Relationship between bile acid malabsorption and pancreatic insufficiency in cystic fibrosis

An in vitro medium for modeling gut dysbiosis associated with cystic fibrosis

The gut physiology of pediatric and adult persons with cystic fibrosis (pwCF) is altered relative to healthy persons. The CF gut is characterized, in part, as having excess mucus, increased fat content, acidic pH, increased inflammation, increased antibiotic perturbation, and the potential for increased oxygen availability. These physiological differences shift nutritional availability and the local environment for intestinal microbes, thus likely driving significant changes in microbial metabolism, colonization, and competition with other microbes. The impact of any specific change in this physiological landscape is difficult to parse using human or animal studies. Thus, we have developed a novel culture medium representative of the CF gut environment, inclusive of all the aforementioned features. This medium, called CF-MiPro, maintains CF gut microbiome communities, while significantly shifting nonCF gut microbiome communities toward a CF-like microbial profile, characterized by low Bacteroidetes and high Proteobacteria abundance. This medium is able to maintain this culture composition for up to 5 days of passage. Additionally, microbial communities passaged in CF-MiPro produce significantly less immunomodulatory short-chain fatty acids (SCFA), including propionate and butyrate, than communities passaged in MiPro, a culture medium representative of healthy gut physiology, confirming not only a shift in microbial composition but also altered community function. Our results support the potential for this in vitro culture medium as a new tool for the study of CF gut dysbiosis. IMPORTANCE Cystic fibrosis is an autosomal recessive disease that disrupts ion transport at mucosal surfaces, leading to mucus accumulation and altered physiology of both the lungs and the intestines, among other organs, with the resulting altered environment contributing to an imbalance of microbial communities. Culture media representative of the CF airway have been developed and validated; however, no such medium exists for modeling the CF intestine. Here, we develop and validate a first-generation culture medium inclusive of features that are altered in the CF colon. Our findings suggest this novel medium, called CF-MiPro, as a maintenance medium for CF gut microbiome samples and a flexible tool for studying key drivers of CF-associated gut dysbiosis.

An In Vitro Medium for Modeling Gut Dysbiosis Associated with Cystic Fibrosis

The gut physiology of pediatric and adult persons with cystic fibrosis (pwCF) is altered relative to healthy persons. The CF gut is characterized, in part, as having excess mucus, increased fat content, acidic pH, increased inflammation, increased antibiotic perturbation and the potential for increased oxygen availability. These physiological differences shift nutritional availability and the local environment for intestinal microbes, thus likely driving significant changes in microbial metabolism, colonization and competition with other microbes. The impact of any specific change in this physiological landscape is difficult to parse using human or animal studies. Thus, we have developed a novel culture medium representative of the CF gut environment, inclusive of all the aforementioned features. This medium, called CF-MiPro, maintains CF gut microbiome communities, while significantly shifting non-CF gut microbiome communities toward a CF-like microbial profile, characterized by low Bacteroidetes and high Proteobacteria abundance. This medium is able to maintain this culture composition for up to 5 days of passage. Additionally, microbial communities passaged in CF-MiPro produce significantly less immunomodulatory short chain fatty acids (SCFA), including propionate and butyrate, than communities passaged in MiPro, a culture medium representative of healthy gut physiology, confirming not only a shift in microbial composition but altered community function. Our results support the potential for this in vitro culture medium as a new tool for the study of gut dysbiosis in CF.

Elevated Levels of Toxic Bile Acids in Serum of Cystic Fibrosis Patients with CFTR Mutations Causing Pancreatic Insufficiency

Hepatobiliary involvement is a hallmark in cystic fibrosis (CF), as the causative CF Transmembrane Conductance Regulator (CFTR) defect is expressed in the biliary tree. However, bile acid (BA) compositions in regard to pancreatic insufficiency, which is present at an early stage in about 85% of CF patients, have not been satisfactorily understood. We assess the pattern of serum BAs in people with CF (pwCF) without CFTR modulator therapy in regard to pancreatic insufficiency and the CFTR genotype. In 47 pwCF, 10 free and 12 taurine- and glycine-conjugated BAs in serum were prospectively assessed. Findings were related to genotype, pancreatic insufficiency prevalence (PIP)-score, and hepatic involvement indicated by serum liver enzymes, as well as clinical and ultrasound criteria for CF-related liver disease. Serum concentrations of total primary BAs and free cholic acid (CA) were significantly higher in pwCF with higher PIP-scores (p = 0.025, p = 0.009, respectively). Higher total BAs were seen in pwCF with PIP-scores ≥0.88 (p = 0.033) and with pancreatic insufficiency (p = 0.034). Free CA was higher in patients with CF-related liver involvement without cirrhosis, compared to pwCF without liver disease (2.3-fold, p = 0.036). pwCF with severe CFTR genotypes, as assessed by the PIP-score, reveals more toxic BA compositions in serum. Subsequent studies assessing changes in BA homeostasis during new highly effective CFTR-modulating therapies are of high interest.

Serum bile acids in cystic fibrosis patients - glycodeoxycholic acid as a potential marker of liver disease

BACKGROUND

Cystic fibrosis (CF) and CF-related liver disease can lead to disturbances in bile acid metabolism.

AIM

This study determined serum bile acid concentrations in CF to define their usefulness in liver disease assessment.

METHODS

Primary, secondary and conjugated bile acid levels were measured in three CF groups (25 patients each) exhibiting: liver cirrhosis, other liver disease, no liver disease, and in 25 healthy subjects (HS).

RESULTS

Bile acid levels were higher in CF patients than in HS, except for glycodeoxycholic acid (GDCA). However, bile acid concentrations did not differ between patients with cirrhosis and other liver involvement. GDCA and deoxycholic acid (DCA) differentiated CF patients with non-cirrhotic liver disease from those without liver disease (GDCA-AUC: 0.924, 95%CI 0.822-1.000, p<0.001; DCA-AUC: 0.867, 95%CI: 0.731-1.000, p<0.001). Principal component analysis revealed that in CF liver disease was related to GDCA, GGTP activity, severe genotype and pancreatic insufficiency.

CONCLUSIONS

A CF-specific bile acid profile was defined and shown to relate to liver disease. GDCA differentiates patients with non-cirrhotic liver involvement from those with no detectable liver disease. Hence, GDCA is a candidate for validation as a biomarker of non-cirrhotic progression of liver disease in CF.

Rational Use of Pancreatic Enzymes for Pancreatic Insufficiency and Pancreatic Pain

We describe the rational use of enteric coated and unprotected replacement pancreatic enzymes for treatment of malabsorption due to pancreatic insufficiency and for pancreatic pain. Enteric coated formulations mix poorly with food allowing separation of enzymes and nutrients when emptying from the stomach. The site of dissolution of the enteric coating in the intestine is also unpredictable and enzymes may not be released until the distal intestine. Together, these barriers result in the lack of dose-response such that the strategy of increasing the dosage following a suboptimal effect is often ineffective. The ability to maintain the intragastric pH ≥4 with the combination of proton pump inhibitors and antacids suggests that it should be possible to reliably obtain a good response with uncoated enzymes. We also discuss the recognition, treatment and prevention of nutritional deficiencies associated with pancreatic insufficiency and recommend a test and treat strategy to identify and resolve nutritional deficits. Finally, we focus on mechanisms causing pain that may be amenable to therapy with pancreatic enzymes. Pain due to malabsorbed digestive contents can be prevented by successful therapy of malabsorption. Feedback inhibition of endogenous pancreatic secretion can prevent pain associated with pancreatic secretion but requires use of non-enteric coated formulations.

Endogenous praecaecal and total tract losses of nitrogen in pancreatic duct-ligated minipigs

The pancreatic duct-ligated minipig (PL) is an established model of pancreatic exocrine insufficiency (PEI) with a significant decrease of nutrient digestibility. This study aimed to quantify and compare endogenous losses of nitrogen (N) (ileal and faecal) in minipigs receiving an almost N-free diet. Altogether, 12 Göttingen minipigs (7 PL and 5 control animals) fitted with an re-entrant ileo-caecal fistula were used. In Study 1, ileal digesta was collected over a period of 12 h on seven consecutive days, including one 24 h collection, when animals were fed a diet containing 0.49 g N/kg dry matter (DM). In Study 2, faeces were collected for 10 consecutive days. In Group PL, the amount and DM content of ileal digesta were higher (p < 0.05), while N concentration was lower than in the Control. The ileo-caecal N flux [g/kg DM intake] was about 2.5 times higher in Group PL (5.47 ± 1.15) than in the Control (1.91 ± 0.59) (p < 0.05). The amount of faeces did not differ, but faecal N losses were higher in Group PL (p < 0.05). Endogenous faecal N losses [g N/kg DM intake] of the Control group (1.17 ± 0.72) were comparable with earlier studies, while those of Group PL were 2.6 times higher (3.09 ± 1.34). In contrast, urinary excretion of N did not differ between the Control and Group PL. In conclusion, PEI caused markedly increased endogenous N losses. Therefore, the impact of reduced digestibility of nutrients on endogenous N losses might be relevant for apparent protein digestibility rates and should be taken into account.

Pancreatic enzyme replacement therapy for pancreatic exocrine insufficiency in the 21st century

Restitution of normal fat absorption in exocrine pancreatic insufficiency remains an elusive goal. Although many patients achieve satisfactory clinical results with enzyme therapy, few experience normalization of fat absorption, and many, if not most, will require individualized therapy. Increasing the quantity of lipase administered rarely eliminates steatorrhea but increases the cost of therapy. Enteric coated enzyme microbead formulations tend to separate from nutrients in the stomach precluding coordinated emptying of enzymes and nutrients. Unprotected enzymes mix well and empty with nutrients but are inactivated at pH 4 or below. We describe approaches for improving the results of enzyme therapy including changing to, or adding, a different product, adding non-enteric coated enzymes, (e.g., giving unprotected enzymes at the start of the meal and acid-protected formulations later), use of antisecretory drugs and/or antacids, and changing the timing of enzyme administration. Because considerable lipid is emptied in the first postprandial hour, it is prudent to start therapy with enteric coated microbead prior to the meal so that some enzymes are available during that first hour. Patients with hyperacidity may benefit from adjuvant antisecretory therapy to reduce the duodenal acid load and possibly also sodium bicarbonate to prevent duodenal acidity. Comparative studies of clinical effectiveness of different formulations as well as the characteristics of dispersion, emptying, and dissolution of enteric-coated microspheres of different diameter and density are needed; many such studies have been completed but not yet made public. We discuss the history of pancreatic enzyme therapy and describe current use of modern preparations, approaches to overcoming unsatisfactory clinical responses, as well as studies needed to be able to provide reliably effective therapy.

Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies

BACKGROUND & AIMS

Patients with cystic fibrosis (CF) have poorly defined defects in biliary function. We evaluated the effects of cystic fibrosis transmembrane conductance regulator (CFTR) deficiency on the enterohepatic disposition of bile acids (BAs).

METHODS

Bile secretion and BA homeostasis were investigated in Cftr(tm1Unc) (Cftr-/-) and CftrΔF508 (ΔF508) mice.

RESULTS

Cftr-/- and ΔF508 mice did not grow to normal size, but did not have liver abnormalities. The gallbladders of Cftr-/- mice were enlarged and had defects in emptying, based on (99m)technetium-mebrofenin scintigraphy or post-prandial variations in gallbladder volume; gallbladder contraction in response to cholecystokinin-8 was normal. Cftr-/- mice had abnormal gallbladder bile and duodenal acidity, and overexpressed the vasoactive intestinal peptide-a myorelaxant factor for the gallbladder. The BA pool was larger in Cftr-/- than wild-type mice, although there were no differences in fecal loss of BAs. Amounts of secondary BAs in portal blood, liver, and bile of Cftr-/- mice were much lower than normal. Expression of genes that are induced by BAs, including fibroblast growth factor-15 and BA transporters, was lower in the ileum but higher in the gallbladders of Cftr-/- mice, compared with wild-type mice, whereas enzymes that synthesize BA were down-regulated in livers of Cftr-/- mice. This indicates that BAs underwent a cholecystohepatic shunt, which was confirmed using cholyl-(Ne-NBD)-lysine as a tracer. In Cftr-/- mice, cholecystectomy reversed most changes in gene expression and partially restored circulating levels of secondary BAs. The ΔF508 mice overexpressed vasoactive intestinal peptide and had defects in gallbladder emptying and in levels of secondary BAs, but these features were less severe than in Cftr-/- mice.

CONCLUSIONS

Cftr-/- and CftrΔF508 mice have defects in gallbladder emptying that disrupt enterohepatic circulation of BAs. These defects create a shunt pathway that restricts the amount of toxic secondary BAs that enter the liver.

Review: Management of postprandial diarrhea syndrome

Unexpected, urgent, sometimes painful bowel movements after eating are common complaints among adults. Without a clear etiology, if pain is present and resolves with the movements, this is usually labeled "irritable bowel syndrome-diarrhea" based solely on symptoms. If this symptom-based approach is applied exclusively, it may lead physicians not to consider treatable conditions: celiac disease, or maldigestion due to bile acid malabsorption, pancreatic exocrine insufficiency, or an a-glucosidase (sucrase, glucoamylase, maltase, or isomaltase) deficiency. These conditions can be misdiagnosed as irritable bowel syndrome-diarrhea (or functional diarrhea, if pain is not present). Limited testing is currently available to confirm these conditions (antibody screens for celiac disease; fecal fat as a surrogate marker for pancreatic function). Therefore, empirical treatment with alpha amylase, pancreatic enzymes, or a bile acid-binding agent may simultaneously treat these patients and serve as a surrogate diagnostic test. This review will summarize the current evidence for bile acid malabsorption, and deficiencies of pancreatic enzymes or a-glucosidases as potential causes for postprandial diarrhea, and provide an algorithm for treatment options.

Comparative biology of cystic fibrosis animal models

Animal models of human diseases are critical for dissecting mechanisms of pathophysiology and developing therapies. In the context of cystic fibrosis (CF), mouse models have been the dominant species by which to study CF disease processes in vivo for the past two decades. Although much has been learned through these CF mouse models, limitations in the ability of this species to recapitulate spontaneous lung disease and several other organ abnormalities seen in CF humans have created a need for additional species on which to study CF. To this end, pig and ferret CF models have been generated by somatic cell nuclear transfer and are currently being characterized. These new larger animal models have phenotypes that appear to closely resemble human CF disease seen in newborns, and efforts to characterize their adult phenotypes are ongoing. This chapter will review current knowledge about comparative lung cell biology and cystic fibrosis transmembrane conductance regulator (CFTR) biology among mice, pigs, and ferrets that has implications for CF disease modeling in these species. We will focus on methods used to compare the biology and function of CFTR between these species and their relevance to phenotypes seen in the animal models. These cross-species comparisons and the development of both the pig and the ferret CF models may help elucidate pathophysiologic mechanisms of CF lung disease and lead to new therapeutic approaches.

[Measurement of 75Se-SeHCAT abdominal retention in the initial diagnosis of Bile Acid Absorption (BAM)]

AIM

To evaluate the usefulness of the (75)SeHCAT abdominal retention (AR) measurement in the early diagnosis of diarrhea syndrome (DS).

METHODS

Thirty-seven patients with diarrhea syndrome within the first month of evolution were prospectively evaluated. The (75)Se-SeHCAT abdominal retention was measured 4 and 7 days post-administration of 0.01 mCi of (75)SeHCAT. The test was performed prior to treatment and at 3 months when the baseline study was positive. The test was considered positive if the RA was <25% at 4(th) and <10% on the 7th day. The patients were visited at 3 months. Depending on the response, 3 groups were established: a) complete response: normalization of stool frequency, b) partial response, decrease of frequency or c) no response.

RESULTS

Group A: The AR of (75)Se-SEHCAT was normal in 21 patients. Six were diagnosed of colonic diverticulosis, 8 of irritable bowel syndrome, 1 of lymphocytic colitis, 1 of post-gastroenteritis syndrome, 1 of celiac disease and 1 of stenosis of the cardia. Four are still under study. Group B: The AR of (75)Se-SEHCAT decreased in 16 patients. All showed abnormal AR at day 7 and all but 1 at day 4. Following administration of cholestyramine resin, 8 (50%) presented partial response and 8 (50%) complete response. At 3 months, AR had increased at day 4 and 9 at day 7.

CONCLUSION

The measurement of (75)SEHCAT abdominal retention allows the early diagnosis of bile acid malabsorption in 43% of the patients with DS. Measurement at 7 days seems more accurate than that at 4 days.

Persistent fat malabsorption in cystic fibrosis; lessons from patients and mice

Fat malabsorption in pancreatic insufficient cystic fibrosis (CF) patients is classically treated with pancreatic enzyme replacement therapy (PERT). Despite PERT, intestinal fat absorption remains insufficient in most CF patients. Several factors have been suggested to contribute to the persistent fat malabsorption in CF (CFPFM). We reviewed the current insights concerning the proposed causes of CFPFM and the corresponding intervention studies. Most data are obtained from studies in CF patients and CF mice. Based on the reviewed literature, we conclude that alterations in intestinal pH and intestinal mucosal abnormalities are most likely to contribute to CFPFM. The presently available data indicate that acid suppressive drugs and broad spectrum antibiotics could be helpful in individual CF patients for optimizing fat absorption and/or nutritional status.

Pilot study: a randomised, double blind, placebo controlled trial of pancrealipase for the treatment of postprandial irritable bowel syndrome-diarrhoea

OBJECTIVE: To evaluate the efficacy of pancrealipase (PEZ) compared with placebo in the reduction of postprandial irritable bowel syndrome-diarrhoea (IBS-D). DESIGN: An intention to treat, double blind, randomised, crossover trial comparing PEZ to placebo for reduction of postprandial IBS-D. Patients had to recognise at least two different triggering foods, be willing to consume six baseline 'trigger meals' and again blinded with PEZ and placebo. Patients then chose which drug they preferred for another 25 meals. SETTING: Outpatient internal medicine practice clinic. PATIENTS: 255 patients were screened; 83 met the criteria, including 5 years of symptoms, recognised 'food triggers', no other identifiable cause for the symptoms, either a normal colonoscopy or barium enema while symptomatic and able to discontinue all anticholinergic medications. 69 patients were enrolled, 20 withdrew before randomisation, leaving 49 patients: 14 men, 35 women, mean age 52 years (SD 15.3). Over 60% had experienced symptoms for 11-30 years and 16% for more than 40 years. INTERVENTIONS: After completing six baseline meals, patients were randomised in blocks of four to receive either identical PEZ or a placebo for another six meals, and after a washout period of time received the alternative drug. MAIN OUTCOME MEASURES: The primary analysis was number of patients who chose PEZ over placebo for the extended use. RESULTS: Overall, 30/49 (61%) would have chosen PEZ (p=0.078), with first drug preference for PEZ at 0.002. Among the PEZ subgroup, PEZ use compared with placebo, demonstrated improvement in all symptoms (p≤0.001) for cramping, bloating, borborygami, urge to defecate, global pain and decrease stooling with increase in stool firmness. CONCLUSIONS: PEZ was found in a small group of patients to reduce postprandial IBS-D symptoms and deserves further evaluation.

Bile acids: short and long term effects in the intestine

Bile acids have secretory, motility and antimicrobial effects in the intestine. In patients with bile acid malabsorption the amount of primary bile acids in the colon is increased compared to healthy controls. Deoxycholic acid is affecting the intestinal smooth muscle activity. Chenodeoxycholic acid has the highest potency to affect intestinal secretion. Litocholic acid has little effect in the lumen of intestine compared to both deoxycholic acid and chenodeoxycholic acid. There is no firm evidence that clinically relevant concentrations of bile acids induce colon cancer. Alterations in bile acid metabolism may be involved in the pathophysiology of constipation.

Limitations in the Clinical Usefulness of Single-Dose Pharmacokinetic Studies of Drugs and a Bayesian Approach for the Estimation of Kinetic Parameters

This review presents several clinical examples indicating that physiological changes in the body dependent and/or independent of developmental age, genetic polymorphisms, different disease states, acute and/or chronic inflammations, and physicochemical properties of drugs as well as some environmental factors, such as viral infections, may exert a significant effect on the first-time assessment of kinetic parameters of drug absorption, disposition, metabolism, and excretion after a single-dose administration in children and adults. The available pharmacokinetic data in the literature suggest that one must be cautious in interpretation and practical use of pharmacokinetic variables derived from either single-dose studies or bayesian methods, especially in a pediatric population.

Endogenous fecal losses of calcium compromise calcium balance in pancreatic-insufficient girls with cystic fibrosis

OBJECTIVE

Bone mineral density is compromised in individuals with cystic fibrosis (CF); calcium is the major bone mineral. This study examined the impact of endogenous fecal calcium (V(endo)) losses on calcium balance in girls with CF. Study design V(endo) was measured in 12 girls with CF (aged 7-18 years): 7 younger, premenarcheal girls with compromised nutritional status; and 5 older, postmenarcheal girls with adequate nutritional status. V(endo) was measured as the amount of intravenously administered (42)Ca, a calcium stable isotope, in stool relative to urine over 6 days. V(endo) was compared between pre- and postmenarcheal girls by Student's t test. Actual calcium balance [absorbed calcium-(urinary calcium (V(u))+V(endo))] was compared with estimated balance (assuming V(endo)=1.6 mg/kg/day calcium) by paired t test.

RESULTS

V(endo) was 99.3+/-42.3 mg/day. By body weight, V(endo) was highest among premenarcheal girls (3.37+/-1.09 mg/kg/day), resulting in excess losses (>1.6 mg/kg/day) of 55.0+/-45.7 mg/day. Over 1 year, this represents 20.1+/-16.7 g of unattained bone calcium or 6.7+/-4.2% of the bone calcium content of these girls.

CONCLUSIONS

V(endo) is a significant source of calcium loss in individuals with CF and may limit calcium availability for bone mineral deposition.

Fat malabsorption in cystic fibrosis patients receiving enzyme replacement therapy is due to impaired intestinal uptake of long-chain fatty acids

BACKGROUND

Pancreatic enzyme replacement therapy frequently fails to correct intestinal fat malabsorption completely in cystic fibrosis (CF) patients. The reason for this failure is unknown.

OBJECTIVE

We investigated whether fat malabsorption in CF patients treated with pancreatic enzymes is caused by insufficient lipolysis of triacylglycerols or by defective intestinal uptake of long-chain fatty acids.

DESIGN

Lipolysis was determined on the basis of breath 13CO2 recovery in 10 CF patients receiving pancreatic enzyme replacement therapy after they ingested 1.3-distearoyl,2[1-13C]octanoyl glycerol ([13C]MTG). Intestinal uptake of long-chain fatty acids was determined by analyzing plasma [13C]linoleic acid ([13C]LA) concentrations after patients ingested [13C]LA. For 3 d, dietary intakes were recorded and feces were collected.

RESULTS

Fecal fat excretion ranged from 5.1 to 27.8 g/d (mean+/-SD: 11.1+/-7.0 g/d) and fat absorption ranged from 79% to 93% (89+/-5%). There was no relation between breath 13CO2 recovery and dietary fat absorption (r = 0.04) after ingestion of [13C]MTG. In contrast, there was a strong relation between 8-h plasma [13C]LA concentrations and dietary fat absorption (r = 0.88, P < 0.001).

CONCLUSION

Our results suggest that continuing fat malabsorption in CF patients receiving enzyme replacement therapy is not likely due to insufficient lipolytic enzyme activity, but rather to incomplete intraluminal solubilization of long-chain fatty acids, reduced mucosal uptake of long-chain fatty acids, or both.

Faecal bile acid and dietary residue excretion in cystic fibrosis: age group variations

BACKGROUND

Earlier studies report the excessive faecal excretions of bile acids and dietary residues in cystic fibrosis (CF). However, few of these investigated large groups of patients using modern pancreatin preparations and little data exists reporting carbohydrate excretion. We therefore aimed to characterise the general levels of malabsorption within age groups of 132 patients attending a regional CF centre.

METHODS

The faecal excretions of bile acids, fat, nitrogen and carbohydrate were measured. Most of these patients were treated with either (Creon) (n = 58) or Pancrease (n = 51) and prophylactic antibiotics. The patients were grouped in age ranges 0.5 to 5 years, 6 to 10 years, 11 to 15 years and >16 years. Carbohydrate excretion was determined in the 11 to 15 year group.

RESULTS

Increased excretions with increment in age group were found which, for bile acids, was twice that of age matched controls. Modest relationships were found between the overall excretion of bile acids and fat, and between the excretion of bile acids and nitrogen. Primary bile acids were a feature of cystic fibrosis stools but the patterns of individual bile acid excretion revealed a trend towards a normal bile acid types with increment in age group. Faecal carbohydrate was significantly increased to levels which may significantly alter large bowel microflora.

CONCLUSIONS

The data adds to the evidence that maldigestion initiates bile acid sequestration and consequently, the predominance of primary bile acids.

Cystic fibrosis. Gastrointestinal complications and gene therapy

The gastrointestinal and nutritional complications of cystic fibrosis are diverse. As longevity improves in patients with cystic fibrosis, management of these complications is becoming increasingly important . This article provides overviews of the molecular aspects of the pathogenesis of cystic fibrosis, the current status of gene therapy, and a review of the gastrointestinal manifestations and nutritional care.

Clinical pharmacology of pancreatic enzymes in patients with cystic fibrosis and in vitro performance of microencapsulated formulations

Improving protein and fat absorption in patients with cystic fibrosis relates to the amount of biologically active enzyme reaching the duodenum. Microencapsulated formulations are more effective than conventional products but differ in content, ability to retard acid inactivation and the pH at which they release enzymes. Contaminants in these products contribute to hyperuricosuria.

Intestinal bile acid malabsorption in cystic fibrosis

This study aimed at examining the mechanisms participating in excessive faecal bile acid loss in cystic fibrosis. The study was designed to define the relation between faecal fat and faecal bile acid loss in patients with and without cystic fibrosis related liver disease; to assess terminal ileal bile acid absorption by a seven day whole body retention of selenium labelled homotaurocholic acid (SeHCAT); and to determine if small intestinal bacterial overgrowth contributes to faecal bile acid loss. The study population comprised 40 patients (27 men; median age 18 years) with cystic fibrosis (n = 8) and without (n = 32) liver disease and eight control subjects. Faecal bile acid excretion was significantly higher in cystic fibrosis patients without liver disease compared with control subjects (mean (SEM) 21.5 (2.4) and 7.3 (1.2) micromoles/kg/24 hours respectively; p < 0.01) and patients with liver disease (7.9 (1.3) micromoles/kg/24 hours; p < 0.01). No correlation was found between faecal fat (g fat/24 hours) and faecal bile acid (micromoles 24 hours) excretion. Eight (33%) of cystic fibrosis patients had seven day SeHCAT retention < 10% (normal retention > 20%). SeHCAT retention in cystic fibrosis patients with liver disease was comparable with control subjects (30.0 (SEM) 8.3% v 36.8 (5.9)%; p = NS) while SeHCAT retention in cystic fibrosis patients who did not have liver disease was significantly reduced (19.9 (3.8); p < 0.05). Although evidence of small bowel bacterial overgrowth was present in 40% of patients no relation was found between breath hydrogen excretion, faecal fat, and faecal bile acid loss. The results are consistent with the presence of an abnormality in terminal ideal function in patients with cystic fibrosis who do not have liver disease and that a defect in the ileal absorption of bile acids may be a contributory factor to excessive faecal bile acid loss. Faecal bile acid loss in cystic fibrosis is unrelated to the presence of intraluminal fat or intestinal bacterial overgrowth.

Cholesterol malabsorption in pancreatic insufficiency: effects of enzyme substitution

Defective lipolysis, steatorrhea, and hypocholesterolemia characterize pancreatic insufficiency. Lipid metabolism in pancreatic insufficiency was studied by measuring serum lipoproteins, cholesterol absorption with double labels and serum plant sterols, and bile acid and cholesterol synthesis with fecal and dietary steroid analysis and cholesterol precursor sterols before and during exogenous pancreatic enzyme substitution. Baseline fecal fat, masses, bile acids and neutral steroids, and cholesterol synthesis were increased, whereas cholesterol absorption was markedly reduced. In fact, the present data suggest that sterol absorption may be disturbed more sensitively than fat absorption in pancreatic insufficiency. Enzyme substitution significantly reduced fecal fat, masses, bile acids and neutral steroids, and synthesis of cholesterol and improved cholesterol absorption in relation to serum cholesterol, although normal values were not obtained. Serum level of high-density lipoprotein cholesterol was significantly elevated by exogenous enzymes, whereas levels of cholesterol or triglycerides in other lipoproteins remained unchanged. Improved sterol absorption increased also serum levels of plant sterols and reduced levels of cholesterol precursors and cholesterol synthesis and precursor sterol-plant sterol ratios. Thus, reduced intestinal lipolysis with expanded oil phase appears to be a major reason for impaired cholesterol absorption, causing enhanced cholesterol and, consequently, bile acid synthesis and reduced serum cholesterol level. Exogenous enzyme substitution seems partly to correct these abnormalities, improvements of which can be monitored by the gas-liquid chromatographic determination of serum plant sterols or cholesterol precursor-plant sterol ratios.

Primary bile acid malabsorption: a pathophysiologic and clinical entity?

Primary bile acid malabsorption is defined as chronic diarrhoea with bile acid malabsorption of unknown cause and a symptomatic response to cholestyramine. Convincing evidence of the proposed pathophysiology--a defect of the active bile acid absorption in the distal ileum--has never been substantiated. We found no evidence of a bile acid transport defect across the ileal brush border membrane in 10 patients with primary bile acid malabsorption; moreover, transport was significantly higher than in a control group. In the patients with primary bile acid malabsorption the estimated bile acid pool was significantly larger than in a control group and in a group of patients with ileal disease. In addition, the oro-anal transit time of radiopaque markers was shorter in the primary bile acid malabsorption group than in both other groups. This suggests that the bile acid pool size as well as intestinal motility could play a role in the pathophysiology of primary bile acid malabsorption.

Primary bile acid diarrhoea without an ileal carrier defect: quantification of active bile acid transport across the ileal brush border membrane

Unexplained bile acid malabsorption associated with diarrhoea that responds to cholestyramine was first described in 1973 but convincing evidence of the proposed mechanism--a defective active ileal bile acid transport--has never been substantiated. Active bile acid transport was quantified in vitro using brush border membrane vesicles prepared from terminal ileal biopsy specimens from 10 patients who fulfilled the criteria of idiopathic bile acid diarrhoea. They were recruited from 181 patients with bile acid malabsorption of various causes. Transport was quantified as in vitro Na+ dependent bile acid transport (INBAT), expressed as pmol taurocholate/mg brush border membrane protein/15 seconds, and in vitro Na+ dependent bile acid local transport capacity (INBALTC), expressed as pmol taurocholate/g ileal biopsy tissue/15 seconds. The lowest INBAT and INBALTC values in the 10 patients with idiopathic bile acid diarrhoea were well above the 10th centile values of a control group of 132 patients. Both INBAT (mean (range) 88 (30-136)) and INBALTC (158 (85-268)) values were significantly higher in the 10 patients than in the control group (INBAT: mean (range) 63 (1-244), INBALTC: mean (range) 98 (1-408)). Quantification of active ileal bile acid transport in these 10 patients with idiopathic bile acid malabsorption suggests that a genetic (carrier) defect is rare in adults.

Na+-dependent bile acid transport in the ileum: the balance between diarrhea and constipation

Ileal Na+-dependent bile acid transport was quantified in vitro as the uptake of 3H-taurocholate into brush-border membrane vesicles. Vesicles were prepared from ileal biopsies of 158 patients placed in 10 diagnostic categories. Active bile acid transport (expressed as picomoles taurocholate uptake per milligram brush-border membrane protein per 15 s, median and interquartile ranges indicated) did not differ significantly in 6 categories: irritable bowel syndrome (71, 35-97; n = 21), colon polyps (42, 30-89; n = 29), colitis (62, 33-91; n = 31), postvagotomy or postcholecystectomy (69, 37-97; n = 11), diarrhea without increased bile acid loss (58, 48-85; n = 12), and lack of gastrointestinal pathology (74, 45-103; n = 22). A decreased active bile acid transport was found in 3 categories: ileal disease (4, 1-36; n = 11), partial ileal resection (5, 1-35; n = 5), and constipation (41, 22-50; n = 8). Bile acid transport was increased in patients with bile acid-losing diarrhea with endoscopically and histologically normal ilea (111, 94-135; n = 8). These findings indicate that a low fecal bile acid loss, presumed to be present in constipated patients, is associated with a low Na+-dependent ileal bile acid transport and a high bile acid loss is associated with a high active bile acid transport. Ileal bile acid transport might be regulated by the availability of bile acids to the ileal enterocytes.

Clinical pharmacology of antibiotics and other drugs in cystic fibrosis

The disposition of many drugs in cystic fibrosis is abnormal. In general, changes in pharmacokinetics include: increased volume of distribution, decreased plasma concentration, and enhanced renal and sometimes non-renal elimination of drugs. Pathophysiology of the disease important for drug disposition includes: (a) hypersecretion of gastric acid and duodenal secretions which are of small volume, viscous and low in bicarbonate; (b) increased intestinal permeability to some sugars and probe substances; (c) hypergammaglobulinaemia and sometimes hypoalbuminaemia; (d) significant elevation of free fatty palmitoleic acid level and decreased low-density and high-density serum lipoproteins; (e) an average increase by 30 to 45% in plasma volume in patients with cystic fibrosis who have moderately severe pulmonary disease, right ventricle hypertrophy and dilatation, which occurs in 15 to 35% of patients with a Shwachman score of 81 to 100; (f) abnormal bile acid metabolism and enterohepatic recirculation; and (g) enlarged kidneys and glomerulomegaly with increased glomerular filtration rate, tubular clearance and urine flow rate in some patients with cystic fibrosis. Delayed absorption from the gastrointestinal tract has been reported in patients with cystic fibrosis for cloxacillin, epicillin, clindamycin, ciprofloxacin and probably for cephalexin, para-aminobenzoic acid and chloramphenicol. A possible increased absorption was reported for cimetidine. Of 7 drugs studied only theophylline had significantly decreased plasma protein binding. An increased volume of distribution and increased renal clearance reported for several drugs is caused mainly by increases in plasma volume and urine flow rate in many of these patients. Possible increased elimination of some drugs in bile (which probably results from bile acid malabsorption) and in bronchial secretions (which are abundant in some cystic fibrosis patients with acute pulmonary infection) may explain enhanced non-renal elimination of these drugs. The metabolism of cimetidine in cystic fibrosis was reported not to be changed significantly compared to control subjects.

Liver disease and common-bile-duct stenosis in cystic fibrosis

To determine the incidence of common-bile-duct lesions and their relation to liver disease in cystic fibrosis, we performed hepatobiliary scanning in 50 of 61 patients with cystic fibrosis who had hepatomegaly, abnormal liver function, or both and in 31 of 92 patients with cystic fibrosis who did not have hepatomegaly or abnormal liver function. Ninety-six percent of the patients with liver disease had evidence of biliary tract obstruction, which was defined cholangiographically as a stricture of the distal common bile duct in the majority of cases. All the patients without liver disease had normal intrahepatic and common-duct excretion of tracer. Abdominal pain was significantly more common in patients with common-duct obstruction (P less than 0.001), and enlarged gallbladders occurred only in such patients. Since fasting levels of serum bile acids were elevated in nearly half these patients, irrespective of the severity of their liver disease, serum bile acids may be markers of the severity of the common-duct lesion. We conclude that strictures of the distal common bile duct are common in patients with cystic fibrosis and liver disease. This association requires further study, since surgical relief of common-duct obstruction may prevent or ameliorate the hepatic complications of cystic fibrosis.

Determinants of serum vitamin D levels in preadolescent cystic fibrosis children

The effects of liver disease, fat malabsorption and sunlight exposure on serum vitamin D levels were determined in 21 optimally treated preadolescent cystic fibrosis (CF) children over a 12-month period. Manifest liver disease and fat malabsorption appeared not to affect the vitamin D level. However, the level fell significantly in winter, although not below the normal range, suggesting that sunlight exposure is a more important determinant of vitamin D levels in preadolescent CF children than liver disease and fat malabsorption.

Bile salt malabsorption in pancreatic insufficiency secondary to alcoholic pancreatitis

Twenty patients with exocrine pancreatic insufficiency secondary to alcohol abuse were studied for the presence of bile salt malabsorption. Fecal bile salts and fecal fat excretion were determined in 15 patients receiving pancreatic enzyme therapy, not receiving enzyme therapy, and on a regimen of pancreatic enzymes plus cimetidine. Serum bile salt levels were measured during fasting and postprandial conditions both during enzyme therapy and after it was stopped in 8 cases. In addition, 5 patients underwent [14C]cholylglycine breath testing during and after discontinuation of enzyme therapy. The fecal bile salt excretion varied between 610 and 3460 mg/day in the untreated patients. Treatment with pancreatic enzymes was associated with significant (p less than 0.05) reduction in fecal bile salt and fecal fat excretion. Cimetidine therapy in addition to enzyme therapy further reduced steatorrhea but failed to alter bile salt excretion significantly. Serum cholylglycine level showed significant (p less than 0.05) postprandial increase in patients receiving enzyme therapy, suggesting improved bile salt absorption. These data suggest a wide range of bile salt malabsorption in alcoholic patients with pancreatic insufficiency, which improves with pancreatic enzyme therapy.

Effect of dietary fat and residues on fecal loss of sterols and on their microbial degradation in cystic fibrosis

Although various etiologic factors have been implicated, the mechanism responsible for bile acid malabsorption in CF remains unknown. Eight CF children studied twice on a normal diet supplemented with pancreatic enzymes and once during a one-month period of Vivonex administered by continuous nasogastric infusion were compared to age-matched controls. On the fat and residue-free elemental diet, there was a modest decrease in steatorrhea and no change in the daily excretion of nitrogen and neutral sterols. However, normalization of bile acid output (485.6 +/- 65.0 to 160.6 +/- 29.2 mg/24 hr) to control levels (150.2 +/- 60.7) was noted. Diminished microbial degradation of both neutral and acidic sterols and a smaller amount of bile acids adsorbed to decreased residues were also found. The data do not support the possibility of a bile acid ileal transport defect and suggest that the most important single factor responsible for the intraluminal sequestration of bile acids in CF is dietary residues. Because of significant ongoing losses of nitrogen and lipids, pancreatic enzymes should be given to CF patients on elemental diets.

Bile acid secretion in cystic fibrosis: evidence for a defect unrelated to fat malabsorption

In order to define basic biliary defects not related to steatorrhoea in cystic fibrosis, we studied 12 control and 18 cystic fibrosis subjects, with a wide range of pancreatic function. Duodenal aspirates were collected over three consecutive 20 minute periods, during continuous intravenous infusion of cholecystokinin and secretin using a marker perfusion technique, and analysed for pancreatic enzyme output (colipase, lipase, trypsin), bile acid output and concentration, and biliary lipids. Cystic fibrosis patients, at all levels of pancreatic function, had significantly reduced total bile acid output (mumol/kg/h) with delayed appearance of the bile acid peak, compared with control subjects. Actual duodenal bile acid concentrations were significantly higher in cystic fibrosis subjects than in controls, however, probably because of the markedly reduced water output shown in these patients. The lithogenic index was not raised in cystic fibrosis patients at any level of pancreatic function. The reduced bile acid output and the delayed peak appearance probably reflect a defect in gall bladder responsiveness which is independent of pancreatic function and steatorrhoea. Whether this defect is related to gall bladder filling or a defective peptide hormone response awaits further study.

Conjugated bile acids in serum and secretions in response to cholecystokinin/secretin stimulation in children with cystic fibrosis

More than 80% of patients with cystic fibrosis have poor pancreatic function, and have large daily faecal bile acid losses. This has been postulated to lower luminal bile acid concentrations and adversely affect fat absorption. We studied, for the first time, quantitative individual conjugated duodenal bile acid secretion rates into the duodenum during cholecystokinin/secretin infusion in 55 cystic fibrosis patients and six controls, using a quantitative non-absorbable marker technique. We were able to show adequate duodenal total bile acid concentrations and normal secretion rates in these children. The bile acid secretion pattern in cystic fibrosis patients showed a marked increase in bile acid concentration during cholecystokinin/secretin infusion, to levels which were above the critical micellar concentration indicating that the gall bladder is a functional organ in this disease. The subsequent fall in secretion rate was similar to controls. We have documented a significantly raised glycine/taurine bile acid conjugation ration in duodenal juice from cystic fibrosis patients and suggest that the combined effects of lowered ileal pH and increased glycine conjugated proportion of bile acids may cause precipitation of bile acids leading to decreased fat absorption and large faecal bile acid losses. To further investigate bile acid secretion in children with cystic fibrosis, we modified the high performance thin layer chromatography/densitometry method to enable measurement of individual glycine and taurine conjugates in serum. In comparing cystic fibrosis patients and controls, we were able to determine a group of 18 (36%) with bile acid evidence of liver damage who also showed reduced bile acid secretion into the duodenum. We were unable to study changes in serum bile acids during cholecystokinin/secretin infusion because of the high level of bile acid contamination in Boots Secretin. Some patients showed raised fasting serum bile acid concentrations more than two years before changes in conventional liver function tests or clinically evident liver disease. We have shown fasting serum bile acids to be a sensitive measure of liver dysfunction in cystic fibrosis and postulate that raised proportions of glycine conjugated bile acids may be responsible for the high incidence of liver disease in cystic fibrosis.

Serum bile acid composition in patients with cystic fibrosis

Serum bile acid composition was examined in detail using capillary column gas chromatography and mass spectrometry in 10 children with cystic fibrosis (CF) and 4 healthy children. The mean total bile acid concentration in fasting serum of CF patients was 2.33 +/- 0.84 mumol/l, slightly lower than but not statistically significantly different from healthy controls (mean 2.86 +/- 0.98 mumol/l) and appeared to show no relationship to the degree of exocrine pancreatic insufficiency. Analysis of individual serum bile acids in these children showed that cholic acid represented less than 10% of the total bile acids. Chenodeoxycholic acid was the predominant serum bile acid; the mean concentration in CF patients was 0.98 +/- 0.51 mumol/l, lower than for the healthy controls (1.69 +/- 0.84 mumol/l). Concentrations of lithocholic acid, 3 beta-hydroxy-5-cholenoic, ursodeoxycholic and 3 beta, 7 alpha, 12 alpha-trihydroxy-5 beta-cholanoic acids in fasting serum samples of the CF patients were not significantly different from the healthy control sera but were higher than those normally found in adults. Measurements of fecal bile acid excretion indicated an increased loss of primary bile acids in patients with CF consistent with an impairment of the enterohepatic circulation of bile acids.

Effect of cimetidine on enzyme inactivation, bile acid precipitation, and lipid solubilisation in pancreatic steatorrhoea due to cystic fibrosis

In pancreatic steatorrhoea, both pH-dependent bile acid precipitation and enzyme inactivation may limit the efficacy of pancreatic enzyme supplements and both may be preventable by addition of cimetidine. To separate these effects we compared postprandial jejunal aspirate from eight adults with steatorrhoea due to cystic fibrosis on three randomised treatment regimens (pancreatin, cimetidine, and both together). We also compared the results with those of previous studies of patients on no treatment, and of healthy subjects. On pancreatin 60% of the test meal entered the jejunum at pH less than 5 compared with 17% in health. Lipase concentration and lipolysis increased over the values on no treatment (14.2 vs 4.4 U/l, p less than 0.01; 16% vs 11%, p less than 0.02) but bile acid precipitation was not reduced (38% vs 27%, NS), and aqueous-phase lipid concentration decreased (6.7 vs 8.6 mM/l, p less than 0.05). On cimetidine, bile acid precipitation fell (19% vs 38%, p less than 0.05); although lipase concentration and lipolysis were lower than on pancreatin (4.8 U/l vs 14.2 U/l, p less than 0.01; 9% vs 16%, p less than 0.01) lipid solubilisation increased (8.8 vs 6.7 mM/l, p less than 0.05). On the combination, there was a marked improvement (p less than 0.02) in lipid solubilisation (18.3 mM/l), reflecting the improvement both in lipase (38.4 U/l) and lipolysis (24%), and in bile acid precipitation (5.6%). We conclude that the efficacy of pancreatin is limited by pH-dependent bile acid precipitation in addition to enzyme inactivation. The action of cimetidine in improving the efficacy of pancreatin depends on prevention of both these effects.

Bile acid metabolism in children with cystic fibrosis

Recycling of bile acids through the enterohepatic cycle is very efficacious. Bile acids contribute to bile formation and, by forming micelles, participate in lipid solubilization and absorption. The small fraction which escapes in the feces, is synthesized daily by the liver to compensate for losses. In CF, bile acid malabsorption has been documented; these large losses are accompanied by an interruption in the enterohepatic circulation with concomitant reduction in bile acid pool and disturbances in biliary composition. The various intraluminal factors implicated in bile acid malabsorption include: unhydrolysed triglycerides and phospholipids, precipitation of bile acids in acidic duodenal content, adsorption to residues and modification of colonic microflora. A defect in bile acid ileal uptake has also been advocated. These disturbances in bile acid metabolism associated with CF might lead to aggravation of diarrhea and steatorrhea, cholelithiasis and perhaps liver disease.

Problems in the treatment of malabsorption in CF

Several factors play a role in the cause of malabsorption in CF. Besides the enzyme deficiency in the secretion of the exocrine pancreas, decreased bile-salt concentration in the gut may also be an important factor in the fat malabsorption. The contribution to the fat absorption by other lipases, such as lingual lipase and gastric lipase, remains to be proved. The therapeutic measures are only partly effective because of the breakdown of swallowed enzymes by gastric acid. Some improvement is reached by using a new acid-resistant coating for the enzyme supplement. Newly developed and essential for its success is the application of small coated particles to prevent retention in the stomach, and the easy breakdown of the coating in an alkaline solution. The treatment of the bile salt deficiency has not been successful until now. A trial with additional Tween 80, with the option of supplementing the detergent activity which was found to be successful in Crohn disease, was without marked success.

Effect of intrajejunal acidity on aqueous phase bile acid and lipid concentrations in pancreatic steatorrhoea due to cystic fibrosis

We have investigated whether jejunal hyperacidity leads to bile acid precipitation and thus limits lipid solubilisation in patients with pancreatic steatorrhoea. Jejunal contents from 12 adults with steatorrhoea due to cystic fibrosis were aspirated for three hours after a liquid test meal, and pooled according to their pH. Thirty eight per cent of the total aspirate was collected at pH less than 5 in cystic fibrosis, compared with 18% in healthy controls (p less than 0.05). Forty six per cent of the bile acids were precipitated at pH less than 5, compared with 15% at pH greater than 6 (p less than 0.01), leading to reduced aqueous phase bile acid concentration at low pH (4.7 mmol/l at pH less than 5 vs 12.5 mmol/l at pH greater than 6, p less than 0.01). Aqueous phase lipid concentrations were reduced at low pH (5.6 mmol/l at pH less than 5 vs 10.2 mmol/l at pH greater than 6, p less than 0.01). Lipolysis and total fatty acid concentrations were greatly reduced and did not vary with pH. We therefore conclude that jejunal hyperacidity leads to bile acid precipitation in pancreatic steatorrhoea due to cystic fibrosis, and imposes a further limitation on lipid solubilisation over that of lipase deficiency.

Evaluation of an oral ursodeoxycholic acid load in the assessment of bile acid malabsorption in cystic fibrosis

Serum levels of ursodeoxycholic acid (UDCA) were measured by radioimmunoassay in 20 children with cystic fibrosis (CF) and in eight controls, who had received 300 mg of this bile acid orally. Area under the curve (AUC) after UDCA load was significantly reduced (25.24 +/- 9.54) in CF patients, as compared to controls (52.98 +/- 5.87 mean values +/- SD percent dose/liter X hr X kg body weight, P less than 0.001). AUC values were compared with daily fecal bile acids (BA) and fat excretion, and with serum fasting conjugated cholic (CCA) and chenodeoxycholic (CCDCA) acid levels. Total fecal BA were increased in CF patients (7.84 +/- 5.57 mg/kg/day) as compared to control values (2.7 +/- 1.1 mean +/- SD, P less than 00.5); they were inversely correlated with AUC values (r = 0.48) but not with steatorrhea (r = 0.32). UDCA load seems to be useful in detecting BA malabsorption in CF. Fasting CCA levels did not significantly differ in CF patients (0.87 +/- 0.61 mumol/liter) and in controls (0.60 +/- 0.26 mumol/liter) and did not correlate with fecal BA excretion. Fasting CCDCA mean levels were significantly increased (mainly in CF patients with liver damage), suggesting a lowered first-pass extraction in the liver: their determination may be useful in the follow-up of liver involvement in CF.

Pancreatic enzyme replacement: the effect of antacids or cimetidine

The effect of the addition of sodium bicarbonate, aluminum hydroxide, magnesium hydroxide, calcium carbonate, or cimetidine to supplemental pancreatic enzyme therapy was investigated in patients with severe exocrine pancreatic insufficiency. Steatorrhea was reduced with the administration of three enzyme tablets with meals (73 vs 29 g/24 hr). The coadministration of enzyme tablets with either sodium bicarbonate (16.6 g/24 hr, P = 0.08), or aluminum hydroxide (18.4 g/24 hr, P = 0.029) yielded a greater reduction in steatorrhea than enzymes alone (29 g/24 hr). Neither magnesium-aluminum hydroxide (36.3 g/24 hr, P = 0.22), nor calcium carbonate (39.0 g/24 hr, P = 0.029), improved efficacy of enzyme therapy and, in fact, tended to enhance steatorrhea. With the administration of cimetidine there was no significant effect on steatorrhea compared to enzymes alone (32.1 vs 29 g/24 hr, P greater than 0.3). Intraduodenal lipase activity following test meals was found to be a poor predictor of the effectiveness of antacid therapy in improving the efficacy of supplemental enzymes.

Serum bile acid response to a test meal stimulus: a sensitive test of ileal function

We assessed ileal functional integrity, as reflected in the capacity to reabsorb the bile acid, cholylglycine, by sequential measurement of postprandial serum levels of this compound. A consistent increase in cholylglycine concentration (mean +/- SEM, peak above fasting baseline = 1.86 +/- 0.14 microM) occurred in eight normal children. Five patients with ileal resection and two with primary bile acid malabsorption had a minimal postprandial increase (0.27 +/- 0.08 microM; P less than 0.005 vs controls) and excess bile acid loss in feces. Similarly, in seven patients with Crohn disease involving the ileum the postprandial increase (0.38 +/- 0.06) was less than controls (P less than 0.001). In eight patients with cystic fibrosis, the administration of pancreatic enzymes normalized the blunted response demonstrated when enzymatic therapy was interrupted suggesting an intact ileal active transport mechanism. Meal-stimulated response of serum cholylglycine concentration is a sensitive indicator of altered ileal integrity and bile acid malabsorption due to ileal resection, inflammation, or dysfunction.

Excretion of bile acids in healthy children and children with cystic fibrosis

Urinary bile acid excretion was investigated in twenty-two patients with cystic fibrosis (CF) and in seven healthy children. CF patients with and without antibiotic treatment were compared. Bile acids were determined in 24-h samples after separation into unconjugated, glycine conjugated, taurine conjugated and sulphate conjugated bile acids. In total twenty bile acids were identified of which cholic, chenodeoxycholic, 3 beta-hydroxy-5-cholenoic acid and 24-nor-5 beta-cholan-23-oic acid were routinely present in samples collected from both CF patients and healthy children. None of the other bile acids were preferentially excreted by CF patients. When compared with the normal group, no statistical significance could be attached to the increased total urinary bile acids excreted by the CF patients (due to the large individual variations). The CF patients excreted increased amounts of cholic acid, 3 alpha, 7 beta, 12 alpha-and 3 beta, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acids mainly in the unconjugated state. After administration of 24-[14C]cholic acid to thirteen CF patients the isotope excretion in faeces and urine was studied. Most of the patients had a high faecal excretion indicating great losses of bile acids from enterohepatic circulation. Compared to normal adults CF children excreted isotope in increased amounts in the urine.

A review of the Zollinger-Ellison syndrome--with particular reference to a patient treated with cimetidine

A case of the Zollinger-Ellison syndrome, presented with watery diarrhoea, malabsorption and multiple duodenal ulcers. Resection of a gastrinoma from the head of the pancreas was ineffective. Cimetidine, administered for more than 30 months produced an immediate and sustained relief of symptoms with a gain in weight of 19 kg and improvement of the biochemical features of malabsorption. Gastric acid secretion has been markedly inhibited and duodenal ulceration healed.

The role of gastric lipolysis on fat absorption and bile acid metabolism in the rat

In vivo studies were carried out in young Sprague-Dawley rats to examine the role of gastric lipolysis on fat absorption and bile acid metabolism. When fed by gastric perfusion 5 times (corn oil, 4 g/day) their usual dietary intake of fat, rats deprived of lingual lipase by the creation of an esophageal fistula had a significant degree of fat and bile acid malabsorption as well as a shortened bile acid half-life when compared to animals with a gastrostomy. The % fat absorption, bile acid loss and bile acid pool were normal in 2 groups of esophageal fistula rats fed the same quantity of corn oil or twice (8 g/day) that amount as a fine emulsion. In view of a negligible gastric lipase activity in animals with an esophageal fistula and of decreased hydrolysis of a triglyceride test meal, these data suggest that gastric lipolysis is of physiological importance in situations where lipolytic mechanisms are stressed by a large fat intkae. Its principal role is to potentiate intestinal lipolysis by facilitating the emulsification of dietary lipids through its formed products and, therefore, the contact of pancreatic lipase with its substrates.

Intestinal bile salts in cystic fibrosis: studies in the patient and experimental animal

The quantitative and qualitative distribution of bile salts in the duodenal juice of 13 patients with cystic fibrosis (CF) was studied after a test meal. The effects of triolein (TO), bovine serum albumin (BSA), and ricinoleic acid (RA) on the absorption of taurocholate (TCA) in the distal ileum of the rat in vivo was also studied. The mean (and ranges) of total bile salt concentrations, glycine: taurine conjugate ratios, and percentage of dihydroxy bile salts in the patients with CF and pancreatic insufficiency were 3.5 (1.3--6.6) mmol/l, 8.6 (greater than 10-3.1), and 37 (10--60) compared with control values of 7.4 (3.0--16.0) mmol/l, 3.0 (1.3--4.5), and 61 (52--70) respectively. The differences between the control and CF values were statistically significant (P less than 0.01--P less than 0.001). Three of the 13 CF patients had total bile salt concentrations less than 2 mmol/l, 8 had much higher glycine: taurine ratios, and 8 had a reduced percentage of dihydroxy bile salts. In 2 patients with normal pancreatic enzyme activities, duodenal bile salts were both quantitatively and qualitatively normal. TO (10 and 30 mmol/l), BSA (3%), and RA (5 mmol/l) had no inhibitory effect on the ileal absorption of TCA. These results show pronounced abnormalities of duodenal juice bile salts in CF with pancreatic insufficiency consistent with a broken enterohepatic circulation (EHC); such abnormalities may contribute to defective lipid absorption in CF. The data in the experimental animal do not support the suggestion that unhydrolysed dietary substrates play a role in the pathophysiology of the broken EHC.

Reduction of bile acid loss in cystic fibrosis by dietary means

On a 'normal' diet increased faecal bile acid excretion was found in 14 of 16 children with cystic fibrosis who had steatorrhoea, but excretion was normal in 2 such children without steatorrhoea. The 16 children with steatorrhoea took 3 regimens of diet and therapy: a 'normal' diet with pancreatic enzyme supplements, a diet of reduced long-chain triglycerides with added medium-chain triglycerides, and the same diet with added pancreatic enzyme supplements. On each of these three regimens steatorrhoea and faecal bile acid loss were significantly less than on no treatment, with the lowest excretions occurring on the diet of reduced long-chain triglycerides with added medium-chain triglycerides and pancreatic enzyme supplements. Although a reduction in steatorrhoea was nearly always accompanied by a decrease in bile acid excretion, the initial bile acid loss was very variable and could not be predicted for any given degree of steatorrhoea. This suggests that at least one other factor, possibly liver disease or bile acid pool size, influences bile acid loss in the faeces.

Influence of diets high and low in animal fat on bowel habit, gastrointestinal transit time, fecal microflora, bile acid, and fat excretion

Epidemiological observations and animal experiments suggest that large bowel cancer is related to serveral factors. Among them, high dietary intakes of animal fat, the presence in the colon of relatively high levels of bile acids, specific patterns of intestinal microflora, slow transit through the gut, and low stool weights. Under metabolic conditions we have observed the effect on these variables of dietes containing 62 or 152 g/day of fat mainly of animal origin in six healthy young men over 4-wk periods. No change attributable to the diet was observed in the subjects' bowel habit, fecal weight, mean transit time through the gut, or in the excretion of dry matter. Total fecal bile acid excretion was significantly higher on the high fat diet (320 +/- 120 mg/day) than on the low fat diet (139.7) +/- 63 mg/day) t test = 7.78 P less than 0.001 as also was the total fecal fatty acid excretion, 3.1+/-0.71 and 1.14+/-0.35 g/day, respectively t test = 11.4 P less than 0.001). The fecal microflora including the nuclear dehydrogenating clostridia were unaltered by the dietary changes as was fecal beta-glucuronidase activity. Dietary changes which increase animal fat intake clearly influence fecal bile acid excretion in a way that would favor the development of large bowel cancer if current theories prove to be true. Dietary fat however has no effect on overall colonic function so other components of the diet must be responsible for the observed associations of bowel cancer with slow transit and reduced fecal bulk.

Abnormal biliary lipid composition in cystic fibrosis. Effect of pancreatic enzymes

Because of the increased incidence of gallstones in cystic fibrosis we compared biliary lipid composition in 26 patients with cystic fibrosis, seven children with cholelithiasis but no cystic-fibrosis and 13 controls. Eighteen of the cystic fibrosis group had cholecystograms, and only one had gallstones. In 14 patients with cystic fibrosis who had stopped taking pancreatic enzymes for one week molar percentage of lipid composition accounted for by cholesterol (mean +/- S.E., 16.3 +/- 2.9) and saturation index (2.0 +/- 0.3) were comparable to values of the cholelithiasis group and higher (P less than 0.01) than those of controls. In 12 patients with cystic fibrosis taking pancreatic enzymes, molar percentage of cholesterol (8.6 +/- 1.7) and saturation index (1.0 +/- 0.1) did not differ from those of controls; in cystic fibrosis there was a preponderance of cholic over chenodeoxycholic acid both off (1.7 +/- 0.2) and on (1.9 +/- 0.3) therapy as compared to the cholelithiasis (0.7 +/- 0.1) and control (0.8 +/- 0.0) groups. The glycine/taurine ratio of conjugated bile acids were lower in enzyme-treated patients with cystic fibrosis (3.7 +/- 0.6) than in patients off treatment (6.4 +/- 1.0), but was higher (P less than 0.01) than in controls (1.8 +/- 0.2). Bile is lithogenic in untreated cystic fibrosis and responds to pancreatic enzymes.