In vitro synthesis of DNA in nuclei isolated from herpes simplex virus-infected cells, untreated and treated with metabolic inhibitors

Plasma L-Carnitine and L-Lysine Concentrations in HIV-Infected Patients

Background:

Virus infections are associated with significant alterations in host cells amino acids profiles that support biosynthetic demands necessary for production of viral progeny. Amino acids play an important role in the pathogenesis of all virus-related infections both as basic substrates for protein synthesis and as regulators in many metabolic pathways.

Objective:

Our aim was to determine the changes in plasma L-carnitine levels and its amino acid precursor (L-lysine) in HIV-infected patients.

Methods:

We performed a case-control study of 430 HIV-1 infected males (non-vegetarians) without any restriction in the nourishment, before highly active antiretroviral therapy (HAART) and 125 HIV-1 subjects after the introduction of HAART who were periodically monitored in the Municipal Center of HIV/AIDS prophylaxis, Surgut, Russian Federation

Results:

The plasma total (TC) and free (FC) L-carnitine concentrations markedly decreased with the clinical stages of HIV infection. The mean plasma TC, FC and L-lysine levels were significantly lower in asymptomatic stage (A) and advanced CDC stages (B, C) HIV-infected patients compared with our reference values. The total and free L-carnitine and its amino acid precursor concentrations mild increased in HIV-infected subjects after the introduction of HAART.

Our data revealed that L-lysine amino acid and its derivative (TC) levels were negatively correlated with viral load and inversely with CD4 count lymphocytes in the total cohort.

Conclusion:

The study results show that there was evidence for an association between plasma L-carnitine, L-lysine and HIV-1 RNA levels, immunological markers and clinical stages of HIV infection. The obtained data indicate that level changes of these host essential nutritional elements can play an important role in the HIV life cycle. These findings are important for understanding the pathophysiology of HIV infection and must be considered in further research for the development of new approaches in the treatment of the disease.

Influence of L-lysine amino acid on the HIV-1 RNA replication in vitro

BACKGROUND

Virus replication strongly depends on host metabolic machinery and essential cellular factors, in particular, on amino acid profiles. Amino acids play an important role in the pathogenesis of all virus-related infections both as basic substrates for protein synthesis and as regulators in many metabolic pathways, including gene expression. The inhibitory effects of deficiency or excess of these essential elements on virus replication are widely appreciated. Although the same interrelationship between host cellular factors and HIV have been recognized for a long time, the effects of amino acids on HIV-1 RNA replication dynamic is not yet well documented. Our aim was to determine in this pilot study the direct effect of L-lysine amino acid on HIV-1 RNA replication in vitro in HIV-infected patients.

METHODS

A total of 100 HIV-1-infected males without highly active antiretroviral therapy (HAART) were monitored in our center. The patients were in stage A of the disease according to the 1993 Centers for Disease Control (CDC) classification system for HIV-infection. Patients with HIV were enrolled in one stage (A) of the disease with the average amount CD4 lymphocytes in the range of 200-300 cells/µL at the time of sample acquisition. For evaluation of the effects of essential L-lysine amino acid on HIV-1 RNA replication level, we used a model of amino acid-excess system in vitro following incubation of plasma samples for 24 h at 25 °C. Quantitative HIV-1 RNA assay was performed using (RT-PCR) reverse-transcriptase polymerase chain reaction (Rotor-Gene Q, QIAGEN, Germany).

RESULTS

The mean HIV-1 RNA levels were significantly higher in the enriched peripheral blood mononuclear cells plasma samples HIV-infected subjects after 24 h incubation at 25 °C temperature than in the plasma samples the same patients studied on the date of blood tests (p < 0.0001). The number of HIV-1 RNA copies increased in 1.5 times. We observed that in plasma of the same HIV-infected patients after adding L-lysine and following incubation in vitro, viral load increased significantly in comparison with standard samples (p < 0.0001). The increased viral load was found in 100/92 (92%) of HIV-infected subjects. The average number of HIV-1 RNA copies in samples had increased by 4.0 times. However, we found no difference in HIV-1 RNA levels after replacement of L-lysine for L-arginine in comparison samples in the same HIV-infected patients. It is obvious that the addition of L-arginine does not increase viral replication in vitro as L-lysine amino acid supplement does. Additionally, no increase in viral load was determined after adding L-lysine and non toxic doses of its inhibitor (L-lysine alpha-oxidase) in plasma samples.

CONCLUSIONS

The results show that L-lysine amino acid excess is characterized by significant increased of HIV-1 RNA copies in enriched peripheral blood mononuclear cells plasma samples of HIV-infected patients. There was evidence for an association between L-lysine supplementation and HIV-1 RNA replication and the level changes of this host essential nutritional element play a key role in the synthesis of the virus proteins and in transcription initiation of the retrovirus life cycle. High intake of L-lysine amino acid may increase the risk of high viral load, subsequent acceleration of immunosuppression and HIV progression. Overall results demonstrate that the simple L-lysine-related model in vitro can be widely used for practical purposes to evaluate HIV-1 RNA replication dynamic, disease prognosis and new approaches in treatment of the patients with human immunodeficiency virus. Although the impact mechanism of L-lysine amino acid on the viral load in the pathogenesis of HIV-infection is at present conjectural and requires further development, the results highlight an interesting target in antiviral therapy, and this statement remains to be proved in further research and clinical trials.

DNA polymerase in nuclei isolated from herpes simplex virus type-2-infected cells. Characterization of the reaction product and inhibition by substrate analogs

Nuclei isolated from herpes simplex virus (HSV) type 2-infected KB cells were examined for their capacity to serve as an in situ source of herpes DNA polymerase. In contrast to purified enzymes with added template, approx. 80% of the DNA synthesized in isolated nuclei was viral. The average size of DNA fragments labeled in vitro was 3.2 X 10(6) Da. Based on an increase in DNA density when nuclei were incubated in the presence of BrdUTP rather than dTTP, 16% of the nucleotides were added during the in vitro reaction. Sucrose gradient analysis of DNA polymerase activity in extracts of isolated nuclei demonstrated the nearly exclusive presence of herpes DNA polymerase. Km concentrations for the four dNTPs were from 0.14 to 0.55 microM. DNA synthesis was inhibited competitively by the 5'-triphosphates of ara-A and ara-C (Ki = 0.03 and 0.22 microM, respectively) but not by the 5'-triphosphate of dideoxythymidine. aATP also served as a substrate (Km = 0.014 microM) for the reaction. We conclude that nuclei from HSV-infected cells have significant advantages for the detailed study of inhibitors of herpesvirus replication.

Characteristics of chromatin preparations from herpes simplex virus infected cells

Chromatin isolated from herpes simplex virus type 1-infected baby hamster kidney cells contains a number of tightly associated virus-induced polypeptides. A subset of these proteins bind to immobilized DNA in vitro (Vmw 175, 155, 130, 63, 43, 38/39). Virus-induced polypeptides extractable with acid from infected cell chromatin include Vmw 155, the major capsid protein of herpes simplex virus type 1 virions, and Vmw 63 and 38/39 which are heterogeneous with respect to charge and are phosphorylated. These chromatin preparations, in the presence of deoxynucleoside triphosphates and MgCl2 were capable of synthesizing viral and cell DNA in a reaction which was stimulated by the addition of ATP, riboNTPs and potassium acetate. In vitro synthesized viral DNA co-sedimented with prelabelled parental DNA but the single-stranded product was smaller than parental DNA. Density labelling indicated that extensive synthesis was taking place and all BamHI fragments of viral DNA were represented by the DNA synthesized in vitro.

Synthesis of DNA in cells infected with African swine fever virus

Incorporation of 14C-thymidine by cells infected with African swine fever virus (ASFV) occurs in the nucleus. Part of this DNA is transferred to the cytoplasm and becomes resistant to DNAse. The nuclear fraction washed with Triton X100 retained all labeled DNA and was able to synthesize viral and cellular DNA under in vitro conditions in the presence of the four deoxynucleoside triphosphates, Mg+2, and sucrose. Under similar conditions nuclei from uninfected cells synthesized very little DNA.