Small bowel mucosal dysfunction in patients with cystic fibrosis

Digestive system dysfunction in cystic fibrosis: challenges for nutrition therapy

Cystic fibrosis can affect food digestion and nutrient absorption. The underlying mutation of the cystic fibrosis trans-membrane regulator gene depletes functional cystic fibrosis trans-membrane regulator on the surface of epithelial cells lining the digestive tract and associated organs, where Cl(-) secretion and subsequently secretion of water and other ions are impaired. This alters pH and dehydrates secretions that precipitate and obstruct the lumen, causing inflammation and the eventual degradation of the pancreas, liver, gallbladder and intestine. Associated conditions include exocrine pancreatic insufficiency, impaired bicarbonate and bile acid secretion and aberrant mucus formation, commonly leading to maldigestion and malabsorption, particularly of fat and fat-soluble vitamins. Pancreatic enzyme replacement therapy is used to address this insufficiency. The susceptibility of pancreatic lipase to acidic and enzymatic inactivation and decreased bile availability often impedes its efficacy. Brush border digestive enzyme activity and intestinal uptake of certain disaccharides and amino acids await clarification. Other complications that may contribute to maldigestion/malabsorption include small intestine bacterial overgrowth, enteric circular muscle dysfunction, abnormal intestinal mucus, and intestinal inflammation. However, there is some evidence that gastric digestive enzymes, colonic microflora, correction of fatty acid abnormalities using dietary n-3 polyunsaturated fatty acid supplementation and emerging intestinal biomarkers can complement nutrition management in cystic fibrosis.

Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies

Aspartame is a methyl ester of a dipeptide used as a synthetic nonnutritive sweetener in over 90 countries worldwide in over 6000 products. The purpose of this investigation was to review the scientific literature on the absorption and metabolism, the current consumption levels worldwide, the toxicology, and recent epidemiological studies on aspartame. Current use levels of aspartame, even by high users in special subgroups, remains well below the U.S. Food and Drug Administration and European Food Safety Authority established acceptable daily intake levels of 50 and 40 mg/kg bw/day, respectively. Consumption of large doses of aspartame in a single bolus dose will have an effect on some biochemical parameters, including plasma amino acid levels and brain neurotransmitter levels. The rise in plasma levels of phenylalanine and aspartic acid following administration of aspartame at doses less than or equal to 50 mg/kg bw do not exceed those observed postprandially. Acute, subacute and chronic toxicity studies with aspartame, and its decomposition products, conducted in mice, rats, hamsters and dogs have consistently found no adverse effect of aspartame with doses up to at least 4000 mg/kg bw/day. Critical review of all carcinogenicity studies conducted on aspartame found no credible evidence that aspartame is carcinogenic. The data from the extensive investigations into the possibility of neurotoxic effects of aspartame, in general, do not support the hypothesis that aspartame in the human diet will affect nervous system function, learning or behavior. Epidemiological studies on aspartame include several case-control studies and one well-conducted prospective epidemiological study with a large cohort, in which the consumption of aspartame was measured. The studies provide no evidence to support an association between aspartame and cancer in any tissue. The weight of existing evidence is that aspartame is safe at current levels of consumption as a nonnutritive sweetener.

Intestinal inflammation in cystic fibrosis

BACKGROUND

There is controversy about whether the inflammatory response observed in the cystic fibrosis (CF) lung occurs secondary to bacterial infection or is caused by a dysregulation of the inflammatory response associated with the basic cellular defect of CF.

AIMS

To study the inflammatory response in the gastrointestinal tract of children with CF; and to investigate whether there is increased inflammation in the gastrointestinal tract of CF children with fibrosing colonopathy.

METHODS

Whole gut lavage was performed on 21 pancreatic insufficient children with CF, who were clinically well, five children with CF and fibrosing colonopathy, and 12 controls. Intestinal outputs of plasma derived proteins (albumin, alpha(1) antitrypsin, IgG), secretory immunoglobulins (IgA and IgM), cellular constituents (eosinophil cationic protein and neutrophil elastase), and cytokines (interleukin 8 and interleukin 1beta) were measured.

RESULTS

Compared to controls, the 21 CF patients, with no intestinal complications, had increased intestinal outputs of albumin, IgG, IgM, eosinophil cationic protein, neutrophil elastase, interleukin 1beta, and interleukin 8. Similar values were obtained for the CF patients with fibrosing colonopathy.

CONCLUSIONS

These data suggest that there is immune activation in the gastrointestinal mucosa of children with cystic fibrosis, which may result from the basic cellular defect. Fibrosing colonopathy does not appear to be associated with increased inflammation.

Ultrastructural lesions in the small bowel of patients with cystic fibrosis

In the small bowel of patients with cystic fibrosis, primary defects involving both chloride transport and mucus secretion have been demonstrated, but there is no general consensus about the morphologic counterpart of functional and biochemical abnormalities. We have studied the intestinal mucosa in a group of patients with cystic fibrosis and gastrointestinal symptoms with the aim of evaluating whether the intestinal mucosa is normal as previously described. The results showed that the small bowel involvement is characterized by a typical pattern of lesions with preservation of the mucosal architecture and abundant mucus at the surface. In the villi, the absorbing cells were generally well preserved, but unusual features were found in the apical portion of the goblet cells, which formed sacks containing mucus droplets. Similar sacks were also found detached from the goblet cells. Aspects of degeneration were present in the upper portion of the crypts where elements with an extensive vacuolization of the cytoplasm and swelling were detectable. This study demonstrates that in patients with cystic fibrosis the ultrastructure of the small bowel mucosa is not normal as previously described, but that an ultrastructurally detectable enteropathy exists. This enteropathy seems to be localized mainly in sites where molecular biology studies described the highest expression of cystic fibrosis transmembrane conductance regulator.

Intestinal permeability in cystic fibrosis in relation to genotype

BACKGROUND

The purpose of this study was to investigate whether the increase intestinal permeability (IP) seen in patients with cystic fibrosis (CF) is correlated with the basic defect, as revealed by the patient's genotype, and/or whether the intestinal disturbance reflects secondary abnormalities such as essential fatty acid deficiency.

METHODS

Nineteen CF patients were compared with nine age- and sex-matched healthy controls. IP was evaluated by studying urinary excretion for 5 hours after a test meal containing lactulose, L-rhamnose and xylose in water. Urine was analyzed for carbohydrates, and blood samples were taken for determination of the fatty acid pattern of serum phospholipids. The CF patients were grouped according to genotype: homozygous for delta F508, heterozygous for alpha F508, or unidentified.

RESULTS

Patients who were homozygous (n = 9) or heterzygous (n = 6) for delta F508 had significantly higher lactulose/L-rhamnose excretion ratios (mean(range) values of 0.08(0.05-0.13) and 0.09(0.03-0.13), respectively) than patients (n = 4) with unidentified genotypes [0.03(0.02-0.05); p = 0.005] or healthy controls [0.02(0.003-0.06); p = 0.002]. CF patients with EFAD (n = 6) did not differ from those with a normal pattern of serum phospholipid fatty acids, the lactulose/L-rhamnose excretion ratio being 0.08(0.02-0.13) and 0.07(0.03-0.12), respectively.

CONCLUSIONS

These data show that the IP in CF was related to patient genotype; those homozygozous or heterozygous for delta F508 having a significantly increased IP compared with patients with unidentified genotypes, who had IP values within the normal range.

In vivo measurement of chloride and water secretion in the jejunum of cystic fibrosis patients

In the present study, we have investigated the possible consequences of the chloride channel defect in the intestine of cystic fibrosis (CF) patients for electrolyte and water transport in the jejunum in vivo, using a multilumen, double occluding balloon catheter, and an Ag/AgCl intraluminal electrode. During a chloride-free perfusion, to optimize the sensitivity of our measurements, the transmural potential difference (PD) (lumen with reference to serosal side) was found to be significantly higher in the jejunum of CF patients (+8.0 +/- 2.1 mV; n = 5) than in healthy control subjects (-2.2 +/- 2.0 mV; n = 9). The chloride concentration measured in chloride-free jejunal perfusates of CF patients was significantly lower than in controls (10.9 +/- 2.3 and 41.4 +/- 8.2 mM, respectively). Possible differences in net chloride and water secretion did not reach statistical significance (chloride secretion controls: -2.1 +/- 0.9 mmol/10 cm/h; CF: -0.8 +/- 0.2 mmol/10 cm/h; water secretion controls: -0.8 +/- 2.5 mL/10 cm/h; CF: -11.7 +/- 8.9 mL/10 cm/h). In control subjects, intraluminally applied theophylline stimulated the secretion of water (delta 23.4 +/- 4.6 mL/10 cm/h) and chloride (delta 4.1 +/- 1.1 mmol/10 cm/h), but not in CF patients (respectively delta 3.6 +/- 3.3 mL/10 cm/h and delta 1.1 +/- 1.1 mmol/10 cm/h). In controls, theophylline caused a significant increase in lumen negativity (PD -10.2 +/- 2.6 mV), but no change could be seen in CF patient transmural PD. These observations provide in vivo evidence for a decreased chloride permeability in the jejunum in CF, resulting in a significant reduction in net electrolyte and water secretion in the presence, but not in the absence, of an intestinal secretagogue.

Comparative effects of adjuvant cimetidine and omeprazole during pancreatic enzyme replacement therapy

In a double-blind, randomized crossover study, the hypotheses were tested that more powerful inhibition of gastric acid secretion by adjuvant omeprazole further improves the efficacy of pancreatic enzyme replacement therapy compared to adjuvant cimetidine and that excluding the influence of pH-related factors, by virtually complete inhibition of gastric acid secretion with 60 mg omeprazole daily, does not lead to total elimination of steatorrhea. During both adjuvant cimetidine and omeprazole treatment, fecal fat excretion was significantly lower compared to pancreatin monotherapy (P < 0.01). Omeprazole showed a trend towards a more favorable decrease of fecal fat excretion compared to cimetidine but no statistically significant difference. Steatorrhea was almost never abolished, even during 60 mg omeprazole daily. Generally, pH-related factors are considered to explain an inadequate therapeutic response during pancreatic enzyme replacement therapy. However, this study indicates that in vivo other factors also play a significant role.

A cohort study of cystic fibrosis and malignancy

A cohort of 412 patients first attending a cystic fibrosis (CF) clinic between 1961 and 1989 were followed up to 30 June 1989. The number of malignancies observed in the cohort was compared with the number expected based on the age, sex and calendar-year-specific cancer registration rates for England and Wales. Four CF patients were diagnosed as having malignancies before 30 June 1989. The tumours were: adenocarcinoma of the terminal ileum; adenocarcinoma of the pancreas, testicular teratoma, and B-cell lymphoma. This compares with 0.89 malignancies expected on the basis of rates in England and Wales (Standardised Registration Ratio = 452; 95% confidence interval 122-1150, P = 0.03). The single case of adenocarcinoma of the terminal ileum contrasts with less than 0.001 expected (P = 0.003) and that of the pancreas with 0.007 expected (P = 0.01). A further adenocarcinoma of the pancreas was diagnosed 2 years after the end of the study period. The two cases of pancreatic cancer compare with 0.008 expected (P = 0.0001) during the period to mid 1991. On the basis of the present findings and previous case reports in the literature adenocarcinoma of the pancreas and adenocarcinoma of the terminal ileum may be associated with cystic fibrosis.

Enhanced intestinal glucose and alanine transport in cystic fibrosis

The rise in short-circuit current associated with the active transport of glucose and alanine was measured in intestinal biopsy samples from children with cystic fibrosis. The glucose-induced increase in the short-circuit current was greater in the cystic fibrosis tissues than in control samples over the whole range of concentrations tested (2.5-35 mM), a reflection of an increased maximum rate of transport. Similar results were obtained with alanine. These findings suggest that active Na(+)-linked nutrient transport is enhanced in cystic fibrosis.

Relation between essential fatty acid metabolism and gastrointestinal symptoms in cystic fibrosis

Studies in our laboratory have supported the hypothesis, that the basic defect in cystic fibrosis increases the metabolism of essential fatty acids and thereby gradually gives rise to essential fatty acid deficiency, which is a well documented finding in most cases with this disease. Both the increased metabolism--giving high liberation of arachidonic acid and its metabolic products, i.e. different eicosanoids--and the subsequent essential fatty acid deficiency will cause gastrointestinal symptoms and the sequence of this development will mirror the natural history of the disease. Clinical data and results from animal research are discussed in relation to gastrointestinal symptoms and signs of cystic fibrosis.

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.

Intestinal malabsorption in cystic fibrosis

An oral solution containing lactulose and L-rhamnose was administered to six patients with cystic fibrosis. Intestinal absorption of both sugars was assessed by measurement of their urinary excretion. The lactulose: L-rhamnose excretion ratio was raised, supporting the hypothesis of an intestinal component to the malabsorption of cystic fibrosis.

The role of the small intestine in cystic fibrosis patients

A survey is given of the morphological and biochemical lesions of the small intestine that can be found in cystic fibrosis patients. The available data on the structure and function of the small intestine in CF patients favour the hypothesis that the small intestine itself might contribute to the malabsorption of nutrients in this disease. The most pronounced lesions, i.e. meconium ileus and absent active transport of bile salts are found in the ileum. It might be remembered that the ileum is also the site of intensive exchange of chloride and bicarbonate, a function that is heavily disturbed in the pancreas of CF patients. For this reason, further studies on the ileal function in cystic fibrosis are warranted.

Enhanced glucose absorption in the jejunum of patients with cystic fibrosis

After oral D-xylose ingestion, cystic fibrosis patients have significantly higher blood levels of xylose than controls. The aim of this study was to examine whether nutrient absorption at the mucosal level is altered in cystic fibrosis. Steady-state perfusion experiments using isotonic test solutions were performed in 11 healthy controls and 10 cystic fibrosis patients. Net D-glucose absorption was higher in cystic fibrosis when the perfusate contained a glucose concentration of less than or equal to 50 mM. Kinetic analysis by three different methods, including Lineweaver-Burk analysis, revealed a lower apparent Km as well as a lower apparent Vmax in cystic fibrosis as compared with healthy controls (33.9 mM and 52.5 mmol/20 cm . h vs. 81.8 mM and 68.3 mmol/20 cm . h, respectively, p less than 0.01). Absorption of D-fructose and glycine demonstrated a tendency for increased net absorption in cystic fibrosis but the results were not significantly different. L-Xylose absorption and electrolyte movement were not altered in cystic fibrosis. Among several possible mechanisms investigated, a decrease in the apparent Km for glucose absorption would be consistent with a decrease in diffusion barriers overlying the jejunal mucosa in cystic fibrosis. Using an electrical method, the unstirred water layer thickness was significantly decreased in cystic fibrosis (546 +/- 41 micron in cystic fibrosis vs. 780 +/- 110 micron in controls, p less than 0.05). A decrease in the mucosal surface area in the cystic fibrosis group or an intrinsic defect in the mucosal glucose transport system could account for differences in the apparent Vmax values. We suggest, however, that enhanced absorption in cystic fibrosis is most likely due to a decrease in intestinal diffusion barriers possibly due to abnormal mucus overlying the intestinal mucosa.

Inhibition of Na+-coupled solute transport by calcium in brush border membrane vesicles

Intracellular Ca++ is known to influence Na+ flux in luminal membranes. Abnormally elevated Ca++ levels in some cells is believed to be the primary pathophysiologic defect in cystic fibrosis (CF). This in turn is thought to alter Na+ transport which accounts for certain clinical manifestations of this disease. Two Na+-dependent intestinal transport mechanisms have been reported to be suppressed or missing in CF. To examine whether alterations in cell Ca++ may account for these findings, studies were performed to examine the influence of Ca++ on Na+-solute co-transport across intestinal luminal membranes. Purified brush border membrane vesicles prepared from rat small bowel were preincubated in either Ca++-free buffer or buffer containing 2.5 mM CaCl2. Ca++ loaded vesicles showed marked inhibition of Na+ co-transport of taurocholic acid, taurochenodeoxycholic acid, glucose and valine when compared to controls. The uptake of Na+ was also significantly reduced by intravesicular Ca++. These data demonstrate that intravesicular Ca++ inhibits Na+-coupled solute transport as well as Na+ influx across intestinal brush border membranes. These data suggest that intracellular Ca++ may suppress Na+-dependent solute absorption in the intestine. Results presented here further support the theory that elevated intracellular Ca++ may account for intestinal malabsorption and other altered transport phenomena reported in CF.

Short-term clinical, nutritional, and functional effects of continuous elemental enteral alimentation in children with cystic fibrosis

Ten children with cystic fibrosis, aged 3.5 to 12 years, whose weights were lower than 90% of the expected weight for height, received high-calorie elemental enteral alimentation for four weeks. Clinical, anthropometric, and biochemical evaluations as well as blood gas analyses and chest radiograph scoring were performed in all. Pulmonary function tests were performed in the five older children, and progressive exercise tests in three. These evaluations were done before, immediately after, and two months after termination of therapy. Nutritional therapy resulted in an increase of caloric intake and in dramatic weight gain, which persisted only for a short time and was mainly related to adipose tissue accretion. No functional improvement accompanied the amelioration in nutritional status. This short-term nutritional therapy in malnourished children with cystic fibrosis was effective in increasing relative weight and energy stores, but there was no evidence of any long-term functional benefit.

Small intestinal absorption of amino acids and a dipeptide in pancreatic insufficiency

In this study a perfusion technique has been used to investigate in vivo jejunal absorption and transmural potential difference evoked by the neutral amino acids phenylalanine (56 or 20 mmol/l) and glycine (20 mmol/l), the dibasic amino acid lysine (56 or 5 mmol/l), and a dipeptide glycyl-l-phenylalanine (20 mmol/l) in 11 children with pancreatic insufficiency due to cystic fibrosis and in three children with other causes of exocrine pancreatic insufficiency. Net absorption and potential difference evoked by phenylalanine in both cystic fibrosis and pancreatic insufficiency, and net absorption of glycine in cystic fibrosis were significantly reduced; but the absorption of lysine and glycyl-l-phenylalanine was normal. Absorption of the constituent amino acids from the dipeptide was normal or increased in cystic fibrosis. Thus, these studies show a defect in active absorption of neutral amino acids in cystic fibrosis with pancreatic insufficiency and exocrine pancreatic insufficiency. We speculate that pancreatic factors participate in neutral amino acid absorption.

Cimetidine as an adjunct to oral enzymes in the treatment of malabsorption due to cystic fibrosis

The effects of two doses orally administered Cimetidine on gastric and acid production and on intestinal absorption in 13 patients with cystic fibrosis who were treated with pancreatin supplementation were studied. Although both doses of Cimetidine reduced the acid secretion significantly, no reduction in the steatorrhea and creatorrhea or increase in weight were found, although less pancreatin seemed to be inactivated while on cimetidine. It is concluded that pancreatic extract supplementation alone is not sufficient to normalise the digestion in cystic fibrosis.

One-hour blood-xylose test in diagnosis of cow's milk protein intolerance

In this prospective study, 18 consecutive children suspected of cow's milk protein intolerance (C.M.P.I.) on clinical grounds were investigated before and after challenge with cow's milk. One-hour blood-xylose, serum-IgE, eosinophil count, serum-complement (C3) and a jejunal biopsy specimen for histology and disaccharidase activity were obtained from all patients before challenge. Serum-complement was measured again 24 h after the beginning of the challenge and the first three tests were repeated on the fifth day. A second jejunal biopsy was obtained in 9 of the first 10 children. 15 of the 18 children were considered to have C.M.P.I. The one-hour blood-xylose test emerged as a simple and valuable test in the diagnosis of C.M.P.I. A significant drop (51--81%) in the one-hour blood-xylose level was observed in all 15 patients. In all patients but one it dropped below 25 mg/dl. Mean value (+/- S.D.) for the group was 47.5 +/- 11.1 mg/dl before and 17.2 +/- 4.2 mg/dl after cow's milk ingestion.

The effect of cimetidine on maldigestion in cystic fibrosis

Ten patients (6 to 27 years of age) who had severe pancreatic exocrine insufficiency due to cystic fibrosis were studied to determine whether cimetidine would improve dietary fat and nitrogen absorption. When a constant diet was consumed and oral pancreatic enzymes were administered, the addition of cimetidine (150 or 200 mg taken orally one-half hour before meals) signficantly reduced fecal fat excretion from 25.3 +/- 2.9 to 17.3 +/- 2.1 gm/24 hours and fecal nitrogen excretion from 4.5 +/- 0.6 to 3.4 +/- 0.5 gm/24 hours (P less than 0.05). Lower doses of cimetidine resulted in less significant reductions of steatorrhea and azotorrhea. Cimetidine may be a useful adjunct to oral pancreatic enzyme therapy in patients with cystic fibrosis who continue to have steatorrhea and azotorrhea with enzyme therapy alone.

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.