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Biomedical subjects

B Walker

Publications and source records attributed to B Walker.

At least 73 records · Page 4Linked to original sources
PubMed1998

Synthesis and proteinase inhibitory properties of diphenyl phosphonate analogues of aspartic and glutamic acids.

The synthesis of diphenyl phosphonate analogues of aspartic and glutamic acid, and their inhibitory activity against S. aureus V8 protease and granzyme B, is described. The study has revealed difficulties with protecting group compatibility in the synthesis of these analogues. Two analogues, Acetyl. AspP (OPh)2 and Acetyl.GluP (OPh)2 were found to function as irreversible inactivators of V8 proteinase, yet exhibit no activity against granzyme B.

Aspartic Acid↗
PubMed1998

Inhibitors of the chymotrypsin-like activity of proteasome based on di- and tri-peptidyl alpha-keto aldehydes (glyoxals).

A series of peptidyl alpha-keto aldehydes (glyoxals) have been synthesised as putative inhibitors of the chymotryptic-like activity of proteasome. The most potent peptides, Cbz-Leu-Leu-Tyr-COCHO and Bz-Leu-Leu-Leu-COCHO, function as slow-binding reversible inhibitors, exhibiting final Ki values of approximately 3.0 nM. These are among the lowest values so far reported for (tri)peptide-based aldehyde-related inhibitors.

Chymotrypsin↗
PubMed1998

Randomised comparison of percutaneous angioplasty vs continued medical therapy for hypertensive patients with atheromatous renal artery stenosis. Scottish and Newcastle Renal Artery Stenosis Collaborative Group.

BACKGROUND: Data from randomised studies are lacking on the value of interventional procedures in the management of atheromatous renal artery stenosis. This randomised prospective trial compared the effects on blood pressure (BP) and renal function of percutaneous transluminal angioplasty vs medical therapy in hypertensive patients with both unilateral and bilateral disease. METHODS: A total of 135 eligible patients were identified, of whom 55 (44%) were randomised. Eligible patients had sustained hypertension, with a minimum diastolic BP of 95 mm Hg on at least two anti-hypertensive drugs. Renal artery stenosis was defined by renal angiography as at least 50% stenosis in the affected vessel. All patients were observed during an initial 4-week run-in period on a fixed drug regimen and subsequent changes measured from this 4-week baseline. RESULTS: Blood pressure fell during the run-in period in all groups. In patients with bilateral renal artery stenosis randomised to angioplasty, a statistically significant (P<0.05) fall in BP was observed at latest follow-up (range 3-54 months). The mean fall in BP at latest follow-up in the angioplasty group, corrected for the medical group response, was 26/10 mm Hg. In patients with unilateral renal artery stenosis, no statistically significant or clinically important differences in outcome were observed between the two groups. No significant differences or trends in serum creatinine were observed between or within any group during follow-up. Major outcome events (death, myocardial infarction, heart failure, stroke, dialysis) were similar in the angioplasty and medical groups during follow-up. In the 40/135 patients undergoing angioplasty, serious or potentially serious complications attributable to the procedure were observed in 11 patients, bleeding at the arterial site (8 patients) being the most frequent. CONCLUSIONS: In hypertensive patients with atheromatous renal artery stenosis, percutaneous renal angioplasty results in a modest improvement in systolic BP compared with medical therapy alone. This benefit was confined to patients with bilateral disease. No patient was 'cured', renal function did not improve, and intervention was accompanied by a significant complication rate.

Adult↗
PubMed1998

Regional implementation of a national cancer policy: taking forward multiprofessional, collaborative cancer care.

The vision of the Calman-Hine paper is of patient-centred care, delivered by co-ordinated services which have genuine partnerships with each other. There is integration of other providers of support, to meet psychological and non-clinical needs. There is access to palliative care when required, from diagnosis onwards, and not just in the terminal stage. Effective communications and networks are the keys to making this vision a reality. Our recommendations are based upon in-depth discussions with purchasers, doctors and nurses, and others involved with cancer services within hospitals or the community across the region. They reflect the priorities placed on the development of good practice. Purchasers and providers should work together to implement these guidelines.

Communication↗
PubMed1998

Evaluation of a candidate human immunodeficiency virus type 1 (HIV-1) vaccine in macaques: effect of vaccination with HIV-1 gp120 on subsequent challenge with heterologous simian immunodeficiency virus-HIV-1 chimeric virus.

Human immunodeficiency virus type 1 (HIV-1) envelope vaccines can now be evaluated for efficacy in macaques by challenging with chimeric viruses in which the env, tat and rev genes of simian immunodeficiency virus (SIV) have been replaced by those of HIV-1. Most experiments have so far been conducted using gp120 molecules derived from T-cell-adapted LAI or MN strains of HIV-1, which predominantly use the CXCR-4 co-receptor. These vaccines protect against infection by apathogenic chimeric virus carrying the same envelope sequences. In the experiment described here, four macaques were vaccinated with W61D gp120 derived from a low passage Dutch isolate and capable of inhibiting the binding of MIP1beta to the co-receptor CCR-5. This vaccine was potent, inducing high titres of binding and neutralizing antibodies against the homologous HIV-1 and tenfold lower titres against a heterologous challenge virus (SHIV(SF33)) in which the env, tat and rev genes of SIV had been replaced by those of a San Francisco isolate, HIV-1(SF33). Despite strong immune responses to the vaccine there was no evidence that it protected against challenge with this chimeric virus. The antigenic divergence between vaccine and challenge virus or the increased virulence of the challenge virus may be responsible for the inability of this vaccine to protect against infection by SHIV(SF33).

AIDS Vaccines↗
PubMed1997

Identification of potential activators of proteinase-activated receptor-2.

In order to identify physiological activators of proteinase-activated receptor-2 (PAR-2), a peptide chloromethane inhibitor (biotinyl-Ser-Lys-Gly-Arg-CH2Cl) based on the cleavage site for activation of PAR-2 was synthesised and tested with 12 trypsin-like serine proteinases. The second-order rate constant (ki/Ki) for the formation of the covalent proteinase-inhibitor complex varied by 2 x 10(5)-fold between the proteinases. Biotinyl-Ser-Lys-Gly-Arg-CH2Cl reacted very rapidly with trypsin, acrosin from sperm and tryptase from mast cells: the ki/Ki values with these proteinases were greater than 10(5) M(-1) x s(-1). Thus, the specificity of these proteinases matched the sequence of the activation site of PAR-2 and it can be concluded that these proteinases are potential physiological activators of PAR-2.

Animals↗
PubMed1997

Evaluation of some fluorogenic substrates for continuous assay of aminopeptidase P.

Three potential fluorogenic substrates for assay of aminopeptidase P (AP-P) have been prepared and evaluated, using enzyme purified from porcine kidney. They are based on internal quenching of the synthetic, fluorescent amino acid (R, S)-2-amino-3-(7-methoxy4-coumaryl)propanoic acid ((R,S)-Amp) by a 2, 4dinitrophenyl (DNP) group. The compounds are X-Pro-Pro-(R, S)-Amp-NH2, where X is H-Lys(epsilon-DNP), H-Orn(delta-DNP), or L-2-amino-3-(DNP)aminopropionic acid. The first two were found to be excellent substrates for AP-P, with respective Km values of 4.8 and 5.2 microM. An advantageous feature is that under the conditions of assay, using 4-mm2 cells, the substrates are without noticeable quenching effect on the fluorescence of Pro-Pro-(R,S)-Amp-NH2 (the product liberated by the action of AP-P). At concentrations greater than about 30-50 microM, both substrates appear to inhibit the enzyme, but this has little practical consequence since assays can be carried out at substrate concentrations, giving up to approximately 80% of Vmax without this inhibitory effect being noticeable. The Lys derivative was found to be a very useful substrate for a continuous assay for AP-P and equally good in a discontinuous assay of multiple samples using microtiter plates. The racemic center at the Amp residue did not prevent total hydrolysis of the Lys derivative, suggesting that subsite specificity in AP-P does not extend as far as the P3' position.

Aminopeptidases↗
PubMed1997

Transmembrane beta-barrel of staphylococcal alpha-toxin forms in sensitive but not in resistant cells.

Staphylococcal alpha-toxin is a 293-residue, single-chain polypeptide that spontaneously assembles into a heptameric pore in target cell membranes. To identify the pore-forming domain, substitution mutants have been produced in which single cysteine residues were introduced throughout the toxin molecule. By attaching the environmentally sensitive dye acrylodan to the sulfhydryl groups, the environment of individual amino acid side chains could be probed. In liposomes, a single 23-amino acid sequence (residues 118-140) was found to move from a polar to a nonpolar environment, indicating that this sequence forms the walls of the pore. However, periodicity in side chain environmental polarity could not be detected in the liposomal system. In the present study, the fluorimetric analyses were extended to physiological target cells. With susceptible cells such as rabbit erythrocytes and human lymphocytes, the 23 central amino acids 118-140 were again found to insert into the membrane; in contrast to the previous study with liposomes, the expected periodicity was now detected. Thus, every other residue in the sequence 126-140 entered a nonpolar environment in a striking display of an amphipathic transmembrane beta-barrel. In contrast, human granulocytes were found to bind alpha-toxin to a similar extent as lymphocytes, but the heptamers forming on these cells failed to insert their pore-forming domain into the membrane. As a consequence, nonfunctional heptamers assembled and the cells remained viable. The data resolve the molecular organization of a pore-forming toxin domain in living cells and reveal that resistant cells can prevent insertion of the functional domain into the bilayer.

Adenosine Triphosphate↗
PubMed1997

Peptidyl inverse esters of p-methoxybenzoic acid: a novel class of potent inactivator of the serine proteases.

A series of novel synthetic peptides, containing a C-terminal beta-amino alcohol linked to p-methoxybenzoic acid via an ester linkage, have been prepared and tested as inhibitors against typical members of the serine protease family. For example, the sequences Ac-Val-Pro-NH-CH-(CH2-C6H5)-CH2O-CO-C6H4-OCH3 (I) and Ac-Val-Pro-NH-CH-[CH-(CH3)2]-CH2O-CO-C6H4-OCH3 (II), which fulfil the known primary and secondary specificity requirements of chymotrypsin and elastase respectively, have been found to behave as exceptionally potent irreversible inactivators of their respective target protease. Thus I was found to inactivate chymotrypsin with an overall second-order rate constant (k2/Ki) of approx. 6.6x10(6) M-1. s-1, whereas II is an even more potent inactivator of human neutrophil elastase, exhibiting a second-order rate constant of inactivation of approx. 1.3x10(7) M-1.s-1. These values represent the largest rate constants ever reported for the inactivation of these proteases with synthetic peptide-based inactivators. On prolonged incubation in substrate-containing buffers, samples of the inactivated proteases were found to regain activity slowly. The first-order rate constants for the regeneration of enzymic activity from chymotrypsin and human neutrophil elastase inactivated by I and II respectively were determined to be approx. 5.8x10(-5) s-1 and approx. 4.3x10(-4) s-1. We believe that the most likely mechanism for the inactivation and regeneration of enzymic activity involves the formation and subsequent slow hydrolysis of long-lived acyl enzyme intermediates.

Catalysis↗
PubMed1997

Evasion of cytotoxic T lymphocyte (CTL) responses by nef-dependent induction of Fas ligand (CD95L) expression on simian immunodeficiency virus-infected cells.

Inoculation of macaques with live attenuated SIV strains has been shown to protect against subsequent challenge with wild-type SIV. The protective mechanism(s) remain obscure. To study the effect in more detail, we have investigated the role of virus-specific CTL responses in macaques infected with an attenuated SIV strain (pC8), which has a four-amino acid deletion in the nef gene, as compared with the wild-type SIVmac32H clone (pJ5). Cynomolgus macaques infected with pC8 were protected against subsequent challenge with pJ5 and did not develop any AIDS-like symptoms in the 12 months after infection. The pC8-induced protection was associated with high levels of virus-specific CTL responses to a variety of viral antigens. In contrast, pJ5-infected macaques had little, if any, detectable CTL response to the viral proteins after three months. The latter group of macaques also showed increased Fas expression and apoptotic cell death in both the CD4(+) and CD8(+) populations. In vitro, pJ5 but not pC8 leads to an increase in FasL expression on infected cells. Thus the expression of FasL may protect infected cells from CTL attack, killing viral-specific CTLs in the process, and providing a route for escaping the immune response, leading to the increased pathogenicity of pJ5. pC8, on the other hand does not induce FasL expression, allowing the development of a protective CTL response. Furthermore, interruption of the Fas-FasL interaction allows the regeneration of viral-specific CTL responses in pJ5-infected animals. This observation suggests an additional therapeutic approach to the treatment of AIDS.

Acquired Immunodeficiency Syndrome↗