Glycoprotein degradation in the blind loop syndrome: identification of glycosidases in jejunal contents

LanCL1 promotes motor neuron survival and extends the lifespan of amyotrophic lateral sclerosis mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons. Improving neuronal survival in ALS remains a significant challenge. Previously, we identified Lanthionine synthetase C-like protein 1 (LanCL1) as a neuronal antioxidant defense gene, the genetic deletion of which causes apoptotic neurodegeneration in the brain. Here, we report in vivo data using the transgenic SOD1^G93A mouse model of ALS indicating that CNS-specific expression of LanCL1 transgene extends lifespan, delays disease onset, decelerates symptomatic progression, and improves motor performance of SOD1^G93A mice. Conversely, CNS-specific deletion of LanCL1 leads to neurodegenerative phenotypes, including motor neuron loss, neuroinflammation, and oxidative damage. Analysis reveals that LanCL1 is a positive regulator of AKT activity, and LanCL1 overexpression restores the impaired AKT activity in ALS model mice. These findings indicate that LanCL1 regulates neuronal survival through an alternative mechanism, and suggest a new therapeutic target in ALS.

Clinical picture of hypolactasia and lactose intolerance

Selective adult-type hypolactasia, the main cause of primary malabsorption of lactose, shows considerable variation in terms of its symptoms, which mainly depend on the amount of milk consumption. The article discusses congenital lactase deficiency and familial lactose intolerance. Links between hypolactasia and non-specific abdominal complaints, coronary heart disease and cataract are presented. The decrease in lactase activity in the brush border of jejunal mucosa, associated with diseases of the mucosa or any other condition which damages the enterocytes, is discussed as a cause of secondary hypolactasia. It is shown that adult-type primary hypolactasia and selective lactose malabsorption represent a major problem in the everyday work of general practitioners, particularly in populations where hypolactasia is common. Therefore, the examination and treatment of non-selected patients with vague abdominal complaints is important in primary health care. As the need for calcium in humans is largely met by the intake of milk, the consumption of milk has to be in amounts that are tolerable for the individual.

Differences in blood group B-specific mucinase activity between virulent and avirulent Shigella flexneri 2a strains

Based on our previous findings we postulate that the production of blood group B-degrading mucinase by Shigella flexneri 2a is related to virulence. The virulent S. flexneri 2a strain M4243 produced a blood group B mucinase which decreased the blood group B reactivity of germ-free mouse mucins by a factor of 16 and the B reactivity of human saliva by a factor of 32. Avirulent S. flexneri 2a B-1, serologically similar, but not genetically identical to the M4243 strain, failed to degrade the blood group reactivity. The mucin-degrading ability of S. flexneri 2a M4243 harboring a large virulence-conferring 140 MDa plasmid was then compared with a genetically similar large plasmid-free avirulent S. flexneri 2a M4243A1. Virulent S. flexneri M4243 grew in human salivary mucins while the genetically identical avirulent M4243A1 did not. Supernatant of virulent M4243 culture decreased the blood B reactivity of salivary mucins by a factor of 32 while the avirulent M4243a1 had no effect. Eleven of 12 colonies of the transconjugant hybrid Escherichia coli K12 (7300-1-5) containing the shigella PWR 110 plasmid and chromosomal markers decreased the blood group B reactivity by a factor of 4-32, and two of four colonies of the E. coli strain 7262 containing only the plasmid reduced the B reactivity by a factor of 4-16. These findings suggest that blood group B-specific mucinase production may be related to S. flexneri virulence.

Response of the jejunal mucosa of dogs with aerobic and anaerobic bacterial overgrowth to antibiotic therapy

Dogs with naturally occurring aerobic or anaerobic bacterial overgrowth have been examined before and after antibiotic therapy in order to assess reversibility of damage to the jejunal mucosa. Histological changes in peroral jejunal biopsies were relatively minor before and after treatment, but sucrose density gradient centrifugation revealed specific biochemical abnormalities that responded to antibiotic therapy. Aerobic overgrowth was initially associated with a marked loss of the main brush border component of alkaline phosphatase activity; this recovered following treatment, suggesting that aerobic bacteria may cause reversible damage to the hydrophobic region of the brush border membrane. In contrast, anaerobic overgrowth was initially associated with a marked reduction in brush border density, indicative of a considerable fall in the glycoprotein-to-lipid ratio of the membrane. Density increased from 1.17 to 1.21 g/ml after antibiotic therapy, consistent with recovery from this relatively severe damage to the brush border caused by anaerobic bacteria. Reductions in soluble and peroxisomal catalase activities which could compromise mucosal protection against free radicals in dogs with aerobic overgrowth, and a loss of particulate malate dehydrogenase activity indicative of mitochondrial disruption in dogs with anaerobic overgrowth, were also reversed after treatment. These findings indicate that aerobic and anaerobic bacterial overgrowth can result in contrasting but potentially reversible damage to the jejunal mucosa which would not be detected by conventional investigative procedures.

Comparison of the biochemical changes in the jejunal mucosa of dogs with aerobic and anaerobic bacterial overgrowth

Subcellular biochemical changes in the jejunal mucosa have been compared in dogs with either aerobic or anaerobic bacterial overgrowth to explore relationships between composition of the flora and mucosal damage. Affected animals comprised 17 German shepherd dogs with chronic diarrhea or weight loss, or both. Analysis of duodenal juice demonstrated aerobic overgrowth in 10 cases, most frequently comprising enterococci and Escherichia coli, and obligate anaerobic overgrowth in 7 cases, most frequently including Clostridia spp. Histologic changes were minimal; however, examination of peroral jejunal biopsy specimens by sucrose density gradient centrifugation revealed specific biochemical abnormalities. In the dogs with aerobic overgrowth, there was a selective loss of brush border alkaline phosphatase activity, and gamma-glutamyl transferase activity was increased, whereas activities of disaccharidases and aminopeptidase N were unaltered. In contrast, anaerobic overgrowth was associated with a reduction in brush border density, indicative of a considerable fall in the glycoprotein-to-lipid ratio of the brush border membrane, whereas brush border enzyme activities were unaltered. There was a loss of peroxisomal catalase activity in dogs with aerobic overgrowth, and an indication of mitochondrial disruption in dogs with anaerobic overgrowth, but little evidence for damage to other subcellular organelles. These findings demonstrate that aerobic and anaerobic overgrowth may be associated with distinct but different mucosal abnormalities particularly affecting the brush border membrane.

Intestinal microbial flora after feeding phytohemagglutinin lectins (Phaseolus vulgaris) to rats

Incorporation of purified phytohemagglutinin (PHA) lectins derived from red kidney beans (Phaseolus vulgaris) in the diet of weanling rats will cause growth failure, malabsorption of nutrients, and bacterial overgrowth in the small intestine. These effects are not caused by feeding a similar quantity of PHA to germfree rats. To define the morphological and bacterial changes on the mucosal surfaces of the jejunum, ileum, and cecum in greater detail, we pair fed two groups of weanling rats isocaloric, isonitrogenous diets with or without 0.5% PHA protein. On the jejunal surfaces of control rats, the mucous layer was a confluent covering with sparsely scattered bacteria and protozoa. In PHA-treated rats, the mucous layer was thin and discontinuous, and the microvillous surface of the tissue was extensively populated by bacterial cells of two distinct morphotypes--a gram-negative rod and a gram-positive coccobacillus. In all PHA-treated animals, these bacteria formed adherent monospecific or mixed adherent microcolonies on the tissue surface. Tissue damage was observed in PHA-exposed jejunal tissue as evidenced by vesiculation of the microvillous plasma membrane and by damage to the brush border membrane. On the ileal surfaces of control rats, there was a thick mucous layer within which small numbers of bacteria and protozoa were seen. Segmented filamentous bacteria were anchored in the tissue surface. In PHA-treated rats, the ileal surface was only incompletely covered by a mucous layer, and the overlying mucosal surface was extensively covered by large numbers of protozoan cells (predominantly Hexamita muris). Most of the ileal surfaces not covered by the mucous layer were occupied and virtually occluded by an overgrowth of these protozoan cells with occasional cells of Giardia muris and the tissue-associated segmented bacillus. In the ceca of control rats, the mucosa was incompletely covered by a discontinuous mucous layer and colonized by an unnamed Spirillum sp., other bacteria, and occasional protozoa. The cecal surfaces of PHA-treated rats retained most of their incomplete overlying mucous layer, which was heavily colonized by the same type of Spirillum sp. seen in untreated animals; intestinal crypts were colonized. These descriptive morphological studies demonstrate that exposure to purified PHA in the diet caused characteristic changes in the microbial ecology of the small intestine. The changes in microbial flora contributed to the malabsorption of nutrients in the small intestines of PHA-fed animals.

Mucin degradation in human colon ecosystems. Isolation and properties of fecal strains that degrade ABH blood group antigens and oligosaccharides from mucin glycoproteins

We previously reported that the oligosaccharide chains of hog gastric mucin were degraded by unidentified subpopulations numbering approximately 1% of normal human fecal bacteria. Here we report on the enzyme-producing properties of five strains of mucin oligosaccharide chain-degrading bacteria isolated from feces of four healthy subjects. Four were isolated from the greatest fecal dilutions yielding mucin side chain-degrading activity in culture, and thus were the numerically dominant side chain-degrading bacteria in their respective hosts. Three were Ruminococcus strains and two were Bifidobacterium strains. Two Ruminococcus torques strains, IX-70 and VIII-239, produced blood group A- and H-degrading alpha-glycosidase activities, sialidase, and the requisite beta-glycosidases; these strains released greater than 90% of the anthrone-reacting hexoses from hog gastric mucin during growth in culture. The Bifidobacterium strains lacked A-degrading activity but were otherwise similar; these released 60-80% of the anthrone-reacting hexoses but not the A antigenic structures from hog gastric mucin. Only Ruminococcus AB strain VI-268 produced blood group B-degrading alpha-galactosidase activity, but this strain lacked beta-N-acetylhexosaminidases to complete degradation of B antigenic chains. When this strain was co-cultured with a strain that produced beta-N-acetylhexosaminidases, release of hexoses from blood group B salivary glycoprotein increased from 50 to greater than 90%, and bacterial growth was enhanced. The glycosidases required for side chain degradation were produced by these strains in the absence of mucin substrate, and a substantial fraction of each activity in stationary phase cultures was extracellular. In contrast, none of 16 other fecal Bacteroides, Escherichia coli, Streptococcus faecalis, and Bifidobacterium strains produced ABH blood group-degrading enzymes; other glycosidases produced by these strains were predominantly cell bound except for extracellular beta-N-acetylhexosaminidases produced by the five S. faecalis strains. We conclude that certain Bifidobacterium and Ruminococcus strains are numerically dominant populations degrading mucin oligosaccharides in the human colon due to their constitutive production of the requisite extracellular glycosidases including blood group antigen-specific alpha-glycosidases. These properties characterize them as a functionally distinct subpopulation of normal human enteric microflora comprised of specialized subsets that produce blood group H antigen-degrading glycosidases alone or together with either blood group A- or B-degrading glycosidases.

Bacterial overgrowth

Different aspects of bacterial overgrowth in the small intestine are reviewed. The pathophysiological mechanisms involving both bacterial metabolism of dietary components and secretions and effects on the mucosal cells are discussed in more detail. The current therapy, surgical, medical and supportive, is outlined.

Small-bowel bacterial overgrowth in the postgastrectomy syndrome

Jejunal flora, bile acid deconjugation, and breath hydrogen (H2) and methane (CH4) excretion were studied in 22 Billroth II (BII)-operated patients with chronic postprandial symptoms, dumping (9), vomiting (7), pain (10), and diarrhoea (14). Sixteen were below 90% of desirable weight. Two control groups were included, one comprising 5 symptom-free, BII-operated volunteers and another comprising 12 healthy, unoperated volunteers. The numbers of bacteria recovered from jejunal secretions in the postgastrectomy patients did not differ significantly from those recovered in the symptom-free BII-operated controls but were significantly lower in the unoperated controls. Production of fermentation gas in anaerobic media supplemented with carbohydrates occurred in 17 of 22 postgastrectomy patients and in 4 of 5 BII-operated controls but in none of the unoperated controls. Bacterial bile acid deconjugating activity did not differ significantly between the postgastrectomy patients and the BII-operated controls but was significantly lower in the unoperated controls. Breath H2 excretion after glucose ingestion was significantly higher in the postgastrectomy patients than in both the BII-operated and the unoperated controls. The addition of pectin or guar gum to the glucose meal largely prevented postprandial symptoms and breath hydrogen excretion. Six out of 12 postgastrectomy patients treated with metronidazole recorded symptomatic effects, mainly on diarrhoea. Our findings indicate that jejunal bacterial overgrowth may be a major cause of the symptoms in some postgastrectomy patients. The tests available for demonstration of small-bowel bacterial overgrowth, perhaps with the exception of the glucose H2 breath test, did not differentiate satisfactorily between symptom-producing and non-symptom-producing abnormal jejunal flora. Thus these tests may seem to have a limited practical diagnostic value in such patients.

Bacterial overgrowth in jejunal and ileal disease

The number of bacteria recovered in anaerobic cultures of jejunal secretions was significantly higher in a group of 10 patients with jejunal disease and stagnation of gut content in the proximal small bowel than in a group of 10 patients with similar conditions in the distal ileum. Some overlap in bacterial numbers occurred between patients with jejunal disease, ileal disease, and healthy controls, whereas production of fermentation gas in anaerobic media supplemented with glucose occurred only in cultures from the patients with jejunal disease. The 14C-glycocholic acid test showed increased output of breath 14CO2 in both patient groups, whereas faecal 14C was significantly increased only in patients with ileal disease. Increased breath hydrogen excretion after glucose ingestion was recorded in 8 of 10 patients with jejunal disease only. Breath methane excretion, previously found in 44% of healthy subjects, was absent in all of 28 patients with Crohn's disease of the small, indicating that these patients have a gut flora that is different from that of the healthy population.

Degradation of intestinal glycoproteins by pathogenic Shigella flexneri

Intestinal mucin glycoproteins were examined for their ability to sustain growth of pathogenic shigella. Inoculation of germfree cecal mucin glycoproteins with Shigella flexneri 4b resulted at 48 h in a 940-fold increase in the enteropathogen concentration. Investigation in vitro of enzymatic degradation by the pathogen led to the identification of a blood group B-degrading glycosidase produced by the bacteria. In in vivo experiments, fecal supernatants of mice monocontaminated with S. flexneri 4b contained an alpha-galactosidase active against the p-nitrophenyl-glycoside. This fecal alpha-galactosidase peaked 5 days after shigella contamination, showing 2.8 +/- 1.4 mU of enzyme activity per mg of protein. Contaminated fecal supernatants similarly destroyed the blood group B reactivity of cecal mucin glycoproteins. These data suggested that S. flexneri 4b could proliferate within ileocolonic environment by enzymatically degrading mucin glycoprotein sugars.