Cardiometabolic Effects of Irisin in Patients with End-Stage Renal Disease on Regular Hemo- or Peritoneal Dialysis

The emerging roles of irisin in vascular calcification

Vascular calcification is a common accompanying pathological change in many chronic diseases, which is caused by calcium deposition in the blood vessel wall and leads to abnormal blood vessel function. With the progress of medical technology, the diagnosis rate of vascular calcification has explosively increased. However, due to its mechanism's complexity, no effective drug can relieve or even reverse vascular calcification. Irisin is a myogenic cytokine regulating adipose tissue browning, energy metabolism, glucose metabolism, and other physiological processes. Previous studies have shown that irisin could serve as a predictor for vascular calcification, and protect against hypertension, diabetes, chronic kidney disease, and other risk factors for vascular calcification. In terms of mechanism, it improves vascular endothelial dysfunction and phenotypic transformation of vascular smooth muscle cells. All the above evidence suggests that irisin plays a predictive and protective role in vascular calcification. In this review, we summarize the association of irisin to the related risk factors for vascular calcification and mainly explore the role of irisin in vascular calcification.

The role of irisin in kidney diseases

Irisin is a hormone that is produced mainly by skeletal muscles in response to exercise. It has been found to have a close correlation with obesity and diabetes mellitus for its energy expenditure and metabolic properties. Recent research has revealed that irisin also possesses anti-inflammatory, anti-oxidative and anti-apoptotic properties, which make it associated with major chronic diseases, such as chronic kidney disease (CKD), liver diseases, osteoporosis, atherosclerosis and Alzheimer s disease. The identification of irisin has not only opened up new possibilities for monitoring metabolic and non-metabolic diseases but also presents a promising therapeutic target due to its multiple biological functions. Studies have shown that circulating irisin levels are lower in CKD patients than in non-CKD patients and decrease with increasing CKD stage. Furthermore, irisin also plays a role in many CKD-related complications like protein energy wasting (PEW), cardiovascular disease (CVD) and chronic kidney disease-mineral and bone disorder (CKD-MBD). In this review, we present the current knowledge on the role of irisin in kidney diseases and their complications.

Serum irisin levels are negatively associated with blood pressure in dialysis patients

Elevated blood pressure is highly prevalent among dialysis patients and is associated with high mortality. Irisin is a newly found myokine that has been indicated to be related to blood pressure regulation in animal experiments. Data regarding the effect of serum irisin levels on blood pressure in dialysis patients are limited. To identify the association between serum irisin levels and blood pressure and examine determinant factors of systolic blood pressure in dialysis patients, we recruited 300 dialysis patients at Xuanwu Hospital Capital Medical University. Serum irisin levels were assessed by enzyme-linked immunosorbent assay kits. Blood pressure was self-measured on 7 consecutive days by an automated sphygmomanometer. The Pearson correlation test showed that the natural logarithm of irisin was negatively correlated with systolic blood pressure (r = -0.462, P < 0.001) and pulse pressure (r = -0.487, P < 0.001), but not correlated with diastolic blood pressure (r = -0.022, P = 0.709). Multivariate analysis revealed that the natural logarithm of irisin (β = -0.336, P < 0.001), lean tissue mass (β = 0.164, P = 0.005), diabetes mellitus (β = 0.165, P = 0.003) and serum calcium (β = -0.135, P = 0.019) were significant determinant factors for systolic blood pressure. This study is the first to demonstrate that serum irisin levels are significantly negatively associated with blood pressure in dialysis patients. Further studies are needed to provide possible mechanisms. We demonstrated that serum irisin levels were negatively associated with blood pressure in dialysis patients, which may provide a new target for antihypertensive treatment.

Irisin and Bone in Sickness and in Health: A Narrative Review of the Literature

Irisin is a hormone-like myokine produced by the skeletal muscle in response to exercise. Upon its release into the circulation, it is involved in the browning process and thermogenesis, but recent evidence indicates that this myokine could also regulate the functions of osteoblasts, osteoclasts, and osteocytes. Most human studies have reported that serum irisin levels decrease with age and in conditions involving bone diseases, including both primary and secondary osteoporosis. However, it should be emphasized that recent findings have called into question the importance of circulating irisin, as well as the validity and reproducibility of current methods of irisin measurement. In this review, we summarize data pertaining to the role of irisin in the bone homeostasis of healthy children and adults, as well as in the context of primary and secondary osteoporosis. Additional research is required to address methodological issues, and functional studies are required to clarify whether muscle and bone damage per se affect circulating levels of irisin or whether the modulation of this myokine is caused by the inherent mechanisms of underlying diseases, such as genetic or inflammatory causes. These investigations would shed further light on the effects of irisin on bone homeostasis and bone disease.