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NCT Number: NCT07134673

Mitochondrial Function in Peripheral Blood Mononuclear Cells, Muscle, and Skin of Long COVID Patients

Mitochondria are structures inside cells that are responsible for producing energy from nutrients through a series of steps, using oxygen. To have an idea of how well the mitochondria can produce energy, we can measure how much oxygen they use. The goal of this study is to:

1. To compare the oxygen use between people with long COVID and people who completely recovered after COVID-19, using three techniques that measure the oxygen use in blood cells, on the skin and in the muscle 2. To test how similar these three techniques are in measuring the oxygen used in the three different tissues

Participants will:

* Complete surveys, * Wear an activity tracker (7 days), * Undergo several non-invasive tests, and * Donate a blood sample The study will take place in UZ Brussel hospital and will take 2 study visits, approximately 7 days apart.

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Key information

Conditions

Long COVID COVID-19 Chronic Disease Coronaviridae Infections Coronavirus Infections Disease Attributes Infections Lung Diseases Metabolic Diseases Mitochondrial Diseases Nidovirales Infections Nutritional and Metabolic Diseases Pathologic Processes Pathological Conditions, Signs and Symptoms Pneumonia Pneumonia, Viral Post-Acute COVID-19 Syndrome Post-COVID-19 Condition Post-Infectious Disorders RNA Virus Infections Respiratory Tract Diseases Respiratory Tract Infections Virus Diseases

Age range

18 year and older

Sex eligibility

All sexes

Study type

Observational

Primary location

Laarbeeklaan 101

Jette, Brussels Capital, 1090, Belgium

Location status: Recruiting

Location contact

Berenice G. Jimenez Garcia, MSc.

CONTACT

[email protected]

+3224749624

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Individuals with long COVID:

Inclusion criteria

  • Long COVID diagnosis, based on the WHO definition;
  • Presence of long COVID symptoms for a minimum of 6 months.
  • History of confirmed or documented SARS-CoV-2 infection.
  • Adult (≥18 years of age).
  • Post-COVID-19 Functional Status Scale grade 2-4, while they had a grade 0 before the SARS-CoV-2 infection.

Exclusion criteria

  • Pre-existing chronic diseases potentially affecting the functional status scale.
  • Treatment with metabolism altering drugs.
  • > 10 standard units of alcohol (10 grams of alcohol/glass) per week.
  • Unable to understand oral and written instructions in Dutch, French or English.
  • Allergies to medical adhesive bandages.
  • Porphyria and other skin conditions aggravated by sunlight.

Convalescent individuals

Inclusion criteria

  • History of confirmed or documented SARS-CoV-2 infection.
  • Complete recovery after the SARS-CoV-2 infection, no history of long COVID based on the WHO definition;
  • Post-COVID-19 Functional Status Scale [2] grade 0 both before the infection and currently.
  • Adult (≥18 years of age).

Exclusion criteria

  • Pre-existing chronic non-communicable diseases (e.g. hypertension, chronic respiratory diseases, diabetes).
  • Treatment with metabolism altering drugs.
  • > 10 standard units of alcohol (10 grams of alcohol/glass) per week.
  • Unable to understand oral and written instructions in Dutch, French or English.
  • Allergies to medical adhesive bandages.
  • Porphyria and other skin conditions aggravated by sunlight.

Treatment and study plan

Primary outcomes

  1. Basal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress test analysis of the peripheral blood mononuclear cells (PBMCs)

  2. Tissue Saturation Index (TSI)

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Near-infrared spectroscopy

  3. Mitochondrial oxygen tension (mitoPO2) (mmHg/s)

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Cellular Oxygen Metabolism monitoring

  4. Mitochondrial oxygen consumption (mitoVO2)

    Time frame: Second study visit (minimally 7 days after the first study visit)

    Cellular Oxygen Metabolism monitoring

Secondary outcomes

  1. Proportion of participants meeting the criteria for PEM

    Time frame: Second study visit (minimally 7 days after the first study visit)

    De Paul Symptom Questionnaire - Post-exertional malaise (DSQ-PEM)

  2. General fatigue

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Multidimensional Fatigue Inventory (MFI-20)

  3. Physical fatigue

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Multidimensional Fatigue Inventory (MFI-20)

  4. Mental fatigue

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Multidimensional Fatigue Inventory (MFI-20)

  5. Reduced activities

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Multidimensional Fatigue Inventory (MFI-20)

  6. Reduced motivation

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Multidimensional Fatigue Inventory (MFI-20)

  7. Severity and impact of fatigue on daily life

    Time frame: Second study visit (approximately 7 days after the first study visit)

    The Fatigue Severity Scale (FSS) contains nine statements that rate the severity of the fatigue symptoms. The statements are rated from 1 to 7, with a low value indicating strong disagreement with the statement and a high value indicating strong agreement with the statement. The total score is the sum of the individual scores, with a higher score indicating a greater impact of fatigue on daily life.

  8. Symptom burden (θ)

    Time frame: First study visit

    Item Response Theory (IRT) will be applied to estimate a latent trait representing symptom burden, using Section 2.6 of the WHO Post-COVID-19 Case Report Form. Symptoms will be coded as binary variables (1 = symptom present, 0 = symptom absent). IRT modeling will be used to derive a latent trait estimate (θ) for each individual, reflecting the overall severity or burden of symptoms.

  9. Resting Energy Expenditure (kcal/kg body weight/day)

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Indirect calorimetry will be used to measure the Resting Energy Expenditure (kcal/day). This value will be divided by the body weight (kg) on that same day.

  10. Basal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor Etomoxir is used

  11. Basal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor UK5099 is used

  12. Basal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor BPTES is used

  13. Maximal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress Test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor Etomoxir is used

  14. Maximal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress Test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor UK5099 is used

  15. Maximal Oxygen Consumption rate (pmol O2/min)

    Time frame: Blood sample is taken during the second study visit (approximately 7 days after the first study visit) and the PBMCs are cryopreserved until analysis (after all participants have been recruited, estimated to be within 1 year of the start of the study)

    Seahorse XF Substrate Oxidation Stress Test analysis of the peripheral blood mononuclear cells (PBMCs) after substrate pathway inhibitor BPTES is used

  16. Respiratory Quotient

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Indirect calorimetry

Other outcomes

  1. Weight (kg)

    Time frame: Second study visit (approximately 7 days after the first study visit)

    Body weight (kg) in light indoor clothes without shoes.

Study contacts

Contact information is provided by the study sponsor or research team.

Berenice G. Jimenez Garcia, Master of Science

CONTACT

[email protected]

+3224749624

Sponsors and collaborators

Lead sponsor

Universitair Ziekenhuis Brussel

Other

Registry information

Official study title

Mitochondrial Oxygen Consumption and Substrate Utilisation In Vitro in Peripheral Blood Mononuclear Cells, and In Vivo on Muscle and Skin in Long COVID Patients and Convalescent Individuals: A Case-Control and Diagnostic Accuracy Study

Acronym: MitoLoCo

Important dates

Study start
2026
Primary completion
2026
Study completion
2026
First posted
Aug 21, 2025
Registry last updated
Apr 22, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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