John S Lubel

Upregulation of hepatic angiotensin-converting enzyme 2 (ACE2) and angiotensin-(1–7) levels in experimental biliary fibrosis

Background/Aims Angiotensin-converting enzyme 2 (ACE2), its product, angiotensin-(1–7) and its receptor, Mas, may moderate the adverse effects of angiotensin II in liver disease. We examined the expression of these novel components of the renin angiotensin system (RAS) and the production and vasoactive effects of angiotensin-(1–7) in the bile duct ligated (BDL) rat. Methods BDL or sham-operated rats were sacrificed at 1, 2, 3 and 4 weeks. Tissue and blood were collected for gene expression, enzyme activity and peptide measurements. In situ perfused livers were used to assess angiotensin peptide production and their effects on portal resistance. Results Hepatic ACE2 gene and activity (P <0.0005), plasma angiotensin-(1–7) (P <0.0005) and Mas receptor expression (P <0.01) were increased following BDL compared to shams. Perfusion experiments confirmed that BDL livers produced increased angiotensin-(1–7) (P <0.05) from angiotensin II and this was augmented (P <0.01) by ACE inhibition. Whilst angiotensin II increased vasoconstriction in cirrhotic livers, angiotensin-(1–7) had no effect on portal resistance. Conclusions RAS activation in chronic liver injury is associated with upregulation of ACE2, Mas and hepatic conversion of angiotensin II to angiotensin-(1–7) leading to increased circulating angiotensin-(1–7). These results support the presence of an ACE2-angiotensin-(1–7)-Mas axis in liver injury which may counteract the effects of angiotensin II.

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 (AT1) 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.

Hepatitis B virus reactivation following immunosuppressive therapy: guidelines for prevention and management

It is well known that immunosuppressive drugs or cancer chemotherapy can stimulate replication of hepatitis B virus (HBV) and precipitate severe flares of HBV infection. The risk of this syndrome of ‘reactivation hepatitis B’ is highest in haematopoietic stem cell or solid organ transplant recipients and in those undergoing chemotherapy for haematological malignancies; however, it has been described following almost any form of immunosuppressive treatment. Fortunately, it can be largely prevented by prophylactic therapy with oral anti‐HBV nucleoside/nucleotide analogues. Importantly, chronic HBV infection is usually asymptomatic, and most patients at risk are likely to be unaware that they carry the infection. Thus, the key to avoiding this potentially fatal complication of immunosuppressive treatment is to ensure that all patients at risk of chronic HBV infection are screened for the disease before commencing immunosuppressive treatment or chemotherapy.

Liver fibrosis: a balance of ACEs?

There is an increasing body of evidence to suggest that the RAS (renin-angiotensin system) contributes to tissue injury and fibrosis in chronic liver disease. A number of studies have shown that components of a local hepatic RAS are up-regulated in fibrotic livers of humans and in experimental animal models. Angiotensin II, the main physiological effector molecule of this system, mediates liver fibrosis by stimulating fibroblast proliferation (myofibroblast and hepatic stellate cells), infiltration of inflammatory cells, and the release of inflammatory cytokines and growth factors such as TGF (transforming growth factor)-beta1, IL (interleukin)-1beta, MCP (monocyte chemoattractant protein)-1 and connective tissue growth factor. Furthermore, blockade of the RAS by ACE (angiotensin-converting enzyme) inhibitors and angiotensin type 1 receptor antagonists significantly attenuate liver fibrosis in experimental models of chronic liver injury. In 2000 ACE2 (angiotensin-converting enzyme 2), a human homologue of ACE, was identified. ACE2 efficiently degrades angiotensin II to angiotensin-(1-7), a peptide which has recently been shown to have both vasodilatory and tissue protective effects. This suggests that ACE2 and its products may be part of an alternate enzymatic pathway in the RAS, which counterbalances the generation and actions of angiotensin II, the ACE2-angiotensin-(1-7)-Mas axis. This review focuses on the potential roles of the RAS, angiotensin II and ACE2 in chronic liver injury and fibrogenesis.

Hepatitis B reactivation in patients receiving cytotoxic chemotherapy: Diagnosis and management

Nearly one third of the worlds population have been infected with hepatitis B and the virus is endemic in many Asian countries. With increasing life expectancy and the expected global increase in cancer, chemotherapy induced reactivation of hepatitis B is likely to become an increasing problem. Patients with significant levels of hepatitis B virus (HBV) DNA in serum prior to chemotherapy and patients receiving intensive chemotherapy for hematological malignancies appear particularly at risk. Most patients who suffer reactivation of hepatitis B are positive for hepatitis B surface antigen (HBsAg) prior to chemotherapy and are therefore easily identifiable by routine screening. In addition, the very large population of patients who have been exposed to the virus and have apparently cleared the virus as assessed by serological testing (HBsAg negative/hepatitis B core antibody [HBcAb] positive) may also be at risk of reactivation. These patients should be monitored and in some cases receive prophylaxis during chemotherapy. Published experience with antiviral prophylaxis has largely been limited to the nucleoside analogue, lamivudine. The commencement of antiviral prophylaxis prior to chemotherapy and its continuation until restitution of normal host immunity is the cornerstone to effective prevention of hepatitis B reactivation. This review summarizes the important issues related to HBV reactivation and suggests an algorithm for managing these patients in the clinical setting.

Review article: vitamin D and inflammatory bowel disease – established concepts and future directions

Understanding of the role of vitamin D in health and disease has increased markedly in the past decade, with its involvement extending well beyond traditional roles in calcium and phosphate homeostasis and musculoskeletal health. This conceptual expansion has been underpinned by identification and exploration of components of this axis including vitamin D‐binding protein, key enzymes and receptors in multiple cell types, and a greater recognition of nonclassical autocrine and paracrine effects. Its influence in IBD remains uncertain.

Angiotensin-(1-7), an alternative metabolite of the renin-angiotensin system, is up-regulated in human liver disease and has antifibrotic activity in the bile-duct-ligated rat.

Ang-(1-7) (angiotensin-1-7), a peptide product of the recently described ACE (angiotensin-converting enzyme) homologue ACE2, opposes the harmful actions of AngII (angiotensin II) in cardiovascular tissues, but its role in liver disease is unknown. The aim of the present study was to assess plasma levels of Ang-(1-7) in human liver disease and determine its effects in experimental liver fibrosis. Angiotensin peptide levels were measured in cirrhotic and non-cirrhotic patients with hepatitis C. The effects of Ang-(1-7) on experimental fibrosis were determined using the rat BDL (bile-duct ligation) model. Liver histology, hydroxyproline quantification and expression of fibrosis-related genes were assessed. Expression of RAS (renin-angiotensin system) components and the effects of Ang-(1-7) were examined in rat HSCs (hepatic stellate cells). In human patients with cirrhosis, both plasma Ang-(1-7) and AngII concentrations were markedly elevated (P<0.001). Non-cirrhotic patients with hepatitis C had elevated Ang-(1-7) levels compared with controls (P<0.05), but AngII concentrations were not increased. In BDL rats, Ang-(1-7) improved fibrosis stage and collagen Picrosirius Red staining, and reduced hydroxyproline content, together with decreased gene expression of collagen 1A1, alpha-SMA (smooth muscle actin), VEGF (vascular endothelial growth factor), CTGF (connective tissue growth factor), ACE and mas [the Ang-(1-7) receptor]. Cultured HSCs expressed AT1Rs (AngII type 1 receptors) and mas receptors and, when treated with Ang-(1-7) or the mas receptor agonist AVE 0991, produced less alpha-SMA and hydroxyproline, an effect reversed by the mas receptor antagonist A779. In conclusion, Ang-(1-7) is up-regulated in human liver disease and has antifibrotic actions in a rat model of cirrhosis. The ACE2/Ang-(1-7)/mas receptor axis represents a potential target for antifibrotic therapy in humans.

Association of circulating vitamin D concentrations with intestinal but not systemic inflammation in inflammatory bowel disease.

Background:Vitamin D may mediate immunomodulatory effects in patients with inflammatory bowel disease (IBD). The relationships between disease activity and circulating levels of total, free, and bioavailable 25(OH) vitamin D (25(OH)D) are poorly defined. The aim of this study was to measure circulating components of the vitamin D axis in patients with IBD and healthy controls and to correlate these with markers of disease activity, adjusting for potential confounders. Methods:Clinical data were obtained and serum was analyzed for 25(OH)D and vitamin D–binding protein in patients with IBD and controls. Markers of systemic and intestinal (fecal calprotectin) inflammation were measured. Results:Serum 25(OH)D concentration was similar across 23 controls, 40 patients with Crohns disease, and 31 with ulcerative colitis. An inverse correlation between 25(OH)D and calprotectin was noted in Crohns disease (Pearsons r = −0.35, P = 0.040), ulcerative colitis (r = −0.39, P = 0.039), and all IBD together (r = −0.37, P = 0.003), but not with systemic markers. A similar trend was noted for free and bioavailable 25(OH)D. This inverse correlation remained after partial correlation analysis correcting for sunlight exposure, total oral vitamin D intake, and obesity and was also noted among the subgroup without small intestinal involvement. Conclusions:Despite total, free, and bioavailable 25(OH)D concentrations being similar to those in a healthy control population, they inversely correlated strongly with intestinal inflammation. This was independent of potential malabsorption, sunlight exposure, and total vitamin D intake and obesity. Vitamin D may play an immunomodulatory role in IBD.

Review article: the pathophysiological roles of the renin–angiotensin system in the gastrointestinal tract

The renin‐angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

Natural history of chronic hepatitis B:Phases in a complex relationship

Chronic hepatitis B (CHB) is a condition of global prevalence and its sequelae include cirrhosis and hepatocellular carcinoma. The natural history of CHB is a complex interplay of virological, environmental and host factors. The dynamic relationship between the virus and host evolves over the duration of the infection and different phases of the disease have been observed and described. These have been conceptualized in terms of the state of balance between the host immune system and the hepatitis B virus and have been given the labels immune tolerant, immune clearance, immune control and immune escape although other nomenclature is also used. Host factors, such as age at infection, determine progression to chronicity. Virological factors including hepatitis B viral load, mutations and genotype also have an impact on the adverse outcomes of the infection, as do hepatotoxic cofactors such as alcohol. Our understanding of the natural history of CHB has evolved significantly over the past few decades and characterizing the phase of disease of CHB remains an integral part of managing this virus in the clinic.