Juan J. Martínez-Irujo

Flavonoids Induce Apoptosis in Human Leukemia U937 Cells Through Caspase- and Caspase-Calpain-Dependent Pathways

Abstract: Flavonoids are polyphenolic phytochemicals that are ubiquitous in plants and present in the common human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. In this study we tested the apoptotic activity of 22 flavonoids and related compounds in leukemic U937 cells. Several flavones but none of the isoflavones or flavanones tested induced apoptotic cell death under these conditions, as determined by reduction in cell viability, flow cytometry, and oligonucleosomal DNA fragmentation. Structure-activity relationship showed that at least two hydroxylations in positions 3, 5, and 7 of the A ring were needed to induce apoptosis, whereas hydroxylation in 3′ and/or 4′ of the B ring enhanced proapoptotic activity. At lower concentrations, these compounds were also able to sensitize these cells to apoptosis induced by tumor necrosis factor-α. Regarding the mechanisms, galangin, luteolin, chrysin, and quercetin induced apoptosis in a way that required the activation of caspases 3 and 8, but not caspase 9. In contrast, an active role of calpains in addition to caspases was demonstrated in apoptosis induced by fisetin, apigenin, and 3,7-dihydroxyflavone. Our data show evidence of the proapoptotic properties of some flavonoids that could support their rational use as chemopreventive and therapeutic agents against carcinogenic disease.

A checkerboard method to evaluate interactions between drugs.

A method to evaluate interactions between biologically active agents is presented. Synergism, zero interaction, and antagonism were easily detected with the three-dimensional approach proposed herein. This method is compatible with a checkerboard design to diagnose the interaction between agents and obviate the need to test their mixtures in a fixed concentration ratio as proposed by Chou and Talalay. Dose-response curves for individual agents were obtained, and experimental data fitted to appropriate equations by nonlinear regression. If zero interaction was present, the predicted effect could be calculated for each combination using the classical isobole equation with any spreadsheet having a command to solve mathematical equations by iteration. This allowed the selection of appropriate concentrations for the combination of two or more agents. Interaction between agents could be assessed in two ways: by comparing experimental with expected effects, if zero interaction is present; or by analyzing the reduction or increase in total dose found as a consequence of the interaction. The applicability of both approaches is discussed and, for purposes of comparison with other methods, examples based on published data are analyzed and commented upon.

Indoles and pyridazino[4,5-b]indoles as nonnucleoside analog inhibitors of HIV-1 reverse transcriptase

Summary The synthesis and the study of the activity of new indol-2-carboxamides and pyridazino[4,5- b ]indoles as inhibitors of HIV-1 reverse transcriptase (RT) are presented. The activity of the compounds synthesized as inhibitors of different types of HIV-1 RT (wild type enzyme and mutant forms P236L, Y 181C and P236L/Y181C) was evaluated. The activity of the most active compounds was investigated in the syncytia reduction in vitro assay, in HIV-1 IIIB -infected HT4lacZ-1 cells. Their potential cytotoxicity was determined in parallel. Two lead compounds, N -[1-[2-(3-isopropylamino)pyridyl]piperazin]-5,6-methylenedioxy indol-2-carboxamide 7q and N -[1-[2-(3-ethylamino)pyridyl]piperazin]-5,6-methylenedioxyindol-2-carboxamide 7s have been identified.

Selective excision of chain-terminating nucleotides by HIV-1 reverse transcriptase with phosphonoformate as substrate

A major mechanism for human immunodeficiency virus 1 (HIV-1) reverse transcriptase (RT) resistance to nucleoside analogs involves the phosphorolytical removal of the chain-terminating nucleotide from the 3′-end of the primer. In this work, we analyzed the effect of phosphonoformate (PFA) and other pyrophosphate (PPi) analogs on PPi- and ATP-dependent phosphorolysis catalyzed by HIV-1 RT. Our experimental data demonstrated that PFA did not behave as a linear inhibitor but as an alternative substrate, allowing RT to remove AZT from a terminated primer through a PFA-dependent mechanism. Interestingly, in non-terminated primers, PFA was not a substrate for this reaction and competitively inhibited PPi- and ATP-dependent phosphorolysis. In fact, binding of PFA to the RT·template/primer complex was hindered by the presence of a chain terminator at the 3′-end of the primer. Other pyrophosphate analogs, such as phosphonoacetate, were substrates for the excision reaction with both terminated and nonterminated primers, whereas pamidronate, a bisphosphonate that prevents bone resorption, was not a substrate for these reactions and competitively inhibited the phosphorolytic activity of RT. As expected from their mechanisms of action, pamidronate (but not PFA) synergistically inhibits HIV-1 RT in combination with AZT-triphosphate in the presence of PPi or ATP. These results provide new clues about the mechanism of action of PFA and demonstrate that only certain pyrophosphate analogs can enhance the effect of nucleosidic inhibitors by blocking the excision of chain-terminating nucleotides catalyzed by HIV-1 RT. The relevance of these findings in combined chemotherapy is discussed.

Argentine plant extracts active against polymerase and ribonuclease H activities of HIV-1 reverse transcriptase

Lipophilic and hydrophilic extracts of four Argentine plants (Gamochaeta simplicaulis Cabr. 1, Achyrocline flaccida Wein. D. C. 2, Eupatorium buniifolium H. et A. 3, and Phyllanthus sellowianus Muell. Arg. 4) were examined in vitro for their ability to inhibit the polymerase and ribonuclease H (RNase H) activities of human immunodeficiency virus type 1 (HIV‐1) reverse transcriptase (RT) (wild and Y181C mutant types). The active extracts were also examined as inhibitors of viral replication in HLT4LacZ‐1IIIB cell cultures, evaluating their cytotoxicity in parallel. Infusions 2I and 4I, among the crude extracts, showed the highest activity. These extracts were refractioned into four fractions; 2I4 and 4I4 were active as inhibitors of DNA‐polymerase (wild and Y181C types) and RNase H activities. These fractions were potent as inhibitors of viral replication and were not cytotoxic. Refractionation of 2I4 yielded five new fractions, two of which, 2I4‐4 and 2I4‐5, showed notable activity. Refractionation of 4I4 yielded four new fractions; of these, 4I4‐3 and 4I4‐4 were active. The marked biological activity found in the infusion of A. flaccida and P. sellowianus makes them sufficiently attractive to be considered in the combined chemotherapy of the disease. Copyright

Fibronectin peptides as potential regulators of hepatic fibrosis through apoptosis of hepatic stellate cells.

The turnover of extracellular matrix (ECM) components can generate signals that regulate several cellular functions such as proliferation, differentiation, and apoptosis. During liver injury, matrix metalloproteases (MMPs) production is enhanced and increased levels of peptides derived from extracellular matrix proteins can be generated. Synthetic peptides with sequences present in extracellular matrix proteins were previously found to induce both stimulating and apoptotic effects on several cell types including the inflammatory cells monocytes/macrophages. Therefore, in inflammatory liver diseases, locally accumulated peptides could be also important in regulating hepatic fibrosis by inducing apoptosis of hepatic stellate cells (HSC), the primary cellular source of extracellular matrix components. Here, we describe the apoptotic effect of fibronectin peptides on the cell line of human hepatic stellate cells LX‐2 based on oligonucleosomal DNA fragmentation, caspase‐3 and ‐9 activation, Bcl‐2 depletion, and accumulation of Bax protein. We also found that these peptides trigger the activation of Src kinase, which in turn mediated the increase of JNK and p38 activities. By the use of specific inhibitors we demonstrated the involvement of Src, JNK, and p38 in apoptosis induced by fibronectin peptides on HSC. Moreover, fibronectin peptides increased iNOS expression in human HSC, and specific inhibition of iNOS significantly reduced the sustained activity of JNK and the programmed cell death caused by these peptides. Finally, the possible regulatory effect of fibronectin peptides in liver fibrosis was further supported by the ability of these peptides to induce metalloprotease‐9 (MMP‐9) expression in human monocytes. J. Cell. Physiol. 230: 546–553, 2015.

Recurrent exposure to nicotine differentiates human bronchial epithelial cells via epidermal growth factor receptor activation.

Cigarette smoking is the major preventable cause of lung cancer in developed countries. Nicotine (3-(1-methyl-2-pyrrolidinyl)-pyridine) is one of the major alkaloids present in tobacco. Besides its addictive properties, its effects have been described in panoply of cell types. In fact, recent studies have shown that nicotine behaves as a tumor promoter in transformed epithelial cells. This research focuses on the effects of acute repetitive nicotine exposure on normal human bronchial epithelial cells (NHBE cells). Here we show that treatment of NHBE cells with recurrent doses of nicotine up to 500 muM triggered cell differentiation towards a neuronal-like phenotype: cells emitted filopodia and expressed neuronal markers such as neuronal cell adhesion molecule, neurofilament-M and the transcription factors neuronal N and Pax-3. We also demonstrate that nicotine treatment induced NF-kB translocation to the nucleus, phosphorylation of the epidermal growth factor receptor (EGFR), and accumulation of heparin binding-EGF in the extracellular medium. Moreover, addition of AG1478, an inhibitor of EGFR tyrosine phosphorylation, or cetuximab, a monoclonal antibody that precludes ligand binding to the same receptor, prevented cell differentiation by nicotine. Lastly, we show that differentiated cells increased their adhesion to the extracellular matrix and their protease activity. Given that several lung pathologies are strongly related to tobacco consumption, these results may help to better understand the damaging consequences of nicotine exposure.

Endoplasmic reticulum stress-inducing drugs sensitize glioma cells to temozolomide through downregulation of MGMT, MPG, and Rad51

BACKGROUND Endoplasmic reticulum (ER) stress results from protein misfolding imbalance and has been postulated as a therapeutic strategy. ER stress activates the unfolded protein response which leads to a complex cellular response, including the upregulation of aberrant protein degradation in the ER, with the goal of resolving that stress. O(6)-methylguanine DNA methyltransferase (MGMT), N-methylpurine DNA glycosylase (MPG), and Rad51 are DNA damage repair proteins that mediate resistance to temozolomide in glioblastoma. In this work we sought to evaluate whether ER stress-inducing drugs were able to downmodulate DNA damage repair proteins and become candidates to combine with temozolomide. METHODS MTT assays were performed to evaluate the cytotoxicity of the treatments. The expression of proteins was evaluated using western blot and immunofluorescence. In vivo studies were performed using 2 orthotopic glioblastoma models in nude mice to evaluate the efficacy of the treatments. All statistical tests were 2-sided. RESULTS Treatment of glioblastoma cells with ER stress-inducing drugs leads to downregulation of MGMT, MPG, and Rad51. Inhibition of ER stress through pharmacological treatment resulted in rescue of MGMT, MPG, and Rad51 protein levels. Moreover, treatment of glioblastoma cells with salinomycin, an ER stress-inducing drug, and temozolomide resulted in enhanced DNA damage and a synergistic antitumor effect in vitro. Of importance, treatment with salinomycin/temozolomide resulted in a significant antiglioma effect in 2 aggressive orthotopic intracranial brain tumor models. CONCLUSIONS These findings provide a strong rationale for combining temozolomide with ER stress-inducing drugs as an alternative therapeutic strategy for glioblastoma.

All‐trans‐retinoic acid inhibits collapsin response mediator protein‐2 transcriptional activity during SH‐SY5Y neuroblastoma cell differentiation

Neurons are highly polarized cells composed of two structurally and functionally distinct parts, the axon and the dendrite. The establishment of this asymmetric structure is a tightly regulated process. In fact, alterations in the proteins involved in the configuration of the microtubule lattice are frequent in neuro‐oncologic diseases. One of these cytoplasmic mediators is the protein known as collapsin response mediator protein‐2, which interacts with and promotes tubulin polymerization. In this study, we investigated collapsin response mediator protein‐2 transcriptional regulation during all‐trans‐retinoic acid‐induced differentiation of SH‐SY5Y neuroblastoma cells. All‐trans‐retinoic acid is considered to be a potential preventive and therapeutic agent, and has been extensively used to differentiate neuroblastoma cells in vitro. Therefore, we first demonstrated that collapsin response mediator protein‐2 mRNA levels are downregulated during the differentiation process. After completion of deletion construct analysis and mutagenesis and mobility shift assays, we concluded that collapsin response mediator protein‐2 basal promoter activity is regulated by the transcription factors AP‐2 and Pax‐3, whereas E2F, Sp1 and NeuroD1 seem not to participate in its regulation. Furthermore, we finally established that reduced expression of collapsin response mediator protein‐2 after all‐trans‐retinoic acid exposure is associated with impaired Pax‐3 and AP‐2 binding to their consensus sequences in the collapsin response mediator protein‐2 promoter. Decreased attachment of AP‐2 is a consequence of its accumulation in the cytoplasm. On the other hand, Pax‐3 shows lower binding due to all‐trans‐retinoic acid‐mediated transcriptional repression. Unraveling the molecular mechanisms behind the action of all‐trans‐retinoic acid on neuroblastoma cells may well offer new perspectives for its clinical application.

Unfolded protein response induced by Brefeldin A increases collagen type I levels in hepatic stellate cells through an IRE1α, p38 MAPK and Smad-dependent pathway.

Unfolded protein response (UPR) triggered as a consequence of ER stress has been shown to be involved in the development of different pathologies, including fibrotic disorders. In the present paper we explore the role played by UPR on a key fibrogenic parameter in the liver: collagen type I levels in activated hepatic stellate cells (HSC). Using Brefeldin A (BFA) as an ER stress inducer we found that UPR correlated with enhanced mRNA and protein levels of collagen type I in a cell line of immortalized non-tumoral rat HSC. Analysis of the three branches of UPR revealed the activation of IRE1α, PERK and ATF6 in response to BFA, although PERK activation was shown not to be involved in the fibrogenic action of BFA. BFA also activated p38 MAPK in an IRE1α-dependent way and the p38 MAPK inhibitor SB203580 prevented the increase in collagen type I mRNA and protein levels caused by BFA, suggesting the involvement of this kinase on this effect. Analysis of Smad activation showed that phosphorylated nuclear levels of Smad2 and 3 were increased in response to BFA treatment. Inhibition of Smad3 phosphorylation by SIS3 prevented the enhancement of collagen type I levels caused by BFA. Pretreatment with IRE1α and p38 MAPK inhibitors also prevented the increased p-Smad3 accumulation in the nucleus, suggesting an IRE1α-p38 MAPK-Smad pathway to be responsible for the fibrogenic action of BFA on HSC.