Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite of dietary choline and L-carnitine, has emerged as a leading molecular mediator of the gut-heart-kidney axis in heart failure (HF). Evidence from 14 prospective cohort studies demonstrates consistent associations between elevated circulating TMAO and adverse outcomes including mortality, rehospitalization, and major adverse cardiovascular events. The prognostic independence of TMAO is attenuated after renal function adjustment, reflecting both obligate renal clearance and a bidirectional relationship with kidney injury. Critically, TMAO is not modulated by conventional neurohormonal guideline-directed medical therapy (GDMT), suggesting that gut microbiome dysbiosis represents a pathophysiological axis not reached by current HF treatment. The field has evolved through three conceptual eras: TMAO as a single prognostic biomarker, TMAO as a cardiorenal mediator, and most recently, TMAO as the anchor of a multi-metabolite gut-heart signature encompassing trimethyllysine, choline, crotonobetaine, and acetyl-L-carnitine. Beyond the TMAO pathway, emerging evidence for phenylacetylglutamine, short-chain fatty acids, and protein-bound uremic toxins as parallel gut-derived cardiovascular mediators supports a multidimensional metabolite profiling approach. Panel approaches consistently outperform single-marker TMAO. Ethnic and dietary heterogeneity complicate universal threshold application. Without human interventional data demonstrating that lowering TMAO improves cardiovascular outcomes, TMAO remains a prognostic risk marker rather than a validated clinical target. Clinical translation requires resolving the renal confounding problem, validating multi-metabolite panels across diverse populations, and conducting intervention trials targeting the gut-heart-kidney axis.

Background: Respiratory failure (RF) is a frequently fatal complication of chronic liver disease (CLD), yet population-level data on RF-related mortality trends among adults with CLD are lacking. This study characterized temporal trends and demographic disparities in RF-related mortality among U.S. adults with CLD from 1999 to 2024. Methods: Death certificate data were obtained from the CDC WONDER database for adults aged ≥25 years with both RF (ICD-10: J96) and CLD (ICD-10: K70–K76) listed as an underlying or contributing cause of death. Age-adjusted mortality rates (AAMRs) per 100,000 were calculated using the 2000 U.S. standard population. Joinpoint regression identified temporal inflection points and annual percentage change (APC). Results: Among 241,075 deaths, the overall AAMR increased 3.2-fold from 2.237 (1999) to 7.162 (2021) per 100,000, then declined to 6.132 by 2024. Joinpoint analysis identified four segments: moderate increase (1999–2006; APC +2.40%), accelerated increase (2006–2018; APC +5.37%), late acceleration period (2018–2021; APC +13.10%), and post-pandemic decline (2021–2024; APC −4.32%; all p < 0.001). The 2024 AAMR remained 174.2% above baseline. The male-to-female rate ratio narrowed from 2.02 to 1.50, with females showing steeper acceleration (+14.38% vs. +12.36%). American Indian or Alaska Native individuals had the highest AAMRs and the most dramatic surge (APC +26.90%). Rural areas surpassed urban AAMRs by 2020, with steeper post-2007 acceleration (+8.74% vs. +5.51%). The Western U.S. consistently had the highest regional rates. Younger adults aged 25–34 and 35–44 showed 2.96-fold and 2.37-fold increases in crude mortality rates, respectively. Approximately 80% of deaths occurred in inpatient settings. Conclusions: RF-related mortality among U.S. adults with CLD increased more than threefold from 1999 to 2021, with a dramatic surge followed by incomplete decline. Persistent disparities by sex, race/ethnicity, urbanization, and region highlight the need for targeted interventions, including expanded screening for alcohol-associated and metabolic liver disease and improved access to hepatology services in underserved communities.

Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite of dietary choline and L-carnitine, has emerged as a leading molecular mediator of the gut–heart–kidney axis in heart failure (HF). This state-of-the-art narrative review synthesizes evidence from 14 observational studies (13 prospective cohorts and one cross-sectional analysis), encompassing a heterogeneous range of HF settings, including established chronic HF, acute decompensated HF, incident HF in community cohorts, and subclinical myocardial injury. Across these populations, elevated circulating TMAO has been associated with adverse outcomes, including mortality, rehospitalization, and major adverse cardiovascular events, although the strength and consistency of associations vary by HF phenotype, renal function status, and population ancestry. The prognostic independence of TMAO is attenuated after adjusting for renal function in several cohorts, reflecting both obligatory renal clearance and a potentially bidirectional relationship with kidney injury. TMAO was not reduced during neurohormonal GDMT uptitration in the BIOSTAT-CHF study, suggesting that gut microbiota dysbiosis may represent a pathophysiological axis not reached by current HF treatment. The field has evolved through three thematic stages: TMAO as a single prognostic biomarker, TMAO within cardiorenal pathophysiology, and multimetabolite and multipathway risk profiling. Beyond the TMAO pathway, emerging evidence for phenylacetylglutamine (PAGln), short-chain fatty acids (SCFAs), and protein-bound uremic toxins as parallel gut-derived cardiovascular mediators supports a multidimensional metabolite profiling approach. Several cohorts suggest that selected multimetabolite panels may provide additional prognostic information beyond TMAO alone, although their composition, calibration, and external validity remain uncertain. Population-specific variation in TMAO levels and prognostic thresholds complicates universal clinical application. Without human interventional data demonstrating that lowering TMAO improves cardiovascular outcomes, TMAO remains a prognostic risk marker rather than a validated clinical target. Clinical translation requires resolving the renal confounding problem, validating multimetabolite panels across diverse populations, and conducting intervention trials targeting the gut–heart–kidney axis.

Background: Individuals with inflammatory bowel disease (IBD) are at substantially increased risk for Clostridioides difficile infection (CDI), which leads to significantly higher morbidity and mortality compared to the general population. However, comprehensive national-level analyses of long-term mortality trends in this population remain limited. This study examines mortality trends associated with IBD and CDI in the United States from 1999 to 2023. Methods: This descriptive study utilized the CDC WONDER Multiple Cause-of-Death database. Deaths involving IBD (ICD-10: K50, K51) and CDI (A04.7) were identified among adults aged 25 years and older. Age-adjusted mortality rates (AAMRs) per 100,000 population were calculated with 95% confidence intervals and stratified by sex, race/ethnicity, urbanization, and census region. Joinpoint regression was applied to estimate the annual percent change (APC) in mortality. Results: Between 1999 and 2023, 76,084 deaths were recorded. Medical facilities accounted for 46% of deaths, followed by decedents’ homes (28.3%) and nursing home/long-term care facilities (16.5%). Overall mortality declined gradually from 1999 to 2018 (APC: −0.23, p < 0.05), increased sharply through 2021 (APC: +12.75, p < 0.05), and was then followed by a non-significant change through 2023 (APC: −2.69; 95% CI: −8.24 to 3.19), consistent with a plateau. Men consistently exhibited higher AAMRs than women. Non-Hispanic White individuals had the highest AAMRs (1.844 in 2023), while Non-Hispanic Black individuals experienced a sustained increase from 2016 onward (APC: +7.11, p < 0.05). Hispanic mortality increased steadily throughout the study period (APC: +1.31, p < 0.05). Rural populations had higher overall AAMRs than urban populations. The Midwest recorded the highest regional AAMRs by 2023 (1.867). Conclusions: Mortality increased significantly between 2018 and 2021, coinciding with the COVID-19 pandemic, though our study design cannot prove causation. Disparities by race/ethnicity, urbanization, and region persisted. These findings underscore the need for ongoing antibiotic stewardship, equitable healthcare access, and targeted public health interventions for this vulnerable population.