Oral possibile role of carbonyl stress in ovarian aging

Introduction: Female reproductive aging has been so far deeply characterized in terms of ovarian functional decline associated with gradual depletion of ovarian follicles and reduced oocyte developmental potential [1,2]. However little is known about molecular mechanism underlying age-related cellular modifications. Similarly to somatic aging, the most relevant theory for ovarian aging implies a reduced ability of ovarian follicles to counteract reactive oxygen species (ROS), which are among the most important physiological inducers of cellular injury [3,4]. Also, molecular damage during somatic aging has been ascribed to increased levels of reactive dicarbonyl compounds, which, similarly to ROS, result from normal metabolism but can be responsible for i75 Abstracts of the 23rd Annual Meeting of the ESHRE, Lyon, France, 1–4 July 2007 Downloaded from http://humrep.oxfordjournals.org/ by guest on July 14, 2012 macromolecular damage [5]. In the present study we investigated the hypothesis that aging-associated changes in the ovarian follicles may involve a condition of “carbonyl stess” due to impaired degradation of cytotoxic dicarbonyl compounds such as methylglyoxal (MG), one of the most powerful glycating agents of cellular components [6]. To this end, first we monitored in the mouse model MG cytotoxic effects on the oocyte and characterized in the ovary the system mainly involved in MG degradation, the glyoxalase system, which consists of two enzymes, glyoxalase I (GLOI) and glyoxalase II (GLOII). Second, we evaluated possible changes in this system in relation to reproductive aging. Materials and methods: The study was conducted on CD1 young (4–8 wk old) and old (48–52 wk old) female mice. MG toxicity was evaluated by monitoring oocyte chromosome configuration by Hoechst33342 staining and DNA fragmentation by TUNEL assay following exposure to different MG concentrations (50-300 micromolar) during in vitro maturation. Enzymatic activity of GLOI and GLOII enzymes was measured spectrophotometrically in whole ovaries. Expression of GLOI and GLOII mRNA was analyzed by means of semi-quantitative RT-PCR in (1) whole ovaries, denuded oocytes from (2) early antral (DO) or (3) preovulatory follicles (CEO) and (4) oocytes at MII stage. Results: Exposure of young oocytes MG was responsible for a dose-dependent delay in the kinetic of meiosis resumption, aberrant MII configuration and apoptosis. Specific activity of GLOI measured in whole ovaries from young mice was similar to that present in proliferating tissues, whereas that of GLOII was not detectable. The analysis of gene expression pattern revealed that: 1) GLOII mRNAs were expressed in the ovaries although at levels lower that those of GLOI; 2) in MII oocytes the levels of transcripts for both the enzymes severely reduced when compared with DO and CEO. From the comparison of this pattern of expression with that of old mice we observed that the activity of GLOI and the level of the corresponding mRNA were significantly lowered in old ovaries. Although age-related changes in GLOI and GLOII gene expression were not detectable, old oocytes compared with young oocytes were more sensitive to methylglyoxal, being their maturation severely compromised by the exposure to this compound. Conclusions: Presents results provide evidence that ovarian aging may be associated with the impairment of detoxifying processes of reactive dycarbonyl compounds toxic for the mammalian oocyte suggesting that this condition may jeopardize the development of competent gametes during reproductive aging