Arterial stiffness in non-alcoholic fatty liver disease

. Background. The presence of metabolic-associated pathology, namely obesity, diabetes mellitus, dyslipidemia, and non-alcoholic fatty liver disease (NAFLD), significantly accelerates the development of the cardiovascular continuum. This is associated with an increased risk of major cardiovascular events (myocardial infarction, stroke). An important organ damage in hypertension (HTN) is the remodeling of small arteries and an increase in stiffness of large arteries. The relationship between NAFLD, dyslipidemia, hypertriglyceridemia, obesity (especially abdominal), diabetes, and HTN is well studied, but there is a lack of clinical studies examining changes in arterial stiffness in NAFLD. Aim of the research was to study the parameters of arterial stiffness in patients with NAFLD. Materials and methods. Eighty-two Caucasian patients with NAFLD (mean age (56.8 ± 1.1) years, 59.8 % men) were enrolled. Participants were divided into two groups: group 1 (n = 44) — NAFLD and concomitant HTN, group 2 (n = 38) — HTN without NAFLD. All patients underwent a standard general clinical examination, laboratory and instrumental work-up. In addition, all patients were assessed for the parameters of arterial stiffness via non-invasive arteriography. Results. Patients with NAFLD had significantly higher office systolic and diastolic blood pressure (by 15.2 and 10.4 %, respectively, p < 0.01) despite comparable drug therapy. The same trends were observed in relation to the central aortic pressure, which was 19.3 % higher in patients with NAFLD (p < 0.01), and central pulse pressure that was 35.9 % higher than in patients without NAFLD (p < 0.01). Brachial artery augmentation index in NAFLD turned to be elevated compared to patients without NAFLD (p < 0.01), but aortic augmentation index was comparable between groups. The return time interval in group 1 was 50.3 % higher than in group 2 (p < 0.01). Finally, patients with NAFLD had a significant increase in pulse wave velocity by 52.3 % compared to those without NAFLD with average value exceeding 12 m/sec (p < 0.01). Conclusions. There is an association between NAFLD and worse indices of arterial stiffness in patients with concomitant HTN.


Introduction
Pandemic spread of risk factors for cardiovascular diseases (CVD) and metabolically-associated pathology -obesity, diabetes mellitus, dyslipidemia, and non-alcoholic fatty liver disease (NAFLD) is among the central problems of health care at the global level [1,2].The key common features of these conditions are insulin resistance, inflammation, and oxidative stress, although the relationship between them is more multifaceted and not fully understood.NAFLD exacerbates hepatic and systemic insulin resistance, promotes atherogenic dyslipidaemia, induces hypertension (HTN), and triggers synthesis of proatherogenic, procoagulant and proinflammatory mediators that may contribute to the development of CVD and other cardiac/arrhythmic complications [3].The presence of metabolic-associated pathology significantly accelerates the development of the cardiovascular continuum, which is associated with an increased risk of major cardiovascular events (myocardial infarction, stroke).An important organ damage in HTN is the remodeling of small arteries and increased stiffness of large arteries.It is known that insulin resistance significantly accelerates these processes, as well as leads to NAFLD [4].The relationship Gastroenterologìa, ISSN 2308-2097 (print), ISSN 2518-7880 (online) Патологія печінки і жовчовивідної системи / Pathology of Liver and Biliary Excretion System between NAFLD, dyslipidemia, hypertriglyceridemia, obesity (especially abdominal), diabetes, and HTN is well studied, but there is a lack of clinical studies examining changes in arterial stiffness in NAFLD.
The objective was to study the parameters of arterial stiffness (PAS) in patients with NAFLD.

Materials and methods
Eighty-two Caucasian patients with NAFLD (mean age (56.8 ± 1.1) years, 59.8 % men) were enrolled.Study was conducted in accordance with the Declaration of Helsinki of Human Rights (1975 and its revision of 1983), the Council of Europe Convention on Human Rights and Biomedicine and the legislation of Ukraine.Prior to any assessment in the study, a written informed consent was obtained from all subjects.
Participants were divided into two groups: group 1 (n = 44) -NAFLD and concomitant HTN, group 2 (n = 38) -HTN without NAFLD.The diagnosis of NAFLD was established according to the criteria outlined in the unified clinical protocol (Order of the Ministry of Health of Ukraine No. 826 dated November 6, 2014) and EASL-EASD-EASO clinical practice guidelines for the diag nosis and treatment of NAFLD [5,6].All patients underwent a standard general clinical examination (symptoms and history taking, anthropometry, physical examination, including measurement of office blood pressure (BP), electrocardiography and echocardiography at rest, ultrasonography of the liver, routine laboratory examinations, including determining the levels of total and direct bilirubin and liver transaminases).
Diagnosis of HTN was established when there was a sustained office BP elevation ≥ 140/90 mm Hg or office BP was < 140/90 mm Hg in a subject on antihypertensive medication.Upon enrollment, all participants were required to be on standard medical treatment for hypertension in stable doses for at least 2 weeks.In addition, all patients were assessed for PAS via non-invasive arteriography using the Tensiomed Arteriograph device (Tensiomed, Hungary).The study was conducted at rest, in a supine position, after at least 10 minutes of rest.Using an oscillometric method, BP on the dominant arm was measured, and a corresponding sphygmogram was derived, which was then used to calculate the following parameters of peripheral hemodynamics: systolic (SBPb), diastolic, and pulse blood pressure on the brachial artery, augmentation index on the brachial artery (AIxb).The following parameters of central hemodynamics were also recorded: systolic blood pressure and pulse pressure in the aortic root (SBPao and PPao, respectively), augmentation index in the aorta (AIxao), pulse wave velocity (PWV) and return time (RT) of the reflected wave to the aortic root.The study did not enroll subjects in whom it was technically impossible to obtain high-quality sphygmograms, in particular patients with atrial fibrillation, frequent extrasystoles, hypotension at the time of the examination (SBPb less than 90 mm Hg).Patients with stage III-V chronic kidney disease and liver cirrhosis were also not included in the study.
Quantitative characteristics of the studied samples were described by the median and interquartile range or by the arithmetic mean and standard error of the arithmetic mean (M ± m); comparisons between groups were performed using the Mann-Whitney test (for continuous variables) and the Z-test for proportions.Differences were considered significant at p < 0.05.

Results
Clinical data of the patients are shown in Table 1.The studied groups did not differ significantly in terms of age, gender distribution, prevalence of obesity and dyslipidemia.In group 1, the proportion of patients with a longer history of hypertension was significantly higher, by 25.1 %.In general, the profile of risk factors in the groups was similar.Atherosclerotic CVD was present somewhat more frequently in group 1, although the difference did not reach statistical significance.
The studied groups were comparable in terms of concomitant treatment.Thirty patients (68.2 %) from group 1 and 18 (47.4%) from group 2 received renin-angiotensin-aldosterone inhibitors (angiotensin-converting enzyme inhibi tors or angiotensin II receptor blockers), which was not a signifi- The results of the PAS study are shown in Table 2 and Fig. 1.
Patients with NAFLD had significantly higher office SBP and DBP (by 15.2 and 10.4 %, respectively) despite comparable drug therapy.The same trends were observed in relation to central aortic pressure (SBPao), which was 19.3 % higher in patients with NAFLD, and PPao was 35.9 % higher than in patients without NAFLD.Brachial artery augmentation index in NAFLD turned to be higher compared with NAFLD-negative patients, but aortic augmentation index was comparable between two groups.The value of RT in group 1 was 50.3 % higher compared to group 2. Finally, patients with NAFLD had a significant increase in PWV by 52.3 % compared to patients without NAFLD, with average value exceeding 12 m/sec.

Discussion
NAFLD and HTN are often comorbid, with NAFLD affecting up to 40 % of individuals and HTN affecting up to one third of adult population.Data from contemporary clinical studies consistently showed strong relation-ship between NAFLD and HTN.In one recent study [7], 45.65 and 35.12 % of patients with NAFLD had HTN and uncontrolled HTN, respectively.A multivariate analysis demonstrated that NAFLD with concomitant hypertension was associated with increased risk of all-cause mortality (hazard ratio (HR) 1.39, confidence interval (CI) 1.14-1.68,p < 0.01) and CVD mortality (HR 1.85, CI 1.06-3.21,p = 0.03).The deleterious effect of NAFLD/ HTN comorbidity on all-cause and CVD death was even more pronounced in untreated HTN (HR 1.59, CI 1.28-1.96,p < 0.01 and 2.36, CI 1.36-4.10,p < 0.01, respectively).Even treated HTN in the setting of NAFLD was associated with increased risk of all-cause mortality (HR 1.26, CI 1.03-1.55,p = 0.03).In a recent meta-analysis by Ciardullo et al. [8], which aggregated data from 11 longitudinal studies, the presence of NAFLD was found to be associated with an increased risk of incident HTN by 66 % (HR 1.66, CI 1.38-2.01).HTN and NAFLD are related not only at the populational level -there is data suggesting intimate genetic links between the two.In one study [9], it was shown that there was a network proximity between HTN genes and NAFLD genes in a human interactome and data showed HTN genes were more adjacent to NAFLD genes than random genes in the network, indicating a strong association between these two diseases.In was found that 64 genes were involved in the complex relationship between HTN and NAFLD and ALDH1A1 gene was identified as a potential therapeutic target for the treatment of the comorbidity of HTN and NAFLD.
Our study presents data on middle-aged hypertensive overweight/obese subjects.It is worth noting that proportion of subjects with HTN history longer than 5 years was significantly higher in NAFLD group, which mirrors the abovementioned increased risk of the incident HTN in NAFLD.There was a trend towards larger proportion of patients with diabetes and history of atherosclerotic CVD in group 1, although it did not reach statistical significance.In both groups, there were high-risk patients without known atherosclerotic CVD who had three or more conventional risk factors (15.9 % in group 1, 7.9 % in group 2, p = NS).
Despite similar antihypertensive treatment and comparable HR, group 1 demonstrated significantly higher values of office SBP and DBP.This finding may reflect worse overall control of BP in NAFLD-positive patients, possibly due to inferior efficacy of traditional antihypertensive drugs in  NAFLD.The comorbidity of HTN and NAFLD is wellknown, although causal relationship between the two is not straightforward and likely bidirectional [10,11].One putative link may be the low-grade systemic inflammation.The inflammatory background in NAFLD potentiates hepatocyte injury and releases damage-associated molecular patterns in the circulation thereby triggering chronic inflammation.Inflammation is closely associated with the sympathetic system activation, which promotes the activation of the renin-angiotensin system and maintains increased BP and smooth muscle cells growth and remodeling.This mechanism is supported by data from RNA-sequence and microarray dataset from gene cards that shows a higher expression of the RAS components in patients with NAFLD.Additionally, insulin resistance, oxidative stress, and circulation of advanced glycation end products contribute to vascular aging resulting in a sustained increase in blood pressure.Increased arterial stiffness due to altered ratios of cells, intercellular matrix and collagen fibers within the arterial wall is a hallmark of premature vascular ageing.
Our data suggest that accelerated vascular ageing and accompanying increase in arterial stiffness can be the important feature of the clinical pathophysiology in patients with HTN and NAFLD.We observed a consistent increase in central SBP, central pulse pressure and PWV in NAFLD-positive subjects.Increase in SBPao in patients with HTN and NAFLD may be a result of early return of reflected pulse wave to the aortic root as evidenced by increased PWV and RT in this group.Although central augmentation index did not differ between groups, peripheral augmentation index (AIxb) was unfavorable in group 1, which shows increased peripheral vascular resistance in NAFLD-positive patients.Increase in arterial stiffness can be detected before the onset of clinically apparent vascular disease, and altered arterial stiffness is generally recognized now as a subclinical hypertension-mediated organ damage.Arterial stiffness may act as a marker that predicts development of future atherosclerotic disease or may be more directly involved in the process of atherosclerosis.

Conclusions
Presence of NAFLD is associated with increased office BP and more advanced arterial stiffness: increased central BP, PWV and brachial augmentation index.These associations may mechanistically explain the link between NAFLD and increased cardiovascular risk, but further investigations elucidating the exact mechanisms of these associations are needed.www.gastro.org.ua,https://gastro.zaslavsky.com.ua

Figure 1 -
Figure 1 -Office blood pressure and heart rate