The interplay between non-esterified fatty acids and bovine peroxisome proliferator-activated receptors: results of an in vitro hybrid approach

Sebastiano Busato,Massimo Bionaz

doi:10.1186/s40104-020-00481-y

Abstract

BackgroundIn dairy cows circulating non-esterified fatty acids (NEFA) increase early post-partum while liver and other tissues undergo adaptation to greater lipid metabolism, mainly regulated by peroxisome proliferator-activated receptors (PPAR). PPAR are activated by fatty acids (FA), but it remains to be demonstrated that circulating NEFA or dietary FA activate bovine PPAR. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows.MethodsThe dose-response activation of PPAR by NEFA or dietary FA was assessed using HP300e digital dispenser and luciferase reporter in several bovine cell types. Cells were treated with blood plasma isolated from Jersey cows before and after parturition, NEFA isolated from the blood plasma, FA released from lipoproteins using milk lipoprotein lipase (LPL), and palmitic acid (C16:0). Effect on each PPAR isotype was assessed using specific synthetic inhibitors.ResultsNEFA isolated from blood serum activate PPAR linearly up to ~ 4-fold at 400 μmol/L in MAC-T cells but had cytotoxic effect. Addition of albumin to the culture media decreases cytotoxic effects of NEFA but also PPAR activation by ~ 2-fold. Treating cells with serum from peripartum cows reveals that much of the PPAR activation can be explained by the amount of NEFA in the serum (R2 = 0.91) and that the response to serum NEFA follows a quadratic tendency, with peak activation around 1.4 mmol/L. Analysis of PPAR activation by serum in MAC-T, BFH-12 and BPAEC cells revealed that most of the activation is explained by the activity of PPARδ and PPARγ, but not PPARα. Palmitic acid activated PPAR when added in culture media or blood serum but the activation was limited to PPARδ and PPARα and the response was nil in serum from post-partum cows. The addition of LPL to the serum increased > 1.5-fold PPAR activation.ConclusionOur results support dose-dependent activation of PPAR by circulating NEFA in bovine, specifically δ and γ isotypes. Data also support the possibility of increasing PPAR activation by dietary FA; however, this nutrigenomics approach maybe only effective in pre-partum but not post-partum cows.

Highlights

The period comprised between 21 days before and after parturition, commonly referred to as “transition period” or “peripartum”, is widely regarded as one of the most metabolically challenging events in the life of a dairy cow [1, 2]
Transition dairy cows are routinely exposed to circulating non-esterified fatty acids (NEFA) over 1 mmol/L in the few days after parturition [1]; we were interested in exploring the effect of serum NEFA on peroxisome proliferator-activated receptors (PPAR) activation past the 400 μmol/L threshold
Adjusting the pH of the solution to a physiological level (i.e., 7.4) with sodium hydroxide reduced acute cytotoxicity; the percentage of apoptotic cells was still higher compared to Immortalized mammary alveolar cells (MAC-T) cells treated with only Dulbecco’s Modified Eagle Media (DMEM), suggesting that the cytotoxic effect of NEFA goes beyond the pH change

Summary

Introduction

The period comprised between 21 days before and after parturition, commonly referred to as “transition period” or “peripartum”, is widely regarded as one of the most metabolically challenging events in the life of a dairy cow [1, 2]. NEFA have cytotoxic effects in several cell types including leukocytes [4], as well as contributing to overall oxidative stress via mitochondrial βoxidation [10], increase rates of ketogenesis [11], and have a negative impact on the immune system, typical of early post-partum dairy cows [12]. All these factors, combined with presence of inflammatory-like conditions that stimulate the hepatic acute response (i.e., increase circulating haptoglobin and decrease of albumin and other negative acute phase proteins) [13], result in the overrepresentation of diseases, which about half of early post-partum cows have to endure [14]. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows

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