Vitamin E analogs exhibit antioxidative functions and inhibit production of a cytochrome P450 derived oxylipid

Preventing and controlling disease during the transition period in cattle is the most significant health challenge facing veterinarians and farm managers. In initial studies, it was found that cattle have increased biomarkers of oxidative stress around the time of calving in addition to significant shifts in the abundance of pro-inflammatory lipid inflammatory mediators, known as oxylipids, compared to other stages of lactation. These factors, brought upon by the intense physiological shifts around the time of calving, can become detrimental and contribute to disease predisposition during the transition period in animals that do not properly adapt to such physiological changes. There is a significant need to find means to reduce oxidative stress and the production of pro-inflammatory lipid mediators at this time. One potential way is by augmenting the well-known effects of [alpha]-tocopherol with other analogs of vitamin E which have been shown in other species to have antioxidant functions and share a metabolic pathway with the pro-inflammatory oxylipid 20-HETE. Little is known about this shared metabolic pathway, specially the cytochrome P450 family 4 sub-family F member 2 enzyme, in dairy cattle. Additionally, many other cytochrome P450 enzymes which are involved in the production of other oxylipids and metabolism of fat-soluble vitamins essential to appropriate immune regulation remain mostly unexplored in cattle. A range of such cytochrome P450 enzymes was explored in both bovine tissues and common cell culture models used for oxidative stress and inflammation modeling. These data revealed which models may best represent specific cytochrome P450 metabolic pathways in vivo. A bovine mammary endothelial cell model of oxidative stress was utilized to determine the antioxidative effects of vitamin E analogs in vitro. Gamma-tocopherol was found to not only reduce the accumulation of reactive metabolites but protected cellular health by reducing apoptosis and protecting the endothelial barrier integrity. Further, [gamma]-tocopherol reduced the production of 20-HETE produced from human and bovine-kidney cytochrome P450 microsomes, likely by competitive inhibition. These data provide credence to further explore the functions of [gamma]-tocopherol and other non-[alpha]-tocopherol analogs of vitamin E in cattle. Overall, this dissertation underscores the challenges faced by dairy cattle during the transition period and highlights gaps in knowledge left to be explored regarding the production of inflammatory mediators, especially those from the cytochrome P450 pathway. Given the relative safety of feeding mixed tocopherols to dairy cattle, further efforts should be undertaken to confirm these initial safety assessments and aim to understand their potential contributions to the prevention of oxidative stress and dysfunctional inflammation during the transition period.