https://stacks.cdc.gov/view/cdc/37676/cdc_37676_DS1.pdf

Toxicological Profile for Lead

I. Introduction The concept that proteins, in addition to steroid hormones, of gonadal origin could play a role in the inhibition of gonadatropin secretion from the anterior lobe of the pituitary was proposed more than 65 yr ago. Only recently, however, has the elucidation of the chemistry and physiology of these proposed gonadal hormones actually been achieved. Mottram and Cramer (1) reported pituitary hypertrophy as determined by the appearance of so-called castration cells in the anterior lobe of pituitary after treatment of the testes with radium. The removal of the testes leads to the development of highly vacuolated, signet-shaped basophil cells in the pituitary (2), termed castration cells, demonstrating a reciprocal relationship between the pituitary and the gonads and suggesting that a secretion of the testes has an inhibitory effect on the pituitary (3). The pituitary hypertrophy after castration or irradiation of the testes was postulated to be due to a lack of some substance from the seminal e...

Inhibins, Activins, and Follistatins: Gonadal Proteins Modulating the Secretion of Follicle-Stimulating Hormone

In the past decade there has been considerable progress in the characterization of individual human P450 enzymes. These advances were initiated by early work on the purification of individual enzymes from human liver and other sources. The early work in the area was guided by a focus on the most abundant and easily purified enzymes.1–4It is now apparent, in retrospect, that these proteins were in the 2C and 3A families. Efforts were shifted to attempts to purify individual P450s on the basis of catalytic activities with the evidence that in some cases a single P450 could be identified in this way; e.g., the P450 now known as P450 2D6 was found to be under monogenic control. 5 The approach is technically demanding because of the need to do separations in the presence of detergents and then remove them before analysis of catalytic activity. Nevertheless, human P450s 1A1,6 1A2,7 2A6,8 2C8,9 2C9,9,10 2D67,11,12 2E1 13,14 3A4,15 3A5,16 4A11,17 and lanosterol 14α-demethylase18 were isolated in this general manner. Another approach that has been used, sometimes in a mode complementary to catalytic specificity, is purification on the basis of immunochemical similarity to animal P450s. 7,11,19,20

Human Cytochrome P450 Enzymes

Protamines are the major nuclear sperm proteins. The human sperm nucleus contains two types of protamine: protamine 1 (P1) encoded by a single-copy gene and the family of protamine 2 (P2) proteins (P2, P3 and P4), all also encoded by a single gene that is transcribed and translated into a precursor protein. The protamines were discovered more than a century ago, but their function is not yet fully understood. In fact, different hypotheses have been proposed: condensation of the sperm nucleus into a compact hydrodynamic shape, protection of the genetic message delivered by the spermatozoa, involvement in the processes maintaining the integrity and repair of DNA during or after the nucleohistone-nucleoprotamine transition and involvement in the epigenetic imprinting of the spermatozoa. Protamines are also one of the most variable proteins found in nature, with data supporting a positive Darwinian selection. Changes in the expression of P1 and P2 protamines have been found to be associated with infertility in man. Mutations in the protamine genes have also been found in some infertile patients. Transgenic mice defective in the expression of protamines also present several structural defects in the sperm nucleus and have variable degrees of infertility. There is also evidence that altered levels of protamines may result in an increased susceptibility to injury in the spermatozoan DNA causing infertility or poor outcomes in assisted reproduction. The present work reviews the articles published to date on the relationship between protamines and infertility.

/pdf/protamines-and-male-infertility-2zxvclca2k.pdf

Protamines and male infertility.

The biological chemistry of lead.

Publisher Summary This chapter discusses the role of nonsteroidal regulators in control of oocyte and follicular maturation. The ovarian follicle is bathed in a fluid rich in steroid hormones as well as nonsteroidal regulators which interact to serve to control its maturation, responsiveness to gonadotropins, as well as to lead to control of the maturation of its oocyte. The orderly maturation of an ovarian follicle and its oocyte is controlled by pituitary LH and FSH in concert with local intrafollicular regulators. The principal nonsteroidal follicular regulators are an oocyte maturation inhibitor, a luteinization inhibitor, a luteinization stimulator, FSH receptor binding inhibitor, and inhibin-F. OMI is a polypeptide

The role of nonsteroidal regulators in control of oocyte and follicular maturation.

During spermatogenesis, histones are replaced by protamines, which condense and protect sperm DNA. In humans, zinc contributes to sperm chromatin stability and binds to protamine P2 (HP2). Chemical interactions with nuclear protamines, which prevent normal sperm chromatin condensation, may induce changes in the sperm genome and thus affect fertility and offspring development. Since lead has a high affinity for zinc-containing proteins, we investigated lead interactions with HP2 as a novel mechanism of its toxicity to sperm. UV/vis and CD spectroscopy results indicated that HP2 binds Pb(2+) at two different sites, causing a conformational change in the protein. They also provided evidence that thiol groups are primarily involved in Zn(2+) and Pb(2+) binding to HP2 and that HP2 may have additional binding sites for Pb(2+) not related to Zn(2+). HP2 affinities for Pb(2+) and Zn(2+) were very similar, suggesting that Pb(2+) can compete with or replace Zn(2+) in HP2 in vivo. This interaction of lead with HP2 resulted in a dose-dependent decrease in the extent of HP2-DNA binding, although lead interaction with DNA also contributed to this effect. Therefore, the ability of lead to decrease the level of HP2-DNA interaction may result in alterations to sperm chromatin condensation, and thus in reduced fertility.

Lead interaction with human protamine (HP2) as a mechanism of male reproductive toxicity.

The present studies were conducted to define the pathway(s) by which androstenedione is metabolized in porcine granulosa cells (pGC) and determine whether metabolism of this steroid is affected by in vitro luteinization. pGC isolated from large preovulatory follicles were cultured for up to 2 days, in the presence of 5 μm unlabeled or [4-14C]-labeled androstenedione. Metabolism of androstenedione was assessed by HPLC, using in-line liquid scintillation detection. Metabolite identification was confirmed by gas chromatography-mass spectrometry of HPLC fractions isolated from medium conditioned by granulosa cells (pGCCM) cultured for 48 h in the presence of unlabeled androstenedione. The metabolites identified were 19- oic-androstenedione (3,17-dioxo-4-androsten-19-oic acid), 19- hydroxytestosterone, 19-hydroxyandrostenedione, 19-nor-testosterone, an estrenolone of as yet unproven stereoisomerism, 5(10)-estrene-3β,17β-diol, 17β-estradiol, testosterone, and 19-nor-androstenedione. Results indicate that 19-nor...

Androgen metabolism by porcine granulosa cells during the process of luteinization in vitro: identification of 19-oic-androstenedione as a major metabolite and possible precursor for the formation of C18 neutral steroids.

Dennis J. Hoover

Papers

The role of nonsteroidal regulators in control of oocyte and follicular maturation.

Lead interaction with human protamine (HP2) as a mechanism of male reproductive toxicity.

Androgen metabolism by porcine granulosa cells during the process of luteinization in vitro: identification of 19-oic-androstenedione as a major metabolite and possible precursor for the formation of C18 neutral steroids.

Inhibin Secretion by the Primate Ovary