Plant Sterols

Endpoint summary

Additional information

Data are available from in vitro and in vivo studies on phytosterols (composition not defined). A reliable study on the bacterial mutagenicity of Plant Sterols, as defined in section 1, is available, and is used as weight of evidence, as the study did not include a strain of bacteria capable of detecting cross-linking mutagens, as required by the current guideline. Further weight of evidence for bacterial mutagenicity comes from a study that is compliant with the current guideline which tested the related substance phytosterol esters. Reliable data on the genetic toxicity of phytosterol esters is available for all the required in vitro endpoints and for in vivo endpoints. It is considered appropriate to read-across data from phytosterol esters to Plant Sterols because sterols are reversibly esterified in vivo by steryl-O-acyltransferase (SOAT) (see Section 1.4 of the CSR). This enzyme is present in the endoplasmic reticulum of all animal cells. Therefore exposure to phytosterol esters will lead to exposure to the constituents of Plant sterols. In addition, data are available for the Plant sterol constituent, beta-sitosterol, which supports the conclusions from the studies on Plant sterols and phytosterol esters.

Information for the potential for mutagenicity to bacteria comes from weight of evidence of two reliable studies. A study on the closely related substance, phytosterol esters, was conducted according to OECD 471, not compliant with GLP (Wolfreys, A.M and Hepburn, P.A. (2001)). No evidence of a test-substance related increase in the number of revertants was observed with or without metabolic activation in Salmonella typhimurium strains TA 98, TA 100, TA 1535 and TA 1537, and E. coli WP2 uvrA pKM 101. Appropriate solvent and positive controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test. These authors also reported results for free phytosterols (no composition given), which were not genotoxic to Salmonella typhimurium strains TA 98, TA 100, TA 1535 or TA 1537. In a further study, Generol 102, which is known to fit the substance identity of the registered substance, was tested for mutagenicity to bacteria, in a study which was conducted according to OECD 471 (1983) and in compliance with GLP (Schröder (1995)). No evidence of test substance related increase in the number of revertants was observed with or without activation in the initial or the repeat experiments in Salmonella typhimurium strains TA 98 TA 100, TA 1535 and TA 1537 using the plate incorporation method. Appropriate solvent, negative and positive control substances were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test.

The closely related substance, phytosterol ester has been tested for clastogenicity in human peripheral human lymphocytes, in a study which was conducted according to OECD 473, but not compliant with GLP (Wolfreys, A.M and Hepburn, P.A. (2001)). No evidence of a test-substance related increase in the number of induced chromosomal aberrations was observed with or without activation in the initial or repeat experiments. The maximum concentration tested was limited by the solubility of the substance. Appropriate solvent and positive controls were included and gave expected results. It is concluded that the test-substance is negative for mutagenicity to peripheral human lymphocytes under the conditions of the test. The authors also report that a similar study on phytosterols gave similar results, though full details of the results are not given.

Phytosterol esters has been tested for mammalian mutagenicity with L5178Y TK+/- cells, in a study which was conducted according to OECD 476, but was not compliant with GLP (Wolfreys, A.M and Hepburn, P.A. (2001)). No evidence of a test substance related increase in the mutant frequencies was observed with or without metabolic activation in the initial or repeat experiment. The substance was tested up to precipitating concentrations. Appropriate solvent and positive controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to L5178Y TK +/- cells under the conditions of the test.

In vivo

The plant sterol constituent, beta-sitosterol has been tested for its potential clastogenic effect in a micronucleus assay, in a study which was conducted using a method similar to OECD 474, not compliant with GLP (Paniagua-Perez (2005)). No evidence of a test substance related increase in micronuclei in peripheral mouse blood was observed after intraperitoneal treatment with 200, 400 and 1000 mg/kg bw. Appropriate solvent and positive controls were included and a genotoxic effect was observed with the positive control substance. It is concluded that the test substance is negative for clastogenicity in mice under the conditions of the test. This publication also reports the results of a sister chromatid exchange conducted on the same substance.

Additional evidence for lack of genetic toxicity in vivo comes from a study on the closely related substance, phytosterol esters, which has been tested in a micronucleus assay in rat (Wolfreys, A.M and Hepburn, P.A. (2001)). No evidence of test substance-related increase in the frequency of micronucleated polychromatic erythrocytes was obtained after oral gavage administration of 500, 1000 and 2000 mg/kg bw phytosterol esters, administered twice 24 hours apart. No toxicity to bone marrow was observed. Appropriate positive and vehicle controls were included and gave acceptable results. It is concluded that the test substance is negative for induction of micronuclei (is not clastogenic) under the conditions of the test.

Supporting information for the lack of genetic toxicity of Plant sterols comes from a study on the closely related substance phytosterol esters, which has been tested according to OECD 486 in rats using oral administration by gavage. No evidence of unscheduled DNA synthesis was observed. Appropriate positive and vehicle controls were included and gave expected results. It is concluded that the test substance is negative for damage to DNA under the conditions of the test.

Short description of key information:
In vitro:

Gene mutation (Bacterial reverse mutation assay / Ames test): negative with and without metabolic activation in Salmonella typhimurium strains TA 98 TA 100, TA 1535 and TA 1537 (OECD 471 (1983)) (Schröder (1995)).

Gene mutation (Bacterial reverse mutation assay / Ames test): read-across from structural analogue phytosterol esters: negative with and without metabolic activation in S. typhimurium TA 1535, TA 1537, TA 98 and TA 100 and E. coli WP2 uvrA pKM 101 (OECD TG 471) (Wolfreys, A.M and Hepburn, P.A. (2001)).

Cytogenicity in mammalian cells: read-across from structural analogue phytosterol esters: negative with and without metabolic activation in peripheral human lymphocytes (OECD TG 473) (Wolfreys, A.M and Hepburn, P.A. (2001)).

Mutagenicity in mammalian cells: read-across from structural analogue phytosterol esters: negative in L5178Y mouse lymphoma cells (OECD TG 476) (Wolfreys, A.M and Hepburn, P.A. (2001)).

In vivo:

Micronucleus assay in mouse (ip administration): read-across from constituent substance beta-sitosterol: negative (Paniagua-Perez (2005)).

Micronucleus assay in rat (oral gavage administration): read-across from structural analogue phytosterol esters: negative (OECD 474 (1997)) (Wolfreys, A.M and Hepburn, P.A. (2001)).

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the available in vitro genotoxicity data, Plant sterols is not classified for mutagenicity according to Regulation 1272/2008/EC.