Cultured AIDS-related Kaposi's sarcoma (AIDS-KS) cells demonstrate impaired bioenergetic adaptation to oxidant challenge: implication for oxidant stress in AIDS-KS pathogenesis

Implications for oxidative and nitrative stress in the pathogenesis of AIDS-related Kaposi's sarcoma

AIDS-related Kaposi's sarcoma (AIDS-KS), which is the most prevalent AIDS related cancer, arises in a unique environment characterized by profound immunosuppression in conjunction with sustained immunostimulation. Persistent inflammation and the accompanying increased production of reactive species can promote carcinogenesis by numerous routes including sustained cell proliferation, initiation of nuclear and mitochondrial DNA mutations and induction of a proangiogenic environment. Furthermore, during conditions of continuous inflammation, protein nitration can result in irreversible inactivation of enzymes including the cytoprotective and reactive species degrading enzyme, mitochondrial superoxide dismutase (MnSOD). Because MnSOD serves as a putative tumor suppressor gene in addition to its reactive species inactivating capacities, the loss of MnSOD's cytoprotective functions could markedly facilitate malignant transformation. The purpose of this study was to investigate biochemical and molecular pathways by which reactive species facilitate AIDS-KS pathogenesis. Immunohistochemical studies of AIDS-KS tumors showed intense AIDS-KS lesional cell staining for MnSOD, inducible nitric oxide synthase (NOS 2) and the presence of a cellular 'fingerprint' of nitrative stress, 3-nitrotyrosine. Collectively, these results that imply reactive species stress occurs in situ. Similarly, cultured AIDS-KS cells derived from the AIDS-KS tumors contained both MnSOD protein and the 'high output' isoform, NOS 2. Co-localization studies established that the mitochondria are a primary site for 3-nitrotyrosine localization and immunoprecipitation/immunoblotting experiments confirmed that MnSOD tyrosine nitration occurs in AIDS-KS cells. Functional SOD assays showed that AIDS-KS cells possess significantly lower MnSOD activity relative to matched control cells; findings which correspond with ongoing MnSOD tyrosine nitration and subsequent inactivation within AIDS-KS cells. These results, which show in situ evidence of reactive species stress within AIDS-KS tumors and functional deficits attributable to nitrative stress in tumor-derived AIDS-KS lesional cells, imply that reactive species are intimately associated with AIDS-KS pathogenesis and provide insights for development of novel strategies for AIDS-KS clinical treatments.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.

Modulation of glutathione synthetic enzymes by acidic fibroblast growth factor

Increasing evidence suggests that glutathione (GSH) synthesis is a regulated process. Documented increases in gamma-glutamylcysteine synthetase (GCS) occur in response to oxidants, in tumors, on plating cells at a low cell density, and with nerve growth factor stimulation, suggesting that GSH synthesis may be related to the cell growth and transformation. Previously, extracellular acidic fibroblast growth factor (FGF-1) has been demonstrated to cause transformation and aggressive cell growth in murine embryonic fibroblasts. In the present investigation, we sought to determine whether FGF-1, with its growth inducing properties, resulted in the modulation of GSH biosynthetic enzymes, GCS and GSH synthetase. Murine fibroblasts transduced with (hst/KS)FGF-1, a chimeric human FGF-1 gene containing a signal peptide sequence for secretion, displayed elevated gene expression of both heavy and light subunits of GCS. Activity of GSH synthetase was also elevated in these cells compared with control cells. Nonetheless, GSH was decreased in the FGF-1-transduced cells along with high energy phosphates, adenine nucleotides, NADH, and the redox poise. However, GSSG was not elevated in these cells. Fibroblasts stably expressing human immunodeficiency virus type 1 Tat, which induces intrinsic FGF-1 secretion, resulted in similar changes in GCS, GS, and GSH. The results suggest that although increases in the enzymes of GSH synthesis are a common response to growth factors, an increase in GSH content per se is not required for altered cell growth.

Human papillomavirus type 16 E6-enhanced susceptibility of L929 cells to tumor necrosis factor alpha correlates with increased accumulation of reactive oxygen species

Human papillomavirus type 16 (HPV-16) E6 has been shown to prevent or enhance apoptosis depending on the stimulus and cell type. Here we present evidence that HPV-16 E6 sensitized murine fibrosarcoma L929 cells to tumor necrosis factor alpha (TNF)-induced cytolysis. The E6-enhanced cytolysis correlated with a precedent increase in reactive oxygen species (ROS) level and antioxidant treatment could completely block the E6-dependent sensitization. These findings represent the first demonstration of a link between a viral oncogene-sensitized cytolysis and ROS. Previous studies have shown conflicting results regarding whether TNF-induced cytolysis of L929 cells is through necrosis or apoptosis. Here we report that, although L929 cells underwent DNA fragmentation after exposure to TNF, they retained the morphology of intact nuclei while gaining permeability to propidium iodide, features characteristic of necrosis rather than apoptosis. We confirmed that the broad spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone markedly increased the susceptibility of L929 cells to TNF, and further demonstrated that E6 enhanced this susceptibility, which again correlated with increased ROS accumulation. We showed that the expression of E6 in L929 cells did not alter the stability of p53, and the cells retained a p53 response to actinomycin D. Furthermore, two E6 mutants defective for p53 degradation in other systems exhibited differential effects on TNF sensitization. These results suggest that the enhancement of TNF-induced L929 cytolysis by E6 is independent of p53 degradation. We also found that TNF-induced activation of NF-kappaB did not account for the enhanced TNF susceptibility by E6.

Glutathione depletion associated with the HIV-1 TAT protein mediates the extracellular appearance of acidic fibroblast growth factor

Primary murine embryonic fibroblasts transfected with HIV-1 TAT demonstrated decreased levels of high energy phosphates (ATP, GTP, UTP/CTP), adenine nucleotides (ATP, ADP, AMP), and both NAD+/NADH redox pairs, resulting in a substantial loss of redox poise. A greater than 50% decrease in intracellular reduced glutathione (GSH) concentration was accompanied by the extracellular appearance of acidic fibroblast growth factor (FGF-1). Addition of either N-acetyl-L-cysteine or glutathione ester (GSE), but not L-2-oxothiazolidine 4-carboxylate, partially restored intracellular GSH levels and resulted in loss of extracellular FGF-1. Treatment of FGF-1-transduced cells with buthionine sulfoximine (BSO) resulted in a time- and dose-dependent decrease in total cellular GSH concentration that was accompanied by the extracellular appearance of FGF-1. Inclusion of GSE during BSO treatment eliminated the extracellular appearance of FGF-1. BSO treatment of cells transfected with a mutant form of FGF-1, in which all three cysteine residues were replaced with serines, also decreased total cellular GSH concentration but failed to induce the extracellular appearance of FGF-1. Collectively, these results suggest that HIV-1 TAT induces a condition of oxidative stress, which mediates cellular secretion of FGF-1, an observation relevant to the pathophysiologic development and progression of AIDS-associated Kaposi's sarcoma.

Thiol redox modulation of tumor necrosis factor-alpha responsiveness in cultured AIDS-related Kaposi's sarcoma cells

Both clinical and experimental evidence indicates that AIDS-related Kaposi's sarcoma (AIDS-KS) has a multifactorial pathogenesis with factors such as HIV viral load, latent virus induction, and opportunistic infections contributing to disease progression. However, a consistent feature that unites these apparently diverse putative etiologic agents is sustained serum elevations of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha). While virtually every cell responds to TNF-alpha with gene activation, the extent of TNF-alpha-mediated cellular signaling is regulated by a delicate balance between signal activation and signal arresting events. Reactive oxygen intermediates (ROI), which are generated as a consequence of TNF-alpha membrane interaction, are part of this TNF-alpha-initiated cellular activation cascade. Previous studies in our laboratory have shown that AIDS-KS cells possess impaired oxygen intermediate scavenging capacities, thereby establishing conditions permissive for the intracellular retention of ROI. In this study, we used cellular capacity to upregulate the cytoprotective enzyme superoxide dismutase (SOD) to address the extent of cellular response to TNF-alpha. Concurrent with the SOD analyses, nucleotide profiles were obtained to assess cellular bioenergetic responses during TNF-alpha challenge. Proliferative growth levels of mitochondrial (Mn)SOD activities showed an activity spectrum ranging from lowest activity in AIDS-KS cells, to intermediate levels in matched, nonlesional cells from the AIDS-KS donors, to highest activities in HIV normal fibroblasts. In contrast, following TNF-alpha challenge, the AIDS-KS and KS donor nonlesional cells showed a 11.89- and 5.86-fold respective increase in MnSOD activity, while the normal fibroblasts demonstrated a 1.35-fold decrease. Subsequent thiol redox modulation studies showed that only the normal fibroblast cultures showed a potentiation of TNF-alpha-mediated MnSOD upregulation following GSH depletion. In addition, provision of the GSH precursor, N-acetylcysteine during TNF-alpha challenge only diminished MnSOD activity and mitochondrial compartmentalization in the AIDS-KS cells, a finding that likely reflects the lower levels of reduced thiols in this cellular population. Our data, which show that a perturbation in their cellular thiol redox status accentuates AIDS-KS cellular responsiveness to TNF-alpha, suggest a biochemical rationale for the recognized TNF-alpha AIDS-KS clinical correlation.

Curcumin and curcumin derivatives inhibit Tat-mediated transactivation of type 1 human immunodeficiency virus long terminal repeat

The transcription of HIV1 provirus is regulated by both cellular and viral factors. Various evidence suggests that Tat protein secreted by HIV1-infected cells may have additional action in the pathogenesis of AIDS because of its ability to also be taken up by non-infected cells. Curcumin [diferuloylmethane or 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] is the yellow pigment in turmeric Curcuma longa (Linn). It exhibits a variety of pharmacological effects including antiinflammatory and antiretroviral activities. Here, we demonstrated that curcumin used at 10 to 100 nM inhibited Tat transactivation of HIV1-LTR lacZ by 70 to 80% in HeLa cells. In order to develop more efficient curcumin derivatives, we synthesized and tested in the same experimental system the inhibitory activity of reduced curcumin (C1), which lacks the spatial structure of curcumin; allyl-curcumin (C2), which possesses a condensed allyl derivative on curcumin that plays the role of metal chelator; and tocopheryl-curcumin (C3), which enhances the antioxidant activity of the molecule. Results obtained with C1, C2 and C3 curcumin derivatives showed a significant inhibition (70 to 85%) of Tat transactivation. Despite the fact that tocopheryl-curcumin (C3) failed to scavenge O2.-, this curcumin derivative exhibited the most activity; 70% inhibition was obtained at 1 nM, while only 35% inhibition was obtained with the curcumin.

Protective effects of the lipophilic redox conjugate tocopheryl succinyl-ethyl ferulate on HIV replication

Previously, we demonstrated that ferulate ethyl and tocopherol reduced HIV replication. In this study, we investigate whether the conjugation of both compounds (O-tocopheryl succinyl O-ethyl ferulate) can increase HIV inhibition. We show here for the first time that O-tocopheryl succinyl O-ethyl ferulate inhibits 80% of HIV replication (HIV-1 acute infection and HIV transmission), inhibits cell lipoperoxidation and prevents cellular glutathione consumption. Compared to ferulate ethyl and tocopheryl succinyl, O-tocopheryl succinyl O-ethyl ferulate inhibits more HIV replication. This may be due in part to the great increase in the lipophilicity of this compound.

Clastogenic factors in plasma of HIV-1 infected patients activate HIV-1 replication in vitro: inhibition by superoxide dismutase

The frequent neoplastic disorders present in HIV-infected patients and the implication of oxidative stress in AIDS-Kaposi's sarcoma pathogenesis prompted us to study whether the mechanisms implicated in genotoxic effects of clastogenic factors (CFs) (i.e., chromosome damaging materials released by cells under conditions of oxidant stress) can play a role in HIV-1 expression and whether exogenous superoxide dismutase can inhibit the clastogenic and HIV-inducing effects of CFs. CFs were found in the plasma of all HIV-1 infected patients (n = 21) of this study group, in asymptomatic (CDC II) as well as in symptomatic patients (CDC IV). In addition to their chromosome damaging effect, CFs are able to upregulate HIV-1 expression in U1 cells and in PBMCs activated with PHA and IL2 at all time points (p < .05). Their formation, therefore, is an early event in the disease. It occured despite antiviral medication in these patients. Superoxide dismutase inhibited the clastogenic and the viral inducing effects (p < .05). On the basis of our findings, association of SOD mimetics or superoxide scavengers with antiviral drugs may be a new therapeutic approach. This polytherapy, if started early enough after infection, may prolong the latency period and limit the emergence of drug-resistant viral strains.

Ferryl intermediates of catalase captured by time-resolved Weissenberg crystallography and UV-VIS spectroscopy

Various enzymes use semi-stable ferryl intermediates and free radicals during their catalytic cycle, amongst them haem catalases. Structures for two transient intermediates (compounds I and II) of the NADPH-dependent catalase from Proteus mirabilis (PMC) have been determined by time-resolved X-ray crystallography and single crystal microspectrophotometry. The results show the formation and transformation of the ferryl group in the haem, and the unexpected binding of an anion during this reaction at a site distant from the haem.