Dexamethasone Chemotherapy Does Not Disrupt Orexin Signaling

<div><p>Background</p><p>Steroid-induced sleep disturbance is a common and highly distressing morbidity for children receiving steroid chemotherapy for the treatment of pediatric acute lymphoblastic leukemia (ALL). Sleep disturbance can negatively impact overall quality of life, neurodevelopment, memory consolidation, and wound healing. Hypothalamic orexin neurons are influential wake-promoting neurons, and disturbances in orexin signaling leads to abnormal sleep behavior. A new class of drug, the orexin receptor antagonists, could be an intriguing option for sleep disorders caused by increased orexinergic output. Our aim was to examine the impact of ALL treatment doses of corticosteroids on the orexin system in rodents and in children undergoing treatment for childhood ALL.</p><p>Methods</p><p>We administered repeated injections of dexamethasone to rodents and measured responsive orexin neural activity compared to controls. In children with newly diagnosed standard risk B-cell ALL receiving dexamethasone therapy per Children’s Oncology Group (COG) induction therapy from 2014–2016, we collected pre- and during-steroids matched CSF samples and measured the impact of steroids on CSF orexin concentration.</p><p>Results</p><p>In both rodents, all markers orexin signaling, including orexin neural output and orexin receptor expression, were preserved in the setting of dexamethasone. Additionally, we did not detect a difference in pre- and during-dexamethasone CSF orexin concentrations in children receiving dexamethasone.</p><p>Conclusions</p><p>Our results demonstrate that rodent and human orexin physiology is largely preserved in the setting of high dose dexamethasone. The data obtained in our experimental model fail to demonstrate a causative role for disruption of the orexin pathway in steroid-induced sleep disturbance.</p></div

Human CSF orexin levels.

<p>(a) Individual patient CSF orexin levels at baseline and then 8 days into dexamethasone (DEX) therapy for ALL. Mean baseline orexin concentration is equivalent to mean DEX day 8 orexin concentration. (b) There was no significant change in mean orexin level from baseline to DEX day 8 (<i>n</i> = 22). Data are expressed as mean ± SEM.</p

Mice (a, c-e, i-j) and rats (b, f-h) treated with dexamethasone (DEX) versus saline (vehicle) exhibit largely preserved orexin neuron signaling.

<p>(a) DEX does not cause a measurable difference in mouse orexin neuron gene expression as measured by RT-PCR (Vehicle <i>n</i> = 3, DEX <i>n</i> = 5). (b) DEX does not cause a measurable difference in rat orexin neuron gene expression as measured by RT-PCR (Vehicle <i>n</i> = 4, DEX <i>n</i> = 3). (c) Schematic illustrating the division between LH and PFA/DMH orexin neuron populations. (d, e) DEX does not upregulate mouse orexin neuron gene expression as measured by ISH, as grain clusters per orexin neuron (corresponding to radiolabeled <i>Hcrt</i> mRNA) are equivalent in both the DEX and NS animals in both the PFA/DMH and LH (Vehicle <i>n</i> = 9, DEX <i>n</i> = 8). (f) DEX does not alter total hypothalamic orexin (Ox-A) protein concentration in rats treated with DEX (Vehicle <i>n</i> = 7, DEX <i>n</i> = 7). (g) A disrupted normal diurnal variation of Ox-A by day 5 of DEX-treatment compared to sham (Vehicle <i>n</i> = 8, DEX <i>n</i> = 7) **<i>p</i> < 0.01. (h) On repeat testing, CSF Ox-A concentration on day 5 was equivalent between groups (Vehicle <i>n</i> = 7, DEX <i>n</i> = 7). (i, j) DEX did not cause a measurable difference in mice orexin 1 receptor gene expression (Vehicle <i>n</i> = 4, DEX <i>n</i> = 3) or orexin 2 receptor gene expression (NS <i>n</i> = 4, DEX <i>n</i> = 3) as measured by RT-PCR. Data, unless otherwise specified, represent orexin levels at the expected nadir (evening) on day 5 of DEX or sham treatment. Data are expressed as mean ± SEM.</p