Title: Alternative Sweeteners

176 Kinghorn et al.
Figure 2 Structures of steviol, 15α-hydroxysteviol, and 15-oxosteviol.
sponses in chromosomal aberration and gene mutation tests but was not active
in the reverse mutation assay (Ames test) using S. typhimurium strains TA97,
TA98, TA100, and TA102 (26).
Several steviol analogs have been assessed for mutagenicity under the same
conditions as used for steviol, and it is apparent that the C-13 tertiary hydroxyl
group and the C-16, C-17 exomethylene group must be present to elicit a mutagenic
effect (2). 15α-Hydroxysteviol (Fig. 2) was generated as a major in vitro
metabolite under the same experimental conditions used in the treatment of steviol
but was not mutagenic either in the presence or absence of the activating
system (2). Moreover, a chemical oxidation product of 15α-hydroxysteviol,
namely, 15-oxosteviol (Fig. 2) was proposed as a weak direct-acting mutagen.
15-Oxosteviol was also bactericidal but was not detected as a metabolite of steviol
(2). However, the activity of this compound as a direct-acting mutagen was later
disputed (27). In a more comprehensive study on the potential genotoxicity of
steviol, this compound when metabolically activated produced confirmed activity
in the forward mutation assay using S. typhimurium TM677, as well as chromosomal
aberrations and gene mutations in a Chinese hamster lung fibroblast cell
line (28). Steviol was also weakly positive in the umu test using S. typhimurium
TA1535/pSK1002 either with or without metabolic activation. However, stevioside
was not mutagenic in any of the assays used, whereas steviol, even in the
presence of the S9 metabolic activating system, was inactive in a number of
additional mutagenicity assays (28). It has been shown recently that in S. typhimurium
strain TM677, steviol induces mutations of the guanine phosphoribosyltransferase
(gpt) gene (29).
Accordingly, although recent studies have confirmed the mutagenic activity
of metabolically activated steviol in a forward mutation assay on an unmutated