A study says that an inflammatory factor, already implicated in causing several diseases, like pulmonary disease, lung cancer, and arthritis, may cause insulin resistance linked with obesity.
The researchers behind the study say that an inflammatory protein, known as CXCL5, rises and falls with obesity and subsequent weight loss in humans.
They say that they experiments on mice have provided further evidence linking the inflammatory factor, which is produced and secreted at high levels by fat tissue, to insulin resistance.
The researchers have also shown that treatments designed to block its action improve the animals' sensitivity to insulin.
"Clearly, this finding could be a big development for understanding the side effects of obesity. It offers a new target for therapy and new hope for subjects to improve their pathology," said Lluis Fajas of INSERM in France.
The researchers explained that fat tissue known as white adipose tissue (WAT) is primarily involved in energy storage in the form of triglycerides and energy release in the form of free fatty acids.
WAT, however, is more than a fat storage organ, it also secretes numerous other factors with roles in both health and disease.
In the current study, the researchers showed that CXCL5 is one of those factors, for it is expressed at high levels in WAT, particularly in immune cells known as macrophages.
They also claimed that CXCL5 is dramatically increased in the blood of people who are obese as compared to those who are lean.
The CXCL5 levels drop when obese people lose weight and are also lower in obese individuals that continue to respond to insulin than in those who are insulin resistant.
The researchers further found that treatment with recombinant CXCL5 blocks insulin-stimulated glucose uptake in the muscles of mice.
The mice lacking the CXCL5 receptor were also protected against obesity-induced insulin resistance.
Overall, the findings showed that CXCL5 produced by fat tissue "represents a link between obesity, inflammation, and insulin resistance."
Interestingly, the researchers said that the CXCR2 receptor was active outside of muscle, and thus increased levels of the chemokine as observed in obesity could lead to other problems, including atherosclerosis and other inflammatory diseases.
The study has been published in the latest issue of Cell Metabolism, a Cell Press publication.