An Antioxidant Role by Minocycline Via Enhancing the Activation of LKB1/AMPK Signaling in the Process of Cerebral Ischemia Injury

The mechanisms of minocycline in alleviating ischemic stroke damage and cerebral ischemia-reperfusion injury

Stroke is a group of diseases resulting from cerebral vascular rupture or obstruction and subsequent brain blood circulation disorder, leading to rapid neurological deficits. Ischemic stroke accounts for the majority of all stroke cases. The current treatments for ischemic stroke mainly include t-PA thrombolytic therapy and surgical thrombectomy. However, these interventions aimed at recanalizing cerebral vessels can paradoxically lead to ischemia-reperfusion injury, which exacerbates the severity of brain damage. Minocycline, a semi-synthetic tetracycline antibiotic, has been shown to possess a wide range of neuroprotective effects independent of its antibacterial activity. Here we summarize the mechanisms underlying the protective effects of minocycline against cerebral ischemia-reperfusion injury based on the pathogenesis of cerebral ischemia-reperfusion injury, including its modulation of oxidative stress, inflammatory response, excitotoxicity, programmed cell death and blood-brain barrier injury, and also introduce the role of minocycline in alleviating stroke-related complications, in order to provide a theoretical basis for the clinical application of minocycline in cerebral ischemia-reperfusion injury.

Minocycline as heart conditioning agent in experimental type 2 diabetes mellitus - an antibacterial drug in heart protection

Cardiovascular diseases, and among them certainly myocardial infarction, remain leading cause of death worldwide. Diabetes increases risk of occurrence as well as adverse outcome of myocardial infarction. Conditioning maneuvers are the most attractive method for alleviating both the consequences of ischemia and reperfusion. Minocycline is a tetracycline derivative which exerts antioxidant, anti-inflammatory, and anti-apoptotic effects. The aim of this study was to assess the protective ability of preconditioning and postconditioning of isolated hearts from healthy and rats with experimentally induced type 2 diabetes with minocycline on functional recovery and redox status after ischemia and reperfusion. The hearts from healthy and diabetic rats were excised and retrogradely perfused according to the Langendorff technique. Using sensor in the left ventricle, the cardiodynamic parameters were recorded and in the samples of the coronary venous effluent oxidative stress biomarkers were analyzed. Minocycline was injected directly into the coronary vessels, in preconditioning 5 min before global ischemia, and in postconditioning during the first 5 min of reperfusion. Results of this study clearly show beneficial effects of minocycline applied both before ischemia and in the first minutes of reperfusion fashion in both healthy and diabetic rat hearts. The most prominent protective effect regarding oxidative stress is related to the decreased production of superoxide anion radical due postconditioning with minocycline in diabetic hearts. Cardiodynamic parameters were significantly improved in minocycline conditioned groups. Superoxide anion radical stands out as the most susceptible to changes induced by minocycline.

Combined antioxidants and anti-inflammatory therapies fail to attenuate the early and late phases of cyclodextrin-induced cochlear damage and hearing loss

Niemann-Pick C1 (NPC1) is a fatal neurodegenerative disease caused by aberrant cholesterol metabolism. The progression of the disease can be slowed by removing excess cholesterol with high-doses of 2-hyroxypropyl-beta-cyclodextrin (HPβCD). Unfortunately, HPβCD causes hearing loss; the initial first phase involves a rapid destruction of outer hair cells (OHCs) while the second phase, occurring 4-6 weeks later, involves the destruction of inner hair cells (IHCs), pillar cells, collapse of the organ of Corti and spiral ganglion neuron degeneration. To determine whether the first and/or second phase of HPβCD-induced cochlear damage is linked, in part, to excess oxidative stress or neuroinflammation, rats were treated with a single-dose of 3000 mg/kg HPβCD alone or together with one of two combination therapies. Each combination therapy was administered from 2-days before to 6-weeks after the HPβCD treatment. Combination 1 consisted of minocycline, an antibiotic that suppresses neuroinflammation, and HK-2, a multifunctional redox modulator that suppresses oxidative stress. Combination 2 was comprised of minocycline plus N-acetyl cysteine (NAC), which upregulates glutathione, a potent antioxidant. To determine if either combination therapy could prevent HPβCD-induced hearing impairment and cochlear damage, distortion product otoacoustic emissions (DPOAE) were measured to assess OHC function and the cochlear compound action potential (CAP) was measured to assess the function of IHCs and auditory nerve fibers. Cochleograms were prepared to quantify the amount of OHC, IHC and pillar cell (PC) loss. HPβCD significantly reduced DPOAE and CAP amplitudes and caused significant OHC, IHC and OPC losses with losses greater in the high-frequency base of the cochlea than the apex. Neither minocycline + HK-2 (MIN+ HK-2) nor minocycline + NAC (MIN+NAC) prevented the loss of DPOAEs, CAPs, OHCs, IHCs or IPCs caused by HPβCD. These results suggest that oxidative stress and neuroinflammation are unlikely to play major roles in mediating the first or second phase of HPβCD-induced cochlear damage. Thus, HPβCD-induced ototoxicity must be mediated by some other unknown cell-death pathway possibly involving loss of trophic support from damaged support cells or disrupted cholesterol metabolism.

Minocycline Impact on Redox Homeostasis of Normal Human Melanocytes HEMn-LP Exposed to UVA Radiation and Hydrogen Peroxide

Minocycline is a semisynthetic tetracycline antibiotic. In addition to its antibacterial activity, minocycline shows many non-antibiotic, beneficial effects, including antioxidative action. The property is responsible, e.g., for anti-inflammatory, neuroprotective, and cardioprotective effects of the drug. However, long-term pharmacotherapy with minocycline may lead to hyperpigmentation of the skin. The reasons for the pigmentation disorders include the deposition of the drug and its metabolites in melanin-containing cells and the stimulation of melanogenesis. The adverse drug reaction raises a question about the influence of the drug on melanocyte homeostasis. The study aimed to assess the effect of minocycline on redox balance in human normal melanocytes HEMn-LP exposed to hydrogen peroxide and UVA radiation. The obtained results indicate that minocycline induced oxidative stress in epidermal human melanocytes. The drug inhibited cell proliferation, decreased the level of reduced thiols, and stimulated the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). The described changes were accompanied by an increase in the intracellular level of ROS. On the other hand, pretreatment with minocycline at the same concentrations increased cell viability and significantly attenuated the oxidative stress in melanocytes exposed to hydrogen peroxide and UVA radiation. Moreover, the molecular docking analysis revealed that the different influence of minocycline and other tetracyclines on CAT activity can be related to the location of the binding site.

The possible role of CREB-BDNF signaling pathway in neuroprotective effects of minocycline against alcohol-induced neurodegeneration: molecular and behavioral evidences

Abuse of alcohol triggers neurodegeneration in human brain. Minocycline has characteristics conferring neuroprotection. Current study evaluates the role of the CREB-BDNF signaling pathway in mediating minocycline's neuroprotective effects against alcohol-induced neurodegeneration. Seventy adult male rats were randomly split into groups 1 and 2 that received saline and alcohol (2 g/kg/day by gavage, once daily), respectively, and groups 3, 4, 5, and 6 were treated simultaneously with alcohol and minocycline (10, 20, 30 and 40 mg/kg I.P, respectively) for 21 days. Group 7 received minocycline alone (40 mg/kg, i.p) for 21 days. Morris water maze (MWM) has been used to assess cognitive activity. Hippocampal neurodegenerative and histological parameters as well as cyclic AMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) levels were assessed. Alcohol impaired cognition, and concurrent therapy with various minocycline doses attenuated alcohol-induced cognition disturbances. Additionally, alcohol administration boosted lipid peroxidation and levels of glutathione in oxidized form (GSSG), tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and Bax protein, while decreased reducing type of glutathione (GSH), Bcl-2 protein, phosphorylated CREB, and BDNF levels in rat hippocampus. Alcohol also decreased the activity in the hippocampus of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR). In comparison, minocycline attenuated alcohol-induced neurodegeneration; elevating expression levels of P-CREB and BDNF and inhibited alcohol induced histopathological changes in both dentate gyrus (DG) and CA1 of hippocampus. Thus, minocycline is likely to provide neuroprotection against alcohol-induced neurodegeneration through mediation of the P-CREB/BDNF signaling pathway.

Minocycline Inhibits mTOR Signaling Activation and Alleviates Behavioral Deficits in the Wistar Rats with Acute Ischemia stroke

BACKGROUND

Mammalian target of rapamycin (mTOR) has been evidenced as a multimodal therapy in the pathophysiological process of Acute Ischemic Stroke (AIS). However, the pathway that minocycline targets mTOR signaling is not fully defined in the AIS pathogenesis. This study aims at the roles of minocycline on the mTOR signaling in the AIS process and further discovers the underlying mechanisms of minocycline involved in the following change of mTOR signaling-autophagy.

METHODS

Cerebral ischemia/reperfusion (CIR) rat animal models were established with the transient suture occlusion into the middle cerebral artery. Minocycline (50mg/kg) was given by intragastric administration. The Morris water maze was used to test the cognitive function of animals. Immunohistochemistry and immunofluorescence were introduced for testing the levels of synaptophysin and PSD-95. Western blot was conducted for investigating the levels of mTOR, p-mTOR (Ser2448), p70S6, p-p70S6 (Thr389), eEF2k, p-eEF2k (Ser366), p-eIF4B (Ser406), LC3, p62, synaptophysin and PSD-95.

RESULTS

Minocycline prevents the cognitive decline of the MCAO stroke rats. Minocycline limits the expression of p-mTOR (Ser2448) and the downstream targets of mTOR [p70S6, p-p70S6 (Thr389), eEF2k, p-eEF2k (Ser366) and p-eIF4B (Ser406)] (P<0.01), while minocycline has no influence on mTOR. LC3-II abundance and the LC3-II/I ratio were upregulated in the hippocampus of the MCAO stroke rats by the minocycline therapy (P<0.01). p62 was downregulated in the hippocampus from the MCAO stroke rats administrated with minocycline therapy(P<0.01). The levels of SYP and PSD-95 were upregulated in the brain of the MCAO stroke rats administrated with minocycline therapy.

CONCLUSION

Minocycline prevents cognitive deficits via inhibiting mTOR signaling and enhancing the autophagy process, and promoting the expression of pre- and postsynaptic proteins (synaptophysin and PSD-95) in the brain of the MCAO stroke rats. The potential neuroprotective role of minocycline in the process of cerebral ischemia may be related to mitigating ischemia-induced synapse injury via inhibiting the activation of mTOR signaling.