicated; specific antibiotic treatment is not systematically indicated, except for invasive or dysenteric diarrhea and in immunosuppressed patients.

Side chain contributions to the interconversion of the topological isomers of guanylin-like peptides

The peptide hormones guanylin and uroguanylin are ligands of the intestinal guanylyl cyclase-C (GC-C) that is involved in the regulation of epithelial water and electrolyte transport. The small peptides contain 15 and 16 amino acids, respectively, and two disulfide bonds with a 1-3/2-4 connectivity. This structural feature causes the unique existence of two topological isoforms for each peptide in an approximate 3:2 ratio, with only one of the isoforms exhibiting GC-C-activating potential. The two uroguanylin isomers can be separated by HPLC and are of sufficient stability to be studied separately at ambient temperatures while the two guanylin isomers are rapidly interconverting even at low temperatures. Both isomers show clearly distinguishable (1)H chemical shifts. To investigate the influence of certain amino acid side chains on this isomerism and interconversion kinetics, derivatives of guanylin and uroguanylin (L-alanine scan and chimeric peptides) were designed and synthesized by Fmoc solid-phase chemistry and compared by HPLC and 2D (1)H NMR spectroscopy. Amino acid residues with the most significant effects on the interconversion kinetics were predominantly identified in the COOH-terminal part of both peptides, whereas amino acids in the central part of the peptides only moderately affected the interconversion. Thus, the conformational conversion among the isomers of both peptides is under the control of a COOH-terminal sterical hindrance, providing a detailed model for this dynamic isomerism. Our results demonstrate that kinetic control of the interconversion process can be achieved by the introduction of side chains with a defined sterical profile at suitable sequence positions. This is of potential impact for the future development of GC-C peptide agonists and antagonists.

A study of fructo oligosaccharides in the prevention of travellers' diarrhoea

BACKGROUND

Prebiotic carbohydrates selectively stimulate the growth of bifidobacteria and lactobacilli in the human colon. These bacteria form part of the gut's inherent defence against invading pathogens.

AIM

To test the effectiveness of fructo oligosaccharides in preventing travellers' diarrhoea.

METHODS

A total of 244 healthy subjects, travelling to high and medium risk destinations for travellers' diarrhoea, took part in a randomized, double-blind, placebo-controlled study. The protocol comprised a preliminary week for recording bowel habit by diary, a 2-week pre-holiday period with the diary and consumption of 10 g of fructo oligosaccharides or placebo daily, followed by a 2-week holiday with continuation of treatment and diary. A post-study questionnaire was completed by all subjects on their return to the UK.

RESULTS

The consumption of fructo oligosaccharides led to a small (6%; P < 0.02) increase in stool frequency in the pre-holiday period and gave a significantly better sense of 'well-being' during the holiday, although subjects reported more flatulence. There were non-significant decreases in episodes of diarrhoea with 20% on placebo and 11% on fructo oligosaccharides recording episodes in the post-study questionnaire (P=0.08) and 46% placebo, 38% fructo oligosaccharides recording episodes in the diary (P > 0.1). No change in bowel frequency, consistency or stool size was recorded.

CONCLUSION

Travel to high risk areas increases diarrhoea. Fructo oligosaccharides alone are not sufficient to prevent this, although do have some benefits for the subjects.

Health professionals' attitudes toward acute diarrhea management

BACKGROUND

Travelers' diarrhea is the most frequent health problem in those participating in international journeys, and is responsible for many consultations abroad and on return home.

METHODS

A questionnaire assessing attitudes toward treatment and management of travel-related and nontravel-related diarrhea was administered to 542 GPs, nurses and pharmacists.

RESULTS

Health professionals' attitudes to management of acute diarrhea are variable, with marked divergence regarding adherence to published "good practice" guidelines and recommendations. Inconsistencies exist in stated attitudes toward prescribing antispasmodics and antimotility agents and actual prescribing behavior.

CONCLUSIONS

Current treatment guidelines may be outdated. Inappropriate or delayed treatment disadvantages the patient. Limiting the use of antidiarrheal agents can deny access, for those inflicted with diarrhea, to a medication which may shorten symptomatology and morbidity, and speed the return to normality. Review of guidelines for diarrhea management in adults is overdue, as is standardization of treatment response. Educational initiatives are required to encourage active intervention and improved provision of care.

Travel medicine advice to UK based international motor sport teams

BACKGROUND

International motor sport teams travel extensively. Over the years, the design and build of racing cars has improved so that morbidity and mortality in motor sport has been lessened. Those team members supporting the competitors need to be physically and mentally fit to perform complicated tasks, despite having traveled. This group of travelers has not been studied to any extent previously.

METHOD

An anonymous questionnaire asking some basic travel medicine related questions was distributed to the support team members of a Rally team, and Formula One Grand Prix team. Both teams were based in the UK, and competed in all the rounds of their respective world championships.

RESULTS

Ten Rally team members and 18 Formula One team members responded to the questionnaire. The results showed moderate coverage of commonly used vaccinations; appropriate use of antimalarials and insect repellents, but by no means by all team members; little or no problems with traveler's diarrhea; some tendencies to problems related to jet lag, but no real attempt to prevent the problem; and finally some attempt at skin protection against solar damage.

CONCLUSION

Support teams are reasonably well prepared for the combination of, the rigors of frequent travel, and a demanding job. There is a deficit in vaccine coverage, especially of both hepatitis A and B, some education is needed in preventing skin problems later in life due to sun exposure, and further study of jet lag and its implications might be appropriate.

Preparing patients to travel abroad safely. Part 4: Reducing risk of accidents, diarrhea, and sexually transmitted diseases

OBJECTIVE

To present evidence-based recommendations on traveling abroad safely so family physicians can advise travelers on how to reduce risk of accidents, diarrhea, and sexually transmitted diseases (STDs) and how to treat diarrhea themselves if medical care is unavailable.

QUALITY OF EVIDENCE

A MEDLINE search from 1990 to November 1998 found 163 articles on travel and accidents, 504 on travel and diarrhea, and 42 on travel and STDs. Titles and abstracts were reviewed, and randomized controlled trials (RCTs) and systematic reviews were sought. The Cochrane Collaboration database of systematic reviews and meta-analyses was searched for studies relevant to family physicians.

MAIN MESSAGE

For preventing diarrhea, RCTs demonstrate that bismuth subsalicylate, doxycycline, ciprofloxacin, and trimethoprim-sulfamethoxazole are useful prophylactics. Once travelers have diarrhea, RCTs show that loperamide and zaldaride reduce symptoms and duration; quinolones, ciprofloxacin, norfloxacin, and oral aztreonam reduce abdominal symptoms and time to last liquid stool by several days; azithromycin is effective in treatment of ciprofloxacin-resistant Campylobacter, and trimethoprim-sulfamethoxazole is effective in treating cyclospora. There are no RCTs of preventing accidents and STDs abroad. Health Canada has issued a statement summarizing the risks of acquiring STDs abroad.

CONCLUSION

Family physicians can advise their patients on how to reduce risk of travelers' diarrhea and how to treat it themselves on holiday. There is expert advice on how to reduce risk of STDs.

Sources and appropriateness of medical advice for trekkers

BACKGROUND

Little has previously been published on the sources of health advice used by trekkers. This paper investigates the sources of advice used by a group of British trekkers and the appropriateness of the advice which they were given.

METHODS

A questionnaire was issued to 107 clients of a U.K. trekking operator. Clients were asked which advice sources they had used and how useful they found them. They were also asked about advice which they had received on vaccination, antimalarial drugs, and other health precautions. The appropriateness of such advice was assessed by reference to standard advice sources used in the United Kingdom.

RESULTS

One hundred replies were received, a response rate of 93.5%. Responders had traveled to India (10%), Nepal (45%) and Morocco (45%). The most frequently used advice sources were general medical practitioners or health centers (69%) and the tour operator (68%), many trekkers using more than one source. Specialist travel advice centers and general practitioners were rated most highly by 67% and 59% of users for usefulness and 60% and 52% of users for being informative. Other travelers were also rated highly as a source. Some appropriate vaccinations were under-recommended while others which were not appropriate were recommended. Antimalarial drugs were recommended when needed but they were sometimes recommended when not appropriate. Advice on other health risks was generally inadequate.

CONCLUSIONS

Trekkers need access to more relevant health advice. Tour operators need to have better medical information to pass on to their clients, and health professionals need more education about health risks for and the avoidance of health risks by trekkers.

Regulation of taurine transport by Escherichia coli heat-stable enterotoxin and guanylin in human intestinal cell lines

The human colon carcinoma cell lines Caco-2 and HT-29 take up taurine actively. Treatment of Caco-2 cells with Escherichia coli heat-stable enterotoxin (STa) or with guanylin inhibited taurine uptake by approximately 40%. In contrast, neither STa nor guanylin changed the uptake of taurine in HT-29 cells. The inhibition in Caco-2 cells was associated with a decrease in the maximal velocity as well as in the affinity of the transporter. STa caused a 21-fold increase in guanosine 3',5'-cyclic monophosphate (cGMP) levels in Caco-2 cells with no change in cAMP levels. Neither cGMP nor cAMP levels were affected by STa treatment in HT-29 cells. Experiments with protein kinase inhibitors suggested that protein kinase A may mediate the observed effects of STa on taurine uptake. In accordance with this suggestion, treatment of Caco-2 cells with cholera toxin, which elevated intracellular cAMP levels, was found to inhibit taurine uptake. The steady state levels of the taurine transporter mRNA transcripts were not altered as a result of STa treatment. Studies with Caco-2 cells grown on permeable filters revealed that STa acts from the apical side. The taurine uptake from the apical side was inhibited by STa, but the taurine uptake from the basolateral side remained unaffected. It is suggested that the activity of the intestinal taurine transporter may be regulated by protein kinase A at a posttranslational level and that the intestinal absorption of taurine may be impaired during infection with enterotoxigenic strains of E. coli.

Clinical gastroenterology

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Randomised trial of single-dose ciprofloxacin for travellers' diarrhoea

Diarrhoea is the most common illness affecting travellers to developing countries. Our study was designed to compare the efficacy of a single 500 mg dose of ciprofloxacin with placebo for treatment of acute diarrhoea in travellers. British troops who were within their first 8 weeks of deployment in Belize and who presented within 24 h of the onset of diarrhoea, were randomized to receive either ciprofloxacin 500 mg or placebo. Every subject recorded the number and consistency of stools and presence of any other associated symptoms for 72 h or until recovery. Of 88 subjects enrolled, 83 were evaluable, of whom 45 received ciprofloxacin and 38 placebo. Groups did not differ with regard to duration or severity of diarrhoea at randomisation. Mean (SE) duration of diarrhoea, as assessed by time to the last liquid and last unformed stool, was reduced from 50.4 (4.5) h and 53.5 (4.4) h, respectively, in the placebo group to 20.9 (3.4) h and 24.8 (3.8) h in those receiving ciprofloxacin (p < 0.0001). Mean number of liquid stools was reduced from 11.4 (1.2) in the placebo group to 5.0 (0.7) in the ciprofloxacin-treated group (p < 0.0001). The cumulative percentages of subjects with no unformed stool after 24 h, 48 h, and 72 h were, respectively, 64%, 82%, and 93% in the ciprofloxacin group and 11%, 42%, and 79% in the placebo group (p < 0.0001, p < 0.001, and not significant, respectively). A single 500 mg dose of ciprofloxacin was an effective empirical treatment for reducing the duration and severity of diarrhoea in travellers. The regimen should maximise compliance and reduce the cost and duration of therapy.