Mitochondrial diseases (MDs) are the commonest group of inborn errors resulting from primary dysfunction of mitochondrial respiratory chain (MRC). High phenolics-containing extra-virgin olive oil (EVOO) can be one of the potential dietary supplements for the treatment of MD. Previous reports demonstrated that phenolics including oleuropein, oleocanthal, hydroxytyrosol and tyrosol found in EVOO have strong antioxidant properties against the oxidative stress in brain tissue and showed a protective effect on mitochondria by restoring mitochondrial enzymatic activities.

This proposed study is an open-label pilot/ feasibility clinical trial using hydroxytyrosol (HT) as dietary supplements in a cohort of 12 MD patients recruited from the Hong Kong Children's Hospital (HKCH).

The objective is to explore the longitudinal effect of receiving hydroxytyrosol (HT) as dietary supplements over a 12-month period and the change on a 6-month period after withdrawal. The applicability of the outcome measures will be evaluated in the current trial for future clinical studies and obtain relevant data for the next phase of the clinical trial on hydroxytyrosol (HT) efficacy. Besides, the tolerability of hydroxytyrosol (HT) in MD patients will be evaluated.

The primary outcome measure is the functional assessment of the patient's clinical outcomes by International Paediatric Mitochondrial Disease Score (IPMDS). Secondary outcome measures included the measurement of biochemical and radiological parameters. Besides, tolerability and quality of life of the subjects will be determined.

Relevant data including the feasibility of subject recruitment, withdrawal rate, feasibility of data collection of outcome measures, longitudinal effect of hydroxytyrosol (HT) on the outcome measures in the trial can be collected and analysed in this pilot study providing important information for the future clinical trials. The ultimate goal is to develop effective therapies to lower mortality, improve the clinical outcomes and quality of life in MD patients.

High phenolics-containing extra-virgin olive oil (EVOO) can be one of the potential dietary supplements for the treatment of MD. There is growing evidence to suggest that daily consumption of EVOO in Mediterranean diets have beneficial effects on preventing neurodegeneration. Previous reports demonstrated that phenolics including oleuropein, oleocanthal, hydroxytyrosol and tyrosol found in EVOO have strong antioxidant properties against the oxidative stress in brain tissue and protective effect on both acute and chronic neurodegenerative diseases by in vitro study and animal models. In addition to improvement of arsenic-induced oxidative stress by oleuropein or hydroxytyrosol treatment, hydroxytyrosol also showed a protective effect on mitochondria by restoring mitochondrial enzymatic activities in rat brain. In vitro study also demonstrated the stimulatory effect of hydroxytyrosol on mitochondrial function including in mouse 3T3-L1 adipocytes and human endothelial cells. A recent reported clinical study showed that consumption of olive oil could increase mitochondrial membrane fluidity and ATPase activity in patients with relapsing-remitting multiple sclerosis, a neurodegenerative disease associated with mitochondrial dysfunction.

Mitochondrial diseases (MDs) are the commonest group of inborn errors with a minimal prevalence of 12.5 per 100,000 and 4.7 per 100,000 adults and children respectively. These diseases are resulted from primary dysfunction of mitochondrial respiratory chain (MRC) which is mostly caused by both nuclear and mitochondrial DNA defects. They are progressive, multisystem disorders that can affect many parts of the body including brain, nerve, muscle, kidney, heart, liver, eyes, ears or pancreas and some are devastating or even life threatening. Development of effective treatments for the patients is an unmet need until now. Effective treatment strategies and clinical trials are limited, and therapies are mostly palliative. Drug developments and clinical trials for these diseases are scarce in Hong Kong when compared with other countries.

MDs are extremely heterogeneous phenotypically and genetically with the biochemical dysfunction and pathogenic mechanisms being unique in each individual molecular defect. With the advance in next generation sequencing, over 300 mitochondrial genes are implicated to cause human diseases. This wide heterogeneity has been hindering the development of new therapeutic strategies such as gene therapy which requires long term evaluation and substantial manipulation to improve efficacy and reduce toxicity risk. It is therefore not efficient nor realistic to develop unique therapy targeting at a specific molecular defect.

The future pharmaceutical development for treating mitochondrial dysfunctions will focus on boosting the residual mitochondrial function by non-specific bypassing the defective components of MRC or improving the aberrant cellular consequences. Dietary supplements were demonstrated to treat MD owing to their roles as metabolic cofactors to ameliorate mitochondrial ATP production, bypass mitochondrial complex defects and remove toxic metabolites. However, there are few randomized controlled trials to assess the cause-effect relationship of these dietary supplements.

The present study is a feasibility clinical trial to explore the longitudinal effect of receiving hydroxytyrosol (HT) as dietary supplements on primary and secondary outcomes (clinical, biochemical and radiological parameters and quality of life) and tolerability in MD patients in Hong Kong. The investigators aim to obtain relevant data to determine the sample size and treatment duration for the next phase of the clinical trial on hydroxytyrosol (HT) efficacy. Another aim of this study is to evaluate the applicability of the outcome measures in the current study for future clinical trials on different treatment strategies.

This pilot study will be a longitudinal, open label study. Twelve subjects will be recruited, including MD patients with confirmed MD-associated nuclear DNA or mtDNA mutations, from the Hong Kong Children's Hospital (HKCH). Subjects will receive hydroxytyrosol (HT) daily as dietary supplements for 12 months. After that, patients will be randomly assigned in 1:1 ratio to either continue on or withdraw from receiving hydroxytyrosol (HT) as their dietary supplements for another 6 months.

Hydroxytyrosol (HT) dosage are based on the past clinical trials in humans and the NOAEL. The willingness of the participants to stay in the trial in terms of the percentage of participants completing the whole trial on hydroxytyrosol (HT) dietary supplement will be assessed. The withdrawal rate in different study periods and the reasons of withdrawal will be further studied.

Subjects will visit the trial site at different time points after the start of dietary supplements for clinical follow up, functional assessment including questionnaire, blood and urine sampling and neuroimaging as primary and secondary outcome measures. There will be more frequent follow-up and monitoring after initiation and withdrawal of supplements. Data of primary and secondary outcome measures (except radiological evaluation) will be collected before the trial as baseline, 2 weeks, 6 weeks, 3, 6, 9, 12 months after the commencement of the trial and 2 weeks, 6 weeks, 3 and 6 months after randomization. The investigators will examine the feasibility of collecting data on the primary and secondary outcome measures in a clinical trial condition. The amount of missing data, the reason for the missing and difficulties on those data collection will be evaluated.

An open label trial is used for this proposed study because a matching placebo with the same properties, such as taste, smell, colour, etc, as hydroxytyrosol (HT) to keep blindness is not yet developed at this moment. Therefore, a withdrawal design will be used even though this can be a limitation of this study because of the easy accessibility of hydroxytyrosol (HT) by the patients who can continue to use EVOO on their own after being assigned for withdrawal, which may potentially affect the outcome. Information on any deviation from the study protocol on this issue can be collected from the patients by questionnaires at the end of the study to guide the data analysis and interpretation.

Inclusion criteria

1. Subject (aged 3-18 years) is confirmed to have pathogenic MD-associated nuclear DNA or mtDNA mutations.
2. Subject is willing and able to comply with all requirements of the clinical trial.
3. Subject is given enough time and opportunity to consider his/her participation and has signed his/her written consent.

Exclusion criteria

1. Subject is participating or has participated within the last 2 months in any clinical trial involving hydroxytyrosol (HT) or hydroxytyrosol (HT) -associated phenols as dietary supplements.
2. Subject has a medical condition which can be exacerbated by hydroxytyrosol (HT) or hydroxytyrosol (HT) -associated phenols.
3. Subject has allergy to olive oil.
4. Subject is pregnant.