Biology subjects

Neilson, A. P.

Publications and source records attributed to Neilson, A. P..

5 recordsLinked to original sources

bioRxiv2025

Inhibition of pro-atherogenic trimethylamine production by human gut bacteria is not determined by varying chlorogenic acid content in highbush blueberries

Elevated blood levels of trimethylamine N-oxide (TMAO) are linked to increased risk of atherosclerosis. TMAO is produced when gut bacteria metabolize quaternary amines such as choline to trimethylamine (TMA), which is converted to TMAO in the liver. Chlorogenic acid (CGA), a phenolic abundant in blueberries, inhibits TMA production. Blueberries may be a TMA- (and TMAO)-lowering food. CGA content in blueberries varies significantly. It remains unclear whether variations in CGA levels influence the TMA-lowering activity of different cultivars. We investigated the impact of blueberry CGA content on inhibition of choline-d9 conversion to TMA-d9 in our upper gastrointestinal and in vitro human fecal model. Preliminary experiments indicated near-total inhibition of TMA-d9 production when whole blueberries were tested. Blueberry pulp and sugars recapitulated this complete inhibition, whereas blueberry skins and a fiber had more moderate inhibition. We proceeded with skins (to avoid interferences from sugar-rich pulp, which would not be present in the colon in vivo) from 20 highbush blueberry genotypes, chosen for extremes in CGA content. CGA in whole berries was 2.6-146 mg/100 g fresh weight, while CGA in skins was 13.6-975 mg/100 g fresh weight. No differences were observed in TMA-d9 production among the 4 highest and 4 lowest CGA genotypes in kinetic curves or area under the curve (AUC) values when skin digesta were fermented with choline-d9. However, significant differences were observed between all genotypes compared to blank digesta, with [~]19.4.% reduction in TMA-d9 AUCs, indicating that skins provides similar TMA-lowering benefits across genotypes. Levels of free CGA in fermenta of skin digesta were 0.05-0.3 M, >1000-fold lower than the minimum effective dose we observed for pure CGA in vitro, suggesting that blueberry CGA content is not a crucial factor for lowering TMA. Fiber also does not account for most of the inhibitory activity of blueberry skins. Studies are needed to confirm this in vitro study and understand how blueberries inhibit TMA and potentially TMAO production in vivo.

microbiology↗

bioRxiv2024

Establishing reliable blood biomarkers for trimethylamine N-oxide status in rodents: effects of oral choline challenge, dietary choline and fasting conditions

Circulating concentrations of the gut microbial-mammalian metabolite trimethylamine N-oxide (TMAO) is linked to atherosclerosis risk. TMAO biosynthesis begins when dietary choline is converted to trimethylamine (TMA) by gut microbial TMA lyase. TMA is transported to the liver, where flavin-containing monooxygenases convert it to TMAO. While dietary modifications regulate TMAO production, the impact of different intake methods, including oral gavage, dietary supplementation, and conditions such as fasting versus non-fasting, has not been fully explored. Twelve female Sprague-Dawley rats were divided into three diet groups (n = 4 per group): no-choline (0% choline), low-choline (0.08% choline), and high-choline (1% choline). Choline and TMAO fasting and non-fasting blood concentrations, and their kinetics following an acute choline challenge, were assessed before and after a 2-week dietary intervention with the distinct choline dietary levels. Fasting choline was under tight control, with little effect of dietary choline. Non-fasting choline was more variable, with high dietary choline reflected in higher blood choline. Greater levels of dietary choline were reflected in significantly greater levels of TMAO, particularly for non-fasting levels. Kinetic profiling demonstrated additional information regarding the appearance and clearance of these compounds from blood. These results suggest that acute oral choline gavage is likely most suitable for studies targeting acute (direct) inhibitors, whereas a choline-rich diet with assessment of fasting and non-fasting blood levels is more suitable for studying alterations to TMAO production capacity. Future research should examine the impact on atherosclerosis biomarkers and microbiome diversity to deepen the understanding of TMAO regulation and its cardiovascular implications.

biochemistry↗

bioRxiv2023

Dietary phenolics and their microbial metabolites are poor inhibitors of trimethylamine oxidation to trimethylamine N-oxide by hepatic flavin monooxygenase 3

High circulating levels of trimethylamine N-oxide (TMAO) have been associated with cardiovascular disease risk. TMAO is formed through a microbiome-host pathway utilizing primarily dietary choline as a substrate. Specific gut microbiota transform choline into trimethylamine (TMA), and, when absorbed, host hepatic flavin-containing monooxygenase 3 (FMO3) oxidizes TMA into TMAO. Chlorogenic acid and its metabolites reduce microbial TMA production in vitro. However, little is known regarding the potential for chlorogenic acid and its bioavailable metabolites to inhibit the last step: hepatic conversion of TMA to TMAO. We developed a screening methodology to study FMO3-catalyzed production of TMAO from TMA. HepG2 cells were unable to oxidize TMA into TMAO due to their lack of FMO3 expression. Although Hepa-1 cells did express FMO3 when pre-treated with TMA and NADPH, they lacked enzymatic activity to produce TMAO. Rat hepatic microsomes contained active FMO3. Optimal reaction conditions were: 50 {micro}M TMA, 0.2 mM NADPH and 33 {micro}L microsomes/mL reaction. Methimazole (a known FMO3 competitive substrate) at 200 {micro}M effectively reduced FMO3-catalyzed conversion of TMA to TMAO. However, bioavailable chlorogenic acid metabolites did not generally inhibit FMO3 at physiological (1 {micro}M) nor supra-physiological (50 {micro}M) doses. Thus, the effects of chlorogenic acid in regulating TMAO levels in vivo are unlikely to occur through direct FMO3 enzyme inhibition. Potential effects on FMO3 expression remain unknown. Intestinal inhibition of TMA production and/or absorption are thus likely their primary mechanisms of action.

biochemistry↗

bioRxiv2022

Cocoa Extract Exerts Sex-Specific Effects in an Aggressive Hyperglycemia Model: A Pilot Study

Type 2 diabetes (T2D) is characterized by hyperglycemia and insulin resistance. Cocoa may slow T2D development and progression. This study employed male and female BTBR.Cg-Lepob/ob/WiscJ (ob/ob) and wild type (WT) controls to assess the potential for cocoa to ameliorate progressive T2D and compare responses between sexes. Mice received diet without (WT, ob/ob) or with cocoa extract (ob/ob + c) for 10 weeks. Acute cocoa reduced fasting hyperglycemia in females, but not males, after 2 weeks. Chronic cocoa supplementation (6-10 weeks) ameliorated hyperinsulinemia in males and worsened hyperlipidemia and hyperinsulinemia in females, yet also preserved and enhanced beta cell survival in females. The underlying mechanisms of these differences warrant further study. If sex differences are apparent in subsequent preclinical studies, clinical studies will be warranted to establish whether these differences are relevant in humans. Sex differences may need to be considered when designing human dietary interventions for T2D.

biochemistry↗

bioRxiv2020

Microbial metabolites of flavanols in urine are associated with enhanced anti-proliferative activity in bladder cancer cells in vitro

Dietary flavanols and their metabolites are excreted primarily via the urine, suggesting uroepithelial cells as a site of activity due to lengthy exposure to high concentrations of these compounds. Flavanols are metabolized by the gut microbiota to numerous bioavailable metabolites. The observed effects of flavanols, including cancer chemoprevention, may be due in part to the activities of microbial metabolites. Most in vitro mechanistic work in this area relies on a limited pool of commercially available or synthesized flavanol microbial metabolites, and little work has been done in the area of bladder cancer. The impact of physiologically relevant mixtures of native flavanols and their metabolites generated in vivo remains unknown. Rats were fed various flavanols after which 48 h urine samples, approximating the total bioavailable metabolome, were collected. Urine samples were profiled by UPLC-MS/MS, and their anti-proliferative activities were assayed in vitro in four bladder cancer cell models. Significant interindividual variability was observed for chemical profiles and anti-proliferative activities. Concentrations of microbial metabolites (valerolactones, phenylalkyl acids and hippuric acids) were positively associated with reduced bladder cancer cell proliferation in vitro, while native flavanols were poorly correlated with activity. These results suggest that microbial metabolites may be the primary compounds responsible for chemoprevention in uroepithelial cell following flavanol consumption. Furthermore, this highlights the potential for exploiting knowledge about individual genetics, microbiome profiles, flavonoid metabolism profiles, tumor characteristics, etc. to design personalized dietary interventions for cancer prevention and/or adjuvant therapy to reduce bladder cancer incidence and improve outcomes.

cancer biology↗