Inflammation
Suppression of oxidative stress by β-hydroxybutyrate, an endogenous histone deacetylase inhibitor
Abstract
Concentrations of acetyl-coenzyme A and nicotinamide adenine dinucleotide (NAD(+)) affect histone acetylation and thereby couple cellular metabolic status and transcriptional regulation. We report that the ketone body d-β-hydroxybutyrate (βOHB) is an endogenous and specific inhibitor of class I histone deacetylases (HDACs). Administration of exogenous βOHB, or fasting or calorie restriction, two conditions associated with increased βOHB abundance, all increased global histone acetylation in mouse tissues. Inhibition of HDAC by βOHB was correlated with global changes in transcription, including that of the genes encoding oxidative stress resistance factors FOXO3A and MT2. Treatment of cells with βOHB increased histone acetylation at the Foxo3a and Mt2 promoters, and both genes were activated by selective depletion of HDAC1 and HDAC2. Consistent with increased FOXO3A and MT2 activity, treatment of mice with βOHB conferred substantial protection against oxidative stress.
β-hydroxybutyrate: much more than a metabolite
Abstract
The ketone body β-hydroxybutyrate (βOHB) is a convenient carrier of energy from adipocytes to peripheral tissues during fasting or exercise. However, βOHB is more than just a metabolite, having important cellular signaling roles as well. βOHB is an endogenous inhibitor of histone deacetylases (HDACs) and a ligand for at least two cell surface receptors. In addition, the downstream products of βOHB metabolism including acetyl-CoA, succinyl-CoA, and NAD+ (nicotinamide adenine dinucleotide) themselves have signaling activities. These regulatory functions of βOHB serve to link the outside environment to cellular function and gene expression, and have important implications for the pathogenesis and treatment of metabolic diseases including type 2 diabetes.
Inflammation and insulin resistance
Abstract
Over a hundred years ago, high doses of salicylates were shown to lower glucose levels in diabetic patients. This should have been an important clue to link inflammation to the pathogenesis of type 2 diabetes (T2D), but the antihyperglycemic and antiinflammatory effects of salicylates were not connected to the pathogenesis of insulin resistance until recently. Together with the discovery of an important role for tissue macrophages, these new findings are helping to reshape thinking about how obesity increases the risk for developing T2D and the metabolic syndrome. The evolving concept of insulin resistance and T2D as having immunological components and an improving picture of how inflammation modulates metabolism provide new opportunities for using antiinflammatory strategies to correct the metabolic consequences of excess adiposity.
Inflammatory mechanisms linking obesity and metabolic disease
Abstract
There are currently over 1.9 billion people who are obese or overweight, leading to a rise in related health complications, including insulin resistance, type 2 diabetes, cardiovascular disease, liver disease, cancer, and neurodegeneration. The finding that obesity and metabolic disorder are accompanied by chronic low-grade inflammation has fundamentally changed our view of the underlying causes and progression of obesity and metabolic syndrome. We now know that an inflammatory program is activated early in adipose expansion and during chronic obesity, permanently skewing the immune system to a proinflammatory phenotype, and we are beginning to delineate the reciprocal influence of obesity and inflammation. Reviews in this series examine the activation of the innate and adaptive immune system in obesity; inflammation within diabetic islets, brain, liver, gut, and muscle; the role of inflammation in fibrosis and angiogenesis; the factors that contribute to the initiation of inflammation; and therapeutic approaches to modulate inflammation in the context of obesity and metabolic syndrome.
Type 2 diabetes as an inflammatory disease
Key Points
Type 2 diabetes is associated with obesity, ageing and inactivity. It is due to a progressive failure of pancreatic islet β-cells to compensate for insulin resistance.
The proposed mechanisms to explain impaired insulin secretion and sensitivity in type 2 diabetes include oxidative stress, endoplasmic reticulum stress, amyloid deposition in the pancreas, ectopic lipid deposition in muscle, liver and pancreas, and lipotoxicity and glucotoxicity. All these cellular stresses may induce an inflammatory response or are exacerbated by or associated with inflammation.
Factors that are associated with innate immune responses are present in the circulation, insulin-sensitive tissues and pancreatic islets in type 2 diabetes, and this evidence supports the involvement of inflammation in the pathogenesis of this disease.
Mechanisms thought to be responsible for the inflammatory state in type 2 diabetes include hypoxia and cell death of expanding adipose tissue, activation of the nuclear factor-κB (NF-κB) and JUN N-terminal kinase (JNK) pathways, activation of interleukin-1β (IL-1β), and recruitment and activation of immune cells.
Clinical trials using IL-1 antagonists or salsalate to directly target pro-inflammatory factors in patients with type 2 diabetes show promising preliminary results and support the role of inflammation in this condition.
Existing data suggest a potential role for inflammation in the pathogenesis of type 2 diabetes. The relative importance of this mechanism and the precise therapeutic consequences remain to be elucidated.
Abstract
Components of the immune system are altered in obesity and type 2 diabetes (T2D), with the most apparent changes occurring in adipose tissue, the liver, pancreatic islets, the vasculature and circulating leukocytes. These immunological changes include altered levels of specific cytokines and chemokines, changes in the number and activation state of various leukocyte populations and increased apoptosis and tissue fibrosis. Together, these changes suggest that inflammation participates in the pathogenesis of T2D. Preliminary results from clinical trials with salicylates and interleukin-1 antagonists support this notion and have opened the door for immunomodulatory strategies for the treatment of T2D that simultaneously lower blood glucose levels and potentially reduce the severity and prevalence of the associated complications of this disease.