Curcumin Acts as a Positive Allosteric Modulator of α7-Nicotinic Acetylcholine Receptors and Reverses Nociception in Mouse Models of Inflammatory Pain

Curcumin Improves Neurogenesis in Alzheimer's Disease Mice via the Upregulation of Wnt/β-Catenin and BDNF

Adult neurogenesis in the dentate gyrus (DG) is impaired during Alzheimer's disease (AD) progression. Curcumin has been reported to reduce cell apoptosis and stimulate neurogenesis. This study aimed to investigate the influence of curcumin on adult neurogenesis in AD mice and its potential mechanism. Two-month-old male C57BL/6J mice were injected with soluble β-amyloid (Aβ1-42) using lateral ventricle stereolocalization to establish AD models. An immunofluorescence assay, including bromodeoxyuridine (BrdU), doublecortin (DCX), and neuron-specific nuclear antigen (NeuN), was used to detect hippocampal neurogenesis. Western blot and an enzyme-linked immunosorbent assay (ELISA) were used to test the expression of related proteins and the secretion of brain-derived neurotrophic factor (BDNF). A Morris water maze was used to detect the cognitive function of the mice. Our results showed that curcumin administration (100 mg/kg) rescued the impaired neurogenesis of Aβ1-42 mice, shown as enhanced BrdU+/DCX+ and BrdU+/NeuN+ cells in DG. In addition, curcumin regulated the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) -mediated glycogen synthase kinase-3β (GSK3β) /Wingless/Integrated (Wnt)/β-catenin pathway and cyclic adenosine monophosphate response element-binding protein (CREB)/BDNF in Aβ1-42 mice. Inhibiting Wnt/β-catenin and depriving BDNF could reverse both the upregulated neurogenesis and cognitive function of curcumin-treated Aβ1-42 mice. In conclusion, our study indicates that curcumin, through targeting PI3K/Akt, regulates GSK3β/Wnt/β-catenin and CREB/BDNF pathways, improving the adult neurogenesis of AD mice.

Anti-hyperalgesic and anti-inflammatory effects of 4R-tobacco cembranoid in a mouse model of inflammatory pain

4R is a tobacco cembranoid that binds to and modulates cholinergic receptors and exhibits neuroprotective and anti-inflammatory activity. Given the established function of the cholinergic system in pain and inflammation, we propose that 4R is also analgesic. Here, we tested the hypothesis that systemic 4R treatment decreases pain-related behaviors and peripheral inflammation via modulation of the alpha 7 nicotinic acetylcholine receptors (α7 nAChRs) in a mouse model of inflammatory pain. We elicited inflammation by injecting Complete Freund's Adjuvant (CFA) into the hind paw of male and female mice. We then assessed inflammation-induced hypersensitivity to cold, heat, and tactile stimulation using the Acetone, Hargreaves, and von Frey tests, respectively, before and at different time points (2.5 h - 8d) after a single systemic 4R (or vehicle) administration. We evaluated the contribution of α7 nAChRs 4R-mediated analgesia by pre-treating mice with a selective antagonist of α7 nAChRs followed by 4R (or vehicle) administration prior to behavioral tests. We assessed CFA-induced paw edema and inflammation by measuring paw thickness and quantifying immune cell infiltration in the injected hind paw using hematoxylin and eosin staining. Lastly, we performed immunohistochemical and flow cytometric analyses of paw skin in α7 nAChR-cre::Ai9 mice to measure the expression of α7 nAChRs on immune subsets. Our experiments show that systemic administration of 4R decreases inflammation-induced peripheral hypersensitivity in male and female mice and inflammation-induced paw edema in male but not female mice. Notably, 4R-mediated analgesia and anti-inflammatory effects lasted up to 8d after a single systemic administration on day 1. Pretreatment with an α7 nAChR-selective antagonist prevented 4R-mediated analgesia and anti-inflammatory effects, demonstrating that 4R effects are via modulation of α7 nAChRs. We further show that a subset of immune cells in the hind paw expresses α7 nAChRs. However, the number of α7 nAChR-expressing immune cells is unaltered by CFA or 4R treatment, suggesting that 4R effects are independent of α7 nAChR-expressing immune cells. Together, our findings identify a novel function of the 4R tobacco cembranoid as an analgesic agent in both male and female mice that reduces peripheral inflammation in a sex-dependent manner, further supporting the pharmacological targeting of the cholinergic system for pain treatment.

Nicotinic acetylcholine receptors: Therapeutic targets for novel ligands to treat pain and inflammation

Nicotinic acetylcholine receptors (nAChRs) have been historically defined as ligand-gated ion channels and function as such in the central and peripheral nervous systems. Recently, however, non-ionic signaling mechanisms via nAChRs have been demonstrated in immune cells. Furthermore, the signaling pathways where nAChRs are expressed can be activated by endogenous ligands other than the canonical agonists acetylcholine and choline. In this review, we discuss the involvement of a subset of nAChRs containing α7, α9, and/or α10 subunits in the modulation of pain and inflammation via the cholinergic anti-inflammatory pathway. Additionally, we review the most recent advances in the development of novel ligands and their potential as therapeutics.

Recent Advances in the Discovery of Nicotinic Acetylcholine Receptor Allosteric Modulators

Positive allosteric modulators (PAMs), negative allosteric modulators (NAMs), silent agonists, allosteric activating PAMs and neutral or silent allosteric modulators are compounds capable of modulating the nicotinic receptor by interacting at allosteric modulatory sites distinct from the orthosteric sites. This survey is focused on the compounds that have been shown or have been designed to interact with nicotinic receptors as allosteric modulators of different subtypes, mainly α7 and α4β2. Minimal chemical changes can cause a different pharmacological profile, which can then lead to the design of selective modulators. Experimental evidence supports the use of allosteric modulators as therapeutic tools for neurological and non-neurological conditions.

Formulated Curcumin Prevents Paclitaxel-Induced Peripheral Neuropathy through Reduction in Neuroinflammation by Modulation of α7 Nicotinic Acetylcholine Receptors

Paclitaxel is widely used in the treatment of various types of solid malignancies. Paclitaxel-induced peripheral neuropathy (PIPN) is often characterized by burning pain, cold, and mechanical allodynia in patients. Currently, specific pharmacological treatments against PIPN are lacking. Curcumin, a polyphenol of Curcuma longa, shows antioxidant, anti-inflammatory, and neuroprotective effects and has recently shown efficacy in the mitigation of various peripheral neuropathies. Here, we tested, for the first time, the therapeutic effect of 1.5% dietary curcumin and Meriva (a lecithin formulation of curcumin) in preventing the development of PIPN in C57BL/6J mice. Curcumin or Meriva treatment was initiated one week before injection of paclitaxel and continued throughout the study (21 days). Mechanical and cold sensitivity as well as locomotion/motivation were tested by the von Frey, acetone, and wheel-running tests, respectively. Additionally, sensory-nerve-action-potential (SNAP) amplitude by caudal-nerve electrical stimulation, electronic microscopy of the sciatic nerve, and inflammatory-protein quantification in DRG and the spinal cord were measured. Interestingly, a higher concentration of curcumin was observed in the spinal cord with the Meriva diet than the curcumin diet. Our results showed that paclitaxel-induced mechanical hypersensitivity was partially prevented by the curcumin diet but completely prevented by Meriva. Both the urcumin diet and the Meriva diet completely prevented cold hypersensitivity, the reduction in SNAP amplitude and reduced mitochondrial pathology in sciatic nerves observed in paclitaxel-treated mice. Paclitaxel-induced inflammation in the spinal cord was also prevented by the Meriva diet. In addition, an increase in α7 nAChRs mRNA, known for its anti-inflammatory effects, was also observed in the spinal cord with the Meriva diet in paclitaxel-treated mice. The use of the α7 nAChR antagonist and α7 nAChR KO mice showed, for the first time in vivo, that the anti-inflammatory effects of curcumin in peripheral neuropathy were mediated by these receptors. The results presented in this study represent an important advance in the understanding of the mechanism of action of curcumin in vivo. Taken together, our results show the therapeutic potential of curcumin in preventing the development of PIPN and further confirms the role of α7 nAChRs in the anti-inflammatory effects of curcumin.

Restoration and targeting of aberrant neurotransmitters in Parkinson's disease therapeutics

Neurotransmitters are considered as a fundamental regulator in the process of neuronal growth, differentiation and survival. Parkinson's Disease (PD) occurs due to extensive damage of dopamine-producing neurons; this causes dopamine deficits in the midbrain, followed by the alternation of various other neurotransmitters (glutamate, GABA, serotonin, etc.). It has been observed that fluctuation of neurotransmission in the basal ganglia exhibits a great impact on the pathophysiology of PD. Dopamine replacement therapy, such as the use of L-DOPA, can increase the dopamine level, but it majorly ameliorates the motor symptoms and is also associated with long-term complications (for e.g., LID). While the non-dopaminergic system can efficiently target non-motor symptoms, for instance, the noradrenergic system regulates the synthesis of BDNF via the MAPK pathway, which is important in learning and memory. Herein, we briefly discuss the role of different neurotransmitters, implementation of neurotransmitter receptors in PD. We also illustrate the recent advances of neurotransmitter-based drugs, which are currently under in vivo and clinical studies. Reinstating normal neurotransmitter levels has been believed to be advantageous in the treatment of PD. Thus, there is an increasing demand for drugs that can specifically target the neurotransmission system and reinstate the normal levels of neurotransmitters, which might prevent or delay neurodegeneration in PD.

Neuroprotective Activities of Curcumin in Parkinson's Disease: A Review of the Literature

Parkinson's disease (PD) is a slowly progressive multisystem disorder affecting dopaminergic neurons of the substantia nigra pars compacta (SNpc), which is characterized by a decrease of dopamine (DA) in their striatal terminals. Treatment of PD with levodopa or DA receptor agonists replaces the function of depleted DA in the striatum. Prolonged treatment with these agents often has variable therapeutic effects and leads to the development of undesirable dyskinesia. Consequently, a crucial unmet demand in the management of Parkinson's disease is the discovery of new approaches that could slow down, stop, or reverse the process of neurodegeneration. Novel potential treatments involving natural substances with neuroprotective activities are being developed. Curcumin is a polyphenolic compound isolated from the rhizomes of Curcuma longa (turmeric). It has been demonstrated to have potent anti-inflammatory, antioxidant, free radical scavenging, mitochondrial protecting, and iron-chelating effects, and is considered a promising therapeutic and nutraceutical agent for the treatment of PD. However, molecular and cellular mechanisms that mediate the pharmacological actions of curcumin remain largely unknown. Stimulation of nicotinic receptors and, more precisely, selective α7 nicotinic acetylcholine receptors (α7-nAChR), have been found to play a major modulatory role in the immune system via the "cholinergic anti-inflammatory pathway". Recently, α7-nAChR has been proposed to be a potential therapeutic approach in PD. In this review, the detailed mechanisms of the neuroprotective activities of curcumin as a potential therapeutic agent to help Parkinson's patients are being discussed and elaborated on in detail.

Therapeutic Potential of Curcumin in Reversing the Depression and Associated Pseudodementia via Modulating Stress Hormone, Hippocampal Neurotransmitters, and BDNF Levels in Rats

Depressive state adversely affects the memory functions, especially in the geriatric population. The initial stage of memory deficits associated with depression is particularly called as pseudodementia. It is the starting point of memory disturbance before dementia. The purpose of this research was to study depression and its consequent pseudodementia. For this purpose 24 male albino Wistar rats were divided into four groups. Depression was induced by 14 days of chronic restraint stress (CRS) daily for 4 h. After developing a depression model, pattern separation test was conducted to monitor pseudodementia in rats. Morris water maze test (MWM) was also performed to observe spatial memory. It was observed that model animals displayed impaired pattern separation and spatial memory. Treatment was started after the development of pseudodementia in rats. Curcumin at a dose of 200 mg/kg was given to model rats for one week along with the stress procedure. Following the treatment with curcumin, rats were again subjected to the aforementioned behavioral tests before decapitation. Corticosterone levels, brain derived neurotrophic factor (BDNF) and neurochemical analysis were conducted. Model rats showed depressogenic behavior and impaired memory performance. In addition to this, high corticosterone levels and decreased hippocampal BDNF, 5-HT, dopamine (DA), and acetylcholine (ACh) levels were also observed in depressed animals. These behavioral biochemical and neurochemical changes were effectively restored following treatment with curcumin. Hence, it is suggested from this study that pseudodementia can be reversed unlike true dementia by controlling the factors such as depression which induce memory impairment.

Curcumin Potentiates α7 Nicotinic Acetylcholine Receptors and Alleviates Autistic-Like Social Deficits and Brain Oxidative Stress Status in Mice

Autistic spectrum disorder (ASD) refers to a group of neurodevelopmental disorders characterized by impaired social interaction and cognitive deficit, restricted repetitive behaviors, altered immune responses, and imbalanced oxidative stress status. In recent years, there has been a growing interest in studying the role of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in the CNS. Influence of agonists for α7-nAChRs on the cognitive behavior, learning, and memory formation has been demonstrated in neuro-pathological condition such as ASD and attention-deficit hyperactivity disorder (ADHD). Curcumin (CUR), the active compound of the spice turmeric, has been shown to act as a positive allosteric modulator of α7-nAChRs. Here we hypothesize that CUR, acting through α7-nAChRs, influences the neuropathology of ASD. In patch clamp studies, fast inward currents activated by choline, a selective agonist of α7-nAChRs, were significantly potentiated by CUR. Moreover, choline induced enhancement of spontaneous inhibitory postsynaptic currents was markedly increased in the presence of CUR. Furthermore, CUR (25, 50, and 100 mg/kg, i.p.) ameliorated dose-dependent social deficits without affecting locomotor activity or anxiety-like behaviors of tested male Black and Tan BRachyury (BTBR) mice. In addition, CUR (50 and 100 mg/kg, i.p.) mitigated oxidative stress status by restoring the decreased levels of superoxide dismutase (SOD) and catalase (CAT) in the hippocampus and the cerebellum of treated mice. Collectively, the observed results indicate that CUR potentiates α7-nAChRs in native central nervous system neurons, mitigates disturbed oxidative stress, and alleviates ASD-like features in BTBR mice used as an idiopathic rodent model of ASD, and may represent a promising novel pharmacological strategy for ASD treatment.

Stable desensitization of α7 nicotinic acetylcholine receptors by NS6740 requires interaction with S36 in the orthosteric agonist binding site

NS6740 is an α₇ nicotinic acetylcholine receptor-selective partial agonist with low efficacy for channel activation, capable of promoting the stable conversion of the receptors to nonconducting (desensitized) states that can be reactivated with the application of positive allosteric modulators (PAMs). In spite of its low efficacy for channel activation, NS6740 is an effective activator of the cholinergic anti-inflammatory pathway. We observed that the concentration-response relationships for channel activation, both when applied alone and when co-applied with the PAM PNU-120596 are inverted-U shaped with inhibitory/desensitizing activities dominant at high concentrations. We evaluated the potential importance of recently identified binding sites for allosteric activators and tested the hypotheses that the stable desensitization produced by NS6740 may be due to binding to these sites. Our experiments were guided by molecular modeling of NS6740 binding to both the allosteric and orthosteric activation sites on the receptor. Our results indicate that with α₇C190A mutants, which have compromised orthosteric activation sites, NS6740 may work at the allosteric activation sites to promote transient PAM-dependent currents but not the stable desensitization seen with wild-type α₇ receptors. Modeling NS6740 in the orthosteric binding sites identified S36 as an important residue for NS6740 binding and predicted that an S36V mutation would limit NS6740 activity. The efficacy of NS6740 for α₇S36V receptors was reduced to zero, and applications of the compound to α₇S36V receptors failed to induce the desensitization observed with wild-type receptors. The results indicate that the unique properties of NS6740 are due primarily to binding at the sites for orthosteric agonists.

Apigenin and Structurally Related Flavonoids Allosterically Potentiate the Function of Human α7-Nicotinic Acetylcholine Receptors Expressed in SH-EP1 Cells

Phytochemicals, such as monoterpenes, polyphenols, curcuminoids, and flavonoids, are known to have anti-inflammatory, antioxidant, neuroprotective, and procognitive effects. In this study, the effects of several polyhydroxy flavonoids, as derivatives of differently substituted 5,7-dihydroxy-4H-chromen-4-one including apigenin, genistein, luteolin, kaempferol, quercetin, gossypetin, and phloretin with different lipophilicities (cLogP), as well as topological polar surface area (TPSA), were tested for induction of Ca²⁺ transients by α7 human nicotinic acetylcholine (α7 nACh) receptors expressed in SH-EP1 cells. Apigenin (10 μM) caused a significant potentiation of ACh (30 μM)-induced Ca²⁺ transients, but did not affect Ca²⁺ transients induced by high K⁺ (60 mM) containing solutions. Co-application of apigenin with ACh was equally effective as apigenin preincubation. However, the effect of apigenin significantly diminished by increasing ACh concentrations. The flavonoids tested also potentiated α₇ nACh mediated Ca²⁺ transients with descending potency (highest to lowest) by genistein, gossypetin, kaempferol, luteolin, phloretin, quercetin, and apigenin. The specific binding of α7 nACh receptor antagonist [¹²⁵I]-bungarotoxin remained unchanged in the presence of any of the tested polyhydroxy flavonoids, suggesting that these compounds act as positive allosteric modulators of the α7-nACh receptor in SH-EP1 cells. These findings suggest a clinical potential for these phytochemicals in the treatment of various human diseases from pain to inflammation and neural disease.

Curcumin and its Multi-target Function Against Pain and Inflammation: An Update of Pre-clinical Data

Pain is an unpleasant sensation that has complex and varying causative etiology. Modern drug discovery focuses on identifying potential molecules that target multiple pathways with a safer profile compared to those with a single target. The current treatment of pain and inflammation with the available therapeutics has a number of major side effects. Pain is one of the major clinical problems that need functional therapeutics which act on multiple targets and with low toxicity. Curcumin, a naturally occurring polyphenolic compound from Curcuma longa, has been used for years in Ayurvedic, Chinese, and in many other systems of traditional medicine. Pre-clinical data published thus far demonstrated that curcumin possesses multi-target biological functions, suggesting its potential use to cure different diseases. However, there is no or very brief systematic review of its potential use in pain and inflammation with underlying mechanisms for such activities. Accordingly, the aim of the current review was to update the pre-clinical data of curcumin and its multiple targeting pathways for analgesic and anti-inflammatory effects, and to further propose a molecular mechanism(s). A literature study was conducted using different known databases, including Pubmed, SciFinder, Google Scholar, and Science Direct. Available pre-clinical data suggest the ameliorating effect of curcumin in pain and inflammation is rendered through the modulation of pain pathways, including inhibition of a number of pro-inflammatory mediators, inhibition of oxidative stress and cyclooxygenase-2 (COX-2), down-regulation of Ca2+/calmodulin-depend protein kinase II (CaMKIIα) and calcium channels like transient receptor potential (TRP), modulation of metabotropic glutamate receptor-2 (mGlu2), modulation of monoamine system, inhibition of JAK2/STAT3 signaling pathway, remodeling of extracellular matrix proteins, inhibition of apoptosis, inhibition of JNK/MAPK and ERK/CREB signaling pathway, and activation of the opioid system. Taken all together, it is evident that curcumin is one of the promising, safe, and natural polyphenolic molecules that target multiple molecular pathways in pain and can be beneficial in the treatment and management of pain and inflammation.

Natural Polyhydroxy Flavonoids, Curcuminoids, and Synthetic Curcumin Analogs as α7 nAChRs Positive Allosteric Modulators

The α7 nicotinic acetylcholine receptor (α7 nAChR) is a ligand-gated ion channel that is involved in cognition disorders, schizophrenia, pain, and inflammation. Allosteric modulation of this receptor might be advantageous to reduce the toxicity in comparison with full agonists. Our previous results obtained with some hydroxy-chalcones, which were identified as positive allosteric modulators (PAMs) of α7 nAChR, prompted us to evaluate the potential of some structurally related naturally occurring flavonoids and curcuminoids and some synthetic curcumin analogues, with the aim of identifying new allosteric modulators of the α7 nAChR. Biological evaluation showed that phloretin, demethoxycurcumin, and bis-demethoxicurcuming behave as PAMs of α7 nAChR. In addition, some new curcumin derivatives were able to enhance the signal evoked by ACh; the activity values found for the tetrahydrocurcuminoid analog 23 were especially promising.

Cardioprotective role of GTS-21 by attenuating the TLR4/NF-κB pathway in streptozotocin-induced diabetic cardiomyopathy in rats

The cholinergic anti-inflammatory pathway (CAP) was investigated in a variety of inflammatory conditions and constitutes a valuable line in their treatment. In the current study, we investigated the anti-inflammatory effect of GTS-21 (GTS) as a partial selective α7 nicotinic acetylcholine receptor (α7-nAchR) agonist in diabetic cardiomyopathy model in rats. This mechanism was elaborated to study whether it could alleviate the electrocardiographic, histopathological, and molecular levels of Toll-like receptor 4 (TLR4)/nuclear factor κB (NF-κB) pathway proteins. Diabetes was induced by the injection of streptozotocin (STZ) (50 mg/kg). Diabetic rats were treated with GTS (1 or 2 mg/kg/day), methyllycaconitine (MLA), a selective α7-nAchR antagonist (2 mg/kg/day) plus GTS (2 mg/kg/day), or the vehicle. All treatments were given by the intraperitoneal route. Ventricular rate and different electrocardiograph (ECG) anomalies were detected. Plasma levels of cardiac troponin T (cTnT) and creatine kinase MB (CK-MB) were measured by ELISA. Additionally, we elucidated the levels of several proteins involved in the TLR4/NF-κB pathway. Cardiac levels of TLR4 and phosphorylated protein kinase B (p-Akt) were detected by ELISA. The cardiac expression of myeloid differentiation primary response 88 (Myd88), tumor necrosis factor receptor-associated factor 6 (TRAF6), NF-κB, interleukin 1β (IL-1β), and active caspase-1 were evaluated by immunohistochemical staining. Finally, the cardiac levels of interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) were determined by ELISA. Diabetic rats showed (i) ECG signs of cardiomyopathy such as significant ST segment elevations, prolonged QRS, QT intervals, and ventricular tachycardia; (ii) increased plasma levels of cTnT and CK-MB; (iii) increased expression of cardiac TLR4; (iv) elevated immunohistochemical expression of cardiac, Myd88, TRAF6, and NF-κB; (v) diminution in the cardiac expression of p-Akt; and (vi) adaptive increases in cardiac expression of TNF-α and IL-6. These effects were ameliorated in diabetic rats treated with both doses of GTS. Pretreatment with MLA did not completely reverse the ameliorative effect of GTS on cTnT, TRAF6, TNF-α, and IL-6, thereby reinforcing the presence of possible α7-nAchR-independent mechanisms. The activation of α7-nAchR with GTS offers a promising prophylactic strategy for diabetic cardiomyopathy by attenuating the TLR4/NF-κB pathway.

Drug Development in Channelopathies: Allosteric Modulation of Ligand-Gated and Voltage-Gated Ion Channels

Ion channels have been characterized as promising drug targets for treatment of numerous human diseases. Functions of ion channels can be fine-tuned by allosteric modulators, which interact with channels and modulate their activities by binding to sites spatially discrete from those of orthosteric ligands. Positive and negative allosteric modulators have presented a plethora of potential therapeutic advantages over traditionally orthosteric agonists and antagonists in terms of selectivity and safety. This thematic review highlights the discovery of representative allosteric modulators for ligand-gated and voltage-gated ion channels, discussing in particular their identifications, locations, and therapeutic uses in the treatment of a range of channelopathies. Additionally, structures and functions of selected ion channels are briefly described to aid in the rational design of channel modulators. Overall, allosteric modulation represents an innovative targeting approach, and the corresponding modulators provide an abundant but challenging landscape for novel therapeutics targeting ligand-gated and voltage-gated ion channels.

The effects of oral administration of curcumin-galactomannan complex on brain waves are consistent with brain penetration: a randomized, double-blinded, placebo-controlled pilot study

OVERVIEW

A novel highly bioavailable curcumin-galactomannan (CGM) formulation was shown to have improved blood-brain-barrier (BBB) permeability of free curcuminoids in animal models; however, this has not been established in humans. The present study was conducted to determine the functional effects of CGM on brain waves in healthy individuals, owing to its BBB permeability.

METHODS

A total of 18 healthy volunteers aged 35-65 were randomly assigned to consume 500 mg CGM, Unformulated curcumin (UC) or Placebo capsules twice daily for 30 days. Electroencephalogram (EEG) measurements, audio-visual reaction time tests and a working memory test were conducted at baseline and after 30 days.

RESULTS

Supplementation of CGM resulted in a significant increase in α- and β-waves (p < 0.05) as well as a significant reduction in α/β ratio in comparison with unformulated curcumin and placebo groups. Furthermore, the CGM showed significant reduction in the audio-reaction time (29.8 %; p < 0.05) in comparison with placebo and 24.6% (p < 0.05) with unformulated curcumin. The choice-based visual-reaction time was also significantly decreased (36%) in CGM as compared to unformulated curcumin and placebo which produced 15.36% and 5.2% respectively.

CONCLUSION

The observed increase in α and β waves and reduction in α/β ratio in the CGM group suggest that CGM can influence the brain waves in healthy subjects in a manner consistent with penetration of the blood-brain-barrier. The EEG results correlated with improved audio-visual and working memory tests which further support the role of CGM on memory improvements and fatigue reduction.

Neuroprotective Effect of Curcumin on the Nigrostriatal Pathway in a 6-Hydroxydopmine-Induced Rat Model of Parkinson's Disease is Mediated by α7-Nicotinic Receptors

Parkinson’s disease (PD) is a common neurodegenerative disorder, characterized by selective degeneration of dopaminergic nigrostriatal neurons. Most of the existing pharmacological approaches in PD consider replenishing striatal dopamine. It has been reported that activation of the cholinergic system has neuroprotective effects on dopaminergic neurons, and human α7-nicotinic acetylcholine receptor (α7-nAChR) stimulation may offer a potential therapeutic approach in PD. Our recent in-vitro studies demonstrated that curcumin causes significant potentiation of the function of α7-nAChRs expressed in Xenopus oocytes. In this study, we conducted in vivo experiments to assess the role of the α7-nAChR on the protective effects of curcumin in an animal model of PD. Intra-striatal injection of 6-hydroxydopmine (6-OHDA) was used to induce Parkinsonism in rats. Our results demonstrated that intragastric curcumin treatment (200 mg/kg) significantly improved the abnormal motor behavior and offered neuroprotection against the reduction of dopaminergic neurons, as determined by tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra and caudoputamen. The intraperitoneal administration of the α7-nAChR-selective antagonist methyllycaconitine (1 µg/kg) reversed the neuroprotective effects of curcumin in terms of both animal behavior and TH immunoreactivity. In conclusion, this study demonstrates that curcumin has a neuroprotective effect in a 6-hydroxydopmine (6-OHDA) rat model of PD via an α7-nAChR-mediated mechanism.

Key Developments in the Potential of Curcumin for the Treatment of Peripheral Neuropathies

Peripheral neuropathies (PN) can be triggered after metabolic diseases, traumatic peripheral nerve injury, genetic mutations, toxic substances, and/or inflammation. PN is a major clinical problem, affecting many patients and with few effective therapeutics. Recently, interest in natural dietary compounds, such as polyphenols, in human health has led to a great deal of research, especially in PN. Curcumin is a polyphenol extracted from the root of Curcuma longa. This molecule has long been used in Asian medicine for its anti-inflammatory, antibacterial, and antioxidant properties. However, like numerous polyphenols, curcumin has a very low bioavailability and a very fast metabolism. This review addresses multiple aspects of curcumin in PN, including bioavailability issues, new formulations, observations in animal behavioral tests, electrophysiological, histological, and molecular aspects, and clinical trials published to date. The, review covers in vitro and in vivo studies, with a special focus on the molecular mechanisms of curcumin (anti-inflammatory, antioxidant, anti-endoplasmic reticulum stress (anti-ER-stress), neuroprotection, and glial protection). This review provides for the first time an overview of curcumin in the treatment of PN. Finally, because PN are associated with numerous pathologies (e.g., cancers, diabetes, addiction, inflammatory disease...), this review is likely to interest a large audience.

Impact of Natural Dietary Agents on Multiple Myeloma Prevention and Treatment: Molecular Insights and Potential for Clinical Translation

Chemoprevention is based on the use of non-toxic, pharmacologically active agents to prevent tumor progression. In this regard, natural dietary agents have been described by the most recent literature as promising tools for controlling onset and progression of malignancies. Extensive research has been so far performed to shed light on the effects of natural products on tumor growth and survival, disclosing the most relevant signal transduction pathways targeted by such compounds. Overall, anti-inflammatory, anti-oxidant and cytotoxic effects of dietary agents on tumor cells are supported either by results from epidemiological or animal studies and even by clinical trials. Multiple myeloma is a hematologic malignancy characterized by abnormal proliferation of bone marrow plasma cells and subsequent hypercalcemia, renal dysfunction, anemia, or bone disease, which remains incurable despite novel emerging therapeutic strategies. Notably, increasing evidence supports the capability of dietary natural compounds to antagonize multiple myeloma growth in preclinical models of the disease, underscoring their potential as candidate anti-cancer agents. In this review, we aim at summarizing findings on the anti-tumor activity of dietary natural products, focusing on their molecular mechanisms, which include inhibition of oncogenic signal transduction pathways and/or epigenetic modulating effects, along with their potential clinical applications against multiple myeloma and its related bone disease.