2-Hydroxy-4-oxopentanoic acid is found in alcoholic beverages. 2-Hydroxy-4-oxopentanoic acid is formed in beer wort fermentation Alitretinoin (9-<i>cis</i>-retinoic acid) is a naturally-occurring endogenous retinoid indicated for topical treatment of cutaneous lesions in patients with AIDS-related Kaposi's sarcoma. Alitretinoin inhibits the growth of Kaposi's sarcoma (KS) cells <i>in vitro</i>. Retinoic acid is the oxidized form of Vitamin A. It functions in determining position along embryonic anterior/posterior axis in chordates. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. Retinoic acid acts by binding to heterodimers of the retinoic acid receptor (RAR) and the retinoid X receptor (RXR), which then bind to retinoic acid response elements (RAREs) in the regulatory regions of direct targets (including Hox genes), thereby activating gene transcription. Retinoic acid receptors mediate transcription of different sets of genes of cell differentiation, thus it also depends on the target cells. 2-Hydroxy-4-oxopentanoic acid is one of the target genes is the gene of the retinoic acid receptor itself which occurs during positive regulation. Control of retinoic acid levels is maintained by a suite of proteins. Retinoic acid is the oxidized form of Vitamin A. It functions in determining position along embryonic anterior/posterior axis in chordates. It acts through Hox genes, which ultimately controls anterior/posterior patterning in early developmental stages (PMID: 17495912). It is an important regulator of gene expression during growth and development, and in neoplasms. Tretinoin, also known as retinoic acid and derived from maternal vitamin A, is essential for normal growth and embryonic development. 2-Hydroxy-4-oxopentanoic acid is an excess of tretinoin can be teratogenic. It is used in the treatment of psoriasis; acne vulgaris; and several other skin diseases. It has also been approved for use in promyelocytic leukemia (leukemia, promyelocytic, acute).