It is a cytochrome P450 enzyme, which belongs to the oxidoreductase class, and converts cholesterol to 7-alpha-hydroxycholesterol, the first and rate limiting step in bile acid synthesis.

Advances in mRNA purification in the early 1980s allowed to isolate the first cDNA encoding a complete cytochrome P450 (CYP) protein, and thereafter, results of many cloning studies have revealed a large number of different enzymes.

[8] Bile acids have powerful toxic properties like membrane disruption and there are a wide range of mechanisms to restrict their accumulation in tissues and blood.

[8] The increased abundance of SHP causes it to associate with liver receptor homolog (LRH)-1, an obligate factor required for the transcription of CYP7A1.

These inflammatory cytokines, which include tumor necrosis factor alpha and interleukin-1beta, act upon the liver parenchymal cells causing a rapid repression of the CYP7A1 gene.

Bile acids, steroid hormones, inflammatory cytokines, insulin, and growth factors inhibit CYP7A1 transcription through the 5′-upstream region of the promoter.

[8] In the liver, bile acids bound to FXR induce small heterodimer partner, SHP which binds to LRH-1 and so inhibits the transcription of the enzyme.

[13] Disruption of CYP7A1 from classic bile acid synthesis in mice leads to either increased postnatal death or a milder phenotype with elevated serum cholesterol.

[11] The latter is similar to the case in humans, where CYP7A1 mutations associate with high plasma low-density lipoprotein and hepatic cholesterol content, as well as deficient bile acid excretion.

[14] CYP7A1-rs3808607 and apolipoprotein E (APOE) isoform are associated with the extent of reduction in circulating LDL cholesterol in response to plant sterol consumption and could serve as potential predictive genetic markers to identify individuals who would derive maximum LDL cholesterol lowering with plant sterol consumption.