1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) affects the actin cytoskeleton and calcium level of Swiss 3T3 mouse fibroblasts

Effects of Sub-Chronic MPTP Exposure on Behavioral and Cognitive Performance and the Microbiome of Wild-Type and mGlu8 Knockout Female and Male Mice

Motor dysfunction is a hallmark of Parkinson's disease (PD); however, non-motor symptoms such as gastrointestinal dysfunction often arise prior to motor symptoms. Alterations in the gut microbiome have been proposed as the earliest event in PD pathogenesis. PD symptoms often demonstrate sex differences. Glutamatergic neurotransmission has long been linked to PD pathology. Metabotropic glutamate receptors (mGlu), a family of G protein-coupled receptors, are divided into three groups, with group III mGlu receptors mainly localized presynaptically where they can inhibit glutamate release in the CNS as well as in the gut. Additionally, the gut microbiome can communicate with the CNS via the gut-brain axis. Here, we assessed whether deficiency of metabotropic glutamate receptor 8 (mGlu8), group III mGlu, modulates the effects of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on behavioral and cognitive performance in female and male mice. We studied whether these effects are associated with changes in striatal tyrosine hydroxylase (TH) levels and the gut microbiome. Two-week sub-chronic MPTP increased activity of female and male wild-type (WT) and mGlu8 knockout (KO) mice in the open field. MPTP also showed genotype- and sex-dependent effects. MPTP increased the time WT, but not KO, females and males spent exploring objects. In WT mice, MPTP improved sensorimotor function in males but impaired it in females. Further, MPTP impaired cued fear memory in WT, but not KO, male mice. MPTP reduced striatal TH levels in WT and KO mice but these effects were only pronounced in males. MPTP treatment and genotype affected the diversity of the gut microbiome. In addition, there were significant associations between microbiome α-diversity and sensorimotor performance, as well as microbiome composition and fear learning. These results indicate that specific taxa may directly affect motor and fear learning or that the same physiological effects that enhance both forms of learning also alter diversity of the gut microbiome. MPTP's effect on motor and cognitive performance may then be, at least in part, be mediated by the gut microbiome. These data also support mGlu8 as a novel therapeutic target for PD and highlight the importance of including both sexes in preclinical studies.

Inhibitory effects of β-tricalciumphosphate wear particles on osteocytes via apoptotic response and Akt inactivation

Wear debris-induced osteolysis, a major contributing factor of orthopedic implant aseptic loosening, affects long-term survival of orthopedic prostheses following joint replacement and revision surgery. Pathogenic effects of wear debris on various cell types including macrophages/monocytes, osteoblasts, and osteoclasts have been well studied. However, the interactions between wear debris particles and osteocytes, which make up over 90% of all bone cells, have not been clearly illustrated. Here, we explored the biological effects of endotoxin-free beta-tricalciumphosphate (β-TCP) wear particles with the average diameter of 1.997 μm (range 1.3-3.2 μm) on osteocytes in vitro. Our results showed that 24 h or 48 h incubation of β-TCP particles dose-dependently inhibited cell viability of osteocytes MLO-Y4. Alternatively, β-TCP particles treatment for 24 h significantly increased the osteocytic marker SOST/sclerostin mRNA expression and the release of inflammatory cytokines including TNF-α and IL-1β into the culture media, but decreased the mRNA expression of another osteocytic marker dentin matrix protein-1 (DMP-1). Furthermore, these osteocytes dysfunctions were accompanied by F-actin disassembly, cell apoptosis, sustained enhancement of intracellular reactive oxygen species (ROS) and mitochondrial injury upon β-TCP particles stimulation. In addition, β-TCP particles also caused Akt inactivation at Ser473 resides with a dose- and time-dependent pattern. Taken together, β-TCP wear particles could cause osteocytes dysfunctions, which may be mediated by apoptotic death and Akt inactivation in MLO-Y4 cells. These findings strongly suggest that osteocytes may play an important role in the β-TCP wear particles-induced osteolysis, and provide valuable insights for understanding the molecular mechanisms of osteocytes death involved in tissue damage during bone cement and intolerance of cemented prostheses.

Inhibition of platelet aggregation by 1-methyl-4-phenyl pyridinium ion (MPP+) through ATP depletion: Evidence for the reduced platelet activities in Parkinson's disease

Neuronal accumulation of 1-methyl-4-phenylpyridinium ion (MPP(+)), the metabolite of neural toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine (MPTP), induces a rapid depletion of cellular ATP level and loss of neuronal cell viability which simulates human Parkinson's disease (PD). Since ATP plays an important role in the physiology and function of platelets, which share many biochemical and physiological features with neuronal cells, we examined the effect of MPP(+) on platelet aggregation and viability using freshly isolated rat platelets. While the treatment of MPP(+) to platelets did not induce cytotoxicity, it significantly attenuated agonist-induced platelet aggregation in a concentration dependent manner. The inhibition of aggregation by MPP(+) was mediated by the depletion of the cytoplasmic ATP pool and resultant decreased ATP secretion. Different from the previous reports in neuronal cells, MPP(+) did not affect intracellular levels of glutathione and cytoplasmic Ca(2+) in platelets. The combined treatment with MPP(+) and 2-deoxyglucose, a glycolysis inhibitor, showed the additive effect in the decrease of ATP secretion and intracellular content. Consistent with these findings, inhibitory effects of MPP(+) on platelet aggregation was significantly enhanced by the treatment with 2-deoxyglucose. In conclusion, these results suggested that MPP(+) can induce ATP depletion in platelets and attenuate platelet aggregation providing a new theory on the reduced platelet activities in PD patients.

The role of tissue transglutaminase in 1-methyl-4-phenylpyridinium (MPP+)-induced toxicity in differentiated human SH-SY5Y neuroblastoma cells

Tissue transglutaminase (TG2) can induce post-translational modification of proteins, resulting in protein cross-linking or incorporation of polyamines into substrates, and can also function as a signal transducing G protein. The role of TG2 in the formation of insoluble cross-links has led to its implication in some neurodegenerative conditions. Exposure of pre-differentiated SH-SY5Y cells to the Parkinsonian neurotoxin 1-methyl-4-phenylpyridinium ion (MPP(+)) resulted in significant dose-dependent reductions in TG2 protein levels, measured by probing Western blots with a TG2-specific antibody. Transglutaminase (TG) transamidating activity, on the other hand, monitored by incorporation of a polyamine pseudo-substrate into cellular proteins, was increased. Inhibitors of TG (putrescine) and TG2 (R283) exacerbated MPP(+) toxicity, suggesting that activation of TG2 may promote a survival response in this toxicity paradigm.

Classifying structural alterations of the cytoskeleton by spectrum enhancement and descriptor fusion

A classifier capable of ranking structural alterations of the cytoskeleton is developed. Images of cytoskeletal microtubules obtained from the epifluorescence microscopy of primary culture rat hepatocytes are analyzed. Morphological descriptors are extracted by contour and mass fractal analysis, direct methods, and spectrum enhancement. All methods are designed and tuned to make the extracted morphological descriptors insensitive to absolute fluorescence intensities. Spectrum enhancement is a nonlinear filter that involves spatial differentiation of the gray-scale image followed by conversion of power spectral density to the logarithmic scale and averaging over arcs in the reciprocal domain. Enhanced spectra exhibit local maxima that correspond to the structured microtubule bundles of a normal cytoskeleton. Descriptor fusion for classification is achieved by means of multivariate analysis. The classifier is trained by image sets representing normal ("negative control") microtubules and those altered by exposure to a fungicide at the highest dose of the experiment design. Some sensitivity and validation tests, including discriminant functions analysis, are applied to the classifier. The latter is applied to recognize images of microtubules not used in the training stage and comes from treatments at lower concentrations and shorter times. As a result, structural alterations are ranked and structural recovery after treatment is quantified. The method has potential use in quantitative, morphology-based tests on the cytoskeleton treated either by anticancer drugs or by cytotoxic agents.

Quantitative kinetics of damage and recovery of cytoskeletal structure by means of image analysis

The cytoskeleton is a network of proteins which structurally and dynamically organise the cytoplasm of living cells. Microtubules are among its constituents. Morphological alterations of microtubules are related to functional impairment. Therefore cytoskeletal morphology is a valuable indicator of cell injury and functionality. This paper focuses on the comparison between normal and altered cytoskeletal microtubules by means of image analysis and classification with the aim of replacing visual assessment. Morphology has been quantified by the extraction of some descriptors yielded by spatial differentiation, fractal analysis and Fourier analysis followed by non-linear filtering. The principal component analysis of these descriptors has led to image recognition and has been applied to hepatocytes and fibroblasts exposed to some xenobiotics. In the case of hepatocytes, images have been ranked according to the severity of cytoskeletal damage, a dose-response relation has been derived from the regression of the first principal component and the percentage of structural recovery after exposure has been estimated.

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on differentiating mouse N2a neuroblastoma cells

The effect of the neurotoxin 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) was investigated in mouse N2a neuroblastoma cells, induced to differentiate by serum withdrawal and addition of dibutyryl cyclic AMP, over a 24-h period. Addition of MPTP (10 microM) during differentiation caused a change in cell morphology characterised by an inhibition of axon outgrowth, in the absence of cell death. Biochemical characterisation by western blotting revealed that MPTP had no significant effects on the levels of actin, alpha-tubulin, or total heavy-chain neurofilament (NF-H). However, NF-H phosphorylation appeared to increase following MPTP treatment when blots were probed with the phosphorylation state-specific antibodies RMd09 and Ta51. In addition, indirect immunofluorescence analysis revealed an accumulation of phosphorylated NF-H in the cell perikaryon, suggesting that altered NF-H distribution was associated with the observed effects of MPTP on cell morphology. These changes may represent a useful in vitro marker of MPTP neurotoxicity within a simple differentiating neuronal cell model system.

Characterization of MPP(+)-induced cell death in a dopaminergic neuronal cell line: role of macromolecule synthesis, cytosolic calcium, caspase, and Bcl-2-related proteins

To further characterize MPP(+)-induced cell death and to explore the role of Bcl-2-related proteins in this death paradigm, we utilized a mesencephalon-derived dopaminergic neuronal cell line (MN9D) stably transfected with human bcl-2 (MN9D/Bcl-2), its C-terminal deletion mutant (MN9D/Bcl-2Delta22), murine bax (MN9D/Bax), or a control vector (MN9D/Neo). As determined by electron microscopy and TUNEL assay, MN9D/Neo cells exposed to MPP(+) underwent a cell death that was characterized by mitochondrial swelling and irregularly scattered heterochromatin without accompanying DNA fragmentation. However, cell swelling typically seen in necrosis did not appear. To examine the biochemical events associated with MPP(+)-induced cell death, various analyses were conducted. Addition of a broad-spectrum caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (50-400 microM) or Boc-aspartyl(OMe)-fluoromethylketone (50-200 microM) did not attenuate MPP(+)-induced cell death while the same treatment protected MN9D/Neo cells against staurosporine-induced apoptotic cell death. Concurrent treatment with an inhibitor of macromolecule synthesis such as cycloheximide, emetine, or actinomycin D blocked MPP(+)-induced cell death, suggesting that new protein synthesis is required as demonstrated in many apoptotic cell death. The level of cytosolic calcium in MN9D/Neo cells was unchanged over 24 h following MPP(+) treatment, as monitored by means of the fluorescent probe Fura-2. Western blot analysis indicated that expression level of proapoptotic protein, Bax was not significantly altered after MPP(+) treatment. In this death paradigm, overexpression of Bcl-2 but not its C-terminal deletion mutant attenuated MPP(+)-induced cell death whereas overexpression of Bax had no effect. Taken together, these data indicate that (i) MPP(+) induces a distinct form of cell death which resembles both apoptosis and necrosis; and (ii) full-length Bcl-2 counters MPP(+)-induced morphological changes and cell death via a mechanism that is dependent on de novo protein synthesis but independent of cytosolic calcium changes, Bax expression, and/or activation of caspase(s) in MN9D cells.

Molecular approaches to evaluate pollutants

Many organisms are in use to test pollutants and their extensive variability clearly emerges from reviews since researchers in the world are involved in continuous effort to set up new assays and to improve those already in use. In the present paper we focus the attention on the mixed function oxidase system and the DNA adduct formation which are two biomarkers widely used and extensively studied in mammals and fish by different Authors. We compare their results with the ones we obtained in amphibians, which result to be a good model. Moreover we present some significative results obtained by the use of cultured cell lines to test the herbicide MCPA. The results obtained demonstrate that the amphibian Xenopus is a suitable indicator for induction of cytochrome P-450 by B[a]P as well as for production of DNA adducts. Cultured cells evidenced that cytoskeletal array and thiol proteins are molecular targets of the herbicide used, demonstrating that risk assessment can be properly analysed in in vitro systems.

MPTP produces differential oxidative stress and antioxidative responses in the nigrostriatal and mesolimbic dopaminergic pathways

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to produce a differential toxicity in the nigrostriatal and mesolimbic dopaminergic pathways with the nigrostriatal pathway being more vulnerable. We, therefore, investigated whether oxidative stress and the antioxidant system play a role in this phenomenon. Balb/c mice were treated with either saline or MPTP (30 mg/kg/d) for 7 d, and were sacrificed on the next day. Results revealed that MPTP increased lipid peroxidation in the striatum (ST) and decreased glutathione concentration in the substantia nigra (SN) without markedly affecting these measures in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Further, MPTP produced approximately twofold increases in both manganese superoxide dismutase (MnSOD) and copper-zinc superoxide dismutase (CuZnSOD) activities in the VTA while it only increased MnSOD activity in the SN. Both catalase and glutathione peroxidase (GPx) activities were not markedly altered by MPTP in both systems. However, the basal levels of catalase and GPx activities were higher in the VTA and NAc than in the SN and ST. These results together suggest that a lesser degree of oxidative damage and a more inducible CuZnSOD activity observed in the mesolimbic dopaminergic pathway may partially explain the differential toxicity MPTP produced in these two dopaminergic systems.

Benomyl affects the microtubule cytoskeleton and the glutathione level of mammalian primary cultured hepatocytes

Rat primary hepatocyte cultures have been used to study the effect of Benomyl alone or in combination with Pirimiphos-methyl. The results presented demonstrate that Benomyl alone is responsible for the microtubular disorganization in both a time- and dose-dependent manner, that the effect is reversible after the agent is removed, and that Benomyl is a potent glutathione-depleting agent. Pirimiphos-methyl, alone or combined with Benomyl had no effect on microtubule organization, but reinforced the decrease in glutathione.