Down-regulation of microglial activity attenuates axotomized nigral dopaminergic neuronal cell loss

Ginsenoside Rg1 attenuates cerebral ischemia-reperfusion injury through inhibiting the inflammatory activation of microglia

It is recognized that the cerebral ischemia/reperfusion (I/R) injury triggers inflammatory activation of microglia and supports microglia-driven neuronal damage. Our previous studies have shown that ginsenoside Rg1 had a significant protective effect on focal cerebral I/R injury in middle cerebral artery occlusion (MCAO) rats. However, the mechanism still needs further clarification. Here, we firstly reported that ginsenoside Rg1 effectively suppressed the inflammatory activation of brain microglia cells under I/R conditions depending on the inhibition of Toll-likereceptor4 (TLR4) proteins. In vivo experiments showed that the ginsenoside Rg1 administration could significantly improve the cognitive function of MCAO rats, and in vitro experimental data showed that ginsenoside Rg1 significantly alleviated neuronal damage via inhibiting the inflammatory response in microglia cells co-cultured under oxygen and glucose deprivation/reoxygenation (OGD/R) condition in gradient dependent. The mechanism study showed that the effect of ginsenoside Rg1 depends on the suppression of TLR4/MyD88/NF-κB and TLR4/TRIF/IRF-3 pathways in microglia cells. In a word, our research shows that ginsenoside Rg1 has great application potential in attenuating the cerebral I/R injury by targeting TLR4 protein in the microglia cells.

Construction of 3D-rendering imaging of an ischemic rat brain model using the planar FMMD technique

Occlusion of the major cerebral artery usually results in brain hypoxic-ischemic injury, which evokes neuroinflammation and microglial activation. Activated microglia are considered a source of multiple neurotoxic factors, such as reactive oxygen species (ROS), in the central nervous system (CNS). We herein present a 3D-rendering brain imaging technique in an experimental rodent model of cerebral ischemia based on 2D magnetic images of superparamagnetic iron oxide nanoparticles (SPIONs) using the planar frequency mixing magnetic detection (p-FMMD) technique. A rat model of cerebral ischemia was established by unilateral middle cerebral artery occlusion with reperfusion (MCAO/R) injury. 2,3,5-Triphenyltetrazolium chloride (TTC) staining was performed to demonstrate the irreversibly damaged ischemic brain tissues, and double immunofluorescent labeling of OX6 (activated microglial marker) and ethidium (ROS marker) was conducted to confirm ROS generation in the activated microglia in the infarcted brain region. The ischemic brain sections treated with OX6-conjugated SPIONs were scanned using our p-FMMD system, yielding 2D images on the basis of the nonlinear magnetic characteristics inherent in SPIONs. The p-FMMD signal images representing microglia activation show an infarct ratio of 44.6 ± 7.1% compared to the contralateral counterpart, which is smaller than observed by TTC (60.9 ± 4.9%) or magnetic resonance imaging (MRI, 65.7 ± 2.7%). Furthermore, we developed a 3D-rendering brain imaging process based on the 2D p-FMMD signal images. The 3D reconstructed model showed a decreased ratio of coincidence of the ischemic regions compared with MRI models. In this study, we successfully conducted a feasibility test on whether our p-FMMD technology, a technique for signaling and imaging based on the nonlinearity of SPIONs, can be used to visualize the ischemic brain region in real time by detecting activated microglia in an MCAO/R animal model. Therefore, our method might allow for a different approach to analyze the pathophysiology of ischemic stroke through molecular imaging. Furthermore, we propose that this magnetic particle imaging (MPI) technique that detects the nonlinear magnetization properties of SPIONs could be applied not only to a stroke model but also to various types of pathophysiological studies as a new bioimaging tool.

Use of PEGylated Immunoliposomes to Deliver Dopamine Across the Blood-Brain Barrier in a Rat Model of Parkinson's Disease

AIM

To treat neurodegenerative disorders such as Parkinson's disease (PD), drugs must be able to cross the blood-brain barrier (BBB). Patients with PD are deficient in dopamine (DA), a neurotransmitter that cannot pass through the BBB. Liposomes modified by adding polyethylene glycol (PEGylated liposomes (PLs)) can be conjugated with antibody to form DA-PEGylated immunoliposomes (DA-PILs), and we tested their use as carriers of DA for treating PD.

METHODS

PEGylated liposomes (PLs) were prepared by evaporation method, and [(3) H]dopamine was encapsulated within the dried lipid film using a freeze/thaw cycle to form DA-PL. Thiolated OX26 MAb, an antitransferrin receptor monoclonal antibody, was then conjugated to 46-nm PEGylated liposomes. Particle size, zeta potential, and stability were assessed, and in vivo effects were determined after the intravenous injection of DA, DA-PL, and DA-PIL by examining brain tissue in normal rats and rats that underwent transection of the medial forebrain bundle to induce PD.

RESULTS

The uptake of DA-PIL in the brains of this PD rat model increased about 8-fold compared with that of DA alone and about 3-fold compared with that of encapsulated DA-PEGylated liposomes (DA-PL). The volume of distribution of DA-PIL in the brain by the perfusion method was 4-fold higher than that of DA-PL, indicating that conjugation of OX26 MAb to the transferrin receptor of brain capillary endothelium mediated the effective delivery of DA to brain tissue.

CONCLUSIONS

Dopamine can be effectively delivered to the brain by means of a PIL-based drug delivery system in PD rats.

Lipoic acid protects dopaminergic neurons in LPS-induced Parkinson's disease model

Parkinson's disease (PD) is a chronic neurodegenerative disease of the central nervous system (CNS), characterized by a loss of dopaminergic neurons, which is thought to be caused by both genetic and environmental factors. Recent findings suggest that neuroinflammation may be a pathogenic factor in the onset and progression of sporadic PD. Here we explore the potential therapeutic effect of lipoic acid (LA) on a lipolysaccharide (LPS)-induced inflammatory PD model. Our results for the first time showed that LA administration improved motor dysfunction, protected dopaminergic neurons loss, and decreased α-synuclein accumulation in the substantia nigra (SN) area of brain. Further, LA inhibited the activation of nuclear factor-κB (NF-κB) and expression of pro-inflammatory molecules in M1 microglia. Taken together, these results suggest that LA may exert a profound neuroprotective effect and is thus a promising anti-neuroinflammatory and anti-oxidative agent for halting the progression of PD. Interventions aimed at either blocking microglia-derived inflammatory mediators or modulating the polarization of microglia may be potentially useful therapies that are worth further investigation.

Somatostatin prevents lipopolysaccharide-induced neurodegeneration in the rat substantia nigra by inhibiting the activation of microglia

Somatostatin (SST) is a neuromodulator which is abundant throughout the central nervous system (CNS) and has a crucial role in neurodegenerative disorders. However, little is known about the effects and mechanisms of SST in dopaminergic (DA) neurons in the context of Parkinson's disease (PD). In the present study, a model of PD was generated by injecting lipopolysaccharide (LPS) into the substantia nigra (SN) of rats in order to investigate the effects of SST on LPS-induced degeneration of DA in vivo. Intramural injection of LPS resulted in a significant loss of DA neurons, while reduction of neuronal death by SST pretreatment was confirmed using immunohistochemical staining for tyrosine hydroxylase and Nissl. In parallel, immunohistochemical detection of OX-42 and hydroethidine staining were employed to determine the activation of microglia and production of reactive oxygen species (ROS), respectively. It was found that SST inhibited the LPS-induced microglial activity and ROS production. ELISA revealed a decreased production of pro-inflammatory mediators, including tumor necrosis factor-α, interleukin-1β and prostaglandin E2 when SST was administered prior to LPS treatment. Western blot analysis showed that LPS-induced expression of inducible nitric oxide synthase, cyclooxygenase-2 and nuclear factor κB (NF-κB) p-p65 was attenuated by administration of SST prior to LPS application. The results indicated that LPS-induced loss of nigral DA neurons was inhibited by SST and the observed effects of SST on neuroprotection were associated with suppression of microglial activation and the NF-κB pathway, ensuing decreases of neuroinflammation and oxidative stress. The present study therefore suggested that SST is beneficial for treating neurodegenerative diseases, such as PD, through inhibiting the activation of microglia.