Document Detail

Impact of metformin on endothelial ischemia-reperfusion injury in humans in vivo: a prospective randomized open, blinded-endpoint study.
Jump to Full Text
MedLine Citation:
PMID:  24755906     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
INTRODUCTION: Large prospective studies in patients with type 2 diabetes mellitus have demonstrated that metformin treatment improves cardiovascular prognosis, independent of glycemic control. Administration of metformin potently limits infarct size in murine models of myocardial infarction. This study examined, for the first time in humans, whether metformin limits ischemia-reperfusion (IR) injury in vivo using a well-validated forearm model of endothelial IR-injury.
METHODS: Twenty-eight healthy volunteers (age 41±6 years, 10 male/16 female) were randomized between pretreatment with metformin (500 mg three times a day for 3 days) or no treatment in a Prospective Randomized Open Blinded Endpoint study. Brachial artery flow mediated dilation (FMD) was measured before and after 20 minutes of forearm ischemia and 20 minutes of reperfusion. FMD analysis was performed offline by investigators blinded for the treatment arm.
RESULTS: Baseline FMD did not differ between metformin pretreatment and no pretreatment (6.9±3.6% and 6.1±3.5%, respectively, p = 0.27, n = 26). FMD was significantly lower after forearm IR in both treatment arms (4.4±3.3% and 4.3±2.8%, respectively, P<0.001 in both conditions). A linear mixed model analysis revealed that metformin treatment did not prevent the decrease in FMD by IR.
CONCLUSION: A 3 day treatment with metformin in healthy, middle-aged subjects does not protect against endothelial IR-injury, measured with brachial artery FMD after forearm ischemia. Further studies are needed to clarify what mechanism underlies the cardiovascular benefit of metformin treatment.
TRIAL REGISTRATION: ClinicalTrials.gov NCT01610401.
Authors:
Saloua El Messaoudi; Tim H Schreuder; Roel D Kengen; Gerard A Rongen; Petra H van den Broek; Dick H J Thijssen; Niels P Riksen
Related Documents :
851166 - Ultrastructural changes in the ischemic zone bordering experimental infarcts in rat lef...
17213206 - Dramatic accumulation of triglycerides and precipitation of cardiac hemodynamic dysfunc...
1372536 - Loss of microvascular negative charges accompanied by interstitial edema in septic rats...
19484156 - Cell therapy for ischaemic heart disease: focus on the role of resident cardiac stem ce...
10695466 - Effect of atrial radiofrequency ablation designed to cure atrial fibrillation on atrial...
9330016 - Brain morphometric comparison of first-episode schizophrenia and temporal lobe epilepsy.
Publication Detail:
Type:  Journal Article     Date:  2014-04-22
Journal Detail:
Title:  PloS one     Volume:  9     ISSN:  1932-6203     ISO Abbreviation:  PLoS ONE     Publication Date:  2014  
Date Detail:
Created Date:  2014-04-23     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101285081     Medline TA:  PLoS One     Country:  United States    
Other Details:
Languages:  eng     Pagination:  e96062     Citation Subset:  IM    
Export Citation:
APA/MLA Format     Download EndNote     Download BibTex
MeSH Terms
Descriptor/Qualifier:

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

Full Text
Journal Information
Journal ID (nlm-ta): PLoS One
Journal ID (iso-abbrev): PLoS ONE
Journal ID (publisher-id): plos
Journal ID (pmc): plosone
ISSN: 1932-6203
Publisher: Public Library of Science, San Francisco, USA
Article Information
Download PDF
Copyright: 2014 El Messaoudi et al
License:
Received Day: 5 Month: 12 Year: 2013
Accepted Day: 1 Month: 4 Year: 2014
collection publication date: Year: 2014
Electronic publication date: Day: 22 Month: 4 Year: 2014
Volume: 9 Issue: 4
E-location ID: e96062
PubMed Id: 24755906
ID: 3996005
Publisher Id: PONE-D-13-50260
DOI: 10.1371/journal.pone.0096062

Impact of Metformin on Endothelial Ischemia-Reperfusion Injury in Humans In Vivo: A Prospective Randomized Open, Blinded-Endpoint Study Alternate Title:Metformin and Ischemia-Reperfusion Injury
Saloua El Messaoudi12
Tim H. Schreuder3
Roel D. Kengen1
Gerard A. Rongen14
Petra H. van den Broek1
Dick H. J. Thijssen35
Niels P. Riksen14*
Yoshihiro Fukumotoedit1 Role: Editor
1Department of Pharmacology-Toxicology, Radboud University Medical Center, Nijmegen, The Netherlands
2Department of Cardiology, Radboud University Medical Center, Nijmegen, The Netherlands
3Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands
4Department of General Internal Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
5Research Institute for Sports and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
Kurume University School of Medicine, Japan
Correspondence: * E-mail: N.Riksen@aig.umcn.nl
[conflict] Competing Interests: The authors have declared that no competing interests exist.
Contributed by footnote: Conceived and designed the experiments: NPR GAR DHJT. Performed the experiments: SEM THS RDK PHvdB. Analyzed the data: SEM THS RDK DHJT NPR. Contributed reagents/materials/analysis tools: PHvdB. Wrote the paper: SEM THS RDK GAR NPR DHJT PvdB.

Introduction

Despite optimal reperfusion strategies, morbidity and mortality remain significant in patients suffering an acute myocardial infarction. Therefore, much effort is put into developing novel strategies to limit ischemia-reperfusion (IR) injury.[1] Interestingly, large observational and intervention studies have shown that overall cardiovascular mortality is lower in patients with type 2 diabetes mellitus who are treated with metformin, than in patients treated with alternative glucose-lowering drugs, despite similar glycemic control.[2][6] This observation suggests that metformin has direct cardioprotective effects.[7] Indeed, in murine models of myocardial infarction, performed in diabetic as well as in non-diabetic animals, administration of metformin limits myocardial infarct size.[8][11] This cardioprotective effect is mediated by activation of adenosine monophosphate activated protein kinase (AMPK) and adenosine receptor stimulation.[9], [10] Whether metformin treatment also directly protects against IR injury in humans is currently unknown.

Myocardial IR also induces endothelial dysfunction, causing endothelial swelling and impaired endothelium-dependent relaxation, which can further impede proper tissue reperfusion.[12] Several strategies, including ischemic preconditioning and postconditioning have been reported to limit IR-induced endothelial dysfunction in healthy humans [13], [14].

In this study, we investigate for the first time in humans whether metformin limits endothelial IR injury in vivo by measuring flow mediated dilation (FMD) of the brachial artery before and after prolonged ischemia and reperfusion of the forearm. We test the hypothesis that short-term pretreatment with metformin limits endothelial IR injury in humans in vivo.


Methods
Ethics Statement

The protocol is approved by the Institutional Review Board of the Radboud University Medical Centre, and was performed in the Radboud University Medical Centre in compliance with the recommendations of the Declaration of Helsinki. All patients signed for informed consent before participation. The study is registered at www.clinicaltrials.gov (NCT01610401). The authors confirm that all ongoing and related trials for this drug/intervention are registered. The protocol for this trial and supporting CONSORT checklist are available as supporting information; see Checklist S1 and Protocol S1.

Participants

We included 28 healthy, non-smoking adult volunteers in this study. All subjects were free of cardiovascular disease, diabetes mellitus, hypertension (systolic blood pressure ≥140 and/or diastolic ≥90 mm Hg) and hypercholesterolemia (random total cholesterol>6.5 mmol/L). We also excluded professional athletes and those who were taking concomitant medication. Oral contraceptive use by female participants was permitted and these females were asked to continue their contraceptive throughout the study to maintain stable hormone levels. Females not on oral contraceptives were measured at identical times in their menstrual cycle, to exclude any confounding effects of circulating hormones on endothelial function.[15], [16] Two participants withdrew during the study. Therefore, 26 subjects finished the trial protocol (Figure 1).

Experimental Design

In a prospective randomized open blinded end-point (PROBE) study, subjects were allocated to treatment with either metformin 500 mg (Mylan, Bunschoten, The Netherlands) three times a day for 3 days, to ensure a steady state plasma concentration, or no pretreatment (figure 1). Simple random allocation was performed by an independent researcher by dice-throwing for each individual patient (even number: starting with metformin; uneven number: starting with no treatment). The last dose of metformin was given approximately 3 hours before the experiments. Subjects attended our laboratory twice, separated by at least 14 days to prevent any cross-over effect of metformin. Brachial artery endothelial function was measured with flow-mediated dilation (FMD) in the right arm, before and after 20 minutes of forearm ischemia. Forearm ischemia was induced by inflating a pneumatic cuff around the upper arm for 20 minutes and this was followed by 20 minutes of reperfusion. Patient recruitment was performed between May 15th 2012 and October 4th 2012. The first patient was included on May 15th 2012 and the last visit of the last patient was November 20th 2012.

Measurements

All subjects had to abstain from caffeine consumption and strenuous exercise for at least 24 hours before the measurement. Measurements were performed after an overnight fast of at least 6 hours. Before the test, venous blood was taken to assess metformin and caffeine levels. After removing phospholipids and proteins with HybridSPE-phospholipids columns (Supelco), the plasma metformin concentration was determined with LC-MS/MS, using an Accela U-HPLC (Thermo Fischer Scientific) coupled to a TSQ Vantage (Thermo Fisher Scientific) triple quadropole mass spectrometer. The compounds were separated on a Zorbax HILIC Plus (100×2.1 mm, 3.5 µm particle size; Agilent Technologies). As internal standard we used metformin-d6 (Toronto Research Chemicals Inc.) The elution gradient was as follows: 0 min, 100% B; 5 min, 50% B; and 6 min, 100% B. Solvent A consisted of 2 mM NH4format+0.1% formic acid in H2O and Solvent B consisted of 2 mM NH4format+0.1% formic acid in 90% Acetonitril. The column temperature was set at 40°C, and the flow rate was 200 µl/min. The effluent from the U-HPLC was passed directly into the electrospray ion source. Positive electrospray ionization was achieved using a nitrogen sheath gas with ionization voltage at 3500 Volt. The capillary temperature was set at 290°C. Detection of metformin and the internal standard was based on isolation of the protonated molecular ion, [M+H]+ and subsequent MS/MS fragmentations and a selected reaction monitoring (SRM) were carried out. The following SRM transitions were used: for metformin m/z 130,1(parent ion) to m/z 60,1 and 71,1 (both product ions) and for d6-metformin m/z 136,1 (parent ion) to m/z 77,1 (product ion).

Plasma caffeine concentrations were determined by use of reversed phase HPLC with UV detection set at 273 nm, as previously described [17].

Flow Mediated Dilation (FMD)

Endothelium-dependent vasodilation was assessed using FMD according to recent guidelines.[18] Participants rested in the supine position in a temperature-controlled room (22°C) for at least 15 minutes to allow baseline assessment of heart rate and blood flow. The subjects were tested at the same time of day to prevent diurnal variation in FMD responses. Mean arterial pressure was determined using a manual sphygmomanometer placed around the left arm.

To examine brachial artery FMD, the right arm was extended and positioned at an angle of ∼80° abduction from the torso. A rapid inflation and deflation pneumatic cuff (D.E. Hokanson, Bellevue, WA) was placed distal to the olecranon process to provide an ischemic stimulus distal from the brachial artery. A 10-MHz (T3000, Terason, Aloka, UK) multi-frequency linear array probe attached to a high-resolution ultrasound machine was used to perform imaging. The brachial artery was imaged in the distal third of the upper arm. Ultrasound parameters were set to optimize longitudinal B-mode images of the lumen/arterial wall interface. A continuous Doppler velocity assessment was obtained simultaneously, and data were collected using the lowest possible insonation angle (always <60°), which did not vary during each study. [18] After a resting period of at least 15 minutes, 1 minute of baseline recording of the arterial diameter and velocity was performed. Subsequently, the occlusion cuff was inflated to 220 mmHg for 5 minutes. The arterial diameter and velocity recordings were restarted at least 30 seconds before cuff deflation and continued for at least 3 minutes after deflation. Peak arterial diameter and flow, and the time to reach this peak after cuff deflation, were recorded. Subsequently, the rapid inflation/deflation pneumatic cuff was positioned proximally around the upper arm to provide an occlusion for 20 minutes, so that the brachial artery was within the ischemic zone and was exposed to IR. The cuff was inflated for 20 minutes to 220 mmHg, which was followed by 20 minutes of reperfusion. Finally, the FMD measurement was repeated 20 minutes after reperfusion. All measurements were performed by the same, well-experienced sonographer who was blinded for the treatment allocation.

Brachial Artery Diameter and Blood Flow Analysis

Analysis of the brachial artery diameter was performed by an investigator who was blinded for the experimental treatment, using custom-designed edge-detection and wall-tracking software, which is independent of investigator bias.[19] Baseline data were calculated across the 1 minute preceding cuff inflation. Following cuff deflation, peak diameter was automatically detected according to an algorithm as described in detail elsewhere.[20] Within-subject reproducibility of the FMD using this semi-automated software is 6.7–10.5% (coefficient of variation).[21] Post-deflation shear rate data, derived from velocity and diameter measures, was used to calculate the area under the shear rate curve (SRAUC).

Statistical Analysis

All data were analyzed using the Statistical Package for the Social Sciences (SPSS, version 16). Data are presented as mean±SD unless stated otherwise. Baseline parameters between testing days were compared by paired t-tests.

In a previous study from our laboratory, forearm IR reduced FMD with 2.6% with a SD of 3.7%. Assuming a correlation coefficient of 0.7 in our study, given the cross-over design, the expected SD of the effect of IR on FMD in our study therefore equals 2.85. With n = 26 subjects, we will be able to detect a difference of 1.65% with a power of 80% and a type I error probability of 5%, which is a relevant difference.

In order to evaluate the impact of IR on endothelial function (measured as FMD), and whether metformin can (partially) prevent endothelial IR, we employed a linear mixed model analysis and a two-way repeated measures ANOVA. Furthermore, according to a recent study by Atkinson et al., inadequate scaling for FMD would be present if the upper confidence limit of the regression slope of the relationship between logarithmically transformed base diameter and peak diameter is less than one.[22] In such an event, FMD% is not an appropriate measure to estimate endothelial function. We checked our data for this phenomenon, and subsequently performed the allometric modelling solution proposed by Atkinson et al.[22] Subsequently, the FMD-values were re-analysed with a linear mixed model analysis with random factor subject and fixed factors IR (pre versus post), intervention (metformin versus no treatment), but also whether the type of intervention was associated with the different impact of IR on the change in FMD (i.e. interaction IR*intervention). We used a Kolmogorov-Smirnov test to demonstrate a normal distribution of our outcome measures (FMD% and allometrically scaled FMD; P>0.1). The level of statistical significance was set at 0.05.


Results

Baseline characteristics are presented in Table 1. All values were within the normal range.

The metformin plasma concentration immediately before the experiment averaged 1357±588 ng/ml and were all within the therapeutic range (494–3237 ng/ml). Median plasma caffeine concentration was 0.12 (range 0–2.11) mg/dl, with 7 subjects >1 mg/dl. An overview of the FMD measurements is presented in table 2. There were no serious adverse events during the trial. At baseline, we found no differences in brachial artery characteristics (i.e. baseline diameter, time-to-peak diameter, and shear rate area-under-the-curve) between both testing days (Table 2). Baseline FMD% did not differ between metformin pretreatment and no pretreatment (6.9±3.6% and 6.1±3.5%, respectively, p = 0.27).

The IR protocol induced a significant increase in baseline brachial artery diameter and a decrease in shear rate stimulus that was not affected by metformin treatment (Table 2). Both in absence as well as in presence of metformin, brachial artery FMD% was significantly lower after forearm IR (4.4±3.3% and 4.3±2.7% respectively, p<0.01 in both conditions). A two-way repeated measures ANOVA revealed that metformin treatment did not affect the decrease in FMD by IR (Figure 2; p = 0.52). Subsequent linear mixed model analysis, in which we included baseline diameter and SRAUC as covariates to correct for the changes in these parameters after IR, confirmed our primary finding, in that the decrease in FMD% after IR was not altered by 3-days of metformin intake. A limited number of subjects (n = 7) had a caffeine concentration >1 µg/ml. Exclusion of these subjects did not change our conclusion (data not shown).


Discussion

Our current study is the first to investigate whether metformin limits IR-injury in humans in vivo. Using a well-validated model of forearm endothelial IR-injury in healthy middle-aged subjects, we demonstrated that a three day treatment with metformin does not protect against IR-induced endothelial dysfunction.

Our hypothesis that metformin ameliorates IR-injury is based on previous epidemiological studies and clinical trials in patient with diabetes and on preclinical animal studies. First, the United Kingdom Prospective Diabetes Study (UKPDS) reported that patients with type 2 diabetes mellitus who were treated with metformin had a significant lower cardiovascular mortality than patients treated with alternative glucose-lowering drugs, despite similar glycemic control.[2] Secondly, recent experimental studies in mice and rats showed that acute administration of metformin potently reduced myocardial infarct size. In diabetic and nondiabetic mice, administration of a single dose of metformin either before ischemia or at the moment of coronary reperfusion decreased final infarct size.[8][11] This cardioprotective effect appeared to be mediated by activation of AMPK and endothelial Nitric Oxide Synthase (NOS).[9] In addition, Yellon’s group reported that in diabetic and nondiabetic rat hearts, administration of metformin reduced infarct size.[8], [10], [23] In these studies, the cardioprotective effect was dependent on adenosine receptor stimulation and activation of important signalling molecules of the Reperfusion Injury Salvage Kinase (RISK) pathway. Finally, not only acute single-dose administration of metformin confers cardioprotection, but also chronic administration of metformin limits infarct size [23] and beneficially affects postinfarction myocardial remodelling.[11], [24] Based on these studies, we have recently proposed that metformin treatment is an attractive strategy to limit IR injury in patients suffering a myocardial infarction or patients undergoing cardiac surgery [7], [25].

To test our hypothesis, we used a well-validated model of IR-induced endothelial dysfunction in the forearm. Endothelial IR-injury is relevant for two reasons. First, myocardial ischemia and reperfusion not only inflicts direct injury to cardiomyocytes, but the endothelial cells are also highly susceptible to IR-injury.[12] Indeed, structural endothelial injury occurs during ischemia and reperfusion, which induces cell swelling and impairment of endothelial-dependent relaxation, which contributes to the so-called ‘no-reflow’phenomenon and impedes effective coronary reperfusion.[26], [27] Secondly, endothelial dysfunction is an early sign of cardiovascular disease and is associated with future cardiovascular events.[28][31] Importantly, endothelial dysfunction is associated with a worse outcome in several clinical settings.[32][35] Thus, IR injury to coronary endothelium could contribute to the increased risk of recurrent atherothrombosis as observed in patients who present with an acute coronary event.

Several previous studies have reported that twenty minutes of forearm ischemia impairs subsequent flow mediated dilation (FMD) of the brachial artery.[13], [14] Indeed, this finding was confirmed in our current study, in which post-IR FMD was 36% lower than baseline FMD. This observation of a lower FMD, even after correction for the potential influence of changes in diameter and the eliciting shear rate stimulus, is in agreement with the concept that IR causes endothelial dysfunction. Subsequent studies demonstrated that this IR-induced endothelial dysfunction can be prevented by ischemic preconditioning, postconditioning, and remote conditioning.[13], [14], [36], [37] Also, statins significantly reduced endothelial IR-injury in this model [38].

In contrast to the preclinical studies, we did not observe any protective effect of metformin against endothelial IR-injury in our study. There are several potential explanations for this discrepancy. First, murine models of IR-injury might not reflect the human situation. In this regard, many interventions that are promising in animal models do not appear to be effective in clinical trials.[39] In the field of ischemic stroke, only two of approximately 500 neuroprotective strategies that were beneficial in animal models, improved outcome in patients.[39] This translational failure can be due to differences between animal and human (patho)physiology, due to methodological flaws in animal studies, or due to shortcomings of the clinical trial. In the case of metformin-induced cardioprotection, the evidence is rather strong, with cardioprotection shown in mice and rats, with or without diabetes, and with acute as well as chronic administration. The design of our current study is also robust and uses a well-validated model of endothelial IR-injury. Although the study was not blinded, we used a PROBE design, which is a well-accepted design for this kind of studies.

A second explanation could relate to the duration and dose of metformin pretreatment. Interestingly, in several patient groups, including patients with type 1 diabetes and patients with polycystic ovarian syndrome, long-term administration of metformin improves endothelial function, measured with FMD.[40], [41] In our study, however, a three day treatment with metformin did not improve baseline FMD. Animal studies on the cardioprotective effect of metformin, however, have demonstrated that either an acute single dose administration of metformin[9], [10] as well as chronic administration of metformin confer cardioprotection.[23] The dose of metformin used in these preclinical studies was comparable to or even considerably lower than the dose used to treat patients with diabetes in clinical practice.[9], [10] Based on these studies, we used a dose of 3dd500 mg, which is a dose often used to treat patients in clinical practice. Subjects were pretreated for three days to ensure an effective steady-state plasma concentration and to enable translation of our results to daily clinical practice. The last dose of metformin was taken 3 hours prior to the ischemic episode, which allows for a maximum plasma concentration of metformin at the moment of forearm ischemia. Indeed, the circulating plasma concentration of metformin immediately before the experiment was comparable to the previous animal studies. In our study,

A third potential explanation for the discrepancy between our results and results from previous animal studies is that the mechanism of endothelial IR-injury might differ from IR-injury in cardiomyocytes. However, most strategies that limit myocardial infarct size in animal models also conferred protection against endothelial IR-injury, although some studies could not observe protection [13], [34], [36], [37].

Fourthly, the findings in the brachial artery may not be representative for the coronary circulation. However, previous studies have reported a good correlation between endothelial responses to flow and vasoactive substances between the brachial and coronary arteries [42], [43].

In conclusion, we can state that short-term metformin pretreatment does not protect against endothelial dysfunction induced by ischemia-reperfusion in healthy middle aged subject. However, whether these results predict the effect of metformin on myocardial IR-injury and can be extrapolated to subjects with a history of cardiovascular disease or diabetes mellitus is a matter of debate. It is important to realize that many comorbidities, including diabetes mellitus, and comedications can affect the tolerance against ischemia-reperfusion and the efficacy of cardioprotective strategies. Therefore, with interest we await further studies on the effect of metformin on myocardial injury in patients with a myocardial infarction and patients undergoing coronary artery bypass grafting (NCT01217307 and NCT01438723 respectively).

Clinical Perspectives

In patients with diabetes, treatment with metformin is associated with an improved cardiovascular outcome. In contrast to previous studies in animals, we observed no protective effect of a short term treatment with metformin on forearm IR-induced endothelial dysfunction in healthy individuals. Further studies are needed to clarify what mechanism underlies the cardiovascular benefit of metformin treatment.


Supporting Information Checklist S1

CONSORT Checklist.

(DOCX)


Click here for additional data file (pone.0096062.s001.docx)

Protocol S1

Trial Protocol.

(PDF)



The authors would like to thank Ab Bilos for the determination of the plasma concentration of metformin and caffeine.


References
1. Hausenloy DJ,, Yellon DM, (Year: 2013) Myocardial ischemia-reperfusion injury: a neglected therapeutic target. J Clin Invest123: 92–10023281415
2. The United Kingdom Prospective Diabetes Study (UKPDS) Group (Year: 1998) Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). UK Prospective Diabetes Study (UKPDS) Group. Lancet352: 854–8659742977
3. Roussel R,, Travert F,, Pasquet B,, Wilson PW,, Smith SC Jr,, et al. (Year: 2010) Metformin use and mortality among patients with diabetes and atherothrombosis. Arch Intern Med170: 1892–189921098347
4. Jorgensen CH,, Gislason GH,, Andersson C,, Ahlehoff O,, Charlot M,, et al. (Year: 2010) Effects of oral glucose-lowering drugs on long term outcomes in patients with diabetes mellitus following myocardial infarction not treated with emergent percutaneous coronary intervention–a retrospective nationwide cohort study. Cardiovasc Diabetol9: 5420843380
5. Selvin E,, Bolen S,, Yeh HC,, Wiley C,, Wilson LM,, et al. (Year: 2008) Cardiovascular outcomes in trials of oral diabetes medications: a systematic review. Arch Intern Med168: 2070–208018955635
6. Saenz A, Fernandez-Esteban I, Mataix A, Ausejo M, Roque M, et al. . (2005) Metformin monotherapy for type 2 diabetes mellitus. Cochrane Database Syst Rev: CD002966.
7. El Messaoudi S,, Rongen GA,, de Boer RA,, Riksen NP, (Year: 2011) The cardioprotective effects of metformin. Curr Opin Lipidol22: 445–45321897229
8. Bhamra GS,, Hausenloy DJ,, Davidson SM,, Carr RD,, Paiva M,, et al. (Year: 2008) Metformin protects the ischemic heart by the Akt-mediated inhibition of mitochondrial permeability transition pore opening. Basic Res Cardiol103: 274–28418080084
9. Calvert JW,, Gundewar S,, Jha S,, Greer JJ,, Bestermann WH,, et al. (Year: 2008) Acute metformin therapy confers cardioprotection against myocardial infarction via AMPK-eNOS-mediated signaling. Diabetes57: 696–70518083782
10. Paiva M,, Riksen NP,, Davidson SM,, Hausenloy DJ,, Monteiro P,, et al. (Year: 2009) Metformin prevents myocardial reperfusion injury by activating the adenosine receptor. J Cardiovasc Pharmacol53: 373–37819295441
11. Gundewar S,, Calvert JW,, Jha S,, Toedt-Pingel I,, Ji SY,, et al. (Year: 2009) Activation of AMP-activated protein kinase by metformin improves left ventricular function and survival in heart failure. Circ Res104: 403–41119096023
12. Laude K,, Beauchamp P,, Thuillez C,, Richard V, (Year: 2002) Endothelial protective effects of preconditioning. Cardiovasc Res55: 466–47312160943
13. Loukogeorgakis SP,, Panagiotidou AT,, Yellon DM,, Deanfield JE,, MacAllister RJ, (Year: 2006) Postconditioning protects against endothelial ischemia-reperfusion injury in the human forearm. Circulation113: 1015–101916476844
14. van den Munckhof I,, Riksen N,, Seeger JP,, Schreuder TH,, Borm GF,, et al. (Year: 2013) Aging attenuates the protective effect of ischemic preconditioning against endothelial ischemia-reperfusion injury in humans. Am J Physiol Heart Circ Physiol304: H1727–173223604707
15. Hashimoto M,, Akishita M,, Eto M,, Ishikawa M,, Kozaki K,, et al. (Year: 1995) Modulation of endothelium-dependent flow-mediated dilatation of the brachial artery by sex and menstrual cycle. Circulation92: 3431–34358521564
16. Williams MR,, Westerman RA,, Kingwell BA,, Paige J,, Blombery PA,, et al. (Year: 2001) Variations in endothelial function and arterial compliance during the menstrual cycle. J Clin Endocrinol Metab86: 5389–539511701712
17. Schreiber-Deturmeny E,, Bruguerolle B, (Year: 1996) Simultaneous high-performance liquid chromatographic determination of caffeine and theophylline for routine drug monitoring in human plasma. J Chromatogr B Biomed Appl677: 305–3128704934
18. Thijssen DH,, Black MA,, Pyke KE,, Padilla J,, Atkinson G,, et al. (Year: 2011) Assessment of flow-mediated dilation in humans: a methodological and physiological guideline. Am J Physiol Heart Circ Physiol300: H2–1220952670
19. Woodman RJ,, Playford DA,, Watts GF,, Cheetham C,, Reed C,, et al. (Year: 2001) Improved analysis of brachial artery ultrasound using a novel edge-detection software system. J Appl Physiol91: 929–93711457812
20. Black MA,, Cable NT,, Thijssen DH,, Green DJ, (Year: 2009) Impact of age, sex, and exercise on brachial artery flow-mediated dilatation. American journal of physiology Heart and circulatory physiology297: H1109–111619633208
21. Thijssen DH,, Dawson EA,, Tinken TM,, Cable NT,, Green DJ, (Year: 2009) Retrograde flow and shear rate acutely impair endothelial function in humans. Hypertension53: 986–99219380611
22. Atkinson G,, Batterham AM,, Thijssen DH,, Green DJ, (Year: 2013) A new approach to improve the specificity of flow-mediated dilation for indicating endothelial function in cardiovascular research. J Hypertens31: 287–29123169234
23. Whittington HJ,, Hall AR,, McLaughlin CP,, Hausenloy DJ,, Yellon DM,, et al. (Year: 2013) Chronic metformin associated cardioprotection against infarction: not just a glucose lowering phenomenon. Cardiovasc Drugs Ther27: 5–1623192487
24. Yin M,, van der Horst IC,, van Melle JP,, Qian C,, van Gilst WH,, et al. (Year: 2011) Metformin improves cardiac function in a nondiabetic rat model of post-MI heart failure. Am J Physiol Heart Circ Physiol301: H459–46821572014
25. El Messaoudi S,, Rongen GA,, Riksen NP, (Year: 2013) Metformin therapy in diabetes: the role of cardioprotection. Curr Atheroscler Rep15: 31423423523
26. Kaeffer N,, Richard V,, Francois A,, Lallemand F,, Henry JP,, et al. (Year: 1996) Preconditioning prevents chronic reperfusion-induced coronary endothelial dysfunction in rats. Am J Physiol271: H842–8498853316
27. VanBenthuysen KM,, McMurtry IF,, Horwitz LD, (Year: 1987) Reperfusion after acute coronary occlusion in dogs impairs endothelium-dependent relaxation to acetylcholine and augments contractile reactivity in vitro. J Clin Invest79: 265–2743793926
28. Kharbanda RK,, Peters M,, Walton B,, Kattenhorn M,, Mullen M,, et al. (Year: 2001) Ischemic preconditioning prevents endothelial injury and systemic neutrophil activation during ischemia-reperfusion in humans in vivo. Circulation103: 1624–163011273988
29. Inaba Y,, Chen JA,, Bergmann SR, (Year: 2010) Prediction of future cardiovascular outcomes by flow-mediated vasodilatation of brachial artery: a meta-analysis. Int J Cardiovasc Imaging26: 631–64020339920
30. Yeboah J,, Folsom AR,, Burke GL,, Johnson C,, Polak JF,, et al. (Year: 2009) Predictive value of brachial flow-mediated dilation for incident cardiovascular events in a population-based study: the multi-ethnic study of atherosclerosis. Circulation120: 502–50919635967
31. Kitta Y,, Obata JE,, Nakamura T,, Hirano M,, Kodama Y,, et al. (Year: 2009) Persistent impairment of endothelial vasomotor function has a negative impact on outcome in patients with coronary artery disease. J Am Coll Cardiol53: 323–33019161880
32. Devan AE,, Umpierre D,, Harrison ML,, Lin HF,, Tarumi T,, et al. (Year: 2011) Endothelial ischemia-reperfusion injury in humans: association with age and habitual exercise. Am J Physiol Heart Circ Physiol300: H813–81921239631
33. Charakida M,, Masi S,, Luscher TF,, Kastelein JJ,, Deanfield JE, (Year: 2010) Assessment of atherosclerosis: the role of flow-mediated dilatation. Eur Heart J31: 2854–286120864485
34. Wouters CW,, Wever KE,, Bronckers I,, Hopman MT,, Smits P,, et al. (Year: 2012) Short-term statin treatment does not prevent ischemia and reperfusion-induced endothelial dysfunction in humans. J Cardiovasc Pharmacol59: 22–2821885990
35. Kilian JG,, Nakhla S,, Griffith K,, Harmer J,, Skilton M,, et al. (Year: 2005) Reperfusion injury in the human forearm is mild and not attenuated by short-term ischaemic preconditioning. Clin Exp Pharmacol Physiol32: 86–9015730440
36. Luca MC,, Liuni A,, McLaughlin K,, Gori T,, Parker JD, (Year: 2013) Daily ischemic preconditioning provides sustained protection from ischemia-reperfusion induced endothelial dysfunction: a human study. J Am Heart Assoc2: e00007523525419
37. Bailey TG,, Birk GK,, Cable NT,, Atkinson G,, Green DJ,, et al. (Year: 2012) Remote ischemic preconditioning prevents reduction in brachial artery flow-mediated dilation after strenuous exercise. Am J Physiol Heart Circ Physiol303: H533–53822730390
38. Liuni A,, Luca MC,, Gori T,, Parker JD, (Year: 2010) Rosuvastatin prevents conduit artery endothelial dysfunction induced by ischemia and reperfusion by a cyclooxygenase-2-dependent mechanism. J Am Coll Cardiol55: 1002–100620202516
39. van der Worp HB,, Howells DW,, Sena ES,, Porritt MJ,, Rewell S,, et al. (Year: 2010) Can animal models of disease reliably inform human studies?PLoS Med7: e100024520361020
40. Pitocco D,, Zaccardi F,, Tarzia P,, Milo M,, Scavone G,, et al. (Year: 2013) Metformin improves endothelial function in type 1 diabetic subjects: a pilot, placebo-controlled randomized study. Diabetes Obes Metab15: 427–43123167274
41. Jensterle M,, Sebestjen M,, Janez A,, Prezelj J,, Kocjan T,, et al. (Year: 2008) Improvement of endothelial function with metformin and rosiglitazone treatment in women with polycystic ovary syndrome. Eur J Endocrinol159: 399–40618653546
42. Takase B, Uehata A, Akima T, Nagai T, Nishioka T, et al. . (1998) Endothelium-dependent flow-mediated vasodilation in coronary and brachial arteries in suspected coronary artery disease. Am J Cardiol 82: 1535–1539, A1537–1538.
43. Takase B,, Hamabe A,, Satomura K,, Akima T,, Uehata A,, et al. (Year: 2005) Close relationship between the vasodilator response to acetylcholine in the brachial and coronary artery in suspected coronary artery disease. Int J Cardiol105: 58–6616207546

Figures

[Figure ID: pone-0096062-g001]
doi: 10.1371/journal.pone.0096062.g001.
Figure 1  Consort 2012 flow diagram of the study.

[Figure ID: pone-0096062-g002]
doi: 10.1371/journal.pone.0096062.g002.
Figure 2  Brachial artery flow mediated dilation (presented as percentage change from baseline ±SE) before (black) and after (white) 20-minutes for forearm ischemia and 20-minutes reperfusion preceded by pretreatment with metformin or no pretreatment.

Tables
[TableWrap ID: pone-0096062-t001] doi: 10.1371/journal.pone.0096062.t001.
Table 1  Baseline characteristics.
Variable Value
Age (yrs) 41.3±6.4
Body weight (kg) 74±13
Heigth (cm) 174±8
BMI (kg/m2) 24.2±2.9
Systolic blood pressure (mmHg) 120±9
Diastolic blood pressure (mmHg) 75±6
Creatinine (µmol/L) 73±13
MDRD-GFR (mL/min/1.73 m2) 85±7
Glucose (mmol/L)Cholesterol (mmol/L) 4.5±0.34.7±0.8

BMI; body mass index, MDRD; modification of diet in renal disease, GFR; glomerular filtration rate.


[TableWrap ID: pone-0096062-t002] doi: 10.1371/journal.pone.0096062.t002.
Table 2  Brachial artery characteristics before and after ischemia-reperfusion (IR) when preceded by metformin pretreatment or no pretreatment (n = 26).
No pretreatment Metformin P-values
Baseline IR Baseline IR IR Metformin IR*Metformin
FMD (%) 6.1±3.5 4.3±2.7 6.9±3.6 4.4±3.3 <0.001 0.52 0.23
FMD (mm) 0.19±0.09 0.15±0.09 0.22±0.08 0.15±0.11 <0.001 0.60 0.09
Diameter (mm) 3.5±0.9 3.8±0.9 3.5±0.8 3.7±0.9 <0.001 0.52 0.15
Time-to-peak diameter (s) 49±16 54±25 54±17 48±23 0.94 0.92 0.17
SRAUC (s, 103) 30.2±11.3 21.8±11.7 28.4±11.2 21.1±9.5 <0.001 0.51 0.86

Data is presented as mean±SD.

FMD: flow mediated dilation; FMD (%) percent change to baseline; FMD (mm) absolute change to baseline; IR: ischemia-reperfusion; SRAUC: shear rate area under the curve.



Article Categories:
  • Research Article
Article Categories:
  • Biology and Life Sciences
    • Anatomy
      • Cardiovascular Anatomy
    • Physiology
      • Cardiovascular Physiology
        • Blood Circulation
Article Categories:
  • Medicine and Health Sciences
    • Cardiology
      • Cardiovascular Pharmacology
    • Clinical Medicine
      • Clinical Trials
    • Hematology
      • Hemodynamics
    • Pharmacology
      • Clinical Pharmacology
    • Vascular Medicine
      • Vascular Diseases
        • Peripheral Vascular Disease
      • Atherosclerosis
Article Categories:
  • Research and Analysis Methods
    • Research Design
      • Clinical Research Design


Previous Document:  Comparison of Five Major Trichome Regulatory Genes in Brassica villosa with Orthologues within the B...
Next Document:  Transcriptomic and Functional Analysis of NaCl-Induced Stress in Enterococcus faecalis.