Prolonged use of letrozole causes morphological changes on gonads in Galea spixii

Abstract

Letrozole is used as a therapeutic agent in reproductive disorders caused by high estrogen levels. Letrozole inhibits cytochrome P450 aromatase and reduces estrogen levels. However, the effects of long-term use on reproductive traits are unknown. The aim of this study was to evaluate the prolonged use of letrozole in the gonads of rodents (Spix's yellow-toothed cavy; Galea spixii). Forty-eight rodents (24 males and 24 females) were randomly divided into the treated and control groups. Letrozole administration started at 15 days of age and continued weekly until 30, 45, 90, and 120 days of age. The body, testis, and ovary weights were analyzed, as well as the morphological progression of spermatogenesis and folliculogenesis. Macroscopically, body weight gain and gonads weight were increased in the letrozole group. Microscopically, the ovaries of treated females showed stratified epithelium and a cellular disorder of the tunica albuginea. In the testes of treated males, the development of seminiferous tubules was delayed and sperm was absent. The collective findings indicate that the prolonged use of letrozole alters secondary sexual characteristics, and causes weight gain, reproductive changes, and male infertility.

Keywords: aromatase; estrogens; ovary; rodents; steroidogenesis; testis.

Figure 1. Simplified steroid chain diagram. The highlighted portion is cytochrome P450 aromatase, the enzyme responsible for estrogen biosynthesis from androgens.

Figure 2. Letrozole effect on average body weight gain of female (A) and male (B) Spix's yellow-toothed cavy during sexual development in the letrozole and control groups. */# p<0.05 30 days vs. 45, 90 and 120 days; ♦ p<0.05 letrozole vs. control.

Figure 3. Effect of letrozole effect on mean testis and ovary weight gain during sexual development in the letrozole and control groups.

Figure 4. Effect of letrozole effect on the morphological development of the ovary of Spix's yellow-toothed cavy in the letrozole group (B-30 days, C-45 days, E-90 days, F-120 days) and the control group (A-30 days, D-90 days) groups. The arrow denotes the stratification of the epithelium. (*): Cellular disorder; (CL): corpus luteum; (C): cortical zone; (M): medullar zone; (F): follicles; (a): atresic follicle. A/C – The scale bar in panels A to C denote 100 μm (10× magnification). The scale bars in panels B, C, E, and F denote 20 μm (40× magnification).

Figure 5. Effect of letrozole effect on the morphological development of the testis of Spix’s yellow-toothed cavy in the control (A-D) and letrozole (E-H) groups. The findings are evidence of spermatogenic regression. (c) testicular cords, (i) internal cord with interstitial cells, (st) seminiferous tubules with spermatogonia, (sc) Sertoli cells, (p) primary spermatocytes, (s) spermatids, (*) spermatozoa, and (LG) Leydig cells. Scale bars denote 20 μm (magnification 40×).