Dexmedetomidine attenuates the induction and reverses the progress of 6-hydroxydopamine- induced parkinsonism; involvement of KATP channels, alpha 2 adrenoceptors and anti-inflammatory mechanisms

Dexmedetomidine, an alpha-2 adrenoceptors agonist, provides a neuroprotective effect for dopaminergic neurons in the substantia nigra and attenuates glucose imbalance in the 6-hydroxydopamine animal model of Parkinson's disease

INTRODUCTION

Studies have shown that dexmedetomidine (DEX, an a2-adrenoceptors agonist) provides a neuroprotective effect and influences blood glucose levels. Here, we evaluated the effect of prolonged treatment with low doses of DEX on the survival rate of dopaminergic (DAergic) neurons in the substantia nigra and also serum glucose levels in 6-hydroxydopamine (6-OHDA) - induced Parkinson's disease (PD) in the rat.

MATERIAL AND METHODS

The neurotoxin of 6-OHDA was injected into the medial forebrain bundle by stereotaxic surgery. DEX (25 and 50 µg/kg, i.p) and yohimbine, an a2-adrenoceptor antagonist (1 mg/kg, i.p) were administered before the surgery to the 13 weeks afterward. Apomorphine-induced rotational tests and blood sampling were carried out before the surgery and multiple weeks after that. Thirteen weeks after the surgery, the rats' brain was transcardially perfused to assess the survival rate of DAergic neurons using the tyrosine hydroxylase (TH) immunohistochemistry.

RESULTS

DEX remarkably attenuated the severity of rotational behavior and reversed the progress of the PD. It also increased the number of TH-labeled neurons by up to 60%. The serum glucose levels in 6-OHDA-received rats did not change in the third and seventh weeks after the surgery but decreased significantly in the thirteenth week. Treatment with DEX prevented this decrement in glucose levels. On the other hand, Treatment with yohimbine did not affect PD symptoms and glucose levels.

CONCLUSION

Our data indicate that DEX through neuroprotective activity attenuates the severity of 6-OHDA-induced PD in rats. DEX might also prevent hypoglycemia during the progress of the PD.

Dexmedetomidine on the interplay of IL-6 and STAT3 pathways in adrenal gland damage-induced scalding burns in rats

Scalding burns are a common form of thermal injury that often leads to systemic complications. Pro-inflammatory cytokines like interleukin-6 (IL-6) and the activation of signal transducer and activator of transcription 3 (STAT3) pathways have been linked to the pathophysiology of organ damage caused by burns. This study aimed to investigate the potential therapeutic effects of dexmedetomidine, an α2-adrenergic receptor agonist with anti-inflammatory properties, on the interplay of IL-6 and STAT3 pathways in adrenal gland damage following scalding burns in rats. Twenty-eight rats were divided randomly into four groups. Rats in group 1 (n=7, control) were given only 0.9% intraperitoneal (i.p.) NaCl. Rats in group 2 (n=7, DEX) were exposed to 25°C water for 17 s on day 1 and received 100 mcg/kg/day dexmedetomidine i.p. for 3 days; for rats in group 3 (n=7, Burn), boiling water of 94°C was applied inside for 17 s. Rats in group 4 (n=7, Burn+DEX) were exposed to 94°C water for 17 s and received 100 mcg/kg/day dexmedetomidine i.p. for 3 days. Adrenal gland tissues were histopathological examined, and STAT3, IL-6, and TUNEL staining were performed using immunohistochemically. Our results revealed that scalding burns increased IL-6 and STAT3 expression in the adrenal glands of rats. Histological analysis demonstrated that dexmedetomidine administration ameliorated adrenal gland damage and reduced inflammatory cell infiltration. Our findings suggest that dexmedetomidine protects the adrenal glands in scalding burns. This protection appears to be mediated, at least in part, by its modulation of IL-6 and STAT3 pathways.

Appraisal of the Neuroprotective Effect of Dexmedetomidine: A Meta-Analysis

Dexmedetomidine is an adrenergic receptor agonist that has been regarded as neuroprotective in several studies without an objective measure to it. Thus, the aim of this meta-analysis was to analyze and quantify the current evidence for the neuroprotective effects of dexmedetomidine in animals. The search was performed by querying the National Library of Medicine. Studies were included based on their language, significancy of their results, and complete availability of data on animal characteristics and interventions. Risk of bias was assessed using SYRCLE's risk of bias tool and certainty was assessed using the ARRIVE Guidelines 2.0. Synthesis was performed by calculating pooled standardized mean difference and presented in forest plots and tables. The number of eligible records included per outcome is the following: 22 for IL-1β, 13 for IL-6, 19 for apoptosis, 7 for oxidative stress, 7 for Escape Latency, and 4 for Platform Crossings. At the cellular level, dexmedetomidine was found protective against production of IL-1β (standardized mean difference (SMD) =  - 4.3 [- 4.8; - 3.7]) and IL-6 (SMD =  - 5.6 [- 6.7; - 4.6]), apoptosis (measured through TUNEL, SMD =  - 6.0 [- 6.8; - 4.6]), and oxidative stress (measured as MDA production, SMD =  - 2.0 [- 2.4; - 1.4]) exclusively in the central nervous system. At the organism level, dexmedetomidine improved behavioral outcomes measuring escape latency (SMD = - 2.4 [- 3.3; - 1.6]) and number of platform crossings (SMD = 9.1 [- 6.8; - 11.5]). No eligible study had high risk of bias and certainty was satisfactory for reproducibility in all cases. This meta-analysis highlights the complexity of adrenergic stimulation and sheds light into the mechanisms potentiated by dexmedetomidine, which could be exploited for improving current neuroprotective formulations.

Dopaminergic Neuronal Death in Substantia Nigra Associates with Serum Levels of Total Bilirubin, Selenium, and Zinc: Evidences from 6-Hydroxydopamine Animal Model of Parkinson's Disease

Mild to moderate dopaminergic (DA) neuronal death in substantia nigra pars compacta (SNc) as the main pathological hallmark of Parkinson's disease (PD) is usually silent and does not produce marked clinical symptoms. In this study, we investigated the association between SNc DA neuronal loss and serum levels of total bilirubin (TB), selenium (Se), and zinc (Zn) in 6-hydroxydopamine (6-OHDA) animal model of PD. The neurotoxin of 6-OHDA was injected into the medial forebrain bundle of right hemisphere by stereotaxic surgery. Two conventional behavioral tests were carried out in several steps after the toxin to confirm the model reproduction and quantify severity and progress of 6-OHDA-induced PD. Blood samples were collected within 1 week before the toxin and in the second, fifth, and eighth weeks thereafter. Immunohistochemistry (IHC) assessments were performed on the rat's brain to determine the severity of DA neuronal loss in SNc. The severity of behavioral symptoms and TB levels were progressively increased in 6-OHDA-treated rats. On the other hand, Se and Zn levels in them were lower than control. These changes were observed in rats with severe or mild behavioral symptoms. Also, IHC revealed that changes in TB, Se, and Zn associate with SNc DA neuronal loss but do not correlate with its severity. Significant changes in serum levels of TB, Se, and Zn in the mild SNc DA neuronal loss suggest them as valuable parameters for establishment of a serum profile for early detection of PD.

Dexmedetomidine Can Enhance PINK1/Parkin-Mediated Mitophagy in MPTP-Induced PD Mice Model by Activating AMPK

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the degeneration of dopaminergic (DA) neurons in the substantia nigra (SN). Our previous study has shown that dexmedetomidine (Dex) can protect mitochondrial function and reduce apoptosis in MPP⁺-induced SH-SY5Y cells. Evidences have shown that mitophagy is related to the development of PD. In this study, we investigated whether Dex can enhance mitophagy in MPTP-induced mice to play a neuroprotective effect. In our experiment, mice were injected with MPTP 30 mg/kg intraperitoneally for 5 consecutive days to establish a PD subacute model. Dex (30, 50, and 100 μg/kg) was injected intraperitoneally 30 minutes before each injection of MPTP, respectively. Our results showed that Dex (50 μg/kg) most significantly attenuated MPTP-induced motor dysfunction and restored TH-positive neurons in the SN, increased the expression of the antiapoptotic protein Bcl-2, and decreased the expression of apoptotic proteins cleaved casepase3, cleaved casepase9, and Bax. Moreover, Dex increased the activity of mitochondrial Complexes I-IV and decreased the level of oxidative stress, manifesting as decreased MDA levels and increased SOD and GSH-PX levels. Besides, under transmission electron microscopy, Dex increased the mitophagosome which is an autophagosome with a mitochondrion-like structure inside under the electron microscope. In addition, Dex could also increase the expression of mitophagy-related proteins p-AMPK, LC3II/I, PINK1, and Parkin and decrease P62. However, after using Compound C (CC, 10 mg/kg, AMPK inhibitor), the effects of Dex on increasing PINK1/Parkin-induced mitophagy and neuroprotection were attenuated. In conclusion, Dex may improve mitochondrial function by activating AMPK to enhance PINK1/Parkin-induced mitophagy, thereby protecting dopaminergic neurons.

Chronic and progressive dopaminergic neuronal death in substantia nigra associates with a decrease in serum levels of glucose and free fatty acids, the role of interlokin-1 beta

Human studies indicate that Parkinson's disease (PD) associates with disruption in metabolism of glucose and free fatty acids (FFA). Studies have shown that interlukin-1beta (IL-1β) causes hypoglycemia through insulin- independent mechanisms. Here, we investigated association between dopaminergic neuronal death, as the main pathophysiological mechanism underlying PD, and serum levels of glucose, FFA and IL-1β in 6-hydroxydopamine (6-OHDA) animal model of PD. Neurotoxin of 6-OHDA was injected into medial forebrain bundle and multiple behavioral testes were carried out during eight weeks thereafter. Blood was collected before the toxin and in second and eight weeks thereafter. Then, brain of the animals was perfused to assess survival of dopaminergic (DAergic) neurons in substantia nigra by tyrosine hydroxylase (TH) immunohistochemistry. Glucose, FFA and IL-1β levels were determined using calorimetric method and specific ELISA kits. In compare to control, 6-OHDA- treated rats had less glucose and FFA levels in the eight week and higher IL-1β level in the both second and eight weeks. Based on severity of behavioral symptoms, 6-OHDA- treated rats were divided into two subgroups of severe and mild. Number of TH- positive cells in these subgroups was 83 and 45% less than that in control. Also, both subgroups showed less weight gain, lower glucose and FFA and higher IL-1β in eight week. Our data indicate that moderate to severe progressive DAergic neuronal death in substantia nigra associates with a decrease in serum levels of glucose and FFA. Increase in IL-1β production following neuronal death possibly mediated this decrease.

Dopaminergic neuronal death in the substantia nigra associates with change in serum levels of TNF-α and IL-1β; evidence from early experimental model of Parkinson's disease

PURPOSE

Studies have shown that inflammation plays a key role in etiology of Parkinson's disease (PD). However, human studies which have evaluated association between PD and serum levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) have reported conflicting results. In this study, serum and striatum levels of these cytokines were evaluated in 6-hydroxydopamine (6-OHDA) animal model of PD.

METHOD

The neurotoxin of 6-OHDA was injected into medial forebrain bundle of right hemisphere and behavioral tests were carried out to eight weeks thereafter to evaluate severity of PD and its progress. Blood was collected before the toxin and in second and eight weeks after that. Survival of dopaminergic (DAergic) neurons in substantia nigra was assessed by immunohistochemistry. TNF-α and IL-1β levels were determined using ELISA kits.

RESULT

Severity of behavioral symptoms was gradually increased in 6-OHDA-treated rats. They showed a decrease in serum TNF-α level in the eight week and increase in IL-1β both in the second and eight weeks. They were divided into two subgroups, symptomatic and asymptomatic with severe and moderate degrees in DAergic neuronal death. Significant decrease in serum TNF-α was only observed in the symptomatic subgroup but IL-1β increased in both subgroups. Also, striatal levels of both cytokines were higher in the lesioned hemisphere.

CONCLUSION

Increase in serum IL-1β level can reflect moderate degree of lesion in substantia nigra and thereby is used for prognosis of PD before its clinical symptoms are appeared. On the other hand, an increase in serum TNF-α is appeared in advanced stage of PD.

Chinese Herbal Medicine to Reduce Radiation-Induced Oral Mucositis in Head and Neck Cancer Patients: Evidence From Population-Based Health Claims

BACKGROUND

Subjects with head and neck cancer (HNC) often experience post-treatment side effects, particularly radiation-induced oral mucositis (RIOM). This study aimed to explore the association of Chinese herbal medicine use with the sequent risk of RIOM among them.

METHODS

This cohort study used a nationwide health insurance database to identify subjects newly diagnosed with HNC, aged 20 to 60 years, who received treatment between 2000 and 2007. Among them, a total of 561 cases received CHM after HNC onset (CHM users); the remaining 2395 cases were non-CHM users. All patients were followed to the end of 2012 to identify any treatment for RIOM as the end point. Cox proportional hazards regression was used to compute the adjusted hazard ratio (aHR) of RIOM by CHM use.

RESULTS

During the follow-up period, 183 CHM users and 989 non-CHM users developed RIOM at incidence rates of 40.98 and 57.91 per 1000 person-years, respectively. CHM users had a lower RIOM risk than the non-CHM users (aHR: 0.68; 95% Confidence Interval: 0.58-0.80). The most potent effect was observed in those taking CHM for more than 1 year. Use of Baizhi, Danshen, Shao-Yao-Gan-Cao-Tang, Gan-Lu-Yin, Huangqin, Shu-Jing-Huo-Xue-Tang, and Xin-Yi-Qing-Fei-Tang, was significantly related to a lower risk of RIOM.

CONCLUSION

Findings of this study indicated that adding CHM to conventional clinical care could be helpful in protecting those with HNC against the onset of RIOM. Further clinical and mechanistic studies are warranted.

Hydrogen sulfide attenuates induction and prevents progress of the 6-hydroxydopamine-induced Parkinsonism in rat through activation of ATP-sensitive potassium channels and suppression of ER stress

PURPOSE

Studies argue in favor of hydrogen sulfide (H₂S) as the next potent therapeutic agent for neurodegenerative diseases. In present study, we investigated the effect of long term treatment with NaHS (as donor of H₂S) on induction and progress of the 6-hydroxydopamine (6-OHDA) -induced Parkinsonism in rat.

METHODS

The 6-OHDA was injected into medial forebrain bundle of right hemisphere by stereotaxic surgery. Behavioral tests and treatments were carried out to eight weeks after the toxin. Immunohistochemistry and western blotting were carried out to evaluate the survival of tyrosine hydroxylase (TH) -positive neurons in substantia nigra (SN) and also expression of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP), the markers of endoplasmic reticulum (ER) stress, in striatum and SN.

RESULTS

Eight weeks assessment of the behavioral symptoms showed that NaHS especially at dose of 100 μmol/kg attenuates remarkably induction of the Parkinsonism and prevents its progress. NaHS also increased the survival of TH- positive neurons and suppressed 6-OHDA- induced overexpression of GRP78 and CHOP. Blockade of ATP-sensitive potassium (K-ATP) channels with glibenclamide (Glib) prevented markedly the effect of NaHS on both the induction phase and survival of TH- positive neurons. But Glib did not affect the preventing effect of NaHS on the progress phase and its suppressing effect on the overexpression of ER stress markers.

CONCLUSION

H₂S attenuates induction of the 6-OHDA- induced Parkinsonism and also increases the survival of dopaminergic neurons through activation of K-ATP channels. H₂S also prevents progress of the Parkinsonism probably through suppression of ER stress.

Dexmedetomidine improves postoperative neurocognitive disorder after cardiopulmonary bypass in rats

PURPOSE

To investigate whether dexmedetomidine can improve postoperative neurocognitive function after cardiopulmonary bypass in rats.

METHODS

A total of 45 male Sprague Dawley (SD) rats were randomly divided into sham group, control group, and dexmedetomidine (Dex) group. The rats in the sham group received skin excision and blood vessel ligation treatment, rats in the control group received cardiopulmonary bypass (CPB), and rats in the Dex group received CPB and Dex treatment. Morris water maze test and open-field tests were used to evaluate the rats' cognition. The expression of inflammatory mediators in the rats' central and peripheral regions, Aβ and Tau in the hippocampus and prefrontal cortex, and apoptosis in brain tissue were measured.

RESULTS

The CPB model rats were found to have significantly decreased cognitive function, increased expression of caspase-3 and Bax in the prefrontal cortex and hippocampus DG, increased apoptosis and activated microglia, and increased plasma levels of TNF-α, IL-6, and TNF-α. Dexmedetomidine reduced apoptosis in the prefrontal cortex and hippocampus DG region of rats, decreased the expression of caspase-3 and bax, inhibited microglia activation in the prefrontal cortex and hippocampus DG region of rats, and decreased the plasma levels of IL-β, IL-6, and TNF-α.

CONCLUSIONS

Dexmedetomidine plays a neuroprotective role by inhibiting inflammation, apoptosis, and microglia activation in the prefrontal cortex and hippocampal DG region, and attenuates the cognitive deficit identified in the control group.

Use of Chinese Herbal Medicines Is Related to a Reduction in Depression Risk Among Patients With Insomnia: A Matched Cohort Study

Objective: Subjects with insomnia have a higher risk of depression, thus possibly making them live with serious health conditions. To date, information regarding the effect of Chinese herbal medicines (CHMs), a commonly used complementary and alternative medicine, on depression risk among people with insomnia is still unknown. This study aimed to investigate the effect of CHMs on the risk of depression among individuals with insomnia.

Methods: This cohort study used a national health insurance database to identify 68,573 subjects newly diagnosed with insomnia, aged 20–70 years, who received treatment between 1998 and 2010. Using propensity score matching, we randomly selected 26,743 CHMs users and 26,743 non-CHMs users from this sample. All enrollees were followed to the end of 2012 to identify any treatment for depression as the end point. Cox proportional hazards regression was used to compute the adjusted hazard ratio of depression associated with CHMs use.

Results: After utilizing the propensity score matching, we randomly selected 26,743 CHMs users and 26,743 non-CHMs users from this sample. During follow up, 3,328 CHMs users and 6,988 non-CHMs users developed depression at incidence rates of 17.24 and 37.97 per 1,000 person-years, respectively. CHMs users had a lower depression risk than the non-CHMs users (adjusted hazard ratio = 0.44; 95% Confidence Interval, 0.42–0.46). The greatest effect was observed for those taking CHMs for more than 2 years. Gegen, Huangqin, Dan-Shen, Beimu, Dahuang, Shegan, Shu-jing-huo-xue-tang, Ge-gen-tang, Shao-yao-gan-cao-tang and Píng wèi sǎn were significantly associated with a lower risk of depression.

Conclusions: Findings from this study demonstrated that adding CHMs to conventional treatment significantly reduces depression risk among patients with insomnia.

Dexmedetomidine Provides Cardioprotection During Early or Late Reperfusion Mediated by Different Mitochondrial K+-Channels

BACKGROUND

Cardioprotective interventions-such as pharmacological postconditioning-are a promising strategy to reduce deleterious consequences of ischemia and reperfusion injury (I/RI) in the heart, especially as timing and onset of myocardial infarction are unpredictable. Pharmacological postconditioning by treatment with dexmedetomidine (Dex), an α2-adrenoreceptor agonist, during reperfusion protects hearts from I/RI, independently of time point and duration of application during the reperfusion phase. The mitochondrial ATP-sensitive K (mKATP) and mitochondrial large-conductance calcium-sensitive potassium channel (mBKCa) play a pivotal role in mediating this cardioprotective effect. Therefore, we investigated whether Dex-induced cardioprotection during early or late reperfusion is mediated variously by these mitochondrial K-channels.

METHODS

Hearts of male Wistar rats were randomized into 8 groups and underwent a protocol of 15 minutes adaption, 33 minutes ischemia, and 60 minutes reperfusion in an in vitro Langendorff-system. A 10-minute treatment phase was started directly (first subgroup, early reperfusion) or 30 minutes (second subgroup, late reperfusion) after the onset of reperfusion. Control (Con) hearts received vehicle only. In the first subgroup, hearts were treated with 3 nM Dex, 100 µM mKATP-channel blocker 5-hydroxydecanoate (5HD) or 1 µM mBKCa-channel blocker Paxilline (Pax) alone or with respective combinations (5HD + Dex, Pax + Dex). Hearts of the second subgroup received Dex alone (Dex30') or in combination with the respective blockers (5HD + Dex30', Pax + Dex30'). Infarct size was determined with triphenyltetrazoliumchloride staining. Hemodynamic variables were recorded during the whole experiment.

RESULTS

During early reperfusion (first subgroup), the infarct size reducing effect of Dex (Con: 57% ± 9%, Dex: 31% ± 7%; P< .0001 versus Con) was completely abolished by 5HD and Pax (52% ± 6%; Pax + Dex: 53% ± 4%; each P< .0001 versus Dex), while both blockers alone had no effect on infarct size (5HD: 54% ± 8%, Pax: 53% ± 11%). During late reperfusion (second subgroup) the protective effect of Dex (Dex30': 33% ± 10%, P< .0001 versus Con) was fully abrogated by Pax (Pax + Dex30': 58% ± 7%, P < .0001 versus Dex30'), whereas 5HD did not block cardioprotection (5HD + Dex30': 36% ± 7%). Between groups and within each group throughout reperfusion no significant differences in hemodynamic variables were detected.

CONCLUSIONS

Cardioprotection by treatment with Dex during early reperfusion seems to be mediated by both mitochondrial K-channels, whereas during late reperfusion only mBKCa-channels are involved.