Intestinal function is impaired in patients with Chronic Obstructive Pulmonary Disease

Genetic Insights into the Gut-Lung Axis: Mendelian Randomization Analysis on Gut Microbiota, Lung Function, and COPD

Background

Chronic obstructive pulmonary disease (COPD) is a respiratory disorder with a complex etiology involving genetic and environmental factors. The dysbiosis of gut microbiota has been implicated in COPD. Mendelian Randomization (MR) provides a tool to investigate causal links using genetic variants as instrumental variables. This study aims to employ MR analysis to explore the causal relationship between gut microbiota, lung function, and COPD.

Methods

We utilized genome-wide association study (GWAS) data from MiBioGen, UK Biobank and FinnGen, which were related to gut microbial taxa, lung function parameters including forced vital capacity in one second (FEV1), forced vital capacity (FVC), and percentage of predicted FEV1 (FEV1%pred), as well as GWAS data for COPD. MR analysis was conducted to assess the causal effects of gut microbiota on lung function and the risk of COPD. Sensitivity analysis was utilized to examine the stability of the causal relationships. Multiple testing and reverse analysis were employed to evaluate the robustness of these relationships.

Results

Using the IVW method, 64 causal correlations were identified. Through conducting sensitivity analysis, multiple testing, and reverse analysis, we identified 14 robust and stable causal relationships. The bacterial taxa that showed a positive association with lung function included Desulfovibrionaceae, Erysipelotrichales, Desulfovibrionales, Clostridiales, Clostridia, Deltaproteobacteria and Erysipelotrichia, while Selenomonadales and Negativicutes showed a negative association with lung function. The abundance of Holdemanella were positively correlated with the risk of COPD, while FamilyXIII exhibited a negative correlation with the risk of COPD.

Conclusion

Several microbial taxa were discovered to have a positive causal correlation with lung function, offering potential insights into the development of probiotics. The presence of microbial taxa negatively correlated with lung function and positively correlated with COPD emphasized the potential impact of gut microbiota dysbiosis on respiratory health.

Multiomics was used to clarify the mechanism by which air pollutants affect chronic obstructive pulmonary disease: A human cohort study

Exposure to air pollutants has been associated with various adverse health outcomes, including chronic obstructive pulmonary disease (COPD). However, the precise underlying mechanism by which air pollution impacts COPD through remains insufficiently understood. To elucidated the molecular mechanism by which air pollutant exposure contributes to alterations in the gut microbiome and metabolism in AECOPD patients, we employed metagenomics and untargeted metabolomics to analyse the gut microbial, faecal, and serum metabolites. The correlations among air pollutants, gut microbes, serum metabolites, and blood biochemical markers were assessed using generalised additive mixed models and Spearman correlation analysis. The findings revealed that for every 10 μg/m3 increase in PM2.5 concentration, the α-diversity of the gut flora decreased by 2.16% (95% CI: 1.80%-2.53%). We found seven microorganisms that were significantly associated with air pollutants, of which Enterococcus faecium, Bacteroides fragilis, Ruthenibacterium lactatiformans, and Subdoligranulum sp.4_3_54A2FAA were primarily associated with glycolysis. We identified 13 serum metabolites and 17 faecal metabolites significantly linked to air pollutants. Seven of these metabolites, which were strongly associated with air pollutants and blood biochemical indices, were found in both serum and faecal samples. Some of these metabolites, such as 2,5-furandicarboxylic acid, C-8C1P and melatonin, were closely associated with disturbances in lipid and fatty acid metabolism in AECOPD patients. These findings underscore the impact of air pollutants on overall metabolism based on influencing gut microbes and metabolites in AECOPD patients. Moreover, these altered biomarkers establish the biologic connection between air pollutant exposure and AECOPD outcomes.The identification of pertinent biomarkers provides valuable insights for the development of precision COPD prevention strategies.

Interplay of chronic obstructive pulmonary disease and colorectal cancer development: unravelling the mediating role of fatty acids through a comprehensive multi-omics analysis

BACKGROUND

Chronic obstructive pulmonary disease (COPD) patients often exhibit gastrointestinal symptoms, A potential association between COPD and Colorectal Cancer (CRC) has been indicated, warranting further examination.

METHODS

In this study, we collected COPD and CRC data from the National Health and Nutrition Examination Survey, genome-wide association studies, and RNA sequence for a comprehensive analysis. We used weighted logistic regression to explore the association between COPD and CRC incidence risk. Mendelian randomization analysis was performed to assess the causal relationship between COPD and CRC, and cross-phenotype meta-analysis was conducted to pinpoint crucial loci. Multivariable mendelian randomization was used to uncover mediating factors connecting the two diseases. Our results were validated using both NHANES and GEO databases.

RESULTS

In our analysis of the NHANES dataset, we identified COPD as a significant contributing factor to CRC development. MR analysis revealed that COPD increased the risk of CRC onset and progression (OR: 1.16, 95% CI 1.01-1.36). Cross-phenotype meta-analysis identified four critical genes associated with both CRC and COPD. Multivariable Mendelian randomization suggested body fat percentage, omega-3, omega-6, and the omega-3 to omega-6 ratio as potential mediating factors for both diseases, a finding consistent with the NHANES dataset. Further, the interrelation between fatty acid-related modules in COPD and CRC was demonstrated via weighted gene co-expression network analysis and Kyoto Encyclopedia of Genes and Genomes enrichment results using RNA expression data.

CONCLUSIONS

This study provides novel insights into the interplay between COPD and CRC, highlighting the potential impact of COPD on the development of CRC. The identification of shared genes and mediating factors related to fatty acid metabolism deepens our understanding of the underlying mechanisms connecting these two diseases.

Butyrate inhibits iILC2-mediated lung inflammation via lung-gut axis in chronic obstructive pulmonary disease (COPD)

BACKGROUND

The study investigated the effects and underlying mechanisms of intestinal flora metabolite butyrate on inflammatory ILC2 cells (iILC2s)-mediated lung inflammation in chronic obstructive pulmonary disease (COPD).

METHODS

Mouse models of COPD and acute exacerbation of COPD (AECOPD) were established. Flow cytometry was used to detect natural ILC2 cells (nILC2s) and iILC2s in lung and colon tissues. The 16s rRNA and GC-MS were used to detect microbial flora and short chain fatty acids (SCFAs) in feces. ELISA was used to detect IL-13 and IL-4. Western blot and qRT-PCR were used to detect the relative protein and mRNA levels, respectively. In vitro experiments were performed with sorted ILC2s from colon tissues of control mice. Mice with AECOPD were treated with butyrate.

RESULTS

The nILC2s and iILC2s in lung and colon tissues of AECOPD mice were significantly higher than control groups. The abundance of the flora Clostridiaceae was significantly reduced, and the content of SCFAs, including acetate and butyrate, was significantly reduced. The in vitro experiments showed that butyrate inhibited iILC2 cell phenotype and cytokine secretion. Butyrate treatment reduced the proportion of iILC2 cells in the colon and lung tissues of mice with AECOPD.

CONCLUSIONS

The nILC2s and iILC2s in the colon tissues are involved in the course of COPD. Decreased Clostridiaceae and butyrate in AECOPD mice caused the accumulation of iILC2 cells in the intestines and lungs. Supplementation of butyrate can reduce iILC2 in the intestine and lung tissues. Our data may provide new ideas for prevention and treatment of COPD.

The impact of advanced age on gastrointestinal characteristics that are relevant to oral drug absorption: An AGePOP review

The purpose of this review is to summarize the current knowledge on three physiological determinants of oral drug absorption, i.e., gastric emptying, volumes and composition of luminal fluids, and intestinal permeability, in the advanced age population, so that potential knowledge gaps and directions for further research efforts are identified. Published data on gastric emptying rates in older people are conflicting. Also, there are significant knowledge gaps, especially on gastric motility and emptying rates of drugs and of non-caloric fluids. Compared with younger adults, volumes of luminal contents seem to be slightly smaller in older people. Our understanding on the impact of advanced age on luminal physicochemical characteristics is, at best, very limited, whereas the impact of (co)morbidities and geriatric syndromes in the advanced age population has not been addressed to date. The available literature on the effect of advanced age on intestinal permeability is limited, and should be approached with caution, primarily due to the limitations of the experimental methodologies used.

Short-chain fatty acid production in accessible and inaccessible body pools as assessed by novel stable tracer pulse approach is reduced by aging independent of presence of COPD

BACKGROUND

Production rates of the short-chain fatty acids (SCFA) acetate, propionate, and butyrate, which are beneficial metabolites of the intestinal microbiota, are difficult to measure in humans due to inaccessibility of the intestine to perform measurements, and the high first-pass metabolism of SCFAs in colonocytes and liver. We developed a stable tracer pulse approach to estimate SCFA whole-body production (WBP) in the accessible pool representing the systemic circulation and interstitial fluid. Compartmental modeling of plasma enrichment data allowed us to additionally calculate SCFA kinetics and pool sizes in the inaccessible pool likely representing the intestine with microbiota. We also studied the effects of aging and the presence of Chronic Obstructive Pulmonary Disease (COPD) on SCFA kinetics.

METHODS

In this observational study, we designed a two-compartmental model to determine SCFA kinetics in 31 young (20-29 y) and 71 older (55-87 y) adults, as well as in 33 clinically stable patients with moderate to very severe COPD (mean (SD) FEV₁, 46.5 (16.2)% of predicted). Participants received in the fasted state a pulse containing stable tracers of acetate, propionate, and butyrate intravenously and blood was sampled four times over a 30 min period. We measured tracer-tracee ratios by GC-MS and used parameters obtained from two-exponential curve fitting to calculate non-compartmental SCFA WBP and perform compartmental analysis. Statistics were done by ANCOVA.

RESULTS

Acetate, propionate, and butyrate WBP and fluxes between the accessible and inaccessible pools were lower in older than young adults (all q < 0.0001). Moreover, older participants had lower acetate (q < 0.0001) and propionate (q = 0.019) production rates in the inaccessible pool as well as smaller sizes of the accessible and inaccessible acetate pools (both q < 0.0001) than young participants. WBP, compartmental SCFA kinetics, and pool sizes did not differ between COPD patients and older adults (all q > 0.05). Overall and independent of the group studied, calculated production rates in the inaccessible pool were on average 7 (acetate), 11 (propionate), and 16 (butyrate) times higher than non-compartmental WBP, and sizes of inaccessible pools were 24 (acetate), 31 (propionate), and 55 (butyrate) times higher than sizes of accessible pools (all p < 0.0001).

CONCLUSION

Non-compartmental production measurements of SCFAs in the accessible pool (i.e. systemic circulation) substantially underestimate the SCFA production in the inaccessible pool, which likely represents the intestine with microbiota, as assessed by compartmental analysis.

Relationship among Body Composition, Adipocytokines, and Irisin on Exercise Capacity and Quality of Life in COPD: A Pilot Study

Adipose tissue is an endocrine organ that interferes with the severity of chronic obstructive pulmonary disease (COPD). Although inflammatory markers, body composition, and nutritional status have a significant impact on pulmonary function, the real contribution of adipocytokines and myokines in COPD is still controversial. We aimed to evaluate the role played by the body composition, leptin, adiponectin, haptoglobin, and irisin on the functional exercise capacity, respiratory function, and quality of life (QoL) in COPD. In 25 COPD (20% GOLD-1; 60% GOLD-2; 20% GOLD-3) patients and 26 matched control subjects, we find that leptin, total adiponectin and haptoglobin are significantly increased whereas the 6 min walk test (6MWT) and physical functioning scores are significantly decreased in COPD versus controls. A significant positive relationship is found between leptin and fat mass and between 6MWT and the good health indicators of nutritional status. A significant inverse relationship is found between 6MWT and leptin and fat mass, FEV₁ and haptoglobin, and irisin and haptoglobin. Phase angle and leptin level are significant predictors for functional exercise capacity assessed with 6MWT. Taken altogether, the results of this pilot study further support the role played by body composition and adipocytokines on exercise capacity respiratory function and QoL in COPD.

Butyrate: Connecting the gut-lung axis to the management of pulmonary disorders

Short-chain fatty acids (SCFAs) are metabolites released by bacterial components of the microbiota. These molecules have a wide range of effects in the microbiota itself, but also in host cells in which they are known for contributing to the regulation of cell metabolism, barrier function, and immunological responses. Recent studies indicate that these molecules are important players in the gut-lung axis and highlight the possibility of using strategies that alter their intestinal production to prevent or treat distinct lung inflammatory diseases. Here, we review the effects of the SCFA butyrate and its derivatives in vitro and in vivo on murine models of respiratory disorders, besides discussing the potential therapeutic use of butyrate and the other SCFAs in lung diseases.

Measuring muscle protein synthesis in humans and the influence of nutritional state

In 1982 and 2011, Clinical Science published papers that used infusion of stable isotope-labeled amino acids to assess skeletal muscle protein synthesis in the fasted and fed state and before and after a period of increased intake of omega-3 fatty acids, respectively; both of these papers have been highly cited. An overview of the study designs, key findings and novel features, and a consideration of the lasting impact of these two papers is presented.

The earlier paper introduced stable isotope tracer approaches in humans that showed consuming a meal will increase whole body oxidation, synthesis, and breakdown of protein, but that protein synthesis is greater than breakdown resulting in net accumulation of protein. The paper also demonstrated that consuming a meal promotes net protein synthesis in skeletal muscle.

The later paper introduced the concept that omega-3 polyunsaturated fatty acids are able to improve anabolism by reporting that 8 weeks consumption of high-dose omega-3 fatty acids by healthy young and middle-aged adults increased skeletal muscle protein synthesis during a hyperaminoacidemic–hyperinsulinemic clamp compared with what was seen during the clamp at study entry. Omega-3 fatty acids also increased the phosphorylation of important signaling proteins in muscle, including mammalian target of rapamycin, p70s6k, and Akt, during the clamp.

These two papers remain relevant because they offer experimental approaches to study human (patho)physiology in different contexts, they present novel insights into the impact of nutritional state (feeding) and specific nutrients (omega-3 fatty acids) on muscle protein synthesis, and they suggest ways to explore the potential of interventions to help prevent and reverse the age-, disease-, and disuse-associated decline in muscle mass.

Probiotics: Protecting Our Health from the Gut

The gut microbiota (GM) comprises billions of microorganisms in the human gastrointestinal tract. This microbial community exerts numerous physiological functions. Prominent among these functions is the effect on host immunity through the uptake of nutrients that strengthen intestinal cells and cells involved in the immune response. The physiological functions of the GM are not limited to the gut, but bidirectional interactions between the gut microbiota and various extraintestinal organs have been identified. These interactions have been termed interorganic axes by several authors, among which the gut–brain, gut–skin, gut–lung, gut–heart, and gut–metabolism axes stand out. It has been shown that an organism is healthy or in homeostasis when the GM is in balance. However, altered GM or dysbiosis represents a critical factor in the pathogenesis of many local and systemic diseases. Therefore, probiotics intervene in this context, which, according to various published studies, allows balance to be maintained in the GM, leading to an individual’s good health.

The True Amino Acid Digestibility of 15N-Labelled Sunflower Biscuits Determined with Ileal Balance and Dual Isotope Methods in Healthy Humans

BACKGROUND

Sunflower is a promising protein source but data on amino acid (AA) digestibility are lacking in humans. Classically, the determination of AA digestibility requires ileal digesta sampling. The dual isotope method is minimally invasive but has not been compared to the conventional approach.

OBJECTIVES

This study aimed to determine the true ileal digestibility of sunflower AAs in healthy volunteers who ate biscuits containing 15nitrogen (N) protein isolate, in comparison with the dual isotope method.

METHODS

Twelve healthy volunteers (men and women; 40.4 ± 10.5 years old; BMI, 23.7 ± 2.9 kg/m2) were equipped with a naso-ileal tube. For 4 hours, they consumed 9 repeated meals comprising 15N-sunflower protein biscuits together with 13carbon (C)-AAs, carried either in chocolate (SUN + Ch; n = 7) or apple puree (SUN + P; n = 5). Ileal digesta and blood were sampled throughout 8 hours after ingestion of the first meal. The 15N and 13C AA enrichments were measured in digesta to determine ileal digestibility directly and in plasma to determine lysine and threonine digestibility using the dual isotope method. Differences between methods and between vector groups were analyzed using paired and unpaired t-tests, respectively.

RESULTS

The ileal digestibility of sunflower indispensable AAs (IAA) was 89% ± 5.3%, with threonine and lysine having the lowest digestibility. In the SUN + Ch meal, IAA digestibility was 3% below that of SUN + P (P < 0.05). The mean free 13C-AA ileal digestibility was 98.1% ± 0.9%. No matter which matrix was used to carry 13C-AAs, plasma 15N and 13C-AA kinetics displayed a 1-hour offset. Digestibility obtained with the dual isotope method (70.4% ± 6.0% for threonine and 75.9% ± 22.3% for lysine) was below the target values.

CONCLUSIONS

The ileal digestibility of IAAs from a sunflower isolate incorporated in a biscuit was close to 90% in healthy adults. Under our experimental conditions, the dual isotope method provided lower values than the usual method. Further protocol developments are needed to validate the equivalence between both methods. This trial was registered at clinicaltrials.gov as NCT04024605.

Transorgan short-chain fatty acid fluxes in the fasted and postprandial state in the pig

The short-chain fatty acids (SCFAs) acetate, propionate, butyrate, isovalerate, and valerate are end products of intestinal bacterial fermentation and important mediators in the interplay between the intestine and peripheral organs. To unravel the transorgan fluxes and mass balance comparisons of SCFAs, we measured their net fluxes across several organs in a translational pig model. In multicatheterized conscious pigs [n = 12, 25.6 (95% CI [24.2, 26.9]) kg, 8-12 wk old], SCFA fluxes across portal-drained viscera (PDV), liver, kidneys, and hindquarter (muscle compartment) were measured after an overnight fast and in the postprandial state, 4 h after administration of a fiber-free, mixed meal. PDV was the main releasing compartment of acetate, propionate, butyrate, isovalerate, and valerate during fasting and in the postprandial state (all P = 0.001). Splanchnic acetate release was high due to the absence of hepatic clearance. All other SCFAs were extensively taken up by the liver (all P < 0.05). Even though only 7% [4, 10] (propionate), 42% [23, 60] (butyrate), 26% [12, 39] (isovalerate), and 3% [0.4, 5] (valerate) of PDV release were excreted from the splanchnic area in the fasted state, splanchnic release of all SCFAs was significant (all P values ≤0.01). Splanchnic propionate, butyrate, isovalerate, and valerate release remained low but significant in the postprandial state (all P values <0.01). We identified muscle and kidneys as main peripheral SCFA metabolizing organs, taking up the majority of all splanchnically released SCFAs in the fasted state and in the postprandial state. We conclude that the PDV is the main SCFA releasing and the liver the main SCFA metabolizing organ. Splanchnically released SCFAs appear to be important energy substrates to peripheral organs not only in the fasted but also in the postprandial state.NEW & NOTEWORTHY Using a multicatheterized pig model, we identified the portal-drained viscera as the main releasing compartment of the short-chain fatty acids acetate, propionate, butyrate, isovalerate, and valerate in the fasted and postprandial states. Low hepatic acetate metabolism resulted in a high splanchnic release, whereas all other SCFAs were extensively cleared resulting in low but significant splanchnic releases. Muscle and kidneys are the main peripheral SCFA metabolizing organs during fasting and in the postprandial state.

Prediction of exacerbation frequency of AECOPD based on next-generation sequencing and its relationship with imbalance of lung and gut microbiota: a protocol of a prospective cohort study

INTRODUCTION

Patients with frequent acute exacerbation phenotype chronic obstructive pulmonary disease (AECOPD) have a higher hospitalisation rate than infrequent exacerbation, the disease progresses quickly and treatment is more difficult. At present, it is impossible to predict patients with COPD with frequent acute exacerbation phenotypes. The composition of the lower respiratory tract flora and the intestinal flora is closely related to AECOPD, but the specific association mechanism between them is not very clear. This study used metagenomic next-generation sequencing (mNGS) technology to explore the microbial characteristics of the intestinal tract and airways of patients with COPD, and analyse the correlation between the sequencing results and inflammatory factors, immune factors and nutritional factors.

METHODS AND ANALYSIS

This will be a prospective cohort study. We intend to recruit 152 patients with stable COPD. In the baseline, we will detect the participants' induced sputum and faecal flora through mNGS, and changes in blood immune levels, and the patient's condition is evaluated. Every 2 months, we will check the number of acute exacerbation through the phone range. After 12 months, we will check again the changes in the blood immune level, evaluate the patient's condition and count the number of episodes.

ETHICS AND DISSEMINATION

This study has been approved by the ethics committee of Guangdong Provincial Hospital of Traditional Chinese Medicine (approval number ZF2019-219-03). The results of the study will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Registry (ChiCTR2000032870).

Intestinal dysfunction in chronic disease

PURPOSE OF REVIEW

This review will discuss recent studies showing that patients with chronic wasting diseases suffer from a variety of small intestinal impairments which might negatively impact the colonic microbiota and overall well-being. New insights will be addressed as well as novel approaches to assess intestinal function.

RECENT FINDINGS

Small intestinal dysfunction can enhance the amount and alter the composition of undigested food reaching the colon. As a result of reduced protein digestion and absorption, a large amount of undigested protein might reach the colon promoting the presence of pathogenic colonic bacteria and a switch from bacterial fiber fermentation to protein fermentation. While microbial metabolites of fiber fermentation, such as short-chain fatty acids (SCFA), are mainly considered beneficial for overall health, metabolites of protein fermentation, i.e. ammonia, branched SCFAs, hydrogen sulfide, polyamines, phenols, and indoles, can exert beneficial or deleterious effects on overall health. Substantial advances have been made in the assessment of small intestinal dysfunction in chronic diseases, but studies investigating the connection to colonic microbial metabolism are needed. A promising new stable isotope approach can enable the measurement of metabolite production by the colonic microbiota.

SUMMARY

Several studies have been conducted to assess intestinal function in chronic diseases. Impairments in intestinal barrier function, sugar absorption, protein digestion, and absorption, as well as small intestinal bacterial overgrowth were observed and possibly might negatively impact colonic bacterial metabolism. We suggest that improving these perturbations will improve overall patient health.

Impaired intestinal function is associated with lower muscle and cognitive health and well-being in patients with congestive heart failure

BACKGROUND

Small- and large-intestinal perturbations have been described as prevalent extracardiac systemic manifestations in congestive heart failure (CHF), but alterations in protein digestion and absorption and plasma short-chain fatty acid (SCFA) concentrations and the potential link with other systemic effects (muscle and cognitive health) have not been investigated in CHF.

METHODS

We analyzed protein digestion and absorption with dual stable tracer method in 14 clinically stable, noncachectic CHF outpatients (mean left ventricular ejection fraction: 35.5% [95% CI, 30.9%-40.1%]) and 15 controls. Small-intestinal non-carrier-mediated permeability and active carrier-mediated glucose transport were quantified by sugar permeability test. Plasma SCFA (acetate, propionate, butyrate, isovalerate, valerate) concentrations were measured as intestinal microbial metabolites. Muscle function was assessed by isokinetic dynamometry, cognition by a battery of tests, and well-being by questionnaire.

RESULTS

Protein digestion and absorption were impaired by 29.2% (P = .001) and active glucose transport by 38.4% (P = .010) in CHF. Non-carrier-mediated permeability was not altered. Whereas plasma propionate, butyrate, and isovalerate concentrations were lower in CHF (P < .05), acetate and valerate concentrations did not differ. Overall, intestinal dysfunction was associated with impaired leg muscle quality, emotional distress, and cognitive dysfunction (P < .05).

CONCLUSIONS

We identified impaired protein digestion and absorption and altered SCFA concentrations as additional intestinal dysfunctions in CHF that are linked to reduced muscle and cognitive health and well-being. More research is needed to implement strategies to improve intestinal function in CHF and to investigate the mechanisms underlying its link with other systemic manifestations.

Walking exercise alters protein digestion, amino acid absorption, and whole body protein kinetics in older adults with and without COPD

Gut function is disturbed in older adults with COPD. As exercise is the cornerstone of pulmonary rehabilitation in COPD, knowledge of the response of the gut to aerobic exercise is of importance.