The Contribution of Intestinal Gluconeogenesis to Glucose Homeostasis Is Low in 2-Day-Old Pigs

Background: Active gluconeogenesis is essential to maintain blood glucose concentrations in neonatal piglets because of the high glucose requirements after birth. In several adult mammals, the liver, kidney, and possibly the gut may exhibit gluconeogenesis during fasting and insulinopenic conditions. During the postnatal period, the intestine expresses all of the gluconeogenic enzymes, suggesting the potential for gluconeogenesis. Galactose in milk is a potential gluconeogenic precursor for newborns.Objective: Our aim was to quantify the rate of intestinal glucose production from galactose in piglets compared with the overall rate of glucose production.Methods: A single bolus of [U-¹⁴C]-galactose was injected into 2-d-old piglets (females and males; mean ± SEM weight: 1.64 ± 0.07 kg) through a gastric catheter. Galactosemia, glycemia, and glucose turnover rate (assessed by monitoring d-[6-³H]-glucose) were monitored. Intestinal glucose production from [U-¹⁴C]-galactose was calculated from [U-¹⁴C]-glucose appearance in the blood and isotopic dilution. Galactose metabolism was also investigated in vitro in enterocytes isolated from 2-d-old piglets that were incubated with increasing concentrations of galactose.Results: In piglet enterocytes, galactose metabolism was active (mean ± SEM maximum rate of reaction: 2.26 ± 0.45 nmol · min^-1 · 10⁶ cells^-1) and predominantly oriented toward lactate and pyruvate production (74.0% ± 14.5%) rather than glucose production (26.0% ± 14.5%). In conscious piglets, gastric galactose administration led to an increase in arterial galactosemia (from 0 to 1.0 ± 0.8 mmol/L) and glycemia (35% ± 12%). The initial increase in arterial glycemia after galactose administration was linked to an increase in glucose production rate (33% ± 15%) rather than to a decrease in glucose utilization rate (3% ± 6%). The contribution of intestinal glucose production from galactose was <10% of total glucose production in 2-d-old piglets.Conclusion: Our results indicate that there is a low contribution to glucose homeostasis from intestinal gluconeogenesis in 2-d-old piglets.

Primocolonization is associated with colonic epithelial maturation during conventionalization

Interaction between the gut microbiota and the host starts immediately after birth with the progressive colonization of the sterile intestine. Our aim was to investigate the interactions taking place in the colonic epithelium after the first exposure to gut microbiota. Germ-free (GF) rats were inoculated with two different microbiotas: the first, obtained from suckling rats, was rich in primocolonizing bacteria and the second, obtained from adult rats, was representative of a mature microbiota. Once transferred into GF rats, these two microbiotas evolved such that they converged, and recapitulated the primocolonization pattern, mimicking the chronological scheme of implantation following birth. The two microbiotas induced common responses in the colonic epithelium: a transitory proliferative phase followed by a compensatory phase characterized by increases in the abundance of p21(Cip1) and p27(Kip1) and in the number of goblet cells. The effects of the two microbiotas diverged only through their effects on colonic transporters. Analyses of solute carriers and aquaporins revealed that functional maturation was more pronounced following exposure to adult microbiota than suckling microbiota. The colon matured in parallel with the evolution of the microbiota composition, and we therefore suggest a link between intestinal events regulating homeostasis of the colon and modulation of microbial composition.

Microbiota matures colonic epithelium through a coordinated induction of cell cycle-related proteins in gnotobiotic rat

Previous studies have suggested that intestinal microbiota modulates colonic epithelium renewal. The objective of our work was to study the effects of microbiota on colonic epithelium structure and cell cycle-related proteins by using gnotobiotic rats. Colonic crypts and amount of cell cycle-related proteins were compared between germ-free (GF), conventional (CV), and conventionalized rats by histochemistry and Western blot. Ki67 and proliferating cell nuclear antigen (PCNA) were used as surrogates for proliferative cells; p21(cip1) and p27(kip1) were markers of cell cycle arrest; anti- and proapoptotic proteins, Bcl2 and Bax, respectively, were also studied. We observed 40% increase of the crypt proliferative area 2 days after inoculation of GF rats with a complex microbiota. This recruitment of proliferative cells may account for the 30% increase of crypt depth observed between CV and GF rats. The hyperproliferative boost induced by microbiota was compensated by a fourfold increase of p21(cip1) and p27(kip1) involved in cell cycle arrest and a 30% drop of antiapoptotic Bcl2 protein while Bax was unchanged. Inductions of p21(cip1), p27(kip1), and PCNA protein were not paralleled by an increase of the corresponding mRNA. We also showed that p21(cip1) induction by microbiota was partially restored by Bacteroides thetaiotaomicron, Ruminococcus gnavus, and Clostridium paraputrificum. Colonization of the colon by a complex microbiota increases the crypt depth of colon epithelium. This event takes place in conjunction with a multistep process: a hyperproliferative boost accompanied by compensatory events as induction of p21(cip1) and p27(kip1) and decrease of Bcl2.

Expression of mitochondrial HMGCoA synthase and glutaminase in the colonic mucosa is modulated by bacterial species

The expression of the colonic mitochondrial 3-hydroxy 3-methyl glutaryl CoA (mHMGCoA) synthase, a key control site of ketogenesis from butyrate, is lower in germ-free (GF) than in conventional (CV) rats. In contrast, the activity of glutaminase is higher. The objective of this study was to investigate whether the intestinal flora can affect gene expression through short chain fatty acid (SCFA) and butyrate production. GF rats were inoculated with a conventional flora (Ino-CV) or with a bacterial strain producing butyrate (Clostridium paraputrificum, Ino-Cp) or not (Bifidobacterium breve, Ino-Bb). In the Ino-CV rats, mHMGCoA synthase expression was restored to the CV values 2 days after the inoculation, i.e. concomitantly with SCFA production. In the Ino-Cp group, but not in the Ino-Bb group, mHMGCoA synthase and glutaminase were expressed at the level observed in the CV rats. These data suggest that the intestinal flora, through butyrate production, could control the expression of colonic mHMGCoA synthase and glutaminase. These modifications in gene expression by butyrate in vivo seem unrelated to a modification of histone acetylation.