The mitochondrial bioenergetic profile in response to L-Carnitine as a clue for vitality of in vitro produced bovine embryos cultured under serum enriched conditions

The supplementation of L-Carnitine (LC) to culture medium during bovine in vitro production is known to have beneficial impact on the embryo quality in terms of cryotolerance, accumulation of reactive oxygen species as well as mitochondrial metabolism. In the present study we aimed to investigate the metabolic status of bovine day 7 embryos cultured with or without supplementation of L-Carnitine in serum enriched conditions as well as the bioenergetic profile of their respective mitochondria in order to gain a deeper understanding of metabolic and mitochondrial determinants related to embryo vitality. Therefore, the bioenergetic profile of blastocysts from both culture conditions was analysed by determining the oxygen consumption rate (OCR) via extracellular flux analysis and mitochondrial stress test. The values are ratios that are presented relative to the control group. Our results revealed that, L-Carnitine profoundly modulates the mitochondrial bioenergetic profile in terms of higher mitochondrial respiration (Control: 1.0 ± 0.1 vs. LC: 1.2 ± 0.1; p < 0.05) and maximum respiration (Control: 1.0 ± 0.1 vs LC: 1.3 ± 0.1; p < 0.01). Although ATP production was significantly increased by LC supplementation (Control: 1.0 ± 0.1 vs. LC: 1.2 ± 0.1; p < 0.05), significantly lower proportions of total respirated oxygen was used for ATP-generation, implicating that L-Carnitine supplementation under serum enriched condition accelerates mitochondrial metabolism, without making it more efficient. This study revealed that, L-Carnitine profoundly modulates the mitochondrial bioenergetic profile of in vitro derived bovine embryos and enhance our understanding of bovine embryo vitality paving the way for improvements to in vitro embryo production systems in the future.