Causal Mechanisms in Adolescent Arterial Stiffness

Hardening of the blood vessels, called arterial stiffness, is a risk factor for future heart disease and its causes are unclear. The proposed study will 1) randomly assign adolescents at high risk of stiffening blood vessels to take a protein supplement called carnitine and study its effects on arterial stiffening and 2) study carnitine related genes for their effect on arterial stiffening. The study will definitively establish a role for carnitine action as a cause of stiffening blood vessels and signal a way to treat or prevent stiffening.

Study Overview

• Status: Active, not recruiting
• Conditions: Metabolic Syndrome; Dyslipidemias; Pediatric Obesity; Lipid Disorder; Aortic Stiffness; Insulin Resistance Syndrome
• Intervention / Treatment: Dietary supplement: CS+; Dietary supplement: CS-

Detailed Description

Aortic stiffness measured in adolescence or adulthood determines current hypertension, predicts future incidence of hypertension, and future atherosclerotic cardiovascular disease (ASCVD) events. International hypertension guidelines list severe aortic stiffness as grounds to intensify anti-hypertensive pharmacotherapy. Mechanisms of arterial stiffness beyond aging and obesity warrant further elucidation. In our preliminary data from adolescents attending weight-loss summer camps arterial stiffness improvement was not associated with weight change but was with change in circulating carnitine. Carnitine influences fatty acid oxidation and carbohydrate metabolism. Carnitine could therefore link to arterial stiffness through insulin resistance which in turn affects cellular tone, vascular fibrosis, modification of lipids or glucose metabolism, and/or advanced glycation end products. This proposal leverages 2 instrumental variable study designs to infer a causal relation between carnitine and arterial stiffness. First, in 90 youth 11-21 years old at risk of arterial stiffening due to high serum triglycerides(TG), we will conduct a mechanistic, double blinded, randomized controlled trial for the effect of 6 months of oral carnitine supplementation (CS+, n=45) versus placebo (CS-, n=45) on aortic stiffness measured as carotid femoral pulse wave velocity (CFPWV); serum fatty acid oxidation biomarkers by metabolomics analysis; insulin resistance as homeostatic model assessment of insulin resistance (HOMA-IR); and TG. Aim 1 is to compare CS+ versus CS- on change in arterial stiffness and monitor adverse events. The hypothesis CS+ is associated with lower arterial stiffening, and CS+ effect is not modified by sex or race/ethnicity. Aim 2 is to compare the effect of CS+ versus CS- on fatty acid metabolism, insulin resistance, and lipids. The hypothesis is that CS+ alters long chain fatty acid beta oxidation, measured as lower long chain acylcarnitines, which in turn improves (HOMA-IR), and in turn decreases TG levels. This causal chain will be disentangled for direct versus indirect effects on CFPWV change. Second, naturally randomly assorted carnitine single nucleotide polymorphisms (SNPs) noted above will be used to characterize the relationship of carnitine to arterial stiffness and stratify the effectiveness of CS+.Aim 3a is to obtain the direct effect of carnitine on arterial stiffness using Mendelian randomization of SNPs associated with serum carnitine as instrumental variables with the hypothesis these variant SNPs are associated with lower arterial stiffness, supporting a causal inference. Aim 3b is to identify effect modification of CS+ vs CS- on arterial stiffness by examining if a carnitine genetic risk score will modify the effect of CS+ on change in arterial stiffness. This proposal with 2 instrumental variable projects would evaluate a causal role for carnitine in arterial stiffness at a point when the life course trajectory to hypertension can be modified. The study will also investigate the role of carnitine in insulin resistance and dyslipidemia at this same age, which may serve as grounds for future therapeutic clinical trials. Discovering genetically mediated causes of arterial stiffness or other outcomes may facilitate targeting of future therapies on susceptible youth before atherosclerotic changes are irreversible.

• Study Type: Interventional
• Enrollment (Estimated): 90
• Phase: Phase 2

Contacts and Locations

Study Locations

• United States
  • Texas
    • Houston, Texas, United States, 77030
      • Texas Children's Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 13 years to 19 years (Child, Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

1. 11-21 year old adolescents
2. males and females
3. all ethnicities and races
4. fasting serum triglyceride levels over 130 and less than 500 mg/dL
5. fasting low density lipoprotein cholesterol (LDL-C) less than 160mg/dL.

Exclusion Criteria:

1. known seizure disorder
2. renal failure patients requiring renal replacement therapy like dialysis or renal transplant
3. diabetes mellitus type 1 or 2
4. congenital heart disease requiring surgical or catheterization intervention
5. current pregnancy or planned pregnancy during the active study participation
6. incarceration/institutionalized/wards of the state
7. known metabolic disorders that require carnitine therapy
8. nonadherence to study protocol during run-in phase defined as possessing 25% more than the expected remainder of placebo supplement pro-rated to the day of assessment

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Carnitine supplementation (CS+); Carnitine supplementation in liquid form, sugar free.	Dietary supplement: CS+; Oral carnitine supplementation
Placebo Comparator: Placebo (CS-); Placebo comparator liquid similar in appearance and taste to CS+.	Dietary supplement: CS-; Placebo

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Carotid Femoral Pulse Wave Velocity	Carotid Femoral Pulse Wave Velocity will be measured noninvasively using applanation tonometry.	6 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Fasting Triglyceride	Fasting serum triglycerides to be measured using conventional techniques.	6 months
Change in Insulin Resistance	Insulin resistance will be assessed using fasting serum glucose and fasting serum insulin to calculate homeostatic model assessment of insulin resistance.	6 month

Collaborators and Investigators

• Sponsor: Baylor College of Medicine
• Collaborators: National Heart, Lung, and Blood Institute (NHLBI)
• Investigators: Principal Investigator: Justin P Zachariah, MD MPH, Study Principal Investigator

Study record dates

Study Major Dates

• Study Start (Actual): February 1, 2020
• Primary Completion (Estimated): June 1, 2026
• Study Completion (Estimated): August 31, 2026

Study Registration Dates

• First Submitted: October 11, 2019
• First Submitted That Met QC Criteria: October 14, 2019
• First Posted (Actual): October 16, 2019

Study Record Updates

• Last Update Posted (Estimated): December 10, 2025
• Last Update Submitted That Met QC Criteria: December 4, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: insulin resistance; metabolic syndrome; arterial stiffness; dyslipidemia; pediatric obesity
• Additional Relevant MeSH Terms: Nutrition Disorders; Metabolic Diseases; Overnutrition; Body Weight; Glucose Metabolism Disorders; Hyperinsulinism; Overweight; Obesity; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Metabolic Syndrome; Insulin Resistance; Pediatric Obesity; Dyslipidemias; Lipid Metabolism Disorders
• Other Study ID Numbers: H-45557; R01HL148217 (U.S. NIH Grant/Contract)

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