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Biomedical subjects

A Hallett

Publications and source records attributed to A Hallett.

At least 19 recordsLinked to original sources
PubMed2000

Bradyzide, a potent non-peptide B(2) bradykinin receptor antagonist with long-lasting oral activity in animal models of inflammatory hyperalgesia.

Bradyzide is from a novel class of rodent-selective non-peptide B(2) bradykinin antagonists (1-(2-Nitrophenyl)thiosemicarbazides). Bradyzide has high affinity for the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in NG108-15 cells and in Cos-7 cells expressing the rat receptor with K(I) values of 0.51+/-0.18 nM (n=3) and 0.89+/-0.27 nM (n=3), respectively. Bradyzide is a competitive antagonist, inhibiting B(2) receptor-induced (45)Ca efflux from NG108-15 cells with a pK(B) of 8.0+/-0.16 (n=5) and a Schild slope of 1.05. In the rat spinal cord and tail preparation, bradyzide inhibits bradykinin-induced ventral root depolarizations (IC(50) value; 1.6+/-0.05 nM (n=3)). Bradyzide is much less potent at the human than at the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in human fibroblasts and in Cos-7 cells expressing the human B(2) receptor with K(I) values of 393+/-90 nM (n=3) and 772+/-144 nM (n=3), respectively. Bradyzide inhibits bradykinin-induced [(3)H]-inositol trisphosphate (IP(3)) formation with IC(50) values of 11.6+/-1.4 nM (n=3) at the rat and 2.4+/-0.3 microM (n=3) at the human receptor. Bradyzide does not interact with a range of other receptors, including human and rat B(1) bradykinin receptors. Bradyzide is orally available and blocks bradykinin-induced hypotension and plasma extravasation. Bradyzide shows long-lasting oral activity in rodent models of inflammatory hyperalgesia, reversing Freund's complete adjuvant (FCA)-induced mechanical hyperalgesia in the rat knee joint (ED(50), 0.84 micromol kg(-1); duration of action >4 h). It is equipotent with morphine and diclofenac, and 1000 times more potent than paracetamol, its maximal effect exceeding that of the non-steroidal anti-inflammatory drugs (NSAIDs). Bradyzide does not exhibit tolerance when administered over 6 days. In summary, bradyzide is a potent, orally active, antagonist of the B(2) bradykinin receptor, with selectivity for the rodent over the human receptor. British Journal of Pharmacology (2000) 129, 77 - 86

Administration, Oral↗
PubMed1999

Interleukin-5 transgenic mice show enhanced resistance to primary infections with Nippostrongylus brasiliensis but not primary infections with Toxocara canis.

In this study, interleukin-5 (IL-5) transgenic mice with lifelong eosinophilia were assessed for resistance to primary infections with two tissue-invading nematodes, Nippostrongylus brasiliensis and Toxocara canis. Relative to nontransgenic littermates, three lines of IL-5 transgenic mice with varying degrees of eosinophilia all displayed enhanced resistance to N. brasiliensis. Although the timing of final worm expulsion was similar in transgenic and nontransgenic hosts, intestinal worms in transgenic mice were fewer in number throughout infection, failed to increase in size over the course of the infection, and were much less fecund. In contrast, T. canis larvae were recovered in similar numbers from tissues of transgenic mice with "low" or "high" eosinophilia and from nontransgenic mice. These results and other data suggest that eosinophils can contribute to host resistance to some parasite species. Parasite transit time through the host may correlate with relative sensitivity to eosinophils.

Animals↗
PubMed1996

Managing pressure sores in the community.

A six-month project was undertaken in the Portsmouth HealthCare NHS Trust to identify the prevalence of pressure sores and assess current practice and level of knowledge among nurses working in the community. Questionnaires were returned by 99 nurses and the pressure sore prevalence was found to be 4.4%; 72% of respondents performed pressure sore risk assessment routinely, 49% had access to appropriate equipment and 60% had good or acceptable levels of knowledge. However, 40% had poor knowledge of risk factors for pressure sore development, and 80% did not routinely carry out mattress testing. Eighty-five per cent of nurses stated that they would like a specialist advisory service.

Community Health Nursing↗
PubMed1987

The structure of a synthetic pepsin inhibitor complexed with endothiapepsin.

The conformation of a synthetic polypeptide inhibitor, bound to the active site of the fungal aspartic proteinase endothiapepsin (EC 3.4.23.6), has been determined by X-ray diffraction at 0.20-nm resolution and refined to an agreement factor of 0.20. The inhibitor: Pro Thr Glu Phe-R-Phe Arg Glu (R = -CH2NH-) is based on a chromogenic substrate of pepsin (EC 3.4.23.1). It has, in place of the scissile bond, a reduced peptide group which is resistant to hydrolysis and mimics the tetrahedral transition state. The inhibitor binds in an extended conformation with the reduced bond close to the essential aspartate side-chains of the enzyme. The hydrogen bonds and hydrophobic interactions between the enzyme and the inhibitor do not induce large conformational changes.

Aspartic Acid Endopeptidases↗
PubMed1987

Crystallographic studies of reduced bond inhibitors complexed with an aspartic proteinase.

To aid in the design of an effective inhibitor to human renin, it is essential to have a detailed knowledge of how this aspartic proteinase interacts with its substrate, angiotensinogen. Human renin shows a stringent specificity toward the Leu-Val bond in its natural substrate. The minimal length for an effective substrate has been characterised as an octapeptide sequence derived from the amino terminal portion of angiotensinogen (residues 6----13): His-Pro-Phe-His-Leu-Val-Ile-His (Leu-Val is the scissile bond). This suggests that renin has a fairly extensive active site cleft, as has been observed in homologous enzymes whose three-dimensional structures have been solved using x-ray diffraction methods. The homologous fungal aspartic proteinase, endothiapepsin, has been cocrystallised with human renin inhibitors of the type His-Pro-Phe-His-Leu-R-Val-Ile-His, where R indicates a reduced carbonyl analogue of the scissile peptide bond. The three-dimensional crystallographic structures of two complexes of endothiapepsin with an inhibitor have been solved. The details of inhibitor binding at the active site cleft of endothiapepsin are described. These data allow a rational approach to the design of novel renin inhibitors, through studies of these inhibitors in a three-dimensional model of human renin constructed in our laboratory.

Amino Acid Sequence↗
PubMed1985

A transition-state analogue inhibitor of human renin (H.261): test in vitro and a comparison with captopril in the anaesthetized baboon.

H.261, a new transition state inhibitor of human renin with an IC50 of 6.9 X 10(-10) M, was given by intravenous infusion to six anaesthetized baboons. The inhibitor was infused first at 0.1 mumol/kg/h for 15 min, then at 1.0 mumol/kg/h for a further 15 min. After a recovery period of 2 h in which the animals received 5% dextrose, they were infused with captopril, 25 mumol/kg/h for 15 min. At both rates of infusion H.261 markedly and significantly reduced the enzymatic action of renin in plasma, the blood concentration of angiotensin I, the plasma concentration of angiotensin II and mean arterial pressure. All changes reverted towards or to control values in the subsequent control period. Captopril also lowered plasma angiotensin II concentration and mean arterial pressure markedly and significantly but, as expected for an inhibitor of the angiotensin I-converting enzyme, plasma active renin concentration and blood angiotensin I concentration increased. The changes of angiotensin II and arterial pressure were similar with captopril and H.261.

Angiotensin I↗
PubMed1985

Renin inhibitors: their use in understanding the role of angiotensin II as a pressor hormone.

Infusion of H.261, the inhibitor of human renin in the baboon, lowered blood angiotensin I, plasma angiotensin II, and arterial pressure suggesting that in the sodium-depleted state angiotensin II contributes to the maintenance of arterial pressure. In a second experiment dose-response infusions of angiotensin II were given in conscious sodium-depleted dogs before and during infusion of the renin inhibitor H.77. These suggested that the contribution of angiotensin II to the maintenance of arterial pressure in this state was made mainly by a circulating peptide. Preliminary results in normal humans show that infusion of H.142 intravenously lowered angiotensin I, angiotensin II, and arterial pressure.

Adult↗
PubMed1984

The purification of a high-molecular-weight, enzymatically inactive renin precursor from human kidney.

A high-molecular-weight enzymatically inactive form of renin has been purified to homogeneity from human kidney. It has an Mr of 48 000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate and an Mr of 51 000 by gel filtration on Sephadex G100. It is activated by treatment with trypsin and reversibly activated by exposure to acid. We conclude that this material represents a human prorenin.

Chromatography, Affinity↗
PubMed1984

Peptide inhibitors of renin.

Analogues of renin substrate that incorporated a non-cleavable isostere at the scissile bond are powerful inhibitors of renin both in vitro, and in animals and man.

Animals↗
PubMed1983

Purification of human renin by affinity chromatography using a new peptide inhibitor of renin, H.77 (D-His-Pro-Phe-His-LeuR-Leu-Val-Tyr).

A new affinity column for renin was prepared by coupling the isosteric peptide inhibitor of renin, H.77 (D-His-Pro-Phe-His-LeuR-Leu-Val-Tyr, where R is a reduced isosteric bond, -CH2-NH-), to activated 6-aminohexanoic acid-Sepharose 4B. Chromatography of a crude extract of human kidney cortex on this material resulted in a 5500-fold purification of renin in 76% yield. The purified enzyme (specific activity 871 units/mg) was free of non-specific acid-proteinase activity and was stable at pH 6.8 and -20 degrees C over a period of several weeks.

Chromatography, Affinity↗
PubMed1983

New inhibitors of human renin tested in vitro and in vivo in the anaesthetized baboon.

A new inhibitor of human renin (H. 189) is described. It is a decapeptide analogue of human renin substrate with the amino acid, statine, substituted for leucine in the scissile bond. Its inhibitory potency as shown by IC50 is 1.0 X 10(-8) M with human plasma renin and 1.5 X 10(-8) M with baboon plasma renin. It is less effective with dog and rat renin, but its inhibitory potency with human renin is similar to that of another inhibitor of ours (H. 142) having a reduced isostere in the scissile bond. H. 189 has some inhibitory effect on cathepsin D (IC50 6.5 X 10(-5) M) but H. 142 has no discernible effect. Pepstatin, on the other hand, was highly effective against cathepsin D (IC50 1.2 X 10(-8) M). H. 142 and H. 189 were infused intravenously at 10 mg/kg/h in four anaesthetized salt-deplete baboons (Papio hamadryas). The activity of renin in plasma decreased markedly as did the circulating concentration of its products, angiotensin I and angiotensin II.

Anesthesia, General↗
PubMed1983

Peptide inhibitors of renin.

Three experiments are described using new substrate analogue inhibitors of renin. The first experiment shows that introduction of a reduced isostere in the scissile peptide bond of an analogue greatly increases its ability to inhibit renin of a particular species. However, different species of renin substrate have different amino acids in their scissile bond and variation here also greatly influences the affinity of renin and substrate and hence of renin and substrate analogues. Finally, substitution of amino acids in the C-terminal adjacent to the scissile bond influences the affinity and efficacy of substrate analogues as inhibitors. In our second experiment a peptide inhibitor of dog renin, H.77, was used in an affinity column to produce a one-stage, 2000-fold, and complete purification of human renin. In our third experiment infusion of H.77 was used to lower circulating concentrations of angiotensin I and angiotensin II in conscious sodium-deplete dogs. Captopril was then given in addition to H.77 but blood pressure did not fall further, suggesting that captopril lowers blood pressure wholly or partly by reducing angiotensin II within the circulation and in extravascular sites.

Amino Acid Sequence↗