Laquinimod ameliorates secondary brain inflammation

Laquinimod Inhibits Microglial Activation, Astrogliosis, BBB Damage, and Infarction and Improves Neurological Damage after Ischemic Stroke

Glial activation is involved in neuroinflammation and blood-brain barrier (BBB) damage, which plays a key role in ischemic stroke-induced neuronal damage; therefore, regulating glial activation is an important way to inhibit ischemic brain injury. Effects of laquinimod (LAQ) include inhibiting axonal damage and neuroinflammation in multiple neuronal injury diseases. However, whether laquinimod can exert neuroprotective effects after ischemic stroke remains unknown. In this study, we investigated the effect of LAQ on glial activation, BBB damage, and neuronal damage in an ischemic stroke model. Adult ICR mice were used to create a photothrombotic stroke (PT) model. LAQ was administered orally at 30 min after ischemic injury. Neurobehavioral tests, Evans Blue, immunofluorescence, TUNEL, Nissl staining, and western blot were performed to evaluate the neurofunctional outcome. Quantification of immunofluorescence was evaluated by unbiased stereology. LAQ post-treatment significantly reduced infarction and improved forepaw function at 5 days after PT. Interestingly, LAQ treatment significantly promoted anti-inflammatory microglial activation. Moreover, LAQ treatment reduced astrocyte activation, glial scar formation, and BBB breakdown in ischemic brains. Therefore, this study demonstrated that LAQ post-treatment restricted microglial polarization, astrogliosis, and glial scar and improved BBB damage and behavioral function. LAQ may serve as a novel target to develop new therapeutic agents for ischemic stroke.

Therapeutic effect of combination vitamin D3 and siponimod on remyelination and modulate microglia activation in cuprizone mouse model of multiple sclerosis

Stimulation of remyelination is critical for the treatment of multiple sclerosis (MS) to alleviate symptoms and protect the myelin sheath from further damage. The current study aimed to investigate the possible therapeutic effects of combining vitamin D3 (Vit D3) and siponimod (Sipo) on enhancing remyelination and modulating microglia phenotypes in the cuprizone (CPZ) demyelination mouse model. The study was divided into two stages; demyelination (first 5 weeks) and remyelination (last 4 weeks). In the first 5 weeks, 85 mice were randomly divided into two groups, control (n = 20, standard rodent chow) and CPZ (n = 65, 0.3% CPZ mixed with chow for 6 weeks, followed by 3 weeks of standard rodent chow). At week 5, the CPZ group was re-divided into four groups (n = 14) for remyelination stages; untreated CPZ (0.2 ml of CMC orally), CPZ+Vit D3 (800 IU/kg Vit D3 orally), CPZ+Sipo (1.5 mg/kg Sipo orally), and CPZ+Vit D3 (800 IU/kg Vit D3) + Sipo (1.5 mg/kg Sipo orally). Various behavioral tasks were performed to evaluate motor performance. Luxol Fast Blue (LFB) staining, the expression level of myelin basic protein (MBP), and M1/M2 microglia phenotype genes were assessed in the corpus callosum (CC). The results showed that the combination of Vit D3 and Sipo improved behavioral deficits, significantly promoted remyelination, and modulated expression levels of microglia phenotype genes in the CC at early and late remyelination stages. These results demonstrate for the first time that a combination of Vit D3 and Sipo can improve the remyelination process in the cuprizone (CPZ) mouse model by attenuating the M1 microglia phenotype. This may help to improve the treatment of MS patients.

S100B inhibition protects from chronic experimental autoimmune encephalomyelitis

Studies have correlated excessive S100B, a small inflammatory molecule, with demyelination and associated inflammatory processes occurring in multiple sclerosis. The relevance of S100B in multiple sclerosis pathology brought an emerging curiosity highlighting its use as a potential therapeutic target to reduce damage during the multiple sclerosis course, namely during inflammatory relapses. We examined the relevance of S100B and further investigated the potential of S100B-neutralizing small molecule pentamidine in chronic experimental autoimmune encephalomyelitis. S100B depletion had beneficial pathological outcomes and, based on promising results of a variety of S100B-blockade strategies in an ex vivo demyelinating model we choose pentamidine to assay its role in the in vivo experimental autoimmune encephalomyelitis. We report that pentamidine prevents more aggressive clinical symptoms and improves recovery of chronic experimental autoimmune encephalomyelitis. Blockade of S100B by pentamidine protects against oligodendrogenesis impairment and neuroinflammation by reducing astrocyte reactivity and microglia pro-inflammatory phenotype. Pentamidine also increased regulatory T cell density in the spinal cord suggesting an additional immunomodulatory action. These results showed the relevance of S100B as a main driver of neuroinflammation in experimental autoimmune encephalomyelitis and identified an uncharacterized mode of action of pentamidine, strengthening the possibility to use this drug as an anti-inflammatory and remyelinating therapy for progressive multiple sclerosis.

Recent advances in clinical trials targeting the kynurenine pathway

The kynurenine pathway (KP) is the major catabolic pathway for the essential amino acid tryptophan leading to the production of nicotinamide adenine dinucleotide. In inflammatory conditions, the activation of the KP leads to the production of several bioactive metabolites including kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, kynurenic acid and quinolinic acid. These metabolites can have redox and immune suppressive activity, be neurotoxic or neuroprotective. While the activity of the pathway is tightly regulated under normal physiological condition, it can be upregulated by immunological activation and inflammation. The dysregulation of the KP has been implicated in wide range of neurological diseases and psychiatric disorders. In this review, we discuss the mechanisms involved in KP-mediated neurotoxicity and immune suppression, and its role in diseases of our expertise including cancer, chronic pain and multiple sclerosis. We also provide updates on the clinical trials evaluating the efficacy of KP inhibitors and/or analogues in each respective disease.

TSPO imaging in animal models of brain diseases

Over the last 30 years, the 18-kDa TSPO protein has been considered as the PET imaging biomarker of reference to measure increased neuroinflammation. Generally assumed to image activated microglia, TSPO has also been detected in endothelial cells and activated astrocytes. Here, we provide an exhaustive overview of the recent literature on the TSPO-PET imaging (i) in the search and development of new TSPO tracers and (ii) in the understanding of acute and chronic neuroinflammation in animal models of neurological disorders. Generally, studies testing new TSPO radiotracers against the prototypic [11C]-R-PK11195 or more recent competitors use models of acute focal neuroinflammation (e.g. stroke or lipopolysaccharide injection). These studies have led to the development of over 60 new tracers during the last 15 years. These studies highlighted that interpretation of TSPO-PET is easier in acute models of focal lesions, whereas in chronic models with lower or diffuse microglial activation, such as models of Alzheimer's disease or Parkinson's disease, TSPO quantification for detection of neuroinflammation is more challenging, mirroring what is observed in clinic. Moreover, technical limitations of preclinical scanners provide a drawback when studying modest neuroinflammation in small brains (e.g. in mice). Overall, this review underlines the value of TSPO imaging to study the time course or response to treatment of neuroinflammation in acute or chronic models of diseases. As such, TSPO remains the gold standard biomarker reference for neuroinflammation, waiting for new radioligands for other, more specific targets for neuroinflammatory processes and/or immune cells to emerge.

Cuprizone markedly decreases kynurenic acid levels in the rodent brain tissue and plasma

Background

The kynurenine (KYN) pathway (KP) of the tryptophan (TRP) metabolism seems to play a role in the pathomechanism of multiple sclerosis (MS). Cuprizone (CPZ) treated animals develop both demyelination (DEM) and remyelination (REM) in lack of peripheral immune response, such as the lesion pattern type III and IV in MS, representing primary oligodendrogliopathy.

Objective

To measure the metabolites of the KP in the CPZ treated animals, including TRP, KYN and kynurenic acid (KYNA). We proposed that KYNA levels might be decreased in the CPZ-induced demyelinating phase of the animal model of MS, which model represents the progressive phase of the disease.

Methods

A total of 64 C57Bl/6J animals were used for the study. Immunohistochemical (IHC) measurements were performed to prove the effect of CPZ, whereas high-performance liquid chromatography (HPLC) was used to quantify the metabolites of the KP (n = 10/4 groups; DEM, CO1, REM, CO2).

Results

IHC measurements proved the detrimental effects of CPZ. HPLC measurements demonstrated a decrease of KYNA in the hippocampus (p < 0.05), somatosensory cortex (p < 0.01) and in plasma (p < 0.001).

Conclusion

This is the first evidence of marked reduction in KYNA levels in a non-immune mediated model of MS. Our results suggest an involvement of the KP in the pathomechanism of MS, which needs to be further elucidated.

Natural Molecules and Neuroprotection: Kynurenic Acid, Pantethine and α-Lipoic Acid

The incidence of neurodegenerative diseases has increased greatly worldwide due to the rise in life expectancy. In spite of notable development in the understanding of these disorders, there has been limited success in the development of neuroprotective agents that can slow the progression of the disease and prevent neuronal death. Some natural products and molecules are very promising neuroprotective agents because of their structural diversity and wide variety of biological activities. In addition to their neuroprotective effect, they are known for their antioxidant, anti-inflammatory and antiapoptotic effects and often serve as a starting point for drug discovery. In this review, the following natural molecules are discussed: firstly, kynurenic acid, the main neuroprotective agent formed via the kynurenine pathway of tryptophan metabolism, as it is known mainly for its role in glutamate excitotoxicity, secondly, the dietary supplement pantethine, that is many sided, well tolerated and safe, and the third molecule, α-lipoic acid is a universal antioxidant. As a conclusion, because of their beneficial properties, these molecules are potential candidates for neuroprotective therapies suitable in managing neurodegenerative diseases.

Cuprizone-induced demyelination triggers a CD8-pronounced T cell recruitment

The loss of myelinating oligodendrocytes is a key characteristic of many neurological diseases, including Multiple Sclerosis (MS). In progressive MS, where effective treatment options are limited, peripheral immune cells can be found at the site of demyelination and are suggested to play a functional role during disease progression. In this study, we hypothesize that metabolic oligodendrocyte injury, caused by feeding the copper chelator cuprizone, is a potent trigger for peripheral immune cell recruitment into the central nervous system (CNS). We used immunohistochemistry and flow cytometry to evaluate the composition, density, and activation status of infiltrating T lymphocytes in cuprizone-intoxicated mice and post-mortem progressive MS tissues. Our results demonstrate a predominance of CD8⁺ T cells along with high proliferation rates and cytotoxic granule expression, indicating an antigenic and pro-inflammatory milieu in the CNS of cuprizone-intoxicated mice. Numbers of recruited T cells and the composition of lymphocytic infiltrates in cuprizone-intoxicated mice were found to be comparable to those found in progressive MS lesions. Finally, amelioration of the cuprizone-induced pathology by treating mice with laquinimod significantly reduces the number of recruited T cells. Overall, this study provides strong evidence that toxic demyelination is a sufficient trigger for T cells to infiltrate the demyelinated CNS. Further investigation of the mode of action and functional consequence of T cell recruitment might offer promising new therapeutic approaches for progressive MS.

Molecular Effects of FDA-Approved Multiple Sclerosis Drugs on Glial Cells and Neurons of the Central Nervous System

Multiple sclerosis (MS) is characterized by peripheral and central inflammatory features, as well as demyelination and neurodegeneration. The available Food and Drug Administration (FDA)-approved drugs for MS have been designed to suppress the peripheral immune system. In addition, however, the effects of these drugs may be partially attributed to their influence on glial cells and neurons of the central nervous system (CNS). We here describe the molecular effects of the traditional and more recent FDA-approved MS drugs Fingolimod, Dimethyl Fumarate, Glatiramer Acetate, Interferon-β, Teriflunomide, Laquinimod, Natalizumab, Alemtuzumab and Ocrelizumab on microglia, astrocytes, neurons and oligodendrocytes. Furthermore, we point to a possible common molecular effect of these drugs, namely a key role for NFκB signaling, causing a switch from pro-inflammatory microglia and astrocytes to anti-inflammatory phenotypes of these CNS cell types that recently emerged as central players in MS pathogenesis. This notion argues for the need to further explore the molecular mechanisms underlying MS drug action.