The link between resistin, systemic low-grade inflammation and obstructive sleep apnea

Abstract

Summary. Obstructive sleep apnea is a condition manifested by airway obstruction associated with decreased or complete cessation of air flow in the upper respiratory system. This condition leads to recurrent nocturnal oxygen desaturation, fragmented sleep, and excessive daytime sleepiness. Moreover, increasing evidence suggests that obstructive sleep apnea is a risk factor for various diseases, including: cardiovascular diseases, type 2 diabetes, metabolic syndrome and non-alcoholic fatty liver disease, abdominal obesity and dyslipidemia. Chronic intermittent hypoxia is one of the main consequences of obstructive sleep apnea, and induces oxidative stress that damages endothelial cells, adipocytes and immune system cells. In addition, this condition stimulates the inflammatory response due to increased concentrations of pro-inflammatory cytokines, as well as overactivation of the sympathetic nervous system. Obstructive sleep apnea frequently occurs in obese subjects and promotes inflammation of adipose tissues. Adipose tissue has recently been recognised to be an endocrine organ, and systemic exposure to inflammation and chronic intermittent hypoxia induces structural and functional changes resulting in release of pro-inflammatory cytokines by adipocytes and vascular stromal cells. Resistin, a cysteine-rich peptide, is one such pro-inflammatory molecule whose precise role in inflammation is not well understood.  Resistin is expressed mainly in bone marrow, immune cells, and macrophages, where it functions by binding to Toll-like receptor 4 and adenylyl cyclase-associated protein 1 receptors, promoting inflammation and enhancing transcription of pro-inflammatory cytokines. In humans, resistin has been reported to be associated with the development and progression of insulin resistance, type 2 diabetes, metabolic syndrome, and cardiovascular diseases by participating in pro-inflammatory-associated processes. Obstructive sleep apnea is a chronic, low-grade pro-inflammatory state; and the role of resistin in obstructive sleep apnea has been investigated in numerous studies to explain the connection between inflammation processes that may deteriorate air flow and muscular functions of the upper parts of the respiratory system. This review will discuss the relationship between resistin and obstructive sleep apnea in the context of systemic low-grade inflammation.