Unbounded solutions of the max-type difference equation xn+1 = max {An/xn, Bn/xn-2},n = 0,1,2,...

We investigate the periodic character and the boundedness nature of positive solutions of the difference equation: xn+1=max{An/xn,Bn/xn−2},n=0,1,..., where {An}∞n=0 and {Bn}∞n=0 are periodic sequences of positive real numbers

Role of ammonia in NAFLD: An unusual suspect

Mechanistically, the symptomatology and disease progression of non-alcoholic fatty liver disease (NAFLD) remain poorly understood, which makes therapeutic progress difficult. In this review, we focus on the potential importance of decreased urea cycle activity as a pathogenic mechanism. Urea synthesis is an exclusive hepatic function and is the body’s only on-demand and definitive pathway to remove toxic ammonia. The compromised urea cycle activity in NAFLD is likely caused by epigenetic damage to urea cycle enzyme genes and increased hepatocyte senescence. When the urea cycle is dysfunctional, ammonia accumulates in liver tissue and blood, as has been demonstrated in both animal models and patients with NAFLD. The problem may be augmented by parallel changes in the glutamine/glutamate system. In the liver, the accumulation of ammonia leads to inflammation, stellate cell activation and fibrogenesis, which is partially reversible. This may be an important mechanism for the transition of bland steatosis to steatohepatitis and further to cirrhosis and hepatocellular carcinoma. Systemic hyperammonaemia has widespread negative effects on other organs. Best known are the cerebral consequences that manifest as cognitive disturbances, which are prevalent in patients with NAFLD. Furthermore, high ammonia levels induce a negative muscle protein balance leading to sarcopenia, compromised immune function and increased risk of liver cancer. There is currently no rational way to reverse reduced urea cycle activity but there are promising animal and human reports of ammonia-lowering strategies correcting several of the mentioned untoward aspects of NAFLD. In conclusion, the ability of ammonia-lowering strategies to control the symptoms and prevent the progression of NAFLD should be explored in clinical trials

Hyperammonemia induces mitochondrial dysfunction and neuronal cell death

BACKGROUND & AIMS: In liver cirrhosis, astrocytic swelling is believed to be the principal mechanism of ammonia neurotoxicity leading to hepatic encephalopathy (HE). The role of neuronal dysfunction in HE is not clear. We aimed to explore the impact of hyperammonemia on mitochondrial function in primary co-cultures of neurons and astrocytes and in acute brain slices of cirrhotic rats using live cell imaging. METHODS: To primary co-cultures of astrocytes and neurons, low concentrations (1 and 5μM) of NH4Cl were applied. In rats with bile-duct ligation (BDL)-induced cirrhosis, a model known to induce hyperammonemia and minimal HE, acute brain slices were studied. One group of BDL rats were treated twice daily with the ammonia scavenger ornithine phenylacetate (OP, 0.3g/kg). Fluorescence measurements of changes in mitochondrial membrane potential (ΔΨm), cytosolic and mitochondrial reactive oxygen species (ROS) production, lipid peroxidation (LP) rates, and cell viability were performed using confocal microscopy. RESULTS: Neuronal cultures treated with NH4Cl exhibited mitochondrial dysfunction, ROS overproduction and reduced cell viability (27.8±2.3% and 41.5±3.7%, respectively) compared to untreated cultures (15.7±1.0%, both p<0.0001). BDL led to increased cerebral LP (p=0.0003) and cytosolic ROS generation (p<0.0001), which was restored by OP (both p<0.0001). Mitochondrial function was severely compromised in BDL resulting in hyperpolarization of ΔΨm with consequent overconsumption of ATP and augmentation of mitochondrial ROS production. Administration of OP restored ΔΨm. In BDL animals, neuronal loss was observed in hippocampal areas, which was partially prevented by OP. CONCLUSIONS: Our results elucidate that low-grade hyperammonemia in cirrhosis can severely impact on brain mitochondrial function. Profound neuronal injury was observed in hyperammonemic conditions, which was partially reversible by OP. This points towards a novel mechanism of HE development. LAY SUMMARY: The impact of hyperammonemia, a common finding in patients with liver cirrhosis, on brain mitochondrial function was investigated in this study. The results show that ammonia in concentrations commonly seen in patients induces severe mitochondrial dysfunction, overproduction of damaging oxygen molecules and profound injury and death of neurons in rat brain cells. These findings point towards a novel mechanism of ammonia-induced brain injury in liver failure and potential novel therapeutic targets

Combination of G-CSF and a TLR4 inhibitor reduce inflammation and promote regeneration in a mouse model of ACLF

BACKGROUND & AIMS: Acute-on-chronic liver failure (ACLF) is characterised by high short-term mortality, systemic inflammation, and failure of hepatic regeneration. Its treatment is an unmet medical need. This study was conducted to explore whether combining TAK-242, a Toll-like receptor-4 (TLR4) antagonist, with Granulocyte-Colony Stimulating Factor (G-CSF) targets inflammation whilst enhancing liver regeneration. METHODS: Two mouse models of ACLF were investigated. Chronic liver injury was induced by carbon tetrachloride followed by either lipopolysaccharide (LPS) or galactosamine (GalN) as extrahepatic or hepatic insults, respectively. G-CSF and/or TLR4-antagonist, TAK-242, were administered daily. The treatment duration was 24h and 5d in the LPS model and 48h in the GalN model, respectively. RESULTS: In a LPS-induced ACLF mouse model treatment with G-CSF was associated with a significant mortality of 66% after 48 hours compared with 0% without G-CSF. Addition of TAK-242 to G-CSF abrogated mortality (0%) and significantly reduced liver cell death, macrophage infiltration and inflammation. In the GalN model, both G-CSF and TAK-242, when used individually, reduced liver injury but their combination was significantly more effective. G-CSF treatment, with or without TAK-242, was associated with activation of the pro-regenerative and anti-apoptotic STAT3 pathway. LPS-driven ACLF was characterized by p21 over-expression suggesting hepatic senescence and inhibition of hepatocyte regeneration. While TAK-242 treatment mitigated the effect on senescence, G-CSF, when co-administered with TAK-242, resulted in a significant increase of markers of hepatocyte regeneration. CONCLUSION: TLR4 inhibition with TAK-242 rescued G-CSF-driven cell death, inflammation, enhanced tissue repair, and significantly induced regeneration thus suggesting that the combination of G-CSF and TAK-242 is a novel approach for the treatment of ACLF. LAY SUMMARY: The combinatorial therapy of Granulocyte-Colony Stimulating Factor and TAK-242, a Toll-like Receptor-4 inhibitor, achieves the dual aim of reducing hepatic inflammation and inducing liver regeneration for the treatment of acute-on-chronic liver failure

Toll-like receptor 4 is a therapeutic target for prevention and treatment of liver failure

Background and aims: Toll-like receptor 4 (TLR4) plays an essential role in mediating organ injury in acute liver failure (ALF) and acute-on-chronic liver failure (ACLF). Here we assess whether inhibiting TLR4 signaling can ameliorate liver failure and serve as a potential treatment. / Material and Methods: Circulating TLR4 ligands and hepatic TLR4 expression was measured in plasma samples and liver biopsies from patients with cirrhosis. TAK-242 (TLR4 inhibitor) was tested in vivo with 10mg/Kg, i.p. in rodent models of ACLF (bile duct ligation + lipopolysaccharide (LPS); carbontetrachloride + LPS) and ALF (Galactosamine + LPS) and in vitro on immortalized human monocytes (THP-1) and hepatocytes (HHL5).. The in vivo therapeutic effect was assessed by coma free survival, organ injury and cytokine release and in vitro by measuring IL6, IL1b or cell injury (TUNEL), respectively. / Results: In patients with cirrhosis, hepatic TLR4 expression was upregulated and circulating TLR4 ligands were increased (p<0.001). ACLF in rodents was associated with a switch from apoptotic cell death in ALF to non-apoptotic forms of cell death. TAK-242 reduced LPS induced cytokine secretion and cell death (p=0.002) in hepatocytes and monocytes in vitro. In rodent models of ACLF, TAK-242 administration improved coma free survival, reduced the degree of hepatocyte cell death in liver p<0.001) and kidneys (p=0.048) and reduced circulating cytokine levels (IL1b p<0.001). In a rodent model of ALF TAK-242 prevented organ injury (p<0.001) and systemic inflammation (IL1b p<0.001). / Conclusion: This study shows that TLR4 signaling is a key factor in the development of both ACLF and ALF and its inhibition improves severity of organ injury and outcome. TAK-242 may be of therapeutic relevance in patients with liver failure

Determinants of mortality in patients with cirrhosis and uncontrolled variceal bleeding

BACKGROUND AND AIM: Failure to control oesophago-gastric variceal bleeding (OGVB) and acute-on-chronic liver failure (ACLF) are both important prognostic factors in liver cirrhosis. The aims of this study were to determine whether ACLF and its severity define the risk of death in OGVB and whether insertion of rescue transjugular intrahepatic stent-shunt (TIPSS) improves the survival of patients with failure to control OGVB and ACLF. METHODS: From a prospectively maintained ICU registry, data of 174 consecutive eligible patients with failure to control OGVB between 2005 and 2015, were included. Rescue TIPSS was defined as technically successful TIPSS within 72-hours of presentation with failure to control OGVB. Cox proportional hazards regression analyses were applied to explore the impact of ACLF and TIPSS on survival in failure-to-control OGVB. RESULTS: ACLF patients (n=119) were significantly older, had organ failures and higher white cell count compared with patients with acute decompensation (AD, n=55). Mortality at 42-days and 1-year was significantly higher in ACLF (47.9% and 61.3%) as compared to AD patients (9.1% and 12.7%, p<0.001), whereas there was no difference in the number of endoscopies and transfusion requirements between these groups. TIPSS was inserted in 78 patients [AD: 21 (38.2%); ACLF: 57 (47.8%), p=0.41]. In ACLF, rescue TIPSS insertion was an independent favorable prognostic factor for 42-day mortality. In contrast, rescue TIPSS did not impact on the outcome of AD patients. CONCLUSIONS: This study shows for the first time that in patients with failure to control OGVB, the presence and severity of ACLF determines the risk of 42-day and 1-year mortality. Rescue TIPSS is associated with improved survival of ACLF patients

Copeptin in acute decompensation of liver cirrhosis: relationship with acute-on-chronic liver failure and short-term survival.

BACKGROUND: Acute-on-chronic liver failure (ACLF) is characterized by the presence of acute decompensation (AD) of cirrhosis, organ failure, and high short-term mortality rates. Hemodynamic dysfunction and activation of endogenous vasoconstrictor systems are thought to contribute to the pathogenesis of ACLF. We explored whether copeptin, a surrogate marker of arginine vasopressin, is a potential marker of outcome in patients admitted for AD or ACLF and whether it might be of additional value to conventional prognostic scoring systems in these patients. METHODS: All 779 patients hospitalized for AD of cirrhosis from the CANONIC database with at least one serum sample available for copeptin measurement were included. Presence of ACLF was defined according to the CLIF-consortium organ failure (CLIF-C OF) score. Serum copeptin was measured in samples collected at days 0-2, 3-7, 8-14, 15-21, and 22-28 when available. Competing-risk regression analysis was applied to evaluate the impact of serum copeptin and laboratory and clinical data on short-term survival. RESULTS: Serum copeptin concentration was found to be significantly higher in patients with ACLF compared with those without ACLF at days 0-2 (33 (14-64) vs. 11 (4-26) pmol/L; p < 0.001). Serum copeptin at admission was shown to be a predictor of mortality independently of MELD and CLIF-C OF scores. Moreover, baseline serum copeptin was found to be predictive of ACLF development within 28 days of follow-up. CONCLUSIONS: ACLF is associated with significantly higher serum copeptin concentrations at hospital admission compared with those with traditional AD. Copeptin is independently associated with short-term survival and ACLF development in patients admitted for AD or ACLF

Plasma ammonia levels predict hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis

BACKGROUND AND AIMS: Hyperammonaemia is central in the pathogenesis of hepatic encephalopathy, but also has pleiotropic deleterious effects on several organ systems, impacting on immune function, sarcopenia, energy metabolism and portal hypertension. This study was performed to test the hypothesis that severity of hyperammonaemia is a risk factor for liver-related complications in clinically stable outpatients with cirrhosis. METHODS: We collected data from 754 clinically stable outpatients with cirrhosis from 3 independent liver units. Baseline ammonia levels were corrected to the upper limit of normal (AMM-ULN) for the reference laboratory. The primary endpoint was hospitalisation with liver-related complications (a composite endpoint of bacterial infection, variceal bleeding, overt hepatic encephalopathy, or new onset or worsening of ascites). Multivariable competing risk frailty analysis and fast unified random forest were performed to predict complications and mortality. External validation was carried out using prospective data from 130 cirrhotic patients in an independent tertiary liver centre. RESULTS: Overall, 260 (35%) patients were hospitalised with liver-related complications. On multivariable analysis, AMM-ULN was an independent predictor of both liver-related complications (HR=2.13; 95%CI=1.89-2.40; p<0.001) and mortality (HR=1.45; 95%CI=1.20-1.76; p<0.001). AUROC of AMM-ULN was 77.9% for 1-year complications, higher than traditional severity scores. Statistical differences in survival were found between high and low levels of AMM-ULN both for complications and mortality (p<0.001) using 1.4 as the optimal cut-off from the training set. AMM-ULN remained a key variable for the prediction of complications within the random forests model in the derivation cohort and upon external validation. CONCLUSION: Ammonia is an independent predictor of hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis and performs better than traditional prognostic scores in predicting complications. LAY SUMMARY: We conducted a prospective cohort study evaluating the association of blood ammonia levels with the risk of adverse outcomes in 754 patients with stable cirrhosis across 3 independent liver units. We found that ammonia is a key determinant that helps to predict which patients will be hospitalised, develop liver-related complications and die; this was confirmed in an independent cohort of patients

Hemodynamic response to primary prophylactic therapy with nonselective beta-blockers is related to a reduction of first variceal bleeding risk in liver cirrhosis: a meta-analysis

Development and application of statistical models for medical scientific researc