| Many studies show a correlation between high-fructose consumption and the metabolic syndrome, a known harbinger of cardiovascular disease. My study explores the role of oxidative stress, specifically the overproduction of superoxide (O2-) and subsequent lowering of nitric oxide (NO) bioavailability, in the development of fructose-induced metabolic syndrome. My work is divided into three specific aims: 1) To characterize the effects of high-fructose consumption on the cardiovascular system and explore the involvement of NO and O2-, 2) To determine the consequences of high-fructose consumption during pregnancy and exercise, two states of elevated cardiac work, and 3) To ascertain the development of the metabolic syndrome as a consequence of high-fructose consumption in the dog and explore its effects on cardiovascular progenitor cells. For Specific Aim 1, female SD rats were fed either a basal (N=8) or 60% fructose diet (N=8) for 21 days. Cardiovascular alterations were observed in fructose-fed (FF) animals, including an elevation of diastolic blood pressure (DBP) and mean arterial pressure (MAP, from 104 +/- 2 to 115 +/- 4 mmHg) , and changes in myocardial O2 consumption (MVO2), represented by impaired response to bradykinin (BK), an eNOS activator. This response was rescued with the addition of tiron, a O2- scavenger, or apocynin, an NADPH oxidase inhibitor, ?indicating the involvement of excess O2- produced by NADPH oxidase. On the other hand, addition of L-NAME, an eNOS inhibitor, to control tissue resulted in an impaired BK response similar to FF samples. Insulin resistance was indicated in FF animals, as normoglycemia was maintained at significantly higher plasma insulin concentration (3.10 +/- 0.42 to 5.47 +/- 0.44 ng/mL). There was a tendency for plasma NOx concentration to increase in FF rats, paralleled by an increase in phosphorylated eNOS, phosphorylated p47 (an NADPH oxidase subunit), and N-Tyr, suggesting an increase in NO and O2- production. Finally, cross-analysis of mRNA and miRNA microarrays revealed corresponding changes, where downregulated miRNAs are associated with upregulated mRNAs, and vice versa. These changes demonstrate that high-fructose consumption affects gene regulation and may reveal the mechanism behind phenotypic changes in FF animals. In Specific Aim 2, pregnant SD rats were fed a basal (N=8) or 60% fructose diet (N=8) for 21 days, the length of gestation. Significant elevations in systolic blood pressure (SBP), DBP, and MAP (93 +/- 3 to 110 +/- 2 mmHg) were observed. Plasma insulin concentration was significantly increased, as well as plasma uric acid and Ang II (236 +/- 11 to 311 +/- 16 pg/mL). Intrauterine growth restriction was indicated, as fetal weight of FF rats was found to be approximately 20% lower than control. Surprisingly, exercise capacity was significantly enhanced in pregnant FF rats though at the cost of increased O2 consumption and altered RER profile. Ex vivo VO2 measurements of the LV and gastrocnemius muscles revealed a reduced NO bioavailability and increased O2- production by NADPH oxidase as the cause behind impaired response to BK. Finally, significant increases in productions of NO and O2- were demonstrated by measurement of plasma nitrate/nitrite, O2- quantification by lucigenin chemiluminescence and Western blots of eNOS and NADPH oxidase subunits. For Specific Aim 3, male mongrel dogs (N=6) were fed 60% fructose diet for 7 weeks. FF dogs developed metabolic syndrome, characterized by hypertension, insulin resistance, and dyslipidemia. Furthermore, though cardiac function was maintained, wall stress and cardiac work were significantly increased with fructose feeding. Hearts of FF animals also showed impaired contractile response to ?-adrenergic stimulation and displayed substrate utilization shift commonly seen in heart failure. Finally, impaired growth was observed in endothelial progenitor cells (EPCs) cultured from FF animals. This impairment can be induced by the addition of Ang II to control EPCs. Supplementation with losartan, apocynin, or tiron rescued FF and Ang II-treated control EPCs, confirming the role of AT1R, NADPH oxidase, and excess O2-. In all, my study has shown the many deleterious effects of fructose on the cardiovascular system. Effectiveness of losartan, tiron, or apocynin in reversing fructose-induced changes indicate the importance of NO-O2- interaction in the mechanism behind the effects of fructose feeding. As fructose consumption continues to climb, it is prudent to consider the cellular changes and physiological consequences of this additive. Ultimately, while studies of fructose feeding can provide valuable insight into the cellular workings of physiological consequences, it seems reasonable to call for the reduction of this simple monosaccharide in our diet. |
