Monitoring the skin NADH changes during ischaemia and reperfusion in humans

Abstract

Nicotinamide adenine dinucleotide (NADH/NAD+) is involved in many important biochemical reactions in human metabolism, including participation in energy production by mitochondria. Flow Mediated Skin Fluorescence (FMSF) is a non-invasive method to study dynamic changes in the content of the reduced form of NADH by measuring the optical properties of NADH related to the emission of the autofluorescent light (460 nm) after an earlier excitation by ultraviolet light. This review summarises the available studies using this method to describe its potential and limitations.

Non‐invasive in vivo human model of post‐ischaemic skin preconditioning by measurement of flow‐mediated 460‐nm autofluorescence

“…However, the total amount of NAD (sum of NADH and NAD+) should remain stable over a short time in our experiment. 23 Thus we may indirectly conclude on the NAD+ content.…”

“…21,47 We have previously reported that the brachial artery's occlusion increases the intensity of skin 460-nm fluorescence accompanied by a cessation of microvascular blood flow as measured by laser Doppler. 18,23 During reperfusion, the restoration of arterial blood flow to the forearm causes an immediate increase in the microvascular blood flow with a short, approximately 20-second, hyperaemic response. Although the 460-nm fluorescence drops instantly at the beginning of reperfusion, this signal's intensity does not recover to the baseline level for over 2-5 minutes.…”

“…Further screening involved detailed history, physical examination, including brachial blood pressure measurement at rest in a sitting position and a 12‐lead standard ECG. Thirty individuals were excluded for one of the following reasons: current smoker or nicotine vape user; a suspicion of hypertension (systolic blood pressure (SBP) at least 140 mmHg or diastolic blood pressure (DBP) at least 90 mmHg); recent viral infection of the respiratory tract; skin rash or skin tattooing on the left forearm; no visible increase of the 460‐nm fluorescence curve during ischaemia phase (typically, ischaemia induces an increase of this fluorescence); 23 or movement of the forearm during any stage of the fluorescence signal recording. All participants were asked to avoid caffeine and alcohol consumption in any form and avoid intensive physical exercise 24 hours before the study.…”

“…Inflation of the brachial cuff is designed to induce transient ischaemia. The cuff is inflated for 100 seconds with the pressure set at 60 mmHg above pre‐test resting SBP 16,23 . Such cuff pressure compresses the brachial artery, effectively stopping the blood flow to the forearm distal to the occlusion.…”

“…The cuff is inflated for 100 seconds with the pressure set at 60 mmHg above pre-test resting SBP. 16,23 Such cuff pressure compresses the brachial artery, effectively stopping the blood flow to the forearm distal to the occlusion. Next, the brachial cuff's instant deflation restores blood flow through the brachial artery and its peripheral branches with rapid reperfusion.…”