Effect of two mutations of human CYP1B1, G61E and R469W, on stability and endogenous steroid substrate metabolism

Estrogen dysregulation, intraocular pressure, and glaucoma risk

Characterized by optic nerve atrophy due to retinal ganglion cell (RGC) death, glaucoma is the leading cause of irreversible blindness worldwide. Of the major risk factors for glaucoma (age, ocular hypertension, and genetics), only elevated intraocular pressure (IOP) is modifiable, which is largely regulated by aqueous humor outflow through the trabecular meshwork. Glucocorticoids such as dexamethasone have long been known to elevate IOP and lead to glaucoma. However, several recent studies have reported that steroid hormone estrogen levels inversely correlate with glaucoma risk, and that variants in estrogen signaling genes have been associated with glaucoma. As a result, estrogen dysregulation may contribute to glaucoma pathogenesis, and estrogen signaling may protect against glaucoma. The mechanism for estrogen-related protection against glaucoma is not completely understood but likely involves both regulation of IOP homeostasis and neuroprotection of RGCs. Based upon its known activities, estrogen signaling may promote IOP homeostasis by affecting extracellular matrix turnover, focal adhesion assembly, actin stress fiber formation, mechanosensation, and nitric oxide production. In addition, estrogen receptors in the RGCs may mediate neuroprotective functions. As a result, the estrogen signaling pathway may offer a therapeutic target for both IOP control and neuroprotection. This review examines the evidence for a relationship between estrogen and IOP and explores the possible mechanisms by which estrogen maintains IOP homeostasis.

Challenges and Opportunities in P450 Research on the Eye

Of the 57 cytochrome P450 enzymes found in humans, at least 30 have ocular tissues as an expression site. Yet knowledge of the roles of these P450s in the eye is limited, in part because only very few P450 laboratories expanded their research interests to studies of the eye. Hence the goal of this review is to bring attention of the P450 community to the eye and encourage more ocular studies. This review is also intended to be educational for eye researchers and encourage their collaborations with P450 experts. The review starts with a description of the eye, a fascinating sensory organ, and is followed by sections on ocular P450 localizations, specifics of drug delivery to the eye, and individual P450s, which are grouped and presented based on their substrate preferences. In sections describing individual P450s, available eye-relevant information is summarized and concluded by the suggestions on the opportunities in ocular studies of the discussed enzymes. Potential challenges are addressed as well. The conclusion section outlines several practical suggestions on how to initiate eye-related research. SIGNIFICANCE STATEMENT: This review focuses on the cytochrome P450 enzymes in the eye to encourage their ocular investigations and collaborations between P450 and eye researchers.

The molecular genetics of anterior segment dysgenesis

Anterior segment dysgenesis is a severe developmental eye disorder that leads to blindness in children. The exact mechanisms underlying this condition remain elusive. Recently, an increasing amount of studies have focused on genes and signal transduction pathways that affect anterior segment dysgenesis;these factors include transcription factors, developmental regulators, extracellular matrix genes, membrane-related proteins, cytoskeleton proteins and other associated genes. To date, dozens of gene variants have been found to cause anterior segment dysgenesis. However, there is still a lack of effective treatments. With a broader and deeper understanding of the molecular mechanisms underlying anterior segment development in the future, gene editing technology and stem cell technology may be new treatments for anterior segment dysgenesis. Further studies on the mechanisms of how different genes influence the onset and progression of anterior segment dysgenesis are still needed.

Animal Model Contributions to Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is an ocular disease characterized by congenital anterior segmental maldevelopment with progressive optic nerve degeneration. Certain genes, such as cytochrome P450 family 1 subfamily B member 1 and latent TGF-β-binding protein 2, are involved in the pathogenesis of PCG, but the exact pathogenic mechanism has not yet been fully elucidated. There is an urgent need to determine the etiology and pathophysiology of PCG and develop new therapeutic methods to stop disease progression. Animal models can simulate PCG and are essential to study the pathogenesis and treatment of PCG. Various animal species have been used in the study of PCG, including rabbits, rats, mice, cats, zebrafish, and quails. These models are formed spontaneously or by combining with genetic engineering technology. The focus of the present study is to review the characteristics and potential applications of animal models in PCG and provide new approaches to understand the mechanism and develop new treatment strategies for patients with PCG.

Geographical Variability in CYP1B1 Mutations in Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is a rare type of glaucoma that is inherited in an autosomal recessive manner. PCG can lead to blindness if not detected early in children aged 3 or younger. PCG varies in presentation among various populations, where disease presentation and disease severity vary by mutation. The most common gene implicated in PCG is cytochrome p450 1B1 (CYP1B1). Here, we sought to review the literature for mutations in CYP1B1 and their presentation among different populations. Areas of interest include recent findings on disease presentation and potential implications on our understanding of PCG pathophysiology.

Prenatal diagnosis of primary congenital glaucoma and histopathological features in a fetal globe with cytochrome p4501B1 mutations

BACKGROUND/OBJECTIVES

This study aims to report the developmental and histopathological features of ocular tissues from an electively aborted human fetus with mutations in cytochrome p4501B1, and thus predisposed to primary congenital glaucoma in comparison to an age-matched healthy fetal globe.

SUBJECTS/METHODS

Both eyes of two 17-week gestational aged fetuses, the first with CYP1B1 mutations and the second as healthy control fetus, were studied. Hematoxylin and eosin, Periodic acid-Schiff, Gomori's trichrome, and Verhoeff-Van Gieson staining protocols in addition to immunohistochemistry staining using anti-cytochrome p4501B1, anti-fibrillin-1, and anti-4-hydroxy-2-nonenal antibodies, as primary antibodies, were performed to assess the effect of the mutations on tissue development, cytochrome p4501B1 protein expression, extracellular matrix structure, and oxidative stress in the developing fetus eye. Quantitative analyses were performed using ImageJ software. Student's t-test was used for statistical analysis and P-values <0.05 were considered as significant.

RESULTS

Delayed development in ocular tissues, decreased expression of cytochrome p4501B1 protein, irregular extracellular matrix structure, and increased oxidative stress biomarker were evident in the ocular tissues of the fetus with cytochrome p4501B1 mutations as compared to a normal globe from an age-matched fetus.

CONCLUSION

To the best of our knowledge, this is the first report of prenatal diagnosis of primary congenital glaucoma. We also describe histopathological changes in the primary congenital glaucoma-affected globes revealing the effect of cytochrome p4501B1 deficiency on ocular tissues during early fetal development contributing to the glaucoma phenotype.

Identification of Estrogen Signaling in a Prioritization Study of Intraocular Pressure-Associated Genes

Elevated intraocular pressure (IOP) is the only modifiable risk factor for primary open-angle glaucoma (POAG). Herein we sought to prioritize a set of previously identified IOP-associated genes using novel and previously published datasets. We identified several genes for future study, including several involved in cytoskeletal/extracellular matrix reorganization, cell adhesion, angiogenesis, and TGF-β signaling. Our differential correlation analysis of IOP-associated genes identified 295 pairs of 201 genes with differential correlation. Pathway analysis identified β-estradiol as the top upstream regulator of these genes with ESR1 mediating 25 interactions. Several genes (i.e., EFEMP1, FOXC1, and SPTBN1) regulated by β-estradiol/ESR1 were highly expressed in non-glaucomatous human trabecular meshwork (TM) or Schlemm’s canal (SC) cells and specifically expressed in TM/SC cell clusters defined by single-cell RNA-sequencing. We confirmed ESR1 gene and protein expression in human TM cells and TM/SC tissue with quantitative real-time PCR and immunofluorescence, respectively. 17β-estradiol was identified in bovine, porcine, and human aqueous humor (AH) using ELISA. In conclusion, we have identified estrogen receptor signaling as a key modulator of several IOP-associated genes. The expression of ESR1 and these IOP-associated genes in TM/SC tissue and the presence of 17β-estradiol in AH supports a role for estrogen signaling in IOP regulation.

CYP1B1 as a therapeutic target in cardio-oncology

Cardiovascular complications have been frequently reported in cancer patients and survivors, mainly because of various cardiotoxic cancer treatments. Despite the known cardiovascular toxic effects of these treatments, they are still clinically used because of their effectiveness as anti-cancer agents. In this review, we discuss the growing body of evidence suggesting that inhibition of the cytochrome P450 1B1 enzyme (CYP1B1) can be a promising therapeutic strategy that has the potential to prevent cancer treatment-induced cardiovascular complications without reducing their anti-cancer effects. CYP1B1 is an extrahepatic enzyme that is expressed in cardiovascular tissues and overexpressed in different types of cancers. A growing body of evidence is demonstrating a detrimental role of CYP1B1 in both cardiovascular diseases and cancer, via perturbed metabolism of endogenous compounds, production of carcinogenic metabolites, DNA adduct formation, and generation of reactive oxygen species (ROS). Several chemotherapeutic agents have been shown to induce CYP1B1 in cardiovascular and cancer cells, possibly via activating the Aryl hydrocarbon Receptor (AhR), ROS generation, and inflammatory cytokines. Induction of CYP1B1 is detrimental in many ways. First, it can induce or exacerbate cancer treatment-induced cardiovascular complications. Second, it may lead to significant chemo/radio-resistance, undermining both the safety and effectiveness of cancer treatments. Therefore, numerous preclinical studies demonstrate that inhibition of CYP1B1 protects against chemotherapy-induced cardiotoxicity and prevents chemo- and radio-resistance. Most of these studies have utilized phytochemicals to inhibit CYP1B1. Since phytochemicals have multiple targets, future studies are needed to discern the specific contribution of CYP1B1 to the cardioprotective and chemo/radio-sensitizing effects of these phytochemicals.

The Ocular Neural Crest: Specification, Migration, and Then What?

During vertebrate embryonic development, a population of dorsal neural tube-derived stem cells, termed the neural crest (NC), undergo a series of morphogenetic changes and extensive migration to become a diverse array of cell types. Around the developing eye, this multipotent ocular NC cell population, called the periocular mesenchyme (POM), comprises migratory mesenchymal cells that eventually give rise to many of the elements in the anterior of the eye, such as the cornea, sclera, trabecular meshwork, and iris. Molecular cell biology and genetic analyses of congenital eye diseases have provided important information on the regulation of NC contributions to this area of the eye. Nevertheless, a complete understanding of the NC as a contributor to ocular development remains elusive. In addition, positional information during ocular NC migration and the molecular pathways that regulate end tissue differentiation have yet to be fully elucidated. Further, the clinical challenges of ocular diseases, such as Axenfeld-Rieger syndrome (ARS), Peters anomaly (PA) and primary congenital glaucoma (PCG), strongly suggest the need for better treatments. While several aspects of NC evolution have recently been reviewed, this discussion will consolidate the most recent current knowledge on the specification, migration, and contributions of the NC to ocular development, highlighting the anterior segment and the knowledge obtained from the clinical manifestations of its associated diseases. Ultimately, this knowledge can inform translational discoveries with potential for sorely needed regenerative therapies.

Girl Power in Glaucoma: The Role of Estrogen in Primary Open Angle Glaucoma

Estrogen is essential in maintaining various physiological features in women, and a decline in estrogen levels are known to give rise to numerous unfortunate symptoms associated with menopause. To alleviate these symptoms hormone replacement therapy with estrogen is often used, and has been shown to be fruitful in improving quality of life in women suffering from postmenopausal discomforts. An often forgotten condition associated with menopause is the optic nerve disorder, glaucoma. Thus, estrogen may also have an impact in maintaining the retinal ganglion cells (RGCs), which make up the optic nerve, thereby preventing glaucomatous neurodegeneration. This review aims to provide an overview of possible associations of estrogen and the glaucoma subtype, primary open-angle glaucoma (POAG), by evaluating the current literature through a PubMed-based literature search. Multiple in vitro and in vivo studies of RGC protection, as well as clinical and epidemiological data concerning the well-defined retinal neurodegenerative disorder POAG have been reviewed. Over all, deficiencies in retinal estrogen may potentially instigate RGC loss, visual disability, and eventual blindness. Estrogen replacement therapy may therefore be a beneficial future treatment. However, more studies are needed to confirm the relevance of estrogen in glaucoma prevention.

Investigation of CYP1B1 Gene Involvement in Primary Congenital Glaucoma in Iraqi Children

PURPOSE

Primary congenital glaucoma (PCG) is a severe type of glaucoma that occurs early in life. PCG is usually inherited in an autosomal recessive pattern. Cytochrome P450, family 1, subfamily B, polypeptide 1 (CYP1B1) gene is reported to be PCG-related gene. It codes for the CYP1B1 enzyme which is considered as phase I xenobiotic-metabolizing enzyme and its function is related to the eye oxidative homeostasis and correspondingly to the normal development of the eye. This is the first genetic study in Iraq that investigates the CYP1B1 polymorphisms behind the PCG disease.

METHODS

Genomic DNA was extracted from the whole blood of 100 unrelated Iraqi PCG patients and 100 healthy children, all of them were aged between 1 month and 3 years. All the coding sequence of CYP1B1 gene was amplified using polymerase chain reaction; restriction fragment length polymorphism was used to follow G61E and E229K mutations. Direct sequencing was performed to screen for other mutations.

RESULTS

CYP1B1 mutations were identified in 78 (78%) of the patients. We detected a total of eight mutations: Four missense mutations (c.182G>A, c.685G>A, g.6813G>A, and g.6705G>A), one silence mutation (D449D) and three insertions (g.10068ins10069, g.10138ins10139, and g.10191ins10192). Five mutations (g.6813G>A, g.6705G>A, g.10068ins10069, g.10138ins10139, and g.10191ins10192) are novel. G61E is the only mutation that was detected in patients merely.

CONCLUSIONS

CYP1B1 mutation (G61E) is considered as PCG-related allele in the Iraqi population.

Mutational analysis of the CYP1B1 gene in Pakistani primary congenital glaucoma patients: Identification of four known and a novel causative variant at the 3' splice acceptor site of intron 2

Primary congenital glaucoma (PCG) causes blindness in early age. It has an autosomal recessive pattern of inheritance, hence is more prevalent in populations with frequent consanguineous marriages that occur in the Pakistani population. Mutations in the CYP1B1 gene are commonly associated with PCG. The aim of the present study was to identify genetic mutations in the CYP1B1 gene in PCG cases belonging to 38 Pakistani families. DNA was extracted using blood samples collected from all enrolled patients, their available unaffected family members and controls. Direct sequencing of the CYP1B1 gene revealed a novel 3' splice acceptor site causative variant segregating in an autosomal recessive manner in a large consanguineous family with four PCG-affected individuals. The novel variant was not detected in 93 ethnically matched controls. Furthermore, four already reported mutations, including p.G61E, p.R355X, p.R368H, and p.R390H were also detected in patients belonging to nine different families. All identified causative variants were evaluated by computational programs, that is, SIFT, PolyPhen-2, and MutationTaster. Pathogenicity of the novel splice site variant identified in this study was analyzed by Human Splicing Finder and MaxEntScan. Ten out of 38 families with PCG had the disease due to CYP1B1 mutations, suggesting CYP1B1 was contributing to PCG in these Pakistani patients. Identification of this novel 3' splice acceptor site variant in intron 2 is the first report for the CYP1B1 gene contributing to genetic heterogeneity of disease.

Structure-Based Drug Design for Cytochrome P450 Family 1 Inhibitors

Cytochromes P450 are a class of metalloproteins which are responsible for electron transfer in a wide spectrum of reactions including metabolic biotransformation of endogenous and exogenous substrates. The superfamily of cytochromes P450 consists of families and subfamilies which are characterized by a specific structure and substrate specificity. Cytochromes P450 family 1 (CYP1s) play a distinctive role in the metabolism of drugs and chemical procarcinogens. In recent decades, these hemoproteins have been intensively studied with the use of computational methods which have been recently developed remarkably to be used in the process of drug design by the virtual screening of compounds in order to find agents with desired properties. Moreover, the molecular modeling of proteins and ligand docking to their active sites provide an insight into the mechanism of enzyme action and enable us to predict the sites of drug metabolism. The review presents the current status of knowledge about the use of the computational approach in studies of ligand-enzyme interactions for CYP1s. Research on the metabolism of substrates and inhibitors of CYP1s and on the selectivity of their action is particularly valuable from the viewpoint of cancer chemoprevention, chemotherapy, and drug-drug interactions.

Primary congenital and developmental glaucomas

Glaucoma is the leading cause of irreversible blindness worldwide. Although most glaucoma patients are elderly, congenital glaucoma and glaucomas of childhood are also important causes of visual disability. Primary congenital glaucoma (PCG) is isolated, non-syndromic glaucoma that occurs in the first three years of life and is a major cause of childhood blindness. Other early-onset glaucomas may arise secondary to developmental abnormalities, such as glaucomas that occur with aniridia or as part of Axenfeld-Rieger syndrome. Congenital and childhood glaucomas have strong genetic bases and disease-causing mutations have been discovered in several genes. Mutations in three genes (CYP1B1, LTBP2, TEK) have been reported in PCG patients. Axenfeld-Rieger syndrome is caused by mutations in PITX2 or FOXC1 and aniridia is caused by PAX6 mutations. This review discusses the roles of these genes in primary congenital glaucoma and glaucomas of childhood.

Characterizing the "POAGome": A bioinformatics-driven approach to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a genetically, physiologically, and phenotypically complex neurodegenerative disorder. This study addressed the expanding collection of genes associated with POAG, referred to as the "POAGome." We used bioinformatics tools to perform an extensive, systematic literature search and compiled 542 genes with confirmed associations with POAG and its related phenotypes (normal tension glaucoma, ocular hypertension, juvenile open-angle glaucoma, and primary congenital glaucoma). The genes were classified according to their associated ocular tissues and phenotypes, and functional annotation and pathway analyses were subsequently performed. Our study reveals that no single molecular pathway can encompass the pathophysiology of POAG. The analyses suggested that inflammation and senescence may play pivotal roles in both the development and perpetuation of the retinal ganglion cell degeneration seen in POAG. The TGF-β signaling pathway was repeatedly implicated in our analyses, suggesting that it may be an important contributor to the manifestation of POAG in the anterior and posterior segments of the globe. We propose a molecular model of POAG revolving around TGF-β signaling, which incorporates the roles of inflammation and senescence in this disease. Finally, we highlight emerging molecular therapies that show promise for treating POAG.

Potential role of CYP1B1 in the development and treatment of metabolic diseases

Cytochrome P450 1B1 (CYP1B1), a member of CYP superfamily, is expressed in liver and extrahepatic tissues carries out the metabolism of numerous xenobiotics, including metabolic activation of polycyclic aromatic hydrocarbons. Surprisingly, CYP1B1 was also shown to be important in regulating endogenous metabolic pathways, including the metabolism of steroid hormones, fatty acids, melatonin, and vitamins. CYP1B1 and nuclear receptors including peroxisome proliferator-activated receptors (PPARs), estrogen receptor (ER), and retinoic acid receptors (RAR) contribute to the maintenance of the homeostasis of these endogenous compounds. Many natural flavonoids and synthetic stilbenes show inhibitory activity toward CYP1B1 expression and function, notably isorhamnetin and 2,4,3',5'-tetramethoxystilbene. Accumulating evidence indicates that modulation of CYP1B1 can decrease adipogenesis and tumorigenesis, and prevent obesity, hypertension, atherosclerosis, and cancer. Therefore, it may be feasible to consider CYP1B1 as a therapeutic target for the treatment of metabolic diseases.

Functional characterization of eight rare missense CYP1B1 variants involved in congenital glaucoma and their association with null genotypes

PURPOSE

To evaluate the function of eight missense CYP1B1 single nucleotide variants (SNVs) previously identified in patients with primary congenital glaucoma (PCG).

METHODS

The eight variants were obtained by site-directed mutagenesis and transiently expressed in human embryonic kidney 293-T (HEK-293T) cells. The catalytic activity, protein stability and subcellular localization of the different recombinant CYP1B1 variants were assessed in this cell line.

RESULTS

Six of the mutant CYP1B1 proteins (p.L89P, p.A106D, p.R390S, p.P437L, p.C470Y and S485F) showed catalytic activity values ranging from 0% to 4% of those of the wild-type protein and were considered null variants. The activity values of the two remaining variants (p.F123L and p.A237E) were close to 20% of that of the wild-type enzyme and were classified as hypomorphic variants. Reduced protein stability contributed partially to the decreased catalytic activity of two of the mutant enzymes (p.L89P and p.A106D). None of the CYP1B1 variants showed intracellular aggregation and they all displayed a normal subcellular localization in the endoplasmic reticulum, suggesting that they had folded into a wild-type-like structure. The enzymatic activity associated with the different genotypes in which these CYP1B1 variants were present was estimated to range from 0% to 10% of that of the wild-type genotype.

CONCLUSION

These results confirm the pathogenicity of the analysed missense CYP1B1 variants and further support the concept that either absent or very low CYP1B1 activity levels are the primary molecular defect involved in PCG pathogenesis.

Microfluidic array for simultaneous detection of DNA oxidation and DNA-adduct damage

Exposure to chemical pollutants and pharmaceuticals may cause health issues caused by metabolite-related toxicity. This paper reports a new microfluidic electrochemical sensor array with the ability to simultaneously detect common types of DNA damage including oxidation and nucleobase adduct formation. Sensors in the 8-electrode screen-printed carbon array were coated with thin films of metallopolymers osmium or ruthenium bipyridyl-poly(vinylpyridine) chloride (OsPVP, RuPVP) along with DNA and metabolic enzymes by layer-by-layer electrostatic assembly. After a reaction step in which test chemicals and other necessary reagents flow over the array, OsPVP selectively detects oxidized guanines on the DNA strands, and RuPVP detects DNA adduction by metabolites on nucleobases. We demonstrate array performance for test chemicals including 17β-estradiol (E2), its metabolites 4-hydroxyestradiol (4-OHE2), 2-hydroxyestradiol (2-OHE2), catechol, 2-nitrosotoluene (2-NO-T), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and 2-acetylaminofluorene (2-AAF). Results revealed DNA-adduct and oxidation damage in a single run to provide a metabolic-genotoxic chemistry screen. The array measures damage directly in unhydrolyzed DNA, and is less expensive, faster, and simpler than conventional methods to detect DNA damage. The detection limit for oxidation is 672 8-oxodG per 106 bases. Each sensor requires only 22 ng of DNA, so the mass detection limit is 15 pg (∼10 pmol) 8-oxodG.

The Aryl Hydrocarbon Receptor Relays Metabolic Signals to Promote Cellular Regeneration

While sensing the cell environment, the aryl hydrocarbon receptor (AHR) interacts with different pathways involved in cellular homeostasis. This review summarizes evidence suggesting that cellular regeneration in the context of aging and diseases can be modulated by AHR signaling on stem cells. New insights connect orphaned observations into AHR interactions with critical signaling pathways such as WNT to propose a role of this ligand-activated transcription factor in the modulation of cellular regeneration by altering pathways that nurture cellular expansion such as changes in the metabolic efficiency rather than by directly altering cell cycling, proliferation, or cell death. Targeting the AHR to promote regeneration might prove to be a useful strategy to avoid unbalanced disruptions of homeostasis that may promote disease and also provide biological rationale for potential regenerative medicine approaches.

Functional and Structural Analyses of CYP1B1 Variants Linked to Congenital and Adult-Onset Glaucoma to Investigate the Molecular Basis of These Diseases

Glaucoma, the leading cause of irreversible blindness, appears in various forms. Mutations in CYP1B1 result in primary congenital glaucoma (PCG) by an autosomal recessive mode of inheritance while it acts as a modifier locus for primary open angle glaucoma (POAG). We investigated the molecular basis of the variable phenotypes resulting from the defects in CYP1B1 by using subclones of 23 CYP1B1 mutants reported in glaucoma patients, in a cell based system by measuring the dual activity of the enzyme to metabolize both retinol and 17β-estradiol. Most variants linked to POAG showed low steroid metabolism while null or very high retinol metabolism was observed in variants identified in PCG. We examined the translational turnover rates of mutant proteins after the addition of cycloheximide and observed that the levels of enzyme activity mostly corroborated the translational turnover rate. We performed extensive normal mode analysis and molecular-dynamics-simulations-based structural analyses and observed significant variation of fluctuation in certain segmental parts of the mutant proteins, especially at the B-C and F-G loops, which were previously shown to affect the dynamic behavior and ligand entry/exit properties of the cytochrome P450 family of proteins. Our molecular study corroborates the structural analysis, and suggests that the pathologic state of the carrier of CYP1B1 mutations is determined by the allelic state of the gene. To our knowledge, this is the first attempt to dissect biological activities of CYP1B1 for correlation with congenital and adult onset glaucomas.

Glaucoma in iran and contributions of studies in iran to the understanding of the etiology of glaucoma

Epidemiologic and genetic/molecular research on glaucoma in Iran started within the past decade. A population-based study on the epidemiology of glaucoma in Yazd, a city in central Iran, revealed that 4.4% of studied individuals were affected with glaucoma: 1.6% with high tension primary open angle glaucoma (POAG), 1.6% with normal tension POAG, and 0.4% each with primary angle closure glaucoma (PACG) and pseudoexfoliation glaucoma (PEXG), and other types of secondary glaucoma. Two notable observations were the relatively high frequency of normal tension glaucoma cases (1.6%) and the large fraction of glaucoma affected individuals (nearly 90%) who were unaware of their condition. The first and most subsequent genetic studies on glaucoma in Iran were focused on primary congenital glaucoma (PCG) showing that cytochrome P450 1B1 (CYP1B1) is the cause of PCG in the majority of Iranian patients, many different CYP1B1 mutations are present among Iranian patients but only four mutations constitute the vast majority, and the origins of most mutations in the Iranians are identical by descent (IBD) with the same mutations in other populations. Furthermore, most of the PCG patients are from the northern and northwestern provinces of Iran. A statistically significant male predominance of PCG was observed only among patients without CYP1B1 mutations. Clinical investigations on family members of PCG patients revealed that CYP1B1 mutations exhibit variable expressivity, but almost complete penetrance. A great number of individuals harboring CYP1B1 mutations become affected with juvenile onset POAG. Screening of JOAG patients showed that an approximately equal fraction of the patients harbor CYP1B1 and (myocilin) MYOC mutations; MYOC is a well-known adult onset glaucoma causing gene. Presence of CYP1B1 mutations in JOAG patients suggests that in some cases, the two conditions may share a common etiology. Further genetic analysis of Iranian PCG patients led to identification of Latent-transforming growth factor beta-binding protein 2 (LTBP2) as a causative gene for both PCG and several diseases which are often accompanied by glaucomatous presentations, such as Weill-Marchesani syndrome 3 (WMS3). The findings on LTBP2 have contributed to recognize the importance of the extracellular matrix in pathways leading to glaucoma.

Regioselective hydroxylation of steroid hormones by human cytochromes P450

This article reviews in vitro metabolic activities [including Michaelis constants (Km), maximal velocities (Vmax) and Vmax/Km] and drug-steroid interactions [such as induction and cooperativity (activation)] of cytochromes P450 (P450 or CYP) in human tissues, including liver and adrenal gland, for 14 kinds of endogenous steroid compounds, including allopregnanolone, cholesterol, cortisol, cortisone, dehydroepiandrosterone, estradiol, estrone, pregnenolone, progesterone, testosterone and bile acids (cholic acid). First, we considered the drug-metabolizing P450s. 6β-Hydroxylation of many steroids, including cortisol, cortisone, progesterone and testosterone, was catalyzed primarily by CYP3A4. CYP1A2 and CYP3A4, respectively, are likely the major hepatic enzymes responsible for 2-/4-hydroxylation and 16α-hydroxylation of estradiol and estrone, steroids that can contribute to breast cancer risk. In contrast, CYP1A1 and CYP1B1 predominantly metabolized estrone and estradiol to 2- and 4-catechol estrogens, which are endogenous ultimate carcinogens if formed in the breast. Some metabolic activities of CYP3A4, including dehydroepiandrosterone 7β-/16α-hydroxylation, estrone 2-hydroxylation and testosterone 6β-hydroxylation, were higher than those for polymorphically expressed CYP3A5. Next, we considered typical steroidogenic P450s. CYP17A1, CYP19A1 and CYP27A1 catalyzed steroid synthesis, including hydroxylation at 17α, 19 and 27 positions, respectively. However, it was difficult to predict which hepatic drug-metabolizing P450 or steroidogenic P450 will be mainly responsible for metabolizing each steroid hormone in vivo based on these results. Further research is required on the metabolism of steroid hormones by various P450s and on prediction of their relative contributions to in vivo metabolism. The findings collected here provide fundamental and useful information on the metabolism of steroid compounds.

Ocular cytochrome P450s and transporters: roles in disease and endobiotic and xenobiotic disposition

Drug metabolism and transport processes in the liver, intestine and kidney that affect the pharmacokinetics and pharmacodynamics of therapeutic agents have been studied extensively. In contrast, comparatively little research has been conducted on these topics as they pertain to the eye. Recently, however, catalytic functions of ocular cytochrome P450 enzymes have gained increasing attention, in large part due to the roles of CYP1B1 and CYP4V2 variants in primary congenital glaucoma and Bietti's corneoretinal crystalline dystrophy, respectively. In this review, we discuss challenges to ophthalmic drug delivery, including Phase I drug metabolism and transport in the eye, and the role of three specific P450s, CYP4B1, CYP1B1 and CYP4V2 in ocular inflammation and genetically determined ocular disease.

Identification of estrogen target genes during zebrafish embryonic development through transcriptomic analysis

Estrogen signaling is important for vertebrate embryonic development. Here we have used zebrafish (Danio rerio) as a vertebrate model to analyze estrogen signaling during development. Zebrafish embryos were exposed to 1 µM 17β-estradiol (E2) or vehicle from 3 hours to 4 days post fertilization (dpf), harvested at 1, 2, 3 and 4 dpf, and subjected to RNA extraction for transcriptome analysis using microarrays. Differentially expressed genes by E2-treatment were analyzed with hierarchical clustering followed by biological process and tissue enrichment analysis. Markedly distinct sets of genes were up and down-regulated by E2 at the four different time points. Among these genes, only the well-known estrogenic marker vtg1 was co-regulated at all time points. Despite this, the biological functional categories targeted by E2 were relatively similar throughout zebrafish development. According to knowledge-based tissue enrichment, estrogen responsive genes were clustered mainly in the liver, pancreas and brain. This was in line with the developmental dynamics of estrogen-target tissues that were visualized using transgenic zebrafish containing estrogen responsive elements driving the expression of GFP (Tg(5xERE:GFP)). Finally, the identified embryonic estrogen-responsive genes were compared to already published estrogen-responsive genes identified in male adult zebrafish (Gene Expression Omnibus database). The expressions of a few genes were co-regulated by E2 in both embryonic and adult zebrafish. These could potentially be used as estrogenic biomarkers for exposure to estrogens or estrogenic endocrine disruptors in zebrafish. In conclusion, our data suggests that estrogen effects on early embryonic zebrafish development are stage- and tissue- specific.

Cyp1b1 mediates periostin regulation of trabecular meshwork development by suppression of oxidative stress

Mutation in CYP1B1 has been reported for patients with congenital glaucoma. However, the underlying mechanisms remain unknown. Here we show increased diurnal intraocular pressure (IOP) in Cyp1b1-deficient (Cyp1b1(-/-)) mice. Cyp1b1(-/-) mice presented ultrastructural irregular collagen distribution in their trabecular meshwork (TM) tissue along with increased oxidative stress and decreased levels of periostin (Postn). Increased levels of oxidative stress and decreased levels of Postn were also detected in human glaucomatous TM tissues. Furthermore, Postn-deficient mice exhibited TM tissue ultrastructural abnormalities similar to those of Cyp1b1(-/-) mice. Administration of the antioxidant N-acetylcysteine (NAC) restored structural abnormality of TM tissue in Cyp1b1(-/-) mice. In addition, TM cells prepared from Cyp1b1(-/-) mice exhibited increased oxidative stress, altered adhesion, and decreased levels of Postn. These aberrant cellular responses were reversed in the presence of NAC or by restoration of Cyp1b1 expression. Cyp1b1 knockdown or inhibition of CYP1B1 activity in Cyp1b1(+/+) TM cells resulted in a Cyp1b1(-/-) phenotype. Thus, metabolic activity of CYP1B1 contributes to oxidative homeostasis and ultrastructural organization and function of TM tissue through modulation of Postn expression.

Genetic variability of drug-metabolizing enzymes: the dual impact on psychiatric therapy and regulation of brain function

Polymorphic drug-metabolizing enzymes (DMEs) are responsible for the metabolism of the majority of psychotropic drugs. By explaining a large portion of variability in individual drug metabolism, pharmacogenetics offers a diagnostic tool in the burgeoning era of personalized medicine. This review updates existing evidence on the influence of pharmacogenetic variants on drug exposure and discusses the rationale for genetic testing in the clinical context. Dose adjustments based on pharmacogenetic knowledge are the first step to translate pharmacogenetics into clinical practice. However, also clinical factors, such as the consequences on toxicity and therapeutic failure, must be considered to provide clinical recommendations and assess the cost-effectiveness of pharmacogenetic treatment strategies. DME polymorphisms are relevant not only for clinical pharmacology and practice but also for research in psychiatry and neuroscience. Several DMEs, above all the cytochrome P (CYP) enzymes, are expressed in the brain, where they may contribute to the local biochemical homeostasis. Of particular interest is the possibility of DMEs playing a physiological role through their action on endogenous substrates, which may underlie the reported associations between genetic polymorphisms and cognitive function, personality and vulnerability to mental disorders. Neuroimaging studies have recently presented evidence of an effect of the CYP2D6 polymorphism on basic brain function. This review summarizes evidence on the effect of DME polymorphisms on brain function that adds to the well-known effects of DME polymorphisms on pharmacokinetics in explaining the range of phenotypes that are relevant to psychiatric practice.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Null CYP1B1 genotypes in primary congenital and nondominant juvenile glaucoma

PURPOSE

To assess the mutation spectrum, enzymatic activity, and phenotypic features associated with CYP1B1 genotypes in primary congenital glaucoma (PCG) and nondominant juvenile glaucoma (ndJG).

DESIGN

CYP1B1 genotyping, segregation analysis, and functional evaluation of mutations in a cohort of patients.

PARTICIPANTS

A total of 177 probands clinically diagnosed with PCG (161) or ndJG (16).

METHODS

Automatic DNA sequencing of the promoter (-1 to -867) and the 3 CYP1B1 exons. CYP1B1 enzymatic activity was evaluated using an ethoxyresorufin O-deethylation assay in transfected HEK-293T cells.

MAIN OUTCOME MEASURES

Screening and functional evaluation of CYP1B1 mutations. Glaucoma diagnosis based on slit-lamp examination, measurement of intraocular pressure, gonioscopy, and fundus examination.

RESULTS

Thirty-one different mutations were identified in 56 PCG and 7 ndJG index cases. To the best of our knowledge, 3 of the identified mutations were novel (-337G>T, F123L, and I399_P400del). Approximately 56% of all mutation carriers were compound heterozygotes, 25% were homozygotes, and both groups inherited glaucoma as an autosomal recessive trait. Nineteen percent of carriers were heterozygotes and showed non-Mendelian segregation. In vitro and inferred functional analysis showed that no less than approximately 74% of the recessive genotypes result in null enzymatic activity. We detected variable expressivity in relation to age of onset and a possible case of incomplete penetrance in 3 of 6 families (50%), with more than 1 affected child or more than 1 subject carrying 2 CYP1B1 mutant alleles. Altogether, these data support that PCG is not a simple monogenic disease. In addition, most patients with PCG carrying null or putative null genotypes showed severe bilateral phenotypes featured by early disease onset, frequently at birth. The mean number of trabeculectomies per eye was significantly higher in carriers than in noncarriers.

CONCLUSIONS

This is the largest analysis of CYP1B1 mutations performed in European patients with PCG to date. Our data show that null CYP1B1 genotypes, and therefore complete absence of CYP1B1 activity, frequently lead to severe phenotypes. Our results support that CYP1B1 glaucoma is not a simple monogenic disease and that CYP1B1 activity levels could influence the phenotype.

Genetics of primary glaucoma

PURPOSE OF REVIEW

To provide an overview of the genetics of the primary open-angle glaucomas with particular attention to congenital, infantile, and juvenile forms.

RECENT FINDINGS

Mutations in CYP1B1, in addition to being the most common identifiable cause of autosomal recessive primary congenital/infantile glaucoma, can infrequently underlie juvenile and even primary adult-onset open-angle glaucoma, particularly in certain consanguineous populations. In 2009, patients diagnosed with congenital/infantile glaucoma were found to have recessive mutations in a second gene, LTBP2, with a phenotypic spectrum that includes primary megalocornea, spherophakia with ectopia lentis, and lens-related glaucoma. The most common identifiable cause of primary juvenile open-angle glaucoma across most populations remains heterozygous (autosomal dominant) MYOC mutation, underlying up to one-third of cases and possibly sometimes involved in earlier and later onset glaucomas Although primary adult-onset open-angle glaucoma usually does not follow simple Mendelian genetics and is etiologically complex, genome-wide association studies are uncovering genetic susceptibility factors. In some cases, primary adult-onset open-angle glaucoma can be caused by heterozygous mutation in MYOC, OPTN, or WDR36. In addition, in 2009, heterozygous NTF4 mutation was associated with the phenotype in a small percentage of patients from a German cohort.

SUMMARY

Seemingly unaffected siblings of children with CYP1B1-related primary congenital/infantile glaucoma should undergo genetic testing because of variable expressivity for the phenotype; such testing should also be considered for other asymptomatic relatives, especially in consanguineous families. In western populations, dominant MYOC mutation remains a common cause of primary open-angle juvenile glaucoma and infrequently can be implicated in congenital/infantile or adult-onset forms; identified families should undergo genetic counseling. Primary adult-onset open-angle glaucoma rarely follows simple Mendelian genetics, but genomic studies in different populations are revealing potential genetic risk factors for the phenotype.

Primary Congenital Glaucoma and the Involvement of CYP1B1

Primary congenital glaucoma (PCG) is an autosomal recessive disorder in children due to the abnormal development of the trabecular meshwork and the anterior chamber angle. With an onset at birth to early infancy, PCG is highly prevalent in inbred populations and consanguinity is strongly associated with the disease. Gene mapping of PCG-affected families has identified three chromosomal loci, GLC3A, GLC3B and GLC3C, of which, the CYP1B1 gene on GLC3A harbors mutations in PCG. The mutation spectra of CYP1B1 vary widely across different populations but are well structured based on geographic and haplotype backgrounds. Structural and functional studies on CYP1B1 have suggested its potential role in the development and onset of glaucomatous symptoms. A new locus (GLC3D) harboring the LTBP2 gene has been characterized in developmental glaucoma but its role in classical cases of PCG is yet to be understood. In this review, we provide insight into PCG pathogenesis and the potential role of CYP1B1 in the disease phenotype.

Familial juvenile glaucoma with underlying homozygous p.G61E CYP1B1 mutations

We describe siblings with familial primary juvenile glaucoma from a consanguineous Saudi Arabian family. The phenotype segregated with homozygous p.G61E CYP1B1 mutations while MYOC mutation was not detected, illustrating that mutations in CYP1B1 rather than mutation in MYOC can underlie familial primary juvenile glaucoma in certain populations.

Expression of CYP2A6, CYP2D6 and CYP4A11 Polymorphisms in COS7 Mammalian Cell Line

The cytochrome P450 (P450, CYP) are the superfamily of heme-containing monooxygenase enzymes, found throughout all nature including mammals, plants, and microorganisms. Mammalian P450 enzymes are involved in oxidative metabolism of a wide range of endo- and exogenous chemicals. Especially P450s involved in drug metabolisms are important for drug efficacy and polymorphisms of P450s in individuals reflect differences of drug responses between people. To study the functional differences of CYP2A6, CYP2D6, and CYP4A11 variants, we cloned the four CYP2A6, three CYP2D6, and three CYP4A11 variants, which were found in Korean populations, in mammalian expression vector pcDNA by PCR and examined their expressions in COS-7 mammalian cells using immunoblots using P450 specific polyclonal antibodies. Three of four CYP2A6, two of three CYP4A11, and two of three CYP2D6 variants showed expressions in COS-7 cells but the relative levels of expressions are remarkably different in those of each variants. Our findings may help to study and explain the differences between functions of CYP variants and drug responses in Korean populations.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

CYP1B1, a developmental gene with a potential role in glaucoma therapy

The association of CYP1B1 gene alterations in primary congenital glaucoma individuals has been known for about a decade. Recent evidence has shown the involvement of CYP1B1 mutations in a number of forms of glaucoma and anterior segment disorders. This suggests a wide role for CYP1B1 in ocular physiology. Histochemical studies of eyes from individuals with primary congenital glaucoma revealed abnormalities in the anterior chamber angle, the region between the cornea and the iris, containing the trabecular meshwork. The cells of the trabecular meshwork serve as a filter to allow drainage of the aqueous humour, the fluid formed by the ciliary body that fills the anterior chamber. Mutations in CYP1B1 that affect its activity have frequently been shown to influence development of the trabecular meshwork, and it is thought that CYP1B1, a monooxygenase, acts to form or degrade some endobiotic compound that is necessary for proper development of the filtering structures. The rapidly developing area of stem cell research suggests a potential therapeutic approach for glaucomas resulting from deleterious mutations in CYP1B1, that is, the transfer of stem cells, differentiated to a specific lineage, containing wild-type CYP1B1 to specific regions of the eye, where they will develop into normal cells of that region and rectify the defect.

Functional analysis of CYP1B1 mutations and association of heterozygous hypomorphic alleles with primary open-angle glaucoma

Glaucoma is an inherited complex and heterogeneous disease, and one of the most prevalent causes of definitive blindness in the world. Recent reports have indicated that heterozygous mutations of the CYTOCHOROME P4501B1 (CYP1B1) gene are present in 4-10% of patients with primary open-angle glaucoma (POAG). To further evaluate the role of CYP1B1 mutations in POAG we extended our previous association study and carried out a functional analysis of the mutations identified by polymerase chain reaction (PCR) DNA sequencing of the three exons of the gene in a total of 245 unrelated Spanish patients and 326 control subjects. Eight of nine different mutations identified in these patients were cloned and functionally assessed by measuring ethoxyresorufin O-deethylation activity and CYP1B1 stability in transiently transfected HEK-293T cells. All these mutants showed reduced catalytic activity, ranging from 20% to 60% of wild-type and/or decreased protein stability and, therefore, they were classified as hypomorphic alleles. No null alleles were identified in these patients. We found heterozygous hypomorphic CYP1B1 mutations in 17 (6.7%) patients and in seven controls (2.1%) showing that these mutations are associated with an increased risk of POAG (p = 0.005; odds ratio = 3.2; 95% confidence interval = 1.30-9.19). Our data suggest that hypomorphic CYP1B1 mutations are, to date, the main known genetic risk factor in POAG.

Comparative docking studies of CYP1b1 and its PCG-associated mutant forms

Molecular docking has been used to compare and contrast the binding modes of oestradiol with the wild-type and some disease-associated mutant forms of the human CYP1b1 protein.The receptor structures used for docking were derived from molecular dynamics simulations of homology-modelled structures. Earlier studies involving molecular dynamics and principal component analysis indicated that mutations could have a disruptive effect on function,by destabilizing the native properties of the functionally important regions, especially those of the haem-binding and substrate-binding regions,which constitute the site of catalytic activity of the enzyme.In order to gain more insights into the possible differences in substrate-binding and catalysis between the wild-type and mutant proteins,molecular docking studies were carried out. Mutants showed altered protein -ligand interactions compared with the wild-type as a consequence of changes in the geometry of the substrate-binding region and in the position of haem relative to the active site. An important difference in ligand -protein interactions between the wild-type and mutants is the presence of stacking interaction with phenyl residues in the wild-type,which is either completely absent or considerably weaker in mutants.The present study revealed essential differences in the interactions between ligand and protein in wild-type and disease mutants,and helped in understanding the deleterious nature of disease mutations at the level of molecular function.

Characterization of the biochemical and structural phenotypes of four CYP1B1 mutations observed in individuals with primary congenital glaucoma

OBJECTIVE

The objective of this study was to examine the biochemical and physical properties of cytochrome P450 1B1 (CYP1B1) mutants, test our hypothesis that primary congenital glaucoma (PCG)-causing mutants have altered metabolic activity, and correlate these to structural changes in the molecule.

METHODS

CYP1B1.1 cDNA was mutated to four forms found in individuals with the PCG phenotype, Y81N, E229K, A330F, and R368H. Expression and stability of the mutant hemoproteins and their ability to metabolize beta-estradiol, arachidonic acid, and retinoids, were determined. Alterations in mutant properties were related to structural changes by in silico examination, on the basis of the CYP1A2 crystal structure.

RESULTS

CYP1B1 mutations strongly affected the stability, ease of heterologous expression, and enzymatic properties of the protein. These were related to the location of the amino acid substitutions in the CYP1B1 structure. Three of the mutations involve residues located on the surface of CYP1B1, Y81N, and E229K near the distal surface, and R368H near the proximal surface. The former two substitutions, Y81N and E229K, caused greatly reduced stability at 4 degrees C. Y81N severely inhibited all substrate turnover, but E229K only inhibited arachidonate turnover and exhibited minimal effect on efficiency of retinoid metabolism and estradiol metabolism. The R368H mutation is relatively conservative, affecting charge-pairing with the deeper-located D374, but it severely inhibited metabolism of all substrates tested, and, like Y81N, expression of the enzyme is less facile than CYP1B1wt. The A330F mutation replaces a small alanine by a bulky phenylalanine in the enzyme active site and had major impact on substrate binding, turnover, uncoupling, and metabolite pattern.

CONCLUSION

Consistent with the hypothesis, these PCG-related mutations cause identifiable structural changes negatively impacting CYP1B1 biochemistry and stability.

Physiological Significance and Expression of P450s in the Developing Eye

Expression of 10 CYP orthologs (Families 1-3) in developing mouse conceptus is constitutive. These forms have specific temporal and spatial expression. Studies on CYP1B1 indicate its requirement for normal eye development, both in human and mouse. The distribution of the enzyme in the mouse eye is in three regions, which may reflect three different, perhaps equally important, functions in this organ. Its presence in the inner ciliary and lens epithelia appears to be necessary for normal development of the trabecular meshwork and its function in regulating intraocular pressure. Its expression in the retinal ganglion and inner nuclear layers may reflect a role in maintenance of the visual cycle. Its expression in the corneal epithelium may indicate a function in metabolism of environmental xenobiotics.

Accurate DNA fragment sizing by capillary electrophoresis with laser-induced fluorescence array for detection of sequence specificity of DNA damage

Cancer has been linked to mutations within specific codons in genes that code for critical biomolecules such as tumor suppressor proteins (e.g., p53). Activated metabolites like benzo[a]pyrenediol epoxide act on preferred nucleotide sequences of DNA, and such mutations have been identified in cancers. DNA reaction site identification depends on accurate analysis of oligonucleotide fragment sizes produced by strand breakage at the damaged sites. Herein, we report a new method for DNA fragment sizing using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). Absolute sizing accuracy and speed are achieved by utilizing a CE-LIF array with two-color fluorescence detection. Accuracy depends on correcting results with commercial standards by referring them to primary standards with the same sequences and identical labels as sample fragments. The method is demonstrated by detection of a [...GGCGCGCAG...] G reaction site for styrene oxide on an oligonucleotide representing the CYP1B1 gene. This approach avoids the need for radioactive isotopes and is less labor intensive and faster than the alternative PAGE with (32)P end labeling.

Role of CYP1B1 in Glaucoma

Glaucoma is a leading cause of blindness, estimated to affect 60 million people by 2010, and represents a heterogeneous group of neurodegenerative disease. The two major types of glaucoma include primary open-angle glaucoma (POAG) and primary congenital glaucoma (PCG). A genetically heterogeneous group of developmental disorders known as anterior segment dysgenesis (ASD) have been reported to be associated with increased intraocular pressure (IOP) and glaucoma. These include Peters' anomaly, Rieger's anomaly, aniridia, iris hypoplasia, and iridogoniodysgenesis. Genetic linkage analysis and mutation studies have identified CYP1B1 as a causative gene in PCG, as a modifier gene in POAG, and, on rare occasions, as causative gene in POAG as well as in several ASD disorders. CYP1B1-deficient mice exhibit abnormalities in their ocular drainage structure and trabecular meshwork that are similar to those reported in human PCG patients. Accordingly, it is speculated that diminished or absent metabolism of key endogenous CYP1B1 substrates adversely affects the development of the trabecular meshwork. CYP1B1 protein is involved in the metabolism of steroids, retinol and retinal, arachidonate, and melatonin. The conserved expression of CYP1B1 in both murine and human eyes, its higher expression in fetal than adult eyes, and its biochemical properties are consistent with this hypothesis. The exact role of CYP1B1 in the pathogenesis of glaucoma and other ASD disorders remains to be elucidated.

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants

Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4'-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala(119)Ser, Pro(379)Leu, Ala(443)Gly, Arg(48)Gly/Leu(432)Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp(57)Cys, Gly(61)Glu, Arg(48)Gly/Ala(119)Ser, Arg(48)Gly/Ala(119)Ser/Leu(432)Val, Arg(48)Gly/Ala(119)Ser/Leu(432)Val/Ala(443)Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V(max)/K(m)) for both N- and 4-hydroxylation of PhIP. Six variants (Gly(365)Trp, Glu(387)Lys, Arg(390)His, Pro(437)Leu, Asn(453)Ser, Arg(469)Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp(365), Lys(387), and His(390) variants and was not detectable for the Ser(453) variant. In contrast, there was no difference between the Trp(469) variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp(469) variant totally lost its metabolic activity toward PhIP. The Leu(437) variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.

Genetic polymorphisms in cytochrome P4501B1 and susceptibility to head and neck cancer

Cytochrome P4501B1 (CYP1B1), a polycyclic aromatic hydrocarbon (PAH) metabolizing CYP, is genetically polymorphic in humans and may be involved in the individual susceptibility to chemical-induced cancer. In the present study, genotype and haplotype frequencies of four single nucleotide polymorphisms (SNPs) in CYP1B1 that cause amino acid changes (Arg-Gly at codon 48, Ala-Ser at codon 119, Leu-Val at codon 432 and Asn-Ser at codon 453) were studied in 150 cases suffering from head and neck squamous cell carcinoma (HNSCC) and in an equal number of controls. A significant difference was observed for the distribution of variant genotypes of Arg48Gly (CYP1B1*2) and Ala119Ser (CYP1B1*2) polymorphisms of CYP1B1 in cases versus controls. No significant differences were observed for the distribution of variant genotypes-Leu432Val (CYP1B1*3) and Asn453Ser (CYP1B1*4), respectively. When the four SNPs were analyzed using a haplotype approach, SNPs at codon 48 (Arg48Gly) and codon 119 (Ala119Ser) exhibited complete linkage disequilibrium (LD) in all the cases and controls. Significant differences in the distribution of the two haplotypes (G-T-C-A and G-T-G-A) were observed both in the cases and in controls. Furthermore, our data indicates a several fold increase in risk in the cases who use tobacco (cigarette smoking or tobacco chewing) or alcohol with the variant genotypes of CYP1B1 (CYP1B1*2 and CYP1B1*3) suggesting the role of gene-environment interaction in the susceptibility to HNSCC.

Electrochemiluminescent arrays for cytochrome P450-activated genotoxicity screening. DNA damage from benzo[a]pyrene metabolites

Arrays suitable for genotoxicity screening are reported that generate metabolites from cytochrome P450 enzymes (CYPs) in thin-film spots. Array spots containing DNA, various human cyt P450s, and electrochemiluminescence (ECL) generating metallopolymer [Ru(bpy)2PVP10]2+ were exposed to H2O2 to activate the enzymes. ECL from all spots was visualized simultaneously using a CCD camera. Using benzo[a]pyrene as a test substrate, enzyme activity for producing DNA damage in the arrays was found in the order CYP1B1 > CYP1A2 > CYP1A1 > CYP2E1 > myoglobin, the same as the order of their metabolic activity. Thus, these arrays estimate the relative propensity of different enzymes to produce genotoxic metabolites. This is the first demonstration of ECL arrays for high-throughput in vitro genotoxicity screening.

Cytochrome P450-catalyzed pathways in human brain: Metabolism meets pharmacology or old drugs with new mechanism of action?

The true importance of cytochrome P450 enzymes, not just in drug metabolism but also in pharmacology, is only beginning to be appreciated. Though originally discovered through their role in the biotransformation of xenobiotics, the P450 enzyme super family is ubiquitous in nature and necessarily evolved around endogenous pathways. The extent of tissue- and cell-specific expression of individual P450 isoforms has led many investigators to hypothesize localized roles in endogenous biochemical pathways for isoforms traditionally thought of as drug-metabolizing. In some cases, direct evidence from humanized transgenic animal models can confirm the degree to which such enzymes modulate endogenous pathways. However, overlapping P450 substrate specificities may mask genetic or biochemical deficiencies, such that many of these reactions appear nonessential. Nonetheless, the drug-induced alteration of local biochemical concentrations in extrahepatic tissues due to metabolism by and inhibition of P450 isoforms has tremendous potential for introducing unexpected pharmacological effects. Nowhere is this truer than in the CNS. On the other hand, if we can harness the power of in silico modeling to create highly specific inhibitors of identified brain isoforms, a novel avenue for drug design using P450 as drug targets may be at hand. This article highlights some notable examples in which the catalytic state of specific P450 isoforms involved in endogenous biochemical reaction pathways are influenced by pharmacological agents. The implications of inhibition of P450-catalzyed oxidation steps that are known or speculated to influence arachadonic acid, cholesterol, and catecholamine neurotransmitters pathways in human brain will be considered.