Dual effects of the tryptophan-derived bacterial metabolite indole on colonic epithelial cell metabolism and physiology: comparison with its co-metabolite indoxyl sulfate

Indole, which is produced by the intestinal microbiota from L-tryptophan, is recovered at millimolar concentrations in the human feces. Indoxyl sulfate (IS), the main indole co-metabolite, can be synthesized by the host tissues. Although indole has been shown to restore intestinal barrier function in experimental colitis, little is known on the effects of indole and IS on colonic epithelial cell metabolism and physiology. In this study, we compared the effects of indole and IS on the human colonic epithelial HT-29 Glc^-/+ and Caco-2 cell lines, exposed to these compounds for 1-48 h. Indole, but not IS, was cytotoxic at 5 mM, altering markedly colonocyte proliferation. Both molecules, used up to 2.5 mM, induced a transient oxidative stress in colonocytes, that was detected after 1 h, but not after 48 h exposure. This was associated with the induction after 24 h of the expression of glutathione reductase, heme oxygenase, and cytochrome P450 (CYP)1B1. Indole and IS used at 2.5 mM impaired colonocyte respiration by diminishing mitochondrial oxygen consumption and maximal respiratory capacity. Indole, but not IS, displayed a slight genotoxic effect on colonocytes. Indole, but not IS, increased transepithelial resistance in colonocyte monolayers. Indole and IS used at 2.5 mM, induced a secretion of the pro-inflammatory interleukin-8 after 3 h incubation, and an increase of tumor necrosis factor-α secretion after 48 h. Although our results suggest beneficial effect of indole on epithelial integrity, overall they indicate that indole and IS share adverse effects on colonocyte respiration and production of reactive oxygen species, in association with the induction of enzymes of the antioxidant defense system. This latter process can be viewed as an adaptive response toward oxidative stress. Both compounds increased the production of inflammatory cytokines from colonocytes. However, only indole, but not IS, affected DNA integrity in colonocytes. Since colonocytes little convert indole to IS, the deleterious effects of indole on colonocytes appear to be unrelated to its conversion to IS.

In vitro impact of amino acid-derived bacterial metabolites on colonocyte mitochondrial activity, oxidative stress response and DNA integrity

BACKGROUND

4-hydroxyphenylacetic acid (HO-PAA) is produced by intestinal microbiota from L-tyrosine. High concentrations in human fecal water have been associated with cytotoxicity, urging us to test HO-PAA's effects on human colonocytes. We compared these effects with those of phenylacetic acid (PAA), phenol and acetaldehyde, also issued from amino acids fermentation.

METHODS

HT-29 Glc^-/+ human colonocytes were exposed for 24 h to metabolites at concentrations between 350 and 1000 μM for HO-PAA and PAA, 250-1500 μM for phenol and 25-500 μM for acetaldehyde. We evaluated metabolites'cytotoxicity with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide and DNA quantification assays, reactive oxygen species (ROS) production with H2DCF-DA, and DNA damage with the comet assay. We measured cell oxygen consumption and mitochondrial complexes activity by polarography.

RESULTS

Although HO-PAA displayed no cytotoxic effect on colonocytes, it decreased mitochondrial complex I activity and oxygen consumption. This was paralleled by an increase in ROS production and DNA alteration. Cells pretreatment with N-acetylcysteine, a ROS scavenger, decreased genotoxic effects of HO-PAA, indicating implication of oxidative stress in HO-PAA's genotoxicity. PAA and phenol did not reproduce these effects, but were cytotoxic towards colonocytes. Last, acetaldehyde displayed no effect in terms of cytotoxicity and mitochondrial metabolic activity, but increased DNA damage.

CONCLUSIONS

Several bacterial metabolites produced from amino acids displayed deleterious effects on human colonocytes, in terms of genotoxicity (HO-PAA and acetaldehyde) or cytotoxicity (PAA and phenol).

GENERAL SIGNIFICANCE

This study helps understanding the consequences of intestinal microbiota's metabolic activity on the host since amino acids fermentation can lead to the formation of compounds toxic towards colonic epithelial cells.

Antioxidant and antigenotoxic activities of Ginkgo biloba L. leaf extract are retained after in vitro gastrointestinal digestive conditions

PURPOSE

The recognized biological properties of Ginkgo biloba extracts potentiate their utilization as an ingredient for functional foods. However, the digestive conditions can affect the chemical composition of the extracts and consequently their biological properties, which can lead to food safety problems. Thus, the impact of in vitro-simulated upper gastrointestinal tract digestion on the chemical composition and bioactivity of Ginkgo biloba leaf extract (GBE) was evaluated.

METHODS

Physicochemical conditions of human digestion were simulated in vitro, and its impact on the chemical composition of GBE was investigated by electrospray ionization-mass spectrometry. The persistence of bioactivity was investigated by subjecting GBE and the in vitro digested extract (DGBE) to the same methodology. Antioxidant properties were assessed using 2',7'-dichlorofluorescein diacetate to measure the intracellular oxidation of Schizosaccharomyces pombe cells pre-incubated with GBE or DGBE and exposed to H₂O₂. Antigenotoxicity was tested by comet assay in HT-29 colon cancer cells pre-incubated with GBE or DGBE and challenged with H₂O₂.

RESULTS

The chemical analysis revealed a considerable change in chemical composition upon digestion. Pre-incubation with GBE or DGBE attenuated the H₂O₂-imposed intracellular oxidation in wild-type S. pombe cells, unlike the oxidative stress response-affected mutants sty1 and pap1, and decreased H₂O₂-induced DNA damage in HT-29 cells. The extracts did not induce toxicity in these eukaryotic models.

CONCLUSION

The chemical composition of GBE was affected by in vitro digestion, but the antioxidant and antigenotoxic activities persisted. Therefore, G. biloba extract may be suitable for use as food additive and contribute to a healthy colon.

Toll like receptors (TLRs) in response to human gut microbiota of Indian obese and lean individuals

Background:

The rising incidence of obesity is one of the most serious public health issues in the developed as well as in developing countries like India. Obesity and overweight are most important risk factors for many chronic diseases, including cardiovascular diseases, diabetes and cancer. In this study the body mass index (BMI) cut off was taken as 18.5-22.9 kg/m² for normal, 23.0-24.9 kg/m² for Overweight and >25 kg/m² for obese as per WHO recommendation for Asian Indians, which is different for developed and developing countries. Role of gut microbiota mediated immune response in the development of obesity has been studied but the literature on Indian population are lacking. Therefore, a study was conducted to determine Toll like receptors (TLRs) in response to human gut microbiota of Indian obese and lean individuals using viable colonocytes in a Non invasive technique and Flowcytometry.

Methods:

A total of 20 healthy volunteer (10 obese and 10 lean) were enrolled in the study as per inclusion and exclusion criteria. Viable colonocytes were isolated from fecal samples using a Non invasive technique (SCSR Method). Toll like receptors (TLRs) and immunoglobulin (IgA &IgG) receptor concentration were measured by standard Flowcytometry methods using specific fluorochrome conjugated antibodies.

Results:

Average TLR2 receptor concentration was significantly higher in obese (6.35 %) as compared to lean (2.9 %) (P = 0.01). TLR4 receptor concentration was 1.4 % in obese and 1.65 % in lean although the difference was not statistically significant (P = 0.59). IgA & IgG receptor concentration was 49.6 % & 11.2 % in the obese and 67.15 % & 8.05 % in the lean respectively but the differences among both the group were not statistically significant.

Conclusion:

The results of the present study will be helpful for physicians and researchers to find some biomarkers which can determine predisposition of the obesity in Indian population and helps to use alternative therapeutics such as probiotics to maintain gut homeostasis and immune modulation to prevent obesity.

Toward Cell Type-Specific In Vivo Dual RNA-Seq

Dual RNA-seq has emerged as a genome-wide expression profiling technique, simultaneously measuring RNA transcript levels in a given host and its pathogen during an infection. Recently, the method was transferred from cell culture to in vivo models of bacterial infections; however, specific host cell-type resolution has not yet been achieved. Here we present a detailed protocol that describes the application of Dual RNA-seq to murine colonocytes isolated from mice infected with the enteric pathogen Salmonella Typhimurium. At day 5 after oral infection, the mice were humanely euthanized, their colons extracted, and colonocytes isolated and fixed. Upon antibody staining of cell type-specific surface markers, the fraction of Salmonella-invaded colonocytes was collected by fluorescence-activated cell sorting based on a fluorescent signal emitted by the internalized bacteria. Total RNA was extracted from cells enriched by this method, and ribosomal transcripts from host and microbial cells were removed prior to cDNA synthesis and library generation. We compared different protocols for library preparation and discuss their respective advantages and caveats when applied to minute RNA amounts that constitute an inherent challenge for in vivo transcriptomics. Our results introduce an ultralow input protocol that holds promise for cell type-specific in vivo Dual RNA-seq for charting gene expression of a bacterial pathogen within its respective in vivo niche, along with the consequent host response.

Stool DNA Integrity Method for Colorectal Cancer Detection

Fluorescence long DNA (FL-DNA) is a non-invasive and simple-to-perform stool DNA test. This assay consists of a qualitative and quantitative real-time PCR (RT PCR) analysis. FL-DNA has great potential in colorectal cancer (CRC) lesions detection used alone or in combination with the standard CRC screening tool: immunochemical fecal occult blood test (iFOBT).