The regulation of fat synthesis

The synthesis of fatty acids mainly uses acetyl coenzyme A (CoA) and reduced coenzyme II (NADPH) as substrates. The citric acid-pyruvate cycle provides acetyl-CoA for fatty acid synthesis, and acetyl-CoA carboxylase (ACC) catalyzes the formation of malonyl-CoA. Huang et al. (2008) found that betaine could reduce the activities of acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS) and malic enzyme (ME) in subcutaneous adipose tissue of finishing pigs.

The decrease of ACC activity leads to the weakening of malonyl-CoA synthesis. The content of malonyl-CoA can regulate the efficiency of fatty acid transport into mitochondria. FAS and ME are the key enzymes for the synthesis of NADPH. Attenuates fat synthesis. Xing et al. (2009, 2010) found that betaine could reduce lipoprotein lipase (LPL) mRNA expression in both broiler and laying hen studies. LPL is a key enzyme in the regulation of adipose tissue deposition in broilers, and a decrease in LPL activity leads to a decrease in fat deposition.
 
The regulation of lipolysis

Betaine metabolism can produce lysine, which provides a skeleton for the synthesis of carnitine, and at the same time can provide active methyl group as a synthetic raw material, which has the ability to increase the synthesis of carnitine. The active form of carnitine is long-chain fatty phthalocarnitine, that is, acid-insoluble carnitine. The increase of methyl content in animals can promote the conversion of carnitine to acid-insoluble carnitine. Long-chain fatty acids can be transported into mitochondria for β-oxidation only after being combined with carnitine to form fatty acylcarnitines. The synthesis of free carnitine in the liver increases, which enhances the transport of fatty acids, thereby promoting fatty acid oxidation, and thus feedback. It enhances the activity of lipolytic enzymes in different stages of pigs and accelerates fat decomposition.

Triacylglycerols are broken down into glycerol and fatty acids by hormone-sensitive lipase (HSL). The addition of betaine increased the activity of HSL in the adipose tissue of growing pigs, resulting in the increase of free fatty acid content in serum, thereby reducing the thickness of the backfat and improving the carcass quality. Wang Yizhen et al. (2001) and Feng Jie et al. (2001) found that adding betaine increased the carnitine content in liver and longissimus dorsi and the ratio of carnitine to fatty acylcarnitine, reduced carcass fat, and improved carcass quality.
 
The regulation of fat transport
 
With the participation of diacylglycerol, choline can synthesize phosphatidylcholine (PC), which is an essential component of lipoproteins such as VLDL. During the transport process, choline and other carrier proteins are insufficient and fat will be stored locally in the form of droplets. in tissues and organs. As an efficient methyl donor, betaine can save the consumption of choline in animals. The serine produced by betaine demethylation provides the backbone for choline synthesis, and provides methyl for choline synthesis by increasing the content of active methyl donors. base.

Cao Huabin et al. (2010) showed that adding betaine to high-energy and low-protein diets of laying hens can increase the expression of apoA1 and ApoB100 mRNA in the liver, and enhance the transport of lipids in the liver, thereby preventing fatty liver.
 
Indirect regulation of fat metabolism through endocrine
 
The known endocrine hormones that can regulate fat metabolism mainly include: growth hormone (GH), thyroxine and insulin, etc. Adding betaine to the diet of growing pigs can increase the levels of GH, insulin-like growth factor I (IGF-I) in plasma. ).