MedicalResearch.com Interview with:
Jing Liu, Ph.D.
College of Environmental & Resource Sciences
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: In addition to consistent observations of earlier pubertal onset in female since late 19th century, acceleration in male pubertal development also has been reported in more recent studies. Improved nutrition, health and living conditions may contribute to the secular trend towards an earlier pubertal onset. However, the potential role of environmental agents, specifically endocrine-disrupting chemicals (EDCs), also has been emphasized.
Pyrethroids are among the currently used pesticide classes placed on the list of the US Environmental Protection Agency (EPA) as potential EDCs. Pyrethroids are one of the top 10 classes of pesticides and account for greater than 30% of global insecticide usage. Increased human exposure to pyrethroids is thought to occur mainly via residues in diets and indoor residential use. The metabolites of pyrethroids have been widely identified in urine samples of adults, children and adolescents worldwide and the detection rate is usually more than 60% in human populations.
Here, we recognize pyrethroids as a new environmental contributor to the observed secular trend toward earlier male sexual maturity. For the first time to our knowledge, this work reveal a significant and positive association between pyrethroids exposure and gonadotropins levels in 463 Chinese boys, in which a 10% increase in 3-PBA (a common urinary metabolite of pyrethroids) is associated with more than 2% increase in both LH and FSH. Boys with increased urinary levels of 3-PBA have a significantly increased risk of earlier pubertal development, in which the odds of being in an advanced testicular volume and genitalia stage are increase by 113% and 268%, respectively.
Because it is difficult to test the direct causality of environmental risk factors in humans, we further sought to identify in animals how pyrethroids alter the timing of puberty. Postnatal exposure to a widely used pyrethroid pesticide, cypermethrin, can accelerate pubertal timing and induce circulating levels of gonadotropins and testosterone in male mice. Our findings reveal the activation of voltage-gated calcium channels pathway in pituitary gonadotropes and testicular Leydig cells as a newly discovered mechanism of pyrethroid-induced early pubertal development in the male.