The mechanisms underlying the negative effect and high variability of systemic behavioural side effects of glucocorticoid therapy are not completely understood. This study is the first to explore possible PK, serum albumin, and pharmacogenomic mechanisms that contribute to poor sleep and increased fatigue in children with ALL receiving dexamethasone. As one would expect, dexamethasone clearance was higher in younger children and decreased with age. This lower clearance and higher dosing of steroids in the higher risk groups resulted in a higher exposure (AUC) in older children and adolescents and in those in the higher-risk groups.
The mean apparent oral clearance of dexamethasone was slightly higher in our study (20.9 L/h/m2
) than in the only previously published dexamethasone PK study of children with ALL by Yang and colleagues8
In that study, the 214 patients were in reinduction therapy and received more intensive therapy, including recent administration of asparaginase. Clearance in that patient group was 14 L/h per m2
and most likely reflective of poorer organ function due to more intensive treatment during remission induction. In that earlier study, the variability of dexamethasone PK parameters (46% inter-patient, 53% intra-patient) was comparable to that in our results.
In our study, older participants were usually in the standard-risk group, and they received higher doses of dexamethasone; thus, it was difficult to distinguish between the effects of dose, disease risk, and age. In an exploratory analysis, we attempted to control for dosing schedules (BID vs TID) and observed that children on TID dosing had more awakenings and a longer duration of WASO. It is difficult to determine whether the difference in dose or the timing of the third dose closer to bedtime explains the difference in sleep outcomes. The actual timing of the last dose was not recorded in this study. We theorize that the later the dose is given in the evening, the more likely the peak of dexamethasone will interfere with sleep. The current data cannot test if dose frequency (BID vs TID) has an independent effect on sleep, while adjusting for the total dose, because of multicolinearity. Future studies should explore the effect of timing of dexamethasone dosing on disturbed sleep and fatigue.
We retrospectively measured albumin levels in stored serum from time 0 samples. In the Yang study8
, albumin concentration was the largest covariate contributing to dexamethasone clearance. In our patient population, most albumin levels were in the normal range, and PK analysis did not find a significant correlation with albumin. Children with lower albumin levels appeared to experience greater fatigue, but our small patient group and normal albumin levels prevented us from determining whether a true relationship exists. In patients with a normal albumin level, other factors (i.e., age, risk group, etc.) most likely account for the large inter-patient variability of systemic dexamethasone side effects.
Using candidate genes, we explored 99 gene loci and their association with sleep and fatigue. There were no genotypes associated with fatigue; however, four genotypes on three genes to be associated with sleep measures. The AHSG
C>G (Thr238Ser) exon 7 genotype (rs4918) showed a significant association with sleep measures both OFF and ON DEX with a significant difference in sleep duration and actual sleep time for those with the GG genotype. While the effect of the described SNP on gene expression within this patient population is not known, a previous genomic analysis identified two common SNPs associated with circulating AHSG
levels, one being the C/G in exon 7 (rs4918), as described in this study.32
is a major hepatic protein that regulates inflammation and recovery and calcium levels. ASHG
also inhibits insulin receptor tyrosine kinase activity, thereby regulating insulin signaling and energy homeostasis.33 ASHG
has been identified as a susceptibility locus for type 2 diabetes and the metabolic syndrome.34-36
A study by Siddiq and colleaugues37
found the AHSG
SNP rs1071592 to be associated with type 2 diabetes and the SNPs rs2248690 and rs4918 to have borderline association. Along with insulin resistance, high AHSG
plasma levels have been implicated in the accumulation of fat in the human liver.38
Wöltje and colleagues39
found that in the presence of dexamethasone, the expression of AHSG
was upregulated indirectly via glucocorticoid hormone–induced transcriptional upregulation in the CCAAT enhancer binding protein β (C/EBP-β) in mouse hepatocytes and mouse hepatoma cells. This murine model may explain a possible upregulation of expression of AHSG
in the presence of dexamethasone, which is further potentiated in the presence of the GG genotype.
We found the wild-type (normal) AHSG
CC genotype to be significantly associated with better sleep during the OFF DEX week, providing sleep protection with higher sleep efficiency and shorter WASO. During the ON DEX period, the homozygous variant AHSG
GG genotype was associated with longer actual sleep time and longer sleep duration. Patients with the AHSG
GG genotype experienced significantly longer sleep duration during ON DEX than during OFF DEX. These sleep parameters, longer actual sleep time and longer sleep duration have been associated with fatigue during dexamethasone use in treatment of paediatric ALL.10
The rs4918 polymorphism interaction with dexamethasone may further increase the expression of AHSG
, which may result in longer sleep duration in compensation for the negative effect of fatigue.
Cytokines, most specifically IL-6, have been implicated in the inflammatory process and contribute to cancer-related symptomatology.40, 41
IL-6 is a known mediator of sleepiness and increased levels may increase one's drive for sleep.42 IL-6
(174) wild type G allele has been associated with higher production of the cytokine.43, 44
Our analysis found that OFF DEX, patients with the IL-6
(174) GG genotype experienced longer actual sleep time and longer total daily sleep minutes. These results suggest that IL-6
(174) GG contributes to an increased need for sleep. However, ON DEX there was no significant difference in sleep measures and IL-6
genotype. The IL-6
(C634G) CG genotype was also associated with longer actual sleep time and longer total daily sleep minutes during the OFF DEX week than those with the CC genotype. This specific IL-6
genotype has not yet been associated with sleep as the IL-6
(174). The association of IL-6
and sleep disappeared during the ON-DEX week, suggesting that the anti-inflammatory actions of steroids may influence IL-6
interactions with sleep.
Lastly, the POLDIP3
AA and AG genotypes were protective with significantly longer actual sleep time and better sleep efficiency during the OFF DEX week. The POLDIP3
AA genotype also was associated with fewer nocturnal awakenings and decreased WASO during the OFF DEX week. Although the POLDIP3
gene has not been previously associated with sleep, it plays a role in autoimmune disorders.45
This is an exciting new finding as the POLDIP3
A allele was significantly associated four sleep variables, but further exploration of this gene and its role in sleep is necessary.
This study has several limitations. First, the original study was powered to elucidate the effect of dexamethasone on sleep and fatigue variables; the additional analysis presented here is lacking in power, most specifically for discerning the effects of the associated genotypes. Second, the analysis of serum albumin concentration was conducted retrospectively; thus, adequate samples were not available from all 100 participants.
In conclusion, risk group had the most significant influence on sleep variables; however, it is impossible to distinguish the true impact of PK factors with risk group being highly correlated to dexamethasone dose and age, influencing both AUC and clearance. We did not identify a direct relationship of fatigue to dexamethasone pharmacokinetics or serum albumin. However, we identified candidate genes that may help explain the adverse events of disrupted sleep and increased fatigue in patients on dexamethasone. Most specifically, the regulatory effects of AHSG
expression on insulin metabolism and energy homeostasis may play a role in the increased fatigue and poorer sleep quality that was noted by Hinds and colleagues10
in patients prior to dexamethasone. Dexamethasone may then potentiate AHSG
expression and contribute to poor sleep quality, prolonged sleep as a compensatory mechanism to increased fatigue during dexamethasone treatment and account for the significant differences in sleep quality in these patients between the OFF DEX and ON DEX weeks. Further genetic exploration is needed to validate the association between AHSG
expression and sleep in paediatric patients with ALL.