Sweetener System Intervention Shifted Neutrophils from Homeostasis to Priming.

BACKGROUND: Non-nutritive sweeteners (NNS) are part of personalized nutrition strategies supporting healthy glycemic control. In contrast, the consumption of non-nutritive sweeteners has been related to person-specific and microbiome-dependent glycemic impairments. Reports on the effects of NNS on our highly individual cellular immune system are sparse. The recent identification of taste receptor expression in a variety of immune cells, however, suggested their immune-modulatory relevance. METHODS: We studied the influence of a beverage-typical NNS system on the transcriptional profiling of sweetener-cognate taste receptors, selected cytokines and their receptors, and on Ca2+ signaling in isolated blood neutrophils. We determined plasma concentrations of saccharin, acesulfame-K, and cyclamate by HPLC-MS/MS, upon ingestion of a soft drink-typical sweetener surrogate. In an open-labeled, randomized intervention study, we determined pre- versus post-intervention transcript levels by RT-qPCR of sweetener-cognate taste receptors and immune factors. RESULTS: Here we show that the consumption of a food-typical sweetener system modulated the gene expression of cognate taste receptors and induced the transcriptional regulation signatures of early homeostasis- and late receptor/signaling- and inflammation-related genes in blood neutrophils, shifting their transcriptional profile from homeostasis to priming. Notably, sweeteners at postprandial plasma concentrations facilitated fMLF (N-formyl-Met-Leu-Phe)-induced Ca2+ signaling. CONCLUSIONS: Our results support the notion of sweeteners priming neutrophils to higher alertness towards their adequate stimuli.

Modeling the Orthosteric Binding Site of the G Protein-Coupled Odorant Receptor OR5K1.

With approximately 400 encoding genes in humans, odorant receptors (ORs) are the largest subfamily of class A G protein-coupled receptors (GPCRs). Despite its high relevance and representation, the odorant-GPCRome is structurally poorly characterized: no experimental structures are available, and the low sequence identity of ORs to experimentally solved GPCRs is a significant challenge for their modeling. Moreover, the receptive range of most ORs is unknown. The odorant receptor OR5K1 was recently and comprehensively characterized in terms of cognate agonists. Here, we report two additional agonists and functional data of the most potent compound on two mutants, L1043.32 and L2556.51. Experimental data was used to guide the investigation of the binding modes of OR5K1 ligands into the orthosteric binding site using structural information from AI-driven modeling, as recently released in the AlphaFold Protein Structure Database, and from homology modeling. Induced-fit docking simulations were used to sample the binding site conformational space for ensemble docking. Mutagenesis data guided side chain residue sampling and model selection. We obtained models that could better rationalize the different activity of active (agonist) versus inactive molecules with respect to starting models and also capture differences in activity related to minor structural differences. Therefore, we provide a model refinement protocol that can be applied to model the orthosteric binding site of ORs as well as that of GPCRs with low sequence identity to available templates.

An evolutionary conserved olfactory receptor for foodborne and semiochemical alkylpyrazines.

Molecular recognition is a fundamental principle in biological systems. The olfactory detection of both food and predators via ecological relevant odorant cues are abilities of eminent evolutionary significance for many species. Pyrazines are such volatile cues, some of which act as both human-centered key food odorants (KFOs) and semiochemicals. A pyrazine-selective odorant receptor has been elusive. Here we screened 2,3,5-trimethylpyrazine, a KFO and semiochemical, and 2,5-dihydro-2,4,5-trimethylthiazoline, an innate fear-associated non-KFO, against 616 human odorant receptor variants, in a cell-based luminescence assay. OR5K1 emerged as sole responding receptor. Tested against a comprehensive collection of 178 KFOs, we newly identified 18 pyrazines and (2R/2S)-4-methoxy-2,5-dimethylfuran-3(2H)-one as agonists. Notably, OR5K1 orthologs in mouse and domesticated species displayed a human-like, potency-ranked activation pattern of pyrazines, suggesting a domestication-led co-evolution of OR5K1 and its orthologs. In summary, OR5K1 is a specialized olfactory receptor across mammals for the detection of pyrazine-based key food odors and semiochemicals.

Food sources and biomolecular targets of tyramine.

Tyramine is a biogenic trace amine that is generated via the decarboxylation of the amino acid tyrosine. At pico- to nanomolar concentrations, it can influence a multitude of physiological mechanisms, exhibiting neuromodulatory properties as well as cardiovascular and immunological effects. In humans, the diet is the primary source of physiologically relevant tyramine concentrations, which are influenced by a large number of intrinsic and extrinsic factors. Among these factors are the availability of tyrosine in food, the presence of tyramine-producing bacteria, the environmental pH, and the salt content of food. The process of fermentation provides a particularly good source of tyramine in human nutrition. Here, the potential impact of dietary tyramine on human health was assessed by compiling quantitative data on the tyramine content in a variety of foods and then conducting a brief review of the literature on the physiological, cellular, and systemic effects of tyramine. Together, the data sets presented here may allow both the assessment of tyramine concentrations in food and the extrapolation of these concentrations to gauge the physiological and systemic effects in the context of human nutrition.

Ratio of T-Helper Type 1 (Th1) to Th17 Cytokines in Whole Blood Is Associated With Human ß-Defensin 3 Expression in Skin and Persistent Staphylococcus aureus Nasal Carriage.

BACKGROUND: Nasal colonization has gained attention as an effect modifier in Staphylococcus aureus vaccine trials, suggesting interference of carriage with T-cell immunity. Likewise, T-cell signals may be involved in regulating effectors of epithelial innate defense. METHODS: Whole blood from 43 persistent carriers and 49 noncarriers was stimulated with viable S. aureus T-helper type 1 (Th1), Th2, and Th17 cytokine expression was measured, compared between carrier groups, and linked with data on human ß-defensin 3 (hBD-3) messenger RNA (mRNA) in skin while adjusting for transcriptionally relevant promoter haplotypes. RESULTS: Compared with carriers, stimulated whole blood from noncarriers contained on average 60% more interferon γ mRNA (P = .031) and 19% less interleukin 17A (IL-17A) mRNA (P = .11), resulting in, on average, a 90% higher IFN-γ to IL-17A mRNA ratio (P = .003). In a multivariable model, per duplication of the mRNA template, the risk of being a carrier increased by 93% for IL-17A (odds ratio [OR], 1.93; 95% confidence interval [CI], 1.10-3.41; P = .023) and decreased by 35% for IFN-γ (OR, 0.65; 95% CI, 0.47-0.91; P = .01). Independent of carriage and DEFB promotor haplotype, a 1-unit increase in the IFN-γ to IL-17A mRNA ratio (mean ± SD, 5.93 ± 1.60) led to a 24% increase in hBD-3 transcription in experimentally wounded human skin (P = .003). CONCLUSIONS: A low Th1 to Th17 mRNA ratio increases the propensity for persistent S. aureus nasal colonization, with downregulated hBD-3 transcription providing a potential link.

Hepatitis E Virus Superinfection and Clinical Progression in Hepatitis B Patients.

Hepatitis E virus (HEV) infection may cause acute hepatitis and lead to hepatic failure in developing and developed countries. We studied HEV seroprevalences in patients with hepatitis B virus (HBV) infection to understand the consequences of HEV superinfection in a Vietnamese population. This cross-sectional study was conducted from 2012 to 2013 and included 1318 Vietnamese patients with HBV-related liver diseases and 340 healthy controls. The case group included patients with acute (n = 26) and chronic hepatitis B (n = 744), liver cirrhosis (n = 160), hepatocellular carcinoma (n = 166) and patients with both liver cirrhosis and hepatocellular carcinoma (n = 222). Anti-HEV IgG and IgM antibodies were assessed in patients and controls by ELISA. HEV-RNA was identified by PCR assays and sequencing. Seroprevalences of anti-HEV IgG among hepatitis B patients and controls were 45% and 31%, respectively (adjusted P = 0.034). Anti-HEV IgM seroprevalences were 11.6% and 4.7% in patients and controls, respectively (adjusted P = 0.005). Seroprevalences were higher among the elder individuals. When stratifying for patient groups, those with liver cirrhosis had the highest anti-HEV IgG (52%) and anti-HEV IgM (19%) seroprevalences. Hepatitis B patients with current HEV infection had abnormal liver function tests compared to patients with past or without HEV infection. One HEV isolate was retrieved from a patient with both liver cirrhosis and hepatocellular carcinoma and identified as HEV genotype 3. This study indicates high prevalences of HEV infection in Vietnamese HBV patients and among healthy individuals and shows that HEV superinfection may influence the outcome and progression of HBV-related liver disease.

LRRK2 and RIPK2 variants in the NOD 2-mediated signaling pathway are associated with susceptibility to Mycobacterium leprae in Indian populations.

In recent years, genome wide association studies have discovered a large number of gene loci that play a functional role in innate and adaptive immune pathways associated with leprosy susceptibility. The immunological control of intracellular bacteria M. leprae is modulated by NOD2-mediated signaling of Th1 responses. In this study, we investigated 211 clinically classified leprosy patients and 230 ethnically matched controls in Indian population by genotyping four variants in NOD2 (rs9302752A/G), LRRK2 (rs1873613A/G), RIPK2 (rs40457A/G and rs42490G/A). The LRRK2 locus is associated with leprosy outcome. The LRRK2 rs1873613A minor allele and respective rs1873613AA genotypes were significantly associated with an increased risk whereas the LRRK2 rs1873613G major allele and rs1873613GG genotypes confer protection in paucibacillary and leprosy patients. The reconstructed GA haplotypes from RIPK2 rs40457A/G and rs42490G/A variants was observed to contribute towards increased risk whereas haplotypes AA was observed to confer protective role. Our results indicate that a possible shared mechanisms underlying the development of these two clinical forms of the disease as hypothesized. Our findings confirm and validates the role of gene variants involved in NOD2-mediated signalling pathways that play a role in immunological control of intracellular bacteria M. leprae.

Genetic evidence of TAP1 gene variant as a susceptibility factor in Indian leprosy patients.

The heterodimeric transporter associated with antigen processing (TAP) gene loci is known to play a vital role in immune surveillance. We investigated a possible association of gene polymorphisms both in TAP1 and TAP2 in a cohort of clinically classified leprosy patients (n=222) and in ethnically matched controls (n=223). The TAP1 and TAP2 genes were genotyped for four single nucleotide polymorphisms TAP1 (rs1057141 Iso333Val and rs1135216 Asp637Gly) and TAP2 (rs2228396 Ala565Thr and rs241447 Ala665Thr) by direct sequencing and ARMS-PCR. The minor allele of TAP1 637G contributes to an increased risk to leprosy compared to controls (OR: 1.68, 95% CI 1.2-2.36, P=0.0057). An increased risk for the variant minor allele of the TAP1 637G to multibacillary (BL+LL) or paucibacillary (BT+TT) infections was also observed [multibacillary vs. controls (OR: 1.56, 95% CI 1.07-2.28, P=0.054); paucibacillary vs. controls (OR: 1.92, 95% CI 1.21-3.01, P=0.013)]. In the dominant model, the genotypes of the TAP1 rs1135216AG+GG additionally contributed to an increased risk. Overall our findings demonstrate that the TAP1 gene variant (rs1135216 Asp637Gly) influences the susceptibility to clinically classified leprosy patients in Indian population.