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Biomedical subjects

I G Robertson

Publications and source records attributed to I G Robertson.

At least 37 records · Page 2Linked to original sources
PubMed1991

Fetal phenytoin exposure, hypoplastic nails, and jitteriness.

In a prospective study infants born to mothers with epilepsy (n = 61) were found to have an unexpectedly high incidence of congenital anomalies (26/61, 43%) and neonatal conditions (26/61, 43%) compared with controls (0/62, and 6/62, 10%, respectively). There were two neonatal deaths in the study group but none among the controls. Hypoplasia of the finger or toenails was a common congenital anomaly in those infants whose mothers had received phenytoin alone or in combination with other anticonvulsant drugs (11 of 40, 28%). The mean serum phenytoin concentration was higher among mothers of infants with hypoplastic nails than among those with normal nails. Jitteriness was a common neonatal condition affecting infants of epileptic mothers (11 of 61, 18%) but not controls The mean cord serum phenytoin concentrations were similar among jittery and non-jittery infants. At follow up (after excluding one infant with Down's syndrome from the study group) the infants seemed to have developed normally, though one had serious learning difficulties at school. We suggest that hypoplasia of the nails is related to high maternal serum concentrations of phenytoin, and though 18% of infants born to epileptic mothers were jittery compared with no control infants this may not be the result of withdrawal of the drug in all cases.

Abnormalities, Drug-Induced↗
PubMed1990

Disposition of amsacrine and its analogue 9-([2-methoxy-4-[(methylsulfonyl)amino]phenyl]amino)-N,5-dimethyl-4- acridinecarboxamide (CI-921) in plasma, liver, and Lewis lung tumors in mice.

9-([2-Methoxy-4-[(methylsulfonyl)amino]phenyl]amino)-N,5-dimethyl-4- acridinecarboxamide (CI-921), an analogue of the clinical antileukemia drug amsacrine with improved solid tumor activity in mice, is currently being evaluated in patients. In order to determine whether CI-921 possesses any advantages over amsacrine in terms of tissue delivery, the pharmacokinetics of amsacrine and CI-921 were determined following i.v. injection in male B6D2F1 mice. Plasma kinetics in normal mice were measured following administration of 14.4, 28.9, and 57.7 mumol/kg. The kinetics in s.c. Lewis lung tumors, and in plasma and livers of normal and tumor-bearing mice were measured following administration of 57.7 mumol/kg. CI-921 and amsacrine were quantitated by high-performance liquid chromatography after extraction from plasma and from liver and tumor homogenates. In experiments with appropriate 3H-labeled compounds, both total and covalently bound radioactivity (determined after precipitation and washing with acetonitrile) were measured in plasma and in liver homogenates. Over this dose range, nonlinear kinetics were observed in plasma for unchanged CI-921 and amsacrine, and a reasonable fit was obtained with Michaelis-Menten kinetics to a one-compartment model for CI-921 (Km 3.7 mumol/liter; Vmax 18 mumol/h/kg; V ss 3.3 liter/kg) and a two-compartment model for amsacrine (Km 3.6 mumol/liter; Vmax 76 mumol/h/kg; Vss 4.8 liter/kg). The area under the concentration-time curve (AUC) for plasma following a dose of 57.7 mumol/kg was 31 mumol.h/liter for CI-921 and 6.3 mumol.h/liter for amsacrine. However, equilibrium dialysis measurements indicated high plasma protein binding with free drug fractions for CI-921 and amsacrine of 0.63 and 6.7%, respectively. In the liver, unchanged drug concentrations and total radioactivity for both compounds were approximately 10-fold those in plasma, and the tissue half-life of CI-921 was approximately 4-fold longer for CI-921 than for amsacrine. Plasma and liver kinetics in mice with s.c. Lewis lung tumors were similar to those in normal mice. Tumor half-lives of unchanged CI-921 and amsacrine were 3.9 and 2.7 h, respectively, considerably longer than those for plasma (1.2 and 0.30 h respectively) or liver (1.2 and 0.28 h, respectively). Tumor AUC values for CI-921 and amsacrine were 68 and 37 mumol.h/liter, respectively, as compared to the calculated AUC values for free drug in plasma of 0.19 and 0.42 mumol.h/liter, respectively. It is concluded that the uptake into tumors from the plasma free drug fraction is more efficient for CI-921 than for amsacrine.

Amsacrine↗
PubMed1989

Differences in detection of DNA adducts in the 32P-postlabelling assay after either 1-butanol extraction or nuclease P1 treatment.

The use of nuclease P1 treatment and 1-butanol extraction to increase the sensitivity of the 32P-postlabelling assay for DNA adducts have been compared. Although similar results were obtained with the two methods for standard adducts formed with benzo[a]pyrene diol epoxide I (BPDE-I), nuclease P1 treatment resulted in a significant reduction in detection of major adducts from 1-amino-6-nitropyrene (1-amino-6-NP), 1-amino-8-nitropyrene (1-amino-8-NP), 2-aminofluorene (2-AF), 2-naphthylamine (2-NA) and 4-aminobiphenyl (4-ABP) modified DNAs, but not following the 32P-postlabelling analysis of 2-acetylaminofluorene (2-AAF) modified DNA. These results suggest that, at least initially, both modifications of the 32P-postlabelling assay should be used for the detection of unknown adducts or for adducts derived from nitroaromatics and aromatic amines.

1-Butanol↗
PubMed1988

The relationship between lipophilic-hydrophilic balance, uptake and anti-bacteriophage lambda activity of experimental anti-tumour bisquaternary salts.

The uptake by Escherichia coli of a series of bisquaternary experimental anti-tumour agents (quinolinium 4-[p-9(-pyridylamino)phenylcarbamoyl]-aniline-bisalkyl dibromides) has been measured both by association of radiolabelled compounds and their inhibition of the vegetative replication of bacteriophage lambda (after heat inactivation of the phage repressor) as a measure of biologically effective intracellular drug concentration. Uptake of these compounds was correlated with biological effect, and was a function of both incubation temperature and the lipophilic-hydrophilic balance of the compound. At 30 degrees C uptake was drug concentration-dependent and was not readily reversible. No saturation of uptake was apparent over the concentration range tested. Preliminary experiments indicated that time-dependent drug uptake was also related to growth inhibition in cultured L1210 murine leukaemia cells. These results are consistent with the hypothesis that uptake occurs by diffusion across the plasma membrane followed by strong binding to cell constituents such as DNA. The approximate range of uptake of the most active compounds, using an external drug concentration of 1 microM, are 100 and 2400 molecules/s respectively for bacteria and murine leukemia cells. For bacteria, the uptake of approx. 2 X 10(5) molecules of drug/cell inhibits the yield of phage lambda by 90%.

Animals↗
PubMed1988

Thiolytic cleavage and binding of the antitumour agent CI-921 in blood.

The antitumour agent 9-[[2-methoxy-4-[methylsulphonylamino]-phenyl]amino]-N,5-dimethyl- 4-acridinecarboxamide (CI-921; NSC 343499) is currently undergoing clinical evaluation. The plasma disposition of this compound together with its ability to bind to plasma proteins has been investigated in the mouse. Five minutes after intravenous administration of [acridinyl-G-3H]-CI-921 (57.7 mol/kg) to male BDF1 mice, plasma samples were taken and precipitated with acetonitrile. 17% of the total plasma radioactivity was found to be bound to plasma proteins, increasing to 31% by 30 min. To ascertain the mechanism of binding, [acridinyl-G-3H]-CI-921 was incubated at 37 degrees C in mouse blood or plasma and the radioactivity analysed after precipitation with acetonitrile. CI-921 and the cleavage product 4-amino-3-methoxy-methanesulphonanilide (MSA) were detected in the acetonitrile supernatants by HPLC using electrochemical and ultraviolet detection. After incubation for 1 h with blood, extensive association of radioactivity (80% of total) with plasma proteins, together with a rapid decrease in CI-921 concentration and a concomitant increase in MSA concentration, was observed. In blood samples from mice given CI-921, low concentrations (1 to 2 mumol/l) of MSA were detected up to 1 h after injection. The results suggest that in vivo at least part of the covalent binding in blood arises from the nucleophilic attack by protein thiols at the C-9 position of the acridine ring resulting in covalent protein adducts and release of MSA.

Acetonitriles↗
PubMed1988

Involvement of glutathione in the metabolism of the anilinoacridine antitumour agents CI-921 and amsacrine.

4'-(9-Acridinylamino)methanesulphon-m-anisidide (amsacrine) and CI-921, the 4-methyl-5-(N-methyl-carboxamide) derivative of amsacrine, are two anilinoacridine antitumour agents in clinical use or trial. The elimination of these agents has been investigated in male BDF1 mice. 74% and 86% of the dose of [acridinyl-G-3H]-amsacrine and -CI-921, respectively, was excreted in the faeces of mice by 72 hr after i.v. injection. Administration of both compounds also resulted in significant depletion of glutathione (GSH) in mouse liver, although the effect of CI-921 was delayed and reduced compared with amsacrine. In mouse bile, radiolabelled products which cochromatographed with amsacrine GSH conjugates at both the 5'- and 6'-positions of the anilino ring were present in similar amounts and constituted approximately 70% of the excreted radioactivity, the balance being minor, more polar metabolites. With hepatic microsomal fractions, both conjugates of amsacrine were formed but only the 6'- and not the 5'-conjugate was increased in the presence of cytosol. Preliminary evidence indicates the presence in mouse bile of at least the 5'-GSH conjugate of CI-921, and several other GSH derived products not seen with amsacrine. It is concluded that the elimination of CI-921 occurs by a mechanism similar to that of amsacrine. Further, the possible involvement of GSH transferase in the conjugation of amsacrine may have consequences for the hepatotoxicity of this agent.

Amsacrine↗
PubMed1986

The importance of 2-aminofluorene in the mutagenic activation of 2-acetylaminofluorene.

The mutagenic activation of 2-acetylaminofluorene (AAF) and its derivatives N-hydroxy-AAF and 2-aminofluorene (AF) by pulmonary and hepatic microsomal fractions from untreated rabbits was investigated using Salmonella strain TA98. The mutagenicity of AAF in the presence of hepatic microsomes followed typical saturation kinetics. However, in the presence of pulmonary microsomes, the mutagenic activity increased linearly with increasing substrate concentration and approximated that obtained with low concentrations of AF. N-Hydroxy-AAF was 1/10th as mutagenic as AF in the presence of pulmonary microsomes, but 2-2.5 times more mutagenic than AF in the presence of hepatic microsomes. The activation of AAF by both fractions was completely inhibited by the deacetylase inhibitor paraoxon. Although AAF does not appear to be a substrate for cytochrome P450 form 5, antibodies to this form inhibited the activation of AAF by pulmonary and hepatic microsomes by 90% and 60%, respectively. These results indicate that the mutagenic activation of AAF by these fractions primarily involves deacetylation to AF, followed by cytochrome P450 form 5-mediated activation of AF.

2-Acetylaminofluorene↗
PubMed1986

The enzymatic conjugation of glutathione with bay-region diol-epoxides of benzo[a]pyrene, benz[a]anthracene and chrysene.

The kinetics of the enzymatic conjugation of glutathione (GSH) with the anti-diastereoisomers of trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE), trans-3,4-dihydroxy-1,2-epoxy-1,2,3, 4-tetrahydrobenz[a]anthracene (BADE) and trans-1,2- dihydroxy-3,4-epoxy-1,2,3,4-tetrahydrochrysene (CDE) catalyzed by transferase 4-4 from rat liver have been compared. When the concentration of these diol-epoxides was varied (using 2 mM GSH) the apparent Vmax values were 560, 2100 and 1500 nmol/mg/min for (+/-)-anti-BPDE, (+/-)-anti-BADE and (+/-)-anti-CDE, respectively, with corresponding apparent Km values of 11, 125 and 105 microM. The catalytic efficiency of transferase 4-4 in the GSH conjugation of (+/-)-anti-BADE and (+/-)-anti-CDE is thus approximately one-third of (+/-)-anti-BPDE (0.014 and 0.012 s-1 microM-1 respectively versus 0.042 s-1 microM-1). Similar non-linear Lineweaver-Burk plots were obtained with each diol-epoxide when the concentration of GSH was varied, and two apparent Km values of 0.02-0.04 and 0.4-0.9 mM GSH were estimated. The GSH-conjugates formed with the individual enantiomers of the racemic substrates used were resolved by h.p.l.c. The data indicate that with each diol-epoxide transferase 4-4 is highly selective (greater than or equal to 95%) towards the biologically most active (+)-enantiomer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Glutathione transferases in rat lung: the presence of transferase 7-7, highly efficient in the conjugation of glutathione with the carcinogenic (+)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

The enzyme-catalysed conjugation of (+/-)-7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+/-)-anti-BPDE] with glutathione (GSH) by cytosolic GSH transferases isolated primarily from rat lung has been studied. GSH transferase 4-4 was active in the GSH conjugation of anti-BPDE, whereas transferases 2-2 and 3-3 showed little activity. GSH transferase 1-1 did not contribute to the activity since significant amounts were not detected in the rat lung. Activity was also obtained with several acidic pulmonary GSH transferases and with a newly described form, transferase 7-7, also isolated from rat kidney and from hyperplastic liver nodules. The catalytic efficiency (kcat/Km) of transferase 7-7 was seven times that of transferase 4-4, the most active rat transferase previously identified. When the GSH concentration was varied at constant (+/-)-anti-BPDE concentration in the presence of transferases 4-4, 7-7 or the major acidic transferase, non-linear Lineweaver-Burk plots were obtained. Resolution of the GSH conjugates of the two enantiomers of (+/-)-anti-BPDE by h.p.l.c. showed that all isoenzymes with notable activity were selective (greater than or equal to 97%) for the (+)-enantiomer of anti-BPDE, which is generally considered to be the most carcinogenic form of BPDE. The possibility that one enantiomer inhibits the conjugation of the other enantiomer with GSH cannot be excluded and may quantitatively affect the results obtained.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Differences in stereoselectivity and catalytic efficiency of three human glutathione transferases in the conjugation of glutathione with 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene.

The kinetics of the enzyme-catalyzed conjugation of glutathione with (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha -oxy-7,8,9,10 -tetrahydrobenzo(a)pyrene [(+/-)-anti-BPDE] have been studied with the following human cytosolic glutathione transferases: the basic (alpha-epsilon) and near-neutral (mu) isoenzymes from liver, and the acidic (pi) isoenzyme from placenta. When the BPDE concentration was varied (using 5 mM glutathione) the apparent Vmax values for transferases alpha-epsilon, mu, and pi were 38, 570, and 825 nmol X mg-1 X min-1, respectively, with corresponding apparent Km values of 88, 27, and 54 microM. The apparent Km values for glutathione [using 80 microM (+/-)-anti-BPDE] were 0.4, 0.7, and 0.1 mM for transferase alpha-epsilon, mu, and pi, respectively. The glutathione conjugates formed with the two enantiomers of (+/-)-anti-BPDE were resolved by high performance liquid chromatography. The percentages of conjugates derived from the highly carcinogenic (+)-enantiomer were 59, 60, and greater than or equal to 90% for transferases alpha-epsilon, mu, and pi, respectively. The separate enantiomers of anti-BPDE were assayed in experiments with transferases mu and pi. Both enantiomers were substrates for transferase mu, but only the (+)-enantiomer gave measurable activity with transferase pi. A 3-fold increase in Vmax and Km values for transferase pi was obtained with (+)-anti-BPDE as compared with the racemic substrate and could be quantitatively accounted for by the finding that (-)-anti-BPDE serves as a competitive inhibitor for transferase pi.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Prescribing in pregnancy. Epilepsy in pregnancy.

In women with epilepsy, seizure control during pregnancy can be improved by maintaining the serum anticonvulsant drug concentration within the therapeutic range. Treatment with one anticonvulsant drug plus folic acid supplementation 5 mg per day seems appropriate in most cases. This should be achieved before conception whenever possible. No anticonvulsant drug seems free of teratogenic risk. With the commonly used anticonvulsant drugs-phenytoin, phenobarbitone, carbamazepine and sodium valproate-the risk is relatively low and represents less potential harm to the fetus than might occur with uncontrolled seizures.

Abnormalities, Drug-Induced↗
PubMed1985

Differences in the occurrence of glutathione transferase isoenzymes in rat lung and liver.

Cytosolic GSH transferases have been purified from rat lung by affinity chromatography followed by chromatofocusing. On the criteria of order of elution, substrate specificity, apparent subunit Mr, sensitivity to inhibitors, and reaction with antibodies, transferase subunits equivalent to subunits 2, 3, and 4, in the binary combinations occurring in liver, were identified. However, subunit 1 (and therefore transferases 1-1 and 1-2) was not detected. The most conspicuous difference is the presence in lung of a new form, eluting at pH 8.7, which is not detected in rat liver. This isoenzyme (transferase "pH 8.7") is characterized by its low apparent subunit Mr and high efficiency in the conjugation of glutathione with anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide, considered the ultimate carcinogen of benzo(a)-pyrene.

Animals↗
PubMed1983

Interactions between xenobiotics that increase or decrease the levels of cytochrome P-450 isozymes in rabbit lung and liver.

Isozyme-specific enzymatic activities, radial immunodiffusion, and Western blotting were used to study the effects of phenobarbital, Aroclor 1260, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on microsomal levels of cytochrome P-450 forms 2, 5, and 6. The pulmonary concentration of form 2 was decreased to trace levels by the administration of Aroclor 1260 but not TCDD; co-administration of phenobarbital did not mitigate the decrease. The pulmonary concentration of form 5 was not significantly changed following treatment with Aroclor 1260, phenobarbital, or TCDD. The pulmonary content of form 6 was increased 5- and 10-fold by administration of Aroclor 1260 and TCDD, respectively, and decreased 2-fold by treatment with phenobarbital. Further, phenobarbital antagonized the induction of form 6 by Aroclor 1260 but not by TCDD. In the liver, increases and decreases in form 2-mediated benzphetamine N-demethylation were observed following treatment with Aroclor 1260 depending on the time after dose and individual rabbit response. Hepatic induction of form 2 by phenobarbital was significantly decreased by co-administration of Aroclor 1260. However, form 5 was induced in the liver by either Aroclor 1260 or phenobarbital or both. Thus, the effect of Aroclor 1260 on the control of the concentration of form 2 is independent of that of form 5 in the lung and liver. Fractionation of the Aroclor 1260 to remove co-planar polychlorinated biphenyls and dibenzofurans was useful in demonstrating that the pulmonary induction of form 6 was dependent on these components and unrelated to the repression of form 2 in the lung and liver. The apparent repressive effect of phenobarbital on form 6 in the lung is interesting as it suggests an interaction between phenobarbital and polycyclic hydrocarbon-mediated induction.

Animals↗
PubMed1983

Specificity of rat liver cytochrome P-450 isozymes in the mutagenic activation of benzo[a]pyrene, aromatic amines and aflatoxin B1.

The ability of three purified forms of rat liver cytochrome P-450 to metabolically activate benzo[a]pyrene, trans-benzo-[a]pyrene-7,8-dihydrodiol, 2-aminofluorene, aflatoxin B1, dimethylnitrosamine, and a pyrolysis product of tryptophan(3-amino-1-methyl-5H-pyrido(4,3-b)indole) (Trp-P-2) to mutagenic products was examined using Salmonella typhimurium strains TA98 and G46 in a reconstituted monooxygenase system. The isozymes examined were cytochrome P-450-PB (the major phenobarbital inducible form), and the two major 3-MC inducible forms (cytochromes P-448(52) and P-448(55)). Cytochromes P-448(52) and P-448(55) preferentially metabolize 2-aminofluorene and Trp-P-2 to mutagenic products. However, only cytochrome P-448(55) metabolizes benzo[a]pyrene and its 7,8-dihydrodiol derivative to mutagenic products. Both cytochrome P-448(52) and P-448(55) metabolize aflatoxin B1 to mutagenic products at a much faster rate than cytochrome P-450-PB. Dimethylnitrosamine was not activated by any of the isozymes tested.

Aflatoxin B1↗
PubMed1983

Activation of some aromatic amines to mutagenic products by prostaglandin endoperoxide synthetase.

Cooxidation of xenobiotics may occur during prostaglandin biosynthesis. The ability of prostaglandin endoperoxide synthetase to cooxidize several aromatic amines and other chemicals to mutagenic products was tested with the standard Salmonella tester strains. The microsomal fraction of ram seminal vesicles, a rich source of prostaglandin endoperoxide synthetase, in the presence of the prostaglandin endoperoxide synthetase substrate arachidonic acid metabolized benzidine, 2-aminofluorene, 2-naphthylamine, and 2,5-diaminoanisole to mutagenic products. 1-Napthylamine, 2-aminoanthracene, 2-acetylaminofluorene, and 2,4-diaminoanisole were negative or weakly mutagenic. N-Nitrosodimethylamine, N-nitrosomorpholine, the pesticide Aminocarb, and di(2-ethylhexyl)phthalate were not activated to mutagenic products by the ram seminal vesicle microsomal fraction.

Amines↗
PubMed1983

The relationship between increases in the hepatic content of cytochrome P-450, form 5, and in the metabolism of aromatic amines to mutagenic products following treatment of rabbits with phenobarbital.

Treatment of rabbits with phenobarbital is followed by increases in the hepatic microsomal concentration of cytochrome P-450, form 5, and in the hepatic microsomal metabolism of aromatic amines to mutagenic products. Inhibition by antibodies to form 5 of the activation of 2-aminoanthracene and 2-aminofluorene demonstrates that these increases are directly related. The extent of the apparent induction of form 5 by phenobarbital is determined from single radial immunodiffusion, immunostaining of form 5 on nitrocellulose sheets containing microsomal proteins transferred from polyacrylamide gels, and the amount of antibody required for 50% of maximal inhibition of activity. The results indicate that phenobarbital increases the hepatic microsomal concentration of cytochrome P-450, form 5, to the same extent that it increases form 5-mediated metabolism of aromatic amines to mutagenic products: 10- to 12-fold. In contrast to the effects of phenobarbital, treatment of rabbits with beta-naphthoflavone decreases the hepatic microsomal concentration of cytochrome P-450, form 5, to less than detectable levels and has little effect on the metabolism of aromatic amines to mutagenic products. Our findings, along with the known effects of phenobarbital on cytochrome P-450, form 2, and the known catalytic activity of cytochrome P-450, form 4, lead to the following conclusions: (a) treatment of rabbits with phenobarbital results in increases in the hepatic microsomal concentrations of at least two structurally, immunochemically, and catalytically distinct isozymes of cytochrome P-450, forms 2 and 5; (b) the metabolism of aromatic amines to mutagenic products in rabbit hepatic microsomal preparations depends on the relative concentrations of at least two isozymes of cytochrome P-450, forms 4 and 5, that change in response to different inducers.

Amines↗
PubMed1982

Age-related changes in mutagen activation by rat tissues.

Age-related changes in drug metabolism of the liver, lung and kidney of adult female Long-Evans rats were determined by measuring changes in mutagen formation. Activation of aflatoxin B1 (AFB1), 2-aminofluorene (AF) and 2-acetylaminofluorene (AAF) to mutagenic derivatives was assayed using the Ames Salmonella test system. The promutagens were incubated with tissue fractions from rats ranging in age from 2.5 to 25 months. With all three compounds, hepatic, renal and pulmonary activation was lower in the senescent than in the young adult animals. The largest decrease, however, occurred prior to middle-age, i.e. before 9-13 months. In liver and kidney, little change was detectable between the middle-aged and the old (20-25 months) animals. However, pulmonary metabolism in the oldest animals was slightly higher than in the extracts from the middle-aged rats. The observed decline in mutagen activation may thus be a function of maturation rather than senescence.

2-Acetylaminofluorene↗