Obesity - Inflammation - Metabolic Disease: Effect of Lactobacillus Casei Shirota

Obesity and metabolic disorders (type 2 diabetes and insulin resistance) are tightly linked to inflammation. Obesity, a pandemic affecting 30-50% of the adult population, is mediated by a variety of genetic and environmental factors. It is well described that cytokines cause insulin resistance which causes hyperinsulinemia and excessive fat storage in adipose tissue and the liver. However, the triggering factor, linking inflammation to metabolic syndrome has not been fully elucidated yet.

Recently it has been hypothesized that the gut flora is an important factor in this vicious cycle of obesity, metabolic disease and inflammation. Firstly, metabolic activities of the gut microbiota facilitates the extraction of calories from ingested dietary substances and helps to store these calories in host adipose tissue for later use. Second, the gut bacterial flora of obese mice and humans include fewer Bacteroidetes and correspondingly more Firmicutes than that of their lean counterparts, suggesting that differences in caloric extraction of ingested food substances may be due to the composition of the gut microbiota. Furthermore, bacterial lipopolysaccharide derived from the intestinal microbiota may trigger inflammation, linking it to high-fat diet-induced metabolic syndrome. High-fat diet induces insulin resistance and oxidative stress in mice and is associated with increased gut permeability. high fat diet induces a low-grade endotoxemia in mice ("metabolic endotoxemia) and infusing endotoxin causes weight gain and insulin resistance. This has also been shown in humans, where patients with fatty liver had a susceptibility to higher gut permeability, possibly causing increased endotoxin levels.

Endotoxin and Lipopolysaccharide-binding protein (LBP) is elevated in obese patients, patients with type 2 diabetes and patients with liver steatosis. Endotoxin causes a significant increase in proinflammatory cytokine production in adipocytes via a TLR mediated pathway, contribution to the proinflammatory state in obesity. Endotoxin levels correlate with adiponectin and insulin suggesting a pathophysiological link between obesity, inflammation and metabolic disease.

As described above, endotoxin is related to increased inflammation and oxidative stress, causing insulin resistance. Adipocytes have been shown to play a dynamic role in regulation of inflammation by producing cytokines via a Toll-like receptor (TLR)/Nuclear Factor kappa B (NFkB) mediated pathway.But not only adipocytes are in a proinflammatory state - also circulating mononuclear cells have been described to be activated. Clinical evidence suggests immune dysfunction in obesity, since obese patients are more prone to infections after surgery, higher incidence of lower respiratory infection which is also underlined by impairment of cell-mediated immune responses in vivo and in vitro and a reduced intracellular killing by neutrophils.

A similar situation has been recently described in alcoholic cirrhosis and alcoholic hepatitis, which is also a proinflammatory condition with impaired innate immunity, leading to infection. Endotoxin has been described as a key mediator and inadequate activation of neutrophils leading to high oxidative burst and energy depletion of the cells with consecutive impaired phagocytic capacity has been described.