Feedback inhibition of fully unadenylylated glutamine synthetase from Salmonella typhimurium by glycine, alanine, and serine.

Bacterial glutamine synthetase (GS; EC 6.3.1.2) was previously shown to be inhibited by nine end products of glutamine metabolism. Here we present four crystal structures of GS, complexed with the substrate Glu and with each of three feedback inhibitors. The GS of the present study is from Salmonella typhimurium, with Mn2+ ions bound, and is fully unadenylylated. From Fourier difference maps, we find that L-serine, L-alanine, and glycine bind at the site of the substrate L-glutamate. In our model, these four amino acids bind with the atoms they share in common (the "main chain" +NH3-CH-COO-) in the same positions. Thus on the basis of our x-ray work, glycine, alanine, and serine appear to inhibit GS-Mn by competing with the substrate glutamate for the active site.     

Nucleos(t)ide analogues for hepatitis B virus: Strategies for long-term success

Nucleoside and nucleotide analogues are potent HBV suppressors, but these agents rarely eradicate HBV. Therefore, the durability of viral response is a problem, and long-term therapy is usually required to ensure maintained HBV suppression. Studies have shown that long-term therapy starting with lamivudine may significantly improve survival, reduce the risk of liver-related major complications, and prevent the development of cirrhosis and HCC in chronic hepatitis B patients. However, drug resistance is a critical challenge during long-term nucleos(t)ide analogue maintenance therapy. The emergence of these mutants is characterized by an increasing level of serum HBV DNA, elevation of ALT level, and even hepatitis flare or decompensation. The prevention and proper management of drug resistance are crucial to ensure long-term success. To start treatment in the right patients at the right time with the right drug is essential in minimizing the problem of drug resistance. Each of these agents has a different profile of resistant mutations. In choosing a direct antiviral agent to initiate therapy, resistance profile is a crucial factor to consider, apart from potency and cost. In the case of drug resistance emerging, timely institution of a drug without cross-resistance may rescue the adverse effects of drug resistance and ensure the long-term success of nucleos(t)ide analogue therapy. To develop strategies for enhancing the therapeutic response and shortening the duration of therapy is an ultimate goal to avoid the problems of drug resistance.⁶⁸

• nucleos(t)ide analogues for hepatitis B virus (HBV) are highly effective in suppressing HBV replication but rarely eliminate the virus

• long-term therapy is usually required

• emergence of drug-resistant HBV mutations is a critical challenge

• to treat the right patient at the right time with the drug with highest genetic barrier to drug resistance is essential to minimize the problem with drug resistance

• the strategy of on-treatment adjustment based on level of suppression of HBV DNA needs to be clarified

• studies are needed to find the optimal combination therapy for both better therapeutic efficacy and less drug resistance

• oral antiviral agents able to attack cccDNA are urgently needed

Therapy of chronic hepatitis B: current challenges and opportunities

Better understanding of hepatitis B virus (HBV) replication, natural history and the immunopathogenesis of chronic hepatitis B, together with the introduction of effective agents with different mechanisms of action are the basis for better therapeutic strategies against chronic hepatitis B. Among currently available drugs, interferon-alpha and thymosin-alpha1 have only modest efficacy (approximately 40% vs 9-20% in controls). In the past decade, lamivudine has dominated in the treatment of chronic HBV infection because it is easy to use, safe, and is effective in terms of hepatitis B e antigen and/or HBV-DNA loss, ALT normalization, and improvement in histology. The response rate increases with increasing pretherapy alanine aminotransferase (ALT) levels, suggesting that patients with stronger endogenous immune response against HBV have a better response to direct antiviral agents. Lamivudine is also beneficial in decompensated cirrhotics with HBV replication. Hepatitic flares may occur after stopping lamivudine therapy in nonresponders and also in responders. Therefore, prolonged therapy is usually required. However, tyrosine-methionine-aspartate-aspartate (YMDD) mutations conferring resistance to lamivudine start to emerge after 6-9 months of therapy, and hepatitis flare, even decompensation, may develop after viral breakthrough. Thus the benefits of long-term lamivudine therapy must be balanced against the concern about YMDD mutations and the durability of treatment response. Adefovir dipivoxil, entecavir, emtricitabine, clevudine and other nucleoside/ nucleotide analogues have shown encouraging results and some agents appear effective in patients with YMDD mutants. Further development of new drugs and new strategies may help to improve treatment in the new century.     

Betulinic acid exerts anti-hepatitis C virus activity via the suppression of NF-κB- and MAPK-ERK1/2-mediated COX-2 expression

Background and Purpose

This study was designed to evaluate the effect of betulinic acid (BA), extracted from Avicennia marina, on the replication of hepatitis C virus (HCV) and to investigate the mechanism of this BA-mediated anti-HCV activity.

Experimental Approach

HCV replicon and infectious systems were used to evaluate the anti-HCV activity of BA. Exogenous COX-2 or knock-down of COX-2 expression was used to investigate the role of COX-2 in the anti-HCV activity of BA. The effects of BA on the phosphorylation of NF-κB and on kinases in the MAPK signalling pathway were determined. The anti-HCV activity of BA in combination with other HCV inhibitors was also determined to assess its use as an anti-HCV supplement.

Key Results

BA inhibited HCV replication in both Ava5 replicon cells and in a cell culture-derived infectious HCV particle system. Treatment with a combination of BA and IFN-α, the protease inhibitor telaprevir or the NS5B polymerase inhibitor sofosbuvir resulted in the synergistic suppression of HCV RNA replication. Exogenous overexpression of COX-2 gradually attenuated the inhibitory effect of BA on HCV replication, suggesting that BA reduces HCV replication by suppressing the expression of COX-2. In particular, BA down-regulated HCV-induced COX-2 expression by reducing the phosphorylation of NF-κB and ERK1/2 of the MAPK signalling pathway.

Conclusions and Implications

BA inhibits HCV replication by suppressing the NF-κB- and ERK1/2-mediated COX-2 pathway and may serve as a promising compound for drug development or as a potential supplement for use in the treatment of HCV-infected patients.     

Predictors of HBeAg loss after lamivudine treatment for chronic hepatitis B

Elevated alanine transaminase (ALT) levels and low serum hepatitis B virus (HBV) DNA predict a higher likelihood of hepatitis B e antigen (HBeAg) loss in patients with chronic hepatitis B treated with interferon. Predictors of HBeAg loss in patients treated with lamivudine are not known. The objective of this analysis of 4 lamivudine-controlled Phase III trials was to determine patient-dependent or laboratory variables that predict HBeAg loss. Predictors of HBeAg loss in patients treated with interferon, lamivudine plus interferon, or placebo are also described. A total of 805 adults with chronic hepatitis B were treated either with lamivudine (n = 406), matching placebo (n = 196), interferon (n = 68), or the combination of lamivudine plus interferon (n = 135). Demographic and baseline disease characteristics were used in stepwise multivariate analyses to identify features that were predictive of lamivudine-induced HBeAg loss. HBeAg loss correlated with increased pretreatment ALT levels in all groups. The rate of HBeAg loss was highest among patients with pretreatment ALT levels greater than 5 times the upper limit of normal (ULN) and was most pronounced in the lamivudine group (56%). Multivariate modeling indicated that elevated baseline ALT levels (P <.001) and histologic activity index (HAI) score (P <.001) were important predictors of HBeAg loss in response to lamivudine. The effect of pretreatment ALT levels on HBeAg loss was similar for Asians and Caucasians. In conclusion, elevated pretreatment ALT levels and/or active histologic disease were the most important predictors of lamivudine-induced HBeAg loss. Asians and Caucasians had similar rates of response to lamivudine at comparable ALT levels.     

Acute exacerbation in patients with liver cirrhosis: a clinicopathological study

ABSTRACT— The incidence, clinicopathologic features and etiology of acute exacerbation occurring in patients with liver cirrhosis were assessed prospectively among 332 hepatitis B surface antigen (HBsAg) positive and 71 HBsAg negative patients. During an 11-year period and a mean follow-up duration of 26.8 months, 148 acute exacerbation occurred in 107 HBsAg positive patients and 32 episodes occurred in 18 HBsAg negative patients. The calculated annual incidence was 11.5%. The clinical, laboratory and histologic features were similar to those in patients with chronic hepatitis. Confluent hepatic necrosis and alphafetoprotein elevation over 100 ng/ml occurred frequently, particularly in HBeAg positive patients. In general, acute exacerbations in HBsAg negative patients were less severe than their HBsAg positive counterparts. Of the exacerbations in HBsAg positive patients, 54.8% of the HBeAg positive ones and 38.6% of the HBeAg negative ones were attributable to hepatitis B virus reactivation, while 4.8% and 7.9%, respectively, were due to hepatitis delta virus superinfection. The others might be the results of hepatitis non-A, non-B virus superinfection or increased piecemeal necrosis. The immediate outcome of acute exacerbations in cirrhotic patients was usually good, although 13.8% developed hepatic decompensation and 4.4% died. Further follow-up study is required to evaluate the long-term effect of the frequent occurrence of bridging hepatic necrosis, high elevation of alphafetoprotein and hepatic decompensation during acute exacerbation in cirrhotic patients.     

Prognostic significance of in vitro marrow culture growth pattern in untreated acute nonlymphocytic leukemia

The growth pattern of marrow cells in agar culture was studied in 90 adult patients with acute nonlymphocytic leukemia (ANLL) at diagnosis. We classified the abnormal growth patterns into 4 groups, A: no growth, B: decreased growth, C: excessive microcluster formation and D: excessive cluster growth with more than 20 colonies. There was a good correlation between growth pattern and FAB subtype. A predominance of group A growth was observed in M1, while group B growth was found in 50% of patients with M2 and M5. No relationships between the growth patterns and other clinical parameters were detected. Sixty-six patients were evaluable for treatment outcome. The growth pattern significantly correlated with complete remission rate. The remission rates were 52, 87, 80, and 25% for patients with group A, B, C and D growth, respectively. Analyses of remission duration and survival curves showed significant differences among the different growth patterns. Patients with D growth experienced a shorter remission duration and a lower survival rate than other groups. These results indicate that the in vitro culture growth pattern in untreated ANLL is of prognostic significance in predicting the response to therapy.