Stimulation of butyrate absorption in the human rectum in vivo

Intraperitoneal administration of butyrate prevents the severity of acetic acid colitis in rats

Intrarectal infusion of butyrate improves colorectal disorders including ulcerative colitis (UC). However, it is not established whether systemically administered butyrate benefits such patients. The current study aimed at exploring and comparing the potential of intraperitoneally, intrarectally, and orally administered butyrate against acetic acid (AA)-induced UC in rats. Intrarectal administration of 2 ml of 50% AA was done after or without prior treatment of rats for 7 consecutive days with 100 mg/kg sodium butyrate (SB) intraperitoneally, intrarectally, or orally. Rats were sacrificed after 48 h of AA-treatment. Subsequently, colon sections were processed routinely for histopathological examination. We clinically observed diarrhea, loose stools, and hemoccult-positive stools, and histologically, epithelial loss and ulceration, crypt damage, goblet cell depletion, hemorrhage, and mucosal infiltration of inflammatory cells. The changes were significantly reduced by intraperitoneal, intrarectal, or oral butyrate, with intraperitoneal butyrate exhibiting the highest potency. It is concluded that intraperitoneal administration of butyrate abrogates the lesions of AA-induced UC and its potency surpasses that of intrarectal or oral butyrate.

Estimation and interpretation of fermentation in the gut: coupling results from a 24 h batch in vitro system with fecal measurements from a human intervention feeding study using fructo-oligosaccharides, inulin, gum acacia, and pea fiber

Gut bacteria ferment fiber at different rates to primarily short chain fatty acids (SCFA) and gas while proteins are metabolized to SCFA, branched chain fatty acids (BCFA), gas, and undesirable metabolites. Large volumes of gas produced in vivo may contribute to bloating and flatulence in an individual. The objectives of this trial were to (1) compare the in vitro fermentation profiles of fructo-oligosaccharides (FOS), inulin, gum acacia, and pea fiber alone or blended using a 24 h batch model and (2) relate these findings to a human study that fed enteral formula fortified with fiber blend (FB) or no fiber (FF). The in vitro fermentation of the fiber blend resulted in a delayed pH decrease and gas and SCFA production compared to the FOS and inulin. Human samples had higher SCFA on FB compared to FF (p = 0.029). BCFA were not different between formulas. By using a blend of fibers, we observed a slower fermentation in vitro but still increased fecal SCFA when fed to human subjects.

Dietary sodium gluconate protects rats from large bowel cancer by stimulating butyrate production

Butyrate has an antitumorigenic effect on colorectal cancer cell lines. Dietary sodium gluconate (GNA) promotes butyrate production in the large intestine. Accordingly, we examined the effect of dietary GNA on tumorigenesis in the large intestine in rats. Male Fisher-344 rats (n = 32) were divided into 4 groups: 2 diets (with or without 50 g GNA/kg basal diet) x 2 treatments (with or without carcinogen administration). Colonic tumors were induced by 3 intraperitoneal injections of azoxymethane (15 mg/kg body wt, 1 time/wk) and dietary deoxycholic acid (2 g/kg basal diet). The experiment was conducted for 33 wk except for a few rats. Ingestion of GNA increased cecal butyrate concentration at the end of experiment (P < 0.01). No tumor development occurred in the untreated groups. Ingestion of GNA decreased the incidence of tumors in rats administered the carcinogen (37.5 vs. 100%, P < 0.05). Ingestion of GNA also decreased the mean number of tumors per rat (0.5 +/- 0.8 vs. 2.8 +/- 1.5, P < 0.01). beta-Catenin accumulation and TdT-mediated dUTP nick end labeling (TUNEL) positive cells in tumors were histochemically examined. The results of this study suggested that the antitumorigenic effect of GNA may involve the stimulation of apoptosis through enhanced butyrate production in the large intestine.

Relationships between fecal consistency and colonic microstructure and absorptive function in dogs with and without nonspecific dietary sensitivity

OBJECTIVE

To determine relationships between fecal consistency and colonic microstructure and absorptive function in dogs with and without nonspecific dietary sensitivity.

ANIMALS

12 dogs with nonspecific dietary sensitivity (affected) and 9 healthy dogs (controls).

PROCEDURE

Affected dogs were fed 4 test diets and control dogs, 3 diets for 4 weeks each in a crossover design. Fecal consistency was assessed daily. At the end of each feeding period, electrolyte and water transport were assessed, and colonic biopsy specimens were obtained for histologic examination and measurement of crypt water uptake by use of confocal microscopy.

RESULTS

Feces were consistently looser in affected dogs. In control dogs, we detected net colonic absorption of sodium and chloride and secretion of potassium and bicarbonate. Absorption of sodium and chloride was less in affected dogs, compared with controls, indicating that electrolyte transport was disrupted in affected dogs. This disruption was accentuated during feeding of diets associated with significantly poorer fecal consistency (ie, loose feces). Fecal consistency was inversely correlated with crypt water absorption, which was reduced in affected dogs. Colonic crypts were shorter and less dense in affected dogs fed diets associated with poor fecal consistency, compared with affected dogs fed other diets or with control dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Colonic transport function is a major determinant of fecal consistency in dogs. Dogs with nonspecific dietary sensitivity are particularly susceptible to diet-induced changes in absorptive function. Such changes are associated with damage to colonic microstructure, disrupted electrolyte transport, and failure to dehydrate luminal contents.

Mechanism of n-butyrate uptake in the human proximal colonic basolateral membranes

Current studies were undertaken to characterize the mechanism of short-chain fatty acid (SCFA) transport in isolated human proximal colonic basolateral membrane vesicles (BLMV) utilizing a rapid-filtration n-[(14)C]butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO(3)(-)/SCFA exchanger in these membranes, are summarized as follows: 1) n-[(14)C]butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO(3)(-) and an inwardly directed pH gradient; 2) n-[(14)C]butyrate uptake was markedly inhibited (approximately 40%) by anion exchange inhibitor niflumic acid (1 mM), but SITS and DIDS (5 mM) had no effect; 3) structural analogs e.g., acetate and propionate, significantly inhibited uptake of HCO(3)(-) and pH-gradient-driven n-[(14)C]butyrate; 4) n-[(14)C]butyrate uptake was saturable with a K(m) for butyrate of 17.5 +/- 4.5 mM and a V(max) of 20.9 +/- 1.2 nmol x mg protein(-1) x 5 s(-1); 5) n-[(14)C]butyrate influx into the vesicles demonstrated a transstimulation phenomenon; and 6) intravesicular or extravesicular Cl(-) did not alter the anion-stimulated n-[(14)C]butyrate uptake. Our results indicate the presence of a carrier-mediated HCO(3)(-)/SCFA exchanger on the human colonic basolateral membrane, which appears to be distinct from the previously described anion exchangers in the membranes of colonic epithelia.

In vivo absorption of medium-chain fatty acids by the rat colon exceeds that of short-chain fatty acids

BACKGROUND AND AIMS

Short-chain fatty acids (SCFAs) are main fuels of the colonic epithelium, and are avidly absorbed by the colon of animal and man. The current knowledge on colonic metabolism and absorption of medium-chain fatty acids (MCFAs) is limited. In some clinical situations, colonic absorption of high-energy substances could compensate for reduced absorptive capacity because of a shortened or malfunctioning small bowel. We evaluated and compared colonic absorption and metabolism of MCFAs (octanoate, decanoate, and dodecanoate), SCFAs (acetate and butyrate), and long-chain fatty acids (LCFAs) (oleate).

METHODS

Rats were surgically operated on to cannulate a 7-cm segment of proximal colon, isolate the vasculature, and cannulate the right colic vein draining this segment. The lumen was perfused with (14)C-labeled substrates for 100 minutes. Right colic vein blood was analyzed for total (14)C, (14)CO(2), and metabolites by scintillation counting and high-performance liquid chromatography.

RESULTS

The transport from the colonic lumen to mesenteric blood of substrate carbon from MCFAs exceeded by 2-13-fold that of SCFAs and LCFAs. The CO(2) production from the oxidation of MCFAs was as high as or higher than that from SCFAs. CO(2) produced from the LCFA, oleate, was lower than from SCFAs or MCFAs. In addition to CO(2), ketone bodies were major metabolites of SCFAs and MCFAs. Ketogenesis from butyrate and the MCFAs was significantly higher than from acetate and oleate. A substantial proportion (50%-90%) of all substrates was absorbed without being metabolized.

CONCLUSIONS

The colonic epithelium serves to absorb and partially metabolize MCFAs. For patients with a compromised small-bowel function, colonic absorption of MCFAs could represent an important way of receiving calories.

The characterization of butyrate transport across pig and human colonic luminal membrane

1. Luminal membrane vesicles (LMV) were isolated from human and pig colonic tissues. They were characterized in terms of purity and ability to transport [14C]butyrate. 2. The activity of cysteine-sensitive alkaline phosphatase, and the abundance of villin, NHE2 and NHE3 proteins, markers of the colonic luminal membrane, were significantly enriched in the LMV compared with the original cellular homogenate. The LMV were free from contamination by other cellular organelles and basolateral membranes, as revealed by the negligible presence of either specific marker enzyme activity or characteristic immunogenic protein. 3. The transport of butyrate into the luminal membrane vesicles was enhanced 5-fold at pH 5.5 compared with pH 8.0. Butyrate transport was temperature dependent, and was stimulated in the presence of an outward-directed anion gradient in the order of butyrate > bicarbonate > propionate > chloride. Kinetic analysis of increasing substrate concentration showed saturation kinetics with an apparent Km value of 14.8 +/- 3.6 mM and a Vmax of 54 +/- 14 nmol min-1 (mg protein)-1. 4. Butyrate transport was significantly reduced in the presence of short chain fatty acids (SCFA), acetate, propionate and other monocarboxylates (pyruvate and L-lactate). Butyrate uptake was inhibited by several cysteine group modifying reagents such as p-chloromercuribenzosulphonic acid (pCMBS), p-chloromercuribenzoate (pCMB), mersalyl acid and HgCl2, but not by the stilbene anion exchange inhibitors, 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS) and 4,4'-dinitrostilbene-2,2'-disulphonate (SITS). 5. The described properties of butyrate transport across the luminal pole of the colon suggest the involvement of a carrier protein, in the form of a pH-activated anion exchange process. The transporter is distinct from the erythrocyte band-3 type anion exchanger and may belong to the monocarboxylate-type transport proteins (MCT1).

Short-chain fatty acids in the human colon: relation to gastrointestinal health and disease

Fermentation, the process whereby anaerobic bacteria break down carbohydrates to short-chain (C2-C6) fatty acids (SCFAs), is an important function of the large bowel. SCFAs constitute approximately two-thirds of the colonic anion concentration (70-130 mmol/l), mainly as acetate, propionate, and butyrate. Gastroenterologists have, in spite of these facts, addressed this scientific field surprisingly late, in contrast to veterinarians, for whom the fermentative production of SCFAs has been acknowledged as a principal mechanism of intestinal digestion in plant-eating animals for decades. Interest in the effects of SCFA production on the human organism has been growing rapidly in the last 10 years, because gastrointestinal functions and beneficial effects are associated with these acids. SCFAs are of major importance in the understanding of the physiological function of dietary fibre and their possible role for colonic neoplasia. SCFA production and absorption are closely related to the nourishment of the colonic mucosa and sodium and water absorption, and mechanisms of diarrhoea. Patients with severe malabsorption compensate by the fermentation of otherwise osmotic active saccharides to SCFAs, which are readily absorbed and used as energy fuels in the organism. SCFA production from dietary carbohydrates is a mechanism whereby considerable amounts of calories can be salvaged in short-bowel patients with remaining colonic function if dietary treatment is adjusted. SCFA enemas are a new and promising treatment modality for patients with ulcerative colitis. The effect has been attributed to the oxidation of SCFAs in the colonocytes. An impressive number of papers have described the effects of butyrate on various cell functions, the significance of which is still unknown. Up until now, attention has been related especially to cancer prophylaxis and treatment. Diminished production of SCFAs appears to be involved in antibiotic-associated diarrhoea, diversion colitis, and possibly in pouchitis. The interaction between bacterial fermentation, ammonia metabolism, and bacterial growth and protein synthesis appears to be the main mechanism of action of lactulose treatment in hepatic coma. Pathological and extremely high rates of saccharide fermentation explain the severe deterioration in patients with D-lactate acidosis. Hence, this scientific field has come late to clinical working gastroenterologists, but as work is progressing the production of SCFAs in the large bowel becomes involved in several well-known intestinal disorders.

Butyrate absorption and lactate secretion in ulcerative colitis

PURPOSE

Fecal electrolytes and organic anion concentrations are altered in ulcerative colitis, presumably reflecting changes in colon epithelial transport. Information of mucosal absorption of butyrate in active ulcerative proctosigmoiditis is not available.

METHODS

Dialysis bags containing 70 mmol/liter of butyrate in an isotonic electrolyte solution were placed in the rectum for 30 minutes. Net absorption or secretion rates of butyrate, lactate, and electrolytes were determined in the rectum of 12 patients with active ulcerative colitis (UC) and in 10 patients with quiescent UC and then compared with 10 healthy controls.

RESULTS

Net flux rates demonstrated a considerable absorption of butyrate in patients with active inflammation of 7.5 +/- 0.4 mumol/cm2/h and quiescent colitis of 6.6 +/- 0.4 mumol/cm2/h, equal to absorption in healthy controls of 6.3 +/- 0.5 mumol/cm2/h, P = 0.12. Despite normal butyrate absorption, sodium absorption was compromised in active ulcerative colitis (11.5 +/- 1.4 mumol/cm2/h) compared with quiescent (15.4 +/- 1.0 mumol/cm2/h) and controls (18.7 +/- 0.8 mumol/cm2/h) (P = 0.0006). Mucosal secretion of L-lactate was minimal in both healthy controls and quiescent UC but significantly increased in patients with proctosigmoiditis (0.2 +/- 0.1 mumol/cm2/h, 0.2 +/- 0.1 mumol/cm2/h vs. 0.9 +/- 0.2 mumol/cm2/h; P = 0.0001). Appearance of D-lactate was negligible in all three groups.

CONCLUSIONS

This study demonstrates that rectal butyrate absorption is normal in UC, and it follows that butyrate supplied in enemas can be expected to be absorbed. The inflamed colonic mucosa secretes L-lactate, and the increased fecal lactate concentrations can be explained by mucosal origin of lactate.