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Biomedical subjects

F J Evans

Publications and source records attributed to F J Evans.

At least 19 recordsLinked to original sources
PubMed1992

Role of protein kinase C in induction of gene expression and inhibition of cell proliferation by interferon alpha.

Recent studies have suggested that protein kinase C (PKC) may be involved in the mechanism of signal transduction by which members of the interferon (IFN) family regulate gene expression and cell phenotype. We have investigated the role of PKC in the control of cell growth and gene expression by IFN alpha in Daudi cells. Treatment of these cells with two analogues of staurosporine, which are potent inhibitors of PKC, completely blocked the induction by IFN alpha of the mRNA for 2',5'-oligoadenylate synthetase and the 6-16 gene. These compounds also inhibited cell proliferation and thymidine incorporation in this system. In contrast, the protein kinase inhibitor 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H7) did not significantly inhibit the induction of these genes by IFN alpha and had no effect on Daudi cell growth or thymidine incorporation in the presence or absence of IFN alpha. No effect of IFN alpha on total PKC activity could be observed, and there were no significant changes in the overall levels of individual PKC isoforms or their mRNA following IFN alpha treatment. In contrast, treatment of Daudi cells with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate, which also inhibits cell proliferation, strongly down-regulated PKC. These data suggest that the activity of a PKC species, or a closely related enzyme, may be required both for continued cell proliferation and the response to IFN alpha in Daudi cells, but that IFN-induced growth inhibition does not involve overall down-regulation or change in activity of PKC.

Amino Acid Sequence↗
PubMed1992

The potent irritancy of the daphnane orthoester, resiniferatoxin, exhibits features of a mixed aetiology.

Resiniferatoxin-induced erythema of mouse ear was shown to possess characteristics of both a phorbol ester-mediated response and that induced by the neurogenic irritant, capsaicin. Whereas the response to the phorbol ester, sapintoxin D, was delayed and prolonged, and was augmented by capsaicin pretreatment, the response to resiniferatoxin was biphasic, with the early phase being antagonized by capsaicin desensitization. However, resiniferatoxin was most potent in inducing a delayed erythema which, unlike the capsaicin response, was sensitive to inhibition by low dose hydrocortisone treatment, but not to chronic capsaicin desensitization. It is concluded that the erythema response to resiniferatoxin has a mixed aetiology, which may explain the unique potency of this toxin.

Animals↗
PubMed1991

Activation of the PKC-isotypes alpha, beta 1, gamma, delta and epsilon by phorbol esters of different biological activities.

Phorbol esters, tetradecanoylphorbolacetate, sapintoxin-A, 12-deoxyphorbol-phenylacetate, 12-deoxyphorbol-phenylacetate-20-acetate, thymeleatoxin and resiniferatoxin were investigated for their abilities to activate the PKC-isotypes alpha, beta 1, gamma, delta and epsilon. PKC-isotypes were grouped into two classes on the basis of Ca2+ requirements for activation by phorbol esters; alpha, beta 1, and gamma being Ca(2+)-dependent forms and delta and epsilon being Ca(2+)-independent. PKC-isotype selective activation by phorbol esters was observed in that SAPA failed to activate PKC-delta up to a concentration of 1000 ng.ml-1 and DOPPA only activated PKC-beta 1 over the same range of concentrations.

Animals↗
PubMed1991

NADPH-oxidase activation by protein kinase C-isotypes.

The cell free activation of NADPH-Oxidase in membranes of mouse peritoneal macrophages by purified PKC-isotypes was investigated. Unstimulated intrinsic activity of PKC-isotypes showed little dependence on Ca2+ for activation of the oxidase. In the presence of TPA, the activation of the oxidase was greatly enhanced, and alpha-, and gamma-subtypes were strongly Ca2+ dependent in this system. Beta-, delta- and epsilon-subtypes were active both in the presence and absence of free Ca2+ ions. The results suggest that at resting Ca2+ levels certain PKC-isotypes can activate NADPH-oxidase.

Animals↗
PubMed1991

Natural products as probes for new drug target identification.

One traditional aspect of natural products in medical research has been their use in the identification and investigation of the physiological/pathological role of receptors and enzymes as possible targets for drug design programmes. Classical examples of this function of natural products in drug research can be seen in the investigation of the cholinergic system. For example, the importance of alkaloids such as nicotine, physostigmine and curare for research into the nicotine receptor and muscarine, pilocarpine and the tropane alkaloids on the muscarinic receptor. On binding of a ligand to its cell surface membrane receptor and prior to a physiological/pharmacological response two mechanisms are currently known to be involved in membrane signal transductance. In the minority of cases signal transductance involves the direct opening of an ion channel, for example sodium ion influx, but in the majority of cases involves stimulation of a family of G-proteins and subsequent activation of second messenger systems. For example, the cyclic-AMP/adenylate cyclase system and the phosphoinositol cycle. In this communication, the part played currently by the tumour-promoting and pro-inflammatory phorbol esters from the plant family Euphorbiaceae in furthering our understanding of the role of a group of related kinases from one arm of the phosphoinositol cycle as a signal transduction pathway will be illustrated. The possibilities of using these new receptors as targets for future drug development will also be described.

Animals↗
PubMed1991

Induction of Epstein-Barr virus lytic cycle by tumor-promoting and non-tumor-promoting phorbol esters requires active protein kinase C.

Exposure to the tiglian 12-O-tetradecanoylphorbol-13-acetate (TPA) represents one of the most efficient and widely used protocols for inducing Epstein-Barr virus (EBV)-infected cells from latent into lytic cycle. Since TPA is both a potent tumor promoter and a potent activator of the cellular protein kinase C (PKC), we sought to determine whether either of these activities was closely linked to EBV lytic cycle induction. A panel of TPA structural analogs, encompassing tiglians with different spectra of biological activities, was assayed on a number of EBV-positive B-lymphoid cell lines. Lytic cycle induction correlated with the capacity to activate PKC, not with tumor promoter status; some nonpromoting tiglians were as efficient as TPA in inducing lytic cycle antigen expression. We then sought more direct evidence for an involvement of PKC in the induction process. In initial experiments, 1-(5-isoquinolinyl sulphonyl)-2-methylpiperazine (H-7), the best available pharmacological inhibitor of PKC, completely blocked the induction of the lytic cycle by TPA and its active analogs. This is consistent with, but does not prove, a requirement for active PKC in the induction process, since H-7 targets PKC preferentially but also has some effects on other kinases. We therefore turned to the synthetic pseudosubstrate peptide PKC(19-36) as a means of specific PKC inhibition and to the closely related but inactive peptide PKC(19-Ser-25-36) as a control. Using the technique of scrape loading to deliver the peptides into cells of an adherent EBV-positive target line, we found that the pseudosubstrate peptide PKC(19-36) completely and specifically blocked tiglian-induced entry of the cells into the lytic cycle. The evidence both from TPA analogs and from enzyme inhibition studies therefore indicates that the pathway linking TPA treatment to lytic cycle induction involves active PKC. Interestingly, inhibition of PKC had no effect upon the spontaneous entry into lytic cycle which occurs in naturally productive cell lines, suggesting that spontaneous entry is signalled by another route.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Cannabinoids: the separation of central from peripheral effects on a structural basis.

A brief history of the therapeutic uses and legal problems of cannabis as well as the component cannabinoids is given. This is followed by a discussion of drug development from delta 1-tetrahydrocannabinol and its synthetic analogues. The controversy of whether the pharmacological effects are of central or peripheral origin is included. Then, the potentials for the development of new drugs based on the cannabinoid structure for the treatment of pain, inflammation, and related conditions are outlined. It is concluded that the central activity of cannabinoids is confirmed and that the presence of a C-5 hydroxy group confers potent peripheral activity.

Animals↗
PubMed1990

Platelet protein phosphorylation and protein kinase C activation by phorbol esters with different biological activity and a novel synergistic response with Ca2+ ionophore.

Phorbol esters with different biological activities have been tested for their ability to induce the phosphorylation of human platelet proteins. We have shown that only the potent platelet aggregatory phorbol esters were able to stimulate the phosphorylation of proteins of 76, 68, 47, 30 and 20 kDa in intact platelets. The ability of these esters to stimulate phosphorylation of the 47-kDa protein ('p47') correlated with their ability to cause platelet aggregation. When a non-platelet aggregatory deoxyphorbol (12-deoxyphorbol 13-phenylacetate 20-acetate) was combined with a subthreshold dose of the Ca2+ ionophore, A23187, a large increase in phosphorylation of p47 and a fourfold decrease in Ka was observed. This was in contrast to a barely detectable stimulation of phosphorylation at micromolar levels of this phorbol ester in the absence of the ionophore. This synergism was not evident for the potent platelet aggregatory derivatives. The Ka for DOPPA with a mixture of total platelet protein kinase C was 530 nM in the absence of calcium decreasing to 120 nM in the presence of calcium. In the presence of calcium, 12-deoxyphorbol 13-phenylacetate 20-acetate was shown to stimulate preferentially one of the isoforms of protein kinase C.

Blood Platelets↗
PubMed1979

An assay procedure for the comparative irritancy testing of esters in the tigliane and daphnane series.

A method is described for testing of diterpene esters for irritancy. The technique involves the application of acetone solutions of the toxins to the inside ears of female LACA mice. The number of mice responding per group and the log10 dose data were evaluated using probit analysis with the assistance of a computer program. This evaluation has the advantage that approximations inherent with an arithmetical evaluation were eliminated, and limits may be placed upon the standard deviation of the irritant dose 50% (ID50). In addition, the use of a chi2 test automatically eliminated results which were not attributed to random biological variation. Observations of the time to onset and the persistence of the inflammation have led to the suggestion that daphnane orthoester diterpenes may elicit their effect by means of a direct action at a receptor site in skin, whereas the tigliane O-acyl esters may in part act by causing more general tissue damage.

Animals↗
PubMed1979

Investigations into the skin-irritant properties of resiniferonol ortho esters.

A series of esters were produced by partial synthesis from 9,13,14-orthophenylacetyl-resiniferonol. These compounds were tested for irritant effects by means of a mouse ear assay. All of the derivatives, including the parent compound, produced short-term inflammation of mice ears within 1-2 h and the effects did not persist for 24 h. This is in contrast to esters of structurally related tigliane diterpenes which produce a longer-term on mice ears. Highly potent irritants were synthesized which exhibited irritant doses 50% in the 0.0012-0.00021 nmol range. These esters were all substituted phenylacetates of the C-20 position of 9,13,14-orthophenylacethyl-resiniferonol. The meta or para positions of the phenylacetate moiety were substituted with electronegative groups for maximum activity. Compounds exhibiting substituted phenyl propionates at C20 were not irritants in the test used.

Animals↗
PubMed1979

The succulent euphorbias of Nigeria. III. Structure and potency of the aromatic ester diterpenes of Euphorbia poissonii Pax.

The latex of Euphorbia poissonii was found to contain irritant aromatic diterpene esters based upon resiniferonol, 12-deoxy-16-hydroxy-phorbol and 12-deoxyphorbol. Four resiniferonol esters, 9,13,14-ortho-phenylacetyl-resiniferonol-20-0-[p-hydroxy-phenylacetate]; 9,13,14-orthophenylacetyl-resiniferonol-20-0-[m-methoxy-m'-hydroxy-phenylacetate]; 9,13,14-orthophenylacetyl-resiniferonol-20-0-acetate and resiniferonol-14-0-phenylacetate-20-0-[m-methoxy-m'-hydroxy-phenylacetate], were identified. Two further esters were identified as 12-deoxy-16-0-[2-methylbutyroyl]-phorbol-13-0-phenylacetate-20-0-acetate and 12-deoxy-16-0-[2-methylbutyroyl]-phorbol-13-0-phenylacetate. These compounds represent the first aromatic esters of this parent diterpene to be obtained from natural sources. The third group of compounds were identified as 12-deoxyphorbol-13-0-[p-hydroxy-phenylacetate]-20-0-acetate; 12-deoxyphorbol-13-0-[p-acetoxy-phenylacetate]-20-0-acetate; 12-deoxyphorbol-13-0-phenylacetate-20-0-acetate and 12-deoxyphorbol-13-0-phenylacetate. The irritant potency of the ten pure compounds was obtained using a mouse ear method for assessment of the irritant dose 50%.

Animals↗