Sodium para-aminosalicylate protected cultured basal ganglia astrocytes from manganese-induced DNA damages and alteration of amino acid neurotransmitter levels

Therapeutic Effects of Sodium Para-Aminosalicylic Acid on Cognitive Deficits and Activated ERK1/2-p90RSK/NF-κB Inflammatory Pathway in Pb-Exposed Rats

Lead (Pb) is a toxic heavy metal and environmental pollutant that adversely affects the nervous system. However, effective therapeutic drugs for Pb-induced neurotoxicity have yet to be developed. In the present study, we investigated the ameliorative effect of sodium para-aminosalicylic acid (PAS-Na) on Pb-induced neurotoxicity. Male Sprague-Dawley rats were treated with (CH₃COO)₂ Pb•4H₂O (6 mg/kg) for 4 weeks, followed by 3 weeks of PAS-Na (100, 200, and 300 mg/kg). The results showed that subacute Pb exposure significantly decreased rats body-weight gains and increased liver coefficient, and impaired spatial learning and memory. HE staining showed that Pb damaged the structure of the hippocampus. Moreover, Pb activated the ERK1/2-p90^RSK/ NF-κB pathway concomitant with increased inflammatory cytokine IL-1β levels in rat hippocampus. PAS-Na reversed the Pb-induced increase in the liver coefficient as well as the learning and memory deficits. In addition, PAS-Na reduced the phosphorylation of ERK1/2, p90^RSK and NF-κB p65, decreasing IL-1β levels in hippocampus. Our findings indicated that PAS-Na showed efficacy in reversing Pb-induced rats cognitive deficits and triggered an anti-inflammatory response. Thus, PAS-Na may be a promising therapy for treating Pb-induced neurotoxicity.

Sodium Para-aminosalicylic Acid Reverses Changes of Glutamate Turnover in Manganese-Exposed Rats

Sodium para-aminosalicylic acid (PAS-Na) has been used to treat patients with manganism, a neurological disease caused by manganese (Mn) toxicity, although the exact molecular mechanisms are yet unclear. The present study aims to investigate the effect of PAS-Na on glutamate (Glu) turnover of Mn-exposed rats. The results showed that Mn concentrations in the hippocampus, thalamus, striatum, and globus pallidus were increased in Mn-exposed rats. Moreover, the results also demonstrated that subacute Mn exposure (15 mg/kg for 4 weeks) interrupted the homeostasis of Glu by increasing Glu levels but decreasing glutamine (Gln) levels in the hippocampus, thalamus, striatum, and globus pallidus in male Sprague-Dawley rats. These effects lasted even after Mn exposure had been ceased for a period of 6 weeks. Meanwhile the main Glu turnover enzymes [Gln synthetase (GS) and phosphate-activated glutaminase (PAG)] and transporters [Glu/aspartate transporter (GLAST) and Glu transporter-1 (GLT-1)] were also affected by Mn treatment. Additionally, PAS-Na treatment recovered the aforementioned changes induced by Mn. Taken together, these results indicate that Glu turnover might be involved in Mn-induced neurotoxicity. PAS-Na treatment could promote Mn excretions and recover the changes in Glu turnover induced by Mn, and a prolonged PAS-Na treatment may be more effective.

Secretogranin III upregulation is involved in parkinsonian toxin-mediated astroglia activation

Environmental neurotoxins such as paraquat (PQ), manganese, and 1-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are associated with a higher risk of Parkinson's disease (PD). These parkinsonian toxins exert certain common toxicological effects on astroglia; however, their role in the regulatory functions of astroglial secretory proteins remains unclear. In a previous study, we observed that secretogranin II (SCG2) and secretogranin III (SCG3), which are important components of the regulated secretory pathway, were elevated in PQ-activated U118 astroglia. In the current study, we used the parkinsonian toxins dopamine (DA), active metabolite of MPTP (MPP⁺), MnCl₂, and lipopolysaccharide (LPS) as inducers, and studied the potential regulation of SCG2 and SCG3. Our results showed that all the parkinsonian toxins except LPS affected astroglial viability but did not cause apoptosis. Exposure to DA, MPP⁺, and MnCl₂ upregulated glial fibrillary acidic protein (GFAP), a marker for astrocyte activation, and stimulated the levels of several astrocytic-derived factors. Further, DA, MPP⁺, and MnCl₂ exposure impeded astroglial cell cycle progression. Moreover, the expression of SCG3 was elevated, while its exosecretion was inhibited in astroglia activated by parkinsonian toxins. The level of SCG2 remained unchanged. In combination with our previous findings, the results of this study indicate that SCG3 may act as a cofactor in astrocyte activation stimulated by various toxins, and the regulation of SCG3 could be involved in the toxicological mechanism by which parkinsonian toxins affect astroglia.

Preventive impacts of PAS-Na on the slow growth and activated inflammatory responses in Mn-exposed rats

BACKGROUND

Sodium para-aminosalicylic acid (PAS-Na), an anti-tuberculosis drug, has been demonstrated its function in facilitating the Mn elimination in manganism patients and Mn-exposed models in vivo and improving the symptoms of Mn poisoning. But whether it can improve the growth retardation and inflammatory responses induced by Mn have not been reported.

OBJECTIVES

This study was designed to investigate the preventive effects of PAS-Na on the development of retardation and inflammatory responses in Mn-exposed rats.

METHODS

Male Sprague Dawley (SD) rats (8 weeks old, weighing 180 ± 20 g) were randomly divided into normal control group and Mn-exposed group in the 4 weeks experiment observation and normal control group, Mn-exposed group, PAS-Na preventive group and PAS-Na control group in the 8 weeks experiment observation. The Mn-exposed group received an intraperitoneal injection (i.p.) of 15 mg/kg MnCl₂ and the normal control group i.p. physiological Saline in the same volume once a day for 4 or 8 weeks, 5 days per week. The PAS-Na preventive group i.p. 15 mg/kg MnCl₂ along with back subcutaneous (s.c.) injection of 240 mg/kg PAS-Na once a day for 8 weeks, 5 days per week. PAS-Na control group received s.c. injection of 240 mg/kg PAS-Na along with i.p. injection of saline once daily. The body weight was determined once a week until the end of the experiment. The manganese contents in the blood were detected by graphite furnace atomic absorption spectrometry. The inflammatory factor levels (TNF-α, IL-1β, IL-6, and PGE2) in the blood were detected by using enzyme-linked immunosorbent assay (Elisa) and each organ taking from rats were weighed and recorded.

RESULTS

Mn exposure significantly suppressed the growth in rats and increased heart, liver, spleen and kidney coefficients as compared with the control group. The whole blood Mn level and serum levels of IL-1β, IL-6, PGE2, and TNF-α in sub-chronic Mn-exposure group were markedly higher than those in the control group. However, preventive treatment with PAS-Na obviously reduced the whole blood Mn level, the spleen and liver coefficients of the Mn-exposed rats. And serum levels of IL-1β and TNF-α were significantly reduced by 33.9% and 14.7% respectively in PAS-Na prevention group.

CONCLUSIONS

PAS-Na could improve the growth retardation and alleviate inflammatory responses in Mn-exposed rats.

Sodium p-Aminosalicylic Acid Reverses Sub-Chronic Manganese-Induced Impairments of Spatial Learning and Memory Abilities in Rats, but Fails to Restore γ-Aminobutyric Acid Levels

Excessive manganese (Mn) exposure is not only a health risk for occupational workers, but also for the general population. Sodium para-aminosalicylic acid (PAS-Na) has been successfully used in the treatment of manganism, but the involved molecular mechanisms have yet to be determined. The present study aimed to investigate the effects of PAS-Na on sub-chronic Mn exposure-induced impairments of spatial learning and memory, and determine the possible involvements of γ-aminobutyric acid (GABA) metabolism in vivo. Sprague-Dawley male rats received daily intraperitoneal injections MnCl₂ (as 6.55 mg/kg Mn body weight, five days per week for 12 weeks), followed by daily subcutaneous injections of 100, 200, or 300 mg/kg PAS-Na for an additional six weeks. Mn exposure significantly impaired spatial learning and memory ability, as noted in the Morris water maze test, and the following PAS-Na treatment successfully restored these adverse effects to levels indistinguishable from controls. Unexpectedly, PAS-Na failed to recover the Mn-induced decrease in the overall GABA levels, although PAS-Na treatment reversed Mn-induced alterations in the enzyme activities directly responsible for the synthesis and degradation of GABA (glutamate decarboxylase and GABA-transaminase, respectively). Moreover, Mn exposure caused an increase of GABA transporter 1 (GAT-1) and decrease of GABA A receptor (GABA_A) in transcriptional levels, which could be reverted by the highest dose of 300 mg/kg PAS-Na treatment. In conclusion, the GABA metabolism was interrupted by sub-chronic Mn exposure. However, the PAS-Na treatment mediated protection from sub-chronic Mn exposure-induced neurotoxicity, which may not be dependent on the GABA metabolism.