Lipopolysaccharides (LPS / endotoxins)

Cell wall components of gram-negative bacteria. When the gut barrier is more permeable, more LPS can reach the bloodstream and stimulate a low-grade inflammatory response there ("metabolic endotoxaemia"). It has been observed in studies with excess weight and insulin resistance.

What LPS trigger in the body

Lipopolysaccharides (LPS) form the outer envelope of gram-negative bacteria, which make up a large part of the gut flora. The gut therefore constantly contains large amounts of LPS; the mucus layer, tight junctions, secretory IgA and the enzyme alkaline phosphatase of the gut cells keep them away from the inside of the body. Small amounts that nevertheless arrive via the portal vein are captured by the scavenger cells of the liver, and lipoproteins in the blood bind LPS. When LPS reach immune cells, these recognise the component lipid A via LPS-binding protein, CD14 and the receptor TLR4 – and release inflammatory messengers such as TNF-alpha, interleukin-1 and interleukin-6. This recognition is an early-warning system against bacterial infections.

Low LPS – what does it mean?

A low value is the normal case: the gut barrier largely keeps LPS inside the gut, and whatever still gets through is captured by the liver and lipoproteins before immune cells react to it on a larger scale.

Raised LPS – what happens in the body?

When more LPS pass through the gut wall than the liver and lipoproteins can capture, immune cells in the gut wall, liver, fat tissue and blood vessels are persistently and mildly stimulated via TLR4. They release inflammatory messengers, the liver produces acute-phase proteins such as CRP, and the messengers disrupt insulin signalling in the liver, muscle and fat tissue. This low-grade burden is called metabolic endotoxaemia; it has been observed in studies with excess weight, insulin resistance and fatty liver. More LPS pass through when the tight junctions are loosened, when the gut flora shifts in favour of gram-negative bacteria, and temporarily after very fatty meals, because LPS are absorbed with the fat droplets via the lymph. Large amounts in the blood, as in a severe bacterial infection, cause fever and a drop in blood pressure – that is an emergency.

The interpretation is given in your report.