Biochemical and Biophysical Research Communications
CYP2D7 splice variants in human liver and brain: Does CYP2D7 encode functional protein?☆
Section snippets
Methods
Source of DNA and RNA. Tissue samples were obtained through NICHD-supported tissue retrieval programs, the University of Maryland Brain and Tissue Bank for Developmental Disorders (Baltimore, MD), and the Central Laboratory for Human Embryology at the University of Washington (Seattle, WA). RNA from 26 liver specimens (n = 3, prenatal; n = 23, postnatal) was used for the study. Of six subjects, brain tissue was also available (n = 3, prenatal; n = 3 postnatal). The use of these tissues was approved by
Cloning and identification of splice variants
Amplification of full-length CYP2D7 and CYP2D6 cDNA from liver and brain revealed multiple PCR products (Fig. 1). While fragments larger than full-length cDNA were visible in all subjects for liver, a shift towards larger bands (>2 kb) was especially evident in brain. In these latter cases, almost all amplicons were considerably larger than the expected 1.6 kb transcript. Since these initial results confirmed the existence of numerous alternative splice products, full-length liver and brain cDNA
Discussion
A recent report describing a functional CYP2D7 protein expressed in brain with kinetic characteristics distinct from those of CYP2D6 offers promise for novel therapeutic strategies targeting opiate receptors in the treatment of pain [3]. Other potential applications can be envisioned within the context of drug abuse and other areas where a role for CYP2D6 involvement is suggested or implied, such as the serotonin salvage pathway [2] and personality traits [19]. Moreover, the presence of
Acknowledgments
We gratefully acknowledge the technical assistance of Darren W. Baker and Liliane Ndjountché.
References (24)
- et al.
A frameshift mutation and alternate splicing in human brain generate a functional form of the pseudogene cytochrome P4502D7 that demethylates codeine to morphine
J. Biol. Chem.
(2004) - et al.
Discriminative quantification of cytochrome P4502D6 and 2D7/8 pseudogene expression by TaqMan real-time reverse transcriptase polymerase chain reaction
Anal. Biochem.
(2002) - et al.
Alternative splicing of CYP2D mRNA in human breast tissue
Arch. Biochem. Biophys.
(1997) - et al.
Inter-individual variation of several cytochrome P450 2D6 splice variants in human liver
Biochem. Biophys. Res. Commun.
(2005) - et al.
Ultrarapid metabolizers of debrisoquine: characterization and PCR-based detection of alleles with duplication of the CYP2D6 gene
FEBS Lett.
(1996) - et al.
Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response
Mol. Psychiatry
(2004) - et al.
Screening for endogenous substrates reveals that CYP2D6 is a 5-methoxyindolethylamine O-demethylase
Pharmacogenetics
(2003) - et al.
The human debrisoquine 4-hydroxylase (CYP2D) locus: sequence and identification of the polymorphic CYP2D6 gene, a related gene, and a pseudogene
Am. J. Hum. Genet.
(1989) - et al.
Characterization of the common defect in humans deficient in debrisoquin metabolism
Nature
(1988) - et al.
Comparison of CYP2D messenger RNA splice variant profiles in human lung tumors and normal tissues
Cancer Res.
(1997)
Analysis of CYP2D6 expression in human lung: implications for the association between CYP2D6 activity and susceptibility to lung cancer
Pharmacogenetics
Only truncated, not complete cytochrome P450 2D6 RNA transcript and no detectable enzyme activity are expressed in human lymphocytes
Drug Metab. Dispos.
Cited by (30)
Cytochrome P450 enzymes in drug metabolism: Regulation of gene expression, enzyme activities, and impact of genetic variation
2013, Pharmacology and TherapeuticsCitation Excerpt :A recent quantitative comparison of hepatic CYP2D6 protein by Western blot and mass spectrometric analysis demonstrated comparability of the results which ranged from undetectable in genetic PMs up to ~70 pmol/mg of microsomal protein in carriers of three alleles (Langenfeld et al., 2009). CYP2D6 and the CYP2D7 pseudogene are found at low mRNA levels in most extrahepatic tissues (Table 2), and expression of protein has been shown in the gastrointestinal tract (Glaeser et al., 2005) and in different areas of the human brain (Table 2; Siegle et al., 2001; Miksys et al., 2002; Gaedigk et al., 2005; Dutheil et al., 2009; Ferguson & Tyndale, 2011). At the RNA level, CYP2D6 expression is characterized by the occurrence of numerous splice variants.
Cytostatic drugs in infants: A review on pharmacokinetic data in infants
2012, Cancer Treatment ReviewsCitation Excerpt :Based on the discrepancies of protein content and m-RNA expression in children it is suggested that at younger age more variants appear. This indicates that the findings of Treluyer et al. do reflect expression of CYP2D6 m-RNA, but merely reflect activity.65,66 In relation to cancer treatment in childhood, CYP2D6 might in the future be important, since it is involved, as CYP3A4 is, in the metabolism of the EGFR-inhibitor gefitinib (Iressa®).
The ontogeny of drug metabolism enzymes and implications for adverse drug events
2008, Pharmacology and TherapeuticsXenobiotic metabolizing enzymes in the central nervous system: Contribution of cytochrome P450 enzymes in normal and pathological human brain
2008, BiochimieCitation Excerpt :Indeed, Pai et al. showed that the CYP2D7 brain-specific protein, corresponding to a functional splice variant, metabolizes codeine to morphine with greater efficiency than CYP2D6, suggesting the existence of tissue-specific isoforms, particularly in brain, to mediate selective metabolism and to generate active drugs [72]. However, a more recent study did not confirm the existence of such functional CYP2D7 enzyme in brain [73]. Altogether, since the presence of CYPs in the central nervous system has been proven and, as the brain is the target of centrally active drugs, its expression may be particularly important in determining an individual response to centrally acting substances [11].
Cytochrome P450-catalyzed pathways in human brain: Metabolism meets pharmacology or old drugs with new mechanism of action?
2007, Pharmacology and TherapeuticsReply
2006, Clinical Pharmacology and Therapeutics
- ☆
This work was supported by RO1 ES10855-04 from the National Institute of Environmental Health Sciences.