Elevated Neuroimmune Biomarkers in Sweat Patches and Plasma of Premenopausal Women with Major Depressive Disorder in Remission: The POWER Study

Abstract

Background-Major depressive disorder (MDD) is inconsistently associated with elevations in pro-inflammatory cytokines and neuropeptides. We used a skin sweat patch, recently validated in healthy controls, and recycling immunoaffinity chromatography (RIC), to measure neuroimmune biomarkers in patients with MDD mostly in remission.

The detection and measurement of interleukin-6 in venous and capillary blood samples, and in sweat collected at rest and during exercise

“…In addition, we have shown that IL-6 does not appear in sweat in concentrations similar to, or even above that of plasma, counter to previous reports (Cizza et al 2008;Marques-Deak et al 2006). Therefore, in agreement with previous proteomic analysis of sweat (Raiszadeh et al 2012), it is unlikely that sweat acts as a plasma transudate, at least in the case of IL-6.…”

“…The assay was sensitive enough to detect IL-6 in human sweat and plasma at concentrations greater than 0.31 pg.ml -1 , which is well below the normal physiological plasma range of this cytokine. Therefore, it is somewhat surprising that we were unable to replicate the findings of others that IL-6 is present in sweat at concentrations above that of blood plasma (Cizza et al 2008;Marques-Deak et al 2006).This is especially so given that female participants were used for this part of the study, in order to directly replicate the subject group of the previous work and that plasma IL-6 was detected at all time points within the expected physiological range.…”

“…In view of previous reports showing that IL-6 was present in sweat at concentrations comparable to that of plasma (Cizza et al 2008;Marques-Deak et al 2006) a secondary proof of concept study was conducted. Only trace amounts of IL-6 were detected in any of the sweat samples.…”

“…Attempts have been made to detect cytokines in a variety of other body fluids using non-invasive methods including saliva (Cox et al 2008;Minetto et al 2005;Minetto et al 2007) and sweat (Cizza et al 2008;Marques-Deak et al 2006) with varying degrees of success. Saliva has been shown to be a poor medium for cytokine measurement, as there is no correlation between IL-6 concentrations in blood versus saliva either at rest (Cox et al 2008) or following strenuous exercise (Minetto et al 2005).…”

“…However, sweat may present a more promising conduit for non-invasive measurement of systemic IL-6. Marques-Deak et al, collected sweat from females over a 24 hour period and reported that IL-6 was present in measurable concentrations, above those of plasma IL-6 (Cizza et al 2008;Marques-Deak et al 2006). Importantly, the IL-6 concentrations detected in sweat and from venous plasma were correlated and the concentrations appeared comparable (Marques-Deak et al 2006), suggesting that sweat may be a potential vehicle for biomarker measurement.…”