Biomedical subjects

D Nelson

Publications and source records attributed to D Nelson.

At least 91 records · Page 5Linked to original sources

PubMed1998

Tubular antithrombin at transplantation determines subsequent renal allograft function.

BACKGROUND: Antithrombin is found in the microvasculature and tubules of normal and transplanted human kidneys. Although depletion of vascular antithrombin is associated with renal allograft dysfunction, neither the distribution nor clinical significance of tubular antithrombin is known. METHODS: Changes in tubular antithrombin in biopsy specimens (n=41) obtained from donor kidneys at transplantation were studied immunohistochemically. The relationship between these changes and subsequent graft function was analyzed. RESULTS: Granular intracellular antithrombin was found only within the proximal tubular epithelium. Allografts with depleted tubular antithrombin at transplantation (n=20) had significantly greater plasma creatinine concentrations at posttransplant days 3 (P < 0.001) and 5 (P < 0.03) than allografts with normal tubular antithrombin (n=21). Indeed, depletion of tubular antithrombin at transplantation correlated with the degree of graft dysfunction at 3 days after transplantation. CONCLUSIONS: Depleted tubular antithrombin at transplantation is associated with reduced early graft function, and this may identify patients at risk of a complicated follow-up.

Antithrombins↗

PubMed1998

Comparative properties of two cysteine proteinases (gingipains R), the products of two related but individual genes of Porphyromonas gingivalis.

Proteolytic enzymes produced by Porphyromonas gingivalis are important virulence factors of this periodontopathogen. Two of these enzymes, referred to as arginine-specific cysteine proteinases (gingipains R), are the product of two related genes. Here, we describe the purification of an enzyme translated from the rgpB/rgp-2 gene (gingipain R2, RGP-2) and secreted as a single chain protein of 422 residues. The enzyme occurs in several isoforms differing in pI, molecular mass, mobility in gelatin zymography gels, and affinity to arginine-Sepharose. In comparison to the 95-kDa gingipain R1, a complex of catalytic and hemagglutinin/adhesin domains, RGP-2 showed five times lower proteolytic activity, although its activity on various P1-arginine p-nitroanilide substrates was generally higher. Gingipains R amidolytic activity, but not general proteolytic activity, was stimulated by glycyl-glycine. However, in cases of limited proteolysis, such as the inactivation of alpha-1-antichymotrypsin, glycyl-glycine potentiated inhibitor cleavage. In contrast, alpha-1-proteinase inhibitor was not inactivated by gingipains R and only underwent proteolytic degradation during boiling in reducing SDS-polyacrylamide gel electrophoresis treatment buffer. Similarly, native type I collagen was completely resistant to cleavage by gingipains but readily degraded after denaturation. Together, these data explain much of the controversy regarding gingipains structure and substrate specificity and indicate that these enzymes function as P. gingivalis virulence factors by proteolysis of selected target proteins rather than random degradation of host connective tissue components.

Adhesins, Bacterial↗

PubMed1998

Inactivation of alpha1-proteinase inhibitor as a broad screen for detecting proteolytic activities in unknown samples.

The need for a quick, simple screening method for the detection of general proteolytic activity prompted us to determine whether cleavage within the reactive site loop region (RSL) of alpha1-proteinase inhibitor (alpha1-PI), a well-characterized member of the serpin family known to be susceptible to proteolytic inactivation, can be utilized for this purpose. Inactivation of alpha1-PI in the RSL region can be measured by loss of residual inhibitory capacity of alpha1-PI against its target proteinase. While we originally utilized this assay to detect a new proteinase from culture supernatants of Porphyromonas gingivalis, the feasibility of extending this assay to scan for proteolytic activity from other systems was also assessed. As an example, we found that the serine proteinase from Staphylococcus aureus (SSP) had virtually the same catalytic efficiency in inactivating alpha1-PI in our assay as it did in the hydrolysis of the synthetic substrate Z-Phe-Leu-Glu-pNA (kcat/Km value of 2 x 10(4) M-1 s-1 vs 2.6 x 10(4) M-1 s-1, respectively). Additionally, in both assays activity could be readily detected in less than a 1 h incubation at SSP concentrations in the picomolar range. This assay is unique in that proteinases which hydrolyze peptide bonds within the RSL of alpha1-PI can readily be detected as measured by loss of alpha1-PI inhibitory activity.

Amino Acid Sequence↗

PubMed1998

Cotinine: effects with and without nicotine.

The purpose of this study was to examine the effects of the metabolite of nicotine, cotinine, in comparison to the effects of the nicotine patch, and a combination thereof during cigarette abstinence. More specifically, this study examined the effects of cotinine on physiological measures, subjective measures assessing craving, withdrawal symptoms and mood, and performance measures. A between-subject, 2 x 2 factorial design was used, with the daily administration of a 15-mg nicotine patch (Nicotrol) versus placebo patch as one factor and 80 mg of oral cotinine fumarate versus placebo drug as the other factor. Baseline measures were obtained while the subjects smoked cigarettes on an ad lib basis for 1 week. Subjects (n = 106) were then randomly assigned to one of four treatment conditions and for the next 14 days were required to be abstinent from cigarettes and take the study drugs. Cotinine administration, with or without nicotine patch, produced serum cotinine concentrations 3 4 times higher than during ad lib smoking. Results showed a reduction of self-reported tobacco withdrawal symptoms using the nicotine patch alone. Cotinine alone had no effect on withdrawal symptoms. However, when nicotine patch was combined with cotinine, the beneficial effect of the nicotine patch on withdrawal symptoms was absent. Therefore, cotinine appears to antagonize the effects of nicotine in the alleviation of withdrawal symptoms at concentrations higher than that attained from normal smoking. This effect does not appear to be mediated by changes in nicotine disposition.

Administration, Topical↗

PubMed1998

Effects of cotinine on cigarette self-administration.

Previous studies have shown that cotinine, a metabolite of nicotine, antagonizes some of the effects of nicotine. One study showed that cotinine eliminates the beneficial effects of the nicotine patch in reducing cigarette withdrawal symptoms. The purpose of this study was to examine the effects of various doses of cotinine on cigarette self-administration. Subjects were randomly assigned to one of three doses of cotinine fumarate (40, 80 and 160 mg) and placebo, each for a period of 10 days, in a randomized order. Outcome variables included measures of nicotine intake and subjective responses to smoked cigarettes. Results showed no differences in the number of cigarettes smoked, carbon monoxide levels, and weights of cigarette butts across the various doses of cotinine and placebo. However, higher nicotine serum levels were observed in the 160 mg cotinine fumarate condition compared to placebo and to 40 mg cotinine fumarate. No systematic effects of cotinine on subjective responses to cigarettes were observed. Cotinine appears potentially to have a selective modulatory effect on nicotine withdrawal symptoms but not on cigarette smoking.

Adult↗

PubMed1998

Newer antidepressants. Beyond selective serotonin reuptake inhibitor antidepressants.

This article outlines the use of alternative agents to TCAs and SSRIs. Features of the more commonly used alternative antidepressant agents are outlined. In addition, antidepressant agents that are currently either under development or used in other countries are indicated for completeness because it seems likely that many of these will be introduced in the United States within the next few years. Many of these agents will be used by pediatricians and child psychiatrists for treatment of depression in children, and although much further research is needed, the future for alternative antidepressants and augmenting strategies is extremely promising.

Adolescent↗

PubMed1998

Methylmalonate toxicity in primary neuronal cultures.

Several inhibitors of mitochondrial complex II cause neuronal death in vivo and in vitro. The goal of the present work was to characterize in vitro the effects of malonate (a competitive blocker of the complex) which induces neuronal death in a pattern similar to that seen in striatum in Huntington's disease. Exposure of striatal and cortical cultures from embryonic rat brain for 24 h to methylmalonate, a compound which produces malonate intracellularly, led to a dose-dependent cell death. Methylmalonate (10 mM) caused >90% mortality of neurons although cortical cells were unexpectedly more vulnerable. Cell death was attenuated in a medium containing antioxidants. Further characterization revealed that DNA laddering could be detected after 3 h of treatment. Morphological observations (videomicroscopy and Hoechst staining) showed that both necrotic and apoptotic cell death occurred in parallel; apoptosis was more prevalent. A decrease in the ATP/ADP ratio was observed after 3 h of treatment with 10 mM methylmalonate. In striatal cultures it occurred concomitantly with a decline in GABA and a rise in aspartate content and the aspartate/glutamate ratio. Changes in ion concentrations were measured in similar cortical cultures from mouse brain. Neuronal [Na+]i increased while [K+]i and membrane potential decreased after 20 min of continuous incubation in 10 mM methylmalonate. These changes progressed with time, and a rise in [Ca2+]i was also observed after 1 h. The results demonstrate that malonate collapses cellular ion gradients, restoration of which imposes an additional load on the already compromised ATP-generation machinery. An early elevation in [Ca2+]i may trigger an increase in activity of proteases, lipases and endonucleases and production of free radicals and DNA damage which, ultimately, leads to cells death. The data also suggest that maturational and/or extrinsic factors are likely to be critical for the increased vulnerability of striatal neurons to mitochondrial inhibition in vivo.

Adenosine Diphosphate↗

PubMed1998

Toxicity of dopamine to striatal neurons in vitro and potentiation of cell death by a mitochondrial inhibitor.

Intrastriatal injections of the mitochondrial toxins malonate and 3-nitropropionic acid produce selective cell death similar to that seen in transient ischemia and Huntington's disease. The extent of cell death can be attenuated by pharmacological or surgical blockade of cortical glutamatergic input. It is not known, however, if dopamine contributes to toxicity caused by inhibition of mitochondrial function. Exposure of primary striatal cultures to dopamine resulted in dose-dependent death of neurons. Addition of medium supplement containing free radical scavengers and antioxidants decreased neuronal loss. At high concentrations of the amine, cell death was predominantly apoptotic. Methyl malonate was used to inhibit activity of the mitochondrial respiratory chain. Neither methyl malonate (50 microM) nor dopamine (2.5 microM) caused significant toxicity when added individually to cultures, whereas simultaneous addition of both compounds killed 60% of neurons. Addition of antioxidants and free radical scavengers to the incubation medium prevented this cell death. Dopamine (up to 250 microM) did not alter the ATP/ADP ratio after a 6-h incubation. Methyl malonate, at 500 microM, reduced the ATP/ADP ratio by approximately 30% after 6 h; this decrease was not augmented by coincubation with 25 microM dopamine. Our results suggest that dopamine causes primarily apoptotic death of striatal neurons in culture without damaging cells by an early adverse action on oxidative phosphorylation. However, when combined with minimal inhibition of mitochondrial function, dopamine neurotoxicity is markedly enhanced.

Adenosine Triphosphate↗

PubMed1998

Increased platelet microvesicle formation is associated with mortality in a porcine model of endotoxemia.

BACKGROUND: Gram-negative sepsis in humans and endotoxemia in pigs induce the formation of platelet microvesicles. These microvesicles are active in homeostasis and may thus contribute to the outcome in patients with activated coagulation and fibrinolysis. We decided to prospectively evaluate the effects of endotoxemia on microvesicle formation and some common physiologic variables against survival in a porcine model. METHODS: Nineteen included pigs were anesthetized, monitored and subjected to an infusion of E. coli endotoxin. Microvesicle formation was determined by flow cytometry. RESULTS: The formation of microvesicles was significantly increased in the 6 pigs that died during endotoxin exposure. This increased formation became significant from the 3rd hour of endotoxemia. Microvesicle formation did not increase in surviving endotoxemic pigs. Cardiac index, mean arterial blood pressure, base excess and systemic vascular resistance index were distinctly reduced in the animals that died as compared to those surviving the endotoxemic period. CONCLUSION: The increased formation of platelet microvesicles seems to be associated with poor prognosis in porcine endotoxemia. Since microvesicles are active in coagulation, they may contribute to the derangement of the coagulation system caused by endotoxemia. Different degrees of microvesicle formation may reflect inter-individual responses to a given challenge.

Acidosis↗

PubMed1998

The B-subunit of cholera toxin induces immunoregulatory cells and prevents diabetes in the NOD mouse.

The B-subunit of the cholera toxin molecule (CT-B) has T-cell immunomodulatory properties. Because the pathogenesis of diabetes in the nonobese diabetic (NOD) mouse model of IDDM is thought to be a T-cell-mediated process due to an imbalance of immunoregulatory and anti-islet effector cells, we examined the effect of CT-B administration on the development of diabetes in the NOD mouse and assessed whether this potential diabetes-sparing effect of CT-B is mediated by changes in immunoregulatory and/or anti-islet cytotoxic effector cell activity. The administration of either intravenous or intraperitoneal CT-B decreased the development of diabetes with no apparent drug toxicity. At 6 months of age, only 18% of CT-B vs. 75% of saline-treated animals had diabetes. Histopathological examination revealed less islet atrophy in CT-B-treated animals. The in vitro proliferative responses of mononuclear splenocytes and thymocytes to concanavalin A and lipolysaccharide and the proportion of B-cells and T-cell subsets were not altered by CT-B treatment. CT-B administration did not inhibit the primary immunization of mice to tetanus toxoid. The development of diabetes in irradiated NOD mice was slower in the animals injected with spleen cells (SC) from CT-B-treated than from saline-treated NOD mice, suggesting that CT-B decreases anti-islet effector cell activity. The injection of SC from CT-B-treated mice inhibited the adoptive transfer of diabetes by SC from diabetic mice into irradiated NOD mice, documenting that CT-B administration induces regulatory cell activity. In conclusion, CT-B administration prevents the development of diabetes in NOD mice by inhibiting the immune destruction of islets. This islet-sparing activity appears mediated, at least in part, by the induction of regulatory cells and, in turn, suppression of anti-islet effector cells, which is not associated with generalized immunosuppression or T- or B-cell depletion.

Adoptive Transfer↗

PubMed1998

Comparing i.v. and non-i.v. cocaine users. Characteristics of a sample of cocaine users seeking to participate in research.

The authors examined differences between current intravenous (i.v.), past i.v., and no i.v. cocaine use among a sample of cocaine users on measures of drug use, medical history, psychiatric history, and criminal history. Past i.v. cocaine users were older than non-i.v. cocaine users. The current i.v. cocaine-using group included more white participants, and the non-i.v. group included more African Americans. Those with past or current i.v. use had more extensive drug use histories than non-i.v. users. Also, more current and past i.v. cocaine-using groups reported having been tested for HIV and reported testing positive for hepatitis. Former i.v. cocaine users reported more emergency room visits for complications stemming from cocaine use. They also reported more treatment for substance abuse and were convicted of more crimes. These results suggest that the route of administration is important in studying the characteristics of drug users.

Adult↗

PubMed1998