Overview and recent trends of systematic reviews and meta-analyses in hepatology

Liver

The discovery that renin–angiotensin system (RAS) components are locally expressed in the liver tissue, pointed out to a role for this system in the pathogenesis of hepatic fibrosis and cirrhosis. The RAS counter-regulatory axis composed by the angiotensin converting enzyme 2 (ACE2), angiotensin-(1-7) [Ang-(1-7)] and Mas receptor mediates pro-inflammatory, pro-thrombotic, and pro-fibrotic processes, frequently opposing the classical RAS arm (ACE-Ang II-AT₁ receptor) actions. Therefore, the balance between both RAS axes most likely affects the clinical and histopathological expression of liver diseases. It is worth noticing that liver diseases are major causes of morbidity and mortality worldwide. Without proper treatment, all types of chronic hepatitis will progress to end-stage liver diseases, including cirrhosis, liver failure, and hepatocellular carcinoma, which ultimately lead to death. In this context, to better comprehend the role of RAS components in liver failure might pave the way for the search of potential predictive biomarkers as well as the development of novel therapeutic approaches. Valuable data have been generated from preclinical and clinical studies. Herein, we summarize the current evidence, mainly focusing in the ACE2-Ang-(1-7)-Mas receptor arm, regarding the role of RAS in liver diseases. The therapeutic potential of the modulation of RAS molecules in liver diseases is also discussed.

Serum levels of angiotensin converting enzyme as a biomarker of liver fibrosis

The renin angiotensin system (RAS) is classically conceived as a circulating hormonal system involved in blood pressure control and hydroelectrolyte balance. The discovery that RAS components are locally expressed in a wide range of organs and tissues, including the liver, pointed to a role for this system in the pathogenesis of several conditions including hepatic fibrosis and cirrhosis. It has been widely reported that the classical RAS axis composed by the angiotensin converting enzyme (ACE)-angiotensin (Ang) II-Ang type 1 (AT1) receptor mediates pro-inflammatory, pro-thrombotic, and pro-fibrotic processes. On the other hand, the alternative axis comprising ACE2-Ang-(1-7)-Mas receptor seems to play a protective role by frequently opposing Ang II action. Chronic hepatitis B (CHB) is one of the leading causes of liver fibrosis, accounting for the death of nearly one million people worldwide. Liver fibrosis is a key factor to determine therapeutic interventions for patients with CHB. However, the establishment of non-invasive and accurate methods to detect reversible stages of liver fibrosis is still a challenge. In an elegant study published in the 36^th issue of the World Journal of Gastroenterology, Noguchi et al showed the predictive value of serum ACE levels in detecting not only advanced stages of liver fibrosis but also initial and intermediate fibrotic stages. The serum levels of ACE might represent an accurate, non-invasive, widely available, and easy method to evaluate fibrosis related to CHB. Moreover, therapies involving the inhibition of the classical RAS axis components might be promising in the control of CHB-related liver fibrosis.

Diagnostic Accuracy of Hepatic Vein Arrival Time Performed with Contrast-Enhanced Ultrasonography for Cirrhosis: A Systematic Review and Meta-Analysis

Background/Aims

We identified reports in the literature regarding the diagnostic accuracy of hepatic vein arrival time (HVAT) measured by contrast-enhanced ultrasonography (CEUS) to assess hepatic fibrosis in cirrhosis.

Methods

The Ovid MEDLINE, Embase, and Cochrane databases were searched for all studies published up to 23 July 2015 that evaluated liver status using CEUS and liver biopsy (LB). The QUADAS-II (quality assessment of diagnostic accuracy studies-II) was applied to assess the internal validity of the diagnostic studies. Selected studies were subjected to a meta-analysis with MetaDisc 1.4 and RevMan 5.3.

Results

A total of 12 studies including 844 patients with chronic liver disease met our inclusion criteria. The overall summary sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of the HVAT measured by CEUS for the detection of cirrhosis compared to LB were 0.83 (95% confidence interval [CI], 0.77 to 0.89), 0.75 (95% CI, 0.69 to 0.79), 3.45 (95% CI, 1.60 to 7.43), and 0.28 (95% CI, 0.10 to 0.74), respectively. The summary diagnostic odds ratio (random effects model) was 15.23 (95% CI, 3.07 to 75.47), the summary receiver operator characteristics area under the curve was 0.74 (standard error [SE]=0.14), and the index Q was 0.69 (SE=0.11).

Conclusions

Based on a systematic review, the measurement of HVAT by CEUS exhibited an increased accuracy and correlation for the detection of cirrhosis.

Renin angiotensin system in liver diseases: Friend or foe?

In the last three decades, the understanding of the renin angiotensin system (RAS) has been changed by the discoveries of functional local systems, novel biologically active peptides, additional specific receptors, alternative pathways of angiotensin (Ang) II generation, and new roles for enzymes and precursor components other than those in Ang II synthesis. In this regard, the discovery that Ang-(1-7) opposes the pressor, proliferative, pro-fibrotic, and pro-inflammatory effects mediated by Ang II has contributed to the realization that the RAS is composed of two axes. The first axis consists of the angiotensin-converting enzyme (ACE), with Ang II as the end product, and the angiotensin type 1 (AT₁) receptor as the main effector mediating the biological actions of Ang II. The second axis results from ACE2-mediated hydrolysis of Ang II, leading to the production of Ang-(1-7), with the Mas receptor as the main effector conveying the vasodilatory, anti-proliferative, anti-fibrotic, and anti-inflammatory effects of Ang-(1-7). Experimental and clinical studies have shown that both axes of the RAS may take part in the pathogenesis of liver diseases. In this manuscript, we summarize the current evidence regarding the role of RAS in hepatic cirrhosis and its complications, including hemodynamic changes and hepatorenal syndrome. The therapeutic potential of the modulation of RAS molecules in liver diseases is also discussed.

Transient elastography versus hepatic venous pressure gradient for diagnosing portal hypertension: a systematic review and meta-analysis

Background/Aims

Transient elastography (TE) has been proposed as a promising noninvasive alternative to hepatic venous pressure gradient (HVPG) for detecting portal hypertension (PH). However, previous studies have yielded conflicting results. We gathered evidence from literature on the clinical usefulness of TE versus HVPG for assessing PH.

Methods

We conducted a systematic review by searching databases for relevant literature evaluating the clinical usefulness of non-invasive TE for assessing PH in patients with cirrhosis. A literature search in Ovid Medline, EMBASE and the Cochrane Library was performed for all studies published prior to December 30, 2015.

Results

Eight studies (1,356 patients) met our inclusion criteria. For the detection of PH (HVPG ≥6 mmHg), the summary sensitivity and specificity were 0.88 (95% confidence interval [CI] 0.86-0.90) and 0.74 (95% CI 0.67-0.81), respectively. Regarding clinically significant PH (HVPG ≥10 mmHg), the summary sensitivity and specificity were 0.85 (95% CI 0.63-0.97) and 0.71 (95% CI 0.50-0.93), respectively. The overall correlation estimate of TE and HVPG was large (0.75, 95% CI: 0.65; 0.82, P<0.0001).

Conclusions

TE showed high accuracy and correlation for detecting the severity of PH. Therefore, TE shows promise as a reliable and non-invasive procedure for the evaluation of PH that should be integrated into clinical practice.

Renin-angiotensin system inhibitors and fibrosis in chronic liver disease: a systematic review

BACKGROUND AND AIMS

The renin-angiotensin system (RAS) has an important role in hepatic fibrosis and portal hypertension. RAS inhibitors are already accepted in clinical fields for antihypertensive management, but their effects on hepatic fibrosis are controversial. The aim of this study was to systematically review the effects of RAS inhibitors on hepatic fibrosis based on histological assessment.

METHODS

We performed a systematic review and meta-analysis (MA) of the literature using the Ovid-MEDLINE, EMBASE, and Cochrane Library databases (up to January 2015) to identify clinical studies evaluating the effects of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers on hepatic fibrosis or cirrhosis patients based on histological assessment. Of the 455 studies identified, we analyzed 7, including a total of 1066 patients, which met our selection criteria.

RESULTS

According to the MA, patients treated with RAS inhibitors had significantly lower fibrosis scores (SMD -0.68, 95 % CI -1.03, -0.34, I (2) = 0 %, p < 0.0001) and smaller fibrosis areas (SMD -0.80, 95 % CI -1.18, -0.41, I (2) = 0 %, p < 0.0001) than controls. Serum fibrosis markers such as TGF-β1, collagen I, IV, TIMP-1, and MMP2 were significantly reduced in the intervention group. In two studies, mean arterial pressures were significantly decreased in RAS inhibitor users, but there were no reports about symptoms related to decreased blood pressure. No significant difference was found in serum creatinine levels between the intervention and control groups, and significant renal dysfunction was not observed after administration of RAS inhibitors.

CONCLUSIONS

RAS inhibitors are potential therapeutic agents for hepatic fibrosis, which can be safely used in patients with chronic liver disease.

Assessment for Risk of Bias in Systematic Reviews and Meta-Analyses in the Field of Hepatology

A systematic review (SR) provides the best and most objective analysis of the existing evidence in a particular field. SRs and derived conclusions are essential for evidence-based strategies in medicine and evidence-based guidelines in clinical practice. The popularity of SRs has also increased markedly in the field of hepatology. However, although SRs are considered to provide a higher level of evidence with greater confidence than original articles, there have been no reports on the quality of SRs and meta-analyses (MAs) in the field of hepatology. Therefore, we performed a quality assessment of 225 SRs and MAs that were recently published in the field of hepatology (January 2011 to September 2014) using A MeaSurement Tool to Assess systematic Reviews (AMSTAR). Using AMSTAR, we revealed both a shortage of assessments of the scientific quality of individual studies and a publication bias in many SRs and MAs. This review addresses the concern that SRs and MAs need to be conducted in a stricter and more objective manner to minimize bias and random errors. Thus, SRs and MAs should be supported by a multi-disciplinary approach that includes clinical experts, methodologists, and statisticians.

The need for histological subclassification of cirrhosis: a systematic review and meta-analysis

BACKGROUND & AIMS

The need for further histological subclassification of cirrhosis has been increasingly recognized because of the heterogeneity of severity within cirrhosis. We sought to identify evidence in the literature regarding the histological subclassification of cirrhosis using the Laennec stage.

METHODS

We conducted a systematic review and meta-analysis by searching databases, including MEDLINE, EMBASE and the COCHRANE library, for relevant studies.

RESULTS

Of 208 studies identified, 16 were eligible according to the inclusion criteria. With higher grades of the Laennec stage, clinical stages of cirrhosis and Child-Pugh scores/Model for end-stage liver disease scores increased (P < 0.05). Higher Laennec stages were statistically associated with the development of liver-related events, such as liver-related death, liver cancer progression and variceal haemorrhage, as well as higher hepatic venous pressure gradients and higher liver stiffness values (P < 0.05). Two open-labelled studies showed the usefulness of the Laennec system with regard to the evaluation of whether antifibrotic treatments were effective. The mean kappa value was 0.81 (range 0.61-0.87) for inter-observer agreement.

CONCLUSIONS

Based on this systematic review and meta-analysis, histological subclassification of cirrhosis using the Laennec system is useful to better predict prognosis and complications of portal hypertension.

Therapeutic Effects of Mesenchymal Stem Cells for Patients with Chronic Liver Diseases: Systematic Review and Meta-analysis

Based on their ability to differentiate into multiple cell types including hepatocytes, the transplantation of mesenchymal stem cells (MSCs) has been suggested as an effective therapy for chronic liver diseases. The aim of this study was to evaluate the safety, efficacy and therapeutic effects of MSCs in patients with chronic liver disease through a literature-based examination. We performed a systematic review (SR) and meta-analysis (MA) of the literature using the Ovid-MEDLINE, EMBASE and Cochrane Library databases (up to November 2014) to identify clinical studies in which patients with liver diseases were treated with MSC therapy. Of the 568 studies identified by the initial literature search, we analyzed 14 studies and 448 patients based on our selection criteria. None of the studies reported the occurrence of statistically significant adverse events, side effects or complications. The majority of the analyzed studies showed improvements in liver function, ascites and encephalopathy. In particular, an MA showed that MSC therapy improved the total bilirubin level, the serum albumin level and the Model for End-stage Liver Disease (MELD) score after MSC treatment. Based on these results, MSC transplantation is considered to be safe for the treatment of chronic liver disease. However, although MSCs are potential therapeutic agents that may improve liver function, in order to obtain meaningful insights into their clinical efficacy, further robust clinical studies must be conducted to evaluate the clinical outcomes, such as histological improvement, increased survival and reduced liver-related complications, in patients with chronic liver disease.