Molecular heterogeneity of gamma delta T-cell antigen receptors expressed by CD4- CD8- T-cell clones from normal donors: both disulfide- and non-disulfide-linked receptors are delta TCS1+

We investigated the molecular heterogeneity of gamma delta T-cell antigen receptors (TCR) expressed on T-cell clones generated from peripheral blood lymphocytes of normal donors. Extensive molecular heterogeneity was seen at the gamma-chain level and, to a lesser extent, at the delta-chain level. Both disulfide and non-disulfide gamma delta TCR were found and use different gamma chains with similar molecular masses (range, 41-43 kDa). In contrast, gamma chains of 55-60 kDa, which are expressed on T-cell lines derived from the peripheral blood of patients with immunodeficiency disorders, were not found on T-cell clones derived from the peripheral blood of normal donors. delta chains expressed on these T-cell clones had a molecular mass of 37 kDa and were either disulfide or nondisulfide linked. Significant delta-chain heterogeneity was identified in these clones using the anti-delta TCS1 and the anti-TCR delta 1 monoclonal antibodies. All clones tested were TCR delta 1+, whereas only 25% of the clones were delta TCS1+. The anti-delta TCS1 monoclonal antibody stained and immunoprecipitated both disulfide- and non-disulfide-linked gamma delta TCRs from different T-cell clones from normal donors.

Metabolic activation of polycyclic aromatic hydrocarbons to mutagens in the Ames test by various animal species including man

6 polycyclic aromatic hydrocarbons were assayed for mutagenicity in the Ames test, in the presence of hepatic post-mitochondrial preparations isolated from the mouse, rat, hamster, pig and man. Benzo[a]pyrene, dibenzo[a,i]pyrene and benz[a]anthracene gave a positive mutagenic response only in the presence of activation systems derived from the hamster. With the exception of the pig, activation systems derived from all animal species could convert 3-methylcholanthrene to mutagens, the hamster being the most efficient. With the exception of the rat and pig, all animal species activated 7,12-dimethylbenz[a]-anthracene to mutagens, the human preparation being the most effective followed by the hamster and mouse. Dibenz[a,h]anthracene was not activated by any of the hepatic preparations. It is concluded that, among the animal species studied the hamster is generally the most efficient in activating polycyclic aromatic hydrocarbons to mutagens in the Ames test.

Metabolic activation of chemical carcinogens by hepatic preparations from streptozotocin-treated rats

The effect of insulin-dependent diabetes on the hepatic microsomal activation of chemical carcinogens to mutagenic intermediates in the Ames test was investigated in rats pretreated with streptozotocin. In order to discern between the effects of streptozotocin itself and that of the resulting diabetes, groups of streptozotocin-treated rats received either nicotinamide simultaneously with the diabetogenic agent to prevent the onset of diabetes or daily treatment with insulin in order to antagonise the effects of diabetes. The activation of two nitrosamines, nitrosopiperidine and nitrosopyrrolidine was markedly increased following treatment of the animals with streptozotocin, the effect being preventable by nicotinamide and effectively antagonised by insulin. A similar increase in mutagenic response was also seen when Glu-P-1, a carcinogen generated during the cooking of proteinaceous food, was employed as the mutagen. In contrast, the diabetic rats were less efficient than control animals in activating the aromatic amine 2-aminofluorene to mutagenic intermediates. Concomitant administration of nicotinamide with streptozotocin prevented the decrease in mutagenicity, and daily treatment of diabetic rats with insulin partially restored mutagenic response to control levels. Streptozotocin-induced diabetes had no effect on the mutagenicity of 4-aminobiphenyl and the two polycyclic aromatic hydrocarbons, benzo(a)pyrene and 3-methylcholanthrene. The present findings clearly illustrate that diabetes modulates the metabolic activation of carcinogenic chemicals, the effect being dependent on the nature of the carcinogen.

Prediction of chemical carcinogenicity from molecular and electronic structures: a comparison of MINDO/3 and CNDO/2 molecular orbital methods

Molecular orbital methods have been used to calculate the electronic structures of a number of chemical carcinogens and non-carcinogens using the MINDO/3 (Modified Intermediate Neglect of Differential Overlap, version 3) and CNDO/2 (Complete Neglect of Differential Overlap) procedures; results from the two methods show good agreement. Spatial conformations of the same series of chemicals have also been determined. High affinity for cytochromes P-448 (P450 I) and high potential for chemical carcinogenicity/toxicity show good correlation with molecular planarity (high values of area/depth2) and low values of the difference between the frontier orbital energies (delta E) of the chemical. This computer graphic procedure identifies substrates of the cytochromes P-448 and is highly suited for the rapid screening of new chemicals for potential mutagenicity, carcinogenicity and certain other forms of toxicity. The implications of these findings to the mechanism of chemical carcinogenicity are discussed.

Molecular orbital studies of oxygen activation and mechanisms of cytochromes P-450-mediated oxidative metabolism of xenobiotics

Molecular dimensions and molecular orbital calculations of the electronic structures of 56 substrates, inhibitors and inducers of the cytochromes P-448 and other families of the cytochromes P-450 are reported. Substrates of the cytochromes P-448 are shown to be planar molecules with relatively large values of area/depth2, and to have electronic structures with relatively low values for delta E, the difference in energy between the frontier orbitals (E(LEMO)- E(HOMO)). Substrates of other families of the cytochromes P-450 are globular molecules, with relatively low values of area/depth2 and relatively high values of delta E. Molecular orbital calculations of the active oxygen species, singlet oxygen and superoxy anion, have also been made. Singlet oxygen is a poor electron donor (low values of E(HOMO)) but a good electron acceptor (low values of E(LEMO)), whereas superoxy anion is a good electron donor and a poor electron acceptor. Cytochrome P-448 substrates, which are good electron donors, would preferentially accept singlet oxygen, a good electron acceptor; substrates of the other families of cytochrome P-450, which are less effective electron donors, would preferentially accept superoxy anion, a good electron donor, although substrates of both cytochromes P-448 and other P-450s may accept both species of active oxygen. Together with recent published evidence, these data provide a greater understanding of the mode of activation of oxygen by the various families of the cytochromes P-450, and to the insertion of active oxygen into the substrates. Mechanisms are proposed for the oxygenation of substrates, namely, epoxidation involving singlet oxygen and hydroxylation by superoxy anion. Finally, a detailed explanation of the cytochrome P-450 cycle is discussed, and mechanisms of the different types of oxidative metabolism are presented.

Adverse reactions of imidazole antifungal agents: computer graphic studies of cytochrome P-450 interactions

The imidazole antifungal agents give rise to adverse reactions and clinically relevant drug interactions. This is due to lack of specificity of the antifungal agents that interact avidly not only with the fungal but also with mammalian cytochrome P-450 proteins. A computer graphic technique capable of predicting the interaction of these structurally-related imidazoles with fungal and mammalian cytochrome P-450 proteins is described. This prediction is achieved by comparing the molecular conformation of these drugs with lanosterol, the substrate of the fungal cytochrome P-450, and with phenobarbitone, an inducing agent of a family of mammalian cytochrome P-450, toward which the antifungal agents show highest inhibitory activity.

A study of the mutagenicity of melatonin and 6-hydroxymelatonin

The mutagenicity of melatonin and its major metabolite 6-hydroxymelatonin were evaluated using the Ames test and three strains of Salmonella typhimurium--TA 97, TA 98, and TA 100. Neither compound exhibited mutagenicity whether in the presence or absence of an activation system derived from rats induced with Aroclor 1254. Positive controls were employed throughout and gave the expected response. We conclude that melatonin, 6-hydroxymelatonin, and their microsomal metabolites are not mutagenic in the Ames test.

Organic nitrate reductase: reassessment of its subcellular localization and tissue distribution and its relationship to the glutathione transferases

1. Using a specific and sensitive GLC method for the determination of glyceryl trinitrate (GTN), its subcellular and tissue distribution were reassessed. Liver was the most active tissue, but activity was also detected in the heart, kidney and gut. In all tissues activity was localized in the soluble fraction. The activity of soluble glutathione S-transferase followed the same pattern, liver exhibiting the highest and the heart the lowest activity. 2. Pretreatment with phenobarbitone and 3-methylcholanthrene stimulated both the glutathione S-transferase and organic nitrate reductase activities. 3. Glutathione S-transferase activity was competitively inhibited by GTN. 4. A comparison of the plasma and hepatic metabolism of GTN revealed higher drug affinity for the hepatic enzyme.

Induction of the rat hepatic microsomal mixed-function oxidases by two aza-arenes. A comparison with their non-heterocyclic analogues

The ability of the aza-aromatic polycyclic aromatic hydrocarbons 10-azobenz(a)pyrene and benz(a)acridine to induce the rat hepatic microsomal mixed-function oxidases was compared to that of their non-heterocyclic analogues benz(a)pyrene and benz(a)anthracene respectively. All four hydrocarbons markedly increased the O-deethylations of ethoxyresorufin and ethoxycoumarin, the non-heterocyclic analogues being the more potent. A more modest increase was seen in the O-dealkylation of pentoxyresorufin. All four hydrocarbons induced proteins recognised by antibodies to cytochrome P-450IAI but no increase was seen when antibodies to cytochrome P-450IIB1 were employed. The metabolic activation of benz(a)pyrene and Glu-P-1 to mutagenic intermediates in the Ames test was enhanced by all pretreatments. It is concluded that the aza-aromatic polycyclic hydrocarbons, like their non-heterocyclic analogues, selectively induce the cytochrome P-450I family of proteins.

Role of ketone bodies in the diabetes-induced changes in hepatic mixed-function oxidase activities

In order to assess the role of ketone bodies in the diabetes-induced changes in hepatic mixed-function oxidase activity, rats rendered hyperketonaemic by dietary administration of medium chain triacylglycerols were compared with streptozotocin treated rats. Both groups of animals became hyperketonaemic but only the latter were hyperglycaemic. Treatment with streptozotocin or medium chain triacylglycerols gave rise to marked increases in the O-dealkylations of ethoxyresorufin, ethoxycoumarin and pentoxyresorufin, the p-hydroxylation of aniline and the N-demethylation of dimethylnitrosamine. It is concluded that the streptozotocin-induced changes in hepatic mixed-function oxidases are mediated, at least partly, by the high levels of ketone bodies.

Replacement of the interarticular disc of the craniomandibular joint with fresh autogenous sternal or auricular cartilage. An experimental study in guinea pigs

Meniscectomy has proved to be a disadvantageous therapeutic method for the surgical treatment of patients with internal derangement of the TMJ. A few authors have reported on the replacement of the removed disc with dermis, fascia and auricular cartilage in clinical reports. To the best of our knowledge no experimental work has ever been published on this subject. The interarticular disc of six young adult albino guinea pigs was removed and replaced with fresh autogenous sternal cartilage and in nine others with fresh autogenous auricular cartilage. After having been followed clinically, the animals were sacrificed after 3, 6, 12 and 24 weeks. Transplantation of sternal cartilage resulted clinically in moderate to marked discomfort. However, histologically no spectacular changes in the joints were found. The auricular cartilage transplants clinically did rather well. Histologically, some changes were found which became less pronounced with time. The use of sternal cartilage is not advisable as a replacement material because of technical reasons. The protective role of the auricular transplants could not be fully evaluated because of their tendency to warp and become displaced, although they retained their original microscopic structure and did not show reactive or resorptive changes. Further studies using larger groups of experimental animals and intermaxillary fixation are justified.

Induction of rat hepatic cytochrome P-450 I proteins by the antimutagen anthraflavic acid

Administration of the antimutagen anthraflavic acid to rats gave rise to significant increases in the hepatic microsomal O-deethylations of ethoxyresorufin and ethoxycoumarin, but not in the O-dealkylation of pentoxyresorufin nor in cytosolic glutathione S-transferase activity. Immunoblot studies of solubilized microsomes from anthraflavic acid-treated rats revealed that anthraflavic acid induced the apoproteins P-450 I A1 and A2 but not P-450 B1 and B2. Pretreatment with anthraflavic acid resulted in a marked increase in the in vitro bioactivation of 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole and 2-amino-3,2-amino-3-methylimidazomethylimidazo[4,5-f]-quinoline (IQ) to mutagenic intermediate(s); IQ is a carcinogen against which anthraflavic acid has displayed strong antimutagenic effect in the Ames test when incorporated into the metabolic activation system. The increase in mutagenicity of IQ was the result of enhancement of both the microsomal and cytosolic activation steps. It is concluded that anthraflavic acid is a specific inducer of P-450 I proteins in the rat and this compound is not only unlikely to exhibit any anticarcinogenic effect in vivo but may act as a co-carcinogen.

Lyophilized auricular cartilage as a replacement for the interarticular disc of the craniomandibular joint. An experimental study in guinea pigs

Meniscectomy has major disadvantages and should be abandoned. Replacement of the removed interarticular disc is mandatory. As the harvesting of autogenous transplants requires the creation of a donor site defect, the use of preserved allogenic material seems justified. The interarticular disc of six young adult albino guinea pigs was replaced with preserved allogenic auricular cartilage. From the clinical and histological results we concluded that the postoperative clinical course of all animals paralleled the histological appearance of the joints. The transplants showed marked degree of resorption, but were replaced by fibrous connective tissue with focal cartilage formation. This newly formed structure resembled the original disc and protected the articular components of the joints, which, 24 weeks postoperatively, hardly differed from the controls. The role of the synovia in the formation of the "new disc" was quite evident.

Metabolic activation of carcinogens and toxic chemicals

1. The spatial parameters and electronic structures of 100 exogenous and endogenous chemicals have been determined by computer graphics, from which their oxidative metabolism by the cytochrome P-448 (activation) or the other families of cytochromes P-450 (generally detoxication) have been predicted. 2. The spatial parameters of these chemicals primarily determine the family of cytochrome P-450 by which the chemicals are metabolized and the electronic structures primarily determine their ease of oxidative metabolism. 3. The role of oxidative metabolism of xenobiotics by the cytochromes P-448, and their binding to the cytosolic Ah receptor, are considered in relationship to the mechanisms of chemical toxicity, mutagenicity, carcinogenicity, and co-carcinogenicity. 4. The mechanisms of chemical toxicity and carcinogenesis are considered in respect of activation through cytochrome P-448-mediated, conformationally-hindered oxygenation to reactive intermediates which, unlike most cytochrome P-450-oxygenated metabolites, are not acceptable substrates for conjugation and detoxication and therefore react with essential intracellular macromolecules. 5. The computer graphic method of determining the molecular conformations and electronic structures of molecules is a rapid, scientifically-based procedure for evaluation of the potential toxicity, mutagenicity and carcinogenicity of chemicals.

Replacement of the damaged interarticular disc of the TMJ

Meniscectomy should be abandoned and the removed, damaged disc of the TMJ should be replaced in patients suffering from internal derangement of the TMJ. In seventeen patients the disc which was removed, was replaced with fresh autogenous auricular cartilage. The follow-up period ranged from one to six years with a mean of almost three years. From the analysis of the results we concluded that all patients showed a postoperative improvement in their symptoms and joint function and that the use of intermaxillary fixation for a short period postoperatively had a significant effect on the subsequent increase in mouth opening.

Induction of the rat hepatic microsomal mixed-function oxidases by 3 imidazole-containing antifungal agents: selectivity for the cytochrome P-450IIB and P-450III families of cytochromes P-450

Administration of the imidazole antifungal agents ketoconazole, miconazole and clotrimazole gave rise to increases in the microsomal cytochrome P-450 levels and the NADPH-dependent reduction of cytochrome c. Clotrimazole, and to a much lesser extent miconazole and ketoconazole, stimulated the dealkylation of pentoxyresorufin. All 3 agents gave rise to small, but significant increases in the O-deethylation of ethoxycoumarin and ethoxyresorufin. The antifungal-induced O-deethylation of ethoxycoumarin was much more sensitive to inhibition by metyrapone rather than by alpha-naphthoflavone. The binding of metyrapone to reduced microsomes was enhanced by treatment of animals with the 3 antifungal agents, clotrimazole being clearly the most potent. Immunoquantitation of cytochrome P-450 proteins using an ELISA procedure and employing anti-cytochrome P-450c (P-450IA1, P-448 low spin) and P-450b (P-450IIB1) antisera revealed that clotrimazole and miconazole, but not ketoconazole, induced the levels of phenobarbital-induced cytochromes P-450, while none of the antifungal agents increased the levels of cytochrome of P-448 proteins. Similar results were obtained using Western blots employing the above antibodies. On SDS-polyacrylamide gel electrophoresis microsomes derived from animals pretreated with clotrimazole showed intensification of a band at 51 kDa which was identified by Western blotting as the PCN-inducible form of cytochrome P-450 (cytochrome P-450p, P-450III family). Similar, but less pronounced intensification was seen with microsomes from animals pretreated with miconazole and ketoconazole. Furthermore, microsomes from clotrimazole- and ketoconazole-treated animals interacted with erythromycin to yield type I spectra. It is concluded that the imidazole-containing agents clotrimazole and miconazole, and to a much lesser extent ketoconazole, are potent inducers of the rat hepatic microsomal mixed-function oxidases, displaying selectivity towards the P-450IIB (phenobarbital-inducible) and P-450III (PCN-inducible) families of cytochrome P-450 proteins.

A comparison of bisoprolol and atenolol in the treatment of mild to moderate hypertension

1. Fourteen patients (mean age 56.0, range 37-61 years; eight females) with mild essential hypertension (DBP greater than 90 mm Hg on placebo) completed a randomised, double-blind placebo controlled crossover study comparing the hypotensive effects of bisoprolol (10-20 mg) and atenolol (50-100 mg) each taken once daily. 2. Bisoprolol had a significantly greater antihypertensive effect than atenolol, reducing sitting blood pressures by 15.9 mm Hg (diastolic) and 21.9 mm Hg (systolic) compared with placebo. Corresponding figures for atenolol were 10.7 and 5.7 mm Hg respectively. Bisoprolol reduced standing blood pressures by 15.9 mm Hg (diastolic) and 22.8 mm Hg (systolic) compared with 7.3 and 8.6 mm Hg respectively for atenolol. 3. Examination of the pharmacokinetic data showed that bisoprolol had a median elimination half-life of 11.2 h during chronic dosing, compared with 6.4 h for atenolol. For bisoprolol, the median clearance fell from 264 ml min-1 after a single dose to 212 ml min-1 during chronic dosing, although clinically significant accumulation would not be expected during chronic administration. 4. Overall, the results suggest that bisoprolol may be a more effective antihypertensive agent than atenolol but larger studies are necessary to confirm these findings.

Ocular injuries associated with fractures involving the orbit

Ocular injuries often accompany periorbital fractures. The incidence reported by various authors varies greatly. The charts of 509 patients operated on because of a fracture involving the orbit were reviewed and the intra- and extraocular injuries were recorded. Subconjunctival haematoma, corneal abrasions and mild retinal oedema were not considered. It appeared that 26% of the injured suffered concomitant lesions of the eye and/or its adnexae. The incidence is discussed and certain hints are given, which can help non-ophthalmologists assess the severity of the trauma in cases where obvious signs are absent.

Inhibition of the rat hepatic mixed-function oxidases by in vivo administration of clotrimazole

The ability of the 1-substituted imidazole antifungal agent clotrimazole to inhibit the rat hepatic microsomal mixed-function oxidases was investigated in rats pretreated with either phenobarbital or 3-methylcholanthrene. When administered to 3-methylcholanthrene-pretreated animals, clotrimazole inhibited the O-deethylations of ethoxyresorufin and ethoxycoumarin. An even more marked inhibition of the dealkylation of pentoxyresorufin and O-deethylation of ethoxycoumarin was observed in phenobarbital-pretreated rats. It is concluded that administration of clotrimazole to rats gives rise to a marked inhibition of the hepatic mixed-function oxidases, and especially of the cytochrome P450 II B family of haemoproteins.

Anthraflavic acid inhibits the mutagenicity of the food mutagen IQ: mechanism of action

The ability of anthraflavic acid to inhibit the mutagenicity of IQ was investigated using the Ames test and employing hepatic activation systems from Aroclor 1254-pretreated rats. Incorporation of anthraflavic acid into the S9 mix caused a concentration-dependent decrease in the mutagenicity of IQ. A similar effect was seen when microsomes only were employed as activation systems. Cytosol, as we have previously demonstrated, potentiated the microsome-mediated mutagenicity of IQ and this potentiation was also inhibited by anthraflavic acid. In contrast, anthraflavic acid had no effect on the mutagenicity of the direct-acting microsome-generated metabolites of IQ. It is concluded that anthraflavic acid is a potent inhibitor of IQ mutagenicity by virtue of its ability to inhibit both its microsomal and cytosolic activation pathways.

Streptozotocin-induced diabetes modulates the metabolic activation of chemical carcinogens

The effect of chemically-induced diabetes on the hepatic microsomal mixed-function oxidase system and the activation of chemical carcinogens was investigated in animals treated with streptozotocin (STZ). In order to distinguish between the effects of the diabetogenic chemical per se and that of the diabetic state, groups of STZ-treated animals received either nicotinamide simultaneously with STZ to prevent the onset of diabetes, or daily treatment with insulin in order to reverse the effects of diabetes. STZ-treated animals exhibited higher pentoxyresorufin O-dealkylase, ethoxy-resorufin O-deethylase, ethoxycoumarin O-deethylase, aniline p-hydroxylase and NADPH-cytochrome c reductase activities; similarly, increases were seen in cytochrome P-450 and b5 levels. All of these effects were prevented by nicotinamide and, at least partly, antagonised by insulin therapy. Treatment of animals with STZ markedly increased the activation, by liver microsomes in vitro, of Trp-P-1 and Trp-P-2 to mutagens, the effect being totally preventable by nicotinamide and successfully antagonised with insulin therapy. The diabetic animals were similarly more efficient in activating MeIQ but the effect was not preventable by nicotinamide or reversed by insulin. In contrast no changes were seen in the activation of IQ and only a modest increase in the case of MeIQx. It is concluded that diabetes may modulate the metabolic activation of some chemical carcinogens, presumably by changing the ratio of the various cytochrome P-450 isoenzymes.

Effect of vitamin A on rat hepatic mixed-function oxidases, glutathione transferase activity and generations of oxygen radicals

Rat hepatic microsomal mixed-function oxidase activities were not significantly affected by vitamin A deficiency. Similarly cytosolic glutathione S-transferase and glutathione reductase activities as well as total glutathione levels were unaffected by the vitamin A status. Induction of the mixed-function oxidases by 3-methylcholanthrene or phenobarbitone was independent of the vitamin A status. No significant differences in microsomal chemiluminescence, before and following challenge with tertiary butyl hydroperoxide, were evident between the vitamin-A-deficient animals and those maintained on vitamin-A-supplemented diets. The present findings indicate that the protective action of vitamin A against chemical carcinogens is unlikely to involve modulation of the enzyme systems responsible for their metabolism.

Anthraflavic acid is a potent and specific inhibitor of cytochrome P-448 activity

Consideration of the computer-optimised dimensions of anthraflavic acid indicates that it is essentially a planar molecule with a large area/depth ratio, that would preferentially interact with the polycyclic aromatic hydrocarbon-induced family of cytochrome P-450 proteins (cytochromes P-448). Anthraflavic acid was a potent inhibitor of the O-deethylations of ethoxycoumarin and ethoxyresorufin, both catalysed primarily by cytochromes P-448, in Arochlor-1254-induced hepatic microsomes. Similarly anthraflavic acid markedly inhibited the mutagenicity of 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-I) in the Ames test. In contrast, it has no effect on the dealkylation of pentoxyresorufin, a reaction catalysed primarily by the phenobarbital-induced cytochromes P-450, and NADPH-dependent reduction of cytochrome c. It is concluded that anthraflavic acid is a potent and specific inhibitor of cytochrome P-448 activity.

Interactions of imidazole antifungal agents with purified cytochrome P-450 proteins

The imidazole N-substituted antifungal agents ketoconazole, miconazole and clotrimazole have been shown to be potent inhibitors of oxidative metabolism by both a phenobarbital-induced cytochrome P-450 (P-450b) and a 3-methylcholanthrene-induced cytochrome P-448-protein (P-450c) in reconstituted systems. All three compounds inhibited the cytochrome P-450b-dependent 7-pentoxyresorufin-O-dealkylase and the cytochrome P-450c-dependent 7-ethoxyresorufin-O-deethylase activities. When 7-benzyloxyresorufin and 7-ethoxycoumarin were employed as substrates with both cytochrome preparations, all three antifungal compounds exhibited selective inhibition of the cytochrome P-450b preparation; ketoconazole was always the weakest inhibitor. The three antifungal agents were also shown to elicit a type II difference spectral interaction with both isoenzymes, the magnitude of the spectral interaction being greater with the cytochrome P-450b preparation.

The single dose pharmacokinetics of bisoprolol (10 mg) in renal insufficiency: the clinical significance of balanced clearance

The pharmacokinetics of the beta-blocking agents presently available render some subject to accumulation in renal or hepatic failure. Bisoprolol is one of the beta blockers possessing balanced clearance (both renal and hepatic clearance) which prevents such accumulation even in the case of complete failure of kidneys or liver. The single dose pharmacokinetics of bisoprolol were studied in patients with varying degrees of renal impairment and in healthy controls. Correlations were demonstrated between creatinine clearance and elimination half-life, mean residence time, area under the curve, total clearance and maximum concentration in those with renal dysfunction. The elimination half-life increased by a factor of 1.96 in those with severe renal dysfunction. Because of its balanced clearance, it is unlikely that accumulation of bisoprolol would occur beyond a factor of 2 on dosing to a steady state. The 48 hour plasma levels in the patients on dialysis were similar to those of the patients with severe renal dysfunction. This suggest that accumulation is unlikely, even in end stage renal failure. Bisoprolol may be used safely in patients with renal dysfunction. No adjustment of dose is necessary for those with mild to moderate dysfunction, but in severe or end stage renal failure the dose should not exceed 10 mg once daily.

Single oral dose pharmacokinetics of bisoprolol 10 mg in liver disease

The pharmacokinetic profile of an oral single dose of the new cardioselective beta-blocking agent, bisoprolol, was studied in patients with moderate and severe liver disease (Pugh group B and C, respectively) and normal subjects. In patients with liver disease a significant increase in the drug elimination half-life, mean residence time, area under the curve, and time to reach maximum plasma concentration (Tmax) was observed with a significant reduction in the oral clearance compared with the control population. There was significant positive correlation between the Pugh Score (an objective measurement of hepatic dysfunction) and the volume of distribution. The drug was well tolerated although a rise in blood urea and creatinine of over 50% was observed in 4 of 9 patients with severe liver disease. In conclusion, the delayed absorption in these patients results in lower plasma concentrations and indicates that dose adjustment is not necessary but it is recommended that the upper limit for the daily dose should be set at 10 mg; this also applies under chronic dosing of bisoprolol.

Induction of the hepatic mixed-function oxidases by Aroclor 1254 in the hamster: comparison of Aroclor-induced rat and hamster preparations in the activation of pre-carcinogens in the Ames test

Hepatic microsomal mixed-function oxidase activities and the metabolic activation of chemical carcinogens to mutagens in the Ames test were investigated using Aroclor 1254-induced rat and hamster preparations. Benzphetamine N-demethylase, NADPH-cytochrome c reductase and cytochromes P-450 and b5 were induced in both animals to the same extent by pre-treatment with Aroclor. However, the O-deethylation of ethoxyresorufin was markedly induced in the rat (147-fold) but only modestly in the hamster (3-fold). 1,2-Benzanthracene and 4-aminobiphenyl were more efficiently activated by the rat preparations while, in contrast, 2-acetylaminofluorene, 2-aminoanthracene, nitrosopiperidine, nitrosopyrrolidine, cyclophosphamide and phenacetin were more efficiently activated by the hamster preparations. No significant difference was observed in the activation of 3-methylcholanthrene, benzo[a]pyrene and 2-aminofluorene. It is concluded that (a) the hamster is relatively refractive to cytochrome P-448 induction, and (b) Aroclor 1254-induced rat and hamster S9 preparations differ in their ability to convert chemical carcinogens to mutagens in the Ames test.

Spectral and kinetic studies of the interaction of imidazole anti-fungal agents with microsomal cytochromes P-450

1. The imidazole antifungal agents, ketoconazole, miconazole and clotrimazole have been shown to be potent inhibitors of the phenobarbital-induced cytochromes P-450 and the 3-methylcholanthrene-induced cytochromes P-448-dependent rat hepatic microsomal mixed-function oxidases. 2. All three drugs were more potent inhibitors of the phenobarbital-induced O-deethylation of ethoxycoumarin than of the 3-methylcholanthrene-induced activity indicating selective inhibition of the phenobarbital-induced cytochromes P-450. In both types of microsomes ketoconazole was always the weakest inhibitor. 3. All three compounds elicited type II spectral interactions with both types of microsomes, and had similar Ks values. Miconazole and clotrimazole, and to a lesser extent ketoconazole, also interacted with the substrate binding sites of both phenobarbital-induced cytochromes P-450 and to a lesser extent with the 3-methylcholanthrene-induced cytochrome P-448. 4. It is concluded that at least part of the inhibitory effect of these antifungal agents may reflect competitive inhibition at the substrate binding site.

Bioactivation of N-nitrosopiperidine to mutagens: role of hepatic cytochrome P-450 proteins and contribution of cytosolic fraction

In the present study the role of two families of cytochrome P-450 proteins and the contribution of the cytosolic fraction in the activation of N-nitrosopiperidine to mutagens in the Ames test were investigated. The bioactivation of this nitrosamine was preferentially catalysed by the phenobarbitone-induced cytochromes P-450, in contrast to the 3-methylcholanthrene-induced cytochromes P-448. The mutagenicity of nitrosopiperidine catalysed by microsomes, in the absence of cytosol, was lower when compared with that observed with S9 fractions. Cytosol itself could not activate nitrosopiperidine but potentiated the microsome-mediated mutagenicity of the carcinogen. The cytosolic potentiation was still evident when microsomal metabolism was terminated, indicating that cytosolic enzyme(s) can further convert the microsome-generated metabolites to more potent mutagens. The cytosolic enzyme(s) was inducible by prior treatment of the rats with phenobarbitone or Arochlor 1254 but not 3-methylcholanthrene. The microsome-mediated activation of nitrosopiperidine could be supported by NADH in the absence of NADPH. It is therefore concluded that the activation of nitrosopiperidine to mutagen(s) involves, in addition to NADH- and NADPH-dependent microsomal enzymes, cytosolic proteins.

Cytosolic potentiation of the rat hepatic microsome mediated mutagenicity of benzidine

The role of the cytosolic fraction in the S9-mediated metabolic activation of benzidine to mutagens in the Ames test was investigated using hamster and rat hepatic preparations. Rat microsomes alone were poor activators of benzidine compared to hamster microsomes, at least partly explaining the well known superiority of S9 preparations from the latter species in activating this amine. Supplementation of rat microsomal preparations with the cytosolic fraction from hamsters and to a lesser extent from rats enhanced the bioactivation of benzidine. When hamster microsomal preparations were supplemented with rat or hamster cytosolic fractions no significant effect was observed. Cytosolic fractions from either species could not activate benzidine to mutagens in the absence of microsomes. The cytosolic potentiation of the microsome-mediated activation of the amine was not inducible by Aroclor 1254. Similarly, the microsome-mediated activation of benzidine was not enhanced by Aroclor 1254 pre-treatment of the rats, when mutagenicity is expressed per nmol of cytochrome P-450. It is concluded that (i) the cytosolic fraction may play an important role in the metabolic activation by S9 preparations of chemical carcinogens such as benzidine, and (ii) the Aroclor-induced isozymes of cytochrome P-450 do not catalyse the N-hydroxylation of benzidine.

Effect of syngeneic anti-idiotypic antibody on influenza virus neuraminidase antibody response

Influenza viruses possess two major surface glycoproteins - hemagglutinin (HA) and neuraminidase (NA). Py203, a monoclonal antibody (Ab) specific for the neuraminidase of the PR8 (H1N1) influenza virus, was used to prepare syngeneic monoclonal anti-idiotypic (anti-Id) Abs. From a BALB/c mouse immunized with Py203 (anti-N1), we obtained RM1, a monoclonal anti-Id Ab. The Py203-Id was detected in a significant fraction of immunoglobulins (Igs) in the primary and secondary responses elicited by PR8 (H1N1) and X31 (H3N2) viruses. In animals injected with minute amounts of RM1 and subsequently boosted with an identical dose of RM1, no detectable anti-NA activity was noted, but a significant increase in Py203-Id-bearing Igs was observed. In the sera of animals injected with minute amounts of RM1 and subsequently boosted with PR8 (H1N1) or X31 (H3N2) viruses, an increase in anti-NA activity and in the level of Py203-Id was noted. Animals injected with large amounts of RM1 and boosted with PR8 and X31 showed a marked suppression of the Py203-Id but no alteration in the anti-NA response. The anti-Id recognizes an idiotope (the Py203 idiotope) shared by antibodies specific for the N1 and N2 neuraminidase variants.

Structural requirements for substrates of cytochromes P-450 and P-448

Distinct and different molecular structural features are manifested by substrates, inhibitors and inducers of the two families of liver microsomal enzymes, the phenobarbital-induced cytochromes P-450 and the 3-methylcholanthrene-induced cytochromes P-448. In a theoretical study based on molecular orbital calculations and molecular graphics, it is established that cytochrome P-448 substrates contain fused aromatic or heteroaromatic rings giving rise to overall molecular planarity with relatively small molecular depth. In contrast, substrates of the cytochromes P-450 have greater conformational freedom and an ability to bind at more than one point of attachment, as a result of possession of certain characteristic functions, namely, a carbonyl and/or amine moiety coupled with an iso-propyl group, or similar function of equivalent shape and hydrophobicity. The implications are that the binding sites of cytochromes P-448 contain a number of hydrophobic aromatic amino acid residues orientated so as to allow occupation by similar substrates containing co-planar aromatic rings, whereas those of the phenobarbital-induced cytochromes P-450 contain hydrophilic amino acid residues capable of hydrogen bonding to greater than C = O moieties and at least one leucine or valine residue, as these contain the complementary isopropyl function. The corollary of these findings is the possibility of prediction of the toxicity of new chemicals on the basis of their molecular dimensions.

Effect of tryptamine on the mutagenic activity of 2-amino-3-methylimidazo(4,5-f) quinoline (IQ) and related azaarenes in the Ames test

The bioactivation of the azaarenes 2-amino-3-methylimidazo(4,5-f) quinoline (IQ), 2-amino-3,4-dimethylimidazo(4,5-f) quinoline (MeIQ) and 2-amino-3,8-dimethylimidazo(4,5-f) quinoxaline (MeIQx) to mutagens by hepatic S9 preparations derived from Aroclor-pretreated Wistar rats was inhibited by tryptamine (2-50 microM). However, with similar preparations derived from Sprague-Dawley rats, bioactivation of IQ and MeIQx was less markedly inhibited by tryptamine while metabolic activation of MeIQ was enhanced. In the absence of cytosol, activation of IQ by microsomal preparations of both rat strains was inhibited by tryptamine. Cytosolic fractions from both rat strains were incapable of activation of IQ per se but increased the mutagenicity of the microsomal metabolite(s). This potentiation of the mutagenic activity by cytosol derived from Wistar rats was also inhibited by tryptamine whereas no significant inhibition was observed with cytosolic preparations from Sprague-Dawley rats. There appear to be two alternative pathways of microsomal metabolism of IQ: a tryptamine-sensitive pathway, probably involving the formation of the N-hydroxymetabolite; and a tryptamine-insensitive pathway producing weakly mutagenic or non-mutagenic metabolites which are activated to a potent mutagen by the cytosol. The tryptamine-insensitive pathway appears to be the major route of activation of the azaarenes in microsomal preparations from Sprague-Dawley rats and the principal activation route for MeIQ in both rat strains.

Induction of cytochrome P-448 activity as exemplified by the O-deethylation of ethoxyresorufin. Effects of dose, sex, tissue and animal species

The effects of tissue, sex, animal species and dose on the induction of cytochrome P-448 activity by various inducing agents were investigated using O-ethoxyresorufin as a model substrate. The liver was by far more effective in catalysing the O-deethylation of ethoxyresorufin (EROD) than the lung and kidney. The extent of induction was also highest in the liver, with the exception of benzo(a)pyrene and 3-methylcholanthrene where inducibility was more pronounced in the kidney. The benzo(a)pyrene-induced hepatic EROD activity in the rat decayed to reach control levels four days after a single administration. Rat hepatic EROD activity was induced in both sexes but tended to be higher in the male. Marked species differences in the inducibility of hepatic EROD activity by various chemicals was observed, the rat being always more responsive when compared to the hamster or mouse. The induction of rat hepatic EROD activity by benzo(a)pyrene, 2-acetylaminofluorene and safrole was dose-dependent, maximum induction being achieved with single doses of 5, 2 and 5 mg/kg, respectively.

Alkoxyresorufin O-dealkylases: association with the murine Ah locus

The hepatic microsomal dealkylation of a series of alkoxyresorufins and the oxidation of phenoxazone to resorufin were investigated in C57BL/6 and DBA/2 mice of both sexes. In both strains of mice and in both sexes the dealkylation rate decreased with increasing length of the alkyl chain. With all alkoxyresorufins the dealkylation rates were higher in the C57BL mice than the DBA mice, whereas the rate of phenoxazone hydroxylation was higher in the latter. In the C57BL mice, and to a lesser extent in the DBA mice, females were more efficient in dealkylating the resorufin ethers. Treatment with 3-methylcholanthrene (3MC) enhanced the rates of dealkylation of all alkoxyresorufins in the C57BL mice but not in the DBA mice, the extent of stimulation being highest for the propoxy- and butoxyresorufins and least for pentoxy-, heptoxy- and benzyloxyresorufins. The same treatment had no effect on the oxidation of phenoxazone in either strain of mice. It is concluded that the dealkylation of alkoxyresorufins, not the oxidation of phenoxazone, is associated with the murine Ah locus.

The metabolic activation of 2-naphthylamine to mutagens in the Ames test

The mutagenicity of 2-naphthylamine and its major metabolites in the Ames test was determined in the absence and presence of activation systems derived from rats and hamsters. In the absence of an activation system only N-hydroxy-2-naphthylamine and 2-nitrosonaphthalene were mutagenic. In the presence of activation systems derived from control and 3-methylcholanthrene-treated hamsters and Arochlor 1254-treated rats only 2-naphthylamine exhibited a mutagenic response while its hydroxy-derivatives and 2-acetamidonaphthalene were devoid of mutagenicity. Pretreatment of rats with 3-methylcholanthrene or Arochlor 1254 enhanced the mutagenicity of 2-naphthylamine while treatments with phenobarbitone, safrole and clofibrate had no significant effect. In the hamster treatment with only 3-methylcholanthrene increased the mutagenicity of 2-naphthylamine. It is concluded that the metabolic activation of 2-naphthylamine proceeds via N-hydroxylation which is preferentially catalysed by the 3-methylcholanthrene inducible forms of cytochrome P-450, whereas ring-hydroxylation appears to be a deactivation pathway.

Metabolic activation of 2-amino-3-methylimidazo(4,5-f)quinoline by hepatic preparations--contribution of the cytosolic fraction and its significance to strain differences

In accordance with previous studies the bioactivation of 2-amino-3-methylimidazo(4,5-f)quinoline (IQ) to mutagens in the Ames test was preferentially catalysed by the 3-methyl-cholanthrene-induced cytochromes P-448, in contrast to the phenobarbital-induced forms of the cytochrome. The mutagenicity of IQ catalysed by microsomes, in the absence of cytosol, was much lower when compared with that observed with S9 fractions. Cytosol itself could not activate IQ but markedly potentiated the microsome-mediated mutagenicity of the carcinogen. The effect of the cytosol was still evident when microsomal metabolism was terminated, indicating that the cytosol contains enzyme(s) that can further convert the microsome-generated metabolites of IQ to more potent mutagens. The cytosolic enzyme(s) were inducible by pre-treatment of the rats with Aroclor 1254. The higher efficiency of activation of IQ to mutagens by Sprague-Dawley S9 mixes when compared with similar preparations from the Wistar rat could be attributed not only to differences in the rate of microsomal metabolism but also to the higher ability of the Sprague-Dawley cytosolic fraction in further metabolizing the microsome-generated metabolite(s). The present study demonstrates clearly that the mutagenic response of this compound in the Ames test may be profoundly modulated by the cytosolic fraction and its role in the metabolic activation of pre-mutagens merits further investigation.

Hepatic microsomal mixed-function oxidase activity in ethanol-treated hamsters and its consequences on the bioactivation of aromatic amines to mutagens

Male golden Syrian hamsters were maintained on ethanol-containing liquid diets for 4 weeks, corresponding to an average daily intake of 17 g/kg body wt. The p-hydroxylation of aniline was markedly enhanced by this treatment while minimal effects were seen in benzphetamine N-demethylase and ethoxyresorufin O-deethylase activities; there was no change in the microsomal levels of cytochromes P-450. Hepatic microsomal preparations from the ethanol-treated hamsters were more efficient than controls fed isocaloric diets in converting 2-aminofluorene, 4-aminobiphenyl, benzidine and 2-acetylaminofluorene into mutagens in the Salmonella mutagenicity test. The same treatment had no effect on the metabolic activation of 2-naphthylamine and even inhibited the mutagenicity of 2-aminoanthracene. No increase was seen in the activation of the two polycyclic aromatic hydrocarbons, benzo[a]pyrene and 3-methylcholanthrene to mutagens and an inhibitory effect was seen with the former. The ethanol-induced increase in the mutagenicity of 2-aminofluorene was inhibited by 2-butanol but not by the hydroxyl radical scavenger dimethylsulphoxide. It is concluded that chronic ethanol ingestion modulates the bioactivation of aromatic amines and amides to mutagens, the effect being substrate dependent. This effect of ethanol may be catalysed by unique form(s) of cytochrome P-450 whose synthesis is induced by such treatment.

Induction of rat hepatic mixed function oxidases by aromatic amines and its relationship to their bioactivation to mutagens

Hepatic microsomal mixed-function oxidase activities were determined in rats pretreated with the aromatic amines 2-aminoanthracene, 2-naphthylamine or 4-aminobiphenyl. All three amines stimulated the O-deethylation of ethoxyresorufin (cytochromes P-448) but none had any effect on the p-hydroxylation of aniline. 2-Aminoanthracene and 4-aminobiphenyl also stimulated the NADPH-dependent reduction of cytochrome c and 2-naphthylamine inhibited the N-demethylation of benzphetamine. Hepatic preparations from animals pretreated with 2-aminoanthracene were more efficient in converting this carcinogen to mutagens while in contrast pretreatment with Aroclor 1254 caused a marked decrease in mutagenicity. 4-Aminobiphenyl also enhanced its own activation but Aroclor-pretreated preparations were the most effective. The latter preparations were also more efficient than controls in activating 2-naphthylamine to mutagens. It is concluded that 4-aminobiphenyl and 2-aminoanthracene enhance their own activation at least partly, by inducing the synthesis of cytochromes P-448.

Molecular dimensions of the substrate binding site of cytochrome P-448

The molecular geometries of specific substrates, inhibitors and inducers of cytochrome P-448 activity were determined using computer-graphic techniques for use in defining the molecular dimensions of the substrate binding site of this enzyme. Specific substrates of cytochrome P-448 are essentially planar molecules characterised by a small depth and a large area/depth ratio. In contrast, compounds that do not serve as substrates of cytochrome P-448 are bulky, non-planar molecules characterised by small area/depth ratios and greater flexibility in molecular conformation. Specific inhibitors of cytochrome P-448 whose effect is mediated through interaction with the haem still meet the dimensional criteria for substrates indicating that they must also interact with the substrate binding-site, which is probably located in proximity to the haem. Inducers of cytochrome P-448 activity exhibit similar molecular geometries to the substrates from which it may be inferred that the cytosolic receptor associated with the induction of cytochrome P-448 activity is structurally related to the active site of the cytochrome.

Effects of brotizolam on mixed-function oxidases and glutathione metabolism in the rat

Intra-gastric administration of brotizolam (0.1-200 mg/kg) daily for three days to rats resulted in no significant changes in the hepatic and intestinal cytochrome P-450-dependent or P-448-dependent mixed-function oxidases, or in the hepatic flavoprotein dimethylaniline N-oxidase. Liver microsomes from mouse, rat and man metabolized brotizolam by hydroxylation of the diazepine ring and of the methyl group at rates which were greater for mouse greater than rat greater than man. Brotizolam and its metabolites generated by rat-liver microsomes in vitro were not mutagenic in the Ames' test. Brotizolam, at 200 mg/kg per day for two to six weeks, depleted liver glutathione concentration and markedly increased liver gamma-glutamyl transpeptidase, glutathione reductase and glutathione transferase activities. Similar changes were not seen at the lower dose of 0.3 mg/kg. The observed increases in glutathione metabolism and the decreased tissue concentration of glutathione are indicative of high levels of glutathione conjugation, and provide a possible explanation for the equivocal increase in tumorigenicity seen in rats receiving brotizolam at high dosage.

Differential effects of chronic alcohol administration to rats on the activation of aromatic amines to mutagens in the Ames test

Male Wistar albino rats were maintained on alcohol-containing liquid diets for 4 weeks. Hepatic post-mitochondrial preparations derived from these animals were more efficient than control in activating 4-aminobiphenyl and 2-aminofluorene to mutagens in the Ames test. The alcohol-induced enhancement in mutagenicity was not inhibited by dimethylsulphoxide indicating that the generation of hydroxyl radicals is not involved. The activation of 2-naphthylamine was not affected by the treatment with alcohol but the mutagenicities of 2-aminoanthracene, benzo[a]pyrene and 3-methylcholanthrene were inhibited. The same treatment markedly increased hepatic microsomal aniline p-hydroxylase and ethoxyresorufin O-de-ethylase activities and to a lesser extent benzphetamine N-demethylase and microsomal levels of total cytochromes P-450. It is concluded that chronic alcohol administration to rats modulates the metabolic activation of pre-carcinogens to their reactive intermediates presumably by causing the redistribution of cytochrome P-450 isozymes.

Mechanism of the protective action of n-acetylcysteine and methionine against paracetamol toxicity in the hamster

The mechanism of the protective action of methionine and N-acetylcysteine against the toxicity of paracetamol was investigated in vivo. N-acetylcysteine inhibited the O-deethylation of ethoxyresorufin (cytochrome P-448) while methionine enhanced the N-demethylation of benzphetamine (cytochrome P-450) and increased hepatic microsomal levels of cytochrome P-450. These observations indicate that N-acetylcysteine, but not methionine, could afford protection against paracetamol hepatotoxicity, at least partly, by inhibiting cytochrome P-448 activity and thus the generation of the reactive intermediate. However, previous studies demonstrating no decrease in the urinary excretion of glutathione conjugates of paracetamol (derived from the reactive intermediate) in animals treated with N-acetylcysteine suggest that this is unlikely to be the prevailing mechanism of action. Administration of a large dose of paracetamol, as expected, depleted glutathione levels and inhibited cytosolic glutathione transferase activity. Administration of either N-acetylcysteine or methionine 1 h after paracetamol prevented both effects. On the basis of the present work and previously published observations, it is concluded that the major mechanism of action of N-acetylcysteine and methionine in vivo is by acting as precursors of intracellular glutathione.

Inhibition of the mutagenicity of aromatic amines by the plant flavonoid (+)-catechin

Addition of the plant phenolic flavonoid (+)-catechin to rat liver microsomes inhibited the mutagenicity of the aromatic amines 2-aminofluorene and 4-aminobiphenyl in the Ames test. Similarly, (+)-catechin decreased the mutagenicity of N-hydroxy-4-amino-biphenyl, the proximate carcinogen, but, in contrast, had no effect on the mutagenicity of other direct-acting carcinogens such as N-methyl-N'-nitro-N-nitrosoguanidine and 9-aminoacridine. In vitro addition of (+)-catechin gave rise to a dose-dependent inhibition of the cytochrome P-450-dependent benzphetamine N-demethylase and ethoxyresorufin O-deethylase activities. This was achieved by impairment of the electron flow from the reduced pyridine nucleotide to the cytochrome. However, administration of (+)-catechin to rats had no effect on the in vitro mixed-function oxidase activities. It is concluded that the (+)-catechin inhibits the mutagenicity of aromatic amines in the Ames test by interfering with their cytochrome P-450-dependent bioactivation and by direct interaction with the proximate carcinogen, but the former mechanism is unlikely to occur in vivo because the high doses of the flavonoid required are not achieved.

Foetal and neonatal development of cytochrome P-450 and cytochrome P-448 catalysed mixed function oxidases in the rat: induction by 3-methylcholanthrene

Benzphetamine N-demethylase (cytochrome P-450) and ethoxyresorufin O-deethylase activities (cytochrome P-448) were determined in the growing neonate and foetus of control and 3-methylcholanthrene-pretreated rats. Ethoxyresorufin O-deethylase activity was highest in the 1-2-week-old animals and then decreased with age. The inducibility of this activity by 3-methylcholanthrene was low in the young animals, but increased with age. In contrast, benzphetamine N-demethylase activity in the control animals was low at birth and increased with age, and was not induced by 3-methylcholanthrene. In the foetal liver, ethoxyresorufin O-deethylase was the only activity present at higher levels than in the maternal liver. Transplacental administration of 3-methylcholanthrene failed to induce the foetal activities while the maternal liver showed the expected response. These observations demonstrate that cytochrome P-448 may be a predominant hepatic form in the foetus and neonate but cytochrome P-450 becomes a major form as the animal grows. The implications of these findings in chemical toxicity are discussed.

Interactions of safrole and isosafrole and their metabolites with cytochromes P-450

The structural features which determine interaction of safrole and related methylenedioxyphenyl compounds with cytochromes P-450 or P-448, and determine the induction of these two classes of the cytochrome, have been studied. All methylenedioxyphenyl compounds studied interact with both cytochromes P-450 and P-448 eliciting type I spectral changes and it has been found that the allyl 4-substituent is important in these interactions. Methylenedioxyphenyl compounds with an oxidised allyl 4-substituent exhibited higher affinity for cytochrome P-448 while those possessing an intact allyl or methylvinyl group generally showed higher affinity for cytochrome P-450. Compounds possessing intact allyl and methylenedioxyphenyl groups (safrole, isosafrole and myristicine) were the most potent inducers of cytochromes P-450 and P-448; compounds containing an intact allyl group only (estragole, allybenzene and eugenol methyl ether) or an oxidized allyl group and an intact methylenedioxyphenyl group (epoxysafrole) were inducers of P-448 only.

Ligand-complex formation between cytochromes P-450 and P-448 and methylenedioxyphenyl compounds

The formation of ligand complexes between hepatic microsomal cytochrome P-450 and safrole, isosafrole and other methylenedioxyphenyl compounds was studied in vivo and in vitro in rats pretreated with either phenobarbital or 3-methylcholanthrene. Both the phenobarbital-induced cytochrome P-450 and the 3-methylcholanthrene-induced cytochrome P-448 metabolically convert safrole, isosafrole, and those metabolites possessing an intact methylenedioxy group, to reactive metabolites which then interact with the cytochromes to form ligand complexes. Formation of these ligand complexes was accompanied by loss of mixed-function oxidase activities, and dissociation of the complexes with the type I substrate biphenyl restored activities. Safrole and, to a lesser extent, 1'-hydroxysafrole formed complexes in vivo when administered to phenobarbital-pretreated rats; none was obtained with epoxysafrole. However, when administered to 3-methylcholanthrene-pretreated animals all three compounds formed complexes, safrole being the least effective. Epoxysafrole and 1'-hydroxysafrole administered to phenobarbital-pretreated rats resulted in slight inhibition of the type I binding of safrole to liver microsomal P-450 in vitro; in contrast, with 3-methylcholanthrene-pretreated animals marked competitive inhibition was observed. This study shows that oxidation of the allyl chain of safrole analogues enhances their affinity for cytochrome P-448, but not for cytochrome P-450, and further demonstrates that these cytochromes possess distinctly different binding sites.

Perforation of the intra-articular disc diagnosed by arthro-tomography of the temporomandibular joint

Arthrography was first used almost 40 years ago for evaluation of the non-osseous parts of the TMJ. It did not find wide application and only during the last decade have certain authors re-introduced its use as a diagnostic approach in TMJ pathology. Among the other pathological conditions which can be diagnosed, is a perforation of the intra-articular disc. Four such cases are presented and the value of this method is shown.

The homogeneity of rat liver microsomal cytochrome P-448 activity and its role in the activation of benzo[a]pyrene to mutagens

The O-deethylation of ethoxyresorufin and the metabolic activation of benzo[a]pyrene to mutagens were determined in hepatic microsomal preparations from control and induced animals. An excellent direct correlation (r = 0.95) has been observed between ethoxyresorufin O-deethylase and the metabolic activation of benzo[a]pyrene to mutagens when the fraction of cytochromes P-450 present as cytochrome P-448 was altered by the administration of phenobarbitone and 3-methylcholanthrene alone or in combination with 9-hydroxyellipticine. The correlation between these activities was maintained following treatment of animals with Arochlor 1254, benzo[a]pyrene, benzo[e]pyrene, 7,12-dimethylbenzo[a]anthracene,2-anthramine and 2-naphthylamine.