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Diabetes Care 30:2922-2927, 2007
DOI: 10.2337/dc07-1110
© 2007 by the American Diabetes Association
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Pathophysiology/Complications |
Dehydroepiandrosterone Administration Counteracts Oxidative Imbalance and Advanced Glycation End Product Formation in Type 2 Diabetic Patients
1 Oncological Endocrinology Unit, San Giovanni Battista Hospital, Turin, Italy
2 Department of Internal Medicine, University of Turin, Turin, Italy
3 Department of Experimental Medicine and Oncology, University of Turin, Turin, Italy
4 Department of Clinical Pathophysiology, University of Turin, Turin, Italy
Address correspondence and reprint requests to Prof. Giuseppe Boccuzzi, Dipartimento di Fisiopatologia Clinica, Via Genova, 3-10126 Torino, Italy. E-mail: giuseppe.boccuzzi{at}unito.it
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
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OBJECTIVE—Dehydroepiandrosterone (DHEA) has been shown to prevent oxidative stress in several in vivo and in vitro models. This study aimed to evaluate the effects of DHEA administration on oxidative stress, pentosidine concentration, and tumor necrosis factor (TNF)-
/TNF- receptor system activity in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS—Twenty patients were enrolled in the study and randomly assigned to the DHEA (n = 10) or placebo (n = 10) group. Twenty healthy sex- and age-matched subjects with normal glucose levels served as control subjects. DHEA was given as a single daily dose of 50 mg for 12 weeks.
RESULTS—Oxidative stress parameters were significantly higher in diabetic patients versus control subjects. Pentosidine levels, as well as soluble TNF receptor (sTNF-R)I and sTNF-RII, were also higher in diabetic patients. After DHEA, plasma levels of reactive oxygen species and hydroxynonenal dropped by 53 and 47%, respectively, whereas the nonenzymatic antioxidants glutathione and vitamin E increased (+38 and +76%, respectively). The same changes in oxidative parameters were detected in peripheral blood mononuclear cells (PBMCs). DHEA treatment also induced a marked decrease of pentosidine plasma concentration in diabetic patients (–50%). Moreover, the TNF-/TNF- receptor system was shown to be less activated after DHEA treatment, in both plasma and PBMCs.
CONCLUSIONS—Data indicate that DHEA treatment ameliorates the oxidative imbalance induced by hyperglycemia, downregulates the TNF-/TNF- receptor system, and prevents advanced glycation end product formation, suggesting a beneficial effect on the onset and/or progression of chronic complications in type 2 diabetic patients.
Abbreviations: AGE, advanced glycation end product • DHEA, dehydroepiandrosterone • DHEAS, DHEA sulfate • GSH, glutathione • HNE, hydroxynonenal • HOMA, homeostasis model assessment • PBMC, peripheral blood mononuclear cell • ROS, reactive oxygen species • sTNF-R, soluble tumor necrosis factor receptor • TNF, tumor necrosis factor
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
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The onset and progression of diabetes complications involves a complex interplay between ranges of pathogenic mechanisms. However, emerging evidence suggests that a single early phenomenon, i.e., the overproduction of superoxide by the respiratory chain, plays a key role in the pathogenesis of both microvascular and macrovascular chronic complications (1–3).
The production of advanced glycation end products (AGEs) is among the main mechanisms recruited by oxidative stress and is involved in the pathogenesis of tissue injury (3,4). AGEs progressively accumulate with time at the sites of diabetic microvascular disease and mediate tissue damage by activation of specific receptors at distant sites, via circulation (3,5). Moreover, the AGE/AGE receptor interaction, along with hyperglycemia-induced oxidative stress, possibly serves as a key activator of upstream kinases, leading to increased production of inflammatory cytokines thought to be involved in the progression of chronic diabetes complications (6).
Interruption of free radical overproduction by antioxidants counteracts AGE formation (2). Nevertheless, despite convincing experimental results, clinical trials with traditional antioxidants have been disappointing (7)—the activity of the antioxidants used in those trials is limited to scavenging already-formed oxidants and is stoichiometric. A compound of physiological origin that possesses multi-targeted antioxidant properties is dehydroepiandrosterone (DHEA), a multifunctional steroid that has been shown to prevent tissue damage induced by hyperglycemia in several in vivo and in vitro models (8,9). It also prevents the upregulation of AGE receptors observed in the hippocampus of streptozotocin-induced diabetic rats (10).
This study aimed to examine the effects of DHEA administration on oxidative stress, pentosidine (a marker of AGE-biogenesis) concentration, and tumor necrosis factor (TNF)-/TNF- receptors in patients with recently diagnosed type 2 diabetes, controlled with diet alone, and without any evidence of chronic complications, i.e., with the disease at a very early stage.
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RESEARCH DESIGN AND METHODS— |
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TOPABSTRACTINTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
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The study was approved by the ethics committee at our institution, and written informed consent was obtained from all recruited subjects. It was a randomized, double-blind, placebo-controlled, small-scale study of 12-week duration.
The study group comprised 20 patients with recently diagnosed type 2 diabetes treated with diet alone, having good glycemic control, and taking no drugs potentially interfering with redox status. All patients were nonsmokers and showed no evidence of chronic diabetes complications. The control group comprised 20 healthy subjects, matched by sex and age, with normal glucose levels.
After consent, patients were randomly assigned to the DHEA (n = 10) or the placebo (n = 10) group. DHEA was purchased from DHEAPharma (Miami, FL) and given as a single daily oral dose of 50 mg at 0800 h for 12 weeks. The 10 patients enrolled in the placebo group received pills that were identical in appearance to the DHEA formulation. Compliance was checked by pill counts. At baseline and at the end of the treatment, all patients were subjected to complete physical examination and fasting blood samples collected to evaluate oxidative stress parameters, pentosidine levels, and TNF-/TNF receptors.
Serum DHEA, DHEA sulfate, glucose, serum insulin, homeostasis model assessment, and A1C
Serum DHEA and DHEA sulfate (DHEAS) were determined by specific radioimmunoassay (Diagnostic System Laboratories, Oxford, U.K.). Fasting serum glucose was measured by the glucose oxidase method (HITACHI 911 Analyzer; Sentinel Ch., Milan, Italy), and fasting serum insulin by immunoradiometric assay (Radim S.p.A., Pomezia, Italy). A1C was determined by standardized affinity high-performance liquid chromatography (BioRad). The homeostasis model assessment (HOMA) of insulin resistance index was calculated as the product of basal glucose and insulin levels divided by 22.5 (11).
Cytosol extracts from PBMCs
To isolate peripheral blood mononuclear cells (PBMCs), heparin-anticoagulated blood was subjected to density-gradient centrifugation on Lymphoprep (Fresenius Kabi Norge, Oslo, Norway). The cytosolic extracts were prepared as reported elsewhere (12). PBMCs were resuspended in buffer containing 20 mmol/l HEPES, pH 7.9, 1 mmol/l MgCl2, 0.5 mmol/l EDTA, 1% NP-40, 1 mmol/l EGTA, 1 mmol/l DTT, 0.5 mmol/l PMSF, 5 µg/ml aprotinin, and 2.5 µg/ml leupeptin, then centrifuged at 1,000g for 5 min at 4°C. Supernatants were centrifuged at 105,000g at 4°C for 40 min to obtain cytosolic fraction, and protein content was determined.
Pentosidine
Plasma samples (200 µl) were treated with 6 mol/l hydrochloric acid for 2 h at 40°C and centrifuged (4,000 rpm), and 20 µl supernatant was injected.
A Thermo-Finnigan Surveyor instrument (Thermo Electron, Rodano, Italy), equipped with autosampler and PDA-UV 6,000 LP detector, was used. Mass spectrometry analyses were performed using a LCQ Deca XP Plus spectrometer, with electrospray interface and ion trap as mass analyzer.
The chromatographic separations were run on a Varian Polaris C18-A column (150 x 2 mm, particle size 3 µm) (Varian, Leinì, Italy), with a flow rate of 200 µl/min. Gradient mobile phase composition was adopted: 95/5 to 0/100 vol/vol 5 mmol/l heptafluorobutanoic acid in water/methanol for 13 min.
The liquid chromatography column effluent was delivered to a UV detector (200–400 nm) and then to the ion source using nitrogen as sheath and auxiliary gas (Claind Nitrogen Generator apparatus; Claind, Lenno, Italy). The tuning parameters adopted for the electrospray ionization source were as follows: source current 80.00 µA, capillary voltage 3.00 V, and tube lens offset 15 V; and for ions optics, multipole one offset –5.25 V, intermultipole lens voltage –16.00 V, and multipole two offset –9.00 V. Mass spectra were collected in tandem mass spectrometry (MS) mode: MS2 of (+) 379 m/z with 33% capillary electrophoresis in the range 100–400 m/z.
Oxidative biochemical parameters
Reduced glutathione (GSH), hydroxynonenal (HNE), and reactive oxygen species (ROS) levels were evaluated as reported elsewhere (12). For GSH levels, a mixture was directly prepared in a cuvette: 2.25 ml of 0.1 mol/l K-phosphate buffer, pH 8.0; 0.2 ml of the sample (plasma or PBMCs cytosol fractions); and 25 µl of Ellman’s reagent (10 mmol/l dithionitrobenzoic acid in methanol). After 1 min, the assay absorbance was measured at 412 nm and the GSH concentration calculated by comparison with a standard curve.
HNE was determined on plasma or PBMC cytosol fractions. An aliquot of cytosol (0.5 ml) was added to an equal volume of acetonitrile:acetic acid (96:4 vol:vol). After centrifugation, the supernatant was injected into a high-performance liquid chromatography (HPLC; Waters Associated, Milford, MA) Symmetry C18 column (5 mm, 3.9 x 150 mm). The mobile phase was acetonitrile:bidistilled water (42% vol:vol). The HNE concentration was calculated by comparison with a standard solution of HNE of known concentration.
ROS was measured in plasma or PBMC cytosol fractions using probe 2',7'-dichlorofluorescin diacetate (DCFH-DA). DCFH-DA is a stable, nonfluorescent molecule that readily crosses the cell membrane and is hydrolyzed by intracellular esterases to the nonfluorescent 2',7'-dichlorofluorescin (DCFH), which is rapidly oxidized, in the presence of peroxides, to highly fluorescent 2',7'-dichlorofluorescein (DCF); DCF is measured fluorimetrically.
-Tocopherol (vitamin E) was assayed using the method described by Burton et al. (13)—after extraction of 0.5 ml plasma with 1 ml n-heptane and centrifugation, the heptane phase was collected for HPLC analysis. A Supercosil-LC-Si column (25 cm x 4.6 mm; Supelco, Bellefonte, PA) was used, the mobile phase being n-hexane-isopropanol (99:1, vol:vol) and the flow rate 2.0 ml/min; the fluorescence detector was set to 298 nm excitation and 325 nm emission.
TNF- and TNF receptors I and II
Serum levels
Serum levels of TNF-, its soluble receptors TNF-RI (sTNF-RI) and TNF-RII (sTNF-RII) were measured using enzyme-linked immonosorbent assay tests (for TNF-: Immunotech, Marseille, France; for sTNF-RI and sTNF-RII: Quantikine HS, R&D Systems, Minneapolis, MN) following the manufacturers’ instructions.
Real-time RT-PCR
Total RNA was extracted from PBMCs using TRIzol Reagent (Invitrogen, Groningen, the Netherlands), as reported elsewhere (12). DNase was added to remove remaining genomic DNA. RNA was reverse transcribed using the iScript cDNA Synthesis Kit (BioRad Laboratories).
Primers were designed using the Beacon 5 program. Primers used were as follows: for TNF-, forward 5'-CGC CAC CAC GCT CTT CTG C, reverse 5'-GGG CTA CAG GCT TGT CAC TCG; for TNF-RI, forward 5'-CTG CCA GGA GAA ACA GAA CAC C, reverse 5'-GCG TCC TCA GTG CCC TTA ACA TTC; for TNF-RII: forward 5'-CGG TGT GGG CTG TGT CGT AG, reverse 5'- GAG GCT GCG GCT GTG GAG; and for β-actin, forward 5'-GCG AGA AGA TGA CCC AGA TC, reverse 5'-GGA TAG CAC AGC CTG GAT AG.
Real-time PCR was performed using a BioRad iQ iCycler Detection System with SYBR green fluorophore. Reactions were run in a total volume of 25 µl including 12.5 µl IQ SYBR Green Supermix (BioRad Laboratories), 1 µl of each primer at 10 µmol/l concentration, and 5 µl of the reverse-transcribed cDNA template. The protocol is as follows: denaturation (95°C for 5 min) and amplification repeated 40 times (95°C for 15 s, 60°C for 1 min). A melt curve analysis was performed to ensure a single amplified product for every reaction. All reactions were carried out in at least triplicate. Analysis of relative gene expression was performed using Gene Expression Macro software (BioRad Laboratories).
Statistical analysis
Results are presented as means ± SE. Differences between means were analyzed for significance using the Student’s t test. A P value <0.05 was considered significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
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Oxidative stress was significantly higher in diabetic patients than control subjects, as demonstrated by higher levels of ROS and HNE and reduced levels of GSH and vitamin E (Table 1). Pentosidine levels, as well as sTNF-RI and sTNF-RII, were also higher in diabetic patients than in control subjects, whereas serum TNF-
levels were within the normal range (Table 1).
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Effects of DHEA on BMI and glycemic control
DHEA treatment had no effect on patients’ BMI. Basal glucose concentration, A1C level, and HOMA index were also unaffected (Table 2).
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Effects of DHEA on oxidative state
After DHEA treatment, DHEA and DHEAS levels were significantly increased (P < 0.05, Table 3). Oxidative stress parameters were significantly modified by DHEA treatment, both in plasma and in PBMCs. Plasma levels of ROS dropped by 53% (Table 3 and Fig. 1A). Likewise, a 47% reduction of plasma HNE was observed after DHEA treatment (Table 3 and Fig. 1A), whereas plasma levels of the nonenzymatic antioxidants GSH and vitamin E increased by 38 and 76%, respectively (Table 3 and Fig. 1A). The same trends were found in PBMCs (Table 3 and Fig. 1B). No correlation was found between DHEA or DHEAS levels and both oxidative and antioxidant parameters either before or after DHEA treatment.
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Effects of DHEA on pentosidine levels
DHEA treatment markedly decreased pentosidine plasma concentration in diabetic patients (–50%; Table 3 and Fig. 1A).
Effects of DHEA on TNF- and TNF- receptors
After DHEA treatment, no modification of serum TNF- and sTNF-RI was observed (Table 3), whereas in PBMCs mRNA expression was reduced by 33 and 29%, respectively (Fig. 1C). On the contrary, serum sTNF-RII levels were reduced after DHEA treatment (Table 3), without any modification in mRNA expression (Fig. 1C).
All the above parameters were unchanged in diabetic patients given placebo (data not shown).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
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Type 2 diabetic patients with good glycemic control and no evidence of chronic diabetes complications, such as those enrolled in this study, show a redox imbalance characterized by increased production of highly reactive oxygen species and lower-than-normal antioxidant potential. We show here that DHEA treatment counteracts this oxidative imbalance—after 12 weeks, the concentrations of ROS and HNE were greatly reduced in both plasma and cytosol of PBMCs, whereas levels of the nonenzymatic antioxidants GSH and vitamin E were increased. These results are in agreement with the multi-targeted antioxidant effect of DHEA previously reported by our group (9,10,12). We could not find any correlation between serum DHEA or DHEAS levels and both the oxidative and the antioxidant parameters either before or after DHEA treatment. This result is not surprising, since DHEA is not a scavenger compound acting in a stoichiometric manner and exerts its antioxidants effects in a complex and non–completely defined way (10,12).
Moreover, DHEA treatment significantly reduced the plasma concentration of pentosidine in these patients, in line with its effects on AGEs and AGE receptors, which have been reported in experimental diabetes (12). AGEs, whose production is triggered by oxidative stress, are clearly implicated in the development and progression of chronic diabetes complications (3,4). Among AGEs, pentosidine is a well-characterized compound and is used as a marker of AGE biogenesis (14); it is considered a good predictor for the development of microvascular complications in diabetic patients (15). Interestingly, DHEA reduces pentosidine concentration in type 2 diabetic patients without any influence on glycemic control, strongly suggesting that this effect can involve its ability to improve redox balance.
Hyperglycemia-induced oxidative stress may, either directly or through the AGE/AGE receptor interaction, serve as a key activator of upstream kinases, leading to an increase in the plasma inflammatory cytokine concentrations that is thought to be involved in the progression of chronic diabetes complications (6), as well as in the development of insulin resistance (16).
Compared with control subjects, diabetic patients showed higher levels of sTNF-RI and sTNF-RII, whereas TNF- plasma concentrations were similar. After binding of TNF- to its receptors, cleavage of the extracellular parts elicits the soluble forms, known as sTNF-RI and sTNF-RII, which are thought to reflect the degree of TNF system activation (17). TNF- is not a very stable protein, and its serum level may not adequately reflect its activity. On the contrary, serum concentration of soluble TNF- receptors have been shown to be increased in diabetic patients (18) and the level of sTNF-RII has been considered the best predictor of TNF- system activation, as well as a marker of insulin resistance (19). DHEA treatment reduced the serum concentration of sTNF-RII and mRNA expression of TNF- and TNF-RI in PBMCs. A reduction in mRNA expression of TNF- indicates a downregulation of this system, which is reflected by a concomitant reduction in TNF-RI expression. As far as TNF-RII is concerned, our observation of a reduction in its serum levels without any change in its mRNA expression implies reduced shedding of the protein, suggesting improved insulin sensitivity after DHEA treatment. A relationship between TNF- system and insulin resistance has indeed been reported (20), as has a negative correlation between TNF-RII shedding and insulin sensitivity (21). Moreover, ROS, which are markedly reduced by DHEA treatment, have recently been reported to play a causal role in insulin resistance (16). In accordance with previous observations (22), the present data suggest that DHEA treatment might influence insulin sensitivity in type 2 diabetic patients, through its effects on the TNF- system, despite the absence of HOMA index modifications that we observed.
In conclusion, these data, together with the experimental data from rodents, suggest that DHEA treatment might prevent many of the events that lead to cellular damage induced by hyperglycemia, thus counteracting the onset and/or progression of chronic complications in type 2 diabetic patients. Of interest, this result was obtained in the absence of any improvement of glycemic control. Present management of hyperglycemia is based upon the assumption that the best way to reduce the risk of diabetes complications is to achieve optimal glycemic control. However, it should be pointed out that patients receiving intensive therapy designed to achieve glycemic control still develop diabetes complications, even though their prevalence is reduced (23). If hyperglycemia cannot be effectively prevented, the only way to impede diabetes complications will be to interrupt the pathways that lead from hyperglycemia to target organ damage. AGEs clearly represent one such pathway.
A similar preventive activity against hyperglycemia-induced oxidative stress has been postulated for drugs such as statins, ACE inhibitors, angiotensin II type 1 receptor blockers, calcium channel blockers, and thiazolidinediones, and their clinical use to prevent chronic complications in diabetic patients has been suggested (24). Compared with these drugs, DHEA has the advantage of being a physiologic steroid without side effects at the dosage used in this study. The usefulness of this novel approach to protect diabetic patients against tissue damage appears to be worth further exploration through multicenter clinical trials.
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Acknowledgments |
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This study was supported by the Special Project "Oncology," Compagnia San Paolo, Turin, by MIUR (Ministero Università e Ricerca), and by Regione Piemonte.
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Footnotes |
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Published ahead of print at http://care.diabetesjournals.org on 17 August 2007. DOI: 10.2337/dc07-1110.
A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C Section 1734 solely to indicate this fact.
Received for publication June 22, 2007. Accepted for publication August 9, 2007.
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References |
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TOPABSTRACTINTRODUCTIONRESEARCH DESIGN AND METHODS--RESULTSCONCLUSIONSReferences |
|---|
- Baynes JW: Role of oxidative stress in development of complications in diabetes. Diabetes 40: 405–412, 1991[Abstract]
- Nishikawa T, Edelstein D, Du XL, Yamagishi S, Matsumura T, Kaneda Y, Yorek MA, Beebe D, Oates PJ, Hammes HP, Giardini I, Brownlee M: Normalizing mitochondrial superoxide production blocks three pathways of hyperglycaemic damage. Nature 404: 787–790, 2000[Medline]
- Brownlee M: Biochemistry and molecular cell biology of diabetic complications. Nature 414: 813–820, 2001[Medline]
- Vlassara H: The AG: E-receptor in the pathogenesis of diabetic complications. Diabete Metab Res Rev 17: 436–443, 2001
- Forbes JM, Yee LT, Thallas V, Lassila M, Candido R, Jandeleit-Dahm KA, Thomas MC, Burns WC, Deemer EK, Thorpe SM, Cooper ME, Allen TJ: Advanced glycation end product interventions reduce diabetes-accelerated atherosclerosis. Diabetes 53: 1813–1823, 2004
[Abstract/Free Full Text] - Esposito K, Nappo F, Marfella R, Giugliano G, Giugliano F, Ciotola M, Quagliaro L, Ceriello A, Giugliano D: Inflammatory cytokine concentrations are acutely increased by hyperglycemia in humans: Role of oxidative stress. Circulation 106: 2067–2072, 2002
[Abstract/Free Full Text] - Lonn E, Yusuf S, Hoogwerf B, Pogue J, Yi Q, Zinman B, Bosch J, Gagenais G, Mann JFE, Gerstein HC: Effects of vitamin E on cardiovascular and microvascular outcomes in high-risk patients with diabetes. Diabetes Care 25: 1919–1927, 2002
[Abstract/Free Full Text] - Brignardello E, Beltramo E:, Molinatti PA, Aragno M, Gatto V, Tamagno E, Danni O, Porta M, Boccuzzi G: Dehydroepiandrosterone protects bovine retinal capillary pericytes against glucose toxicity. J Endocrinol 158: 21–26, 1998[Abstract]
- Aragno M, Parola S, Brignardello E, Mauro A, Tamagno E, Manti R, Danni O, Boccuzzi G: Dehydroepiandrosterone prevents oxidative injury induced by transient ischemia/reperfusion in the brain of diabetic rats. Diabetes 49: 1924–1931, 2000[Abstract]
- Aragno M, Mastrocola R, Medana C, Restivo F, Catalano MG, Pons N, Danni O, Boccuzzi G: Up-regulation of advanced glycated products receptors in the brain of diabetic rats is prevented by antioxidant treatment. Endocrinology 146: 561–5567, 2005
- Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC: Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 28: 412–419, 1985[Medline]
- Aragno M, Mastrocola R, Medana C, Catalano MG, Vercellinatto I, Danni O, Boccuzzi G: Oxidative stress-dependent impairment of cardiac-specific transcription factors in experimental diabetes. Endocrinology 147: 5967–5974, 2006
[Abstract/Free Full Text] - Burton GW, Traber MG, Acuff RV, Walters DN, Kayden H, Hughes L, Ingold KU: Human plasma and tissue alpha-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E. Am J Clin Nutr 67: 669–684, 1998[Abstract]
- Raj DSC, Choudhury D, Welbourne TC, Levi M: Advanced glycation end products: a nephrologist’s perspective. Am J Kidney Dis 35: 365–380, 2000[Medline]
- Monnier VM, Bautista O, Kenny D, Sell DR, Fogarty J, Dahms W, Cleary PA, Lachin J, Genuth S, the DCCT Skin Collagen Ancillary Study Group: Skin collagen glycation, glycoxidation, and crosslinking are lower in subjects with long-term intensive versus conventional therapy of type 1 diabetes: relevance of glycated collagen products versus HbA1c as markers of diabetic complications. Diabetes 48: 870–880, 1999[Abstract]
- Houstis N, Rosen ED, Lander ES: Reactive oxygen species have a causal role in multiple forms of insulin resistance. Nature 440: 944–948, 2006[Medline]
- Nophar Y, Kemper O, Brakebusch C, Englemann H, Zwang R, Aderka D, Holtmann H, Wallach D: Soluble forms of tumor necrosis factor receptors (TNF-Rs): the cDNA for the type I TNF-R, cloned using amino acid sequence data of its soluble form, encodes both the cell surface and a soluble form of the receptor. EMBO J 9: 3269–3278, 1990[Medline]
- Fernandez-Real JM, Brich M, Ricart W, Casamitjana R, Gutierrez C, Vendrell J, Richart C: Plasma levels of the soluble fraction of tumor necrosis factor receptor 2 and insulin resistance. Diabetes 47: 1757–1762, 1998[Abstract]
- Hotamisligil GS, Arner P, Atkinson RL, Spiegelman BM: Differential regulation of the p80 tumor necrosis factor receptor in human obesity and insulin resistance. Diabetes 46: 451–455, 1997[Abstract]
- Winkler G, Lakatos P, Salamon F, Nagy Z, Speer G, Kovacs M, Harmos G, Dworak O, Cseh K: Elevated serum TNF-alpha level as a link between endothelial dysfunction and insulin resistance in normotensive obese patients. Diabet Med 16: 207–211, 1999[Medline]
- Fernandez-Real JM, Lainez B, Vendrell J, Rigla M, Castro A, Penarroja G, Broch M, Perez A, Richart C, Engel P, Ricart W: Shedding of TNF-alpha receptors, blood pressure, and insulin sensitivity in type 2 diabetes mellitus. Am J Physiol Endocrinol Metab 282: E952–E959, 2002
[Abstract/Free Full Text] - Kawano H, Yasue H, Kitagawa A, Hirai N, Yoshida T, Soejima H, Miyamoto S, Nakano M, Ogawa H: Dehydroepiandrosterone supplementation improves endothelial function and insulin sensitivity in men. J Clin Endocrinol Metab 88: 3190–3195, 2003
[Abstract/Free Full Text] - Soro-Paavonen A, Forbes JM: Novel therapeutics for diabetic micro- and macrovascular complications. Curr Med Chem 13: 1777–1788, 2006[Medline]
- Ceriello A: Controlling oxidative stress as a novel molecular approach to protecting the vascular wall in diabetes. Curr Opin Lipidol 17: 510–518, 2006[Medline]
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