Inhibition of intracellular cathepsin activities and suppression of immune responses mediated by helper T lymphocyte type-2 by peroral or intraperitoneal administration of vitamin B6

What We Know So Far about the Metabolite-Mediated Microbiota-Intestinal Immunity Dialogue and How to Hear the Sound of This Crosstalk

Trillions of microorganisms, termed the "microbiota", reside in the mammalian gastrointestinal tract, and collectively participate in regulating the host phenotype. It is now clear that the gut microbiota, metabolites, and intestinal immune function are correlated, and that alterations of the complex and dynamic host-microbiota interactions can have deep consequences for host health. However, the mechanisms by which the immune system regulates the microbiota and by which the microbiota shapes host immunity are still not fully understood. This article discusses the contribution of metabolites in the crosstalk between gut microbiota and immune cells. The identification of key metabolites having a causal effect on immune responses and of the mechanisms involved can contribute to a deeper insight into host-microorganism relationships. This will allow a better understanding of the correlation between dysbiosis, microbial-based dysmetabolism, and pathogenesis, thus creating opportunities to develop microbiota-based therapeutics to improve human health. In particular, we systematically review the role of soluble and membrane-bound microbial metabolites in modulating host immunity in the gut, and of immune cells-derived metabolites affecting the microbiota, while discussing evidence of the bidirectional impact of this crosstalk. Furthermore, we discuss the potential strategies to hear the sound of such metabolite-mediated crosstalk.

Pyridoxine supplementation during oocyte maturation improves the development and quality of bovine preimplantation embryos

Recently, inhibition of cathepsin B (CTSB) activity during in vitro maturation (IVM) and culture (IVC) improved the developmental competence and quality of bovine oocytes and embryos. E-64 is a widely used inhibitor to inhibit CTSB activity, however, E-64 inhibits not only CTSB activity but also the activities of other proteases including cathepsin L (CTSL), papain, calpain, and trypsin. Pyridoxine, the catalytically active form of vitamin B6, plays a crucial role in several cellular processes and has the ability to inhibit CTSB activity. However, whether pyridoxine has an improving effect during IVM of bovine oocytes is still unknown. In this study, we investigated the effect of pyridoxine supplementation during IVM on the developmental competence of bovine oocytes and the quality of the produced blastocysts. Supplementation of pyridoxine to the maturation medium significantly decreased the activity of CTSB in both bovine cumulus cells and oocytes. Moreover, pyridoxine improved both the blastocyst and hatched blastocyst rates. In addition, the presence of pyridoxine during IVM also significantly improved the quality of the produced embryos by increasing the total cell number as well as decreasing the CTSB mRNA expression and apoptotic rate. These results indicate that pyridoxine is a promising tool to improve the developmental competence of bovine oocytes and subsequent embryo quality.

High dose dietary pyridoxine induces T-helper type 1 polarization and decreases contact hypersensitivity response to fluorescein isothiocyanate in mice

Pyridoxine (vitamin B(6)) is commonly used as a dietary supplement and beneficial effects of it are expected. However, excess ingestion of pyridoxine has been shown to cause a severe sensory neuropathy in humans and experimental animals. We have been studying the linkage between the nervous and immune systems using a fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) mouse model. We have found that activation of transient receptor potential ankyrin 1 (TRPA1), which is expressed on sensory neurons, enhances skin sensitization to FITC. Another feature of FITC-induced CHS is its dependence on T helper 2 (Th2) type responses. We hypothesized that the excess intake of pyridoxine may affect sensitization to FITC and influence helper T-cell polarization. We examined FITC-induced CHS in BALB/c mice fed a diet containing excess pyridoxine (120 mg/kg diet) for 3 weeks. We found that mice fed on the excess-pyridoxine diet exhibited a lower response as to FITC-induced CHS compared with ones fed on a diet with a standard pyridoxine content (6.0 mg/kg diet). Moreover, the interferon (IFN)-γ/interleukin (IL)-4 ratio produced by draining lymph node cells was significantly higher with the excess-pyridoxine diet. This suggested that the cytokine balance was shifted toward Th1 with the excess-pyridoxine diet. Consistently, Th1-dependent oxazolone-induced CHS was enhanced with the excess-pyridoxine diet. These results suggested that an excess pyridoxine intake actively influences the immune system by altering helper T cell polarization.

Dietary factors impact on the association between CTSS variants and obesity related traits

Background/Aims

Cathepsin S, a protein coded by the CTSS gene, is implicated in adipose tissue biology–this protein enhances adipose tissue development. Our hypothesis is that common variants in CTSS play a role in body weight regulation and in the development of obesity and that these effects are influenced by dietary factors–increased by high protein, glycemic index and energy diets.

Methods

Four tag SNPs (rs7511673, rs11576175, rs10888390 and rs1136774) were selected to capture all common variation in the CTSS region. Association between these four SNPs and several adiposity measurements (BMI, waist circumference, waist for given BMI and being a weight gainer–experiencing the greatest degree of unexplained annual weight gain during follow-up or not) given, where applicable, both as baseline values and gain during the study period (6–8 years) were tested in 11,091 European individuals (linear or logistic regression models). We also examined the interaction between the CTSS variants and dietary factors–energy density, protein content (in grams or in % of total energy intake) and glycemic index–on these four adiposity phenotypes.

Results

We found several associations between CTSS polymorphisms and anthropometric traits including baseline BMI (rs11576175 (SNP N°2), p = 0.02, β = −0.2446), and waist change over time (rs7511673 (SNP N°1), p = 0.01, β = −0.0433 and rs10888390 (SNP N°3), p = 0.04, β = −0.0342). In interaction with the percentage of proteins contained in the diet, rs11576175 (SNP N°2) was also associated with the risk of being a weight gainer (p_interaction = 0.01, OR = 1.0526)–the risk of being a weight gainer increased with the percentage of proteins contained in the diet.

Conclusion

CTSS variants seem to be nominally associated to obesity related traits and this association may be modified by dietary protein intake.

Vitamin B6 protects primate retinal neurons from ischemic injury

Vitamin B6 derivatives protect the retinal neurons from excitotoxic injury in vitro. However, their in vivo role in a process involving excitotoxicity, such as ischemia, remains unknown. We studied potential protective effects of pyridoxal 5'-phosphate (PLP) and pyridoxal hydrochloride (pyridoxal) on the retinal neurons in a monkey model of transient global ischemia. Daily intravenous injections (15 mg/kg) of pyridoxal and PLP were performed for consecutive 10 days. On the sixth day, whole brain complete ischemia was produced by clipping the innominate and the left subclavian arteries for 20 min. The monkeys were sacrificed 5 days after ischemia and their retinas were processed for histological analysis. The ischemia induced a marked cellular injury in the retina as shown by the loss of ganglion cells and the reduction of thickness of the ganglion cell, inner plexiform, and inner nuclear layers. PLP significantly prevented the ganglion cell loss and the reduction of thickness of the ganglion cell layer. Pyridoxal significantly prevented the ganglion cell loss as well as the reduction of thickness of ganglion cell, inner plexiform and inner nuclear layers. These results suggest that PLP and pyridoxal counteract the postischemic neuronal death in the adult primate retina, offering a potential for a novel pharmacotherapy of retinal ischemic injury.