The lipid profile: a window into metabolism and inflammation
What are Biomarkers?
Biomarkers are measurable indicators of biological processes, health conditions, or responses to treatment. They can be molecules circulating in the blood, proteins found in tissues, genetic signatures, or even physiological measurements such as heart rate or blood pressure. Biomarkers are essential tools in modern medicine, as they support diagnosis, help predict disease risk, guide treatment decisions, and allow researchers to understand how diseases develop and progress. By examining biomarkers, clinicians and scientists can take steps toward more personalised and precise healthcare.
Among the many biomarker categories currently studied, lipid-based biomarkers have gained increasing attention, especially in the context of chronic inflammation and metabolic dysfunction.
Why look at lipids as biomarkers of inflammation?
Lipids, often simply called “fats”, play key roles in the body. They form cell membranes, are used as an energy source, help produce hormones, support metabolism, and ensure normal organ function. But lipids also interact closely with the immune system. Changes in lipid levels can reflect biological stress, inflammatory activity, or disturbances in metabolism.
Increasing scientific evidence links lipid alterations not only to cardiovascular disease but also to chronic inflammation, insulin resistance, autoimmune diseases, and gut barrier dysfunction. Because these processes are also central to rheumatic conditions such as rheumatoid arthritis (RA) and osteoarthritis (OA), lipid biomarkers may also provide insights relevant to the ENDOTARGET goals of understanding the health-to-disease transition.
The lipid profile: a window into metabolism and inflammation
The standard lipid profile measures four major blood lipid components:
- Total cholesterol
- Low-density lipoprotein (LDL)
- High-density lipoprotein (HDL)
- Triglycerides
These parameters are routinely used in cardiovascular diagnostics but also have strong connections to inflammation and gut health.
Total Cholesterol: Total cholesterol is the sum of all cholesterol molecules circulating in the bloodstream, including both LDL and HDL. Cholesterol is required for:
- Building cell membranes
- Producing hormones
- Synthesising vitamin D
- Forming bile acids for digestion
While cholesterol is essential, elevated total cholesterol may signal metabolic imbalance. However, its interpretation always depends on the combination of LDL and HDL levels. High total cholesterol is associated with chronic inflammation and increased cardiovascular risk, especially when accompanied by high LDL or low HDL.
Low-Density Lipoprotein (LDL): LDL particles transport cholesterol from the liver to the rest of the body. LDL supports cell membrane repair, production of hormones, vitamin D synthesis and certain immune functions. However, excess LDL can accumulate in artery walls, leading to plaque formation, oxidative stress, and inflammation. Elevated LDL is also associated with:
- Atherosclerosis
- Chronic low-grade inflammation
- Metabolic syndrome
- Higher cardiovascular risk
LDL can also cross-link with inflammatory molecules, amplifying immune responses. In inflammatory conditions, LDL becomes more susceptible to oxidation, a process closely tied to endothelial dysfunction and systemic inflammation.
High-Density Lipoprotein (HDL): HDL is often described as “good cholesterol.” Its key functions include (i) removing excess cholesterol from cells and tissues, (ii) transporting cholesterol back to the liver for excretion, (iii) protecting blood vessels from inflammation, and (iv) supporting endothelial (blood vessel lining) health. HDL has anti-inflammatory, anti-oxidative, and immune-modulating properties. Low HDL levels are linked to:
- Increased systemic inflammation
- Insulin resistance
- Greater cardiovascular risk
- Metabolic dysfunction
Interestingly, inflammation can also impair HDL quality, reducing its ability to protect blood vessels even when levels appear normal. Thus, HDL is not only a quantity marker but also a marker of lipid functionality.
Triglycerides: Triglycerides are the primary form of stored fat in the body. They are essential for energy storage, metabolism and the transport of fat-soluble vitamins. However, high triglycerides are associated with insulin resistance, obesity, metabolic syndrome, increased cardiovascular risk, chronic inflammation, alcohol overconsumption, and sedentary behaviour. Elevated triglycerides can also reflect gut–microbiome imbalances (dysbiosis) and poor intestinal barrier function, both of which are key contributors to systemic inflammation and endotoxemia.
How lipids and inflammation interact
The relationship between lipid levels and inflammation is bidirectional:
- Inflammation alters lipid metabolism, changing the balance of LDL, HDL, and triglycerides.
- Abnormal lipid levels can promote inflammation, feeding into metabolic and immune dysfunction.
Three main mechanisms link lipids to inflammation:
- Gut inflammation and intestinal permeability. Gut inflammation can disrupt tight junction proteins such as claudins and occludin, leading to increased intestinal permeability (“leaky gut”). This allows bacterial toxins like lipopolysaccharides (LPS) to enter the bloodstream, influencing liver metabolism and altering lipid levels.
- Dysbiosis and altered bile acid metabolism. An imbalanced gut microbiome affects bile acid pathways, lipid absorption, and cholesterol metabolism. People with dysbiosis often exhibit elevated triglycerides and LDL and lowered HDL.
- Inflammatory cytokines and liver function. Chronic inflammation activates cytokines such as IL-6 and TNF-α, which stimulate triglyceride synthesis, decrease HDL, and promote LDL oxidation. These processes contribute to atherosclerosis, metabolic syndrome, and systemic inflammation.
Together, these mechanisms show why the lipid profile is a sensitive marker of chronic inflammatory conditions.
Lipid profiles in ENDOTARGET
The ENDOTARGET project investigates lipid biomarkers to better understand how inflammation develops and how the gut–joint axis contributes to rheumatic disease progression. The lipid profile is used to:
- Identify metabolic patterns linked to systemic inflammation
- Study interactions between lipids and endotoxemia
- Compare inflammatory and metabolic markers across patient cohorts
- Support precision-medicine approaches exploring the health-to-disease transition
Glossary
Biomarker: A measurable indicator of a biological process, condition, or response to treatment.
Cholesterol: A lipid molecule essential for cell structure, hormone production, and vitamin D synthesis.
Dysbiosis: An imbalance in the gut microbiome, often linked to inflammation.
Endotoxemia: The presence of bacterial toxins, such as LPS, in the bloodstream.
HDL (High-Density Lipoprotein): A “good” lipoprotein that removes excess cholesterol and protects against inflammation.
Inflammatory Cytokines: Signalling proteins (e.g., IL-6, TNF-α) produced during inflammation.
LDL (Low-Density Lipoprotein): A “delivery” lipoprotein carrying cholesterol to tissues; elevated levels can promote inflammation.
Leaky Gut: Increased intestinal permeability allowing bacteria or toxins to enter the bloodstream.
Metabolic Syndrome: A cluster of conditions linked to inflammation, including obesity, insulin resistance, and abnormal lipid levels.
Triglycerides: The main form of stored fat in the body, often elevated during metabolic or inflammatory stress.
References
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