Li You Chen

Melatonin inhibits microglial activation, reduces pro-inflammatory cytokine levels, and rescues hippocampal neurons of adult rats with acute Klebsiella pneumoniae meningitis.

Abstract:  Acute bacterial meningitis caused by Klebsiella pneumoniae (K. pneumoniae) is a major health threat with a high mortality rate and severe neuro‐cognitive sequelae. The intense pro‐inflammatory cytokine released from calcium‐mediated microglial activation plays an important role in eliciting neuronal damage in the hippocampal region. Considering melatonin possesses anti‐inflammatory and immuno‐modulatory properties, the present study determined whether melatonin can effectively decrease inflammatory responses and prevent hippocampal damage in animals subjected to K. pneumoniae. Adult rats inoculated with K. pneumoniae received a melatonin injection immediately thereafter at doses of 5, 25, 50, or 100 mg/kg. Following 24 h of survival, all experimental animals were processed for time‐of‐flight secondary ion mass spectrometry (for detecting glial calcium intensity), isolectin‐B4 histochemistry (reliable marker for microglial activation), pro‐inflammatory cytokine measurement as well as cytochrome oxidase and in situ dUTP end‐labeling (representing neuronal bio‐energetic status and apoptotic changes, respectively). Results indicate that in K. pneumoniae‐infected rats, numerous calcium‐enriched microglia, enhanced pro‐inflammatory cytokine, and various apoptotic neurons with low bio‐energetic activity were detected in hippocampus. Following melatonin administration, however, all parameters including glial calcium intensity, microglial activation, pro‐inflammatory cytokine levels, and number of apoptotic neurons were successfully decreased with maximal change observed at a melatonin dose of 100 mg/kg. Enzymatic data corresponded well with above findings in which all surviving neurons displayed high bio‐energetic activity. As effectively reducing glia‐mediated inflammatory response is neuro‐protective to hippocampal neurons, the present study supports the clinical use of melatonin as a potential therapeutic agent to counteract K. pneumoniae meningitis‐induced neuro‐cognitive damage.

Proliferative effects of melatonin on Schwann cells: implication for nerve regeneration following peripheral nerve injury

Activation of proliferation of Schwann cells is crucial for axonal guidance and successful nerve regeneration following peripheral nerve injury (PNI). Considering melatonin plays an important role in proliferative regulation of central glial cells, the present study determined whether melatonin can effectively promote Schwann cell proliferation and improve nerve regeneration after PNI. The spontaneous immortalized rat Schwann cell line (RSC 96 cells) was first analyzed by quantitative polymerase chain reaction (QPCR) to detect the potential existence of melatonin receptors. The melatonin receptor‐mediated signaling responsible for proliferation was examined by measuring the phosphorylation of extracellular signal‐regulated kinases (ERK1/2) pathway. The in vivo model of PNI was performed by the end‐to‐side neurorrhaphy. The quantity of Schwann cells as well as the number of re‐innervated motor end plates (MEP) on target muscles was examined to represent the functional recovery of injured nerves. QPCR results indicated that MT1 is the dominant receptor in Schwann cells. Immunoblotting and proliferation assay revealed an enhanced phosphorylation of ERK1/2 and increased number of RSC 96 cells following melatonin administration. Nonselective melatonin receptor antagonist (luzindole) treatment significantly suppressed all the above findings, suggesting that the proliferative effects of melatonin were mediated by a receptor‐dependent pathway. In vivo results corresponded well with in vitro findings in which melatonin effectively increased the amount of proliferated Schwann cells and re‐innervated MEP on target muscles following PNI. As melatonin successfully improves nerve regeneration by promoting Schwann cell proliferation, therapeutic use of melatonin may thus serve as a promising strategy to counteract the PNI‐induced neuronal disability.

Resveratrol suppresses calcium-mediated microglial activation and rescues hippocampal neurons of adult rats following acute bacterial meningitis

Acute bacterial meningitis (ABM) is a serious disease with severe neurological sequelae. The intense calcium-mediated microglial activation and subsequently pro-inflammatory cytokine release plays an important role in eliciting ABM-related oxidative damage. Considering resveratrol possesses significant anti-inflammatory and anti-oxidative properties, the present study aims to determine whether resveratrol would exert beneficial effects on hippocampal neurons following ABM. ABM was induced by inoculating Klebsiella pneumoniae into adult rats intraventricularly. The time-of-flight secondary ion mass spectrometry (TOF-SIMS), Griffonia simplicifolia isolectin-B4 (GSA-IB4) and ionized calcium binding adaptor molecule 1 (Iba1) immunohistochemistry, enzyme-linked immunosorbent assay as well as malondialdehyde (MDA) measurement were used to examine the calcium expression, microglial activation, pro-inflammatory cytokine level, and extent of oxidative stress, respectively. In ABM rats, strong calcium signaling associated with enhanced microglial activation was observed in hippocampus. Increased microglial expression was coincided with intense production of pro-inflammatory cytokines and oxidative damage. However, in rats receiving resveratrol after ABM, the calcium intensity, microglial activation, pro-inflammatory cytokine and MDA levels were all significantly decreased. Quantitative data showed that much more hippocampal neurons were survived in resveratrol-treated rats following ABM. As resveratrol successfully rescues hippocampal neurons from ABM by suppressing the calcium-mediated microglial activation, therapeutic use of resveratrol may act as a promising strategy to counteract the ABM-induced neurological damage.

Comprehensive Application of Time-of-flight Secondary Ion Mass Spectrometry (TOF-SIMS) for Ionic Imaging and Bio-energetic Analysis of Club Drug-induced Cognitive Deficiency

Excessive exposure to club drug (GHB) would cause cognitive dysfunction in which impaired hippocampal Ca2+-mediated neuroplasticity may correlate with this deficiency. However, the potential changes of in vivo Ca2+ together with molecular machinery engaged in GHB-induced cognitive dysfunction has never been reported. This study aims to determine these changes in bio-energetic level through ionic imaging, spectrometric, biochemical, morphological, as well as behavioral approaches. Adolescent rats subjected to GHB were processed for TOF-SIMS, immunohistochemistry, biochemical assay, together with Morris water maze to detect the ionic, molecular, neurochemical, and behavioral changes of GHB-induced cognitive dysfunction, respectively. Extent of oxidative stress and bio-energetics were assessed by levels of lipid peroxidation, Na+/K+ ATPase, cytochrome oxidase, and [14C]-2-deoxyglucose activity. Results indicated that in GHB intoxicated rats, decreased Ca2+ imaging and reduced NMDAR1, nNOS, and p-CREB reactivities were detected in hippocampus. Depressed Ca2+-mediated signaling corresponded well with intense oxidative stress, diminished Na+/K+ ATPase, reduced COX, and decreased 2-DG activity, which all contributes to the development of cognitive deficiency. As impaired Ca2+-mediated signaling and oxidative stress significantly contribute to GHB-induced cognitive dysfunction, delivering agent(s) that improves hippocampal bio-energetics may thus serve as a promising strategy to counteract the club drug-induced cognitive dysfunction emerging in our society nowadays.

Prophylactic supplement with melatonin successfully suppresses the pathogenesis of periodontitis through normalizing RANKL/OPG ratio and depressing the TLR4/MyD88 signaling pathway.

Periodontitis (PD) is an inflammatory disease characterized by gingival inflammation and resorption of alveolar bone. Impaired receptor activator of nuclear factor‐kappa B ligand/osteoprotegerin (RANKL/OPG) signaling caused by enhanced production of pro‐inflammatory cytokines plays an essential role in the pathogenesis of PD. Considering melatonin possesses significant anti‐inflammatory property, this study aimed to determine whether prophylactic treatment with melatonin would effectively normalize RANKL/OPG signaling, depress toll‐like receptor 4/myeloid differentiation factor 88 (TLR4/MyD88)‐mediated pro‐inflammatory cytokine activation, and successfully suppress the pathogenesis of PD. PD was induced in adult rats by placing the ligature at molar subgingival regions. Fourteen days before PD induction, 10, 50, or 100 mg/kg of melatonin was intraperitoneally injected for consecutive 28 days. Biochemical and enzyme‐linked immunosorbent assay were used to detect TLR4/MyD88 activity, RANKL, OPG, interleukin 1β, interleukin 6, and tumor necrosis factor‐α levels, respectively. The extent of bone loss, bone mineral intensity, and calcium intensity was further evaluated by scanning electron microscopy, micro‐computed tomography, and energy‐dispersive X‐ray spectroscopy. Results indicated that high RANKL/OPG ratio, TLR4/MyD88 activity, and pro‐inflammatory cytokine levels were detected following PD. Impaired biochemical findings paralleled well with severe bone loss and reduced calcium intensity. However, in rats pretreated with melatonin, all above parameters were successfully returned to nearly normal levels with maximal change observed in rats receiving 100 mg/kg. As prophylactic treatment with melatonin effectively normalizes RANKL/OPG signaling by depressing TLR4/MyD88‐mediated pro‐inflammatory cytokine production, dietary supplement with melatonin may serve as an advanced strategy to strengthen oral health to counteract PD‐induced destructive damage.

Melatonin Successfully Rescues Hippocampal Bioenergetics and Improves Cognitive Function following Drug Intoxication by Promoting Nrf2-ARE Signaling Activity

Prolonged exposure to gamma‐hydroxybutyric acid (GHB) would cause drug intoxication in which impaired cognitive function results from enhanced hippocampal oxidative stress may serve as a major symptom in this deficiency. Considering melatonin possesses significant anti‐oxidative efficacy, this study aimed to determine whether melatonin would successfully promote the nuclear factor erythroid 2‐related factor 2 and antioxidant responsive element (Nrf2‐ARE) signaling, depress oxidative stress, and rescue hippocampal bioenergetics and cognitive function following drug intoxication injury. Adolescent rats subjected to 10 days of GHB were received melatonin at doses of either 10 or 100 mg/kg. Time‐of‐flight secondary ion mass spectrometry, biochemical assay, quantitative histochemistry, [14C]‐2‐deoxyglucose analysis, together with Morris water maze were employed to detect the molecular signaling, oxidative status, bioenergetic level, as well as the cognitive performances, respectively. Results indicated that in GHB‐intoxicated rats, enhanced oxidative stress, increased cholesterol level, and decreased anti‐oxidative enzymes activities were detected in hippocampal regions. Intense oxidative stress paralleled well with reduced bioenergetics and poor performance in behavioral testing. However, in rats treated with melatonin following GHB intoxication, all above parameters and cognitive function were gradually returned to nearly normal levels. Melatonin also remarkably promoted the translocation of Nrf2 from cytoplasm to nucleus in a dose‐dependent manner, thereby increased the Nrf2‐ARE signaling‐related downstream anti‐oxidative enzymes activities. As melatonin effectively rescues hippocampal bioenergetics through depressing the oxidative stress by promoting Nrf2‐ARE molecular machinery, this study thus highlights for the first time that clinical use of melatonin may serve as a therapeutic strategy to improve the cognitive function in unsuspecting victims suffered from GHB intoxication injury.

Redistribution of Cav2.1 channels and calcium ions in nerve terminals following end-to-side neurorrhaphy: ionic imaging analysis by TOF–SIMS

The P/Q-type voltage-dependent calcium channel (Cav2.1) in the presynaptic membranes of motor nerve terminals plays an important role in regulating Ca2+ transport, resulting in transmitter release within the nervous system. The recovery of Ca2+-dependent signal transduction on motor end plates (MEPs) and innervated muscle may directly reflect nerve regeneration following peripheral nerve injury. Although the functional significance of calcium channels and the levels of Ca2+ signalling in nerve regeneration are well documented, little is known about calcium channel expression and its relation with the dynamic Ca2+ ion distribution at regenerating MEPs. In the present study, end-to-side neurorrhaphy (ESN) was performed as an in vivo model of peripheral nerve injury. The distribution of Ca2+ at regenerating MEPs following ESN was first detected by time-of-flight secondary ion mass spectrometry, and the specific localization and expression of Cav2.1 channels were examined by confocal microscopy and western blotting. Compared with other fundamental ions, such as Na+ and K+, dramatic changes in the Ca2+ distribution were detected along with the progression of MEP regeneration. The re-establishment of Ca2+ distribution and intensity were correlated with the functional recovery of muscle in ESN rats. Furthermore, the re-clustering of Cav2.1 channels after ESN at the nerve terminals corresponded with changes in the Ca2+ distribution. These results indicated that renewal of the Cav2.1 distribution within the presynaptic nerve terminals may be necessary for initiating a proper Ca2+ influx and shortening the latency of muscle contraction during nerve regeneration.