Pharmacokinetic, neurochemical, stereological and neuropathological studies on the potential effects of paraquat in the substantia nigra pars compacta and striatum of male C57BL/6J mice

AbstractThe pharmacokinetics and neurotoxicity of paraquat dichloride (PQ) were assessed following once weekly administration to C57BL/6J male mice by intraperitoneal injection for 1, 2 or 3 weeks at doses of 10, 15 or 25mg/kg/week. Approximately 0.3% of the administered dose was taken up by the brain and was slowly eliminated, with a half-life of approximately 3 weeks. PQ did not alter the concentration of dopamine (DA), homovanillic acid (HVA) or 3,4-dihydroxyphenylacetic acid (DOPAC), or increase dopamine turnover in the striatum. There was inconsistent stereological evidence of a loss of DA neurons, as identified by chromogenic or fluorescent-tagged antibodies to tyrosine hydroxylase in the substantia nigra pars compacta (SNpc). There was no evidence that PQ induced neuronal degeneration in the SNpc or degenerating neuronal processes in the striatum, as indicated by the absence of uptake of silver stain or reduced immunolabeling of tyrosine-hydroxylase-positive (TH+) neurons. There was no evidence of apoptotic cell death, which was evaluated using TUNEL or caspase 3 assays. Microglia (IBA-1 immunoreactivity) and astrocytes (GFAP immunoreactivity) were not activated in PQ-treated mice 4, 8, 16, 24, 48, 96 or 168h after 1, 2 or 3 doses of PQ.In contrast, mice dosed with the positive control substance, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 10mg/kg/dose×4 doses, 2h apart), displayed significantly reduced DA and DOPAC concentrations and increased DA turnover in the striatum 7 days after dosing. The number of TH+ neurons in the SNpc was reduced, and there were increased numbers of degenerating neurons and neuronal processes in the SNpc and striatum. MPTP-mediated cell death was not attributed to apoptosis. MPTP activated microglia and astrocytes within 4h of the last dose, reaching a peak within 48h. The microglial response ended by 96h in the SNpc, but the astrocytic response continued through 168h in the striatum.These results bring into question previous published stereological studies that report loss of TH+ neurons in the SNpc of PQ-treated mice. This study also suggests that even if the reduction in TH+ neurons reported by others occurs in PQ-treated mice, this apparent phenotypic change is unaccompanied by neuronal cell death or by modification of dopamine levels in the striatum

International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways.

Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined<5 × 10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist

Inhibition of a calcium-activated, non-selective cation channel, in a rat insulinoma cell line, by adenine derivatives

AbstractThe effects of adenosine and adenine nucleotides on a calcium-activated non-selective cation channel, present in the plasma membrane of an insulin-secreting cell line CRI-G1 were investigated. Single-channel currents were recorded from inside-out membrane patches and the adenine derivatives applied to the solution bathing the cytoplasmic aspect of the membrane surface. The activity of this channel is shown to be inhibited by all the derivatives tested. The potency sequence for inhibition was found to be AMP > ADP > ATP > adenosine

Dietary Administration of Paraquat for 13 Weeks Does Not Result in a Loss of Dopaminergic Neurons in the \u3cem\u3eSubstantia nigra\u3c/em\u3e of C57BL/6J Mice

Several investigations have reported that mice administered paraquat dichloride (PQ·Cl2) by intraperitoneal injection exhibit a loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). In this study, male and female C57BL/6J mice were administered PQ·Cl2 in the diet at concentrations of 0 (control), 10, and 50 ppm for a duration of 13 weeks. A separate group of mice were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) during week 12 as positive controls to produce a loss of dopaminergic neurons in the SNpc. The comparative effects of PQ and MPTP on the SNpc and/or striatum were assessed using neurochemical, neuropathological, and stereological endpoints. Morphological and stereological assessments were performed by investigators ‘blinded’ to the origin of the tissue. Neither dose of PQ·Cl2 (10 or 50 ppm in the diet) caused a loss of striatal dopamine or dopamine metabolite concentrations in the brains of mice. Pathological assessments of the SNpc and striatum showed no evidence of neuronal degeneration or astrocytic/microglial activation. Furthermore, the number of tyrosine hydroxylase-positive (TH+) neurons in the SNpc was not reduced in PQ-treated mice. In contrast, MPTP caused a decrease in striatal dopamine concentration, a reduction in TH+ neurons in the SNpc, and significant pathological changes including astrocytic and microglial activation in the striatum and SNpc. The MPTP-induced effects were greater in males than in females. It is concluded that 13 weeks of continuous dietary exposure of C57BL/6J mice to 50 ppm PQ·Cl2 (equivalent to 10.2 and 15.6 mg PQ ion/kg body weight/day for males and females, respectively) does not result in the loss of, or damage to, dopaminergic neurons in the SNpc

Pathological assessment of SNpc and striatum in PQ- or MPTP-treated mice.

<p>Microscopic appearance of the SNpc (G-L) and striatum (A-F) in control (column 1), PQ- (column 2) or MPTP-treated (column 3) mice, 48 hours after dosing. Tyrosine hydroxylase (TH) immunostaining was decreased in the striatum (C) and SNpc (I) of the MPTP-treated animal but was unchanged in the PQ-treated mouse (B, H) compared to the control (A, G). Amino cupric silver (AmCuAg) staining was used to reveal degenerating neurons in the SNpc (J-L) and degenerating fibers in the striatum (D-F). There were no differences in AmCuAg staining in either the SNpc or striatum after PQ treatment compared to the control (D,J). AmCuAg staining was increased in the SNpc and striatum of the MPTP-treated mouse (F,L). The scale bar shown in Panel L represents 400 μm in panels A-C, G-I and 40 μm in panels D-F and J-L.</p

Mean histopathological severity scores in control, paraquat and MPTP-treated groups of C57BL/6J male mice.

<p>Mice were 16 weeks of age at the time of treatment initiation. Mice were administered 10 mg/kg/dose PQ·Cl₂ by ip injection, twice a week for 3 weeks and were sacrificed 8, 16, 24, 48, 96 or 168 hours after the last dose. Control mice were given the vehicle while MPTP-treated mice received four injections of MPTP (16 mg/kg/dose; expressed as free base) at 2-hour intervals, and then euthanized 48 hours after the final dose. Serial sections through the SNpc were evaluated qualitatively and the group mean severity grades are plotted. Grades 0 to 5 reflect increasing intensity of staining for Iba-1, AmCuGg, GFAP and decreased staining intensity of TH.</p