Pathway Human Homo sapiens

Synthesis of bile acids and bile salts via 24-hydroxycholesterol

R-HSA-193775 in Reactome release 97: under Synthesis of bile acids and bile salts, with 13 genes placed in it by the mapping files and 0 child pathways in the hierarchy.

The same number in the other species

Reactome writes the mouse and rat events it infers from a human pathway under the human number with the species token. A door opens only where that species' own list in this release holds the id: R-MMU-193775 (mouse), R-RNO-193775 (rat). Whether the event was inferred from this one is what the record says.

The record
The genes
Parents and children

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This page reads the pathway's record from its source while you read the rest; with scripts off the card stays at its loading line. Reload with scripts on to see it, or open the source's own page from the link in the card.

01The record

Reactome's own record of this pathway

What this tells you

The pathway list, the hierarchy and the genes on this page are read from the files Reactome publishes for Reactome release 97, built into this site on 2026-09-09: the pathway list, the hierarchy relationship file and the two gene mapping files. The record card is the one live read, Reactome's own record of this pathway.

Reactome's download page describes the mapping files: Mapping files link the source database identifier to the lowest level pathway diagram or subset of the pathway, all levels of the pathway hierarchy or database identifier to all reactions. [R13] The gene list here is the all-levels mapping of NCBI Gene ids, filled from the all-levels mapping of Ensembl ids where the NCBI file has no row for a gene; each row names which file it came from by the shape of its source id. Each row carries the evidence codes the file writes for it, as written and unranked, and both where the file writes both; no page of Reactome's documentation the survey read defines the codes, so this page does not expand them. A gene id the identity files do not name is kept as the source's own id with no door rather than turned into a symbol.

On citing what a search finds, Reactome says: It should be remembered that while we strive to contain the most current and accurate data, Reactome should not be used in citations where other primary sources of information are available. [R12] The record card prints the literature Reactome attaches to a curated pathway for that reason. The data are public domain: All data in the Reactome database and files derived from that data are licensed under the Creative Commons Public Domain Dedication (CC0). User may copy, modify, and distribute these data, even for commercial purposes, without asking for permission. Attribution is encouraged but not required. [R10] The pathway illustrations are licensed apart, under CC BY 4.0, and none is shown here.

A gene on this list is one Reactome places in this pathway in this release, and that is all the row says: it does not say the gene is expressed in a tissue or associated with a disease, which are the other two explorers' questions, read from other sources. Reactome's papers of record are [R01] [R02].

[R01] Ragueneau E, Gong C, Sinquin P, Sevilla C, Beavers D, Grentner A, et al. (2026). The Reactome Knowledgebase 2026. Nucleic Acids Research 54:D673-D681. PMID 41251150, doi 10.1093/nar/gkaf1223.
[R02] Milacic M, Beavers D, Conley P, Gong C, Gillespie M, Griss J, et al. (2024). The Reactome Pathway Knowledgebase 2024. Nucleic Acids Research 52:D672-D678. PMID 37941124, doi 10.1093/nar/gkad1025.
[R10] Reactome, reactome.org. License Agreement. https://reactome.org/license, read 2026-09-09.
[R12] Reactome, reactome.org. Citing us. https://reactome.org/cite, read 2026-09-09.
[R13] Reactome, reactome.org. Download. https://reactome.org/download-data, read 2026-09-09.

Stable id: R-HSA-193775.4
Class: Pathway
Species: Homo sapiens (human)
Inferred: no: a curated human pathway
Disease pathway: no
Released: 2007-05-15
Last updated: 2018-03-26
Events inside: 16, counted from the record

In the body, 24-hydroxycholesterol is synthesized in the brain, exported to the liver, and converted there to bile acids and bile salts. This pathway is only a minor source of bile acids and bile salts, but appears to be critical for the disposal of excess cholesterol from the brain (Bjorkhem et al. 1998; Javitt 2002).

In the liver, conversion of 24-hydroxycholesterol to bile acids and bile salts is initiated with hydroxylation and oxidoreductase reactions to form 4-cholesten-7alpha,24(S)-diol-3-one. The pathway then branches: hydroxylation of 4-cholesten-7alpha,24(S)-diol-3-one to 4-cholesten-7alpha,12alpha,24(S)-triol-3-one leads ultimately to the formation of cholate, while its reduction to 5beta-cholestan-7alpha,24(S)-diol-3-one leads to chenodeoxycholate formation. In both branches, reactions in the cytosol, the mitochondrial matrix, and the peroxisomal matrix result in modifications to the ring structure, shortening and oxidation of the side chain, conversion to a Coenzyme A derivative, and conjugation with the amino acids glycine or taurine (Russell 2003). These reactions are outlined in the figure below. The final three reactions are identical to ones of bile salt synthesis initiated by 7alpha-hydroxylation and are shown as arrows with no substrates.

Literature Reactome attaches

Cholesterol, hydroxycholesterols, and bile acidsBiochem Biophys Res Commun, 2002, vol. 292, p. 1147-53PubMed 11969205
The enzymes, regulation, and genetics of bile acid synthesisAnnu Rev Biochem, 2003, vol. 72, p. 137-74PubMed 12543708
Cholesterol homeostasis in human brain: turnover of 24S-hydroxycholesterol and evidence for a cerebral origin of most of this oxysterol in the circulationJ Lipid Res, 1998, vol. 39, p. 1594-600PubMed 9717719

Reactome's record lists 13 orthologous events, R-MMU-193775 (Mus musculus), R-RNO-193775 (Rattus norvegicus) among the species this site serves, and 11 in species this site opens no page for.

Reactome ContentService, this pathway's record · Reactome v97 · read 2026-09-30 ET · Reactome pathway browser"Synthesis of bile acids and bile salts via 24-hydroxycholesterol". Reactome, release 97, https://reactome.org/PathwayBrowser/#/R-HSA-193775 with StableID: R-HSA-193775.4 (accessed 2026-09-30 ET). Reactome version 97 (CC0).

Reading this pathway's record from Reactome (the pathway record).Still reading. A first read of a pathway can take a while; this page waits up to 35 seconds for it, and its scripts then bring in the panel, or a line saying what did not arrive.

02The genes

Genes Reactome places in this human pathway

The mapping files place 13 genes in this human pathway; showing 1 to 13, in pages of 100, sorted by symbol for reading. The order carries no ranking.

Genes Reactome places in this human pathway, page 1 of 1
Gene	Authority id	Mapping file id	Evidence codes
GeneABCD3	AuthorityHGNC:67	Mapping file id5825 NCBI file	EvidenceTAS
GeneAKR1C1	AuthorityHGNC:384	Mapping file id1645 NCBI file	EvidenceTAS
GeneAKR1C2	AuthorityHGNC:385	Mapping file id1646 NCBI file	EvidenceTAS
GeneAKR1C3	AuthorityHGNC:386	Mapping file id8644 NCBI file	EvidenceTAS
GeneAKR1C4	AuthorityHGNC:387	Mapping file id1109 NCBI file	EvidenceTAS
GeneAKR1D1	AuthorityHGNC:388	Mapping file id6718 NCBI file	EvidenceTAS
GeneAMACR	AuthorityHGNC:451	Mapping file id23600 NCBI file	EvidenceTAS
GeneCYP27A1	AuthorityHGNC:2605	Mapping file id1593 NCBI file	EvidenceTAS
GeneCYP39A1	AuthorityHGNC:17449	Mapping file id51302 NCBI file	EvidenceTAS
GeneCYP46A1	AuthorityHGNC:2641	Mapping file id10858 NCBI file	EvidenceTAS
GeneHSD3B7	AuthorityHGNC:18324	Mapping file id80270 NCBI file	EvidenceTAS
GeneSLC27A2	AuthorityHGNC:10996	Mapping file id11001 NCBI file	EvidenceTAS
GeneSLC27A5	AuthorityHGNC:10999	Mapping file id10998 NCBI file	EvidenceTAS

Evidence codes on this page: TAS, as the mapping file writes them; a row carrying two was written twice by the file, once under each. The mapping file id says which file placed the gene: an NCBI Gene id from NCBI2Reactome_All_Levels.txt, an Ensembl gene id from Ensembl2Reactome_All_Levels.txt. The two files can disagree about a code, so a row's codes are the one file's view. Measured by this site's build over this release on 2026-09-09: of the 138,908 human pathway-gene pairs both files place, 207 (0.149 per cent, over 47 genes) carry TAS in the Ensembl file where the NCBI rows carry IEA alone.

Reactome mapping files, the human rows for this pathway · Reactome release 97 · read 2026-09-09 · Reactome downloads"NCBI2Reactome_All_Levels.txt" and "Ensembl2Reactome_All_Levels.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.

03The hierarchy

Parents and children in this release's hierarchy

Parents

Synthesis of bile acids and bile saltsR-HSA-19210534 genes

Children

None: no pathway of this release's list names this one as a parent.

Reactome's hierarchy is a graph rather than a tree: a pathway can sit under more than one parent, and the gene counts are each pathway's own placements at every level under it, so a parent's count is not the sum of its children's.

Reactome, the human pathway list and hierarchy relationship file · Reactome release 97 · read 2026-09-09 · Reactome downloads"ReactomePathways.txt" and "ReactomePathwaysRelation.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.