Association of OSAHS Hypoxia Indicators with Early Renal Injury and Serum Fibroblast Growth Factor 21 in Obese Type 2 Diabetic Patients

Continuous Positive Airway Pressure Effect on Albuminuria Progression in Patients with Obstructive Sleep Apnea and Diabetic Kidney Disease: A Randomized Clinical Trial

Rationale: Obstructive sleep apnea (OSA) is associated with impaired glycemic control and a higher risk of vascular complications, such as diabetic kidney disease (DKD). However, the effect of apnea-hypopnea suppression on DKD progression is unclear. Objectives: To assess the effect of continuous positive airway pressure (CPAP) on the urinary albumin-to-creatinine ratio (UACR) in patients with DKD and OSA. Methods: In a 52-week, multicentric, open-label, parallel, and randomized clinical trial, 185 patients with OSA and DKD were randomized to CPAP and usual care (n = 93) or usual care alone (n = 92). Measurements and Main Results: UACR, estimated glomerular filtration rate, serum concentrations of creatinine and glycated hemoglobin, insulin resistance, lipid concentrations, sleepiness, and quality of life. A 52-week change in UACR from baseline did not differ significantly between the CPAP group and the usual-care group. However, in per-protocol analyses that included 125 participants who met prespecified criteria for adherence, CPAP treatment was associated with a great reduction in UACR (mean difference, -10.56% [95% confidence interval, -19.06 to -2.06]; P = 0.015). CPAP effect on UACR was higher in nonsleepy patients with more severe OSA, worse renal function, and a more recent diagnosis of DKD. CPAP treatment also improved glycemic control and insulin resistance, as well as sleepiness and health-related quality of life. Conclusions: In patients with OSA and DKD, the prescription of CPAP did not result in a statistically significant reduction in albuminuria. However, good adherence to CPAP treatment in addition to usual care may result in long-term albuminuria reduction compared with usual care alone. Clinical trial registered with www.clinicaltrials.gov (NCT02816762).

Fibroblast growth factor 21 is an independent predictor of prevalent and incident obstructive sleep apnea

Fibroblast growth factor 21 (FGF21) is a metabolic regulator and a potential biomarker of metabolic diseases. Limited data are available on the association between FGF21 and obstructive sleep apnea (OSA), which is considered as a manifestation of metabolic syndrome. In the present cross-sectional and longitudinal analyses, the FGF21 level was associated with OSA. This analysis of two clinical cohorts is the first to show that the FGF21 level increased significantly with OSA severity and was an independent predictor of incident OSA in Chinese adults. The circulating FGF21 level could serve as a potential serum biomarker of OSA and its comorbidities and thus aid risk evaluation and early intervention.

Obstructive sleep apnea is associated with impaired renal function in patients with diabetic kidney disease

Obstructive sleep apnea (OSA) is a recognized risk factor for the development of diabetic kidney disease (DKD). Our objectives were to compare the urinary albumin-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) of patients with DKD according to OSA severity, and to evaluate the contribution of sleep parameters to their renal function. In a multicenter, observational, cross-sectional study, 214 patients with DKD were recruited. After a sleep study, UACR and eGFR were measured, as well as serum creatinine, fasting glucose, glycated hemoglobin, insulin resistance, lipid profile and C-reactive protein. UACR was higher in severe OSA patients (920 ± 1053 mg/g) than in moderate (195 ± 232 mg/g, p < 0.001) or mild OSA/non-OSA subjects (119 ± 186 mg/g, p < 0.001). At the same time, eGFR showed an OSA severity-dependent reduction (48 ± 23 vs. 59 ± 21 vs. 73 ± 19 ml/min per 1.73 m², respectively; p < 0.001). Apnea-hypopnea index (AHI and desaturation index (ODI) were identified as independent predictors for UACR and eGFR, respectively. Therefore, in patients with DKD under optimized treatment, severe OSA is associated with a higher UACR and a lower eGFR, reflecting an additional contribution to the impairment of their renal function, although no causality can be inferred.

Hypoxia-Induced Adipose Lipolysis Requires Fibroblast Growth Factor 21

Fibroblast growth factor 21 (FGF21) is a recently discovered hepatokine that regulates lipid and glucose metabolism and is upregulated in response to numerous physiological and pathological stimuli. Herein, we demonstrate that both physical and chemical hypoxia increase the systemic and hepatic expression of FGF21 in mice; by contrast, hypoxia induces a reduction of FGF21 expression in hepatocytes, indicating that hypoxia-induced FGF21 expression is differentially regulated in intact animals and in hepatocytes. Furthermore, we demonstrate that hypoxia treatment increases hormone-sensitive lipase-mediated adipose tissue lipolysis in mice, which is reduced in Fgf21 knockout mice, thereby implying that FGF21 plays a critical role in hypoxia-related adipose lipolysis. Adipose tissue lipolysis causes an increase in the amount of circulating free fatty acids, which leads to the activation of peroxisome proliferators-activated receptor alpha and an increased expression of FGF21 in hepatocytes. We further show that hypoxia-induced elevation of reactive oxygen species, but not the hypoxia-inducible factor, is responsible for the lipolysis and FGF21 expression. In conclusion, our data clearly demonstrate that FGF21 plays a critical role in hypoxia-induced adipose lipolysis, which induces hepatic expression of FGF21. Clarification of hypoxia-regulated FGF21 regulation will enhance our understanding of the pathophysiology of hypoxia-related diseases, such as sleep disorders and metabolic diseases.