Phthalate-induced Leydig cell hyperplasia is associated with multiple endocrine disturbances

Abstract

The possibility that exposures to environmental agents are associated with reproductive disorders in human populations has generated much public interest recently. Phthalate esters are used most commonly as plasticizers in the food and construction industry, and di-(2-ethylhexyl) phthalate (DEHP) is the most abundant phthalate in the environment. Daily human exposure to DEHP in the U.S. is significant, and occupational and clinical exposures from DEHP-plasticized medical devices, e.g., blood bags, hemodialysis tubing, and nasogastric feeding tubes, increase body burden levels. We investigated the effects of chronic exposures to low environmentally relevant DEHP levels on testicular function. Our data show that prolonged exposures to this agent induced high levels of the gonadotropin luteinizing hormone and increased the serum concentrations of sex hormones [testosterone and 17␤-estradiol (E2)] by >50%. Increased proliferative activity in Leydig cells was evidenced by enhanced expression of cell cycle proteins, as determined by RT-PCR. The numbers of Leydig cells in the testis of DEHP-treated rats were 40 -60% higher than in control rats, indicating induction of Leydig cell hyperplasia. DEHP-induced elevations in serum testosterone and E2 levels suggest the possibility of multiple crosstalks between androgen, estrogen, and steroid hormone receptors, whereas the presence of estrogen receptors in nonreproductive tissues, e.g., cardiovascular system and bones, implies that the increases in serum E2 levels have implications beyond reproduction, including systemic physiology. Analysis of the effects of phthalate exposures on gonadotropin and steroid hormone levels should form part of overall risk assessment in human populations. R eports of a higher incidence of urogenital anomalies of the newborn, such as cryptorchidism, hypospadias, and reproductive abnormalities in wild life exposed to high levels of chemicals in the environment, have generated public concern that these agents may impair human reproductive health (1, 2). Phthalates are used as plasticizers in certain infant toys and consumer products (e.g., containers for soaps, shampoos, and perfumes) and medical devices such as tubings and catheters. The U.S. Department of Health and Human Services in 1985 (3) estimated the total daily human consumption of di-(2-ethylhexyl) phthalate (DEHP) from all sources of exposure at 5.8 mg in the U.S. In a report just published by the Center for Disease Control and Prevention, the urinary levels of mono-(ethylhexyl) phthalate (MEHP) (micrograms per liter), which is the chief metabolite of DEHP, ranged from 3.26 to 4.15 in males and 2.93 to 3.51 in females; these levels are thought to represent only one-tenth of the ingested DEHP dose within the previous 24 h (4). In a recent review of laboratory studies, the U.S. National Toxicology Program's Center for the Evaluation of Risks to Human Reproduction Expert Panel concluded that DEHP has the potential to produce adverse reproductive effects in humans (5). Indeed, several propo...

Involvement of testicular growth factors in fetal Leydig cell aggregation after exposure to phthalate in utero

“…Controversy exists over whether DEHP, at the levels found in the environment, is harmful to humans, because most studies have been conducted in rodents administered high doses. In previous studies, we showed that the administration of low-dose (10 mg/kg body weight) DEHP for 28 days during pubertal development caused elevations in testosterone (T) (8,9). This was in contrast to doses Ͼ750 mg/kg, which significantly reduced serum and testicular T (10).…”

“…Thus, one possibility is that increases in IGF-1 and KITL may explain the significant elevations of T in animals exposed to 10 mg/kg DEHP. It should be pointed out that elevations in T levels in response to low-dose DEHP exposures also were noted in DEHP-treated pubertal rats (9,11,12).…”

“…To enumerate FLC numbers, testicular tissues were sampled according to the Fractionator technique, as described in ref. 9. The total number of FLCs per testis was calculated by multiplying the number of FLCs counted in a known fraction of the testis by the inverse of the sampling probability, and average FLC numbers per testis per treatment group were determined.…”

Evidence suggesting that di‐n‐butyl phthalate has antiandrogenic effects in fish

“…Although several mammalian studies have also reported elevated plasma androgen concentrations following phthalate exposure at lower doses [30,31], the majority of studies report significant decreases in plasma testosterone concentrations at doses of >500 mg/kg/d [32,33]. It is currently unclear why apparently contradictory effects occur.…”

Di‐(2‐ethylhexyl)phthalat (DEHP) [MAK Value Documentation in German language, 2016]

“…Postnataltag für mindestens zehn Wochen gegen DEHP exponiert wurden, waren ab 10 mg/kg KG und Tag die Serumkonzentrationen von Testosteron und 17-beta-Östradiol erhöht. Damit erwies sich DEHP als indirekt östrogen, wobei dies vermutlich auf die verstärkte Aromataseaktivität durch die Induktion von LH in den Leydigzellen zurückzuführen ist (Akingbemi et al 2004). Reduzierte Testosteronkonzentrationen sowie histologische Veränderungen in den Hoden von Ratten korrelierten mit der veränderten Genexpression von sieben Proteinen, die zu einem Netzwerk gehören, das direkt oder indirekt von Östradiol reguliert wird (Klinefelter et al 2012).…”