Selective serotonin reuptake inhibitors, tricyclic antidepressants, various psychoactive drugs, as well as endogenous steroids and cannabinoid-like compounds are metabolized by the polymorphic cytochrome P450 2C19 (CYP2C19). Absence of this enzyme has been recently shown to associate with lower levels of depressive symptoms in human subjects. To investigate endogenous functions of CYP2C19 and its potential role in brain function, we have used a transgenic mouse model carrying the human CYP2C19 gene. Here, CYP2C19 was expressed in the developing fetal, but not adult brain and was associated with altered fetal brain morphology, where mice homozygous for the CYP2C19 transgenic insert had severely underdeveloped hippocampus and complete callosal agenesis and high neonatal lethality. CYP2C19 expression was also found in human fetal brain. In adult hemizygous mice we observed besides decreased hippocampal volume, an altered neuronal composition in the hippocampal dentate gyrus. Reduced hippocampal volumes have been reported in several psychiatric disorders, supporting the relevance of this model. Here we found that adult hemizygous CYP2C19 transgenic mice demonstrate behavior indicative of increased stress and anxiety based on four different tests. We hypothesize that expression of the CYP2C19 enzyme prenatally may affect brain development by metabolizing endogenous compounds influencing this development. Furthermore, CYP2C19 polymorphism may have a role in interindividual susceptibility for psychiatric disorders.

In vitro work shows CYP2C19 and CYP2D6 contribute to the metabolism of escitalopram to its primary metabolite, N-desmethylescitalopram. We report the effect of CYP2C19 and CYP2D6 genotypes on steady state morning concentrations of escitalopram and N-desmethylescitalopram and the ratio of this metabolite to the parent drug in 196 adult patients with depression in GENDEP, a clinical pharmacogenomic trial. Subjects who had one CYP2D6 allele associated with intermediate metabolizer phenotype and one associated with poor metabolizer (i.e. IM/PM genotypic category) had a higher mean logarithm escitalopram concentration than CYP2D6 extensive metabolizers (EMs) (p = 0.004). Older age was also associated with higher concentrations of escitalopram. Covarying for CYP2D6 and age, we found those homozygous for the CYP2C19*17 allele associated with ultrarapid metabolizer (UM) phenotype had a significantly lower mean escitalopram concentration (2-fold, p = 0.0001) and a higher mean metabolic ratio (p = 0.0003) than EMs, while those homozygous for alleles conferring the PM phenotype had a higher mean escitalopram concentration than EMs (1.55-fold, p = 0.008). There was a significant overall association between CYP2C19 genotypic category and escitalopram concentration (p = 0.0003; p = 0.0012 Bonferroni corrected). In conclusion, we have demonstrated an association between CYP2C19 genotype, including the CYP2C19*17 allele, and steady state escitalopram concentration.

Cytochrome P450 2C19 (CYP2C19) is a polymorphic enzyme active in the metabolism of for example diazepam and the antidepressants sertraline, citalopram, and escitalopram, whereby allelic variants cause increased (CYP2C19*17) or abolished (mainly CYP2C19*2) enzymatic activity in drug metabolism. In light of the importance of CYP2C19 in the metabolism of psychoactive substances we considered it of interest to investigate the relationship between CYP2C19 polymorphisms and depressive symptoms in 1,472 subjects of European ancestry (45-98 years old) from the Swedish Twin Registry. Depressive symptoms were assessed using the Center of Epidemiologic Studies Depression (CES-D) scale. We found that poor metabolizers lacking CYP2C19 activity (PMs, CYP2C19*2/*2) had significantly lower levels of depressive symptoms than extensive metabolizers (EMs, CYP2C19*1/*1) (P = 0.0018). The size of this difference was in the same range as that between subjects reported taking antidepressants (n = 104) and those without antidepressant treatment (P < 0.0001). Our results suggest for the first time that the CYP2C19 polymorphism might be of importance for depressive symptoms, as here shown for older European adults.

Cytochrome P450 2W1 (CYP2W1) is expressed predominantly in colorectal and also in hepatic tumors, whereas the levels are insignificant in the corresponding normal human adult tissues. CYP2W1 has been proposed as an attractive target for colorectal cancer (CRC) therapy by exploiting its ability to activate duocarmycin prodrugs to cytotoxic metabolites. However, its endogenous function, regulation and developmental pattern of expression remain unexplored. Here we report the CYP2W1 developmental expression in the murine and human gastrointestinal tissues. The gene expression in the colon and small intestine commence at early stages of embryonic life and is completely silenced shortly after the birth. Immunohistochemical analysis of human fetal colon revealed that CYP2W1 expression is restricted to the crypt cells. The silencing of CYP2W1 after birth correlates with the increased methylation of CpG-rich regions in both murine and human CYP2W1 genes. Analysis of CYP2W1 expression in the colon adenocarcinoma cell line HCC2998 revealed that the gene expression can be induced by e.g. the antitumor agent imatinib, linoleic acid and its derivatives. The imatinib mediated induction of CYP2W1 suggests an adjuvant therapy to treatment with duocarmycins that thus would involve induction of tumor CYP2W1 levels followed by the CYP2W1 activated duocarmycin prodrugs. Taken together these data strongly support further exploration of CYP2W1 as a specific drug target in CRC.

Environmental factors had a strong impact on the presence and course of MDD, but no evidence for gene-by-environment interaction was found.