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Non-alcoholic fatty liver disease (NAFLD) is a metabolic liver disease, which classically includes a spectrum of progressive pathological conditions, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH) with different grades of fibrosis and cirrhosis. NAFLD is also a “multisystemic” disease, NAFLD is independently associated with serious hepatic complications (e.g., hepatic decompensation, hepatocellular carcinoma [HCC]), but also with an increased risk of developing cardiovascular disease (CVD).
(a) hepatic lipid accumulation (e.g., di-acyl glycerol [DAG]) in NAFLD patients impairs insulin signalling, thereby conditioning insulin resistance (IR) through different mechanisms, including the inhibition of phosphorylation of insulin receptor substrate-1 (IRS-1) [1] and the activation of protein kinase C (PKC)-e that can inhibit the action of insulin receptor and promote the lipid accumulation [2]. In particular, hepatic and systemic insulin resistance is one of the primary mechanisms for inducing atherogenic lipoproteins and dysglycaemia. Notably, both atherogenic dyslipidemia and dysglycaemia mediate CVD risk in NAFLD patients with T2DM;
(b) the release into the bloodstream of several pro-inflammatory (e.g., tumour necrosis factor-a [TNF-a], interleukin-6 [IL-6]), pro-oxidant and pro-coagulant factors (e.g., fibrinogen, factor VIII, plasminogen activator inhibitor-1) as well as pro-fibrogenic mediators. In particular, the synthesis of lipids, including DAG, may also contribute to the hepatic production of inflammatory cytokines and pro-coagulant factors [3][4][5][6];
(c) the bidirectional relationship between NAFLD and hypertension [7]. Several observational studies and some meta-analyses have reported that patients with NAFLD have an increased risk of developing hypertension [8], thus suggesting that this association may partly mediate the relationship between NAFLD and cardiac complications and that that NAFLD may be a consequence, but also a cause of hypertension [7];
(d) patients with NAFLD have early changes in myocardial substrate metabolism inducing cardiac functional disturbances, probably conditioning a higher risk of heart failure [9] and arrhythmias [6][10];
(e) chronic hyperglycemia induces an inflammatory and osteoblastic phenotype in valvular interstitial cells in experimental models of aortic valve sclerosis [11]. Increased valvular inflammation, through a systemic inflammatory state, could also mediate the increased cardiac valve sclerosis in NAFLD patients, independent of the presence of T2DM;
(f) experimental data also indicate that NAFLD, mainly when advanced stages occur, may contribute to the activation of multiple pathways involved in the pathophysiology of CKD [12][13]. In this regard, atherogenic dyslipidaemia, hypertension, insulin resistance, oxidative stress and pro-inflammatory factors that, as mentioned above, are promoted and exacerbated by NAFLD status, may directly contribute to the vascular and renal damage [13]. Moreover, impaired activation of the renin-angiotensin system (RAS) may also contribute to the renovascular injury by inflammation pathways [13]. Finally, accumulating evidence also suggests a potential and independent association between PNPLA3 (patatin like phospholipase domain containing-3) rs738409, which is the most important polymorphism associated with NAFLD and its advanced forms [14], and kidney dysfunction [13].
Author, Ref. | Main Study Characteristics | Main Results |
---|---|---|
Fatal and non-fatal cardiovascular events | ||
Targher G et al. J. Hepatol. 2016; 65: 589–600. | 16 observational studies were included for a total of 34,043 individuals with and without T2DM | NAFLD was associated with an increased risk of fatal and/or non-fatal CVD (random-effects odds ratio 1.64, 95% confidence interval 1.26–2.13). Patients with more severe forms of NAFLD were also more likely to develop fatal and non-fatal CVD events (random-effects odds ratio 2.58; 95% confidence interval 1.78–3.75) |
Morrison AE et al. Liver Int. 2019; 39: 557–567. | 13 observational studies were included | NAFLD was not associated with an increased risk of CVD (random-effects risks ratio 1.48, 95% confidence interval 0.96–2.29) |
Liu Y et al. Sci Rep. 2019; 9: 11124 | 14 observational studies were included for a total of 498,501 individuals with and without T2DM | NAFLD was associated with an increased risk of all-cause mortality (random-effects hazard ratio 1.34; 95% confidence interval 1.17–1.54), but not with an increased risk of CVD (random-effects hazard ratio 1.13; 95% confidence interval 0.92–1.38) |
Mantovani A et al. Lancet Gastroenterol Hepatol. 2021; 6: 903–913 | 36 longitudinal studies were included for a total of 5,802,226 middle-aged individuals with and without T2DM | NAFLD was associated with an increased risk of fatal or non-fatal CVD events (random-effects hazard ratio 1.45, 95% confidence interval 1.31–1.61). This risk increased progressively across the severity of NAFLD, especially the stage of fibrosis (random-effects hazard ratio 2.50, 95% confidence interval 1.68–3.72) |
Alon L et al. Eur J Prev Cardiol. 2021 Dec 22: zwab212. doi: 10.1093/eurjpc/zwab212. | 20 observational studies were included | NAFLD was associated with an increased risk of myocardial infarction (random-effects odds ratio 1.66, 95% confidence interval 1.39–1.99), ischemic stroke (random-effects odds ratio 1.41, 95% confidence interval 1.29–1.55), atrial fibrillation (random-effects odds ratio 1.27, 95% confidence interval 1.18–1.37), and heart failure (random-effects odds ratio 1.62, 95% confidence interval 1.43–1.84) |
Cardiac function and structure | ||
Borges-Canha M et al. Endocrine 2019; 66: 467–476. | 16 observational studies were included | NAFLD was associated with increased risk of (a) higher left ventricle mass and ratios between left ventricle mass and both height and body surface area; (b) higher left ventricular end diastolic diameter; (c) higher left atrium diameter and ratio between left atrial volume and body surface area; (d) higher posterior wall and septum thickness; (e) lower E/A wave ratio; (f) higher E/E′ ratio; (g) longer deceleration time and (h) longer relaxation time |
Cardiac arrhythmias | ||
Minhas AM et al. Cureus 2017; 9: e1142. | 3 observational studies were included for a total of 1,044 with NAFLD and 1,016 without NAFLD | Patients with NAFLD had a higher risk of AF (random-effects odds ratio 2.47, 95% confidence interval 1.30–4.66) |
Wijarnpreecha K et al. Clin Res Hepatol Gastroenterol. 2017; 41: 525–532 | 5 observational studies (2 cross-sectional ones and 3 cohort ones) were included for a total of 238,129 participants with and without T2DM | Patients with NAFLD had a higher risk of AF (random-effects risks ratio 2.06, 95% confidence interval 1.10–3.85) |
Mantovani A. et al. Liver Int. 2019; 39: 758–769 | 9 observational studies (5 cross-sectional ones and 4 cohort ones) were included for a total of 364,919 individuals with and without T2DM | NAFLD was associated with an increased risk of prevalent AF (random-effects odds ratio 2.07, 95% confidence interval 1.38–3.10). Conversely, NAFLD was associated with increased risk of incident AF only in T2DM patients (random-effects hazard ratio 4.96, 95% confidence interval 1.42–17.3). |
Gong H et al. J. Int. Med. Res. 2021; 49: 3000605211047074 | 19 observational studies were included for a total of 7,012,960 individuals with and without T2DM | NAFLD was associated with higher risks of AF (random-effects odds ratio 1.71, 95% confidence interval 1.14–2.57), prolonged QT interval (random-effects odds ratio 2.86, 95% confidence interval 1.64–4.99), premature atrial/ventricular contraction (random-effects odds ratio 2.53, 95% confidence interval 1.70–3.78) and heart block (random-effects odds ratio 2.65, 95% confidence interval 1.88–3.72) |
Chronic kidney disease (CKD) | ||
Mantovani A et al. Metabolism 2018; 79: 64–76 | 9 observational studies were included for a total of 96,595 individuals with and without T2DM | NAFLD was associated with a higher risk of incident CKD (random-effects hazard ratio 1.37, 95% confidence interval 1.20–1.53). Patients with severe forms of NAFLD were more likely to develop incident CKD (random-effects hazard ratio 1.50, 95% confidence interval 1.25–1.74) |
Mantovani A et al. Gut 2022; 71: 156–162 | 13 observational studies were included for a total of 1,222,032 individuals with and without T2DM | NAFLD was associated with an increased risk of incident CKD (random-effects hazard ratio 1.43, 95% confidence interval 1.33–1.54) |