Assessment of the In Vivo Mutagenic Potential of Methyl Tertiary‐butyl Ether

Abstract

Methyl tertiary‐butyl ether (MTBE) is one of the highest production volume chemicals in the USA. Previous results from in vitro genetic toxicity studies suggested that it was not mutagenic. However, chronic exposure at high levels resulted in liver tumors in female mice and kidney tumors in male rats. The current program assessed in vivo genotoxicity and also explored the possibility that a mutagenic mechanism was involved in the carcinogenic process. The specific tests used included the Drosophila sex‐linked‐recessive‐lethal test, the rat bone marrow cytogenetics test, the mouse bone marrow micronucleus test and the in vivo–in vitro hepatocyte unscheduled DNA synthesis test in the mouse. All tests produced negative results, indicating that the potential for in vivo mutagenic activity was low. These data also suggest that the tumorigenic activity was probably the result of a non‐genotoxic process. © 1997 by John Wiley & Sons, Ltd.

Carcinogenicity Studies on MTBE: Critical Review and Interpretation

“…MTBE has been repeatedly tested in both mammalian and nonmammalian models using in vitro and in vivo protocols. (23) Under the conditions of those experiments MTBE has been consistently negative with respect to genotoxic potential. Similarly, NTP (20) reported that TBA was without genotoxic effects in a testing battery that assessed in vitro and in vivo activity.…”

Carcinogenicity Studies on MTBE: Critical Review and Interpretation

“…MTBE has been repeatedly tested in both mammalian and nonmammalian models using in vitro and in vivo protocols. (23) Under the conditions of those experiments MTBE has been consistently negative with respect to genotoxic potential. Similarly, NTP (20) reported that TBA was without genotoxic effects in a testing battery that assessed in vitro and in vivo activity.…”

Systematic evaluation of the evidence base on methyl tert-butyl ether supporting a lack of concern for carcinogenic hazard in humans based on animal cancer studies and mechanistic data

“…In vivo reliable studies in experimental animal models reported consistently negative data for genotoxic and mutagenic endpoints ( ARCO Chemical Company, 1980 , Vergnes and Morabit, 1989 , Vergnes and Kintigh, 1993 , McKee et al, 1997 , Kado et al, 1998 , Gollapudi et al, 2024 ) with only one study, not considered reliable, showing activity (chromosomal aberrations) ( Darwish and Mosallam, 2019 ). In vivo studies are more useful in assessing the potential mutagenic and genotoxic potential of chemicals considering metabolism is ongoing.…”

“…Several studies reported negative micronucleus formation in the bone marrow in MTBE exposed mice. This included male and female mice administered a single intraperitoneal MTBE injection at doses ranging from 0.25 to 1.75 g/kg-bw ( Kado et al, 1998 ), in mice exposed via inhalation to 400, 3000, 8000 ppm (6 h/day for 2 days) ( Vergnes et al, 1989 ), and in mice exposed to MTBE via inhalation for 2 days (6 hr/day) ( McKee et al, 1997 ). In a recent inhalation study reported in transgenic male F344 Big Blue rats exposed to 0, 400, 1000, 3000 ppm MTBE for 28 days (6 h/day), no changes in the mutant frequencies at the cll locus of the transgene in liver, bone marrow, kidney, or nasal epithelium were reported by Gollapudi et al, 2024 , confirming the lack of mutagenicity of MTBE following high concentrations of exposure.…”

“… Assay Endpoint a Species, Tissue MTBE Dose a , c Dose Regimen (route); Study Duration Results Comments/Quality Assessment Reference Chromosomal Aberrations (CA) Fischer 344 Rat, Bone Marrow 0, 800, 1600 mg/kg Oral Gavage; 14, 28 days +/- Increased CA after 14 days exposure at highest dose; no significant effects at 28-day exposure Method states 50 metaphases evaluated, whereas Table 1 states 300 metaphases evaluated: inconsistent reporting, unable to evaluate. Klimisch = 3 Darwish and Mosallam, 2019 Chromosomal Aberrations (CA) Rat, Bone Marrow 0, 800, 4000 and 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/d for 5 days − NC Vergnes et al, 1989 Micronucleus CD-1 Mouse, Bone Marrow 0, 400, 3000, 8000 ppm [400–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Vergnes et al, 1993 Micronucleus CD-1 Mouse, Bone Marrow 0, 800, 4000, 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Mckee et al, 1997 Micronucleus Mouse, Bone Marrow 0, 0.25, 0.5, 1, 1.5, 1.75 g/kg-bw [250–1750 mg/kg-bw] IP injection; single dose − NC Kado et al, 1998 DNA breaks (Comet assay) Kunming mice, Liver, Kidney, Lung 0, 108 , 1440, and 4968 mg/m 3 [0.146–6.71 mg/kg] Inhalation; 4 h/day for 20 days + Scored 25 cells vs. 150 recommended in OECD 489. Scoring was manual, rather than automated as recommended in TG 489.…”

Risk Characterization of Methyl tertiary Butyl Ether (MTBE) in Tap Water

“…MTBE has been tested in 12 genotoxicity assays, including in vitro bacterial and mammalian cell assays, and in vivo micronucleus and bone marrow assays. (33) The scientific strength of evidence demonstrates that MTBE is not a genotoxicant and thus is unlikely to damage DNA directly. For a more extensive discussion of MTBE genotoxicity, see Rudenko et u1.…”

Carcinogenicity Studies on MTBE: Critical Review and Interpretation

“…MTBE has been repeatedly tested in both mammalian and nonmammalian models using in vitro and in vivo protocols. (23) Under the conditions of those experiments MTBE has been consistently negative with respect to genotoxic potential. Similarly, NTP (20) reported that TBA was without genotoxic effects in a testing battery that assessed in vitro and in vivo activity.…”

Systematic evaluation of the evidence base on methyl tert-butyl ether supporting a lack of concern for carcinogenic hazard in humans based on animal cancer studies and mechanistic data

“…In vivo reliable studies in experimental animal models reported consistently negative data for genotoxic and mutagenic endpoints ( ARCO Chemical Company, 1980 , Vergnes and Morabit, 1989 , Vergnes and Kintigh, 1993 , McKee et al, 1997 , Kado et al, 1998 , Gollapudi et al, 2024 ) with only one study, not considered reliable, showing activity (chromosomal aberrations) ( Darwish and Mosallam, 2019 ). In vivo studies are more useful in assessing the potential mutagenic and genotoxic potential of chemicals considering metabolism is ongoing.…”

“…Several studies reported negative micronucleus formation in the bone marrow in MTBE exposed mice. This included male and female mice administered a single intraperitoneal MTBE injection at doses ranging from 0.25 to 1.75 g/kg-bw ( Kado et al, 1998 ), in mice exposed via inhalation to 400, 3000, 8000 ppm (6 h/day for 2 days) ( Vergnes et al, 1989 ), and in mice exposed to MTBE via inhalation for 2 days (6 hr/day) ( McKee et al, 1997 ). In a recent inhalation study reported in transgenic male F344 Big Blue rats exposed to 0, 400, 1000, 3000 ppm MTBE for 28 days (6 h/day), no changes in the mutant frequencies at the cll locus of the transgene in liver, bone marrow, kidney, or nasal epithelium were reported by Gollapudi et al, 2024 , confirming the lack of mutagenicity of MTBE following high concentrations of exposure.…”

“… Assay Endpoint a Species, Tissue MTBE Dose a , c Dose Regimen (route); Study Duration Results Comments/Quality Assessment Reference Chromosomal Aberrations (CA) Fischer 344 Rat, Bone Marrow 0, 800, 1600 mg/kg Oral Gavage; 14, 28 days +/- Increased CA after 14 days exposure at highest dose; no significant effects at 28-day exposure Method states 50 metaphases evaluated, whereas Table 1 states 300 metaphases evaluated: inconsistent reporting, unable to evaluate. Klimisch = 3 Darwish and Mosallam, 2019 Chromosomal Aberrations (CA) Rat, Bone Marrow 0, 800, 4000 and 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/d for 5 days − NC Vergnes et al, 1989 Micronucleus CD-1 Mouse, Bone Marrow 0, 400, 3000, 8000 ppm [400–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Vergnes et al, 1993 Micronucleus CD-1 Mouse, Bone Marrow 0, 800, 4000, 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Mckee et al, 1997 Micronucleus Mouse, Bone Marrow 0, 0.25, 0.5, 1, 1.5, 1.75 g/kg-bw [250–1750 mg/kg-bw] IP injection; single dose − NC Kado et al, 1998 DNA breaks (Comet assay) Kunming mice, Liver, Kidney, Lung 0, 108 , 1440, and 4968 mg/m 3 [0.146–6.71 mg/kg] Inhalation; 4 h/day for 20 days + Scored 25 cells vs. 150 recommended in OECD 489. Scoring was manual, rather than automated as recommended in TG 489.…”

Risk Characterization of Methyl tertiary Butyl Ether (MTBE) in Tap Water

“…MTBE has been tested in 12 genotoxicity assays, including in vitro bacterial and mammalian cell assays, and in vivo micronucleus and bone marrow assays. (33) The scientific strength of evidence demonstrates that MTBE is not a genotoxicant and thus is unlikely to damage DNA directly. For a more extensive discussion of MTBE genotoxicity, see Rudenko et u1.…”

Carcinogenicity Studies on MTBE: Critical Review and Interpretation

“…MTBE has been repeatedly tested in both mammalian and nonmammalian models using in vitro and in vivo protocols. (23) Under the conditions of those experiments MTBE has been consistently negative with respect to genotoxic potential. Similarly, NTP (20) reported that TBA was without genotoxic effects in a testing battery that assessed in vitro and in vivo activity.…”

Systematic evaluation of the evidence base on methyl tert-butyl ether supporting a lack of concern for carcinogenic hazard in humans based on animal cancer studies and mechanistic data

“…In vivo reliable studies in experimental animal models reported consistently negative data for genotoxic and mutagenic endpoints ( ARCO Chemical Company, 1980 , Vergnes and Morabit, 1989 , Vergnes and Kintigh, 1993 , McKee et al, 1997 , Kado et al, 1998 , Gollapudi et al, 2024 ) with only one study, not considered reliable, showing activity (chromosomal aberrations) ( Darwish and Mosallam, 2019 ). In vivo studies are more useful in assessing the potential mutagenic and genotoxic potential of chemicals considering metabolism is ongoing.…”

“…Several studies reported negative micronucleus formation in the bone marrow in MTBE exposed mice. This included male and female mice administered a single intraperitoneal MTBE injection at doses ranging from 0.25 to 1.75 g/kg-bw ( Kado et al, 1998 ), in mice exposed via inhalation to 400, 3000, 8000 ppm (6 h/day for 2 days) ( Vergnes et al, 1989 ), and in mice exposed to MTBE via inhalation for 2 days (6 hr/day) ( McKee et al, 1997 ). In a recent inhalation study reported in transgenic male F344 Big Blue rats exposed to 0, 400, 1000, 3000 ppm MTBE for 28 days (6 h/day), no changes in the mutant frequencies at the cll locus of the transgene in liver, bone marrow, kidney, or nasal epithelium were reported by Gollapudi et al, 2024 , confirming the lack of mutagenicity of MTBE following high concentrations of exposure.…”

“… Assay Endpoint a Species, Tissue MTBE Dose a , c Dose Regimen (route); Study Duration Results Comments/Quality Assessment Reference Chromosomal Aberrations (CA) Fischer 344 Rat, Bone Marrow 0, 800, 1600 mg/kg Oral Gavage; 14, 28 days +/- Increased CA after 14 days exposure at highest dose; no significant effects at 28-day exposure Method states 50 metaphases evaluated, whereas Table 1 states 300 metaphases evaluated: inconsistent reporting, unable to evaluate. Klimisch = 3 Darwish and Mosallam, 2019 Chromosomal Aberrations (CA) Rat, Bone Marrow 0, 800, 4000 and 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/d for 5 days − NC Vergnes et al, 1989 Micronucleus CD-1 Mouse, Bone Marrow 0, 400, 3000, 8000 ppm [400–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Vergnes et al, 1993 Micronucleus CD-1 Mouse, Bone Marrow 0, 800, 4000, 8000 ppm [800–8000 mg/kg] Inhalation; 6 h/day for 2 days − NC Mckee et al, 1997 Micronucleus Mouse, Bone Marrow 0, 0.25, 0.5, 1, 1.5, 1.75 g/kg-bw [250–1750 mg/kg-bw] IP injection; single dose − NC Kado et al, 1998 DNA breaks (Comet assay) Kunming mice, Liver, Kidney, Lung 0, 108 , 1440, and 4968 mg/m 3 [0.146–6.71 mg/kg] Inhalation; 4 h/day for 20 days + Scored 25 cells vs. 150 recommended in OECD 489. Scoring was manual, rather than automated as recommended in TG 489.…”

Risk Characterization of Methyl tertiary Butyl Ether (MTBE) in Tap Water

“…MTBE has been tested in 12 genotoxicity assays, including in vitro bacterial and mammalian cell assays, and in vivo micronucleus and bone marrow assays. (33) The scientific strength of evidence demonstrates that MTBE is not a genotoxicant and thus is unlikely to damage DNA directly. For a more extensive discussion of MTBE genotoxicity, see Rudenko et u1.…”