At first sight one may wonder why a paper published in the British Journal of Clinical Pharmacology is being highlighted on this web site. Yet Dr Guiney and his colleagues have evolved a very elegant approach to complex metabolically relevant data collection using a simple, non-invasive test that should be celebrated as an example a combination of science, economics and human/animal care, sometimes assumed not to exist in large research establishments. This paper expanded on a previous study published in 2010.
Familiar as we are that the biliary tree offers a route of elimination for both endogenous and exogenous metabolites collected in the bile and stored in the gall bladder, it is the elimination and capture of the bile in order to understand the absorption, distribution, metabolism and elimination of drugs, with particular reference to help better understanding of the potential for drug-drug interactions, that is of most relevance to this paper.
Collecting bile in humans is generally regarded as a combination of ‘highly invasive, difficult and expensive’ (approx. £30k per sample)– hence the interest generated by the novel use of a simple and very economical string test, called the Entero-Test.
How was it done?
This was undertaken, after the ingestion of the cholesterol manipulating medication simvastatin was undertaken. Simvastatin is a drug which is known to undergo metabolism by the liver and to be eliminated as metabolites into the bile. The authors therefore selected simvastatin as the tool compound with which to test the ‘proof of utility’ of their technique. Twenty subjects (15 male and five female) with a mean age of 36 years participated in this study) underwent non-invasive bile capture using a peroral string test (Entero-Test) device prior to and following a single oral dose of simvastatin (80 mg). The device, consisting of a weighted gelatine capsule containing a highly absorbent nylon string, was swallowed by each subject with the proximal end of the string taped to the face.
Once the weighted string was judged to have reached the duodenum, gallbladder contraction was stimulated in order to release bile. The string was then retrieved via the mouth, and bile samples were analysed for drug-related material using spectrometric and spectroscopic techniques following solvent extraction. Numerous metabolites of simvastatin were detected, and the major metabolites were consistent with those reported from studies where bile was collected using invasive techniques from patients dosed with simvastatin. The results from this study demonstrate the utility of deploying the Entero-Test in human studies to provide structural information on biliary metabolites. This can be readily applied in drug development studies, including those in the target patient population and may eliminate the need for more invasive sampling techniques.
Of interest the authors used a somewhat novel means of stimulating biliary flow, a concept that may be applicable in cases where biliary stasis is indicated for Nutritional Therapists, but immediately relevant for researchers looking to repeat the process.
Biliary Provocation strategy
Five and a half hours following oral dosing of simvastatin (the string test having been swallowed 2 hours post drug dosing in order to avoid contamination of the device with swallowed drug), each subject was given a food stimulus (each subject was allowed to visualize photographic images of different favourite food types and asked to imagine for approximately 60 s that they were eating the food; following this, each subject had orange peel squeezed under their nose which they inhaled for several seconds). Each subject was then given a small, high fat food morsel which comprised either a small cocktail sausage (12 subjects) or up to 3 French fries (8 subjects) in order to stimulate bile release from the gallbladder. One hour later, the strings were withdrawn from each subject for analysis. The timings described were designed to ensure sufficient time for transit of the string from the stomach into the duodenum and adequate exposure to released bile, prior to withdrawal.
The authors conclude this paper by stating: Notwithstanding the present limitations, given the simplicity, low-cost and non-invasive nature of the technique, we believe the device is worthy of investigation ahead of invasive techniques in order to provide limited information on the biliary disposition of a drug and its metabolites in humans to complement metabolite information derived from other matrices, such as plasma and excreta.
The simplicity of the technique favours its deployment in both healthy subjects and patients at any stage of the drug development process including the post-marketing phase, and it has now been deployed within our organization (GSK) to collect biliary information from first administration to human, clinical drug– drug interaction and radiolabelled human absorption, distribution, metabolism and elimination (ADME) studies.
The Entero-Test and Gastro-test may be purchased from Nutri-Link Ltd in the UK.
 Guiney WJ, Beaumont C, Thomas SR, Robertson DC, McHugh SM, Koch A, Richards D. Use of Entero-Test, a simple approach for non-invasive clinical evaluation of the biliary disposition of drugs. Br J Clin Pharmacol. 2011 Jul;72(1):133-42. doi: 10.1111/j.1365-2125.2011.03956.x. View Abstract
 Guiney WJ, Beaumont C, Thomas SR. Use of the entero-test, a novel approach for the noninvasive capture of biliary metabolites in dogs. Drug Metab Dispos. 2010 May;38(5):851-6. Epub 2010 Jan 28. View Full Paper