Protection by protein A of apoptotic cell death caused by anti-AIDS drug zidovudine

Gene therapy for neuropathic pain using dorsal root ganglion-targeted helper-dependent adenoviral vectors with GAD67 expression

INTRODUCTION

Currently available medications for neuropathic pain are of limited efficacy. Moreover, they are administered systemically and are associated with significant side effects. Ideally, one can circumvent systemic side effects if such treatment can be administered by delivery of the therapeutic agent directly to the diseased neurons. Towards this end, we previously reported the production of a recombinant helper-dependent adenovirus (HDAd) armed with a tissue-specific homing peptide to deliver transgenes targeting sensory neurons with high efficacy.

OBJECTIVES

To develop an effective gene therapy for neuropathic pain by producing a dorsal root ganglion (DRG)-targeted HDAd vector that specifically expresses glutamic acid decarboxylase (GAD) 67 (HDAd-DRG-GAD67).

METHODS

We produced spinal nerve transection (SNT) mice as a neuropathic pain model and delivered HDAd-DRG-GAD67 by injection into spinal nerve or intrathecally to these animals. We evaluated the therapeutic efficacy by measuring ion channel gene expression and quantifying mechanical allodynia, a representative symptom of neuropathic pain, in treated animals.

RESULTS

Glutamic acid decarboxylase expression by HDAd-DRG-GAD67 reduced allodynia significantly in SNT mice. In addition, HDAd-DRG-GAD67 had a much greater transduction efficacy and expressed the therapeutic gene for a much longer time and at a lower dose of viral particles than wild-type HDAd. We found that SNT induced the upregulation of Cav3.2 mRNA in the DRG and GAD67 overexpression suppressed the elevation. Furthermore, the HDAd-DRG-GAD67-induced allodynia amelioration occurred even when we delayed intrathecal delivery of the therapeutic vector to day 7 after SNT.

CONCLUSION

HDAd-mediated DRG-targeted gene therapy delivering GAD67 is an efficacious treatment for neuropathic pain in SNT mice.

Gene therapy for neuropathic pain by silencing of TNF-α expression with lentiviral vectors targeting the dorsal root ganglion in mice

Neuropathic pain can be a debilitating condition. Many types of drugs that have been used to treat neuropathic pain have only limited efficacy. Recent studies indicate that pro-inflammatory mediators including tumor necrosis factor α (TNF-α) are involved in the pathogenesis of neuropathic pain. In the present study, we engineered a gene therapy strategy to relieve neuropathic pain by silencing TNF-α expression in the dorsal root ganglion (DRG) using lentiviral vectors expressing TNF short hairpin RNA1-4 (LV-TNF-shRNA1-4) in mice. First, based on its efficacy in silencing TNF-α in vitro, we selected shRNA3 to construct LV-TNF-shRNA3 for in vivo study. We used L5 spinal nerve transection (SNT) mice as a neuropathic pain model. These animals were found to display up-regulated mRNA expression of activating transcription factor 3 (ATF3) and neuropeptide Y (NPY), injury markers, and interleukin (IL)-6, an inflammatory cytokine in the ipsilateral L5 DRG. Injection of LV-TNF-shRNA3 onto the proximal transected site suppressed significantly the mRNA levels of ATF3, NPY and IL-6, reduced mechanical allodynia and neuronal cell death of DRG neurons. These results suggest that lentiviral-mediated silencing of TNF-α in DRG relieves neuropathic pain and reduces neuronal cell death, and may constitute a novel therapeutic option for neuropathic pain.

Inhibition of cation channels and suicidal death of human erythrocytes by zidovudine

Zidovudine, a drug widely used in the treatment of AIDS, has been shown to influence cytosolic calcium activity in HIV-infected lymphocytes. Thus, zidovudine may modify the activity of Ca(2+)-permeable ion channels. In erythrocytes, activation of Ca(2+)-permeable cation channels stimulates eryptosis, the suicidal erythrocyte death. Eryptosis is characterized by cell shrinkage (apparent from a decrease of forward scatter) and phosphatidylserine (PS) exposure (apparent from annexin V-binding) at the erythrocyte surface. Triggers of eryptosis include isotonic cell shrinkage (Cl(-) replacement by gluconate), energy depletion (removal of glucose) or exposure to a variety of drugs including azathioprine. The present study explored, whether zidovudine influences the activity of erythrocytic Ca(2+)-permeable cation channels and eryptosis. Whole-cell patch-clamp recordings indeed revealed that zidovudine blocked the Ca(2+)-permeable cation channels activated by Cl(-) removal. In the presence of Cl(-) and glucose, the percentage of annexin V-binding cells was low and not significantly modified by the presence of zidovudine. Both, Cl(-) removal and glucose depletion increased annexin V-binding and decreased forward scatter, effects significantly blunted by zidovudine (2 microg/ml). According to Fluo3 fluorescence, zidovudine (2 microg/ml) did not significantly modify cytosolic Ca(2+) concentration under control conditions, but significantly blunted the increase in cytosolic Ca(2+) activity following glucose depletion. Furthermore, zidovudine significantly inhibited azathioprine-induced eryptosis. The present observations disclose a completely novel effect of zidovudine, i.e. its inhibitory influence on Ca(2+) entry and subsequent suicidal erythrocyte death during isotonic cell shrinkage or energy depletion.

Zidovudine induces S-phase arrest and cell cycle gene expression changes in human cells

Antiretroviral therapy for the human immunodeficiency virus-1 (HIV-1) typically includes two nucleoside reverse transcriptase inhibitors (NRTIs). 3'-Azido-3'-deoxythymidine (AZT, Zidovudine) plus 2'-deoxy-3'-thiacytidine (3TC, Lamivudine) is a combination that is used frequently. The NRTIs are mutagenic nucleoside analogs that become incorporated into DNA and terminate replication. We therefore hypothesized that exposure to this class of drug may alter cell cycle parameters. We used flow cytometry to examine the cell cycle in human epithelioid carcinoma (HeLa) cells exposed to AZT and 3TC alone, as well as a series of AZT/3TC dose combinations: (A) 125.0 microM AZT/12.5 microM 3TC; (B) 250.0 microM AZT/25.0 microM 3TC; and (C) 500 microM AZT/50 microM 3TC. At 24 h, at all doses, there was a good cell viability (>/=68%), and incorporation of AZT into nuclear DNA. Using flow cytometry, a dose-related increase in the percentage of cells in S phase, from 9.5% with no drug, to 36.0% with dose C, was observed in cells exposed for 24 h (P = 0.001, ANOVA). A concomitant decrease in the percentage of cells in G(1) phase, from 82.6% with no drug to 58.5% with dose C, was observed in cells exposed for 24 h (P = 0.017, ANOVA). A similar S phase arrest was seen in cells exposed to 125, 250 and 500 microM AZT alone, but there was no S phase alteration with 50 microM 3TC alone, suggesting that AZT is responsible for the accumulation of cells in S phase. To elucidate the accumulation of cells in S phase and explore the cell cycle gene expression changes induced by AZT and 3TC, we used c-DNA microarray, Cell Cycle Super Array and real-time PCR. There was a strong upregulation of the DNA damage-inducible transcript 3 (DDIT3 or GADD153) in NRTI-exposed cells. In addition, AZT induced an upregulation of cyclin D1 accompanied by a downregulation of the cyclin D1-associated inhibitors P18 and P57, and the G(1)-S check point gene P21, the net effect of which would be to foster a cell progression into S phase. Cyclin A2 was down-regulated in cells exposed to AZT, suggesting a block in S-G(2)-M progression that would also be consistent with the accumulation of cells in S phase. Overall, the study demonstrates that AZT, but not 3TC, causes an arrest of cells in S phase with a consistent alteration in the expression of several cell cycle genes.

Caspase signalling in neuropathic and inflammatory pain in the rat

Whereas small-fibre sensory neuropathies might ultimately lead to cell death and loss of sensation, they first progress through a phase, which might last for years, characterized by the presence of analgesia-resistant neuropathic dysesthesias and pain. Much previous research has addressed these two phases as separate phenomena mediated by presumably discrete biochemical mechanisms. We hypothesized that activity in signalling pathways that ultimately lead to apoptosis plays a critical role in the generation of neuropathic pain, before death of sensory neurons becomes apparent. We have tested the hypothesis that activator and effector caspases, defining components of programmed cell death (apoptosis) signalling pathways, also contribute to pain-related behaviour in animals with small-fibre peripheral neuropathies and that the death receptor ligand, tumour necrosis factor-alpha, and its downstream second messenger, ceramide, also produce pain-related behaviour via this mechanism. In two models of painful peripheral neuropathy, HIV/AIDS therapy (induced by the nucleoside reverse transcriptase inhibitor, dideoxycytidine), and cancer chemotherapy (induced by vincristine) peripheral neuropathy, and for pain-related behaviour induced by tumour necrosis factor-alpha and its second messenger, ceramide, inhibition of both activator (1, 2, 8 and 9) and effector (3) caspases attenuates neuropathic pain-related behaviour, although has no effect in streptozotocin-diabetic neuropathy and control rats. We conclude that during a latent phase, before apoptotic cell death is manifest, the caspase signalling pathway can contribute to pain in small-fibre peripheral neuropathies, and that inflammatory/immune mediators also activate these pathways. This suggests that these pathways are potential targets for novel pharmacological agents for the treatment of inflammatory as well as neuropathic pain.

Disruption of the p53 gene results in preserved trabecular bone mass and bone formation after mechanical unloading

We tested the hypothesis that mechanical unloading facilitates signaling of p53, an important modulator of cell cycling and apoptosis, in bone marrow cells and thereby reduces trabecular bone volume (BV). We performed histomorphometric analyses and bone marrow cell cultures in tail-suspended (TS) p53 null (p53-/-) and wild-type (p53+/+) mice. Eight-week-old male mice were assigned to four groups after 1-week acclimatization: p53+/+ + ground control (GC), p53+/+ + TS, p53-/- + GC, and p53-/- + TS. Bilateral tibial samples were used for analysis. The histomorphometric parameters of trabecular structure, formation and resorption did not differ between the p53-/- + GC and p53+/+ + GC groups. Trabecular BV in p53+/+ + TS mice was significantly reduced to 45% of that in the p53+/+ + GC group after one week of TS. In contrast, BV in p53-/- + TS mice was preserved at the same level as that in the p53-/- + GC group. The bone formation rate (BFR) was significantly reduced in p53+/+ + TS but not in p53-/- + TS mice. Unloading significantly increased trabecular osteoclast number (Oc.N) and surface in p53+/+ + TS mice compared with the p53+/+ + GC group, but the difference was not significant between p53-/- + TS and p53-/- + GC mice. In bone marrow cell culture, the numbers of alkaline phosphatase-positive (ALP+) colony-forming units fibroblastic (CFU-f) and mineralized nodules were significantly reduced in p53+/+ + TS, but not p53-/- + TS mice. [3H]thymidine incorporation into bone marrow cells was higher in p53-/- mice than in p53+/+ mice, independent of mechanical loading or unloading. Flow cytometric cell cycle analysis revealed that unloading significantly increased the percentage of hypoploid bone marrow cells in p53+/+ mice relative to that in p53+/+ + GC mice, but there was no significant difference in ploidy between p53-/- + TS and p53-/- + GC mice. Expression levels of p53 and p21 mRNAs were enhanced after TS in bone marrow cells from p53+/+ mice. Our data show that trabecular bone mass and bone formation were preserved after tail-suspension in p53-/- mice, closely associated with ALP+ CFU-f and mineralized nodule formation in marrow cultures obtained from tibias of p53-/- mice. We speculate that bone loss due to mechanical unloading may be related to facilitation of intracellular p53-p21 signaling.

Synergistic immunopotentiating effects induced by T-cell and B-cell superantigen in mice

Staphylococcal Enterotoxin-A(SEA), a 27kDa monomeric protein, produced by some strains of Staphylococcus aureus, is a prototype T-cell superantigen which causes proliferation of cytotoxic T-lymphocytes and produces cytokines like TNF-alpha and IFN-gamma. Recently Protein A (PA), a 42 kDa membrane protein of the Staphylococcus aureus Cowan-I strain, has been termed a B-cell super antigen. It has been shown to cause multiple immunological responses. In the present study we examined the effect of these two superantigens used separately as well as combination in a normal mouse system. It has been shown that combination treatment of PA and SEA is more effective than that of each individual one. FACS analyses of cell cycles showed that a finely turned cellular collaboration occurred in various phases of cell growth and proliferative response compared with controls (P<0.01). It has also been shown that the percentage of various cell types bearing different clusters of differentiation markers, e.g., CD8+, CD34+ increases considerably due to the combined effect of PA and SEA. We also observed that co-administration of both the elicits different soluble mediators like cytokines (TNF-alpha, INF-gamma, IL-1beta). No apoptotic phenomenon was observed (from the cell cycle analysis) for the dose of PA and SEA, used for the experiments, suggesting that these doses of PA and SEA should be non-toxic.