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Background: Dietary polyunsaturated fatty acids influence the natural history of intestinal inflammatory diseases. Varying the types of long-chain fatty acids that are exposed to cells alters the physicochemical properties of cell membranes. This study aimed to determine whether such variations alter transcellular and paracellular permeability in intestinal epithelium. Methods: Monolayers of Caco-2 cells, allowed to differentiate by culturing for 7 days following confluence, were used as the model for intestinal epithelium. Paracellular permeability was assessed by measurement of transepithelial resistance, while transcellular permeability was assessed by the transepithelial flux of horseradish peroxidase. Results: Exposure of the cells to 100 μmol/L of palmitic acid, oleic acid, eicosapentaenoic acid, or linoleic acid, was not toxic to cells (measured by leakage of lactate dehydrogenase), and altered cell membrane fatty acid composition (as measured by gas chromatography). Flux of horseradish peroxidase was significantly affected by 24 h fatty acid exposure (P = 0.038, ANOVA), being decreased by 23 ± 6% (mean ± SEM) by eicosapentaenoic acid and 25 ± 3% by linoleic acid. Oleic acid, palmitic acid and butyrate, had no effect. Transepithelial resistance also varied significantly across the treatment groups (P < 0.001) due to a 28 ± 5% increase induced by butyrate. The long-chain fatty acids had no effect. Conclusions: Both ω-3 and ω-6 polyunsaturated fatty acids reduce transcellular, non-receptor-mediated permeation of proteins across differentiated Caco2 cell monolayers, without altering paracellular permeability. Alteration of intestinal barrier function should be considered as a possible mechanism of action of dietary polyunsaturated fatty acids.

The relationships between changes induced by diet in colonic epithelial kinetics and in the activities of brush border hydrolases are poorly defined. The aims of this study are to define these relationships, as changes in kinetics would be expected to influence differentiation, and to determine whether the type of ingested dietary indigestible carbohydrates influences hydrolase activities.Groups of eight rats were fed a low fibre diet +/- supplements of different types of indigestible carbohydrates for 4 weeks. Alkaline phosphatase (ALP) and dipeptidyl peptidase IV (DPPIV) activities and epithelial kinetics were measured in distal colonic mucosa.Median ALP activities correlated positively and DPPIV activity negatively with the median proportion of cells entering metaphase (r = 0.58 and -0.58, respectively; P0.05) and number of metaphase arrests per crypt column across the diets (r = 0.59 and 0.58, respectively; P0.05). Stepwise regression analysis showed that both hydrolases independently predicted these kinetic indices (R263% for each). Mucosal ALP activities were markedly elevated during consumption of raw potato starch, guar gum and methylcellulose, while only potato starch caused a significant elevation of DPPIV activities.The type of indigestible carbohydrate in the diet influences colonic mucosal hydrolase activities. The opposite relationship between kinetics and each of the two hydrolases indicates that these hydrolases do not reflect the same event; dipeptidyl peptidase IV might relate to differentiation status while ALP could also be influenced by epithelial irritation due to changes in luminal conditions.

The amount and type of dietary fibre ingested influences colonic luminal characteristics, especially the concentration of carbohydrate fermentation products such as butyrate. This study aimed to assess whether diets supplemented with fibres of differing fermentability (delivering different amounts of butyrate to the colon) influence mucosal activities of urokinase and brush border hydrolases, and epithelial turnover. Groups of five rats were fed one of four diets containing low (2%), highly fermented (guar 10% or oat bran 10%) or slowly fermented fibre (wheat bran 10%) for 4 weeks. Activities of urokinase, alkaline phosphatase, dipeptidyl peptidase IV and maltase were measured in mucosal homogenates of proximal and distal colon and from rectum. Proliferative kinetics were assessed in distal and proximal colon by the metaphase arrest technique. Hydrolase activities were similar across all four dietary groups but a significant difference was found for urokinase (P = 0.014). This was due to a reduction in urokinase activities of > 30% at the three sites in the wheat bran group compared with the other groups. Of proliferative indices, only crypt column height differed across the groups (P = 0.038) and was highest in rats fed wheat bran and lowest in those fed the low fibre diet (P = 0.047). The proportion of mitoses in the top one-fifth of the crypt also differed across groups (P = 0.038) due to the high values in the distal colon of the low fibre group. Thus, addition of a slowly fermented (but not highly fermented) fibre to the diet of rats reduces net urokinase activity in large bowel mucosa and increases the life span of colonic epithelial cells without changing activities of brush border hydrolases.