Role of calorie restriction on pathophysiological changes in tongue fat and its relation to increased risk factors of obstructive sleep apnea in WNIN/Ob obese rats

Purpose Obstructive sleep apnea is an outcome of obesity, resulting from abnormal upper airway structures. Our main objective was to assess the fat infiltration into the tongue of calorie-restricted rats and its consequences on upper airway obstruction in comparison with lean and obese rats. Methods A total of 24 adults lean, obese and CR obese rats were included in the study. Body fat and lean body mass were determined by TOBEC, DXA measured fat depositions around the neck region, and radiographs of upper airway structure were analysed by digital X-ray. Ex vivo biochemistry was carried out for leptin, and lipids in blood/tissues, and fat infiltration by ORO staining. The tongue, masseter muscle fat, fibre and taste bud morphology was assessed by SEM. Results Body composition analysis showed higher body fat and low lean body mass in obese animals; DXA results showed excess fat around the neck region of obese rats. Higher triglyceride and reduced leptin levels were observed in CR obese rats compared to lean and obese rats. ORO and SEM analysis showed varying degree of fat accumulation among the groups. Tongue muscle fibres of obese rats showed rugged abnormal folding with an increase in width in comparison with calorie-restricted obese rats. The distance and width between the taste buds of calorie-restricted obese rats were reduced to the levels of lean rats. Conclusion The calorie restriction in obese rats reduced the fat deposition around the neck and improves the upper airway structures, the morphology of tongue fibre and increased the stiffness of the tongue, thereby reducing the risk of obstructive sleep apnea.