Betaine affects muscle lipid metabolism via regulating the fatty acid uptake and oxidation in finishing pig

Abstract

Background: Betaine affects fat metabolism in animals, but the specific mechanism is still not clear. The purpose of this study was to investigate possible mechanisms of betaine in altering lipid metabolism in muscle tissue in finishing pigs.

Methods: A total of 120 crossbred gilts (Landrace × Yorkshire × Duroc) with an average initial body weight of 70.1 kg were randomly allotted to three dietary treatments. The treatments included a corn-soybean meal basal diet supplemented with 0, 1250 or 2500 mg/kg betaine. The feeding experiment lasted 42 d.

Results: Betaine addition to the diet significantly increased the concentration of free fatty acids (FFA) in muscle (P < 0.05). Furthermore, the levels of serum cholesterol and high-density lipoprotein cholesterol were decreased (P < 0.05) and total cholesterol content was increased in muscle (P < 0.05) of betaine fed pigs. Experiments on genes involved in fatty acid transport showed that betaine increased expression of lipoprotein lipase(LPL), fatty acid translocase/cluster of differentiation (FAT/CD36), fatty acid binding protein (FABP3) and fatty acid transport protein (FATP1) (P < 0.05). The abundance of fatty acid transport protein and fatty acid binding protein were also increased by betaine (P < 0.05). As for the key factors involved in fatty acid oxidation, although betaine supplementation didn't affect the level of carnitine and malonyl-CoA, betaine increased mRNA and protein abundance of carnitine palmitransferase-1(CPT1) and phosphorylated-AMPK (P < 0.05).

Conclusions: The results suggested that betaine may promoted muscle fatty acid uptake via up-regulating the genes related to fatty acid transporter including FAT/CD36, FATP1 and FABP3. On the other hand, betaine activated AMPK and up-regulated genes related to fatty acid oxidation including PPARα and CPT1. The underlying mechanism regulating fatty acid metabolism in pigs supplemented with betaine is associated with the up-regulation of genes involved in fatty acid transport and fatty acid oxidation.

Keywords: Betaine; Fatty acid intake; Fatty acid oxidation; Muscle; Pig.

Fig. 1

Effect of betaine supplementation on serum parameters of lipid metabolism. The levels of serum free fatty acid (FFA, a), triglyceride (b), total cholesterol (c) and high-density lipoprotein cholesterol (HDLC, d). ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 2

Effect of betaine supplementation on total cholesterol, FFA and triglyceride in muscle. The levels of total cholesterol (a), free fatty acid (FFA, b) and triglyceride (c) in muscle. ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 3

The relative gene expression of key factors involved fatty acid uptake in muscle. mRNA expression was performed by RT-PCR and β-actin was chosen as reference gene. aThe relative expression of FAT/CD36, FATP1, LPL and PPARγ in muscle, (b) The relative expression of FABP3 in muscle. ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 4

The relative protein abundance of FATP1 and FABP3 in muscle. Western blot results were shown in a (The control group: 1–1, 1–2, 1–3; Low betaine group: 2–1, 2–2, 2–3; High betaine group: 3–1, 3–2, 3–3). Data were normalized with β-actin as shown in b, c. ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 5

Effect of betaine supplementation on the level of carnitine(a) and malonyl-CoA (b) in muscle. Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 6

The relative mRNA expression of factors involved in fatty acid oxidation in muscle. mRNA expression was performed by RT-PCR and β-actin was chosen as reference gene. ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively

Fig. 7

The relative protein abundance of p-AMPK and M-CPT1. The results of western blot were showed a and b (The control group: 1–1, 1–2, 1–3; Low betaine group: 2–1, 2–2, 2–3; High betaine group: 3–1, 3–2, 3–3). p-AMPK (the activated form of AMPK) was normalized with AMPK (shown in c) and MCPT1(the muscle type of CPT1) was normalized with β-actin (shown in d). ^a,bValues without common superscript letters differ significantly (P < 0.05). Low betaine and high betaine represent 1250 mg/kg and 2500 mg/kg betaine addition, respectively