Therapeutic time window and mechanism of tetramethylpyrazine on transient focal cerebral ischemia/reperfusion injury in rats

Bibliometric analysis of research progress on tetramethylpyrazine and its effects on ischemia-reperfusion injury

In recent decades, natural products have attracted worldwide attention and become one of the most important resources for pharmacological industries and medical sciences to identify novel drug candidates for disease treatment. Tetramethylpyrazine (TMP) is an alkaloid extracted from Ligusticum chuanxiong Hort., which has shown great therapeutic potential in cardiovascular and cerebrovascular diseases, liver and renal injury, as well as cancer. In this review, we analyzed 1270 papers published on the Web of Science Core Collection from 2002 to 2022 and found that TMP exerted significant protective effects on ischemia-reperfusion (I/R) injury that is the cause of pathological damages in a variety of conditions, such as ischemic stroke, myocardial infarction, acute kidney injury, and liver transplantation. TMP is limited in clinical applications to some extent due to its rapid metabolism, a short biological half-life and poor bioavailability. Obviously, the structural modification, administration methods and dosage forms of TMP need to be further investigated in order to improve its bioavailability. This review summarizes the clinical applications of TMP, elucidates its potential mechanisms in protecting I/R injury, provides strategies to improve bioavailability, which presents a comprehensive understanding of the important compound. Hopefully, the information and knowledge from this review can help researchers and physicians to better improve the applications of TMP in the clinic.

Luteolin-7-O-β-d-Glucuronide Attenuated Cerebral Ischemia/Reperfusion Injury: Involvement of the Blood-Brain Barrier

Ischemic stroke is a common cerebrovascular disease with high mortality, high morbidity, and high disability. Cerebral ischemia/reperfusion injury seriously affects the quality of life of patients. Luteolin-7-O-β-d-glucuronide (LGU) is a major active flavonoid compound extracted from Ixeris sonchifolia (Bge.) Hance, a Chinese medicinal herb mainly used for the treatment of coronary heart disease, angina pectoris, cerebral infarction, etc. In the present study, the protective effect of LGU on cerebral ischemia/reperfusion injury was investigated in an oxygen-glucose deprivation/reoxygenation (OGD/R) neuronal model and a transient middle cerebral artery occlusion (tMCAO) rat model. In in vitro experiments, LGU was found to improve the OGD/R-induced decrease in neuronal viability effectively by the MTT assay. In in vivo experiments, neurological deficit scores, infarction volume rates, and brain water content rates were improved after a single intravenous administration of LGU. These findings suggest that LGU has significant protective effects on cerebral ischemia/reperfusion injury in vitro and in vivo. To further explore the potential mechanism of LGU on cerebral ischemia/reperfusion injury, we performed a series of tests. The results showed that a single administration of LGU decreased the content of EB and S100B and ameliorated the abnormal expression of tight junction proteins ZO-1 and occludin and metalloproteinase MMP-9 in the ischemic cerebral cortex of the tMCAO 24-h injury model. In addition, LGU also improved the tight junction structure between endothelial cells and the degree of basement membrane degradation and reduced the content of TNF-α and IL-1β in the brain tissue. Thereby, LGU attenuated cerebral ischemia/reperfusion injury by improving the permeability of the blood-brain barrier. The present study provides new insights into the therapeutic potential of LGU in cerebral ischemia.

Neuroprotection by tetramethylpyrazine and its synthesized analogues for central nervous system diseases: a review

BACKGROUND

Due to the global increase in aging populations and changes in modern lifestyles, the prevalence of neurodegenerative diseases, cerebrovascular disorders, neuropsychiatrcic conditions, and related ailments is rising, placing an increasing burden on the global public health system.

MATERIALS AND METHODS

All studies on tetramethylpyrazine (TMP) and its derivatives were obtained from reputable sources such as PubMed, Elsevier, Library Genesis, and Google Scholar. Comprehensive data on TMP and its derivatives was meticulously compiled.

RESULTS

This comprehensive analysis explains the neuroprotective effects demonstrated by TMP and its derivatives in diseases of the central nervous system. These compounds exert their influence on various targets and signaling pathways, playing crucial roles in the development of various central nervous system diseases. Their multifaceted mechanisms include inhibiting oxidative damage, inflammation, cell apoptosis, calcium overload, glutamate excitotoxicity, and acetylcholinesterase activity.

CONCLUSION

This review provides a brief summary of the most recent advancements in research on TMP and its derivatives in the context of central nervous system diseases. It involves synthesizing analogs of TMP and evaluating their effectiveness in models of central nervous system diseases. The ultimate goal is to facilitate the practical application of TMP and its derivatives in the future treatment of central nervous system diseases.

Tetramethylpyrazine alleviates mitochondrial abnormality in models of cerebral ischemia and oxygen/glucose deprivation Reoxygenation

Traditional herbal medicine Ligusticum wallichii Franchat (Chuan Xiong) is frequently prescribed and highly recommended to patients with stroke. Rodent studies have demonstrated the neuroprotective effects of its active component tetramethylpyrazine against post-stroke brain injury and highlighted its role in antioxidant, anti-inflammation, and anti-apoptosis activity. Using permanent cerebral ischemia in rats and oxygen/glucose deprivation and reoxygenation (OGDR) in rat primary neuron/glia cultures, this study sheds light on the role of mitochondria as crucial targets for tetramethylpyrazine neuroprotection. Tetramethylpyrazine protected against injury and alleviated oxidative stress, interleukin-1β release, and caspase 3 activation both in vivo and in vitro. Reduction of mitochondrial biogenesis- and integrity-related proliferator-activated receptor-gamma coactivator-1 alpha, mitochondrial transcription factor A (TFAM), translocase of outer mitochondrial membrane 20, mitochondrial DNA, and citrate synthase activity, as well as activation of mitochondrial dynamics disruption-related Lon protease, dynamin-related protein 1 (Drp1) phosphorylation, stimulator of interferon genes, TANK-binding kinase 1 phosphorylation, protein kinase RNA-like endoplasmic reticulum kinase phosphorylation, eukaryotic initiation factor 2α phosphorylation, and activating transcription factor 4 were revealed in permanent cerebral ischemia in rats and OGDR in neuron/glia cultures. TMP alleviated those biochemical changes. Our findings suggest that preservation or restoration of mitochondrial dynamics and functional integrity and alleviation of mitochondria-oriented pro-oxidant, pro-inflammatory, and pro-apoptotic cascades are alternative neuroprotective mechanisms of tetramethylpyrazine. Additionally, mitochondrial TFAM and Drp1 as well as endoplasmic reticulum stress could be targeted by TMP to induce neuroprotection. Data of this study provide experimental base to support clinical utility and value of Chuan Xiong towards stroke treatment and highlight an alternative neuroprotective target of tetramethylpyrazine.

Ligustrazine Attenuates Hyperhomocysteinemia-induced Alzheimer-like Pathologies in Rats

Ligustrazine, an alkaloid extracted from the traditional Chinese herbal medicine Ligusticum Chuanxiong Hort, has been clinically applied to treat the cerebrovascular diseases. Hyperhomocysteinemia (Hhcy) is an independent risk factor for Alzheimer's disease (AD). Memory deficits can be caused by Hhcy via pathologies of AD-like tau and amyloid-β (Aβ) in the hippocampus. Here, we investigated whether homocysteine (Hcy) can induce AD-like pathologies and the effects of ligustrazine on these pathologies. The Hcy rat model was constructed by 14-day Hcy injection via vena caudalis, and rats were treated with daily intragastric administration of ligustrazine at the same time. We found that the pathologies of tau and Aβ were induced by Hcy in the hippocampus, while the Hcy-induced tau hyperphosphorylation and Aβ accumulation could be markedly attenuated by simultaneous ligustrazine treatment. Our data demonstrate that ligustrazine may be used as a promising neuroprotective agent to treat the Hcy-induced AD-like pathologies.

A Novel Co-Crystal of Bexarotene and Ligustrazine Improves Pharmacokinetics and Tissue Distribution of Bexarotene in SD Rats

Bexarotene (BEX), a specific retinoic acid X receptor (RXR) agonist granted by Food and Drug Administration (FDA) approval for the clinical treatment of T cell lymphoma, has now been found to exert pharmacological effects in the nervous system, with low bioavailability and poor cerebral distribution limiting its application in treatment on neurological disorders. Pharmaceutical co-crystal was a helpful method to improve the bioavailability and tissue distribution of active pharmaceutical ingredients (APIs). Here, 2bexarotene-ligustrazine (2BEX-LIG), a novel co-crystal system of BEX and ligustrazine (LIG) of which with BEX is an API, was constructed with satisfactory stability and enhanced solubility. The pharmacokinetics characteristics of BEX were detected, and the results showed that the absolute bioavailability and the cerebral concentration of BEX in rats administrated with 2BEX-LIG were enhanced from 22.89% to 42.86% and increased by 3.4-fold, respectively, compared with those in rats administrated an equivalent of BEX. Hence, our present study indicated that the novel co-crystal of 2BEX-LIG contributed to improving BEX oral bioavailability and cerebral distribution, thereby providing significant advantages for clinical application of brain tumors and other neurological diseases.

Loss of thioredoxin reductase function in a mouse stroke model disclosed by a two-photon fluorescent probe

The first two-photon fluorescent probe (TP-TRFS) is reported, and it was successfully used in vivo.

HSPB8 over-expression prevents disruption of blood-brain barrier by promoting autophagic flux after cerebral ischemia/reperfusion injury

Heat-shock protein B8 (HSPB8) has been recently reported to confer neuroprotection against ischemia/reperfusion (I/R)-induced cerebral injury in vivo and in vitro. However, the molecular mechanism is still elusive. This study focused on the effect of intracerebroventricular (i.c.v) delivery of lenti-HSPB8 virus against neurological injury in a rat model of cerebral I/R and explored the underlying mechanism. We found that lentivirus i.c.v injection-induced HSPB8 over-expression strongly alleviated infarct volume, improved neurobehavioral outcomes, and reduced brain edema in rat middle cerebral artery occlusion/reperfusion (MCAO/R) model. Concomitantly, HSPB8 over-expression noticeably prevented blood-brain barrier (BBB) disruption after cerebral I/R injury as indicated by the reduction in Evans blue leakage and IgG detection in the ipsilateral hemisphere compared with the vehicle group. Moreover, immunoblotting and immunofluorescence staining of tight junction proteins claudin-5 and occludin showed that HSPB8 over-expression prevented the degradation of these proteins induced by MCAO/R, which indicated the protective effect of HSPB8 on BBB. Western blotting and immunostaining techniques were also utilized to analyze the expression of the markers of autophagy. We found that HSPB8 over-expression promoted autophagic flux, evidenced by increased ratio of LC3 I/II, accumulation of Beclin-1 expression and enhanced p62 degradation. i.c.v injection of 15 μg autophagy inhibitor 3-methyladenine (3-MA) was applied at the onset of reperfusion. The results showed that 3-MA elicited a significant loss of the protective effect of HSPB8 against MCAO/R-induced neurological defect, Evans blue extravasation, and the loss tight junction proteins, suggesting that the BBB protective role of HSPB8 was, at least in part, mediated through autophagy. Collectively, HSPB8 may represent a potential therapeutic agent for preserving BBB integrity following cerebral I/R injury. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14488.

Synthesis and Evaluation of Novel Ligustrazine Derivatives as Multi-Targeted Inhibitors for the Treatment of Alzheimer's Disease

A series of novel ligustrazine derivatives 8a–r were designed, synthesized, and evaluated as multi-targeted inhibitors for anti-Alzheimer’s disease (AD) drug discovery. The results showed that most of them exhibited a potent ability to inhibit both ChEs, with a high selectivity towards AChE. In particular, compounds 8q and 8r had the greatest inhibitory abilities for AChE, with IC₅₀ values of 1.39 and 0.25 nM, respectively, and the highest selectivity towards AChE (for 8q, IC₅₀ BuChE/IC₅₀ AChE = 2.91 × 10⁶; for 8r, IC₅₀ BuChE/IC₅₀ AChE = 1.32 × 10⁷). Of note, 8q and 8r also presented potent inhibitory activities against Aβ aggregation, with IC₅₀ values of 17.36 µM and 49.14 µM, respectively. Further cellular experiments demonstrated that the potent compounds 8q and 8r had no obvious cytotoxicity in either HepG2 cells or SH-SY5Y cells, even at a high concentration of 500 μM. Besides, a combined Lineweaver-Burk plot and molecular docking study revealed that these compounds might act as mixed-type inhibitors to exhibit such effects via selectively targeting both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChEs. Taken together, these results suggested that further development of these compounds should be of great interest.

Ligustrazine monomer against cerebral ischemia/reperfusion injury

Ligustrazine (2,3,5,6-tetramethylpyrazine) is a major active ingredient of the Szechwan lovage rhizome and is extensively used in treatment of ischemic cerebrovascular disease. The mechanism of action of ligustrazine use against ischemic cerebrovascular diseases remains unclear at present. This study summarizes its protective effect, the optimum time window of administration, and the most effective mode of administration for clinical treatment of cerebral ischemia/reperfusion injury. We examine the effects of ligustrazine on suppressing excitatory amino acid release, promoting migration, differentiation and proliferation of endogenous neural stem cells. We also looked at its effects on angiogenesis and how it inhibits thrombosis, the inflammatory response, and apoptosis after cerebral ischemia. We consider that ligustrazine gives noticeable protection from cerebral ischemia/reperfusion injury. The time window of ligustrazine administration is limited. The protective effect and time window of a series of derivative monomers of ligustrazine such as 2-[(1,1-dimethylethyl)oxidoimino]methyl]-3,5,6-trimethylpyrazine, CXC137 and CXC195 after cerebral ischemia were better than ligustrazine.

Ligustrazine reduces blood-brain barrier permeability in a rat model of focal cerebral ischemia and reperfusion

Ligustrazine, also known as 2,3,5,6-tetramethylpyrazine (TMP), one of the major active compounds of Ligusticum wallichii Franchat., has been shown to reduce neuroinflammation and protect neurons during cerebral ischemia/reperfusion injury. However, whether it reduces blood-brain barrier (BBB) permeability during ischemic stroke is unclear. The aim of the present study was to investigate the role that TMP plays in protecting the BBB integrity in ischemia/reperfusion injury and to investigate the relevant mechanisms involved. Rats received an intraperitoneal injection of 20 mg/kg TMP 15 min before the onset of ischemia, which was induced by middle cerebral artery occlusion. Infarct volume, neurological score, brain edema, BBB permeability and tight junction protein impairment were observed. The results showed that TMP reduced the neurological score and levels of brain infarction and edema. In addition, TMP significantly decreased BBB permeability and prevented the impairment of occludin and claudin-5, two tight junction protein components of the BBB, in rat brains with ischemia/reperfusion injury. In addition, the expression and activity of matrix metalloproteinases, enzymes responsible for the degradation of the extracellular matrix and tight junctions, were reduced in the rat brains by TMP treatment. These results combined suggest that TMP reduces BBB permeability as well as neuronal damage in focal cerebral ischemia/reperfusion injury in rats.

Tetramethylpyrazine protects Schwann cells from ischemia-like injury and increases cell survival in cold ischemic rat nerves

Tetramethylpyrazine (TMP), a major active ingredient of Ligusticum wallichi Franchat extract (a Chinese herb), exhibits neuroprotective properties in ischemia. In this study, we assessed its protective effects on Schwann cells (SCs) by culturing them in the presence of oxygen glucose deprivation (OGD) conditions and measuring cell survival in cold ischemic rat nerves. In the OGD-induced ischemic injury model of SCs, we demonstrated that TMP treatment not only reduced OGD-induced cell viability losses, cell death, and apoptosis of SCs in a dose-dependent manner, and inhibited LDH release, but also suppressed OGD-induced downregulation of Bcl-2 and upregulation of Bax and caspase-3, as well as inhibited the consequent activation of caspase-3. In the cold ischemic nerve model, we found that prolonged cold ischemic exposure for four weeks was markedly associated with the absence of SCs, a decrease in cell viability, and apoptosis in preserved nerve segments incubated in University of Wisconsin solution (UWS) alone. However, TMP attenuated nerve segment damage by preserving SCs and antagonizing the decrease in nerve fiber viability and increase in TUNEL-positive cells in a dose-dependent manner. Collectively, our results indicate that TMP not only provides protective effects in an ischemia-like injury model of cultured rat SCs by regulating Bcl-2, Bax, and caspase-3, but also increases cell survival and suppresses apoptosis in the cold ischemic nerve model after prolonged ischemic exposure for four weeks. Therefore, TMP may be a novel and effective therapeutic strategy for preventing peripheral nervous system ischemic diseases and improving peripheral nerve storage.

Efficacy of some non-conventional herbal medications (sulforaphane, tanshinone IIA, and tetramethylpyrazine) in inducing neuroprotection in comparison with interleukin-10 after spinal cord injury: A meta-analysis

CONTEXT

Inflammation after spinal cord injury (SCI) may be responsible for further neural damages and therefore inhibition of inflammatory processes may exert a neuroprotection effect.

OBJECTIVES

To assess the efficacy of some non-conventional herbal medications including sulforaphane, tanshinone IIA, and tetramethylpyrazine in reducing inflammation and compare them with a known effective anti-inflammatory agent (interleukin-10 (IL-10)).

METHODS

We searched relevant articles in Ovid database, Medline (PubMed) EMBASE, Google Scholar, Cochrane, and Scopus up to June 2013. The efficacy of each treatment and study powers were compared using random effects model of meta-analysis. To our knowledge, no conflict of interest exists.

RESULTS

Eighteen articles entered into the study. The meta-analysis revealed that exogenous IL-10 was more effective in comparison with the mentioned herbal extracts. The proposed pathways for each medication's effect on reducing the inflammation process are complex and many overlaps may exist.

CONCLUSION

IL-10 has a strong effect in the induction of neuroprotection and neurorecovery after SCI by multiple pathways. Tetramethylpyrazine has an acceptable influence in reducing inflammation through the up-regulation of IL-10. Outcomes of sulforaphane and tanshinone IIA administration are acceptable but still weaker than IL-10.

Tetramethylpyrazine, a natural alkaloid, attenuates pro-inflammatory mediators induced by amyloid β and interferon-γ in rat brain microglia

Neuroinflammation has been consistently reported as a pathological hallmark of Alzheimer׳s disease and other neurodegenerative diseases. Microglial cells are activated by diverse pathological stimuli and play key roles in development of neuroinflammation. Amyloid β peptide (Aβ), the major constituent of amyloid plaques in Alzheimer׳s brain, is known to activate cultured microglial cells to produce increased amounts of proinflammatory and neurotoxic factors. Tetramethylpyrazine (TMP) is the main bioactive alkaloid isolated from Ligusticum chuanxiong. TMP has multiple pharmacological activities, including anti-oxidant, anti-inflammatory, and anti-cancer effects. Neuroprotective potential of TMP has been demonstrated in animal models of neuropathologies. However, the efficacy of this compound for controlling Aβ-related neuropathology has not been explored yet. We examined the efficacy of TMP in the repression of inflammatory response in cultured microglial cells stimulated with Aβ25-35 in the presence of interferon (IFN)-γ. TMP significantly inhibited the Aβ25-35 and IFN-γ-stimulated productions of nitric oxide, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, monocyte chemoattractant protein-1, and intracellular reactive oxygen species from primary microglial cells. TMP also effectively reduced Aβ25-35 and IFN-γ-elicited NF-κB activation. In organotypic hippocampal slice cultures (OHSCs), TMP significantly blocked Aβ25-35-induced reactive oxygen species generation and phosphorylation of Akt. Furthermore, TMP also inhibited Aβ1-42-induced TNF-α and IL-1β production in primary microglial cells and neuronal death in OHSCs. These results suggest that TMP provide a possible therapeutic approach for alleviating the inflammatory progression of Alzheimer׳s disease.

Tetramethylpyrazine promotes the proliferation and migration of brain endothelial cells

The aim of the present study was to investigate the role of tetramethylpyrazine (TMP), one of the alkaloids isolated from the Chinese herb Chuanxiong, on the proliferation and migration of brain endothelial cells. A different dosage of TMP was employed to stimulate the mouse microvascular cell line bEnd.3 in vitro. TMP at lower concentrations (0.25 ng/ml), however not at high concentrations (100 ng/ml) could promote the proliferation and migration of endothelial cells, which was further enhanced if combined with soluble Fas ligand (sFasL). TMP alone, or combined with sFasL, increased the autocrine signaling of vascular endothelial growth factor (VEGF) by endothelial cells and TMP improved the expression of Fas on endothelial cells, which may explain the effect of the sFasL. These results provide insight into the underlying mechanisms of the effects of TMP on stroke and other vascular diseases.

Effects of Tetramethylpyrazine on Microglia Activation in Spinal Cord Compression Injury of Mice

Secondary mechanisms, including inflammation and microglia activation, serve as targets for the development and application of pharmacological strategies in the management of spinal cord injury (SCI). Tetramethylpyrazine (TMP), an active ingredient of Ligusticum wallichii (chuanxiong), has shown anti-inflammatory and neuroprotective effects against SCI. However, it remains uncertain whether the inflammation-suppressive effects of TMP play a modulatory role over microglia activation in SCI. The present study investigated the effects of TMP on microglia activation and pro-inflammatory cytokines in spinal cord compression injury in mice. For a real-time PCR measurement of pro-inflammatory cytokines, SCI was induced in mice by the clip compression method (30 g force, 1 min) and TMP (15 or 30 mg/kg, i.p.) was administered once, 30 minutes before the SCI induction. For immunohistochemistry, TMP (30 mg/kg, i.p.) treatment was given three times during the first 48 hours after the SCI. 30 mg/kg of TMP treatment reduced the up-regulation of TNF-α, IL-1β and COX-2 mRNA in the spinal tissue at four hours after the SCI induction. TMP also significantly attenuated microglia activation and neutrophil infiltration at 48 hours after the SCI induction. In addition, iNOS expression in the spinal tissue was attenuated with TMP treatment. These results suggest that TMP plays a modulatory role in microglia activation and may protect the spinal cord from or potentially delay secondary spinal cord injury.

Intravenous administration of tetramethylpyrazine reduces intestinal ischemia-reperfusion injury in rats

Intestinal ischemia-reperfusion injury (IIRI) is a life-threatening condition requiring prompt medical intervention. Tetramethylpyrazine (TMP) is a biologically active alkaloid isolated from Ligusticum wallichii. Previously, it was shown that TMP causes vasodilatation and inhibition of platelet aggregation as well as exhibits significant antioxidant effects. Therefore, the aim of the present study was to evaluate possible therapeutic effects of TMP in the prevention of IIRI. Wistar rats (n = 80) were randomly divided into eight experimental groups and subjected to a 1 h occlusion of cranial mesenteric artery followed by 0, 1, 12, and 24 h period of reperfusion. Thirty minutes before the IIRI animals received either TMP (30 mg/kg, i.v.) or identical volume of saline. In addition, a control group of 10 animals was not exposed to IIRI. Intestine morphology was evaluated by using histopathological injury index examination (HII), goblet and Paneth cells quantification as well as by applying immunofluorescent methods such as InSitu TUNEL and caspase-3 positivity assessment. Here we showed that preconditioning with TMP prior IIRI decreases the grade of injury. Significant reduction of HII was detected in TMP pretreated groups after 0, 1, and 12 h of reperfusion where injury reduction up to 75% was found. Lower histopathological damage in preconditioned groups was accompanied with increased number of secretory epithelial cells and decreased number of apoptotic cells. These results demonstrate the protective effect of TMP on the small intestine mucosa, suggesting administration of TMP as a molecule for pharmacological intervention against IIRI.

Baicalin's Therapeutic Time Window of Neuroprotection during Transient Focal Cerebral Ischemia and Its Antioxidative Effects In Vitro and In Vivo

We investigated the effects of baicalin on an ischemia-reperfusion-induced brain injury model in rats and its antioxidative activities in vitro and in vivo. An ischemia-reperfusion injury of the brain via a middle cerebral artery occlusion (MCAO) was induced in rats. Baicalin was injected at different time points (0, 2, 4, and 6 h) after the MCAO was induced. Baicalin can improve neurological function and significantly decrease brain infarction within a time window of 4 h. Moreover, baicalin was able to reduce cell apoptosis and had the strong antioxidative effect of reducing reactive oxygen species production and malondialdehyde generation. In contrast, baicalin interfered with superoxide dismutase and nicotinamide adenine dinucleotide 2′-phosphate oxidase activities. Moreover, baicalin also exhibited strong neuroprotective effects against H₂O₂-mediated injury and improved the SOD activity of neurons. Furthermore, baicalin demonstrated good scavenging of hydroxyl radicals, superoxide anions, and DPPH radicals and exerted an additional effect of inhibiting xanthine oxidase. Baicalin showed beneficial effects against MCAO-induced injury within a 4 h time window, and its antioxidative effects both in vitro and in vivo may partly elucidate its mechanism of action.

Ligustrazine phosphate ethosomes for treatment of Alzheimer's disease, in vitro and in animal model studies

In the present study, we have investigated transdermal administration of ligustrazine phosphate (LP), as an antioxidant, for the treatment of Alzheimer's disease (AD). The LP transdermal ethosomal system was designed and characterized. Franz-type diffusion cells and confocal laser scanning microscopy were used for the in vitro permeation studies. Furthermore, the effect of LP transdermal ethosomal system on AD was evaluated in the scopolamine-induced amnesia rats by evaluating the behavioral performance in the Morris water maze test. The activities of the antioxidant enzymes and the levels of the lipid peroxidation product malondialdehyde (MDA) in the brain of rats were also determined. The results showed that both the penetration ability and the drug deposition in skin of the LP ethosomal system were significantly higher than the aqueous one. The LP transdermal ethosomal system could recover the activities of the antioxidant enzymes and the levels of MDA in the brain of the amnesic rats to the similar status of the normal rats, which was also indirectly reflected by the improvement in the behavioral performance. In conclusion, LP might offer a potential alternative therapeutic drug in the fight against AD, and ethosomes could be vesicles of choice for transdermal delivery of LP.

Effect of Xiongbing compound on the pharmacokinetics and brain targeting of tetramethylpyrazine

Objectives

To investigate the effect of the Xiongbing compound (XBC) on the pharmacokinetics and brain targeting of tetramethylpyrazine (TMP).

Methods

Three microemulsions containing the same TMP concentration were prepared. XBC microemulsions were made from Rhizoma ligustric Chuanxiong extracts, borneol and TMP. TMP microemulsions were made with TMP only. Borneol microemulsions contained borneol and TMP. Microdialysis with high performance liquid chromatography (HPLC) was used to measure the concentration of TMP in the blood and striatum after intravenous (i.v.) or intragastric (i.g.) administration of the three different microemulsions.

Key findings

The pharmacokinetics of free TMP concentration in the blood and the striatum fit a first-order rate, open two-compartment model after intravenous and intragastric microemulsion administration. The maximal concentration (Cmax) and area under curve (AUC) values in the XBC microemulsion i.v. group were significantly higher than that in the TMP microemulsion and borneol microemulsion i.v. groups. After XBC microemulsion i.g. administration, the t1/2, mean residence time (MRT) and AUC of TMP in both plasma and brain tissues were greater than those with TMP microemulsion and borneol microemulsion administration. The relative brain targeting efficiency of TMP for the XBC microemulsion i.v and i.g. groups relative to the TMP microemulsion and borneol microemulsion groups were greater than 1.

Conclusion

XBC microemulsion can enhance TMP oral bioavailability, brain targeting and tissue distribution, mainly through a synergistic action of Rhizoma ligustric Chuanxiong extracts and borneol.

TMP prevents retinal neovascularization and imparts neuroprotection in an oxygen-induced retinopathy model

PURPOSE

To evaluate the effects of tetramethylpyrazine (TMP) on retinal neovascularization (NV) and neuroprotection in an oxygen-induced retinopathy (OIR) model.

METHODS

Neonatal C57BL/6J mice were subjected to 75% oxygen from postnatal day 7 (P7) to P12 and then returned to room air. TMP (200 mg/kg) or normal saline was given daily from P12 to P17. Immunostaining, HE staining, TUNEL assay, and RT-PCR were used to assess the effects of TMP on retinal neurovascular repair.

RESULTS

TMP effectively prevented pathologic NV and accelerated physiologic revascularization by enhancing the formation of endothelial tip cells at the edges of the repairing capillary networks and preserving the astrocytic template in the avascular retina. TMP also prevented morphologic changes and significantly decreased TUNEL-positive cells in the avascular retina by rescuing neurons such as amacrine, rod bipolar, horizontal, and Müller cells. In TMP-treated mice retinas, there was a less obvious loss of amacrine cell bodies and their distinct bands; the number of both rod bipolar and horizontal cell bodies, as well as the density of their dendrites in the outer plexiform layer, was greater than that in OIR control mice. TMP not only decreased the loss of alignment of Müller cell bodies and distortion of processes but reduced the reactive expression of GFAP in Müller cells. Furthermore, HIF-1α and VEGF mRNA expression were downregulated in TMP-treated mice retinas.

CONCLUSIONS

TMP improved neurovascular recovery by preventing NV and protecting retinal astroglia cells and neurons from ischemia-induced cell death partially due to its downregulation of HIF-1α and VEGF mRNA expression.

Microemulsion-based novel transdermal delivery system of tetramethylpyrazine: preparation and evaluation in vitro and in vivo

Objective

To deliver 2,3,5,6-tetramethylpyrazine (TMP) in a relatively large dose through a transdermal route and facilitate the practical application of microemulison in transdermal drug delivery.

Methods

The pseudo-ternary phase diagram for microemulsion regions was constructed using isopropyl myristate as oil phase, Labrasol^® as surfactant, and Plurol^® Oleique CC 497 as cosurfactant. A uniform experimental design was applied for formulation optimization. In vitro skin permeation experiments of six formulations were undertaken with TMP transdermal patch (EUDRAGIT^® E100 as matrix) and TMP saturated solution as controls. We prepared TMP-oil dispersed in water-ethylene vinyl acetate-transdermal therapeutic system (TMP-O/W-EVA-TTS) with microemulsion as reservoir and EVA membrane as release liner; pharmacokinetic and brain distribution studies in rats were conducted with TMP transdermal patches as control.

Results

The skin fluxes of TMP from microemulsions were 8.2- to 26.7-fold and 0.9- to 4.7-fold higher than those of TMP transdermal patch and TMP saturated solution, respectively, and were strongly affected by the microemulsion composition. The improvement in TMP solubility as well as the skin permeation enhancement effect of microemulsion components contributed mainly to transdermal delivery facilitation. In the pharmacokinetic study, the relative bioavailability of TMP-O/W-EVA-TTS was 350.89% compared with the TMP transdermal patch. Higher and more stable TMP contents in rat plasma were obtained after administration of TMP-O/WEVA- TTS than after application of TMP transdermal patch. In the brain distribution study, higher rate and extent of TMP distribution to brain, and lower rate of TMP clearance from brain were observed after transdermal administration of TMP-O/W-EVA-TTS than after application of TMP transdermal patch.

Conclusion

The novel transdermal delivery system prepared in this study showed a remarkable skin permeation improvement of microemulsion and facilitated its practical application in transdermal drug delivery. With this system as a vehicle, a relatively large dose of TMP could enable successful drug delivery via the transdermal route.

Kainic acid-induced neurodegenerative model: potentials and limitations

Excitotoxicity is considered to be an important mechanism involved in various neurodegenerative diseases in the central nervous system (CNS) such as Alzheimer's disease (AD). However, the mechanism by which excitotoxicity is implicated in neurodegenerative disorders remains unclear. Kainic acid (KA) is an epileptogenic and neuroexcitotoxic agent by acting on specific kainate receptors (KARs) in the CNS. KA has been extensively used as a specific agonist for ionotrophic glutamate receptors (iGluRs), for example, KARs, to mimic glutamate excitotoxicity in neurodegenerative models as well as to distinguish other iGluRs such as α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors and N-methyl-D-aspartate receptors. Given the current knowledge of excitotoxicity in neurodegeneration, interventions targeted at modulating excitotoxicity are promising in terms of dealing with neurodegenerative disorders. This paper summarizes the up-to-date knowledge of neurodegenerative studies based on KA-induced animal model, with emphasis on its potentials and limitations.