Human Dopamine Transporter Function Following Exposure to Heavy Metals and Psychostimulants

Abstract

Background

Environmental exposure to heavy metals plus the use of psychostimulants may pose a unique threat to the neurological health of the user at the level of dopamine transporter (DAT) function.

Objectives

These studies examined the effects of low-concentration heavy metal and psychostimulant (co)exposure on human DAT density and function.

Materials and Methods

Neuro2A neuroblastoma cells (N2A) were exposed to PbCl2 (Pb), HgCl2 (Hg), cocaine (COC), and methamphetamine (MA) to assess alterations in cell viability as well as human dopamine transporter (hDAT) density and function. Assays included Lactate Dehydrogenase activity (cell viability), [3H] GBR12935 binding (hDAT density), and [3H] dopamine (DA) uptake (hDAT functionality). The threshold for changes in cell viability of a metal or stimulant is the concentration used in mixture exposure studies (10 μM for Hg and Pb; 100 nM for COC and MA) with an optimum exposure time of 72 h.

Results

Both Hg and Pb reduced cell viability related to exposure time and concentration. N2A cells demonstrated greater resistance to COC- and MA-induced cytotoxicity. The density of hDAT increased (115-175%) following exposure to Hg, Pb, COC, or MA compared to vehicle values. After exposure to metal-psychostimulant mixtures, hDAT density increased 161-288% compared to control values. We observed the largest increase in [3H] DA uptake in the MA group (35-81%), whereas COC groups inhibited uptake (17-20%). Collectively, exposures to each compound (alone or mixture) increased hDAT density. Our observations suggest that increased protein present did not translate to increased functionality, since changes in [3H] DA uptake did not parallel density changes.

Conclusion

Although more hDAT protein is at the cell surface, altered function results in an inability to clear [3H] DA from the extracellular space. Thus, exposure to low-levels of heavy metals may increase the risk for altered DA neurotransmission/turnover following psychostimu-lant use, resulting in an exaggerated response or increased risk for toxicity.