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H Shimada

Publications and source records attributed to H Shimada.

At least 145 records · Page 8Linked to original sources
PubMed2000

The effects of sulfhydryl blockers and metal ions on nickel accumulation by rat primary hepatocyte cultures.

Previously, we found that nickel (Ni) accumulation by rat hepatocytes involves Ca channel transport processes. However, other mechanisms responsible for Ni accumulation are still unclear. Therefore, in the present study we examined the effects of sulfhydryl (SH) blockers on Ni accumulation by hepatocytes. Hepatocytes were exposed to various concentrations of N-ethylmaleimide (NEM) (0.5, 1 or 2 mM) or monoiodoacetic acid (MIA) (0.1, 0.25 or 0.5 mM), potent blockers of SH ligands, for 30 min and subsequently exposed to 10 microM NiCl(2) for an additional 60 min. Pretreatment with NEM and MIA enhanced the Ni accumulation by hepatocytes to maximum of 156 and 73%, respectively. The effects of essential and nonessential metal ions on Ni accumulation were also investigated. Pretreatment with 10 microM of Cu, Zn, Co, Cd and Mn, decreased Ni accumulation by 46, 30, 20, 18 and 11%, respectively. In contrast, pretreatment with Hg (10 and 20 microM) enhanced the Ni accumulation by almost 81 and 140%, respectively. Furthermore, significant decrease in SH concentration in the hepatocyte membrane was observed by the treatment with NEM, MIA and Hg, but not with Cu, Zn and Cd. These results suggest that Ni accumulation by hepatocytes does not appear to be dependent on the SH carrier-mediated transport processes, and that to block the SH ligands in the plasma membrane may facilitate the Ni crossing of the cell membrane.

Animals↗
PubMed2000

Chloroplast development in Arabidopsis thaliana requires the nuclear-encoded transcription factor sigma B.

Development of plastids into chloroplasts, the organelles of photosynthesis, is triggered by light. However, little is known of the factors involved in the complex coordination of light-induced plastid gene expression, which must be directed by both nuclear and plastid genomes. We have isolated an Arabidopsis mutant, abc1, with impaired chloroplast development, which results in a pale green leaf phenotype. The mutated nuclear gene encodes a sigma factor, SigB, presumably for the eubacterial-like plastid RNA polymerase. Our results provide direct evidence that a nuclear-derived prokaryotic-like SigB protein, plays a critical role in the coordination of the two genomes for chloroplast development.

Arabidopsis↗
PubMed2000

Formation of compound I in the reaction of native myoglobins with hydrogen peroxide.

Reaction of ferric native myoglobin (Mb) with hydrogen peroxide (H(2)O(2)) was studied by the aid of stopped-flow rapid-scan spectrophotometry. In contrast to the results in previous studies where compound I was reported to be undetectable, both sperm whale and horse heart metmyoglobins (metMbs) formed a significant quantity of compound I, an oxoferryl porphyrin pi-cation radical (Por(+)-Fe(IV)(O)), during their reactions with H(2)O(2). With both kinds of Mbs, formation of compound I was more clearly observed in D(2)O than in H(2)O. The compound thus formed was capable of performing monooxygenation of thioanisole to methyl phenyl sulfoxide and a 2-electron oxidation of H(2)O(2) giving O(2) and H(2)O as products. It was also converted into ferryl myoglobin (Por-Fe(IV)(O)-globin(+)) spontaneously. Rate constants for these reactions and that for a direct conversion of metMb to ferryl Mb through the homolysis of H(2)O(2) were determined. These results established unambiguously that native metMb can form both compound I and ferryl Mb upon reaction with H(2)O(2) and that these high valent iron compounds serve as essential intermediates in Mb-assisted peroxidative reactions. The observed deuterium effect on the apparent stability of compound I was attributable to that effect on the hydrogen abstraction step in the 2-electron oxidation of H(2)O(2) by compound I.

Animals↗
PubMed2000

Correlation of Indocyanine Green Angiography Findings and Expression of Vascular Endothelial Growth Factor in Surgically Excised Age-related Macular Degeneration-related Choroidal Neovascular Membranes.

Purpose: We investigated the relationship between clinical classification by indocyanine green angiography (IA) and pathologic findings including the expression of vascular endothelial growth factor (VEGF) in age-related macular degeneration-related choroidal neovascular membranes.Subject and Methods: The subjects were 15 patients with age-related macular degeneration who underwent surgical excision for choroidal neovascular membrane. The patients were classified into 4 types: Type I, hyperfluorescence in both early and late phases (n = 7); Type II, hyperfluorescence in the early phase only (n = 2); Type III, hyperfluorescence in the late phase only (n = 3); and Type IV, no hyperfluorescence in any phase (n = 3). The excised choroidal neovascular membranes were fixed and stained by hematoxylin-eosin and azan. They were also examined by immunohistochemical staining for VEGF.Results: VEGF was expressed markedly in vascular endothelial cells and fibroblast-like cells of interstitial tissue of Types I, II and III. Its expression was weak in Type IV.Conclusion: Clinical classification by IA for age-related macular degeneration is consistent with the pathologic findings including the expression of VEGF.

Journal Article↗
PubMed2000

Acetaldehyde production by non-pathogenic Neisseria in human oral microflora: implications for carcinogenesis in upper aerodigestive tract.

Many epidemiological studies have identified chronic alcohol consumption as a significant risk factor for cancer of the upper aerodigestive tract (UAT) in human. Although acetaldehyde, the first metabolite from ethanol by alcohol dehydrogenase (ADH), is regarded as a carcinogen, how systemic production of acetaldehyde particularly affects the UAT remains unclear. In our study, we searched for the regional source of acetaldehyde in UAT, especially the involvement of bacteria in the human normal oral microflora. Here we demonstrate that, among the bacterial species identified from the human oral cavity, genus Neisseria had extremely high ADH activity and produced significant amounts of acetaldehyde when cultured with medium containing ethanol in vitro. The ability to produce acetaldehyde was more than 100-fold higher than that produced by any other genera we studied. Furthermore, alcohol ingestion influences the bacterial composition of the oral microflora, resulting in an increased proportion of Neisseria. Although Neisseria present in normal oral microflora is generally non-pathogenic, these findings suggest that this microbe can be a regional source of carcinogenic acetaldehyde and thus potentially play an important role in alcohol-related carcinogenesis in human UAT.

Acetaldehyde↗
PubMed2000

Serum p53 antibody is a useful tumor marker in superficial esophageal squamous cell carcinoma.

BACKGROUND: Patients with superficial (mucosal or submucosal) esophageal carcinoma (SEC) have significantly better survival rates than patients with advanced carcinoma. Some patients with advanced esophageal carcinoma have been reported to test positive for serum p53 antibodies (Abs). Because very few patients with superficial carcinoma have been examined, the aim of this study was to evaluate the clinical significance of serum p53-Abs in patients with superficial esophageal squamous cell carcinoma (SESCC). METHODS: Thirty-five consecutive patients with SESCC were studied for serum p53-Abs by enzyme-linked immunoabsorbent assay before and after treatment. The clinicopathologic features of p53 seropositive and p53 negative patients were compared. The relation between the presence of serum p53-Abs and p53 immunoreactivity of the resected specimens was examined. Three tumor markers (squamous cell carcinoma antigen [SCC-Ag], CYFRA21-1, and carcinoembryonic antigen [CEA]) were assessed to compare their sensitivities with serum p53-Abs. RESULTS: Fourteen of 35 patients (40%) were p53 seropositive. Relatively few patients tested positive for the other tumor markers: CEA, 11.4%; SCC-Ag, 14.3%; CYFRA21-1, 5.7%. There were no significant correlations between clinicopathologic features and p53 seropositivity except for tumor location. A strong correlation between p53 immunostaining and the presence of serum p53-Abs was observed (P = 0.003). Of the 14 patients with seropositive results, 12 turned seronegative after resection, and the other 2 experienced disease recurrence. CONCLUSIONS: Surveillance of serum p53-Abs is superior to the three tumor markers for detecting SESCC. This serum marker is also useful for the detection of p53 protein overexpression and for the monitoring of residual tumor cells.

Aged↗
PubMed2000

Current mirror effect and correlated cooper-pair transport in coupled arrays of small Josephson junctions.

We have measured the transport properties of capacitively coupled one-dimensional arrays of small aluminum Josephson junctions. Under suitable biasing conditions, the samples act as current mirrors; the currents in the two arrays couple to each other and become equally large. The coupling is found both for currents flowing in the same direction and in opposite directions. We have also measured the time dependent fluctuations of the currents in the two arrays, and we find a strong correlation or anticorrelation of the fluctuations depending on the relative direction of the two currents.

Journal Article↗
PubMed2000

Relation between vascular morphologic changes during stent implantation and the magnitude of in-stent neointimal hyperplasia.

Intimal hyperplasia usually occurs after balloon overstretch injury or wire coil stimuli to coronary arteries. We examined whether the degree of vessel wall stretch during coronary stent placement could predict the amount of in-stent neointimal hyperplasia after a 6-month follow-up. Serial (preintervention, postballooning, poststent implantation, and a follow-up after 6 months) intravascular ultrasound (IVUS) was used to study 457 consecutive cross-sectional areas in 28 patients. IVUS imaging, using a motorized pullback system at 0.5 mm/s, allowed 1-mm axial increment measurements of the total vascular, stent, and lumen cross-sectional areas. The mean total vascular area changed from 10.89 +/- 2.50 mm2 before to 11.27 +/- 2.49 mm2 after ballooning, to 12.80 +/- 2.59 mm2 after stenting, and to 12.58 +/- 2.41 mm2 at follow-up (p < 0.0001). The mean lumen area changed from 3.36 +/- 1.95 mm2 before to 4.21 +/- 1.65 mm2 after ballooning, to 5.16 +/- 1.09 mm2 after stenting, and to 3.57 +/- 1.23 mm2 at follow-up (p < 0.0001). The mean stent area decreased from 5.25 +/- 1.17 mm2 after stenting to 5.09 +/- 0.90 mm2 at follow-up (p < 0.0001). Stepwise logistic regression analysis showed that delta total vascular area (after stent implantation - before intervention) was a strong predictor of the amount of intimal hyperplasia (r = 0.57, p < 0.0001). Vascular overstretch caused by the stenting procedure promotes intimal hyperplasia in proportion to the degree of sectional vascular stretch.

Aged↗
PubMed2000

A Case of Proliferative Sarcoid Retinopathy with Sarcoid Nodules in Tissue Obtained During Vitrectomy.

Background: In previous studies, intraocular proliferative tissues obtained from proliferative sarcoid retinopathy cases during vitrectomy have been examined histopathologically. However, there is no report of identification of sarcoid nodules in examined tissues. We performed vitrectomy for a case of proliferative sarcoid retinopathy with extensive proliferative changes. Histopathologically, sarcoid nodules were identified in the fibrovascular membranes.Case: A 25-year-old man was treated for sarcoid uveitis in the right eye by his local ophthalmologist. Lens aspiration was performed for complicated cataract. He was referred to our hospital with vitreous opacity and traction retinal detachment which occurred after the surgery.Findings: The vitreous opacity was so severe that details of the fundus were not visible. Traction retinal detachment was suspected from findings of B-mode echography. Vitrectomy was performed, and total retinal detachment due to contraction of the fibrovascular membrane around the optic disc and posterior pole was observed. Sarcoid nodules were identified histopathologically in fibrovascular membranes obtained during vitrectomy.Conclusion: In proliferative sarcoid retinopathy cases, sarcoid lesions may be one of the causes of fibrovascular membrane formation.

Journal Article↗
PubMed2000

Histopathology defines prognostic subsets of ganglioneuroblastoma, nodular.

BACKGROUND: Ganglioneuroblastoma, nodular (GNBn) is a rare subtype of the family of neuroblastic tumors (neuroblastoma, ganglioneuroblastoma, and ganglioneuroma) that are classified in the unfavorable histology group according to the International Neuroblastoma Pathology Classification (Shimada system). Tumors of this subtype have been considered to represent a prototypic example of biologically and clinically nonaggressive (Schwannian stroma-rich and stroma-dominant) components combined with biologically and clinically aggressive nodular (Schwannian stroma-poor) components. However, detailed histopathologic analysis as well as thorough prognostic evaluation of patients with this subtype has not been reported. METHODS: Pathology slides and reports from a total of 70 GNBn patients from the Children's Cancer Group (CCG)-3881 and CCG-3891 studies were reviewed. Sixty-eight tumors were classified in the favorable subset (FS) or the unfavorable subset (US) based on the evaluation of nodular components by applying the same histopathologic criteria (patient age, grade of neuroblastic differentiation, mitosis-karyorrhexis index) that are used for neuroblastomas in the International Neuroblastoma Pathology Classification. Patient prognosis as well as clinical and biologic characteristics within the subsets were analyzed, and the results were compared with those from 654 non-GNBn patients who were enrolled in the same CCG studies during the same period. RESULTS: Patients with GNBn tumors, usually diagnosed at age > 1 year, had a significantly lower overall 5-year event free survival (EFS) rate than patients with non-GNBn subtypes (44.7% EFS vs. 65.0% EFS; P = 0. 0073). A significant difference in the outcome of the patients between the FS (22 patients; 86.1% EFS; 95.0% survival rate) and the US (46 patients; 29.0% EFS; 40.7% survival rate) of the GNBn subtype (P < 0.0005) was shown. When the cohort of patients with GNBn tumors was subdivided into FS and US, the outcomes were similar to those of patients with tumors of favorable histology (397 patients; 90.5% EFS; 97.6% survival rate) and with tumors of unfavorable histology (257 patients; 27.0% EFS; 35.7% survival rate) of the non-GNBn type. The patients with US tumors frequently (63.0%) presented with distant metastasis. CONCLUSIONS: The current study demonstrates that the nodular components in GNBn tumors are not always aggressive. The prognosis of these patients can be determined by the analysis of age-linked histopathologic features.

Age Factors↗
PubMed2000

Analysis of genes under the downstream control of the t(8;21) fusion protein AML1-MTG8: overexpression of the TIS11b (ERF-1, cMG1) gene induces myeloid cell proliferation in response to G-CSF.

The AML1-MTG8 fusion transcription factor generated by t(8;21) translocation is thought to dysregulate genes that are crucial for normal differentiation and proliferation of hematopoietic progenitors to cause acute myelogenous leukemia (AML). Although AML1-MTG8 has been shown to repress the transcription of AML1 targets, none of the known targets of AML1 are probably responsible for AML1-MTG8-mediated leukemogenesis. In this study, 24 genes under the downstream control of AML1-MTG8 were isolated by using a differential display technique. Analysis with deletion mutants of AML1-MTG8 demonstrated that the regulation of the majority of these genes requires the region of 51 residues (488-538) containing the Nervy homology region 2 (NHR2), through which AML1-MTG8 interacts with MTGR1. Among the 24 genes identified, 10 were considered to be genes under the control of AML1, because their expression was altered by AML1b or AML1a or both. However, the other 14 genes were not affected by either AML1b or AML1a, suggesting the possibility that AML1-MTG8 regulates a number of specific target genes that are not normally regulated by AML1. Furthermore, an up-regulated gene, TIS11b (ERF-1, cMG1), was highly expressed in t(8;21) leukemic cells, and the overexpression of TIS11b induced myeloid cell proliferation in response to granulocyte colony-stimulating factor. These results suggest that the high-level expression of TIS11b contributes to AML1-MTG8-mediated leukemogenesis. (Blood. 2000;96:655-663)

Animals↗
PubMed2000

Identification and light-induced expression of a novel gene of NADPH-protochlorophyllide oxidoreductase isoform in Arabidopsis thaliana.

In Arabidopsis thaliana, we identified a novel gene of a NADPH-protochlorophyllide oxidoreductase (POR) isoform, which catalyzes the light-dependent protochlorophyllide a reduction in the chlorophyll (Chl) biosynthetic pathway. The deduced amino acid sequence of the novel POR isoform (PORC) showed significant identities ( approximately 75%) with the previously isolated two POR isoforms of A. thaliana. Contrasting with these POR isoforms, the PORC transcript increased in etiolated seedlings by illumination, and was dominantly expressed in immature and mature tissues. The present results demonstrated that Chl biosynthesis and chloroplast biogenesis in A. thaliana are controlled by three POR isoforms, which are differentially controlled by light and development.

Amino Acid Sequence↗
PubMed2000

Methioninase gene therapy of human cancer cells is synergistic with recombinant methioninase treatment.

Results obtained over the past 40 years have demonstrated that tumor cells of all types tested have an elevated growth requirement for methioninase compared with normal cells. Recombinant methioninase (rMETase) cloned from Pseudomonas putida has been found previously to be an effective antitumor agent attributable to deprivation of the extracellular methionine source of the tumor. To degrade intracellular methioninase, we have now developed an adenoviral vector inserted with the P. putida methioninase (MET) gene (rAd-MET). The in vitro efficacy of rAd-MET was tested on the OVCAR-8 human ovarian cancer cell line, the HT1080 human fibrosarcoma cell line, and human normal fibroblasts. rAd-MET transduction of OVACAR-8 and HT1080 resulted in high levels of methioninase expression up to 10% or more of the total protein of the cells, depending on the multiplicity of infection. The IC50 of rAd-MET for OVCAR-8 cells in 96-well plates was approximately 2 x 106 plaque-forming units (pfu)/well. The IC50 of control adenovirus (control-rAd) was 4 x 10(7) pfu/well, 20 times higher than rAd-MET. In the presence of the IC50 of 2 x 10(6) pfu/well of rAd-MET, the addition of 0.025 units/ml of rMETase, which is 25% of the IC50, resulted in a 90% inhibition of tumor cell number. This indicated that rAd-MET enhanced the efficacy of rMETase. In contrast, 2 x 10(6) pfu/well of control-rAd in combination with 0.025 units/ml of rMETase had an efficacy of only 10% inhibition of cell number. The synergistic effect of the combination of rMETase and rAd-MET was quantitated by calculating the combination index (CI). The CIs for all combinations of rAd-MET and rMETase tested on OVCAR-8 were <0.7 with a mean of 0.5, indicating synergy. Similar synergy of rAd-MET and rMETase was seen on HT1080 human fibrosarcoma cells with a mean of 0.74. In contrast, the CIs of all combinations of rMETase and control adenovirus concentrations tested on both cell lines had a mean CI of approximately 1, which indicated that this combination had only an additive effect. The normal fibroblasts, on the other hand, appeared relatively resistant to the MET gene because in the presence of rMETase, 2.5 x 10(7) pfu/well of rAd-MET or control rAd had almost an identical effect on cell survival. The selectively strong synergy of rAd-MET and rMETase on cancer cells allows reduced levels of each agent to be used, thus decreasing potential side effects.

Carbon-Sulfur Lyases↗
PubMed2000

An isozyme of the NADP-malic enzyme of a CAM plant, Aloe arborescens, with variation on conservative amino acid residues.

In Aloe arborescens, an obligate CAM plant, Western analysis detected three major isoforms of NADP-malic enzyme (NADP-ME), 72kDa with a pI of 6.0, 65kDa with a pI of 5.6 and 65kDa with a pI of 5.5. Among them, the 65kDa protein with a pI of 5.5 was leaf-specific, and the 65kDa protein with a pI of 5.6 was found only in roots, whereas the 72kDa protein was uniformly detected in both organs. Activity staining indicated enzyme activity of both 65kDa NADP-MEs but little activity of the 72kDa protein. A cDNA clone encoding a leaf-abundant NADP-ME, AME1, was isolated. Deduced amino acid sequence of AME1 showed a high degree of homology to known NADP-MEs, but it was also found that AME1 contained substitutions on five conservative amino acid residues, some of which have been predicted to be important for their enzyme activity. Transgenic rice carrying the aloe AME1 gene efficiently produced an additional 65kDa protein with a pI of 5.5 as an active NADP-ME. These results indicate that AME1 corresponds to the leaf-specific 65kDa NADP-ME, which may be involved in CAM photosynthesis. It was also shown that substitutions of these conservative amino acid residues identified in AME1 still allowed it to give enzyme activity.

Aloe↗
PubMed2000

Whole-body optical imaging of green fluorescent protein-expressing tumors and metastases.

We have imaged, in real time, fluorescent tumors growing and metastasizing in live mice. The whole-body optical imaging system is external and noninvasive. It affords unprecedented continuous visual monitoring of malignant growth and spread within intact animals. We have established new human and rodent tumors that stably express very high levels of the Aequorea victoria green fluorescent protein (GFP) and transplanted these to appropriate animals. B16F0-GFP mouse melanoma cells were injected into the tail vein or portal vein of 6-week-old C57BL/6 and nude mice. Whole-body optical images showed metastatic lesions in the brain, liver, and bone of B16F0-GFP that were used for real time, quantitative measurement of tumor growth in each of these organs. The AC3488-GFP human colon cancer was surgically implanted orthotopically into nude mice. Whole-body optical images showed, in real time, growth of the primary colon tumor and its metastatic lesions in the liver and skeleton. Imaging was with either a trans-illuminated epifluorescence microscope or a fluorescence light box and thermoelectrically cooled color charge-coupled device camera. The depth to which metastasis and micrometastasis could be imaged depended on their size. A 60-microm diameter tumor was detectable at a depth of 0.5 mm whereas a 1, 800-microm tumor could be visualized at 2.2-mm depth. The simple, noninvasive, and highly selective imaging of growing tumors, made possible by strong GFP fluorescence, enables the detailed imaging of tumor growth and metastasis formation. This should facilitate studies of modulators of cancer growth including inhibition by potential chemotherapeutic agents.

Adenocarcinoma↗
PubMed2000

Integrins alpha(v)beta3 and alpha(v)beta5 are expressed by endothelium of high-risk neuroblastoma and their inhibition is associated with increased endogenous ceramide.

Inhibition of the RGD-binding integrins, alpha(v)beta3 and alpha(v)beta5, prevents endothelial cell anchorage and induces endothelial apoptosis, which results in disruption of tumor angiogenesis and inhibition of tumor growth in animal models. In this study, we demonstrate by immunohistochemical analysis that integrin alpha(v)beta3 was expressed by 61% (mean) of microvessels in high-risk neuroblastomas (stage IV and MYCN-amplified stage III; n = 28) but only by 18% (mean) of microvessels in low-risk tumors (stages I and II and non-MYCN-amplified stage III; n = 12). Integrin alpha(v)beta5 was found on 60% (mean) of microvessels in 21 Stage IV tumors. These data suggest that neuroblastomas may be targeted for antiangiogenic treatment directed against endothelial integrins alpha(v)beta3 and alpha(v)beta5. In cell culture, inhibition of integrin-dependent endothelial cell anchorage to vitronectin by RGDfV, an RGD function-blocking cyclic peptide, induced apoptosis in bovine brain endothelial cells compared with the control peptide, RADfV (37.5% versus 8.7%, respectively), as detected by chromatin condensation and nuclear fragmentation. Treatment with RGDfV but not with RADfV, which prevented attachment of endothelial cells to vitronectin or fibronectin, was associated with up to a 50% increase in endogenous ceramide, a lipid second messenger that can mediate cell death. Furthermore, exogenous C2-ceramide was cytotoxic to bovine brain endothelial cells and induced activation of C-jun N-terminal kinase (JNK), a MAP kinase that can be activated in stress-induced apoptosis pathways. This suggests that ceramide may function in detachment-induced endothelial cell apoptosis, originating from inhibition of vitronectin binding to integrins such as alpha(v)beta3 and alpha(v)beta5. This is the first report to demonstrate expression of integrins alpha(v)beta3 and alpha(v)beta5 by microvascular endothelium of a childhood tumor and association of their expression with neuroblastoma aggressiveness. Furthermore, our data provide the first suggestion that inhibition of endothelial cell anchorage, resulting from specific blockade of RGD-binding integrins, increases endogenous ceramide, which may contribute to endothelial cell death.

Angiogenesis Inhibitors↗
PubMed2000

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.

Animals↗