elegansSMF-1 or SMF-2 may be more likely to be involved in Mn2+transport

elegansSMF-1 or SMF-2 may be more likely to be involved in Mn2+transport. an essential trace element that is necessary for normal growth and development. The heavy metal is usually required for a number of biological processes, including amino acid, lipid, and carbohydrate production, and metabolism, and is a cofactor for a diverse set of proteins, including arginases, transferases, hydrolases, ligases, and oxidoreductases (1,2). Deficiencies in Mn2+, although rare, have been linked with bone malformation, hypertension, osteoporosis, and epilepsy (3,4). Mn2+is usually also a potent neurotoxicant, and occupational exposure to high concentrations of the metal can result in a neurological condition called manganism (1,5). Symptoms of manganism include tremors, bradykinesia, rigidity, and facial muscle spasms (1,6,7). Mn2+neurotoxicity has been associated with a number of occupational and environmental exposures. High incidence of manganism has been found in manganese miners and smelters (710). Welders appear to be particularly vulnerable to Pyridoxamine 2HCl the disorder as manganese alloys used in the heating and joining of metals may result in the production and inhalation of manganese particles (11). Exposure to Mn2+-based pesticides, including maneb and mancozeb, has also been associated with the development of manganism (1214). Furthermore, significant environmental exposures have been reported with water contamination and possibly with the manganese-containing anti-knock fuel additive methylcyclopentadienyl manganese tricarbonyl (12). Recently, high exposures to Mn2+have also been associated with psychoactive stimulant preparations for recreational drug use (15,16). Epidemiological studies suggest a significant correlation of exposure to high concentrations of Mn2+and Pyridoxamine 2HCl the propensity to develop Parkinson disease (PD)2(6,11). PD is usually characterized by the loss of DA neurons in the substantia nigra and other basal ganglia (17). Individuals with occupational exposure to Mn2+greater than 20 years have an increased probability to develop PD (18). Combinatorial long term exposures to Mn2+, Fe2+, and aluminum (greater than 30 years) have also been shown to lead to increased likelihood of PD (19). Acute Mn2+toxicity results in symptoms comparable (but not identical) to those seen in patients with PD, including rigidity, tremors, and bradykinesia (1,7,11,20). As in PD, oxidative stress appears to play a significant role in the disorder, and the brain region most Pyridoxamine 2HCl susceptible to Mn2+injury is also sensitive to oxidative stress (2126). Mn2+toxicity can confer damage to the striatum, reduction of the DA precursor tyrosine hydroxylase, and DA neurodegeneration (2729). The PD-associated pre-synaptic Pyridoxamine 2HCl protein -synuclein has also been proposed to contribute to the pathogenesis of both disorders (3033). Although Pyridoxamine 2HCl the molecular bases of manganism and Mn2+-induced toxicity has not been elucidated,in vitrostudies of Mn2+treatments suggest inhibition of the electron transport chain complex-I within the mitochondria and increase in production of reactive oxygen species (ROS) (21,23,34). Furthermore, there are significant changes in intracellular antioxidant levels, including GSH, thiols, and catalase (35,36). Mn2+is usually believed to be transported into the cell via several routes, including voltage-gated and glutamate receptor calcium channels, the transferrin receptor, and the proton-coupled electrogenic divalent metal transporter-1, DMT-1 (37,38). DMT-1 mediates the transport of divalent ions, including Mn2+, Fe2+, copper, cobalt, lead, and zinc. In yeast, DMT-1 isoforms Smf1p and Smf2p transport Mn2+across the plasma membrane and intracellular vesicles, respectively (3942). In vertebrates, two of four isoforms of DMT-1 have been identified and are the major transporters involved in absorption of Fe2+in the intestines (37,43). Also known as Nramp2 (natural resistance-associated macrophage protein), the transporters are expressed in most tissues and are capable of transporting divalent metal cations (38). Recently, DMT-1 has been implicated in Fe2+-mediated DA neuronal death in PD and vertebrate model systems (44). The nematodeCaenorhabditis elegansis a IP1 powerful model system to explore the molecular basis of PD-associated DA neuronal vulnerability and death (45,46). All of the genes responsible for DA biosynthesis, packaging, and reuptake have recognizable homologs in the worm genome, and genetic, cellular, and functional studies confirm their participation in dopaminergic function (47). Transcriptional green fluorescent protein (GFP) fusions allow the eight DA neurons to be clearly visiblein vivounder a fluorescent dissecting scope,.