Abnormal Growth and Feeding Behavior Persist After Removal of Upper Airway Obstruction in Juvenile Rats

Changes in energy metabolism and respiration in different tracheal narrowing in rats

Why obstructive sleep apnea (OSA) treatment does not completely restore healthy metabolic physiology is unclear. In rats, the need for respiratory homeostasis maintenance following airway obstruction (AO) is associated with a loss of thermoregulation and abnormal metabolic physiology that persists following successful obstruction removal. Here, we explored the effect of two different types of tracheal narrowing, i.e., AO and mild airway obstruction (mAO), and its removal on respiratory homeostasis and metabolic physiology. We show that after ten weeks, mAO vs. AO consumes sufficient energy that is required to maintain respiratory homeostasis and thermoregulation. Obstruction removal was associated with largely irreversible increased feeding associated with elevated serum ghrelin, hypothalamic growth hormone secretagogue receptor 1a, and a phosphorylated Akt/Akt ratio, despite normalization of breathing and energy requirements. Our study supports the need for lifestyle eating behavior management, in addition to endocrine support, in order to attain healthy metabolic physiology in OSA patients.

Improvement in BMI z-score following adenotonsillectomy in adolescents aged 12-18 years: a retrospective cohort study

BACKGROUND

Characteristics of obstructive sleep apnea (OSA) changes with age. Infants, toddlers and prepubertal children with OSA are usually underweight and may suffer from failure to thrive (FTT). Adenotonsillectomy (T&A) is the first line of treatment for OSA in childhood. In adults OSA is commonly associated with obesity and the metabolic syndrome. The change in body mass index (BMI) in adolescents with OSA following T&A was only sporadically studied. Thus, we peruse to examine the BMI z-score change following T&A in adolescents.

METHODS

Clalit Health Services is the largest health care organization in Israel with the largest patient registry (more than 50% of the population). Two hundred and forty two adolescents aged 12-18 who underwent T&A between 2006 and 2015 were identified in the Clalit registry and their characteristics including height and weight were retrieved. The BMI z-score of these adolescents at baseline (up to 3 months prior to T&A) and during the consecutive 3 years after T&A were analyzed and compared.

RESULTS

Changes in BMI Z-score were observed to all directions following T&A with overall small increase, not statistically significant (P = 0.26) from a median of 0.79 prior to T&A to a median of 0.835 after it. There was a minimal trend toward BMI z-score reduction in overweight children (n = 74) from 1.508 to 1.48 following T&A (p = NS), and in obese children (n = 33) from 2.288 to 2.000 (P = 0.06, 2 tailed). Interestingly thin individuals (n = 6) increased their BMI z-score following T&A from - 2.4 to - 0.59 (p = 0.046).

CONCLUSIONS

Adolescents show variable changes in their BMI z-score following T&A. In this aspect their BMI z-score change is closer to the change seen in adults treated for OSA and not that of young children. The changes observed show a trend toward normalization of the BMI z-score such that overweight children tend to decrease their BMI z-score while thin individuals tend to increase it.

Upper Airway Obstruction Elicited Energy Imbalance Leads to Growth Retardation that Persists after the Obstruction Removal

Upper airway obstruction can lead to growth retardation by unclear mechanisms. We explored the effect of upper airway obstruction in juvenile rats on whole-body energy balance, growth plate metabolism, and growth. We show that after seven weeks, obstructed animals’ ventilation during room air breathing increased, and animals grew less due to abnormal growth plate metabolism. Increased caloric intake in upper airway-obstructed animals did not meet increased energy expenditure associated with increased work of breathing. Decreased whole-body energy balance induced hindrance of bone elongation following obstruction removal, and array pathways regulating growth plate development and marrow adiposity. This is the first study to show that rapidly growing animals cannot consume enough calories to maintain their energy homeostasis, leading to an impediment in growth in the effort to save energy.

Irreversible metabolic abnormalities following chronic upper airway loading

STUDY OBJECTIVES

Treatment of obstructive sleep apnea increases obesity risk by an unclear mechanism. Here, we explored the effects of upper airway obstruction and its removal on respiratory homeostasis, energy expenditure, and feeding hormones during the sleep/wake cycle from weaning to adulthood.

METHODS

The tracheas of 22-day-old rats were narrowed, and obstruction removal was performed on post-surgery day 14. Energy expenditure, ventilation, and hormone-regulated feeding were analyzed during 49 days before and after obstruction.

RESULTS

Energy expenditure increased and body temperature decreased in upper airway obstruction and was only partially recovered in obstruction removal despite normalization of airway resistance. Increased energy expenditure was associated with upregulation of ventilation. Decreased body temperature was associated with decreased brown adipose tissue uncoupling protein 1 level, suppressed energy expenditure response to norepinephrine, and decreased leptin level. Upper airway obstructed animals added less body weight, in spite of an increase in food intake, due to elevated hypothalamic orexin and neuropeptide Y and plasma ghrelin. Animals who underwent obstruction removal fed more due to an increase in hypothalamic neuropeptide Y and plasma ghrelin.

CONCLUSIONS

The need to maintain respiratory homeostasis is associated with persistent abnormal energy metabolism and hormonal regulation of feeding. Surgical treatment per se may not be sufficient to correct energy homeostasis, and endocrine regulation of feeding may have a larger effect on weight change.

Abnormal Growth and Feeding Behavior in Upper Airway Obstruction in Rats

Pediatric obstructive sleep apnea (OSA) is a syndrome manifesting with snoring and increased respiratory effort due to increased upper airway resistance. In addition to cause the abnormal sleep, this syndrome has been shown to elicit either growth retardation or metabolic syndrome and obesity. Treating OSA by adenotonsillectomy is usually associated with increased risk for obesity, despite near complete restoration of breathing and sleep. However, the underlying mechanism linking upper airways obstruction (AO) to persistent change in food intake, metabolism, and growth remains unclear. Rodent models have examined the impact of intermittent hypoxia on metabolism. However, an additional defining feature of OSA that is not related to intermittent hypoxia is enhanced respiratory loading leading to increased respiratory effort and abnormal sleep. The focus of this mini review is on recent evidence indicating the persistent abnormalities in endocrine regulation of feeding and growth that are not fully restored by the chronic upper AO removal in rats. Here, we highlight important aspects related to abnormal regulation of metabolism that are not related to intermittent hypoxia per se, in an animal model that mimics many of the clinical features of pediatric OSA. Our evidence from the AO model indicates that obstruction removal may not be sufficient to prevent the post-removal tendency for abnormal growth.