Biomedical subjects

S Stack

Publications and source records attributed to S Stack.

At least 37 records · Page 2Linked to original sources

PubMed1995

Limited sequence diversity of the HIV type 1 protease gene from clinical isolates and in vitro susceptibility to HIV protease inhibitors.

Proviral DNAs from 3 laboratory strains and 21 clinical isolates of HIV-1 were extracted from infected cells after proteinase K digestion and the protease gene was PCR amplified and sequenced directly by the Sanger method. In vitro susceptibilities of the virus isolates to protease inhibitors were determined by the ACTG/DoD consensus assay. Four different HIV protease inhibitors were tested including P9941, a C2 symmetrical diol (Du Pont-Merck); A80987, an asymmetric mono-ol (Abbott); XM323, a cyclic urea (Du Pont-Merck); and Ro31-8959, an asymmetric hydroxyethylene isostere (Roche). Maximum sequence variation was 10% at both the nucleic and amino acid levels. Purine-purine substitutions were most common. Five noncontiguous regions were conserved across all isolates and corresponded to amino acids 1-9 (amino terminal), 21-32 (catalytic site), 47-56 ("flap" region), 78-88 (substrate-binding region), and 94-99 (carboxy terminal). All clinical isolates demonstrated in vitro susceptibility to the protease inhibitors. There was no significant difference between the susceptibility of the reference strains and the clinical isolates. These data suggest that the variable regions of protease do not contain sites that are important for interactions with the inhibitors tested.

Amino Acid Sequence↗

PubMed1995

Protein adsorption and macrophage activation on polydimethylsiloxane and silicone rubber.

Static and dynamic human blood adsorption studies on polydimethylsiloxane, PDMS, and silicone rubber show that these materials are similar, but not identical, in their protein adsorption behavior. Fibrinogen, immunoglobulin G, and albumin were the predominant proteins identified on the material surfaces with fibronectin, Hageman factor (factor XII), and factor VIII/vWF adsorbing at intermediate levels. While the protein adsorption characteristics for the two materials were similar, higher levels of the respective proteins were identified on silicone rubber compared to PDMS. Monocytes/macrophages incubated on PDMS, silicone rubber and low density polyethylene, LDPE, with or without protein adsorption produced variable levels of IL-1 beta, IL-6 and TNF-alpha dependent on the polymer and adsorbed protein. PDMS showed lower levels of the cytokines when compared to the polystyrene control and polyethylene. Protein preadsorption on the PDMS, polystyrene, and LDPE surfaces showed lower levels of cytokines when compared to the respective quantities produced with no protein adsorption suggesting a passivating effect by the protein adsorption phenomenon on monocyte/macrophage activation. Preadsorption of IgG, fibrinogen or fibronectin decreased the quantitative expression of IL-1 beta but increased the functional activity in the thymocyte proliferation assay indicating the presence of monocyte/macrophage activation products which either downregulated the activity of IL-1 beta or upregulated thymocyte proliferation in an independent fashion.

Adsorption↗

PubMed1995

Marital status, alcohol abuse and attempted suicide: a logit model.

Research on suicide and marital status has neglected the impact of alcohol abuse. Given that nonmarried people are more apt to abuse alcohol than married people, the often cited relationship between low marital integration and suicide may either be spurious, or it may involve a complicated interaction between the two variables. Married individuals consume less alcohol than unmarried individuals, but within marriage alcohol abuse does occur, and when it leads to family abuse it may trigger suicide. Also, over the life course individuals experience stressors (e.g., unemployment, illness) that may influence alcohol abuse and suicide. The present study explores the causal linkage between marital status, alcohol abuse and suicide at the micro level, employing data from the Epidemiological Catchment Area surveys. Logistic regression results indicate that marital status affects the odds of attempting suicide independent of indicators of alcohol abuse. Alcohol abuse is, however, a better predictor of attempted suicide than marital status.

Adolescent↗

PubMed1994

Age, birthdays, and suicide.

The present study, which contained a sample of 3,948 suicides and controls for seasonal effects, did not replicate the results of Barraclough and Hughes's (1987) study. People are not significantly more likely to die near the time of their birthdays than they are at other times of the year.

Age Factors↗

PubMed1994

The heavy metal subculture and suicide.

The impact of the heavy metal music subculture on suicide has been the subject of much public debate but little scholarly research. The present paper assesses this relationship with data on heavy metal magazine subscriptions and youth suicide in the 50 states. We find that, controlling for other predictors of suicide, the greater the strength of the metal subculture, the higher the youth suicide rate. The music perhaps nurtures suicidal tendencies already present in the subculture. The model explains 51% of the variance in youth suicide.

Adolescent↗

PubMed1993

Protein adsorption and endothelial cell attachment and proliferation on PAPI-based additive modified poly(ether urethane ureas).

To better understand vascular interactions with poly(ether urethane urea) (PEUU) materials, protein adsorption, and endothelial cell attachment and proliferation assays were performed on a base PEUU formulation, on PEUU formulations loaded with hydrophobic and amphiphilic poly(methylene-[polyphenyl isocyanate]) (PAPI) based additives, and on PEUU formulations in which some of the polymer chains had been endcapped with either diisopropylaminoethyl (DIPAA) or decyl (DA) moieties. Protein adsorption experiments with PAPI-based additives showed that additive loaded PEUU formulations adsorbed significantly lower amounts of the studied proteins than did the unloaded PEUU. Protein adsorption to the DA and DIPAA endcapped PEUU films was found not to vary consistently from that of the unloaded PEUU film. Endothelial cell attachment and proliferation experiments with PAPI-DA and polyethylene glycol-PAPI-DA (PEG-PAPI-DA) loaded PEUU films showed that many of the films exhibited attachment and proliferation that was significantly enhanced compared to PEUU A' and that approached or equaled that of the tissue culture polystyrene control. Experiments with PAPI-DIPAA and PEG-PAPI-DIPAA loaded PEUU films exhibited attachment and proliferation data that was often below 10% of the tissue culture polystyrene control values. Experiments with the DA and DIPAA endcapped PEUU films showed endothelial cell attachment and proliferation that was statistically indistinguishable from the PEUU A' values. Contact angle analysis was carried out on the endcapped PEUU films, on the PAPI-based additive loaded PEUU films, and on PEUU A' using the sessile drop method. The advancing and receding contact angle behavior of the PAPI-based additive loaded PEUU films deviated markedly from the behavior of PEUU A', suggesting that the additives were present at the PEUU-water interface. The contact angle behavior of the endcapped PEUUs was similar to that of PEUU A', suggesting that the DA and DIPAA endcap moieties did not exist at the hydrated PEUU surface in appreciable quantities. To explain the differences in protein adsorption and endothelial cell behavior on the air side of additive loaded PEUUs when compared to the base PEUU, it was assumed that the additives near this region of the solvent swollen PEUU matrix may have migrated to, at, or near the PEUU-air interface during film formation, creating an additive enriched PEUU surface region.(ABSTRACT TRUNCATED AT 400 WORDS)

Adsorption↗

PubMed1993

The media and suicide: a nonadditive model, 1968-1980.

Unlike previous work, the present investigation tests a nonadditive model of the suggestion/imitation. Suicide stories are predicted to have the greatest effect on suicide in times of high suicidogenic conditions. The latter are measured in terms of unemployment. Data on the American monthly suicide rate are analyzed using Cochrane Orcutt techniques. While support was found for the nonadditive model based on an interaction effect between media stories and the rate of unemployment, it did not prove more powerful than an additive model. Future work is needed, however, for a systematic testing of the nonadditive thesis.

Adolescent↗

PubMed1992

Ionic modulation of the effects of heparin on plasminogen activation by tissue plasminogen activator: the effects of ionic strength, divalent cations, and chloride.

Ionic strength, divalent cations, and Cl- modulate the ability of the glycosaminoglycan heparin to stimulate the activation of human plasminogen (Pg) by tissue-type Pg activator. Kinetic analysis of Pg activation indicates that heparin is inhibitory, stimulatory, or nonstimulatory as a function of ionic strength. While increasing ionic strength inhibits Pg activation in the absence of heparin, in it presence an activation phase followed by an inhibitory phase is observed. Divalent cations, inhibitors of activation in the absence of heparin, increase the rate of activation in its presence. Kinetic analysis demonstrates that divalent cations augment the heparin stimulatory effect a maximum of 60-fold due to increases in kcat without changes in Km of the reaction. This effect is heparin-specific, since activation is not affected by Ca2+ in the presence of heparan sulfate or de-N-sulfated heparin. Also, Cl- inhibits Pg activation in the presence of heparin by acting as a competitive inhibitor (Kic of 100 mM). Furthermore, inhibition by Cl- reduces the overall magnitude of heparin stimulation of Pg activation. These results suggest that physiologic ions in combination with heparin may be significant effectors of Pg activation in the vascular microenvironment.

Binding, Competitive↗

PubMed1992

Divorce and sex.

Studies on the sex lives of the divorced are relatively few and somewhat dated. Although they give a rather optimistic view of the subject, this research is flawed by high respondent refusal rates and poor representativeness of samples. Further, a major gap in this literature is that the possible predictors of sexual activity of the divorced remain largely unexplored. The present study, using national data on 340 divorced people, indicates a much lower level of sexual activity than found in past research. Regression analyses find that both number of partners and sex frequency are related to religiosity, education, and political liberality. Future research can explore the impact of low sexual activity among the divorced on indicators of emotional well-being.

Adaptation, Psychological↗

PubMed1992

Staining plant cells with silver. III. The mechanism.

Silver does not stain all cytological structures with the same intensity. The chemical basis for differential silver staining is unclear, but differences in protein side groups available to react with silver are likely involved. These include amine, carboxyl, phosphate, sulfhydryl and hydroxyl moieties. Here we report an investigation of the chemical groups that could be involved in salt-nylon silver staining of onion root tip squashes. Based on the results, we conclude that SN silver staining primarily depends on the presence of tyrosine hydroxyl groups, and we propose a mechanism for staining.

Allium↗

PubMed1992

The effect of the media on suicide: the Great Depression.

Previous work on the media and suicide has neglected the mood of the audience in its models. The present study tests the thesis from symbolic interaction theory that the degree of media influence is contingent on audience receptivity. Audience receptivity to suicide stories is assumed to be high in the Great Depression given widespread unemployment, a condition thought to promote suicidogenic mood such as anomie. A taxonomy of stories is developed using classic imitation, social learning, and differential identification theories. Analysis of monthly data on suicide and publicized stories finds, however, little supporting evidence. Only stories concerning political leaders were associated with suicide. Stories concerning other categories of victims, such as villains, entertainers, and foreigners, were not associated with suicide. Possibly the potential impact was offset by other factors such as the absence of television to echo for the messages carried by the newspapers and radio and heightened political integration.

Cross-Sectional Studies↗

PubMed1991

Plasmin binding to the plasminogen receptor enhances catalytic efficiency and activates the receptor for subsequent ligand binding.

Specific cell surface receptors for plasminogen (Pg) are expressed by a wide variety of cell types. The colocalization of receptors for Pg and its activators restricts plasmin (Pm) activity to specific sites and serves to promote fibrinolysis and local Pg activation. These studies show that both Pg and Pm bind to cellular receptors on monocytoid U937 cells. Limited Pm pretreatment of the cells enhances total Pg binding and alters the kinetics of Pm binding. Furthermore, surface-bound Pg is converted to Pm in the absence of exogenous activators. Cell-bound Pm exhibits a 12-fold increase in catalytic efficiency (kcat/Km) relative to Pm free in solution. These studies demonstrate that Pg/Pm receptor occupancy can be regulated by Pm in the microenvironment and may play a significant regulatory role in fibrinolysis and extravascular proteolysis.

Cell Line↗

PubMed1991

Modulation of plasminogen activation and type IV collagenase activity by a synthetic peptide derived from the laminin A chain.

Laminin is a large multidomain glycoprotein with diverse biological activities which include stimulation of neurite outgrowth, enhancement of tumor metastasis, and promotion of cell growth, adhesion, and differentiation. A 19 amino acid synthetic peptide derived from the E8 fragment of the laminin A chain (Cys-Ser-Arg-Ala-Arg-Lys-Gln-Ala-Ala-Ser-Ile-Lys-Val-Ala-Val-Ser-Ala-Asp -Arg- NH2) was identified which promotes metastasis and stimulates collagenase IV activity in the culture medium of B16 melanoma cells (Kanemoto et al., 1990). We report that this peptide, here designated LamA2091-2108, is also a potent stimulator of tissue plasminogen activator (t-PA)-catalyzed plasminogen activation, resulting in a 22-fold increase in the kcat/Km of the activation reaction. The activity of purified type I and type IV collagenase was inhibited by LamA2091-2108 with IC50 values of 3 and 43 microM, respectively. These data support an alternative mechanism for the appearance of collagenase activity in the culture media of melanoma cells, namely, that the peptide stimulates plasminogen activation, subsequently generating collagenase activity.

Amino Acid Sequence↗

PubMed1991

The effect of religion on suicide ideation.

Work on the impact of religion on suicide has not yielded consistent results. Classic Durkheimian models stressing religious affiliation (Catholic vs Protestant) have been questioned in recent years and some authors have argued for a model based on the alternative conception of religious commitment (e.g. religiosity per se) as a prophylactic against suicide. Almost all of this work has been based on highly aggregated data where it is not known if nonreligious people account for the suicides. The present study tests both models with national data on 1,687 respondents. No support is found for the Durkheimian model at the individual level, but some is found for the religious commitment model: the greater the church attendance the lower the approval of suicide. The effect of religiosity on suicide ideation is independent of education, gender, marital status, and age.

Humans↗

PubMed1991

The effect of divalent cations on the conformation and function of human plasminogen.

The activation of native human plasminogen (Glu1-Pg) by tissue plasminogen activator, urinary plasminogen activator (u-PA), and streptokinase is inhibited by the divalent cations Ca2+, Mg2+, and Mn2+. This inhibition is accompanied by a conformational change in the molecule as evidenced by a decrease in Stokes' radius and intrinsic fluorescence. Kinetic analysis indicates that Mn2+ acts as an uncompetitive inhibitor of u-PA-catalyzed Glu1-Pg activation. In contrast to the inhibitory effects of divalent cations on Glu1-Pg, Ca2+ and Mg2+ stimulate the activation of proteolytically modified Lys77-Pg. These observations provide further evidence that Glu1-Pg and Lys77-Pg exhibit differential responses to ligands in the microenvironment.

Cations, Divalent↗

PubMed1991

Staining plant cells with silver. I. The salt-nylon technique.

A technique is described for selectively silver staining nucleoli, active nucleolus organizers, nucleolar material attached to chromosomes, kinetochores, synaptonemal complexes, and chromosome cores in plant cells. The technique, called salt-nylon silver staining, involves spreading cells on glass slides, treating the cells with a solution of saline sodium citrate, and incubating the cells in a silver nitrate solution covered with nylon screen. Selected variables important for achieving reliable silver staining are considered.

Allium↗

PubMed1990

Regulation of plasminogen activation by components of the extracellular matrix.

The kinetics of activation of Glu-plasminogen (Glu-Pg) and Lys77-Pg by two-chain recombinant tissue plasminogen activator (t-PA) were determined in the presence of isolated protein components of the extracellular matrix (ECM) and compared to activation in the presence of fibrinogen and fibrinogen fragments and in the absence of added protein. Several ECM protein components were as effective as fibrinogen fragments at stimulating Pg activation. Stimulation of Glu-Pg activation resulted from both a decrease in Km and an increase in Vmax, whereas stimulation of Lys77-Pg was due primarily to increases in Vmax. The most effective stimulators of activation were basement membrane type IV collagen and gelatin which resulted in a 21- and 55-fold increase, respectively, in the kcat/Km of Glu-Pg (relative to a 10-fold increase observed with fibrinogen fragments). Amidolytic activity of t-PA was also enhanced up to 12-fold by ECM proteins. However, plasmin amidolytic activity was unaffected by the presence of added proteins. These data suggest that several ECM-associated proteins can enhanced the activation of Pg in the absence of fibrin.

Collagen↗

PubMed1990

A reanalysis of the impact of non celebrity suicides. A research note.

Previous work on suicide and the media has neglected theoretical issues. Some work has implied that only celebrity suicides can be expected to trigger additional suicides in the real world. The present study focuses on non celebrity suicides. Correcting coding errors in a previous work, it finds that the suicides of non celebrities are associated with increases in the national suicide rate. An index of publicized celebrity suicide stories was, however, more closely associated to increases in suicide than the publicized non celebrity stories. The model explains 90 percent of the variance in monthly suicide rates.

Cross-Sectional Studies↗