W. E. W. Roediger

Reducing sulfur compounds of the colon impair colonocyte nutrition: Implications for ulcerative colitis

BACKGROUND Mercaptides (sodium hydrogen sulfide and sodium methanethiol) and mercapto-fatty acid (sodium mercaptoacetate) are reducing agents that help to maintain anaerobic conditions in the colonic lumen. The metabolic effect of these agents on n-butyrate and glucose oxidation in human colonocytes is unknown. METHODS Isolated human colonocytes were prepared from 31 colectomy specimens, and generation of oxidative metabolites from [1-14C]n-butyrate and [6-14C]glucose was measured in the presence and absence of reducing agents. Injury to cells was judged by diminished production of metabolites. RESULTS The injurious action of mercaptides at all sites of the colon was of the order of sodium hydrogen sulfide > methanethiol > mercaptoacetate. Significant inhibition of n-butyrate (< 0.005) but not glucose oxidation was observed with sodium hydrogen sulfide in the ascending colon, splenic flexure, and rectosigmoid region. Hydrogen sulfide more significantly inhibited fatty acid oxidation in the rectosigmoid than in the ascending colon (P < 0.02). CONCLUSIONS Metabolic effects of sodium hydrogen sulfide on butyrate oxidation along the length of the colon closely mirror metabolic abnormalities observed in active ulcerative colitis, and the increased production of sulfide in ulcerative colitis suggests that the action of mercaptides may be involved in the genesis of ulcerative colitis.

Colonic Sulfide in Pathogenesis and Treatment of Ulcerative Colitis

A role for colonic sulfide in the pathogenesisand treatment of ulcerative colitis (UC) has emergedbased on biochemical, microbiological, nutritional,toxicological, epidemiological, and therapeuticevidence. Metabolism of isolated colonic epithelial cellshas indicated that the bacterial short-chain fatty acidn-butyrate maintains the epithelial barrier and thatsulfides can inhibit oxidation of n-butyrate analogous to that observed in active UC. Sulfurfor fermentation in the colon is essential forn-butyrate formation and sulfidogenesis aids disposal ofcolonic hydrogen produced by bacteria. The numbers of sulfate-reducing bacteria and sulfidogenesisis greater in UC than control cases. Sulfide is mainlydetoxified by methylation in colonic epithelial cellsand circulating red blood cells. The enzyme activity of sulfide methylation is higher in red bloodcells of UC patients than control cases. Patients withUC ingest more protein and thereby sulfur amino acidsthan control subjects. Removing foods rich in sulfur amino acids (milk, eggs, cheese) has proventherapeutic benefits in UC. 5-Amino salicylic acidreduces fermentative production of hydrogen sulfide bycolonic bacteria, and aminoglycosides, which inhibit sulfate-reducing bacteria, are of therapeuticbenefit in active UC. Methyl-donating agents are acategory of drugs of potential therapeutic use in UC. Acorrelation between sulfide production and mucosal immune responses in UC needs to be undertaken.Control of sulfidogenesis and sulfide detoxification maybe important in the disease process of UC, althoughwhether their roles is in an initiating or promoting capacity has yet to be determined.

The starved colon—Diminished mucosal nutrition, diminished absorption, and colitis

Nutrition of colonic epithelial cells is mainly from short chain fatty acids (SCFAs) produced by bacterial fermentation in the colonic lumen. n-Butyrate contributes more carbon of oxidation to epithelial cells than glucose or glutamine from the vasculature. Incomplete starvation of colonic epithelial cells through lack of luminal SCFAs leads, in the short term, to mucosal hypoplasia with either diminished absorption or diarrhea. A chronic lack of SCFAs or complete organ starvation in conjunction with other factors leads to nutritional colitis, either “diversion colitis” or “starvation colitis”. Whether predominantly diarrhea or colitis develops in mucosal malnutrition appears to depend upon the severity and duration of starvation. Ulcerative colitis may be classified as a nutritional colitis in that colonic epithelial cells are unable to utilize SCFAs reflecting epithelial starvation despite abundant SCFAs.

SULFIDES IMPAIR SHORT CHAIN FATTY ACID BETA -OXIDATION AT ACYL-COA DEHYDROGENASE LEVEL IN COLONOCYTES : IMPLICATIONS FOR ULCERATIVE COLITIS

The disease process of ulcerative colitis (UC) is associated with a block in β-oxidation of short chain fatty acid in colonic epithelial cells which can be reproduced by exposure of cells to sulfides. The aim of the current work was to assess the level in the β-oxidation pathway at which sulfides might be inhibitory in human colonocytes. Isolated human colonocytes from cases without colitis (n = 12) were exposed to sulfide (1.5 mM) in the presence or absence of exogenous CoA and ATP. Short chain acyl-CoA esters were measured by a high performance liquid chromatographic assay. 14CO2 generation was measured from [1-14C]butyrate and [6-14C]glucose. 14CO2 from butyrate was significantly reduced (p < 0.001) by sulfide. When colonocytes were incubated with hydrogen sulfide in the presence of CoA and ATP, butyryl-CoA concentration was increased (p < 0.01), while crotonyl-CoA (p < 0.01) and acetyl-CoA (p < 0.01) concentrations were decreased. These results show that sulfides inhibit short chain acyl-CoA dehydrogenase. As oxidation of n-butyrate governs the epithelial barrier function of colonocytes the functional activity of short chain acyl-CoA dehydrogenase may be critical in maintaining colonic mucosal integrity. Maintaining the functional activity of dehydrogenases could be an important determinant in the expression of ulcerative colitis.

Human colonocyte detoxification

Detoxification or biotransformation of drugs and xenobiotics are usually linked with liver metabolism, yet colonocytes of the gastrointestinal tract have an equal capacity to mediate these processes.1 2 This brief overview specifically discusses the ability of human colonocytes, but not other tissues, to detoxify chemical agents and relates pertinent findings to ulcerative colitis and some aspects of colon cancer. Failure to detoxify, leading to epithelial cell damage, or an exaggerated capacity to biotransform, leading to carcinogen formation in colonocytes, have been the main implications in disease processes. In general, two categories of detoxification processes are recognised (table 1)3 4: phase I reactions concern oxidation, reduction and hydrolysis within the cytosol, and phase 2 reactions require ATP and concern conjugation with a donor substrate synthesised in the cell. Both reactions need enzymes such as oxidoreductases, hydrolases, transferases, and lyases. Amongst these may be subclasses, genetic polymorphism and variability of enzyme activity in organs and along the gastrointestinal tract. Particularly, differences in enzyme activity in the proximal and distal colon may occur.5 6 View this table: Table 1 Detoxification and biotransformation reactions found in human colonocytes Biochemists, pharmacologists, toxicologists, molecular biologists, geneticists, oncologists, and gastroenterologists are involved in this field of study, from each of which information is now drawn together. Many new toxicological advances made with liver and lung tissues still have to be applied to colonocytes and would be a fruitful area of future research. The subject of clinical gastrointestinal toxicology7 makes it possible to bridge a gap between colonic disease, genetics and the ability to detect initiating or promoting factors in ulcerative colitis and colon cancer. Cytochrome P-450 are a superfamily of haem containing mono-oxygenases8 acting in the metabolism of foreign compounds, as well as synthesis of steroids and bile components. The P-450 superfamily of enzymes is …

Nitrite from inflammatory cells—A cancer risk factor in ulcerative colitis?

Elevated levels of luminal nitrite and a lowered luminal pH were found in 77 percent of patients with acute ulcerative colitis. No luminal nitrite was found in healthy control subjects. Nitrites are a secretory product of activated macrophages and neutrophils of the lamina propria, whereas the lowered luminal pH is due to diminished bicarbonate formation by impaired colonocytes. A hypothesis is put forward that nitrites, lowered pH, and bacterial amines are conducive to formation of carcinogenic n-nitroso compounds, which reflect a cancer risk in patients with ulcerative colitis dependent on the type and extent of inflammatory cell activation as well as metabolic impairment of colonic epithelial cells.

Colonic Luminal Hydrogen Sulfide Is Not Elevated in Ulcerative Colitis

It has been proposed that the reduction inn-butyrate oxidation by colonic epithelial cellsobserved in ulcerative colitis may be related toexposure to reduced forms of sulfur derived fromdissimilatory sulfate reduction by luminal microflora. Thisstudy aims to compare stool sulfide concentrations incontrol and colitic subjects. Control subjects hadsignificant colorectal disease excluded by virtue of their selection. Patients with ulcerativecolitis were stratified by disease extent and activity,and by salicylate drug use. Stool sulfide was measuredusing a direct spectrophotometric method on NaOH (free sulfide) and zinc acetate (total sulfide)stool slurries. Fifteen control and 19 colitic subjectswere studied. There was no significant difference instool sulfide between control and colitic patients (free sulfide, control =0.52 (0.17), colitic0.45 (0.10), t = 0.36, P = 0.71, total sulfide, control1.33 (0.21), colitic 0.96 (0.15), t = 1.44, P = 0.16).Disease extent or activity did not significantlyinfluence stool sulfide. These results do not support aprimary etiologic role for luminal sulfide in ulcerativecolitis.

Nitric oxide effect on coloncyte metabolism: Co-action of sulfides and peroxide

Luminal levels of nitric oxide/nitrite are high in colitis. Whether nitric oxide is injurious or protective to human colonocytes is unknown and the role of nitric oxide in the genesis of colitis unclear. The aims were to establish whether nitric oxide was injurious to oxidation of substrates (n-butyrate and D-glucose) in isolated human and rat colonocytes both alone and in the presence of hydrogen sulfide and hydrogen peroxide, agents implicated in cell damage of colitis. Nitric oxide generation from S-nitrosoglutathione was measured by nitrite appearance. Colonocytes were isolated and incubated with [1-14C] butyrate or [6-14C] glucose and 2.6 μM nitric oxide, 1.5 mM sodium hydrogen sulfide or 2.5 mM hydrogen peroxide. Acyl-CoA esters were measured by high performance liquid chromatography, 14CO2 radiochemically and lactate/ketones by enzymic methods. Results indicate that nitric oxide very significantly (p < .001) reduced acyl-CoA formation but did not impair 14CO2 generation. Peroxide and sulfide with nitric oxide resulted in significant reduction (p < 0.01) of substrate oxidation to CO2. Sulfide significantly stimulated release of nitric oxide from S-nitrosoglutathione. The principal conclusion is that nitric oxide diminishes CoA metabolism in colonocytes. CoA depletion has been observed in chronic human colitis for which a biochemical explanation has been lacking. For acute injurious action in human colonocytes nitric oxide requires co-action of peroxide and sulfide to impair oxidation of substrates in cells. From current observations treatment of colitis should aim to reduce simultaneously nitric oxide, peroxide and sulfide generation in the colon.

Effect of sulphide on short chain acyl-CoA metabolism in rat colonocytes.

BACKGROUND: It has been proposed that the diminished n-butyrate oxidation observed in ulcerative colitis may be the result of sulphide induced inhibition of short chain acyl-coenzyme A (acyl-CoA) dehydrogenase activity. AIM: To examine the acyl-CoA ester profiles in isolated rat colonic epithelial cells treated in vitro with sodium hydrogen sulphide (NaHS). METHODS: Isolated rat colonic epithelial cell suspensions were incubated for 10 minutes in the presence of [1-14C] n-butyrate (5 mM), with and without NaHS (1.5 mM). Incubations were carried out both in the presence and the absence of exogenous CoA and ATP. Metabolic performance was assessed by 14CO2 production and by acyl-CoA ester production measured by HPLC with ultraviolet detection. RESULTS: Results are given as mean (SEM). For colonocytes incubated in the presence of exogenous CoA and ATP, treatment with NaHS significantly diminished 14CO2 production (control 0.97 (0.06) mumol/g dry weight cells/min, treated 0.26 (0.09) mumol/g dry weight cells/min, p = 0.0019), was associated with an increase in butyryl-CoA concentrations in the final reaction mixture at 10 minutes (control 2.55 (0.28) mumol/g dry weight cells, treated 3.32 (0.32) mumol/g dry weight cells, p = 0.002), and a reduction in crotonyl-CoA concentrations (control 0.274 (0.02) mumol/g dry weight cells, treated 0.120 (0.04) mumol/g dry weight cells, p = 0.008). The mean concentration of acetyl-CoA in the reaction mixture at 10 minutes was not significantly different between control and sulphide treated incubations. There were no significant differences in acyl-CoA ester profiles observed when cells were incubated in the absence of exogenous CoA and ATP. CONCLUSIONS: These results support the view that sulphides inhibit n-butyrate oxidation in colonic epithelial cells by inhibiting short chain acyl dehydrogenation of activated fatty acids.

Methionine derivatives diminish sulphide damage to colonocytes--implications for ulcerative colitis.

BACKGROUND: Bacterial production of anionic sulphide is increased in the colon of ulcerative colitis and sulphides can cause metabolic damage to colonocytes. AIMS: To assess the reversal of the damaging effect of sulphide to isolated colonocytes by methionine and methionine derivatives. METHODS AND SUBJECTS: Isolated colonocytes were prepared from rat colons and 12 human colectomy specimens. In cell suspensions 14CO2/acetoacetate generation was measured from [1-14C]-butyrate (5.0 mmol/l) in the presence of 0-2.0 mmol/l sodium hydrogen sulphide. The effect of 5.0 mmol/l L-methionine, S-adenosylmethionine 1,4 butane disulphonate and DL-methionine-S-methylsulphonium chloride on sulphide inhibited oxidation was observed. RESULTS: In rat colonocytes sodium hydrogen sulphide dose dependently reduced oxidative metabolite formation from n-butyrate, an action reversed in order of efficacy by S-adenosylmethionine 1,4 butane disulphonate > DLmethionine-S-methyl-sulphonium chloride > L-methionine. In human colonocytes S-adenosylmethionine 1,4 butane disulphonate most significantly improved 14CO2 production (p = < 0.005) suppressed by sodium hydrogen sulphide. CONCLUSION: Sulphide toxicity in colonocytes is reversible by methyl donors. The efficiency of sulphide detoxification may be an important factor in the pathogenesis and treatment of ulcerative colitis for which S-adenosylmethionine 1,4 butane disulphonate may be of therapeutic value.