Angiotensin II type 1 receptor blocker inhibits fibrosis in rat nonalcoholic steatohepatitis

Current and future anti-fibrotic therapies for chronic liver disease

Chronic injury results in a wound healing response that eventually leads to fibrosis. The response is generalized, with features common among multiple organ systems. In the liver, various different types of injury lead to fibrogenesis, implying a common pathogenesis. Although several specific therapies for patients who have different liver diseases have been successfully developed, including antiviral therapies for those who have hepatitis B and hepatitis C virus infection, specific and effective antifibrotic therapy remains elusive. Over the past 2 decades, great advances in the understanding of fibrosis have been made and multiple mechanisms underlying hepatic fibrogenesis uncovered. Elucidation of these mechanisms has been of fundamental importance in highlighting novel potential therapies. Preclinical studies have indicated several putative therapies that might abrogate fibrogenesis. This article emphasizes mechanisms underlying fibrogenesis and reviews available and future therapeutics.

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.

Angiotensin receptor blockers in the treatment of NASH/NAFLD: could they be a first-class option?

Nonalcoholic fatty liver disease (NAFLD) is a condition pathogenically linked to metabolic syndrome (MS) by insulin resistance (IR), and characterized by hepatic steatosis in the absence of significant alcohol use, hepatotoxicity, and/or other known liver diseases.The principles of NAFLD therapy target IR: the key point of MS. As the renin-angiotensin system (RAS) plays a central role in IR, and subsequently in NAFLD and nonalcoholic steatohepatitis (NASH), an attempt to block the deleterious effects of RAS overexpression seems a logical target. While many potential therapies tested in NASH target only the consequences of this condition, or try to "get rid" of excessive fat, angiotensin receptor blockers (ARBs) could act as an elegant tool for adequate correction of the various imbalances that act in harmony in NASH/NAFLD. Indeed, by inhibiting RAS we can improve the intracellular insulin signaling pathway, better control adipose tissue proliferation and adipokine production, and produce more balanced local and systemic levels of various cytokines. At the same time, by controlling the local RAS in the liver we might be able to prevent at least fibrosis and also slow down the vicious cycle that links steatosis to necroinflammation. By targeting the pancreatic effects of angiotensin we should be able to preserve an adequate insulin secretion and acquire a better metabolic balance.In our opinion there are two major advantages of ARBs that make them a possible therapeutic option for treating NASH and MS: their specific antihypertensive effect, and their impact on liver fibrosis. In light of this, and based on the current evidence (including existent human studies), we can speculate that some ARBs like telmisartan, candesartan, and losartan can be beneficial in treating NASH/NAFLD and its consequences, and further larger controlled clinical trials will bring consistent data into this field.

Treatment options for nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease comprises a range of disorders from steatosis and steatohepatitis through to cirrhosis. Nonalcoholic steatohepatitis can progress to cirrhosis and liver-related death. Therefore, managing this common disorder is becoming an important public health issue. Lifestyle measures are commonly suggested but robust data are lacking. Trials with antioxidants (vitamin E, betaine) as well as cytoprotectants (ursodeoxycholic acid) have been disappointing. While data for insulin sensitizers such as metformin are less conclusive, thiazolidinediones appear promising. However, not all patients respond to thiazolidinediones. Moreover, issues related to weight gain, cardiovascular risk need to be addressed. The use of endocannabinoid antagonists and insulin secretagogues are novel strategies to combat this disorder.

Olmesartan medoxomil: a review of its use in the management of hypertension

Olmesartan medoxomil (Olmetec, Benicar) is an angiotensin II type 1 (AT(1)) receptor antagonist (angiotensin receptor blocker [ARB]) that inhibits the actions of angiotensin II on the renin-angiotensin-aldosterone system, which plays a key role in the pathogenesis of hypertension. Oral olmesartan medoxomil 10-40 mg once daily is recommended for the treatment of adult patients with hypertension. In those with inadequate BP control using monotherapy, fixed-dose olmesartan medoxomil/hydrochlorothiazide (HCTZ) [Olmetec plus, Benicar-HCT] combination therapy may be initiated. Extensive clinical evidence from several large well designed trials and the clinical practice setting has confirmed the antihypertensive efficacy and good tolerability profile of oral olmesartan medoxomil, as monotherapy or in combination with HCTZ, in patients with hypertension, including elderly patients with isolated systolic hypertension (ISH). Notably, BP control is sustained throughout the 24-hour dosage interval, including during the last 4 hours of this period. In clinical trials, olmesartan medoxomil monotherapy provided better antihypertensive efficacy than losartan, candesartan cilexetil or irbesartan monotherapy, and was at least as effective as valsartan treatment, with a faster onset of action than other ARBs in terms of reductions from baseline in diastolic BP (DBP) and, in most instances, systolic BP (SBP). Combination therapy with olmesartan medoxomil plus HCTZ was superior to that with benazepril plus amlodipine, as effective as that with losartan plus HCTZ, noninferior to that with atenolol plus HCTZ, but less effective than that with telmisartan plus HCTZ, in individual trials. Data from ongoing clinical outcome trials are required to more fully determine the relative position of olmesartan medoxomil therapy in the management of hypertension. In the meantime, the consistent antihypertensive efficacy during the entire 24-hour dosage interval and good tolerability profile of olmesartan medoxomil, with or without HCTZ, make it a valuable option for the treatment of adult patients with hypertension, including the elderly.

[Non-alcoholic fatty liver disease and cardiovascular risk]

Non-alcoholic fatty liver disease is present in 15-25% of the general population. The fundamental derangement in non-alcoholic fatty liver disease is insulin resistance, a key component of the metabolic syndrome, which includes type 2 diabetes mellitus, dyslipidemia, hypertension, and obesity. The natural history of non-alcoholic fatty liver disease is not always benign, and causality for chronic liver disease and cirrhosis is well known in clinical practice and sometimes it is accompanied by hepatocellular carcinoma. Non-alcoholic fatty liver disease is likely to be associated with increased cardiovascular disease risk, and it raises the possibility that non-alcoholic fatty liver disease may be not only a marker but also an early mediator of atherosclerosis. Therapy is currently directed at treating components of the metabolic syndrome which may be beneficial also for the liver.

Angiotensin II-induced non-alcoholic fatty liver disease is mediated by oxidative stress in transgenic TG(mRen2)27(Ren2) rats

BACKGROUND/AIMS

Non-alcoholic fatty liver disease (NAFLD) is a common health problem and includes a spectrum of hepatic steatosis, steatohepatitis and fibrosis. The renin-angiotensin system (RAS) plays a vital role in blood pressure regulation and appears to promote hepatic fibrogenesis. We hypothesized that increased RAS activity causes NAFLD due to increased hepatic oxidative stress.

METHODS

We employed the transgenic TG(mRen2)27(Ren2) hypertensive rat, harboring the mouse renin gene with elevated tissue Angiotensin II (Ang II).

RESULTS

Compared with normotensive Sprague-Dawley (SD) control rats, Ren2 developed significant hepatic steatosis by 9 weeks of age that progressed to marked steatohepatitis and fibrosis by 12 weeks. These changes were associated with increased levels of hepatic reactive oxygen species (ROS) and lipid peroxidation. Accordingly, 9-week-old Ren2 rats were treated for 3 weeks with valsartan, an angiotensin type 1 receptor blocker, or tempol, a superoxide dismutase/catalase mimetic. Hepatic indices for oxidative stress, steatosis, inflammation and fibrosis were markedly attenuated by both valsartan and tempol treatment.

CONCLUSIONS

This study suggests that Ang II causes development and progression of NAFLD in the transgenic Ren2 rat model by increasing hepatic ROS. Our findings also support a potential role of RAS in prevention and treatment of NAFLD.

Review article: diagnosis and treatment of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent condition affecting adults and children, leading to significant morbidity. It is often associated with the metabolic syndrome, although multiple pathogenetic mechanisms have been suggested. In the coming decades, it promises to be the leading cause of liver disease in industrial countries.

AIM

To provide a comprehensive, updated review of diagnosis and management of NAFLD and to appraise the evolution of new modalities in these areas.

METHODS

An Ovid MEDLINE search was performed to identify pertinent original research and review articles. Selected references in these articles were also evaluated.

RESULTS

The diagnosis of hepatic steatosis and steatohepatitis or non-alcoholic steatohepatitis (NASH) is not yet possible without liver biopsy. This is impractical given the large numbers affected by the condition. Current therapy has focused on improving insulin resistance and mediators of inflammation, factors probably associated with disease progression.

CONCLUSIONS

There are no proven non-invasive diagnostic modalities to distinguish NAFLD and NASH, but new biomarker panels are approximating the liver biopsy in accuracy. Therapeutic targets of drug development are in early stages, but a multifaceted approach will probably yield several treatment options in the years to come.

Liver disease and the renin-angiotensin system: recent discoveries and clinical implications

The renin-angiotensin system (RAS) is a key regulator of vascular resistance, sodium and water homeostasis and the response to tissue injury. Historically, angiotensin II (Ang II) was thought to be the primary effector peptide of this system. Ang II is produced predominantly by the effect of angiotensin converting enzyme (ACE) on angiotensin I (Ang I). Ang II acts mainly through the angiotensin II type-1 receptor (AT(1)) and, together with ACE, these components represent the 'classical' axis of the RAS. Drug therapies targeting the RAS by inhibiting Ang II formation (ACE inhibitors) or binding to its receptor (angiotensin receptor blockers) are now in widespread clinical use and have been shown to reduce tissue injury and fibrosis in cardiac and renal disease independently of their effects on blood pressure. In 2000, two groups using different methodologies identified a homolog of ACE, called ACE2, which cleaves Ang II to form the biologically active heptapeptide, Ang-(1-7). Conceptually, ACE2, Ang-(1-7), and its putative receptor, the mas receptor represent an 'alternative' axis of the RAS capable of opposing the often deleterious actions of Ang II. Interestingly, ACE inhibitors and angiotensin receptor blockers increase Ang-(1-7) production and it has been proposed that some of the beneficial effects of these drugs are mediated through upregulation of Ang-(1-7) rather than inhibition of Ang II production or receptor binding. The present review focuses on the novel components and pathways of the RAS with particular reference to their potential contribution towards the pathophysiology of liver disease.

Development from simple steatosis to liver cirrhosis and hepatocellular carcinoma: a 27-year follow-up case

Nonalcoholic fatty liver disease (NAFLD) is classified as nonalcoholic steatohepatitis (NASH) or simple steatosis (SS) according to histological findings. It is well recognized that NASH may develop into cirrhosis and hepatocellular carcinoma (HCC), both with unfavorable prognoses. Although the outlook of SS is reported to be better than that of NASH, the long-term prognosis of SS remains unclear. Here, we report the case of a patient who was diagnosed as having SS by a first liver biopsy, and later developed into cirrhosis and HCC over a period of 27 years. In 1980, a 42-year-old Japanese man was admitted because of abnormal liver function tests. He had no history of alcohol intake and was negative for hepatitis virus markers and autoantibodies. A liver biopsy specimen showed macrovesicular steatosis without ballooned hepatocytes, Mallory hyaline, lobular inflammation, or perisinusoidal/perivenular fibrosis, confirming the diagnosis of SS. The patient's serum aminotransferase levels did not normalize despite repeated dietary instruction, and in 2001, liver histology demonstrated cirrhosis with mild steatosis and hepatocyte ballooning, leading to the diagnosis of NASH-related cirrhosis. HCC appeared in 2007. Overall, this patient progressed to cirrhosis and HCC in 20 and 27 years, respectively, following initial diagnosis. Platelet counts and degree of steatosis, as assessed by periodic ultrasonography, were seen to gradually reduce with progression of fibrosis. This case demonstrates that even a diagnosis of SS does not guarantee non-progression to cirrhosis and HCC, and careful follow-up is needed not only in patients with NASH, but also in those with SS.

Non-alcoholic fatty liver disease: the mist gradually clears

Non-alcoholic fatty liver disease (NAFLD) is now the commonest liver disorder in the developed world affecting up to a third of individuals. It is closely associated with features of the metabolic syndrome, particularly obesity and diabetes. It can progress to cirrhosis, hepatocellular carcinoma and liver failure and is an increasing indication for transplantation. Dietary and genetic factors determine susceptibility to NAFLD and its progression. NAFLD may also be involved in the pathogenesis of cardiovascular disease. Most patients present with incidentally found abnormal liver blood tests. Diagnosis is usually one of exclusion. Liver biopsy is required for disease staging, but new imaging modalities and biomarkers are emerging which may eventually fulfil this role. There is, as yet no firm evidence-based treatment for NAFLD. Therapy is currently directed at treating components of the metabolic syndrome which may also be beneficial for the liver. The recent elucidation of the mechanisms leading to progressive disease suggests a variety of novel targets worthy of testing in animal models of NAFLD and subsequently in pilot studies in humans.

Significance of chymase-dependent angiotensin II formation in the progression of human liver fibrosis

AIM

Angiotensin II may contribute to liver fibrogenesis. In addition to angiotensin-converting enzyme (ACE), chymase, which is expressed by mast cells, is also known to be an angiotensin II-forming enzyme. However, it is unclear which of these two angiotensin II-forming enzymes plays a more important role in liver cirrhosis progression. In the present study, the role of angiotensin II-forming enzymes in the progression of liver cirrhosis was clarified.

METHODS

A total of 77 patients (16 in F0 stage, 10 in F1 stage, 22 in F2 stage, 12 in F3 stage, and 17 in F4 stage) were classified according to the new Inuyama classification into a non-cirrhosis (F0) group, an early cirrhosis (F1 + F2) group, and a chronic cirrhosis (F3 + F4) group.

RESULTS

Both chymase and total angiotensin II-forming activities were significantly higher in chronic cirrhosis patients than in the other two groups. However, there was nodifference among the three groups in ACE activity. On immunohistology, the number of chymase- and angiotensin II-positive cells was significantly higher in the chronic cirrhosis group than in the non-cirrhosis and early cirrhosis groups. There were significant correlations between the number of chymase-positive cells and the number of angiotensin II-positive cells, between the number of chymase-positive cells and the degree of fibrosis, and between the number of angiotensin II-positive cells and the degree of fibrosis.

CONCLUSION

These results suggest that chymase-dependent angiotensin II formation may play an important role in hepatic fibrosis of patients with cirrhosis.

Diagnosis and therapy of nonalcoholic steatohepatitis

The increasing prevalence of obesity, insulin resistance, and the metabolic syndrome has significant implications for the future of chronic liver disease. The resultant increase in the number of patients with nonalcoholic fatty liver disease (NAFLD) is expected to translate into increased numbers of patients with end-stage liver disease (cirrhosis), liver failure, and hepatocellular carcinoma. It is particularly important to identify the patients who are at greatest risk of these aforementioned complications of chronic liver disease, those nonalcoholic fatty liver disease patients with nonalcoholic steatohepatitis. Currently liver biopsy is the gold standard for diagnosis, but less invasive, highly accurate, and affordable screening tools are required. These tools may include radiologic or laboratory studies to identify patients noninvasively who may benefit from therapeutic interventions. Clinical scoring systems that may be used in general practice as initial screening tools also may prove useful. Most therapeutic modalities available or under development target the major pathways thought essential in the pathogenesis of nonalcoholic steatohepatitis and often are directed at reducing body mass index and improving insulin resistance via pharmacologic, surgical, dietary, or exercise regimens. Other potential therapeutic agents directed at cytoprotection or reduction of fibrosis are under investigation. This article focuses on diagnosis and therapy available and under development for this chronic liver disease.

Liver fibrosis

Liver damage leads to an inflammatory response and to the activation and proliferation of mesenchymal cell populations within the liver which remodel the extracellular matrix as part of an orchestrated wound-healing response. Chronic damage results in a progressive accumulation of scarring proteins (fibrosis) that, with increasing severity, alters tissue structure and function, leading to cirrhosis and liver failure. Efforts to modulate the fibrogenesis process have focused on understanding the biology of the heterogeneous liver fibroblast populations. The fibroblasts are derived from sources within and out with the liver. Fibroblasts expressing alpha-smooth muscle actin (myofibroblasts) may be derived from the transdifferentiation of quiescent hepatic stellate cells. Other fibroblasts emerge from the portal tracts within the liver. At least a proportion of these cells in diseased liver originate from the bone marrow. In addition, fibrogenic fibroblasts may also be generated through liver epithelial (hepatocyte and biliary epithelial cell)-mesenchymal transition. Whatever their origin, it is clear that fibrogenic fibroblast activity is sensitive to (and may be active in) the cytokine and chemokine profiles of liver-resident leucocytes such as macrophages. They may also be a component driving the regeneration of tissue. Understanding the complex intercellular interactions regulating liver fibrogenesis is of increasing importance in view of predicted increases in chronic liver disease and the current paucity of effective therapies.

Nonalcoholic fatty liver disease: diagnosis and relation to metabolic syndrome and approach to treatment

Nonalcoholic fatty liver disease is an increasingly prevalent disorder that spans a range of conditions from hepatic steatosis to cirrhosis. It is commonly associated with obesity and diabetes, two components of the metabolic syndrome. Although hepatic steatosis may be reversible, disease progression appears to be triggered by overproduction of reactive oxygen species and mitochondrial injury in hepatocytes. Evolving treatments are focused on reversing insulin resistance, which underlies many of the metabolic derangements in this disease.

Nonalcoholic fatty liver disease as a component of the metabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is an important cause of liver-related morbidity and mortality. The association between NAFLD and the metabolic syndrome is well established: the presence of the metabolic syndrome signifies advanced histology in NAFLD patients. Emerging data indicate that patients with NAFLD have a significantly higher prevalence of cardiovascular disease. This article reviews the definitions of the two syndromes, their association, and the cardiovascular risk conferred by both when they occur separately and together. This review also discusses management options for the syndromes, including treating the individual components of the metabolic syndrome in NAFLD patients.

Natural history of chronic hepatitis B: special emphasis on disease progression and prognostic factors

The natural history of chronic hepatitis B virus (HBV) infection and disease is complex and highly variable. We review the natural history of chronic hepatitis B with emphasis on the rates of disease progression and factors influencing the course of the liver disease. Chronic hepatitis B is characterized by an early replicative phase (HBeAg positive chronic hepatitis) and a late low or non-replication phase with HBeAg seroconversion and liver disease remission (inactive carrier state). Most patients become inactive carriers after spontaneous HBeAg seroconversion with good prognosis, but progression to HBeAg negative chronic hepatitis due to HBV variants not expressing HBeAg occurs at a rate of 1-3 per 100 person years following HBeAg seroconversion. The incidence of cirrhosis appears to be about 2-fold higher in HBeAg negative compared to HBeAg positive chronic hepatitis. In the cirrhotic patient the 5-year cumulative risk of developing hepatocellular carcinoma is 17% in East Asia and 10% in the Western Europe and the United States and the 5-year liver related death rate is 15% in Europe and 14% in East Asia. There is a growing understanding of viral, host and environmental factors influencing disease progression, which ultimately could improve the management of chronic hepatitis B.