Elsevier

European Urology

Volume 53, Issue 6, June 2008, Pages 1272-1281
European Urology

Sexual Medicine
Daily Treatment with Sildenafil Reverses Endothelial Dysfunction and Oxidative Stress in an Animal Model of Insulin Resistance

https://doi.org/10.1016/j.eururo.2007.11.018Get rights and content

Abstract

Objectives

Patients with insulin resistance exhibit endothelial dysfunction with decreased nitric oxide (NO) production and increased oxidative stress. We postulated that daily sildenafil improved endothelial function in fructose-fed rats.

Methods and results

Wistar rats were fed a standard or fructose-enriched diet (FFR) for 9 wk. From weeks 6–8, sildenafil was administered twice daily (sc, 20 m g/kg), followed by a 1-wk washout. Concentration-response curves (CRCs) to endothelium-dependent (acetylcholine [Ach] and A23187) and -independent (sodium nitroprusside [SNP]) relaxing agents were performed on isolated precontracted aortas and superior mesenteric arteries (SMAs). Vascular cyclic guanosine monophosphate (cGMP) content, urinary excretion of nitrates/nitrites (NOx) and 8-isoprostanes (IPT), and plasma levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were evaluated. Relaxations to ACh were significantly reduced in aortas and SMAs of FFR. Sildenafil restored ACh-induced relaxations in aortas and provoked a significant leftward shift of the CRC to ACh in SMAs, whereas it did not modify the enhanced relaxations to SNP in FFR. IL-6, TNF-α, vascular cGMP, and urinary NOx levels were not modified by the fructose or sildenafil treatment. Urinary IPT levels were significantly elevated in FFR and normalized by sildenafil.

Conclusions

Endothelial dysfunction and oxidative stress associated with insulin resistance can be reversed by daily sildenafil, even 1 wk after treatment cessation.

Introduction

Insulin resistance (IR) has been implicated in the pathogenesis of obesity and the metabolic syndrome (MetS) as defined either by the International Diabetes Federation (IDF), National Cholesterol Education Program—Adult Treatment Panel III (NCEP-ATPIII), or European Group for the study of Insulin Resistance (EGIR) criteria [1]. In fact, MetS in both children and adults is a known independent cardiovascular risk factor [1], and patients with MetS exhibit impaired endothelium-dependent vasodilation [2]. It is now recognized that these disturbances in endothelial function are principal players in cardiovascular diseases [3]. It was reported that fructose consumption might be a contributing factor to the development of obesity and the accompanying metabolic abnormalities observed in MetS [4], and fructose has also been associated with angiopathy in patients with diabetes [5]. Interestingly, high fructose consumption by animals leads to impaired glucose tolerance, IR, hyperinsulinemia, and hypertriglyceridemia [6], with even a mild elevation of blood pressure found by some authors [7] but not confirmed by others [8].

In a previous study, we evidenced the beneficial effects of daily sildenafil on erectile function in normal rats and further characterized these effects in vitro to be via improved cavernosal endothelial function [9]. Because previous work had shown the central role of the Akt-dependent phosphorylation of endothelial nitric oxide synthase (eNOS) in mediating penile erection [10], we hypothesized that chronic sildenafil may actually exert a direct or indirect effect beyond phosphodiesterase (type) 5 (PDE5) inhibition and thus modulate the transduction pathway leading to the activation of eNOS. Indeed, the serine/threonine–specific protein kinase Akt could be involved in the upregulation of eNOS activity by a calcium-independent mechanism, resulting in the phosphorylation of eNOS and increase in eNOS activity [11]. Thus, a plausible explanation of the beneficial effects of daily sildenafil on endothelial reactivity may be that it leads to an increased expression of phosphorylated eNOS over total eNOS and active Akt over total Akt, as recently evidenced in cavernosal tissues [12]. Furthermore, it was suggested that daily treatment with PDE5 inhibitors could have additional and prolonged beneficial effects on endothelial function in patients with increased cardiovascular risks [13]. The benefit of this therapy could even be sustained 2 wk after discontinuation of therapy [13].

In this study, we aimed to investigate whether chronic sildenafil could improve systemic endothelium-dependent relaxations in an experimental model of IR by in vitro isometric tension studies on aortic and superior mesenteric arterial (SMA) rings. Moreover, because oxidative stress has been suggested to contribute to IR [14] and associated endothelial dysfunction [15], we sought to determine the effects of chronic sildenafil on a potentially relevant biomarker of endothelial dysfunction, urinary 8-isoprostanes (IPT) content, a direct marker of nonenzymatic in vivo lipid peroxidation and the most reliable and clinically relevant marker of oxidative stress available to date [16].

Section snippets

Chronic treatment of rats and monitoring of endothelial biomarkers

All procedures were performed in accordance with the legislation on the use of laboratory animals (NIH publication No 85-23, revised 2002) and animal care regulations in force in France. Male Wistar rats (Charles River, L’Arbresle, France, 180–220 g) were given standard chow (Reference TD.03102; CONT) or an isocaloric fructose-enriched diet containing 18.3% protein, 60.3% fructose, and 5.2% lard expressed in % diet by weight (Reference TD.89247; fructose-fed rats, FFR) for the following 9 wk

Results

Body weight changes, fasting glycemia, and plasma IL-6 and TNF-α levels remained statistically unchanged in the various treatment groups (Table 1). Conversely, FFR displayed an impaired OGTT as indicated by a greater hyperglycemic response and AUC compared with control rats both at weeks 8 and 9. Strikingly, chronic treatment with sildenafil corrected this hyperglycemic response while treatment lasted (p < 0.05, one-way ANOVA; Fig. 1). This effect, however, wore off 1 wk after cessation of

Discussion

A high-fructose diet in rats leads to impaired glucose tolerance, IR, hyperinsulinemia, and hypertriglyceridemia [6], with even a mild elevation of blood pressure found by some authors [7] but not confirmed by others [8], a set of symptoms that resembles MetS in humans. In humans, each of the above abnormalities is associated with endothelial dysfunction, let alone when all these risk factors are combined. Here, we confirmed the elevation of triglycerides and the lack of fasting hyperglycemia

Conflicts of interest

This work was supported by a restricted grant from Pfizer Ltd.

References (36)

  • H.A. Ghofrani et al.

    Differences in hemodynamic and oxygenation responses to three different phosphodiesterase-5 inhibitors in patients with pulmonary arterial hypertension: a randomized prospective study

    J Am Coll Cardiol

    (2004)
  • S. Morano et al.

    Antioxidant treatment associated with sildenafil reduces monocyte activation and markers of endothelial damage in patients with diabetic erectile dysfunction: a double-blind, placebo-controlled study

    Eur Urol

    (2007)
  • A.J. Bella et al.

    Daily administration of phosphodiesterase type 5 inhibitors for urological and nonurological indications

    Eur Urol

    (2007)
  • S. Ückert et al.

    Update on phosphodiesterase (PDE) isoenzymes as pharmacologic targets in urology: present and future

    Eur Urol

    (2006)
  • P.M. Nilsson et al.

    The metabolic syndrome and incidence of cardiovascular disease in non-diabetic subjects—population-based study comparing three different definitions

    Diabet Med

    (2007)
  • A.D. Baron

    Vascular reactivity

    Am J Cardiol

    (1999)
  • D. Galipeau et al.

    Chronic thromboxane synthase inhibition prevents fructose-induced hypertension

    Hypertension

    (2001)
  • M.J. Reed et al.

    Salt-sensitive and carbohydrate-sensitive rodent hypertension: evidence of strain differences

    Blood Press

    (1994)
  • Cited by (0)

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