Lack of association between early atherosclerotic carotid artery wall lesions and serum level of homocysteine

The present study evaluated the possible association of high serum levels of homocysteine with ultrasonographic manifestations of carotid atherosclerosis in 65-year-old Finnish subjects drawn from a population-based cohort. Carotid ultrasonographic measurements were performed on 54 diabetic subjects, 97 subjects with impaired glucose tolerance and 57 normoglycaemic subjects. There were no statistically significant differences between the groups in the homocysteine levels. The median homocysteine level was higher in the subjects with a history of myocardial infarction (MI) (n=9) than in the subjects with no history of MI (14.8 [range 8.7—18.3] vs.12.3 [range 6.4—49.0] µmol/L, p=0.045). In the subjects without a history of MI or stroke, the maximal intima-media thickness (IMT) of the common carotid artery did not differ in the homocysteine quintiles. There was no association between the number of atheromatous plaques and the homocysteine level. In conclusion, although high levels of serum homocysteine were not associated with early atherosclerotic changes (i.e. increased carotid IMT or the number of plaques), high homocysteine concentrations were associated with advanced atherosclerosis (i.e. a history of MI).

Axillary lymph node biopsy in newly diagnosed invasive breast cancer: comparative accuracy of fine-needle aspiration biopsy versus core-needle biopsy

PURPOSE

To compare the diagnostic accuracy of ultrasonographically (US)-guided fine-needle aspiration biopsy (FNAB) and core-needle biopsy (CNB) of the axillary lymph nodes (LNs) of patients with newly diagnosed invasive breast cancer.

MATERIALS AND METHODS

This prospective single-center study had institutional review board approval, and written informed consent was obtained. Between April 2011 and March 2012, 178 consecutive patients (182 axillae) were evaluated by using axillary US. Sixty-six axillae fulfilled the inclusion criteria (cortical thickness greater than 2 mm or abnormal morphologic characteristics), and patients with these axillae underwent US-guided axillary LN biopsy. Both FNAB and CNB were obtained from the same suspicious LN. Patients with biopsy-proved metastasis underwent axillary clearance, and those with a negative biopsy underwent sentinel LN biopsy with completion axillary clearance if needed. Diagnostic performance was calculated separately for US, FNAB, and CNB. Statistical differences in sensitivities were evaluated by using the McNemar test.

RESULTS

From the total study population, 45.6% (83 of 182 axillae) had metastases. A total of 66 axillae underwent both FNAB and CNB. The sensitivity for US was 61.4% (51 of 83 axillae), and specificity was 84.8% (84 of 88 axillae). The sensitivities for FNAB and CNB were 72.5% (37 of 51 axillae) and 88.2% (45 of 51 axillae), respectively (P = .008). Specificity for both was 100% (15 of 15 axillae). The negative predictive value for FNAB was 81.7%, and that for CNB was 91.2%. The positive predictive value was 100% for both methods.

CONCLUSION

When accurate preoperative staging of the axilla is needed in patients with newly diagnosed invasive breast cancer, CNB is more sensitive than FNAB.

Risk of retinal microembolism after off-pump and on-pump coronary artery bypass surgery

AIM

In order to investigate the neuroprotective efficacy of off-pump coronary artery bypass surgery (OPCAB) over conventional on-pump coronary artery bypass surgery (CCAB), we have performed a prospective randomized study evaluating retinal circulation changes after OPCAB and CCAB.

METHODS

Twenty patients were randomized to OPCAB or CCAB. Retinal fluorescein angiography and 60 degrees black-and-white as well as color fundus photographs of both eyes of each patient were taken 1 to 24 h before and 5 to 6 days after the operation.

RESULTS

Patients undergoing OPCAB had more severely stenosed carotid arteries (P=0.075), higher incidence of slightly diseased ascending aorta (P=0.087) and higher Northern New England Cardiovascular Study Group stroke risk score (P=0.075). Neither stroke nor transient ischemic attack occurred postoperatively in these patients. Inferotemporal retinal arterial embolization and microinfarction was detected in one patient after CCAB, but in none of the OPCAB group.

CONCLUSION

The risk of retinal embolism can be minimized by the use of OPCAB and, most likely, by adequate epiaortic ultrasound scanning of the ascending aorta and avoiding clamping in case of severely diseased aorta.

Predictive value of animal models for human cytochrome P450 (CYP)-mediated metabolism: a comparative study in vitro

One major challenge in drug development is defining of the optimal animal species to serve as a model of metabolism in man. The study compared the hepatic drug metabolism characteristics of humans and six widely used experimental animal species. Classical in vitro model enzyme assays with known human cytochrome P450 (CYP) enzyme selectivity were employed and optimized to target human hepatic CYP forms. The profile of CYP activities best resembling the human was seen in mouse followed by monkey, minipig, and dog liver microsomes, with rats displaying the most divergent. The widest interindividual variability was found in CYP3A-mediated midazolam -hydroxylase, and omeprazole sulphoxidase activities in human and monkey liver microsomes. These data demonstrate that if hepatic xenobiotic-metabolizing characteristics were to be the sole reason for the selection of animal species for toxicity studies, then the rat might not be the most appropriate model to mimic human CYP activity patterns.

Identification of inhibitors of the nicotine metabolising CYP2A6 enzyme--an in silico approach

The compulsive nature of tobacco use is attributable to nicotine addiction. Nicotine is eliminated by metabolism through the cytochrome P450 2A6 (CYP2A6) enzyme in liver. Inhibition of CYP2A6 by chemical compounds may represent a potential supplement to anti-smoking therapy. The purpose of this study was to rationally design potent inhibitors of CYP2A6. 3D-QSAR models were constructed to find out which structural characteristics are important for inhibition potency. Specifically located hydrophobic and hydrogen donor features were found to affect inhibition potency. These features were used in virtual screening of over 60,000 compounds in the Maybridge chemical database. A total of 22 candidate molecules were selected and tested for inhibition potency. Four of these were potent and selective CYP2A6 inhibitors with IC(50) values lower than 1 muM. They represent novel structures of CYP2A6 inhibitors, especially N1-(4-fluorophenyl)cyclopropane-1-carboxamide. This compound can be used as a lead in the design of CYP2A6 inhibitor drugs to combat nicotine addiction.

New potent and selective cytochrome P450 2B6 (CYP2B6) inhibitors based on three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis

BACKGROUND AND PURPOSE

The cytochrome P450 2B6 (CYP2B6) enzyme metabolises a number of clinically important drugs. Drug-drug interactions resulting from inhibition or induction of CYP2B6 activity may cause serious adverse effects. The aims of this study were to construct a three-dimensional structure-activity relationship (3D-QSAR) model of the CYP2B6 protein and to identify novel potent and selective inhibitors of CYP2B6 for in vitro research purposes.

EXPERIMENTAL APPROACH

The inhibition potencies (IC(50) values) of structurally diverse chemicals were determined with recombinant human CYP2B6 enzyme. Two successive models were constructed using Comparative Molecular Field Analysis (CoMFA).

KEY RESULTS

Three compounds proved to be very potent and selective competitive inhibitors of CYP2B6 in vitro (IC(50)<1 microM): 4-(4-chlorobenzyl)pyridine (CBP), 4-(4-nitrobenzyl)pyridine (NBP), and 4-benzylpyridine (BP). A complete inhibition of CYP2B6 activity was achieved with 0.1 microM CBP, whereas other CYP-related activities were not affected. Forty-one compounds were selected for further testing and construction of the final CoMFA model. The created CoMFA model was of high quality and predicted accurately the inhibition potency of a test set (n=7) of structurally diverse compounds.

CONCLUSIONS AND IMPLICATIONS

Two CoMFA models were created which revealed the key molecular characteristics of inhibitors of the CYP2B6 enzyme. The final model accurately predicted the inhibitory potencies of several structurally unrelated compounds. CBP, BP and NBP were identified as novel potent and selective inhibitors of CYP2B6 and CBP especially is a suitable inhibitor for in vitro screening studies.

Pulsatile tinnitus as a symptom of cervicocephalic arterial dissection

The aim of this study was to investigate pulsatile tinnitus as a presenting symptom in cervicocephalic arterial dissection (CCAD). Of the 136 consecutive patients with confirmed CCAD, 16 presented with pulsatile tinnitus. On admission 10 patients presented with subjective tinnitus and five with objective tinnitus, tinnitus being the only presenting symptom in one case. In one further case with bilateral ICA dissection (ICAD) subjective tinnitus appeared three months after the initial symptoms of arterial dissection, despite a contralateral cervical bruit being evident on admission. Thirteen patients presented with headache or neck pain. Ischaemic symptoms were detected in six and Horner’s syndrome in four patients. Vertigo and dysgeusia were reported in two patients each. Arterial dissection involved unilateral ICA in 11, bilateral ICA in two, unilateral vertebral artery (VA) in two and bilateral ICA and bilateral VA in one patient. In angiography the most common finding was irregular stenosis, and the majority of these abnormalities normalized during follow-up. To avoid delay in diagnosis a high index of suspicion and early angiography (digital subtraction or magnetic resonance angiography) are warranted.

Associations of microalbuminuria and blood pressure with carotid, aortic and femoral atheromatous plaques in elderly Finns

AIMS

To evaluate the possible associations of microalbuminuria (MA) and blood pressure (BP) with the ultrasonographic manifestations of carotid, aortic and femoral atherosclerosis in 65-year-old Finns.

METHODS

Ultrasonographic measurements were performed on 54 diabetic subjects, 97 subjects with impaired glucose tolerance (IGT) and 57 normoglycemic subjects (NGT). Urinary albumin and creatinine concentrations were measured from an early morning spot urine sample, and the urinary albumin-to-creatinine ratio (ACR) of > or = 2.5 mg/mmol in men and > or = 3.5 mg/mmol in women was used as a measure of MA. Hypertension was defined as either a systolic BP of > or = 160 mmHg or a diastolic BP of > or = 95 mmHg or being on antihypertensive medication.

RESULTS

Eighteen subjects were microalbuminuric and 176 subjects normoalbuminuric. MA was associated with diabetes mellitus and high systolic and diastolic BP. The subjects were divided into two groups according to the median total number of carotid, aortic and femoral plaques: > or = 9 versus 0-8 plaques. A high number of plaques were associated with hypertension, male gender, smoking and MA. When the study subjects were stratified according to hypertension, it turned out that MA was associated with a high number of plaques in hypertensive, but not in nonhypertensive subjects. According to the results of logistic regression analysis with a high number of plaques as the dependent variable, the unadjusted OR for smoking was 6.0 (95% CI 2.4-15.3) in hypertensive subjects. Microalbuminuria was of borderline statistical significance (OR 4.5, 95% CI 0.9-22.9). After adjustment for systolic blood pressure and fasting glucose concentration, the OR for microalbuminuria was reduced to 3.3 (95% CI 0.6-18.4).

Human placenta: a human organ for developmental toxicology research and biomonitoring

Pregnant mothers are exposed to a wide variety of foreign chemicals. This exposure is most commonly due to maternal medication, lifestyle factors, such as smoking, drug abuse, and alcohol consumption, or occupational and environmental sources. Foreign compounds may interfere with placental functions at many levels e.g. signaling, production and release of hormones and enzymes, transport of nutrients and waste products, implantation, cellular growth and maturation, and finally, at the terminal phase of placental life, i.e. delivery. Placental responses may also be due to pharmaco-/toxicodynamic responses to foreign chemicals, e.g. hypoxia. On the other hand, placental xenobiotic-metabolizing enzymes can detoxify or activate foreign chemicals, and transporters either enhance or prevent cellular accumulation and transfer across the placenta. The understanding of what xenobiotics do to the placenta and what the placenta does to the xenobiotics should provide the basis for the use of placenta as a tool to investigate and predict some aspects of developmental toxicity. This review aims to give an update of the fate and behavior of xenobiotics in the placenta from the viewpoint of xenobiotic-metabolizing enzymes and transporters. Their response levels will be described according to gestational status and methods used. The effects of foreign chemicals on placental metabolizing enzymes will be discussed. Also, interactions in the transporter protein level will be covered. The role of the placenta in contributing to developmental effects and fetotoxicity will be examined. The toxicological effects of maternal medications, smoking, and environmental exposures (dioxins, pesticides) as well as some possibilities for biomonitoring will be highlighted.

Diabetic retinopathy: sonographically measured hemodynamic alterations in ocular, carotid, and vertebral arteries

PURPOSE

To compare local ophthalmic blood flow changes with flow changes in carotid and vertebral arteries in diabetic patients with retinopathy of different grades.

MATERIAL AND METHODS

Ten patients with proliferative or preproliferative retinopathy, 10 with mild retinopathy, and 10 matched controls were prospectively studied with ultrasound. Color and duplex Doppler imaging was used to quantitate blood flow in the central retinal arteries (CRA), ophthalmic arteries (OA), common carotid (CCA) and vertebral arteries (VA). Peak systolic velocity (PSV), mean velocity (MV), and resistance index (RI) in CRA, OA, CCA and VA, and volume flow (VF) were measured in CCA and VA.

RESULTS

There was a non-significant increase in the CRA and OA velocities in mild retinopathies, a decrease of about 30% in MV, and a slightly increased RI in proliferative or preproliferative retinopathies. There was a decrease of about 15% in the carotid MV and a 20% decrease in the vertebral MV and a decrease of about 30% in VF in the CCA and VA in severe retinopathies. The MV ratio of CRA/CCA was lower in the severe retinopathy group than in the controls.

CONCLUSION

The study showed a non-significant increase of ocular blood flow velocities in mild diabetic retinopathy and a significant decrease of flow velocities in severe diabetic retinopathy. This decrease in flow primarily seems to reflect the general decrease of blood flow in the cervical arteries.

Cerebral CT and MRI findings in cervicocephalic artery dissection

PURPOSE

To explore the frequency and patterns of brain infarction and other brain manifestations in cervicocephalic artery dissection (CCAD) and to evaluate the correlation between vessel wall findings and infarctions.

MATERIAL AND METHODS

The medical records and films of 136 consecutive CCAD patients diagnosed in Oulu University Hospital during the 20-year period since 1982 were reviewed. Five patients with no brain imaging were excluded.

RESULTS

One-hundred-and-twenty-seven patients underwent cerebral CT and four patients MRI. Brain infarction was detected in 73 patients (56%), 43 of whom had cerebral infarction associated with anterior circulation dissection and 30 cerebellar infarction associated with posterior circulation dissection. Occlusion of the dissected vessel was accompanied by infarction in 76%, irregular stenosis in 40%, and other findings in 12%. Of the anterior circulation infarctions, territorial and subcortical infarctions and territorial infarctions with fragmentation, which are considered embolic, accounted for 95%, while only 5% were in the watershed area and considered hemodynamic. Intracranial posterior circulation dissection rarely caused infarction (in 1/11 of the dissected vessels), whereas intracranial anterior circulation dissection resulted in infarction more commonly (9/12). Altogether 23% of patients with intracranial CCAD had subarachnoid hemorrhage. Hemorrhagic transformation was present in five patients.

CONCLUSIONS

More than half of CCAD patients have cerebral or cerebellar infarction at CT or conventional MR imaging. Occlusion of the dissected vessel is accompanied by infarction more often than other vessel wall abnormalities. Most cerebral infarctions caused by arterial dissections are of embolic origin. Intracranial dissections cause subarachnoid hemorrhage in more than 20% of patients.

Associations of blood pressure with carotid intima-media thickness in elderly Finns with diabetes mellitus or impaired glucose tolerance

The aim of the present study was to evaluate the associations of ultrasonographic manifestations of carotid atherosclerosis with systolic (SBP) and diastolic blood pressure (DBP) and pulse pressure (PP) in 65-year-old Finns drawn from a population-based cohort. Carotid ultrasonographic measurements were performed on 54 diabetic subjects, 97 subjects with impaired glucose tolerance (IGT) and 57 normoglycaemic subjects (NGT). The subjects were classified into four quartiles of SBP, DBP and PP. SBP, DBP, PP and the use of antihypertensive drugs increased along with the deterioration of glucose status. The maximal intima-media thickness (IMT) of the common carotid artery (CCA) from the lowest to the highest quartiles of SBP was 0.98+/-0.34, 1.00+/-0.35, 1.03+/-0.29, 1.18+/- 0.52 mm (P=0.038), respectively. SBP was higher (161+/-22 mmHg) in the subjects with severe intima-media thickening (maximal IMT CCA > or =1.2 mm) than in those with maximal IMT CCA of <1.2 mm (153+/- 20 mmHg) (P=0.030). DBP and PP tended to be higher in the former than the latter group (DBP: 89+/-9 mmHg vs 86+/-9 mmHg, P=0.055 and PP: 72+/-18 mmHg vs 67+/-17 mmHg, P=0.159). The prevalence of severe intima-media thickening was 39% in the subjects in the highest SBP quartile (> or =170 mmHg) and 20% in the subjects with lower SBP (P=0.008). In multiple regression analysis, the adjusted OR for severe intima-media thickening was 2.9 (95% CI 1.1-7.9) in the subjects in the highest SBP quartile compared to the subjects with lower SBP. In the present study, high SBP was associated with severe carotid intima-media thickening. We suggest that the results can be generalized to apply to elderly Finnish subjects with DM and IGT, but not to normoglycaemic subjects, on the basis of this study.

Cardiac arrest after interscalene brachial plexus block with ropivacaine and lidocaine

Serious adverse reactions to ropivacaine and lidocaine are rare. In this report, we describe a case of sudden cardiac arrest after an interscalene brachial plexus block with a mixture of 150 mg of ropivacaine and 360 mg of lidocaine in a previously healthy, 34-year-old, 97-kg man. Severe hypotension occurred after successful resuscitation, necessitating an infusion of epinephrine. The patient developed pulmonary oedema, and was mechanically ventilated for 22 h. He eventually made a good recovery. We conclude that although ropivacaine and lidocaine are often considered relatively safe local anesthetics, serious cardiovascular complications can occur after the use of these drugs.

Extracranial internal carotid and vertebral artery dissections: angiographic spectrum, course and prognosis

We reviewed the clinical and radiological findings of 93 consecutive patients with 111 extracranial internal carotid (ICAD) and vertebral artery (VAD) dissections and one concomitant intracranial VAD; 83% of the patients had unilateral and 17% multiple vessel dissections. The diagnosis was made by intra-arterial digital subtraction angiography in 92 patients and MR angiography in one. Follow-up angiography was performed in 77 cases (83%): of 49 initially stenotic arteries, 40 became completely or almost completely normal, while three showed slight improvement. Of 30 initially occluded arteries, nine had completely or partly recanalised. Of 12 pseudoaneurysms eight were unchanged at follow-up. The proximal vertebral artery was involved as often as the C1-C2 level. Recurrences were rare: a new dissection in another vessel was found in three patients. Kinking or coiling was found in 23% of the dissected internal carotid arteries.

Low insulin sensitivity measured by both quantitative insulin sensitivity check index and homeostasis model assessment method as a risk factor of increased intima-media thickness of the carotid artery

The present study evaluated the association of ultrasonographic manifestations of carotid atherosclerosis with glucose status, various components of the insulin resistance syndrome, and insulin sensitivity measured by a novel quantitative insulin sensitivity check index (QUICKI = 1/[log(I0) + log (G0)]). Carotid ultrasonographic measurements were performed on 54 diabetic subjects, 97 subjects with impaired glucose tolerance and 57 normoglycemic subjects. QUICKI and insulin resistance measured by a HOMA (homeostasis model assessment) method had a high negative correlation (r = -0.995, P < 0.001). QUICKI was lower in diabetic subjects (0.319 +/- 0.022) than in subjects with impaired glucose tolerance (0.334 +/- 0.027) or normoglycemia (0.335 +/- 0.022, P = 0.002). There was an increasing trend in the mean and maximal intima-media thickness (IMT) of the common carotid artery (CCA) with worsening of glucose status. The maximal IMT of the CCA correlated inversely with QUICKI (r = -0.158, P = 0.027). The prevalence of severe CCA atherosclerosis (maximal IMT of the CCA > or = 1.2 mm) was 41% in men and 16% in women (P < 0.001). It was also associated with a long (> or =26 yr) smoking history. The prevalence of severe CCA atherosclerosis was 11% in the highest QUICKI tertile, 36% in the middle tertile, and 33% in the lowest tertile (P = 0.002). Systolic blood pressure was higher and high-density lipoprotein cholesterol lower in subjects with severe CCA atherosclerosis, compared with those without it. In multiple regression analysis, the adjusted odds ratio for severe CCA atherosclerosis was 5.7 (95% confidence interval, 2.2-15.1) in subjects in the two lowest tertiles of QUICKI, compared with those in the highest tertile.

Cytochrome P450 3A expression in the human fetal liver: evidence that CYP3A5 is expressed in only a limited number of fetal livers

CYP3A is the major cytochrome P450 subfamily constitutively expressed in the human liver. CYP3A4 is the predominant hepatic P450 form in adults and it is expressed at high but very variable levels among individuals. The fetal liver contains mainly CYP3A7, while the presence of the other CYP3A enzymes in fetal liver has remained controversial. In this study, the relative levels of CYP3A4, CYP3A5 and CYP3A7 expression were determined in a panel of 9-11 fetal livers with a similar gestation age (9-12 weeks) and compared to adult livers. CYP3A7 was found to be the major CYP3A form in all the fetal liver samples. The abundance of CYP3A7 varied more at the mRNA (77-fold variation) than at the protein level (4.8-fold variation). CYP3A5 mRNA was also detected in all of the fetal liver samples, but the average level was 700-fold lower than that of CYP3A7. CYP3A5 protein was detected by immunoblot analysis in only 1 fetal liver out of the 9 investigated, the level of expression being moderately high in this sample. CYP3A4 mRNA was detected in only a subset of the fetal liver samples and its level was the lowest of the CYP3A forms. This is the first study to demonstrate the polymorphic expression of CYP3A5 and the variability of CYP3A7 expression in fetal liver and suggests that significant interindividual differences in the metabolism of xenobiotics may already exist at the prenatal stage. These differences may contribute to individual pharmacological and/or toxicological responses in the fetus.

The expression of cytochrome P450 enzymes in human breast tumours and normal breast tissue

Environmental chemicals are one of the risk factors in breast cancer genesis. Cytochrome P450 (CYP) enzymes play a major role in the activation of these chemicals. Using highly specific and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. the expression profile of all major xenobiotic metabolizing CYP forms was screened in breast tumour and surrounding tumour free (control) breast tissue in a series of 20 sample pairs obtained from females with infiltrating ductal carcinoma. The levels of CYPIAI mRNA were very low in both tumour and normal tissue. CYP1B1, CYP2B6, CYP2C, CYP2D6, CYP2E1, CYP4B1, and CYP11A1 expressions were positive in both tumours and control tissue. CYP2A6, CYP2A7, CYP2A13, CYP2F1, CYP3A4, CYP3A5. and CYP3A7 mRNAs were expressed neither in tumours nor in control tissue. These results show that several CYPs. responsible for the activation of a quite large number of procarcinogens and genotoxic estrogen metabolites. are expressed in breast tissue with a lack of qualitative differences in CYP expression at mRNA level between breast tumours and surrounding normal breast.

CYP2B6 and CYP2C19 as the major enzymes responsible for the metabolism of selegiline, a drug used in the treatment of Parkinson's disease, as revealed from experiments with recombinant enzymes

In view of conflicting data in the literature regarding the enzyme(s) responsible for metabolism of selegiline, a drug used in the treatment of Parkinson's disease, investigations were carried out in vitro using the human cytochrome P450 enzymes CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 recombinantly expressed in yeast to elucidate the enzyme specificity in selegiline metabolism. In the yeast microsomes used, desmethylselegiline and levomethamphetamine were formed from selegiline at significant rates. The highest contribution to the hepatic clearance of selegiline was calculated to be exerted by CYP2B6 (124 l/h) CYP2C19 (82 l/h), whereas CYP3A4 (27 l/h) and CYP1A2 (21 l/h) were of less importance. Antibodies against CYP2B6 inhibited metabolism of selegiline in microsomes containing CYP2B6 but not in microsomes without significant amounts of the enzyme. In contrast to previous reports, we could not find any role for CYP2D6 in the metabolism of selegiline. The data strongly indicate that the high extent of interindividual variation seen in vivo for selegiline clearance is caused by the metabolism of the compound by the highly polymorphic CYP2B6 and CYP2C19.

In vitro prediction of gastrointestinal absorption and bioavailability: an experts' meeting report

The most convenient route of drug administration is peroral. To reach their target, drug molecules must be absorbed from the gastrointestinal tract and enter the systemic circulation in sufficient quantities. For this reason, understanding and anticipating the mechanisms and factors affecting gastrointestinal absorption and metabolism are of the utmost importance in developing new drugs. In contrast to drugs, which are administered intentionally for therapeutic reasons, chemical residues in food and other matrices enter the body unintentionally. Hence, in this case, a low systemic availability would be advantageous. For many reasons, but particularly because of financial and ethical (reduced used of animals) considerations, in vitro and ex vivo approaches to this problem have been pursued over the last few years. The use of in vitro methods, however, inherently creates questions about the validity of extrapolation to the in vivo situation. The purpose of this report is to review the current status of the field and to identify major gaps in our knowledge. Currently, there are a number of in silico, in vitro, cultured cell-based and ex vivo approaches available to predict the cell permeation, absorption and gastrointestinal metabolism of molecules. Some strengths and weaknesses of these approaches are presented, together with a discussion of genetic, environmental, physiological and pathological factors responsible for interspecies and inter-individual variability in these processes. Recent advances in our understanding of active processes such as gut epithelial transporters, involved in absorption, and drug-metabolising enzymes, responsible for intestinal presystemic metabolism, are highlighted. Some major research priorities are identified, including the need for high-quality, information-rich databases against which testing methods being developed can be prevalidated and validated. Preclinical drug development is changing rapidly, and the role of in vitro and ex vivo approaches in this process is becoming increasingly more important. Methods available now are very useful in the drug discovery and development process, including lead compound selection and optimisation and in the design of very early clinical studies, but whether any of them will eventually obviate the need for clinical trials of bioavailability is still very debatable and will require their full validation. It is clear, however, that the results from such in vitro tests are important in shaping drug discovery and the early preclinical drug development process. For other environmental, industrial and household chemicals to which humans are exposed, in particular new chemicals, results from in vitro studies might be the only source of information concerning systemic availability.

Polymorphisms of CYP2A6 and its practical consequences

CYP2A6 is an hepatic enzyme predominantly with some expression in specialized extrahepatic cell types. The CYP2A6 enzyme has a somewhat restricted active site, accepting only a few xenobiotics as substrates. Interest in CYP2A6 has risen considerably after nicotine and some tobacco specific nitrosamines were established as high-affinity substrates for this enzyme. Recently, the organization and structures of the CYP2A gene cluster and several polymorphic alleles of the CYP2A6 gene have been characterized. Two alleles with a point mutation and at least three different types of gene deletion, all leading to deficient gene function, have been found. The frequencies of these alleles vary considerably among different ethnic populations, the deletion alleles being most common in Orientals (up to 20%). The frequency of point mutations are low in all populations studied thus far (< 3%). Several case-control studies have addressed the relationship between CYP2A6 status and smoking habits as well as the role of CYP2A6 polymorphism in lung cancer risk. Studies in Japanese suggest that CYP2A6 poor metabolizer genotypes result in altered nicotine kinetics and may lower cigarette smoking elicited lung cancer risk, whereas similar studies in Caucasian populations have not revealed any clear associations between variant CYP2A6 genotypes and smoking behaviour or lung cancer predisposition.

Expression of xenobiotic-metabolizing enzymes in human pulmonary tissue: possible role in susceptibility for ILD

The lung is a major target for all inhaled toxicants. Many inhaled chemicals are not hazardous as such, but are biotransformed to reactive intermediates. Therefore, the pathogenesis of interstitial and other lung diseases is intimately linked to exposure to environmental and other chemicals, which may be causative or modifying factors in the cellular pathways and mechanisms mediating oxidative stress and cell protection in the pulmonary tissue. Several different xenobiotic-metabolizing cytochrome P450 (CYP) and phase II enzymes (i.e. conjugation enzymes including several transferases) are present in the human lung and lung-derived cell lines, possibly contributing to in situ activation and inactivation of chemical toxicants. This paper describes the expression and localization of individual CYP-forms in the lung. Interindividual differences in the expression of these enzymes may contribute to the risk of developing interstitial and other lung diseases initiated by agents that require metabolic activation.

Interstitial lung disease induced by exogenous agents: factors governing susceptibility

The purpose of this review is to describe the present state of knowledge regarding host susceptibility factors that may determine the occurrence, development and severity of interstitial lung disease (ILD) caused by exogenous agents. First, host susceptibility may pertain to differences in the delivery and/or persistence of the noxious agent in the lung. The deposition and clearance of inhaled particles or fibres may vary depending on innate anatomical or physiological characteristics, and on acquired changes, such as nasal disease or smoking-induced alterations. Genetically- or environmentally-induced interindividual differences in the expression of pulmonary biotransformation enzymes may form the basis for, or contribute to the risk of, drug-induced interstitial lung disease. Secondly, there are genetic and acquired variations in various enzymatic and nonenzymatic defence systems that protect cells and tissues against oxidative stress, which is often involved in the pathogenesis of interstitial lung disease caused by particles, fibres, metals, organic agents and drugs. Thirdly, the occurrence of immunological sensitization is dependent on both genetic and environmental factors. This has been demonstrated in chronic beryllium lung disease and in hypersensitivity pneumonitis. Fourthly, the propensity of individuals to develop particular types of inflammation, such as granulomas, is probably under genetic control. The regulation and resolution of inflammation and fibrogenesis caused by dust particles are also partly determined by genetic factors, involving cytokine networks and growth factors. In conclusion, although the issue of genetics pervades the entire discussion of host susceptibility, genes are not the only determinants of health and disease. Environmental factors may be equally important in shaping host susceptibility. Therefore, research must be focused on both the genetic bases and the environmental determinants of interstitial lung disease, in order to provide mechanism-based prevention strategies, early detection of, and improved therapy for these conditions.

Distribution of cytochrome P4501A (CYP1A) in the tissues of Baltic ringed and grey seals

Information about the expression of CYP1A in wildlife species is essential for understanding the impact of organochlorine exposure on the health status of an exposed population. Therefore, we aimed at characterising a putative CYP1A enzyme expression in both hepatic and extrahepatic tissues of ringed and grey seals from the Baltic Sea and from less polluted waters. The cellular localisation of CYP1A was identified using a monoclonal antibody against scup P4501A1 (MAb 1-12-3). Immunohistochemical staining showed the highest level of CYP1A expression in liver hepatocytes, and the second highest level in the endothelial cells of capillaries and larger blood vessels in the liver and other organs. The most frequent and strongest staining was found in Baltic ringed seals. Although CYP1A-positive staining was observed in only a few tissues in the other seal populations, it was more intense in Baltic grey seals than in Canadian grey seals. The CYP1A enzyme activity, expressed as ethoxyresorufin O-deethylation (EROD), followed a similar tissue distribution and geographical pattern as the immunohistochemistry with clearly elevated EROD activities in most tissues of both Baltic seal populations. Immunochemical characterisation by immunoblotting confirmed the presence and elevation pattern of a putative CYP1A protein in ringed and grey seals, supporting our findings using other methods. The evenly distributed elevation of CYP1A expression among most of the tissues examined indicates that Baltic seals are exposed to CYP1A inducing agents affecting the whole body. This may result in an increased or decreased toxic potential of foreign substances, which may ultimately determine the biological effects of the contaminants.

Carbamazepine: a 'blind' assessment of CVP-associated metabolism and interactions in human liver-derived in vitro systems

1. The ability of various in vitro systems for CYP enzymes (computer modelling, human liver microsomes, precision-cut liver slices, hepatocytes in culture, recombinant enzymes) to predict various aspects of in vivo metabolism and kinetics of carbamazepine (CBZ) was investigated. 2. The study was part of the EUROCYP project that aimed to evaluate relevant human in vitro systems to study drug metabolism. 3. CBZ was given to the participating laboratories without disclosing its chemical nature. 4. The most important enzyme (CYP3A4) and metabolic route (10,11-epoxidation) were predicted by all the systems studied. 5. Minor enzymes and routes were predicted to a different extent by various systems. 6. Prediction of a clearance class, i.e. slow clearance, was correctly predicted by microsomes, slices, hepatocytes and recombinant enzymes (CYP3A4). 7. The 10,11-epoxidation of CBZ by the recombinant CYP3A4 was enhanced by the addition of exogenous cytochrome-b5, leading to a considerable over-prediction. 8. Induction potency of CBZ was predicted in cultured hepatocytes in which 7-ethoxycoumarin O-deethylase was used as an index activity. 9. It seems that for a principally CYP-metabolized substance such as CBZ, all liver-derived systems provide useful information for prediction of metabolic routes, rates and interactions.

An assessment of human liver-derived in vitro systems to predict the in vivo metabolism and clearance of almokalant

The ability of various human derived in vitro systems to predict various aspects of the in vivo metabolism and kinetics of almokalant have been investigated in a multicenter collaborative study. Although almokalant has been withdrawn from further clinical development, its metabolic and pharmacokinetic properties have been well characterized. Studies with precision-cut liver slices, primary hepatocyte cultures, and hepatic microsomal fractions fortified with UDP-glucuronic acid all suggested that almokalant is mainly glucuronidated to the stereoisomers M18a and M18b, which is in good agreement with the results in vivo. Both in vivo and in vitro studies indicate that the formation of M18b dominates over that of M18a, although the difference is more pronounced with the in vitro systems. Molecular modeling, cDNA-expressed enzyme analysis, correlation analysis, and inhibition studies did not clearly indicate which P450 enzymes catalyze the oxidative pathways, which may indicate a problem in identifying responsible enzymes for minor metabolic routes by in vitro methods. All of the in vitro systems underpredicted the metabolic clearance of almokalant, which has previously been reported to be a general problem for drugs that are cleared by P450-dependent metabolism. Although few studies on in vivo prediction of primarily glucuronidated drugs have appeared, in vitro models may consistently underpredict in vivo metabolic clearance. We conclude that in vitro systems, which monitor phase II metabolism, would be beneficial for prediction of the in vivo metabolism, although all of the candidate liver-derived systems studied here, within their intrinsic limitations, provided useful information for predicting metabolic routes and rates.

In vitro inhibition of cytochrome P450 enzymes in human liver microsomes by a potent CYP2A6 inhibitor, trans-2-phenylcyclopropylamine (tranylcypromine), and its nonamine analog, cyclopropylbenzene

Currently, there are no selective, well characterized inhibitors for CYP2A6. Therefore, the effects of trans-(+/-)-2-phenylcyclopropylamine (tranylcypromine), a potent CYP2A6 inhibitor, on human liver microsomal cytochromes P450 (CYP) were studied to elucidate its selectivity. The IC50 value of tranylcypromine in coumarin 7-hydroxylation (CYP2A6 model activity) was 0.42 +/- 0.07 microM and in chlorzoxazone 6-hydroxylation (CYP2E1 model activity) 3.0 +/- 1.1 microM. The IC50 values for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 activities were >10 microM. Potency and selectivity of tranylcypromine were strongly dependent on the amine group, because its nonamine analog cyclopropylbenzene was much less potent inhibitor of CYP1A, CYP2A6, CYP2C19, and CYP2E1 activities and did not inhibit at all CYP2C9, CYP2D6, or CYP3A4 activities. In human liver microsomes tranylcypromine induced type II and cyclopropylbenzene type I difference spectrum. According to the double reciprocal analysis of these spectral responses both tranylcypromine and cyclopropylbenzene may have at least two P450-related binding sites in liver microsomes. The K(a) values of tranylcypromine varied from 4.5 to 15.1 microM and -34.3 to 167 microM in microsomes derived from three different livers and of cyclopropylbenzene from -1.6 to 10.1 microM and -34.6 and 75.2 microM in the same liver microsomes. Based on these results, tranylcypromine seems an adequately selective CYP2A6 inhibitor for in vitro use.

cAMP mediated upregulation of CYP2A5 in mouse hepatocytes

CYP2A5 is induced by a large number of chemicals including some cAMP modifiers. In a primary hepatocyte model, stimulation of the cAMP signal transduction pathway by glucagon and isoproterenol, acting via specific G-protein coupled plasma membrane receptors, produced up to 17-fold increases in the marker activity of CYP2A5, coumarin 7-hydroxylase. In contrast, glucagon and isoproterenol caused no significant effects on two other major CYP forms, CYP2B10 and CYP1A1/2. Phenobarbital (PB) elicited a 3-fold increase in CYP2A5 expression (catalytic activity and mRNA), while the cAMP and protein kinase A (PKA) stimulators dibutyryl-cAMP, forskolin and Sp-cAMPs caused up to 18-fold increases in the amount of CYP2A5 mRNA. Coadministration of PB and cAMP/PKA stimulating agents produced an additive inducing effect. The expression of CYP2A5, but not CYP2B10 or CYP1A1/2, in DBA/2 mice displayed a marked circadian rhythm, the level of expression being highest in the evening. These results suggest that among xenobiotic metabolizing CYP enzymes, CYP2A5 is uniquely upregulated by cAMP, possibly having the physiological function of priming the olfactory and digestive systems for nocturnal feeding.

Characterization of xenobiotic-metabolizing cytochrome P450 (CYP) forms in ringed and grey seals from the Baltic Sea and reference sites

Earlier studies have shown that members of the cytochrome P4501 (CYP1) enzyme family are constitutively expressed, and are elevated in the livers of ringed seals (Phoca hispida) and grey seals (Halichoerus grypus) living in the heavily polluted Baltic Sea. In this study, we compared the expression profiles of several additional CYP enzymes in the liver and extrahepatic tissues of Baltic ringed and grey seals with the corresponding CYP expression in seals from relatively unpolluted waters. We used marker enzyme activity levels, diagnostic inhibitors and immunoblot analysis to assess members of the CYP2A, CYP2B, CYP2C, CYP2D, CYP2E and CYP3A sub-families. Coumarin 7-hydroxylation (COH), a marker of CYP2A activity, was high in the liver and the lungs of all the studied seal populations. The presence of a putative CYP2A form in these seals was further supported by the strong inhibition of COH activity by a chemical inhibitor and by an anti-CYP2A5 antibody. However, antibodies to human and rodent CYP2B, CYP2C and CYP2E forms did not recognize any proteins in these seal species. Dextromethorphan O-demethylation (marker for CYP2D activity) and chlorzoxazone 6-hydroxylation (marker for CYP2E activity) were measurable in the livers of all the seals we studied. Both activities were elevated in the Baltic seal populations, showed a strong positive correlation with CYP1A activity and were at least partly inhibited by a typical CYP1A inhibitor, alpha-naphthoflavone. Further studies are needed to determine the presence and characteristics of CYP2D and CYP2E enzymes in ringed and grey seals. Testosterone 6beta-hydroxylation, a CYP3A marker, showed a relatively high level of activity in the livers of both seal species and was potently inhibited by ketoconazole, a CYP3A-selective inhibitor. The putative CYP3A activity showed an opposing geographical trend to that of CYP2D and CYP2E, since it was elevated in the control area. CYP3A protein levels, revealed by immunoblotting, showed a positive correlation with testosterone 6beta-hydroxylation. We conclude tentatively that CYP2A- and CYP3A-like enzymes are expressed in ringed and grey seals, but that CYP2B- and CYP2C-like ones are not. Further information on the individual contaminant profile is needed before any conclusions can be drawn on a possible connection between the varying CYP expressions and the contaminant load.

CYP2A5/CYP2A6 expression in mouse and human hepatocytes treated with various in vivo inducers

Induction of coumarin 7-hydroxylation, catalyzed by CYP2A5 in mice and CYP2A6 in humans by various known in vivo murine inducers and modifiers, was compared in human and mouse hepatocytes in culture. Phenobarbital and rifampicin were efficient inducers (up to 10-fold induction) after 48-h treatment in murine cultured hepatocytes, whereas the enzyme activity in human hepatocytes was much more refractory to induction. However, a prolongation of incubation time to 72 h in human hepatocytes led to a modest restoration of inducibility by phenobarbital. Of the three porphyrinogenic inducers studied, griseofulvin induced the murine enzyme efficiently, but not the human enzyme, whereas aminotriazole and thioacetamide had no effect on either species. Pyrazole produced substantial induction in both human and murine hepatocytes, whereas cobalt chloride, which is also an in vivo inducer of the mouse enzyme, had no effect. Clofibric acid, an in vivo depressor of coumarin 7-hydroxylase, also depressed hepatocyte activities. In both murine and human hepatocytes, changes in CYP2A5/6 mRNA levels correlated roughly with enzyme changes, except in the case of cobalt chloride, which increased mRNA levels despite a lack of effect on enzyme activity. In general, human and mouse hepatocytes gave a similar response to CYP2A inducers. However, some differences were found, which means that, although CYP2A isozymes are probably regulated in a similar manner in both species, it is necessary to be cautious before extrapolating to human the results found in mouse models.

Differential maintenance of cytochrome P450 enzymes in cultured precision-cut human liver slices

The maintenance of the major hepatic cytochrome P450 (CYP) enzymes has been studied in precision-cut human liver slices cultured for up to 72 h in supplemented RPMI 1640 medium. The relative apoprotein levels of 11 CYP enzymes were determined using a panel of antipeptide antibodies. In addition, 7-ethoxyresorufin O-deethylase, tolbutamide methylhydroxylase, debrisoquine 4-hydroxylase, and testosterone 6beta-hydroxylase activities were determined as enzymatic markers for CYP1A2, CYP2C9, CYP2D6, and CYP3A4, respectively. There was a large variation in the rate of decline of different CYP levels with time in culture. Based on the rate of decrease, CYP enzymes could be separated into two groups, with CYP2C9, CYP2D6, CYP3A4, and CYP4A11 being relatively stable (half-lives between 70 and 104 h), compared with CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, and CYP3A5, which were relatively unstable (half-lives between 23 and 36 h). Enzyme activities decreased at rates similar to those of their corresponding apoproteins. There was also a large difference in the stability of individual CYP enzymes from different liver donors, particularly for the most rapidly declining CYP enzymes. Similar losses of CYP enzymes were found when human liver slices were cultured in supplemented Williams' medium E for 72 h, except that CYP2E1 apoprotein levels were better maintained. Because of the variable decreases of CYP enzymes, xenobiotic metabolism studies are best performed with freshly cut rather than cultured human liver slices.

Synthesis of new potent and selective aromatase inhibitors based on long-chained diarylalkylimidazole and diarylalkyltriazole molecule skeletons

A series of long-chained diarylalkylimidazoles and diarylalkyltriazoles were synthesized and evaluated for the inhibitory potency for aromatase (estrogen synthetase) activity in human placental microsomes. The relative specificity of inhibition was evaluated by measuring the inhibition of cholesterol side-chain cleavage enzyme (desmolase) in human placental mitochondria and the inhibition of 7-ethoxycoumarin O-deethylase (a typical drug-metabolizing enzyme activity) in rat liver microsomes. The structural requirements including substituent effects for the strongest potency and for the highest specificity were delineated. alpha,omega-Diarylalkyltriazoles and imidazoles were the most interesting molecules, in which the geometric and optical isomerism displayed remarkable selectivity for aromatase inhibition.

Expression and inducibility of members in the cytochrome P4501 (CYP1) family in ringed and grey seals from polluted and less polluted waters

The expression and inducibility of cytochrome P4501A (CYP1A) were investigated in hepatic microsomes of ringed seals (Phoca hispida) and grey seals (Halichoerus grypus) from polluted (Baltic Sea) and less polluted (Svalbard and Sable Island) areas. Liver CYP1A protein levels and activities were assessed by immunoblot analysis and determining catalytic activities towards ethoxyresorufin (EROD) and pentoxyresorufin (PROD). The amount of CYP1A apoprotein and its catalytic activity were increased up to 5-fold in Baltic ringed and grey seal populations in comparison with ringed seals from Svalbard and grey seals from Sable Island. EROD and PROD activities correlated in all seal groups, indicating catalysis by the same CYP form(s). Enzyme kinetic studies suggested that PROD activity is catalysed by CYP1A enzymes in both ringed and grey seals. In immunoblot analysis, a protein was revealed in liver with an antibody against human CYP1B1, indicating that a CYP1B1 like protein could be present in ringed and grey seals. In conclusion, these data strengthen the concept that CYP1A is markedly induced in seals living in polluted waters and that both EROD and PROD activities are mediated by CYP1A forms in the seal liver. In addition, this study provides the first evidence for the presence of a CYP1B like protein in seal liver.

In vitro inhibition screening of human hepatic P450 enzymes by five angiotensin-II receptor antagonists

OBJECTIVE

Metabolic interactions at the level of drug-metabolising enzymes are important for drug therapy. We investigated potential interactions of losartan, irbesartan, valsartan, eprosartan and candesartan with cytochrome P450 (CYP) enzymes in human liver microsomes.

METHODS

In incubations with human liver microsomes in vitro, the inhibitory potency of angiotensin-II receptor antagonists (sartans) on CYP-specific model activities were compared by measuring the IC50 and, with respect to more potent inhibition, Ki values.

RESULTS

None of the five sartans inhibited CYP2A6-, CYP2D6- or CYP2E1-associated activities (coumarin 7-hydroxylation, dextromethorphan O-demethylation and chlorzoxazone 6-hydroxylation, respectively) to any significant extent. Losartan and irbesartan inhibited the CYP2C9-associated tolbutamide methylhydroxylation more potently (Ki values 4.1 microM and 24.5 microM), than valsartan, candesartan or eprosartan (Ki values 135 microM, 155 microM and > 1000 microM, respectively). Losartan and irbesartan inhibited CYP1A2- and CYP3A4-associated activities (ethoxyresorufin O-deethylation and testosterone 6beta-hydroxylation) with relatively weak affinities (IC50 values between 200 microM and 500 microM). CYP2C1OFF S-mephenytoin 4'-hydroxylation activity was inhibited by losartan (IC50 value 138 microM) and much less or not at all by the other sartans tested.

CONCLUSION

All sartans except eprosartan have at least some affinity for CYP2C9, but only losartan has an affinity for CYP2C19. Losartan and irbesartan have modest affinity for CYP1A2 and CYP3A4. This would suggest that the theoretical potential for drug interactions is likely to be quite low, with the possible exceptions of losartan and irbesartan for CYP2C9. Based on these findings, further studies on the interaction potential of losartan and irbesartan are warranted.

Selegiline metabolism and cytochrome P450 enzymes: in vitro study in human liver microsomes

Although being a drug therapeutically used for a long time, the enzymatic metabolism of selegiline has not been adequately studied. In the current work we have studied the cytochrome P450 (CYP)-catalyzed oxidative metabolism of selegiline to desmethylselegiline and 1-methamphetamine and the effects of selegiline, desmethylselegiline and 1-methamphetamine on hepatic CYP enzymes in human liver microsomes in vitro. The apparent Km values for desmethylselegiline and 1-methamphetamine formation were on an average 149 microM and 293 microM, and the apparent Vmax values, 243 pmol/min./mg and 1351 pmol/min./mg, respectively. Furafylline and ketoconazole, the known reference inhibitors for CYP1A2 and CYP3A4, respectively, inhibited the formation of desmethylselegiline with Ki value of 1.7 microM and 15 microM. Ketoconazole inhibited also the formation of 1-methamphetamine with Ki of 18 microM. Fluvoxamine, an inhibitor of CYP1A2, CYP2C19 and CYP3A4, inhibited the formation of desmethylselegiline and 1-methamphetamine with Ki values of 9 and 25 microM, respectively. On the basis of these results we suggest that CYP1A2 and CYP3A4 contribute to the formation of desmethylselegiline and that CYP3A4 participates in the formation of 1-methamphetamine. In studies with CYP-specific model activities, both selegiline and desmethylselegiline inhibited the CYP2C19-mediated S-mephenytoin 4'-hydroxylation with average IC50 values of 21 microM and 26 microM, respectively. The Ki for selegiline was determined to be around 7 microM. Selegiline inhibited CYP1A2-mediated ethoxyresorufin O-deethylation with a Ki value of 76 microM. Inhibitory potencies of selegiline, desmethylselegiline and 1-methamphetamine towards other CYP-model activities were much lower. On this basis, selegiline and desmethylselegiline were shown to have a relatively high affinity for CYP2C19, but no evidence about selegiline metabolism by CYP2C19 was obtained.

CYP2A6: a human coumarin 7-hydroxylase

Coumarin 7-hydroxylation is catalysed by a high-affinity CYP2A6 enzyme in human liver microsomes. CYP2A6 is the only enzyme catalysing this reaction and consequently the formation of 7-hydroxycoumarin can be used as 'an in vitro and in vivo probe' for CYP2A6. CYP2A6 is a major contributor to the oxidative metabolism of nicotine and cotinine, and it also contributes, to a larger or smaller extent, to the metabolism of a few pharmaceuticals (e.g. fadrozole), nitrosamines, other carcinogens (e.g. aflatoxin B1) and a number of coumarin-type alkaloids. CYP2A6 may be inducible by antiepileptic drugs and it is decreased in alcohol-induced severe liver cirrhosis. Several mutated or deleted CYP2A6 alleles have been characterized. Although CYP2A6 represent up to 15% of human microsomes P450 proteins, it is still one of the less well characterised cytochrome P450 enzymes.

Antepartum glucocorticoid therapy suppresses human placental xenobiotic and steroid metabolizing enzymes

We investigated the effects of maternal gestational corticosteroid therapy on placental xenobiotic and steroid metabolizing enzymes at term in 20 glucocorticoid/betamethasone treated (with various doses) and control (n=10) women. A single dose of betamethasone (12 mg i.m. twice at a 24-h interval) was given to 15 mothers at risk of preterm delivery to prevent respiratory syndrome in their premature newborns. Five mothers were treated more than once. The gestation time in mothers receiving the glucocorticoid therapy varied from 22-38 gestational weeks. Compared with controls, a significant decrease in placental aromatase activity (53.6+/-18.0 pmol/mg/min versus 119+/-30 pmol/mg/min, P=0.0007) and placental CYP19 mRNA content (by 50 per cent ) was observed in mothers treated with glucocorticoids. Also the formation of androstenedione (13.2+/-8.1 pmol/mg/min, steroids versus 30.03+/-5.2 pmol/mg/min, controls, P< 0.001), using testosterone as the substrate, and 7-ethoxycoumarin O-deethylase (P< 0.05) and 7-ethoxyresorufin O-deethylase (P< 0.09) were slightly decreased in the glucocorticoid treated compared to control patients' values. The changes were not dependent on the number of treatments or the time between treatment and delivery. Our results demonstrate that even a single dose of glucocorticoid given to expectant mothers is associated with diminished placental steroid hormone and xenobiotic metabolizing enzymes at term. Further studies are needed to assess whether these changes affect the well-being of the fetus and its later development.