Melatonin inhibits postischemic matrix metalloproteinase-9 (MMP-9) activation via dual modulation of plasminogen/plasmin system and endogenous MMP inhibitor in mice subjected to transient focal cerebral ischemia

Magnolol reduces glutamate-induced neuronal excitotoxicity and protects against permanent focal cerebral ischemia up to 4 hours

Neuroprotective efficacy of magnolol, 5,5′-dially-2,2′-dihydroxydiphenyl, was investigated in a model of stroke and cultured neurons exposed to glutamate-induced excitotoxicity. Rats were subjected to permanent middle cerebral artery occlusion (pMCAO). Magnolol or vehicle was administered intraperitoneally, at 1 hr pre-insult or 1–6 hrs post-insult. Brain infarction was measured upon sacrifice. Relative to controls, animals pre-treated with magnolol (50–200 mg/kg) had significant infarct volume reductions by 30.9–37.8% and improved neurobehavioral outcomes (P<0.05, respectively). Delayed treatment with magnolol (100 mg/kg) also protected against ischemic brain damage and improved neurobehavioral scores, even when administered up to 4 hrs post-insult (P<0.05, respectively). Additionally, magnolol (0.1 µM) effectively attenuated the rises of intracellular Ca²⁺ levels, [Ca²⁺](i), in cultured neurons exposed to glutamate. Consequently, magnolol (0.1–1 µM) significantly attenuated glutamate-induced cytotoxicity and cell swelling (P<0.05). Thus, magnolol offers neuroprotection against permanent focal cerebral ischemia with a therapeutic window of 4 hrs. This neuroprotection may be, partly, mediated by its ability to limit the glutamate-induced excitotoxicity.

Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 expression in early focal cerebral infarction following urokinase thrombolysis in rats

Activity of matrix metalloproteinase-9 increases following cerebral ischemia/reperfusion, and is associated with cerebral microvascular permeability, blood-brain barrier destruction, inflammatory cell infiltration and brain edema. Matrix metalloproteinase-9 also likely participates in thrombolysis. A rat model of middle cerebral artery infarction was established by injecting autologous blood clots into the internal carotid artery. At 3 hours following model induction, urokinase was injected into the caudal vein. Decreased neurological severity score, reduced infarct volume, and increased expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 were observed in the cerebral cortex 24 hours after urokinase thrombolysis. These results suggest that urokinase can suppress damage in the acute-early stage of cerebral infarction.

Evidence that membrane-bound G protein-coupled melatonin receptors MT1 and MT2 are not involved in the neuroprotective effects of melatonin in focal cerebral ischemia

Melatonin is synthesized and released by the pineal gland in a circadian rhythm, and many of its peripheral actions are mediated via membrane MT1 and MT2 receptors. Apart from its metabolic functions, melatonin is a potent neuroprotective molecule owing to its antioxidative actions. The roles of MT1 and MT2 in the neuroprotective effects of melatonin and cell signaling after cerebral ischemia remain unknown. With the use of MT1 and MT2 knockout (mt1/2(-/-) ) mice treated with melatonin, we evaluated brain injury, edema formation, inducible nitric oxide synthase (iNOS) activity, and signaling pathways, including CREB, ATF-1, p21, Jun kinase (JNK)1/2, p38 phosphorylation, resulting from ischemia/reperfusion injury. We show that the infarct volume and brain edema do not differ between mt1/2(-/-) and wild-type (WT) animals, but melatonin treatment decreases infarct volume in both groups and brain edema in WT animals after middle cerebral artery occlusion. Notably, melatonin's neuroprotective effect was even more pronounced in mt1/2(-/-) animals compared to that in WT animals. We also demonstrate that melatonin treatment decreased CREB, ATF-1, and p38 phosphorylation in both mt1/2(-/-) and WT mice, while p21 and JNK1/2 were reduced only in melatonin-treated WT animals in the ischemic hemisphere. Furthermore, melatonin treatment lowered iNOS activity only in WT animals. We provide evidence that the absence of MT1 and MT2 has no unfavorable effect on ischemic brain injury. In addition, the neuroprotective effects of melatonin appear to be mediated through a mechanism independent of its membrane receptors. The underlying mechanism(s) should be further studied using selective melatonin receptor agonists and antagonists.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Melatonin protects liver against ischemia and reperfusion injury through inhibition of toll-like receptor signaling pathway

This study investigated the immunomodulating effect of melatonin on toll-like receptor (TLR)-stimulated signal transduction. Rats were subjected to 60 min of ischemia followed by 1 or 5 hr of reperfusion. Melatonin (10 mg/kg) or the vehicle was administered intraperitoneally 15 min prior to ischemia and immediately before reperfusion. Melatonin treatment significantly reduced the level of serum alanine aminotransferase activity. Increased levels of TLR3 and TLR4 protein expression induced by ischemia/reperfusion (I/R) were attenuated by melatonin. Serum level of high-mobility group box 1 (HMGB1), a potent alarmin of the TLR system, increased significantly in the I/R group, and melatonin inhibited this release. Melatonin suppressed the increase in myeloid differentiation factor 88 (MyD88) protein expression, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) phosphorylation and nuclear translocation of nuclear factor κB (NF-κB) and phosphorylated c-Jun, a component of activator protein 1. The increased level of toll-receptor-associated activator of interferon (TRIF) expression, phosphorylation of interferon (IFN) regulatory factor 3 (IRF3) and serum IFN-β was attenuated by melatonin. Melatonin attenuated the levels of tumor necrosis factor alpha (TNF-α), interleukin (IL)-6 and inducible nitric oxide synthase (iNOS) protein and mRNA expression, while the level of heme oxygenase-1 (HO-1) was augmented. Our results suggest that melatonin ameliorates I/R-induced liver damage by modulation of TLR-mediated inflammatory responses.

Melatonin protects against transient focal cerebral ischemia in both reproductively active and estrogen-deficient female rats: the impact of circulating estrogen on its hormetic dose-response

Melatonin (5-15 mg/kg) protects male animals against ischemic stroke. We explored the potential interactions and synergistic neuroprotection of melatonin and estrogen using a panel of lipid peroxidation and radical-scavenging assays, primary neuronal cultures subjected to oxygen-glucose deprivation (OGD), and lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Neuroprotective efficacy of melatonin was also evaluated in both reproductively active and ovariectomized female rats subjected to transient focal cerebral ischemia. Relative to melatonin or estradiol (E2) alone, a combination of the two agents exhibited robust, synergistic antioxidant and radical-scavenging actions (P<0.05, respectively). Additionally, the two agents, when combined at large doses, showed synergistic inhibition in the production of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) in the LPS-stimulated RAW 264.7 cells (P<0.05, respectively). Alternatively, co-treatment with melatonin and E2 independently, but not combined, showed a U-shaped dose-responsive (hormetic) cytoprotection for neuronal cultures subjected to OGD. When combined at a dosage either positively or negatively skewed from each optimal dosage, however, co-treatment caused synergistic neuroprotection. Relative to vehicle-injected controls, melatonin given intravenously at 1-5 mg/kg, but not 0.1 or 15 mg/kg, significantly reduced brain infarction and improved neurobehavioral outcomes (P<0.05, respectively) in reproductively active female rats. In ovariectomized stroke rats, melatonin was only effective at a large dosage (15-50 mg/kg). These results demonstrate complex interactions and synergistic antioxidant, radical-scavenging, and anti-inflammatory actions between estradiol and melatonin, and highlight the potential need to rectify the melatonin's hormetic dose-response by the level of circulating estradiol in the treatment of female stroke patients.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.