Interaction of terfenadine and its primary metabolites with cytochrome P450 2D6

The substrate structure-activity relationships described for the major human drug-metabolizing cytochrome P450 (P450 or CYP) enzymes suggest that the H1 receptor antagonist terfenadine could interact with CYP2D6 either as a substrate or as an inhibitor, in addition to its known ability to act as a substrate for CYP3A4. Based on this substrate structure-activity relationship, computer modeling studies were undertaken to explore the likely interactions of terfenadine with CYP2D6. An overlay of terfenadine and dextromethorphan, a known substrate of CYP2D6, showed that it was possible to superimpose the site of hydroxylation (t-butyl group) and the nitrogen atom of terfenadine with similar regions in dextromethorphan. These observations were substantiated by the ease of docking of terfenadine into a protein model of CYP2D6. Experimentally, terfenadine inhibited CYP2D6 activity in human liver microsomes with an IC50 of 14-27 microM, depending on the CYP2D6 substrate used. The inhibition of CYP2D6 was further defined by determining the Ki for terfenadine against bufuralol 1'-hydroxylase activity in four human livers. Terfenadine inhibited bufuralol 1'-hydroxylase activity with a Ki of approximately 3.6 microM. The formation of the hydroxylated metabolite (hydroxyterfenadine) in microsomes prepared from human liver and specific P450 cDNA-transfected B lymphoblastoid cells indicated that only CYP2D6 and CYP3A4 were involved in this transformation. As expected, the rate of formation was greatest with CYP3A4 (Vmax = 1257 pmol/min/nmol of P450), with CYP2D6 forming the metabolite at a 6-fold lower rate (Vmax = 206 pmol/min/nmol of P450). The two enzymes had similar KM values (9 and 13 microM, respectively). These data indicate that, as predicted from modeling studies, terfenadine has the structural features necessary for interaction with CYP2D6.

Contribution of sex and genetics to neuroendocrine adaptation to stress in mice

Male and female C57BL/6 (B6) and DBA/2 (D2) mice were subjected to either acute or 5 days of repeated restraint in ventilated, 50 ml centrifuge tubes. Control animals were not disturbed. The acute restraint animals were killed immediately following 15, 30 or 60 min of restraint and blood collected for corticosterone (CORT) analysis. The results of the acute restraint procedure revealed a strain difference in time to peak CORT in plasma with D2 animals showing an earlier peak. The males of both strains evinced similar maximum response and similar to B6 females; however, the D2 females showed a 2-fold greater CORT response than did the B6 females. Repeated restraint consisted of 5 days of 12 h in the tubes. At the end of 5 days, the animals were weighted and adrenalectomized in preparation for determination of brain corticosteroid receptors. Upon sacrifice, brains, thymus, adrenals and blood were harvested, the last for corticosteroid binding globulin (CBG). Five days of repeated restraint produced body weight loss in both strains, with B6s less affected than D2s. Repeated restraint reduced the mass of the adrenals in the B6s only. Restraint also reduced the mass of the thymus in both strains and sexes, but to a greater extent in the B6s. Plasma CBG densities were also sensitive to restraint, but only in females, showing a restraint-related decrease. Repeated restraint had no effect on hippocampal glucocorticoid or mineralocorticoid receptors; however for the latter, we observed significant strain and sex effects with D2 having higher Bmax than B6 and females having higher Bmax than males. In the pituitary, glucocorticoid receptors (GR) were reduced by repeated restraint in males, but increased in females, especially in the B6. These findings lend preliminary evidence for involvement of sex and genetics as sources of individual differences in bioadaptation to stress.

The effect of age and testosterone on the expression of glial fibrillary acidic protein in the rat cerebellum

Testosterone reversed the age-related increase in glial fibrillary acidic protein (GFAP) in the male rat cerebellum, a brain region not generally associated with gonadal steroid hormone sensitivity. This supports the hypothesis that a decrease in circulating testosterone contributes to age-related increase in GFAP. These data also suggest that reductions in circulating gonadal steroids during aging could render the brain more susceptible to neurodegeneration and that hormone replacement therapy might have value in neurodegenerative disease intervention.

A genetic basis for neuroendocrine-immune interactions

Psychoneuroimmunology is an exciting, complex field that elucidates interactions among the nervous, endocrine, and immune systems. The contribution of psychosocial factors and behavioral processes to these interactions has been the focus of numerous studies designed to investigate the intricate pathways that are involved in the "mind-body connection." In addition, the effects of this connection on the development and progression of various disease conditions are of considerable interest. Although efforts have been made to identify the cellular and molecular mechanisms underlying these relationships, the impact of genetic makeup on the communication among these systems has yet to be fully realized. The development of sophisticated genetic analytical methods and gene mapping techniques now provide the "tools" to determine the influence of genetics on behavior-neuroendocrine-immune interactions--an area of study that may represent the next frontier in psychoneuroimmunology.

Ethanol modulates cocaine-induced behavioral change in inbred mice

We recently conducted a study of the behavioral effects of combined cocaine and ethanol in genetically defined mice. Male and female C57BL/6 (B6) and DBA/2 (D2) were tested in an automated activity monitor on 2 consecutive days. On day 1, all animals received an IP injection of sterile saline and were placed into the activity monitor for 30 min. Behaviors measured were total distance traveled, stereotypy, nosepokes, and wall-seeking. On day 2, all animals were tested again for 15 min following injection of one of the following: saline, 10% v/v ethanol at 2.0 g kg(-1) or 2.0 g kg(-1) ethanol plus 5, 15, or 30 mg kg(-1) cocaine. Cocaine alone at the same doses was injected into separate groups of animals. For the B6 strain, the overall effect of ethanol was to reduce cocaine-induced locomotor stimulation; no consistent effect of ethanol on cocaine-induced locomotion was observed in D2 mice. Cocaine-induced inhibition of nosepokes in both strains and sexes was partially reversed by ethanol. Ethanol also partially reversed cocaine-elevated stereotypy in both strains and both sexes. In B6 mice, cocaine-increased wall seeking tended to be reversed by coadministration of ethanol, whereas no consistent pattern was observed in the D2s. Results from this study suggest that the several measures affected by cocaine (locomotor activity, stereotypy, exploration, thigmotaxis) were, in turn, differentially affected by concurrent treatment with ethanol. Furthermore, our results point to genetic-based differences in ethanol's effects on cocaine-related behaviors. We address the implications for combined ethanol and cocaine use in humans.

Distribution and clearance of cocaine in brain is influenced by genetics

The purpose of this study was to examine the pharmacokinetics of cocaine in two inbred mouse strains, C57BL/6 (B6) and DBA/2 (D2). Male and female mice were administered 30 mg kg(-1) cocaine IP and killed after 5, 15, 30, or 60 minutes postinjection. Brains were removed quickly and assayed for total brain cocaine concentration. Quantification of cocaine was conducted using gas chromatography and mass spectrometry. The results of this study revealed a strain difference in total brain cocaine kinetics. Specifically, we observed that at 5 min onward, B6 mice cleared cocaine from the brain with a t1/2 estimated at 22.3 min, while distribution in D2 mice appeared to be incomplete until 15 min with a subsequent t1/2 estimated at 11.2 min. These results show that despite faster clearance by D2 mice, the prolonged time to distribution in this strain may help explain why D2 mice show initial greater locomotor activation by cocaine, compared to B6s.

Differential effects of stress-induced adrenal function on components of the herpes simplex virus-specific memory cytotoxic T-lymphocyte response

We have previously demonstrated in a murine model system that psychological stress, applied in the form of physical restraint, suppresses both the activation of splenic-derived, herpes simplex virus (HSV)-specific memory cytotoxic T-lymphocytes (CTLm) to the lytic phenotype and the production of cytokines associated with CTL activation and function. In the studies described herein, we investigated the hypothesis that an adrenal-dependent event is responsible, either in whole or in part, for these observations. While adrenalectomy was shown to abrogate stress-induced suppression of both HSV-specific CTLm activation and the production of IL-6 and IFN-gamma, the reduction in splenic cellularity associated with restraint stress remained, In addition, a role for adrenal function in the regulation of splenic cellularity and IFN-gamma production in non-stressed mice was observed. Together, these results indicate that both adrenal-dependent and adrenal-independent events, operative under both baseline and stress conditions, mediate control of the memory component of the cellular immune response to HSV infection. Overall, these studies provide insight into the mechanisms by which psychological stress modulates immune responsiveness to viral pathogens.

Mapping of provisional quantitative trait loci influencing temporal variation in locomotor activity in the LS x SS recombinant inbred strains

The finding that stress-induced locomotor activity exhibited a significant strain x time interaction in the LS x SS RI strains prompted examination of QTL influencing this behavior as a function of time. The degree of genetic determination for locomotor activity was 0.26 for the first 5 min and decreased to 0.16 for the last 5 min of a 30-min test but the number of genetic factors stayed relatively constant (three or four) across time. A QTL point analysis revealed a total of 15 QTL, 5-8 per 5-min time block. Few of the QTL were detected across all time points and different combinations of QTL were evident for each time period. Five of the QTL were in common with those reported by other investigators for similar behaviors. The results suggest that locomotor behavior is under a greater degree of genetic control during the initial part of the test but environmental factors become increasingly important as the test progresses. Furthermore, different genetic factors appear to be mediating genetic variation in locomotor behavior at any given time point.

Hypervascular liver metastases: do unenhanced and hepatic arterial phase CT images affect tumor detection?

PURPOSE

To evaluate the relative roles of unenhanced and hepatic arterial phase (HAP) computed tomographic (CT) imaging in the detection of hypervascular liver metastases.

MATERIALS AND METHODS

Eighty-four patients with biopsy-proved liver metastases from hypervascular primary tumors other than hepatocellular carcinoma underwent unenhanced and HAP and portal venous phase (PVP) helical CT studies. Three blinded radiologists evaluated each series of images separately for the number, size, and enhancement characteristics of lesions. Sixty-nine patients had follow-up imaging proof of tumor burden.

RESULTS

The three readers detected 381-402 lesions on the PVP images and 397-416 lesions on the unenhanced images. Unenhanced images allowed detection of 72%-80% of the lesions seen on PVP images. They detected 94-137 additional lesions on unenhanced but not PVP images. On the HAP images, 375-395 lesions were identified. HAP images allowed detection of 81%-90% of the lesions seen on PVP images. Forty-five to 78 additional lesions were detected on HAP but not on PVP images. In the 69-patient subset, maximal detection of tumor foci occurred in 94% of patients with unenhanced plus PVP images and in 78% with HAP plus PVP images. Unenhanced plus PVP images allowed detection of 96% of the 322 tumors in the subset population.

CONCLUSION

Unenhanced plus PVP CT images allow detection of statistically significantly more hypervascular liver metastases than do HAP plus PVP images or imaging only in the PVP.

Sex and strain influence the effect of ethanol on central monoamines

OBJECTIVE

We recently investigated the effects of EtOH on the mesolimbic dopamine and serotonin systems in male and female C57BL/6 (B6) and DBA/2J (D2) mice.

METHOD

Male and female rodents from the B6 and D2 mouse strains (n = 11 per strain, sex and dose) were used in this study. Doses of EtOH (vs saline) administered were 1.0, 2.0 or 3.0 g/kg.

RESULTS

Treatment with saline or EtOH produced both strain- and sex-dependent differences in patterns of monoamine response. For example, D2s exhibited significantly higher overall dopamine (DA) levels than did B6s in the frontal cortex (FC), nucleus accumbens (NA) and caudate-putamen (CP). In the FC, female D2 evinced elevated 5HIAA at 1.0 g/kg. In the NA, D2 females showed dose related increases in levels of DA up to 3.0 g/kg, whereas in the D2 males and in B6 males and females we observed no response. Also in the NA, B6 males showed increases in dihydroxyphenyacetic acid (DOPAC) at 1.0 and 3.0 g/kg. In the CP, B6 males showed higher DA levels than B6 females at the saline, and all EtOH doses. For serotoninergic activity in the CP as well as the NA, EtOH produced a distinctive triphasic response, with the 1.0 and 3.0 g/kg doses of EtOH producing higher levels than saline and 2.0 g/kg of 5HIAA in B6 males than in B6 females.

CONCLUSIONS

Our findings indicate strain and sex differences in monoamine response to acute doses of ethanol, and further implicate (via changes in DOPAC) presynaptic mechanisms in the effects of ethanol on dopamine.

Identification of the cytochrome P450 isoforms involved in the O-demethylation of 4-nitroanisole in human liver microsomes

1. 4-Nitroanisole is O-demethylated to 4-nitrophenol by human liver microsomes. Kinetic studies indicate that this metabolic route is mediated by two cytochrome P450 isoforms, one with a K(m) = 2.1 microM and the other with a K(m) = 220 microM. 2. Chemical inhibition and correlation studies in human liver microsomes indicate that the low K(m) enzyme is CYP2A6 and the high K(m) enzyme is CYP2E1 suggesting that44-nitroanisole is not a general cytochrome P450 substrate. 3. Studies using expressed recombinant cytochrome P450s indicated that all the cytochrome P450s investigated metabolized 4-nitroanisole but CYP2A6 and CYP2E1 produced the highest rates. Kinetic studies with these two isoforms produced a K(m) for CYP2A6 of 9 microM and 54 microM for CYP2E1. 4. The involvement of these two isoforms in the O-demethylation of 4-nitroanisole can be rationalized in terms of a hydrogen bond interaction with the nitro group and the active site of CYP2A6 and a hydrophobic interaction with the active site of CYP2E1.

The prediction of human pharmacokinetic parameters from preclinical and in vitro metabolism data

We describe a comprehensive retrospective analysis in which the abilities of several methods by which human pharmacokinetic parameters are predicted from preclinical pharmacokinetic data and/or in vitro metabolism data were assessed. The prediction methods examined included both methods from the scientific literature as well as some described in this report for the first time. Four methods were examined for their ability to predict human volume of distribution. Three were highly predictive, yielding, on average, predictions that were within 60% to 90% of actual values. Twelve methods were assessed for their utility in predicting clearance. The most successful allometric scaling method yielded clearance predictions that were, on average, within 80% of actual values. The best methods in which in vitro metabolism data from human liver microsomes were scaled to in vivo clearance values yielded predicted clearance values that were, on average, within 70% to 80% of actual values. Human t1/2 was predicted by combining predictions of human volume of distribution and clearance. The best t1/2 prediction methods successfully assigned compounds to appropriate dosing regimen categories (e.g., once daily, twice daily and so forth) 70% to 80% of the time. In addition, correlations between human t1/2 and t1/2 values from preclinical species were also generally successful (72-87%) when used to predict human dosing regimens. In summary, this retrospective analysis has identified several approaches by which human pharmacokinetic data can be predicted from preclinical data. Such approaches should find utility in the drug discovery and development processes in the identification and selection of compounds that will possess appropriate pharmacokinetic characteristics in humans for progression to clinical trials.

Synthetic strategies to lower affinity for CYP2D6

There are several models for the CYP2D6 active site with the characteristics of their substrates and inhibitors well defined. Imipramine possesses such characteristics and is both a substrate and an inhibitor of the CYP2D6 enzyme. Possible synthetic strategies to avoid interaction with the enzyme have been investigated, including: attenuation of basicity; and alteration of rigidity and length of the alkyl chain. Imipramine inhibited the 1'-hydroxylation of bufuralol (10 microM), an in vitro marker of CYP2D6 activity, in a CYP2D6 cell line (IC50 = 2.4 microM). Inhibitory potency was attenuated by the removal of the basic centre; imipramine N-oxide had no inhibitory effect on bufuralol 1'-hydroxylation. However, removal of this basic centre, as a strategy to decrease CYP2D6 interaction, may well have a detrimental effect on pharmacological efficacy. Both an increase and decrease in the N-N carbon chain length [2C,4C] caused a reduction in inhibitory potency. In addition, introduction of a carbonyl adjacent to the amino dibenzyl moiety into 2C, 3C and 4C compounds brought about a further reduction in inhibitory potency. These data demonstrate that changes to the molecule, distal to the basic centre, can attenuate the affinity of the molecule for CYP2D6 and are in keeping with the known characteristics of the enzyme.

Genotypic selection provides experimental confirmation for an alcohol consumption quantitative trait locus in mouse

Quantitative genetic research has produced a wealth of basic information concerning genetic influence on alcohol-related processes. Recent developments in quantitative trait locus (QTL) methodology were promptly applied to the task of individuating polygenes affecting alcohol-related attributes in animal models and a body of reliable data is gradually coming into focus as a result of replication and convergence of evidence from a variety of methods. A key issue in QTL research is the need to distinguish true positive results from the false positive results that are inherent in analytical procedures requiring large numbers of significance tests. One school of thought holds that stringent significance levels should be imposed; another suggests more modest criteria for QTL nomination, with subsequent confirmation trials with independent samples. Recombinant inbred strains and various types of intercrosses have been used in correlational designs, both for nomination and confirmation studies. Alternative experimental procedures include knockout preparations and short-term phenotypic selective breeding. We present here results from a third experimental method-that of marker-based genotypic selection--in evaluation of two nominated QTLs for alcohol acceptance in mice.

A second catalytic metal ion in group I ribozyme

Although only a subset of protein enzymes depend on the presence of a metal ion for their catalytic function, all naturally occurring RNA enzymes require metal ions to stabilize their structure and for catalytic competence. In the self-splicing group I intron from Tetrahymena thermophila, several divalent metals can serve structural roles, but only Mg2+ and Mn2+ promote splice-site cleavage and exon ligation. A study of a ribozyme reaction analogous to 5'-splice-site cleavage by guanosine uncovered the first metal ion with a definitive role in catalysis. Substitution of the 3'-oxygen of the leaving group with sulphur resulted in a metal-specificity switch, indicating an interaction between the leaving group and the metal ion. Here we use 3'-(thioinosylyl)-(3'-->5')-uridine, IspU, as a substrate in a reaction that emulates exon ligation. Activity requires the addition of a thiophilic metal ion (Cd2+ or Mn2+), providing evidence for stabilization of the leaving group by a metal ion in that step of splicing. Based on the principle of microscopic reversibility, this metal ion activates the nucleophilic 3'-hydroxyl of guanosine in the first step of splicing, supporting the model of a two-metal-ion active site.

Inhibition of replication of hepatitis B virus by cytallene in vitro

The acyclic cytosine nucleoside analog cytallene [1-(4'-hydroxy-1',2'-butadienyl)cytosine], which has both (+)- and (-)-enantiomers, was evaluated for its anti-hepatitis B virus (HBV) activity in 2.2.15 cells and was found to have potent activity against HBV DNA synthesis. The R-(-)-enantiomer was found to be the more active of the cytallene enantiomers, with a 50% inhibition concentration against HBV synthesis (HBIC50) of 0.08 microM. Its antiviral activity could be reversed by deoxycytidine (dC) and less efficiently by cytidine. Upon removal of the R-(-)-enantiomer from culture medium, the synthesis of HBV DNA could reinitiate, which suggested that the antiviral action is reversible. The R-(-)-enantiomer was also found to be more cytotoxic than the S-(+)-enantiomer. The degree of cytotoxicity varied among the cell lines, with a 50% inhibition of cell growth at greater than 10 microM. The R-(-)-enantiomer had no effect on HBV RNA synthesis and mitochondrial DNA synthesis at a concentration of 10 times or more than the HBIC50. The two enantiomers cannot be deaminated by dC deaminase, and they can be phosphorylated by cytoplasmic dC kinase. The R-(-)-enantiomer of cytallene is the first acyclic cytosine analog with potent inhibitory activity against HBV similar to those of other L-(-)-ddC analogs.

Common quantitative trait loci for alcohol-related behaviors and central nervous system neurotensin measures: hypnotic and hypothermic effects

Genetic correlations were found between high-affinity neurotensin receptor (NTR(H)) densities and NT-immunoreactivity (NT-ir) levels in specific brain regions and sensitivity to hypnotic and hypothermic effects of ethanol in LSXSS recombinant inbred strains of mice. Simple sequence length polymorphisms were used to identify quantitative trait loci (QTL) influencing hypnotic and hypothermic sensitivity to ethanol, NTR(H) and low-affinity neurotensin receptor densities and NT-ir levels in LSXSS recombinant inbred strains. Common QTL for NTR(H) receptor densities, NT-ir levels and these ethanol actions were identified. One of the QTL (chromosome 2, 80 cM) for NTR(H) density and hypnotic sensitivity is linked to the NTR(H) gene, Ntsr. Also, QTL for NTR(H) density were found in common with confirmed QTL for hypnotic sensitivity on chromosomes 1 (43 cM), 11 (57 cM) and 15 (56 cM) and with an unconfirmed QTL on chromosome 3 (19 cM). Two common QTL for NT-ir levels, but not NTR(H) or low-affinity neurotensin receptor receptors, and ethanol-induced hypothermia were observed on chromosomes 4 (43 cM) and 6 (41 cM). Two common QTL for NT-ir levels and sleep time were identified on chromosomes 3 (19 cM) and 9 (55 cM). Common QTL indicate that genes regulating NT receptor and/or NT-ir expression may be the same as those regulating sensitivity to ethanol.

Common quantitative trait loci for alcohol-related behaviors and central nervous system neurotensin measures: locomotor activation

We have analyzed LSXSS recumbinant inbred for ethanol-induced activity using 2.0 g/kg ethanol and a new method we call ethanol activation slope. The ethanol activation slope provides a robust dose-response measure of ethanol activation, independent of both activity after saline and the inhibitory effects of ethanol on locomotor activity. These behavioral data were used in a quantitative trait locus analysis to map chromosomal loci involved in ethanol-induced locomotor activity. We tentatively identified seven loci that mediate the low-dose stimulatory effect of ethanol and six loci involved in locomotion after 2.0 g/kg ethanol. Only one of the loci are in common between the two behaviors. We also compared the behavioral quantitative trait locus to those previously identified that are involved in regulating central nervous system neurotensin levels and neurotensin receptor densities. Six chromosomal regions were identified that regulate at least one central nervous system neurotensin measure and an ethanol-induced locomotor behavior. The identification of loci controlling both central nervous system neurotensin levels or neurotensin receptor densities and ethanol-induced locomotor activity strengthens the proposal that neurotensin regulates, in part, ethanol-induced behaviors and central nervous system sensitivity to ethanol.

Design of drugs involving the concepts and theories of drug metabolism and pharmacokinetics

Drug metabolism input to the discovery process had historically been on an empirical case-by-case basis, since, detailed descriptors of the effect on pharmacokinetics of a change in structure or physicochemical property were not available. Considerable advances have been made in recent years, such that basic rules can be applied to predict the behavior of a compound in man based on physicochemistry and structure. This is particularly true in the areas of absorption, distribution, and clearance. In particular, knowledge of the reactions catalyzed by the enzymes of drug metabolism, including the cytochrome P450 super family, can be used in the design of new chemical entities, together with the usual pharmacological-derived SAR. The combination of both pharmacokinetics and pharmacodynamics at the discovery stage leads to drugs with optimum performance characteristics. Such drugs are easier to develop, representing a huge saving in resources. Moreover, the marketed compound is much more likely to find high clinical utilization. This review uses dofetilide, fluconazole, and amlodipine to highlight the multifaceted consequences of changing chemical structure, in terms of drug disposition, and reinforces these principles with examples from the literature.

Enhancement of benzo[a]pyrene diol epoxide mutagenicity by sulfite in a mammalian test system

Sulfur dioxide, a ubiquitous air pollutant, is a co-carcinogen for benzo[a]pyrene (BP). We have demonstrated previously that the interaction between sulfite, the physiological form of sulfur dioxide, and (+/-) -7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), the ultimate carcinogenic form of BP, results in an enhanced mutagenic effect in Salmonella typhimurium strains TA98 and TA100. We report here that this same co-mutagenic effect of sulfite occurs in a mammalian cell line. Treatment of Chinese hamster V79 cells with 50 nM anti-BPDE, a concentration on the linear portion of the dose-response, resulted in a four-fold increase in mutations at the hprt locus relative to the spontaneous rate. When V79 cells were exposed to 1 or 10 mM sulfite immediately prior to the addition of anti-BPDE, the mutation rate increased by 73% and 210%, respectively, over that elicited by anti-BPDE alone. Sulfite itself was moderately cytotoxic, but caused no increase in mutation over the spontaneous rate. Characterization of the dose- and time-dependance of this enhancement of diol epoxide mutagenicity by sulfite closely resembled the effects seen previously in the bacterial system. In particular, enhancement by sulfite was evident when sulfite was added to the cells between 60 min and 1 min prior to the addition of the diol epoxide. Concurrent addition of sulfite and the diol epoxide attenuated the enhancement, and the effect was lost altogether when sulfite was added 10 min after the diol epoxide. The specificity of this effect of sulfite was shown by comparison with sulfate, which at concentrations of either 1 or 10 mM exhibited modest cytotoxicity, but neither was directly mutagenic nor able to enhance the mutagenic effect of anti-BPDE. Binding studies with labeled anti-BPDE showed that the addition of 10 mM sulfite increased binding of anti-BPDE to DNA by over 43%, corresponding to the observed increase in mutant frequency. Interestingly, this difference in level of DNA modification was not apparent after 30 min to 2 h exposures, but only emerged at the 4 h time point. The 4 h point was routinely used for all mutagenicity studies. Binding of anti-BPDE-derived materials to cellular RNA was not altered by 10 mM sulfite. The emergence of increased DNA modification at the latest time point suggests either a more prolonged period of active DNA binding than would occur with diol epoxide, or a difference in the ability to recognize and clear specific DNA adducts. Both possibilities are discussed in regard to the observed formation of 7r,8t,9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a] pyrene-10c-sulfonate (BPT-10-sulfonate) in those incubations. BPT-10-sulfonate is a relatively stable BP derivative which retains the ability to covalently modify DNA. The role of this derivative in the enhancement of diol epoxide mutagenicity by sulfite is strongly suggested by these data.

Significance of metabolism in the disposition and action of the antidysrhythmic drug, dofetilide. In vitro studies and correlation with in vivo data

Dofetilide, a class III antidysrhythmic agent, undergoes both renal and metabolic clearance. Characterization of the metabolism in vitro allows explanation of species differences, whereas identification of the human enzymes involved permits assessment of potential drug interaction. In liver microsomes, the rate of oxidative metabolism of dofetilide is in the order: male rat > female rat > dog > humans, which correlates with the metabolic clearance seen in vivo. In vitro products of oxidative metabolism, formed by N-dealkylation, are the same as those formed in vivo, with the N-desmethyl being the major product. This route of dofetilide metabolism is mediated by cytochrome P450 (CYP). In humans, N-demethylation has a high KM of 657 +/- 116 microM, indicating low affinity for the enzyme's active site. In a number of human liver microsomal preparations, this rate correlated (r = 0.903) with the activity of CYP3A4. There was no correlation with the activities of other isozymes. Specific isozyme inhibitors also indicated the involvement of CYP3A4, with partial inhibition being observed with ketoconazole and troleandeomycin, whereas the activator, alpha-naphthaflavone, caused increased turnover. No inhibition was observed with specific inhibitors or competing substrates for other isozymes. Dofetilide did not significantly inhibit CYP2C9, CYP2D6, or CYP3A4 at concentrations up to 100 microM in vitro. In contrast, amiodarone (IC50, 25 microM) and flecainide (49 microM) inhibited CYP2C9 and quinidine (0.26 microM), and flecainide (0.44 microM) inhibited CYP2D6. Many antidysrhythmic drugs have active, circulating metabolites, complicating the relationship of dose and clinical response. In vitro pharmacology studies allow assessment of the potential contribution to the pharmacological profile by metabolites. Potency of dofetilide and metabolites has been compared for class III (K+ channel blockade) and class I (Na+ channel blockade) antidysrhythmic activities. Three of the metabolites of dofetilide displayed class III activity, but at concentrations at least 20-fold higher than dofetilide. Dofetilide N-oxide showed class I activity, but only at high concentration. Neither resting membrane potential or action potential amplitude were affected by any metabolite. This lack of biologically relevant activity is in accord with the close correlation between plasma concentrations of dofetilide and pharmacological response.

Putative active site template model for cytochrome P4502C9 (tolbutamide hydroxylase)

Binding of substrates to the active site of cytochrome P450 enzymes largely relies on hydrophobic interactions. However, other binding interactions can take place giving the enzyme high regioselectivity and even stereoselectivity. For instance, within the major human cytochrome P450s involved in drug metabolism, cytochrome P4502D6 (CYP2D6) relies on an ion-pair interaction as a major binding factor. There are now a number of substrates reported that have routes of metabolism ascribed specifically to cytochrome P4502C9 (CYP2C9), the isoform mainly responsible for tolbutamide hydroxylation. Although chemically diverse, these substrates have the capability to be hydrogen bond donors (or acceptors). The substrate specificity has been rationalized in terms of a hydrogen bond donor/acceptor model and, by use of molecular modeling, an active site template model for CYP2C9 has been generated. The substrates modeled were phenytoin, warfarin, ibuprofen, naproxen, diclofenac, delta 1-tetrahydrocannabinol, 58C80, and tolbutamide. In addition to the substrates, the potent, selective inhibitor sulfaphenazole was also included in the modeling. An initial hydrogen bond donor site (N2) was identified on phenytoin, the most rigid of the substrates. Corresponding hydrogen bond donation sites were then identified on all of the molecules studied. Using molecular modeling, the site of metabolism and the hydrogen bond donation sites of the molecules were then overlaid on phenytoin to produce the putative active site model. The resultant model is described by a, the distance between the site of metabolism (Y), and the hydrogen bond donor heteroatom (X) and C, the angle between this and the hydrogen bond. The mean dimensions (+/- SD) for the nine substrates and one inhibitor (a = 6.7 +/- 1.0 A, C = 133 +/- 21 degrees) illustrate the degree of overlap achieved.

Effect of exposure to novelty on brain monoamines in C57BL/6 and DBA/2 mice

Male and female mice from two inbred strains, C57BL/6 (B6) and DBA/2 (D2), were exposed to a novel environment (vs. undisturbed control) for 10 min. Immediately after this treatment, the animals were sacrificed by cervical dislocation, and the brains were removed and dissected into ventral midbrain (VMB), caudate-putamen (CP), nucleus accumbens (NA), and medial prefrontal cortex (FC). Analyses of dopamine (DA) and its metabolites, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were made by high-performance liquid chromatography. Utilization of the parent amines was estimated by the ratios, DOPAC/DA, HVA/DA, and 5-HIAA/5-HT. Novelty increased DOPAC levels in NA of both strains of mice and in CP of D2 males; however, it did not induce significant changes in DA, or 5-HT levels or utilization of the latter. The results did, however, reveal large strain differences in DA and its metabolites. The data suggest that genetically based neurophysiological and neurochemical differences exist in dopaminergic and serotonergic systems in mice, and that the DA systems in NA may be more sensitive to novelty than other DA systems.

Behavioral responses to low doses of cocaine are affected by genetics and experimental history

We recently conducted a set of two experiments to investigate the possible co-operation between genetics and exposure to novelty on the putative locomotor inhibiting effects of low doses of cocaine in male and female C57BL/6 and DBA/2 mice. Experiment one examined the effects of three low doses of cocaine (0.1, 0.5, and 1.0 mg/kg) on locomotion, exploration, stereotypy and wall-seeking in an automated activity monitor. Testing occurred on two consecutive days, with subjects receiving an IP injection of saline on day one, and one dose of cocaine on day 2 (S-C). Immediately following injection, subjects were placed into automated activity monitors, where four behaviors were recorded; total distance, nosepokes, stereotypy and margin time. Using this S-C injection regimen, we found significant decreases in measures of total distance and stereotypy when compared to saline in both male and female C57 mice. Experiment two was designed to determine if the observed decrease in locomotor activity was the result of low-dose cocaine or pre-exposure to the test procedure and apparatus. All conditions and procedures were identical to those in experiment one, with the exception of the injection regimen. In this experiment, we injected all subjects IP with 0.1 mg/kg cocaine on day one, followed by saline on day two (C-S). Additionally, a group of subjects receiving saline on both days (S-S) served as the control. In contrast to experiment one results, cocaine produced locomotor activation. Furthermore, significant sex and strain differences were found in both experiments. The results of our experiments suggest that the behavioral effects of low doses of cocaine are markedly influenced by both the genetic constitution of the experimental animal and by familiarity with the test apparatus.

An investigation of the interaction between halofantrine, CYP2D6 and CYP3A4: studies with human liver microsomes and heterologous enzyme expression systems

1. We have assessed the interaction of the antimalarial halofantrine with cytochrome P450 (CYP) enzymes in vitro, with the use of microsomes from human liver and recombinant cell lines. 2. Rac-halofantrine was a potent inhibitor (IC50 = 1.06 microM, Ki = 4.3 microM) of the 1-hydroxylation of bufuralol, a marker for CYP2D6 activity. Of a group of structurally related antimalarials tested, only quinidine (IC50 = 0.04 microM) was more potent. 3. Microsomes prepared from recombinant CYP2D6 and CYP3A4 cell lines were shown to catalyse halofantrine N-debutylation. 4. The metabolism of halofantrine to its N-desbutyl metabolite by human liver microsomes showed no correlation with CYP2D6 genotypic or phenotypic status and there was no consistent inhibition by quinidine. 5. The rate of halofantrine metabolism showed a significant correlation with both CYP3A4 protein levels (r = 0.88, P = 0.01) and the rate of felodipine metabolism (r = 0.86, P = 0.013), a marker substrate for CYP3A4 activity. Inhibition studies showed that ketoconazole is a potent inhibitor of halofantrine metabolism (IC50 = 1.57 microM). 6. In conclusion, we have demonstrated that halofantrine is a potent inhibitor of CYP2D6 in vitro and can also be metabolised by the enzyme. However, in human liver microsomes it appears to be metabolised largely by CYP3A4.

Pharmacogenetics of cocaine: a critical review

The development of genetic models to help explain individual differences in sensitivity to and susceptibility to misuse certain CNS active substances, like ethanol and psychostimulants, spans a brief, thirty-plus years. The first animal models involved inbred strains and selected lines of mice and rats and predicted genetic-based differential sensitivity to ethanol and its misuse in humans found a few years later. With drugs like cocaine, tracking genetic differences in sensitivity and misuse liability in humans is difficult because of legal problems. Genetically-defined animals, however, have shown most if not all of cocaine-related behavioural, neurophysiological and toxicological effects to evince wide variation with most effects being influenced by several genes. Thus, we argue that animal and human studies of individual differences in drug sensitivity be studied from both quantitative and molecular genetic approaches. For the former, new techniques involving recombinant inbred strains of rodents, genetic correlational analysis and quantitative trait loci analysis are particularly useful, especially as genetic synteny between rodents and humans becomes better described. Also, because drug effects are highly labile to environmental conditions as well as genetic-based individual differences, multivariate, systems level studies should be developed to provide more complete descriptive and mechanistic views of a multifaceted problem.

Synthesis, absolute configuration, and enantioselectivity of antiretroviral effect of (R)-(-)- and (S)-(+)-cytallene. Lipase-catalyzed enantioselective acylations of (+/-)-N4-acylcytallenes

Enantioselectivity of acylations of (+/-)-cytallene (1b), (+/-)-N4-acetylcytallene (11a), (+/-)-N4-benzoylcytallene (11b), and (+/-)-N4-(9-fluorenylmethoxycarbonyl)cytallene (11c) using vinyl butyrate or acetate catalyzed by lipases in organic solvents was investigated. Reactions with 1b, 11a, and adenallene (1a) did not display a high enantioselectivity but all resulted in a predominant acylation of the (-)-enantiomers. Application of the Lowe-Brewster rule led to a tentative assignment of the R-configuration to all acylated products. Studies of the time course of acylation of (+/-)-N4-benzoylcytallene (11b) in chloroform, tetrahydrofuran (THF), tetrahydropyran (THP), tetrahydrothiophene (THT), and dioxane with lipase PS30 and/or AK showed that the reaction in THF catalyzed by lipase AK was the most promising for resolution of 11b. Indeed, a large-scale acylation afforded, after separation and deprotection of intermediates 3e and 10d, (+)- and (-)-cytallene (3c and 2b) in high yield and enantioselectivity. Acylation of 11c in THF led also to formation of 3c and 2b in high enantioselectivity. Single crystal X-ray diffraction established the S-configuration of (+)-cytallene (3c), thus confirming the assignment made on the basis of Lowe-Brewster rule. An improved large-scale synthesis of (+/-)-cytallene (1b) is also described. The R-enantiomer 2b inhibited the replication of a primary human immunodeficiency virus (HIV-1) isolate in phytohemagglutinin-activated peripheral blood mononuclear cells (PHA-PBM) with IC50 0.4 and IC90 1.7 microM. (+/-)-Cytallene (1b) exhibited IC50 0.8 and IC90 3.4 microM. Both compounds completely suppressed replication of HIV-1 at 10 microM with no detectable cytotoxicity. The S-enantiomer (3c) was inactive.

Alcohol acceptance, preference, and sensitivity in mice. II. Quantitative trait loci mapping analysis using BXD recombinant inbred strains

Quantitative trait loci (QTL) mapping of complex phenotypes has emerged as an important feature of the recombinant inbred (RI) strain methodology. In this second study of our series on alcohol-related behaviors in mice, we examine alcohol acceptance, preference, and hypnotic dose sensitivity (HDS) to a standard dose of alcohol measured in BXD RI strains to identify candidate QTL regions responsible for their heritability. We detected highly significant marker associations for acceptance on chromosome 12 (Eif4e), for preference on chromosome 1 (D1Rti2) and chromosome 7 (D7Mit7), and for HDS on chromosome 7 (Mpmv1). These are the strongest QTL associations that we detected, but several other candidate QTL regions are reported. Given the limited number of BXD RI strains available, the large number of markers used herein, and the consequent chance of identifying false marker associations, these RI QTL mapping results must be seen as tentative, but an important first step toward identifying QTL for alcohol-related behaviors.

Alcohol acceptance, preference, and sensitivity in mice. I. Quantitative genetic analysis using BXD recombinant inbred strains

Although the recombinant inbred strain method was designed for molecular genetic analysis of linkage, it also provides powerful quantitative genetic analyses of heritability and genetic correlations. Measures of alcohol acceptance, alcohol preference, and hypnotic dose sensitivity (HDS) were assessed in 21 strains of mice from the BXD RI series. Sex differences were found to be significant at a phenotypic level. However, heritability estimates for acceptance, preference, and HDS are similar in males and females. Heritability estimates for the three measures are approximately 0.20 for acceptance and preference, and 0.10 for HDS. Analyses of genetic correlations reveal that acceptance and preference share some degree of genetic influence, although they mostly operate under different genetically mediated mechanisms. HDS did not show a significant genetic relationship to either acceptance or preference. Strong correlations were obtained when acceptance, preference, and HDS strain means were correlated across male and female recombinant inbreds, suggesting substantial genetic similarity across sexes.

Effects of acute and chronic ethanol administration on neurotensinergic systems

A summary of pharmacogenetic studies designed to test the hypothesis that NT receptors might mediate or regulate some of the actions of ethanol is presented. Indeed, there are significant genetic correlations between ethanol-induced locomotor activation and high-affinity NT receptor densities in the FC. The results suggest that further studies are needed to determine the role of NT receptors in the FC and MPFC in regulating locomotor activity. In other studies, chronic ethanol treatment, under conditions that produced tolerance to ethanol and caused NT receptor downregulation in the NA and VMB, caused tolerance to locomotor inhibitory effects of centrally administered NT and blunted the effects of intra-VTA NT on dopamine metabolism in the NA and CP. The results show a relationship between NT receptor densities and pharmacological effects of ethanol.

Inhibition of p-nitrophenol hydroxylase in rat liver microsomes by small aromatic and heterocyclic molecules

The cytochrome P450 isoenzyme P4502E1 is constitutively expressed in human liver and catalyzes the oxidation of many known or suspected carcinogens of low molecular weight. In this structure-metabolism study, the role that heteroatoms in heterocyclic compounds play in determining their affinity for P4502E1 was investigated. The ability of 16 six-membered and 10 five-membered compounds to inhibit the hydroxylation of p-nitrophenol, which is specifically catalyzed by P4502E1, was studied in suspensions of microsomes from rat livers in which P4502E1 had been induced by inclusion of acetone in the drinking water. Apparent Ki values were extrapolated from kinetic models of Dixon or Cornish-Bowden plots for enzyme inhibition. Enzyme inhibition was generally of the non-or uncompetitive type. Pyridine was the most potent and benzene one of the least potent inhibitors, with Ki values of 0.4 microM and 8,400 microM, respectively. Pyridazine was less inhibitory than 1,3,5-triazine, which inhibited P4502E1 to a lesser degree than pyrazine and pyrimidine. Among the unsubstituted unsaturated five-membered ring molecules, pyrrole was a better inhibitor than furan or thiophene. 4-Methylimidazole was a much stronger inhibitor than imidazole or 1-and 2-methylimidazole. The ability of compounds to inhibit P4502E1 seems to depend in the main on the presence of a nitrogen atom in the molecule and on the ability of the nitrogen lone pair of electrons to ligand to the heme.

Comprehensive health care reform: an imperative

A public relations marketing strategy is essential to the consensus building for the enactment of health care reform legislation. As Governor of Kentucky, the author reflects on the complex legislative experience that he went through in his state, while attempting to enact a health care reform bill similar to President Clinton's proposal. This article draws the parallel in the politics of health reform between the political reality of an individual state, as compared to the one operating on the national scene.

Altered monamine metabolism in caudate-putamen of iron-deficient rats

The effect of iron deficiency on brain monoamine metabolism using in vivo microdialysis techniques has not been previously reported. We, therefore, examined the monoamines, dopamine and norepinephrine, and their metabolites at steady state by in vivo microdialysis in rat brain caudate-putamen in 11-week-old iron-deficient anemic (hemoglobin < 7 g/dl) and control rats (Hb > 14 g/dl). Caudate-putamen dopamine (DA), dihydroxyphenyl acetic acid (DOPAC), and homovanillic acid (HVA) concentrations were increased by 53%, 57%, and 30% (p < 0.001), respectively, in iron-deficient rats in samples collected over a 4-h period. While diminished numbers of D2 receptors have been previously reported, the present findings suggest an additional defect in monoamine uptake and catabolism.

Characterization of dopamine transporter and locomotor effects of cocaine, GBR 12909, epidepride, and SCH 23390 in C57BL and DBA mice

C57BL/6 and DBA/2 mice were used to examine genetic differences in locomotor activating effects of acute cocaine administration and to determine whether differences were mediated by dopaminergic systems. C57BL/6 mice were less activated than DBA/2 mice at 5 and 10 min after 10 and 15 mg/kg cocaine. HPLC analysis showed equivalent brain cocaine concentrations in the two strains at 5 and 10 min after 10, 15, or 20 mg/kg doses. The selective dopamine uptake inhibitor, GBR 12909, at 5 and 7.5 mg/kg, produced greater locomotor activation in DBA/2 mice than in C57BL/6 mice. However, binding studies with the selective dopamine uptake ligand [3H]GBR 12935, revealed no between-strain difference in Kd or Bmax in caudate putamen (CP) or nucleus accumbens (NA) membranes. Competition assays using unlabeled dopamine to compete for [3H]GBR 12935 binding in CP or NA membranes showed no between-strain difference by brain region. The specific D1 or D2 antagonists, SCH 23390 or epidepride, respectively, produced dose-dependent decreases in locomotor activity but there were no between-strain differences. However, epidepride, at a dose of 0.003 mg/kg, completely reversed cocaine-induced (15 mg/kg) activation in both strains. These findings show that C57BL/6 and DBA/2 mice differ in dopamine-related behaviors and suggest that dopaminergic processes may mediate genetic differences in cocaine sensitivity.

Effects of sulfite on the uptake and binding of benzo[a]pyrene diol epoxide in cultured murine respiratory epithelial cells

Sulfur dioxide (SO2) may act as a cocarcinogen with benzo[a]pyrene (BaP) in the respiratory tract. We have modeled this effect by examining the interactions of 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) with sulfite, the physiological form of SO2, in a murine respiratory epithelial cell line (C10). We exposed C10 cells to [3H]-anti-BPDE and determined the effects of 1 and 10 mM sulfite on the uptake and subcellular localization of labeled products. Autoradiographic analysis showed that sulfite doubled the nuclear localization of anti-BPDE-derived materials after a 4-hr incubation period. The net nuclear localization of anti-BPDE-derived materials was not affected by sulfite during the first 60 min, but nuclear localization continued to increase in the sulfite-containing incubations throughout the 4-hr incubation period. Little increase in nuclear localization of anti-BPDE-derived material was noted in the incubations without sulfite after 60 min. Subcellular fractionation was performed to determine the amount of label associated with cytosolic and nuclear fractions and to determine covalent binding to protein and DNA. Sulfite produced a modest increase in the amount of [3H]-anti-BPDE-derived products bound to protein; however, binding to nuclear DNA increased by more than 200% with 10 mM sulfite. Analysis of the supernatants from the cytosolic and nuclear fractions of cells exposed to anti-BPDE and sulfite demonstrated the presence of 7r,8t,9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10c-su lfonate (BPT-10-sulfonate). [3H]-BPT-10-sulfonate was unable to enter C10 cells, suggesting that it is formed intracellularly.(ABSTRACT TRUNCATED AT 250 WORDS)

Synovial sarcoma: MR imaging findings in 34 patients

OBJECTIVE

MR imaging is considered the procedure of choice for detecting and staging soft-tissue tumors. Its ability to show differences between benign and malignant soft-tissue tumors and its usefulness in suggesting a specific histologic diagnosis remain controversial. We studied the MR features of synovial sarcoma in 34 patients to determine if these tumors have specific MR findings that can be used to suggest the diagnosis.

MATERIALS AND METHODS

MR imaging studies of 34 patients with synovial sarcoma were collected from two institutions and studied to determine the following characteristics of the tumor: size, shape, location, signal intensity and homogeneity, margin definition, presence of hemorrhage, and relationships to adjacent structures. These findings were then correlated with pathologic findings.

RESULTS

The tumors tended to be deep, large (85% were > or = 5 cm in diameter), and located in the extremities with epicenters close to joints (63% within 7 cm of a joint). The lesions were usually inhomogeneous on T2-weighted images (82%) and clearly delineated from surrounding tissues (91%). Forty-four percent had high signal consistent with hemorrhage on both T1- and T2-weighted images. Fluid-fluid levels, best visualized on T2-weighted images, were present in 18% of patients. Thirty-five percent of the lesions had areas that were hyper-, iso-, and hypointense relative to fat on T2-weighted images, constituting a triple signal intensity. The tumors frequently involved adjacent bone, with 71% invading, eroding, or touching bone. No association of pathologic subtypes with specific imaging findings was noted.

CONCLUSION

Our results show a spectrum of MR imaging findings in synovial sarcoma. Nevertheless, the results suggest that synovial sarcoma should be considered when MR images show a relatively well-defined but inhomogeneous hemorrhagic lesion near a joint and in contact with bone. Fluid-fluid levels and areas hyper-, hypo-, and isointense relative to fat (triple signal) on T2-weighted sequences support the diagnosis.

Strain and housing affect cocaine self-selection and open-field locomotor activity in mice

We recently conducted an experiment to investigate the possible cooperation between genetic makeup and differential housing on cocaine self-administration in male and female C57BL/6J and DBA/2J mice. Cocaine self-selection was measured in a two-choice test with one choice being cocaine-HCl solution of 40 mg% in tap water and the other choice being plain tap water. Housing conditions began at weaning (21-23 days of age) and consisted of group housed (GH) with 2-3 mice per cage, and isolated housed (IH) with 1 mouse per cage. The results of this study revealed overall strain, sex and housing differences, with C57BL/6Js consuming more cocaine solution than DBA/2J subjects, females consuming more cocaine solution than males, and group housed consuming more than isolate housed subjects. In a second study, the effect of differential housing on open-field locomotor activity was investigated. Testing was conducted on two consecutive days, with subjects receiving an IP injection of saline on day 1, and 15 mg/kg cocaine HCl on day 2. Four behaviors were recorded, including: total distance, nosepokes, stereotypy, and margin time. Overall, the results revealed significant strain differences for stereotypy and nosepokes, and males were found to be more activated by cocaine than females. Additionally, DBA males tended to be differentially affected by housing condition, with IH showing suppressed locomotor activity as compared to GH subjects. Last, significant strain by housing interactions occurred in nosepokes and stereotypy time.

Pharmacogenetics of cocaine: I. Locomotor activity and self-selection

We investigated the effects of cocaine on multiple activity measures and cocaine self-selection in C57BL/6Ibg and DBA/2Ibg mice. Male mice were tested in an automated activity monitor at three doses of cocaine, 5, 15 and 30 mg kg-1. Activity measures included locomotion, rearings, stereotyped movements and wall-seeking. Testing was conducted on 2 days with saline injection, i.p. on day one and cocaine i.p. injected on day two. We also tested other mice of both strains for cocaine ingestion in a two-choice test, pairing tap water with 40 mg% cocaine HCl in tap water. Two separate groups of mice received 15 or 30 mg kg-1 of cocaine i.p., killed at 5 min and brain cocaine levels were determined by HPLC. Cocaine produced dose-related increases in locomotion in both strains, with a delay in initial activation noticed at 30 mg kg-1 in C57s but not in DBAs. In DBAs, cocaine suppressed rearings and increased stereotyped movements while having no consistent effect on either behaviour in C57s. At all doses, cocaine produced moderate increases in proximity to the wall in DBAs and 30 mg kg-1 produced pronounced wall-seeking in C57s. At 15 and 30 mg kg-1 DBAs tended to have higher levels of cocaine in whole brain than did C57s. Finally, C57s consumed significantly more cocaine than did the DBAs.

Pharmacogenetics of cocaine: II. Mesocorticolimbic and striatal dopamine and cocaine receptors in C57BL and DBA mice

Studies were conducted to determine whether genetic differences in behavioural effects of cocaine in C57BL/6 and DBA/2 mice might be mediated by strain differences in dopamine and serotonin transporters and dopamine D1 and D2 receptors in specific brain regions. Binding characteristics of [3H]CFT, a cocaine analogue, in the presence of either GBR12909, a dopamine uptake blocker or fluoxetine, a serotonin uptake blocker and binding of [3H]-paroxetine, a specific serotonin uptake receptor antagonist, were evaluated. We observed regional differences in [3H]CFT binding parameters in the presence of GBR12909 or fluoxetine, but no strain differences by brain region were observed. There were no differences in [3H]paroxetine binding characteristics between corresponding brain regions from C57BL and DBA/2 mice. The D1 antagonist, [3H]SCH23390 and the D2 ligands [3H]sulpiride or [125I]epidepride were used to determine dopamine receptor characteristics. Regional differences were found in [3H]SCH23390 and [3H]sulpiride, with higher affinities and lower densities in frontal cortex compared to striatum; with no differences in [3H]SCH23390 binding in corresponding tissues from C57BL and DBA/2 brains. There were strain-related differences in [3H]sulpiride and in [3H]epidepride binding in striatal membranes with higher densities in C57BL than in DBA/2. Our findings suggest striatal D2 receptor differences are possibly involved in genetic differences in cocaine-related behaviours.

Brain iron: location and function

This review has a focus on the distribution and function of iron in human brain and appropriate animal models. Data are presented on the consequences of abnormalities of iron status with regard to neural development, neurotransmitter metabolism, and cognition.

Genetic-based differences in neurotensin levels and receptors in brains of LS x SS mice

Levels of endogenous neurotensin (NT-IR) in the LS x SS RI strains differed by 3.0-, 4.7-, 5.4-, and 6.9-fold in the ventral midbrain (VMB), hypothalamus (HY), nucleus accumbens (NA), and caudate putamen (CP), respectively. Frequency distributions and estimates of the number of genes indicate that differences in NT-IR are polygenically influenced. The NT-IR levels in NA and CP were significantly correlated, but levels in the VMB did not correlate with those in the NA or CP. Specific binding to either low (NTL)- or high (NTH)-affinity receptors as measured in the absence or presence of levocabastine differed significantly in brain regions from among LS X SS mouse strains. Results indicate a polygenic influence mediating the differences in receptor densities and suggest differences in genetic regulation of NTL and NTH receptors.

Iron in the brain

The location and function of iron in the central nervous system are reviewed with particular emphasis on human biology. Iron is distributed to different cell types in the brain in a heterogeneous fashion through the action of transferrin, transferrin receptors, and the metabolic needs of those cells. The function of this iron and its storage is documented in states of growth and development as well as during pathological states associated with aging. The information relating this biology to current observations of attention deficits in iron-deficient humans is also reviewed.

Inhibitor-induced conformational change in cytochrome P-450CAM

The X-ray crystal structures of cytochrome P-450CAM complexed with both enantiomers of a chiral, multifunctional inhibitor have been refined to R-factors of 21.0% [(+)-enantiomer] and 19.6% [(-)-enantiomer] at approximately 2.1-A resolution. Binding of either enantiomer, both considerably larger than the natural substrate camphor, results in similar, dramatic structural changes in the enzyme. In contrast to all previous P-450CAM crystallographic structures, the Tyr96 side chain is not pointing "down" toward the heme but is rather directed "up" into the proposed substrate access channel. This conformational change is accompanied by the displacement of the Phe193 side chain out into the solvent at the enzyme surface. These changes are consistent with the assignment of this region of the enzyme as the access channel [Poulos et al. (1986) Biochemistry 25, 5314-5322] and suggest that several aromatic residues lining the channel may be involved in substrate recognition and channeling to the active site. The cation usually observed coordinated to the Tyr96 carbonyl oxygen is missing in the presence of the (+)-enantiomer but is present with the (-)-enantiomer. The Phe87 side chain, located near the inhibitor binding site, adopts different orientations depending upon which enantiomer is bound. Finally, electron density reveals that although the inhibitor enantiomers were dichlorinated as provided, when bound to P-450CAM the chlorine atoms are present at only 0-20% occupancy, probably reflecting selective binding of impurities in the samples. Coordinates of these inhibited P-450CAM complexes have been deposited in the Brookhaven Protein Data Bank [Bernstein et al. (1977) J. Mol. Biol. 112, 535-542].

Genetic correlations among ethanol-related behaviors and neurotensin receptors in long sleep (LS) x short sleep (SS) recombinant inbred strains of mice

Studies were designed to examine the hypothesis that genetic based differences in sensitivity to several behavioral effects of ethanol are mediated, in part, by shared genes and that some of ethanol's actions are mediated by brain neurotensinergic processes. In these studies we have used recombinant inbred (RI) strains of mice derived from Long Sleep (LS/Ibg) and Short Sleep (SS/Ibg) lines of mice. The LS and SS mice were selectively bred to differ in hypnotic sensitivity but also differ in hypothermia and locomotor effects of ethanol. Therefore LS x SS RI strains were used to answer the question whether there are shared genetic influences on these diverse ethanol actions. Moreover, since the LS and SS mice were found to differ in neurotensin (NT) receptor densities in various brain regions, the LS x SS RI strains were used to determine associations between NT receptor densities and ethanol actions. The results showed a significant genetic correlation (r = .38) between hypnotic sensitivity and low-dose locomotor effects of ethanol and indicated multigenetic influences, with estimates of seven, four and three genes being responsible for mediating differences in hypnotic, hypothermic, and locomotor effects of ethanol, respectively. The findings are consistent with one or more genes having pleiotropic effects on these ethanol actions.

Hepatocyte ultrastructure following exposure to aroclors and pure polychlorinated biphenyls

Three agriculturally important minor species, the goat, rabbit, and duck, were exposed to various subclinical levels of pure polychlorinated biphenyls (PCBs) and/or PCB mixtures (Aroclors) for short periods of time. Upon sacrifice, liver samples were prepared for ultrastructural observation. Regardless of species, hepatocytes displayed qualitatively similar morphological responses to PCB exposure. At lower exposure levels, cellular changes included increased density of mitochondrial matrix and proliferation of endoplasmic reticulum. At higher exposure levels, degradative changes such as cytoplasmic loss and peripheralization of cytoplasm and organelles became more obvious. When compared quantitatively, it was obvious that goats were much more sensitive to PCB exposure than either rabbits or ducks. Goats showed extensive hepatocyte degradation (cytoplasmic and nucleoplasmic leaching) at exposures of 2 mg/kg body weight of Aroclor 1254. Such species-related differences in response to chlorinated biphenyls cautions against the use of single species animal models in xenobiotic exposure studies.

Speculations on the substrate structure-activity relationship (SSAR) of cytochrome P450 enzymes

This brief review attempts to define the SSAR of two families of cytochrome P450. With P4502D catalytic competence is achieved by tight ionic binding which gives the enzyme high regioselectivity. In contrast P4503A achieves catalytic competence by a flexible binding site relying on hydrophobic forces that allow chemically vulnerable sites to be the principal sites of metabolism. In general, the different binding mechanism should be reflected in the enzyme, such that substrates of P4502D should have lower Km values than substrates of P4503A. Thus, routes of metabolism catalysed by P4502D may be saturated at substrate concentrations lower than routes catalysed by P4503A. The apparent differences between P4502D and P4503A in terms of substrate specificity bring into question what relationships govern other families of cytochrome P450. Our analysis of data suggests that the other principal form involved, generally, in the metabolism of pharmaceuticals in humans is P4502C9 (possibly 2C8 and 2C10). The enzyme is responsible for the metabolism of phenytoin, tolbutamide, tienilic acid [4], naproxen, ibuprofen, diclofenac [38], the 7-hydroxylation of S-warfarin [39] and the 7-hydroxylation of delta 1-tetrahydrocannabinol [40]. These compounds all have areas of strong hydrogen bond [4] forming potential (Fig. 8), all distanced 5-10A from the site of metabolism. Moreover the carboxylic acid function of naproxen, ibuprofen and diclofenac (pKa 4.5) and the sulfonylurea of tolbutamide (pKa 5.4) render the compounds ionized at physiological pH. The ionised group is positioned 7-11A from the site of metabolism. It is likely, therefore, that hydrogen bonding and possibly ion-pair interactions play a major role in determining the SSAR of the P4502C isoenzymes. These interactions would suggest that the P4502C enzymes are analogous to P4502D rather than P4503A. In this regard it is noteworthy that P4502C9 is selectively and potently inhibited by sulfaphenazole (IC50 of 0.6 microM), a compound that is structurally related (Fig. 8) to the substrates in terms of potential hydrogen bonding regions [4, 41]. Simplistically we suggest that the SSAR of the various P450 enzymes ranges from the highly selective enzymes dealing with endogenous substrates, through the enzymes metabolising exogenous substrates with narrow substrate structure requirements such as P4502D to P4503A with its broad substrate structure range. It would seem logical that animals and humans would evolve such combinations of isoenzymes to deal with the vast array of exogenous xenobiotics.

Chronic ethanol consumption produces genotype-dependent tolerance to ethanol in LS/Ibg and SS/Ibg mice

It is well known that chronic ethanol administration produces tolerance to the sedative-hypnotic and hypothermic effects as well as low-dose locomotor inhibitory effects of ethanol. We report herein characterization of a convenient method of producing genotype-dependent functional tolerance to ethanol-induced locomotor inhibition. Mice, LS/Ibg (LS) and SS/Ibg (SS), which differ markedly in acute effects of ethanol on locomotor activity, hypothermia, and hypnotic sensitivity, were required to consume solutions of ethanol in water as the sole source of liquid. Mice were provided lab chow ad lib. and the following regimen of ethanol in water, v/v: 10% for 4 days, 15% for 4 days, 20% for 7 days, followed by 15% for periods longer than 2 weeks. Control animals received water only or were pair-fed sucrose (isocaloric with ethanol) solutions plus lab chow; both control and ethanol-consuming (15 g ethanol/kg/24 h) mice maintained similar body weights for up to 4 weeks. Blood ethanol concentrations from 10-200 mg% were obtained during a 12 L:12 D cycle. At 6 h following withdrawal, LS and SS mice showed differential dose-dependent tolerance to locomotor inhibitory effects of ethanol. However, low-dose locomotor activation was unaltered in either line of mice, and results indicate that an apparent sensitization in SS mice is secondary to development of tolerance to locomotor inhibition. Maximum tolerance to locomotor inhibition was observed after 2 weeks of chronic ethanol consumption, with responses returning to control values within 1-2 weeks after withdrawal. Rates of acquisition of tolerance were similar in LS and SS mice.(ABSTRACT TRUNCATED AT 250 WORDS)