New Insights Into the Anticonvulsant Effects of Essential Oil From Melissa officinalis L. (Lemon Balm)

Melissa officinalis L. is used in traditional European and Iranian folk medicines to treat a plethora of neurological diseases including epilepsy. We utilized the in vitro and in vivo models of epilepsy to probe the anticonvulsant potentials of essential oil from M. officinalis (MO) to gain insight into the scientific basis for its applications in traditional medicine for the management of convulsive disorders. MO was evaluated for effects on maximal electroshock (MES) and pentylenetetrazole (PTZ) -induced seizures in mice, on 4–aminopyridine (4-AP)-brain slice model of epilepsy and sustained repetitive firing of current clamped neurons; and its ameliorative effects were examined on seizure severity, anxiety, depression, cognitive dysfunction, oxidative stress and neuronal cell loss in PTZ-kindled rats. MO reversibly blocked spontaneous ictal-like discharges in the 4-AP-brain slice model of epilepsy and secondary spikes from sustained repetitive firing, suggesting anticonvulsant effects and voltage-gated sodium channel blockade. MO protected mice from PTZ– and MES–induced seizures and mortality, and ameliorated seizure severity, fear-avoidance, depressive-like behavior, cognitive deficits, oxidative stress and neuronal cell loss in PTZ–kindled rats. The findings warrant further study for the potential use of MO and/or its constituent(s) as adjunctive therapy for epileptic patients.

Protective Effects of Anthocleista djalonensis Extracts against Pentylenetetrazole-Induced Epileptic Seizures and Neuronal Cell Loss: Role of Antioxidant Defense System

Oxidative stress and neurodegeneration are involved in the initiation of epileptogenesis and progression of epileptic seizures. This study was aimed at investigating the anticonvulsant, antioxidant, and neuroprotective properties of active fractions isolated from Anthocleista djalonensis root barks in pentylenetetrazole mouse models of epileptic seizures. Bioactive-guided fractionation of Anthocleista djalonensis (AFAD) extracts using acute pentylenetetrazole (90 mg/kg) induced generalised tonic-clonic seizures, which afforded a potent anticonvulsant fraction (FPool 5). Further fractionation of AFAD was performed by high-performance liquid chromatography, which yielded fifteen subfractions, which were chemically characterised. In addition, AFAD was tested against convulsions or spontaneous kindled seizures induced, respectively, by acute (50 mg/kg) or subchronic (30 mg/kg) injection of pentylenetetrazole. Finally, oxidative stress markers, brain GABA content, and neuronal cell loss were evaluated in AFAD-treated pentylenetetrazole-kindled mice. Administration of AFAD significantly protected mice against acute pentylenetetrazole (90 mg/kg)-induced convulsions. In acute pentylenetetrazole (50 mg/kg)-induced hippocampal and cortical paroxysmal discharges, AFAD significantly decreased the number of crisis, the cumulative duration of crisis, and the mean duration of crisis. Additionally, AFAD significantly decreased the number of myoclonic jerks and improved the seizure score in subchronic pentylenetetrazole-induced kindled seizures. The pentylenetetrazole-induced alteration of oxidant-antioxidant balance, GABA concentration, and neuronal cells in the brain were attenuated by AFAD treatment. This study showed that AFAD protected mice against pentylenetetrazole-induced epileptic seizures possibly through the enhancement of antioxidant defence and GABAergic signalling. These events might be correlated with the amelioration of neuronal cell loss; hence, AFAD could be a potential candidate for the treatment of epilepsy.

Neuroinflammation and Neuronal Loss in the Hippocampus Are Associated with Immediate Posttraumatic Seizures and Corticosterone Elevation in Rats

Hippocampal damage after traumatic brain injury (TBI) is associated with late posttraumatic conditions, such as depression, cognitive decline and epilepsy. Mechanisms of selective hippocampal damage after TBI are not well understood. In this study, using rat TBI model (lateral fluid percussion cortical injury), we assessed potential association of immediate posttraumatic seizures and changes in corticosterone (CS) levels with neuroinflammation and neuronal cell loss in the hippocampus. Indices of distant hippocampal damage (neurodegeneration and neuroinflammation) were assessed using histological analysis (Nissl staining, Iba-1 immunohistochemical staining) and ELISA (IL-1β and CS) 1, 3, 7 and 14 days after TBI or sham operation in male Wistar rats (n = 146). IL-1β was elevated only in the ipsilateral hippocampus on day 1 after trauma. CS peak was detected on day 3 in blood, the ipsilateral and contralateral hippocampus. Neuronal cell loss in the hippocampus was demonstrated bilaterally; in the ipsilateral hippocampus it started earlier than in the contralateral. Microglial activation was evident in the hippocampus bilaterally on day 7 after TBI. The duration of immediate seizures correlated with CS elevation, levels of IL-1β and neuronal loss in the hippocampus. The data suggest potential association of immediate post-traumatic seizures with CS-dependent neuroinflammation-mediated distant hippocampal damage.

Enhancing calmodulin binding to ryanodine receptor is crucial to limit neuronal cell loss in Alzheimer disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by progressive neuronal cell loss. Recently, dysregulation of intracellular Ca2+ homeostasis has been suggested as a common proximal cause of neural dysfunction in AD. Here, we investigated (1) the pathogenic role of destabilization of ryanodine receptor (RyR2) in endoplasmic reticulum (ER) upon development of AD phenotypes in AppNL-G-F mice, which harbor three familial AD mutations (Swedish, Beyreuther/Iberian, and Arctic), and (2) the therapeutic effect of enhanced calmodulin (CaM) binding to RyR2. In the neuronal cells from AppNL-G-F mice, CaM dissociation from RyR2 was associated with AD-related phenotypes, i.e. Aβ accumulation, TAU phosphorylation, ER stress, neuronal cell loss, and cognitive dysfunction. Surprisingly, either genetic (by V3599K substitution in RyR2) or pharmacological (by dantrolene) enhancement of CaM binding to RyR2 reversed almost completely the aforementioned AD-related phenotypes, except for Aβ accumulation. Thus, destabilization of RyR2 due to CaM dissociation is most likely an early and fundamental pathogenic mechanism involved in the development of AD. The discovery that neuronal cell loss can be fully prevented simply by stabilizing RyR2 sheds new light on the treatment of AD.

Microglial gene signature reveals loss of homeostatic microglia associated with neurodegeneration of Alzheimer’s disease

Microglia-mediated neuroinflammation has been implicated in the pathogenesis of Alzheimer’s disease (AD). Although microglia in aging and neurodegenerative disease model mice show a loss of homeostatic phenotype and activation of disease-associated microglia (DAM), a correlation between those phenotypes and the degree of neuronal cell loss has not been clarified. In this study, we performed RNA sequencing of microglia isolated from three representative neurodegenerative mouse models, AppNL-G-F/NL-G-F with amyloid pathology, rTg4510 with tauopathy, and SOD1G93A with motor neuron disease by magnetic activated cell sorting. In parallel, gene expression patterns of the human precuneus with early Alzheimer’s change (n = 11) and control brain (n = 14) were also analyzed by RNA sequencing. We found that a substantial reduction of homeostatic microglial genes in rTg4510 and SOD1G93A microglia, whereas DAM genes were uniformly upregulated in all mouse models. The reduction of homeostatic microglial genes was correlated with the degree of neuronal cell loss. In human precuneus with early AD pathology, reduced expression of genes related to microglia- and oligodendrocyte-specific markers was observed, although the expression of DAM genes was not upregulated. Our results implicate a loss of homeostatic microglial function in the progression of AD and other neurodegenerative diseases. Moreover, analyses of human precuneus also suggest loss of microglia and oligodendrocyte functions induced by early amyloid pathology in human.

Application of AOP networks in human health risk assessment: Increasing confidence in rodent olfactory nasal lesions as the point of departure for hydrogen sulfide exposure limits

Acute exposure to hydrogen sulfide initiates a series of hallmark biological effects that occur progressively at increasing exposure levels: odor perception, conjunctivitis, olfactory paralysis, “knockdown”, pulmonary edema, and paralysis of breathing. Although effects of exposure to high concentrations of hydrogen sulfide are clear, effects associated with chronic, low-level exposure in humans is under debate, leading to uncertainty in the critical effect used in regulatory risk assessments addressing low dose exposures. This study integrates experimental animal, observational epidemiology, and occupational exposure evidence by applying a pathway-based approach. A hypothesized adverse outcome pathway (AOP) network was developed from 34 studies, comprised of 5 AOPs sharing 2 molecular initiating events (MIEs) and culminating in 5 adverse outcomes. A comparative assessment of effect levels and weight of evidence identified an AOP leading to a biologically-plausible, low-dose outcome relative to the other outcomes (nasal lesions, 30 ppm vs neurological effects, >80 ppm; pulmonary edema, >80 ppm; cardiovascular related mortality, >400 ppm; mortality via central nervous system depression, >400 ppm). This AOP (i.e., AOP1) consists of the following key events: cytochrome oxidase inhibition (>10 ppm), neuronal cell loss (>30 ppm), and olfactory nasal lesions (defined as both neuronal cell loss and basal cell hyperplasia; >30 ppm) in rodents or olfactory paralysis (>100 ppm) in humans. The key event relationships in this pathway were supported by high empirical evidence and have high biological plausibility due to known mechanistic understanding and consistency in observations for diverse chemicals. Based on assessment using the human relevance framework, this biological pathway (or, mode of action) is qualitatively possible in humans and is likely to share the same set of key event leading to olfactory paralysis in humans. This approach provides a basis to link the known observations in humans with the subchronic animal data, reducing the overall uncertainty of the human health risk assessment of H2S.

The Neuroprotective Effect of Zingiber cassumunar Roxb. Extract on LPS-Induced Neuronal Cell Loss and Astroglial Activation within the Hippocampus

The systemic administration of lipopolysaccharide (LPS) has been recognized to induce neuroinflammation which plays a significant role in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. In this study, we aimed to determine the protective effect of Zingiber cassumunar (Z. cassumunar) or Phlai (in Thai) against LPS-induced neuronal cell loss and the upregulation of glial fibrillary acidic protein (GFAP) of astrocytes in the hippocampus. Adult male Wistar rats were orally administered with Z. cassumunar extract at various doses (50, 100, and 200 mg/kg body weight) for 14 days before a single injection of LPS (250 μg/kg/i.p.). The results indicated that LPS-treated animals exhibited neuronal cell loss and the activation of astrocytes and also increased proinflammatory cytokine interleukin- (IL-) 1β in the hippocampus. Pretreatment with Z. cassumunar markedly reduced neuronal cell loss in the hippocampus. In addition, Z. cassumunar extract at a dose of 200 mg/kg BW significantly suppressed the inflammatory response by reducing the expression of GFAP and IL-1ß in the hippocampus. Therefore, the results suggested that Z. cassumunar extract might be valuable as a neuroprotective agent in neuroinflammation-induced brain damage. However, further investigations are essential to validate the possible active ingredients and mechanisms of its neuroprotective effect.