Muhammad Qasim Memon ( Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, The University of Nottingham, Nottingham, UK. )
Elizabeth Jane Simpson ( Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, The University of Nottingham, Nottingham, UK. )
Ian Andrew Macdonald ( Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, The University of Nottingham, Nottingham, UK. )
Objective: To assess how acute consumption of fructose affects flow-mediated dilatation in brachial artery.
Methods: The randomised cross-over study was conducted at the University of Nottingham\'s Medical School, Nottingham, United Kingdom in July 2009. Ten healthy, white European males visited the laboratory twice, on separate mornings. On each visit, the volunteers consumed water (3ml/kg bodyweight) and rested semi-supine on the bed. After 30 minutes, baseline diastolic brachial artery diameter and blood velocity was measured. At 60 minutes, blood velocity and five scans of brachial artery diameter were recorded before a blood pressure cuff was inflated on the forearm for 5 minutes and at 50-60-70-80 and 90 sec after cuff deflation. Fifteen minutes later, the volunteers consumed 500ml of test-drink containing either fructose (0.75 g/kg bodyweight) or sucralose (sweetness-matched with fructose drink); 45 minutes later, baseline and flow-mediated dilatation was re-measured.
Results: Pre-drink and post-drink baseline values were similar on two occasions (p> 0.05). Brachial artery diameter increased (p < 0.05) by 7±3% pre-fructose and by 6.9±3% above baseline values post-fructose with no significant difference in these responses (p < 0.15). It increased (p < 0.05) by 5.9±3% above baseline before and by 6.7±2% (p < 0.01) after sucralose; a significant difference was noted in these flow-mediated dilatation responses (p < 0.02). Responses before and after sucralose were not different from those before and after fructose (p < 0.294).
Conclusion: Acute ingestion of fructose or sucralose had no effect on flow-mediated dilatation measured at brachial artery.
Keywords: Endothelium, Brachial artery, Vasodilatation, Fructose, Nitric oxide, Cardiovascular. (JPMA 64: 743; 2014)
The endothelium is a single layer of cells lining the intimal surface of blood vessels. By its production of various chemical substances in response to physical and chemical stimuli, the endothelium enables vessels to adapt to changes in the local environment by dilatation or contraction.1-5 A normally functioning endothelium is an index of healthy cardiovascular (CV) status. Endothelial dysfunction in the brachial artery (BA) is closely related to impairment of coronary arterial endothelial function6 and is a predictor of adverse CV health. In addition, the degree of arterial stiffness is directly related to the extent of endothelial dysfunction reflected in a reduced endothelial capacity to produce nitric oxide (NO).7,8
Flow-mediated dilatation (FMD) is a non-invasive method employed for the assessment of endothelial function by evaluating changes in BA diameter resulting from a sheer stress stimulus. This is achieved by the use of an occlusion cuff (typically applied for 5 minutes) on the forearm whereby release of the cuff leads to reactive hyperaemia. The resulting increase in BA diameter in response to this increase in blood flow can be measured by ultrasound imaging.9 FMD measurements have diagnostic and prognostic value and repeated measurements are possible because of the procedure\'s non-invasive nature.10
Animal studies suggest that fructose ingestion induces hyperinsulinaemia as a consequence of the sympathetic nervous system stimulation11 and fructose induced hypertriglyceridaemia12 leads to the production of superoxide radicals which contributes to oxidative stress (OS) and leads to reduced amount of NO in the vasculature. This results in altered vascular function and defective vasodilatation.13-15 Acute fructose consumption in human subjects is reported to have detrimental CV effects, such as increase in blood pressure (BP).16-18 However, effects produced by fructose in humans remain controversial, as it has been reported that ingestion of 64g of fructose, i.e., fructose equivalent to that contained in 5 apples, may bring about beneficial effects by increasing plasma anti-oxidant levels.19 Using sucralose (a synthetic sweetener) as a control, the purpose of the present study was to assess how acute consumption of fructose affected the FMD of the BA by employing ultrasound imaging for FMD measurements.
Subjects and Methods
The study of six-month duration was conducted at the University of Nottingham\'s Medical School, Nottingham, United Kingdom in July 2009. It was approved by the institutional ethics committee and conformed to the Declaration of Helsinki for experimentation on humans.
Ten healthy, non-smoking, white, European males were recruited for the study which involved 2 visits in a randomised, cross-over design. The volunteers fasted overnight and avoided sugar-containing soft drinks, caffeinated drinks, bakery products, fruit or fruit products, alcohol, fatty food, vitamin C supplements and strenuous exercise for 24 hours before the visit. The subjects were advised to consume the same type of meal on the night before each experimental visit. All experiments took place at the same time in the morning. Upon arrival, the volunteers were weighed and were offered water (3ml/kg bodyweight) to ensure that they were adequately hydrated. They rested on a bed, semi-recumbent in a thermo-regulated room (27°C) and their arms were positioned at the same height relative to their heart. Electrocardiogram (ECG) leads on the ultrasound machine (Toshiba Diagnostic Ultrasound System — Model SSA-770A; Toshiba Medical Systems Corporation, Japan) were attached to the volunteer to allow ECG-gating of subsequent scans, and a BP cuff was applied over a single layer of Soffban orthopaedic padding (Smith & Nephew; Hull , UK) at a pre-determined position on the right lower arm of the volunteer. After resting for 30 minutes, the BA was located and 3 baseline BA diameter measurements and blood velocity (BV) readings were taken. Cine images of all scans were stored for subsequent comparison and analysis. BA position was marked on the volunteer\'s skin to ensure reproducibility of measurements. A further baseline measurement was made a few minutes before the occlusion at 60 minutes; the BP cuff was inflated to 50 mmHg above the volunteer\'s systolic BP and it remained inflated for 5 min (occlusion period). Upon completion of the 5 minutes, the BP cuff was deflated and 15 seconds later, a BV measurement was made. Five scans of BA diameter were recorded at 50, 60, 70, 80 and 90 seconds after cuff deflation and the change in diameter was expressed as per cent change from the baseline diameter.
Fifteen min after the FMD measurement, volunteers were offered 500ml of a lemon-flavoured drink (to be consumed over 5 minutes) containing either fructose (0.75g per kg bodyweight) (Fruisana; Danisco Sweeteners OY. Kotka, Finland) or sucralose (having matched sweetness to that of the fructose drink; Splenda; McNeil Nutritionals Ltd). At 120 minutes (45 minutes after the drink), baseline diameter and BV were measured before a second FMD measurement was made. The above procedure was followed on the second study day, at least 3 days later and usually within one week, with the exception that the drink was different from the one consumed on the first experimental visit.
BA diameter change was analysed from the stored cine images and FMD was calculated by taking an average of the 3 baseline diastolic diameter measurements (A) and the average of diastolic diameter measurements taken over 3 cardiac cycles at 60, 70 and 80 sec (B) after the occlusion was released. The following equation was used to calculate the FMD:
B-A = C
(C/A) x 100 = FMD %
Intra-group statistical analyses were carried out using paired student\'s t-test after determination of normality of the data. Comparisons made between the 2 visits i.e., the FMD measurements before and after consumption of either sucralose or fructose, were carried out using a 2-way analyses of variance (ANOVA) with repeated measures. Statistical significance was set as p<0.05.
The present study employed a randomised, cross-over, single-blind design and used non-invasive techniques, e.g., ultrasound, to assess the effects of acute consumption of fructose and that of sucralose on the FMD of BA.
FMD responses before fructose or sucralose consumption (7% and 5.9% respectively) were similar and compared well with the literature and were indicative of a healthy endothelial function.20-22 A significant FMD response was observed before and after fructose was consumed, but there was no significant difference in these FMD responses. Other interventions reported in the literature show changes from such values — for example, both increases of FMD after flavanols, as contained in cocoa and reversal of smoking-induced endothelial dysfunction23 and decreases after cigarette smoking24 and saturated fat meal.25 A possible reason for the absence of an effect of fructose is either because it does not have the purported effects proposed in the literature, that fructose induces hyperuricaemia which leads to endothelial dysfunction26 or the dose was too small or the timing of the post-fructose measurement inappropriate. Ample time was allowed between the measurements (1h) which was sufficient for the vessel to recover and for a repeat measurement to be made and for fructose to reach peak serum level, i.e., 30-60 minutes after oral ingestion.17 Evidence suggests that timing for post-fructose FMD measurement, i.e., 45 minutes after the drink, was appropriate for fructose effects to become apparent as a study reported CV effects of fructose to become noticeable within 30 minutes, whereas another study reported peak changes evident after 20 minutes post-drink.18,27 The quantity of fructose used in the present study was 0.75g per kg bodyweight, which amount was determined after personal experience, which indicated that 1g per kg may cause gastrointestinal upset. Volunteers participating in this study weighed 73±9kg, so fructose used in the study ranged between 48g- 61.5g, an amount consistent with fructose dose used in a study determining fructose effects.27
There was a decrease in per cent diameter change of the BA after fructose was consumed compared to pre-drink in 6 of the 10 volunteers, while for the rest the values increased. Thus, it is possible that fructose may affect FMD, but the present study did not show this to be significant because of either wide variability (range of 0.20 to 19.2% between individuals) in FMD response among healthy volunteers or the sample size was too small.20,21 Sucralose consumption resulted in decreased per cent diameter change of the BA in half of the volunteers with the other half showing an increase and sucralose responses (pre- and post-drink) were similar to fructose. The results were consistent with earlier reports that showed similarity in effects of fructose and sucralose.18
Acute ingestion of fructose and sucralose had no effects on the dilatation of the BA after 5 minutes of occlusion and the effects of sucralose were not different from that of fructose.
1. Burnstock G. Release of vasoactive substances from endothelial cells by shear stress and purinergic mechanosensory transduction. J Anat 1999; 194: 335- 42.
2. Furchgott RF, Zawadzki JV. The obligatory role of the endothelium in the relaxation of arterial smooth muscle by acetylcholine. Nature 1980; 288: 373-6.
3. Parnavelas JG, Kelly W, Burnstock G. Ultrastructural localization of choline acetyltransferase in vascular endothelial cells in rat brain. Nature 1985; 316: 724-5.
4. Pohl U, Holtz J, Busse R, Bassenge E. Crucial role of endothelium in the vasodilator response to increased flow in vivo. Hypertension 1986; 8: 37-44.
5. Yanagisawa M, Kurihara H, Kimura S, Tomobe Y, Kobayashi M, Mitsui Y, et al. A novel potent vasoconstrictor peptide produced by vascular endothelial cells. Nature 1988; 332: 411-5.
6. Teragawa H, Ueda K, Matsuda K, Kimura M, Higashi Y, Oshima T, et al., Relationship between endothelial function in the coronary and brachial arteries. Clin Cardiol 2005; 28: 460-6.
7. Sözmen B, Uysal F, Gazitepe D, Aslan L and Sözmen EY. A novel clinical and laboratory based approach to coronary heart disease: relationship between angiography findings, antioxidant enzymes and NO. Turk J Med Sci 1999; 29: 117-23.
8. Soga J, Nakamura S, Nishioka K, Umemura T, Jitsuiki D, Hidaka T, et al. Relationship between augmentation index and flow-mediated vasodilation in the brachial artery. Hypertens Res 2008; 31: 1293-8.
9. Ulusoy RE, Yokusoglu M, Baysan O, Kirilmaz A, Kilicaslan F, Cebeci BS. Ventricular functions, aortic elastic properties, and endothelial functions in patients with hypertensive response to treadmill exercise testing. Turk J Med Sci 2011; 41: 781-7.
10. Corretti MC, Anderson TJ, Benjamin EJ, Celermajer D, Charbonneau F, Creager MA, et al. Guidelines for the ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery: A report of the International Brachial Artery Reactivity Task Force. J Am Coll Cardiol 2002; 39: 257-65.
11. Verma S, Bhanot S, McNeill JH. Sympathectomy prevents fructose-induced hyperinsulinemia and hypertension. Eur J Pharmacol 1999; 373: R1-4.
12. Sleder J, Chen YD I, Cully MD, Reaven GM. Hyperinsulinemia in fructose-induced hypertriglyceridemia in the rat. Metabolism 1980; 29: 303-5.
13. Higashi Y, Sasaki S, Nakagawa K, Matsuura H, Oshima T, Chayama K. Endothelial function and oxidative stress in renovascular hypertension. N Engl J Med 2002; 346: 1954-62.
14. Hsieh PS. Attenuation of insulin-mediated pressor effect and nitric oxide release in rats with fructose-induced insulin resistance. Am J Hypertens 2004; 17: 707-11.
15. Oudot A, Behr-Roussel D, Compagnie S, Caisey S, Le Coz O, Gorny D, et al. Endothelial dysfunction in insulin resistant rats is associated with oxidative stress and cox pathway dysregulation. Physiol Res 2009; 58: 499-509.
16. Brown CM, Dulloo AG, Yepuri G, Montani JP. Fructose ingestion acutely elevates blood pressure in healthy young humans. Am J Physiol Regul Integr Comp Physiol 2008; 294: R730-37.
17. Gaby AR. Adverse effects of dietary fructose. Altern Med Rev 2005; 10: 294-306.
18. Memon MQ, Bennett T, Macdonald IA. Haemodynamic effects of fructose and sucralose in healthy, white Caucasian males. J Liaquat Uni Med Health Sci 2011; 10: 3-10.
19. Lotito SB, Frei B. The increase in human plasma antioxidant capacity after apple consumption is due to the metabolic effect of fructose on urate, not apple-derived antioxidant flavonoids. Free Radical Bio Med 2004; 37: 251-8.
20. Bots ML, Westerink J, Rabelink TJ, de Koning EJ. Assessment of flow-mediated vasodilatation (FMD) of the brachial artery: effects of technical aspects of the FMD measurement on the FMD response. Eur Heart J 2005; 26: 363-8.
21. Corretti MC, Plotnick GD, Vogel RA. Technical aspects of evaluating brachial artery vasodilatation using high-frequency ultrasound. Am J Physiol 1995; 268: H1397-404.
22. De Roos NM, Bots ML, Schouten EG, Katan MB. Within-subject variability of flow-mediated vasodilation of the brachial artery in healthy men and women: implications for experimental studies. Ultrasound Med Biol 2003; 29: 401-6.
23. Heiss C, Finis D, Kleinbongard P, Hoffmann A, Rassaf T, Kelm M, et al. Sustained increase in flow-mediated dilation after daily intake of high-flavanol cocoa drink over 1 week. J Cardiovasc Pharm 2007; 49: 74-80.
24. Karatzi K, Papamichael C, Karatzis E, Papaioannou TG, Stamatelopoulos K, Zakopoulos NA, et al., Acute smoke-induced endothelial dysfunction is more prolonged in smokers than in non-smokers. Int J Cardiol 2007; 120: 404-6.
25. Keogh JB, Grieger JA, Noakes M, Clifton PM. Flow-mediated dilatation is impaired by a high saturated fat diet but not by a high-carbohydrate diet. Arterioscler Thromb Vasc Biol 2005; 25: 1274-9.
26. Nakagawa T, Tuttle KR, Short RA, Johnson RJ. Hypothesis: fructose-induced hyperuricemia as a causal mechanism for the epidemic of the metabolic syndrome. Nat Clin Pract Neph 2005; 1: 80-6.
27. Brown CM, Dulloo AG, Yepuri G, Montani JP. Fructose ingestion acutely elevates blood pressure in healthy young humans. Am J Physiol Regul Integr Comp Physiol 2008; 294: R730-7.