Drug discrimination by humans compared to nonhumans: current status and future directions

In drug discrimination (DD) procedures, behavior is differentially reinforced depending on the presence or absence of specific drug stimuli. The DD paradigm has been widely adopted by behavioral pharmacologists because of its specificity of stimulus control, concordance with drug action at cellular levels and its use as a preclinical model of subject-rated effects in humans. With the successful extension of DD to humans, a comparison of human and nonhuman DD will help place each in the context of the other. Twenty-eight studies of DD in humans are reviewed, including studies of amphetamine, opioid, benzodiazepine, caffeine, nicotine, marijuana and ethanol discriminative stimuli. Comparison of procedures between studies in humans and nonhumans reveals a common tradition, except the use of instructions appears to facilitate greatly DD acquisition in humans. Findings were qualitatively similar between humans and nonhumans. Potency relationships were quantitatively similar between humans and most, but not all, other species. Areas of human DD needing additional empirical evaluation include the influence of instructions, the effects of training dose and the effects of antagonists. Additionally, antihistamines, barbiturates, nicotine and marijuana are under-represented in human DD.

The nurse executive in Operation Desert Shield/Desert Storm

The Army Medical Department's Chief Nurse describes a corporate nurse executive's role in the Persian Gulf campaign to free Kuwait in early 1991. Although language and cultural barriers presented problems, U.S. Army and Host Nation nurses were able to integrate their resources to assure smooth operations during wartime.

Prevalence and serovars of leptospira involved in equine abortions in central Kentucky during the 1990 foaling season

A study to determine the prevalence of leptospira-induced abortions in the central Kentucky equine population during the 1990 foaling season and to determine the leptospira serovars responsible was conducted. From July 1, 1989 through June 30, 1990, 32 (4.4%) of 726 submissions (fetuses, stillborn foals, and/or placentas) were diagnosed as leptospirosis by the fluorescent antibody test and/or microscopic agglutination test. Attempts were made to isolate leptospires from the fetal tissues and/or the dam's urine in 31 of these cases. Leptospira interrogans serovar kennewicki was isolated from 11 (35.5%) and serovar grippotyphosa from 2 (6.5%) of the 31 cases. Of 12 cases that were culture negative with serologically positive fetal fluids, 8 had titers against serovar pomona, 1 against bratislava, 1 against grippotyphosa, 1 against hardjo, and 1 against both bratislava and pomona.

The oxidation of 4-aminobiphenyl by horseradish peroxidase

The oxidation of the carcinogen 4-aminobiphenyl (4-ABP) catalyzed by the model peroxidase enzyme horseradish peroxidase (HRP) was investigated. 4-ABP served as a reducing cosubstrate for HRP during the enzyme-catalyzed reduction of the synthetic hydroperoxide, 5-phenyl-4-penten-1-yl hydroperoxide, to its corresponding alcohol. Spectral analysis during the incubation of HRP, 4-ABP, and H2O2 showed an increase in absorbance at 230 and 325 nm and decrease at 270 nm, suggesting metabolite formation. Oxygen consumption was not detected in incubations of HRP, 4-ABP, and H2O2. However, oxygen uptake was observed after the addition of glutathione, which indicated that a free radical metabolite of 4-ABP was formed by the peroxidase. The 4-ABP free radical reacted with glutathione forming a glutathionyl radical which, in turn, reacted with and consumed oxygen. HPLC analysis of organic extracts of incubations with HRP, [3H]-4-ABP, and H2O2 showed the formation of one major peak identified by mass spectroscopy as 4,4'-azobis(biphenyl). The addition of glutathione to the incubations decreased the formation of 4-ABP metabolites, suggesting a reduction of the 4-ABP free radical and/or the formation of glutathione conjugates. Subsequent HPLC analysis of incubations including [35S]glutathione indicated formation of several unidentified 4-ABP-glutathione conjugates as well as recovery of parent compound. These studies suggest that HRP metabolizes 4-ABP by a one-electron oxidation mechanism, resulting in formation of a free radical. This radical can either react with a second radical to form azobis(biphenyl), be reduced by glutathione back to parent, or react with glutathione to form glutathione conjugates.

Mutagenic activation of benzidine requires prior bacterial acetylation and subsequent conversion by prostaglandin H synthase to 4-nitro-4'-(acetylamino)biphenyl

We have used the Ames test in combination with prostaglandin H synthase (PHS) to study the bioactivation of benzidine as well as other aromatic amines. Previous investigations established that the formation of benzidine mutagens by PHS is dramatically enhanced in Salmonella typhimurium strains with high levels of acetyl CoA-dependent arylamine N-acetyltransferase/arylhydroxylamine O-acetyltransferase activity despite the fact that acetylation of aromatic amines decreases their susceptibility to oxidation by peroxidases. In this study, we used a new strain (YG1012) that has very high acetylation capability to investigate the metabolism and mutagenicity of benzidine and N-acetylbenzidine catalyzed by PHS (from ram seminal vesicle microsomes) and horseradish peroxidase (HRP). YG1012 bacteria rapidly acetylated benzidine to N-acetylbenzidine and N,N'-diacetylbenzidine. Preincubation of the bacteria with benzidine before addition of PHS increased the mutagenicity. Under conditions identical to those used to assess mutagenicity, PHS metabolized benzidine rapidly, but the substrate was not totally consumed, with about 40% of the original concentration remaining intact. These data suggest that conversion to N-acetylbenzidine may be the initial step in the bioactivation of benzidine in the PHS-mediated Ames assay. N-Acetylbenzidine is a cosubstrate for PHS peroxidase activity as measured by 5-phenyl-4-pentenyl hydroperoxide reduction, spectral changes, and formation of protein adducts. N-Acetylbenzidine was converted to mutagens by PHS but not HRP, with enhanced mutagenicity observed in bacteria with high acetylation activity. We used reverse- phase HPLC to characterize the metabolites of N-acetylbenzidine formed by PHS and HRP.(ABSTRACT TRUNCATED AT 250 WORDS)

The humeroscapular bone of the great horned owl (Bubo virginianus) and other raptors

A small, separate, bony density dorsal to the shoulder joint is radiographically visible in several species of large hawks and owls. Gross dissection and histological examination show the bone to lie on the deep surface of the major deltoid muscle in intimate association with the dorsal coracohumeral ligament of the shoulder joint. The tendon of the supracoracoideus muscle passes immediately cranial to the humeroscapular bone. Two ligaments distinct from the shoulder joint capsule attach the humeroscapular bone to the proximal humerus: one passes to the proximal edge of the pectoral crest of the humerus, and the other passes to the ventral tubercle of the humerus. The bone was described as the humeroscapular bone in reference to a similar fibrocartilaginous structure possessed by some birds. The humeroscapular bone is present in the great horned owl (Bubo virginianus), the screech owl (Otus asio), the barred owl (Strix varia), the red-tailed hawk (Buteo jamaicencis), the Cooper's hawk (Accipiter cooperii), and the sharp-shinned hawk (Accipiter striatus). The bone is absent in the barn owl (Tyto alba), the osprey (Pandion haliaetus), the golden eagle (Aquila chysaetos), and the turkey vulture (Cathartes aura), though some of these species possessed a similar fibrocartilaginous structure. Whether the humeroscapular structure develops as bone or cartilage in a given species may be related to other morphological features of the wing, and/or to characteristics of the predatory behavior of the species. Clinicians and anatomists dealing with birds of prey must be aware of the presence of the humeroscapular bone to avoid misinterpreting it as a fracture fragment.

The Heat of Formation of Formaldimine

Ab initio molecular orbital theory at the G 2 level has been used to predict new values for the heat of formation of formaldimine (CH2=NH): ?Hfº0 = 94 ±10 kJ mol-1 and ?Hfº298 = 86 ±10 kJ mol-1.

Uncoupling thermotolerance from the induction of heat shock proteins

Exposure of cells to elevated temperatures causes a rapid increase in the synthesis of heat shock proteins (hsps) and induces thermotolerance, the increased ability of cells to survive exposure to lethal temperatures; however, the connection between hsp induction and the acquisition of thermotolerance is unclear. hsp induction in the yeast Saccharomyces cerevisiae is mediated by the activation of heat-shock transcription factor, and recently we have described a mutation, hsf1-m3, in heat-shock transcription factor that prevents the factor's activation. We now demonstrate that this mutation results in a general block in heat-shock induction but does not affect the acquisition of thermotolerance. Our results indicate that high-level induction of the major hsps is not required for cells to acquire thermotolerance.

Matrix-assisted UV-laser desorption/ionization mass spectrometric analysis of monoclonal antibodies for the determination of carbohydrate, conjugated chelator, and conjugated drug content

The chemically averaged molecular weights of a variety of native and conjugated monoclonal antibodies, approximately 150,000, were measured by matrix-assisted UV-laser desorption/ionization mass spectrometry. The average mass of the carbohydrate present in a monoclonal antibody was estimated from the difference between the measured mass of the monoclonal antibody and the mass of the protein present in the monoclonal antibody computed from the amino acid translation of the DNA sequence. The loading of chelators and anticancer drugs conjugated to a monoclonal antibody was quantitated from the difference in the measured masses for the conjugated and untreated monoclonal antibody relative to the expected mass change upon conjugation of 1 mol of chelator or drug. The loading results obtained by mass spectrometry were consistent in most cases with measurements obtained by radioactivity trace assay or UV spectrometry. Similar matrix-assisted UV-laser desorption/ionization mass spectrometric studies were also made after reducing untreated and conjugated monoclonal antibodies with dithiothreitol to determine the distribution of carbohydrate and chelator between the light and heavy chains of the molecules. Matrix-assisted UV-laser desorption/ionization mass spectra were used to compute loading values for covalently bound drugs and proteins, while the loading values obtained by use of gel-filtration HPLC and UV spectrometry cannot distinguish between covalently and noncovalently bound drugs and proteins.

Epoxidation of 4-vinylcyclohexene by human hepatic microsomes

Carcinogenicity studies have shown that chronic administration of 4-vinylcyclohexene (VCH) will induce ovarian tumors in B6C3F1 mice but not F-344 rats. This occurs because the blood level of the ovotoxic VCH metabolite, VCH-1,2-epoxide, is dramatically higher in VCH-treated female mice compared with rats. This species difference in VCH epoxidation is also reflected in the rate of VCH metabolism by hepatic microsomes (female mouse greater than female rat). The present study assessed the ability of microsomes obtained from human liver to metabolize VCH to epoxides since humans are exposed to VCH in certain occupational settings. The production of VCH-1,2-epoxide and VCH-7,8-epoxide from VCH (1 mM) by human hepatic microsomes was linear with respect to microsomal protein concentration (0.25-1.0 mg/ml) and incubation time (5-20 min). VCH-1,2-epoxide was the major metabolite, while the rate VCH-7,8-epoxide formation was about 6-fold lower and in some cases was below the limit of detection. There was no dramatic difference in the rate of VCH epoxidation by hepatic microsomes obtained from male and female humans. The rate of VCH-1,2-epoxide formation by female human hepatic microsomes was 0.71 +/- 0.35 nmol/mg microsomal protein/min (n = 4). This is 13- and 2-fold lower than the rate of VCH-1,2-epoxide formation by female mouse and rat hepatic microsomes, respectively. Therefore, if the rate of hepatic VCH epoxidation is the main factor which determines the ovotoxicity of VCH, then the results of these studies suggest that rats are the more appropriate animal model for extrapolation of animal data to humans.

A mutation in the yeast heat-shock factor gene causes temperature-sensitive defects in both mitochondrial protein import and the cell cycle

Yeast cells containing the recessive mas3 mutation display temperature-sensitive defects in both mitochondrial protein import and the cell division cycle. The import defect is characterized by two pools of mitochondrial precursors and a dramatically slower rate of posttranslational import. The effect of mas3 on cell cycle progression occurs within one cell cycle at the nonpermissive temperature and retards progression through the G2 stage. The mas3 mutation maps to the gene encoding yeast heat-shock transcription factor (HSF), and expression of wild-type HSF complements the temperature-sensitive defects. The mas3 lesion has no apparent effect on protein secretion. In mas3 cells, induction of a major heat-shock gene, SSA1, is defective at 37 degrees C. The properties of the mas3 mutant cells indicate that HSF mediates the response to stress of two basic cellular processes: mitochondrial protein import and cell cycle progression.

Diagnosis and prevalence of leptospira infection in aborted and stillborn horses

A study was conducted to evaluate a recently available fluorescent antibody test (FAT) conjugate for the detection of leptospires in tissues of aborted and stillborn horses, to determine the leptospira antibody titers and compare serologic test results with FAT results, and to determine the prevalence of leptospira-induced abortions and stillbirths in the equine population of central Kentucky. From July 1, 1988 through June 30, 1989, 15 (2.5%) of 594 submissions (fetuses, stillborn foals, and/or placentas) were diagnosed as leptospirosis by the FAT (14 of 15 tested) and/or microscopic agglutination test (12 of 14 tested). Of the 12 serologically positive fetal fluids, 10 had high tigers against Leptospira interrogans serovar pomona and 2 against serovar grippotyphosa.

Comparison of random and serial sections in assessment of ovarian toxicity

Assessment of ovarian toxicity by follicle quantitation and morphometric analysis of serial sections is time consuming and expensive. This report compares the estimation of follicle number obtained from counting oocytes in serial sections or 5 random sections of mouse ovaries. Ovaries were obtained from C57BL/6N and B6C3F1 mice treated with ovarian toxicants. C57BL/6N mice were treated with cyclophosphamide (0, 75, 200, and 500 mg/kg, ip) and killed at 24, 72, and 168 h. B6C3F1 mice were treated daily, ip, with 4-vinylcyclohexene (0, 100, 400, and 800 mg/kg/day for 30 days), vinylcyclohexene diepoxide (0, 10, 40, and 80 mg/kg/day for 30 days), or benzo(a)pyrene (100 mg/kg, single dose) and killed on day 31. Ovarian serial sections were prepared and oocytes counted in every tenth section. When serial sections were evaluated, 30 to 60 sections were counted. Random section counting involved randomly selecting 5 sections from the 30 to 60 sections previously counted by the serial method. Chemically-induced follicle loss was evident by the reduction in follicle counts relative to control animals when estimating follicle number using serial or random section counting. Furthermore, a linear regression analysis of follicle counts over all treatment groups showed that the highest correlation between random and serial section counting and was for primordial follicles. Correlation coefficients (R2) for each follicle type were: primordial--C57BL/6N 0.82, B6C3F1 0.86; growing--C57BL/6N 0.16, B6C3F1 0.46; antral--C57BL/6N 0.07, B6C3F1 0.11. Although other screens may need to be developed for growing and antral follicles, primordial follicle toxicity is adequately defined by counting 5 random sections.

Bioactivation of xenobiotics by prostaglandin H synthase

Prostaglandin H synthase (PHS) catalyzes the oxidation of arachidonic acid to prostaglandin H2 in reactions which utilize two activities, a cyclooxygenase and a peroxidase. These enzymatic activities generate enzyme- and substrate-derived free radical intermediates which can oxidize xenobiotics to biologically reactive intermediates. As a consequence, in the presence of arachidonic acid or a peroxide source, PHS can bioactivate many chemical carcinogens to their ultimate mutagenic and carcinogenic forms. In general, PHS-dependent bioactivation is most important in extrahepatic tissues with low monooxygenase activity such as the urinary bladder, renal medulla, skin and lung. Mutagenicity assays are useful in the detection of compounds which are converted to genotoxic metabolites during PHS oxidation. In addition, the oxidation of xenobiotics by PHS often form metabolites or adducts to cellular macromolecules which are specific for peroxidase- or peroxyl radical-dependent reactions. These specific metabolites and/or adducts have served as biological markers of xenobiotic bioactivation by PHS in certain tissues. Evidence is presented which supports a role for PHS in the bioactivation of several polycyclic aromatic hydrocarbons and aromatic amines, two classes of carcinogens which induce extrahepatic neoplasia. It should be emphasized that the toxicities induced by PHS-dependent bioactivation of xenobiotics are not limited to carcinogenicity. Examples are given which demonstrate a role for PHS in pulmonary toxicity, teratogenicity, nephrotoxicity and myelotoxicity.

The biochemical basis for the species difference in hepatic microsomal 4-vinylcyclohexene epoxidation between female mice and rats

Mice but not rats are susceptible to 4-vinylcyclohexene (VCH)-induced ovarian toxicity and carcinogenicity. This is due in part to a 4- to 6-fold greater rate of hepatic microsomal bioactivation of VCH to the ovotoxicant VCH-1,2-epoxide. The biochemical basis for this difference was investigated in microsomes using enzyme induction, enzyme inhibition with chloramphenicol or specific inhibitory antibodies, and correlation with marker steroid hydroxylase activities to associate VCH epoxidation with particular cytochrome P450 forms. Testosterone 6 beta- and 15 alpha-hydroxylase activities and VCH epoxidation were decreased in microsomes from chloramphenicol-treated mice, initially suggesting the possible involvement of P450IIIA and P450IIA forms in VCH metabolism. Although both testosterone 6 beta-hydroxylase and VCH epoxidase activities were increased by dexamethasone treatment (P450IIIA inducer), anti-rat P450IIIA IgG inhibited testosterone 6 beta-hydroxylase (68%) but not VCH epoxidase activity. These latter results do not support the involvement of mouse P450IIIA forms in VCH epoxidation. However, results were obtained which indicated that mouse P450IIA forms are involved in VCH epoxidation. In microsomes from untreated female mice VCH epoxidase activity was inhibited 48% by antibodies to mouse P45015 alpha (P450IIA3) at a concentration that inhibited testosterone 15 alpha-hydroxylase activity by 86%. No protein immunochemically related to mouse P45015 alpha was detected in female rat hepatic microsomes. VCH epoxidation by hepatic microsomes was increased in female mice and rats by phenobarbital treatment and was inhibited by approximately one-third by anti-rat-P450IIB1 IgG in microsomes from untreated animals of both species. Furthermore, microsomal VCH epoxidase and testosterone 16 alpha-hydroxylase activities were lower (34%) in female 129/J mice (deficient in constitutive expression of P450IIB forms) than in B6C3F1 mice. These results suggested partial involvement of P450IIB forms in the microsomal epoxidation of VCH. Therefore, P450 forms IIA and IIB account for the majority of VCH bioactivation in female mouse liver, which explains in part the susceptibility of mice to VCH-induced ovarian toxicity and carcinogenicity.

Comparison of the disposition and in vitro metabolism of 4-vinylcyclohexene in the female mouse and rat

4-Vinylcyclohexene (VCH) is a chemical to which humans are exposed in the rubber industry. A chronic carcinogenicity bioassay conducted by the National Toxicology Program showed that oral administration of VCH induced tumors in the ovaries of mice but not in those of rats. The hypothesis tested was that the species and organ specificity of VCH toxicity was due to differences in the disposition of VCH between the female rat and mouse. Therefore, the disposition of a single oral dose of 400 mg/kg [14C]VCH was studied in female B6C3F1 mice and Fischer 344 rats. Mice eliminated greater than 95% of the dose in 24 hr, whereas rats required 48 hr to eliminate greater than 95% of the dose. The major routes of excretion of [14C]VCH-derived radioactivity were in the urine (50-60%) and expired air (30-40%). No evidence was obtained to indicate that the ovaries of either species retained VCH as a parent compound or as radioactive equivalents. A dramatic difference was observed between the rat and mouse in the appearance of a monoepoxide of VCH in blood from 0.5 to 6 hr after VCH administration (800 mg/kg, ip). VCH-1,2-epoxide was present in the blood of mice with the highest concentration at 2 hr (41 nmol/ml). The blood concentration of VCH-1,2-epoxide in rats was less than 2.5 nmol/ml at all times examined. VCH-7,8-epoxide was not present in the blood of either species at the level of detection. These findings were supported by in vitro studies of VCH epoxidation by liver microsomes. The rate of epoxidation of VCH (1 mM) to VCH-1,2-epoxide was 6.5-fold greater in mouse liver microsomes than that in rat liver microsomes. The species difference in the rate of epoxide formation by the liver may be an important factor in the species difference in susceptibility to VCH-induced ovarian tumors.

The role of epoxidation in 4-vinylcyclohexene-induced ovarian toxicity

4-Vinylcyclohexene (VCH) is present in gases discharged during synthetic rubber production. Chronic treatment of B6C3F1 mice and F-344 rats with VCH by gavage has been shown to induce ovarian tumors in mice but not in rats. Our objective was to understand the mechanism of the species difference in VCH-induced ovarian tumors. Since a critical step in the induction of ovarian tumors is destruction of the small oocyte, small oocyte counts obtained from serially sectioned ovaries were used as an index of toxicity. VCH or its epoxide metabolites [VCH-diepoxide, VCH-1,2-epoxide, and VCH-7,8-epoxide (in mice only)] were given to 28-day-old female mice and rats in corn oil, ip, at doses ranging from 0.07 to 7.4 mmol/kg body wt/day for 30 days. The dose which reduced the small oocyte count to 50% that of control was defined as the ED50. In mice, the ED50 for the reduction in small oocytes by VCH was 2.7 mmol/kg, whereas, no detectable oocyte loss occurred in rats at the highest dose of VCH (7.4 mmol/kg). The potency of the epoxides of VCH was greater than that of VCH in both species. The ED50 for oocyte loss by VCH-1,2-epoxide in mice and rats was 0.5 and 1.4 mmol/kg, respectively. In mice, VCH-7,8-epoxide had comparable potency to VCH-1,2-epoxide (ED50 = 0.7). VCH diepoxide was even more potent with ED50 values of 0.2 and 0.4 mmol/kg, in mice and rats, respectively. The dose response of the blood concentration of VCH-1,2-epoxide in mice after VCH showed that doses of VCH which caused minimal toxicity had the lowest blood level of this ovotoxic epoxide. Pretreatment of mice with the cytochrome P450 inhibitor chloramphenicol (200 mg/kg, ip) inhibited VCH epoxidation in vivo and in vitro and partially protected mice from VCH toxicity. Thus it appears that metabolism of VCH to epoxides and their subsequent destruction of oocytes are critical steps in VCH-induced ovarian tumors. Rats may be resistant to ovarian tumor induction by VCH because the amount of VCH converted to epoxides is insufficient to produce oocyte destruction.