In aged laying hens, adding taurine to feed at 0.05% to 0.2% increases the activity of two liver proteins, ABCG5 and ACAT2, which leads to more cholesterol being moved out of the liver and turned...
Mechanism
Synthesis from 1 study
Taurine tells the liver to stop making so much cholesterol, push more out through bile, and store the rest as stable esters. This leaves less cholesterol in the blood and less available to go into egg yolks.
Most probable mechanism
Taurine tells liver cells to make more proteins that push cholesterol out into bile and turn it into a stored form, while also slowing down the liver's production of new cholesterol. This reduces the amount of cholesterol circulating in the blood and available to be put into egg yolks.
Taurine enters hepatocytes and upregulates the expression of ABCG5, increasing the transport of cholesterol from liver cells into bile ducts for excretion.
Taurine upregulates ACAT2, increasing the conversion of free cholesterol into cholesteryl esters for storage in lipid droplets or packaging into lipoproteins, reducing the pool of free cholesterol available for secretion.
Taurine downregulates SREBP2, reducing the transcriptional activation of HMGCR, the rate-limiting enzyme in cholesterol biosynthesis, thereby decreasing de novo cholesterol production in the liver.
The combined reduction in cholesterol synthesis and increase in biliary excretion and esterification lower the hepatic cholesterol pool, limiting the amount of cholesterol packaged into very low-density lipoproteins for transport to the ovary.
Reduced circulating cholesterol decreases the delivery of cholesterol to developing oocytes during vitellogenesis, resulting in lower cholesterol content in egg yolks.
Less supported by current evidence, but not ruled out
At higher doses, taurine increases the liver's ability to convert cholesterol into bile acids, which are then excreted, further reducing cholesterol levels in the body.
Taurine upregulates CYP7A1, increasing the conversion of cholesterol into 7α-hydroxycholesterol, the first step in bile acid synthesis.
Bile acids are secreted into the intestine and excreted, removing cholesterol from the enterohepatic circulation.
Reduced hepatic cholesterol burden limits cholesterol availability for egg yolk deposition.
Evidence from Studies
Supporting (1)
Community contributions welcome
Effects of dietary taurine supplementation on polyunsaturated fatty acids, cholesterol, and egg quality of egg of hens
Contradicting (0)
Community contributions welcome
Gold Standard Evidence Needed
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