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Biomedical subjects

R L Yu

Publications and source records attributed to R L Yu.

14 recordsLinked to original sources
PubMed1999

Lack of response to multiple genotoxic agents at the hprt locus in peripheral blood T-lymphocytes of cynomolgus monkeys.

We tested the ability of a series of known genotoxic agents to cause mutations at the hprt locus in peripheral blood T-lymphocytes of cynomolgus monkeys as measured by the ability to form clones in the presence of 6-thioguanine. Ethylmethane sulfonate (EMS, 300 mg/kg i.p.), chloroethylmethane sulfonate (CI-EMS, 35 or 50 mg/kg i.p.), and the Pharmacia & Upjohn antitumor agents adozelesin (1.6, 4, 6, or 8 microg/kg i.v.) and CC-1065 (6 microg/kg i.v.) were all negative in the hprt mutation test. Results with cyclophosphamide (CP, 75 mg/kg i.v.) were equivocal. Adozelesin, CC-1065, and CI-EMS treatments increased the percentage of T-lymphocytes with chromosome aberrations, as well as inducing types of aberrations not seen in control cells. EMS and CP were not tested for chromosome aberrations. We have previously shown that treatment of monkeys with 77 mg/kg ENU substantially increased the hprt mutant frequency, with a lag time of approximately 77 days between treatment and peak MF values. The results of the present study suggest a low sensitivity of the hprt mutation assay to certain classes of genotoxic agents in cynomolgus monkeys.

Animals↗
PubMed1998

Antiendotoxin strategies for the prevention and treatment of septic shock. New approaches and future directions.

Therapy for Gram-negative sepsis remains unsatisfactory despite a concerted effort to develop new treatments for this common, life-threatening syndrome. Current research continues on several fronts to improve the treatment options available to clinicians in the management of these critically ill patients. Recently, a greater understanding of the complex molecular basis of endotoxin-mediated pathophysiological effects in humans has generated a number of novel therapeutic agents for sepsis. Several of these treatment strategies have already entered clinical trials and it is hoped that some of these therapies will become widely available in the near future. In this review, the current status of the most promising new antiendotoxin agents is summarised, and the major obstacles to the successful clinical development of these therapies are described. New antiendotoxin therapies include those which interrupt the synthesis of endotoxin, bind and neutralise its activity, prevent endotoxin interactions with host effector cells and interfere with endotoxin-mediated signal transduction pathways. Potential therapeutic strategies involving these agents consist of endotoxin analogues, antibodies, subunit vaccines, binding columns, recombinant human proteins and small molecule inhibitors of endotoxin synthesis and intracellular signalling. The pitfalls of previous antiendotoxin clinical investigations and the perils of future clinical trial designs are discussed in the context of unmet needs and realistic expectations for success. While considerable progress has been made, effective and new treatments for Gram-negative bacterial sepsis continues to elude us at the present time. This has been to the detriment of patients, investigators and pharmaceutical companies alike. It will require focused efforts by basic scientists, continued support by industry and enlightened study designs by clinical investigators to successfully develop antiendotoxin in therapies for use in septic patients in the future.

Anti-Bacterial Agents↗
PubMed1996

End points for biomonitoring: assay sensitivity/selectivity.

Estimation of population exposure and biological impact of potential hazards are central reasons for performing biomonitoring. The sensitivity of the biomonitoring methods and the linkage of the measured phenomenon to human disease are also important, but often overlooked, considerations. We are conducting experiments to evaluate the sensitivity of hprt mutation measurement in the nonhuman primate, the cynomolgus monkey. Our findings demonstrate in the monkey that hypoxanthine guanine phosphoribosyltransferase (hprt) mutations produced in vivo can be detected using technique originally worked out using human cells; cynomolgus monkeys were chosen to avoid many of the complications encountered in studying humans. Sequencing of mutants from the monkey using reverse transcriptase polymerase chain reaction methods has led us to conclude that there is similarity of the spectra observed between the spontaneous mutations detected in the two species. However, more recent data suggest that due to low sensitivity, the method is probably not appropriate for routine biomonitoring of randomly selected populations. For example, the inability of the hprt mutation assay to detect some very potent mutagens in the monkey and the effects of the time-dependent pattern of mutant occurrence serve to urge caution in interpretation of elevation or lack of elevation in mutant frequency. Mechanisms for splitting and archiving samples of human tissues/blood from populations at risk may prove valuable as methods improve.

Animals↗
PubMed1995

Micronuclei in mice treated with monocrotaline with and without phenobarbital pretreatment.

Monocrotaline is a very potent toxin, producing significant effects of pneumotoxicity, hepatotoxicity, and teratogenicity, as well as carcinogenicity. In addition, the compound has been clearly shown to be mutagenic after metabolic activation. The goal of the experiments reported here was to confirm the reported clastogenesis induced by this agent in vivo and to evaluate the impact of modulation of metabolic activity by phenobarbital, a potent P-450 inducer (both Phase I and Phase II enzymes). The method used in addressing this problem relied on a new technique for monitoring clastogenesis in vivo, i.e., the acridine orange micronucleus assay method originally exploited by Hayashi et al. [1990]. The result of our experiments confirmed monocrotaline to be an effective clastogen in vivo, using the acridine orange method of assessment. The peak in induction of micronuclei occurred on the second day following intraperitoneal administration of the drug. Administration of phenobarbital prior to monocrotaline did appear to modulate the micronucleus induction. At 30 mg/kg bw monocrotaline, the pretreatment with phenobarbital appears to increase the intensity of monocrotaline clastogenesis, while the effect at higher doses (60 and 125 mg/kg bw) is a reduction in potency, presumably reflecting increased importance of Phase II metabolism for monocrotaline at these doses. Thus the study reported here confirms the potent in vivo clastogenesis of monocrotaline, and provides evidence for a dose-related shift in mechanism for the phenomenon.

Analysis of Variance↗
PubMed1995

Lung tumor induction in A/J mice and clastogenic effects in CD-1 mice of the sequence-selective DNA alkylating agents (+)-CC-1065 and (-)-CC-1065.

The in vivo genotoxic effects of the antitumor antibiotic, (+)-CC-1065, and its unnatural enantiomer, (-)-CC-1065, were investigated in two mouse models. These two compounds alkylate AT-rich regions of double stranded DNA with distinct sequence selectivities. (+)-CC-1065 dose-dependently increased the chromosomal aberration frequency in bone marrow cells of CD-1 mice from 1.2 +/- 0.8% in vehicle control animals to 5.0 +/- 1.2%, 11.4 +/- 3.9%, and 20.6 +/- 2.3% 24 hours following single intravenous doses of 2, 4, and 8 micrograms/kg, respectively. (-)-CC-1065 was significantly less potent with a maximal response at 8 micrograms/kg approximately one-third of that observed for (+)-CC-1065. (+)-CC-1065 induced a significant (P < or = 0.05), three-fold increase in the number of lung tumors/mouse in strain A/J mice from 0.27 +/- 0.15 for vehicle control animals to 0.83 +/- 0.15 24 weeks following a single intravenous dose of 8 micrograms/kg. This effect was paralleled by corresponding threefold increases in the percentage of mice with tumors and the percentage of mice with multiple tumors, compared to vehicle controls. (-)-CC-1065 at 8 micrograms/kg induced 0.67 +/- 0.15 tumors/mouse and resulted in slightly smaller increases in the tumor incidence and multiple tumor incidence, compared to (+)-CC-1065. The above results demonstrate that single intravenous doses of (+)- CC-1065 and (-)-CC-1065 which cause chromosomal damage in CD-1 mice also induce an increased incidence of lung tumors in A/J mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Risk and benefit evaluation in development of pharmaceutical products.

Pharmaceutical products are intended to cure disease, reduce pain and suffering, prolong life, and correct metabolic deficits in patients. However, the potential patient population is intrinsically genetically heterogenous, and this factor complicates the evaluation of data on all aspects of safety evaluation of new drugs. Often the genetic heterogeneity is related to drug metabolizing capacity, but recent evidence suggests that heterogeneity in repair capacity as well as structural integrity of the chromatin (fragile X) have been shown to be relevant. Because drugs are biologically active and may have more than one type of effect, the evaluation of a large number of parameters is necessary in arriving at a rational estimate of potential risk. In this paper, several specific examples of risk assessments and some generic genotoxicity questions that are recurrent, including the question of the relevance of in vitro chromosomal aberration induction at high dose/sampling time, are raised. Other examples of the kinds of concerns from the safety evaluation of U-48753E, U-54461, and U-68,553B are discussed. The drug U-48753E was discovered to be slightly mutagenic in the AS52 assay, and significant efforts were expended in evaluation of the metabolism-based generation of a reactive intermediate. The drug U-54,461 was shown to be capable of breaking chromosomes in vitro but extensive in vivo data as well as a variety of other studies served to reduce the level of concern substantially.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-Related Side Effects and Adverse Reactions↗
PubMed1992

Chromosomal breakage following treatment of CHO-K1 cells in vitro with U-68,553B is due to induction of undercondensation of heterochromatin.

Preferential breakage of chromosomes at specific sites (so-called "fragile sites") has been observed to occur spontaneously, and has been induced by some metal salts and chemicals. Furthermore, a heterochromatic region of the long arm of the Chinese hamster ovary (CHO) X-chromosome is known to be susceptible to a disproportionately high frequency of spontaneous breakage; unless there is physical displacement of chromatin the resulting achromatic lesions are not scored as structural aberrations. We have encountered such anomalous breakage associated with C-band positive regions of the chromosomes of a CHO-K1 cell line following exposure of the cells to toxic doses of U-68,553B and in this report present evidence that the apparent breaks are due to undercondensed heterochromatin (UH) and evidence that the phenomenon appears to occur at higher frequency in a particular cell line of Chinese hamster. This finding has important implications on the assessment of potential risk due to exposure to the drug. Such apparent breaks at sites of UH in chromosome 1 was not observed in an alternate CHO cell line (CHO-WBL) which supports the notion that the UH associated achromatic lesions in the CHO-K1 line may be a cell line specific phenomenon. Furthermore, careful electron microscopy of the chromosomes revealed chromatin fibers connecting the apparently broken chromosomes. The UH was not observed in the presence of added metabolic activation (S9), and thus the significance of the phenomenon in risk assessment is further reduced. The data presented here provide evidence that sites of UH occur preferentially at locations of C-band positive constitutive heterochromatin in CHO cells; we believe that this is the first report of induced fragile sites in rodent cells in vitro documented in this way. In addition, evidence is presented that U-68,553B lacks the ability to induce breakage in vivo in rodents and lacks the ability to induce chromosome breakage in human peripheral lymphocytes in vitro. Therefore, it is concluded that the positive results with CHO-K1 cells treated with U-68,553B are unlikely to be predictive of a genotoxic hazard. This is a specific example of the importance of careful followup to an in vitro result in risk assessment.

Animals↗
PubMed1983

The detection of viable heritable translocations by chromosome banding procedures.

Ethyl methanesulfonate was tested for its ability to induce viable heritable translocations in progeny of male rats given a single IP injection prior to breeding. Reproductively competent Wistar rats were used as the test animals. Males were treated with either 75 or 150 mg/kg EMS or vehicle control. Neonates were used for primary tissue culture; the fibroblasts were harvested for cytogenetic analysis of chromosomes banded by Giemsa banding procedures. Since the cells examined were somatic cells, it was necessary to karyotype only two to three per neonate to ascertain inherited translocations. A reduction in fertility was observed in males treated with EMS. A statistically significant (p less than 0.05) dose-related increase in heritable translocations was observed in the F1 generation of treated animals.

Animals↗