Background
Fabry disease (FD) is a rare, X-linked hereditary disease of lipid metabolism. The genetic change in the GLA gene results in the absence or reduced activity of the lysosomal enzyme α-galactosidase A (α-Gal A). As a result, glycosphingolipids, mainly globotriaosylceramide (Gb3) and its deacylated toxic metabolite lyso-Gb3, accumulate in many cells in the body, leading to damage of many organs. The lifespan of patients is significantly shortened, in men by about 15 years and in women by about 5 years. The cause of mortality is mainly cardiovascular complications. There are conflicting and deficient data in the literature on the involvement of the cardiovascular system in FD, especially regarding the presence of atherosclerosis.
Telomeres are specialized DNA structures that are located at the ends of chromosomes and protect them from damage and prevent them from sticking to adjacent chromosomes. Telomerase is an enzyme that maintains the length of the telomere. Leukocyte telomere length (LTL) and telomerase activity (TA) are used as markers of “cellular” aging. There is more evidence of an association between LTL and age-related diseases, such as: cancer, atherosclerosis, diabetes, and heart failure. The main cause of LTL shortening in chronic diseases is thought to be inflammation and oxidative stress. Despite the fact that FD is characterized by premature death, the possible premature and / or accelerated aging in FD has not yet been studied. Accelerated aging has been described in chronic diseases with chronic inflammation, oxidative stress, immune system dysfunction, telomere shortening, and the development of progressive kidney and heart disease. All of these factors, except telomere shortening, have been shown to play an important role in pathophysiology and in FD progression.
Aim and hypotheses of study
Telomere length has been shown to be shorter in a variety of conditions associated with cellular stress, including oxidative stress and inflammation. In untreated patients with FD, chronic renal failure, cardiovascular and cerebrovascular complications cause premature mortality. The central purpose of the doctoral thesis is to define the cardiovascular risk of patients with FD and its association with biological markers of inflammation, oxidative stress, and telomere lengths. In patients with FD, we would like to define the links between these parameters according to gender, treatment, and the degree of disease most commonly expressed by the degree of renal impairment. With this we want to test the following hypotheses:
1. Telomere length is shorter in patients with FD than in healthy subjects of the same age.
2. Patients with FD differ from the healthy population in cardiovascular impairment assessed by noninvasive examinations.
3. Cardiovascular impairment and LTL also differ between patients with FD according to gender, enzyme replacement therapy (ERT) and the degree of disease expressed by the degree of renal impairment.
We expect to use LTL measurements to prove an older biological age than their chronological one. LTL could be a biomarker of cardiovascular risk and biological vascular aging in FD. By measuring LTL and TA, which have not yet been studied in FD, we could, together with chronological years, explain interindividual variations in susceptibility to cardiovascular disease in FD. LTL measurements could also be used to infer the prognosis of the disease in an individual patient.
Methods and subjects
The study included 33 patients with FD (13 men and 20 women, mean ages 44.6 years and 45.3 years) and 66 healthy subjects matched by age, sex, body mass index, smoking status, and presence. arterial hypertension. We performed anthropological measurements on all of them, took blood to determine basic laboratory blood tests, serological markers of inflammation, and blood to determine LTL and TA. We performed ultrasound examinations of the carotid arteries, arteries of the extremities and heart in addition to stress testing on a bicycle. The functional status of the vessels was assessed by measuring endothelial function (FMD). The described parameters in Fabry patients were compared with healthy controls. In addition, patients with FD were also compared with each other according to gender, enzyme replacement therapy (ERT) and disease stage defined as the degree of renal impairment.
Results
Telomere length and telomerase activity
Patients with FD had a statistically shorter (p = 0.015) mean LTL (0.68; IQR 0.58–0.81) than healthy controls (0.72; IQR 0.52–0.98). This difference was present only in male patients (p = 0.02) and not in female patients, which could be due to the fact that men with FD are generally more affected.
TA was statistically significantly higher in patients (1.55 ± 1.002) compared to the control group (1.19 ± 0.104) (p = 0.047). However, the differences were statistically significant (p = 0.005) higher values only in patients, while the differences were not statistically significant in the patients. There were no statistically significant differences in LTL and TA between patients. Renal impairment did not affect LTL, and TA was statistically significantly (p = 0.003) reduced in the group of patients with advanced renal impairment. LTL and TA were not affected by ERT treatment. The LTL of patients with FD decreased statistically significantly with age, but only in male patients. LTL and TA were not associated with any of the observed cardiovascular or inflammatory parameters. TA was inversely related to age in patients with FD.
Morphological and functional examinations of the cardiovascular system
Patients had statistically larger common carotid artery (ACC), internal carotid artery (ACI) diameters (p <0.001), and aortic bulb diameter (p = 0.001). IMT (intima - media thickness) was thickened in most of the measured arteries, but important only in ACC (p = 0.021) compared to controls. Atherosclerotic deposits in the carotid arteries were found in only three elderly female patients with FD, which was significantly less than in controls (p <0.001). FMD (measurement of endothelium-dependent dilatation) was statistically lower than in controls (p = 0.001). Patients had statistically significant cardiac muscle hypertrophy and left ventricular diastolic dysfunction. Systolic function was preserved. Functional parameters (maximum physical activity, maximum load, maximum heart rate) were significantly reduced in patients. In men with FD, the changes were more pronounced than in women. In patients with advanced renal impairment, significant differences were noted with increased diameters in all examined vessels and biochemical, morphological, and functional signs of advanced heart disease present.
Patients had statistically higher plasma levels of the following circulating markers of inflammation: TNF-α, IL-6, hsCRP, VCAM-1, and lower levels of E-selectin than controls. The values of these parameters were higher in patients than in female patients. All markers of inflammation were elevated in patients with advanced compared with those with mild renal impairment.
Conclusions
Our study is the first in the field of rare metabolic diseases, where we demonstrated that patients with FD have significantly shorter LTL and higher TA than the healthy population. With shortened LTL, TA was increased, but this increase was statistically significant only in female patients and not in male patients who were also more affected by the disease. The probable influence of the disease stage is also indicated by the fact that elevated TA values were present only in patients with a milder form of the disease, while in patients with more advanced disease the TA values were significantly reduced. One possible explanation could be that the increased TA is a protective mechanism against shortening of the LTL, which is depleted as the disease progresses over the years. The results of the study also showed differences in the measured TA values according to the degree of renal impairment.
This study is also the first presentation of the morphological and functional characteristics of the cardiovascular system in patients with FD in Slovenia. Cardiovascular involvement in our patients with FD is manifested by dilated arterial diameters, thickened IMT, impaired endothelial function in the absence of atherosclerotic plaques, left ventricular hypertrophy and diastolic dysfunction, and elevated TNF-h, ILP 6 -1 and reduced E-selectin content. Most of these changes were more pronounced in male patients and in patients with a more advanced stage of renal impairment. As a rule, FD affects men more than women, and we also found a more pronounced form of the disease in men as expected in our subjects. Given the proven extensive morphological and functional changes of the arteries (especially impaired endothelial function), a high rate of atherosclerotic changes would be expected in patients with FD, while atherosclerotic plaques were not present in our patients. It is possible that FD has a different phenotype of vascular involvement as well as atherosclerosis. Since it is known that the advanced form of the disease involves extensive irreversible fibrotic changes also in the blood vessels, we explained that these changes in the intima and media prevent the accumulation of cholesterol and the formation of plaques. However, further research will be needed to confirm this hypothesis, as these observations are also clinically very important.
We found that in patients with FD there are some changes that show signs of premature aging: signs of cellular aging (decreased LTL), arterial phenotype (dilated arteries with thickened wall and endothelial dysfunction) and cardiac (left ventricular hypertrophy and diastolic dysfunction) and signs of activation of pathophysiological mechanisms of aging (activation of inflammation and oxidative stress).
The study identified some new features of FD that could be useful in the pathophysiology and assessment of FD progression.
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