Exercise and microvascular health in an ageing population : the EXAMIN AGE study

Background
Cardiovascular (CV) disease remains a major health care burden worldwide. Exercise has a preventive effect on CV disease risk. Risk factors for CV disease include higher age, higher inactivity levels as well as reduced cardiorespiratory fitness. The retinal microcirculation is a valid vascular bed to detect vascular alterations in an early and subclinical stage. Alterations in retinal microvascular phenotype, defined as narrower central retinal arteriolar equivalents(CRAE), wider central retinal venular equivalents (CRVE) as well as reduced flicker light induced dilatation (FID), are associated with increased CV risk. Reactive oxygen species (ROS)production, modulated by DNA methylation of p66Shc, is a key driver for vascular alterations. To date no study exists that investigates the influence of physical activity (PA) or the effect of an exercise intervention on the ageing process of the retinal microcirculation in healthy individuals and patients with increased CV risk.
Aims
The aims of my PhD project were: 1) to investigate the association of long-term PA or inactivity on retinal microvascular phenotype in healthy older individuals, 2) to investigate the association of CV risk on retinal microvascular phenotype in long-term physical inactive older individuals and 3) to investigate the effects of twelve-weeks HIIT on retinal microvascular phenotype in older CV risk patients.
Methods
This PhD based on the “Exercise, Arterial Crosstalk-Modulation, and Inflammation in an Ageing Population” study (EXAMIN AGE). This study investigated the exercise effects in a systems physiology approach with a cross-sectional and an interventional study design. In the crosssectional approach 38 healthy active (HA), 36 healthy sedentary (HS) and 84 sedentary individuals at increased CV risk (SR) were included. SR were randomised into a twelve-week high-intensity interval training (HIIT) or a control condition with standard PA recommendations after the baseline assessment. The Retinal Vessel Analyser was used to measure the retinal microvascular phenotype. Enzyme-linked immunosorbent assay kits were used to analyse plasma 3-nitrotyrosine (3-NT) as a marker of oxidative stress. Gene expression of p66Shc and DNA methylation analysis were assessed in mononuclear cells by real-time quantitative polymerase chain reaction and Methylminer quantitative polymerase chain reaction to detect the epigenetic pathway of oxidative stress, one potential mechanism that affect retinal microvascular phenotype.
Results
Our results demonstrated wider CRAE and narrower CRVE in HA compared to HS resulting in a higher arteriolar-to-venular diameter ratio (AVR). By contrast, SR showed narrower CRAE and wider CRVE compared to HS resulting in a lower AVR compared to HS and HA. HS showed higher FID compared to SR and HA. FID in SR and HA did not significantly differ. A significant correlation between CRVE and maximal oxygen consumption (VO2peak) as well as between AVR and VO2peak were observed. In both sedentary groups, higher p66Shc expression and increased plasma levels of 3-NT were associated with hypomethylation of p66Shc promoter. HIIT reduced body mass index, fat mass, low-density lipoprotein and increased muscle mass and VO2peak. HIIT increased CRAE, decreased CRVE and increased arteriolar FID compared to the control group. A significant association between ΔCRAE and ΔVO2peak, ΔAVR and ΔVO2peak as well as between Δarteriolar FID and ΔVO2peak were observed. HIIT restored promoter methylation, blunting p66Shc expression and 3-NT levels.
Conclusion
Higher PA seems to be associated with favourable microvascular phenotype compared to sedentary individuals, with a further decline in sedentary individuals with increased CV risk. However, the use of FID seems to be limited in highly active individuals, eventually due to predilated arterioles. Therefore, our recommendation is to combine FID with analysis of retinal vessel diameters to differentiate functional non-responders from manifest microvascular endothelial dysfunction and thereby improve individual microvascular risk stratification. Exercise treatment has the potential to counteract microvascular dysfunction in older patients at increased CV risk. Exercise-induced reprogramming of DNA methylation on p66Shc gene promoter may represent a putative mechanistic link whereby exercise protects against age-related oxidative stress. Retinal vessel analysis seems to be a sensitive tool for detecting longterm PA as well as short-term exercise effects on retinal microvascular health in an ageing population.