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Biomedical subjects

W Howson

Publications and source records attributed to W Howson.

At least 19 recordsLinked to original sources
PubMed1999

Prevalence of the C282Y mutation of the hemochromatosis gene in liver transplant recipients and donors.

Hemochromatosis heterozygotes may be predisposed to end-stage liver disease from other causes. The aims of this study were to determine the prevalence of the hemochromatosis mutation, C282Y, in end-stage liver disease and to determine if transplantation of C282Y heterozygous livers adversely affected survival. The C282Y status of patients who underwent hepatic transplantation and, whenever possible, their donors, was determined and correlated with hepatic iron status. Survival was compared in patients who received livers from heterozygotes and normals. Prevalence of C282Y in recipients was compared with 5,211 voluntary blood donors. Twenty-six C282Y heterozygotes were detected among 304 transplant recipients (8.6%) compared with a prevalence of 8.4% in blood donors. Six of 26 heterozygous recipients (23%) had >/=2+ iron staining in their explanted livers compared with 40 of 277 wild-type livers (14%) (P = ns). There was no significant difference in mean hepatic iron concentration between C282Y heterozygotes and wild-type explanted livers with >/=2+ iron staining. Seven of 31 patients (23%) with alcoholic liver disease were C282Y heterozygotes. Twenty-four heterozygotes were detected in 141 donors (17.0%). Survival did not differ between recipients who received heterozygous or normal livers. The prevalence of C282Y heterozygotes in patients requiring liver transplantation does not differ significantly from the general population. Heterozygotes are not at increased risk of developing end-stage liver disease. Transplantation of C282Y heterozygous livers is a safe, effective practice.

Adolescent↗
PubMed1998

Evaluation of a targeted prodrug strategy of enhance oral absorption of poorly water-soluble compounds.

PURPOSE: The purpose of this research was to examine a targeted prodrug strategy to increase the absorption of a poorly water-soluble lipophilic compound. METHODS: Three water-soluble prodrugs of Cam-4451 were synthesized. The amino acid (Cam-4562, Cam-4580) or phosphate (Cam-5223) ester prodrugs introduced moieties ionized at physiological pH and targeted intestinal brush-border membrane enzymes for reconversion to the parent. Selectivity for reconversion of the three prodrugs was examined in rat intestinal perfusate and brush-border membrane suspensions. Bioavailability of Cam-4451 in rats was evaluated after administering orally as the parent or as prodrugs in a cosolvent vehicle or in methylcellulose. RESULTS: Cam-5223 was highly selective for reconversion at the brush-border, but was rapidly reconverted in intestinal perfusate. Cam-4562 was not as selective but was more stable in the perfusate, whereas Cam-4580 was neither selective nor stable. Oral bioavailability of Cam-4451 was 14% after dosing as the parent in the cosolvent vehicle, 39% and 46%, respectively, as Cam-4562 and Cam-5223. Oral bioavailability was only 3.6% when the parent was dosed in methylcellulose, whereas the bioavailability was 7-fold higher when dosed as the phosphate prodrug. CONCLUSIONS: Water-soluble prodrugs that target brush-border membrane enzymes for reconversion can be useful in improving drug oral bioavailability.

Administration, Oral↗
PubMed1998

The development of rheumatoid arthritis after recombinant hepatitis B vaccination.

OBJECTIVE: Hepatitis B vaccination has been associated with reactive arthritis and rarely rheumatoid arthritis (RA). We defined the clinical, serologic, and immunogenetic background of patients developing RA, soon after recombinant hepatitis B vaccination. METHODS: The clinical, serologic, and HLA antigens of a cluster of firefighters who developed arthritis after prophylactic recombinant hepatitis B vaccination (5 subjects), as well as a second group of sporadic cases of arthritis (6 patients) after hepatitis B vaccination are described. RESULTS: Ten of 11 patients fulfilled revised American College of Rheumatology criteria for RA. All cases had persistent arthritis for more than 6 months; at 48 months followup 2 cases no longer had inflammatory arthritis. Nine patients required disease modifying antirheumatic drugs. Five subjects were HLA-DR4 positive. HLA class II genes expressing the RA shared motif were identified in 9/11 patients genotyped for HLA-DRbeta1 and DQbeta1 alleles (0401, 0101, or 0404). All the firefighters shared the HLA-DRbeta1 allele 0301 and the DQbeta1 allele 0201, with which it is in linkage disequilibrium. CONCLUSION: These polymorphic residues in the binding site of the MHC class II molecules of the affected patients appear capable of binding some peptide sequences of the recombinant vaccine peptides they received and may be responsible for hepatitis B vaccine triggering development of RA in these cases. Recombinant hepatitis B vaccine may trigger the development of RA in MHC class II genetically susceptible individuals.

Adult↗
PubMed1997

Temporal and Quantitative Analysis of Chimerism in Liver and Kidney Transplant Patients: An Enhanced Fluorescence Detection System Allows for More Sensitive Quantitative Detection.

Background: Because spontaneous microchimerism has been reported in stable renal and hepatic allografts, the presence of donor-derived cells in recipient tissues was investigated in kidney and liver tranplant recipients. Methods and Results: Human lymphocyte antigen class II markers and Y-chromosome sequences in male donor-to-female recipient transplants were used for chimeric analysis. Human lymphocyte antigen typing was performed by group-specific polymerase chain reaction amplification and restriction fragment length polymorphism analysis, X-chromosome- and Y-chromosome-specific primers were used in a multiplex polymerase chain reaction analysis. Quantitative Y-chromosome analysis was performed using energy-transfer fluorescence from a nested primer system. Patients who had rejected their grafts were also analyzed, as were a group who were analyzed for chimerism at the time of transplant (day 1) and sequentially at various intervals for up to 3 months. Of 23 long-term kidney patients analyzed, 16 were chimeric by human lymphocyte antigen or sex-determination analysis. In 2 patients whose graft had failed no chimerism was observed. Chimerism in liver patients was detectable on the day of transplant and was maintained for 30 to 120 days as measured at 5-day intervals (these patients continue to be monitored). Quantititative analysis suggested that the ratio of donor to recipient cells was variable in a patient and ranged from greater than 1 in 10(4) to less than 1 in 10(5). An enhanced fluorescence energy-transfer detection system was adopted to increase sensitivity of the polymerase chain reaction detection of chimerism and to quantitate the results. Conclusions: The results indicate that cells from the donor organ migrate into recipient tissues early after transplantation. These cells persist in a majority of patients for at least 3 to 4 years. It has been proposed that tolerance is related to the presence of these "passenger" leukocytes and that dendritic cells play the most important role. The data suggest that the establishment of chimerism plays an important role in graft acceptance in a majoritiy of the kidney and liver patients in this study. These findings also suggest that the levels of chimeric cells, "a quantitative chimerism," may be important in establishing tolerance but further studies are required to support this contention.

Journal Article↗
PubMed1996

The design of dipeptide helical mimetics: the synthesis, tachykinin receptor affinity and conformational analysis of 1,1,6-trisubstituted indanes.

The design and synthesis of conformationally constrained, nonpeptide templates (1,1,6-trisubstituted indanes) which allow the incorporation of two adjacent amino acid side chains, plus a third binding group in an orientation similar to that found in alpha-helices are reported. Six racemic and two homochiral Phe-Phe and Trp-Phe mimetics were synthesised and evaluated in tachykinin receptor binding assays as molecular probes for the binding conformation of the endogenous peptides. Several were found to bind with micromolar affinity to the NK1 and/or NK3 receptor. The conformation of one of the homochiral indanes, (1R)-N-((S)-1-hydroxymethylbenzyl)-1,6-dibenzylindan-1-carbo xamide, was analysed by X-ray crystallography and was found to be in an alpha-helix conformation.

Amino Acid Sequence↗
PubMed1996

Absorption of Cam-2445, and NK1 neurokinin receptor antagonist: in vivo, in situ, and in vitro evaluations.

Cam-2445 is a selective, high-affinity NK1 receptor antagonist that is a potentially useful treatment for arthritis, asthma, migraine, anxiety, psychosis, and emesis. Cam-2445 exhibits low aqueous solubility and high lipophilicity and has a molecular weight of 470. Cam-2445 has poor oral bioavailability and the purpose of this research was to examine the potential barriers to the oral bioavailability of Cam-2445. Cam-2445 was relatively stable at 37 degrees C in 0.1 N HCl, 5 microM alpha-chymotrypsin, rat intestinal perfusate, and in rat jejunal brush border membrane suspension. High permeability was observed from CACO-2 cells and from rat single-pass intestinal perfusions. Cam-2445 was administered as a solution to rats by intravenous (i.v.), oral (p.o.), intraduodenal (i.d.), and intraportal (i.p.v.) routes. The total oral bioavailability was poor at 1.4%. Absorption appeared to be rapid after i.d. dosing; bioavailability was 26%, and 54% of the dose was absorbed intact into the portal system. After i.p.v. dosing, 48% of the dose was available to the systemic circulation. The elimination t1/2 after i.d. dosing (2.91 h) was comparable to that i.v. dosing (2.93 h), whereas it was significantly longer after p.o. dosing (12.4 h). The p.o. dose apparently precipitated in the gastrointestinal (GI) tract, resulting in low oral bioavailability. These results indicated that neither stability in the GI tract nor membrane transport were major obstacles to the absorption of Cam-2445. While hepatic extraction of 52% was significant, the low aqueous solubility of Cam-2445, as well as the differences noted between p.o. and i.d. studies, strongly support GI dissolution and/or precipitation as the limiting factor for the oral bioavailability of the compound.

Animals↗
PubMed1996

Alanine scan and N-methyl amide derivatives of Ac-bombesin[7-14]. Development of a proposed binding conformation at the neuromedin B (NMB) and gastrin releasing peptide (GRP) receptors.

Alanine and N-methylation scans together with molecular modelling were implemented in order to propose a binding conformation of the minimum active fragment of bombesin (BB), Ac-BB[7-14], to the gastrin releasing peptide (GRP) and neuromedin B (NMB) receptors. These data are also used to critically evaluate the previously proposed binding conformations such as alpha-helix and antiparallel beta-sheets. This shows that the previously reported conformations do not satisfy the experimental data. A new binding conformation of Ac-BB[7-14] is proposed consisting of three consecutive gamma-turns followed by a bend and finishing with two gamma-turns. This low energy conformation (analogous to a fragment of thymidylate synthase, 2TSC) of bombesin stabilized by five internal hydrogen bonds, and with the side chains of residues Trp8 and Leu13 held on the same side of the peptide, is in agreement with the experimentally observed data. This and the results of molecular modelling may aid in the synthesis of conformationally restricted high affinity bombesin analogues and/or high affinity template-based GRP or NMB receptor agonists and antagonists.

Amides↗
PubMed1995

Quantitative structure-activity relationships (QSARs) of N-terminus fragments of NK1 tachykinin antagonists: a comparison of classical QSARs and three-dimensional QSARs from similarity matrices.

The ability of three-dimensional quantitative structure-activity relationships (QSARs) derived from classical QSAR descriptors and similarity indices to rationalize the activity of 28 N-terminus fragments of tachykinin NK1 receptor antagonists was examined. Two different types of analyses, partial least squares and multiple regression, were performed in order to check the robustness of each derived model. The models derived using classical QSAR descriptors lacked accurate quantitative and predictive abilities to describe the nature of the receptor-inhibitor interaction. However models derived using 3D QSAR descriptors based on similarity indices were both robust and significantly predictive. The best model was obtained through the statistical analysis of molecular field similarity indices (n = 28, r2 = 0.846, r(cv)2 = 0.737, s = 0.987, PRESS = 7.102) suggesting that electronic and size-related properties are the most relevant in explaining the affinity data of the training set. The overall quality and predictive ability of the models applied to the test set appear to be very high, since the predicted affinities of three test compounds agree with the experimentally determined affinities obtained subsequently within the experimental error of the binding data.

Carbamates↗
PubMed1994

Rational design of high affinity tachykinin NK2 receptor antagonists.

The rational discovery of a high affinity NK2 receptor antagonist is described utilizing a general strategy for peptoid design. The contribution to NK2 receptor binding affinity for each amino acid of the hexapeptide 'minimum fragment': Leu-Met-Gln-Trp-Phe-GlyNH2 (8c), was examined by preparing derivatives where each amino acid in turn was replaced with Ala in an 'alanine scan'. The results from this study indicated the primary importance of the Trp and Phe side-chain for binding and led to the observation that Z-Trp-PheNH2 (9a) is a micromolar affinity NK2 receptor dipeptide lead. Further exploration of structure-affinity via conformationally restricted analogues and N- and C-terminus modifications gave a selective, nanomolar affinity NK2 receptor antagonist, (2,3di-CH3OPh)CH2OCO(S)Trp(S)alpha-MePheGlyNH2, PD 147714 (19) with an K(i) = 1.4 nM (hamster urinary bladder membranes and using [125I]-iodohistidyl-NKA (0.1 nM) as the radioligand).

Amino Acid Sequence↗
PubMed1994

Rational design of high affinity tachykinin NK1 receptor antagonists.

The rational design of a non-peptide tachykinin NK1 receptor antagonist, [(2-benzofuran)-CH2OCO]-(R)-alpha-MeTrp-(S)-NHCH(CH3)P h (28, PD 154075) is described. Compound 28 has a Ki = 9 and 0.35 nM for the NK1 receptor binding site in guinea-pig cerebral cortex membranes and human IM9, cells respectively (using [125I] Bolton-Hunter-SP as the radioligand). It is a potent antagonist in vitro where it antagonises the contractions mediated by SPOMe in the guinea-pig ileum (KB = 0.3 nM). Compound 28 is active in vivo in the guinea-pig plasma extravasation model, where it is able to block the SPOMe-induced protein plasma extravasation (monitored by Evans Blue) in the bladder with an ID50 of 0.02 mg kg-1 iv.

Animals↗
PubMed1994

'Peptoid' design.

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Amino Acid Sequence↗
PubMed1993

Structure-activity requirements of bombesin for gastrin-releasing peptide- and neuromedin B-preferring bombesin receptors in rat brain.

The pharmacological profile of [125I][Tyr4]bombesin binding to gastrin-releasing peptide- and neuromedin B-preferring sites has been investigated in rat cerebral cortex and olfactory bulb membranes, respectively. [125I][Tyr4]bombesin specific binding to cerebral cortex membranes was displayed biphasically by gastrin releasing peptide and [D-Phe6]bombesin-(6-13)-ethyl amide. In the presence of 10 mM neuromedin B, displacement curves for bombesin-related peptides were monophasic with gastrin releasing peptide displaying approximately 100-fold higher affinity than neuromedin B. In olfactory bulb membranes, [125I][Tyr4]bombesin binding was also displaced biphasically by gastrin releasing peptide, [D-Phe6]bombesin-(6-13)-ethyl amide and neuromedin B. In the presence of 10 microM [D-Phe6]bombesin-(6-13)-ethyl ester, displacement curves were monophasic with neuromedin B possessing approximately 10-fold higher affinity than gastrin-releasing peptide. Under these conditions, successive deletion of N-terminal amino acids from bombesin-(1-14) was well tolerated at both sites, with little loss in affinity up to bombesin-(5-14). A 5- to 10-fold drop in affinity was observed at both sites with bombesin-(6-14), whilst the octapeptide acetyl-bombesin-(7-14) displayed similar affinities to bombesin-(1-14). Bombesin-(8-14), -(9-14) and -(10-14) were essentially inactive (IC50 > 10 microM). C-terminal deletion of Met24 (bombesin-(1-13)) resulted in 100-fold loss of affinity at the gastrin-releasing peptide site and complete loss of affinity at the neuromedin B site. Fragments smaller than bombesin-(1-13) were virtually inactive at either site.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Typing of serum-soluble HLA-B27 antigen by ELISA.

An ELISA using serum as soluble HLA antigen source was developed for HLA-B27 typing. Two sandwich assays were run in parallel. The first assay utilized a monoclonal antibody (mAb) reacting with a determinant expressed by both HLA-B7 and B27 antigens; the other assay utilized a mAb reactive with HLA-B7 antigens but not with HLA-B27 antigens. After incubation with serum samples, bound HLA antigen was detected using an anti-beta 2m antibody conjugated to peroxidase and a chromogenic substrate. Absorbance of each well was measured at 490 nm. Based on analysis of absorbances obtained with panels of specimens of known HLA phenotypes, a mathematical algorithm was developed to derive the specimen HLA-B27 phenotype from its ELISA absorbance values. Despite the lack of monospecific mAb, an accurate HLA-B27 typing was possible. 362 specimens (including 151 HLA-B27-positive) were tested. Agreement between microlymphocytotoxicity and ELISA was 99.2%. No correlation between the level of HLA-B27 antigen reactivity and the amount of total HLA class I antigen in serum was observed. This report demonstrates the possibility of using serum-soluble HLA antigen and ELISA technology for histocompatibility testing. The assay offers several significant advantages over microlymphocytotoxicity: no need for cell preparation, batch testing capabilities and objective, reproducible interpretation of results.

Algorithms↗
PubMed1991

Subpopulations of GABA-mediated synaptic potentials in slices of rat dorsal striatum are differentially modulated by presynaptic GABAB receptors.

gamma-Aminobutyric acid (GABA)-mediated synaptic potentials in rat dorsal striatum in vitro were reduced in amplitude by the GABAB receptor agonists baclofen and 3-aminopropyl-(methyl)-phosphinic acid (SK&F 97541), without any detectable postsynaptic effect. Synaptic potentials in 40% of neurones were distinctly multiphasic, the components of which exhibited a differential sensitivity to GABAB agonists. One population of GABA-releasing neurones within the striatum had presynaptic GABAB autoreceptors, whereas others were not directly affected by GABAB agonists.

Animals↗
PubMed1991

Phosphinic acid analogues of GABA are antagonists at the GABAB receptor in the rat anococcygeus.

CGP 35348 (3-aminopropyl(diethoxymethyl)phosphinic acid) and 3-aminopropyl(n-hexyl)phosphinic acid (3-APHPA) were tested in the rat anococcygeus muscle against CGP 27492 (3-aminopropylphosphinic acid), a selective GABAB agonist, for their antagonist activity. Their antagonist potency was compared with that of 2-hydroxysaclofen. The pA2 values for CGP 35348, 3-APHPA and 2-hydroxysaclofen were 5.38, 4.86, 4.45 respectively in the rat anococcygeus muscle. These results confirm the previous reports of GABAB antagonist activity for these compounds and show a marginal improvement in potency over 2-hydroxysaclofen.

Animals↗
PubMed1991

A comparison of the relative activities of a number of GABAB antagonists in the isolated vas deferens of the rat.

1. A series of GABAB receptor antagonists were tested against (+/-)-baclofen for activity on the presynaptic GABAB receptor in the rat vas deferens. 2. All the antagonists tested caused a rightward shift in the concentration-response curve to (+/-)-baclofen. 3. pA2 values calculated from full Schild analysis were as follows: phaclofen, pA2 = 4.3; delta-amino valeric acid, pA2 = 4.4; 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP 35348), pA2 = 5.0; 3-amino-propyl(n-hexyl)phosphinic acid (3-APHPA), pA2 = 4.5. 4. These results show that none of the above compounds possess potent antagonist activity at the GABAB receptor (i.e. pA2 > 6) in this peripheral tissue. In addition, the more recently available phosphinic acid antagonists, appear to offer no great advance over the GABAB antagonists previously available.

Animals↗