Pesticide residues in food — 2006: Toxicological ... - ipcs inchem

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increase in peroxisome proliferation, a decrease in replicative DNA synthesis and an increase in
apoptosis in cultured guinea-pig hepatocytes (Elcombe, 2002b).
A study with similar protocol to the studies in mouse and guinea-pig hepatocytes in vitro was
performed in human hepatocytes using the same batch of racemic haloxyfop acid. Concentrations
of 0, 30, 300 and 1000 μmol/l were used. Samples of human liver were obtained from three patients
undergoing resections for the removal of tumours. The liver cultures from each donor were tested
separately. This time, WY14,643 was used as a positive control for induction of peroxisome proliferation
only and not for replicative DNA synthesis or apoptosis. The results showed no consistent effect of
racemic haloxyfop acid on peroxisome proliferation, although there was a significant increase for one
donor at 30 μmol/l and a significant decrease for another donor at 100 μmol/l. The positive control
(WY14,643 at 100 μmol/l) had no effect on peroxisome proliferation in cells from any of the donors,
suggesting that human hepatocytes are not responsive (or, at least, not as responsive as mouse or
guinea-pig hepatocytes) to peroxisome proliferators. There was a dose-related decrease in replicative
DNA synthesis that was significant (p < 0.05) in all three sets of cells from different donors at
300 μmol/l or more, and at 30 μmol/l there was a significant decrease with the cell culture from one
of the donors. The positive control (EGF at 25 ng/ml) caused a highly significant (p < 0.001) increase
in replicative DNA synthesis in all three sets of cells. There were significant (p < 0.05) increases
in apoptosis in all three donors at concentrations of 300 μmol/l or more and in two of the donors
at 30 μmol/l, and significant increases were seen in cells from all three donors in response to the
positive-control material (TGFβ 1
at 5 ng/ml) (Elcombe, 2002c).
The results of in-vitro studies in hepatocytes from different species showed that human
hepatocytes responded to racemic haloxyfop acid in a different way to hepatocytes from the other two
species, in that they did not show the increase in peroxisome proliferation that was seen in mice and
guinea-pigs (Table 6). The hepatocytes from all three species showed a decrease in replicative DNA
synthesis and an increase in the number of cells undergoing apoptosis. The direction of the effect on
replicative DNA synthesis was opposite to the direction of the response to the positive control (EGF).
The finding of decreased replicative DNA synthesis at S-phase was unexpected and no explanation
for it was available.
Table 6. Effects of haloxyfop acid on hepatocytes from different species in vitro
Effect
Species
Mouse Guinea-pig Human
Haloxyfop acid
Peroxisome proliferation + + 0
Replicative DNA synthesis − − −
Number of cells undergoing apoptosis + + +
Positive controls
Peroxisome proliferation (WY14,643) + + 0
Replicative DNA synthesis (EGF) + + +
Number of cells undergoing apoptosis (TGFβ 1
) + + +
From Elcombe (2002a), (2002b) & (2002c)
EGF, epidermal growth factor; TGFβ 1
, transforming growth factor beta-1.
+ Increase in this parameter when compared with untreated controls.
0 No consistent increase or decrease (similar to untreated control).
− Decrease in this parameter when compared with untreated controls.
HALOXYFOP X-X JMPR 2006