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Yorek M. Combination therapy is it in the future for successfully treating peripheral diabetic neuropathy? Front Endocrinol (Lausanne) 2024; 15:1357859. [PMID: 38812811 PMCID: PMC11133577 DOI: 10.3389/fendo.2024.1357859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Accepted: 04/16/2024] [Indexed: 05/31/2024] Open
Abstract
In 2022, the Center for Disease Control and Prevention reported that 11.3% of the United States population, 37.3 million people, had diabetes and 38% of the population had prediabetes. A large American study conducted in 2021 and supported by many other studies, concluded that about 47% of diabetes patients have peripheral neuropathy and that diabetic neuropathy was present in 7.5% of patients at the time of diabetes diagnosis. In subjects deemed to be pre-diabetes and impaired glucose tolerance there was a wide range of prevalence estimates (interquartile range (IQR): 6%-34%), but most studies (72%) reported a prevalence of peripheral neuropathy ≥10%. There is no recognized treatment for diabetic peripheral neuropathy (DPN) other than good blood glucose control. Good glycemic control slows progression of DPN in patients with type 1 diabetes but for patients with type 2 diabetes it is less effective. With obesity and type 2 diabetes at epidemic levels the need of a treatment for DPN could not be more important. In this article I will first present background information on the "primary" mechanisms shown from pre-clinical studies to contribute to DPN and then discuss mono- and combination therapies that have demonstrated efficacy in animal studies and may have success when translated to human subjects. I like to compare the challenge of finding an effective treatment for DPN to the ongoing work being done to treat hypertension. Combination therapy is the recognized approach used to normalize blood pressure often requiring two, three or more drugs in addition to lifestyle modification to achieve the desired outcome. Hypertension, like DPN, is a progressive disease caused by multiple mechanisms. Therefore, it seems likely as well as logical that combination therapy combined with lifestyle adjustments will be required to successfully treat DPN.
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Affiliation(s)
- Mark Yorek
- Department of Internal Medicine, University of Iowa, Iowa City, IA, United States
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA, United States
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, United States
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Wang AN, Carlos J, Fraser GM, McGuire JJ. Zucker Diabetic Sprague Dawley rat (ZDSD): type 2 diabetes translational research model. Exp Physiol 2022; 107:265-282. [PMID: 35178802 PMCID: PMC9314054 DOI: 10.1113/ep089947] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 02/02/2022] [Indexed: 11/30/2022]
Abstract
New Findings What is the topic of this review? The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is in the early adoption phase of use by researchers in the fields of diabetes, including prediabetes, obesity and metabolic syndrome. It is essential that physiology researchers choose preclinical models that model human type 2 diabetes appropriately and are aware of the limitations on experimental design. What advances does it highlight? Our review of the scientific literature finds that although sex, age and diets contribute to variability, the ZDSD phenotype and disease progression model the characteristics of humans who have prediabetes and diabetes, including co‐morbidities.
Abstract Type 2 diabetes (T2D) is a prevalent disease and a significant concern for global population health. For persons with T2D, clinical treatments target not only the characteristics of hyperglycaemia and insulin resistance, but also co‐morbidities, such as obesity, cardiovascular and renal disease, neuropathies and skeletal bone conditions. The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is a rodent model developed for experimental studies of T2D. We reviewed the scientific literature to highlight the characteristics of T2D development and the associated phenotypes, such as metabolic syndrome, cardiovascular complications and bone and skeletal pathologies in ZDSD rats. We found that ZDSD phenotype characteristics are independent of leptin receptor signalling. The ZDSD rat develops prediabetes, then progresses to overt diabetes that is accelerated by introduction of a timed high‐fat diet. In male ZDSD rats, glycated haemoglobin (HbA1c) increases at a constant rate from 7 to >30 weeks of age. Diabetic ZDSD rats are moderately hypertensive compared with other rat strains. Diabetes in ZDSD rats leads to endothelial dysfunction in specific vasculatures, impaired wound healing, decreased systolic and diastolic cardiac function, neuropathy and nephropathy. Changes to bone composition and the skeleton increase the risk of bone fractures. Zucker Diabetic‐Sprague Dawley rats have not yet achieved widespread use by researchers. We highlight sex‐related differences in the ZDSD phenotype and gaps in knowledge for future studies. Overall, scientific data support the premise that the phenotype and disease progression in ZDSD rats models the characteristics in humans. We conclude that ZDSD rats are an advantageous model to advance understanding and discovery of treatments for T2D through preclinical research.
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Affiliation(s)
- Andrea N Wang
- Departments of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
| | - Joselia Carlos
- Departments of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
| | - Graham M Fraser
- Division of Biomedical Sciences, Faculty of Medicine, Memorial University, St. John's, Newfoundland, Canada
| | - John J McGuire
- Departments of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.,Physiology & Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
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Impaired Corneal Sensation and Nerve Loss in a Type 2 Rat Model of Chronic Diabetes Is Reversible With Combination Therapy of Menhaden Oil, α-Lipoic Acid, and Enalapril. Cornea 2018; 36:725-731. [PMID: 28476051 DOI: 10.1097/ico.0000000000001182] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
PURPOSE This study investigated the efficacy of monotherapy versus combination of menhaden oil, α-lipoic acid, and enalapril on corneal sensation and morphometry and other neuropathy-related endpoints in a rat model of type 2 diabetes. METHODS Male Sprague-Dawley rats (aged 12 weeks) were fed a high-fat diet for 8 weeks followed by 30 mg/kg streptozotocin. After 16 weeks of hyperglycemia, 12-week treatments consisting of menhaden oil, α-lipoic acid, enalapril, or their combination were initiated. Before and after treatments, we performed analyses of multiple neural and vascular endpoints including corneal sensitivity, corneal nerve density, vascular reactivity of epineurial arterioles, motor and sensory nerve conduction velocity, intraepidermal nerve fiber density, and thermal nociception. RESULTS Before treatment, all the neural and vascular endpoints in diabetic rats were impaired. Treating diabetic rats with monotherapy was effective in improving neural and vascular deficits with menhaden oil being most efficacious. However, the combination therapy provided the greatest benefit and improved/reversed all nerve and vascular deficits. The effect of combination therapy on corneal relative sensitivity and structure (in mm/mm), primary endpoints for this study, for control, diabetic, and diabetic treated rats was 4.2 ± 1.4 and 7.5 ± 0.5, 12.1 ± 1.3* and 3.8 ± 0.2*, and 6.6 ± 2.3 and 7.3 ± 0.5, respectively (*P < 0.05 compared with control rats; P < 0.05 compared with diabetic rats). CONCLUSIONS These studies suggest that a combination therapeutic approach may be most effective for treating vascular and neural complications of type 2 diabetes.
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Marche P, Dubois S, Abraham P, Parot-Schinkel E, Gascoin L, Humeau-Heurtier A, Ducluzeau PH, Mahe G. Neurovascular microcirculatory vasodilation mediated by C-fibers and Transient receptor potential vanilloid-type-1 channels (TRPV 1) is impaired in type 1 diabetes. Sci Rep 2017; 7:44322. [PMID: 28287157 PMCID: PMC5347083 DOI: 10.1038/srep44322] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 02/06/2017] [Indexed: 01/20/2023] Open
Abstract
Microvascular dysfunction may have an early onset in type 1 diabetes (T1D) and can precede major complications. Our objectives were to assess the endothelial-dependent (acetylcholine, ACh; and post-occlusive hyperemia, PORH), non-endothelial-dependent (sodium nitroprusside, SNP) and neurovascular-dependent (local heating, LH and current induced vasodilation, CIV) microcirculatory vasodilation in T1D patients compared with matched control subjects using a laser speckle contrast imager. Seventeen T1D patients - matched with 17 subjects according to age, gender, Body-Mass-Index, and smoking status - underwent macro- and microvascular investigations. The LH early peak assessed the transient receptor potential vanilloid type 1 channels (TRPV1) mediated vasodilation, whereas the plateau assessed the Nitirc-Oxyde (NO) and endothelium-derived hyperpolarizing factor (EDHF) pathways. PORH explored sensory nerves and (EDHF), while CIV assessed sensory nerves (C-fibers) and prostaglandin-mediated vasodilation. Using neurological investigations, we observed that C-fiber and A-delta fiber functions in T1D patients were similar to control subjects. PORH, CIV, LH peak and plateau vasodilations were significantly decreased in T1D patients compared to controls, whereas there was no difference between the two groups for ACh and SNP vasodilations. Neurovascular microcirculatory vasodilations (C-fibers and TRPV 1-mediated vasodilations) are impaired in TD1 patients whereas no abnormalities were found using clinical neurological investigations. Clinicaltrials: No. NCT02538120.
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Affiliation(s)
- P Marche
- Endocrinology Department, University Hospital of Angers, Angers, France
| | - S Dubois
- Endocrinology Department, University Hospital of Angers, Angers, France
| | - P Abraham
- Laboratory of Vascular Investigations, University Hospital of Angers, UMR CNRS6214/INSERM1083, LUNAM Université, Angers, France
| | - E Parot-Schinkel
- Methodology and Biostatistics Unit, University Hospital of Angers, Angers, France
| | - L Gascoin
- Laboratory of Vascular Investigations, University Hospital of Angers, UMR CNRS6214/INSERM1083, LUNAM Université, Angers, France
| | - A Humeau-Heurtier
- University of Angers, LARIS - Laboratoire Angevin de Recherche en Ingénierie des Systèmes, Angers, France
| | - P H Ducluzeau
- Endocrinology Department, University Hospital of Tours, Tours, France
| | - G Mahe
- INSERM Clinical Investigation Center (CIC 14 14), Rennes, France, Université de Rennes 1 and LUNAM University, Inserm 1083/CNRS 6214, Faculty of Medicine, Angers, France
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Jia G, Durante W, Sowers JR. Endothelium-Derived Hyperpolarizing Factors: A Potential Therapeutic Target for Vascular Dysfunction in Obesity and Insulin Resistance. Diabetes 2016; 65:2118-20. [PMID: 27456617 PMCID: PMC4955984 DOI: 10.2337/dbi16-0026] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Guanghong Jia
- Diabetes and Cardiovascular Research Center, Columbia, MO Harry S. Truman Memorial Veterans Hospital, Columbia, MO
| | - William Durante
- Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, MO
| | - James R Sowers
- Diabetes and Cardiovascular Research Center, Columbia, MO Harry S. Truman Memorial Veterans Hospital, Columbia, MO Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, MO Dalton Cardiovascular Research Center, Columbia, MO
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Yorek MA. Vascular Impairment of Epineurial Arterioles of the Sciatic Nerve: Implications for Diabetic Peripheral Neuropathy. Rev Diabet Stud 2015; 12:13-28. [PMID: 26676659 PMCID: PMC5397981 DOI: 10.1900/rds.2015.12.13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 04/30/2015] [Indexed: 12/11/2022] Open
Abstract
This article reviews the impact of diabetes and its treatment on vascular function with a focus on the reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve. Another focus is the relationship between the dysregulation of neurovascular function and diabetic peripheral neuropathy. Diabetic peripheral neuropathy is a debilitating disorder that occurs in more than 50 percent of patients with diabetes. The etiology involves metabolic, vascular, and immunologic pathways besides neurohormonal growth factor deficiency and extracellular matrix remodeling. In the light of this complex etiology, an effective treatment for diabetic peripheral neuropathy has not yet been identified. Current opinion postulates that any effective treatment for diabetic peripheral neuropathy will require a combination of life style and therapeutic interventions. However, a more comprehensive understanding of the factors contributing to neurovascular and neural dysfunction in diabetes is needed before such a treatment strategy can be developed. After reading this review, the reader should have gained insight into the complex regulation of vascular function and blood flow to the sciatic nerve, and the impact of diabetes on numerous elements of vascular reactivity of epineurial arterioles of the sciatic nerve.
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Affiliation(s)
- Mark A Yorek
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA 52246, USA
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Davidson EP, Coppey LJ, Holmes A, Lupachyk S, Dake BL, Oltman CL, Peterson RG, Yorek MA. Characterization of diabetic neuropathy in the Zucker diabetic Sprague-Dawley rat: a new animal model for type 2 diabetes. J Diabetes Res 2014; 2014:714273. [PMID: 25371906 PMCID: PMC4211210 DOI: 10.1155/2014/714273] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 09/09/2014] [Indexed: 01/22/2023] Open
Abstract
Recently a new rat model for type 2 diabetes the Zucker diabetic Sprague-Dawley (ZDSD/Pco) was created. In this study we sought to characterize the development of diabetic neuropathy in ZDSD rats using age-matched Sprague-Dawley rats as a control. Rats were examined at 34 weeks of age 12 weeks after the onset of hyperglycemia in ZDSD rats. At this time ZDSD rats were severely insulin resistant with slowing of both motor and sensory nerve conduction velocities. ZDSD rats also had fatty livers, elevated serum free fatty acids, triglycerides, and cholesterol, and elevated sciatic nerve nitrotyrosine levels. The corneas of ZDSD rats exhibited a decrease in subbasal epithelial corneal nerves and sensitivity. ZDSD rats were hypoalgesic but intraepidermal nerve fibers in the skin of the hindpaw were normal compared to Sprague-Dawley rats. However, the number of Langerhans cells was decreased. Vascular reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve, to acetylcholine and calcitonin gene-related peptide was impaired in ZDSD rats. These data indicate that ZDSD rats develop many of the neural complications associated with type 2 diabetes and are a good animal model for preclinical investigations of drug development for diabetic neuropathy.
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Affiliation(s)
- Eric P. Davidson
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
| | - Lawrence J. Coppey
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
| | - Amey Holmes
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA 52246, USA
| | - Sergey Lupachyk
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
| | - Brian L. Dake
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
| | - Christine L. Oltman
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA 52246, USA
| | | | - Mark A. Yorek
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA 52246, USA
- Iowa City Veterans Administration Center for the Prevention and Treatment of Visual Loss, Iowa City, IA 52246, USA
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA 52242, USA
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Cellek S, Cameron NE, Cotter MA, Fry CH, Ilo D. Microvascular dysfunction and efficacy of PDE5 inhibitors in BPH–LUTS. Nat Rev Urol 2014; 11:231-41. [DOI: 10.1038/nrurol.2014.53] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Van Dam PS, Cotter MA, Bravenboer B, Cameron NE. Pathogenesis of diabetic neuropathy: focus on neurovascular mechanisms. Eur J Pharmacol 2013; 719:180-186. [PMID: 23872412 DOI: 10.1016/j.ejphar.2013.07.017] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Accepted: 07/11/2013] [Indexed: 02/08/2023]
Abstract
Neuropathies of the peripheral and autonomic nervous systems affect up to half of all people with diabetes, and are major risk factors for foot ulceration and amputation. The aetiology is multifactorial: metabolic changes in diabetes may directly affect neural tissue, but importantly, neurodegenerative changes are precipitated by compromised nerve vascular supply. Experiments in animal models of diabetic neuropathy suggest that similar metabolic sequelae affect neurons and vasa nervorum endothelium. These include elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes such as elevated protein kinase C, nuclear factor κB and p38 mitogen activated protein kinase signalling. These mechanisms do not work in isolation but strongly interact in a mutually facilitatory fashion. Nitrosative stress and the induction of the enzyme poly (ADP-ribose) polymerase form one important link between physiological stressors such as reactive oxygen species and the pro-inflammatory mechanisms. Recently, evidence points to endoplasmic stress and the unfolded protein response as forming another crucial link. This review focuses on the aetiopathogenesis of neurovascular changes in diabetic neuropathy, elucidated in animal studies, and on putative therapeutic targets the majority of which have yet to be tested for efficacy in clinical trials.
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Affiliation(s)
- P Sytze Van Dam
- Onze Lieve Vrouwe Gasthuis, Department of internal Medicine, PO Box 95500, 1090HM Amsterdam, The Netherlands
| | - Mary A Cotter
- School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland UK
| | | | - Norman E Cameron
- School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland UK.
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Gao X, Martinez-Lemus LA, Zhang C. Endothelium-derived hyperpolarizing factor and diabetes. World J Cardiol 2011; 3:25-31. [PMID: 21286215 PMCID: PMC3030734 DOI: 10.4330/wjc.v3.i1.25] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Revised: 11/30/2010] [Accepted: 12/07/2010] [Indexed: 02/06/2023] Open
Abstract
In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemia-reperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetes-related endothelial dysfunction.
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Affiliation(s)
- Xue Gao
- Xue Gao, Department of Physiology, Chinese Academy of Medical Science and Peking Union Medical College, Beijing 100005, China
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Cotter MA, Gibson TM, Nangle MR, Cameron NE. Effects of interleukin-6 treatment on neurovascular function, nerve perfusion and vascular endothelium in diabetic rats. Diabetes Obes Metab 2010; 12:689-99. [PMID: 20590746 DOI: 10.1111/j.1463-1326.2010.01221.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
AIM Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, participates in neural development and has neurotrophic activity. Recent research has also indicated actions to improve vasa nervorum function in diabetes. Both these facets are potentially relevant for treatment of diabetic neuropathy. The aim of this study was to determine whether IL-6 treatment corrected changes in neurovascular function in streptozotocin-induced diabetic rats. METHODS After 1 month of diabetes, rats were given IL-6 for 1 month. The rats were subjected to sensory testing and measurements of nerve conduction velocities and nerve blood flow by hydrogen clearance microelectrode polarography. Further groups were used to study responses of the isolated gastric fundus and renal artery. Results were statistically analysed using ANOVA and post hoc tests. RESULTS Diabetic rats showed mechanical hyperalgesia, thermal hyperalgesia, and tactile allodynia. The former was unaffected by IL-6 treatment, whereas the latter two measures were corrected. Immunohistochemical staining of dorsal root ganglia for IL-6 did not reveal any changes with diabetes or treatment. The results showed that 22 and 17.4% slowing of sciatic motor and saphenous sensory nerve conduction velocities, respectively, with diabetes were improved by IL-6. Sciatic endoneurial perfusion was halved by diabetes and corrected by IL-6. A 40.6% diabetic deficit in maximal non-adrenergic, non-cholinergic relaxation of gastric fundus to nerve stimulation was unaffected by IL-6. Renal artery endothelium-dependent relaxation was halved by diabetes, the endothelium-derived hyperpolarizing factor (EDHF) component being severely attenuated. IL-6 did not affect nitric oxide-mediated vasorelaxation, but markedly improved EDHF responses. CONCLUSIONS IL-6 improved aspects of small and large nerve fibre and vascular endothelium dysfunction in diabetic rats. The functional benefits related to increased nerve blood flow via an EDHF mechanism, and IL-6 could have therapeutic potential in diabetic neuropathy and vasculopathy, which should be further evaluated.
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Affiliation(s)
- M A Cotter
- School of Medical Sciences, University of Aberdeen, Aberdeen, UK
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Matsumoto T, Ishida K, Taguchi K, Kobayashi T, Kamata K. Losartan normalizes endothelium-derived hyperpolarizing factor-mediated relaxation by activating Ca2+-activated K+ channels in mesenteric artery from type 2 diabetic GK rat. J Pharmacol Sci 2010; 112:299-309. [PMID: 20168046 DOI: 10.1254/jphs.09308fp] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
Ca(2+)-activated K(+) (K(Ca)) channels are important for endothelium-derived hyperpolarizing factor (EDHF) signaling. Since treatment with angiotensin II receptor blockers (ARBs) improves vasculopathies in type 2 diabetic patients, we asked whether the EDHF-type relaxation and its associated K(Ca) channels [small (SK(Ca))-, intermediate (IK(Ca))-, and large (BK(Ca))-conductance channels] are abnormal in mesenteric arteries isolated from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes (34 - 38 weeks) and whether an ARBs (losartan, 25 mg . kg(-1) . day(-1) for 2 weeks) might correct these abnormalities. Although the acetylcholine chloride-induced EDHF-type relaxation in mesenteric arteries from GK rats was reduced versus the Wistar controls, it was significantly restored by losartan treatment. The SK(Ca)-blocker apamin or the IK(Ca)-blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) inhibited such relaxations in the losartan-treated or -untreated Wistar groups and in the losartan-treated GK group, but not in the losartan-untreated GK group. The BK(Ca)-blocker iberiotoxin had a significant inhibitory effect in only one of these groups, the losartan-treated GK. The relaxations induced by the SK(Ca)/IK(Ca) activator NS309 and the BK(Ca) activator NS1619, which were impaired in GK rats, were normalized by losartan treatment. We conclude that losartan improves EDHF-type relaxation in GK rats at least partly by normalizing SK(Ca)/IK(Ca) activities and increasing BK(Ca) activity.
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Affiliation(s)
- Takayuki Matsumoto
- Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Tokyo, Japan
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Hanif K, Bid HK, Konwar R. Reinventing the ACE inhibitors: some old and new implications of ACE inhibition. Hypertens Res 2009; 33:11-21. [PMID: 19911001 DOI: 10.1038/hr.2009.184] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Since their inception, angiotensin-converting enzyme (ACE) inhibitors have been used as first-line therapy for the treatment of cardiovascular and renal diseases. They restore the balance between the vasoconstrictive salt-retentive and hypertrophy-causing peptide angiotensin II (Ang II) and bradykinin, a vasodilatory and natriuretic peptide. As ACE is a promiscuous enzyme, ACE inhibitors alter the metabolism of a number of other vasoactive substances. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have been proven effective in the treatment of hypertension, and reduce mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction. They inhibit ischemic events and stabilize plaques. Furthermore, they delay the progression of diabetic nephropathy and neuropathy and act as antioxidants. Ongoing studies have elucidated protective roles for them in both memory-related disorders and cancer. Lastly, N- and C-domain selective ACE inhibitors have led to new uses for ACE inhibitors.
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Affiliation(s)
- Kashif Hanif
- Division of Pharmacology, Central Drug Research Institute (CSIR), Lucknow, Uttar Pradesh, India.
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Vascular and neural dysfunctions in obese Zucker rats: effect of AVE7688. EXPERIMENTAL DIABETES RESEARCH 2009; 2009:912327. [PMID: 19536347 PMCID: PMC2695958 DOI: 10.1155/2009/912327] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Accepted: 05/12/2009] [Indexed: 12/23/2022]
Abstract
The purpose of this study was to determine whether AVE7688 a drug that inhibits both angiotensin converting enzyme and neutral endopeptidase activity protects vascular and nerve functions in an animal model of metabolic syndrome. Obese Zucker rats at 20 weeks of age were treated for 12 weeks with AVE7688. Vasodilation in epineurial arterioles was measured by videomicroscopy and nerve conduction velocity was measured following electrical stimulation. Treatment with AVE7688 improved vascular relaxation in response to acetylcholine and motor and sensory nerve conduction velocity. In obese Zucker rats superoxide levels and nitrotyrosine staining were elevated in the aorta and treatment corrected both conditions. Obese Zucker rats were hypoalgesic in response to a thermal stimulus and demonstrated signs of impaired tactile response and both conditions were significantly improved with treatment. Even though obese Zucker rats are normoglycemic vascular and neural dysfunctions develop with age and can be improved by treatment with AVE7688.
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Oltman CL, Davidson EP, Coppey LJ, Kleinschmidt TL, Yorek MA. Treatment of Zucker diabetic fatty rats with AVE7688 improves vascular and neural dysfunction. Diabetes Obes Metab 2009; 11:223-33. [PMID: 18564175 PMCID: PMC2667677 DOI: 10.1111/j.1463-1326.2008.00924.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
AIM Vasopeptidase inhibitors are drugs that inhibit angiotensin-converting enzyme and neutral endopeptidase (NEP). The latter is a protease that degrades vasoactive peptides and is increased in diabetes. We have previously shown that treating streptozotocin-induced diabetic rats, an animal model of type 1 diabetes, with AVE7688, a vasopeptidase inhibitor, improves neurovascular and neural function. In this study, we determined the effect of treating Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes, with AVE7688 on vascular and neural function. METHODS ZDF rats at 12 weeks of age were treated for 12 weeks with AVE7688 (500 mg/kg diet). Afterwards, vascular reactivity of epineurial arterioles of the sciatic nerve and nerve conduction velocity and blood flow was determined. RESULTS Vascular and neural function was significantly impaired in ZDF rats compared with age-matched lean (control) rats. Treating ZDF rats with AVE7688 improved vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineurial arterioles. Motor and sensory nerve conduction velocity, endoneurial blood flow and thermal nociception end-points were also improved by treatment compared with untreated ZDF rats. Superoxide and expression of NEP were increased in epineurial arterioles from ZDF rats and attenuated by treatment with AVE7688. CONCLUSIONS AVE7688 is an effective treatment for microvascular and neural disease in ZDF rats. Thus, vasopeptidase inhibitors may be an effective treatment for diabetic microvascular and neural complication in type 2 diabetes.
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Affiliation(s)
- C L Oltman
- Veteran Affairs Medical Center, Iowa City, IA 52246, USA
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Young EJ, Hill MA, Wiehler WB, Triggle CR, Reid JJ. Reduced EDHF responses and connexin activity in mesenteric arteries from the insulin-resistant obese Zucker rat. Diabetologia 2008; 51:872-81. [PMID: 18324386 DOI: 10.1007/s00125-008-0934-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Accepted: 12/17/2007] [Indexed: 01/18/2023]
Abstract
AIMS/HYPOTHESIS The objective of this study was to examine the effect of insulin resistance on endothelium-derived hyperpolarising factor (EDHF) and small mesenteric artery endothelial function using 25-week-old insulin-resistant obese Zucker rats (OZRs) and lean littermate control rats (LZRs). The involvement of gap junctions and their connexin subunits in the EDHF relaxation response was also assessed. METHODS Mesenteric arteries were evaluated using the following assays: (1) endothelial function by pressure myography, with internal diameter recorded using video microscopy; (2) connexin protein levels by western blotting; and (3) Cx mRNA expression by real-time PCR. RESULTS Relaxations in response to acetylcholine were significantly smaller in mesenteric arteries from the OZRs than the LZRs, whereas there was no difference in relaxations in response to levcromakalim. Responses to acetylcholine were not altered by nitric oxide inhibitors, but were abolished by charybdotoxin in combination with apamin, which blocked the EDHF component of the response. 40Gap27 significantly attenuated the response to acetylcholine in the LZRs, but had no effect in the OZRs. Connexin 40 protein and Cx40 mRNA levels in mesenteric vascular homogenates were significantly smaller in the OZRs than in the LZRs, with no difference in connexin 43 or Cx43 mRNA levels. CONCLUSIONS/INTERPRETATION These findings demonstrate that endothelial dysfunction in mesenteric arteries from the insulin-resistant OZRs can be attributed to a defect in EDHF. The results also suggest that the defective EDHF is at least partly related to an impairment of connexin 40-associated gap junctions, through a decrease in connexin 40 protein and Cx40 mRNA expression in the OZRs.
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Affiliation(s)
- E J Young
- School of Medical Sciences, RMIT University, Melbourne, Victoria, Australia.
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17
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Abstract
The arterial supply to the sciatic nerve was investigated in 20 human lower limbs (10 right, 10 left) from 20 cadavers (14 females, aged 84 +/- 9.6 years, range 66-95 years: 6 males, aged 80 +/- 8.2 years, range 70-90 years). In all limbs examined at least 1 sciatic artery could be identified supplying the sciatic nerve in the gluteal region. In total 28 sciatic arteries were identified, of which 14 arose from the medial circumflex femoral artery, 11 from the inferior gluteal artery, 2 from the first perforating artery, and 1 from the internal pudendal artery. In 5 limbs, 2 sciatic arteries were observed, being independent branches from the medial circumflex femoral and inferior gluteal arteries in 4 limbs and separate branches of the medial circumflex femoral artery in 1 limb. In 1 limb, 4 sciatic arteries were observed: 1 from the inferior gluteal artery, 2 from the medial circumflex femoral artery, and 1 from the first perforating artery. In the remaining 14 limbs a single sciatic artery was observed, which in one case arose from the internal pudendal artery, a previously unreported observation.
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18
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Davidson EP, Kleinschmidt TL, Oltman CL, Lund DD, Yorek MA. Treatment of streptozotocin-induced diabetic rats with AVE7688, a vasopeptidase inhibitor: effect on vascular and neural disease. Diabetes 2007; 56:355-62. [PMID: 17259379 DOI: 10.2337/db06-1180] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In epineurial arterioles, acetylcholine-mediated vascular relaxation is mediated by nitric oxide and endothelium-derived hyperpolarizing factor (EDHF), and both mechanisms are impaired by diabetes. The mediator responsible for the effect of EDHF is unknown. In epineurial arterioles, C-type natriuretic peptide (CNP) has properties consistent with EDHF-like activity. Epineurial arterioles express CNP, and exogenous CNP causes a concentration-dependent vascular relaxation. In streptozotocin-induced diabetic rats, CNP-mediated vascular relaxation in epineurial arterioles is decreased. Since CNP may be a regulator of vascular function, a vasopeptidase inhibitor may be an effective treatment for diabetes-induced vascular and neural disease. Vasopeptidase inhibitors inhibit ACE activity and neutral endopeptidase, which degrades natriuretic peptides. Streptozotocin-induced diabetic rats were treated with AVE7688 (450 mg/kg in the diet), a vasopeptidase inhibitor, for 8-10 weeks after 4 weeks of untreated diabetes. Treatment of diabetic rats corrected the diabetes-induced decrease in endoneurial blood flow, significantly improved motor and sensory nerve conduction velocity, prevented the development of hypoalgesia in the hind paw, and reduced superoxide and nitrotyrosine levels in epineurial arterioles. The diabetes-induced decrease in acetylcholine-mediated vascular relaxation by epineurial arterioles was significantly improved with treatment. These studies suggest that vasopeptidase inhibitors may be an effective approach for the treatment of diabetic vascular and neural dysfunction.
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Affiliation(s)
- Eric P Davidson
- Department of Veterans Affairs Iowa City Health Care System, Iowa City, IA 52246, USA
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Burnham MP, Johnson IT, Weston AH. Impaired small-conductance Ca2+-activated K+ channel-dependent EDHF responses in Type II diabetic ZDF rats. Br J Pharmacol 2006; 148:434-41. [PMID: 16682967 PMCID: PMC1751791 DOI: 10.1038/sj.bjp.0706748] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2005] [Revised: 02/10/2006] [Accepted: 03/14/2006] [Indexed: 01/08/2023] Open
Abstract
We have examined the relative contributions of small- and intermediate-conductance Ca(2+)-activated K(+) channels (SK(Ca) and IK(Ca)) to the endothelium-derived hyperpolarizing factor (EDHF) pathway response in small mesenteric arteries of Zucker Diabetic Fatty (ZDF) rats, before and after the development of Type II diabetes, together with Lean controls. Smooth muscle membrane potential was recorded using sharp microelectrodes in the presence of 10 microM indomethacin plus 100 microM N(omega)-nitro-L-arginine. SK(Ca) was selectively inhibited with 100 nM apamin, whereas IK(Ca) was blocked with 10 microM TRAM-39 (2-(2-chlorophenyl)-2,2-diphenylacetonitrile). Resting membrane potentials were similar in arteries from 17- to 20-week-old control and diabetic rats (approximately -54 mV). Responses elicited by 1 and 10 microM acetylcholine (ACh) were significantly smaller in the diabetic group (e.g. hyperpolarizations to -69.5 +/- 0.8 mV (ZDF; n = 12) and -73.2 +/- 0.6 mV (Lean; n = 12; P < 0.05) evoked by 10 microM ACh). The IK(Ca)-mediated components of the ACh responses were comparable between groups (hyperpolarizations to approximately -65 mV on exposure to 10 microM ACh). However, SK(Ca)-mediated responses were significantly reduced in the diabetic group (hyperpolarizations to -63.1 +/- 1.0 mV (ZDF; n = 6) and -71.5 +/- 1.2 mV (Lean; n = 6; P < 0.05) on exposure to 10 microM ACh. Impaired ACh responses were not observed in arteries from 5- to 6-week-old (pre-diabetic) animals. SK(Ca) subunit mRNA expression was increased in the diabetic group. The EDHF pathway, especially the SK(Ca)-mediated response, is impaired in Type II diabetic ZDF rats without a reduction in channel gene expression. These results may be particularly relevant to the microvascular complications of diabetes. The functional separation of SK(Ca) and IK(Ca) pathways is discussed.
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Affiliation(s)
- Matthew P Burnham
- Faculty of Life Sciences, The University of Manchester, G38 Stopford Building.
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Coppey LJ, Davidson EP, Rinehart TW, Gellett JS, Oltman CL, Lund DD, Yorek MA. ACE inhibitor or angiotensin II receptor antagonist attenuates diabetic neuropathy in streptozotocin-induced diabetic rats. Diabetes 2006; 55:341-8. [PMID: 16443766 DOI: 10.2337/diabetes.55.02.06.db05-0885] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ACE inhibition and/or blocking of the angiotensin II receptor are recognized as first-line treatment for nephropathy and cardiovascular disease in diabetic patients. However, little information is available about the potential benefits of these drugs on diabetic neuropathy. We examined vascular and neural activity in streptozotocin-induced diabetic rats that were treated for 12 weeks with enalapril, an ACE inhibitor, or L-158809, an angiotensin II receptor blocker. A prevention protocol (group 1) as well as three intervention protocols (treatment was initiated after 4, 8, or 12 weeks of diabetes [groups 2, 3, and 4, respectively]) were used. Endoneurial blood flow and motor nerve conduction velocity (MNCV) were impaired in all groups of untreated diabetic rats. In group 1, treatment of diabetic rats with enalapril or L-158809 partially prevented the diabetes-induced decrease in endoneurial blood flow and MNCV. In groups 2-4, intervention with enalapril was more effective in reversing the diabetes-induced impairment in endoneurial blood flow and MNCV than L-158809. The superoxide level in the aorta and epineurial arterioles of diabetic rats was increased. Treatment of diabetic rats with enalapril or L-158809 reduced the superoxide level in the aorta in all groups but was less effective in epineurial arterioles. Acetylcholine and calcitonin gene-related peptide (CGRP) cause vasodilation in epineurial arterioles of the sciatic nerve, which was impaired by diabetes. Treatment of diabetic rats (all groups) with enalapril or L-158809 completely prevented/reversed the diabetes-induced impairment in CGRP-mediated vascular relaxation. Treatment with enalapril or L-158809 was also effective in improving impaired acetylcholine-mediated vasodilation, but the efficacy was diminished from groups 1 to 4. These studies suggest that ACE inhibitors and/or angiotensin II receptor blockers may be effective treatments for diabetes and vascular and neural dysfunction. However, the efficacy of these treatments may be dependent on when the treatment is initiated.
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Affiliation(s)
- Lawrence J Coppey
- Department of Internal Medicine, University of Iowa and Veterans Affairs Medical Center, Iowa City, 52246, USA
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Srivastava S, Tammali R, Chandra D, Greer DA, Ramana KV, Bhatnagar A, Srivastava SK. Regulation of lens aldose reductase activity by nitric oxide. Exp Eye Res 2005; 81:664-72. [PMID: 15967436 DOI: 10.1016/j.exer.2005.04.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Revised: 04/04/2005] [Accepted: 04/05/2005] [Indexed: 02/02/2023]
Abstract
To examine the regulation of aldose reductase (AR) activity by nitric oxide (NO) in human lens epithelial cells (HLEC), cultured rat lens, and normal and diabetic rat lens, we have incubated HLEC or cultured rat lenses with 1 mm of the NO donors S-nitroso-N-acetylpenicillamine (SNAP) or S-nitrosoglutathione (GSNO), and the AR activity and sorbitol content were measured. Non-diabetic and diabetic (treated with streptozotocin 65 mg kg(-1) body wt, i.p.) rats were injected with the nitric oxide synthase (NOS) inhibitor, L-NAME (50 mg kg(-1) body wt day(-1), x 10 days i.p.) or NOS substrate, L-arginine (200 mg kg(-1) body wt day(-1), x 10 days i.p.). In a separate group of rats, a nitroglycerin (NG)-patch that releases 200 ng min(-1) NO was applied to the dorsal neck region. After 10 days of treatment, the lenses were removed and their AR activity and sorbitol content were measured. Incubation of HLEC with SNAP or GSNO reduced AR activity. A similar reduction in AR activity and sorbitol accumulation was observed when diabetic and non-diabetic rat lenses were cultured in the presence of SNAP and GSNO. Total protein-SSG in diabetic lens was lower compared to normal lens. Treatment of diabetic and non-diabetic rats with L-NAME enhanced AR activity and sorbitol accumulation, whereas NG patch and L-arginine significantly decreased AR activity and sorbitol accumulation in diabetic lenses compared to non-diabetic. Increased S-glutathiolation of AR was observed in the presence of SNAP. These results suggest that decreased glutathiolation of cellular proteins in diabetic rat lens compared to non-diabetic lens is related to decreased NO availability in diabetic rats which would decrease GSNO. Restoring the NO levels in diabetic animals increases glutathiolation of cellular proteins, inhibits AR activity and prevents sorbitol accumulation. Exogenous delivery of NO may represent a potentially useful strategy for preventing or delaying diabetic cataractogenesis and the development of other diabetic complications.
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Affiliation(s)
- Seema Srivastava
- Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, TX 77555-0647, USA
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Cheng ZJ, Grönholm T, Louhelainen M, Finckenberg P, Merasto S, Tikkanen I, Mervaala E. Vascular and renal effects of vasopeptidase inhibition and angiotensin-converting enzyme blockade in spontaneously diabetic Goto-Kakizaki rats. J Hypertens 2005; 23:1757-70. [PMID: 16093923 DOI: 10.1097/01.hjh.0000179765.48324.b4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND The renin-angiotensin system plays an important role in the pathogenesis of diabetes-induced vascular and renal complications. Vasopeptidase inhibitors simultaneously inhibit angiotensin-converting enzyme (ACE) and neutral endopeptidase. OBJECTIVE To compare the effectiveness of vasopeptidase inhibition and ACE inhibition in preventing hypertension, endothelial dysfunction and diabetic nephropathy in spontaneously diabetic Goto-Kakizaki (GK) rats. METHODS Eight-week-old GK rats received omapatrilat (40 mg/kg) or enalapril (30 mg/kg) for 12 weeks, either during a normal-sodium or high-sodium diet (7% w/w). Blood pressure, arterial functions and renal morphology were determined. RESULTS Blood pressure and albuminuria were increased in GK rats compared to non-diabetic Wistar controls. Endothelium-dependent vascular relaxation in response to acetylcholine (ACh) and endothelium-independent vascular relaxation in response to sodium nitroprusside (SNP) were impaired in GK rats. Experiments with N-nitro-L-arginine methyl ester (L-NAME), diclofenac, and L-NAME + diclofenac suggested that cyclooxygenase and endothelium-derived hyperpolarizing factor components of endothelium-dependent vascular relaxation were also impaired. A high-sodium diet aggravated hypertension and diabetes-induced vascular and renal complications. Omapatrilat and enalapril normalized blood pressure and albuminuria during the normal-sodium diet, and effectively ameliorated diabetes-induced renal complications also during the high-sodium diet. However, omapatrilat improved endothelium-dependent relaxation to ACh to a greater extent (85 +/- 5%) than enalapril (68 +/- 6%, P < 0.05). Diclofenac pre-incubation eliminated this difference between omapatrilat and enalapril in ACh-induced vascular relaxation, suggesting that it was mediated, at least in part, via the cyclooxygenase pathway. CONCLUSIONS Despite comparable blood pressure-lowering and renoprotective properties, omapatrilat may be more effective in preventing vascular dysfunction during diabetes compared to enalapril in GK rats.
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Affiliation(s)
- Zhong Jian Cheng
- Institute of Biomedicine, Pharmacology, University of Helsinki, FIN-00014 Helsinki, Finland
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Fitzgerald SM, Kemp-Harper BK, Tare M, Parkington HC. ROLE OF ENDOTHELIUM-DERIVED HYPERPOLARIZING FACTOR IN ENDOTHELIAL DYSFUNCTION DURING DIABETES. Clin Exp Pharmacol Physiol 2005; 32:482-7. [PMID: 15854163 DOI: 10.1111/j.1440-1681.2005.04216.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Under normal conditions, the endothelium plays a major role in the maintenance of vasodilatory tone via the production of endothelium-derived vasodilator agents, such as prostacyclin, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). Inhibition of endothelium-dependent relaxation features prominently in a range of cardiovascular diseases, including hypertension, coronary artery disease and diabetes. 2. Endothelium-derived hyperpolarizing factor is a prominent vasodilator, particularly in smaller arteries and arterioles. There is now emerging evidence to suggest that EDHF may play a role in the endothelial dysfunction in diabetes. 3. Since the first description of endothelium-dependent hyperpolarization some 20 years ago, it has emerged that EDHF is heterogeneous in nature, consisting of diffusible factors and contact-mediated mechanisms. The specific identity of EDHF in any particular vascular bed may influence the impact of diabetes on vascular function. 4. There is accumulating evidence in diabetic rat models and humans showing impaired EDHF activity in small resistance vessels. In contrast, studies in mice suggest that EDHF activity is actually enhanced under diabetic conditions. 5. It is clear that alterations in EDHF activity may have an important contribution in diabetes, more specifically in contributing to microvascular complications observed under diabetic conditions.
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Affiliation(s)
- Sharyn M Fitzgerald
- Department of Physiology, Monash University, Melbourne, Victoria, Australia.
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Li F, Obrosova IG, Abatan O, Tian D, Larkin D, Stuenkel EL, Stevens MJ. Taurine replacement attenuates hyperalgesia and abnormal calcium signaling in sensory neurons of STZ-D rats. Am J Physiol Endocrinol Metab 2005; 288:E29-36. [PMID: 15585600 DOI: 10.1152/ajpendo.00168.2004] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The etiology of painful diabetic neuropathy is poorly understood, but may result from neuronal hyperexcitability secondary to alterations of Ca2+ signaling in sensory neurons. The naturally occurring amino acid taurine functions as an osmolyte, antioxidant, Ca2+ modulator, inhibitory neurotransmitter, and analgesic such that its depletion in diabetes may predispose one to neuronal hyperexcitability and pain. This study reports the effects of taurine replacement on hyperalgesia and sensory neuron Ca2+ homeostasis in streptozotocin-diabetic (STZ-D) rats. Nondiabetic and STZ-D rats were treated with a 2% taurine-supplemented diet for 6-12 wk. Thermal hyperalgesia and mechanical allodynia were determined by measuring hindpaw withdrawal latency to radiant heat and the withdrawal threshold to the von Frey anesthesiometer. Intracellular Ca2+ signaling was explored in neurons from L4-L6 dorsal root ganglia (DRG), using fura 2 fluorescence. Taurine replacement of diabetic rats attenuated deficits of nerve conduction and prevented reductions of mechanical and thermal withdrawal threshold and latency, respectively. In small DRG sensory neurons from diabetic rats, recovery of intracellular Ca2+ concentration ([Ca2+]i) in response to KCl was slowed and 73% corrected by taurine. The amplitudes of caffeine and ATP-induced [Ca2+]i transients were decreased by 47 and 27% (P < 0.05), respectively, in diabetic rat DRG sensory neurons and corrected by 74 and 93% (P < 0.05), respectively, by taurine replacement. These data indicate that taurine is important in the regulation of neuronal Ca2+ signaling and that taurine deficiency may predispose one to nerve hyperexcitability and pain, complicating diabetes.
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Affiliation(s)
- Fei Li
- Department of Internal Medicine, Michigan Diabetes Research and Training Center, University of Michigan, Ann Arbor Veterans Administration Hospitals, Ann Arbor, Michigan, USA
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