Dopaminergic toxicity of the herbicide atrazine in rat striatal slices

Abstract

A possible link between Parkinson's disease and pesticide exposure has been suggested, and recently it was shown that the herbicide atrazine (ATR) modulates catecholamine metabolism in PC12 cells and affects basal ganglia function in vivo. Hence, the objectives of this study were to: (i) determine if ATR is capable of modulating dopamine (DA) metabolism in striatal tissue slices in vitro and (ii) to explore possible mechanisms of its effects. Striatal tissues from adult male Sprague Dawley rats were incubated with up to 500 μM ATR in a metabolic shaker bath at 37 °C and an atmosphere of 95% O 2 and 5% CO 2 for 4 h. At the end of incubation, samples were collected for both tissue and media levels of DA and its metabolites (3,4-dihydroxyphenylacetic acid, DOPAC and homovanillic acid, HVA), which were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). To gain some mechanistic insight in to the way ATR affects DA metabolism, several pharmacological manipulations were performed. Striata exposed to ATR at concentrations of 100 μM and greater had a dose-dependent decrease of tissue levels of DA. At doses of ATR 50 μM and greater, the DOPAC+HVA/DA ratio was dose-dependently increased. Tyrosine hydroxylase (TH, the rate-limiting enzyme in DA synthesis) protein levels and activity were not affected by ATR treatment. However, high potassium induced DA release into the medium was decreased, whereas the increase in media DA observed in the presence of the DA uptake inhibitor nomifensine was increased even further by ATR in a dose-dependent manner. All of these effects of ATR were observed at levels that were not toxic to the tissue, as LDH release into the medium (lactate dehydrogenase, an index of non-specific cytotoxicity) was not affected by ATR. Taken together, results from this study suggest that ATR decreases tissue DA levels not by affecting TH activity, but possibly by interfering with the vesicular storage and/or cellular uptake of DA.

Alteration of dopamine uptake into rat striatal vesicles and synaptosomes caused by an in vitro exposure to atrazine and some of its metabolites

“…The doses (0.1-250 μM) used in this study are lower or in the range to those used in previous studies (Das et al, 2000;Das et al, 2003;Filipov et al, 2007). In vivo studies reported that DACT is the major urinary metabolite of ATR in mice (Ross and Filipov, 2006), rats (McMullin et al, 2003) and, apparently, humans (Barr et al, 2007).…”

“…In the present study, at the higher concentrations, DE and DIP were similar to ATR in their ability to decrease vesicular uptake. Considering the fact that in PC 12 cells (Das et al, 2001) and in striatal slices we observed that these metabolites of ATR are not as potent and/ or had differential effects with ATR (Filipov et al, 2004), it is conceivable that ATR has effects that are in addition to its ability to decrease the vesicular uptake of DA.…”

“…The risk of PD or PD-like pathology in animal models associated with exposure to pesticides has been reported in multiple studies (i.e., Morato et al, 1989;Takahashi et al, 1989;Fredriksson et al, 1993;Alam and Schmidt, 2002;McCormack et al, 2002;Gao et al, 2003). With respect to ATR, several studies indicate that both in vivo (Rodriguez et al, 2005;Coban and Filipov, 2007) and in vitro (Das et al, 2000;Das et al, 2003;Filipov et al, 2007) exposure to this herbicide causes dopaminergic neurotoxicity manifested with decreased DA. In order to clarify the mechanism underlying this reduction, we investigated the effects of in vitro exposure to ATR and its major metabolites, DACT, DE, and DIP on DA uptake into rat striatal synaptosomes and vesicles.…”

“…However, a recent study found that exposure to ATR results in apoptosis of ZC 7901 cells which is associated with a disruption of the mitochondrial membrane potential (Liu et al, 2006). Thus, direct mitochondrial effects of ATR, but not if its metabolites, especially at higher exposure levels, may provide one possible explanation for the greater effects of ATR than DIP and DE on tissue/cellular DA levels (Das et al, 2000;Das et al, 2001;Filipov et al, 2004;Filipov et al, 2007).…”

“…Our data indicate that ATR, DIP and DE, but not its major mammalian metabolite, DACT, decrease striatal DA levels by inhibiting VMAT-2 while moderately activating the membrane DA transporter (DAT). As TH was not affected by ATR (Das et al, 2003;Filipov et al, 2007) other possible ATR targets such as aromatic amino acid decarboxylase (AAAD), monoamine oxidase (MAO), and mitochondrial function, in particular, remain to be investigated in future studies.…”