Dose Response for the Stimulation of Cell Division by Caffeic Acid in Forestomach and Kidney of the Male F344 Rat
Ursula Lutz
0
1
Serena Lugli.t Annette Bitsch
0
1
Josef Schlatter
0
Werner K. Lutz
0
1
0
1997 Soday of Toxicology
1
Department of Toxicology, University of WUrzburg
,
D-97078 WUrzburg
,
Germany
2
Institute of Toxicology, ETH and University of Zurich
,
CH-8603 Schwerzenbach
,
Switzerland;
and $Swiss Federal Office of Public Health, Food Sciences Division, do Institute of Veterinary Pharmacology
,
CH-8057 Zurich
,
Switzerland
Caffeic acid (CA, 3,4-dihydroxycinnamic acid), at 2% in the diet, had been shown to be carcinogenic in forestomach and kidney of F344 rats and B6C3F1 mice. Based on its occurrence in coffee and numerous foods and using a linear interpolation for cancer incidence between dose 0 and 2%, the cancer risk in humans would be considerable. In both target organs, tumor formation was preceded by hyperplasia, which could represent the main mechanism of carcinogenic action. The dose-response relationship for this effect was investigated in male F344 rats after 4-week feeding with CA at different dietary concentrations (0, 0.05, 0.14, 0.40, and 1.64%). Cells in S-phase of DNA replication were visualized by immunohistochemical analysis of incorporated 5-bromo-2'-deoxyuridine (BrdU), 2 hr after intraperitoneal injection. In the forestomach, both the total number of epithelial cells per millimeter section length and the unit length labeling index of BrdU-positive cells (ULLI) were increased, about 2.5-fold, at 0.40 and 1.64%. The lowest concentration (0.05%) had no effect. At 0.14%, both variables were decreased by about one-third. In the kidney, the labeling index in proximal tubular cells also indicated a J-shaped (or U-shaped) dose response with a 1.8-fold increase at 1.64%. In the glandular stomach and in the liver, which are not target organs, no dose-related effect was seen. The data show a good correlation between the organ specificity for cancer induction and stimulation of cell division. With respect to the dose-response relationship and the corresponding extrapolation of the animal tumor data to a human cancer risk, a linear extrapolation appears not to be
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Caffeic acid (3,4-dihydroxycinnamic acid; CA), a natural
phenolic antioxidant, is widely distributed in vegetables,
fruits, and beverages (Herrmann, 1989). It occurs mainly in
conjugated forms. In chlorogenic acid, the most abundant
derivative, the carboxylic acid function of CA is linked with
a hydroxyl group of quinic acid.
CA, as other polyphenols, has attracted attention for
having both hazardous and beneficial effects [review (Stich,
1991)]. Administered at 2% in the diet for 2 years, CA was
shown to induce hyperplasia and tumors in the forestomach
and kidney of F344 rats and B6C3F1 mice (Hagiwara et al,
1991). When administered to male F344 rats after initiation
with 7V-methyl-W-nitro-/V-nitrosoguanidine (MNNG), 0.5%
CA in the diet for 35 weeks (Hirose et al., 1991) or 1% CA
for 51 weeks (Hirose et al, 1992) increased the incidence
of forestomach tumors observed after initiation with MNNG
alone. Treatment of female Sprague-Dawley rats with 0.5%
CA for 51 weeks after initiation with
7,12-dimethylbenz[a]anthracene also resulted in a higher incidence of forestomach
tumors (Hirose et al, 1988). On the other hand, CA at 0.05%
for 32 weeks inhibited the formation of squamous epithelial
carcinomas of the rat tongue induced by
4-nitroquinoline-loxide given for 5 weeks (Tanaka et at, 1993) and of mouse
forestomach tumors induced by benzo(a)pyrene (at 0.54%
CA) (Wattenberg et al, 1980). Thus, CA was shown to be
carcinogenic at 2%, tumor-promoting activity was shown at
0 . 5 - 1 % , and anticarcinogenic effects at 0.05-0.5%.
Exposure of humans to CA strongly depends on the coffee
consumption. Moderately high consumers may ingest about
9 mg/kg body wt per day. The intake from foods, mainly
from tomatoes and potatoes, was estimated to be about 0.2
mg/kg body wt per day (National Research Council, 1996).
The human cancer risk, linearly extrapolated from the animal
tumor data to a dose of 1 mg/kg body wt per day would
result in a value as high as 1 in 1000 lives (Lutz and
Schlatter, 1992). A linear extrapolation to the human exposure
level might be appropriate for DNA-reactive carcinogens.
For CA, this mechanism of action is unlikely. CA showed
no mutagenic effects in different bacterial test systems. On
the other hand, forward mutations were induced in cultured
mouse lymphoma L5178Y cells, and chromosomal
aberrations were induced in cultured Chinese hamster ovary cells
0272-0590/97 $25.00
Copyright 1997 by the Society of Toxicology.
All rights of reproduction in any form reserved.
(Hanham et al, 1983). In the IARC monograph on CA it
was concluded that indirect genotoxicity via reactive oxygen
species or tumor-promoting activity, possibly based on the
stimulation of cell division, might be more relevant than
DNA reactivity (IARC, 1993). For this mechanism of action,
nonlinear dose-response relationships are more widely
accepted. Therefore, (...truncated)