Pretreatment with saturated and unsaturated fatty acids regulates fatty acid oxidation in Madin-Darby bovine kidney cells

Abstract

Metabolic fates of fatty acids in tissue may be influenced by extracellular concentration and profile of fatty acids. Previous work has demonstrated the ability of C18:3n-3 cis to ameliorate the effects of C16:0- or C18:0-induced depression of pyruvate carboxylase (PC) mRNA expression. Pyruvate carboxylase catalyzes oxaloacetate synthesis and connects gluconeogenesis from lactate and fatty acid metabolism. Our objective was to determine the effects of co-presence of saturated and unsaturated fatty acids on cellular partitioning of [1-¹⁴C]C16:0 metabolism to CO₂ or acid-soluble products (ASP) in Madin-Darby bovine kidney cells and the role of PC in this relationship. We hypothesized that the ratio of saturated to unsaturated fatty acid pretreatments regulates [1-¹⁴C]C16:0 partitioning to CO₂ or ASP. Cells were exposed for 21 h to either individual fatty acids, C16:0, C18:0, C18:1n-9 cis, or C18:3n-3 cis, or to fatty acid combinations in 10:90, 25:75, 50:50, 75:25, or 90:10 ratios for 3 combinations: C16:0/C18:3n-3 cis, C18:0/C18:3n-3 cis, or C18:1n-9 cis/C18:3n-3 cis. Total fatty acid concentration was 1.0 mM during the 21-h pretreatment phase. Following the 21-h incubation phase with fatty acid combinations, cells were incubated in the presence of 1.0 mM [1-¹⁴C]C16:0 for 3 h to determine the rate of metabolism to CO₂ and ASP collection (per µg DNA^-1·h^-1). Pretreatment with either C16:0 or C18:0 alone significantly depressed subsequent oxidation of [1-¹⁴C]C16:0 to ASP by 62.7 and 41.2%, respectively, compared with C18:3n-3 cis pretreatment. Similar patterns were observed for [1-¹⁴C]C16:0 oxidation to CO₂. Expression of PC mRNA was significantly decreased with exposure to either C16:0 or C18:0 compared with expression after exposure to either C18:3n-3 cis or control 1% BSA in Dulbecco's modified Eagle's medium. Expression of cytosolic phosphoenolpyruvate carboxykinase (PCK1) mRNA followed a similar pattern. Fatty acid treatments containing C18:1n-9 cis did not alter PC or PCK1 expression from control or C18:3n-3 cis results. Pearson coefficient correlations were determined for PC mRNA expression and rate of [1-¹⁴C]C16:0 metabolism to CO₂ or ASP, including ketones, and for PCK1 mRNA expression and rate of [1-¹⁴C]C16:0 metabolism to CO₂ or ASP. Production of CO₂ from [1-¹⁴C]C16:0 was positively correlated (r = 0.63) with PC expression, whereas ASP production from [1-¹⁴C]C16:0 only tended to positively correlate (r = 0.51) with PC mRNA expression. Production of CO₂ or ASP from [1-¹⁴C]C16:0 were both positively correlated (r = 0.80 and r = 0.69, respectively) with PCK1 expression. Results show a regulation of ketone production by Madin-Darby bovine kidney cells in response to saturated and unsaturated fatty acid pretreatments.

Keywords: bovine; fatty acid oxidation; ketogenesis.