Richard H.C. San

d-Methylphenidate is non-genotoxic in in vitro and in vivo assays

D-Methylphenidate (dexmethylphenidate; D-MPH) and its racemate D,L-methylphenidate (D,L-MPH) are currently prescribed for the chronic treatment of attention deficit hyperactivity disorder (ADHD) in children. Studies have shown that D-MPH is the pharmacologically active enantiomer for ADHD and is therefore the preferred drug for the treatment of ADHD symptoms. Although studies on the mutagenicity of D,L-MPH have been conducted, similar data for D-MPH are lacking. Therefore, D-MPH was evaluated in the bacterial reverse mutation and mouse lymphoma assays with and without S9 and in a bone marrow micronucleus test in male and female CD-1 mice. As a comparison, the L-enantiomer and racemate were also included in the assessments. While MPH-associated toxicity was observed in the mammalian tests, none of the three compounds tested induced mutagenic or clastogenic effects. Our present results along with published epidemiological data from patient populations are consistent with the conclusion that D-MPH and D,L-MPH do not present a carcinogenic risk to humans.

Mouse Lymphoma thymidine kinase locus gene mutation assay : International Workshop on Genotoxicity Test Procedures Workgroup Report

The Mouse Lymphoma Assay (MLA) Workgroup addressed and reached consensus on a number of issues. Discussion focused on five areas: (1) acceptable assay versions; (2) cytotoxicity measure; (3) 24‐hr treatment; (4) microwell colony counting and sizing; and (5) data acceptability/statistical analysis. Although the International Conference on Harmonisation (ICH) indicated a preference for the microwell over the soft agar method, all of the workgroup members agreed that both versions of the MLA are equally acceptable. The workgroup agreed that it is desirable for both assay versions to use the same measure of cytotoxicity to define the acceptable and required concentration range. Currently, laboratories using the microwell version use the relative survival (RS) determined by cloning immediately after the treatment. Laboratories using the soft agar method do not obtain an RS but use the relative total growth (RTG), a combination of the relative suspension growth (RSG) during the expression period and the relative cloning efficiency determined at the time of mutant selection. The workgroup agreed to investigate the RSG, the RS, and the RTG and to develop further guidance. In the interim, the workgroup reached consensus that the RTG be used as the standard measure of cytotoxicity. The ICH recommended a 24‐hr treatment in the absence of S9 when negative results are obtained with short (3–4 hr) treatments. The workgroup agreed to retain this requirement but acknowledged that more data are needed prior to making final recommendations concerning the need for and the specific protocol for the 24‐hr treatment. Environ. Mol. Mutagen. 35:185–190, 2000 Published 2000 Wiley‐Liss, Inc.

Genotoxicity of iron compounds in Salmonella typhimurium and L5178Y mouse lymphoma cells.

The mutagenic activity of elemental and salt forms of iron (Fe), including compounds currently being used in dietary supplements and for food fortification, were evaluated for mutagenicity in Salmonella typhimurium and L5178Y mouse lymphoma cells. Except for the weak response obtained with ferrous fumarate, none of the compounds induced a mutagenic response in Salmonella. In the mouse lymphoma assay, responses were related to the Fe compound and/or reduction of ferric (Fe+3) to ferrous (Fe+2). Responses with the elemental forms of Fe were divergent. Electrolytic Fe with a relatively larger particle size and irregular shape was negative. The smaller‐sized carbonyl Fe, which after 4 hr attached to and was taken up by the cells, induced mutagenic responses both with and without S9. With ferric chloride (FeCl3) and ferric phosphate (FePO4), there was an increase in mutant frequency only with S9. With the Fe+2 compounds, ferrous sulfate (FeSO4) and ferrous fumarate (FeC4H2O4), positive responses were observed without S9. The Fe chelate, sodium Fe(III)EDTA was positive in both the presence and absence of S9. The lowest effective doses (LED) for induction of mutagenicity were identified for these compounds and an LED ratio calculated. The LED ratio ranges from 1 for FeSO4 to 30 for carbonyl Fe, which are similar to oral LD50 values obtained in animal studies. Environ. Mol. Mutagen. 33:28–41, 1999

Re-evaluation of the mutagenic potential of quinacrine dihydrochloride dihydrate.

Quinacrine has been used for voluntary female non-surgical sterilization for its ability to produce tubal occlusion. Safety issues regarding quinacrine have been raised because it has been shown to intercalate with DNA. Therefore, safety issues need to be resolved by appropriate toxicology studies to support a review for human transcervical use. Such toxicology studies include mutagenicity assays. Here we report an evaluation of the genotoxicity of quinacrine dihydrochloride dihydrate (QH) using a battery of assays. In the bacterial mutagenicity assay, QH was strongly positive in Salmonella typhimurium tester strain TA1537 with and without S9-activation and in S. typhimurium tester strain TA98 with S9-activation; QH was also strongly positive in Escherichia coli WP2 uvrA without S9-activation. QH was not mutagenic in S. typhimurium tester strains TA100 and TA1535 with and without S9-activation. QH was mutagenic in the mouse lymphoma assay in the absence of S9-activation. QH was clastogenic in Chinese hamster ovary (CHO) cells, with and without S9-activation. QH was negative for polyploidy in the same chromosome aberration test. Using a triple intraperitoneal injection treatment protocol in both male and female mice, QH was negative in the in vivo mouse micronucleated erythrocyte (micronucleus) assay. These results confirm that QH is mutagenic and clastogenic in vitro and suggest a potential risk to human health due to QH exposure after intrauterine exposure.

Evaluation of the butter flavoring chemical diacetyl and a fluorochemical paper additive for mutagenicity and toxicity using the mammalian cell gene mutation assay in L5178Y mouse lymphoma cells

Diacetyl (2,3-butanedione) is a yellowish liquid that is usually mixed with other ingredients to produce butter flavor or other flavors in a variety of food products. Inhalation of butter flavoring vapors was first associated with clinical bronchiolitis obliterans among workers in microwave popcorn production. Recent findings have shown irreversible obstructive lung disease among workers not only in the microwave popcorn industry, but also in flavoring manufacture, and in chemical synthesis of diacetyl, a predominant chemical for butter flavoring. It has been reported that perfluorochemicals utilized in food packaging are migrating into foods and may be sources of oral exposure. Relatively small quantities of perfluorochemicals are used in the manufacturing of paper or paperboard that is in direct contact with food to repel oil or grease and water. Because of recent concerns about perfluorochemicals such as those found on microwave popcorn bags (e.g. Lodyne P208E) and diacetyl in foods, we evaluated both compounds for mutagenicity using the mammalian cell gene mutation assay in L5178Y mouse lymphoma cells. Lodyne P208E was less toxic than diacetyl and did not induce a mutagenic response. Diacetyl induced a highly mutagenic response in the L5178Y mouse lymphoma mutation assay in the presence of human liver S9 for activation. The increase in the frequency of small colonies in the assay with diacetyl indicates that diacetyl causes damage to multiple loci on chromosome 11 in addition to functional loss of the thymidine kinase locus.

Evaluation of potential genotoxicity of pulsed electric and electromagnetic fields used for bone growth stimulation

Medical devices emitting pulsed electric and electromagnetic fields have been found to be effective for a number of clinical applications including stimulation of bone and tissue growth. To determine whether pulsed fields of the type used in these clinical applications present a mutagenic hazard, electric and electromagnetic fields at two exposure levels were tested in the Ames test, CHO cell chromosomal aberration assay, BALB/3T3 cell transformation assay and unscheduled DNA synthesis assay in primary rat hepatocytes. For both field types, initial and independent repeat studies were performed for each assay at both clinical and supra clinical doses. In all assays, the results show a lack of cytotoxic, transforming and mutagenic activity. The data suggest that pulsed electric and electromagnetic fields of the type and dose levels used in bone growth stimulation lack mutagenic and transforming activity.

Syrian hamster embryo (SHE) cell transformation assay with conditioned media (without X-ray irradiated feeder layer) using 2,4-diaminotoluene, 2,6-diaminotoluene and chloral hydrate

The Syrian hamster embryo (SHE) cell transformation assay has traditionally been conducted with a feeder layer of X-ray irradiated cells to provide growth support to the target cells seeded in low numbers. The feeder layer of cells consists of X-ray irradiated cells which are still viable but unable to replicate. We have tried seeding the target cells in conditioned media prepared from the stock culture flasks in lieu of plating them on a feeder layer. Three SHE cell isolates were tested to investigate the feasibility of this approach. With freshly prepared conditioned medium (LeBoeufs Dulbeccos Modified Eagles Medium with 2 mM L-glutamine and 20% fetal bovine serum), used within 2 weeks of preparation, there was essentially no difference in the number of target cell colonies in the conditioned medium and in the plates with the X-ray irradiated feeder cell layer. The plating efficiencies of the vehicle controls were within the historical range for the standard SHE cell transformation assay. In each experiment, the positive control benzo(a)pyrene [B(a)P] elicited a significant increase in morphological transformation frequency (MTF), with or without feeder cells. Three compounds, 2,4-diaminotoluene (2,4-DAT), 2,6-diaminotoluene (2,6-DAT), and chloral hydrate were tested in the SHE cell transformation assay without an X-ray irradiated feeder layer and using a 7-day exposure regimen. The results were comparable to those reported in the published literature using the standard methodology with feeder cells, with 2,4-DAT and chloral hydrate eliciting a significant increase in MTF, and 2,6-DAT not eliciting any increase in MTF. The results of this study demonstrate the feasibility of conducting the SHE cell transformation assay without the use of an X-ray irradiated feeder layer, thereby simplifying the test procedure and facilitating the scoring of morphologically transformed colonies.

Syrian Hamster Embryo (SHE) cell transformation assay with and without X-ray irradiation of feeder cells using Di(2-ethylhexyl)phthalate (DEHP) and N-nitroso-N-methylnitroguanidine (MNNG).

The SHE cell transformation assay has traditionally been conducted with a feeder layer of X-ray irradiated cells to provide growth support to the target cells seeded in low numbers. The need for an X-ray irradiated feeder cell layer necessitates the maintenance of an X-ray machine and the additional step to seed feeder cells prior to plating target cells. This laboratory has previously reported a method allowing target cells to be seeded in conditioned media prepared from the stock culture flasks in lieu of plating them on a feeder layer (Pant et al. [1,2,4]). In order to expand the data base for chemicals tested using this method, we describe in this paper the results obtained testing Di(2-ethylhexyl)phthalate (DEHP) and N-nitroso-N-methylnitroguanidine (MNNG) which are known to give positive responses in the standard SHE cell transformation assay. With freshly prepared conditioned medium (used within 2 weeks of preparation), there was essentially no difference in the number of target cell colonies in the conditioned medium and in the plates with the X-ray irradiated feeder cell layer. The plating efficiencies of the vehicle controls were within the historical range for the standard SHE cell transformation assay. In more than ten experiments the positive control benzo(a)pyrene [B(a)P] elicited a significant increase in morphological transformation frequency (MTF), with or without X-ray irradiated feeder cells. Compounds, DEHP and MNNG, were tested in the SHE cell transformation assay with and without an X-ray irradiated feeder layer and using a 7-day exposure regimen. The results were comparable between experiments performed using either method. These results demonstrate the feasibility of conducting the SHE cell transformation assay without the use of an X-ray irradiated feeder layer, thereby simplifying the test procedure and assisting the scoring of morphologically transformed colonies.

Genetic toxicology assessment of HI-6 dichloride.

The oxime HI‐6 dichloride [1‐(2 hydroxyiminomethyl‐1‐pyridino)‐3‐(4‐carbamoyl‐1‐pyridino)‐2‐oxapropane dichloride monohydrate] has shown to be a potent reactivator of cholinesterase activity and may have efficacy for the treatment of organo‐phosphate intoxication [SIPRI, 1976; Schenk et al.; Arch Toxicol 36:71–81, 1976]. As part of a preclinical safety assessment program, the genetic toxicology of HI‐6 dichloride was evaluated in a series of assays designed to measure induction of gene mutations and chromosomal aberrations. HI‐6 dichloride gave negative responses in the Salmonella mutagenicity assay and in the CHO/HGPRT gene mutation assay. Dose‐dependent increases in the frequency of chromosomal aberrations were noted when HI‐6 dichloride was tested in cultured CHO cells and in cultured human peripheral blood lymphocytes. The mouse lymphoma gene mutation assay, reputed to measure both gene mutations and chromosomal deletions, was negative in the absence of metabolic activation. Depending on the criteria employed, a negative or equivocal response was seen in the presence of rat liver‐derived S‐9 mix. An in vivo rat bone marrow metaphase assay performed to further investigate the in vitro clastogenic responses was negative. The results from these studies indicate that HI‐6 dichloride does not induce gene mutations in vitro; however, it is clastogenic in vitro but does not appear to be clastogenic in vivo.