Effects of Sub-Acute Manganese Exposure on Thyroid Hormone and Glutamine (Gln)/Glutamate (Glu)-γ- Aminobutyric Acid (GABA) Cycle in Serum of Rats.

Excessive manganese (Mn) exposure may adversely affect the central nervous system, and cause an extrapyramidal disorder known as manganism. The glutamine (Gln)/glutamate (Glu)-γ-aminobutyric acid (GABA) cycle and thyroid hormone system may be involved in Mn-induced neurotoxicity. However, the effect of Mn on the Gln/Glu-GABA cycle in the serum has not been reported. Herein, the present study aimed to investigate the effects of sub-acute Mn exposure on the Gln/Glu-GABA cycle and thyroid hormones levels in the serum of rats, as well as their relationship. The results showed that sub-acute Mn exposure increased serum Mn levels with a correlation coefficient of 0.733. Furthermore, interruption of the Glu/Gln-GABA cycle in serum was found in Mn-exposed rats, as well as thyroid hormone disorder in the serum via increasing serum Glu levels, and decreasing serum Gln, GABA, triiodothyronine (T3) and thyroxine (T4) levels. Additionally, results of partial correlation showed that there was a close relationship between serum Mn levels and the detected indicators accompanied with a positive association between GABA and T3 levels, as well as Gln and T4 levels in the serum of Mn-exposed rats. Unexpectedly, there was no significant correlation between serum Glu and the serum T3 and T4 levels. In conclusion, the results demonstrated that both the Glu/Gln-GABA cycle and thyroid hormone system in the serum may play a potential role in Mn-induced neurotoxicity in rats. Thyroid hormone levels, T3 and T4, have a closer relationship with GABA and Gln levels, respectively, in the serum of 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 (GABAA) 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.

Sodium P-Aminosalicylic Acid Improved Manganese-Induced Learning and Memory Dysfunction via Restoring the Ultrastructural Alterations and γ-Aminobutyric Acid Metabolism Imbalance in the Basal Ganglia.

Excessive intake of manganese (Mn) may cause neurotoxicity. Sodium para-aminosalicylic acid (PAS-Na) has been used successfully in the treatment of Mn-induced neurotoxicity. The γ-aminobutyric acid (GABA) is related with learning and memory abilities. However, the mechanism of PAS-Na on improving Mn-induced behavioral deficits is unclear. The current study was aimed to investigate the effects of PAS-Na on Mn-induced behavioral deficits and the involvement of ultrastructural alterations and γ-aminobutyric acid (GABA) metabolism in the basal ganglia of rats. Sprague-Dawley rats received daily intraperitoneally injections of 15 mg/kg MnCl2.4H2O, 5d/week for 4 weeks, followed by a daily back subcutaneously (sc.) dose of PAS-Na (100 and 200 mg/kg), 5 days/week for another 3 or 6 weeks. Mn exposure for 4 weeks and then ceased Mn exposure for 3 or 6 weeks impaired spatial learning and memory abilities, and these effects were long-lasting. Moreover, Mn exposure caused ultrastructural alterations in the basal ganglia expressed as swollen neuronal with increasing the electron density in the protrusions structure and fuzzed the interval of neuropil, together with swollen, focal hyperplasia, and hypertrophy of astrocytes. Additionally, the results also indicated that Mn exposure increased Glu/GABA values as by feedback loops controlling GAT-1, GABAA mRNA and GABAA protein expression through decreasing GABA transporter 1(GAT-1) and GABA A receptor (GABAA) mRNA expression, and increasing GABAA protein expression in the basal ganglia. But Mn exposure had no effects on GAT-1 protein expression. PAS-Na treatment for 3 or 6 weeks effectively restored the above-mentioned adverse effects induced by Mn. In conclusion, these findings suggest the involvement of GABA metabolism and ultrastructural alterations of basal ganglia in PAS-Na's protective effects on the spatial learning and memory abilities.

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

Sodium para-aminosalicylate (PAS-Na) was first applied successfully in clinical treatment of two manganism patients with good prognosis. However, the mechanism of how PAS-Na protects against Mn-induced neurotoxicity is still elusive. The current study was conducted to explore the effects of PAS-Na on Mn-induced basal ganglia astrocyte injury, and the involvement of amino acid neurotransmitter in vitro. Basal ganglia astrocytes were exposed to 500 µM manganese chloride (MnCl2) for 24 hr, following by 50, 150, or 450 µM PAS-Na treatment for another 24 hr. MnCl2 significantly decreased viability of astrocytes and induced DNA damages via increasing the percentage of tail DNA and Olive tail moment of DNA. Moreover, Mn interrupted amino acid neurotransmitters by decreasing Gln levels and increasing Glu, Gly levels. In contrast, PAS-Na treatment reversed the aforementioned Mn-induced toxic effects on basal ganglia astrocytes. Taken together, our results demonstrated that excessive Mn exposure may induce toxic effects on basal ganglia astrocytes, while PAS-Na could protect basal ganglia astrocytes from Mn-induced neurotoxicity.

Sodium Para-aminosalicylic Acid Protected Primary Cultured Basal Ganglia Neurons of Rat from Manganese-Induced Oxidative Impairment and Changes of Amino Acid Neurotransmitters.

Manganese (Mn), an essential trace metal for protein synthesis and particularly neurotransmitter metabolism, preferentially accumulates in basal ganglia. However, excessive Mn accumulation may cause neurotoxicity referred to as manganism. Sodium para-aminosalicylic acid (PAS-Na) has been used to treat manganism with unclear molecular mechanisms. Thus, we aim to explore whether PAS-Na can inhibit Mn-induced neuronal injury in basal ganglia in vitro. We exposed basal ganglia neurons with 50 µM manganese chloride (MnCl2) for 24 h and then replaced with 50, 150, and 450 µM PAS-Na treatment for another 24 h. MnCl2 significantly decreased cell viability but increased leakage rate of lactate dehydrogenase and DNA damage (as shown by increasing percentage of DNA tail and Olive tail moment). Mechanically, Mn reduced glutathione peroxidase and catalase activity and interrupted amino acid neurotransmitter balance. However, PAS-Na treatment reversed the aforementioned Mn-induced toxic effects. Taken together, these results showed that PAS-Na could protect basal ganglia neurons from Mn-induced neurotoxicity.

[Effect of sodium para-aminosalicylic on concentrations of amino acid neurotransmitters in basal ganglia of manganese-exposed rats].

OBJECTIVE: To probe the effect of sodium para-aminosalicylate (PAS-Na) on concentration of amino acid neurotransmitters including glutamate (Glu), glutamine (Gln), glycine (Gly) and gamma-aminobutyric acid (GABA) in basal ganglia of subacute manganese (Mn)-exposed rats. METHODS: Forty Sprague-Dawley male rats were randomly divided into the control, Mn-exposed, low dose PAS-Na (L-PAS) and high dose PAS-Na (H-PAS) groups. Rats in experiment groups received daily intraperitoneally injections of manganese chloride (MnCl2 · 4H2O, 15 mg/kg), while rats in control group received daily intraperitoneally injections of normal saline (NS), all at 5 days/week for 4 weeks. Then the rats in PAS groups followed by a daily subcutaneously dose of PAS-Na (100 and 200 mg/kg as the L-PAS and H-PAS groups, respectively) for another 3 and 6 weeks; while the rats in Mn-exposed and control group received NS. The concentrations of Glu, Gln, Gly and GABA in basal ganglia of rat was detected by the high performance liquid chromatography fluorescence detection technique. RESULTS: After treating with PAS-Na for 3 weeks, the concentration of Gly in the Mn-exposed rats decreased to (0.165 ± 0.022) µmol/L (control = (0.271 ± 0.074) µmol/L, Mn vs control, t = 4.65, P < 0.05). After the further 6-week therapy with PAS-Na, the concentrations of Glu, Gln, Gly in the Mn-exposed rats were lower than those of the control rats ((0.942 ± 0.121), (0.377 ± 0.070), (0.142 ± 0.048), (1.590 ± 0.302), (0.563 ± 0.040), (0.247 ± 0.084) µmol/L; t = 7.72, 5.85, 4.30, P < 0.05); and also lower than in L-PAS and H-PAS groups, whose concentrations were separately (1.268 ± 0.124), (1.465 ± 0.196), (0.497 ± 0.050), (0.514 ± 0.103), (0.219 ± 0.034) µmol/L (L-PAS Glu and Gln vs Mn, t = 3.87, 3.77, P < 0.05; H-PAS Glu, Gln and Gly vs Mn, t = 6.78, 4.70, 3.42, P < 0.05). CONCLUSION: The toxic effect of manganese on Glu, Gln and Gly in basal ganglia of Mn-exposed rats is obvious, especially appears earlier on Gly. The toxic effect still continues to develop when relieved from the exposure. PAS-Na may play an antagonism role in toxic effect of manganese on concentration of Glu, Gln and Gly in basal ganglia of Mn-exposed rats.

[Application of multi-coeffieient of variation significance test for toxicology study].

OBJECTIVE: To establish the methods of calculating and analyzing the multi-coefficient of variation significance test for the toxicology study. METHODS: The paper aimed to confirm the significance level with the method of Bonferroni and then compared the methods of calculating and analyzing of the experiment groups with the control group respectively. RESULTS: The significance level of multi-coefficient of variation significance test was confirmed as alpha1=0.0167. Compared with the control groups, the activity of ALT in serum both in 30 mg/kg and 60 mg/kg groups did not change in the average significance test, which was not statistically significant (P>0.05), while it changed in the variation significance test, which was of statistical significance (P<0.0167). The activity of AST in serum in 60 mg/kg group did not change in the average significance test (P>0.05), while it changed in the variation significance test (P<0.0167). CONCLUSION: The complete changes of the indexes can only be shown by use of both the average significance test and the variation significance test together.