Preclinical Toxicology Studies with Acyclovir: Genetic Toxicity Tests

Preclinical Toxicology Studies with Acyclovir: Genetic ToxicityTests. Clive, D., Turner, N.T., Hozier, J., Batson, A.G. andTucker, W.E., Jr. (1983). Fundam. Appl. Toxicol 3: 587–602.Acyclovir (ACV), an antiviral drug active in the treatment oforal and genital Herpes infections, has been evaluated for mutagenicand carcinogenic potential in a battery of in vitro and in vivoshort-termassays. Negative results were obtained in the following in vitrotests: Ames Salmonella, plate incorporation and preincubationmodification assays; E. coli polA⁺/polA^– DNA repair; yeast(S. cerevisiae D4) gene conversion; Chinese hamster ovary cells(HGPRT, APRT loci and ouabain-resistance marker); L5178 Y mouselymphoma cells (HGPRT locus and ouabain-resistance marker);and C3H/10Tmouse fibroblast neo-plastic transformation assay.All except the last assay were performed in the presence andabsence of an exogenous metabolic activation system. ACV waspositive at high concentrations x exposure times in the absenceof exogenous metabolic activation in the following in vitrosystems and at the indicated concentrations: BALB/c-3T3 neoplastictransformation (50 /µg/mL, 72 h exposure); human lymphocytecytogenetics (250–500 µg/mL, 48 h exposure); andL5178Y mouse lymphoma cells (TK locus, 400–2400 µg/mL,4 h exposure; predominantly small colony mutants of chromosomalorigin produced). No effects were seen in vivo (mouse dominantlethal assay; rat and Chinese hamster bone marrow cytogenetics)at up to maximum tolerated doses (MTD). An unusual clastogeniceffect was seen in Chinese hamsters at 5 times the MTD. Overall,positive effects were seen only at either high concentrations(250 µg/mL in vitro or plasma levels) or prolonged exposure(72 hr in the BALB/ c-3T3 neoplastic transformation assay).These studies support the view that ACV is a chromosomal mutagen,i.e., one which causes multi-locus damage but not single geneeffects. The significance of these results for the genetic riskof ACV to man is discussed.     

Chronic Marijuana Smoke Exposure in the Rhesus Monkey I. Plasma Cannabinoid and Blood Carboxyhemoglobin Concentrations and Clinical Chemistry Parameters

Chronic Marijuana Smoke Exposure in the Rhesus Monkey I. PlasmaCannabinoid and Blood Carbxyhemoglobin Concentrations and ClinicalChemistry Parameters SLIKKER, W., JR., PAULE, M. G., ALI, S.F., SCALLET, A. C., AND BAILEY, J. R (1991). Fundam. Appl Toxicol17, 321–334. This report is the first in a series abouta large multidisciplinary study designed to determine whetherchronic marijuana (MJ) smoke exposure results in residual behavioraland/or neuropathological alterations in the rhesus monkey. Priorto the initiation of a year of chronic MJ smoke exposure, 64periadolescent male rhesus monkeys were trained for 1 year toperform five operant behavioral tasks and then divided, accordingto their performance in these tasks, into four exposure groups(n=15–16/group): (1) a high dose (HI) group, exposed 7days/week to the smoke of one standard MJ cigarette; (2) a lowd m (LO) group, exposed on weekend days only to the smoke ofa standard MJ cigarate; (3) an extracted MJ cigarette (EX) group,exposed 7 days/week to the smoke of one ethanol-extracted MJcigarette; and (4) a sham group (SH), exposed 7 days/week tosham exposure conditions. Daily exposures for 1 year were accomplishedusing a mask that covered the subjects' nose and mouth. Averagebody weights (initially 3.7?0.5 kg, mean?SD) and rates of weightgain (approximately 0.1 kg/month) were the same for all groupsthroughout the entire experiment. During the first week of expsure,plasma concentrations of -9-tetrahydrocannabinol and 11-nor-9-carboxy-THCin the HI group were 59?7 (mean?SE) and 5.5?1.5 ng/ml, respectively,45 min after MJ smoke administration and did not change significantlyat similar times after exposure throughout the remainder ofthe year. Whole blood carboxyhemoglobin levels increased toapproximately 13% 1 min after expsure to smoke in either theMJ or the EX groups. Comparison of blood chemistry and hematologyvalues before, during, and after exposure indicated no differencesfor most parameters. During exposure, lymphocytes, alkalinephosphatase and -glutamyl transferase were depressed in theHI group compared to in the SH group. During exposure, aspartateaminotransferase was elevatd for both the HI and EX groups,suggesting a general effect of smoke exposure. Because theseeffects were transient and remained within the range of reportednormal values, these data indicate that long-term, experimentalexperimental exposure to MJ smoke is feasible and does not compromisethe general health of the rhesus monkey.     

Immunogenic Properties of Structurally Modified Human Tissue Plasminogen Activators in Chimpanzees and Mice

Immunogenic properties of second generation human tissue plasminogenactivator (tPA) derivatives were examined in chimpanzee andmouse systems. Five species of modified tPAs (mtPAs) (designated2660, 2663, 2810, 8000, and 9200), recombinant native tPA orbovine serum albumin (BSA) as a positive control were subcutaneouslyinjected nine times at suitable intervals into chimpanzees,genetically the closest species to man. These animals were testedfor antigen(Ag)-specific antibodies to the corresponding proteinsby means of enzyme-linked immunosorbent assay and Western blotanalysis. Neither 9200, one of the five mtPAs tested, nor tPAwas immunogenic, although BSA and the other four mtPAs wereimmunogenic under these conditions. Thus, an antigenic determinant was not exposed by the modification on 9200 and thismodified tPA is expected not to be immunogenic in humans. Inthe mouse studies, mice were immunized with mtPAs. Serum sam-piesfrom these animals were tested for antibodies to the mtPAs whichdid not concomitantly recognize native tPA by immune ad sorptionof the antibodies to tPA. The amount of such antibodies alterthe elimination of native tPA-reactive antibodies was littleor none when the serum samples from 9200 and from the othermtPAs, except 8000, were tested. Taking into consideration theresults of the chimpanzee studies, it can be concluded thatAg-specific antibodies are dominantly produced to unchangedepitopes present in modified proteins in the mouse system, inwhich the native protein is immunogenic. These results suggestthat the chimpanzee model should be useful to predict immunogenicityof second generation recombinant proteins in man, while themouse system adopted by us, which determines the newly generatedepitopes of the modified proteins, is not sufficient.     

Hydrodynamic Function of Second Generation Porcine Bioprosthetic Heart Valves

The hydrodynamic function and leaflet dynamics of second generation porcine valves prepared with low- or zero-pressure fixation have been studied and compared to first generation porcine bioprostheses, bileaflet, and tilting disc mechanical valves. The Carpentier-Edwards Supra-Annular and Hancock II valves showed lower pressure drops than the Medtronic Intact valve and first generation porcine valves, and comparable overall energy losses to mechanical valves at normal cardiac outputs. Only the zero-pressure fixed Intact valve showed synchronous leaflet opening. Delayed leaflet opening and high opening pressures were found in both low- and high-pressure fixed porcine valves. All porcine bioprostheses showed high open leaflet bending strains. Fixation of valve leaflets with "near zero" pressure fixation and a more physiological neutral geometry is necessary to ensure synchronous leaflet opening at low flows and a reduction in commissural bending strains.     

CONTROL OF BREATHING AFTER FENTANYL AND INNOVAR ANAESTHESIA

Ventilation (VI), end-tidal (Pco₂), mixed venous (PVco₂) andthe ventilatory response to carbon dioxide were measured beforesurgery, and during the first 4h of recovery in 18 adult patientswho underwent elective limb surgery under fentanyl or Innovaranaesthesia. End-tidal and mixed venous PCO₂ were increasedsignificantly in the first 150 min after the last dose of drug(P<0.001, P<0.01). but had returned to control valuesby 4 h. Ventilation and ventilatory response to carbon dioxidewere significantly depressed in all patients (P < 0.001),but returned to near control values at 4 h. Fentanyl and Innovaranaesthesia displaced the carbon dioxide response to the right,but no correlation was found between either the magnitude ofthe displacement of the response curve or the alteration inslope and the control values. This suggests that patients witha low value of VI/Pco₂ are not more susceptible to the ventilatorydepressant action of narcotic anaesthetics. Recovery of ventilatoryresponsiveness towards normal during the 4 h after anaesthesia,occurred in a graded and progressive manner; there was no evidenceof a biphasic pattern of recovery. ^*Present address: Centre for Advanced Studies in Health Sciences,Western Australian Institute of Technology, Bentley, WesternAustralia. Presented to the annual meeting of the Canadian AnaesthetistsSociety, Ottawa, Ontario, June 1978.     

Peptide formation in the presence of metal ion protecting groups

A quantitative study of the degree of racemization induced by the [(NH₃)₅Co-(III)-] protecting group when bound to the C-terminal of the amino acids Leu, Phe, and His, as has been carried out. Racemization was determined by forming the diastereomeric cobalt dipeptides [(Leu)(AA)Co(III)(NH3)₅] where AA = L-Leu, L-Phe, and L-His; after cobalt removal (using NaBH₄), the peptide diastereomers were analyzed quantitatively using an amino acid analyzer. No racemization was observed within experimental error (0.3%) as a result of the substitution of the [(NH3)₅Co(III)-] group on the amino acids and peptides studied.     

Maintaining a balanced perspective on risk

This paper discusses the psychological approach to the treatment of sexual problems. The focus is on sexual dysfunctions, rather than sexual deviations. The history of psychological therapy for sexual dysfunction is briefly outlined, and the major approaches commented on. The current status of this field is reviewed. It is argued that a broad-based behavioural approach is the treatment of choice for these problems, with contributions from cognitive therapy and the systems theory approach where appropriate. A discussion of the practice of therapy is also provided.