Suprazero cooling conditions significantly influence subzero permeability parameters of mammalian ovarian tissue

Freezing of Solute-Laden Aqueous Solutions: Kinetics of Crystallization and Heat- and Mass-Transfer-Limited Model

Following an earlier study, we reexamined the latent heat of fusion during freezing at 5 K/min of twelve different pre-nucleated solute-laden aqueous solutions using a Differential Scanning Calorimeter (DSC) and correlated it with the amount of initially dissolved solids or solutes in the solution. In general, a decrease in DSC-measured heat release (in comparison to that of pure water, 335 mJ/mg) was observed with an increasing fraction of dissolved solids or solutes, as observed in the earlier study. In addition, the kinetics of ice crystallization was also obtained in three representative biological media by performing additional experiments at 1, 5 and 20 K/min. A model of ice crystallization based on the phase diagram of a water–NaCl binary solution and a modified Avrami-like model of kinetics was then developed and fit to the experimental data. Concurrently, a heat and mass transfer model of the freezing of a salt solution in a small container is also presented to account for the effect of the cooling rate as well as the solute concentration on the measured latent of freezing. This diffusion-based model of heat and mass transfer was non-dimensionalized, solved using a numerical scheme and compared with experimental results. The simulation results show that the heat and mass transfer model can predict (± 10%) the experimental results.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

Fertility preservation through gonadal cryopreservation

Fertility preservation is an area of immense interest in today's society. The most effective and established means of fertility preservation is cryopreservation of gametes (sperm and oocytes) and embryos. Gonadal cryopreservation is yet another means for fertility preservation, especially if the gonadal function is threatened by premature menopause, gonadotoxic cancer treatment, surgical castration, or diseases. It can also aid in the preservation of germplasm of animals that die before attaining sexual maturity. This is especially of significance for valuable, rare, and endangered animals whose population is affected by high neonatal/juvenile mortality because of diseases, poor management practices, or inbreeding depression. Establishing genome resource banks to conserve the genetic status of wild animals will provide a critical interface between ex-situ and in-situ conservation strategies. Cryopreservation of gonads effectively lengthens the genetic lifespan of individuals in a breeding program even after their death and contributes towards germplasm conservation of prized animals. Although the studies on domestic animals are quite promising, there are limitations for developing cryopreservation strategies in wild animals. In this review, we discuss different options for gonadal tissue cryopreservation with respect to humans and to laboratory, domestic, and wild animals. This review also covers recent developments in gonadal tissue cryopreservation and transplantation, providing a systematic view and the advances in the field with the possibility for its application in fertility preservation and for the conservation of germplasm in domestic and wild species.

Dual dependence of cryobiogical properties of Sf21 cell membrane on the temperature and the concentration of the cryoprotectant

The Sf21 cell line is extensively used for virus research and producing heterologous recombinant proteins. To develop optimal strategies for minimizing cell injury due to intracellular ice formation and excessive volume shrinkage during cryopreservation, the fundamental transport properties including the osmotic inactive volume (V_b), the hydraulic conductivity (L_p), and the glycerol permeability (P_s) of Sf21 cell membrane at 25, 15, 5 and −2°C were characterized using a micro-perfusion chamber. The effects of temperature on the hydraulic conductivity and the glycerol permeability of Sf21 cell membrane, reflected by the activation energies, were quantitatively investigated. It was found that the hydraulic conductivity decreases along with the increase of the final CPA concentration at a given temperature, and quantitative analysis indicates that the hydraulic conductivity has a significant linear attenuation along with the increase of the concentration of glycerol. Therefore, we incorporate the concentration dependence of the hydraulic conductivity into the classic Arrhenius relationship by replacing the constant reference value of the hydraulic conductivity at the reference temperature with a function that is linearly dependent on the CPA concentration. Consequently, the prediction of the Arrhenius relationship is improved, and the novel Arrhenius relationship could be very important to the development of optimal strategies for cell cryopreservation.

Membrane Transport Properties of Equine and Macaque Ovarian Tissues Frozen in Mixtures of Dimethylsulfoxide and Ethylene Glycol

The rate at which equine and macaque ovarian tissue sections are first cooled from +25°Cto+4°C has a significant effect on the measured water transport when the tissues are subsequently frozen in 0.85M solutions of glycerol, dimethylsulfoxide (DMSO), or ethylene glycol (EG). To determine whether the response of ovarian tissues is altered if they are suspended in mixtures of cryoprotective agents (CPAs), rather than in solutions of a single CPA, we have now measured the subzero water transport from ovarian tissues that were suspended in mixtures of DMSO and EG. Sections of freshly collected equine and macaque ovaries were suspended either in a mixture of 0.9M EG plus 0.7M DMSO (equivalent to a mixture of ∼5%v∕v of EG and DMSO) or in a 1.6M solution of only DMSO or only EG. The tissue sections were cooled from +25°Cto+4°C and then frozen to subzero temperatures at 5°C∕min. As the tissues were being frozen, a shape-independent differential scanning calorimeter technique was used to measure water loss from the tissues and, consequently, the best fit membrane permeability parameters (Lpg and ELp) of ovarian tissues during freezing. In the mixture of DMSO+EG, the respective values of Lpg and ELp for equine tissue first cooled at 40°C∕min between +25°C and +4°C before being frozen were 0.15μm∕minatm and 7.6kcal∕mole. The corresponding Lpg and ELp values for equine tissue suspended in 1.6M DMSO were 0.12μm∕minatm and 27.2kcal∕mole; in 1.6M EG, the values were 0.06μm∕minatm and 21.9kcal∕mole, respectively. For macaque ovarian tissues suspended in the mixture of DMSO+EG, the respective values of Lpg and ELp were 0.26μm∕minatm and 26.2kcal∕mole. Similarly, the corresponding LLg and ELp values for macaque tissue suspended in 1.6M DMSO were 0.22μm∕minatm and 31.4kcal∕mole; in 1.6M EG, the values were 0.20μm∕minatm and 27.9kcal∕mole. The parameters for both equine and macaque tissue samples suspended in the DMSO+EG mixture and first cooled at 0.5°C∕min between +25°C and +4°C were very similar to the corresponding values for samples cooled at 40°C∕min. In contrast, the membrane parameters of equine and macaque samples first cooled at 0.5°C∕min in single-component solutions were significantly different from the corresponding values for samples cooled at 40°C∕min. These results show that the membrane properties of ovarian cells from two species are different, and that the membrane properties are significantly affected both by the solution in which the tissue is suspended and by the rate at which the tissue is cooled from +25°Cto+4°C before being frozen. These observations suggest that these variables ought to be considered in the derivation of methods to cryopreserve ovarian tissues.

Subzero water transport characteristics and optimal rates of freezing rhesus monkey (Macaca mulatta) ovarian tissue

The purpose of the present study was to examine the effect of two different suprazero (room temperature +25 degrees C to +4 degrees C) cooling conditions on the measured water transport response of primate (Macaca mulatta) ovarian tissue in the presence and absence of cryoprotective agents (CPAs). Freshly collected Macaca mulatta (rhesus monkey) ovarian tissue sections were cooled at either 0.5 degrees C/min or 40 degrees C/min from 25 to 4 degrees C. A shape independent differential scanning calorimeter (DSC) technique was then used to measure the volumetric shrinkage during freezing of ovarian tissue sections at a freezing rate of 5 degrees C/min in the presence and absence of three different CPAs (0.85 M glycerol, 0.85 M dimethylsulfoxide, and 0.85 M ethylene glycol). Thus, water transport during freezing of primate ovarian tissue was obtained at eight different conditions (i.e., at four different freezing media with two different suprazero cooling conditions). The water transport response of ovarian tissue cooled rapidly from 25 to 4 degrees C was significantly different (P < 0.01) than that of slow cooled tissue, in the freezing media without CPAs and with dimethylsulfoxide. However, the differences in the measured water transport response due to the imposed suprazero cooling conditions were reduced with the addition of glycerol and ethylene glycol (statistically different with P < 0.05). By fitting a model of water transport to the experimentally obtained volumetric shrinkage data the best-fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The best-fit parameters of water transport in primate ovarian tissue sections ranged from: L(pg) = 0.7 to 0.15 microm/min-atm and E(Lp) = 22.1 to 32.1 kcal/mol (the goodness of fit parameter, R(2) > 0.96). These parameters suggest that the "optimal rates of cryopreservation" for ovarian tissue are significantly dependent upon suprazero cooling conditions and the choice of CPA.