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      α-lipoic acid suppresses neuronal excitability and attenuates colonic hypersensitivity to colorectal distention in diabetic rats

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          Abstract

          Aim

          Patients with long-standing diabetes often demonstrate intestinal dysfunction, characterized as constipation or colonic hypersensitivity. Our previous studies have demonstrated the roles of voltage-gated sodium channels NaV1.7 and NaV1.8 in dorsal root ganglion (DRG) in colonic hypersensitivity of rats with diabetes. This study was designed to determine roles of antioxidant α-lipoic acid (ALA) on sodium channel activities and colonic hypersensitivity of rats with diabetes.

          Methods

          Streptozotocin was used to induce diabetes in adult female rats. Colonic sensitivity was measured by behavioral responses to colorectal distention in rats. The excitability and sodium channel currents of colon projection DRG neurons labeled with DiI were measured by whole-cell patch-clamp recordings. The expressions of NaV1.7 and NaV1.8 of colon DRGs were measured by western blot analysis.

          Results

          ALA treatment significantly increased distention threshold in responding to colorectal distension in diabetic rats compared with normal saline treatment. ALA treatment also hyper-polarized the resting membrane potentials, depolarized action potential threshold, increased rheobase, and decreased frequency of action potentials evoked by ramp current stimulation. Furthermore, ALA treatment also reduced neuronal sodium current densities of DRG neurons innervating the colon from rats with diabetes. In addition, ALA treatment significantly downregulated NaV1.7 and NaV1.8 expression in colon DRGs from rats with diabetes.

          Conclusion

          Our results suggest that ALA plays an analgesic role, which was likely mediated by downregulation of NaV1.7 and NaV1.8 expressions and functions, thus providing experimental evidence for using ALA to treat colonic hypersensitivity in patients with diabetic visceral pain.

          Most cited references42

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          Lipoic acid as an anti-inflammatory and neuroprotective treatment for Alzheimer's disease.

          Alzheimer's disease (AD) is a progressive neurodegenerative disorder that destroys patient memory and cognition, communication ability with the social environment and the ability to carry out daily activities. Despite extensive research into the pathogenesis of AD, a neuroprotective treatment - particularly for the early stages of disease - remains unavailable for clinical use. In this review, we advance the suggestion that lipoic acid (LA) may fulfil this therapeutic need. A naturally occurring cofactor for the mitochondrial enzymes pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, LA has been shown to have a variety of properties which can interfere with the pathogenesis or progression of AD. For example, LA increases acetylcholine (ACh) production by activation of choline acetyltransferase and increases glucose uptake, thus supplying more acetyl-CoA for the production of ACh. LA chelates redox-active transition metals, thus inhibiting the formation of hydroxyl radicals and also scavenges reactive oxygen species (ROS), thereby increasing the levels of reduced glutathione. In addition, LA down-regulates the expression of redox-sensitive pro-inflammatory proteins including TNF and inducible nitric oxide synthase. Furthermore, LA can scavenge lipid peroxidation products such as hydroxynonenal and acrolein. In human plasma, LA exists in an equilibrium of free and plasma protein bound form. Up to 150 muM, it is bound completely, most likely binding to high affinity fatty acid sites on human serum albumin, suggesting that one large dose rather than continuous low doses (as provided by "slow release" LA) will be beneficial for delivery of LA to the brain. Evidence for a clinical benefit for LA in dementia is yet limited. There are only two published studies, in which 600 mg LA was given daily to 43 patients with AD (receiving a standard treatment with choline-esterase inhibitors) in an open-label study over an observation period of up to 48 months. Whereas the improvement in patients with moderate dementia was not significant, the disease progressed extremely slowly (change in ADAScog: 1.2 points=year, MMSE: -0.6 points=year) in patients with mild dementia (ADAScog<15). Data from cell culture and animal models suggest that LA could be combined with nutraceuticals such as curcumin, (-)-epigallocatechin gallate (from green tea) and docosahexaenoic acid (from fish oil) to synergistically decrease oxidative stress, inflammation, Abeta levels and Abeta plaque load and thus provide a combined benefit in the treatment of AD.
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            The vanilloid receptor initiates and maintains colonic hypersensitivity induced by neonatal colon irritation in rats.

            Robust chemical or mechanical irritation of the colon of neonatal rats leads to chronic visceral hypersensitivity. The clinical and physiologic relevance of such noxious stimulation in the context of human irritable bowel syndrome is questionable. The aims of this study were to determine whether mild chemical irritation of the colon of neonatal rats produced persistent changes in visceral sensitivity and to evaluate the role of transient receptor potential vanilloid 1 (TRPV1) in the initiation and maintenance of visceral hypersensitivity. Ten-day-old rat pups received an intracolonic infusion of 0.5% acetic acid in saline. TRPV1 inhibitors were administered 30 minutes before acetic acid sensitization. Sensitivity of the colon to balloon distention (CRD) in adults was measured by grading their abdominal withdrawal reflex and electromyographic responses. In adult rats, TRPV1 antagonist was injected intraperitoneally 30 minutes before CRD. Neonatal acetic acid treatment resulted in higher sensitivity to CRD in adult rats compared with controls in the absence of histopathologic signs of inflammation. Treatment of colons of adult rats with acetic acid did not produce persistent sensitization. Antagonism of the TRPV1 before neonatal administration of acetic acid and after established visceral hypersensitivity attenuated sensitivity to CRD. TRPV1 expression was increased in dorsal root ganglia-containing colon afferent neurons. We have described a new model for persistent colonic sensory dysfunction following a transient noxious stimulus in the neonatal period and a potentially important role for TRPV1 in initiation and maintenance of persistent visceral hypersensitivity.
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              New molecular mechanisms on the activation of TRPM2 channels by oxidative stress and ADP-ribose.

              The Na(+) and Ca(2+)-permeable melastatin related transient receptor potential (TRPM2) cation channels can be gated either by ADP-ribose (ADPR) in concert with Ca(2+) or by hydrogen peroxide (H(2)O(2)), an experimental model for oxidative stress, and binding to the channel's enzymatic Nudix domain. Since the mechanisms that lead to TRPM2 inhibiting in response to ADPR and H(2)O(2) are not understood, I reviewed the effects of various inhibitors such as flufenamic acid and PARP inhibitors on ADPR, NAD(+) and H(2)O(2)-induced TRPM2 currents. In our experimental study, TRPM2 cation channels in chinese hamster ovary transected cells were gated both by ADPR and NAD(+). In addition, H(2)O(2) seems to activate TRPM2 by changing to the hydroxyl radical in the intracellular space after passing the plasma membrane. Experimental studies with respect to patch-clamp and Ca(2+) imaging, inhibitor roles of antioxidants are also summarized in the review.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                Journal of Pain Research
                Journal of Pain Research
                Dove Medical Press
                1178-7090
                2017
                14 July 2017
                : 10
                : 1645-1655
                Affiliations
                [1 ]Department of Endocrinology, The Second Affiliated Hospital of Soochow University, Suzhou, People’s Republic of China
                [2 ]Department of Endocrinology, The East District of Suzhou Municipal Hospital, Suzhou, People’s Republic of China
                [3 ]Jiangsu Key Laboratory of Translational Research and Therapy for Neuro-Psycho-Diseases, Institute of Neuroscience, Soochow University, Suzhou, People’s Republic of China
                Author notes
                Correspondence: Hong-Hong Zhang, Department of Endocrinology, The Second Affiliated Hospital of Soochow University, 1055 San-Xiang Road, Suzhou 215000, People’s Republic of China, Tel/Fax +86 512 6778 4167, Email miqihh@ 123456sina.com
                [*]

                These authors contributed equally to this work

                Article
                jpr-10-1645
                10.2147/JPR.S135017
                5529097
                28769585
                d9bd994d-ab04-4820-a28f-1df9ebf70ed7
                © 2017 Sun et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                History
                Categories
                Original Research

                Anesthesiology & Pain management
                diabetes,colonic hypersensitivity,dorsal root ganglion,voltage-gated sodium channels,α-lipoic acid

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