Search PubMed⌕ Search

Biomedical subjects

M McLaughlin

Publications and source records attributed to M McLaughlin.

At least 37 records · Page 2Linked to original sources
PubMed2000

A role for complement in the rejection of porcine ventral mesencephalic xenografts in a rat model of Parkinson's disease.

Vascularized whole organ discordant xenografts placed in the periphery are rejected by a rapid "hyperacute" process that involves preformed antibody binding to the xeno-antigens on the donor endothelial cells with complement activation. In the CNS, xenografts are classically thought to be rejected more slowly by a T-cell-dependent process. We now report that xenografts of embryonic porcine ventral mesencephalic tissue in the 6-hydroxydopamine-lesioned, nonimmunosuppressed rat induce both a humoral and a cell-mediated response. Over the first 10 d after implantation, the xenografts matured with identifiable TH neurons and pig-specific neurofilament fibers extending along host white matter tracts. During this period of time, IgM and complement binding were observed within the graft, as well as a CD8 cellular infiltrate, leading to rejection of the transplant over the next 25 d. These intracerebral xenografts were not associated with an early systemic antibody response. A role for complement in this rejection process was further investigated using cobra venom factor (CVF), which systemically depleted the rats of complement for 7 d. CVF treatment, when given in the period immediately before and after grafting, delayed but did not prevent the cellular immune response induced by the graft, demonstrating that xenografted neural tissue can activate the humoral arm of the rejection process, in particular the complement cascade. This suggests that interventions targeting this aspect of the immune rejection process may be of great importance for the future development of xenotransplantation for neurodegenerative conditions.

Adrenergic Agents↗
PubMed2000

Characterization of peptidyl boronic acid inhibitors of mammalian 20 S and 26 S proteasomes and their inhibition of proteasomes in cultured cells.

Proteasomes are large multisubunit proteinases which have several distinct catalytic sites. In this study a series of di- and tri-peptidyl boronic acids have been tested on the chymotrypsin-like activity of purified mammalian 20 S and 26 S proteasomes assayed with succinyl-Leu-Leu-Val-Tyr-amidomethylcoumarin (suc-Leu-Leu-Val-Tyr-AMC) as substrate. The inhibition of 20 S proteasomes is competitive but only slowly reversible. The K(i) values for the best inhibitors were in the range 10-100 nM with suc-Leu-Leu-Val-Tyr-AMC as substrate, but the compounds tested were much less effective on other proteasome activities measured with other substrates. Free boronic acid inhibitors exhibited equivalent potency to their pinacol esters. Both benzoyl (Bz)-Phe-boroLeu and benzyloxycarbonyl (Cbz)-Leu-Leu-boroLeu pinacol ester inhibited 20 S and 26 S proteasomes with non-ideal behaviour, differences in inhibition of the two forms of proteasomes becoming apparent at high inhibitor concentrations (above 3xK(i)). Both of these compounds were also potent inhibitors of 20 S and 26 S proteasomes in cultured cells. However, gel filtration of cell extracts prepared from cells treated with radiolabelled phenacetyl-Leu-Leu-boroLeu showed that only 20 S proteasomes were strongly labelled, demonstrating differences in the characteristics of inhibition of 20 S and 26 S proteasomes. The usefulness of peptidyl boronic acid inhibitors for investigations of proteasome-mediated protein degradation was confirmed by the observation that Bz-Phe-boroLeu and Cbz-Leu-Leu-boroLeu pinacol ester inhibited NFkappaB activation with IC(50) values comparable to their K(i) values for purified proteasomes. The latter result supports the view that the chymotrypsin-like activity of proteasomes assayed with suc-Leu-Leu-Val-Tyr-AMC is a critical one for protein degradation in cells.

Animals↗
PubMed2000

2H-Thieno[3,2-e]- and [2,3-e]-1,2-thiazine-6-sulfonamide 1,1-dioxides as ocular hypotensive agents: synthesis, carbonic anhydrase inhibition and evaluation in the rabbit.

Novel non-chiral 2H-thieno[3,2-e]- and [2,3-e]-1,2-thiazine-6-sulfonamide 1,1-dioxides were synthesized for evaluation as potential candidates for the treatment of glaucoma. All of the compounds prepared were potent high affinity inhibitors of human carbonic anhydrase II, Ki < 0.5 nM. Additionally, inhibition of recombinant human carbonic anhydrase IV was determined for selected compounds; these were shown to be moderate to potent inhibitors of this isozyme with IC50 values ranging from 4.25 to 73.6 nM. Of the compounds evaluated for their ability to lower intraocular pressure in naturally hypertensive Dutch-belted rabbits, 5a, 17a3, 17b1, 17b2, 17h2 and 17i1 showed significant efficacy (> 20% decrease) in this model following topical ocular administration.

Animals↗
PubMed2000

Activation of phospholipase D by metabotropic glutamate receptor agonists in rat cerebrocortical synaptosomes.

The pharmacological profile of metabotropic glutamate receptor (mGluR) activation of phospholipase D (PLD), and the associated signalling pathways, were examined in rat cerebrocortical synaptosomes. The assay was conducted using a transphosphatidylation reaction in synaptosomes which were pre-labelled with either [(3)H]-arachidonic acid or [(32)P]-orthophosphate. The mGluR agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S, 3R-ACPD) and (RS)-3,5-dihydroxyphenylglycine (DHPG), both activated PLD, while phorbol 12,13-dibutyrate (PDBu) treatment caused receptor-independent activation of PLD and had an additive effect on 1S,3R-ACPD induced PLD activity. A protein kinase C (PKC) inhibitor, GF109203X, failed to antagonize mGluR receptor-coupled PLD activity. We could not detect any increase in the products of PI (phosphoinositide)-specific phospholipase C (PI-PLC), inositol(1,4, 5)trisphosphate or diacylglycerol, by 1S, 3R-ACPD at 15 s. However, diacylglycerol increased monophasically in response to mGluR agonists and remained elevated for at least 15 min. Phosphatidic acid phosphohydrolase (PAP) activity, which converts PA to DAG, was present in the synaptosomes. These data suggest that, in rat cerebrocortical synaptosomes, the 1S,3R-ACPD-sensitive mGluR is coupled to PLD through a mechanism that is independent of both PKC and PI-PLC.

Animals↗
PubMed2000

Nitric oxide and atrial natriuretic factor stimulate cGMP-dependent membrane insertion of aquaporin 2 in renal epithelial cells.

In collecting duct principal cells, aquaporin 2 (AQP2) is shuttled from intracellular vesicles to the plasma membrane upon vasopressin (VP) stimulation. VP activates adenylyl cyclase, increases intracellular cAMP, activating protein kinase A (PKA) to phosphorylate AQP2 on the COOH-terminal residue, serine 256. Using rat kidney slices and LLC-PK1 cells stably expressing AQP2 (LLC-AQP2 cells), we now show that AQP2 trafficking can be stimulated by cAMP-independent pathways. In these systems, the nitric oxide (NO) donors sodium nitroprusside (SNP) and NONOate and the NO synthase substrate L-arginine mimicked the effect of VP, stimulating relocation of AQP2 from cytoplasmic vesicles to the plasma membrane. Unlike VP, these other agents did not increase intracellular cAMP. However, SNP increased intracellular cGMP, and exogenous cGMP stimulated AQP2-membrane insertion. Atrial natriuretic factor, which signals via cGMP, also stimulated AQP2 translocation. The VP and SNP effects were blocked by the kinase inhibitor H89. SNP did not stimulate membrane insertion of AQP2 in LLC-PK1 cells expressing the phosphorylation-deficient mutant 256SerAla-AQP2, indicating that phosphorylation of Ser256 is required for signaling. Both PKA and cGMP-dependent protein kinase G phosphorylated AQP2 on this COOH-terminal residue in vitro. These results demonstrate a novel, cAMP-independent and cGMP-dependent pathway for AQP2 membrane insertion in renal epithelial cells.

Amino Acid Sequence↗
PubMed2000

Safety and efficacy of high-dose adenosine-induced asystole during endovascular AAA repair.

PURPOSE: To assess the safety and efficacy of high-dose adenosine administration to increase the precision of endovascular abdominal aortic aneurysm (AAA) repair using a balloon deployed stent-graft. METHODS: From January 1997 to March 1999, 98 AAA patients (79 men; mean age 71 years, range 62-91) were treated with balloon-expandable stent-grafts under an approved protocol. After placing a temporary transvenous ventricular lead or an external transthoracic pacing electrode, adenosine (24 mg initially) was administered in an escalating dose fashion to induce at least 10 seconds of asystole, during which the proximal stent was expanded. RESULTS: Adenosine dosages ranged from 24 to 90 mg (median 24 mg). Nine (9.2%) self-limiting cardiac events were observed: 2 (2.0%) episodes of transient myocardial ischemia, 2 (2.0%) cases of atrial fibrillation requiring cardioversion, 1 (1.0%) transient left bundle branch block lasting <10 seconds, and 4 (4.1%) prolonged periods of asystole requiring temporary pacemaker activation. There were no cases of bronchospasm or worsening obstructive pulmonary disease, and no patients required inotropic support after adenosine-induced asystole. CONCLUSIONS: Cardiac events following adenosine-induced asystole are infrequent, mild, and easily treated. The perioperative use of high-dose adenosine to ensure precise stent-graft placement appears to be a safe method of inducing temporary asystole during endovascular aortic repair.

Adenosine↗
PubMed1999

Modest cholinergic deafferentation fails to alter hippocampal G-proteins.

The integrity of hippocampal G-protein mediated signalling following ibotenate induced lesion of the medial septum was examined. The lesion was confined histologically to the septum and induced a 23% reduction in hippocampal choline acetyltransferase (ChAT) activity and G-proteins levels and related enzyme activities were measured in the hippocampus following a 21 day survival period. The relative levels of five G-protein subunits (Gbeta, G(alpha)o, G(alpha)i1, G(alpha)i2, and G(alpha)s-L), basal GTPase, the degree of carbachol- or baclofen-stimulated GTPase activities, and the basal and fluoroaluminate-stimulated adenylate cyclase activities were apparently unaffected. To determine if our assay methodology was sensitive to changes in pre-synaptic signalling, we compared G-protein density in synaptosomes with total hippocampal homogenates. The concentration of G(alpha)q/11, G(alpha)i1, and G(alpha)i2. were significantly lower in synaptosomes, while G(alpha)o, was only marginally reduced. Thus, modest lesions of the medial-septal nucleus fail to alter G-protein signalling. However, our findings that G-protein density is lower in synaptosomal membranes than in total homogenates, indicates that the analysis of signalling events in synaptosomes following deafferentation could clarify adaptive changes which may occur at the presynaptic level.

Adenylyl Cyclases↗
PubMed1999

Capillary gas chromatographic detection of invert sugar in heated, adulterated, and adulterated and heated apple juice concentrates employing the equilibrium method.

The equilibrium method is introduced for the detection of invert sugar addition to apple juice. The method consists of a pre-equilibration of the sample with dry pyridine at 50 degrees C for 20 min followed by the addition of trimethylsilylimidazole and heating at 75 degrees C for 40 min. The resulting derivatized carbohydrates are then analyzed by capillary gas chromatography. This method was successfully used by independent laboratories to distinguish heated pure, intentionally adulterated (with invert sugar), and intentionally adulterated and then heated apple juice concentrates. The equilibrium method was shown to give significantly lower coefficients of variation for this sample set when compared to the original capillary gas chromatographic method. In addition, these results indicate that it may also be an effective method for the detection of medium invert sugar, depending on the level of the fingerprint oligosaccharides in this sweetener.

Beverages↗
PubMed1999

Association between variants at the GABAAbeta2, GABAAalpha6 and GABAAgamma2 gene cluster and alcohol dependence in a Scottish population.

A role for the GABA/benzodiazepine receptor complex in alcohol dependence syndrome has been suggested by several lines of evidence. To elucidate the role of GABAA subunits in human alcohol dependence syndrome, we identified polymorphisms in the GABAAbeta2 and GABAAalpha6 receptor subunit genes on 5q33 and assessed their potential contribution in an association study, together with a NciI RFLP at the GABAAgamma2 receptor subunit gene. One hundred and eight alcohol-dependent subjects and 54 unrelated controls were recruited from Scotland. Two novel genetic markers were identified at the GABAAbeta2 and GABAAalpha6 receptor subunit genes and examined for association with the alcohol dependence syndrome and subgroups of subjects with Korsakoff's psychosis and without Korsakoff's psychosis, together with a NciI RFLP at the GABAAgamma2 receptor subunit gene. The chi2 tests demonstrated associations between all alcohol-dependent subjects (not stratified) and the BanI RFLP at the GABAAbeta2 receptor subunit gene (P = 0.015), and the AlwNI RFLP at the GABAAalpha6 receptor gene (P = 0.013). Significant associations were also found between the alcohol-dependent subjects with Korsakoff's psychosis and the BanI RFLP (P = 0.039) and the AlwNI RFLP (P = 0.003). Haplotype analysis also provided evidence of association when all alcohol-dependent subjects (P = 0.013) and the subjects with Korsakoff's psychosis (P = 0.007) were compared with controls. Our findings provide evidence for a role for the GABAA receptor subunit cluster on chromosome 5q33 in susceptibility to the alcohol dependence syndrome and Korsakoff's psychosis.

Adult↗
PubMed1999

Protein kinase C modulates field-evoked transmitter release from cultured rat cerebellar granule cells via a dendrotoxin-sensitive K+ channel.

The role of protein kinase C (PKC) in the control of neurotransmitter release from cultured rat cerebellar granule cells was investigated. Release of preloaded [3H]-D-aspartate which is incorporated into synaptic vesicles in this preparation was evoked by electrical field stimulation or elevated KCl. PKC activation by phorbol esters resulted in a large facilitation of field-evoked Ca(2+)-dependent [3H]-D-aspartate release and a lesser enhancement of KCl-stimulated release. Inhibition of PKC by Ro 31-8220 or staurosporine virtually abolished field-evoked release but had no effect on KCl-evoked release. Field-evoked, but not KCl-evoked, synaptic vesicle exocytosis monitored by the fluorescent vesicle probe FM2-10 was inhibited by staurosporine. PKC was not directly modulating neurite Ca2+ channels coupled to release, as Ro 31-8220 did not inhibit these channels. Activation or inhibition of PKC modulated field-evoked plasma membrane depolarization, but had no effect on KCl-evoked depolarization, consistent with a regulation of Na+ or K+ channels activated by field stimulation. No modulation of field-evoked neurite Na+ influx was seen using phorbol esters. Phorbol ester-induced facilitation of field-evoked [3H]-D-aspartate release and neurite Ca2+ entry was non-additive with that produced by the specific K+ channel antagonist dendrotoxin-1, suggesting that PKC modulates transmitter release from field-stimulated cerebellar granule cells by inhibiting a dendrotoxin-1-sensitive K+ channel.

Animals↗
PubMed1999

Differential coupling of G-protein-linked receptors to Ca2+ mobilization through inositol(1,4,5)trisphosphate or ryanodine receptors in cerebellar granule cells in primary culture.

Rat cerebellar granule cells in primary culture possess muscarinic, metabotropic glutamatergic, histaminergic and alpha-adrenergic receptors which couple to phosphoinositide-specific phospholipase C. We have determined the ability of these receptors to elevate inositol(1,4,5)trisphosphate and to release intracellular calcium, in order to establish the correlation between these two responses. In resting cerebellar granule cells, only the muscarinic agonist carbachol evoked significant increases in both inositol(1,4, 5)trisphosphate and cytoplasmic free Ca2+. Mild depolarization (20 mM KCl) enhanced inositol(1,4,5)trisphosphate elevation by carbachol and histamine, but not by noradrenaline or the metabotropic glutamate agonist 1S,3R ACPD. In contrast, Ca2+-release responses were modified differently by 20 mM KCl-depolarization: the responses to carbachol, histamine and 1S,3R ACPD, but not the responses to noradrenaline, were markedly enhanced. The contribution of ryanodine-sensitive Ca2+-release channels (ryanodine receptors) to the calcium release signal in depolarized cells was determined. Ryanodine (10 microM) inhibited most effectively the cytoplasmic Ca2+ elevation evoked by 1S,3R ACPD (> 90%), while Ca2+ release upon stimulation by carbachol and histamine was only inhibited by approximately 60% and remained larger than in the absence of KCl. Our data are consistent with a specific coupling between metabotropic glutamate receptors and ryanodine-sensitive Ca2+-release channels which may not require generation of inositol(1, 4,5)trisphosphate.

Animals↗
PubMed1999

Alzheimer's disease: correlation of the suppression of beta-amyloid peptide secretion from cultured cells with inhibition of the chymotrypsin-like activity of the proteasome.

Peptide aldehyde inhibitors of the chymotrypsin-like activity of the proteasome (CLIP) such as N-acetyl-Leu-Leu-Nle-H (or ALLN) have been shown previously to inhibit the secretion of beta-amyloid peptide (A beta) from cells. To evaluate more fully the role of the proteasome in this process, we have tested the effects on A beta formation of a much wider range of peptide-based inhibitors of CLIP than published previously. The inhibitors tested included several peptide boronates, some of which proved to be the most potent peptide-based inhibitors of beta-amyloid production reported so far. We found that the ability of the peptide aldehyde and boronate inhibitors to suppress A beta formation from cells correlated extremely well with their potency as CLIP inhibitors. Thus, we conclude that the proteasome may be involved either directly or indirectly in A beta formation.

Aldehydes↗
PubMed1999

An epidemiological review of red cell transfusions in cancer chemotherapy.

OBJECTIVE: The objective of this chart review was to determine the frequency of transfusion and prevalence of anemia (hemoglobin result < 100 g/L) in patients receiving chemotherapy. DESIGN: This study was a retrospective review of medical charts. SETTING: Patients receiving chemotherapy were included from 12 tertiary care comprehensive cancer centres across Canada. MAIN OUTCOME MEASURE: The primary study outcome measure was red blood cell transfusion rate, controlling for patient variables. RESULTS: The 616 patients included had started chemotherapy in January-June 1992. For each subject, data collection finished 4 weeks after the end of the first regimen or after a maximum follow-up period of 26 weeks. Seventy-two patients (12%; 95% confidence interval 9.5% to 14.5%) were transfused for anemia (reasons other than blood loss), and 28% (95% confidence interval 24.5% to 31.5%) of the subjects were anemic during treatment. The univariate analyses of transfusion for anemia yielded significant associations with prognostic factors. In the multivariate analyses, platinum (odds ratio [OR] = 6.69) and anthracycline (OR = 3.56) chemotherapy, baseline hemoglobin (OR = 0.96) and disease stage (OR = 1.72) were statistically significant contributors. CONCLUSION: In this patient cohort, red blood cell transfusion was infrequent (12%). However, patient groups at high risk of transfusion could be identified, with platinum-based chemotherapy being the most significant contributing factor. The information obtained from this multicentre study may prove helpful in developing supportive care guidelines for the management of chemotherapy-related anemia requiring transfusion.

Adolescent↗
PubMed1999

Protein kinase C activation potentiates the rapid secretion of the amyloid precursor protein from rat cortical synaptosomes.

In this study we have used the presynaptic-rich rat cerebrocortical synaptosomal preparation to investigate the proteolytic cleavage of the amyloid precursor protein (AbetaPP) by the alpha-secretase pathway within the betaA4 domain to generate a soluble secreted N-terminal fragment (AbetaPPs). AbetaPP was detected in crude cortical synaptosomal membranes, although at a lower density than that observed in whole-tissue homogenates. Protein kinase C (PKC) activation induced a translocation of the conventional PKC isoform beta1 and novel PKCepsilon from cytosol to membrane fractions, but there was no alteration in the proportion of AbetaPP associated with the Triton-soluble and -insoluble fractions. AbetaPPs was constitutively secreted from cortical synaptosomes, with this secretion being enhanced significantly by the direct activation of PKC with phorbol ester. The PKC-induced secretion of AbetaPPs was only partially blocked by the PKC inhibitor GF109203X (2.5 microM), whereas the phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein was significantly inhibited by GF109203X. The differential sensitivities of the MARCKS phosphorylation and AbetaPPs secretion to GF109203X may imply that different PKC isoforms are involved in these two events in the synaptosomal system. These findings strongly suggest that the alpha-secretase activity leading to the secretion of AbetaPPs can occur at the level of the presynaptic terminal.

Alzheimer Disease↗
PubMed1998

A protective effect of apolipoprotein E e2 allele on dementia in Down's syndrome.

BACKGROUND: The apolipoprotein E (ApoE) e4 allele has been associated with an increased risk for Alzheimer's disease, whereas the e2 allele has been shown to be protective. Similar effects in Down's syndrome (DS) have been postulated but not yet demonstrated. METHODS: We obtained DNA from 221 DS individuals and from 162 population controls, and 77 DS children. Older DS subjects were evaluated for dementia and compared to age-matched DS controls. RESULTS: The DS sample with dementia (n = 31) had a significantly lower frequency of the ApoE e2 allele compared to age-matched nondemented DS controls (0% vs. 8.3%, p = .0136). The older DS population had a significantly lower frequency of ApoE e4 compared to population controls (11.7% vs. 20.6%, chi-square 8.9, p = .0028). CONCLUSIONS: The lower frequency of the e2 allele in demented DS subjects compared to age-matched nondemented DS controls suggests a protective effect for ApoE e2 in the development of dementia in DS. The lower frequency of ApoE e4 in our older DS sample compared to population controls points to a detrimental effect of the e4 allele on longevity.

Adult↗
PubMed1998

Vasopressin regulated trafficking of a green fluorescent protein-aquaporin 2 chimera in LLC-PK1 cells.

Aquaporin 2 (AQP2) transfected into LLC-PK1 cells functions as a vasopressin-regulated water channel that recycles between intracellular vesicles and the plasma membrane upon vasopressin stimulation. The green fluorescent protein (GFP) of the jellyfish, Aequorea victoria, was used as an autofluorescent tag to monitor AQP2 trafficking in transfected LLC-PK1 cells. Two chimeras were constructed, one in which GFP was fused to the amino-terminus of AQP2 [GFP-AQP2(NT)] and the second in which it was fused to the carboxyl-terminus [AQP2-GFP(CT)]. The GFP-AQP2(NT) chimera trafficked in a regulated pathway from intracellular vesicles to the basolateral plasma membrane in response to vasopressin or forskolin stimulation of cells. In contrast, the AQP2-GFP(CT) chimera expressed in LLC-PK1 cells was localized constitutively on both apical and basolateral plasma membranes. The cellular location of this chimera was not modified by vasopressin or forskolin. Thus, while the GFP-AQP2(NT) chimera will be useful to study AQP2 trafficking in vitro, the abnormal, constitutive membrane localization of the AQP2-GFP(CT) chimera suggests that one or more trafficking signals exist on the carboxyl-terminus of the AQP2 protein.

Amino Acid Sequence↗