Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lamivudine is a nuleoside analog with potent inhibitory effects on hepatitis B virus (HBV) replication. Prolonged therapy is required for sustained suppression. However, HBV species with mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) locus of the HBV-RNA-dependent DNA polymerase confering resistance to lamivudine may emerge after 6-9 months therapy with an incidence of 38% and 67% after 2 and 4 years of lamivudine therapy, respectively. During continued lamivudine therapy, patients with YMDD mutant HBV usually show serum alanine aminotransferase (ALT) and HBV-DNA elevations at lower median levels than their baseline. Marked flare of serum ALT or acute exacerbation may occurred as the results of cytotoxic T lymphocyte mediated immune response directed against YMDD mutant. Although viral clearance with or without emergence of distinct lamivudine resistant mutants may occur after such exacerbations, 20% of the exacerbations are complicated with decompensation or even fatality. The exacerbations appear to be more severe than those occur during the natural course of wild type HBV chronic infection. The current practice of continuing lamivudine therapy, therefore, requires careful evaluation. Alternatives include interferon therapy but this seems ineffective. Adefovir dipivoxil and entecavir may effectively suppress the YMDD mutant but these treatments have not yet been available for use. Recent studies have shown no benefit to continuing lamivudine therapy in patients with YMDD mutantions. Before a rescue drug becomes available, the most cost-effective strategy is to select patients with stronger endogenous anti-HBV immunity to increase efficacy and to shorten the duration of lamivudine therapy to avoid the emergence of YMDD mutations.
 ...
PMID:Management of YMDD mutations during lamivudine therapy in patients with chronic hepatitis B. 1247 59

All classes of antiretroviral (ARV) therapy have been associated with asymptomatic elevations of alanine aminotransferase/aspartate aminotransferase (ALT/AST) levels, and much less frequently with serious, and at times life threatening, clinical liver hepatotoxicity. The relationship between the risk of developing serious clinical liver injury and the rate and severity of elevated asymptomatic ALT/AST levels is poorly understood. Boehringer Ingelheim has recently completed the Viramune Hepatic Safety Project; its primary objective was to identify risk factors for antiretroviral-associated hepatotoxicity. Data from 1731 nevirapine-treated patients and 1912 control patients who took part in Boehringer Ingelheim-controlled clinical trials as well as 814 nevirapine-treated patients in uncontrolled trials were analyzed. Risk factors for asymptomatic ALT/AST elevations during nevirapine therapy included baseline elevations of ALT/AST levels > 2.5x upper limit of normal (RR = 4.3, p < .01) and co-infection with hepatitis B (RR = 2.3, p < .01) or hepatitis C (RR = 5.2, p < .01). An analysis of ALT/AST elevations > 5x ULN for patients stratified by baseline CD4 cell count demonstrated that men with > or = 400 CD4 cells/mm3 were at increased risk of asymptomatic transaminase elevations while taking nevirapine (RR = 1.6, p < .01). No consistent CD4 cell count cutoff could be identified in women that was associated with an increased risk of ALT/AST elevations. Analyses from five large observational cohorts (N = 8711) demonstrated no significant differences in the rate of serious hepatic events among antiretroviral regimens, including between the non-nucleoside reverse transcriptase inhibitors nevirapine and efavirenz. Use of nevirapine was not associated with a significantly increased risk of clinical hepatotoxic events, including liver failure or liver related death, compared to therapy with other antiretroviral drugs.
 ...
PMID:A comprehensive hepatic safety analysis of nevirapine in different populations of HIV infected patients. 1502 21

The use of all potent drugs is associated with toxicities and antiretroviral (ARV) drugs are no exception. Antiretroviral therapy-associated hepatic toxicity is of increasing concern in the management of patients with HIV/AIDS. Liver toxicity has been reported in some HIV-infected patients being treated with drugs from all of these classes of ARV drugs: protease inhibitors (PIs), nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Although the majority of cases involve asymptomatic elevations of liver enzymes (alanine aminotransferase [ALT] and aspartate aminotransferase [AST]), severe, and, in a minority of cases, life threatening, liver disease has been reported in patients treated with ARV drugs. The exact causes of elevated plasma levels of AST and ALT are complex and, in many cases, obscure. The combination of viral hepatic disease, drugs that act adversely directly on the liver and drugs that act on other systems of the body which in turn, adversely affect the liver, can result in hepatic toxicity. Such toxicity may be inappropriately attributed solely to the direct effect of a drug. Knowledge of the possible causes of liver toxicity, and ways to avoid it, should reduce the risk of developing hepatotoxicity. The physician's task is to prevent the development of liver toxicity, e.g., by choosing appropriate therapeutic regimens and by careful management of the patient. This involves frequent monitoring of the patient, both clinically and by utilizing liver function tests on a regular basis. If signs and symptoms of liver disease do develop, prompt and expert management is essential. This review discusses the influence of a number of factors on hepatic toxicity including viral hepatitis, insulin resistance and the specific ARV drugs used in the treatment of patients with HIV/AIDS.
 ...
PMID:Managing antiretroviral-associated liver disease. 1456 56

Breakthroughs during lamivudine therapy were assessed according to hepatitis flares and mutational polymorphism of hepatitis B virus (HBV) infecting patients. Of 42 patients with chronic hepatitis B and positive for hepatitis B e antigen in serum, 13 (30%) harbored HBV mutants with lamivudine resistance after a mean duration of 29 months on lamivudine. The virological breakthrough occurred 14.5 months after the start of lamivudine treatment, and all the patients with it developed breakthrough hepatitis 3 months later. The clinical course of breakthrough hepatitis was self-limited except in one patient who had already developed cirrhosis at the baseline. One year after breakthrough hepatitis, serum ALT, albumin, prothrombin time and platelet counts were maintained well on conventional treatments without resorting to interferon. Major HBV mutants during breakthrough hepatitis were those with M552I in the YMDD motif of viral DNA polymerase/reverse transcriptase in 7 patients (54%), M552I/L528M in 4 patients (31%) and M552V/L528M in 2 patients (15%). There were no patients in whom mutations at nucleotide 529 occurred including the 2 who later developed hepatocellular carcinoma. There was no clear relationship between distinct mutational patterns and clinical courses. Further studies are needed for making out the effects of lamivudine-resistant mutants on clinical outcomes, taking into considerations genotypes of HBV.
 ...
PMID:Subclones of drug-resistant hepatitis B virus mutants and the outcome of breakthrough hepatitis in patients treated with lamivudine. 1468 51

Lamivudine is a nucleoside analogue with potent inhibitory effects on hepatitis B virus (HBV) polymerase/reverse transcriptase activity. The rate of hepatitis B e antigen (HBeAg) seroconversion in a large series of Asian patients treated with lamivudine 100 mg daily for 1 year was only 16% and the incidence of YMDD mutants was 14%. Further analysis of this Asian trial has shown that patients with a pretreatment alanine aminotransferase (ALT) level higher than 5-fold the upper limit of normal (ULN) have a much higher HBeAg seroconversion rate as compared with patients with a pretreatment ALT level <2 x upper limit of normal (64 vs. 5%; p < 0.001). In order to avoid the development of YMDD mutants, we selected 186 patients with acute exacerbation for treatment with lamivudine during 9 months, if possible, and not more than 15 months. They were all seropositive for both hepatitis B surface antigen and HBeAg for more than 6 months and also had serum HBV DNA; 138 (74%) of them were male. HBV genotypes were A in 2 (1%), B in 115 (62%), C in 65 (35%), D in 2 (1%) and F in the remaining 2 (1%). Four patients (2%) had liver cirrhosis. They had mean pretreatment levels of ALT at 608 IU/l (range: 184-2,400 IU/l), total bilirubin at 1.5 mg/dl (0.3-14.8 mg/dl), and HBV DNA at 2,246 pg/ml (0.5-25,903 pg/ml). After a median of 8.2 months (3-15 months) on lamivudine, 96 patients (51%) achieved HBeAg seroconversion, while the other 90 (48%) patients did not. Genotype B was detected comparably frequently in seroconverters and nonconverters (63 vs. 61%). During 1-year follow-up after withdrawal of lamivudine, 56 (58%) of the 96 seroconverters experienced flare-ups with ALT levels elevated higher than 5 x ULN in 50 (89%). Of 90 patients who remained HBeAg-positive, in contrast, 80 (86%) experienced ALT flares (with ALT >5 x ULN in 84%) within 1 year. YMDD mutants did not develop in any of these 186 patients during the course of lamivudine therapy. In conclusion, short-term lamivudine therapy in patients with chronic active hepatitis B can reduce the incidence of YMDD mutants and achieve an acceptable HBeAg seroconversion rate. However, the relapse rate was high (60% during 1-year follow-up). Further study is needed to establish how to improve a sustained HBeAg response.
 ...
PMID:Short-term lamivudine therapy in patients with chronic hepatitis B. 1468 53

Although it seems to be rather unlikely, it still remains unclear whether hepatitis G virus (HGV) is involved in post-transfusion hepatitis. Prevalence of HGV viremia and persistence in blood donors was determined. ALT and AST values of viremic and non-viremic donations of the donors were compared. 25,006 blood donations were tested for the presence of HGV RNA by reverse transcriptase polymerase chain reaction. ALT and AST were determined for every donation. Sequential serum samples of 105 HGV RNA-positive donors were tested for both HGV RNA and antibodies to the HGV-E2 antigen (anti-E2) by enzyme-linked immunosorbent assay. Stored serum samples of 66 patients from before and after transfusion of HGV RNA-positive units were also tested. 1.6% of the 25,006 blood donations were HGV RNA-positive. One of 105 HGV RNA-positive blood donors showed viremia for more than 6 years. Three donors showed viremia and HGV antibody at the same time. There is no significant difference in ALT and AST activity in HGV RNA-positive donors compared to a control group of healthy donors and also before and after seroconversion to HGV RNA-negative (p > 0.05). Transmission of HGV by blood components has been shown in transfused patients. The prevalence of HGV infection in patients (n = 66) is 17%. Transmission of HGV by blood components does occur. Patients have a significantly higher prevalence of HGV viremia compared to blood donors. In blood donors no liver affection by means of ALT or AST elevation can be seen. Long persistence of HGV viremia is common and the presence of anti-E2 does not exclude viremia.
 ...
PMID:Prevalence, persistence and liver enzyme levels of HGV RNA-positive blood donors determined by large-scale screening and transmission by blood components. 1500 Feb 18

Our previous study demonstrated that polycationic liposomes are highly stable in the bloodstream and represent an effective agent for liver gene delivery. We report here that liposome-mediated extracellular superoxide dismutase (EC-SOD) gene delivery successfully prevented acute liver injury in mice. The therapeutic efficacy of EC-SOD gene delivery by polycationic liposomes was determined against the toxicity of superoxide anions and hydroxyethyl radicals in HepG2 cells and in a mouse model of acute liver injury caused by D-galactosamine and lipopolysaccharide intoxication. Transfection of HepG2 cells with an EC-SOD plasmid led to a striking increase in superoxide dismutase activity in the medium. The transfected cells had much less cell death after reactive oxygen species exposure compared with untransfected or control plasmid-transfected cells. In a model of acute liver injury, serum alanine aminotransferase levels in mice receiving portal vein injections of EC-SOD lipoplexes were much lower than in those receiving normal saline, liposomes alone, or control lipoplexes. Liver histology confirmed that there was less cell death in the EC-SOD lipoplex-treated group. Quantitative reverse transcriptase polymerase chain reaction showed a 55-fold increase in human EC-SOD gene expression in the liver of mice injected with EC-SOD lipoplexes. Serum superoxide dismutase activity in EC-SOD lipoplex-treated mice was higher than in the control groups; this was associated with higher liver glutathione levels and reduced lipid peroxidation. In conclusion, polycationic liposome-mediated EC-SOD gene delivery protects against reactive oxygen species toxicity in vitro and against lipopolysaccharide-induced acute liver injury in D-galactosamine-sensitized mice.
 ...
PMID:Liposome-mediated extracellular superoxide dismutase gene delivery protects against acute liver injury in mice. 1523 3

For cells on the path to carcinogenesis, the key to unlimited growth potential lies in overcoming the steady loss of telomeric sequence commonly referred to as the 'end-replication problem' that occurs with each cell division. Most human tumors have reactivated telomerase, a specialized reverse transcriptase that directs RNA-templated addition of telomeric repeats on to chromosomal termini. However, approximately 10% of tumors maintain their telomeres through a recombination-based mechanism, termed alternative lengthening of telomeres or ALT. Here we demonstrate that telomeric DNA undergoes a high rate of a particular type of recombination visualized cytogenetically as sister chromatid exchange (SCE), and that this rate is dependent on genotype. A novel model of ALT is presented in which it is argued that telomeric exchanges, if they are unequal and occur at a sufficiently high frequency, will allow cells to proliferate indefinitely without polymerase-mediated extension of telomeric sequence.
 ...
PMID:Frequent recombination in telomeric DNA may extend the proliferative life of telomerase-negative cells. 1525 49

Abnormal liver function tests are frequently observed in HIV-infected individuals receiving nevirapine (NVP). Here we investigate the relationship between total and unbound plasma concentrations of NVP and the liver enzymes alanine aminotransferase (ALT) and gamma-glutamyl transferase (gammaGT). HIV-infected individuals [n = 85, 22 female, 34 hepatitis C or B virus (HCV or HBV(+))] receiving NVP (200 mg bd; median duration 66 weeks, range 3-189) and two nucleoside reverse transcriptase inhibitors (NRTIs) were enrolled into this study. Blood samples were taken at C(trough) (12 hr postdose) for measurement of NVP and liver function tests (ALT and gammaGT). Plasma protein bound and unbound drug was separated using ultrafiltration and NVP concentrations quantified using HPLC-MS/MS. A linear relationship was observed between total and unbound NVP C(trough) (r(2) = 0.77, p < 0.0001). Patients with elevated ALT (>37 IU/liter; n = 31) had higher NVP unbound C(trough) than those with ALT within the normal range (median 2268 vs. 1694 ng/ml, p = 0.04) but there was no difference in total C(trough). Logistic regression revealed no association between higher NVP C(trough) and ALT elevations. Significantly higher NVP total and unbound C(trough) were observed in patients with increased gammaGT (>40 IU/liter; n = 63; total 6747 vs. 4530 ng/ml, p = 0.001; unbound 2113 vs. 1557 ng/ml, p = 0.03). Significantly higher unbound NVP C(trough) was observed in HCV/HBV(+) (median 2275 vs. 1726 ng/ml, p = 0.02) and on bivariate analysis, higher NVP C(trough) was associated with HCV/HBV coinfection (chi(2) = 4.228; p = 0.04). Overall we found no strong association between NVP concentrations and hepatotoxicity. Although in this study NVP was well tolerated in HCV/HBV coinfected patients, higher plasma concentrations were observed.
 ...
PMID:The relationship between nevirapine plasma concentrations and abnormal liver function tests. 1530 17

In the present study, we investigated the protective effect of Lycium chinense Miller (Solanaceae) fruit (LFE) against CCl(4)-induced hepatotoxicity and the mechanism underlying these protective effects in rats. The pretreatment of LFE has shown to possess a significant protective effect by lowering the serum aspartate and alanine aminotransferase (AST and ALT) and alkaline phosphatase (ALP). This hepatoprotective action was confirmed by histological observation. In addition, pretreatment of LFE prevented the elevation of hepatic malondialdehyde (MDA) formation and the depletion of reduced glutathione (GSH) content and catalase activity in the liver of CCl(4)-injected rats. The LFE also displayed hydroxide radical scavenging activity in a dose-dependent manner (IC(50) = 83.6 microg/ml), as assayed by electron spin resonance (ESR) spin-trapping technique. The expression level of cytochrome P450 2E1 (CYP2E1) mRNA and protein, as measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot analysis, was significantly decreased in the liver of LFE-pretreated rats when compared with that in the liver of control group. Based on these results, it was suggested that the hepatoprotective effects of the LFE might be related to antioxidative activity and expressional regulation of CYP2E1.
 ...
PMID:Protective effect of Lycium chinense fruit on carbon tetrachloride-induced hepatotoxicity. 1561 74


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>