The Intravenous Amino Acid Therapy for Vascular Rigidity in End Stage Renal Disease

Background and Rationale Patients with end-stage renal disease (ESRD) who require chronic hemodialysis (HD) face one of the highest cardiovascular mortality rates of any patient population. Despite advances in dialysis technology, medications, and supportive therapies, cardiovascular disease (CVD) accounts for approximately 40-50% of deaths in this group. The excess risk reflects not only traditional risk factors such as hypertension, diabetes, and dyslipidemia but also non-traditional mechanisms that are unique to uremic conditions. Among these, protein carbamylation has emerged as a key biochemical driver of vascular dysfunction and accelerated aging.

Carbamylation is a post-translational modification caused by the reaction of isocyanic acid, a urea-derived metabolite, with free amino groups of proteins. In ESRD, chronically elevated urea concentrations amplify this process. Carbamylation alters structural proteins of the extracellular matrix (collagen, elastin, fibronectin), lipoproteins (LDL, HDL), and clotting factors (fibrinogen, von Willebrand factor), leading to impaired vascular compliance, thrombogenicity, and inflammation. In parallel, carbamylation of endothelial enzymes reduces nitric oxide bioavailability, tipping the balance toward vasoconstriction and hypertension.

Another consequence of carbamylation is the acceleration of cellular senescence. Vascular endothelial and smooth muscle cells exposed to carbamylation undergo growth arrest, increased oxidative stress, and adopt a pro-inflammatory secretory phenotype. Senescent cells amplify vascular inflammation, promote calcification, and further stiffen arteries. Together, these mechanisms establish a vicious cycle of vascular aging in HD patients.

Why Amino Acid Supplementation? During each dialysis session, patients lose 5-12 g of free amino acids into the dialysate. This loss deprives the circulation of natural carbamylation scavengers. Without sufficient free amino acids, reactive isocyanates are more likely to modify proteins. Replacing amino acids intravenously during dialysis directly addresses this imbalance.

• Biochemical rationale: Free amino acids act as competitive substrates for isocyanates, reducing carbamylation of critical structural and functional proteins.
• Physiological rationale: Amino acids, especially arginine, contribute to nitric oxide production, improving vasodilation and endothelial function.
• Clinical evidence: Small pilot studies have shown that amino acid supplementation reduces levels of carbamylated albumin and improves surrogate markers of vascular health. However, no adequately powered randomized trial has tested whether this strategy improves hard outcomes in ESRD.

The NASCAR-PLUS trial (The Intravenous Amino Acid Therapy for Vascular Rigidity in End-Stage Renal Disease) is designed to fill this gap by testing whether intravenous amino acid therapy administered during dialysis can reduce vascular stiffness, improve cardiovascular outcomes, and prolong survival in ESRD patients.

Study Design

The NASCAR-PLUS trial is a multicenter, randomized, double-blind, placebo-controlled clinical trial conducted at five dialysis centers in Norway.

• Population: 104 patients with ESRD undergoing chronic HD or online hemodiafiltration (HDF), on stable treatment regimens for at least 90 days prior to enrollment.
• Randomization: 1:1 allocation to amino acid supplementation or placebo, stratified by site and diabetes status.
• Blinding: Double-blind design, with indistinguishable infusion bags prepared by an unblinded pharmacist.
• Treatment duration: 12 months of intervention, followed by 6 months of observational follow-up.
• Sample size: Powered to detect a clinically meaningful reduction in pulse wave velocity of 0.5 m/s with 80% power at a significance level of 0.05, accounting for dropouts.

Interventions

• Intervention arm: Intravenous Synthamin 9® (Baxter), 250 ml containing 13.7 g amino acids. Administered during the first hour of two weekly dialysis sessions.
• Placebo arm: Intravenous infusion of 0.9% NaCl, 250 ml, under identical conditions.

Infusions are delivered via the venous line of the dialysis circuit. Patients are observed during and after administration for infusion-related reactions.

Clinical Assessments The trial integrates state-of-the-art cardiovascular phenotyping to capture structural, functional, and biochemical effects of the intervention.

Imaging and Functional Assessments

• Pulse Wave Velocity (cf-PWV) and Augmentation Index: Non-invasive gold-standard measures of arterial stiffness performed at baseline, 6 months, and 12 months.
• Coronary Artery Calcium (CAC) Scoring and CT Angiography: Performed at baseline and 12 months to quantify coronary calcification and plaque burden.
• Echocardiography: Comprehensive transthoracic assessments including left ventricular ejection fraction (LVEF), global longitudinal strain (GLS), LV mass, diastolic function (E/e'), and left atrial volume.
• 24-hour Holter ECG: Conducted in a subset of patients at baseline and 12 months to detect arrhythmias and evaluate heart rate variability.

Biomarkers and Biobanking

Blood samples are collected at baseline, months 3, 6, 12, and 18. Analyses include:

• Carbamylation markers: Carbamylated albumin, carbamylated LDL, and free amino acid profiles.
• Inflammation markers: CRP, IL-6, TNF-α, myeloperoxidase.
• Oxidative stress markers: F2-isoprostanes, malondialdehyde, oxidized LDL.
• Vascular injury markers: ICAM-1, VCAM-1, E-selectin.
• Senescence markers: p16^INK4a, p21^CIP1, and senescence-associated secretory phenotype cytokines.

All samples are stored in the Haukeland University Hospital Biobank, creating a long-term research resource for secondary and exploratory studies.

Patient-Reported Outcomes

Quality of life and functional capacity are assessed with validated questionnaires:

• MacNew Heart Disease Health-Related Quality of Life Questionnaire.
• SF-36 Health Survey.
• EQ-5D-5L.

Assessments are performed at baseline, 12 months, and 18 months.

Data Management and Analysis

Data are collected in electronic case report forms (eCRFs) with built-in monitoring and quality checks. All data are anonymized and stored securely in compliance with GDPR and Norwegian data protection laws.

• Primary endpoint analysis: All-cause mortality at 12 months, analyzed with Cox proportional hazards regression, Kaplan-Meier survival curves, and log-rank tests.
• Secondary endpoint analyses: Mixed-effects models for repeated measures (PWV, echocardiography, biomarkers), linear regression for CAC progression, and non-parametric tests for biomarker distributions.
• Subgroup analyses: Pre-specified by diabetes status, baseline inflammation, and dialysis modality.
• Interim analyses: Performed by an independent monitoring board, focusing on safety and feasibility.

Safety Monitoring

Safety is overseen by the clinical investigator team and an independent safety monitoring board. Key elements include:

• Continuous monitoring for infusion-related reactions (hypotension, flushing, nausea, chest discomfort).
• Regular recording of vital signs pre- and post-infusion.
• Adverse events graded according to CTCAE criteria.
• Immediate discontinuation of study drug in cases of serious adverse reaction, with continued safety follow-up.

Patients may withdraw at any time without impact on their standard medical care.

Risk Assessment and Feasibility

The trial builds on strong feasibility data:

• Pilot studies show that amino acid infusions are well tolerated and feasible in the dialysis setting.
• Recruitment is supported by five collaborating centers across Norway, ensuring diversity and robust enrollment.
• Sample size is moderate, but endpoints are designed to capture both survival and mechanistic improvements.

Potential risks include under-recruitment, infusion-related reactions, and dropouts. To mitigate these risks, the trial employs centralized coordination, trained dialysis staff, and standardized operating procedures.

Significance and Impact

If successful, the NASCAR-PLUS trial will provide the first definitive evidence that intravenous amino acid therapy can:

• Reduce carbamylation and its downstream vascular effects.
• Improve vascular stiffness and cardiac function in ESRD.
• Lower mortality and cardiovascular events in a high-risk population.
• Enhance patient-reported quality of life.

This low-cost, easily implementable therapy could be rapidly integrated into clinical practice worldwide. The mechanistic insights and biobank data will also guide the development of future therapies targeting carbamylation and vascular senescence, with potential relevance not only to kidney disease but also to aging-related cardiovascular and neurodegenerative disorders.

Inclusion criteria

• Age ≥18 years.
• Diagnosis of end-stage renal disease (ESRD) and undergoing maintenance hemodialysis (HD) or online hemodiafiltration (HDF).
• On a stable dialysis regimen for a minimum of 90 consecutive days prior to enrollment.
• Serum albumin level ≥30 g/L.
• Documented dialysis adequacy: single-pool Kt/V (spKt/V) > 1.2.
• Able to understand study procedures and provide written informed consent.

Exclusion criteria

• Administration of parenteral amino acids or intravenous nutrition within the past 90 days.
• Severe hypertension (e.g., SBP >180 mmHg despite antihypertensive therapy).
• Advanced liver disease classified as Child-Pugh class C.
• Diagnosis of active malignancy or cancer treatment within the last 5 years.
• Current participation in another interventional study or within the past 30 days.
• Pregnant or breastfeeding women.
• Psychiatric or cognitive impairment that interferes with informed consent or study compliance.
• Life expectancy <12 months due to unrelated comorbidities.