Nutrition support in clinical practice: review of published data and recommendations for future research directions. National Institutes of Health, American Society for Parenteral and Enteral Nutrition, and American Society for Clinical Nutrition

In the last 30 years, marked advances in enteral feeding techniques, venous access, and enteral and parenteral nutrient formulations have made it possible to provide nutrition support to almost all patients. Despite the abundant medical literature and widespread use of nutritional therapy, many areas of nutrition support remain controversial. Therefore, the leadership at the National Institutes of Health, The American Society for Parenteral and Enteral Nutrition, and The American Society for Clinical Nutrition convened an advisory committee to perform a critical review of the current medical literature evaluating the clinical use of nutrition support; the goal was to assess our current body of knowledge and to identify the issues that deserve further investigation. The panel was divided into five groups to evaluate the following areas: nutrition assessment, nutrition support in patients with gastrointestinal diseases, nutrition support in wasting diseases, nutrition support in critically ill patients, and perioperative nutrition support. The findings from each group are summarized in this report. This document is not meant to establish practice guidelines for nutrition support. The use of nutritional therapy requires a careful integration of data from pertinent clinical trials, clinical expertise in the illness or injury being treated, clinical expertise in nutritional therapy, and input from the patient and his/her family.

Association between a functional polymorphism in the serotonin transporter gene and diarrhoea predominant irritable bowel syndrome in women

BACKGROUND AND AIMS

Serotonin (5-hydroxtryptamine, 5-HT) is an important factor in gut function, playing key roles in intestinal peristalsis and secretion, and in sensory signalling in the brain-gut axis. Removal from its sites of action is mediated by a specific protein called the serotonin reuptake transporter (SERT or 5-HTT). Polymorphisms in the promoter region of the SERT gene have effects on transcriptional activity, resulting in altered 5-HT reuptake efficiency. It has been speculated that such functional polymorphisms may underlie disturbance in gut function in individuals suffering with disorders such as irritable bowel syndrome (IBS). The aim of this study was to assess the potential association between SERT polymorphisms and the diarrhoea predominant IBS (dIBS) phenotype.

SUBJECTS

A total of 194 North American Caucasian female dIBS patients and 448 female Caucasian controls were subjected to genotyping.

METHODS

Leucocyte DNA of all subjects was analysed by polymerase chain reaction based technologies for nine SERT polymorphisms, including the insertion/deletion polymorphism in the promoter (SERT-P) and the variable tandem repeat in intron 2. Statistical analysis was performed to assess association of any SERT polymorphism allele with the dIBS phenotype.

RESULTS

A strong genotypic association was observed between the SERT-P deletion/deletion genotype and the dIBS phenotype (p = 3.07x10(-5); n = 194). None of the other polymorphisms analysed was significantly associated with the presence of disease.

CONCLUSIONS

Significant association was observed between dIBS and the SERT-P deletion/deletion genotype, suggesting that the serotonin transporter is a potential candidate gene for dIBS in women.

Nutrition support in clinical practice: review of published data and recommendations for future research directions. Summary of a conference sponsored by the National Institutes of Health, American Society for Parenteral and Enteral Nutrition, and American Society for Clinical Nutrition

In the last 30 years, marked advances in enteral feeding techniques, venous access, and enteral and parenteral nutrient formulations have made it possible to provide nutrition support to almost all patients. Despite the abundant medical literature and widespread use of nutritional therapy, many areas of nutrition support remain controversial. Therefore, the leadership at the National Institutes of Health, The American Society for Parenteral and Enteral Nutrition, and The American Society for Clinical Nutrition convened an advisory committee to perform a critical review of the current medical literature evaluating the clinical use of nutrition support; the goal was to assess our current body of knowledge and to identify the issues that deserve further investigation. The panel was divided into five groups to evaluate the following areas: nutrition assessment, nutrition support in patients with gastrointestinal diseases, nutrition support in wasting diseases, nutrition support in critically ill patients, and perioperative nutrition support. The findings from each group are summarized in this report. This document is not meant to establish practice guidelines for nutrition support. The use of nutritional therapy requires a careful integration of data from pertinent clinical trials, clinical expertise in the illness or injury being treated, clinical expertise in nutritional therapy, and input from the patient and his/her family. (Journal of Parenteral and Enteral Nutrition 21:133-156, 1997).

Cloning of a cDNA encoding rat intestinal fatty acid binding protein

Intestinal fatty acid binding protein mRNA is one of the most abundant mRNA species in the rat small intestinal epithelium. RNA transfer blot analyses disclosed that the mRNA encoding intestinal fatty acid binding protein is approximately equal to 900 nucleotides long and not represented in liver RNA. We have identified 564 nucleotides of this mRNA, including 12 nucleotides of the 5' nontranslated region, the coding portion, and 155 nucleotides of the 3' nontranslated domain. The primary translation product encoded by this mRNA contains 132 amino acids and has a Mr of 15,062. The derived protein sequence was verified by automated sequential Edman degradation of the intact polypeptide isolated from a wheat germ cell-free system. The in vitro product is NH2-terminally acetylated, a finding that is consistent with its ultimate cytoplasmic destination. Comparison of the amino acid sequence of this protein with liver fatty acid binding protein, a polypeptide specified by the most abundant small intestinal epithelial mRNA, revealed significant homology and similarity in the predicted secondary structures of their NH2-terminal domains.

Oleic acid stimulation of apolipoprotein B secretion from HepG2 and Caco-2 cells occurs post-transcriptionally

HepG2 and Caco-2 cells were studied to compare the regulation of liver and intestinal apolipoprotein (apo) biosynthesis and secretion by fatty acids. Incubation with fatty acid consistently stimulated apoB production by both HepG2 and Caco-2 cells. Media concentrations of apoB, determined by radioimmunoassay, were approx. 3-fold greater for cells incubated for 24 h in serum-free medium containing oleic acid bound to albumin than for cells incubated with albumin alone. Oleic acid also resulted in a 2-3-fold accumulation of cellular triacylglycerol for HepG2 cells and Caco-2 cells. Cellular apoB and media and cellular apoA-I concentrations were not affected by oleic acid. Immunoblotting with a monoclonal antibody against human apoB confirmed a greater mass of apoB in media from HepG2 and Caco-2 cells incubated with oleic acid. Radiolabeled apoB-100 was also increased in media from HepG2 and Caco-2 cells incubated with [35S]methionine for 24 h in the presence of oleic acid, suggesting enhanced apoB synthesis. However, apoB mRNA concentrations were unchanged in response to oleic acid. Gel filtration of media by fast protein liquid chromatography (FPLC) revealed a redistribution of apoB from LDL-sized particles to VLDL or chylomicrons in media from Caco-2 cells incubated with oleic acid, whereas apoB remained in LDL for HepG2 cells. ApoA-I in media from HepG2 and Caco-2 cells eluted as free or lipid-poor apoA-I, and the apoA-I distribution was unaltered by incubation with oleic acid. These data demonstrate that HepG2 and Caco-2 cells maintained in supplemented serum-free medium respond to oleic acid by a similar post-transcriptional increase in apoB synthesis, but different packaging of apoB into triacylglycerol-rich lipoproteins.

Caco-2 cells express a combination of colonocyte and enterocyte phenotypes

Caco-2 cells are derived from a human colonic adenocarcinoma, but differentiate into small intestinal-like cells after confluence. While this enterocytic differentiation has been well studied, the presumed parallel loss of colonocyte function has not been as thoroughly examined. To follow the phenotype for both tissues, Western blots were performed using antisera recognizing liver/bone/kidney alkaline phosphatase and surfactant-like particle proteins found in normal human colon, along with antisera against the small bowel representatives of the same proteins. Antisera against proteins enriched in either enterocytes (alpha1-antitrypsin) or colonocytes (surfactant protein A) were also evaluated. Alkaline phosphatase activity increased from 3 to 18 days post-confluence. Activity at 3 days post-confluence derived substantially from both isomers. Thereafter, the colonic (liver/bone/kidney) isomer declined to low levels as the content of the enterocytic isomer rose. A similar pattern was found with colonic (decreasing expression) and enterocytic (increasing expression) surfactant-like particle proteins. In particular, the content of larger enterocytic particle proteins (97 and 116 kDa) increased with time in culture. Expression of alpha1-antitrypsin increased early and remained high, whereas surfactant protein A generally declined after the third day post-confluency. In summary, undifferentiated Caco-2 cells express very low levels of proteins characteristic of either colonocytes or enterocytes. Immediately after confluence, they expressed proteins characteristic of both cell types. Thereafter, the content of colonocyte-specific proteins decreased, whereas those specific for the enterocyte increased. The timing and degree of this phenotypic switch have implications for the interpretation of experiments using Caco-2 cells as a model of small intestinal function.

Fundamentals of neurogastroenterology

Current concepts and basic principles of neurogastroenterology in relation to functional gastrointestinal disorders are reviewed. Neurogastroenterology is emphasized as a new and advancing subspecialty of clinical gastroenterology and digestive science. As such, it embraces the investigative sciences dealing with functions, malfunctions, and malformations in the brain and spinal cord, and the sympathetic, parasympathetic and enteric divisions of the autonomic innervation of the digestive tract. Somatomotor systems are included insofar as pharyngeal phases of swallowing and pelvic floor involvement in defecation, continence, and pelvic pain are concerned. Inclusion of basic physiology of smooth muscle, mucosal epithelium, and the enteric immune system in the neurogastroenterologic domain relates to requirements for compatibility with neural control mechanisms. Psychologic and psychiatric relations to functional gastrointestinal disorders are included because they are significant components of neurogastroenterology, especially in relation to projections of discomfort and pain to the digestive tract.

Do life events or depression exacerbate inflammatory bowel disease? A prospective study

OBJECTIVE

To determine whether depressed mood or life events are associated with an exacerbation of inflammatory bowel disease.

DESIGN

A prospective study of a consecutive sample of patients with relapsing inflammatory bowel disease, followed by monthly questionnaires and periodic office visits.

SETTING

A referral-based gastroenterology clinic at a medical school.

PATIENTS

A consecutive sample of 32 patients with inflammatory bowel disease who had had at least one relapse in a 2-year period after entry into the study.

MEASUREMENTS AND MAIN RESULTS

The Social Readjustment Rating Scale (measuring life events), the Beck Depression Inventory (a visual analog scale for depressed mood) and an inventory of intestinal symptoms were completed monthly by each subject with a 78% rate of compliance. A mean of 2.2 exacerbations was seen per subject during the study period. Life events were not temporally associated with changes in intestinal symptoms. Significant associations were found between intestinal symptoms and the two mood scales (P less than 0.05 for each), but no directionality in symptom occurrence could be detected in a time-lagged analysis. The results were similar when the months preceding exacerbations of inflammatory bowel disease were analyzed separately.

CONCLUSIONS

Although these findings suggest that mood changed concurrently with exacerbation of inflammatory bowel disease, no evidence indicated that stressful life events or depressed mood precipitated exacerbations in this study group.

Antidepressant therapy in 138 patients with irritable bowel syndrome: a five-year clinical experience

BACKGROUND

Antidepressant agents may have a therapeutic role in functional gastroenterologic disorders, but controlled investigations in irritable bowel syndrome (IBS) have not provided satisfactory practice recommendations. To help with future study design, we reviewed a five-year clinical experience with antidepressant agents in out-patients with IBS.

METHODS

Presenting features, treatment course, and clinical outcome were determined from a chart review of 138 patients attending a university-based gastroenterology practice.

RESULTS

Patients were treated with up to five antidepressants in separate, consecutive trials if a satisfactory end-point had not been reached. Tricyclic antidepressants were utilized 130 times, newer antidepressants 39 times, and anxiolytic-antidepressants 47 times. Improvement and complete remission in bowel symptoms occurred in 89% and 61% of patients, respectively, during antidepressant therapy. Median dosages being prescribed when remission occurred were less than those conventionally used in clinical psychiatry (50 mg/day for several tricyclic antidepressants). Age, gender, symptom duration, and presence of psychological symptoms did not discriminate those who remitted from those who did not, whereas a pain predominant symptom pattern was more commonly associated with symptom remission (P < 0.05 comparing symptom patterns). Symptom remission was more likely during the first antidepressant treatment than with subsequent trials in the group with continued symptoms (P = 0.01), but nearly half of the patients with side effects or no benefit from the first agent who went on to subsequent trials remitted during treatment with an alternative antidepressant.

CONCLUSIONS

The design of this retrospective review is not capable of determining the efficacy of antidepressants for IBS. Our observations in conjunction with other available data suggest that future trials should employ low daily dosages, carefully assess pain response, include patients with and without active psychiatric symptoms, and utilize a second agent for subjects intolerant or unresponsive to the first.

Intestinal apoproteins during fat absorption

To compare the roles of apolipoprotein (Apo) A-I, B, and E (or arginine-rich apoprotein, ARP) in the intracellular production of intestinal chylomicrons (and/or VLDL), these apoproteins were localized in rat intestinal mucosa by the light microscope method of indirect immunofluorescence. In addition, tissue levels of ApoA-I and ApoB were measured during fat absorption by radioimmunoassay. Antisera were produced using ApoA-I isolated from rat plasma high density lipoprotein, and ApoB and ARP from plasma VLDL by column chromatography. The apoproteins yielded single bands on polyacrylamide disc gel electrophoresis in urea and in sodium dodecyl sulfate. Anti-apoprotein antisera were produced in rabbits. These antisera appeared to be monospecific on double-antibody immunoprecipitation of 125I-labeled apoproteins. In fasted animals granular staining of ApoA-I was noted in the supranuclear (Golgi) regions of epithelial cells in the top third of the villus. At 30 min, when fat droplets were seen in the supranuclear cytoplasm of the cells along the top two-thirds of the villus, intense ApoA-I staining surrounded droplets in the cytoplasm. At later times when epithelial cells and lamina propria both contained fat droplets, bright ApoA-I stain surrounded many droplets in the supranuclear cytoplasm of cells and in the lamina propria. Over the same period of time, tissue levels of ApoA-I rose 10-fold. The distribution and time-course of ApoB staining was nearly identical with that of ApoA-I. Concomitantly, tissue ApoB levels doubled. By contrast, in fasting rat intestine, staining of ARP was sparse, punctate, and confined to the lower quarter of the villus. After fat feeding, stained droplets were seen only in the lamina propria near the base of the villus even though abundant ARP was found in cells along most of this length of the villus. Stain was never seen to surround any droplets inside cells. Thus, ApoA-I and ApoB appeared to participate in the intracellular assemply of lipoproteins in gut, whereas ARP did not, although ARP was found within mucosal cells. Liver and intestine differed in their stainable contents of ApoA-I and ARP. Whereas intestine stained heavily for ApoA-I and lightly for ARP, liver stained heavily for ARP and lightly for ApoA-I. Both organs stained for ApoB. These findings suggest that there may be some quantitative "specialization" of the two organs which secrete lipoproteins.

Effect of proteolytic enzymes on the binding of cobalamin to R protein and intrinsic factor. In vitro evidence that a failure to partially degrade R protein is responsible for cobalamin malabsorption in pancreatic insufficiency

Cobalamin (Cbl; vitamin B(12)) malabsorption in pancreatic insufficiency can be partially corrected by bicarbonate and completely corrected by pancreatic proteases but the mechanisms involved are unknown. Because saliva contains enough R-type Cbl-binding protein (R protein) to bind all of the dietary and biliary Cbl, it is possible that R protein acts as an inhibitor of Cbl absorption and that pancreatic proteases are required to alter R protein and prevent such inhibition. To test this hypothesis we studied the ability of R protein and intrinsic factor (IF) to compete for Cbl binding and ability of pancreatic proteases to alter this competition. Human salivary R protein bound Cbl with affinities that were 50- and 3-fold higher than those of human IF at pH 2 and 8, respectively. Cbl bound to IF was transferred to an equal amount of R protein with t((1/2))'s of 2 and 90 min at pH 2 and 8, respectively, and within several hours respective ratios of R protein-Cbl/IF-Cbl of 50 and 2 were observed. Cbl bound to R protein was not transferred to IF at either pH 2 or 8. Incubation of R protein with pancreatic proteases at pH 8 led to a 150-fold decrease in its affinity for Cbl. Incubation of R protein-Cbl with pancreatic proteases led to complete transfer of Cbl to IF within 10 min. Gel filtration studies with R protein-[(57)Co]Cbl and (125)I-R protein showed that pancreatic proteases partially degraded R protein. Pancreatic proteases differed in their ability to effect these changes with trypsin > chymotrypsin > elastase. Pancreatic proteases did not alter IF in any of the parameters mentioned above. Pepsin failed to alter either R protein or IF. THESE STUDIES SUGGEST THE FOLLOWING: (a) that Cbl is bound almost exclusively to R protein in the acid milieu of the stomach, rather than to IF as has been assumed previously; (b) that Cbl remains bound to R protein in the slightly alkaline environment of the intestine until pancreatic proteases partially degrade R protein and enable Cbl to become bound exclusively to IF; and (c) that the primary defect in Cbl absorption in pancreatic insufficiency is a lack of pancreatic proteases and a failure to alter R protein and effect the transfer of Cbl to IF. These studies also suggest that the partial correction of Cbl malabsorption observed with bicarbonate is due to neutralization of gastric HCl, since at slightly alkaline, pH IF can partially compete with R protein for the initial binding and retention of Cbl.

The possible role of pancreatic proteases in the turnover of intestinal brush border proteins

1. Intestinal brush border enzymes have heterogeneous rates of turnover, the largest proteins having the fastest turnover. Since the membrane faces the intestinal lumen, the effects of pancreatic factors were examined in mediating this turnover. Surgical subtotal pancreatectomy was used as an experimental model to study the turnover of brush border proteins in the absence of most pancreatic secretions. 2. Subtotal (95%) pancreatectomy of rats was found to cause elevations by about 50% of total activity and specific activities of certain brush border enzymes (maltase, sucrase, lactase), but not of others (alkaline phosphatase, trehalase). Rats were judged to be functionally deficient in pancreatic proteolytic enzymes (a) by demonstration of vitamin B-12 malabsorption, which was corrected by trypsin, and (b) by the finding of only about 20% of proteolytic activity appearing in the lumen after a test meal when compared to control. 3. To measure protein turnover in vivo the method of double labelling was used, where [3H]- and [14C]valine were administered intraduodenally in sequence 10 h apart. With this technique, a high 3H/14C ratio is correlated with rapid turnover. Proteins with apparent molecular weights of about 200 000-270 000 were found to turn over more rapidly than smaller proteins. 3H/14C ranged from 4.7 to 6.2 in animals without pancreatic insufficiency. In the face of decreased pancreatic proteolysis, the 3H/14C ratio was 2.3-3.1, similar to that of proteins with a slow half life. 4. Estimates of relative synthetic rates of large brush border proteins were lower than normal in pancreatectomized animals, but were constant over the period of the labelling experiment. The high enzyme levels in the face of lower synthetic rates confirms that, at the new steady rate, degradation rates must be slower for large brush border proteins in pancreatic insufficiency. 5. In vitro, using purified brush borders, unfractionated pancreatic enzymes were found to remove sucrase, maltase and lactase, but not alkaline phosphatase and trehalase. The enzyme most potent in this respect was the pancreatic protease, elastase. Non-proteolytic enzymes (amylase, lipase, phospholipase A) were inactive in removing enzyme from the brush border. The addition of elastase to pancreatectomized animals in vivo restored the rapid turnover rate of large brush border proteins. 6. A model is thus proposed for the normal catabolism of some large intestinal brush border proteins. It is suggested that the surface of intestinal absorptive cells is being constantly remodelled, and that certain surface enzymes are in part removed from the membrane by the action of pancreatic proteases. A possible special role for elastase is suggested.

Highly reliable genetic identification of individual northern hairy-nosed wombats from single remotely collected hairs: a feasible censusing method

The highly endangered northern hairy-nosed wombat (Lasiorhinus krefftii) is extremely difficult to study in the wild, and its numbers correspondingly difficult to estimate. Disturbance to the animals caused by trapping and radio-tracking may not only constitute an excessive risk to the population's viability, but may also yield biased data. The results of a pilot study are presented, which clearly show noninvasive genotyping to be a highly feasible and reliable alternative censusing method for L. krefftii. The protocol can identify individual wombats from single hairs collected remotely at burrow entrances, using: (i) a panel of microsatellite markers giving individual-specific genotypes; and (ii) a Y-linked sexing marker in combination with a single-copy X-linked amplification control. Using just the eight most variable microsatellites (of 20 available), only one in 200 pairs of full-sibs are predicted to share the same genotype. From 12 wombat hair samples collected on tape suspended over burrow entrances, three known female, two known male and an unknown wombat of each sex were identified. The approach will allow censusing of individuals that evade capture, and will also reveal some otherwise problematic aspects of the behaviour of this elusive animal.

Protein synthesis in intestinal mucosa: the effect of route of administration of precursor amino acids

All cells in the intestinal villus of the rat are capable of synthesizing protein from amino acid precursors (l-leucine). Moreover, polyribosomes from both crypts and villi are equally able to incorporate l-leucine into protein. Unlike other tissues, e.g. liver, there is no diurnal variation of protein synthesis in the intestine of the unfed rat, whether leucine is administered intraluminally or intravenously. The route of administration of precursor (l-leucine) is important in determining which part of the villus incorporates the label into protein. After intravenous administration, protein from cells near the villus-crypt junction is most heavily labeled, whereas after intraluminal administration protein from cells near the villus tip is most heavily labeled. The pattern of proteins most heavily labeled by radioactive precursor is different in the villus when compared with proteins from the crypt cells. Smaller molecular weight membrane-bound proteins are preferentially labeled in the crypt cells, whereas on the villus the pattern of labeling is more evenly distributed among the various proteins. Moreover, intraluminal leucine is utilized for protein synthesis to a greater extent than that in the blood, when the concentration in both compartments is similar. Thus, intraluminal and intravenous injections of labeled precursor are not equivalent. Both routes should be considered in data for experiments measuring intestinal protein synthesis.

The relation of ulcerative colitis to psychiatric factors: a review of findings and methods

The authors reviewed all known English-language literature on the association between psychiatric factors and ulcerative colitis to ascertain the evidence for such an association and evaluate the methods used in these studies. Most of the 138 studies contained serious flaws in research design, such as lack of control subjects, unspecified manner of data collection, and absence of diagnostic criteria. Analysis revealed that methodological flaws were significantly related to the finding of a positive association between psychiatric factors and ulcerative colitis. Seven studies represented solid systematic investigation, and all seven failed to find such an association.

Cloning of a complementary deoxyribonucleic acid encoding a portion of rat intestinal preapolipoprotein AIV messenger ribonucleic acid

Apolipoprotein AIV is one of the principal apolipoproteins synthesized by the rat small intestine. We have cloned a cDNA encoding a portion of preapolipoprotein AIV mRNA. A kinetically fractionated cDNA probe highly enriched for the abundant intestinal mucosal mRNA sequences was used to screen a library of recombinants containing cDNA generated from total intestinal epithelial mRNA. The abundant class of mRNA sequences was defined by hybridization analyses. This frequency class had an aggregate complexity of 5300 nucleotides and represented 25% of accumulated mRNA sequences.l The mRNAs comprising this class were identified by in vitro translation and included preapolipoprotein AIV, preproapolipoprotein AI, intestinal fatty acid binding protein, and liver fatty acid binding protein. A cDNA-containing clone derived from preapolipoprotein AIV mRNA was identified among probe-positive recombinants. This cDNA was used to establish that apolipoprotein AIV mRNA has a mass of 550000 daltons (equivalent to 1780 nucleotides) and represents 0.013% of total cellular RNA in the fasting state. Acute feeding with triglyceride-rich meals resulted in a 2-fold increase in preapolipoprotein AiV mRNA after 4 h.

A controlled study of the association between ulcerative colitis and psychiatric diagnoses

Fifty consecutive patients with ulcerative colitis were personally examined to determine the lifetime prevalence of specific psychiatric diagnoses. A personality assessment and a tabulation of recently occurring stressful events were done. A matched control sample with chronic nongastrointestinal medical illnesses was evaluated in the same way. The two groups were compared so as to quantify the relative association and impact of psychiatric disorder in ulcerative colitis. We found no greater frequency of diagnosable psychiatric disorder in ulcerative colitis patients than in the control population. Those with ulcerative colitis and a psychiatric illness did not appear to have more serious gastrointestinal involvement, nor did severity of the ulcerative colitis predict more frequent or more serious psychiatric disorder. Personality profiles were similar in probands and controls, and there was no correlation between the frequency of potentially stressful life events within the six months prior to interview and severity of ulcerative colitis at the time of interview. We did find slightly higher levels of obsessional symptomatology in ulcerative colitis cases, but this association appeared to be weak and unrelated to the severity of the gastrointestinal disorder. Despite the fact that more than a quarter of the ulcerative colitis patients had some diagnosable psychiatric illness, the occurrence of psychiatric disorder was rarely documented in the medical charts.

Effect of secreted Bacteroides proteases on human intestinal brush border hydrolases

Selected bacteroides species secreted various amounts of protease and glycosidase into their growth medium. Bacteroides vulgatus, distasonis, and ovatus secreted the most (31-60% of total). The secreted protease was similar in action to the protease within the organism, in that it had a broad pH optimum of 6-9, a K(m app.) for casein of 0.1 muM, and was inhibited by benzamidine, phenylmethylsulfonyl fluoride, diisopropylfluorophosphate (DIFP), and by an elastase inhibitor, Ac(Ala)(3)AlaCH(2)Cl. Exposure of human brush border preparations to the secreted protease reduced maltase and sucrase activities; the reduction could be prevented by DIFP. In contrast, brush border alkaline phosphatase activity either did not change or increased after exposure to bacterial secretions. >90% inhibition of secreted glycosidase using EDTA and p-chloromercuribenzoic acid did not prevent the reduction of brush border maltase and sucrase activity, suggesting that glucosidases were not likely to be involved in the destruction of brush border enzymes. Moreover, the bacterial proteases caused only a small net release of active maltase or sucrase from the brush border. Most of the loss of activity was due to destruction of the enzyme. Proximal bowel fluid of three patients with overgrowth contained DIFP-inhibitable protease that destroyed sucrase in isolated brush borders. A Bacteroides species was isolated from each sample that secreted protease and destroyed brush border sucrase. We conclude that in bacterial overgrowth syndromes, brush border damage may occur from protease(s) secreted by Bacteroides.

ERK and p38 MAP kinase pathways are mediators of intestinal epithelial wound-induced signal transduction

Repair of gastrointestinal epithelial injury involves cell migration, proliferation, and specific gene expression. The pathways responsible for epithelial wound signal transduction are poorly understood. Mechanical wounding of IEC-6 cell monolayers resulted in rapid activation of the extracellular signal-regulated kinase (ERK) and p38 MAP kinase pathways, while c-Jun amino-terminal protein kinases were not significantly activated. Two minutes after wounding cells at the wound edge strongly expressed cytoplasmic phospho-ERK. By five minutes, immunostaining was concentrated within the nucleus. Consistent with activated MAP kinase signaling cascades (which phosphorylate transcription factors implicated in immediate-early gene induction), monolayer wounding resulted in greater than 30- and 8-fold increases in c-Fos and early growth response-1 mRNA by Northern blot analysis, peaking at 20 minutes. Only slight increases in c-Jun mRNA were detected. Thus, intestinal epithelial wound signal transduction is, at least in part, mediated by activation of ERK and p38 MAP kinase signaling cascades. ERK and p38 pathways may regulate pathophysiologically relevant genes in wound repair by the induction of transcription factors.

The relation of size to the relative rates of degradation of intestinal brush border proteins

Proteins associated with intestinal brush borders and their various fractions were solubilized with sodium dodecyl sulfate and beta-mercaptoethanol, and separated by electrophoresis on acrylamide gels containing sodium dodecyl sulfate. Brush borders contain at least 15 proteins or subunits, ranging in molecular weight from 19,000 to 270,000. The largest proteins (170-270,000 mol wt), including the disaccharidases, are removed from the brush borders by papain. Proteins belonging to the remaining membrane, including alkaline phosphatase, have an intermediate size (53-140,000 mol wt). The proteins corresponding to the filamentous "core" of the microvilli are the smallest (19-45,000). The relative rates of degradation of these proteins were studied by following the rate of decline of (14)C-labeled leucine activity in specific proteins, and by the double isotope technique of Schimke in which leucine-(14)C was given to intact rats intraluminally 10 hr before an intraluminal dose of leucine-(3)H. Heterogeneity of (3)H/(14)C ratios and thus of rates of turnover of brush border proteins was noted. In general, the largest proteins (including the disaccharidases), were turning over the fastest. Other membrane proteins (i.e. alkaline phosphatase) had an intermediate rate of degradation, and "core" proteins turned over slowly. Thus, there was a general correlation between relative degradation rate and size.

Barostat testing of rectal sensation and compliance in humans: comparison of results across two centres and overall reproducibility

We assessed reproducibility of measurements of rectal compliance and sensation in health in studies conducted at two centres. We estimated samples size necessary to show clinically meaningful changes in future studies. We performed rectal barostat tests three times (day 1, day 1 after 4 h and 14-17 days later) in 34 healthy participants. We measured compliance and pressure thresholds for first sensation, urgency, discomfort and pain using ascending method of limits and symptom ratings for gas, urgency, discomfort and pain during four phasic distensions (12, 24, 36 and 48 mmHg) in random order. Results obtained at the two centres differed minimally. Reproducibility of sensory end points varies with type of sensation, pressure level and method of distension. Pressure threshold for pain and sensory ratings for non-painful sensations at 36 and 48 mmHg distension were most reproducible in the two centres. Sample size calculations suggested that crossover design is preferable in therapeutic trials: for each dose of medication tested, a sample of 21 should be sufficient to demonstrate 30% changes in all sensory thresholds and almost all sensory ratings. We conclude that reproducibility varies with sensation type, pressure level and distension method, but in a two-centre study, differences in observed results of sensation are minimal and pressure threshold for pain and sensory ratings at 36-48 mmHg of distension are reproducible.