Elevated asymmetric dimethylarginine in plasma: an early marker for endothelial dysfunction in non-alcoholic fatty liver disease?

Metabolic Derangement in Non-Alcoholic Fatty Liver Disease: Opportunities for Early Diagnostic and Prognostic Markers

Non-alcoholic fatty liver disease is a globally prevalent disorder that can rapidly progress if not detected early. Currently, no accepted markers exist for early diagnosis and prognosis of NAFLD. This review describes derangement in major metabolic pathways of lipid, carbohydrate, and amino acids in NAFLD. It suggests that measuring levels of thrombospondin, TyG index, asymmetric dimethylarginine, LAL-A, GLP-1, FGF-21, and GSG index are potential markers for early diagnosis of NAFLD. A single marker may not indicate early NAFLD, and further large-scale studies on correlating levels of Thrombospondin-2, triglyceride-glucose index, and FGF-21 with NAFLD are warranted.

The relationship between liver enzymes, prehypertension and hypertension in the Azar cohort population

BACKGROUND

The incidence of hypertension (HTN) as a worldwide health problem is rising rapidly. Early identification and management of pre-HTN before HTN development can help reduce its related complications. We evaluated the relationship between liver enzymes levels and pre-HTN/HTN in the Azar cohort population.

METHOD

This cross-sectional study was based on data from the large Azar cohort study and a total of 14,184 participants were included. Pre-HTN and HTN were defined based on the American Heart Association guideline. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT) levels were measured by Pars Azmoon kits. The relationship between pre-HTN/HTN and liver enzyme levels was evaluated by logistic regression.

RESULTS

Of 14,184 participants, 5.7% and 39.6% had pre-HTN and HTN, respectively. In the adjusted model, AST levels of 19-23 IU/l were associated with an elevated risk of pre-HTN (OR [95% CI]: 1.24 [1.04-1.48]). A dose-response increase was seen in pre-HTN in relation to ALT, with the highest OR in the third tertile (1.34 [1.09-1.63]). The odds of pre-HTN also increased with GGT in the third tertile (1.25[1.03-1.52]). In addition, the odds of HTN increased with increased levels of AST, ALT, ALP, and GGT, such that the highest ORs were recorded in the third tertile (OR 1.22 [1.09-1.37], 1.51 [1.35-1.70], 1.19 [1.07-1.34], and 1.68 [1.49-1.89], respectively). Among these enzymes, GGT had the highest OR regarding HTN.

CONCLUSION

This study indicates that AST, ALT, ALP and GGT levels were associated with pre-HTN (except for ALP) and HTN, independent of known risk factors. Hence, it may be possible to use liver enzymes to predict the incidence of pre-HTN and HTN, empowering primary care providers to make the necessary interventions promptly.

Endothelial dysfunction and cardiovascular risk in non-alcoholic fatty liver disease – a systematic review and meta-analysis

Background

Nonalcoholic fatty liver disease (NAFLD) is a prevalent metabolic disorder that has been associated with an increased risk of cardiovascular diseases. Endothelial dysfunction, characterized by impaired flow-mediated dilation (FMD) of the brachial artery, is a known predictor of cardiovascular risk. However, the relationship between NAFLD and endothelial dysfunction, as well as the impact of NAFLD on clinical cardiovascular events, remains unclear.

Objective

The aim of this systematic literature review was to determine the association between endothelial dysfunction, as measured by FMD of the brachial artery, and NAFLD. Additionally, we aimed to investigate the relationship between NAFLD and clinical cardiovascular events (CVE).

Methods

A systematic search was conducted in PubMed, Scopus, ScienceDirect, and Google Scholar for articles published between 2000 and July 2023. The reference lists of the included studies were also searched to retrieve possible additional studies. Original studies published in English focusing on adults with NAFLD and endothelial dysfunction are included. Editorials, commentaries, letters and studies focusing on pediatric populations and non-NAFLD liver diseases were excluded. The quality of included studies was appraised using the Newcastle–Ottawa scale. Meta-analyses were performed using Review Manager 5.4 software.

Results

The initial search yielded a total of 1792 articles and ultimately only 20 studies met the criteria. A total 6396 NAFLD patients were studied. Meta-analysis showed that individuals diagnosed with NAFLD had significantly lower brachial FMD values compared to their respective control groups (standardized mean difference: -4.63, 95% confidence interval: -5.68 to -3.58, p < 0.0001). Furthermore, NAFLD patients exhibited a significantly higher risk of clinical cardiovascular events compared to controls (odds ratio: 2.61; 95% CI: 1.41–4.83, p < 0.002). Subgroup analysis of studies focusing on non-alcoholic steatohepatitis (NASH) versus pure steatosis demonstrated that individuals with NASH had even lower FMD values than those with pure steatosis (standardized mean difference: -3.84, 95% confidence interval: -7.56 to -0.13, p = 0.03, I2 = 66%).

Limitations, bias and heterogeneity

The review included studies published in English language, over last 23 years and specified database resulted in language bias and might have missed older pertinent studies from another important database. The overall heterogeneity is attributed to variations in study populations, outcome measurements, differences in methodological approaches among included studies, and diverse diagnostic criteria for NAFLD.

Conclusion

Individuals with NAFLD exhibited impaired brachial FMD, indicating compromised endothelial function. Furthermore, NAFLD patients had an elevated risk of clinical cardiovascular events.

Relation between non-alcoholic fatty liver disease and carotid artery intimal media thickness as a surrogate for atherosclerosis: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD), characterized by hepatic steatosis without heavy alcohol consumption or other chronic conditions, encompasses a spectrum from non-alcoholic fatty liver to non-alcoholic steatohepatitis leading to cirrhosis. This analysis aimed to investigate the correlation between NAFLD and carotid intimal media thickness (C-IMT), a non-invasive surrogate for atherosclerosis.

METHODOLOGY

Database searches, including PubMed, EMBASE and Cochrane Library, yielded studies up to April 2023. Included were studies exploring the NAFLD-C-IMT relationship in populations aged >18 years. Exclusions comprised non-English papers, those involving animals or pediatric populations and studies lacking control groups.

RESULTS

No statistical significance was noted between mild and moderate NAFLD compared to the control group regarding C-IMT [95% confidence intervals (CI): -0.03, 0.12] and (95% CI: -0.03, 0.21), respectively. There was a statistically significant difference only in the Severe NAFLD group ( P value 0.03). NAFLD with and without metabolic syndrome showed statistically significant differences compared to control regarding C-IMT (95% CI: 0.04, 0.12) and (95% CI: 0.01, 0.07), respectively. Fifty-nine studies were mentioned without classification of NAFLD severity and revealed a high statistically significant difference between NAFLD and controls regarding C-IMT with (95% CI: 0.09, 0.12, P < 0.00001). Stratified analysis according to sex was done in two studies and revealed statistical differences between NAFLD and control regarding C-IMT in both groups.

CONCLUSION

This meta-analysis underscores a significant association between NAFLD and increased C-IMT, emphasizing the importance of assessing C-IMT in NAFLD patients to identify cardiovascular risk and tailor therapeutic interventions for improved patient outcomes.

Association of nonalcoholic fatty liver disease and carotid media-intima thickness: A systematic review and a meta-analysis

Introduction

The relationship between cardiovascular disorders and nonalcoholic fatty liver disease (NAFLD) has been extensively studied. To better pool this data and make a more definite conclusion, we performed a meta-analysis to evaluate the association between NAFLD and the thickness of media and intima of carotid artery (CIMT) and cardiovascular disorders.

Methods

We searched PubMed, Ovid, Scopus, ProQuest, Web of Science, and the Cochrane Library, and analyzed the pooled data using R studio and the "metafor" package.

Results

The final analysis included a total of 59 studies with 16,179 cases and 26,120 control individuals. NAFLD was shown to be associated with an increase of 0.1231 mm (20.6%) in carotid artery intima-media thickness (CIMT) (p = 0.002, 95% confidence interval [CI]: 0.0462-0.2000) in individuals with NAFLD. The prevalence of atherosclerotic plaques in the carotid arteries and the occurrence of NAFLD are significantly correlated, according to a meta-analysis based on 17 distinct studies (p = 0.001, 1.28-1.43, 95% CI, odds ratio = 1.356).

Conclusion

Patients with increased CIMT are considerably more likely to have NAFLD. Large prospective investigations are required to corroborate these findings and their prognostic significance, along with the effectiveness of the available interventions.

Nonalcoholic fatty liver disease and risk of incident young-onset hypertension: Effect modification by sex

BACKGROUND AND AIMS

Although nonalcoholic fatty liver disease (NAFLD) and hypertension are increasingly common among young adults, it is uncertain if NAFLD affects incidence of young-onset hypertension, and if the association is modified by sex. We investigated potential effect modification by sex on the association between NAFLD and incident hypertension in young adults (<40 years).

METHOD AND RESULTS

This cohort study comprised 85,789 women and 67,553 men aged <40 years without hypertension at baseline. Hepatic steatosis was assessed by liver ultrasound and classified as mild or moderate/severe. Hypertension was defined as blood pressure (BP) ≥130/80 mmHg; self-reported history of physician-diagnosed hypertension; or current use of BP-lowering medications. Cox proportional hazard models were used to estimate hazard ratios (HRs; 95% confidence intervals [CIs]) for incident hypertension by NAFLD status (median follow-up 4.5 years). A total of 25,891 participants developed incident hypertension (incidence rates per 10³ person-years: 15.6 for women and 63.5 for men). Multivariable-adjusted HRs (95% CIs) for incident hypertension comparing no NAFLD (reference) with mild or moderate/severe NAFLD were 1.68 (1.56-1.80) and 1.83 (1.60-2.09) for women and 1.21 (1.17-1.25) and 1.23 (1.17-1.30) for men, respectively. Stronger associations were consistently observed between NAFLD and incident hypertension in women, regardless of obesity/central obesity (all p-values for interaction by sex <0.001).

CONCLUSIONS

NAFLD is a potential risk factor for young-onset hypertension with a relatively greater impact in women and in those with more severe hepatic steatosis.

Hepatic DDAH1 mitigates hepatic steatosis and insulin resistance in obese mice: Involvement of reduced S100A11 expression

Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is an important regulator of plasma asymmetric dimethylarginine (ADMA) levels, which are associated with insulin resistance in patients with nonalcoholic fatty liver disease (NAFLD). To elucidate the role of hepatic DDAH1 in the pathogenesis of NAFLD, we used hepatocyte-specific Ddah1-knockout mice (Ddah1HKO) to examine the progress of high-fat diet (HFD)-induced NAFLD. Compared to diet-matched flox/flox littermates (Ddah1f/f), Ddah1HKO mice exhibited higher serum ADMA levels. After HFD feeding for 16 weeks, Ddah1HKO mice developed more severe liver steatosis and worse insulin resistance than Ddah1f/f mice. On the contrary, overexpression of DDAH1 attenuated the NAFLD-like phenotype in HFD-fed mice and ob/ob mice. RNA-seq analysis showed that DDAH1 affects NF-κB signaling, lipid metabolic processes, and immune system processes in fatty livers. Furthermore, DDAH1 reduces S100 calcium-binding protein A11 (S100A11) possibly via NF-κB, JNK and oxidative stress-dependent manner in fatty livers. Knockdown of hepatic S100a11 by an AAV8-shS100a11 vector alleviated hepatic steatosis and insulin resistance in HFD-fed Ddah1HKO mice. In summary, our results suggested that the liver DDAH1/S100A11 axis has a marked effect on liver lipid metabolism in obese mice. Strategies to increase liver DDAH1 activity or decrease S100A11 expression could be a valuable approach for NAFLD therapy.

Contribution of Hepatic Steatosis-Intensified Extracellular Vesicle Release to Aggravated Inflammatory Endothelial Injury in Liver-Specific Asah1 Gene Knockout Mice

To study the mechanism by which nonalcoholic fatty liver disease (NAFLD) contributes to vascular endothelial Nod-like receptor pyrin domain 3 (NLRP3) inflammasome activation and neointima hyperplasia, NAFLD was established in high-fat diet (HFD)-treated Asah1fl/fl/Albcre (liver-specific deletion of the acid ceramidase gene Asah1) mice. Compared with Asah1 flox [Asah1fl/fl/wild type (WT)] and wild-type (WT/WT) mice, Asah1fl/fl/Albcre mice exhibited significantly enhanced ceramide levels and lipid deposition on HFD in the liver. Moreover, Asah1fl/fl/Albcre mice showed enhanced expression of extracellular vesicle (EV) markers, CD63 and annexin II, but attenuated lysosome-multivesicular body fusion. All these changes were accompanied by significantly increased EV counts in the plasma. In a mouse model of neointima hyperplasia, liver-specific deletion of the Asah1 gene enhanced HFD-induced neointima proliferation, which was associated with increased endothelial NLRP3 inflammasome formation and activation and more severe endothelial damage. The EVs isolated from plasma of Asah1fl/fl/Albcre mice on HFD were found to markedly enhance NLRP3 inflammasome formation and activation in primary cultures of WT/WT endothelial cells compared with those isolated from WT/WT mice or normal diet-treated Asah1fl/fl/Albcre mice. These results suggest that the acid ceramidase/ceramide signaling pathway controls EV release from the liver, and its deficiency aggravates NAFLD and intensifies hepatic EV release into circulation, which promotes endothelial NLRP3 inflammasome activation and consequent neointima hyperplasia in the mouse carotid arteries.

Severity of non-alcoholic fatty liver disease is a risk factor for developing hypertension from prehypertension

BACKGROUND

There is little published evidence about the role of non-alcoholic fatty liver disease (NAFLD) in the progression from prehypertension to hypertension. This study was conducted to investigate the association of NAFLD and its severity with the risk of hypertension developing from prehypertension.

METHODS

The study cohort comprised 25, 433 participants from the Kailuan study with prehypertension at baseline; those with excessive alcohol consumption and other liver diseases were excluded. NAFLD was diagnosed by ultrasonography and stratified as mild, moderate, or severe. Univariable and multivariable Cox proportional hazard regression was used to calculate the hazard ratios (HRs) and 95% confidence intervals (CIs) of incident hypertension according to the presence and 3 categories of severity of NAFLD.

RESULTS

During a median of 12.6 years of follow-up, 10,638 participants progressed to hypertension from prehypertension. After adjusting for multiple risk factors, patients with prehypertension and NAFLD had a 15% higher risk of incident hypertension than those without NAFLD (HR = 1.15, 95% CI 1.10-1.21). Moreover, the severity of NAFLD was associated with the incidence of hypertension, which was higher in patients with more severe NAFLD (HR = 1.15 [95% CI 1.10-1.21] in the mild NAFLD group; HR = 1.15 [95% CI 1.07-1.24] in the moderate NAFLD group; and HR = 1.20 [95% CI 1.03-1.41] in the severe NAFLD group). Subgroup analysis indicated that age and baseline systolic blood pressure may modify this association.

CONCLUSIONS

NAFLD is an independent risk factor for hypertension in patients with prehypertension. The risk of incident hypertension increases with the severity of NAFLD.

Endothelial Cell Dysfunction and Nonalcoholic Fatty Liver Disease (NAFLD): A Concise Review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. It is strongly associated with obesity, type 2 diabetes (T2DM), and other metabolic syndrome features. Reflecting the underlying pathogenesis and the cardiometabolic disorders associated with NAFLD, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has recently been proposed. Indeed, over the past few years, growing evidence supports a strong correlation between NAFLD and increased cardiovascular disease (CVD) risk, independent of the presence of diabetes, hypertension, and obesity. This implies that NAFLD may also be directly involved in the pathogenesis of CVD. Notably, liver sinusoidal endothelial cell (LSEC) dysfunction appears to be implicated in the progression of NAFLD via numerous mechanisms, including the regulation of the inflammatory process, hepatic stellate activation, augmented vascular resistance, and the distortion of microcirculation, resulting in the progression of NAFLD. Vice versa, the liver secretes inflammatory molecules that are considered pro-atherogenic and may contribute to vascular endothelial dysfunction, resulting in atherosclerosis and CVD. In this review, we provide current evidence supporting the role of endothelial cell dysfunction in the pathogenesis of NAFLD and NAFLD-associated atherosclerosis. Endothelial cells could thus represent a "golden target" for the development of new treatment strategies for NAFLD and its comorbid CVD.

Non-Alcoholic Fatty Liver Disease and Extrahepatic Cancers: A Wolf in Sheep’s Clothing?

Non-alcoholic fatty liver disease (NAFLD) is now considered the main driver and leading cause of chronic liver disease globally. The umbrella term NAFLD describes a range of liver conditions closely related to insulin resistance, metabolic syndrome, diabetes mellitus, obesity, and dyslipidemia. At the same time, several malignancies, including hepatocellular carcinoma and colorectal cancer, are considered to be common causes of death among patients with NAFLD. At first, our review herein aims to investigate the role of NAFLD in developing colorectal neoplasms and adenomatous polyps based on the current literature. We will also explore the connection and the missing links between NAFLD and extrahepatic cancers. Interestingly, any relationship between NAFLD and extrahepatic malignancies could be attributable to several shared metabolic risk factors. Overall, obesity, insulin resistance, metabolic syndrome, and related disorders may increase the risk of developing cancer. Therefore, early diagnosis of NAFLD is essential for preventing the progression of the disease and avoiding its severe complications. In addition, cancer screening and early detection in these patients may improve survival and reduce any delays in treatment.

Coagulation and Endothelial Dysfunction Associated with NAFLD: Current Status and Therapeutic Implications

Non-alcoholic fatty liver disease (NAFLD) is closely related to insulin resistance, type 2 diabetes mellitus and obesity. It is considered a multisystem disease and there is a strong association with cardiovascular disease and arterial hypertension, which interfere with changes in the coagulation system. Coagulation disorders are common in patients with hepatic impairment and are dependent on the degree of liver damage. Through a review of the literature, we consider and discuss possible disorders in the coagulation cascade and fibrinolysis, endothelial dysfunction and platelet abnormalities in patients with NAFLD.

Impact of Helicobacter pylori-Related Metabolic Syndrome Parameters on Arterial Hypertension

Arterial hypertension is a risk factor for several pathologies, mainly including cardio-cerebrovascular diseases, which rank as leading causes of morbidity and mortality worldwide. Arterial hypertension also constitutes a fundamental component of the metabolic syndrome. Helicobacter pylori infection is one of the most common types of chronic infection globally and displays a plethora of both gastric and extragastric effects. Among other entities, Helicobacter pylori has been implicated in the pathogenesis of the metabolic syndrome. Within this review, we illustrate the current state-of-the-art evidence, which may link several components of the Helicobacter pylori-related metabolic syndrome, including non-alcoholic fatty liver disease and arterial hypertension. In particular, current knowledge of how Helicobacter pylori exerts its virulence through dietary, inflammatory and metabolic pathways will be discussed. Although there is still no causative link between these entities, the emerging evidence from both basic and clinical research supports the proposal that several components of the Helicobacter pylori infection-related metabolic syndrome present an important risk factor in the development of arterial hypertension. The triad of Helicobacter pylori infection, the metabolic syndrome, and hypertension represents a crucial worldwide health problem on a pandemic scale with high morbidity and mortality, like COVID-19, thereby requiring awareness and appropriate management on a global scale.

Nonalcoholic Fatty Liver Disease and Non-Alcoholic Steatohepatitis: Current Issues and Future Perspectives in Preclinical and Clinical Research

Nonalcoholic fatty liver disease (NAFLD) is a continuum of liver abnormalities often starting as simple steatosis and to potentially progress into nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular carcinoma. Because of its increasing prevalence, NAFLD is becoming a major public health concern, in parallel with a worldwide increase in the recurrence rate of diabetes and metabolic syndrome. It has been estimated that NASH cirrhosis may surpass viral hepatitis C and become the leading indication for liver transplantation in the next decades. The broadening of the knowledge about NASH pathogenesis and progression is of pivotal importance for the discovery of new targeted and more effective therapies; aim of this review is to offer a comprehensive and updated overview on NAFLD and NASH pathogenesis, the most recommended treatments, drugs under development and new drug targets. The most relevant in vitro and in vivo models of NAFLD and NASH will be also reviewed, as well as the main molecular pathways involved in NAFLD and NASH development.

Abnormal metabolic processes involved in the pathogenesis of non-alcoholic fatty liver disease (Review)

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases and can lead to liver cirrhosis or liver cancer in severe cases. In recent years, the incidence of NAFLD has increased substantially. The trend has continued to increase and has become a key point of concern for health systems. NAFLD is often associated with metabolic abnormalities caused by increased visceral obesity, including insulin resistance, diabetes mellitus, hypertension, dyslipidemia, atherosclerosis and systemic microinflammation. Therefore, the pathophysiological mechanisms of NAFLD must be clarified to develop new drug treatment strategies. Recently, researchers have conducted numerous studies on the pathogenesis of NAFLD and have identified various important regulatory factors and potential molecular mechanisms, providing new targets and a theoretical basis for the treatment of NAFLD. However, the pathogenesis of NAFLD is extremely complex and involves the interrelationship and influence of multiple organs and systems. Therefore, the condition must be explored further. In the present review, the abnormal metabolic process, including glucose, lipid, amino acid, bile acid and iron metabolism are reviewed. It was concluded that NAFLD is associated with an imbalanced metabolic network that involves glucose, lipids, amino acids, bile acids and iron, and lipid metabolism is the core metabolic process. The current study aimed to provide evidence and hypotheses for research and clinical treatment of NAFLD.

Nonalcoholic Fatty Liver Disease: An Emerging Driver of Hypertension

Hypertension, a multifactorial disorder resulting from the interplay between genetic predisposition and environmental risk factors, affects ≈30% of adults. Emerging evidence has shown that nonalcoholic fatty liver disease (NAFLD), as an underestimated metabolic abnormality, is strongly associated with an increased risk of incident prehypertension and hypertension. However, the role of NAFLD in the development of hypertension is still obscure and is highly overlooked by the general public. Herein, we highlight the epidemiological evidence and putative mechanisms focusing on the emerging roles of NAFLD in hypertension, with the purpose of reinforcing the notion that NAFLD may serve as an independent risk factor and an important driving force in the development and progression of hypertension. Finally, we also briefly summarize the current potential treatments for NAFLD that might also be beneficial approaches against hypertension.

Nonalcoholic fatty liver disease: implications for cardiovascular risk

Nonalcoholic fatty liver disease (NAFLD) is a growing epidemic in the USA affecting ∼30% of the population. It has been closely linked to metabolic syndrome and type 2 diabetes, with strong implications for cardiovascular disease (CVD). This review focuses on the relationship between NAFLD and CVD and the proposed interactions interlinking these two diseases. This appraisal also discusses treatments targeting NAFLD in the context of CVD. NAFLD is a multisystem disease and ultimately the goals of therapy are to ameliorate CVD and prevent coronary artery disease morbidity and mortality.

Dimethylarginine Dimethylaminohydrolase 1 Protects Against High-Fat Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice

AIMS

High plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with hepatic dysfunction in patients with nonalcoholic fatty liver disease (NAFLD). However, it is unknown whether ADMA is involved in the pathogenesis of NAFLD. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is an enzyme that degrades ADMA. In this study, we used Ddah1^-/- mice to investigate the effects of the ADMA/DDAH1 pathway on high-fat diet (HFD)-induced hepatic steatosis.

RESULTS

After HFD feeding for 20 weeks, Ddah1^-/- mice were more obese and had developed more severe hepatic steatosis and worse insulin resistance compared with wild-type (WT) mice. In the livers of HFD-fed mice, loss of DDAH1 resulted in higher levels of lipogenic genes, lower expression of β-oxidation genes, and greater induction of oxidative stress, endoplasmic reticulum stress, and inflammation than in the WT livers. Furthermore, ADMA treatment in HepG2 cells led to oxidative stress and steatosis, whereas overexpression of DDAH1 attenuated palmitic acid-induced steatosis, oxidative stress, and inflammation. Innovation and Conclusion: Our results provide the first direct evidence that the ADMA/DDAH1 pathway has a marked effect on hepatic lipogenesis and steatosis induced by HFD feeding. Our findings suggest that strategies to increase DDAH1 activity in hepatocytes may provide a novel approach to attenuate NAFLD development. Antioxid. Redox Signal. 26, 598-609.

Emerging Liver-Kidney Interactions in Nonalcoholic Fatty Liver Disease

Mounting evidence connects non-alcoholic fatty liver disease (NAFLD) to chronic kidney disease (CKD). We review emerging mechanistic links between NAFLD and CKD, including altered activation of angiotensin converting enzyme (ACE)-2, nutrient/energy sensors sirtuin-1 and AMP-activated kinase, as well as impaired antioxidant defense mediated by nuclear factor erythroid 2-related factor-2 (Nrf2). Dietary fructose excess may also contribute to NAFLD and CKD. NAFLD affects renal injury through lipoprotein dysmetabolism and altered secretion of the hepatokines fibroblast growth factor-21, fetuin-A, insulin-like growth factor-1, and syndecan-1. CKD may mutually aggravate NAFLD and associated metabolic disturbances through altered intestinal barrier function and microbiota composition, the accumulation of uremic toxic metabolites, and alterations in pre-receptor glucocorticoid metabolism. We conclude by discussing the implications of these findings for the treatment of NAFLD and CKD.

MCD diet-induced steatohepatitis is associated with alterations in asymmetric dimethylarginine (ADMA) and its transporters

Using an experimental model of NASH induced by a methionine-choline-deficient (MCD) diet, we investigated whether changes occur in serum and tissue levels of asymmetric dimethylarginine (ADMA). Male Wistar rats underwent NASH induced by 8-week feeding with an MCD diet. Serum and hepatic biopsies at 2, 4 and 8 weeks were taken, and serum enzymes, ADMA and nitrate/nitrite (NOx), were evaluated. Hepatic biopsies were used for mRNA and protein expression analysis of dimethylarginine dimethylaminohydrolase-1 (DDAH-1) and protein methyltransferases (PRMT-1), enzymes involved in ADMA metabolism and synthesis, respectively, and ADMA transporters (CAT-1, CAT-2A and CAT-2B). Lipid peroxides (TBARS), glutathione, ATP/ADP and DDAH activity were quantified. An increase in serum AST and ALT was detected in MCD animals. A time-dependent decrease in serum and tissue ADMA and increase in mRNA expression of DDAH-1 and PRMT-1 as well as higher rates of mRNA expression of CAT-1 and lower rates of CAT-2A and CAT-2B were found after 8-week MCD diet. An increase in serum NOx and no changes in protein expression in DDAH-1 and CAT-1 and higher content in CAT-2 and PRMT-1 were found at 8 weeks. Hepatic DDAH activity decreased with a concomitant increase in oxidative stress, as demonstrated by high TBARS levels and low glutathione content. In conclusion, a decrease in serum and tissue ADMA levels in the MCD rats was found associated with a reduction in DDAH activity due to the marked oxidative stress observed. Changes in ADMA levels and its transporters are innovative factors in the onset and progression of hepatic alterations correlated with MCD diet-induced NASH.

Diet-induced dyslipidemia leads to nonalcoholic fatty liver disease and oxidative stress in guinea pigs

Chronic dyslipidemia imposed by a high-fat and high-caloric dietary regime leads to debilitating disorders such as obesity, nonalcoholic fatty liver disease (NAFLD), and insulin resistance. As disease rates surge, so does the need for high validity animal models to effectively study the causal relationship between diet and disease progression. The dyslipidemic guinea pig displays a high similarity with the human lipoprotein profile and may in this aspect be superior to other rodent models. This study investigated the effects of 2 long-term Westernized diets (0.35% cholesterol, 18.5% vegetable oil and either 15% or 20% sucrose) compared with isocaloric standard chow in adult guinea pigs. Biochemical markers confirmed dyslipidemia in agreement with dietary regimens; however, both high-fat groups displayed a decreased tissue fat percentage compared with controls. Macroscopic appearance, histopathologic evaluation, and plasma markers of liver function confirmed NAFLD in high-fat groups, supported by liver redox imbalance and markers suggesting hepatic endothelial dysfunction. Plasma markers indicated endothelial dysfunction in response to a high-fat diet, although atherosclerotic lesions were not evident. Evaluation of glucose tolerance showed no indication of insulin resistance. The 5% increase in sucrose between the 2 high-fat diets did not lead to significant differences between groups. In conclusion, we find the dyslipidemic guinea pig to be a valid model of diet imposed dyslipidemia, particularly with regards to hepatic steatosis and endothelial dysfunction. Furthermore, the absence of obesity supports the present study setup as targeting NAFLD in nonobese individuals.

Low- and high-density lipoprotein subclasses in subjects with nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with increased cardiometabolic risk. Although dyslipidemia represents a key factor in this disease, its impact on serum levels of distinct lipoprotein subfractions is largely unknown.

OBJECTIVE

To assess the full low-density lipoprotein (LDL) and high-density lipoprotein (HDL) profiles in patients with NAFLD.

METHODS

Seven LDL and 10 HDL subfractions were assessed by gel electrophoresis (Lipoprint, Quantimetrix Corporation, USA) in men with biopsy proven NAFLD (simple steatosis [n = 17, age, 34 ± 7 years] and nonalcoholic steatohepatitis [NASH; n = 24, age, 32 ± 6 years]). Exclusion criteria included robust alcohol consumption, infection with hepatitis B or C virus, body mass index ≥ 40 kg/m(2), diabetes mellitus, and hypertension.

RESULTS

Compared with simple steatosis, NASH patients had similar body mass index, homeostasis model assessment of insulin resistance index and plasma lipids, with increased levels of both aspartate aminotransferase and alanine transaminase. NASH subjects had lower levels of larger LDL1 (10 ± 4 vs 13 ± 4%, P = .010) and increased smaller LDL3 and LDL4 particles (9 ± 5 vs 5 ± 5%, P = .017 and 3 ± 3 vs 1 ± 2%, P = .012, respectively). No changes were found in the HDL subclass profile. By multiple regression analysis, we found that NASH was associated only with increased levels of LDL3 (P = .0470).

CONCLUSIONS

The increased levels of small, dense LDL3 and LDL4 in NASH may help to at least partly explain the increased risk for atherosclerosis and cardiovascular diseases in these patients.

Nonalcoholic fatty liver disease and cardiovascular disease

Nonalcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD) are two diseases that are common in the general population. To date, many studies have been conducted and demonstrate a direct link between NAFLD and CVD, but the exact mechanisms for this complex relationship are not well established. A systematic search of the PubMed database revealed that several common mechanisms are involved in many of the local and systemic manifestations of NAFLD and lead to an increased cardiovascular risk. The possible mechanisms linking NAFLD and CVD include inflammation, oxidative stress, insulin resistance, ectopic adipose tissue distribution, dyslipidemia, endothelial dysfunction, and adiponectin, among others. The clinical implication is that patients with NAFLD are at an increased risk of CVD and should undergo periodic cardiovascular risk assessment.

Association between endothelial dysfunction and frailty: the Toledo Study for Healthy Aging

Cardiovascular disease (CVD), both clinical and subclinical, has been proposed as one of the mechanisms underlying frailty. However, there is no evidence addressing the relationship between the earliest stage of CVD (endothelial dysfunction) and frailty. The goal of the study was to analyze the association between endothelial dysfunction, evaluated by asymmetric dimethylarginine (ADMA) levels, and frailty. We used data from the Toledo Study for Healthy Aging, a prospective Spanish cohort study. Biological samples were obtained and ADMA levels were determined using an enzyme immunoassay method. Logistic regression was used to estimate the odds ratio (OR) and 95 % confidence intervals of frailty associated with ADMA. Adjustments were made for age, gender, cardiovascular risk factors, and presence of atherosclerotic disease (assessed by ankle–brachial index; ABI). One thousand two hundred eighty-seven community-dwelling elderly were included. One hundred seven (8.3 %) were identified as frail, 542 (42.1 %) as pre-frail, and 638 (49.6 %) as non-frail. ADMAvalues were higher in frail subjects than in non-frail ones. In addition, an interaction between the presence of atherosclerotic disease and ADMA on the odds of frailty (p=0.045) was detected. After adjustments for age, classical cardiovascular risk factors, and ABI, the risk of frailty was associated with increasing levels of ADMA in subjects without atherosclerotic disease [OR for 1 standard deviation increase in ADMA=1.14 (1.01–1.28), p=0.032] but not in those with atherosclerotic disease. In our study, endothelial dysfunction, assessed by ADMA levels, is associated with frailty. These findings provide additional support for a relevant role of vascular system since its earliest stage in frailty.

A systematic review: burden and severity of subclinical cardiovascular disease among those with nonalcoholic fatty liver; should we care?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is an emerging disease and a leading cause of chronic liver disease. The prevalence in the general population is approximately 15-30% and it increases to 70-90% in obese or diabetic populations. NAFLD has been linked to increased cardiovascular disease (CVD) risk. It is therefore critical to evaluate the relationship between markers of subclinical CVD and NAFLD.

METHOD

An extensive search of databases; including the National Library of Medicine and other relevant databases for research articles meeting inclusion criteria: observational or cohort, studies in adult populations and clearly defined NAFLD and markers of subclinical CVD.

RESULTS

Twenty-seven studies were included in the review; 16 (59%) presented the association of NAFLD and carotid intima-media thickness (CIMT), 7 (26%) the association with coronary calcification and 7 (26%) the effect on endothelial dysfunction and 6 (22%) influence on arterial stiffness. CIMT studies showed significant increases among NAFLD patients compared to controls. These were independent of traditional risk factors and metabolic syndrome. The association was similar in coronary calcification studies. The presence of NAFLD is associated with the severity of the calcification. Endothelial dysfunction and arterial stiffness showed significant independent associations with NAFLD. Two studies argued the associations were not significant; however, these studies were limited to diabetic populations.

CONCLUSION

There is evidence to support the association of NAFLD with subclinical atherosclerosis independent of traditional risk factors and metabolic syndrome. However, there is need for future longitudinal studies to review this association to ascertain causality and include other ethnic populations.

Influence of non-alcoholic fatty liver disease on autonomic changes evaluated by the time domain, frequency domain, and symbolic dynamics of heart rate variability

Background

Non-alcoholic fatty liver disease (NAFLD) is associated with cardiovascular atherosclerosis independent of classical risk factors. This study investigated the influence of NAFLD on autonomic changes, which is currently unknown.

Methods

Subjects without an overt history of cardiovascular disease were enrolled during health checkups. The subjects diagnosed for NAFLD using ultrasonography underwent 5-min heart rate variability (HRV) measurements that was analyzed using the following indices: (1) the time domain with the standard deviation of N-N (SDNN) intervals and root mean square of successive differences between adjacent N-N intervals (rMSSD); (2) the frequency domain with low frequency (LF) and high frequency (HF) components; and (3) symbolic dynamics analysis. Routine blood biochemistry data and serum leptin levels were analyzed. Homeostasis model assessment of insulin resistance (HOMA-IR) was measured.

Results

Of the 497 subjects (mean age, 46.2 years), 176 (35.4%) had NAFLD. The HRV indices (Ln SDNN, Ln rMSSD, Ln LF, and Ln HF) were significantly decreased in the NAFLD group (3.51 vs 3.62 ms, 3.06 vs 3.22 ms, 5.26 vs 5.49 ms², 4.49 vs 5.21 ms², respectively, all P<0.05). Ln SDNN was significantly lower in the NAFLD group after adjustment for age, sex, hypertension, dyslipidemia, metabolic syndrome, body mass index, smoking, estimated glomerular filtration rate, HOMA-IR, and leptin (P<0.05). In the symbolic dynamic analysis, 0 V percentage was significantly higher in the NAFLD group (33.8% vs 28.7%, P = 0.001) and significantly correlated with linear HRV indices (Ln SDNN, Ln rMSSD, and Ln HF).

Conclusions

NAFLD is associated with decreased Ln SDNN and increased 0 V percentage. The former association was independent of conventional cardiovascular risk factors and serum biomarkers (insulin resistance and leptin). Further risk stratification of autonomic dysfunction with falls or cardiovascular diseases by these HRV parameters is required in patients with NAFLD.

Assessment of endothelial function in patients with nonalcoholic fatty liver disease

In this study, we aimed to evaluate the endothelial functions in patients with nonalcoholic fatty liver disease (NAFLD). In this observational case-control study, a total of 51 patients with NAFLD in study group and a total of 21 with age- and sex-equivalent individuals in control group were enrolled. In both patients and control groups, levels of asymmetric dimethylarginine (ADMA), systemic endothelial function (brachial artery flow-mediated dilation) (FMD) and carotid artery intima-media thickness (C-IMT) were measured. FMD and C-IMT were evaluated by vascular ultrasound. Plasma levels of ADMA were measured by ELISA. C-IMT was significantly higher in patients with NAFLD group than control group (0.67 ± 0.09 vs. 0.52 ± 0.11 mm, P < 0.001). The average C-IMT measurements were found in groups of control, simple steatosis, and NAFLD with (borderline and definite) NASH as 0.52 ± 0.11, 0.63 ± 0.07, and 0.68 ± 0.1 mm, respectively. The differences between groups were significant (P < 0.001). Measurement of brachial artery FMD was significantly lower in patients with NAFLD group compared to control group (7.3 ± 4.8 vs. 12.5 ± 7.1 %, P < 0.001). FMD measurements in groups of control, the simple steatosis, and NAFLD with NASH as 12.5 ± 7.1, 9.64 ± 6.63, and 7.03 ± 4.57 %, respectively, and the differences were statistically significant (P < 0.001). The increase in C-IMT and decrease in FMD was independent from metabolic syndrome and it was also more evident in patients with simple steatosis and NASH compared to control group. There was no significant difference between the control and NAFLD groups in terms of plasma ADMA levels (0.61 ± 0.11 vs. 0.69 ± 0.37 μmol/L, P = 0.209). Our data suggested that NAFLD is associated with endothelial dysfunction and increased earlier in patients with atherosclerosis compared to control subjects.

Atorvastatin modulates the DDAH1/ADMA system in high-fat diet-induced insulin-resistant rats with endothelial dysfunction

Dimethylarginine dimethyl-aminohydrolase 1 (DDAH1) is a metabolic enzyme for asymmetric dimethylarginine (ADMA), both of which are closely related to endothelial function. Endothelial dysfunction, a main risk factor of cardiovascular diseases, can be attributed to insulin resistance. We aimed to determine the effects of atorvastatin, an endothelium-protective drug, on DDAH1/ADMA in insulin-resistant rats. Insulin resistance in male Sprague-Dawley rats was induced with a high-fat diet for 8 weeks. Some rats received atorvastatin (30 mg/kg/day) for an additional 8 weeks. Insulin-resistant rats exhibited not only decreases in the DDAH activity and aortic expression of DDAH1 and sterol regulatory element-binding protein 1 (SREBP1) but also increases in plasma ADMA levels, all of which were inhibited by atorvastatin. Insulin sensitivity and DDAH activity showed a significant positive correlation. In conclusion, our results suggest that atorvastatin may modulate DDAH1/ADMA to improve endothelial function in insulin-resistant rats; SREBP1 may also play a role in this.