Antifreeze protein type I in the vitrification solution improves the cryopreservation of immature cat oocytes

Oocyte cryopreservation is not yet considered a reliable technique since it can reduce the quality and survival of oocytes in several species. This study determined the effect of different concentrations of antifreeze protein I (AFP I) on the vitrification solution of immature cat oocytes. For this, oocytes were randomly distributed in three groups and vitrified with 0 μg/mL (G0, 0 μM); 0.5 μg/mL (G0.5, 0.15 μM), or 1 μg/mL (G1, 0.3 μM) of AFP I. After thawing, oocytes were evaluated for morphological quality, and compared to a fresh group (FG) regarding actin integrity, mitochondrial activity and mass, reactive oxygen species (ROS) and glutathione (GSH) levels, nuclear maturation, expression of GDF9, BMP15, ZAR-1, PRDX1, SIRT1, and SIRT3 genes (normalized by ACTB and YWHAZ genes), and ultrastructure. G0.5 and G1 presented a higher proportion of COCs graded as I and while G0 had a significantly lower quality. G1 had a higher percentage of intact actin in COCs than G0 and G0.5 (P < 0.05). There was no difference (P > 0.05) in the mitochondrial activity between FG and G1 and they were both higher (P < 0.05) than G0 and G0.5. G1 had a significantly lower (P < 0.05) mitochondrial mass than FG and G0, and there was no difference among FG, G0, and G0.5. G1 had higher ROS than all groups (P < 0.05), and there was no difference in GSH levels among the vitrified groups (P > 0.05). For nuclear maturation, there was no difference between G1 and G0.5 (P > 0.05), but these were both higher (P < 0.05) than G0 and lower (P < 0.05) compared to FG. Regarding gene expression, in G0 and G0.5, most genes were downregulated compared to FG, except for SIRT1 and SIRT3 in G0 and SIRT3 in G0.5. In addition, G1 kept the expression more similar to FG. Regardless of concentration, AFP I supplementation in vitrification solution of immature cat oocytes improved maturation rates, morphological quality, and actin integrity and did not impact GSH levels. In the highest concentration tested (1 μg/mL), AFP maintained the mitochondrial activity, reduced mitochondrial mass, increased ROS levels, and had the gene expression more similar to FG. Altogether these data show that AFP supplementation during vitrification seems to mitigate some of the negative impact of cryopreservation improving the integrity and cryosurvival of cat oocytes.