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Biomedical subjects

M Lees

Publications and source records attributed to M Lees.

30 records · Page 2Linked to original sources
PubMed1993

Catabolism of intact type VI collagen microfibrils: susceptibility to degradation by serine proteinases.

We present the first direct biochemical evidence for the turnover of intact type VI collagen microfibrils. Matrix-degrading enzymes of the serine proteinase class, including rat mast cell chymases I and II, human mast cell tryptase, neutrophil elastase, cathepsin G and trypsin, were able to catabolize intact type VI collagen microfibrils isolated from foetal bovine skin and metabolically labelled intact type VI collagen immunoprecipitated from fibroblast culture medium. By contrast, intact type VI collagen was not degraded by the human matrix metalloproteinases, MMP-1, MMP-2, MMP-3 and MMP-9. These data have important implications for the stability of type VI collagen in connective tissues and highlight the potential role of serine proteinases both in normal type VI collagen turnover and in inflammatory conditions characterized by matrix degradation.

Animals↗
PubMed1993

Differential expression of gelatinase B (MMP-9) and stromelysin-1 (MMP-3) by rheumatoid synovial cells in vitro and in vivo.

Primary cultures of adherent rheumatoid synovial cells (ASC) are comprised of variable proportions of fibroblasts, macrophages and stellate cells (activated fibroblasts). These cultures were shown to produce the metalloproteinases stromelysin-1 (MMP-3), gelatinase A (MMP-2) and gelatinase B (MMP-9) by Western blotting and zymography techniques. Immunolocalisation studies showed that MMP-3 was mainly produced by the fibroblastic cells whereas MMP-9 was restricted to macrophages (CD68 positive). Subcultured synovial fibroblasts, devoid of macrophages, did not produce MMP-9 as judged by zymography and immunolocalisation; but when stimulated with phorbol myristate acetate and interleukin-1 alpha both MMP-9 and MMP-3 were co-expressed. These 'activated' fibroblasts assumed a dendritic or stellate morphology, which in localisation studies was usually associated with enhanced enzyme production. Immunolocalisation studies of rheumatoid synovial tissue showed that relatively few cells were positive for MMP-3 and MMP-9. Localisation of MMP-9 corresponded to a proportion of macrophages positive for the CD68 marker throughout the synovial tissue. MMP-3 localisation was not associated with the macrophage marker, but was observed in both the synovial lining layer and deeper stromal locations. Widespread distribution of both enzymes was not observed in fresh tissues, but this increased in tissues subjected to short-term explant cultures. Thus, both in vitro and in vivo studies indicated that synovial fibroblasts or B-cells are effective producers of MMP-3 whereas macrophages elaborate MMP-9, observations that demonstrated different metalloproteinase phenotypes under similar environmental conditions.

Arthritis, Rheumatoid↗
PubMed1991

Combining binocular and monocular curvature features.

A study is reported of the perception of visual surfaces in wire-frame stimuli generated by combinations of monocular surface contours and binocular disparity that provide differing information about 3-D relief. Observers vary considerably in the relative contribution made by the binocular and monocular cues to the perception of overall 3-D form. Without training, many observers may entirely fail to perceive surface curvature from the binocular disparity patterns, interpreting the form of the surface only according to the monocular information. For other observers, both cues contribute to the end percept, with the monocular interpretation dominating where the disparity information indicates planarity and with disparity dominating where disparity information suggests curvature and the monocular interpretation suggests planarity. Where stereo and monocular interpretations indicate inconsistent surface curvature features at a common location, more complex resolution strategies are suggested.

Cues↗
PubMed1990

Influence of atrial natriuretic peptide on mammalian large intestine.

Atrial natriuretic peptide is distributed in a number of organs including the large intestine. Atrial natriuretic peptide has potent diuretic and natriuretic properties and appears to play a central role in fluid and electrolyte homeostasis by an action on the kidney. We examined the influence of atrial natriuretic peptide on mammalian colon because this organ is also intimately involved in homeostasis. Segments of the distal colons of male Sprague-Dawley rats were stripped of muscle layers and mounted in flux chambers. Atrial natriuretic peptide, when added to the serosal side of the mucosa, in concentrations ranging from 10(-8)-10(-5) M, caused a rapid, concentration-dependent increase in short-circuit current, transmucosal electrical potential difference, and conductance. The response to atrial natriuretic peptide was inhibited by (a) chloride-free solution on the serosal surface; (b) pretreatment of the tissues with the chloride channel blocker, diphenylamine-2-carboxylate (10(-3) M mucosally); (c) pretreatment with d,l-verapamil (10(-4) M mucosally and serosally); (d) calcium-free solution on the serosal surface; (e) pretreatment with tetrodotoxin (10(-7) M to serosal surface); and (f) pretreatment with atropine (10(-5) M serosally). However, the response to atrial natriuretic peptide was not influenced by pretreatment with amiloride (10(-4) M to mucosal and serosal surfaces) or piroxicam (10(-5) M serosally). Atrial natriuretic peptide did not elicit an increase in short-circuit current and potential difference across T84 cells derived from a human colonic carcinoma cell line, suggesting that the response to atrial natriuretic peptide is not due to a direct effect on colonocytes. These findings suggest that atrial natriuretic peptide acts by a calcium-mediated secretory mechanism involving cholinergic nerves and is likely to be involved in the endogenous neurohumoral regulation of ion transport in the mammalian colon.

Animals↗
PubMed1988

Activation of protein kinase C attenuates prostaglandin E2 responses in a colonic cell line.

We examined the possibility that the protein kinase C pathway may interact with the adenosine 3',5'-cyclic monophosphate (cAMP) pathway in intestinal epithelium by studying the influence of phorbol esters on the response to prostaglandin E2 (PGE2) in a colonic epithelial cell line. Pretreatment of T84 cells with 4 beta-phorbol 12,13-dibutyrate (PDB) markedly attenuated the rise in short-circuit current provoked by PGE2, a receptor-mediated cAMP agonist. The EC50 of this effect was 52 nM PDB with a half time of 4-6 min. The responses to nonreceptor-mediated agonists, forskolin and dibutyryl cAMP, were unaffected by phorbol ester. PDB also reduced the ability of PGE2 to stimulate adenylate cyclase activity in these cells. The accumulation of cAMP in response to PGE2 was inhibited by PDB (EC50 38 nM), an effect mimicked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol. In addition, PGE2 stimulation of adenylate cyclase in membranes from PDB-treated cells was reduced by 30-40%. Inhibition was not mediated via the catalytic or regulatory subunit of the adenylate cyclase, implying an action involving desensitization of PGE2 receptors. These results provide evidence of a complex interrelationship between protein kinase C- and cAMP-mediated pathways that might be important in regulating the cellular response to secretagogues.

Animals↗
PubMed1987

Evidence that PGE2 stimulates intestinal epithelial cell adenylate cyclase by a receptor-mediated mechanism.

These studies were performed to examine whether prostaglandin E2 stimulates intestinal epithelial secretion via a receptor-mediated or non-receptor-mediated activation of adenylate cyclase. Solubilization of epithelial cell adenylate cyclase with Lubrol PX, which separates the receptor moiety of the cyclase from the remainder of the complex, inhibited the prostaglandin E2 stimulation of the cyclase. A similar result was obtained with VIP, which activates adenylate cyclase via a receptor-mediated mechanism, whereas fluoride, gamma S-GTP, and forskolin, which activate the cyclase via non-receptor-mediated mechanisms, all stimulated solubilized adenylate cyclase. In addition, prostaglandin E2 and VIP both showed a dependence on GTP for adenylate cyclase stimulation while fluoride and forskolin did not. These data suggest that prostaglandin E2 activates intestinal mucosal adenylate cyclase by a receptor-mediated mechanism. The presence of such receptors lends support to the possibility that prostaglandins have a physiological role in the control of mucosal transport.

Adenylyl Cyclases↗
PubMed1987

Site and mechanisms of action of kinins in rat ileal mucosa.

Kinin-induced secretion in the intestine is accompanied by marked increases in mucosal adenosine 3', 5'-cyclic monophosphate (cAMP) and prostanoids that undoubtedly contribute to the overall secretory response. The cellular site at which these effects are initiated is unclear although a recent hypothesis has suggested the epithelial cell as the target for kinin action (6). We have investigated the effects of kallidin on the phospholipase-prostanoid-cAMP pathway in whole ileal mucosa and in epithelial cells isolated from the same tissue in the rat. Kallidin (1 microM) stimulated a marked rise (24 to 30-fold) in PG (prostaglandin) E2 release from the serosal surface of stripped ileal mucosa within 1-2 min, which correlated closely with the rise in mucosal short-circuit current. Mucosal cAMP levels were also increased two to threefold by kallidin. However, kinins were unable to elicit effects under the same conditions in suspensions of viable epithelial cells. PGE2 release was unaffected by kallidin or bradykinin at concentrations up to 100 microM, whereas cAMP levels could be stimulated by forskolin and PGE2 but not by kinin. Studies of intestinal phospholipase A2 (PLA2) activity also suggest a nonepithelial site for kinin action. This enzyme is responsible for liberating arachidonic acid from cellular phospholipids and has been shown to be activated by kinins in several tissues. In the intestine, PLA2 activity was found to be concentrated within the subepithelium with significantly lower levels in the epithelium itself. In addition, kallidin was unable to influence phospholipid labeling (an indirect measure of PLA2 activity) in cells incubated with [14C]arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Cost-effectiveness of pergolide compared to bromocriptine in the treatment of Parkinson's disease: a decision-analytic model.

OBJECTIVE: To develop a decision-analytic model to assess the cost-effectiveness of pergolide versus bromocriptine in the treatment of Parkinson's disease (PD). METHODS: A Markov decision-analytic model is used to examine cost-effectiveness. The model ran for 20 cycles of 6 months' duration, and the patients progress through six stages: Hoehn-Yahr stages 1-5 and death. The transitional probabilities for each stage are derived from a 12-year longitudinal study of patients with PD. The costs in the model are derived from an expert panel containing six Australian neurologists. A review of the randomized controlled trials comparing the efficacy and safety of pergolide versus bromocriptine was undertaken. Five studies were identified, with four showing that pergolide offers superior efficacy when compared to bromocriptine. The Mizuno et al. (1995) study was the largest of the controlled trials and also measured patient Hoehn-Yahr status before and after treatment. This was identified as the most appropriate source of relative efficacy data for the model. The model examined various scenarios based on alternate durations of superior clinical benefit with pergolide compared to bromocriptine. The main analysis assumed that patients in each arm of the model would have identical Hoehn-Yahr status by the fifth year. Sensitivity analysis was used to determine cost-effectiveness in the case where the therapeutic benefit was of a shorter duration. RESULTS: The Mizuno study indicates that an additional 19.09% of patients improved by at least one stage on pergolide over bromocriptine, with an odds ratio of 2.26 (p < .01). The total health care cost per patient over the 10-year period was $46,323 in the pergolide treatment arm and $47,351 in the bromocriptine treatment arm, an incremental saving of $1028. Patients also spent extra time in Hoehn-Yahr stages 1, 2, and 3. In sensitivity analyses, when the benefit from pergolide expired between 6 months and 5 years after treatment cessation, cost savings ranged from $68 to $2535. CONCLUSION: Pergolide is cost saving and more efficacious than bromocriptine, and is therefore cost-effective.

Antiparkinson Agents↗
PubMedDate not supplied

Interpretation of combined 2H SNIF/NMR and 13C SIRA/MS analyses of fruit juices to detect added sugar.

The site-specific natural isotopic fractionation studied by nuclear magnetic resonance (SNIF/NMR) method measures site-specific isotope contents in a variety of organic compounds by deuterium nuclear magnetic resonance spectroscopy. This technique, together with SIRA/MS (stable isotope ratio analysis/mass spectrometry) provides a powerful tool for food authentication and characterization. By using the ethanol resulting from sugar fermentation as a molecular probe, SNIF/NMR (deuterium) and SIRA/MS (13C) have been used together for authentication of fruit juices. The influence of deuterium content of the fermentation water on the isotopic parameters is shown and a means for normalizing the results is proposed. A large number of authentic juices have been analyzed to define the variation of isotopic ratios in natural juices. On the basis of these data, a set of rules was designed to enable interpretation of isotopic parameters in terms of possible adulteration of fruit juices by sugar addition. Results of analyses of Florida orange juice are presented. Orange juice samples from Brazil and Israel are included as 2 extreme cases. Assignment limits for a sample of orange juice of unknown origin also are given. These assignment limits are also provided for apple and grapefruit juices.

Beverages↗