Levels of insulinlike factor 3 (INSL3) drop noticeably in men who have abused anabolic androgenic steroids (AAS), even well after stoppage. The results suggest that the effects of AAS use on testosterone-producing Leydig cells may be long-lasting, as some clinicians have suspected. Although there is some variation of INSL3 levels among AAS users, the metric is more accurate than testosterone levels and could be a key element of future diagnostic tests.
Dr. Jon Rasmussen
Those are the conclusions of a new study, led by Jon Jarløv Rasmussen, MD, PhD, of the department of endocrinology at Rigshospitalet in Copenhagen*, published March 9, 2021, in the Journal of Clinical Endocrinology & Metabolism.
Results mirror clinical experience
The drop in levels, both among current and past users, is in keeping with clinical experience of endocrinologists, according to Channa Jayasena, MD, PhD, a reproductive endocrinologist at Imperial College London. He suspects lasting damage in former and current users who come to him when they discover their sperm count is low. "How long that damage lasts is another matter," Dr. Jayasena, who was not involved in the study, said in an interview.
Dr. Channa Jayasena
Dr. Jayasena hopes that INSL3 could find use in tracking damage to Leydig cells from AAS use, as well as to monitor improvements in the event that treatments are found, though he noted that the scatter plots in the study showed quite a bit of variation of INSL3 levels. "So it's a great first step showing that these men, users and past users, have lower INSL3 levels, but it's going to have to be part of a broader suite of factors such as the other hormone [levels], testicular volume, duration of steroid use, etc.," said Dr. Jayasena.
In search of a reliable measure
Low testosterone levels have been shown to be associated with AAS use in some studies, but not in others. That inconsistency led the researchers in search of a more reliable measure. "Serum testosterone is not a stable marker but can fluctuate considerably within minutes to hours, whereas serum insulinlike factor 3 [levels] do not," said Dr. Rasmussen.
INSL3 appears to be involved in bone metabolism regulation as well as spermatogenesis.
Dr. Rasmussen agreed that INSL3 levels could be clinically useful for tracking Leydig cell function, especially in combination with other hormone markers like serum testosterone and gonadotropins. The group is now considering a clinical trial for treatment of hypogonadal men following illicit use of anabolic steroids, which will include INSL3 serum levels as a planned endpoint.
The researchers conducted a cross-sectional study of men aged 18-50 years who had participated in recreational strength training. Cohort 1 included 37 AAS users, 33 former users, and 30 never users. Cohort 2 included 9 current users, 9 former users, and 14 never users. They assigned participant AAS use status based on self-reporting, along with measurement of biomedical parameters including gonadotropins, sexual hormone-binding globulin (SHBG), and hematocrit.
Compared with never users' median value of 0.59 mcg/L, INSL3 serum levels were lower among current AAS (median, 0.04 mcg/L; P < .001) and former AAS (0.39 mcg/L; P = .005) users. A linear multivariate regression that adjusted for luteinizing hormone, SHBG, age, body-fat percentage, smoking status, use of other illicit drugs found lower levels among former users, compared with never users (mean difference, -0.16 mcg/L; P = .011).
An analysis of elapsed duration since AAS cessation found longer duration of AAS use was associated with reduced INSL3 levels (mean difference, -0.08; P = .022).
Although serum inhibin B levels reached the levels of never users after about 21 months, and luteinizing hormone levels recovered in about 12 months, neither serum testosterone nor INSL3 levels recovered in former users.
The study authors received funding from Anti Doping Denmark. Dr. Jayasena has no relevant financial disclosures.
*Dr. Rasmussen's affiliation has been corrected.