Impact of altering gut microbiota metabolism on osteomyelitis severity in obesity-related type 2 diabetes

Staphylococcus aureus is an opportunistic pathogen causing osteomyelitis through hematogenous seeding or contamination of implants and open wounds following orthopedic surgeries. The severity of S. aureus-mediated osteomyelitis is enhanced in obesity-related type 2 diabetes (obesity/T2D) due to chronic inflammation impairing both adaptive and innate immunity. Obesity-induced inflammation is linked to gut dysbiosis, with modification of the gut microbiota by high-fiber diets leading to a reduction in the symptoms and complications of obesity/T2D. However, our understanding of the mechanisms by which modifications of the gut microbiota alter host infection responses is limited. To address this gap, we monitored tibial S. aureus infections in obese/T2D mice treated with the inulin-like fructan fiber, oligofructose. Treatment with oligofructose significantly decreased S. aureus colonization and lowered proinflammatory signaling post-infection in obese/T2D mice, as observed by decreased circulating inflammatory cytokines (TNF-α) and chemokines (IP-10, KC, MIG, MCP-1, and RANTES), indicating partial reduction in inflammation. Oligofructose markedly shifted diversity in the gut microbiota of obese/T2D mice mice, with notable increases in the anti-inflammatory bacterium, Bifidobacterium pseudolongum. Analysis of the cecum and plasma metabolome suggested polyamine production was increased, specifically spermine and spermidine. Oral administration of these polyamines to obese/T2D mice resulted in reduced infection severity similar to oligofructose supplementation, suggesting polyamines can mediate the beneficial effects of fiber on osteomyelitis severity. These results demonstrate the contribution of gut microbiota metabolites to the control of bacterial infections distal to the gut and polyamines as an adjunct therapeutic for osteomyelitis in obesity/T2D.

Chronic kidney disease is associated with attenuated plasma metabolome response to oral glucose tolerance testing

Chronic kidney disease (CKD), a major public health problem, is associated with decreased anabolic response to insulin contributing to protein-energy wasting. Targeted metabolic profiling of the response to oral glucose tolerance testing (OGTT) may help identify metabolic pathways contributing to disruptions to insulin response in CKD. Using targeted metabolic profiling, we examined plasma metabolome in 41 moderate-to-severe non-diabetic CKD patients with estimated glomerular filtration rate (eGFR)<60ml/min per 1.73m2 (38.9+-12.7) and 20 healthy controls with normal eGFR (87.2+-17.7) before and after 2h of 75g oral glucose load. Compared to controls, CKD participants had higher lactate: pyruvate (L:P) ratio both at fasting and after oral glucose challenge. Total energy production estimated through GTP:GDP ratio was impaired during OGTT despite similar fasting GTP:GDP ratio. CKD group had sustained elevation of vitamin B family members, TCA cycle metabolites, and purine nucleotides in response to glucose challenge. Metabolic profiling in response to OGTT suggests a broad disruption of mitochondrial energy metabolism in CKD patients. These findings motivate further investigation into insulin sensitizers in patients with non-diabetic CKD and their impact on energy metabolism.

Gut Microbiome and Plasma Metabolome Signatures in Middle-Aged Mice With Cognitive Dysfunction Induced by Chronic Neuropathic Pain

Patients with chronic neuropathic pain (CNP) often complain about their terrible memory, especially the speed of information processing. Accumulating evidence suggests a possible link between gut microbiota and pain processing as well as cognitive function via the microbiota-gut-brain axis. This study aimed at exploring the fecal microbiome and plasma metabolite profiles in middle-aged spared nerve injury (SNI) mice model with cognitive dysfunction (CD) induced by CNP. The hierarchical cluster analysis of performance in the Morris water maze test was used to classify SNI mice with CD or without CD [i.e., non-CD (NCD)] phenotype. 16S rRNA sequencing revealed a lower diversity of gut bacteria in SNI mice, and the increase of Actinobacteria, Proteus, and Bifidobacterium might contribute to the cognitive impairment in the CNP condition. The plasma metabolome analysis showed that the endocannabinoid (eCB) system, disturbances of lipids, and amino acid metabolism might be the dominant signatures of CD mice. The fecal microbiota transplantation of the Sham (not CD) group improved allodynia and cognitive performance in pseudo-germ-free mice via normalizing the mRNA expression of eCB receptors, such as cn1r, cn2r, and htr1a, reflecting the effects of gut bacteria on metabolic activity. Collectively, the findings of this study suggest that the modulation of gut microbiota and eCB signaling may serve as therapeutic targets for cognitive deficits in patients with CNP.

Metabolomic Profiling Identifies Exogenous and Microbiota-Derived Metabolites as Markers of Methotrexate Efficacy in Juvenile Idiopathic Arthritis

Variability in methotrexate (MTX) efficacy represents a barrier to early and effective disease control in the treatment of juvenile idiopathic arthritis (JIA). This work seeks to understand the impact of MTX on the plasma metabolome and to identify metabolic biomarkers of MTX efficacy in a prospective cohort of children with JIA. Plasma samples from a cohort of children with JIA (n = 30) collected prior to the initiation of MTX and after 3 months of therapy were analyzed using a semi-targeted global metabolomic platform detecting 673 metabolites across a diversity of biochemical classes. Disease activity was measured using the 71-joint count juvenile arthritis disease activity score (JADAS-71) and clinical response to MTX was based on achievement of ACR Pedi 70 response. Metabolomic analysis identified 50 metabolites from diverse biochemical classes that were altered following the initiation of MTX (p &lt; 0.05) with 15 metabolites reaching a false-discovery rate adjusted p-value (q-value) of less than 0.05. Enrichment analysis identified a class-wide reduction in unsaturated triglycerides following initiation of MTX (q = 0.0009). Twelve of the identified metabolites were significantly associated with disease activity by JADAS-71. Reductions in three metabolites were found to be associated with clinical response by ACR Pedi 70 response criteria and represented several microbiota and exogenously derived metabolites including: dehydrocholic acid, biotin, and 4-picoline. These findings support diverse metabolic changes following initiation of MTX in children with JIA and identify metabolites associated with microbial metabolism and exogenous sources associated with MTX efficacy.

Plasma Metabolome Normalization in Rheumatoid Arthritis Following Initiation of Methotrexate and the Identification of Metabolic Biomarkers of Efficacy

Methotrexate (MTX) efficacy in the treatment of rheumatoid arthritis (RA) is variable and unpredictable, resulting in a need to identify biomarkers to guide drug therapy. This study evaluates changes in the plasma metabolome associated with response to MTX in RA with the goal of understanding the metabolic basis for MTX efficacy towards the identification of potential metabolic biomarkers of MTX response. Plasma samples were collected from healthy control subjects (n = 20), and RA patients initiating MTX therapy (n = 20, 15 mg/week) before and after 16 weeks of treatment. The samples were analyzed by a semi-targeted metabolomic analysis, and then analyzed by univariate and multivariate methods, as well as an enrichment analysis. An MTX response was defined as a clinically significant reduction in the disease activity score in 28 joints (DAS-28) of greater than 1.2; achievement of clinical remission, defined as a DAS-28 < 2.6, was also utilized as an additional measure of response. In this study, RA is associated with an altered plasma metabolome that is normalized following initiation of MTX therapy. Metabolite classes found to be altered in RA and corrected by MTX therapy were diverse and included triglycerides (p = 1.1 × 10−16), fatty acids (p = 8.0 × 10−12), and ceramides (p = 9.8 × 10−13). Stratification based on responses to MTX identified various metabolites differentially impacted in responders and non-responders including glucosylceramides (GlcCer), phosphatidylcholines (PC), sphingomyelins (SM), phosphatidylethanolamines (PE), choline, inosine, hypoxanthine, guanosine, nicotinamide, and itaconic acid (p < 0.05). In conclusion, RA is associated with significant alterations to the plasma metabolome displaying at least partial normalization following 16 weeks of MTX therapy. Changes in multiple metabolites were found to be associated with MTX efficacy, including metabolites involved in fatty acid/lipid, nucleotide, and energy metabolism.

Effect of Dairy Matrix on the Postprandial Blood Metabolome

This study investigated the postprandial plasma metabolome following consumption of four dairy matrices different in texture and structure: cheddar cheese (Cheese), homogenized cheddar cheese (Hom. Cheese), and micellar casein isolate (MCI) with cream (MCI Drink) or a MCI Gel. An acute, randomized, crossover trial in male participants (n = 25) with four test days was conducted. Blood samples were collected during an 8-h postprandial period after consumption of a meal similar in micro- and macronutrients containing one of the four dairy matrices, and the metabolome was analyzed using nuclear magnetic resonance (NMR) spectroscopy. A liquid dairy matrix (MCI Drink) resulted in a faster absorption of amino acids compared to products, representing either a semi-solid (MCI Gel and Hom. Cheese) or solid (Cheese) dairy matrix. For the MCI Gel, plasma concentration of acetic acid and formic acid increased approximately 2 h following consumption, while 3-hydroxybyturate and acetoacetic acid increased approximately 6 h after consumption. The structure and texture of the dairy matrix affected the postprandial absorption of amino acids, as revealed by the plasma metabolome. Our study furthermore pointed at endogenous effects associated with consumption of dairy products containing glucono-δ-lactone.

Neutrophil Metabolic Rewiring in Severe and Mild COVID-19

SARS-CoV-2 infection can cause severe respiratory disease resulting in hospitalization and death in some people, but in others it causes a mild disease or is asymptomatic. The causes of severe COVID-19 are of profound public health importance. Severe COVID-19 is marked by an exacerbated innate immune response leading to hyperinflammation which damages host tissues. Broad inhibition of hyperinflammation by dexamethasone is a mainstay of severe COVID-19 treatment. However, more targeted therapeutic approaches to dampen hyperinflammation are lacking. Patients typically exhibit increased neutrophil numbers in the blood and lung, and increased formation of neutrophil extracellular traps. Previous work profiled the metabolome of plasma in severe COVID-19 patients and found several metabolic aberrations as compared to mild COVID-19 patients or healthy controls. However, the metabolome of immune cell populations in COVID-19 has not been characterized to our knowledge. In addition, it is not known if metabolic changes observed in severe COVID-19 mechanistically contribute to hyperinflammation and host tissue damage or if they are simply markers of pathology. To understand how metabolism can regulate the innate immune system in COVID-19 and to explore possible therapeutic targets, we carried out a comprehensive metabolomic study of neutrophils purified from healthy controls, mild/moderate COVID-19 patients, and severe COVID-19 patients. Severe COVID-19 patients were defined as having Acute Respiratory Distress and being treated in the intensive care unit. Plasma from the same patients and healthy controls was also collected and metabolomics was performed to study how COVID-19 impacts the neutrophil and plasma metabolome in tandem. Several metabolic pathways were significantly different between mild COVID-19 patients, severe COVID-19 patients, and healthy controls, consistent with rewired neutrophil and plasma metabolome in severe COVID-19. Differentially abundant metabolites belonged to central carbon metabolism, nucleotide metabolism, amino acid metabolism and other pathways. Variation in the PMN metabolome was largely independent from variation in the plasma metabolome. This suggests that processes internal to neutrophils drive changes in neutrophil metabolism. Metabolomics in 3 mouse models of hyperinflammation showed common or distinct metabolic features that change in inflammation compared to metabolomics of severe COVID-19 patients. Therefore changes in some metabolites comprise a general hyperinflammatory metabolic signature while others are more specific to severe COVID-19. Isotope tracing experiments were carried out to understand how nutrients were utilized in neutrophils in context of inflammation. We will describe mechanistic work testing whether metabolic features we observe in severe COVID-19 patients regulate the inflammatory response of human neutrophils. Disclosures No relevant conflicts of interest to declare.

Metabolomic differences in lung function metrics: evidence from two cohorts

RationaleThe biochemical mechanisms underlying lung function are incompletely understood.ObjectivesTo identify and validate the plasma metabolome of lung function using two independent adult cohorts: discovery—the European Prospective Investigation into Cancer–Norfolk (EPIC-Norfolk, n=10 460) and validation—the VA Normative Aging Study (NAS) metabolomic cohort (n=437).MethodsWe ran linear regression models for 693 metabolites to identify associations with forced expiratory volume in one second (FEV1) and the ratio of FEV1 to forced vital capacity (FEV1/FVC), in EPIC-Norfolk then validated significant findings in NAS. Significance in EPIC-Norfolk was denoted using an effective number of tests threshold of 95%; a metabolite was considered validated in NAS if the direction of effect was consistent and p<0.05.Measurements and main resultsOf 156 metabolites that associated with FEV1 in EPIC-Norfolk after adjustment for age, sex, body mass index, height, smoking and asthma status, 34 (21.8%) validated in NAS, including several metabolites involved in oxidative stress. When restricting the discovery sample to men only, a similar percentage, 18 of 79 significant metabolites (22.8%) were validated. A smaller number of metabolites were validated for FEV1/FVC, 6 of 65 (9.2%) when including all EPIC-Norfolk as the discovery population, and 2 of 34 (5.9%) when restricting to men. These metabolites were characterised by involvement in respiratory track secretants. Interestingly, no metabolites were validated for both FEV1 and FEV1/FVC.ConclusionsThe validation of metabolites associated with respiratory function can help to better understand mechanisms of lung health and may assist the development of biomarkers.

Effects of Tirzepatide, a Dual GIP and GLP-1 RA, on Lipid and Metabolite Profiles in Subjects with Type 2 Diabetes

Context Tirzepatide substantially reduced HbA1c and body weight in subjects with type 2 diabetes (T2D) compared with the GLP-1 receptor agonist dulaglutide. Improved glycemic control was associated with lower circulating triglycerides and lipoprotein markers and improved markers of beta-cell function and insulin resistance (IR), effects only partially attributable to weight loss. Objective Assess plasma metabolome changes mediated by tirzepatide. Design Phase 2b trial participants were randomly assigned to receive weekly subcutaneous tirzepatide, dulaglutide, or placebo for 26 weeks. Post hoc exploratory metabolomics and lipidomics analyses were performed. Setting Post hoc analysis. Patients or Other Participants 259 subjects with T2D. Intervention(s) Tirzepatide (1, 5, 10, 15 mg), dulaglutide (1.5 mg), placebo. Main Outcome Measure(s) Changes in metabolite levels in response to tirzepatide were assessed against baseline levels, dulaglutide, and placebo using multiplicity correction. Results At 26 weeks, higher dose tirzepatide modulated a cluster of metabolites and lipids associated with IR, obesity, and future T2D risk. Branched-chain amino acids, direct catabolic products glutamate, 3-hydroxyisobutyrate, branched-chain ketoacids, and indirect byproducts like 2-hydroxybutyrate decreased compared to baseline and placebo. Changes were significantly larger with tirzepatide compared with dulaglutide, and directly proportional to reductions of HbA1c, HOMA2-IR indices, and proinsulin levels. Proportional to metabolite changes, triglycerides and diglycerides were lowered significantly compared to baseline, dulaglutide, and placebo, with a bias towards shorter and highly saturated species. Conclusions Tirzepatide reduces body weight and improves glycemic control and uniquely modulates metabolites associated with T2D risk and metabolic dysregulation in a direction consistent with improved metabolic health.