Metabolic endotoxemia as a contributing pathogenetic factor in atherosclerotic cardiovascular disease with an adverse outcome

A new publication was released by the ENDOTARGET consortium, which investigates the role of intestinal permeability and ensuing endotoxemia in cardiovascular diseases (CVD) and to discover whether traditional risk factors mediate or modulate its effects. This scientific work was published in April 2025 in the Atherosclerosis Journal from Elsevier. Authors of this study are: J. Parantainen, G. Barreto, T.E. Strandberg, N. Mars, K. Nurmi, and K.K. Eklund.

 

Why should we study metabolic endotoxemia in the context of cardiovascular diseases?

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of death worldwide. Despite advancements in ASCVD prevention and treatment, our understanding of the underlying mechanisms remains incomplete. Several lines of evidence suggest that low-grade chronic inflammation is a pathogenetic factor in ASCVD, and thus, anti-inflammatory agents are used to treat patients. However, knowledge on the factors provoking the inflammation in ASCVD is lacking and prevents sufficient treatment and prevention.

One possible factor provoking such an inflammation might be metabolic endotoxemia, which describes the circulation of inflammatory-active bacterial compounds, esp. lipopolysaccharides (LPS), in the blood. Increased release of bacterial compounds from the microbiota residing in the gut is the most obvious source of metabolic endotoxemia. Here, the translocation of LPS from the gut into the blood is driven by an increased permeability of the gut and an alteration in the composition of the gut microbiota. The mechanisms through which endotoxemia could increase cardiovascular morbidity are yet to be elucidated in detail, but several pathways have been suggested, including endothelial cell activation and a wide range of pro-thrombotic effects.

Thus, this study aimed to explore the role of intestinal permeability and ensuing metabolic endotoxemia as risk factors for cardiovascular mortality.

 

What does the study population look like?

The study population was a random sub-cohort of the Helsinki Businessmen Study (HBS) cohort. Participants of the HBS cohort were recruited in the 1960s in Finland and originally comprised 3,490 male individuals of executive and business occupations who participated in several health check-ups. Available data and samples (i.e., blood, questionnaire information about disease and lifestyle factors, anthropomorphic measurements, biochemical measurements, and indices related to physical and cognitive function) were derived from three follow-up visits in 2002-2003, 2011 and 2017-2018. The mean age of the cohort at the 2002–2003 visit was 75.3 years. Previous studies on the cohort have focused on cardiovascular diseases, thus generating an extensive dataset relevant to the study hypothesis.

 

What kind of measurements were done?

Blood samples were used to analyse:

• Metabolic risk factors: lipoprotein, triglyceride, C-reactive protein (CRP), insulin, fasting glucose levels and low-density lipoprotein (LDL) cholesterol
• Endotoxemia-surrogate biomarkers: lipopolysaccharide binding protein (LBP) and soluble CD14 (sCD14)
• Intestinal permeability and inflammation biomarkers: zonulin, S100A8/A9 and intestinal type fatty acid binding protein (I-FABP)
• TRL-4 activation

 

What does the analysis show us?

1. Biomarkers of metabolic endotoxemia correlate with metabolic risk factors but not with prevalent ASCVD: TLR4 bioactivity, zonulin, and LBP levels were higher in individuals with metabolic syndrome, and esp. zonulin correlated with low-grade inflammation and with most traditional metabolic risk factors. Although an association between endotoxemia and prevalent ASCVD was hypothesised, no endotoxemia-related biomarker was elevated in individuals with a history of CAD or other ASCVD as compared with those without a diagnosis of ASCVD.
2. Biomarkers of intestinal permeability and metabolic endotoxemia as risk factors of incident ASCVD: As many pathogenetic effects of endotoxemia are expected to take years to become apparent, the related biomarkers could be important predictors of an enhanced future risk of metabolic diseases or ASCVD. Thus, the potential of endotoxemia-related biomarkers to predict incident ASCVD or metabolic diseases during the available 15-year follow-up period was studied. Although the biomarkers could not identify individuals with incident CAD, they did show some correlation with other health issues, i.e., diabetes and peripheral artery disease. These results suggest that these markers might help predict who is at risk of developing metabolic diseases in the future, especially in larger or more diverse groups of people.
3. Metabolic endotoxemia predicts CAD mortality: In the analysed sub-cohort, 40% of the 692 individuals of the 2002-2003 follow-up cohort had died. In 21%, the cause of death was CAD. Analysing the predictive values of the endotoxemia-related biomarkers one by one, both zonulin and LBP were associated with an increased risk of death from CAD during the 10-year follow-up time after sample collection. This risk stayed steady over time, suggesting that high levels of these markers may indicate a long-term health issue. Interestingly, almost half of those who died from CAD had never been diagnosed with it before, showing that many cases were unexpected. Even though traditional risk factors like LDL cholesterol were managed in many of the men, having higher LDL was still linked to CAD mortality. However, even after accounting for LDL levels, zonulin and LBP remained important predictors of risk. Taken together, these analyses suggest that while lowering LDL cholesterol levels is a crucial target to reduce CAD mortality, endotoxemia may account for a significant proportion of the residual CAD mortality risk that remains after the traditional risk factors have been managed.

 

What can we learn from the study?

The results support the suggestion of metabolic endotoxemia as a contributing pathogenetic factor in ASCVD with an adverse outcome. Of the surrogate biomarkers studied, zonulin was the most robust predictor of mortality in CAD. Levels of zonulin, LBP, and I-FABP remained relatively stable in individuals over the 15-year follow up, suggesting a potential role for them as biomarkers for ASCVD risk.

Read the full publication here: Increased intestinal mucosal permeability and metabolic endotoxemia predict the risk of cardiovascular mortality

 

Glossary

Atherosclerotic cardiovascular disease (ASCVD): is a condition where arteries become narrowed and hardened due to a buildup of plaque, which can lead to heart attacks, strokes, and other serious heart problems.

Biomarker: a measurable biological indicator (e.g., a molecule, gene, or physiological characteristic) that provides information about a biological process, disease state, or response to treatment

Cardiovascular diseases (CVD): are a group of disorders affecting the heart and blood vessels, including conditions like heart attacks, strokes, and hypertension, often caused by blocked or narrowed blood vessels.

C-reactive protein (CRP): is a substance produced by the liver in response to inflammation, and its levels in the blood are commonly used as a marker to detect inflammation or infection in the body.

Endotoxemia: a condition characterised by the presence of endotoxins, primarily lipopolysaccharides from Gram-negative bacteria, in the bloodstream, leading to systemic inflammation and potentially contributing to various chronic diseases.

Fasting glucose levels: refer to the amount of sugar (glucose) in the blood after not eating for at least 8 hours, and they are used to assess how well the body regulates blood sugar, often in diagnosing diabetes or prediabetes.

Helsinki Businessmen Study (HBS) cohort: is a long-term study group consisting of originally 3.490 Finnish men, mostly executives and professionals, recruited in the 1960s. It was originally a convenience cohort of executives and businessmen (born 1919-34) who participated in voluntary health check-up in Helsinki during the 1960s. The dataset comprises a wide range of phenotypic and environmental measures, biological samples, genetic information and linkage to health and administrative records. Cohort profile can be found here.

Inflammatory-active: Irefers to the ability of a substance to trigger or promote inflammation in the body by activating immune responses or signaling pathways.

Insulin: is a hormone produced by the pancreas that helps regulate blood sugar levels by allowing glucose to enter the body’s cells for energy or storage.

Intestinal type fatty acid binding protein (I-FABP): is a small protein found in cells lining the intestine, and it serves as a marker of intestinal cell damage or increased gut permeability.

Lipopolysaccharide (LPS): a large molecule found in the outer membrane of Gram-negative bacteria, composed of lipids and polysaccharides, that acts as an endotoxin and can trigger strong immune and inflammatory responses.

Lipopolysaccharide binding protein (LBP): is a protein in the blood that helps detect and respond to lipopolysaccharides (LPS), components of certain bacterial cell walls, by delivering them to immune receptors to trigger inflammation.

Lipoproteins: are molecules made of fat and protein that transport cholesterol and other lipids through the bloodstream to be used or stored by the body.

Low-density lipoprotein (LDL) cholesterol: is a type of cholesterol that can build up in the walls of arteries, increasing the risk of heart disease and stroke.

Metabolic syndrome: is a group of conditions (incl. high blood pressure, high blood sugar, excess abdominal fat, and abnormal cholesterol levels) that together increase the risk of heart disease, stroke, and type 2 diabetes.

Microbiota: a specific community of microorganisms, including bacteria, viruses, fungi, and archaea, residing in a defined habitat, like the human gut or soil.

S100A8/A9: also known as calprotectin, is a protein complex released by immune cells during inflammation and serves as a biomarker for various inflammatory diseases.

Soluble CD14 (sCD14): is a protein released by immune cells that helps detect bacterial components like lipopolysaccharides (LPS) and plays a key role in triggering inflammatory responses

Triglycerides: are a type of fat found in the blood that the body uses for energy, and high levels can increase the risk of heart disease.

Toll-like receptor 4 (TRL4): is a protein on the surface of immune cells that recognises specific bacterial molecules and triggers an immune response to defend against infections.

Zonulin: is a protein that helps regulate the tight junctions between cells in the gut lining, and elevated levels are associated with increased intestinal permeability.