Anti-apoptotic properties of carbon monoxide in porcine oocyte during in vitro aging

Carbon Monoxide Exposure Does Not Improve The In Vitro Fertilization Rate of Oocytes Obtained from Heterozygous Hmox1 Knockout Mice

In our experimental study we explored the impact of maternal reduced heme oxygenase-1 (HO-1) gene (Hmox1) expression on the in vitro fertilization (IVF) rate through the use of heterozygous Hmox1 knockout mice models (HET/Hmox1+/ -). Also, we hypothesized a beneficial role of gametes exposure during fertilization to carbon monoxide (CO), one of HO-1 by-products, that might be relevant for the improvement of IVF rates. IVF technique was performed by using oocytes obtained from wild-type (WT) or Hmox1+/ - dams fertilized with WT, Hmox1+/ - or Hmox1-/ - mice-derived sperm. The fertilization step occurred either in a conventional incubator (37°C, 5% CO2) or in an incubator implemented with CO (500 ppm). The superovulation yield of WT and Hmox1+/ - mice and the number of fertilized oocytes was assessed using an optical microscope. The dams' Hmox1 heterozygous knockout neither impact the superovulation yield, nor did influence the fertilization success rate. Moreover, CO exposure during fertilization could not significantly improve the outcome. Our study showed that the maternal Hmox1+/ -condition is not affecting the IVF rate in mice. Furthermore, we discovered that CO exposure cannot be exploited to ameliorate this critical step of the IVF protocol.

Prolonged hypothermic storage of oocytes of the European common frog Rana temporaria in a gas mixture of oxygen and carbon monoxide

The maximum hypothermic storage time of amphibian oocytes is several hours, which is due to the peculiarities of the structure of the cell envelope. The authors of this paper have already demonstrated the possibility of increasing the storage period of unfertilized oocytes of the common frog (Rana temporaria) up to 5-7 days. The aim of the current study was to determine the possibility of using a 6.5 atm gaseous mixture of carbon monoxide and oxygen, for prolonged hypothermic preservation of unfertilized oocytes for 4 to 12 days. After four days, oocytes stored under CO+O2 conditions exhibited fertilization and hatching rates that were 1.6 and 2.2-fold higher than control, respectively. While no oocytes in the control group survived to day twelve, oocytes held under CO +O2 gas exhibited a 39±14% (38 out of 99 oocytes in total) fertilization rate, however only 1±2% (1/99) of those hatched. This approach is promising for the storage of genetic material from female amphibians, particularly in respect to managing and restoring endangered species, but may also be applicable to oocytes of other classes of vertebrates.

Comparison of three antioxidants in chemical and biological assays on porcine oocytes during ageing in vitro

Our previous studies have already revealed that β-cryptoxanthin (BCX), hesperetin (HES), and icariin (ICA) antioxidants are effective for in vitro maturation (IVM) of porcine oocytes. In this study, we investigated which of BCX, HES, or ICA was more effective for IVM of porcine oocytes. The antioxidant properties were assessed with aged porcine oocytes and embryos by comparing 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH), reducing power, and H2O2 scavenging activity assays. The chemical assay results demonstrated that BCX had a greater DPPH scavenging activity and reducing power than HES and ICA, compared with controls. However, the H2O2 scavenging activity of the antioxidants was similar when tested at the optimal concentrations of 1 μM BCX (BCX-1), 100 μM HES (HES-100), and 5 μM ICA (ICA-5). The biological assay results showed that BCX-1 treatment was more effective in inducing a significant reduction in reactive oxygen species (ROS), improving glutathione levels, and increasing the expression of antioxidant genes. In addition, BCX-1 inhibited apoptosis by increasing the expression of anti-apoptotic genes and decreasing pro-apoptotic genes in porcine parthenogenetic blastocysts. BCX-1 also significantly increased the blastocyst formation rate compared with the ageing control group, HES-100 and ICA-5. This study demonstrates that damage from ROS produced during oocyte ageing can be prevented by supplementing antioxidants into the IVM medium, and BCX may be a potential candidate to improve assisted reproductive technologies.

"CO in a pill": Towards oral delivery of carbon monoxide for therapeutic applications

Along with the impressive achievements in understanding the endogenous signaling roles and mechanism(s) of action of carbon monoxide (CO), much research has demonstrated the potential of using CO as a therapeutic agent for treating various diseases. Because of CO's toxicity at high concentrations and the observed difference in toxicity profiles of CO depending on the route of administration, this review analyzes and presents the benefits of developing orally active CO donors. Such compounds have the potential for improved safety profiles, enhancing the chance for developing CO-based therapeutics. In this review, the difference between inhalation and oral administration in terms of toxicity, CO delivery efficiency, and the potential mechanism(s) of action is analyzed. The evolution from CO gas inhalation to oral administration is also extensively analyzed by summarizing published studies up to date. The concept of "CO in a pill" can be achieved by oral administration of novel formulations of CO gas or appropriate CO donors.

The effect of carbon monoxide on meiotic maturation of porcine oocytes

Oxidative stress impairs the correct course of meiotic maturation, and it is known that the oocytes are exposed to increased oxidative stress during meiotic maturation in in vitro conditions. Thus, reduction of oxidative stress can lead to improved quality of cultured oocytes. The gasotransmitter carbon monoxide (CO) has a cytoprotective effect in somatic cells. The CO is produced in cells by the enzyme heme oxygenase (HO) and the heme oxygenase/carbon monoxide (HO/CO) pathway has been shown to have an antioxidant effect in somatic cells. It has not yet been investigated whether the CO has an antioxidant effect in oocytes as well. We assessed the level of expression of HO mRNA, using reverse transcription polymerase chain reaction. The HO protein localization was evaluated by the immunocytochemical method. The influence of CO or HO inhibition on meiotic maturation was evaluated in oocytes cultured in a culture medium containing CO donor (CORM-2 or CORM-A1) or HO inhibitor Zn-protoporphyrin IX (Zn-PP IX). Detection of reactive oxygen species (ROS) was performed using the oxidant-sensing probe 2′,7′-dichlorodihydrofluorescein diacetate. We demonstrated the expression of mRNA and proteins of both HO isoforms in porcine oocytes during meiotic maturation. The inhibition of HO enzymes by Zn-PP IX did not affect meiotic maturation. CO delivered by CORM-2 or CORM-A1 donors led to a reduction in the level of ROS in the oocytes during meiotic maturation. However, exogenously delivered CO also inhibited meiotic maturation, especially at higher concentrations. In summary, the CO signaling molecule has antioxidant properties in porcine oocytes and may also be involved in the regulation of meiotic maturation.

Laminarin enhances the quality of aged pig oocytes by reducing oxidative stress

Laminarin (LAM) is a β-glucan oligomer known to possess biological activities such as anticancer and antioxidant effects. This study explored the influence of LAM supplementation on in vitro aged porcine oocytes and the underlying mechanisms behind this influence. We found that LAM delayed the aging process and improved the quality of aged oocytes. LAM supplementation enhanced the subsequent developmental competence of aged oocytes during the in vitro aging process. The blastocyst formation rate was significantly increased in aged oocytes treated with 20 µg/ml LAM compared to non-treated aged oocytes (45.3% vs. 28.7%, P < 0.01). The mRNA levels of apoptosis-related genes, B cell lymphoma-2-associated X protein (Bax) and Caspase-3, were significantly lower in blastocysts derived from the LAM-treated aged oocytes during the in vitro aging process. Furthermore, the level of intracellular reactive oxygen species was significantly decreased and that of glutathione was significantly increased in aged oocytes following LAM treatment. Mitochondrial membrane potential was increased, and the activities of caspase-3 and cathepsin B were significantly reduced in the LAM-treated aged oocytes compared with the non-treated aged oocytes. Taken together, these results suggest that LAM is beneficial for delaying the aging process in porcine oocytes.

Inhibition of cathepsin B activity prevents deterioration in the quality of in vitro aged porcine oocytes

The activity of cathepsin B, a member of the lysosomal protease family, directly correlates with oocyte quality and subsequent embryonic development. However, its biological function during the progression of in vitro aging of oocytes in pigs has not been demonstrated. Here, we showed that cathepsin B activity was dramatically increased during in vitro aged oocytes. The inhibition of cathepsin B activity prevented the decline of the quality of aged oocytes and improved their subsequent developmental competence. Moreover, the inhibition of cathepsin B activity reduced aging-induced mitochondrial dysfunction and attenuated oxidative stress. The inhibition of cathepsin B activity also markedly decreased early apoptosis levels and the frequency of spindle anomalies during in vitro aging of oocytes. These results demonstrate that in vitro aging of oocytes induces cathepsin B activity, which is associated with a decline in oocyte quality. The inhibition of cathepsin B activity has a beneficial effect on oocytes during the process of in vitro aging.