Chelation therapy of manganese intoxication with para-aminosalicylic acid (PAS) in Sprague-Dawley rats

Abstract

Para-aminosalicylic acid (PAS), an FDA-approved anti-tuberculosis drug, has been used successfully in the treatment of severe manganese (Mn)-induced Parkinsonism in humans [Jiang Y-M, Mo X-A, Du FQ, Fu X, Zhu X-Y, Gao H-Y, et al. Effective treatment of manganese-induced occupational Parkinsonism with p-aminosalicylic acid: a case of 17-year follow-up study. J Occup Environ Med 2006;48:644-9]. This study was conducted to explore the capability of PAS in reducing Mn concentrations in body fluids and tissues of Mn-exposed animals. Sprague-Dawley rats received daily intraperitoneally (i.p.) injections of 6mg Mn/kg, 5 days/week for 4 weeks, followed by a daily subcutaneously (s.c.) dose of PAS (100 and 200mg/kg as the PAS-L and PAS-H group, respectively) for another 2, 3 or 6 weeks. Mn exposure significantly increased the concentrations of Mn in plasma, red blood cells (RBC), cerebrospinal fluid (CSF), brain and soft tissues. Following PAS-H treatment for 3 weeks, Mn levels in liver, heart, spleen and pancreas were significantly reduced by 25-33%, while 3 weeks of PAS-L treatment did not show any effect. Further therapy with PAS-H for 6 weeks reduced Mn levels in striatum, thalamus, choroid plexus, hippocampus and frontal cortex by 16-29% (p<0.05). Mn exposure greatly increased iron (Fe) and copper (Cu) concentrations in CSF, brain and liver. Treatment with PAS-H restored Fe and Cu levels comparable with control. These data suggest that PAS likely acts as a chelating agent to mobilize and remove tissue Mn. A high-dose and prolonged PAS treatment appears necessary for its therapeutic effectiveness.

Figure 1

% Reduction of Mn concentrations in selected brain regions and RBC following PAS chelation therapy. Sprague-Dawley rats in the Mn-alone group received ip. injections of 6 mg Mn/kg, 5 days/week for 4 weeks, followed by sc. saline for 2, 3, or 6 weeks. Rats in the Mn-PAS groups received ip. injections of 6 mg Mn/kg, 5 days/week for 4 weeks, followed by sc. injections of 200 mg PAS/kg for 2, 3, or 6 weeks. Mn concentrations were determined by AAS (n=5–8 in each group). The values in the Mn-PAS group were compared with those in the Mn-alone group and expressed as % of reduction.

Figure 2

Changes of Mn concentrations in major organs of animals exposed to Mn and treated with PAS. Rats in the control group received daily ip. saline injections throughout the entire experiment. Animals in the Mn-alone group received ip. injections of 6 mg Mn/kg, 5 days/week for 4 weeks, followed by sc. saline for 2, 3, or 6 weeks. Rats in the Mn-PAS groups received ip. injections of 6 mg Mn/kg, 5 days/week for 4 weeks, followed by sc. injection of 200 mg PAS/kg for another 2, 3, or 6 weeks. Data represent mean ± SD, n=6–8.*: p<0.05,**: p<0.01 as compared to the saline group; #: p<0.05, ##: p<0.01 as compared to the Mn-alone group.