CYP26B1 and its implications in lymphangiogenesis: Literature review and study of rare variants in two families.

CYP26B1 is a member of the cytochrome P450 family and is responsible for the break-down of retinoic acid for which appropriate levels are important for normal development of the cardiovascular and lymphatic systems. In a cohort of 235 patients with lymphatic malformations, we performed genetic testing for the CYP26B1 gene. These probands had previously tested negative for known lymphedema genes. We identified two heterozygous missense CY-P26B1 variants in two patients. Our bioinformatic study suggested that alterations caused by these variants have no major effect on the overall stability of CYP26B1 protein structure. Balanced levels of retinoic acid maintained by CYP26B1 are crucial for the lymphatic system. We identified that CYP26B1 could be involved in predisposition for lymphedema. We propose that CYP26B1 be further explored as a new candidate gene for genetic testing of lymphedema patients.

Biallelic mutations in CYP26B1: A differential diagnosis for Pfeiffer and Antley-Bixler syndromes.

Recently, a newly identified autosomal recessive skeletal dysplasia was described characterized by calvarial abnormalities (including cranium bifidum, coronal, and lambdoid synostosis), oligodactyly, femoral bowing, narrow thorax, small pelvic bones, and radiohumeral synostosis. In the two families described, a more severe phenotype led to in utero lethality in three siblings while in a single patient in a second family the phenotype was sufficiently mild to allow survival to 5 months of age. The disorder is caused by biallelic missense mutations in CYP26B1, which encodes for a cytochrome P450 enzyme responsible for the catabolism of retinoic acid in a temporally and spatially restricted fashion during embryonic development. Here, we provide the third family affected by the disorder and the first affected individual to survive beyond infancy. This woman homozygous for c.1303G>A; p.(Gly435Ser) in CYP26B1, which was associated with multisutural synostosis, radiohumeral synostosis, normal bone mineral density, and apparent intellectual disability, a phenotype with significant similarities to Antley-Bixler and Pfeiffer syndromes. © 2016 Wiley Periodicals, Inc.

9-cis ß-Carotene Increased Cholesterol Efflux to HDL in Macrophages.

Cholesterol efflux from macrophages is a key process in reverse cholesterol transport and, therefore, might inhibit atherogenesis. 9-cis-ß-carotene (9-cis-ßc) is a precursor for 9-cis-retinoic-acid (9-cis-RA), which regulates macrophage cholesterol efflux. Our objective was to assess whether 9-cis-ßc increases macrophage cholesterol efflux and induces the expression of cholesterol transporters. Enrichment of a mouse diet with ßc from the alga Dunaliella led to ßc accumulation in peritoneal macrophages. 9-cis-ßc increased the mRNA levels of CYP26B1, an enzyme that regulates RA cellular levels, indicating the formation of RA from ßc in RAW264.7 macrophages. Furthermore, 9-cis-ßc, as well as all-trans-ßc, significantly increased cholesterol efflux to high-density lipoprotein (HDL) by 50% in RAW264.7 macrophages. Likewise, food fortification with 9-cis-ßc augmented cholesterol efflux from macrophages ex vivo. 9-cis-ßc increased both the mRNA and protein levels of ABCA1 and apolipoprotein E (APOE) and the mRNA level of ABCG1. Our study shows, for the first time, that 9-cis-ßc from the diet accumulates in peritoneal macrophages and increases cholesterol efflux to HDL. These effects might be ascribed to transcriptional induction of ABCA1, ABCG1, and APOE. These results highlight the beneficial effect of ßc in inhibition of atherosclerosis by improving cholesterol efflux from macrophages.

Direct protein-protein interactions and substrate channeling between cellular retinoic acid binding proteins and CYP26B1.

Cellular retinoic acid binding proteins (CRABPs) bind all-trans-retinoic acid (atRA) tightly. This study aimed to determine whether atRA is channeled directly to cytochrome P450 (CYP) CYP26B1 by CRABPs, and whether CRABPs interact directly with CYP26B1. atRA bound to CRABPs (holo-CRABP) was efficiently metabolized by CYP26B1. Isotope dilution experiments showed that delivery of atRA to CYP26B1 in solution was similar with or without CRABP. Holo-CRABPs had higher affinity for CYP26B1 than free atRA, but both apo-CRABPs inhibited the formation of 4-OH-RA by CYP26B1. Similar protein-protein interactions between soluble binding proteins and CYPs may be important for other lipophilic CYP substrates.

Improved Homology Model of the Human all-trans Retinoic Acid Metabolizing Enzyme CYP26A1.

A new CYP26A1 homology model was built based on the crystal structure of cyanobacterial CYP120A1. The model quality was examined for stereochemical accuracy, folding reliability, and absolute quality using a variety of different bioinformatics tools. Furthermore, the docking capabilities of the model were assessed by docking of the natural substrate all-trans-retinoic acid (atRA), and a group of known azole- and tetralone-based CYP26A1 inhibitors. The preferred binding pose of atRA suggests the (4S)-OH-atRA metabolite production, in agreement with recently available experimental data. The distances between the ligands and the heme group iron of the enzyme are in agreement with corresponding distances obtained for substrates and azole inhibitors for other cytochrome systems. The calculated theoretical binding energies agree with recently reported experimental data and show that the model is capable of discriminating between natural substrate, strong inhibitors (R116010 and R115866), and weak inhibitors (liarozole, fluconazole, tetralone derivatives).