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Glu298Asp polymorphism influences the effects of beetroot bread on diastolic blood pressure in healthy men: A pilot study

Published online by Cambridge University Press:  30 August 2013

D. A. Hobbs ,
T. W. George  and
J. A. Lovegrove
D. A. Hobbs
Affiliation:
Hugh Sinclair Unit of Human Nutrition, University of Reading, Whiteknights, PO Box 226, Reading, RG6 6AP Institute for Cardiovascular and Metabolic Research (ICMR), University of Reading, Whiteknights, PO Box 226, Reading, RG6 6AP
T. W. George
Affiliation:
Department of Biology, Food and Nutritional Sciences, Ellison Building, Ellison Place, Northumbria University, NE1 8ST, UK
J. A. Lovegrove
Affiliation:
Hugh Sinclair Unit of Human Nutrition, University of Reading, Whiteknights, PO Box 226, Reading, RG6 6AP Institute for Cardiovascular and Metabolic Research (ICMR), University of Reading, Whiteknights, PO Box 226, Reading, RG6 6AP
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Abstract

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Proceedings of the Nutrition Society , Volume 72 , Issue OCE4: Summer Meeting, 15–18 July 2013, Nutrition and healthy ageing , 2013 , E227
Copyright
Copyright © The Authors 2013 

Glu298Asp polymorphism of the endothelial nitric oxide synthase eNOS gene (NOS3) has previously been identified as a risk factor for hypertension( Reference Hingorani 1 ) and coronary artery disease( Reference Miyamoto 2 ). Studies suggest that the higher risk observed in thymine (T) allele carriers is due to endothelial dysfunction associated with lower eNOS activity( Reference Casas 3 ). It has been proposed that acute consumption of nitrate ameliorates postprandial endothelial dysfunction possibly by the donation of nitric oxide by a mechanism that does not rely on eNOS( Reference Lundberg 4 ). Nevertheless, how these factors interact has yet to be determined. Therefore, the aim of this study was to investigate whether the presence of NOS3 Glu298Asp polymorphism interacts with the nitrate content of beetroot-enriched bread to influence postprandial blood pressure.

An acute, randomised, single-blind, controlled, crossover pilot study was performed in fourteen healthy men (mean age 34 (sd 9) years and BMI 22.8 (sd 2) kg/m2) who were retrospectively genotyped for NOS3 Glu298asp polymorphism (7 GG; 7 GT/TT – T carriers). Volunteers were randomised to receive 200 g beetroot-enriched bread (1.1 mmol nitrate) or control bread (no beetroot; 0.01 mmol nitrate) on two separate occasions 10 days apart. Baseline and incremental area under the curve of blood pressure and nitrate/nitrite (NOx) were measured fasted and postprandially for a total period of 6 hours.

A treatment by genotype interaction was observed for diastolic blood pressure (DBP; P<0.01), in which the DBP was significantly lower in the T carriers (P<0.01) only after beetroot compared with control bread. No significant treatment by genotype interaction was observed for SBP. However, there was a significant effect of treatment (P<0.01) on plasma NOx regardless of genotype and a near significant treatment by genotype interaction (P<0.06), with Bonferroni post-hoc tests revealing the T carriers had significantly higher plasma NOx (P<0.01) after beetroot-enriched bread compared with control bread.

Diastolic BP (A) and plasma NOx (B) responses in GG (n=7) and T carriers (n=7) of the NOS3 Glu298Asp polymorphism after acute ingestion of either control or beetroot-enriched bread. Data expressed as mean±se. Significant treatment by genotype interaction for DBP (**P<0.01) and near significant treatment by genotype interaction for plasma NOx (P<0.06) using 2-way ANOVA, with the T carriers showing significantly lower DBP and NOx responses (both **P<0.01) after beetroot-enriched vs. control bread after Bonferroni post-hoc test.

In conclusion, beneficial DBP reduction was observed only in the T carriers of the NOS3 Glu298Asp polymorphism after consumption of nitrate-rich beetroot bread. This data requires confirmation in a larger population group.

References

1. Hingorani, AD et al. (1999) Circulation 100, 1515–20.CrossRefGoogle Scholar
2. Miyamoto, Y et al. (1998) Hypertension 32, 3–8.CrossRefGoogle ScholarPubMed
3. Casas, JP et al. (2006) Am J Epidemiol 164, 921–35.Google Scholar
4. Lundberg, JO et al. (2006) Nitric Oxide 15, 359–62.Google Scholar