1 Institute of Biological Chemistry Giorgio Fornaini, Via Saffi, 2; 2 Institute of Hygiene, Via S. Chiara, 27, University of Urbino, 61029 Urbino (PU); 3 Institute of Microbiology, University of Rome La Sapienza, 00185 Rome; 4 Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor Vergata, 00133 Rome, Italy
Keywords: antivirals, drug delivery, macrophages, RBCs
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Introduction |
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In HIV-1-infected patients, highly active antiretroviral therapies (HAART) have been used both to reduce viral load in plasma to un-detectable levels, and to increase the number of CD4 cells in the majority of infected individuals. Nonetheless, HIV-1 has not been eradicated by HAART, as demonstrated by virus rebound from latent viral reservoirs, principally CD4 cells and macrophages, after cessation of HAART.1,2 Cells of the macrophage lineage play an important role in HIV-1 pathogenesis. They are the initial HIV-1 cellular targets, and following infection they resist the cytopathic effects of HIV-1. As a consequence, they persist throughout the course of the disease as long-term stable reservoirs of HIV-1 capable of disseminating the virus in other cells and tissues. In fact, infectious virus can be recovered from blood monocytes obtained from patients receiving HAART with no detectable HIV-1 in blood,3 or from macrophages from SHIV-infected monkeys upon lymphocyte depletion.4 Macrophages are also the most important targets for HIV in the CNS, and alterations in neuronal metabolism induced by infected macrophages play a crucial role in the pathogenesis of HIV-related encephalopathy.3 These and other considerations underline the importance of therapeutic approaches able to interfere with HIV infection and replication in macrophages. Among drugs prescribed today, protease inhibitors inhibit HIV replication in chronically infected macrophages (i.e. cells carrying the proviral genome already integrated in the host genome), although at concentrations higher than those effective in de novo infected CD4 lymphocytes. Nucleoside analogues, the first anti-HIV drugs, although very potent in vitro, possess limited penetration in sequestered districts and are poorly phosphorylated in macrophages while non-nucleoside reverse transcriptase inhibitors possess an antiviral activity similar to that found in lymphocytes.5
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Selective delivery of antiviral drugs to macrophages |
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Potential role of reduced glutathione as an antiviral agent |
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Erythrocytes as carriers of GSH to macrophages |
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The importance of this approach is also supported by recent studies demonstrating that the neurodegenerative phenomena observed in HIV-1-associated dementia can be linked to intracellular GSH depletion and loss of mitochondrial function. Hence, restoring both GSH concentration and mitochondrial integrity are possible therapeutic strategies for slowing disease progression and dementia in AIDS patients.23
Moreover, if on the one hand the administration of GSH-loaded RBCs potentiates the antiviral effect of AZT, on the other it can also mitigate the GSH deficiency observed upon AZT treatment.24
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Conclusions |
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Results obtained in the murine model of AIDS have been confirmed in in vitro HIV-1 chronically infected macrophages where one nights treatment with GSH-loaded RBCs (14 mM GSH inside RBCs) caused a 50%70% reduction of p24 production. This result is comparable to the inhibition obtained with twice the addition of 20 mM GSH in the medium (data not shown).
In addition to the significant antiviral effect observed, another advantage of the selective delivery of high doses of GSH is the absence of toxic side effects in vitro and in vivo in the mouse model used.
Moreover, it has been demonstrated25 that the intracellular thiol redox status of macrophages influences the ability to generate a Th1- or Th2-type response, and, more precisely, that GSH depletion inhibits Th1-associated cytokine production and/or favours Th2-associated responses; therefore, alterations in immune function because of GSH depletion in macrophages may play a key role in exacerbating HIV and other infectious diseases.25 In our opinion, the specific targeting of GSH-loaded RBCs to macrophages should be useful in restoring immune functions altered by GSH depletion in these cells, and addressing an immune response of wide interest in vaccination studies.
Because of the advantageous properties of RBCs and the availability of a specially designed
apparatus to perform the loading procedure under blood banking conditions,26 we consider that RBCs may be used in a variety of pathological conditions to deliver drugs that do not cross cell membranes and/or are not very stable in biological fluids and/or must be targeted to cells or organs. Furthermore, carrier RBCs can also deliver antisense oligonucleotides to block translation of target mRNA. This may have an application in human cancer gene therapy or peptide delivery.26,27
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Acknowledgements |
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Footnotes |
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References |
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