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Biomedical subjects

F J Evans

Publications and source records attributed to F J Evans.

At least 37 records · Page 2Linked to original sources
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

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.

Journal Article↗
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

TPA and resiniferatoxin-mediated activation of NADPH-oxidase. A possible role for Rx-kinase augmentation of PKC.

The non-tumour promoting irritant, resiniferatoxin, was capable of activating the NADPH-oxidase respiratory burst of starch-elicited, but not resident mouse peritoneal macrophages in vitro. Unlike TPA, the response was synergised by incubation with zymosan. The Rx-stimulated NADPH-oxidase activity in a cell-free assay was selectively enhanced in the presence of exogenous Rx-kinase rather than PKC and in the absence of Ca2+. Since resiniferatoxin is a poor activator of PKC, it is probable that the Ca2(+)-independent Rx-kinase plays a role in activation of the macrophage respiratory burst following stimulation by zymosan.

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↗
PubMed1990

Inhibition of protein kinase C prevents phorbol ester- but not muscarine-induced depolarizations in the rat superior cervical ganglion.

The role of protein kinase C (PKC) activation in mediating muscarinic depolarization was assessed in the rat superior cervical ganglion. Staurosporine, an inhibitor of PKC, abolished a depolarization elicited by the direct PKC activator beta-phorbol 12,13-dibutyrate, but had little effect on the response to muscarine. Thus, activation of PKC may not be an obligatory transduction step between muscarinic receptor stimulation and depolarization.

Action Potentials↗
PubMed1990

Non-promoting diterpene esters can induce Epstein-Barr virus early antigen expression in the Raji cell line.

A range of diterpene ester ligands with selective biological activity (e.g., irritant but not tumour promoting) were tested for their ability to induce Epstein-Barr virus (EBV) early antigen expression in the lymphoblastoid Raji cell line. All C12/C13 substituted compounds were found to be capable of inducing some antigen expression at nM-microM levels, including desacetyl-alpha-sapinine, a compound largely devoid of biological activity. The non-promoting, fluorescent compound, sapintoxin A, was virtually equipotent with promoting compounds. It was concluded that, although the assay has relevance to the specific condition of chronic diterpene ester exposure occurring in conjunction with high EBV infection rates, there was relatively poor correlation with mouse skin tumour promoting potential.

Antigens, Viral↗
PubMed1990

Hypnotizability of psychiatric inpatients according to two different scales.

Data on the hypnotizability of 113 psychiatric inpatients and 58 normal control subjects were compared. The patients' mean score on the Hypnotic Induction Profile was significantly lower than that of the control subjects, but on the Stanford Hypnotic Susceptibility Scale: Form C, these patients and control subjects did not differ significantly. On both scales rank-ordered scores of different diagnostic groups of the patients supported the theory that hypnotizability varies according to type of psychopathology. Some results, such as the hypnotizability of the schizophrenic patients, depended on which scale was used. This finding may explain the conflicting literature on the hypnotic potential of schizophrenic patients.

Adolescent↗
PubMed1989

A phorbol ester and a daphnane ester stimulate a calcium-independent kinase activity from human mononuclear cells.

TPA and a non-promoting, pro-inflammatory ester RX were used to stimulate the forms of PKC isolated from human mononuclear cells. Three peaks of kinase activity corresponding to gamma, beta and alpha PKC were stimulated by TPA in the presence and absence of calcium and/or phosphatidylserine (PS) but were not activated by RX. A fourth peak eluted at high phosphate concentration was activated by TPA and RX in the presence of PS and the absence of calcium. Activity in this fraction was labile to freezing and thawing and was inhibited by staurosporine.

Alkaloids↗
PubMed1989

Suggested posthypnotic amnesia in four diagnostic groups of hospitalized psychiatric patients.

We studied the parameters of suggested posthypnotic amnesia (initial deficit in recall, reversibility, and temporal disorganization of the initial material partially recalled during amnesia) in 132 psychiatric inpatients with DSM-III diagnoses of schizophrenia (N = 25), eating disorders (N = 77), alcoholism (N = 12), and major affective disorder (depression) (N = 18). We compared the findings on these patients with normal student control groups on the Stanford Hypnotic Susceptibility Scale (SHSS:C) posthypnotic suggestion item. In general, the small patient subgroups showed posthypnotic amnesia on each of these criteria in similar fashion to normal student populations. Highly hypnotizable patients were more likely to recall their hypnotic experiences in a more random order than the temporally more accurate sequence shown by low-hypnotizable subjects. Schizophrenic patients initially recalled fewer of their hypnotic experiences (indicating some cognitive deficit), and eating disorder patients initially recalled more of their experiences than other patient groups or normal subjects. Nevertheless, all patient subgroups showed significant additional recall after the reversibility cue. The results support the robustness of posthypnotic amnesia in psychiatric patients.

Adult↗
PubMed1989

Tumour-promoting and hyperplastic effects of phorbol and daphnane esters in CD-1 mouse skin and a synergistic effect of calcium ionophore with the non-promoting activator of protein kinase C, sapintoxin A.

Using an 18 week two-stage protocol we have compared the tumour-promoting properties of a range of phorbol and daphnane esters on female CD-1 mice. The induction of epidermal hyperplasia in this mouse strain by these compounds has also been assessed by comparison with the standard phorbol ester, 12-O-tetradecanoylphorbol-13-O-acetate (TPA). Two compounds, sapintoxin D (SAP D) and thymeleatoxin A (TA) (a daphnane structurally related to the second-stage promoter mezerein) were shown to be second-stage promoters using 5 nmol TPA as a first-stage promoter and 0.2 mumol 7,12-dimethylbenz[a]anthracene (DMBA) as initiator. Both compounds at a dose of 17 nmol were hyperplasiogenic. Two further derivatives, sapintoxin C (SAP C) and 4 alpha-sapinine (alpha-SAP) were inactive as promoters and hyperplastic agents. 4 alpha-sapinine, which prevents in vitro stimulation of protein kinase C (PKC), by 12-O-tetradecanoylphorbol-13-O-acetate (TPA) failed to inhibit significantly TPA-induced promotion and hyperplasia at a dose of 20 nmol and 100 nmol respectively. Sapintoxin A (SAP A), a potent activator of PKC, was neither a complete nor second-stage promoter at doses of up to 20 nmol. A series of in vivo and in vitro experiments which were carried out to determine the metabolic fate of this compound under experimental conditions showed that SAP A was not metabolized to any significant extent up to 48 h. When SAP A was co-administered with sub-hyperplastic doses of the calcium ionophore A23187 (5 micrograms and 10 micrograms) tumours appeared in a dose-dependent manner. This combination was also hyperplasiogenic in mouse skin. SAP A may be a useful probe for studying the involvement of PKC isozymes in tumour promotion and cell proliferation.

Animals↗