In this study, we used four independent cohorts to demonstrate the translational utility of metabolomics. We identified significant and robust reductions in steroid metabolites among asthma cases using ICS that place them at serious risk for adrenal suppression with as many as thirty percent reaching clinically diagnosable levels. There were three key findings. First, seventeen steroid metabolites had substantially reduced levels in prevalent asthma cases compared with controls, including marked reductions in the two primary hypothalamic-pituitary-adrenal axis (HPA) steroid hormones that are biomarkers for adrenal suppression34, DHEA-S and cortisol. Second, we observed that this reduction in steroids was primarily, but not exclusively driven by ICS use in asthmatics, suggesting that the reduced steroid levels represent both a fundamental characteristic of the asthma phenotype and a result of ICS use. Third, not only were cortisol levels consistently reduced among asthmatics on ICS compared with all other groups throughout an entire 24-hour diurnal period, but this group had the largest variation in levels throughout the day, with a steep reduction in cortisol levels during the early morning hours, a peak time for asthma exacerbations to occur31,32 Prior studies have correlated low cortisol with decreased asthma control35, suggesting that this reduction may pose a further threat during this vulnerable time31,32. The global reduction in cortisol levels was so pronounced that on average, peak cortisol levels among asthmatics on ICS during an entire 24-hour period, were lower than the average minimum cortisol levels among any of the other groups at any time.
To date, multiple studies have investigated the potential adverse side effects of ICS use for asthma; however, the overall utility of these studies to assess adrenal suppression has been hampered by small or modest samples sizes, short trial periods22,25, and a limited range of ICS dose22,36, with few resounding conclusions; a more comprehensive interrogation is therefore recommended27. While acknowledged as a potential harmful side effect, clinical suppression of the HPA-axis from ICS therapy alone has been considered unusual with minimal long-term systemic ramifications on adrenal function22,23 that may only be apparent at high doses25,26. In contrast to the existing scientific literature, in our population there was a consistent, pronounced, and clinically relevant reduction (as defined by a pronounced in increase in adrenal suppression diagnoses) in adrenal function over a range of ICS use and dose. The utilization of 25 years of EMRs from individuals diagnosed with asthma and ICS use, cortisol measurements from a 4-year ICS trial, and extensive clinical-grade cortisol testing from over 2,000 individuals enables a robust evaluation of the long-term impact of ICS use on adrenal function and suggests increased rates of adrenal and sub-adrenal suppression among asthmatics as a result of ICS use.
The majority of moderate to severe asthmatics use ICS as the first line of treatment to improve control of persistent asthma. It remains an integral part of their long-term treatment protocol37,38 and one of the most effective and efficacious treatments to date. In the short term, these benefits likely outweigh the long-term side effects. However, patient treatment is optimized with proactive monitoring of circulating steroid levels to prevent permanent adrenal suppression. We observed that 31 percent of asthma cases with ICS use tested met the clinical criteria for an adrenal suppression diagnosis. While this is likely an overestimate due to potential selection bias in ordering tests for adrenal suppression when clinically suspected, if these were the only diagnosable cases out of all the entire RPDR, including the other 74.3 percent of asthmatics using ICS who were not tested, this would still suggest that eight percent of all asthmatics using ICS have cortisol levels low enough to classify as adrenal insufficiency diagnosis.
The degree of pronounced steroid suppression upon extended ICS use among asthma cases suggests that proactive monitoring of cortisol levels has the potential to identify and prevent adrenal suppression through altered treatment approaches. This becomes even more imperative, as cases of adrenal suppression are often problematic to diagnose, symptoms can be missed due to the range of presentation of the disease, and the broad range of negative side effects can even result in life-threatening complications that are critical to avoid27,38–42. The institution of regular cortisol testing enables the identification of marked decreases in steroid levels prior to significant and potentially permanent long-term complications from clinical-grade adrenal suppression. Moreover, yearly monitoring is inexpensive (adrenocorticotropic hormone test (ACTH) simulation test)43 and manageable in most primary care settings and may decrease the overall public health burden of this ICS adverse effect. Individual optimization of treatment protocols does not necessarily imply omitting ICS use in all cases, but potentially changing the dosage, the frequency, or supplementation with additional medications may result in more efficacious outcomes in some individuals, while preventing adverse adrenal suppression ramifications in others.
While other omic data types are touted for their potential use in precision medicine, this study demonstrates the expediency to clinical translation that metabolomic profiling offers. Because a large number of clinical tests currently in use are measured metabolites, there are often cases where the metabolites of interest from untargeted analyses are already measured in clinical practice. This was the case in the present study, in which the observed reduction of multiple steroid metabolites led to the exploration of the use of cortisol testing to assess adrenal suppression in asthmatics on ICS. This approach enables investigators to more efficiently translate metabolomic findings into clinical practice than for other omic data types that would require substantial follow-up time and resources.
Despite the strengths of the reported findings, several limitations should be noted. First, our discovery cohort (EPIC-Norfolk) did not have information on ICS use. In MGBB, we created a robust algorithm to identify ICS use. We acknowledge that there is likely misclassification; however, this misclassification would result in a bias towards the null hypothesis and the effects we identified would remain highly significant. Therefore, we do not believe that this impacted the overall conclusions of the study. Moreover, we verified our findings in an RCT, which represents a more robust study design. Second, the CAMP RCT utilized children and while at the end of the trial, they were mostly adolescents; this differs from the other cohorts that utilized primarily adults. It is important to note that there may be important differences between ICS response in adults and adolescents that should be studied in more detail. Third, metabolomic profiling was performed in a different laboratory for CAMP and did not have the broader range of steroid metabolites. Despite these differences, we were able to validate and further refine our findings over the four populations we utilized. Finally, while it is important to realize the potential of large EMR databases, it is equally important to recognize that this information is derived from an overrepresentation of individuals with illness and may bias the data or result in confounding by indication. Acknowledging this limitation, we excluded individuals with common relevant comorbid conditions, such as COPD.
In conclusion, our results suggest regular monitoring of steroid levels among asthma cases with long-term ICS use, which is not currently commonplace, is merited to identify the optimal clinical regimen for individuals with asthma at risk of serious adrenal suppression and determine the clinical impact of low cortisol levels in this population. This could potentially improve overall health and reduce health care spending. Integrating metabolomics data from epidemiological studies with existing clinical biomarkers obtained via EMRs may enhance the interpretation of metabolomic data as it relates to health and current medical practices, in addition to enhancing comprehension both on the side of researchers and of clinicians.