Supplementation with l-carnitine downregulates genes of the ubiquitin proteasome system in the skeletal muscle and liver of piglets

L-Carnitine: an adequate supplement for a multi-targeted anti-wasting therapy in cancer

BACKGROUND & AIMS

Tumour growth is associated with weight loss resulting from both adipose and muscle wasting.

METHODS

Administration of L-carnitine (1 g/kg body weight) to rats bearing the AH-130 Yoshida ascites hepatoma, a highly cachectic rat tumour.

RESULTS

The treatment results in a significant improvement of food intake and in muscle weight (gastrocnemius, EDL and soleus). These beneficial effects are directly related to improved physical performance (total physical activity, mean movement velocity and total travelled distance). Administration of L-carnitine decreases proteasome activity and the expression of genes related with this activity, such as ubiquitin, C8 proteasome subunit and MuRF-1. Interestingly, L-carnitine treatment also decreases caspase-3 mRNA content therefore suggesting a modulation of apoptosis. Moreover, addition of 50 μM of L-carnitine to isolated EDL muscles results in a significant decrease in the proteolytic rate suggesting a direct effect.

CONCLUSIONS

It can be concluded that L-carnitine supplementation may be a good approach for a multi-targeted therapy for the treatment of cancer-related cachexia.

Dietary moderately oxidized oil induces expression of fibroblast growth factor 21 in the liver of pigs

Background

Fibroblast growth factor 21 (FGF21), whose expression is induced by peroxisome proliferator-activated receptor α (PPARα), has been recently identified as a novel metabolic regulator which plays a crucial role in glucose homeostasis, lipid metabolism, insulin sensitivity and obesity. Previous studies have shown that administration of oxidized fats leads to an activation of PPARα in the liver. Therefore, the present study investigated the hypothesis that feeding of oxidized fats causes an induction of FGF21 in the liver.

Methods

Twenty four crossbred pigs were allocated to two groups of 12 pigs each and fed nutritionally adequate diets with either fresh rapeseed oil or oxidized rapeseed oil prepared by heating at a temperature of 175°C for 72 h.

Results

In pigs fed the oxidized fat mRNA abundance and protein concentrations of FGF21 in liver were significantly increased (P < 0.05), and the protein concentrations of FGF21 in plasma tended to be increased (P < 0.1) in comparison to control pigs. Moreover, pigs fed the oxidized fat had increased transcript levels of the PPARα target genes acyl-CoA oxidase, carnitine palmitoyltransferase-1 and novel organic cation transporter 2 in the liver (P < 0.05), indicative of PPARα activation.

Conclusion

The present study shows for the first time that administration of an oxidized fat induces the expression of FGF21 in the liver, probably mediated by activation of PPARα. Induction of FGF21 could be involved in several effects observed in animals administered an oxidized fat.

Dietary moderately oxidized oil activates the Nrf2 signaling pathway in the liver of pigs

Background

Previous studies have shown that administration of oxidized oils increases gene expression and activities of various enzymes involved in xenobiotic metabolism and stress response in the liver of rats and guinea pigs. As these genes are controlled by nuclear factor erythroid-derived 2-like 2 (Nrf2), we investigated the hypothesis that feeding of oxidized fats causes an activation of that transcription factor in the liver which in turn activates the expression of antioxidant, cytoprotective and detoxifying genes.

Methods

Twenty four crossbred pigs were allocated to two groups of 12 pigs each and fed nutritionally adequate diets with either fresh rapeseed oil (fresh fat group) or oxidized rapeseed oil prepared by heating at a temperature of 175°C for 72 h (oxidized fat group).

Results

After 29 days of feeding, pigs of the oxidized fat group had a markedly increased nuclear concentration of the transcription factor Nrf2 and a higher activity of cellular superoxide dismutase and T4-UDP glucuronosyltransferase in liver than the fresh fat group (P < 0.05). In addition, transcript levels of antioxidant and phase II genes in liver, like superoxide dismutase 1, heme oxygenase 1, glutathione peroxidase 1, thioredoxin reductase 1, microsomal glutathione-S-transferase 1, UDP glucuronosyltransferase 1A1 and NAD(P)H:quinone oxidoreductase 1 in the liver were higher in the oxidized fat group than in the fresh fat group (P < 0.05). Moreover, pigs of the oxidized fat group had an increased hepatic nuclear concentration of the transcription factor NF-κB which is also an important transcription factor mediating cellular stress response.

Conclusion

The present study shows for the first time that administration of an oxidized fat activates the Nrf2 in the liver of pigs which likely reflects an adaptive mechanism to prevent cellular oxidative damage. Activation of the NF-κB pathway might also contribute to this effect of oxidized fat.

Effect of L-carnitine on the hepatic transcript profile in piglets as animal model

Background

Carnitine has attracted scientific interest due to several health-related effects, like protection against neurodegeneration, mitochondrial decay, and oxidative stress as well as improvement of glucose tolerance and insulin sensitivity. The mechanisms underlying most of the health-related effects of carnitine are largely unknown.

Methods

To gain insight into mechanisms through which carnitine exerts its beneficial metabolic effects, we fed piglets either a control or a carnitine supplemented diet, and analysed the transcriptome in the liver.

Results

Transcript profiling revealed 563 genes to be differentially expressed in liver by carnitine supplementation. Clustering analysis of the identified genes revealed that most of the top-ranked annotation term clusters were dealing with metabolic processes. Representative genes of these clusters which were significantly up-regulated by carnitine were involved in cellular fatty acid uptake, fatty acid activation, fatty acid β-oxidation, glucose uptake, and glycolysis. In contrast, genes involved in gluconeogenesis were down-regulated by carnitine. Moreover, clustering analysis identified genes involved in the insulin signaling cascade to be significantly associated with carnitine supplementation. Furthermore, clustering analysis revealed that biological processes dealing with posttranscriptional RNA processing were significantly associated with carnitine supplementation.

Conclusion

The data suggest that carnitine supplementation has beneficial effects on lipid and glucose homeostasis by inducing genes involved in fatty acid catabolism and glycolysis and repressing genes involved in gluconeogenesis.