Letter to the Editor From Prickett and Espiner: “Dynamic Response of Musclin, a Myokine, to Aerobic Exercise and Its Interplay With Natriuretic Peptides and Receptor C”

In a recent study (1) the authors report on the response of musclin (also known as osteocrin) to moderate intensity exercise in 21 sedentary male participants. Concentrations of musclin were measured in unextracted serum using an enzyme-linked immunosorbent assay (ELISA) commercial kit. Prior to exercise mean musclin concentrations were 3.88 ng/mL, increasing to peak levels of 6.1 ng/mL after exercise. Using a fully validated and well-characterized musclin (osteocrin) assay, we find concentrations in the low picomolar range (0.02-0.04 ng/mL) in normal resting healthy individuals (2). According to the manufacturer, the ELISA kit used by Nam et al (1) has a detection level ranging from 0.312 to 20 ng/mL, and sensitivity of 0.078 ng/mL—far exceeding concentrations actually observed using fully characterized and sensitive assays in plasma drawn from normal resting humans and sheep (2), or from rats (3). The extremely high concentrations reported by Nam et al (>2 orders of magnitude) are likely to be due to matrix interference—or possibly interactions with one or more of the hundreds of other analytes known to be stimulated and circulate in plasma during intense exercise (4).

It is incumbent on authors—when reporting concentrations of novel peptides in tissue or blood—to authenticate assays used in their research. This is particularly important in the context of putative circulating hormones whose role in humans is unknown.

Funding

None.

Disclosures

There is no potential conflict of interest; the authors have nothing to disclose.

References