Role of the Oral Microbiome in Blood Pressure Regulation in Pregnancy

Investigation of the Oral Microbiome in Pregnancy - do Differences in Oral Bacterial Profiles and Nitrate Metabolism Contribute to Blood Pressure Regulation in Pregnant Women?

High blood pressure in pregnancy is associated with poor outcomes for both mum and baby, increasing the risk of pregnancy complications including pre-eclampsia, fetal growth restriction and preterm birth. The development of new blood pressure lowering interventions suitable for use in pregnancy is a key research priority.

Inorganic nitrate is a compound found in certain types of food, particularly green leafy vegetables and beetroot. Nitrate provides an important source of nitric oxide (NO), a molecule involved in keeping blood vessels healthy and regulating blood pressure. Supplementation with nitrate in the diet, using interventions such as beetroot juice, has been shown to reduce blood pressure and improve blood vessel function.

In order for dietary nitrate to have these beneficial effects, it needs to be converted in the body to nitrite, via bacteria that live in the mouth (oral bacteria). Differences in oral bacteria, and how they metabolise nitrate, are thought to influence blood pressure regulation and potentially response to dietary nitrate supplementation.

This study aims to understand (1) whether pregnant women with high blood pressure have a different composition of oral bacteria compared to healthy pregnant women and women who are not pregnant, and (2) how differences in oral bacteria affect blood pressure responses to a dose of dietary nitrate (in the form of beetroot juice).

Study Overview

• Status: Completed
• Conditions: Gestational Hypertension
• Intervention / Treatment: Dietary supplement: Beetroot juice

• Study Type: Interventional
• Enrollment (Actual): 55
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United Kingdom
  • Manchester, United Kingdom
    • Maternal and Fetal Health Research Centre, St Mary's Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 16 years to 45 years (Child, Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Normotensive or hypertensive women (hypertension as systolic blood pressure >140 mmHg and/or diastolic blood pressure >90 mmHg OR on anti-hypertensive medication)
• For pregnant women, between 20-28 weeks gestation

Exclusion Criteria:

• Multi-fetal pregnancy (for pregnant women)
• Age under 16, or over 45 years of age
• Lacking ability to consent
• Pre-existing diabetes (Type 1/Type 2)
• Previous history of pre-term FGR (delivery before 32 weeks with FGR)
• Current tobacco smoker
• Body Mass Index greater than or equal to 40 or less than or equal to 18
• Use of any of the following drugs in the last 6 months: systemic antibiotics, antifungals, antivirals or antiparasitics (intravenous, intramuscular, or oral)
• Large doses of commercial probiotics (greater than or equal to 108 cfu or organisms per day) including tablets, capsules, lozenges, chewing gum or powders (ordinary dietary components such as yoghurts do not apply)
• Evidence of oral disease, assessed on screening proforma (current conditions of: oral candidiasis (thrush); Dental caries (tooth decay); Halitosis; Oral ulcerations/mouth ulcers; Wisdom tooth pain; Chronic dry mouth)
• Allergy to beetroot juice or lemon juice (both contained within the juice shot)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Non-Randomized
• Interventional Model: Factorial Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Normotensive pregnant women	Dietary supplement: Beetroot juice; Beetroot juice shot (70mL containing 400mg inorganic nitrate)
Experimental: Hypertensive pregnant women	Dietary supplement: Beetroot juice; Beetroot juice shot (70mL containing 400mg inorganic nitrate)
Experimental: Normotensive non-pregnant women	Dietary supplement: Beetroot juice; Beetroot juice shot (70mL containing 400mg inorganic nitrate)
Experimental: Hypertensive non-pregnant women	Dietary supplement: Beetroot juice; Beetroot juice shot (70mL containing 400mg inorganic nitrate)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Quantity of oral nitrate reducing bacterial species	Assessment of oral bacterial profile using next-generation sequencing (bacterial 16S rRNA sequencing)	Baseline
Oral bacterial nitrate reductase activity	Assessment of oral nitrate reductase activity, measured using enzyme assay	Baseline
Difference between groups in nitrate/nitrite concentrations before and after dietary nitrate dose	Measurement of plasma and salivary nitrate and nitrite concentrations, using high-performance liquid chromatography (HPLC)	Baseline to 2.5 hour post-nitrate dose

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Difference between groups in blood pressure response to dietary nitrate dose	Change in blood pressure	Baseline to 2.5 hour post-nitrate dose

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Correlation between salivary nitrate reductase activities and the change in salivary/plasma nitrite concentrations post-nitrate dose	Change in nitrite vs. baseline nitrate reductase activity	Baseline to 2.5 hour post-nitrate dose
Correlation between changes in plasma nitrite concentrations and blood pressure lowering post-nitrate dose	Change in plasma nitrite vs. change in blood pressure	Baseline to 2.5 hour post-nitrate dose

Collaborators and Investigators

• Sponsor: University of Manchester
• Investigators: Principal Investigator: Jenny Myers, BM, PhD, Manchester University NHS Foundation Trust

Study record dates

Study Major Dates

• Study Start (Actual): June 6, 2019
• Primary Completion (Actual): July 12, 2021
• Study Completion (Actual): March 31, 2022

Study Registration Dates

• First Submitted: April 23, 2019
• First Submitted That Met QC Criteria: April 26, 2019
• First Posted (Actual): April 29, 2019

Study Record Updates

• Last Update Posted (Actual): May 16, 2024
• Last Update Submitted That Met QC Criteria: May 13, 2024
• Last Verified: May 1, 2024

More Information

Terms related to this study

• Keywords: Pregnancy; hypertension; nitrate; beetroot juice
• Additional Relevant MeSH Terms: Cardiovascular Diseases; Vascular Diseases; Pregnancy Complications; Female Urogenital Diseases and Pregnancy Complications; Urogenital Diseases; Hypertension; Hypertension, Pregnancy-Induced
• Other Study ID Numbers: 246813

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No