changes that tend to reduce synthesis of polyunsaturated fatty acids
and increase synthesis of saturated fatty acids as well as reduce fatty
acid oxidation and metabolism. A number of other changes in
expression were seen whose significance is less easy to interpret.
In summary, the effects of chilling and the effects of VS exposure
were remarkably similar, as though chilling injury were an extension
of VS toxicity. Chilling injury in rabbit kidneys may also be an
extension of VS toxicity (Fahy et al., unpublished).
Pig oocytes [368] and embryos [369] are particularly sensitive
to chilling injury in part as a consequence of containing globules of
cytoplasmic fat that cause damage to the cell membrane on cooling.
This problem has been reduced by various lipid removal or segregation techniques [368, 370], although birth rates have tended to
be low despite adding additional interventions [368, 371, 372].
Oocytes are in general quite susceptible to cooling injury, and
much of this susceptibility is related to disassembly of the meiotic
spindle and subsequent abnormal or incomplete spindle reassembly
[373, 374]. Cryoprotectants can stabilize [375] but can also damage [376] the spindle. Nevertheless, with proper methodology,
oocytes can be preserved without significant spindle damage [376].
The vitrification of oocytes is motivated in no small part by the
utility of vitrification for “outrunning” chilling injury [66]. The
successful cryopreservation of Drosophila embryos was enabled in
part by the ability of vitrification to allow rapid chilling injury to be
“outrun” in this species [64, 65, 145].
The demonstrated methods mentioned above for altering chilling injury (consisting of modifying plasma membrane composition
or using antifreeze proteins to prevent membrane leakage or preventing protein denaturation) are generally inconvenient or
impractical for many applications and may not be pertinent to
chilling injury below 0
C. McGrath [377] showed, in
non-cryoprotected systems, and Fahy et al. [23, 378] showed, in
cryoprotected systems, that chilling injury can be reduced or prevented by an increase in medium tonicity. In the latter case, the
optimum tonicity for avoiding chilling injury during vitrification
was found to be between about 1.3 and 1.5 times isotonic, whereas
for porcine embryos a tonicity of ~2.8 times isotonic was
effective [377].
Chilling injury is not universally observed in systems prepared
for vitrification [248]. It is seen in rabbit but not rat renal cortical
slices and in rabbit and rat liver slices but not in monkey liver slices
and may be absent in rat and/or rabbit hippocampal slices. Comparing susceptible and non-susceptible tissues of the same type
might offer another way of understanding and seeking new mitigation strategies for chilling injury.
78
Gregory M. Fahy and Brian Wowk
and increase synthesis of saturated fatty acids as well as reduce fatty
acid oxidation and metabolism. A number of other changes in
expression were seen whose significance is less easy to interpret.
In summary, the effects of chilling and the effects of VS exposure
were remarkably similar, as though chilling injury were an extension
of VS toxicity. Chilling injury in rabbit kidneys may also be an
extension of VS toxicity (Fahy et al., unpublished).
Pig oocytes [368] and embryos [369] are particularly sensitive
to chilling injury in part as a consequence of containing globules of
cytoplasmic fat that cause damage to the cell membrane on cooling.
This problem has been reduced by various lipid removal or segregation techniques [368, 370], although birth rates have tended to
be low despite adding additional interventions [368, 371, 372].
Oocytes are in general quite susceptible to cooling injury, and
much of this susceptibility is related to disassembly of the meiotic
spindle and subsequent abnormal or incomplete spindle reassembly
[373, 374]. Cryoprotectants can stabilize [375] but can also damage [376] the spindle. Nevertheless, with proper methodology,
oocytes can be preserved without significant spindle damage [376].
The vitrification of oocytes is motivated in no small part by the
utility of vitrification for “outrunning” chilling injury [66]. The
successful cryopreservation of Drosophila embryos was enabled in
part by the ability of vitrification to allow rapid chilling injury to be
“outrun” in this species [64, 65, 145].
The demonstrated methods mentioned above for altering chilling injury (consisting of modifying plasma membrane composition
or using antifreeze proteins to prevent membrane leakage or preventing protein denaturation) are generally inconvenient or
impractical for many applications and may not be pertinent to
chilling injury below 0
C. McGrath [377] showed, in
non-cryoprotected systems, and Fahy et al. [23, 378] showed, in
cryoprotected systems, that chilling injury can be reduced or prevented by an increase in medium tonicity. In the latter case, the
optimum tonicity for avoiding chilling injury during vitrification
was found to be between about 1.3 and 1.5 times isotonic, whereas
for porcine embryos a tonicity of ~2.8 times isotonic was
effective [377].
Chilling injury is not universally observed in systems prepared
for vitrification [248]. It is seen in rabbit but not rat renal cortical
slices and in rabbit and rat liver slices but not in monkey liver slices
and may be absent in rat and/or rabbit hippocampal slices. Comparing susceptible and non-susceptible tissues of the same type
might offer another way of understanding and seeking new mitigation strategies for chilling injury.
78
Gregory M. Fahy and Brian Wowk