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in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
weight of evidence
1 (reliable without restriction)
Justification for type of information:
This study is taken from a recently-published scientific article by S. Suzuki et al. on "Genetic, acute and subchronic toxicity studies of matured hop extract produced by extraction from heat-treated hops", published in the Journal of Toxicological Sciences (2018) vol. 43, no. 7, pp. 473-484, available freely as full text in the public domain. Matured hop extract contains oxidised alpha and beta acids. This substance is therefore of direct relevance to hop extract, and to alpha acids, iso-alpha acids, and beta acids, as the oxidised alpha and beta acids are common degradation products of hop alpha and beta acids. This article is useful in that it reports a number of toxicological studies, and the in vivo tests on chromosome aberration are reported in this end-point to add as weight of evidence for the lack of genotoxicity expected for hop extract and its constituents.

Data source

Reference Type:
Genetic, acute and subchronic toxicity studies of matured hop extract produced by extraction from heat-treated hops
Shigeo Suzuki, Yumie Morimoto-Kobayashi, Chika Takahashi, Yoshimasa Taniguchi, Mikio Katayama
Bibliographic source:
Report date:

Materials and methods

Test guideline
according to guideline
other: In accordance with a previous protocol, viz. Hayashi, M., Sofuni, T. and Ishidate, M. Jr. (1983): An application of Acridine Orange fluorescent staining to the micronucleus test. Mutat. Res., 120, 241-247.
GLP compliance:
not specified
Type of assay:
mammalian germ cell cytogenetic assay

Test material

Constituent 1
Reference substance name:
Hop, Humulus lupulus, ext.
EC Number:
EC Name:
Hop, Humulus lupulus, ext.
Cas Number:
Molecular formula:
No simple molecular formula for UVCB
Hop, Humulus lupulus, ext.
Test material form:
liquid: viscous
Depending on the extraction conditions and on the hop variety, the colour of the extract can vary from yellow to dark green. It is a semi-fluid paste at room temperature. The product becomes more fluid when heated.
Specific details on test material used for the study:
An aqueous extract of a heat-treated hop extract, designed for production and extraction of oxidised alpha and beta acids.

Test animals

Details on test animals or test system and environmental conditions:
Eight-week-old male rats. Body weight was between 289 - 310 g.

Administration / exposure

Route of administration:
oral: unspecified
Sterlized water
Details on exposure:
High dose group: 2,000 mg/kg bw/day; middle dose group: 1,000 mg/kg bw/day; low dose group: 500 mg/kg bw/day. Once daily for 2 days.
Duration of treatment / exposure:
2 days
Frequency of treatment:
Once daily
Post exposure period:
24 h
Doses / concentrationsopen allclose all
Dose / conc.:
2 000 mg/kg bw/day
High dose group
Dose / conc.:
1 000 mg/kg bw/day
Middle dose group
Dose / conc.:
500 mg/kg bw/day
Low dose group
No. of animals per sex per dose:
Control animals:
yes, concurrent vehicle
Positive control(s):
MMC. This was dissolved in sterilized water and it was injected intraperitoneally at 2 mg/kg bw. One dose only.


Tissues and cell types examined:
Bone marrow cell smears for erythrocytes.
Details of tissue and slide preparation:
Notes from journal: "Bone marrow cell smears were prepared and stained with acridine orange. Numbers of polychromatic erythrocytes (PCEs) per 200 erythrocytes, and micronucleated polychromatic erythrocytes (MNPCEs) per 2,000 PCEs were counted."
Evaluation criteria:
Notes from journal: "Numbers of polychromatic erythrocytes (PCEs) per 200 erythrocytes, and micronucleated polychromatic erythrocytes (MNPCEs) per 2,000 PCEs were counted."

Results and discussion

Test results
Key result
Vehicle controls validity:
Positive controls validity:
Additional information on results:
These results are part of a larger study reported in the article. Results in brief:

• Ames test – negative, up to 5,000 ug per plate, with and without metabolic activation
• In vitro chromosomal aberration test – positive at 3,330 and 5,000 ug per plate without metabolic activation (i.e. elevated structural aberration above negative control) but no increase in polyploid cells
• In vivo micronucleus test in rat bone marrow – no clastogenic potential at max dose of 2,000 mg/kg bw/day, i.e. negative
• Acute toxicity – No noticeable toxic signs at 2,000 mg/kg bw
• 90 days study – NOAEL considered to be over 3,484 mg/kg bw/day for male and 4,022 mg/kg bw/day for female rats.

Authors’ conclusion is that although the structural chromosomal aberration was positive in high dose group for the in vitro test, Ames test and in vivo micronucleus test suggests that the matured hop extract has no potential for mutagenicity and genotoxicity under in vivo conditions.

Further consideration of results noted that cytotoxicity was observed in the in vitro test.If the toxicity mechanism was to slow cell division or similar, it could look like a chromosome aberration. The in vivo test indicates lack of genotoxicity at appropriate doses. The authors' comment was as follows: "From the results mentioned above, it is judged that MHE does not have clastogenic potential in rats at the maximum dose, which is recommended by OECD guidelines (OECD, 1997)."

Applicant's summary and conclusion

The studies reported in this journal article add weight of evidence to the lack of toxicity of hop extract, in particular for substances derived from hop alpha and beta acids.

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