Short-term testosterone use in female mice does not impair fertilizability of eggs: implications for the fertility care of transgender males.

STUDY QUESTION: Does testosterone use in females affect reproductive potential, particularly with regard to the production of fertilizable gametes? SUMMARY ANSWER: Testosterone (T) injections given to post-pubertal female mice caused virilization and although the ovaries were smaller than controls they were still responsive and produced fertilizable eggs when superovulated. WHAT IS KNOWN ALREADY: Studies to examine the effects of testosterone on reproductive potential in transgender males are lacking. Recently, a model was developed that simulates many aspects of testosterone use in transgender males in order to look at reproductive effects of testosterone in female mice. This study found masculinizing effects on the mice but did not find significant deficits on the number of ovarian follicles; however, effects of testosterone use on ovarian stimulation and fertilizability of oocytes were not investigated. STUDY DESIGN, SIZE, DURATION: A total of 66, 6-week-old Hsd:NSA (CF-1) female mice and six Hsd:ICR (CD-1) male mice were used for this study. Mice were injected s.c. with 400 µg T or sesame oil once a week for 6 weeks and were either killed 1 week after the sixth injection (active exposure group), or 6-7 weeks after the final T injection (washout group). PARTICIPANTS/MATERIALS, SETTING, METHODS: Both active exposure and washout groups were further subdivided into three groups: unstimulated, equine CG (eCG)-stimulated or eCG/hCG-stimulated. eCG-stimulated mice were killed 44-48 h after eCG injection. eCG/hCG-stimulated mice were injected with eCG, followed 48 h later with hCG. Mice were killed ∼13-18 h after the hCG injection. Data collected included daily vaginal cytology, terminal testosterone levels, ovary weights and histology, number of oocytes/eggs collected in each group, and cleavage to the two-cell stage following IVF. MAIN RESULTS AND THE ROLE OF CHANCE: Testosterone-treated mice had testosterone levels elevated to the level of male mice and ceased cycling. Ovaries were significantly smaller in testosterone-treated mice, but they contained normal cohorts of follicles and responded to gonadotrophin stimulation by ovulating similar numbers of eggs as controls, that fertilized and cleaved in vitro. LIMITATIONS, REASONS FOR CAUTION: Mice were treated for only 6 weeks, whereas many transgender men use testosterone for many years before considering biological children, and developmental competence was not assessed. Importantly, a mouse system may not perfectly simulate human reproductive physiology. WIDER IMPLICATIONS OF THE FINDINGS: The current standard of care for transgender men who desire biological children is to cease testosterone therapy prior to ovarian stimulation, but the necessity for stopping testosterone is not known. Our model demonstrates that it is possible for testosterone-suppressed ovaries to respond to gonadotrophic stimulation by producing and ovulating fertilizable eggs, thereby obviating the need for testosterone cessation prior to ovarian stimulation. In time, these results may provide insights for future clinical trials of fertility treatment options for transgender men. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the Reproductive Endocrinology and Infertility fellowship program through UConn Health Graduate Medical Education (to C.B.B.). The authors have no competing interests. TRIAL REGISTRATION NUMBER: N/A.

Changes in secondary glutamate release underlie the developmental regulation of excitotoxic neuronal cell death.

Vulnerability to excitotoxicity increases during development in vivo and in vitro. To determine whether the mere presence of mature N-methyl-D-aspartate (NMDA) receptors coincides with the emergence of excitotoxicity or whether post-receptor signaling processes may also contribute, we examined the temporal relationship of NMDA receptor expression, function and toxicity using cortical cell cultures. Surface expression of all NMDA receptor subunits increased with time in culture. This correlated with NMDA receptor function, assessed both biochemically and electrophysiologically, but not with the appearance of excitotoxicity. Specifically, cells at day in vitro (DIV) 10 were less susceptible to NMDA receptor-induced neurotoxicity than those cultured for 14 days, even though receptor expression/function was identical. In addition, cell-attached single channel recordings revealed that NMDA receptor conductance, open probability, and frequency of channel openings were not significantly different between the two days. Intriguingly, depolarization-induced release of glutamate from cultures grown for 10 days was significantly lower than that released from cultures grown for 14 days. Further, exogenous addition of glutamate receptor agonists immediately after removal of NMDA rendered cultures at DIV 10 susceptible to excitotoxicity, while toxicity was significantly reduced by addition of an NMDA receptor antagonist immediately after exposure to NMDA at DIV 14. These data are the first to demonstrate that the subsequent, secondary release of glutamate plays an equal, if not more important, role than NMDA receptor development per se, in mediating the enhanced vulnerability of neurons to excitotoxicity that occurs with age.

SIN-1-induced cytotoxicity in mixed cortical cell culture: peroxynitrite-dependent and -independent induction of excitotoxic cell death.

3-Morpholinosyndnomine (SIN-1) has been reported to be a peroxynitrite (OONO(-)) donor because it produces both nitric oxide (NO) and superoxide (O(2)(-).) upon decomposition in aqueous solution. However, SIN-1 can decompose to primarily NO in the presence of electron acceptors, including those found in biological tissues, making it necessary to determine the release product(s) formed in any given biological system. In a mixed cortical cell culture system, SIN-1 caused a concentration-dependent increase in cortical cell injury with a parallel increase in the release of cellular proteins containing 3-nitrotyrosine into the culture medium. The increase in 3-nitrotyrosine immunoreactivity, a footprint of OONO(-) production, was specific for SIN-1 as exposure to neurotoxic concentrations of an NO donor (Z)-1-[2-aminoethyl)-N-(2-ammonioethyl) aminodiazen-1-ium-1,2-diolate (DETA/NO), or NMDA did not result in the nitration of protein tyrosine residues. Both SIN-1-induced injury and 3-nitrotyrosine staining were prevented by the addition of either 5,10,15,20-Tetrakis (4-sulfonatophenyl) prophyrinato iron (III) [FeTPPS], an OONO(-) decomposition catalyst, or uric acid, an OONO(-) scavenger. Removal of NO alone was sufficient to inhibit the formation of OONO(-) from SIN-1 as well as its cytotoxicity. Removal of O(2)(-). and the subsequently formed H(2)O(2) by superoxide dismutase (SOD) plus catalase likewise prevented the nitration of protein-bound tyrosine but actually enhanced the cytotoxicity of SIN-1, indicating that cortical cells can cope with the oxidative but not the nitrosative stress generated. Finally, neural injury induced by SIN-1 in unadulterated cortical cells was prevented by antagonism of AMPA/kainate receptors, while blockade of the NMDA receptor was without effect. In contrast, activation of both NMDA and non-NMDA receptors contributed to the SIN-1-mediated neurotoxicity when cultures were exposed in the presence of SOD plus catalase. Thus, whether SIN-1 initiates neural cell death in an OONO(-)-dependent or -independent manner is determined by the antioxidant status of the cells. Further, the mode of excitotoxicity by which injury progresses is determined by the NO-related species generated.

Differential modulation of prostaglandin H synthase-2 by nitric oxide-related species in intact cells.

Nitrogen monoxide (NO) has been reported to both activate and inhibit prostaglandin (PG) biosynthesis. This apparent paradox might be explained by the production/action of distinct NO-related species formed as a result of the prevailing redox states of different cellular systems. As such, the effect of NO donors with different redox characteristics on the modulation of prostaglandin H synthase-2 (PGHS-2) in primary mouse cortical astrocytes and COS-7 cells engineered to overexpress PGHS-2 was assessed. In general, compounds that released NO(*) or NO(-) enhanced, while a peroxynitrite (OONO(-)) generator inhibited, PGHS-2-dependent prostaglandin production. While the possibility of altered gene transcription was eliminated in the COS-7 system as PGHS-2 was maximally expressed, in primary astrocytes where PGHS-2 expression was induced by lipopolysaccharide (LPS), effects on protein expression were detected. Compounds that released NO(*) synergistically enhanced LPS-mediated PGHS-2 protein synthesis. None of these effects were mediated by cGMP. All donors lost their ability to modulate PGHS-2 expression and function when decayed. These results indicate that the ultimate effect of NO on PGHS-2 enzyme activity and expression is dictated by the prevalent NO-related species formed, suggesting that important interactions which may exist between NO and prostanoid pathways in vivo will be highly dependent on the inherent redox environment.

A microtiter trypan blue absorbance assay for the quantitative determination of excitotoxic neuronal injury in cell culture.

An automated method for the determination of neuronal cell death using trypan blue is described. Following various excitotoxic insults, murine mixed cortical cell cultures are stained with trypan blue (0.05%; 15 min), followed by SDS (1%) lysis. The absorbance of the dye is measured spectrophotometrically at 590 nm using a microtiter plate reader. When compared to the biochemical lactate dehydrogenase assay, no statistical difference in the calculated levels of excitotoxic neuronal cell death was noted between the assays in any given paradigm. This method is fast and reliable. It eliminates the need for cell counting, thus allowing for high volume sample analysis with a minimum of sample error. Utility of this trypan blue absorbance spectrophotometric assay is likely to extend beyond the study of excitotoxic neuronal injury and should complement existing methods for measuring neuronal viability and cytotoxicity in cell culture.

Cyclooxygenase-2 contributes to N-methyl-D-aspartate-mediated neuronal cell death in primary cortical cell culture.

Cyclooxygenase isozymes (COX-1 and COX-2) are found to be constitutively expressed in brain, with neuronal expression of COX-2 being rapidly induced after numerous insults, including cerebral ischemia. Because overactivation of N-methyl-D-aspartate (NMDA) receptors has been implicated in the cell loss associated with ischemia, we characterized the expression of the COX isozymes in murine mixed cortical cell cultures and used isozyme-selective inhibitors to determine their relative contribution to NMDA receptor-stimulated prostaglandin (PG) production and excitotoxic neuronal cell death. Immunocytochemical analysis of mixed cortical cell cultures revealed that COX-2 expression was restricted to neurons, whereas COX-1 was expressed in both neurons and astrocytes. Brief exposure to NMDA (5 min; 100 microM) elicited a time-dependent accumulation of PGs in the culture medium that preceded neuronal cell death and correlated with the induction of COX-2 mRNA. COX-1 expression remained unchanged. Flurbiprofen, a nonselective COX-1/COX-2 inhibitor, blocked NMDA-stimulated PG production and attenuated neuronal death in a concentration-dependent manner. Similar results were obtained with the specific COX-2 inhibitor NS-398 (10-30 microM) but not with the selective COX-1 inhibitor valeryl salicylate (10-300 microM). Inhibition of total constitutive COX activity with aspirin (100 microM, 1.5 h) before NMDA exposure did not prevent subsequent NMDA-mediated neuronal cell death. However, neuronal injury in aspirin-pretreated cultures was attenuated by flurbiprofen administration after NMDA exposure. Finally, the protection afforded by COX-2 inhibition was specific for NMDA because neither flurbiprofen nor NS-398 protected neurons against kainate-mediated neurotoxicity. Together, these results support the conclusion that newly synthesized COX-2 protein contributes to NMDA-induced neuronal injury.