Quantitation of colonic luminal synthesis of butyric acid in piglets

Maternal amoxicillin affects piglets colon microbiota: microbial ecology and metabolomics in a gut model

Abstract

The first weeks of life represent a crucial stage for microbial colonization of the piglets’ gastrointestinal tract. Newborns’ microbiota is unstable and easily subject to changes under stimuli or insults. Nonetheless, the administration of antibiotics to the sow is still considered as common practice in intensive farming for pathological conditions in the postpartum. Therefore, transfer of antibiotic residues through milk may occurs, affecting the piglets’ colon microbiota. In this study, we aimed to extend the knowledge on antibiotic transfer through milk, employing an in vitro dedicated piglet colon model (MICODE—Multi Unit In vitro Colon Model). The authors’ focus was set on the shifts of the piglets’ microbiota composition microbiomics (16S r-DNA MiSeq and qPCR—quantitative polymerase chain reaction) and on the production of microbial metabolites (SPME GC/MS—solid phase micro-extraction gas chromatography/mass spectrometry) in response to milk with different concentrations of amoxicillin. The results showed an effective influence of amoxicillin in piglets’ microbiota and metabolites production; however, without altering the overall biodiversity. The scenario is that of a limitation of pathogens and opportunistic taxa, e.g., Staphylococcaceae and Enterobacteriaceae, but also a limitation of commensal dominant Lactobacillaceae, a reduction in commensal Ruminococcaceae and a depletion in beneficial Bifidobactericeae. Lastly, an incremental growth of resistant species, such as Enterococcaceae or Clostridiaceae, was observed. To the authors’ knowledge, this study is the first evaluating the impact of antibiotic residues towards the piglets’ colon microbiota in an in vitro model, opening the way to include such approach in a pipeline of experiments where a reduced number of animals for testing is employed.

Key points

• Piglet colon model to study antibiotic transfer through milk.

• MICODE resulted a robust and versatile in vitro gut model.

• Towards the “3Rs” Principles to replace, reduce and refine the use of animals used for scientific purposes (Directive 2010/63/UE).

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12223-3.

Probiotics and necrotizing enterocolitis

One of the most controversial areas in neonatology is whether probiotics should be provided routinely to preterm infants to prevent necrotizing enterocolitis (NEC). This review provides the reader with a brief overview of NEC and current concepts of its pathophysiology, discusses the microbial ecology of the intestine in preterm infants and factors that may lead to a "dysbiosis", summarizes studies of probiotics in preterm infants, elaborates on the need for regulation in this area, and discusses alternatives to probiotics and what is the future for the prevention of NEC.

Butyrate enhances the intestinal barrier by facilitating tight junction assembly via activation of AMP-activated protein kinase in Caco-2 cell monolayers

Butyrate, one of the SCFA, promotes the development of the intestinal barrier. However, the molecular mechanisms underlying the butyrate regulation of the intestinal barrier are unknown. To test the hypothesis that the effect of butyrate on the intestinal barrier is mediated by the regulation of the assembly of tight junctions involving the activation of the AMP-activated protein kinase (AMPK), we determined the effect of butyrate on the intestinal barrier by measuring the transepithelial electrical resistance (TER) and inulin permeability in a Caco-2 cell monolayer model. We further used a calcium switch assay to study the assembly of epithelial tight junctions and determined the effect of butyrate on the assembly of epithelial tight junctions and AMPK activity. We demonstrated that the butyrate treatment increased AMPK activity and accelerated the assembly of tight junctions as shown by the reorganization of tight junction proteins, as well as the development of TER. AMPK activity was also upregulated by butyrate during calcium switch-induced tight junction assembly. Compound C, a specific AMPK inhibitor, inhibited the butyrate-induced activation of AMPK. The facilitating effect of butyrate on the increases in TER in standard culture media, as well as after calcium switch, was abolished by compound C. We conclude that butyrate enhances the intestinal barrier by regulating the assembly of tight junctions. This dynamic process is mediated by the activation of AMPK. These results suggest an intriguing link between SCFA and the intracellular energy sensor for the development of the intestinal barrier.

Cecal infusion of butyrate does not alter cecal concentration of butyrate in piglets fed inulin

BACKGROUND

Cecal or distal colonic concentration of butyrate has been used as an index of butyrate production from various fermentable carbohydrates. However, we previously found that cecal concentration of butyrate does not correlate with the rate of synthesis of butyrate in the cecal lumen. As part of a larger study of the cellular effects of cecal infusions of butyrate, we sought to rule out the null hypothesis that cecal infusion of butyrate also would not alter butyrate concentration in the cecum.

METHODS

Piglets (n = 10) were fed sow milk replacement formula plus inulin (3 g x L(-1)). After 6 days of oral feeding, the piglets were randomly assigned into 2 equal groups: (I) Cecal infusion of phosphate-buffered NaCl and (II) cecal infusion of butyrate (2.13 micromol x kg(-1) x min(-1)). The concentration of butyrate was measured by gas chromatography in the cecum and distal colon.

RESULTS

There was no effect of cecal butyrate infusion on butyrate concentration (mM; I vs II) in the cecum (5.7 +/- 0.4 vs 5.3 +/- 1.1) or distal colon (3.3 +/- 0.6 vs 4.1 +/- 0.8) or on the ratio of cecal butyrate concentration to the sum of the concentrations of butyrate, acetate, propionate, and valerate (0.101 +/- 0.004 vs 0.083 +/- 0.011). There was no effect of cecal butyrate infusion on the concentration of any of these short chain fatty acids.

CONCLUSIONS

At an entry rate into the cecum within the physiological range, butyrate had no effect on cecal or distal colonic luminal concentration of butyrate.

Effects of the in vivo supply of butyrate on histone acetylation of cecum in piglets

BACKGROUND

In vitro, butyrate inhibits histone deacetylase and down-regulates expression of cyclin D1. We hypothesized that an increased entry rate of butyrate into the cecal lumen would have similar effects in vivo.

METHODS

We used frozen cecal tissue and data from previous studies, one showing that lactulose supplementation caused an increased rate of cecal synthesis of butyrate and decreased cecal cell proliferation and density of clostridia and the other showing that cecal cell proliferation was increased by an exogenous cecal butyrate infusion at a comparable rate. The ratio of acetylated to total histones (AH ratio) and cyclin D1 mRNA expression were measured in cecal tissue.

RESULTS

Lactulose supplementation caused a 189% increase in the AH ratio (p = .004), which inversely correlated with cecal cell proliferation (r = -0.782; p = .008). With cecal butyrate infusion, we observed a significant decrease in histone acetylation (p = .02), which also inversely correlated with cecal cell proliferation (r = -0.797; p = .002). Cyclin D1 expression was increased 6.5-fold by lactulose feeding (p = .02) but decreased 50% with cecal butyrate infusion (p = .004).

CONCLUSIONS

The effects on histone acetylation of increased "endogenous" butyrate production produced by lactulose feeding, but not exogenous cecal infusion of butyrate, mirror those in vitro. Thus, bacterial production and exogenous infusion of butyrate have opposite effects on histone acetylation and cyclin D1 expression, suggesting that the composition of bacterial flora may play a role in butyrate's in vivo effects on the cell cycle.

Gaining insight into microbial physiology in the large intestine: a special role for stable isotopes

The importance of the human large intestine for nutrition, health, and disease, is becoming increasingly realized. There are numerous indications of a distinct role for the gut in such important issues as immune disorders and obesity-linked diseases. Research on this long-neglected organ, which is colonized by a myriad of bacteria, is a rapidly growing field that is currently providing fascinating new insights into the processes going on in the colon, and their relevance for the human host. This review aims to give an overview of studies dealing with the physiology of the intestinal microbiota as it functions within and in interaction with the host, with a special focus on approaches involving stable isotopes. We have included general aspects of gut microbial life as well as aspects specifically relating to genomic, proteomic, and metabolomic studies. A special emphasis is further laid on reviewing relevant methods and applications of stable isotope-aided metabolic flux analysis (MFA). We argue that linking MFA with the '-omics' technologies using innovative modeling approaches is the way to go to establish a truly integrative and interdisciplinary approach. Systems biology thus actualized will provide key insights into the metabolic regulations involved in microbe-host mutualism and their relevance for health and disease.

Application of liquid chromatography–mass spectrometry to measure the concentrations and study the synthesis of short chain fatty acids following stable isotope infusions

A new method involving zinc sulphate deproteinization was developed to study short chain fatty acids (SCFA) production in the colon and subsequent occurrence of SCFA in blood. SCFA were baseline separated in a 30 min cycle using ion-exclusion chromatography and detected by mass spectrometry. Concentrations could be measured down to 10 microM and isotopomeric distributions could be assessed, enabling the conduction of tracer studies to study changes in SCFA synthesis. The applicability of the method was tested in an extensively characterized pig model yielding portal SCFA concentrations ranging from 70 microM (butyric acid) to 150 microM (propionic acid) to 440 microM (acetic acid) prior to butyrate tracer infusion, reaching butyric acid isotopic steady state within 2 h.

Lactulose feeding lowers cecal densities of clostridia in piglets

BACKGROUND

In order to understand the consequences of persistent enteral feeding in patients with carbohydrate malabsorption, we fed piglets lactulose in sufficient dosage to produce osmotic diarrhea or inulin, using a conventional dose, to determine if this prebiotic can modulate the effects of lactulose. Feeding lactulose increases cecal luminal synthesis of butyrate, with inulin having an intermediate effect. Because clostridia may be a major source of colonic butyrate production, we hypothesized that feeding piglets lactulose or inulin would increase cecal densities of clostridia.

METHODS

Piglets were assigned to 3 formula study groups for 6 days: (1) control, fed only sow milk replacer (n = 12); (2) inulin, inulin supplement (3 g/L; n = 11); and (3) lactulose, lactulose supplement (66.7 g/L; n = 6). Cecal fluid for bacteriological studies was sampled intraoperatively.

RESULTS

The wet/dry ratio of the cecal contents (mean +/- SEM) was 8.2 +/- 0.5, 6.2 +/- 0.5, and 18.8 +/- 5.5, respectively, in the control, inulin, and lactulose groups (p = .049, Kruskal-Wallis). There were no differences among the diet groups for cecal densities (10(6) colony-forming units [CFU]/g dry wt cecal contents) of total anaerobes, total aerobes, bifidobacteria, or lactobacilli. Densities of clostridia were markedly reduced in the lactulose group (1.14 +/- 0.41) vs the control (18.39 +/- 4.44; p = .001) or inulin groups (8.87 +/- 2.20; p = .04).

CONCLUSIONS

In piglets, feeding lactulose at a dose known to cause diarrhea reduces cecal densities of clostridia.

Cecal infusion of butyrate increases intestinal cell proliferation in piglets

The effects of colon-derived butyrate on intestinal cell proliferation are controversial. In vitro studies suggest an inhibitory effect, and in vivo studies suggest the opposite, but neither type of study has been based on a physiologically relevant, intracolonic supply of butyrate. In this study, piglets (n = 24) were fed sow's milk replacement formula and randomized into 4 equal groups: 1) control; 2) cecal butyrate infusion at a rate equal to that produced in the colon; 3) inulin supplementation at a concentration previously found to lower cecal cell proliferation; and 4) butyrate infusion plus inulin supplementation. After 6 d of oral feeding, cecal butyrate infusions were initiated for a period of 4 d. Cecal, distal colonic, jejunal, and ileal cell proliferation, apoptosis, and morphology were evaluated and serum concentration of glucagon-like peptide-2 (GLP-2) was measured. Butyrate or inulin did not affect GLP-2, weight gain, apoptosis, intestinal injury scores, cecal or colon crypt depth, and jejunal or ileal villus height. For cell proliferation, there was a significant interaction between inulin, butyrate, and tissue (P = 0.007). Inulin modified the effect of butyrate (butyrate x inulin interaction in cecum, P = 0.001; in distal colon, P = 0.018; in ileum, P = 0.001; and in jejunum, P = 0.003). In the absence of inulin, butyrate caused a 78- 119% increase in cell proliferation in the ileum, distal colon, jejunum, and cecum (P < or = 0.002). Thus, at an entry rate into the colon within the physiological range, butyrate caused increased intestinal cell proliferation, but inulin tended to block this effect. Thus, intracolonic butyrate may enhance intestinal growth during infancy.

Beyond diversity: functional microbiomics of the human colon

Molecular tools have revealed wide microbial diversity in the human alimentary tract. Most intestinal microorganisms have not been cultured and the in situ functions of distinct groups of the intestinal microbiota are largely unknown but pivotal to understanding the role of these microorganisms in health and disease. Promising strategies to gain more insight into the functionality of the complex microbial communities in the human alimentary tract, including fermentation processes in the colon, are discussed. These research approaches could provide a basis for the definition of a healthy gut based on key properties of microbial functionality. This will also enable the development of direct nutritional strategies for intestinal disease prevention and health promotion.

Increased colonic luminal synthesis of butyric acid is associated with lowered colonic cell proliferation in piglets

Butyrate inhibits colonic cell proliferation in vitro but reportedly has an opposite effect in vivo. Because lactulose feeding decreases cecal cell proliferation, an effect attenuated by prefeeding inulin, we hypothesized that lactulose feeding would decrease colonic luminal synthesis of butyrate, and that prefeeding and cofeeding inulin would prevent this effect. Piglets (n = 31) were catheterized and randomly assigned to 1 of 4 groups: Control formula (C); control formula + lactulose (L); control formula + lactulose + inulin (L + I); and control formula + inulin (I). At 6 and 7 d postsurgery, the rate of cecal synthesis of butyrate, cecal cell proliferation and apoptosis, and cecal and distal colon butyrate concentration were measured. In groups C, L, L + I, and I, the rates of synthesis of butyrate (mean +/- SEM) were 10.6 +/- 3.2, 23.3 +/- 4.5, 12.4 +/- 3.6, and 14.6 +/- 4.0 micromol/min, respectively (Group Effect, P = 0.1; C vs. L, P = 0.03; L vs. L + I, P = 0.06). The cecal butyrate concentrations did not differ among the 4 groups and were 8.7 +/- 3.2, 2.4 +/- 0.8, 3.4 +/- 1.9, and 2.0 +/- 0.7 micromol/g dry wt, respectively. The total cecal cell proliferation index was higher in C than in L (P = 0.008) or I (P = 0.026) and was higher in L + I than in L (P = 0.013) or I (P = 0.046). The increased supply of butyrate to the cecum was associated with decreased cell proliferation, but cecal butyrate concentration did not reflect synthesis.