Cutaneous Respirometry as Novel Technique to Monitor Mitochondrial Function: A Feasibility Study in Healthy Volunteers

BACKGROUND: The protoporphyrin IX-triplet state lifetime technique (PpIX-TSLT) is proposed as a potential clinical non-invasive tool to monitor mitochondrial function. This technique has been evaluated in several animal studies. Mitochondrial respirometry allows measurement in vivo of mitochondrial oxygen tension (mitoPO(2)) and mitochondrial oxygen consumption (mitoVO(2)) in skin. This study describes the first use of a clinical prototype in skin of humans. METHODS: The clinical prototype was tested in 30 healthy volunteers. A self-adhesive patch containing 2 mg 5-aminolevulinic acid (ALA) was applied on the skin of the anterior chest wall (sternal) for induction of mitochondrial protoporphyrin IX and was protected from light for 5 h. MitoPO(2) was measured by means of oxygen-dependent delayed fluorescence of protoporphyrin IX. MitoVO(2) was determined by dynamic mitoPO(2) measurements on the primed skin, while locally blocking oxygen supply by applying local pressure with the measurement probe. MitoPO(2) was recorded before and during a 60-s period of compression of the microcirculation, at an interval of 1 Hz. Oxygen consumption (i.e. the local oxygen disappearance rate) was calculated from the decay of the mitoPO(2) slope. RESULTS: Oxygen-dependent delayed fluorescence measurements were successfully performed in the skin of 27 volunteers. The average value (± SD) of mitoPO(2) was 44 ± 17 mmHg and mean mitoVO(2) values were 5.8 ± 2.3 and 6.1 ± 1.6 mmHg s(-1) at a skin temperature of 34°C and 40°C, respectively. No major discomfort during measurement and no long-term dermatological abnormalities were reported in a survey performed 1 month after measurements. CONCLUSION: These results show that the clinical prototype allows measurement of mitochondrial oxygenation and oxygen consumption in humans. The development of this clinically applicable device offers opportunities for further evaluation of the technique in humans and the start of first clinical studies.