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Biomedical subjects

S Locarnini

Publications and source records attributed to S Locarnini.

At least 37 records · Page 2Linked to original sources
PubMed2000

A virological perspective on the need for vaccination.

Superinfecton of chronic carriers of hepatitis B virus (HBV) or hepatitis C virus (HCV) with hepatitis A virus (HAV) is often associated with more severe liver disease than infection with HAV alone. Superinfection commonly causes markers of HBV and HCV replication to fall to significantly lower levels. The pathogenesis of acute liver damage characteristic of viral hepatitis is thought to be mediated by host cytotoxic T-lymphocytes (CTLs) directed against virus-infected hepatocytes. It has been proposed that the more aggressive liver disease observed in individuals infected with HAV in addition to chronic HBV/HCV is a result of the induction of interferon (IFN)-alpha during acute HAV infection. This accounts for the antiviral effect on the active markers of HBV/HCV replication, and the enhanced CTL response against HBV/HCV-infected hepatocytes. Alternatively, HAV may indirectly stimulate the T helper 1 (Th1)-type cytokine responses, such as interleukin (IL)-2, IFN-gamma and tumour necrosis factor (TNF)-alpha, which directly promote the antiviral CTL response. Clearance of HBV infection, and possible HAV and HCV, is associated with a specific CTL response, while viral persistence in chronic HBV and HCV infection has been attributed to an imbalance in the Th1-Th2 arms of the immune response. Vaccination against hepatitis A should be considered for patients with chronic HBV/HCV infection, to minimize the risk of exacerbating underlying liver disease.

Carrier State↗
PubMed2000

An efficient extraction method from blood clots for studies requiring both host and viral DNA.

The clot from blood is usually discarded after the collection of serum. Yet, it contains nucleated white blood cells and substantial serum. Here, we have compared four methods to enable quick and efficient extraction of human genomic and viral DNA from clotted blood. Two of these methods, a phenol-based in-house method and Tripure isolation reagent, only achieved a low polymerase chain reaction (PCR) yield. In contrast, the QIAamp blood kit and the High Pure Viral Nucleic Acid kit were equally efficient, with similar sensitivity to serum for extraction of viral DNA.

Blood Coagulation↗
PubMed2000

Effect of nucleoside analogue therapy on duck hepatitis B viral replication in hepatocytes and bile duct epithelial cells in vivo.

BACKGROUND: Recent studies have implicated bile duct epithelial cells (BDEC) as a reservoir of hepatitis B virus (HBV) infection that may be particularly important in the development of post-liver transplant recurrence of hepatitis B. The aim of this study was to compare the effects of antiviral therapy on duck HBV (DHBV) expression in hepatocytes and BDEC and to determine if this was affected by biliary hyperplasia. METHODS: Ducklings congenitally infected with DHBV received penciclovir (10 mg/kg per day) treatment from 9 days of age. In order to mimic the biliary hyperplasia that often accompanies severe post-liver transplant HBV recurrence, half the animals underwent bile duct ligation. Duck HBV-DNA in serum was measured at day 1, and serum and liver DHBV-DNA were determined when the animals were killed on day 17. Intrahepatic expression of viral preS1 antigen and DHBV-DNA was measured by immunohistochemistry and in situ hybridization, respectively. RESULTS: Viraemia became undetectable in the penciclovir-treated animals at day 17, following 8 days of therapy. Examination of liver tissue revealed that all hepatocytes and the majority of BDEC contained DHBV preS1 antigen and DHBV-DNA. Penciclovir greatly reduced the intrahepatic viral burden, but there was no antiviral effect on viral markers within BDEC. Despite the increased number of BDEC after bile duct ligation, the same proportion of BDEC was seen to be infected, and this was unaffected by antiviral therapy. CONCLUSIONS: In the duck model with and without biliary hyperplasia, penciclovir controls DHBV replication and reduces viral burden in hepatocytes, but not in BDEC. The BDEC appear to be an important reservoir of virus that is relatively unaffected by antiviral treatment, and may play an important role in disease persistence and relapse following cessation of therapy.

Acyclovir↗
PubMed2000

Molecular pathogenesis of viral hepatitis.

The global burden of chronic liver disease caused by persistent infection with hepatitis B and C viruses has meant the urgent development of therapeutic strategies designed to control active replication and therefore prevent subsequent clinical sequelae. Advances in these therapeutic strategies are now clearly happening, mainly as a consequence of a better understanding of the viral life cycle and the unique pathogenesis of each disease. Further progress should continue as further insights into the virus-cell relationship are derived, which will sharpen attention on specific viral targets as well as shift and enhance host cytokine responses.

Antiviral Agents↗
PubMed2000

In vitro antihepadnaviral activities of combinations of penciclovir, lamivudine, and adefovir.

Penciclovir (9-[2-hydroxy-1-(hydroxymethyl)-ethoxymethyl]guanine [PCV]), lamivudine ([-]-beta-L-2',3'-dideoxy-3'-thiacytidine [3TC]), and adefovir (9-[2-phosphonylmethoxyethyl]-adenine [PMEA]) are potent inhibitors of hepatitis B virus (HBV) replication. Lamivudine has recently received approval for clinical use against chronic human HBV infection, and both PCV and PMEA have undergone clinical trials against HBV in their respective prodrug forms (famciclovir and adefovir dipivoxil [bis-(POM)-PMEA]). Since multidrug combinations are likely to be used to control HBV infection, investigation of potential interactions between PCV, 3TC, and PMEA is important. Primary duck hepatocyte cultures which were either acutely or congenitally infected with the duck hepatitis B virus (DHBV) were used to investigate in vitro interactions between PCV, 3TC, and PMEA. Here we show that the anti-DHBV effects of all the combinations containing PCV, 3TC, and PMEA are greater than that of each of the individual components and that their combined activities are approximately additive or synergistic. These results may underestimate the potential in vivo usefulness of PMEA-containing combinations, since there is evidence that PMEA has immunomodulatory activity and, at least in the duck model of chronic HBV infection, is capable of inhibiting DHBV replication in cells other than hepatocytes, the latter being unaffected by treatment with either PCV or 3TC. Further investigation of the antiviral activities of these drug combinations is therefore required, particularly since each of the component drugs is already in clinical use.

Acyclovir↗
PubMed2000

Combination chemotherapy for hepatitis B virus: the path forward?

Hepatitis B virus (HBV) was identified as a cause of viral hepatitis more than 30 years ago and hepatitis B vaccines have been available for almost 20 years, but HBV infection continues to be a global health problem, responsible for about 1.2 million deaths annually. By the end of this year, almost 400 million people--about 5% of the world's population and more than ten times the number infected with human immunodeficiency virus (HIV)--will be infected with HBV. Chemotherapy remains the only treatment option for controlling chronic HBV infection once acquired, but none of the many different chemotherapeutic strategies used in the past has proven consistently successful. Prospects for successful treatment of HBV have improved dramatically during the past decade due to the development of new, well tolerated and efficacious anti-HBV drugs, and to advances in our understanding of HBV replication and pathogenesis. The newer anti-HBV drugs are capable of reducing viral loads very rapidly, but the initial response is invariably followed by very much slower elimination of residual virus. As more effective anti-HBV drugs become available, the emergence of drug resistance during the slower phase of HBV elimination will probably become the most significant obstacle in the way of eventual control of HBV infection. Experience with HIV indicates that combination chemotherapy may suppress or eliminate drug resistance and methods for pre-clinical and clinical assessment of anti-HBV drug combinations are being developed. Basic research into mechanisms of drug action and interaction should assist in the design and optimisation of combination chemotherapy for HBV infection, for which additional new anti-HBV drugs will undoubtedly be required in future.

Antiviral Agents↗
PubMed1999

Synthesis and evaluation of 2-amino-9-(3-acyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines and 2-amino-9-(3-alkoxycarbonyloxymethyl-4-alkoxycarbonyloxybut-1- yl)purines as potential prodrugs of penciclovir.

A series of 2-amino-9-(3-acyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purin es (1-8) and 2-amino-9-(3-alkoxycarbonyl-oxymethyl-4-alkoxycarbonyloxybut -1-yl)purines (9-12) were synthesized as potential prodrugs of penciclovir. Treatment of 6-deoxypenciclovir with trimethyl orthoacetate or triethyl orthopropionate (1.2 equiv) in DMF in the presence of p-TsOH.H2O (0.1 equiv) followed by quenching with excess H2O gave the corresponding mono-O-acetyl or mono-O-propionyl compound, 17 or 18, in excellent yields of 95 and 92%, respectively. Reactions of 17 or 18 with an appropriate alkyl (Me, Et, n-Pr, and i-Pr) 4-nitrophenyl carbonate (1.2 equiv) in pyridine in the presence of a catalytic amount of DMAP (0.1 equiv) at 80 degrees C afforded the monoacyl, monocarbonate derivatives of 6-deoxypenciclovir, 1-8, in 86 94% yields. Similar reactions of 6-deoxypenciclovir with 2.1 equiv of alkyl 4-nitrophenyl carbonate produced the dicarbonate derivatives 9 12 in 81-83% yields. Of the prodrugs tested in rats, 2-amino-9-(3-acetoxymethyl-4-isopropoxycarbonyloxybut-1-yl)purine (4) achieved the highest mean urinary recovery of penciclovir (36%), followed in order by compounds 2 (35%), 6 (35%), 7 (34%), 10 (34%), 8 (32%), 3 (32%), and famciclovir (31%). The mean urinary recovery of penciclovir and concentrations of penciclovir in the blood from 4 in mice were also slightly higher than those from famciclovir. The in vivo antiviral efficacy of 4 in HSV-1-infected normal BALB/c mice was higher than those of famciclovir and valaciclovir in terms of mortality (100, 80, and 40%) and mean survival time ( > 21, 13+/-5.0 (SEM), and 13+/-1.6 days). Compound 4 demonstrated an effective anti-hepadnaviral response with intrahepatic viral load being reduced by 90%, the viral supercoiled DNA levels reduced by 70% and Pre-S expression inhibited by 30% against duck hepatitis B virus (DHBV) in vivo, and did not cause any significant hepatotoxicity after 4 weeks of treatment.

Acyclovir↗
PubMed1998

New therapies for the treatment of chronic hepatitis B infection.

Persistent hepatitis B virus infection can lead to the development of chronic liver disease, cirrhosis and primary hepatocellular carcinoma. The only therapy of confirmed benefit in chronic hepatitis B is interferon alpha, which can lead to long-term benefit in only a third of highly selected patients. A number of new therapeutic approaches are being actively developed for treating chronic hepatitis B, including the use of nucleoside analogues, cytokines, antisense oligonucleotides, ribozymes, dominant negative mutants and DNA-based vaccines. Recent clinical trials with the nucleoside analogues have identified several important challenges for future drug development, in which the gene therapy-based approach may prove useful either alone or most probably in various combinations. Future clinical trials should aim to address these challenges using the new therapies so that the goal of substantial and sustained inhibition of viral replication with the accompanying improvement in the underlying liver disease can be achieved.

Journal Article↗
PubMed1998

Long-term therapy with the guanine nucleoside analog penciclovir controls chronic duck hepatitis B virus infection in vivo.

Ducks congenitally infected with duck hepatitis B virus (DHBV) were treated with the antiviral guanine nucleoside analog penciclovir for 12 or 24 weeks at a dosage of 10 mg/kg of body weight per day. By the completion of both 12 and 24 weeks of therapy, molecular hybridization studies of the liver tissue revealed that the viral DNA, RNA, and protein levels were significantly reduced compared to those in the placebo-treated controls. Penciclovir treatment for 12 or 24 weeks was not associated with any toxicity, establishing the efficacy and safety of long-term penciclovir therapy in chronic DHBV infection.

Acyclovir↗
PubMed1998

Targets for inhibition of hepatitis C virus replication.

Considerable progress has been made in characterizing the proteins involved in hepatitis C virus (HCV) replication, despite the lack of a cell culture system. A number of systems have been developed to examine the processes involved in viral replication, including the initiation and processing of the viral proteins required for RNA replication, the unwinding activities of the RNA helicase and the synthesis of RNA by the viral polymerase. These processes have been examined using individually cloned proteins expressed in various in vitro systems, which may be suitable targets for antiviral agents. The viral helicase and protease domains have now been crystallized, which may enable the rational design of specific inhibitors. The recent developments in HCV research in understanding the function of the viral non-structural proteins and the establishment of in vitro screening assays may aid in the development of new antiviral agents.

Antiviral Agents↗
PubMed1997

Hepatitis B virus polymerase mutations during antiviral therapy in a patient following liver transplantation.

BACKGROUND/AIMS: The purpose of this study was to investigate possible resistance mutations which arose in the polymerase gene of hepatitis B virus (HBV) in a patient with severe recurrent HBV infection following liver transplantation. The patient's management included antiviral chemotherapy for almost 4 years comprising ganciclovir, foscarnet and famciclovir. In the last 2.5 years of famciclovir treatment, an increase in serum HBV DNA levels and a reduced sensitivity of the virion-associated DNA polymerase to penciclovir triphosphate were observed. METHODS: The viral polymerase gene and X gene were sequenced from serum samples collected at representative time intervals covering the entire treatment period. RESULTS: No mutations were detected in the X gene. Three nucleotide mutations, each of which resulted in an altered amino acid sequence, were detected in the polymerase gene after 816 days of total antiviral therapy (370 days of famciclovir). Two of these mutations were detected by direct sequencing and the third was detected after cloning and was present in 10% of the clones. All three mutations occurred in "region B" of RNA-dependent DNA polymerases. The HBV polymerase has similarities to both RNA and DNA polymerases. These mutations in the HBV polymerase gene were located in a similar area to the penciclovir-induced mutations observed in the herpes simplex virus DNA polymerase gene. CONCLUSIONS: Three mutations within the HBV polymerase gene were detected which were associated with a reduced penciclovir sensitivity.

2-Aminopurine↗
PubMed1997

Synergistic inhibition of hepadnaviral replication by lamivudine in combination with penciclovir in vitro.

Lamivudine ([-]-beta-L-2',3'-dideoxy-3'-thiacytidine [3TC]) and penciclovir (9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine [PCV]) are potent inhibitors of hepatitis B virus (HBV) replication. Both drugs have entered phase III clinical trials for treatment of chronic HBV infection. 3TC and PCV are deoxycytidine and deoxyguanosine analogs, respectively, and their modes of action and how they interact are matters of both theoretical and practical interest. We compared the antiviral activities of 3TC and PCV alone and in combination in primary duck hepatocyte (PDH) cultures derived from ducklings congenitally infected with the duck hepatitis B virus (DHBV). 3TC and PCV inhibited DHBV replication to a comparable extent when used alone (50% inhibitory concentrations with 95% confidence intervals were 0.55 [0.50-0.59] micromol/L for 3TC and 0.35 [0.27-0.43] micromol/L for PCV), and in combination, the two nucleoside analogs acted synergistically over a wide range of clinically relevant concentrations. Synergy between PCV and 3TC was also observed in acutely infected cells and in "washout" experiments designed to assess the persistence of antiviral activity after drug removal. Furthermore, the combination was more effective in reducing the normally recalcitrant viral covalently closed circular (CCC) DNA form of DHBV than either drug alone. These results suggest that combinations of 3TC and PCV may act synergistically against HBV in vivo.

Acyclovir↗
PubMed1997

Review: Present and future directions in the treatment of chronic hepatitis B infection.

The last decade has witnessed substantial progress in the development of chemotherapeutic agents for chronic hepatitis B. However, the only currently licensed treatment in Australia, interferon-alpha, has low initial response rates and the adverse effects are often unacceptable. Of the newer agents in the class of nucleoside analogues, famciclovir and lamivudine are in phase III clinical trials with encouraging preliminary results, while other agents, such as bis-POM PMEA (Adefovir), are at phase I/II development. Future approaches to therapy will be governed by an understanding of the effects of nucleoside analogues on the natural history of the disease as well as on the hepatitis B virus hepatocyte interaction. Combination antiviral therapy should theoretically offer improved response rates, decrease the development of viral resistance, and provide the greatest reduction in viral load, but it has not yet been widely examined in the clinical setting. In this article, we review the currently available strategies, discuss potential problem areas, and speculate on promising approaches with combination chemotherapy and the features of agents soon to be trialed.

Antiviral Agents↗
PubMed1996

Retransplantation for precore mutant-related chronic hepatitis B infection: prolonged survival in a patient receiving sequential ganciclovir/famciclovir therapy.

Retransplantation for hepatitis B-related liver allograft failure is rarely successful. Recurrence of infection is almost universal, and the second allograft is invariably lost more rapidly than the first. In a recent multicenter study, only 1 of 20 hepatitis B virus (HBV)-positive patients who underwent liver retransplantation survived beyond 6 months. This report describes the long-term effect of antiviral therapy in a 56-year-old man who was retransplanted for HBV-related allograft loss 14 months after his initial liver transplant. He was treated after the second transplant with intravenous daily ganciclovir. After 10 months of this therapy HBV recurrence was detected. After a change to oral famciclovir therapy, there was a decrease in serum HBV DNA and amino-transferase levels and an improvement in the patient's clinical condition. Famiciclovir therapy has now been continued for 26 months, and the patient remains well 3 years after his second transplant, despite persistent HBV infection and progression to cirrhosis. These observations indicate that the use of long-term antiviral therapy offers promise for improving outcomes in patients who undergo retransplantation after HBV-related liver allograft failure.

2-Aminopurine↗