Bile Acids, Gut Microbes, and the Neighborhood Food Environment-a Potential Driver of Colorectal Cancer Health Disparities

A novel near-infrared polymethine dye biosensor for rapid and selective detection of lithocholic acid

Lithocholic acid (LCA), a secondary bile acid, has emerged as a potential early diagnostic biomarker for various liver diseases. In this study, we introduce a novel near-infrared (NIR) polymethine dye-based biosensor, capable of sensitive and selective detection of LCA in phosphate buffer and artificial urine (AU) solutions. The detection mechanism relies on the formation of J-aggregates resulting from the interplay of 3,3-Diethylthiatricarbocyanine iodide (DiSC2(7)) dye molecules and LCA, which induces a distinctive red shift in both absorption and fluorescence spectra. The biosensor demonstrates a detection limit for LCA of 70 μM in PBS solution (pH 7.4), while in AU solution, it responds to an LCA concentration as low as ∼60 μM. Notably, the proposed biosensor exhibits outstanding selectivity for LCA, effectively distinguishing it from common interferents such as uric acid, ascorbic acid, and glucose. This rapid, straightforward, and cost-effective spectrometer-based method underscores its potential for early diagnosis of liver diseases by monitoring LCA concentrations.

Strain-dependent induction of primary bile acid 7-dehydroxylation by cholic acid

BACKGROUND

Bile acids (BAs) are steroid-derived molecules with important roles in digestion, the maintenance of host metabolism, and immunomodulation. Primary BAs are synthesized by the host, while secondary BAs are produced by the gut microbiome through transformation of the former. The regulation of microbial production of secondary BAs is not well understood, particularly the production of 7-dehydroxylated BAs, which are the most potent agonists for host BA receptors. The 7-dehydroxylation of cholic acid (CA) is well established and is linked to the expression of a bile acid-inducible (bai) operon responsible for this process. However, little to no 7-dehydroxylation has been reported for other host-derived BAs (e.g., chenodeoxycholic acid, CDCA or ursodeoxycholic acid, UDCA).

RESULTS

Here, we demonstrate that the 7-dehydroxylation of CDCA and UDCA by the human isolate Clostridium scindens is induced when CA is present, suggesting that CA-dependent transcriptional regulation is required for substantial 7-dehydroxylation of these primary BAs. This is supported by the finding that UDCA alone does not promote expression of bai genes. CDCA upregulates expression of the bai genes but the expression is greater when CA is present. In contrast, the murine isolate Extibacter muris exhibits a distinct response; CA did not induce significant 7-dehydroxylation of primary BAs, whereas BA 7-dehydroxylation was promoted upon addition of germ-free mouse cecal content in vitro. However, E. muris was found to 7-dehydroxylate in vivo.

CONCLUSIONS

The distinct expression responses amongst strains indicate that bai genes are regulated differently. CA promoted bai operon gene expression and the 7-dehydroxylating activity in C. scindens strains. Conversely, the in vitro activity of E. muris was promoted only after the addition of cecal content and the isolate did not alter bai gene expression in response to CA. The accessory gene baiJ was only upregulated in the C. scindens ATCC 35704 strain, implying mechanistic differences amongst isolates. Interestingly, the human-derived C. scindens strains were also capable of 7-dehydroxylating murine bile acids (muricholic acids) to a limited extent. This study shows novel 7-dehydroxylation activity in vitro resulting from the presence of CA and suggests distinct bai gene expression across bacterial species.

Microfluidic gut-axis-on-a-chip models for pharmacokinetic-based disease models

The low success rate of new drugs transitioning from animal testing to human clinical trials necessitates the development of more accurate and representative in vitro models. Recent advances in multi-organ-on-a-chip technology offer promising avenues for studying complex organ-organ interactions. Gut-liver-on-a-chip systems hold particular promise for mimicking the intricate interplay between the gut and liver, which play crucial roles in nutrient absorption, drug metabolism, detoxification, and immune response. Here, we discuss the key components of the gut-liver axis, including the gut epithelium, liver cells, gut microbiota, and their roles in the organ functions. We then explore the potential of gut-liver-on-a-chip models to replicate the intricate interactions between the two organs for pharmacokinetic studies and their expansion to more complicated multi-organ models. Finally, we provide perspectives and future directions for developing more physiologically relevant gut-liver-axis models for more efficient drug development, studying liver diseases, and personalizing treatment strategies.

Naturally nutrient rich (NNR) score and the risk of colorectal cancer: a case-control study

BACKGROUND

The association between colorectal cancer (CRC) and nutrients has been studied frequently. However, the association of nutrient density of diets with the risk of CRC has been less studied. This study aimed to investigate the association between CRC and naturally nutrient rich (NNR) score in Iranian adults.

METHOD

This case-control study included 160 patients with colorectal cancer and 320 controls aged 35-70 years in Tehran, Iran. Dietary intake was assessed using a 168-item food frequency questionnaire. The NNR score was obtained by calculating the average daily value of 14 nutrients including protein, vitamins A, C, D, E, B1, B2, B12, calcium, zinc, iron, folate, potassium and unsaturated fatty acids.

RESULTS

Regarding dietary intake of the components of NNR score, the case group had a lower intake of polyunsaturated fat (15.41±4.44 vs 16.54±4.20 g/day, p=0.01), vitamin E (10.15±4.16 vs 13.1±5.33; p=0.001), vitamin B1 (2±0.86 vs 2.19±0.84 mg/day, p=0.03) and folate (516.45±96.59 vs 571.05±80.31; p=0.001) and a higher intake of oleic acid (8.21±5.46 vs 5.59±3.17 g/day, p=0.01) compared with the control group. Colorectal cancer risk was inversely associated with the NNR score after adjusting for the confounders (OR 0.92; 95% CI 0.88 to 0.97; p=0.03).

CONCLUSION

Low NNR scores may be linked to CRC. If confirmed by future longitudinal research, this result may help prevent CRC by recommending nutrient-rich diets.

Molecular Mechanisms of Western Diet-Induced Obesity and Obesity-Related Carcinogenesis-A Narrative Review

The present study aims to provide a narrative review of the molecular mechanisms of Western diet-induced obesity and obesity-related carcinogenesis. A literature search of the Cochrane Library, Embase and Pubmed databases, Google Scholar and the grey literature was conducted. Most of the molecular mechanisms that induce obesity are also involved in the twelve Hallmarks of Cancer, with the fundamental process being the consumption of a highly processed, energy-dense diet and the deposition of fat in white adipose tissue and the liver. The generation of crown-like structures, with macrophages surrounding senescent or necrotic adipocytes or hepatocytes, leads to a perpetual state of chronic inflammation, oxidative stress, hyperinsulinaemia, aromatase activity, activation of oncogenic pathways and loss of normal homeostasis. Metabolic reprogramming, epithelial mesenchymal transition, HIF-1α signalling, angiogenesis and loss of normal host immune-surveillance are particularly important. Obesity-associated carcinogenesis is closely related to metabolic syndrome, hypoxia, visceral adipose tissue dysfunction, oestrogen synthesis and detrimental cytokine, adipokine and exosomal miRNA release. This is particularly important in the pathogenesis of oestrogen-sensitive cancers, including breast, endometrial, ovarian and thyroid cancer, but also 'non-hormonal' obesity-associated cancers such as cardio-oesophageal, colorectal, renal, pancreatic, gallbladder and hepatocellular adenocarcinoma. Effective weight loss interventions may improve the future incidence of overall and obesity-associated cancer.

Biological tuners to reshape the bile acid pool for therapeutic purposes in non-alcoholic fatty liver disease

Bile acids synthesized within the hepatocytes are transformed by gut microorganisms and reabsorbed into the portal circulation. During their enterohepatic cycling, bile acids act as signaling molecules by interacting with receptors to regulate pathways involved in many physiological processes. The bile acid pool, composed of a variety of bile acid species, has been shown to be altered in diseases, hence contributing to disease pathogenesis. Thus, understanding the changes in bile acid pool size and composition in pathological processes will help to elaborate effective pharmacological treatments. Five crucial steps along the enterohepatic cycle shape the bile acid pool size and composition, offering five possible targets for therapeutic intervention. In this review, we provide an insight on the strategies to modulate the bile acid pool, and then we discuss the potential benefits in non-alcoholic fatty liver disease.