Associations of urinary metal levels with serum hormones, spermatozoa apoptosis and sperm DNA damage in a Chinese population

Abstract

Background: Exposure to metals, including essential and nonessential elements, is widespread and may be associated with male reproductive health.

Objective: To examine whether environmental exposure to metals contributes to reproductive hormone changes, spermatozoa apoptosis and sperm DNA damage in a Chinese population.

Methods: Eighteen metals (aluminum, arsenic, antimony, chromium, cobalt, copper, cadmium, iron, lead, manganese, molybdenum, nickel, selenium, tin, tungsten, thallium, uranium and zinc) were analyzed in two urine samples collected a few hours apart from male partners of couples attending an infertility clinic. Multivariable linear regression models were used to assess the cross-sectional associations of average urinary metal levels with serum hormones (n=511), spermatozoa apoptosis measures (n=460) and sperm DNA damage parameters (n=516).

Results: We found significant inverse dose-dependent trends of urinary tin quartiles with total testosterone (T), and tin, nickel, zinc and molybdenum with the ratio of total T to luteinizing hormone (total T/LH ratio) (all Ptrend<0.05). Additionally, we found significantly dose-dependent trends of increasing urinary manganese quartiles with increasing percentage of Annexin V+/PI- spermatozoa and increasing iron with decreasing percentage of PI+ spermatozoa (both Ptrend<0.05). These dose-dependent trends remained suggestive or significant after controlling for multiple testing and other metals, and they persisted when the metals were modeled as continuous variables in a cubic spline analysis. There were no significant associations between urinary metals and sperm DNA damage after adjustment for multiple testing.

Conclusion: Environmental exposure to tin, nickel, zinc and molybdenum may be associated decreased total T or total T/LH ratio; manganese may induce spermatozoa apoptosis, while iron may be important for living spermatozoa. However, additional prospective research is needed to corroborate these findings in the general population.

Keywords: Apoptosis; DNA damage; Epidemiology; Metals; Reproductive hormone; Spermatozoa.