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The Toxicologist - Society of Toxicology

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tuna, swordfish, or mako shark (3.5, 2.3, and 2.1 nmol Se/g respectively). Diets<br />

were prepared with torula yeast protein or delipidated fish protein isolates added as<br />

10% <strong>of</strong> the total diet to replace an equivalent amount <strong>of</strong> torula yeast protein; (2 Hg<br />

levels x 6 Se diets = 12 dietary treatments, 10 rats per group). Contributions <strong>of</strong><br />

MeHg from the tuna, swordfish, and shark supplemented diets were (1.6, 2.3, and<br />

3.6 nmol MeHg/g respectively). Rats were fed low Se torula yeast based diets for 5<br />

weeks to deplete their tissue Se reserves. Rats were then switched to their assigned<br />

dietary treatments for the duration <strong>of</strong> the study. Results; Rats fed high MeHg, low<br />

Se diets showed growth inhibition after 4 weeks, and hind limb crossing after 9<br />

weeks. Rats fed all other dietary treatments grew normally and did not show symptoms<br />

<strong>of</strong> MeHg toxicity. Conclusion; <strong>The</strong> Se in ocean fish prevented MeHg toxicity<br />

in rats fed otherwise toxic levels <strong>of</strong> MeHg, even though ocean fish contributed additional<br />

MeHg levels in the diets.<br />

2591 IS CHELATION THE MECHANISM OF ACTION OF P-<br />

AMINOSALICYLIC ACID (PAS) IN THE TREATMENT<br />

OF MANGANISM?<br />

V. Petion, J. Rios, J. Mayne, J. Hilaire, D. Nicholson, D. Skeete, K. Ruddock,<br />

M. A. Carroll and E. J. Catapane. Biology, Medgar Evers College, Brooklyn, NY.<br />

Manganese (Mn) is potentially toxic in high concentrations. Mining, welding and<br />

steel manufacturing can expose workers to high levels <strong>of</strong> Mn leading to<br />

Manganism, a Parkinsons-like disorder. <strong>The</strong> mechanism <strong>of</strong> toxicity is not fully understood<br />

and effective treatments are still being developed. Studies indicate the<br />

chelator EDTA is effective in alleviating Manganism. Recently another drug, paminosalicylic<br />

acid (PAS), is being used for treatment. However, the mechanism <strong>of</strong><br />

action is unclear and is debated whether effects <strong>of</strong> PAS are due to anti-inflammation<br />

or chelation. We used dialysis tubing with a 100-500 MWCO pore size to<br />

mimic the passive elements <strong>of</strong> Mn movements across the blood-brain barrier.<br />

Tubing was set up with Mn plus PAS, EDTA, diaminocyclohexane (DACH) or<br />

glucose. Samples were taken outside the bags over time. Mn was measured with an<br />

Atomic Absorption Spectrometer. Less Mn was found to pass across bags containing<br />

Mn and EDTA as compared to control. <strong>The</strong> amounts <strong>of</strong> Mn outside <strong>of</strong> bags<br />

containing Mn with PAS or DACH was higher than controls. <strong>The</strong> paradoxical results<br />

with PAS and DACH are most likely explained because the Mn-PAS and Mn-<br />

DACH chelation complex is able to pass through the pore size, while the Mn-<br />

EDTA complex can not. <strong>The</strong>refore, Mn is diffusing out <strong>of</strong> the bags by 2 driving<br />

forces, that driven by the free Mn concentration gradient and that driven by the<br />

Mn-PAS or Mn-DACH chelation complex gradients. We also used a spectrophotometric<br />

assay to determine Mn chelating properties <strong>of</strong> PAS. Mn solutions were exposed<br />

to varying concentrations <strong>of</strong> PAS. Free Mn was converted to permanganate.<br />

Levels <strong>of</strong> permanganate were measured spectrophotometrically. Results indicate<br />

PAS is an effective chelator <strong>of</strong> Mn. Increasing concentrations <strong>of</strong> PAS reduced levels<br />

<strong>of</strong> free Mn in solution. This information can be <strong>of</strong> importance with respect to passive<br />

transport mechanisms <strong>of</strong> the blood-brain barrier and can help to clarify the<br />

mechanism <strong>of</strong> action <strong>of</strong> PAS in alleviating the symptoms <strong>of</strong> Manganism.<br />

2592 NEUROIMAGING OF MANGANESE TOXICITY:<br />

THERAPEUTIC EFFECT OF PARA-AMINO SALICYLIC<br />

ACID IN A RAT MODEL.<br />

A. Epur 1, 2 , J. Xu 1, 2 , W. Zheng 1 and U. Dydak 1, 2 . 1 School <strong>of</strong> Health Sciences,<br />

Purdue University, West Lafayette, IN and 2 Department <strong>of</strong> Radiology and Imaging<br />

Sciences, Indiana University School <strong>of</strong> Medicine, Indianapolis, IN.<br />

Excessive exposure to Manganese (Mn) is known to cause parkinsonism. Earlier<br />

studies have shown that para-aminosalicylic acid (PAS) effectively alleviates symptoms<br />

in Mn-induced parkinsonism patients and reduces Mn levels in the rat brain.<br />

To study the underlying mechanism, changes in the neurochemical pr<strong>of</strong>ile <strong>of</strong> the<br />

rat brain with or without PAS treatment after Mn exposure were studied using<br />

magnetic resonance spectroscopy (MRS) at 9.4T. <strong>The</strong> rats (220g at start) were divided<br />

into three groups: Group P (N=8) received 6 weeks <strong>of</strong> ip Mn injections (6 mg<br />

Mn/kg bodyweight, 5 d/wk), followed by 4 weeks <strong>of</strong> sc PAS injections at 200<br />

mg/kg, 7 d/wk. Group M (N=8) also received 6 weeks <strong>of</strong> Mn injections, followed<br />

by 4 weeks <strong>of</strong> saline injections. Group C (controls, N=4) received saline injections<br />

throughout the study. Short echo-time MRS data was acquired in all animals at<br />

baseline, wk 6 and wk 10 in the thalamus, frontal cortex and hippocampus. Our<br />

data showed a significant decrease <strong>of</strong> the antioxidant glutathione (GSH) with Mn<br />

exposure in the thalamus (p

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