Minocycline diminishes the rotenone induced neurotoxicity and glial activation via suppression of apoptosis, nitrite levels and oxidative stress

A Novel NOX Inhibitor Alleviates Parkinson's Disease Pathology in PFF-Injected Mice

Oxidative stress-mediated damage is often a downstream result of Parkinson's disease (PD), which is marked by sharp decline in dopaminergic neurons within the nigrostriatal regions of the brain, accounting for the symptomatic motor deficits in patients. Regulating the level of oxidative stress may present a beneficial approach in preventing PD pathology. Here, we assessed the efficacy of a nicotinamide adenine phosphate (NADPH) oxidase (NOX) inhibitor, an exogenous reactive oxygen species (ROS) regulator synthesized by Aptabio therapeutics with the specificity to NOX-1, 2 and 4. Utilizing N27 rat dopaminergic cells and C57Bl/6 mice, we confirmed that the exposures of alpha-synuclein preformed fibrils (PFF) induced protein aggregation, a hallmark in PD pathology. In vitro assessment of the novel compound revealed an increase in cell viability and decreases in cytotoxicity, ROS, and protein aggregation (Thioflavin-T stain) against PFF exposure at the optimal concentration of 10 nM. Concomitantly, the oral treatment alleviated motor-deficits in behavioral tests, such as hindlimb clasping, rotarod, pole, nesting and grooming test, via reducing protein aggregation, based on rescued dopaminergic neuronal loss. The suppression of NOX-1, 2 and 4 within the striatum and ventral midbrain regions including Substantia Nigra compacta (SNc) contributed to neuroprotective/recovery effects, making it a potential therapeutic option for PD.

Minocycline as a Neuroprotective Agent in Arsenic-Induced Neurotoxicity in PC12 Cells

Arsenic is a naturally occurring metalloid that exists in water, soil, food, and air. Humans can be exposed to arsenic through occupational, medical, or nutritional routes. Both acute and chronic forms of toxicity with severe outcomes are likely following arsenic exposure. Neurotoxicity is one of the serious manifestations of arsenic toxicity. In our study, the effect of minocycline, a widely used antimicrobial agent with antioxidant aspects and the ability to cross the blood-brain barrier, was evaluated against arsenic-induced neurotoxicity. PC12 cell line was used as the cellular model of this study. Cells were pre-treated with minocycline (50 nM-1 µM) for 2 h, and then incubated for 24 h after adding sodium arsenite (10 µM). The MTT assay and fluorimetry were performed to study cytotoxicity and reactive oxygen species generation, respectively. Finally, Western blotting was done to determine the levels of caspase-8, Bax, Bcl-2, and caspase-3. Once exposed to arsenic, the cell viability was significantly reduced, the intracellular oxidative balance was significantly disrupted, and the levels of proteins caspase-8, Bax/Bcl-2, and caspase-3 were significantly increased. Minocycline not only attenuated arsenic-induced cytotoxicity and reduced oxidative stress, but also led to lower levels of caspase-8, Bax/Bcl-2, and caspase-3 proteins compared with the arsenic-treated cells. Minocycline can significantly protect cells against arsenic-induced neurotoxicity by antioxidant and anti-apoptosis properties via both intrinsic and extrinsic caspase-dependent apoptotic pathways; therefore, at this point, it's worth considering it as a promising agent for the treatment of arsenic toxicity.

Minocycline Protects PC12 Cells Against Cadmium-Induced Neurotoxicity by Modulating Apoptosis

Cadmium (Cd) is a well-known heavy metal and a neurotoxic agent. Minocycline (Mino) is an anti-microbial agent with a lipophilic structure that crosses the blood-brain barrier and enters the cerebral tissue. In recent studies, Mino has been introduced as an antioxidant and anti-apoptotic chemical compound, and therefore, it was examined as a protective candidate against Cd-induced neurotoxicity. In this study, PC12 cells were exposed to Cd alone, or after being pre-treated with Mino. Initially, the cell viability and oxidative stress were analyzed using the MTT assay and fluorimetry, respectively. Then, Cd-induced apoptosis and Mino anti-apoptotic effect were evaluated in both intrinsic and extrinsic pathways using western blot analysis. Exposing PC12 cells to Cd for 24 h decreased cell viability and increased production of reactive oxygen species in comparison with the control group. Cd (35 μM) also elevated the level of caspase-8, Bax/Bcl-2, and caspase-3 proteins in the cells. Mino pre-treatment for 2 h (100 nM) increased the number of viable cells and decreased the production of reactive oxygen species, and the level of all apoptotic markers in comparison to Cd-treated cells. Considering all the evidence, it appears that Mino holds promising antioxidant and anti-apoptotic activity and can protect cells against Cd-induced oxidative stress and prevent apoptotic cell death.

Minocycline attenuates cholinergic dysfunction and neuro-inflammation-mediated cognitive impairment in scopolamine-induced Alzheimer's rat model

OBJECTIVE

Minocycline, a semisynthetic tetracycline-derived antibiotic, has various pharmacological effect such as anti-inflammatory, anti-oxidative stress, and anti-apoptotic effects. The current study investigated the involvement of neuro-inflammatory, oxidative stress, and cholinergic markers in neuroprotection by minocycline against scopolamine-induced brain damage.

METHODS

Minocycline was administered (oral, 10, 15, and 30 mg/kg, daily) to groups of amnesic rats for 21 days. Passive avoidance memory and spatial learning and memory were assessed. Following that, oxidative stress, cholinergic function, and neuro-inflammation markers were evaluated in the brain tissue.

RESULTS

According to our biochemical data, treatment of the scopolamine-injured rats with minocycline decreased the levels of malondialdehyde and acetylcholinesterase (AChE) as well as mRNA expression of AChE and neuro-inflammation markers (tumor necrosis factor-α, interleukin (IL)-1β, IL-6). It also increased the total thiol levels and superoxide dismutase activity as well as mRNA expression of cholinergic receptor M1 (ChRM1). Moreover, minocycline modified distance and latencies in Morris water maze, prolonged latency to enter the black zone and light time while decreasing time spent and frequency of entries to darkness.

CONCLUSION

Taken together, the data indicate that treatment with minocycline improved memory dysfunction mediated possibly through restoring AChE and ChRM1 levels, oxidant/antioxidant balance, as well as inhibiting inflammatory responses.

Crosstalk between PI3K/AKT/KLF4 signaling and microglia M1/M2 polarization as a novel mechanistic approach towards flibanserin repositioning in parkinson's disease

Balancing microglia M1/M2 polarization has been shown as a prospective therapeutic strategy for Parkinson's disease (PD). Various vital signaling pathways are likely to govern the microglial phenotype. The implication of 5HT1A receptors in neurodegenerative disorders has raised interest in exploring the repositioning of flibanserin (Flib), a 5HT1A agonist, as an effective neuroprotective agent for PD. Therefore, this study was designed to assess the ability of Flib to modulate microglia phenotype switching from M1 to M2 via PI3K/AKT downstream targets in a rotenone model of PD. Rats received rotenone (1.5 mg/kg) every other day and were concurrently treated with Flib (40 mg/kg/day) with or without wortmannin (15 μg/kg/day), a PI3K inhibitor, for 21 days. Flib improved the motor perturbations induced by rotenone, as confirmed by the reversion of histopathological damage and tyrosine hydroxylase immunohistochemical alterations in both the striata and substantia nigra. The molecular signaling of Flib was elaborated by inducing striatal AKT phosphorylation and the expression of its substantial target, KLF4. Flib induced STAT6 phosphorylation to promote M2 polarization as demonstrated by the increased CD163⁺⁺ microglial count with striatal arginase activity. In parallel, it markedly inhibited M1 activation as evidenced by the reduction in CD86⁺⁺ microglia count with striatal proinflammatory mediators, IL-1β and iNOS. The pre-administration of wortmannin mostly negated Flib's neuroprotective effects. In conclusion, Flib AKT/ KLF4-dependently amended M1/M2 microglial imbalance to exert a promising neuroprotective effect, highlighting its potential as a revolutionary candidate for conquering PD.

Microglial Activation Mediates Noradrenergic Locus Coeruleus Neurodegeneration via Complement Receptor 3 in a Rotenone-Induced Parkinson's Disease Mouse Model

Background

Chronic exposure to the insecticide rotenone can damage dopaminergic neurons and lead to an increased risk of Parkinson’s disease (PD). Whereas it is not clear whether rotenone induces neurodegeneration of noradrenergic locus coeruleus (LC/NE) neurons. Chronic neuroinflammation mediated by microglia has been involved in the pathogenesis of PD. Evidence shows that complement receptor 3 (CR3) is a crucial regulator of microglial activation and related neurodegeneration. However, it is not clear whether CR3 mediates rotenone-elicited degeneration of LC/NE neurons through microglia-mediated neuroinflammation.

Materials and Methods

Wild type (WT) and CR3 knockout (KO) mice were treated with rotenone. PLX3397 and minocycline were used to deplete or inactivate the microglia. Leukadherin-1 (LA-1) was used to modulate CR3. LC/NE neurodegeneration, microglial phenotype, and expression of CR3 were determined by using immunohistochemistry, Western blot and real-time polymerase chain reaction (PCR) techniques. The glutathione (GSH) and malondialdehyde (MDA) contents were measured by using commercial kits.

Results

Rotenone exposure led to dose- and time-dependent LC/NE neuronal loss and microglial activation in mice. Depletion of microglia by PLX3397 or inhibition of microglial activation by minocycline significantly reduced rotenone-induced LC/NE neurodegeneration. Mechanistic studies revealed that CR3 played an essential role in the rotenone-induced activation of microglia and neurodegeneration of LC/NE neurons. Rotenone elevated the expression of CR3, and genetic ablation of CR3 markedly reduced rotenone-induced microglial activation and M1 polarization. LA-1 also suppressed rotenone-induced toxic microglial M1 activation. Furthermore, lack of CR3 or treatment with LA-1 reduced oxidative stress in the brainstem of rotenone-intoxicated mice. Finally, we found that mice deficient in CR3 or treated with LA-1 were more resistant to rotenone-induced LC/NE neurodegeneration than WT or vehicle-treated mice, respectively.

Conclusion

Our results indicate that CR3-mediated microglial activation participates in rotenone-induced LC/NE neurodegeneration, providing novel insight into environmental toxin-induced neurotoxicity and related Parkinsonism.

Spinal caspase-3 contributes to tibial fracture-associated postoperative allodynia via up-regulation of LRRTM1 expression in mice

BACKGROUND

Bone fracture may subsequently cause chronic postoperative pain after orthopedic surgery, but mechanisms remain elusive. The necessity of caspase-3 in neuroinflammation and synaptic plasticity has been summarized in pathological pain. Leucine-rich repeat transmembrane protein 1 (LRRTM1) mediates synaptic delivery of AMPA receptor and synaptogenesis. This study evaluated whether caspase-3 and LRRTM1 are required for fracture-associated postoperative allodynia.

METHODS

A model of tibial fracture with intramedullary pinning in mice was established for the induction of postoperative pain, verified by measurement of mechanical paw withdrawal threshold and cold scores response to acetone. The caspase-3 specific inhibitor, recombinant caspase-3 and LRRTM1 knockdown by shRNA were utilized for the investigation of pathogenesis as well as the prevention of allodynia. Also, the activity of caspase-3 and the expression of LRRTM1 in the spinal dorsal horn were examined by Western blot and RT-qPCR.

RESULTS

This study reported that tibial fracture and orthopedic surgery produced long-lasting mechanical allodynia and cold allodynia, along with the up-modulation of spinal caspase-3 activity (but not caspase-3 expression) and LRRTM1 expression. Spinal caspase-3 inhibition prevented fracture-associated behavioral allodynia in a dose-dependent manner. Caspase-3 inhibitor also reduced the spinal increased LRRTM1 level after tibial fracture with pinning. Spinal LRRTM1 deficiency impaired fracture-caused postoperative pain. Intrathecal recombinant caspase-3 facilitated acute pain hypersensitivity and spinal LRRTM1 expression in naïve mice, reversing by LRRTM1 knockdown.

CONCLUSION

Our current results demonstrate the spinal up-regulation of LRRTM1 by caspase-3 activation in the development of tibial fracture-associated postoperative pain in mice.

Immunoproteasome is up-regulated in rotenone-induced Parkinson's disease rat model

The study was to investigate whether immunoproteasome (i-proteasome) and its downstream pathway are related to the pathogenesis of Parkinson's disease (PD). Rats were treated with rotenone showed significant weight loss and dyskinesia, which is consistent with the degeneration of TH-positive neurons and the activation of Iba-1-positive microglia/macrophages. Two major catalytic subunits of i-proteasome (PSMB9 and PSMB8) were seldom expressed in rat substantia nigra (SN) under normal condition, but they were significantly up-regulated with the release of TNF-α and IFN-γ after exposure to rotenone. In addition, compared with control group, the antigen presentation-related proteins antigen peptide transporter (TAP) 1, TAP2, major histocompatibility complex (MHC)-I and MHC-II levels were significantly up-regulated in rotenone group, which was in line with the accumulation of α-syn. These findings suggested that i-proteasome and antigen presentation pathways (related proteins) were upregulated by rotenone in a PD rat model.

Oxidative Stress-Mediated Blood-Brain Barrier (BBB) Disruption in Neurological Diseases

The blood-brain barrier (BBB), as a crucial gate of brain-blood molecular exchange, is involved in the pathogenesis of multiple neurological diseases. Oxidative stress is caused by an imbalance between the production of reactive oxygen species (ROS) and the scavenger system. Since oxidative stress plays a significant role in the production and maintenance of the BBB, the cerebrovascular system is especially vulnerable to it. The pathways that initiate BBB dysfunction include, but are not limited to, mitochondrial dysfunction, excitotoxicity, iron metabolism, cytokines, pyroptosis, and necroptosis, all converging on the generation of ROS. Interestingly, ROS also provide common triggers that directly regulate BBB damage, parameters including tight junction (TJ) modifications, transporters, matrix metalloproteinase (MMP) activation, inflammatory responses, and autophagy. We will discuss the role of oxidative stress-mediated BBB disruption in neurological diseases, such as hemorrhagic stroke, ischemic stroke (IS), Alzheimer’s disease (AD), Parkinson’s disease (PD), traumatic brain injury (TBI), amyotrophic lateral sclerosis (ALS), and cerebral small vessel disease (CSVD). This review will also discuss the latest clinical evidence of potential biomarkers and antioxidant drugs towards oxidative stress in neurological diseases. A deeper understanding of how oxidative stress damages BBB may open up more therapeutic options for the treatment of neurological diseases.

Metformin protects rotenone-induced dopaminergic neurodegeneration by reducing lipid peroxidation

BACKGROUND

Metformin, a widely prescribed antidiabetic drug, has been suggested to have a neuroprotective effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in mice. In this study, we investigated the neuroprotective potential of metformin against rotenone-induced dopaminergic neuron damage and its underlying mechanisms.

METHODS

C57BL/6 mice were given saline or rotenone (2.5 mg/kg/day, ip) injection for 10 days. Metformin treatment (300 mg/kg/day, ip) was started concurrently with rotenone administration and continued for 10 days. The neuroprotective effect of metformin on rotenone-induced dopaminergic toxicity was assessed by tyrosine hydroxylase (TH), cleaved caspase-3 and α-synuclein immunohistochemistry in substantia nigra (SN). SN tissues were extracted for biochemical analysis. Malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) protein levels were measured by spectrophotometric assay.

RESULTS

We found that metformin treatment attenuated the rotenone-induced loss of TH⁺ neurons in the SN. Additionally, metformin significantly decreased the rotenone-induced increase of cleaved caspase-3 and α-synuclein accumulation in the SN; however, there was no difference in motor behaviours between the experimental groups. Meanwhile, the levels of MDA and 4-HNE in SN were significantly reduced in the rotenone-metformin group compared to the rotenone group.

CONCLUSIONS

Results showed that metformin treatment attenuated dopaminergic neuron loss in SN induced by rotenone by decreasing lipid peroxidation.

Metal Chelation Therapy and Parkinson's Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

The present review reports a list of approximately 800 compounds which have been used, tested or proposed for Parkinson’s disease (PD) therapy in the year range 2014–2019 (April): name(s), chemical structure and references are given. Among these compounds, approximately 250 have possible or established metal-chelating properties towards Cu(II), Cu(I), Fe(III), Fe(II), Mn(II), and Zn(II), which are considered to be involved in metal dyshomeostasis during PD. Speciation information regarding the complexes formed by these ions and the 250 compounds has been collected or, if not experimentally available, has been estimated from similar molecules. Stoichiometries and stability constants of the complexes have been reported; values of the cologarithm of the concentration of free metal ion at equilibrium (pM), and of the dissociation constant K_d (both computed at pH = 7.4 and at total metal and ligand concentrations of 10⁻⁶ and 10⁻⁵ mol/L, respectively), charge and stoichiometry of the most abundant metal–ligand complexes existing at physiological conditions, have been obtained. A rigorous definition of the reported amounts is given, the possible usefulness of this data is described, and the need to characterize the metal–ligand speciation of PD drugs is underlined.

Minocycline Prevents the Development of Mechanical Allodynia in Mouse Models of Vincristine-Induced Peripheral Neuropathy

Vincristine is an antineoplastic substance that is part of many chemotherapy regimens, used especially for the treatment of a variety of pediatric cancers including leukemias and brain tumors. Unfortunately, many vincristine-treated patients develop peripheral neuropathy, a side effect characterized by sensory, motoric, and autonomic symptoms. The sensory symptoms include pain, in particular hypersensitivity to light touch, as well as loss of sensory discrimination to detect vibration and touch. The symptoms of vincristine-induced neuropathy are only poorly controlled by currently available analgesics and therefore often necessitate dose reductions or even cessation of treatment. The aim of this study was to identify new therapeutic targets for the treatment of vincristine-induced peripheral neuropathy (VIPN) by combining behavioral experiments, histology, and pharmacology after vincristine treatment. Local intraplantar injection of vincristine into the hind paw caused dose- and time-dependent mechanical hypersensitivity that developed into mechanical hyposensitivity at high doses, and lead to a pronounced, dose-dependent infiltration of immune cells at the site of injection. Importantly, administration of minocycline effectively prevented the development of mechanical hypersensitivity and infiltration of immune cells in mouse models of vincristine induce peripheral neuropathy (VIPN) based on intraperitoneal or intraplantar administration of vincristine. Similarly, Toll-like receptor 4 knockout mice showed diminished vincristine-induced mechanical hypersensitivity and immune cell infiltration, while treatment with the anti-inflammatory meloxicam had no effect. These results provide evidence for the involvement of Toll-like receptor 4 in the development of VIPN and suggest that minocycline and/or direct Toll-like receptor 4 antagonists may be an effective preventative treatment for patients receiving vincristine.

Minocycline Protects against Rotenone-Induced Neurotoxicity Correlating with Upregulation of Nurr1 in a Parkinson's Disease Rat Model

The aim of this study was to investigate the effect of minocycline in rats with rotenone-induced Parkinson's disease (PD). The open field test was performed to determine the motor ability of the rats. Double immunofluorescence staining was used to detect the expression of tyrosine hydroxylase (TH) and Nurr1 in the substantia nigra (SN) of rats. The relative protein levels of TH, Nurr1, and the total- and phosphorylated-cAMP-response element binding protein (CREB) were determined by western blot analysis. The production of reactive oxygen species (ROS) and nitric oxide (NO) was detected by commercial kits. After exposure to rotenone for 28 days, rats exhibited decreased ambulation and rearing frequency and prolonged immobility time with loss of TH positive neurons in the SN. The phosphorylation levels of CREB and Nurr1 expression decreased significantly accompanied with the release of ROS and NO. Minocycline alleviated the motor deficits of rats lesioned by rotenone and elevated the expression of TH, as well as suppressing the release of ROS and NO in the SN. That was in line with the elevated phosphorylation levels of CREB and Nurr1 expression. In conclusion, our present study showed minocycline protected against neurotoxicity in a rotenone-induced rat model of PD, which was correlated with upregulation of Nurr1.