Using 2-aminopurine fluorescence to measure incorporation of incorrect nucleotides by wild type and mutant bacteriophage T4 DNA polymerases. (49/327)

The ability of wild type and mutant T4 DNA polymerases to discriminate in the utilization of the base analog 2-aminopurine (2AP) and the fluorescence of 2AP were used to determine how DNA polymerases distinguish between correct and incorrect nucleotides. Because T4 DNA polymerase incorporates dTMP opposite 2AP under single-turnover conditions, it was possible to compare directly the kinetic parameters for incorporation of dTMP opposite template 2AP to the parameters for incorporation of dTMP opposite template A without the complication of enzyme dissociation. The most significant difference detected was in the K(d) for dTTP, which was 10-fold higher for incorporation of dTMP opposite template 2AP (approximately 367 microm) than for incorporation of dTMP opposite template A (approximately 31 microm). In contrast, the dTMP incorporation rate was reduced only about 2-fold from about 318 s(-1) with template A to about 165 s(-1) for template 2AP. Discrimination is due to the high selectivity in the initial nucleotide-binding step. T4 DNA polymerase binding to DNA with 2AP in the template position induces formation of a nucleotide binding pocket that is preshaped to bind dTTP and to exclude other nucleotides. If nucleotide binding is hindered, initiation of the proofreading pathway acts as an error avoidance mechanism to prevent incorporation of incorrect nucleotides.  (+info)

Fatal hepatitis B reactivation following discontinuation of nucleoside analogues for chronic hepatitis B. (50/327)

BACKGROUND: Nucleoside analogues such as lamivudine for chronic hepatitis B have an excellent safety profile while patients are on therapy but reactivation flares occur in 19-50% of patients after stopping therapy, some of whom develop liver decompensation. AIMS: To describe and report three cases who developed fatal hepatitis B reactivation after stopping nucleoside analogue therapy. SUBJECTS AND RESULTS: Three patients are described who developed hepatitis B reactivation and liver decompensation after stopping therapy. One of the three patients was participating in a famciclovir trial and the other two were receiving lamivudine therapy for active hepatitis B infection. All three patients had documented hepatitis B flares, and all had hepatitis B virus DNA detected at that time. All patients developed decompensated liver disease despite one patient having had a prior liver biopsy showing absence of cirrhosis. Reintroduction of lamivudine therapy failed to halt progression of liver decompensation even after hepatitis B virus DNA had been demonstrated to be absent. Sequencing for lamivudine resistant mutants in two cases where serum was available failed to show evidence of mutations associated with lamivudine resistance. CONCLUSION: Hepatitis B virus reactivation, leading to decompensation and death, are possible complications of treatment withdrawal and patients should be monitored closely if therapy is ceased.  (+info)

Challenges in genital herpes simplex virus management. (51/327)

Development of serologic assays to detect antibodies to herpes simplex virus (HSV) glycoproteins (g)G1 and (g)G2 has allowed accurate definition of the seroprevalence of HSV-2 worldwide. Studies from all continents indicate epidemic proportions of HSV-2 infection. In the United States, 1 in 5 sexually active adults is infected. In Africa and the Caribbean, HSV prevalence is higher. Since the development of the acyclic nucleoside derivatives acyclovir, famciclovir, and valacyclovir, treatment of mucocutaneous HSV is a practice of everyday medical care. Yet, despite effective drugs, there is widespread discontent by clients and providers about care of patients with genital herpes. Much of this relates to transmission complexities and the varied natural history of the infection. However, over time, most patients adjust to their disease and the medical and psychosocial complications. Recent studies show condoms reduce transmission, providing an important tool for counseling the patient with newly diagnosed genital herpes.  (+info)

Progress in meeting today's demands in genital herpes: an overview of current management. (52/327)

Treatment of genital herpes requires accurate diagnosis, patient support, and effective treatment. Diagnosis is usually straightforward for classic presentations characterized by vesicular lesions but can be challenging for atypical presentations, which are more common. Diagnosis of asymptomatic infection requires access to molecular technology or type-specific serologic assays. Misconceptions about herpes simplex infection are common and patient education is essential. Patient concerns extend beyond disease frequency and severity-the psychological impact should not be underestimated. Antiviral therapy is relevant at all stages of infection. Acyclovir, valacyclovir, and famciclovir are effective and well tolerated for genital herpes treatment. Continuous suppressive therapy controls all symptoms of recurrent disease and helps to relieve disease complications. The prodrugs valacyclovir and famciclovir offer easier, less-frequent dosing than required for acyclovir. Valacyclovir achieves effective suppression when taken once a day. Interventions to prevent genital herpes transmission and to control the global problem are urgently required.  (+info)

Understanding pain in herpes zoster: an essential for optimizing treatment. (53/327)

After herpes zoster, immunocompetent persons frequently experience chronic pain and considerable suffering. Zoster-associated pain has a complex pathophysiology that begins with viral damage and increased sensitization of peripheral sensory neurons. The enhanced afferent barrage from these neurons sensitizes spinal neurons and leads to loss of synapses from descending inhibitory fibers, resulting in central neuropathic pain and allodynia. Antiviral therapy of acute zoster limits this sequence of pathophysiologic mechanisms. There is no clear consensus regarding the optimal means of determining the benefits of antiviral therapy in the management of pain of herpes zoster. A novel statistical approach utilizing rates of disappearance of pain of differing pathophysiologic mechanisms is proposed.  (+info)

Hepatitis B: progress in the last 15 years. (54/327)

1. Patients undergoing orthotopic liver transplantation (OLT) for hepatitis B without effective prophylaxis have a high risk for recurrent infection and severe graft damage, leading to death or re-OLT. 2. Long-term prophylaxis with hepatitis B immune globulin (HBIg) significantly reduces the risk for hepatitis B virus (HBV) recurrence and increases survival. Patients with detectable HBV DNA at the time of OLT have a high risk for recurrence despite HBIg prophylaxis. 3. Lamivudine (LAM) therapy for patients with decompensated HBV cirrhosis before OLT results in inhibition of viral replication and clinical improvement. Its efficacy is limited by the frequent emergence of LAM-resistant YMDD mutations. The ideal length of therapy with LAM pre-OLT has not yet been defined. 4. Prophylaxis of HBV recurrence with LAM monotherapy is not recommended because of the reappearance of hepatitis B surface antigen after OLT in approximately 50% of patients. 5. LAM is the best available treatment for patients with established recurrent hepatitis B. Long-term therapy is associated with the emergence of drug-resistant mutants in up to 60% of patients. Severe hepatitis and liver failure have been described among liver transplant recipients with YMDD mutations. 6. Combination therapy with HBIg and LAM prevents HBV recurrence in 90% to 100% of patients who undergo OLT for hepatitis B. The optimal HBIg protocol in the LAM era is yet to be defined. 7. Preliminary studies suggest that adefovir dipivoxil inhibits HBV replication in patients infected with LAM-resistant HBV strains. 8. Fifteen years ago, hepatitis B was regarded as a relative or absolute contraindication for OLT. Today, hepatitis B is a universally accepted indication for OLT.  (+info)

Treatment of recurrent hepatitis B infection in liver transplant recipients. (55/327)

1. Therapeutic decisions are guided by a patient's clinical status (severity of disease and presence of comorbidities) and previous drug-exposure history. 2. Lamivudine is safe and effective in liver transplant recipients with recurrent hepatitis B virus (HBV) infection caused by wild-type virus or failure of hepatitis B immunoglobulin therapy. Lamivudine resistance, developing in approximately 25% after 12 months of therapy, is its main limitation. 3. Famciclovir is safe in liver transplant recipients; however, virological and clinical responses are less consistent than with lamivudine. Thus, lamivudine is favored over famciclovir as first-line therapy in transplant recipients with no previous exposure to nucleoside analogues. 4. Although limited in availability, adefovir dipivoxil appears safe and effective in treating liver transplant recipients with lamivudine-resistant HBV disease. Close monitoring of renal function is recommended, with dose adjustment in patients with reduced creatinine clearances. 5. Limited data suggest that intravenous ganciclovir, tenofovir disoproxil fumarate, and interferon alfa may be useful as rescue therapies for patients with lamivudine- or famciclovir-resistant HBV disease. 6. Antiviral therapy with two or more suitable agents may minimize the chance for viral resistance; therefore, future therapeutic strategies likely will use combination therapy in the long-term management of recurrent HBV disease.  (+info)

Induction of apoptosis in human leukemia cells by the CDK1 inhibitor CGP74514A. (56/327)

We have examined the effects of the CDK1 inhibitor CGP74514A on cell cycle- and apoptosis-related events in human leukemia cells. An 18-hr exposure to 5 microM CGP74514A induced mitochondrial damage (i.e., loss of Delta psi(m)) and apoptosis in multiple human leukemia cell lines (e.g., U937, HL-60, KG-1, CCRF-CEM, Raji, and THP; range 30-95%). In U937 cells, CGP74514A- induced apoptosis (5 microM) became apparent within 4 hr and approached 100% by 24 hr. The pan- caspase inhibitor Boc-fmk and the caspase-8 inhibitor lETD-fmk opposed CGP74514A-induced caspase-9 activation and PARP degradation, but not cytochrome c or Smac/DIABLO release. CGP74514A-mediated apoptosis was substantially blocked by ectopic expression of full-length Bel- 2, a loop-deleted mutant Bcl-2, and Bcl-x(L). CGP74514A treatment (5 microM; 18 hr) resulted in increased p21(CIP1) expression, p27(KIP1) degradation, diminished E2F1 expression, and dephosphorylation of p34(CDC2). It also induced early (i.e., within 2 hr) inhibition of CDK1 activity and dephosphorylation of pRb, followed by pRb degradation, but did not block pRb phosphorylation at CDK2- and CDK4- specific sites. These findings indicate that the selective CDK1 inhibitor, CGP74514A, induces complex changes in cell cycle-related proteins in human leukemia cells accompanied by extensive mitochondrial damage, caspase activation, and apoptosis.  (+info)