Esteban Santiago

Correlation between losses of mitochondrial ATPase activity and cardiolipin degradation

Abstract Peroxidation changes induced by ascorbate or cysteine on phospholipids of isolated rat liver inner mitochondrial membranes are accompanied by losses in some enzyme activities. The rate of degradation for each phospholipid is different and can be also modified by the addition of antioxidant BHT. A close correlation between the alteration of cardiolipin and ATPase activity has been found, indicating the existence of specific association between this enzyme and cardiolipin, independently of other phospholipids.

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.

Inducible nitric oxide synthase in human lymphomononuclear cells activated by synthetic peptides derived from extracellular matrix proteins

Synthetic peptides with sequences present in extracellular matrix proteins are capable of causing the expression of the inducible form of nitric oxide synthase (iNOS), detected by immunocytochemistry, and the release of NO by human lymphomononuclear cells incubated in their presence. Active peptides are 15‐mers containing a characteristic 2‐6‐11 motif in which the amino acid residue at position 2 is Leu, Ile, Val, Gly, Ala or Lys; the residue at position 6 is always Pro; and residue 11 is Glu or Asp. The induction of iNOS in human monocytes and macrophages could be involved in the cytotoxicity against tumor cell lines also elicited by these peptides.

Immunomodulation induced by synthetic peptides derived from Staphylococcus aureus protein A

Peptides from 10 to 22 amino acids containing sequences encompassed by Staphylococcus aureus protein A were synthesized. Some of these peptides, when present in cultures of lymphomononuclear cells from healthy donors or from cancer patients (melanoma, breast carcinoma, non-Hodgkin lymphoma and renal cell carcinoma) promoted: (i) changes in the phenotype of the lymphomononuclear population, (ii) stimulation of monocytes (release of IL-1 and TNF-alpha), and (iii) an increase in cytotoxicity against K562, Daudi and HT-29 cells. Isolated monocytes responded also to those peptides with a release of IL-1 and TNF alpha and an increase of cytotoxicity against HT-29 cells. It was found that the active peptides had the following structural pattern: a length of at least 15 amino-acid residues with a proline at position 6, valine, leucine, isoleucine, glycine, alanine or lysine at position 2, and glutamic or aspartic acid at position 11. Replacement of Pro at position 6 with any other residue turned the peptide inactive. Replacement of residues at positions 2 and 11 with amino-acid residues other than those required for activity resulted in compounds with a marked decrease in the immunomodulating properties described, or lacking these properties altogether.

Activation of human lymphomononuclear cells by peptides derived from extracellular matrix proteins

A series of peptides of 15 amino acids with sequences contained in human extracellular matrix (ECM) proteins (fibronectin, laminin A, laminin B1, tenascin, undulin, alpha 1-chain of type IV and VIII collagen and alpha 2-chain of type VIII collagen) have been synthesized. The selected structures conformed to the following pattern: (i) Pro at position 6, (ii) Leu, Lys, Ile, Val, Ala or Gly at position 2, (iii) Glu or Asp at position 11. Fibronectin and the indicated peptides, when present in cultures of lymphomononuclear cells from healthy donors, promoted stimulation of monocytes manifested by a release of IL-1 alpha, IL-beta, IL-6 and TNF alpha; an increase in the percentage of cells expressing CD14, CD16, CD11b and CD14/CD16; an increase in cytotoxicity against HT-29. Cytotoxicity against K562 and Daudi cells (targets of NK and LAK cells) was also observed together with an increase in the percentage of cells expressing CD56, CD56/CD16 (corresponding to NK cells), and CD56/CD8 (corresponding to NK-like lymphocytes), indicating a stimulation of lymphocytes. Activated monocytes and lymphocytes contained a large number of granules with DNAse activity. These results suggest that at least some of the immunological properties of ECM proteins could be accounted for by motifs fulfilling a characteristic sequence pattern shared by all of them.

cAMP activates transcription of the human glucocorticoid receptor gene promoter

Glucocorticoids and cAMP regulate, either in a synergistic or additive fashion, the transcription of multiple genes, although some antagonistic effects of dexamethasone on cAMP-activated transcription have been described. The increased glucocorticoid receptor (GR) mediated response of some cell types, as a result of augmented cAMP, has been considered to be mainly due to an increased stability of GR mRNA, although other plausible explanations should not be ruled out. We studied the possibility that GR transcription itself could be affected by cAMP levels. HeLa cells were transfected with human GR (hGR) promoter constructs and their transcriptional activity determined after inducing a cAMP increase with forskolin. We found that forskolin almost doubled the transcriptional activity of the promoter construct spanning -2995 to +38 of the hGR, whereas no significant variations were observed with shorter chimeras containing sequences downstream -979. Shift mobility showed binding of CREB in vitro to a putative cAMP responsive element located at -1000, suggesting that hGR may be upregulated by cAMP at the transcriptional level, thus adding a new mechanism ascribable to this second messenger, which in conjunction with the cAMP-induced GR mRNA increased stability, would lead to a more precise control of the amount of GR protein within the cell.

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

Interaction of f1-atpase and its inhibitor peptide effect of pH

1. The inhibition of F1-ATPase by its natural peptide inhibitor is mixed non-competitive with two pH optimum values (5.5 and 8.2). 2. A two-step model for the interaction is suggested in which two enzyme conformations would exhibit different affinities for the peptide. 3. At low pH, interaction would be favoured. At high pH, a conformation (not susceptible to inhibition) changes into another (susceptible to inhibition) through the hydrolytic reaction stimulation, due to high pH.

Effects of free ATP, citrate, and bicarbonate on rat liver mitochondrial ATPase.

Abstract The effects of citrate, free ATP, and bicarbonate on the activity of isolated rat liver mitochondrial ATPase have been studied. Citrate behaved as a weak noncompetitive inhibitor; free ATP at low concentrations was found to be an activator, whereas at high concentrations behaved as an inhibitor. Citrate competed with free ATP. Neither citrate nor free ATP competed with bicarbonate. The results obtained suggest the existence of at least two catalytic sites with ATP hydrolyzing activity and at least three regulatory sites: one for bicarbonate, and two for free ATP, one with low and another with high affinity. Citrate would compete with free ATP for the same sites. The interaction of free ATP with the high affinity site activated the enzyme, whereas its interaction with the low affinity site would lead to an inhibition.