Antiviral therapy in AIDS. Clinical pharmacological properties and therapeutic experience to date

Update on HIV viral-load assays: new technologies and testing in resource-limited settings

Assessment of viral load is one of the best predictors of clinical progression, as well as the main parameter to assess treatment response in HIV-positive patients. Reproducible and sensitive assays based on real-time PCR technology have been developed to quantify HIV in the bloodstream of infected persons. Recent improvements have allowed reliable measurements of viremia in non-B subtypes. Testing of samples other than serum or plasma has been challenging, but is particularly important for developing countries.

Host factors influencing susceptibility to HIV infection and AIDS progression

Transmission of HIV first results in an acute infection, followed by an apparently asymptomatic period that averages ten years. In the absence of antiretroviral treatment, most patients progress into a generalized immune dysfunction that culminates in death. The length of the asymptomatic period varies, and in rare cases infected individuals never progress to AIDS. Other individuals whose behavioral traits put them at high-risk of HIV transmission, surprisingly appear resistant and never succumb to infection. These unique cases highlight the fact that susceptibility to HIV infection and progression to disease are complex traits modulated by environmental and genetic factors. Recent evidence has indicated that natural variations in host genes can influence the outcome of HIV infection and its transmission. In this review we summarize the available literature on the roles of cellular factors and their genetic variation in modulating HIV infection and disease progression.

Lack of muscle toxicity with didanosine (ddI). Clinical and experimental studies

Currently, 2',3'-dideoxyinosine (ddI) is used in AIDS therapy. To investigate the possible myotoxicity of ddI in patients infected with human immunodeficiency virus (HIV), we examined the effect of ddI in vitro in tissue cultures of skeletal muscles of rats exposed to ddI at doses equivalent to plasma ddI levels obtained in the treatment of HIV patients. Control cultures were exposed to normal saline and zidovudine (AZT). After 4 weeks no changes were noted in the ddI and normal saline cultures, but AZT cultures showed abnormal accumulation of mitochondria. The creatine kinase values in culture supernatants were all normal. We also reviewed the clinical, nutritional and biological parameters, AZT and ddI dosage, and histochemical findings in muscle specimens of 14 HIV patients receiving ddI therapy. All patients had previously received AZT. The mean cumulative dose of ddI was 91.6 gm. Two patients had myalgia, 9 muscle atrophy, and 13 weakness. All patients were malnourished. Five patients had mitochondrial myopathy related to AZT, 4 had ddI-associated neuropathy and 2 patients had only selective type 2 fiber atrophy. One patient had necrotizing vasculitis, one had scattered necrotic fibers and type 2 fiber atrophy and 2 had a normal muscle biopsy. On the basis of the results, we have been unable to implicate ddI as a cause of skeletal myopathy.

Therapeutic approaches to HIV infection based on virus structure and the host pathogen interaction

The HIV-1 infection of central nervous system, with attendant neuropathy and dementia, poses a unique challenge for antiviral therapy. For practical considerations, it is important to define carefully the precise therapeutic objectives. (1) Is it necessary to inhibit spreading HIV-1 infection in the central nervous system? (2) What is the role of inflammatory responses in central nervous system disease during HIV-1 infection? (3) Is there a correlation between pathology and dementia? (4) Are virions or virus gene products toxic in the central nervous system? (5) Is there a role for immune suppression and opportunistic pathogens in AIDS dementia? The development of therapeutic agents for HIV-1 infection is guided by our knowledge of virus structure, the function of viral proteins, the interactions with host components, and detailed features of the virus life cycle. In each case, unique features of the virus can be identified and established as targets for unique antiviral compounds. Drugs acting as inhibitors of virus enzymatic functions are plagued by the rapid development in vivo of drug-resistant virus variants, although combination or alternating chemotherapeutic regimens may obviate some of these concerns. Novel approaches to inhibiting virus are flourishing. In vitro studies show the value of agents as diverse as molecular decoys for tat activity to efforts to mutagenize integrated proviruses by modified oligonucleotides that form triple helices with chromosomal genes. As each particular clinical situation is better defined, the design and application of these agents can be refined to inhibit HIV-1 replication and reduce the associated morbidity.

Antiviral therapy in human immunodeficiency virus infections. Current status (Part II)

Part I of this article reviewed the targets against which anti-HIV drugs can be directed, problems in assessing active compounds (e.g. resistance development and use of surrogate end-points). and nucleoside analogues effective against HIV reverse transcriptase. Intensive research is currently being undertaken in laboratories and hospitals to design and evaluate new inhibitors of HIV. In this work, combining different drugs is one important approach, both to decrease toxicity and to offset the rate of resistance development, which seems to be a major problem associated with therapy directed against the ever-changing HIV. Therapeutic vaccines and immunomodulators are other modalities being actively evaluated against HIV and AIDS, although this effort has not yet yielded any licensed treatment. It appears likely that new antiviral drugs and immunotherapies will be forthcoming during the next 5 years, that they will be used in a variety of combinations, and that the treatment options available for opportunistic infections will increase. These developments should improve the survival and the quality of life of patients with HIV infection.

Antiviral drugs

There are only a limited number of effective, non-toxic antiviral drugs for clinical use, whereas there is a great need for such drugs. Especially for the treatment of patients infected with the human immuno-deficiency virus (HIV) anti-HIV drugs are required. At the same time viral infections secondary to AIDS cannot yet be treated effectively. An increasing problem is the development of virus strains resistant to the available drugs. At this moment a great effort is made in the research for new antiviral drugs. In this article the available antiviral drugs are reviewed. Their antiviral properties, mechanism of action, clinical use, pharmacokinetic properties and side-effects are discussed. Some attention is paid to the future directions in the search for new anti-HIV drugs.

Endoretinal biopsy in immunosuppressed and healthy patients with retinitis. Indications, utility, and techniques

Endoretinal biopsies were taken using pars plana vitrectomy techniques in 13 eyes with inflammatory or infectious retinitis complicated by retinal detachment (RD). The surgical technique has evolved over a 4-year period. The authors review the surgical technique including techniques of removal of the vitreous, appropriate hemostasis, selection of the biopsy site, and atraumatic removal of the tissue from the vitreous cavity. Careful processing of the material for histopathology, immunopathology, and electron microscopy is necessary and has provided useful information in patient diagnosis and management. The authors have used the technique in cases of rhegmatogenous RD complicating presumed viral retinitis. The technique has proven to be useful in confirming the clinical diagnosis and is relatively safe when used in selected cases.

Influence of methisoprinol (isoprinosine) on HIV-infected human lymphocytes: in vitro immunological, virological, and ultrastructural studies

Methisoprinol (isoprinosine) is a synthetic compound with reported antiviral and immunomodulating properties. Results of the present study showed that methisoprinol at concentrations greater than or equal to 200 micrograms/ml reduces the p24 and gp120 viral antigen expression on the surface of human immunodeficiency virus (HIV)-infected lymphocytes and the reverse transcriptase levels. In addition, cell viability, the number of the CD4+ cells, and the CD4+/CD8+ cell ratio are higher in methisoprinol-pretreated cell suspensions than in untreated HIV-infected cell cultures. A quantitative freeze-fracture study on the density of the intramembranous particles (IMP) present on both fracture faces of the plasma membrane of lymphocytes has shown that pretreatment with methisoprinol induces a different molecular organization resulting in a nearly three times increase of IMP density.