miR-98 reduces endothelial dysfunction by protecting blood-brain barrier (BBB) and improves neurological outcomes in mouse ischemia/reperfusion stroke model

Most neurological diseases, including stroke, lead to some degree of blood-brain barrier (BBB) dysfunction. A significant portion of BBB injury is caused by inflammation, due to pro-inflammatory factors produced in the brain, and by leukocyte engagement of the brain endothelium. Recently, microRNAs (miRNAs) have appeared as major regulators of inflammation-induced changes to gene expression in the microvascular endothelial cells (BMVEC) that comprise the BBB. However, miRNAs' role during cerebral ischemia/reperfusion is still underexplored. Endothelial levels of miR-98 were significantly altered following ischemia/reperfusion insults, both in vivo and in vitro, transient middle cerebral artery occlusion (tMCAO), and oxygen-glucose deprivation (OGD), respectively. Overexpression of miR-98 reduced the mouse's infarct size after tMCAO. Further, miR-98 lessened infiltration of proinflammatory Ly6C^HI leukocytes into the brain following stroke and diminished the prevalence of M1 (activated) microglia within the impacted area. miR-98 attenuated BBB permeability, as demonstrated by changes to fluorescently-labeled dextran penetration in vivo and improved transendothelial electrical resistance (TEER) in vitro. Treatment with miR-98 improved significantly the locomotor impairment. Our study provides identification and functional assessment of miRNAs in brain endothelium and lays the groundwork for improving therapeutic approaches for patients suffering from ischemic attacks.

let-7g counteracts endothelial dysfunction and ameliorating neurological functions in mouse ischemia/reperfusion stroke model

Stroke is a debilitating disease, accounting for almost 20% of all hospital visits, and 8% of all fatalities in the United States in 2017. Following an ischemic attack, inflammatory processes originating from endothelial cells within the brain microvasculature can induce many toxic effects into the impacted area, from both sides of the blood brain barrier (BBB). In addition to increased BBB permeability, impacted brain microvascular endothelial cells can recruit macrophages and other immune cells from the periphery and can also trigger the activation of microglia and astrocytes within the brain. We have identified a key microRNA, let-7g, which levels were drastically diminished as consequence of transient middle cerebral artery occlusion (tMCAO) in vivo and oxygen-glucose deprivation (OGD) in vitro ischemia/reperfusion conditions, respectively. We have observed that let-7g* liposome-based delivery is capable of attenuating inflammation after stroke, reducing BBB permeability, limiting brain infiltration by CD3+CD4+ T-cells and Ly6G+ neutrophils, lessening microglia activation and neuronal death. These effects consequently improved clinical outcomes, shown by mitigating post-stroke gait asymmetry and extremity motor function. Due to the role of the endothelium in propagating the effects of stroke and other inflammation, treatments which can reduce endothelial inflammation and limit ischemic damage and improving recovery after a stroke are required. Our findings demonstrate a critical link between the CNS inflammation and the immune system reaction and lay important groundwork for future stroke pharmacotherapies.

PARP inhibition in leukocytes diminishes inflammation via effects on integrins/cytoskeleton and protects the blood-brain barrier

Background

Blood-brain barrier (BBB) dysfunction/disruption followed by leukocyte infiltration into the brain causes neuroinflammation and contributes to morbidity in multiple sclerosis, encephalitis, traumatic brain injury, and stroke. The identification of pathways that decreases the inflammatory potential of leukocytes would prevent such injury. Poly(ADP-ribose) polymerase 1 (PARP) controls various genes via its interaction with myriad transcription factors. Selective PARP inhibitors have appeared lately as potent anti-inflammatory tools. Their effects are outside the recognized PARP functions in DNA repair and transcriptional regulation. In this study, we explored the idea that selective inhibition of PARP in leukocytes would diminish their engagement of the brain endothelium.

Methods

Cerebral vascular changes and leukocyte-endothelium interactions were surveyed by intravital videomicroscopy utilizing a novel in vivo model of localized aseptic meningitis when TNFα was introduced intracerebrally in wild-type (PARP^+/+) and PARP-deficient (PARP^−/−) mice. The effects of selective PARP inhibition on primary human monocytes ability to adhere to or migrate across the BBB were also tested in vitro, employing primary human brain microvascular endothelial cells (BMVEC) as an in vitro model of the BBB.

Results

PARP suppression in monocytes diminished their adhesion to and migration across BBB in vitro models and prevented barrier injury. In monocytes, PARP inactivation decreased conformational activation of integrins that plays a key role in their tissue infiltration. Such changes were mediated by suppression of activation of small Rho GTPases and cytoskeletal rearrangements in monocytes. In vitro observations were confirmed in vivo showing diminished leukocyte-endothelial interaction after selective PARP suppression in leukocytes accompanied by BBB protection. PARP knockout animals demonstrated a substantial diminution of inflammatory responses in brain microvasculature and a decrease in BBB permeability.

Conclusions

These results suggest PARP inhibition in leukocytes as a novel approach to BBB protection in the setting of endothelial dysfunction caused by inflammation-induced leukocyte engagement.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0729-x) contains supplementary material, which is available to authorized users.

Dysfunction of brain pericytes in chronic neuroinflammation

Brain pericytes are uniquely positioned within the neurovascular unit to provide support to blood brain barrier (BBB) maintenance. Neurologic conditions, such as HIV-1-associated neurocognitive disorder, are associated with BBB compromise due to chronic inflammation. Little is known about pericyte dysfunction during HIV-1 infection. We found decreased expression of pericyte markers in human brains from HIV-1-infected patients (even those on antiretroviral therapy). Using primary human brain pericytes, we assessed expression of pericyte markers (α1-integrin, α-smooth muscle actin, platelet-derived growth factor-B receptor β, CX-43) and found their downregulation after treatment with tumor necrosis factor-α (TNFα) or interleukin-1 β (IL-1β). Pericyte exposure to virus or cytokines resulted in decreased secretion of factors promoting BBB formation (angiopoietin-1, transforming growth factor-β1) and mRNA for basement membrane components. TNFα and IL-1β enhanced expression of adhesion molecules in pericytes paralleling increased monocyte adhesion to pericytes. Monocyte migration across BBB models composed of human brain endothelial cells and pericytes demonstrated a diminished rate in baseline migration compared to constructs composed only of brain endothelial cells. However, exposure to the relevant chemokine, CCL2, enhanced the magnitude of monocyte migration when compared to BBB models composed of brain endothelial cells only. These data suggest an important role of pericytes in BBB regulation in neuroinflammation.

The dual action of poly(ADP-ribose) polymerase -1 (PARP-1) inhibition in HIV-1 infection: HIV-1 LTR inhibition and diminution in Rho GTPase activity

Multifactorial mechanisms comprising countless cellular factors and virus-encoded transactivators regulate the transcription of HIV-1 (HIV). Since poly(ADP-ribose) polymerase 1 (PARP-1) regulates numerous genes through its interaction with various transcription factors, inhibition of PARP-1 has surfaced recently as a powerful anti-inflammatory tool. We suggest a novel tactic to diminish HIV replication via PARP-1 inhibition in an in vitro model system, exploiting human primary monocyte-derived macrophages (MDM). PARP-1 inhibition was capable to lessen HIV replication in MDM by 60–80% after 7 days infection. Tat, tumor necrosis factor α (TNFα), and phorbol 12-myristate 13-acetate (PMA) are known triggers of the Long Terminal Repeat (LTR), which can switch virus replication. Tat overexpression in MDM transfected with an LTR reporter plasmid resulted in a 4.2-fold increase in LTR activation; PARP inhibition caused 70% reduction of LTR activity. LTR activity, which increased 3-fold after PMA or TNFα treatment, was reduced by PARP inhibition (by 85–95%). PARP inhibition in MDM exhibited 90% diminution in NFκB activity (known to mediate TNFα- and PMA-induced HIV LTR activation). Cytoskeleton rearrangements are important in effective HIV-1 infection. PARP inactivation reduced actin cytoskeleton rearrangements by affecting Rho GTPase machinery. These discoveries suggest that inactivation of PARP suppresses HIV replication in MDM by via attenuation of LTR activation, NFκB suppression and its effects on the cytoskeleton. PARP appears to be essential for HIV replication and its inhibition may provide an effective approach to management of HIV infection.

Selective activation of cannabinoid receptor 2 in leukocytes suppresses their engagement of the brain endothelium and protects the blood-brain barrier

Cannabinoid receptor 2 (CB2) is highly expressed in immune cells and stimulation decreases inflammatory responses. We tested the idea that selective CB2 activation in human monocytes suppresses their ability to engage the brain endothelium and migrate across the blood-brain barrier (BBB), preventing consequent injury. Intravital videomicroscopy was used to quantify adhesion of leukocytes to cortical vessels in lipopolysaccharide-induced neuroinflammation, after injection of ex vivo CB2-activated leukocytes into mice; CB2 agonists markedly decreased adhesion of ex vivo labeled cells in vivo. In an in vitro BBB model, CB2 activation in monocytes largely attenuated adhesion to and migration across monolayers of primary human brain microvascular endothelial cells and diminished BBB damage. CB2 stimulation in monocytes down-regulated active forms of integrins, lymphocyte function-associated antigen 1 (LFA-1), and very late antigen 4 (VLA-4). Cells treated with CB2 agonists exhibited increased phosphorylation levels of inhibitory sites of the actin-binding proteins cofilin and VASP, which are upstream regulators of conformational integrin changes. Up-regulated by relevant stimuli, Rac1 and RhoA were suppressed by CB2 agonists in monocytes. CB2 stimulation decreased formation of lamellipodia, which play a key role in monocyte migration. These results indicate that selective CB2 activation in leukocytes decreases key steps in monocyte-BBB engagement, thus suppressing inflammatory leukocyte responses and preventing neuroinflammation.

Attenuation of HIV-1 replication in macrophages by cannabinoid receptor 2 agonists

Infiltrating monocytes and macrophages play a crucial role in the progression of HIV-1 infection in the CNS. Previous studies showed that activation of the CB₂ can attenuate inflammatory responses and affect HIV-1 infectivity in T cells and microglia. Here, we report that CB₂ agonists can also act as immunomodulators on HIV-1-infected macrophages. First, our findings indicated the presence of elevated levels of CB₂ expression on monocytes/macrophages in perivascular cuffs of postmortem HIV-1 encephalitic cases. In vitro analysis by FACS of primary human monocytes revealed a step-wise increase in CB₂ surface expression in monocytes, MDMs, and HIV-1-infected MDMs. We next tested the notion that up-regulation of CB₂ may allow for the use of synthetic CB₂ agonist to limit HIV-1 infection. Two commercially available CB₂ agonists, JWH133 and GP1a, and a resorcinol-based CB₂ agonist, O-1966, were evaluated. Results from measurements of HIV-1 RT activity in the culture media of 7 day-infected cells showed a significant decrease in RT activity when the CB₂ agonist was present. Furthermore, CB₂ activation also partially inhibited the expression of HIV-1 pol. CB₂ agonists did not modulate surface expression of CXCR4 or CCR5 detected by FACS. We speculate that these findings indicate that prevention of viral entry is not a central mechanism for CB₂-mediated suppression in viral replication. However, CB₂ may affect the HIV-1 replication machinery. Results from a single-round infection with the pseudotyped virus revealed a marked decrease in HIV-1 LTR activation by the CB₂ ligands. Together, these results indicate that CB₂ may offer a means to limit HIV-1 infection in macrophages.

Inhibition of glycogen synthase kinase 3β promotes tight junction stability in brain endothelial cells by half-life extension of occludin and claudin-5

Neuroinflammatory conditions often involve dysfunction of the Blood-Brain Barrier (BBB). Therefore, identifying molecular targets that can maintain barrier fidelity is of clinical importance. We have previously reported on the anti-inflammatory effects that glycogen synthase kinase 3β (GSK3β) inhibition has on primary human brain endothelial cells. Here we show that GSK3β inhibitors also promote barrier tightness by affecting tight junction (TJ) protein stability. Transendothelial electrical resistance (TEER) was used to evaluate barrier integrity with both pharmacological inhibitors and mutants of GSK3β. Inhibition of GSK3β produced a gradual and sustained increase in TEER (as much as 22% over baseline). Analysis of subcellular membrane fractions revealed an increase in the amount of essential tight junction proteins, occludin and claudin-5, but not claudin-3. This phenomenon was attributed to a decrease in TJ protein turnover and not transcriptional regulation. Using a novel cell-based assay, inactivation of GSK3β significantly increased the half-life of occludin and claudin-5 by 32% and 43%, respectively. A correlation was also established between the enhanced association of β-catenin with ZO-1 as a function of GSK3β inhibition. Collectively, our findings suggest the possibility of using GSK3β inhibitors as a means to extend the half-life of key tight junction proteins to promote re-sealing of the BBB during neuroinflammation.

Inhibition of HIV type 1 replication in CD4+ and CD14+ cells purified from HIV type 1-infected individuals by the 2-5A agonist immunomodulator, 2-5A(N6B)

Two major interferon (IFN)-mediated antiviral defense enzymes are double-stranded (ds)RNA-dependent 2',5'-oligoadenylate (2-5A) synthetase (2-5OAS) and p68 kinase (PKR). When activated by dsRNA, 2-5OAS synthesizes 2-5A, which binds to and activates RNase L. Activated RNase L hydrolyzes single-stranded viral RNA, thereby inhibiting viral protein synthesis. HIV-1 inhibits the IFN-mediated intracellular antiviral pathways. We have reported the synthesis and characterization of a nuclease-resistant 2-5A agonist (2-5A(N6B)) that overcomes the HIV-1 induced blockades by restoring the 2-5OAS/RNase L antiviral pathway (Homan JW, et al., J Acquir Immune Defic Syndr 2002;30:9-20). The objective of this study was to test the effect of 2-5A(N6B) on chronically infected CD4(+) T lymphocytes and CD14(+) monocytes derived from HIV-1-seropositive individuals. Wild-type HIV-1 replication was effectively inhibited by 2-5A(N6B) in CD4(+) T lymphocytes and CD14(+) monocytes purified from HIV-1 seropositive individuals (n = 18) compared to untreated cells. We also assessed the cytotoxicity of 2-5A(N6B) and report that 2-5A(N6B) exerts its anti-HIV-1 activity with no evidence of cytotoxicity (IC(90) > 100,000 nM). Furthermore, 2-5A(N6B) did not alter the cellular RNA profile, affect CCR5 or CXCR4 coreceptor expression, or activate caspase-dependent apoptosis. Evidence is also provided to show that 2-5A(N6B), and naturally occurring 2-5A(4), act as ligands to activate human Toll-like receptor 4. These results indicate that the 2-5A agonist 2-5A(N6B) has the potential to enhance host cell innate and acquired immune defense mechanisms against HIV-1 infection.

Lentivirus-mediated transduction of PKR into CD34(+) hematopoietic stem cells inhibits HIV-1 replication in differentiated T cell progeny

Previous studies from this laboratory evaluated the role of p68 kinase (PKR) in the control of HIV-1 replication via retrovirus-mediated gene transfer. PKR was studied because it is a key component of the interferon (IFN)-associated innate antiviral defense pathway in mammalian cells. In this study, CD34(+) hematopoietic stem cells (HSC) were transduced with an HIV-1-based lentiviral vector encoding the PKR transgene (pHIV-PIB) and cultured under conditions that support in vitro differentiation. With high-titer pseudotyped vector stocks, the histogram suggests 100% transduction of the HSC because the cells were blasticidin resistant. Analysis of transduced cells by hybridization revealed an average proviral vector copy number of 1.8 and 2.1 copies of vector sequence per cell. Increased PKR expression and activity (phosphorylation of eukaryotic initiation factor 2alpha [eIF2alpha]) were demonstrated in PKR-transduced, differentiated HSC. There was minimal reduction in cell viability and no induction of apoptosis after transduction of PKR. HSC transduced with the pHIV-PIB lentiviral vector demonstrated normal differentiation into CD34-derived T cell progeny. Two days after HIV-1 infection, lentivirus-mediated transduction of PKR inhibited HIV-1 replication by 72% in T cell progeny compared with cells transduced with the empty vector control (pHIV-IB). By days 5 and 7 post-HIV-1 infection, the surviving PKR-transduced cells were protected from HIV-1 infection, as evidenced by a decrease in p24 antigen expression of at least two orders of magnitude. Our results demonstrate that PKR can be effectively delivered to HSC by a lentiviral vector and can protect CD34-derived T cell progeny from HIV-1 infection. These results provide support for application of the innate antiviral defense pathway in a gene therapy setting to the treatment of HIV-1 infection.

Inhibition of morphine-potentiated HIV-1 replication in peripheral blood mononuclear cells with the nuclease-resistant 2-5A agonist analog, 2-5A(N6B)

Opioids potentiate HIV-1 infection in vitro at least partly by suppressing immunoresponsive processes in human lymphocytes and monocytes. For example, it appears that morphine inhibits the interferon (IFN)-alpha, -beta, and -gamma-mediated natural antiviral defense pathways in human peripheral blood mononuclear cells (PBMC). In this study, we show that restoration of a key component of the antiviral pathway reverses morphine-potentiated HIV-1 infection of human PBMC. The data show that HIV-1 replication is potentiated and RNase L activity is inhibited after morphine administration. Because HIV-1 inhibits the antiviral pathway at the level of 2',5'-oligoadenylate (2-5A) synthetase and p68 kinase, antiviral enzymes that require double-stranded RNA, we overcame this blockade by the addition of the nuclease-resistant, nontoxic 2-5A agonist, 2-5A(N6B), to PBMC in culture. Addition of 2-5A(N6B), but not zidovudine or saquinavir, to morphine-treated PBMC completely reversed the morphine-induced potentiation of HIV-1 infection. Further, 2-5A(N6B) significantly enhanced expression of both IFN-alpha and IFN-gamma. Also, increased expression of IFN-gamma was associated with a significant increase in expression of RANTES and monocyte chemotactic protein (MCP)-1, chemokines that may inhibit HIV-1 infection by blocking viral attachment to CCR2 and CCR5 co-receptors. Our results suggest that reactivation of the antiviral pathway by 2-5A agonists may be useful to inhibit opioid-potentiated HIV-1 replication.

Structural and functional features of the 37-kDa 2-5A-dependent RNase L in chronic fatigue syndrome

A 2',5'-oligoadenylate (2-5A)-dependent 37-kDa form of RNase L has been reported in extracts of peripheral blood mononuclear cells (PBMC) from individuals with chronic fatigue syndrome (CFS). In the current study, analytic gel permeation FPLC, azido photoaffinity labeling, two-dimensional (2-D) gel electrophoresis, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) have been used to examine the biochemical relationship between the 80-kDa RNase L in healthy control PBMC and the 37-kDa RNase L in PBMC from individuals with CFS. Like the 80-kDa RNase L, the 37-kDa RNase L is present as a catalytically inactive heterodimer complex with the RNase L inhibitor (RLI). Formation of a 37-kDa RNase L-RLI complex indicates that the 37-kDa RNase L is structurally similar to the 80-kDa RNase L at the N-terminus, which contains the 2-5A binding domain. The enzymatically active monomer form of 37-kDa RNase L resolved by 2-D gel electrophoresis has a pI of 6.1. RT-PCR and Southern blot analyses demonstrated that the 37-kDa RNase L is not formed by alternative splicing. In-gel tryptic digestion of the 37-kDa RNase L that was excised from 2-D gels and subsequent MALDI-MS analysis identified three peptide masses that are identical to three predicted peptide masses in the 80-kDa RNase L. The electrophoretic mobility of 2-5A azido photolabeled/immunoprecipitated 37-kDa RNase L was the same under reducing and nonreducing conditions. The results presented show that the 37-kDa form of RNase L in PBMC shares structural and functional features with the native 80-kDa RNase L, in particular in the 2-5A binding and catalytic domains.

Biochemical evidence for a novel low molecular weight 2-5A-dependent RNase L in chronic fatigue syndrome

Previous studies from this laboratory have demonstrated a statistically significant dysregulation in several key components of the 2',5'-oligoadenylate (2-5A) synthetase/RNase L and PKR antiviral pathways in chronic fatigue syndrome (CFS) (Suhadolnik et al. Clin Infect Dis 18, S96-104, 1994; Suhadolnik et al. In Vivo 8, 599-604, 1994). Two methodologies have been developed to further examine the upregulated RNase L activity in CFS. First, photoaffinity labeling of extracts of peripheral blood mononuclear cells (PBMC) with the azido 2-5A photoaffinity probe, [32P]pApAp(8-azidoA), followed by immunoprecipitation with a polyclonal antibody against recombinant, human 80-kDa RNase L and analysis under denaturing conditions. A subset of individuals with CFS was identified with only one 2-5A binding protein at 37 kDa, whereas in extracts of PBMC from a second subset of CFS PBMC and from healthy controls, photolabeled/immunoreactive 2-5A binding proteins were detected at 80, 42, and 37 kDa. Second, analytic gel permeation HPLC was completed under native conditions. Extracts of healthy control PBMC revealed 2-5A binding and 2-5A-dependent RNase L enzyme activity at 80 and 42 kDa as determined by hydrolysis of poly(U)-3'-[32P]pCp. A subset of CFS PBMC contained 2-5A binding proteins with 2-5A-dependent RNase L enzyme activity at 80, 42, and 30 kDa. However, a second subset of CFS PBMC contained 2-5A binding and 2-5A-dependent RNase L enzyme activity only at 30 kDa. Evidence is provided indicating that the RNase L enzyme dysfunction in CFS is more complex than previously reported.

Inhibition of growth of estrogen receptor positive and estrogen receptor negative breast cancer cells in culture by AA-etherA, a stable 2-5A derivative

The design, chemical synthesis and biological activities of a nuclease-resistant, nontoxic bioactive 2-5A derivative, AA-etherA [i.e., adenylyl-(2'-5')-adenylyl-(2'-2")-9-[(2'-hydroxyethoxy)-methyl]adenine], are described as a new approach to the inhibition of breast cancer cell growth. AA-etherA inhibits DNA replication and cell division of both estrogen receptor positive (MCF-7) and estrogen receptor negative (BT-20) breast cancer cells in culture in a dose-dependent manner. Maximal inhibition in MCF-7 and BT-20 cells was obtained with 100 microM AA-etherA after four days of treatment, with an GI50 of 58 and 37 microM, respectively. AA-etherA is stable in the cytoplasm. Treated cells accumulate within the late G1/early S phase of the cell cycle and then progress only very slowly through S phase. AA-etherA does not activate RNase L, as do 2-5A and other 2-5A derivatives, nor does it increase p68 kinase (PKR) content of the cells. High resolution, two-dimensional protein gel electrophoresis reveals twofold or greater inhibition of synthesis of 92 proteins out of 682 proteins that were reproducibly detected as high quality spots with average rates of synthesis of > or = 20 p.p.m. in untreated cells. The specificity of the effects of AA-etherA on select proteins and its failure to activate RNase L indicate that AA-etherA does not act through a general effect on mRNA translation or stability, but rather inhibits cell proliferation through a block to DNA replication, with a concommitant reduction in the synthesis of specific proteins, some of which may be required for cell cycle transit. Two likely targets to account for the AA-etherA inhibition of DNA replication are DNA topoisomerase I, which is inhibited by AA-etherA in other cell lines, and thymidine kinase, which could be inhibited in a manner similar to the effect of acyclovir. These data indicate that 2-5A analogs, particularly bifunctional 2-5A analogs like AA-etherA, will be useful for controlling cancer cell growth. Further development of such 2-5A analogs may provide highly specific compounds for chemotherapy and chemoprevention.

Inhibition of HIV-1 replication and activation of RNase L by phosphorothioate/phosphodiester 2',5'-oligoadenylate derivatives

2',5'-Oligoadenylate (2-5A) derivatives have been designed to act distal to the human immunodeficiency virus-1 (HIV-1)-induced blockade in the 2-5A synthetase/RNase L antiviral pathway. Stereochemical modification of individual internucleotide linkages of the 2-5A molecule was accomplished by phosphoramidite and phosphotriester chemical syntheses. Phosphorothioate/phosphodiester trimer and tetramer 2-5A derivatives revealed differences in the stereodynamics of activation of RNase L and inhibition of HIV-1 replication. The first and second internucleotide linkages are critical for activation of recombinant, human RNase L; A(Rp)ApA, A(Sp)ApA and ApA(Rp)A are agonists (IC50 = 2 x 10(-7), 2 x 10(-6) and 8 x 10(-6) M); ApA(Sp)A is an antagonist. The second and third internucleotide linkages are crucial for activation of murine RNase L; ApA(Rp)A, ApA(Rp)ApA, and ApApA(Rp)A are agonists (IC50 = 5 x 10(-7) M); ApA(Sp)A, ApA(Sp)ApA, and ApApA(Sp)A are antagonists. Inhibition of HIV-1-induced syncytia formation by the phosphorothioate/phosphodiester derivatives is specific for derivatives with substitution at the 2',3'-terminus. ApA(Rp)A, ApA(Sp)A, ApApA(Rp)A, and ApApA(Sp)A are potent inhibitors of HIV-1-induced syncytia formation (80-, 10-, 40-, and 15-fold more inhibitory, respectively, than solvent control). HIV-1 infection results in enhanced uptake and accumulation of ApA(Rp)A and ApA(Sp)A (7- and 10-fold, respectively). These stereochemically modified 2-5A derivatives are taken up preferentially by HIV-1-infected cells and show promise in anti-HIV-1 chemotherapy.

Changes in the 2-5A synthetase/RNase L antiviral pathway in a controlled clinical trial with poly(I)-poly(C12U) in chronic fatigue syndrome

Latent 2', 5'-oligoadenylate (2-5A) synthetase activity, bioactive 2-5A and RNase L activity were measured in extracts of peripheral blood mononuclear cells (PMBC) before and during a randomized, multicenter, placebo-controlled, double-blind study of poly(I)-poly(C12U) in individuals with chronic fatigue syndrome (CFS) as defined by the Centers for Disease Control and Prevention. The mean values for bioactive 2-5A and RNase L activity were significantly elevated at baseline compared to controls (p < .0001 and p = .001, respectively). In individuals that presented with elevated RNase L activity at baseline, therapy with poly(I)-poly(C12U) resulted in a significant decrease in both bioactive 2-5A and RNase L activity (p = .09 and p = .005, respectively). Decrease in RNase L activity in individuals treated with poly(I)-poly(C12U) correlated with cognitive improvement (p = .007). Poly(I)-poly(C12U) therapy resulted in a significant decrease in bioactive 2-5A and RNase L activity in agreement with clinical and neuropsychological improvements (Strayer DR, et al., Clin. Infectious Dis. 18:588-595, 1994). The results described show that poly(I)-poly(C12U) is a biologically active drug in CFS.

Upregulation of the 2-5A synthetase/RNase L antiviral pathway associated with chronic fatigue syndrome

Levels of 2',5'-oligoadenylate (2-5A) synthetase, bioactive 2-5A, and RNase L were measured in extracts of peripheral blood mononuclear cells (PBMCs) from 15 individuals with chronic fatigue syndrome (CFS) before and during therapy with the biological response modifier poly(I).poly(C12U) and were compared with levels in healthy controls. Patients differed significantly from controls in having a lower mean basal level of latent 2-5A synthetase (P < .0001), a higher pretreatment level of bioactive 2-5A (P = .002), and a higher level of pretherapy RNase L activity (P < .0001). PBMC extracts from 10 persons with CFS had a mean basal level of activated 2-5A synthetase higher than the corresponding control value (P = .009). All seven pretherapy PBMC extracts tested were positive for the replication of human herpesvirus 6 (HHV-6). Therapy with poly(I).poly(C12U) resulted in a significant decrease in HHV-6 activity (P < .01) and in downregulation of the 2-5A synthetase/RNase L pathway in temporal association with clinical and neuropsychological improvement. The upregulated 2-5A pathway in CFS before therapy is consistent with an activated immune state and a role for persistent viral infection in the pathogenesis of CFS. The response to therapy suggests direct or indirect antiviral activity of poly(I).poly(C12U) in this situation.

HIV-1 reverse transcriptase: inhibition by 2',5'-oligoadenylates

2',5'-Oligoadenylates (2-5A) and derivatives are noncompetitive inhibitors of primer/HIV-1 reverse transcriptase complex formation. The mechanism and specificity of this inhibitory action of 2-5A and 2-5A derivatives have been evaluated with 2-5A molecules modified in ribosyl moiety, chain length, extent of 5'-phosphorylation, and 2',5'-phosphodiester linkage. UV covalent cross-linking of preformed complexes of p66/p66 homodimer or p66/p51 heterodimer recombinant HIV-1 reverse transcriptase and the primer analog pd(T)16 allowed analysis of the initial step in HIV-1 reverse transcriptase-catalyzed DNA synthesis. Utilizing this primer binding assay, it is demonstrated that 2-5A and 2-5A derivatives inhibit the binding of pd(T)16 to HIV-1 reverse transcriptase. This inhibition is specific for the 2',5'-internucleotide linkage in that the corresponding 3',5'-adenylate derivatives do not exhibit inhibitory activity. Enhanced inhibitory properties were observed following modifications of the 2-5A molecule which result in an increase in hydrophobicity. Replacement of the D-ribosyl moiety of 2-5A with the 3'-deoxyribosyl moiety increased the inhibition of primer/HIV-1 reverse transcriptase complex formation 15-20%. 2',5'-Phosphorothioate substitution yielded the most effective inhibitors, with Ki's of 7-13 microM. In all cases, inhibition of primer/HIV-1 reverse transcriptase complex formation showed a preference for the 5'-triphosphate moiety. Nonphosphorylated derivatives were not inhibitory; 5'-monophosphate derivatives exhibited little or no inhibition. The inhibition of primer binding to HIV-1 reverse transcriptase correlated well with the inhibition of DNA-directed DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorothioate and cordycepin analogues of 2',5'-oligoadenylate: inhibition of human immunodeficiency virus type 1 reverse transcriptase and infection in vitro

Natural antiviral activity can be mediated by the interferon-induced synthesis of 2',5'-oligoadenylates (2-5As) and subsequent RNase L activation by these molecules. Analogues of 2-5A that are biologically active and metabolically stable were synthesized and analyzed for antiviral activity against the human immunodeficiency virus type 1 (HIV-1). Replacement of the 3' hydroxyl group of the adenosine moieties of 2-5A with hydrogen atoms (i.e., cordycepin analogues of 2-5A) converted authentic 2-5A trimer into anti-HIV-1 agents in vitro. These cordycepin analogues of 2-5A also inhibited partially purified HIV-1 reverse transcriptase. Introduction of chirality into the 2',5'-phosphodiester internucleotide linkages or 5'-phosphate moieties of the 2-5A molecule (i.e., phosphorothioate analogues of 2-5A) converted authentic 2-5A into more potent inhibitors of HIV-1 reverse transcriptase. However, these phosphorothioate 2-5As demonstrated little or no anti-HIV-1 activity in vitro. Thus, some analogues of 2-5A may form a class of anti-HIV-1 drugs with possible pleiotropic activities that include activation of latent RNase L and inhibition of reverse transcription.

2- and 8-azido photoaffinity probes. 1. Enzymatic synthesis, characterization, and biological properties of 2- and 8-azido photoprobes of 2-5A and photolabeling of 2-5A binding proteins

The 2- and 8-azido trimer 5'-triphosphate photoprobes of 2-5A have been enzymatically synthesized from [gamma-32P]2-azidoATP and [alpha-32P]8-azidoATP by 2-5A synthetase from rabbit reticulocyte lysates. Identification and structural determination of the 2- and 8-azido adenylate trimer 5'-triphosphates were accomplished by enzymatic hydrolyses with T2 RNase, snake venom phosphodiesterase, and bacterial alkaline phosphatase. Hydrolysis products were identified by HPLC and PEI-cellulose TLC analyses. The 8-azido photoprobe of 2-5A displaces p3A4[32P]pCp from RNase L with affinity equivalent to p3A3 (IC50 = 2 X 10(-9) M in radiobinding assays). The 8-azido photoprobe also activates RNase L to hydrolyze poly(U) [32P]pCp 50% at 7 X 10(-9) M in core-cellulose assays. The 2- and 8-azido photoprobes and authentic p3A3 activate RNase L to cleave 28S and 18S rRNA to specific cleavage products at 10(-9) M in rRNA cleavage assays. The nucleotide binding site(s) of RNase L and/or other 2-5A binding proteins in extracts of interferon-treated L929 cells were investigated by photoaffinity labeling. Dramatically different photolabeling patterns were observed with the 2- and 8-azido photoprobes. The [gamma-32P]2-azido adenylate trimer 5'-triphosphate photolabels only one polypeptide with a molecular weight of 185,000 as determined by SDS gel electrophoresis, whereas the [alpha-32P]8-azido adenylate trimer 5'-triphosphate covalently photolabels six polypeptides with molecular weights of 46,000, 63,000, 80,000, 89,000, 109,000, and 158,000. Evidence that the photolabeling by 2- and 8-azido 2-5A photoprobes was highly specific for the p3A3 allosteric binding site was obtained as follows.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased Epstein-Barr virus-induced transformation, and elevated 2-5A synthetase and RNase L activity in peripheral blood mononuclear cells from patients treated with recombinant interferon alfa 2b

Patients with cutaneous T-cell lymphoma (CTCL) were treated with recombinant alfa 2b interferon (rIFN alfa 2b) by intramuscular injection. Therapy-induced changes in Epstein-Barr virus (EBV) induced transformation of patient peripheral blood lymphocytes, 2',5' oligoadenylate (2-5A) synthetase levels and RNase L activation in peripheral blood mononuclear cells were monitored. Inhibition of EBV-induced transformation and elevation of 2-5A synthetase levels correlated with increased activation of RNase L, which provides evidence that intramuscular administration of rIFN alfa 2b induces a sustained anti-EBV state in CTCL patient peripheral blood mononuclear cells which can be detected in vitro.

Phosphorothioate analogues of 2',5'-oligoadenylate. Enzymatically synthesized 2',5'-phosphorothioate dimer and trimer: unequivocal structural assignment and activation of 2',5'-oligoadenylate-dependent endoribonuclease

In continued studies to elucidate the requirements for binding to and activation of the 2',5'-oligoadenylate-dependent endoribonuclease (RNase L), chirality has been introduced into the 2',5'-oligoadenylate (2-5A, p3An) molecule to give the Rp configuration in the 2',5'-internucleotide backbone and the Sp configuration in the alpha-phosphorus of the pyrophosphoryl moiety of the 5'-terminus. This was accomplished by the enzymatic conversion of (Sp)-ATP alpha S to the 2',5'-phosphorothioate dimer and trimer by the 2-5A synthetase from lysed rabbit reticulocytes. The most striking finding reported here is the ability of the 2',5'-phosphorothioate dimer 5'-triphosphate (i.e., p3A2 alpha S) to bind to and activate RNase L. p3A2 alpha S displaces the p3A4[32P]pCp probe from RNase L with an IC50 of 5 X 10(-7) M, compared to an IC50 of 5 X 10(-9) M for authentic p3A3. Further, p3A2 alpha S activates RNase L to hydrolyze poly(U)-3'-[32P]pCp (20% at 2 X 10(-7) M), whereas authentic p3A2 is unable to activate the enzyme. Similarly, the enzymatically synthesized p3A2 alpha S at 10(-6) M activated RNase L to degrade 18S and 28S rRNA, whereas authentic p3A2 was devoid of activity. p3A3 alpha S was as active as authentic p3A3 in the core--cellulose and rRNA cleavage assays. The absolute structural and configurational assignment of the enzymatically synthesized p3A2 alpha S and p3A3 alpha S was accomplished by high-performance liquid chromatography, charge separation, enzymatic hydrolyses, and comparison to fully characterized chemically synthesized (Rp)- and (Sp)-2', 5'-phosphorothioate dimer and trimer cores.(ABSTRACT TRUNCATED AT 250 WORDS)

Plant oligoadenylates: enzymatic synthesis, isolation, and biological activities

An enzyme that converts [3H, 32P]ATP, with a 3H:32P ratio of 1:1, to oligoadenylates with the same 3H:32P ratio was increased in plants following treatment with human leukocyte interferon or plant antiviral factor or inoculation with tobacco mosaic virus. The enzyme was extracted from tobacco leaves, callus tissue cultures, or cell suspension cultures. The enzyme, a putative plant oligoadenylate synthetase, was immobilized on poly(rI) . poly(rC)-agarose columns and converted ATP into plant oligoadenylates. These oligoadenylates were displaced from DEAE-cellulose columns with 350 mM KCl buffer, dialyzed, and further purified by high-performance liquid chromatography (HPLC) and DEAE-cellulose gradient chromatography. In all steps of purification, the ratio of 3H:32P in the oligoadenylates remained 1:1. The plant oligoadenylates isolated by displacement with 350 mM KCl had a molecular weight greater than 1000. The plant oligoadenylates had charges of 5- and 6-. HPLC resolved five peaks, three of which inhibited protein synthesis in reticulocyte and wheat germ systems. Partial structural elucidation of the plant oligoadenylates has been determined by enzymatic and chemical treatments. An adenylate with a 3',5'-phosphodiester and/or a pyrophosphoryl linkage with either 3'- or 5'-terminal phosphates is postulated on the basis of treatment of the oligoadenylates with T2 RNase, snake venom phosphodiesterase, and bacterial alkaline phosphatase and acid and alkaline hydrolyses. The plant oligoadenylates at 8 X 10(-7) M inhibit protein synthesis by 75% in lysates from rabbit reticulocytes and 45% in wheat germ cell-free systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of low molecular weight DNA and changes in chromatin structure in HeLa cells treated with human fibroblast interferon

The addition of human fibroblast interferon (IFN-beta) (100 units/ml) at the S/G2 boundary of the cell cycle of synchronously grown HeLa cells is characterized by the accumulation of newly synthesized low molecular weight DNA and changes in chromatin assembly. In addition, there is a 3-fold stimulation in the incorporation of tracer amounts of [3H]thymidine, but not [3H] deoxyguanosine, into DNA and a 2-fold increase in the incorporation of [3H]dTTP into the DNA of isolated nuclei. Fluorescence-activated cell sorting by laser flow cytometry revealed that IFN-beta-treated cells were delayed in entering and passing through the S phase. The inhibition of proliferation of HeLa cells treated with IFN-beta is characterized by a 3-fold accumulation of newly synthesized DNA of Mr less than 56 X 10(6) compared to untreated cells as determined by alkaline sucrose gradient centrifugation. The newly synthesized DNA in IFN-beta-treated cells was replicative and not repair DNA. The observation that IFN-beta inhibits the processing of newly synthesized low molecular weight DNA into normal DNA might be explained by the intracellular accumulation of S-adenosylhomocysteine in IFN-beta-treated HeLa cells (de Ferra, F., and Baglioni, C. (1983) J. Biol. Chem. 258, 2118-2121) which could change the soluble ribonucleotide and deoxyribonucleotide pool and ultimately affect DNA processing. Interferon may also affect processing of DNA by interfering with normal chromatin assembly. Evidence for the effect of IFN-beta on chromatin assembly is provided; we have observed a more condensed structure in IFN-beta treated cells by circular dichroism spectroscopy. Simultaneous with the affect on chromatin assembly, there is a 70% decrease in poly(ADP-ribosylation) of either histone and/or non-histone proteins. The loss of coordination between the pool size for DNA synthesis, decreased postsynthetic modifications of chromatin, and normal chromatin formation may explain the inability of the cell to differentiate and to continue cell division.

Effect of human fibroblast interferon on the antiviral activity of mammalian cells treated with bleomycin, vincristine, or mitomycin C

Bleomycin, vincristine, or mitomycin C, when added to HeLa cells simultaneously with human fibroblast interferon (IFN-beta), caused a decrease in cell density and inhibited DNA synthesis compared with HeLa cells treated with IFN-beta alone. However, the IFN-beta-induced antiviral processes were unaffected by the presence of these drugs as determined by in vitro enzyme assays and the development of the antiviral state in the intact HeLa cell. HeLa cells treated with IFN-beta alone or with IFN-beta in combination with bleomycin, vincristine, or mitomycin C were able to induce the double-stranded RNA-dependent adenosine triphosphate:2',5'-oligoadenylic acid adenyltransferase (EC 2.2.2.-) and the double-stranded RNA-dependent protein kinase. Furthermore, the antiviral state as measured by the reduction of plaque-forming units after infection of treated cells (with IFN-beta alone or with IFN-beta plus drugs) with vesicular stomatitis virus was not affected. These results indicate that, under these experimental conditions, the double-stranded RNA-dependent adenosine triphosphate:2',5'-oligoadenylic acid adenyltransferase and protein kinase can be induced by IFN-beta in cells treated with bleomycin, vincristine, or mitomycin C. These cells also develop the antiviral state. These experiments could provide a basis for a careful examination of the effects of interferon on the development of the antiviral state when testing potentially active antineoplastic agents. The possibility that IFN-beta potentiates the cytotoxic effects of bleomycin and mitomycin C on HeLa cells is also discussed.

Glutamate as the common precursor for the aglycon of the naturally occurring C-nucleoside antibiotics

Pyrazofurin is one of four naturally occurring C-nucleoside antibiotics; it is elaborated by Streptomyces candidus. The biosynthesis of the pyrazole ring of pyrazofurin has been studied by using 13C- and 14C-labeled acetate. Carbon-13 incorporation into pyrazofurin was observed by proton-decoupled 13C Fourier transform NMR spectroscopy. The incorporation of 14C from [1-14C]acetate was 0.7%. The enrichment of carbons 3, 4, and 5 of pyrazofurin from [2-13C]acetate by S. candidus confirms earlier findings that acetate is converted to glutamate by the combined action of the Krebs cycle and malic enzyme [Elstner, E. F., Suhadolnik, R. J., & Allerhand, A. (1973) J. Biol. Chem. 248, 5385]. Malic enzyme will give rise to [1,2-13C]acetate from [2-13C]acetate. The [1,2-13C]acetate is then converted to glutamate labeled with 13C in carbons 2--5. The 13C incorporation data indicate that carbons 1, 2, 3, and 4, but not 5, of glutamate serve as the four-carbon donor for the carboxamide carbon, C-5, C-4, and C-3, respectively, of the pyrazole ring of pyrazofurin.

Core (2'-5')oligoadenylate and the cordycepin analog: inhibitors of Epstein--Barr virus-induced transformation of human lymphocytes in the absence of interferon

The 3'-deoxyadenosine (cordycepin) analog of (2'-5')oligo(A) [(2'-5')oligoadenylate with a triphosphate at the 5' end], synthesized enzymatically from cordycepin 5'-triphosphate in lysed rabbit reticulocytes or L-cell extracts was (i) inhibitory to translation in lysed rabbit reticulocytes and (ii) metabolically stable in extracts of either L cells or C85-5C lymphoblasts. The 5' dephosphorylated (core) (2'-5')oligo(A) and the core cordycepin analog can replace human fibroblast interferon in preventing the transformation of human lymphocytes after infection with Epstein--Barr virus B95-8 (EBV) as determined by the decreased incorporation of [3H]thymidine into cellular DNA and the inhibition of morphological transformation of EBV-infected lymphocytes. Whereas the naturally occurring core (2'-5')oligo(A) was cytotoxic to uninfected lymphocytes and proliferating lymphoblasts, the core cordycepin analog was not. Human leukocyte interferon was more effective than human fibroblast interferon in the inhibition of EBV-induced transformation of human umbilical cord lymphocytes and adult peripheral blood lymphocytes.