Changes of the liver metabolome following an intravenous lipopolysaccharide injection in Holstein cows supplemented with dietary carnitine

Abstract

Background: Carnitine facilitates the flux of long-chain fatty acids for hepatic mitochondrial beta-oxidation, which acts to ameliorate the negative energy balance commonly affecting high-yielding dairy cows. Inflammation triggered by lipopolysaccharide (LPS) load can however pose a challenge to the metabolic integrity via the expression of pro-inflammatory mediators, leading to immune system activation and respective metabolic alterations. The effect of enhanced carnitine availability on hepatic metabolome profiles during an inflammatory challenge has not yet been determined in dairy cows. Herein, Holstein cows were supplemented with 25 g/d rumen-protected carnitine from 42 d prepartum until 126 d postpartum (n = 16) or assigned to the control group with no supplementation during the same period (n = 14). We biopsied the liver of the cows before (100 d postpartum) and after (112 d postpartum) an intravenous injection of 0.5 µg/kg LPS. Liver samples were subjected to a targeted metabolomics analysis using the AbsoluteIDQ p180 Kit (Biocrates Life Sciences AG, Innsbruck, Austria). RESULTS: Multivariate statistical analyses revealed that hepatic metabolome profiles changed in relation to both the carnitine supplementation and the LPS challenge. Comparing the metabolite profiles on 100 d, carnitine increased the concentration of short- and long-chain acyl-carnitines, which may be explained by an enhanced mitochondrial fatty acid shuttle and hence greater energy availability. The LPS injection affected hepatic metabolite profiles only in the carnitine supplemented group, particularly altering the concentration of biogenic amines.

Conclusions: Our results point to interactions between an acute hepatic inflammatory response and biogenic amine metabolism, depending on energy availability.

Keywords: Acyl-carnitines; Inflammatory response; Lipid metabolism; Liver metabolome; Mitochondrial function.

Fig. 1

The concentration of hepatic carnitine in dairy cows with (CAR group; n = 16) or without (CON group; n = 14) supplementary carnitine. Means ± SD, nmol/g (tissue wet weight). LPS effect: P = 0.31; Carnitine effect: P < 0.01 (mixed model)

Fig. 2

Effect of supplementary carnitine on hepatic metabolome profiles of Holstein cows on d 100 postpartum (before LPS injection). A, Hepatic metabolome profiles of cows with (CAR group) or without (CON group) supplementary carnitine by PLS-DA scores plot. B, Top 15 important hepatic metabolites of the first PLS-DA component. C, The accuracy, the goodness of fit (R²), and predictive ability (Q²) of the PLS-DA model as assessed by cross-validation. In plot B, the blue and red squares indicate lower and higher metabolite concentrations, respectively. Cx: Acylcarnitines of x chain length; PC: Phosphatidylcholine; SM: Sphingomyelin; lysoPC: Lysophosphatidylcholine. The specific abbreviations of these metabolites are available in Additional file 1: Table S1

Fig. 3

Effect of LPS challenge on the hepatic metabolome profiles of Holstein cows without supplementary carnitine (CON group on d 112 postpartum). A, Hepatic metabolome profiles before and after LPS challenge by PLS-DA scores plot. B, Top 15 important hepatic metabolites in the first PLS-DA component. C, The accuracy, the goodness of fit (R²), and predictive ability (Q²) of the PLS-DA model as assessed by cross-validation. In plot B, the blue and red squares indicate lower and higher metabolite concentrations, respectively. Cx: Acylcarnitines of x chain length; PC: Phosphatidylcholine; SM: Sphingomyelin; lysoPC: Lysophosphatidylcholine. The specific abbreviations of these metabolites are available in Additional file 1: Table S1

Fig. 4

Effect of LPS challenge on the hepatic metabolome profiles of dairy cows with supplementary carnitine (CAR group on d 112 postpartum). A, Hepatic metabolome profiles before and after LPS challenge by PLS-DA scores plot. B, Top 15 important hepatic metabolites in the first PLS-DA component. C, The accuracy, goodness of fit (R²), and predictive ability (Q²) of the PLS-DA model as assessed by cross validation. In plot B, the blue and red squares indicate the lower and higher metabolite concentrations, respectively. Cx: Acylcarnitines of x chain length; PC: Phosphatidylcholine; SM: Sphingomyelin; lysoPC: Lysophosphatidylcholine. The specific abbreviations of these metabolites are available in Additional file 1: Table S1