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D J Abraham

Publications and source records attributed to D J Abraham.

At least 55 records · Page 3Linked to original sources
PubMed1998

Different patterns of endothelial cell activation in renal and pulmonary vascular disease in scleroderma.

Abnormal endothelial cell function is implicated in the development of scleroderma, and in major life-threatening complications of the disease. The nature of the stimulus leading to abnormal endothelial cell function in scleroderma, scleroderma renal crisis, and scleroderma-associated pulmonary hypertension was investigated by measurement of soluble adhesion molecules, shed by activated endothelial cells, in sera from patients with these conditions. In scleroderma renal crisis, mean levels of soluble E-selectin (p < 0.05 limited scleroderma, p < 0.0001 diffuse scleroderma), sVCAM-1 (soluble vascular cell adhesion molecule-1) (p < 0.05 limited scleroderma, p < 0.05 diffuse scleroderma), and sICAM-1 (soluble intercellular adhesion molecule-1) (p < 0.0001 limited scleroderma, p < 0.0001 diffuse scleroderma) were raised, supporting a model of endothelial cell activation in this complication. Evidence for endothelial cell activation in scleroderma-associated pulmonary hypertension was inconsistent, with normal sE-selectin and normal sVCAM-1 in sera from patients with limited scleroderma and pulmonary hypertension. The endothelial cell phenotype in scleroderma-associated pulmonary hypertension may resemble that of unstimulated cells. The pulmonary vascular and renal vascular lesions associated with scleroderma may arise by distinct pathogenic mechanisms.

Acute Kidney Injury↗
PubMed1998

Endothelins: effect on matrix biosynthesis and proliferation in normal and scleroderma fibroblasts.

We investigated the effect of endothelin-1 (ET-1) in normal and systemic sclerosis (SSc) dermal fibroblasts. Collagen type I, collagen type III, and MMP-1 levels in culture supernatants were measured by competition ELISA and cellular mRNA expression was examined by Northern blotting. Mitogenic responses to ET-1 were assessed by [3H]TdR incorporation. ET receptor mRNA expression was examined by RT-PCR analysis of fibroblast RNA and with surface binding studies using radiolabeled ET receptor ligands and specific receptor antagonists. ET-1 enhanced release of collagen types I and III by control and SSc fibroblast strains, but the effects were significantly greater for control cells (p < 0.05). This effect appeared to involve both ETA and ETB receptor subtypes. SSc fibroblasts demonstrated lower constitutive MMP-1 production than control fibroblasts (p < 0.01), but ET-1 treatment decreased MMP-1 in normal fibroblasts to levels observed in SSc. Mitogenic response (percent control [3H]TdR incorporation) to ET-1 for SSc fibroblasts was 130 +/- 34, significantly less (p < 0.01) than that for normal fibroblasts strains (290 +/- 25). This response appeared to be predominantly mediated via the ETA receptor subtype. Surface binding studies suggested a significantly lower level of ETA binding sites in SSc compared with normal fibroblasts (p < 0.05). These data suggest that ET-1 induces a fibrogenic phenotype in normal dermal fibroblasts that resembles that seen in fibroblasts grown from lesional SSc skin. Moreover, SSc cells appear to be refractory to these effects, and this reduced responsiveness is associated with an altered ratio of ETA:ETB receptor expression, supporting a role for ET-1 in the fibrotic pathology of SSc.

Cell Division↗
PubMed1998

Endothelin-1 regulation of intercellular adhesion molecule-1 expression in normal and sclerodermal fibroblasts.

We investigated the potential modulation of cell surface intercellular adhesion molecule-1 (ICAM-1) expression and function by ET-1 in fibroblasts grown from skin biopsies of scleroderma (SSc) patients compared with healthy controls. Surface ICAM-1 expression was quantified by cell-bound ELISA and by FACS analysis. ICAM-1 function was investigated by measuring cell adhesion, and we studied ICAM-1 gene expression using RT-PCR. Fibroblast ET-1 binding sites were measured using 125I-labeled ET-1, and the modulation of ICAM-1 function by ET-1 was determined by measuring the binding of human U937 cells to fibroblasts in the presence of a mixed ETA/B receptor antagonist (bosentan) or a neutralizing anti-ICAM-1 antibody. ICAM-1 expression was significantly higher in SSc fibroblasts compared with normal controls. ET-1 increased ICAM-1 on both normal and SSc fibroblasts to comparable levels. RT-PCR demonstrated that ICAM-1 mRNA was upregulated by ET-1, and results from binding studies showed fibroblasts exposed to ET-1 supported more U937 cells than controls, a process that could be inhibited by bosentan and ICAM-1 neutralizing antibody. Autoradiography showed ET-1 receptors on both normal and SSc fibroblasts. Our findings indicate that SSc fibroblasts express intrinsically elevated levels of surface ICAM-1 and message. ET-1 can induce normal fibroblasts to express some SSc phenotypes and may function as a potent proinflammatory mediator, similar to cytokines, and therefore may also have immunoregulatory functions for immune cells infiltrating and binding to connective tissues.

Autoradiography↗
PubMed1998

Effect of an allosteric modifier of hemoglobin, RSR-4, on oxygen affinity and oxygen saturation of hemoglobin in rabbits.

Theoretically, if the arterial partial oxygen pressure (PaO2) does not change, a right shift in the oxygen equilibrium curve (OEC) of hemoglobin should reduce arterial oxygen saturation. In this study we investigate whether a right shift in the OEC of hemoglobin decreases transcutaneous oxygen saturation (Tc-SO2) following the administration of an allosteric effector, 2-[4-(((3, 5-dichloroanilino)-carbonyl) methyl) phenoxy]-2-methylpropionic acid (RSR-4). The effect of RSR-4 on hemoglobin oxygen affinity was studied in four New Zealand white male rabbits. Following intraperitoneal administration of RSR-4, Tc-SO2 decreased in a dose-dependent manner. P50 (partial oxygen pressure at 50% hemoglobin oxygen saturation) in whole blood increased as the concentration of RSR-4 increased. Tc-SO2 decreased as whole-blood affinity (1/P50) decreased. There was no positive correlation between Tc-SO2 and PaO2. We concluded that a decrease in hemoglobin oxygen affinity following RSR-4 administration reduced arterial oxygen saturation. This decrease in the presence of an allosteric effector such as RSR-4 in vivo can be detected and monitored as a reduction in Tc-SO2.

Aniline Compounds↗
PubMed1998

Synthesized allosteric effectors of the hemoglobin molecule: a possible mechanism for improved erythrocyte oxygen release capability in hemoglobinopathy H disease.

Patients with the nondeletion genotype of hemoglobinopathy H (HbH or beta4) disease have higher proportions of HbH and more severe tissue hypoxia than patients with the deletion genotype. Because these patients' red blood cells (RBCs) contain mainly two Hb species, HbH and HbA, the high proportion of HbA can be exploited by lowering its oxygen affinity; this would probably increase oxygen delivery to the RBCs and improve the patients' clinical phenotype. Allosteric effectors that induce a low-affinity Hb may be useful in this regard. We investigated the effect of a bezafibrate derivative, RSR-4, on the oxygen affinity of RBCs and purified hemolysates containing HbA and HbH. This allosteric effector crosses RBC membranes and binds reversibly to the alpha-chains of deoxy-Hb, decreasing hemoglobin oxygen affinity. The blood used was obtained from a patient with HbH disease (alphaTSaudi homozygote) whose HbH level was 33.5% as measured by high-performance liquid chromatography. Oxygen binding studies were performed in RBCs and purified hemolysates. RBCs incubated in the presence of 500 microM RSR-4 (2-[[[(3,5-dichloroanilino)-carbonyl]methyl]phenoxy]-2-methylpropi onic acid) in standard conditions (pH 7.4, 0.14 M NaCl, 37 degrees C) displayed an increase in their P50 value from 14.5 to 35.2 mm Hg. Oxygen binding studies in purified stripped hemolysates (pH 7.2, 0.1 M NaCl, 25 degrees C) showed that addition of both 500 microM RSR-4 and 1 mM of 2,3 diphosphoglycerate (DPG) led to an 11-fold decrease in oxygen affinity, whereas the addition of the natural effector DPG or RSR-4 alone produced a 2.7- and 5.7-fold decrease, respectively. In both cases, the oxygen equilibrium curves (OECs) were biphasic due to the presence of the noncooperative, high-oxygen-affinity HbH (beta4) component. After addition of RSR-4, the lower part of the OEC (corresponding to HbH) was not shifted compared with the upper part (corresponding to HbA). These results were confirmed by kinetic studies of CO recombination. Both experiments demonstrated that RSR-4 does not affect beta4 Hb. Our findings provide an experimental model for lowering the oxygen affinity of HbA in HbH-containing cells and suggest that the oxygen delivery capability of the latter would be thereby improved.

Allosteric Regulation↗
PubMed1997

The rationale for, and effects of oxygen delivery enhancement to ischemic brain in a feline model of human stroke.

Reduced brain tissue oxygenation is frequently seen in severe head injury and after subarachnoid hemorrhage, and this is considered a major cause of secondary ischemic brain injury. In fact, in a previous study, we found a tight correlation between low brain tissue oxygen tension and poor outcome. Therefore, we tested the hypothesis that an allosteric modifier of hemoglobin, which improves oxygen transport to tissue, could reduce the size of an acute infarct in a feline model of human stroke. This compound produces a shift in the hemoglobin dissociation curve to the right and therefore facilitates the unloading of oxygen during low oxygen tension. Seventeen adult cats were studied. Ischemic stroke was induced through a transorbital, permanent, middle cerebral artery occlusion. Seven animals received saline, and 10 received the allosteric Hb modifier RSR-13. Three different endpoints were used to determine the effect of the allosteric modifier. Delta p50 values were measured in the arterial blood; the intra-infarct oxygen tension was measured, and finally, the volume of the infarct was assessed using TTC staining. Mean delta p50 changes varied from 10.4 +/- 9.2 mmHg up to 15.0 +/- 6.8 mmHg. Mean intra-infarct oxygen tension was 27 +/- 6 mmHg for the control group and 33 +/- 7 mmHg for the drug-treated animals. The mean infarct size (measured as percentage of hemisphere volume) in the control group was 32 +/- 9% and for the RSR-13 animals 22 +/- 10% (p < 0.05). A definitive trend towards improvement in brain oxygen tension was seen, such that animals pretreated with RSR-13 showed a higher infarct oxygen tension. Infarct size was significantly reduced in the drug group. Therefore, RSR-13 is potentially beneficial in the treatment of brain ischemia. Since human studies with this compound are already completed, and other compounds which increase oxygen delivery, such as perfluorocarbons, are already being evaluated, it is likely that oxygen delivery enhancement will rapidly become the first 'neuroprotective' modality, employed in patients with severe brain injury, stroke and subarachnoid hemorrhage.

Adult↗
PubMed1997

Hydropathic analysis of the non-covalent interactions between molecular subunits of structurally characterized hemoglobins.

The software program, HINT (Hydropathic INTeractions), which characterizes non-polar-non-polar, polar-polar, and non-polar-polar interactions, has been used to examine subunit interface associations involved in the hemoglobin allosteric transition at a residue and atomic level. HINT differs from many other computational programs in that it is based not on a statistical method or a force-field but employs parameters experimentally determined from solvent transfer experiments. The main focus of this study is to compare HINT scores that are based upon experimentally and thermodynamically derived measurements with experimentally determined thermodynamic results. The HINT analysis yields a good first-order approximation of experimentally measured energies for these interactions as determined by free energies of dimer-tetramer assembly for mutant hemoglobins. The results provide a framework for understanding subunit stabilities based upon individual atom interactions and repulsions. HINT, in agreement with previous analyses, indicates that: (1) the alpha1beta1 and alpha2beta2 subunit contacts are stabilized via several polar and many hydrophobic interactions with few repulsive contact areas in both the T (deoxyhemoglobin) and R (oxyhemoglobin) structures; (2) the alpha1alpha2 subunit contacts are primarily stabilized by polar salt bridge linkages in both T and R states; and (3) the alpha1beta2 and alpha2beta1 contacts have both strong positive and negative interactions in both T and R states with few hydrophobic interactions. The HINT scoring methodology provides a quantitative characterization of the major role of the alpha1beta2 and alpha2beta1 interfaces in the T-->R quaternary transition. HINT also confirms the stronger hydrogen bond formation in mutant Hb Rothschild (Trp 37beta-->Arg) with Asp94alpha1 that gives rise to a low-affinity (deoxy) hemoglobin. HINT shows that the stabilization of the alpha1beta2 interface with mutant Hb Ypsilanti (Asp99alpha-->Tyr) produces a high-affinity (oxy) hemoglobin by reducing hydrophobic-polar contacts in the R state. HINT interaction maps also identified specific sites for mutagenesis at the alpha1beta2 interface that can be explored to shift the allosteric equilibrium in either direction. In addition, the HINT program provides useful diagnostic data for checking the quality of refined crystallographic structures.

Crystallography, X-Ray↗
PubMed1997

Scleroderma lung fibroblasts exhibit elevated and dysregulated type I collagen biosynthesis.

OBJECTIVE: To examine whether scleroderma lung fibroblasts show a pattern of aberrant type I collagen (CI) biosynthesis similar to that observed previously in studies of dermal fibroblasts in this disease. METHODS: CI secretion and steady-state pro alpha1(I) collagen messenger RNA (mRNA) levels and COL1A2 gene activation were examined in fibroblasts grown from lung biopsy specimens obtained from 16 scleroderma patients with lung fibrosis and from 10 histologically normal lung specimens (controls). The effect of culture in a 3-dimensional (3-D) CI gel matrix culture on CI mRNA levels was also examined. RESULTS: The mean (+/- SEM) collagen secretion in monolayer culture for scleroderma lung fibroblasts was 90.9 +/- 56 ng/ml/10(6) cells, significantly greater (P < 0.05) than controls (40.2 +/- 17.5). Pro alpha1(I) collagen mRNA levels in monolayer cultures were higher in scleroderma (mean +/- SEM collagen:GAPDH ratio 3.7 +/- 0.9) compared with control (1.9 +/- 0.8) lung fibroblasts. Transient expression assays confirmed that genes coding for CI are transcriptionally activated in scleroderma lung fibroblasts compared with control strains. Although all lung fibroblasts induced equivalent contraction of 3-D CI gel matrices, scleroderma strains failed to show a reduction in steady-state pro alpha1(I) collagen mRNA levels in gel culture. CONCLUSION: We have demonstrated elevated CI biosynthesis and impaired mRNA down-regulation for CI by scleroderma lung fibroblasts. These properties are likely to be highly relevant to the pathogenesis of scleroderma-associated lung fibrosis.

Adult↗
PubMed1997

Increased levels of endothelin-1 and differential endothelin type A and B receptor expression in scleroderma-associated fibrotic lung disease.

In addition to their vasoactive action, endothelins are potent peptides in the regulation of both cell proliferation and the turnover of extracellular matrix. Using immunohistochemical, autoradiographic, and molecular analyses, we have studied the localization and expression of endothelin-1 and endothelin A (ETA) and B (ETB) receptors in scleroderma-associated fibrotic lung disease. Increased ET-1 immunoreactivity was found in sclerotic tissue compared with control and was associated with the vasculature, pulmonary interstitium, and bronchial and alveolar epithelium. Microautoradiographic analysis after 125I-labeled ET-1 binding showed a two- to threefold increase in the expression of total ET-1 receptors in scleroderma lung tissue localized to the alveolar epithelium and the pulmonary interstitium which was composed of mainly fibroblastic cells with macrophages and some microvessels. RNAse protection assay revealed significantly reduced ETA receptor and slightly raised ETB message levels in systemic sclerosis lung. Surface expression of functional ET receptors was examined by targeted receptor blocking using mixed and receptor-subtype-selective ligands. A consistent decrease in ETA receptor binding sites was noted primarily within the interstitium and vasculature, in contrast to a slight increase in ETB receptors. Elevated ET-1 and the cell-specific pattern of endothelin receptor expression suggest that the endothelins may represent important mediators that influence the pathology of scleroderma-associated lung disease and other fibrotic conditions.

Adult↗
PubMed1996

Low-affinity hemoglobin increases tissue PO2 and decreases arteriolar diameter and flow in the rat cremaster muscle.

The hypothesis that tissue oxygen delivery in excess of metabolic demand results in vasoconstriction and reduced blood flow was tested in the cremaster muscle of anesthetized Sprague-Dawley rats by studying the effects of an intravenous infusion of RSR-13, an allosteric effector of hemoglobin. RSR-13 reduces the affinity of hemoglobin for oxygen, causing a right shift in the oxygen dissociation curve. Thus, oxygen delivery to the tissues was increased without elevations in blood flow or blood pressure. Tissue PO2, arteriolar diameter, and RBC velocity were measured and volume flow was calculated from diameter and RBC velocity in third-order arterioles. In rats receiving RSR-13 at a rate of 200 mg kg-1 in 15 min (n = 18) P50 (the PO2 at which hemoglobin is 50% saturated) increased from 36 +/- 1 to 52 +/- 3 mm Hg, and tissue PO2 increased to a maximum of 146 +/- 12% above its control value. P50 and tissue PO2 did not change in the control group (n = 8) receiving vehicle at a rate equivalent to that in the experimental group. In a separate group of rats receiving RSR-13 (n = 7), P50 increased from 38 +/- 1 to 51 +/- 3 mm Hg, calculated arteriolar flow decreased from 9 +/- 3 to a minimum of 1.4 +/- 1 nl sec-1, and arteriolar diameter decreased from 27 +/- 3 to a minimum of 13 +/- 3 micrograms P50, volume flow, and arteriolar diameter did not change in the control group (n = 10). These results suggest that an increased tissue oxygen delivery, caused by a right shift in the oxygen dissociation curve, may cause an increase in vascular resistance independent of an elevated blood flow.

Aniline Compounds↗
PubMed1996

RSR-13, an allosteric effector of hemoglobin, increases systemic and iliac vascular resistance in rats.

Tissue O2 delivery in excess of metabolic demand may be a factor in the development of high vascular resistance in experimental models of volume-expanded hypertension. This hypothesis was previously tested in rats with an exchange transfusion of red blood cells treated with inositol hexaphosphate or an intravenous infusion of RSR-4, allosteric effectors of hemoglobin. The binding of these drugs with hemoglobin effect a conformational change in the molecule, such that the affinity for O2 is reduced. However, in both preparations, the changes in vascular resistance could have been nonspecific. The present studies used intravenous infusions of RSR-13, which did not share some of the problematic characteristics of RSR-4 and inositol hexaphosphate. Conscious instrumented rats (an electromagnetic flow probe on ascending aorta or an iliac, mesenteric, or renal Doppler flow probe) were studied for 6 h after an RSR-13 infusion of 200 mg/kg in 15 min. This dose significantly increased arterial P50 (PO2 at which hemoglobin is 50% saturated) from 38 +/- 0.8 to 58 +/- 1.4 mmHg at 1 h after the start of the infusion. In the 3rd h cardiac output fell significantly from a control value of 358 +/- 33 to 243 +/- 24 ml.kg-1.min-1 and total peripheral resistance significantly increased from 0.31 +/- 0.03 to 0.43 +/- 0.04 mmHg.ml-1.kg.min. Cardiac output and P50 returned toward control over the next few hours. Neither cardiac output nor total peripheral resistance changed in the group of rats receiving vehicle alone. In a separate group of rats, iliac flow decreased significantly to 60% of control and iliac resistance increased to 160% of control. Iliac flow increased significantly in the group of rats that received vehicle only. Although the mechanism of these changes has not been established, these results suggest that a decreased O2 affinity leads to an increased total peripheral resistance and regional vascular resistance and support the hypothesis that O2 plays a role in the metabolic autoregulation of blood flow.

Allosteric Regulation↗
PubMed1995

How allosteric effectors can bind to the same protein residue and produce opposite shifts in the allosteric equilibrium.

Monoaldehyde allosteric effectors of hemoglobin were designed, using molecular modeling software (GRID), to form a Schiff base adduct with the Val 1 alpha N-terminal nitrogens and interact via a salt bridge with Arg 141 alpha of the opposite subunit. The designed molecules were synthesized if not available. It was envisioned that the molecules, which are aldehyde acids, would produce a high-affinity hemoglobin with potential interest as antisickling agents similar to other aldehyde acids reported earlier. X-ray crystallographic analysis indicated that the aldehyde acids did bind as modeled de novo in symmetry-related pairs to the alpha subunit N-terminal nitrogens. However, oxygen equilibrium curves run on solutions obtained from T- (tense) state hemoglobin crystals of reacted effector molecules produced low-affinity hemoglobins. The shift in the allosteric equilibrium was opposite to that expected. We conclude that the observed shift in allosteric equilibrium was due to the acid group on the monoaldehyde aromatic ring that forms a salt bridge with the guanidinium ion of Arg 141 alpha on the opposite subunit. This added constraint to the T-state structure that ties two subunits across the molecular symmetry axis shifts the equilibrium further toward the T-state. We tested this idea by comparing aldehydes that form Schiff base interactions with the same Val 1 alpha residues but do not interact across the dimer subunit symmetry axis (a new one in this study with no acid group and others that have had determined crystal structures). The latter aldehydes shift the allosteric equilibrium toward the R-state. A hypothesis to predict the direction in shift of the allosteric equilibrium is made and indicates that it is not exclusively where the molecule binds but how it interacts with the protein to stabilize or destabilize the T- (tense) allosteric state.

Aldehydes↗
PubMed1995

Bisaldehyde allosteric effectors as molecular ratchets and probes.

Four new series of monoaldehyde bisacids and bisaldehyde bisacids with varying chain lengths have been synthesized and evaluated as allosteric effectors of hemoglobin. Molecular modeling, oxygen equilibrium, and crystallographic studies were combined for structure/function studies. Crystallographic analyses of the bisaldehydes reveal that Schiff base interaction occurred exclusively between Val 1 alpha and Lys 99 alpha of the opposite alpha chain even though the two terminal Val 1 alpha nitrogens are ideally spaced to also form cross-links. The reason for the observed mode of binding appears to be the influence of chain direction set by key substitutions on the bisaldehyde molecule. Even longer chain derivatives that could overcome the direction set by the key functional groups bind in the same manner. These studies support the general conclusion that long flexible molecules prefer to bind along cavity walls, like double-sided molecular sticky tape, rather than span large open spaces with few chances for interaction. The cross-linked bisaldehydes bind at the same site when incubated under both allosteric states and exhibit reduced cooperativity with a significant decrease in oxygen affinity. The chain length acts as a molecular ratchet and dictates the degree of allosteric effect observed. The tighter the cross-link, the greater the constraint on the tense- (T-) state and the stronger the allosteric effect that is produced. The monoaldehyde bisacids bind in the same fashion with Schiff base formation at Val 1 alpha while the acid that replaces the second aldehyde moiety forms a salt bridge with Lys 99 alpha of the opposite subunit. This class of molecules has weaker allosteric effector activity as would be expected with replacement of one covalent bond by a salt bridge. The importance of Lys 99 alpha on the allosteric equilibrium is confirmed.

Aldehydes↗
PubMed1995

Intrinsic activity at the molecular level: E. J. Ariëns' concept visualized.

The concept of using affinity and intrinsic activity to analyze drug interactions with receptors has had a long history in pharmacological studies. In the simplest case, the biological response will be proportional to the amount of drug bound, i.e. its affinity. However, the biological response is also mediated by the ability of a drug when bound to exert its maximum effectiveness. This effectiveness is termed the intrinsic activity. Physicochemical processes have been thought to be at the basis of intrinsic activity. Detailed oxygen and solution binding experiments combined with X-ray crystallographic studies on allosteric effectors to hemoglobin demonstrate that these potential drug agents bind at the same site in hemoglobin with similar binding constants yet shift the allosteric equilibrium and the oxygen affinity of the T-structure by different degrees. Therefore some of the effectors with similar binding affinities for the same site exhibit varying degrees of affectiveness, i.e. they possess different intrinsic activities. The intrinsic activity of the effector is defined as the ratio of the oxygen affinity constant to the T-state with drug/oxygen affinity constant to the T-state without drug (KT+drug)/(KT control). The source of the intrinsic activity appears to be the ability of the effectors to interact with key residues such as Lys99 alpha at the binding site. These results suggest a general molecular mechanism for allosteric effector modulation of hemoglobin function that might be of use in other allosteric enzyme systems.

Allosteric Regulation↗
PubMed1995

Altered cytokine expression in T lymphocytes from human immunodeficiency virus Tat transgenic mice.

Examination of the interaction between human immunodeficiency virus (HIV) regulatory gene products and the host immune system is fundamental to understanding the pathogenesis of HIV and could reveal possible targets for therapeutic intervention in the treatment of AIDS. The HIV Tat gene is a potential candidate for this type of strategy. Transgenic mice can be used to investigate the in vivo effects of Tat on the developing and dynamic immune system and on cellular gene expression. Thus, we have generated transgenic mice that harbor the HIV type 1 Tat gene under the transcriptional control of the human CD2 gene regulatory elements. This expression cassette results in high-level, tissue-specific transcription of the transgene within the T-cell compartment. In this report, we demonstrate the effects of Tat on the in vivo immune system. CD2-Tat transgenic mice show no signs of aberrant thymic development and have normal levels of T-cell subsets in the thymus and peripheral lymphoid organs. However, activated T cells from transgenic mice contain increased levels of tumor necrosis factor beta mRNA as well as biologically active tumor necrosis factor protein and express elevated levels of transforming growth factor beta and interleukin-4 receptor mRNA. These increased cytokine levels do not appear to alter mitogen- or antigen-stimulated responses or induce the formation of dermal lesions in ageing mice. Such investigations should provide insight into the combination of host immune factors mediating pathogenesis in HIV infection.

Aging↗
PubMed1994

The effect of physical organic properties on hydrophobic fields.

Physical organic structural properties of small molecules and macromolecules such as bond count, branching and proximity between multiple polar fragments contribute significantly to measured hydrophobicity (log P). These structural properties are encoded in the Rekker and Leo methods of calculating log P as structural-dependent factors. Regardless of the size of the atom primitive set, methods predicting log P with only atom primitives can miss subtle structural detail within series of related compounds. The HINT (Hydropathic INTeractions) model for inter- and intramolecular noncovalent interactions calculates atom-based hydrophobic constants, but uses all Leo-type factors in the calculation rather than a large set of atom primitives. Two types of applications of HINT are discussed: evaluation of the binding of an inhibitor (A74704) to HIV-1 protease, where it is shown that modeling of the protonation state (i.e., Asp25, Asp125) in the protein can strongly influence perceived substrate binding; and the use of HINT to calculate a third (hydropathic) field for CoMFA can yield a statistically enhanced and predictive model for molecular design.

Chemical Phenomena↗
PubMed1994

Evaluating docked complexes with the HINT exponential function and empirical atomic hydrophobicities.

Methods that predict geometries of ligands binding to receptor molecules can facilitate ligand discovery and yield information on the factors governing complementarity. Here, the use of atomic hydrophobicities in evaluating binding modes has been examined with four ligand-receptor complexes of known structure. In each system, hundreds of hypothetical binding orientations were generated with DOCK and evaluated using the HINT (Hydropathic INTeractions) exponential function and atomic hydrophobic constants. In three of the four systems, the experimental binding mode received the best HINT score; in the fourth system, the experimental binding mode scored only slightly lower than a similar, apparently reasonable orientation. The HINT function may be generally useful as a scoring method in molecular docking.

Binding Sites↗