The Transient Receptor Potential Melastatin 7 (TRPM7) Inhibitors Suppress Seizure-Induced Neuron Death by Inhibiting Zinc Neurotoxicity

Imipramine, an Acid Sphingomyelinase Inhibitor, Promotes Newborn Neuron Survival in the Hippocampus After Seizure

Epilepsy, a chronic neurological disorder, is triggered by various insults, including traumatic brain injury and stroke. Acid sphingomyelinase (ASMase), an enzyme that hydrolyzes sphingomyelin into ceramides, is implicated in oxidative stress, neuroinflammation, and neuronal apoptosis. Ceramides, which have pro-apoptotic properties, contribute to oxidative damage and lysosomal dysfunction, exacerbating neuronal injury. This study investigates the role of ASMase in epilepsy, hypothesizing that seizure activity upregulates ASMase, increasing ceramide levels, DNA damage, and neuronal apoptosis. We employed a pilocarpine-induced rat seizure model and examined the effects of imipramine, an ASMase inhibitor, administered intraperitoneally (10 mg/kg) for four weeks post-seizure induction. Histological and cognitive analyses showed that while imipramine did not prevent early neuronal death within the first week, it significantly reduced markers of neuronal apoptosis by four weeks. Imipramine also promoted hippocampal neurogenesis and preserved cognitive function, which is often impaired following seizures. These findings suggest that ASMase inhibition could mitigate neuronal apoptosis and improve cognitive recovery after seizures. Imipramine may serve as a promising therapeutic strategy for epilepsy-associated neuronal damage and cognitive deficits. Further studies should delineate the molecular mechanisms of ASMase inhibition and evaluate its long-term efficacy in addressing epilepsy-related neurodegeneration and functional impairments.

TRPM7 Mediates Neuropathic Pain by Activating mTOR Signaling in Astrocytes after Spinal Cord Injury in Rats

In this study, we investigated whether transient receptor melastatin 7 (TRPM7), known as a non-selective cation channel, inhibits neuropathic pain after spinal cord injury (SCI) and how TRPM7 regulates neuropathic pain. Neuropathic pain was developed 4 weeks after moderate contusive SCI and TRPM7 was markedly upregulated in astrocytes in the lamina I and II of L4-L5 dorsal horn. In addition, both mechanical allodynia and thermal hyperalgesia were significantly alleviated by a TRPM7 inhibitor, carvacrol. In particular, carvacrol treatment inhibited mechanistic target of rapamycin (mTOR) signaling, which was activated in astrocytes. When rats were treated with rapamycin, an inhibitor of mTOR signaling, neuropathic pain was significantly inhibited. Furthermore, blocking TRPM7 and mTOR signaling by carvacrol and rapamycin inhibited astrocyte activation in lamina I and II of dorsal spinal cord and reduced the level of p-JNK and p-c-Jun, which are known to be activated in astrocytes. Finally, inhibiting TRPM7/mTOR signaling also downregulated the production of pain-related factors such as tumor necrosis factor-α, interleukin-6, interleukin-1β, chemokine (C-C motif) ligand (CCL) 2, CCL-3, CCL-4, CCL-20, chemokine C-X-C motif ligand 1, and matrix metalloproteinase 9 which are known to be involved in the induction and/or maintenance of neuropathic pain after SCI. These results suggest an important role of TRPM7-mediated mTOR signaling in astrocyte activation and thereby induction and/or maintenance of neuropathic pain after SCI.

A phosphodiesterase 4 (PDE4) inhibitor, amlexanox, reduces neuroinflammation and neuronal death after pilocarpine-induced seizure

Epilepsy, a complex neurological disorder, is characterized by recurrent seizures caused by aberrant electrical activity in the brain. Central to this study is the role of lysosomal dysfunction in epilepsy, which can lead to the accumulation of toxic substrates and impaired autophagy in neurons. Our focus is on phosphodiesterase-4 (PDE4), an enzyme that plays a crucial role in regulating intracellular cyclic adenosine monophosphate (cAMP) levels by converting it into adenosine monophosphate (AMP). In pathological states, including epilepsy, increased PDE4 activity contributes to a decrease in cAMP levels, which may exacerbate neuroinflammatory responses. We hypothesized that amlexanox, an anti-inflammatory drug and non-selective PDE4 inhibitor, could offer neuroprotection by addressing lysosomal dysfunction and mitigating neuroinflammation, ultimately preventing neuronal death in epileptic conditions. Our research utilized a pilocarpine-induced epilepsy animal model to investigate amlexanox's potential benefits. Administered intraperitoneally at a dose of 100 ​mg/kg daily following the onset of a seizure, we monitored its effects on lysosomal function, inflammation, neuronal death, and cognitive performance in the brain. Tissue samples from various brain regions were collected at predetermined intervals for a comprehensive analysis. The study's results were significant. Amlexanox effectively improved lysosomal function, which we attribute to the modulation of zinc's influx into the lysosomes, subsequently enhancing autophagic processes and decreasing the release of inflammatory factors. Notably, this led to the attenuation of neuronal death in the hippocampal region. Additionally, cognitive function, assessed through the modified neurological severity score (mNSS) and the Barnes maze test, showed substantial improvements after treatment with amlexanox. These promising outcomes indicate that amlexanox has potential as a therapeutic agent in the treatment of epilepsy and related brain disorders. Its ability to combat lysosomal dysfunction and neuroinflammation positions it as a potential neuroprotective intervention. While these findings are encouraging, further research and clinical trials are essential to fully explore and validate the therapeutic efficacy of amlexanox in epilepsy management.

Effects of L-Type Voltage-Gated Calcium Channel (LTCC) Inhibition on Hippocampal Neuronal Death after Pilocarpine-Induced Seizure

Epilepsy, marked by abnormal and excessive brain neuronal activity, is linked to the activation of L-type voltage-gated calcium channels (LTCCs) in neuronal membranes. LTCCs facilitate the entry of calcium (Ca2+) and other metal ions, such as zinc (Zn2+) and magnesium (Mg2+), into the cytosol. This Ca2+ influx at the presynaptic terminal triggers the release of Zn2+ and glutamate to the postsynaptic terminal. Zn2+ is then transported to the postsynaptic neuron via LTCCs. The resulting Zn2+ accumulation in neurons significantly increases the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, contributing to reactive oxygen species (ROS) generation and neuronal death. Amlodipine (AML), typically used for hypertension and coronary artery disease, works by inhibiting LTCCs. We explored whether AML could mitigate Zn2+ translocation and accumulation in neurons, potentially offering protection against seizure-induced hippocampal neuronal death. We tested this by establishing a rat epilepsy model with pilocarpine and administering AML (10 mg/kg, orally, daily for 7 days) post-epilepsy onset. We assessed cognitive function through behavioral tests and conducted histological analyses for Zn2+ accumulation, oxidative stress, and neuronal death. Our findings show that AML's LTCC inhibition decreased excessive Zn2+ accumulation, reactive oxygen species (ROS) production, and hippocampal neuronal death following seizures. These results suggest amlodipine's potential as a therapeutic agent in seizure management and mitigating seizures' detrimental effects.

From zinc homeostasis to disease progression: Unveiling the neurodegenerative puzzle

Zinc is a crucial trace element in the human body, playing a role in various physiological processes such as oxidative stress, neurotransmission, protein synthesis, and DNA repair. The zinc transporters (ZnTs) family members are responsible for exporting intracellular zinc, while Zrt- and Irt-like proteins (ZIPs) are involved in importing extracellular zinc. These processes are essential for maintaining cellular zinc homeostasis. Imbalances in zinc metabolism have been linked to the development of neurodegenerative diseases. Disruptions in zinc levels can impact the survival and activity of neurons, thereby contributing to the progression of neurodegenerative diseases through mechanisms like cell apoptosis regulation, protein phase separation, ferroptosis, oxidative stress, and neuroinflammation. Therefore, conducting a systematic review of the regulatory network of zinc and investigating the relationship between zinc dysmetabolism and neurodegenerative diseases can enhance our understanding of the pathogenesis of these diseases. Additionally, it may offer new insights and approaches for the treatment of neurodegenerative diseases.

Drugs acting at TRPM7 channels inhibit seizure-like activity

Transient receptor potential cation subfamily M7 (TRPM7) channels are ion channels permeable to divalent cations. They are abundantly expressed with particularly high expression in the brain. Previous studies have highlighted the importance of TRPM7 channels in brain diseases such as stroke and traumatic brain injury, yet evidence for a role in seizures and epilepsy is lacking. Here, we show that carvacrol, a food additive that inhibits TRPM7 channels, and waixenicin A, a novel selective and potent TRPM7 inhibitor, completely suppressed seizure-like activity in rodent hippocampal-entorhinal brain slices exposed to pentylenetetrazole or low magnesium. These findings support inhibition of TRPM7 channels as a novel target for antiseizure medications.

Pathophysiological Roles of Transient Receptor Potential (Trp) Channels and Zinc Toxicity in Brain Disease

Maintaining the correct ionic gradient from extracellular to intracellular space via several membrane-bound transporters is critical for maintaining overall cellular homeostasis. One of these transporters is the transient receptor potential (TRP) channel family that consists of six putative transmembrane segments systemically expressed in mammalian tissues. Upon the activation of TRP channels by brain disease, several cations are translocated through TRP channels. Brain disease, especially ischemic stroke, epilepsy, and traumatic brain injury, triggers the dysregulation of ionic gradients and promotes the excessive release of neuro-transmitters and zinc. The divalent metal cation zinc is highly distributed in the brain and is specifically located in the pre-synaptic vesicles as free ions, usually existing in cytoplasm bound with metallothionein. Although adequate zinc is essential for regulating diverse physiological functions, the brain-disease-induced excessive release and translocation of zinc causes cell damage, including oxidative stress, apoptotic cascades, and disturbances in energy metabolism. Therefore, the regulation of zinc homeostasis following brain disease is critical for the prevention of brain damage. In this review, we summarize recent experimental research findings regarding how TRP channels (mainly TRPC and TRPM) and zinc are regulated in animal brain-disease models of global cerebral ischemia, epilepsy, and traumatic brain injury. The blockade of zinc translocation via the inhibition of TRPC and TRPM channels using known channel antagonists, was shown to be neuroprotective in brain disease. The regulation of both zinc and TRP channels may serve as targets for treating and preventing neuronal death.

Transient Receptor Potential (TRP) Channels in Pain, Neuropsychiatric Disorders, and Epilepsy

Pharmacomodulation of membrane channels is an essential topic in the study of physiological conditions and disease status. Transient receptor potential (TRP) channels are one such family of nonselective cation channels that have an important influence. In mammals, TRP channels consist of seven subfamilies with a total of twenty-eight members. Evidence shows that TRP channels mediate cation transduction in neuronal signaling, but the full implication and potential therapeutic applications of this are not entirely clear. In this review, we aim to highlight several TRP channels which have been shown to mediate pain sensation, neuropsychiatric disorders, and epilepsy. Recent findings suggest that TRPM (melastatin), TRPV (vanilloid), and TRPC (canonical) are of particular relevance to these phenomena. The research reviewed in this paper validates these TRP channels as potential targets of future clinical treatment and offers patients hope for more effective care.

The blockade of transient receptor potential ankyrin 1 (TRPA1) protects against PTZ-induced seizure

Treatment of epilepsy remains a major problem as some epileptic patients do not respond to the current therapeutics. Transient receptor potential ankyrin 1 (TRPA1) belongs to the TRP channels and has diverse physiological functions in the body. Considering its physiological properties, we aimed to evaluate its role in two experimental models of epilepsy, including pentylenetetrazol (PTZ)-induced acute seizure and PTZ-evoked kindling. Furthermore, the TRPA1 protein levels were assessed in the cerebral cortex, hippocampus, and cerebellum after seizure induction. Three groups of Wistar rats received acute intraperitoneal injection of pentylenetetrazol (PTZ, 85 mg/kg). The groups received intraventricular injections of vehicle (dimethyl sulfoxide, Tween 80, and sterile 0.9% saline), valproate (30 µg/rat), or HC030031 (TRPA1 antagonist, 14 µg/rat) before PTZ injection. In the PTZ-induced kindling model, PTZ was administrated 35 mg/kg every other day for 24 days. PTZ gradually provoked seizure-related behaviors. After experiments, the TRPA1 levels in the brain were assessed using western blot. The results showed that HC030031 reduced the median of seizure scores and S5 duration while increasing S2 and S5 latencies in acute and kindling models. The anticonvulsant effect of HC030031 was comparable with valproate as a standard anticonvulsant drug. Furthermore, induction of seizure, either acute or kindling, enhanced TRPA1 levels in the cerebral cortex, hippocampus, and cerebellum that were prevented by HC030031 or valproate administration. The results of this study showed that HC030031 as a TRPA1 receptor antagonist promoted a significant anticonvulsant effect comparable with valproate. Both drugs prevented TRPA1 upregulation during seizures. These findings imply that TRPA1 is a potential target in treating epilepsy.

Boron-containing compounds on neurons: Actions and potential applications for treating neurodegenerative diseases

Boron-containing compounds (BCC) exert effects on neurons. After the expanding of both the identification and synthesis of new BCC, novel effects in living systems have been reported, many of these involving neuronal action. In this review, the actions of BCC on neurons are described; the effects have been inferred by boron deprivation or addition. Also, the effects can be related to those mediated by interaction on ionic channels, G-protein coupled receptors, or other receptors exerting modification on neuronal behavior. Additionally, BCC have exhibited effects by the modulation of inflammation or oxidative processes. BCC are expanding as drugs. Deprivation of boron sources from the diet shows the role of some natural BCC. However, the observations of several new synthesized compounds suggest their ability to act with attractive potency, efficacy, and long-term action on neuronal receptors or processes related with the origin and evolution of neurodegenerative processes. The details of BCC-target interactions are currently being elucidated in progress, as those observed from BCC-protein crystal complexes. Taking all of the above into account, the expansion is presumably near to having studies on the application of BCC as drugs on specific targets for treating neurodegenerative diseases.

Combined Treatment of Dichloroacetic Acid and Pyruvate Increased Neuronal Survival after Seizure

During seizure activity, glucose and Adenosine triphosphate (ATP) levels are significantly decreased in the brain, which is a contributing factor to seizure-induced neuronal death. Dichloroacetic acid (DCA) has been shown to prevent cell death. DCA is also known to be involved in adenosine triphosphate (ATP) production by activating pyruvate dehydrogenase (PDH), a gatekeeper of glucose oxidation, as a pyruvate dehydrogenase kinase (PDK) inhibitor. To confirm these findings, in this study, rats were given a per oral (P.O.) injection of DCA (100 mg/kg) with pyruvate (50 mg/kg) once per day for 1 week starting 2 h after the onset of seizures induced by pilocarpine administration. Neuronal death and oxidative stress were assessed 1 week after seizure to determine if the combined treatment of pyruvate and DCA increased neuronal survival and reduced oxidative damage in the hippocampus. We found that the combined treatment of pyruvate and DCA showed protective effects against seizure-associated hippocampal neuronal cell death compared to the vehicle-treated group. Treatment with combined pyruvate and DCA after seizure may have a therapeutic effect by increasing the proportion of pyruvate converted to ATP. Thus, the current research demonstrates that the combined treatment of pyruvate and DCA may have therapeutic potential in seizure-induced neuronal death.

Potentials of miR-9-5p in promoting epileptic seizure and improving survival of glioma patients

Background

Epilepsy affects over 70 million people worldwide; however, the underlying mechanisms remain unclear. MicroRNAs (miRNAs) have essential functions in epilepsy. miRNA-9, a brain-specific/enriched miRNA, plays a role in various nervous system diseases and tumors, but whether miRNA-9 is involved in epilepsy and glioma-associated epilepsy remains unknown. Therefore, we aimed to explore the potential role of miR-9-5p in seizures and its effect on the survival of glioma patients, in order to provide new targets for the treatment of epilepsy and glioma.

Methods

The YM500v2 database was used to validate the expression of hsa-miR-9-5p in tissues. Moreover, qRT-PCR was performed to investigate the expression of miR-9-5p in temporal lobe epilepsy patients and rats with lithium-pilocarpine-induced seizures. Recombinant adeno-associated virus containing miR-9-5p was constructed to overexpress miR-9-5p in vivo. The effects of miR-9-5p on the behavior and electroencephalographic activities of the lithium-pilocarpine rat model of epilepsy were tested. Bioinformatics analysis was used to predict the targets of miR-9-5p and explore its potential role in epilepsy and glioma-associated epilepsy.

Results

The expression of miR-9-5p increased at 6 h and 7 days after lithium-pilocarpine-induced seizures in rats. Overexpression of miR-9-5p significantly shortened the latency of seizures and increased seizure intensity at 10 min and 20 min after administration of pilocarpine (P < 0.05). Predicted targets of miR-9-5p were abundant and enriched in the brain, and affected various pathways related to epilepsy and tumor. Survival analysis revealed that overexpression of miR-9-5p significantly improved the survival of patients from with low-grade gliomas and glioblastomas. The involvement of miR-9-5p in the glioma-associated epileptic seizures and the improvement of glioma survival may be related to multiple pathways, including the Rho GTPases and hub genes included SH3PXD2B, ARF6, and ANK2.

Conclusions

miR-9-5p may play a key role in promoting epileptic seizures and improving glioma survival, probably through multiple pathways, including GTPases of the Rho family and hub genes including SH3PXD2B, ARF6 and ANK2. Understanding the roles of miR-9-5p in epilepsy and glioma and the underlying mechanisms may provide a theoretical basis for the diagnosis and treatment of patients with epilepsy and glioma.

Carvacrol Inhibits Expression of Transient Receptor Potential Melastatin 7 Channels and Alleviates Zinc Neurotoxicity Induced by Traumatic Brain Injury

Carvacrol is a monoterpenoid phenol produced by aromatic plants such as oregano. Although the exact mechanism by which carvacrol acts has not yet been established, it appears to inhibit transient receptor potential melastatin 7 (TRPM7), which modulates the homeostasis of metal ions such as zinc and calcium. Several studies have demonstrated that carvacrol has protective effects against zinc neurotoxicity after ischemia and epilepsy. However, to date, no studies have investigated the effect of carvacrol on traumatic brain injury (TBI)-induced zinc neurotoxicity. In the present study, we investigated the therapeutic potential of carvacrol for the prevention of zinc-induced neuronal death after TBI. Rats were subjected to a controlled cortical impact, and carvacrol was injected at a dose of 50 mg/kg. Histological analysis was performed at 12 h, 24 h, and 7 days after TBI. We found that carvacrol reduced TBI-induced TRPM7 over-expression and free zinc accumulation. As a result, subsequent oxidative stress, dendritic damage, and neuronal degeneration were decreased. Moreover, carvacrol not only reduced microglial activation and delayed neuronal death but also improved neurological outcomes after TBI. Taken together, these findings suggest that carvacrol administration may have therapeutic potential after TBI by preventing neuronal death through the inhibition of TRPM7 expression and alleviation of zinc neurotoxicity.

The Inhibition of Zinc Excitotoxicity and AMPK Phosphorylation by a Novel Zinc Chelator, 2G11, Ameliorates Neuronal Death Induced by Global Cerebral Ischemia

AMP-activated protein kinase (AMPK) is necessary for maintaining a positive energy balance and essential cellular processes such as glycolysis, gene transcription, glucose uptake, and several other biological functions. However, brain injury-induced energy and metabolic stressors, such as cerebral ischemia, increase AMPK phosphorylation. Phosphorylated AMPK contributes to excitotoxicity, oxidative, and metabolic problems. Furthermore, brain disease-induced release of zinc from synaptic vesicles contributes to neuronal damage via mechanisms including ROS production, apoptotic cell death, and DNA damage. For this reason, we hypothesized that regulating zinc accumulation and AMPK phosphorylation is critical for protection against global cerebral ischemia (GCI). Through virtual screening based on the structure of AMPK subunit alpha 2, we identified a novel compound, 2G11. In this study, we verified that 2G11 administration has neuroprotective effects via the blocking of zinc translocation and AMPK phosphorylation after GCI. As a result, we demonstrated that 2G11 protected hippocampal neurons against GCI and OGD/R-derived cellular damage. In conclusion, we propose that AMPK inhibition and zinc chelation by 2G11 may be a promising tool for preventing GCI-induced hippocampal neuronal death.

Magnesium in renal fibrosis

PURPOSE

Renal fibrosis (RF) is the main pathological feature of chronic kidney disease (CKD). The main focus of research on treatment for CKD is to develop strategies that delay or prevent RF from progressing to end-stage renal disease (ESRD). Inflammation and oxidative stress occur during all stages of CKD. The magnesium cation (Mg²⁺) can reduce inflammation and oxidative stress, regulate apoptosis, and improve RF, and magnesium-based therapies are promising new treatments that can prevent RF. We reviewed the current evidence on the effects of magnesium in RF and examined the possible mechanism of magnesium in delaying RF.

METHODS

We searched PubMed, Web of Science, and EMBASE for articles on magnesium and fibrosis, with a focus on magnesium and RF.

RESULTS

Inflammation, oxidative stress, and apoptosis are related to the occurrence of CKD. Previous research showed that Mg²⁺ inhibits the differentiation of inflammatory cells, down-regulates the production of inflammatory cytokines, reduces inflammation, and reduces the production of reactive oxygen species (ROS) and oxidative stress. In addition, Mg²⁺ also regulates apoptosis and protects renal tubular function. Magnesium may also regulate TRPM6/7, promote the secretion of klotho protein and improve renal fibrosis. Therefore, Mg²⁺ can protect the kidney from damage and slow down the progression of RF through many molecular and cellular effects. Some of the anti-fibrotic effects of Mg²⁺ may be related to its antagonism of intracellular Ca²⁺.

CONCLUSION

Magnesium may prevent the progression of renal fibrosis and delay CKD by reducing renal inflammation and oxidative stress, and by regulating fibrosis-related signaling pathways and cytokines.

Neuroprotective effects of carvacrol against Alzheimer's disease and other neurodegenerative diseases: A review

Objective

Neurodegenerative diseases are considered an important cause of cognitive deficit and morbidity in old ages. Alzheimer's disease (AD) is one of these disorders affecting about 40 million people in the world at the present time. Available drug therapy is mostly symptomatic and does not modify or stop disease progression. Recently, biologically active chemicals from herbs have been studied to develop new therapeutic drugs. Carvacrol has shown positive properties on many neurological diseases. This compound is expected to have the ability to affect AD pathogenesis and therefore, it is considered an anti-AD agent.

Materials and Methods

This review was conducted using PubMed, Google Scholar and Science Direct bibliographic databases until November 2021. For data collection, the following keywords were used: carvacrol, neuroprotective, cognition, anti-inflammatory, antioxidant, Acetylcolinesterase inhibitor (AChEI), Alzheimer's, Parkinson's, epilepsy, stroke, ischemic brain injury, and neurodegenerative diseases.

Results

This review summarizes in vitro and in vivo studies on protective potential of carvacrol in neurodegenerative disorders and various underlying mechanisms, such as anti-inflammatory, antioxidant, and anticholinesterase effects.

Conclusion

We gave an overview of available literature concerning neuroprotective effects of carvacrol in ameliorating the neurodegenerative diseases symptoms in vivo and in vitro. Particular attention is given to AD. Several neuro-pharmacological actions of carvacrol have been summarized in the current review article including anti-inflammatory, antioxidant, and AChEI properties.

Mechanism of Stat1 in the neuronal Ca2+ overload after intracerebral hemorrhage via the H3K27ac/Trpm7 axis

Intracerebral hemorrhage (ICH) is classified as a subtype of stroke and Calcium (Ca²⁺) overload is a catalyst for ICH. This study explored the mechanisms of Stat1 (signal transducer and activator of transcription 1) in the neuronal Ca²⁺ overload after ICH. ICH mouse models and in vitro cell models were established. Stat1 and transient receptor potential melastatin 7 (Trpm7) were detected up-regulated in ICH models. Afterwards, the mice were infected with the lentivirus containing sh-Stat1, and HT22 cells were treated with si-Stat1 and the lentivirus containing pcDNA3.1-Trpm7. The neurologic functional impairment, histopathological damage, and Nissl body in mice were all measured. HT22 cell viability and apoptosis were identified. The levels of Ca²⁺, Trpm7 mRNA, H3K27 acetylation (H3K27ac), CaMKII-α, and p-Stat1 protein in the tissues and cells were determined. We found that silencing Stat1 alleviated ICH damage and repressed the neuronal Ca²⁺ overload after ICH. H3K27ac enrichment in the Trpm7 promoter region was examined and we found that p-Stat1 accelerated Trpm7 transcription via promoting H3K27ac in the Trpm7 promoter region. Besides, Trpm7 overexpression increased Ca²⁺ overload and aggravated ICH. Overall, p-Stat1 promoted Trpm7 transcription and further aggravated the Ca²⁺ overload after ICH.

Process Optimization for Supercritical Carbon Dioxide Extraction of Origanum vulgare L. Essential Oil Based on the Yield, Carvacrol, and Thymol Contents

Background

Origanum vulgare L. essential oil (OEO) is widely known for its good biological activity, but different extraction methods with significant implications on the yield of OEO and the content of the thymol and carvacrol. As an efficient method for extracting essential oils (EO), the supercritical carbon dioxide extraction (SC-CO2) can improve the yield of EOs while protecting their main active components from loss.

Objective

In this study, the process optimization of SC-CO2 of OEO was carried out. The effects of extraction pressure, temperature, time, and modifier concentration on the composite score of OEO extraction process were investigated.

Method

Response surface analysis was performed using a Box-Behnken design with three levels and four independent variables. Steam distillation (SD) and lipophilic solvents (n-hexane) extraction (LSE) were compared with SC-CO2 for OEO yields. OEOs extracted by the three methods were qualitatively and semi-quantitatively analyzed by gas chromatography quadrupole-time-of-flight mass spectrometry and gas chromatography-flame ionization detector.

Results

The results showed that extraction pressure was the most significant factor affecting the OEO yield, thymol, and carvacrol content. In the optimal conditions (pressure: 217 bar, temperature: 54°C, time: 2 h, modifier concentration: 14%), the yield of OEO reached up to 1.136%, and the contents of thymol and carvacrol reached 53.172  and 41.785 mg/g, respectively.

Conclusions

SC-CO2 was the best extraction method compared to the other two methods. Under the optimal conditions, yield and the content of main components can be effectively improved. It can provide a theoretical basis for the industrial extraction of OEO.

Highlights

Taking the comprehensive score as the index, the interaction between the four independent variables in the supercritical fluid extraction process was evaluated by the response surface method. The effects of extraction parameters on the yield of EOs and the contents of thymol and carvacrol were comprehensively investigated.

A novel antagonist of TRPM2 and TRPV4 channels: Carvacrol

The overload cytosolic free Ca²⁺ (cCa²⁺) influx-mediated excessive generation of oxidative stress in the pathophysiological conditions induces neuronal and cellular injury via the activation of cation channels. TRPM2 and TRPV4 channels are activated by oxidative stress, and their specific antagonists have not been discovered yet. The antioxidant and anti-Covid-19 properties of carvacrol (CARV) were recently reported. Hence, I suspected possible antagonist properties of CARV against oxidative stress (OS)/ADP-ribose (ADPR)-induced TRPM2 and GSK1016790A (GSK)-mediated TRPV4 activations in neuronal and kidney cells. I investigated the antagonist role of CARV on the activations of TRPM2 and TRPV4 in SH-SY5Y neuronal, BV-2 microglial, and HEK293 cells. The OS/ADPR and GSK in the cells caused to increase of TRPM2/TRPV4 current densities and overload cytosolic free Ca²⁺ (cCa²⁺) influx with an increase of mitochondrial membrane potential, cytosolic (cROS), and mitochondrial (mROS) ROS. The changes were not observed in the absence of TRPM2 and TRPV4 or the presence of Ca²⁺ free extracellular buffer and PARP-1 inhibitors (PJ34 and DPQ). When OS-induced TRPM2 and GSK-induced TRPV4 activations were inhibited by the treatment of CARV, the increase of cROS, mROS, lipid peroxidation, apoptosis, cell death, cCa²⁺ concentration, caspase -3, and caspase -9 levels were restored via upregulation of glutathione and glutathione peroxidase. In conclusion, the treatment of CARV modulated the TRPM2 and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting TRPM2 and TRPV4-mediated neurodegenerative diseases associated with the increase of mROS and cCa²⁺. The possible TRPM2 and TRPV4 blocker action of carvacrol (CARV) via the modulation oxidative stress and apoptosis in the SH-SY5Y neuronal cells. TRPM2 is activated by DNA damage-induced (via PARP-1 activation) ADP-ribose (ADPR) and reactive oxygen species (ROS) (H₂O₂), although it is inhibited by nonspecific inhibitors (ACA and 2-APB). TRPV4 is activated by the treatments of GSK1016790A (GSK), although it is inhibited by a nonspecific inhibitor (ruthenium red, RuRe). The treatment of GSK induces excessive generation of ROS. The accumulation of free cytosolic Ca²⁺ (cCa²⁺) via the activations of TRPM2 and TRPV4 in the mitochondria causes the increase of mitochondrial membrane depolarization (ΔΨm). In turn, the increase of ΔΨm causes the excessive generation of ROS. The TRPM2 and TRPV4-induced the excessive generations of ROS result in the increase of apoptosis and cell death via the activations of caspase -3 (Casp-3) and caspase -9 (Casp-9) in the neuronal cells, although their oxidant actions decrease the glutathione (GSH) and glutathione peroxidase (GSHPx) levels. The oxidant and apoptotic adverse actions of TRPM2 and TRPV4 are modulated by the treatment of CARV.