Circulating N-formylmethionine and metabolic shift in critical illness: a multicohort metabolomics study

Formyl-methionine-mediated eukaryotic ribosome quality control pathway for cold adaptation

Protein synthesis in the eukaryotic cytosol can start using both conventional methionine and formyl-methionine (fMet). However, a mechanism, if such exists, for detecting and regulating the incorporation of fMet (instead of Met) during translation, thereby preventing cellular toxicity of nascent fMet-bearing (fMet-) polypeptides, remains unknown. Here, we describe the fMet-mediated ribosome quality control (fMet-RQC) pathway in Saccharomyces cerevisiae. A eukaryotic translation initiation factor 3 subunit c, Nip1, specifically recognizes N-terminal fMet in nascent polypeptides, recruiting a small GTPase, Arf1, to induce ribosome stalling, largely with 41-residue fMet-peptidyl tRNAs. This leads to ribosome dissociation and subsequent stress granule formation. Loss of the fMet-RQC pathway causes the continued synthesis of fMet polypeptides, which inhibits essential N-terminal Met modifications and promotes their coaggregation with ribosomes. This fMet-RQC pathway is important for the adaptation of yeast cells to cold stress by promoting stress granule formation and preventing a buildup of toxic fMet polypeptides.

Development of an enhanced anti-pan-N-formylmethionine-specific antibody

Both bacterial and eukaryotic ribosomes can initiate protein synthesis with formylmethionine (fMet), but detecting fMet-bearing peptides and fMet-bearing proteins has been challenging due to the lack of effective anti-pan-fMet antibodies. Previously, we developed a polyclonal anti-fMet antibody using a fMet-Gly-Ser-Gly-Cys pentapeptide that detects those fMet-bearing peptides and fMet-bearing proteins regardless of their sequence context. In this study, we significantly improved the antibody's specificity and affinity by using a mixture of fMet-Xaa-Cys tripeptides (Xaa, any of the 20 amino acids) as the immunogen. This newly optimized anti-fMet antibody is a powerful, cost-effective tool for detecting fMet-bearing proteins across species. Furthermore, this approach provides a foundation for developing anti-pan-specific antibodies targeting other N-terminal modifications through acylation, alkylation, oxidation, arginylation, etc.

Toward Precision in Nutrition Therapy

Precision in critical care nutrition is paramount, as it focuses nutrition interventions on those patients most likely to benefit, or those who might potentially be harmed. Critical care nutrition must therefore be tailored to individual metabolic needs as determined by factors that control the capacity for tissue homeostasis and anabolic responses. This ideally involves the accurate and timely assessment of macronutrient and micronutrient requirements, a careful evaluation of metabolic response mechanisms and the identification of circumstances that might interfere with the productive utilization of dietary substrates. Specific surrogate markers of metabolic response, such as blood glucose levels, urea levels, or nitrogen balance, might be used to evaluate the metabolic readiness for nutrition and to establish the timing, nature, and clinical effectiveness of nutrition interventions. Despite the pressing need to further develop more targeted approaches in critically ill patients, indices of immediate metabolic responses that correlate with favorable clinical outcomes are lacking. In addition, the development of precision approaches might address timely adjustments in protein, energy, or micronutrient supplementation based on evolving clinical conditions. Here, we review why precision tools are needed in critical care nutrition, our progress thus far, as well as promising approaches and technologies by which multidisciplinary healthcare teams can improve quality of care and clinical outcomes by individualizing nutrition interventions.

Genetically Predicted Leucine Level Mediates Association Between CD4/CD8br T Lymphocytes and Insomnia

Immune and metabolic factors play an important role in the onset and development of insomnia. This study aimed to investigate the causal relationship between insomnia and immune cells and metabolites. Data for 731 immune cell phenotypes, 1400 metabolites, and insomnia in this study were obtained from the GWAS open-access database. Two-way Mendelian randomization was used to (1) detect the causal relationship between immune cells and insomnia and (2) identify potential mediating metabolites. Mendelian randomization analysis identified eight immune cell phenotypes with a causal relationship to insomnia, and two immune cell phenotypes were protective factors for insomnia, namely CD8br %T cells and CD80 on CD62L + myeloid dendritic cells. The other six immune cell phenotypes were risk factors for insomnia, i.e., CD4/CD8br, CD16-CD56 on NKT, CCR2 on myeloid dendritic cells, CD40 on monocytes, CD38 on CD3-CD19-, and CD25 on CD45RA + CD4 not Treg. Further Mendelian randomization revealed 11 metabolites that were causally related to insomnia. Five metabolites were protective factors for insomnia, i.e., 3-hydroxy-3-methylglutarate, cholate, dodecanedioate, N-formylmethionine, and x-26054. Six metabolites were risk factors for insomnia, 3-amino-2-piperidone, 6-oxopiperdine-2-carboxylate, caffeine to theophylline ratio, leucine, maltose, and x-24736. In addition, our analysis showed that leucine mediated the association between CD4/CD8br and insomnia. From genetic information, we confirmed the causal relationship between insomnia, eight immune cell phenotypes, and eleven metabolite levels. Notably, we found a relationship between leucine-mediated CD4/CD8br and insomnia, providing evidence supporting the causal relationship between immune cell and insomnia, with plasma metabolites serving as mediators.

Causal pathways in Lymphoma: The role of serum metabolites and immune cells determined by Mendelian randomization

BACKGROUND

Prior research has demonstrated significant roles of metabolites and immune cells in the progression of lymphoma. Mendelian randomization studies have been conducted to assess the causal relationships among serum metabolites, immune cells, and lymphoma, further exploring the mediating role of serum metabolites.

METHODS

Using summary-level data from genome-wide association studies (GWAS), we applied two-sample Mendelian randomization (TSMR) techniques, including Inverse Variance Weighted (IVW), Weighted Median, MR-Egger, Simple Mode, and Weighted Mode. These methods were employed to examine the causal links between genetically determined serum metabolites, immune cells, and six types of lymphoma. Additionally, reverse MR analysis investigated reverse causality, and two-step MR quantified the proportion of lymphoma effects mediated by immune cells through serum metabolites. MR-Egger regression and leave-one-out sensitivity tests evaluated the stability and reliability of our findings.

RESULTS

The study pinpointed specific serum metabolites and immune cell types causally related to six lymphoma variants. Serum metabolites were identified as mediators in the relationship between immune cells and lymphoma. The two-step Mendelian randomization confirmed this mediated causal relationship, with sensitivity analyses supporting the results' reliability and lack of pleiotropy.

CONCLUSION

The study establishes a causal connection between immune cells and lymphoma, partially mediated by serum metabolites, although the majority of the influence remains undefined. Future research should explore additional potential mediators. Clinically, there should be an increased focus on immune cells biomarkers for lymphoma patients. These results offer valuable insights for identifying lymphoma biomarkers and potential therapeutic targets.

Shared plasma metabolomic profiles of cognitive and mobility decline predict future dementia

Experiencing decline in both cognition and mobility is associated with a substantially higher dementia risk than cognitive decline only. Metabolites associated with both cognitive and mobility declines may be early predictors of dementia and reveal specific pathways to dementia. We analyzed data from 2450 participants initially free of dementia who had 613 metabolites measured in plasma in 1998-1999 (mean age = 75.2 ± 2.9 years old, 37.8% Black, 50% women) from the Health, Aging and Body Composition study. Dementia diagnosis was determined by race-specific decline in 3MS scores, medication use, and hospital records through 2014. Cognition and mobility were repeatedly measured using 3MS and a 20-m walking test up to 10 years, respectively. We examined metabolite associations with changes in 3MS (n = 2046) and gait speed (n = 2019) using multivariable linear regression adjusted for age, sex, race, and baseline performance and examined metabolite associations with dementia risk using Cox regression. During a mean follow-up of 9.3 years, 534 (21.8%) participants developed dementia. On average, 3MS declined 0.47/year and gait declined 0.04 m/sec/year. After covariate adjustment, 75 metabolites were associated with cognitive decline, and 111 metabolites were associated with gait decline (FDR-adjusted p < 0.05). Twenty-six metabolites were associated with both cognitive and gait declines. Eighteen of 26 metabolites were associated with dementia risk (p < 0.05), notably amino acids, glycerophospholipids (lysoPCs, PCs, PEs), and sphingolipids. Results remained similar after adjusting for cardiovascular disease or apolipoprotein E ɛ4 carrier status. During aging, metabolomic profiles of cognitive decline and mobility decline show distinct and shared signatures. Shared metabolomic profiles suggest that inflammation and deficits in mitochondria and the urea cycle in addition to the central nervous system may play key roles in both cognitive and mobility declines and predict dementia. Future studies are warranted to investigate longitudinal metabolite changes and metabolomic markers with dementia pathologies.

High-resolution plasma metabolomics and thiamine status in critically Ill adult patients

INTRODUCTION

Thiamine (Vitamin B1) is an essential micronutrient and is classically considered a co-factor in energy metabolism. The association between thiamine status and whole-body metabolism in critical illness has not been studied.

OBJECTIVES

To determine association between whole blood thiamine pyrophosphate (TPP) concentrations and plasma metabolites and connected metabolic pathways using high resolution metabolomics (HRM) in critically ill patients.

METHODS

Cross-sectional study performed at Erciyes University Hospital, Kayseri, Turkey and Emory University, Atlanta, GA, USA. Participants were critically ill adults with an expected length of intensive care unit stay longer than 48 h and receiving chronic furosemide therapy. A total of 76 participants were included. Mean age was 69 years (range 33-92 years); 65% were female. Blood for TPP and metabolomics was obtained on the day of ICU admission. Whole blood TPP was measured by HPLC and plasma HRM was performed using liquid chromatography/mass spectrometry. Data was analyzed using regression analysis of TPP levels against all plasma metabolomic features in metabolome-wide association studies (MWAS). MWAS using the highest and lowest TPP concentration tertiles was performed as a secondary analysis.

RESULTS

Specific metabolic pathways associated with whole blood TPP levels in regression and tertile analysis included pentose phosphate, fructose and mannose, branched chain amino acid, arginine and proline, linoleate, and butanoate pathways.

CONCLUSIONS

Plasma HRM revealed that thiamine status, determined by whole blood TPP concentrations, was significantly associated with metabolites and metabolic pathways related to metabolism of energy, carbohydrates, amino acids, lipids, and the gut microbiome in adult critically ill patients.

Alterations in metabolome and lipidome in patients with in-stent restenosis

CONTEXT

In-stent restenosis (ISR) can lead to blood flow obstruction, insufficient blood supply to the brain, and may even result in serious complications such as stroke. Endothelial cell hyperproliferation and thrombosis are the primary etiologies, frequently resulting in alterations in intravascular metabolism. However, the metabolic changes related to this process are still undermined.

OBJECTIVE

We tried to characterize the serum metabolome of patients with ISR and those with non-restenosis (NR) using metabolomics and lipidomics, exploring the key metabolic pathways of this pathological phenomenon.

RESULTS

We observed that the cysteine and methionine pathways, which are associated with cell growth and oxidative homeostasis, showed the greatest increase in the ISR group compared to the NR group. Within this pathway, the levels of N-formyl-l-methionine and L-methionine significantly increased in the ISR group, along with elevated levels of downstream metabolites such as 2-ketobutyric acid, pyruvate, and taurocholate. Additionally, an increase in phosphatidylcholine (PC) and phosphatidylserine (PS), as well as a decrease in triacylglycerol in the ISR group, indicated active lipid metabolism in these patients, which could be a significant factor contributing to the recurrence of blood clots after stent placement. Importantly, phenol sulfate and PS(38:4) were identified as potential biomarkers for distinguishing ISR, with an area under the curve of more than 0.85.

CONCLUSIONS

Our study revealed significant metabolic alterations in patients with ISR, particularly in the cysteine and methionine pathways, with phenol sulfate and PS(38:4) showing promise for ISR identification.

Candida albicans accelerates atherosclerosis by activating intestinal hypoxia-inducible factor2α signaling

The gut microbiota is closely linked to atherosclerosis. However, the role of intestinal fungi, essential members of the complex microbial community, in atherosclerosis is poorly understood. Herein, we show that gut fungi dysbiosis is implicated in patients with dyslipidemia, characterized by higher levels of Candida albicans (C. albicans), which are positively correlated with plasma total cholesterol and low-density lipoprotein-cholesterol (LDL-C) levels. Furthermore, C. albicans colonization aggravates atherosclerosis progression in a mouse model of the disease. Through gain- and loss-of-function studies, we show that an intestinal hypoxia-inducible factor 2α (HIF-2α)-ceramide pathway mediates the effect of C. albicans. Mechanistically, formyl-methionine, a metabolite of C. albicans, activates intestinal HIF-2α signaling, which drives increased ceramide synthesis to accelerate atherosclerosis. Administration of the HIF-2α selective antagonist PT2385 alleviates atherosclerosis in mice by reducing ceramide levels. Our findings identify a role for intestinal fungi in atherosclerosis progression and highlight the intestinal HIF-2α-ceramide pathway as a target for atherosclerosis treatment.

Association of mental disorders with sepsis: a bidirectional Mendelian randomization study

Background

Substantial research evidence supports the correlation between mental disorders and sepsis. Nevertheless, the causal connection between a particular psychological disorder and sepsis remains unclear.

Methods

For investigating the causal relationships between mental disorders and sepsis, genetic variants correlated with mental disorders, including anorexia nervosa (AN), attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), bipolar disorder (BD), major depressive disorder (MDD), obsessive-compulsive disorder (OCD), panic disorder (PD), posttraumatic stress disorder (PTSD), schizophrenia (SCZ), and tourette syndrome (TS), were all extracted from the Psychiatric Genomics Consortium (PGC). The causal estimates and direction between these mental disorders and sepsis were evaluated employing a two-sample bidirectional MR strategy. The inverse variance weighted (IVW) method was the primary approach utilized. Various sensitivity analyses were performed to confirm the validity of the causal effect. Meta-analysis, multivariable MR, and mediation MR were conducted to ensure the credibility and depth of this research.

Results

The presence of AN was in relation to a greater likelihood of sepsis (OR 1.08, 95% CI 1.02-1.14; p = 0.013). A meta-analysis including validation cohorts supported this observation (OR 1.06, 95% CI 1.02-1.09). None of the investigated mental disorders appeared to be impacted when sepsis was set as the exposure factor. Even after adjusting for confounding factors, AN remained statistically significant (OR 1.08, 95% CI 1.02-1.15; p = 0.013). Mediation analysis indicated N-formylmethionine levels (with a mediated proportion of 7.47%), cystatin D levels (2.97%), ketogluconate Metabolism (17.41%) and N10-formyl-tetrahydrofolate biosynthesis (20.06%) might serve as mediators in the pathogenesis of AN-sepsis.

Conclusion

At the gene prediction level, two-sample bidirectional MR analysis revealed that mental disorder AN had a causal association with an increased likelihood of sepsis. In addition, N-formylmethionine levels, cystatin D levels, ketogluconate metabolism and N10-formyl-tetrahydrofolate biosynthesis may function as potential mediators in the pathophysiology of AN-sepsis. Our research may contribute to the investigation of novel therapeutic strategies for mental illness and sepsis.

Circulating N-lactoyl-amino acids and N-formyl-methionine reflect mitochondrial dysfunction and predict mortality in septic shock

INTRODUCTION

Sepsis is a highly morbid condition characterized by multi-organ dysfunction resulting from dysregulated inflammation in response to acute infection. Mitochondrial dysfunction may contribute to sepsis pathogenesis, but quantifying mitochondrial dysfunction remains challenging.

OBJECTIVE

To assess the extent to which circulating markers of mitochondrial dysfunction are increased in septic shock, and their relationship to severity and mortality.

METHODS

We performed both full-scan and targeted (known markers of genetic mitochondrial disease) metabolomics on plasma to determine markers of mitochondrial dysfunction which distinguish subjects with septic shock (n = 42) from cardiogenic shock without infection (n = 19), bacteremia without sepsis (n = 18), and ambulatory controls (n = 19) - the latter three being conditions in which mitochondrial function, proxied by peripheral oxygen consumption, is presumed intact.

RESULTS

Nine metabolites were significantly increased in septic shock compared to all three comparator groups. This list includes N-formyl-L-methionine (f-Met), a marker of dysregulated mitochondrial protein translation, and N-lactoyl-phenylalanine (lac-Phe), representative of the N-lactoyl-amino acids (lac-AAs), which are elevated in plasma of patients with monogenic mitochondrial disease. Compared to lactate, the clinical biomarker used to define septic shock, there was greater separation between survivors and non-survivors of septic shock for both f-Met and the lac-AAs measured within 24 h of ICU admission. Additionally, tryptophan was the one metabolite significantly decreased in septic shock compared to all other groups, while its breakdown product kynurenate was one of the 9 significantly increased.

CONCLUSION

Future studies which validate the measurement of lac-AAs and f-Met in conjunction with lactate could define a sepsis subtype characterized by mitochondrial dysfunction.

Association between serum TSH levels and all-cause mortality in critically ill patients

Thyroid dysfunction is common in critical illness and may influence prognosis. However, the value of TSH in patients with severe diseases remains unclear. The aim of this study was to investigate the association between TSH and the clinical prognosis of critically ill patients. Methods: This retrospective study identified patients who were admitted to the ICU in the Medical Information Mart for Intensive Care (MIMIC-IV) database (version 2.2). A total of 6432 patients were divided into four groups based on TSH quartiles (Q1, <0.92 mIU/L; Q2, 0.92-1.07 mIU/L; Q3, 1.07-3.10 mIU/L; Q4, >3.10 mIU/L). The clinical outcomes were defined as all-cause 7-, 30-, and 90-year mortality after ICU admission. Restricted cubic splines (RCSs) for nonlinear associations were generated to visualize the relationship between TSH levels and clinical outcomes. The survival differences among the four groups were also analyzed using Kaplan‒Meier curves and log rank tests. Univariable and multivariable Cox proportional hazards regression were further used to assess the association between TSH levels and clinical outcomes. Results: After multivariate adjustment, a U-shaped relationship was observed between TSH levels and all-cause 7-, 30-, and 90- mortality among patients with severe disease (all P < 0.05 for nonlinearity). The plot showed a risk reduction in the low range of TSH, which reached the lowest risk at approximately 2.9 μIU/mL and then increased thereafter. Compared with patients with Q3 TSH levels, those with Q1, Q2, and Q4 TSH levels had a significantly higher risk of all-cause 30-day mortality (Q1: hazard ratio, 1.28; 95% CI, 1.06-1.54; Q2: hazard ratio, 1.22; 95% CI, 1.01-1.48; Q4: hazard ratio, 1.25; 95% CI, 1.04-1.50). For all-cause 90-day mortality, only the Q4 group had a significantly higher mortality risk than the Q3 group (hazard ratio, 1.24; 95% CI, 1.07-1.44). In subgroup analyses, we found that Q1 TSH levels were associated with higher mortality risk in men and older (≥65 years) patients, while Q4 TSH had a greater risk in men and younger (<65 years) patients. Conclusions: TSH was significantly associated with all-cause 7-, 30-, and 90-day mortality in critically ill patients after admission to the ICU. TSH may serve as a valuable biomarker for risk stratification in critically ill patients.

Mitochondrial N-formyl methionine peptides contribute to exaggerated neutrophil activation in patients with COVID-19

Neutrophil dysregulation is well established in COVID-19. However, factors contributing to neutrophil activation in COVID-19 are not clear. We assessed if N-formyl methionine (fMet) contributes to neutrophil activation in COVID-19. Elevated levels of calprotectin, neutrophil extracellular traps (NETs) and fMet were observed in COVID-19 patients (n = 68), particularly in critically ill patients, as compared to HC (n = 19, p < 0.0001). Of note, the levels of NETs were higher in ICU patients with COVID-19 than in ICU patients without COVID-19 (p < 0.05), suggesting a prominent contribution of NETs in COVID-19. Additionally, plasma from COVID-19 patients with mild and moderate/severe symptoms induced in vitro neutrophil activation through fMet/FPR1 (formyl peptide receptor-1) dependent mechanisms (p < 0.0001). fMet levels correlated with calprotectin levels validating fMet-mediated neutrophil activation in COVID-19 patients (r = 0.60, p = 0.0007). Our data indicate that fMet is an important factor contributing to neutrophil activation in COVID-19 disease and may represent a potential target for therapeutic intervention.

High-Resolution Plasma Metabolomics and Thiamine Status in Critically Ill Adult Patients

BACKGROUND AND AIM

Thiamine (Vitamin B1) is an essential micronutrient and a co-factor for metabolic functions related to energy metabolism. We determined the association between whole blood thiamine pyrophosphate (TPP) concentrations and plasma metabolites using high resolution metabolomics in critically ill patients. Methods Cross-sectional study performed in Erciyes University Hospital, Kayseri, Turkey and Emory University, Atlanta, GA, USA. Participants were ≥ 18 years of age, with an expected length of ICU stay longer than 48 hours, receiving furosemide therapy for at least 6 months before ICU admission. Results Blood for TPP and metabolomics was obtained on the day of ICU admission. Whole blood TPP concentrations were measured using high-performance liquid chromatography (HPLC). Liquid chromatography/mass spectrometry was used for plasma high-resolution metabolomics. Data was analyzed using regression analysis of TPP levels against all plasma metabolomic features in metabolome-wide association studies. We also compared metabolomic features from patients in the highest TPP concentration tertile to patients in the lowest TPP tertile as a secondary analysis. We enrolled 76 participants with a median age of 69 (range, 62.5-79.5) years. Specific metabolic pathways associated with whole blood TPP levels, using both regression and tertile analysis, included pentose phosphate, fructose and mannose, branched chain amino acid, arginine and proline, linoleate, and butanoate pathways. Conclusions Plasma high-resolution metabolomics analysis showed that whole blood TPP concentrations are significantly associated with metabolites and metabolic pathways linked to the metabolism of energy, amino acids, lipids, and the gut microbiome in adult critically ill patients.

Age-associated deficits in social behaviour are microbiota-dependent

Aging is associated with remodelling of immune and central nervous system responses resulting in behavioural impairments including social deficits. Growing evidence suggests that the gut microbiome is also impacted by aging, and we propose that strategies to reshape the aged gut microbiome may ameliorate some age-related effects on host physiology. Thus, we assessed the impact of gut microbiota depletion, using an antibiotic cocktail, on aging and its impact on social behavior and the immune system. Indeed, microbiota depletion in aged mice eliminated the age-dependent deficits in social recognition. We further demonstrate that although age and gut microbiota depletion differently shape the peripheral immune response, aging induces an accumulation of T cells in the choroid plexus, that is partially blunted following microbiota depletion. Moreover, an untargeted metabolomic analysis revealed age-dependent alterations of cecal metabolites that are reshaped by gut microbiota depletion. Together, our results suggest that the aged gut microbiota can be specifically targeted to affect social deficits. These studies propel the need for future investigations of other non-antibiotic microbiota targeted interventions on age-related social deficits both in animal models and humans.