Human microsomal cytochrome P450 2A6 (CYP2A6) contributes extensively to nicotine detoxication but also activates tobacco-specific procarcinogens to mutagenic products. The CYP2A6 structure shows a compact, hydrophobic active site with one hydrogen bond donor, Asn297, that orients coumarin for regioselective oxidation. The inhibitor methoxsalen effectively fills the active site cavity without substantially perturbing the structure. The structure should aid the design of inhibitors to reduce smoking and tobacco-related cancers.

Background/purpose The impact of the pandemic of COVID-19 has a certain influence on various walks of life around the world. Because of the pandemic of this novel coronavirus in terms of COVID-19, the social life global wide has been changed a lot. To keep the social distance between human being to prevent from being infected is the most important strategy for all the countries. Many dental schools have been locked down to minimize the spread out of this coronavirus infection. Close contact between human being are required for all those learning process in traditional dental education. Learning methods should be innovated to keep on the learning process but away from being infected for dental education during pandemic. The purpose of this manuscript is to exchange the information and experience of those dental educators from different countries to prepare for the future demand for dental education during pandemic. Materials and methods By means of three online symposiums, dental educators from different countries were invited to give presentation and discussion regarding to the information and experience in the innovation of dental education during the pandemic. Results The results showed that the impact of the pandemic of COVID-19 affects the dental education a lot. Intelligent technology has certain benefit for the learning process of dental education during the pandemic. Conclusion The impact of the pandemic of COVID-19 affects dental education a lot. The model of dental education should be innovated to suit different situations and novelty intelligent technology should be applied for future dental education.

The gene encoding cytochrome P-450 4A6 (CYP4A6) is transcriptionally activated by peroxisome proliferators. This response is dependent on a strong enhancer element (Z) and weaker elements (X and -27). The peroxisome proliferator response is mediated by the binding of heterodimers containing the peroxisome proliferator-activated receptor alpha (PPAR alpha) and the retinoid X receptor alpha (RXR alpha) to these elements. These peroxisome proliferator response elements (PPREs) contain imperfect direct repeats of the nuclear receptor consensus recognition sequence with a spacing of one nucleotide (DR1) (AGGTCA N AGGTCA). This DR1 motif is seen in the binding sites for other nuclear receptor complexes, such as ARP-1, HNF-4, and RXR alpha homodimers. Mutational analysis of the Z element reveals that the DR1 motif is required for the transcriptional activation of the CYP4A6 gene by peroxisome proliferators; however, deletion of sequences immediately upstream of this motif also abolishes this response. Oligonucleotides corresponding to truncated and mutated Z elements were assayed by gel retardation for binding to RXR alpha, PPAR alpha, and ARP-1. Deletions or mutations within six nucleotides 5' of the DR1 motif dramatically diminish PPAR alpha.RXR alpha binding without reducing the binding of either RXR alpha or ARP-1 homodimers, whereas mutation or deletion of the core DR1 sequences abolishes the binding of PPAR alpha.RXR alpha heterodimers and of RXR alpha or ARP-1 homodimers. Thus, the DR1 motif in the Z element is not sufficient to constitute a PPRE. Moreover, the binding of PPAR alpha.RXR alpha to the Z element requires sequences immediately 5' of the DR1. These sequences are conserved in natural PPREs and promote binding of PPAR alpha.RXR alpha heterodimers in preference to potential competitors such as ARP-1 and RXR alpha.

Cytochromes P450 of the CYP2C and CYP4A gene subfamilies metabolize arachidonic acid to 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) and to 19-and 20-hydroxyeicosatetraenoic acids (HETEs), respectively. Abundant functional studies indicate that EETs and HETEs display powerful and often opposing biological activities as mediators of ion channel activity and regulators of vascular tone and systemic blood pressures. Incubation of 8,9-, 11,12-, and 14,15-EETs with microsomal and purified forms of rat CYP4A isoforms led to rapid NADPH-dependent metabolism to the corresponding 19-and 20-hydroxylated EETs. Comparisons of reaction rates and catalytic efficiency with those of arachidonic and lauric acids showed that EETs are one of the best endogenous substrates so far described for rat CYP4A isoforms. CYP4A1 exhibited a preference for 8,9-EET, whereas CYP4A2, CYP4A3, and CYP4A8 preferred 11,12-EET. In general, the closer the oxido ring is to the carboxylic acid functionality, the higher the rate of EET metabolism and the lower the regiospecificity for the EET -carbon. Analysis of cis-parinaric acid displacement from the ligand-binding domain of the human peroxisome proliferator-activated receptor-␣ showed that -hydroxylated 14,15-EET bound to this receptor with high affinity (K i ‫؍‬ 3 ؎ 1 nM). Moreover, at 1 M, the -alcohol of 14,15-EET or a 1:4 mixture of the -alcohols of 8,9-and 11,12-EETs activated human and mouse peroxisome proliferator-activated receptor-␣ in transient transfection assays, suggesting a role for them as endogenous ligands for these orphan nuclear receptors.Cytochromes P450 of the CYP4A gene subfamily are structurally and functionally conserved fatty-acid hydroxylases that are expressed in most mammalian tissues, including rat and human kidney and liver (1-7). These enzymes are selective for the /-1-hydroxylation of saturated and unsaturated fatty acids (1-7) and lack known roles in drug metabolism. The expression of some CYP4A isoforms is under the control of the peroxisome proliferator-activated receptor-␣ (PPAR␣) 1 (8 -13) and regulated by a variety of physiological and pathophysiological stimuli, including dietary fatty acids, hormones, diabetes, and starvation (9 -13). Interest in the molecular and functional properties of these enzymes has been stimulated by the demonstration of their role in the /-1-hydroxylation of arachidonic acid (AA) (4 -7) and the powerful biological activities of 19-and 20-hydroxyeicosatetraenoic acids (HETEs) as modulators of renal ion fluxes and vasoactivity (14 -18). Based on biochemical and functional correlates of CYP4A renal expression, 20-HETE biosynthesis, and the onset of systemic high blood pressure in the SHR/WKY rat model of spontaneous hypertension, a pro-hypertensive role for 20-HETE and CYP4A isoforms was proposed (14).The cytochrome P450 AA epoxygenase catalyzes the in vivo regio-and enantioselective metabolism of AA to epoxyeicosatrienoic acids (EETs) (16). Studies with microsomal and/or purified cytochrome P450 preparations showed tha...

In mice and other sensitive species, PPAR␣ mediates the induction of mitochondrial, microsomal, and peroxisomal fatty acid oxidation, peroxisome proliferation, liver enlargement, and tumors by peroxisome proliferators. In order to identify PPAR␣-responsive human genes, HepG2 cells were engineered to express PPAR␣ at concentrations similar to mouse liver. This resulted in the dramatic induction of mRNAs encoding the mitochondrial HMG-CoA synthase and increases in fatty acyl-CoA synthetase (3-8-fold) and carnitine palmitoylCoA transferase IA (2-4-fold) mRNAs that were dependent on PPAR␣ expression and enhanced by exposure to the PPAR␣ agonist Wy14643. A PPAR response element was identified in the proximal promoter of the human HMG-CoA synthase gene that is functional in its native context. These data suggest that humans retain a capacity for PPAR␣ regulation of mitochondrial fatty acid oxidation and ketogenesis. Human liver is refractory to peroxisome proliferation, and increased expression of mRNAs for the peroxisomal fatty acyl-CoA oxidase, bifunctional enzyme, or thiolase, which accompanies peroxisome proliferation in responsive species, was not evident following Wy14643 treatment of cells expressing elevated levels of PPAR␣. Additionally, no significant differences were seen for the expression of apolipoprotein AI, AII, or CIII; medium chain acyl-CoA dehydrogenase; or stearoyl-CoA desaturase mRNAs.