The ecdysteroid agonist/antagonist and brassinosteroid-like activities of synthetic brassinosteroid/ecdysteroid hybrid molecules

A series of synthetic hybrid brassinosteroid/ecdysteroid structures has been assessed for their ecdysteroid agonist/antagonist activities in the Drosophila melanogaster B(II) cell bioassay and for brassinosteroid-like activity in the rice lamina inclination test. Most of the compounds proved inactive for ecdysteroid agonist activity, demonstrating the specificity of the ecdysteroid receptor for compounds closely structurally related to 20-hydroxyecdysone. However, compound 18, with 14alpha-hydroxy-7-en-6-one and 22S-hydroxy functionalities (as in most active ecdysteroids), possessed distinct agonist activity (median effective concentration = 1.4 x 10(-5) M), although this is still almost 2000-fold less active than 20-hydroxyecdysone (25). Compounds 13 and 15 possessed weak agonist activity. Compounds 5, 11 and 14 weakly antagonised the action of 20-hydroxyecdysone (at 5 x 10(-8) M) on B(II) cells. In the brassinosteroid bioassay, most of the tested compounds showed activity. This may reflect the metabolic capability of plant tissue to convert test compounds to more active analogues. However, it is clear that biological activity declines as the structure of the test compound deviates further from that of castasterone (16). Three ecdysteroids (25, 26 and 27) are completely inactive in the rice lamina inclination test. These studies demonstrate the high specificities of the insect ecdysteroid receptor and the plant brassinosteroid receptor and indicate that phytoecdysteroids, even in high concentrations, would not interfere with brassinosteroid signalling pathways in plants where the two classes of compounds co-occur. Equally, brassinosteroids would not interfere with ecdysteroid signalling in insects, especially if one takes into account the low concentrations of brassinosteroids in the diet of phytophagous insects.     

Semisynthesis and biological properties of the [B24-leucine]-, [B25-leucine]- and [B24-leucine,B25-leucine]-analogues of human insulin

Summary Trypsin-catalyzed coupling of porcine desoctapeptide-insulin with synthetic octapeptides produced the [Leu^B24]-(I), [Leu^B25]- (II) and [Leu^B24, Leu^B25]- (III)analogues of human insulin. I, II and III displayed respectively 20–30%, 1–2% and 0.5% of the receptor binding activity of the normal hormone. Biological activities of these analogues seemed to be proportional to their binding potencies when assayed in vitro, while in an in vivo assay analogue I was fully active and II exhibited 10–20% of normal activity. III was less active than II in all assays tested.     

Purification of 2 succinic semi-aldehyde reductases from the human brain]

Two succinic semi-aldehyde reductases (A and B) have been purified to electrophoretic homogeneity. Enzyme A, which is a monomer of molecular weight 40,000 +/- 5,000 reduces a wide range of aldehydes and is inhibited by some barbiturates and certain anticonvulsants. Enzyme B, which is a dimer of molecular weight 80,000 +/- 10,000, is very specific for succinic semi-aldehyde and is not inhibited by the aforementioned compounds.     

Laccases of prokaryotic origin: enzymes at the interface of protein science and protein technology

The ubiquitous members of the multicopper oxidase family of enzymes oxidize a range of aromatic substrates such as polyphenols, methoxy-substituted phenols, amines and inorganic compounds, concomitantly with the reduction of molecular dioxygen to water. This family of enzymes can be broadly divided into two functional classes: metalloxidases and laccases. Several prokaryotic metalloxidases have been described in the last decade showing a robust activity towards metals, such as Cu(I), Fe(II) or Mn(II) and have been implicated in the metal metabolism of the corresponding microorganisms. Many laccases, with a superior efficiency for oxidation of organic compounds when compared with metals, have also been identified and characterized from prokaryotes, playing roles that more closely conform to those of intermediary metabolism. This review aims to present an update of current knowledge on prokaryotic multicopper oxidases, with a special emphasis on laccases, anticipating their enormous potential for industrial and environmental applications.     

Phytotoxins as potential herbicides

Phytotoxins are produced in various culture media by many fungi that are pathogenic to weeds. These phytotoxins belong to a wide array of chemical substances including sesquiterpenoids, sesterterpenoids, diketopiperazines, peptides, spirocyclic lactams, isocoumarins, and polyketides. In most cases, the phytotoxin belongs to a family of related compounds produced by the fungus. These related compounds may or may not be phytotoxins. Phytotoxin production, in some cases, is optimized by the addition of a host extract to the culture medium. Biological activity is usually observed in a range of concentrations from 10^–3 to 10^–6 M. The concept of using these molecules, derivatives thereof, or related compounds as herbicides should be explored.     

What’s new in the renin-angiotensin system?

Virtually all existing evidence on the function of angiotensin II (Ang II) in the regulation of tissue homeostasis and blood pressure regulation bears on the more restricted question of what other mechanisms or systems may amplify or inhibit the actions of this important peptide. Whereas there is evidence that Ang II may potentiate the effects of catecholamines, various cytokines and also growth factors, the repertoire of substances which may inhibit the actions of Ang II is more limited and has been restricted primarily to prostacyclin, bradykinin and nitric oxide. Advances in receptor pharmacology and introduction of selective antagonists to two of the receptor subtypes at which Ang II binds permitted a more critical examination of the functions of the renin angiotensin system in physiological and pathophysiological conditions, as well as uncovering the previously unsuspected possibility that within the biochemical pathways leading to the formation of the peptide the renin angiotensin system could process either its immediate precursor (angiotensin I) or the actual Ang II peptide into an alternative form, angiotensin-(1-7) [Ang-(1-7)], the function of which was to antagonize the effects of Ang II. We review here the biological actions of Ang-(1-7) and discuss how this discovery may change altogether the perception of how the renin angiotensin system functions in the regulation of tissue perfusion pressure and the regulation of salt and water metabolism.     

Polarographic activity of the antitumor drug cis-dichlorodiammineplatinum (II). The effect of hydrolysis and trans-isomerization of the drug

Electrochemical activities of cis-dichlorodiammineplatinum (II) (cis-DDP) and its trans isomer were studied by classical and differential pulse polarography (d.p.p.). It was shown that both isomers yielded a polarographic step or peak at about -1.6 V (vs. Ag/AgCl), which corresponded to electroreduction of the complex and to catalytic hydrogen evolution. This signal was easily measurable with the aid of d.p.p. and was suitable for investigation of the extent of hydrolysis and trans-isomerization of cis-DDP leading to the formation of toxic products. The detection limit for determination of cis-DDP and its trans isomer by d.p.p. was 1 X 10(-6) mol/l.     

The pleiotropic functions of aspirin: mechanisms of action

Recent studies have suggested that aspirin and aspirin-like compounds have a variety of actions in addition to their well-studied ability to inhibit cyclooxygenases. These actions include inhibition of the uncoupling of oxidative phosphorylation, decreases in adenosine triphosphate stores, increases in extracellular adenosine, downregulation of the expression and activity of inducible nitric oxide synthetase, inhibition and/or stimulation of various mitogen-activated protein kinase activities and inhibition of nuclear factor binding κB site (NF-κB) activation. Moreover, aspirin-like compounds have recently been shown to have previously unappreciated clinical and biological effects, some apparently independent of cyclooxygenase. In this review we discuss the various mechanisms of action of aspirin-like compounds and their relevance to clinical disease and therapy. Received 1 February 1999; received after revision 1 April 1999; accepted 7 May 1999     

Cellular models for the detection and evaluation of drugs that modulate human phagocyte activity

Simple testing models have been developed for the evaluation of chemical or biological compounds that modulate the activity of human phagocytes. Human neutrophils from buffy coats of donor blood are used. They are stimulated with receptor agonists, and the effects of test compounds on exocytosis of different enzymes, the generation of superoxide (respiratory burst), and cytotoxicity are quantified. All assays are performed in microtiter plates and the responses are evaluated by multi-well photometry or fluorimetry. The models are apt to detect compounds acting on phagocytes as agonists or antagonists, signal transduction activators or inhibitors and primers of agonist responses, and to assess cytotoxic effects.     

Synthesis of three NH2-terminally extended arginine-vasopressins with prolonged biological activities

The synthesis of three novel AVP-analogues, extended by 1-3 amino acids at their NH2-2-termini in accordance with the sequence of the bovine arginine-vasopressin neurophysin II precursor, is reported. The compounds were assayed for their antidiuretic and vasopressor activities with particular attention to the duration of the effects. All compounds showed high potency, based on the intensity, and prolonged effects in both test systems compared with AVP.     

Cellular models for the detection and evaluation of drugs that modulate human phagocyte activity

Summary Simple testing models have been developed for the evaluation of chemical or biological compounds that modulate the activity of human phagocytes. Human neutrophils from buffy coats of donor blood are used. They are stimulated with receptor agonists, and the effects of test compounds on exocytosis of different enzymes, the generation of superoxide (respiratory burst), and cytotoxicity are quantified. All assays are performed in microtiter plates and the responses are evaluated by multi-well photometry or fluorimetry. The models are apt to detect compounds acting on phagocytes as agonists or antagonists, signal transduction activators or inhibitors and primers of agonist responses, and to assess cytotoxic effects.     

Scavenger receptor family proteins: roles for atherosclerosis, host defence and disorders of the central nervous system

In this review, we summarize the structure and function of the scavenger receptor family of proteins including class A (type I and II macrophage scavenger receptors, MARCO), class B (CD36, scavenger receptor class BI), mucinlike (CD68/macrosialin, dSR-CI) and endothelial (LOX-1) receptors. Two motifs have been identified as ligand-binding domains a charged collagen structure of type I and II receptors, and an immunodominant domain of CD36. These structures can recognize a wide range of negatively charged macromolecules, including oxidized low-density lipoproteins, damaged or apoptotic cells, and pathogenic microorganisms. After binding, these ligands can be either internalized by endocytosis or phagocytosis, or remain at the cell surface and mediate adhesion or lipid transfer through caveolae. Under physiological conditions, scavenger receptors serve to scavenge or clean up cellular debris and other related materials, and they play a role in host defence. In pathological states, they mediate the recruitment, activation and transformation of macrophages and other cells which may be related to the development of atherosclerosis and to disorders caused by the accumulation of denatured materials, such as Alzheimer's disease. Received 17 September 1997; received after revision 16 March 1998; accepted 17 March 1998     

Early stimulation of protein kinase activity during hormonal meiosis reinitiation in starfish ovocytes]

Total endogenous protein kinase activity has been compared in homogenates prepared from Marthasterias glacialis and Asterias rubens oocytes treated or not by 1-methyladenine, the hormone which triggers meiosis reinitiation. A 5 mn treatment at the threshold 10(-7) M concentration causes a significant increase (+ 20%) of these activities. This stimulation is maintained or even enhanced when homogenates are complemented with exogenous histones.     

Stereoselectivity of oxotremorine antagonists containing a chiral pyrrolidine group

Summary Oxotremorine (Ia) and its succinimide analogue (IIa) have been substituted in the pyrrolidine ring with a methyl group in the 2- or 3-positions. The compounds are oxotremorine antagonists. The 2-methyl-substituted enantiomers show stereoselectivity, the S-isomers being the most active.     

Tails of unconventional myosins

In addition to the conventional myosins (class II) required for processes such as muscle contraction and cytokinesis, the myosin superfamily of actin-based motor proteins includes at least 14 'unconventional' classes. These unconventional myosins are defined by myosin-like head (motor) domains attached to class-specific tail domains that differ greatly from those of myosin-II. The unconventional myosins account for almost two-thirds of the 28 or more myosin genes currently believed to be expressed in humans and 80-90% of the approximately 10 or more myosin genes expressed in a typical nonmuscle cell. Although these members of the myosin superfamily have not been as intensively investigated as the conventional myosins, unconventional myosins are known or believed to power many forms of actin-based motility and organelle trafficking. The presence of signaling domains such as kinase domains, SH3 domains, PH domains or GTPase-activating domains in the tails of unconventional myosins indicates that these proteins can also be components of signal transduction pathways. Since several classes of the myosin superfamily have been found only in lower eukaryotes or plants (VIII, XI, XIII and XIV), in this review we will focus on the structures and properties of the unconventional myosins found in multicellular animals (excluding classes I and V, which have been reviewed elsewhere recently). Special attention will be focused on the three classes of unconventional myosins that can cause deafness in mouse or humans when mutated. In addition, we discuss the discovery of a pair of intriguing domains, the Myosin Tail Homology 4 (MyTH4) and FERM (band 4.1, Ezrin, Radixin, Moesin) domains, that are present in the tails of otherwise very different myosins as well as a plant kinesin-like protein. Recent progress in the identification of novel unconventional myosins will also be summarized.     

A sigmoidal relationship between liver stearoyl CoA desaturase activity and serum hormone concentrations caused by streptozocin and its antagonists

Stearoyl CoA desaturase activity in liver microsomes, and insulin, thyroxine, and triiodothyronine levels in serum were measured after administration of streptozocin (STZ) and its antagonists to rats. The effect of STZ, which caused hyperglycemia and inhibited the desaturase activity, was antagonized by 2-desoxyglucose and 3-O-methyl-glucose; 1-O-methyl-3-desoxyglucose and 1-O-methyl-3-O-methylglucose were without any effect. The enzyme activity plotted against insulin levels showed a broad sigmoidal curve, whereas the activities versus thyroid hormone levels showed steeper sigmoidal curves.     

Lack of effects of 5-HT3 antagonists on normal and morphine-attenuated sexual behaviours in female and male rats

Although 5-HT₁ and 5-HT₂ receptor activity is known to influence copulation, the effects of 5-HT₃ receptor-selective drugs on sexual activity have yet to be systematically studied. The following experiments investigated the effects of the 5-HT₃-selective antagonists MDL 72222, ondansetron and ICS 205-930 on female sexual behaviour; male rats were studied using ondansetron and granisetron. These compounds influenced neither male nor female copulatory behaviours, suggesting that 5-HT₃ receptors contribute little to the modulation of sexual activity. 5-HT₃ receptor antagonists block certain opioid-induced behaviours and opioids selectively inhibit sexual behaviours; therefore, the ability of ondansetron and ICS 205-930 to modify morphine-attenuated copulatory activity was also tested. While morphine inhibited copulation, 5-HT₃ antagonists failed to reverse the effects.     

Glucocorticoids in T cell apoptosis and function

Glucocorticoids (GCs) are a class of steroid hormones which regulate a variety of essential biological functions. The profound anti-inflammatory and immunosuppressive activity of synthetic GCs, combined with their power to induce lymphocyte apoptosis place them among the most commonly prescribed drugs worldwide. Endogenous GCs also exert a wide range of immunomodulatory activities, including the control of T cell homeostasis. Most, if not all of these effects are mediated through the glucocorticoid receptor, a member of the nuclear receptor superfamily. However, the signaling pathways and their cell type specificity remain poorly defined. In this review, we summarize our present knowledge on GC action, the mechanisms employed to induce apoptosis and the currently discussed models of how they may participate in thymocyte development. Although our knowledge in this field has substantially increased during recent years, we are still far from a comprehensive picture of the role that GCs play in T lymphocytes. Received 20 August 2005; received after revision 27 September 2005; accepted 10 October 2005     

Comparison of bicyclic phosphorous esters with bicuculline and picrotoxin as antagonists of presynaptic inhibition in the rat cuneate nucleus

Summary The effects of 2 of a series of bicyclic phosphorous esters, the ethyl (EPTBO) and isopropyl (IPTBO) compounds, were compared with those of the GABA antagonists, picrotoxin and bicuculline, on presynaptic inhibition in the rat cuneate nucleus. Both EPTBO and IPTBO were found to be effective, reversible antagonists of presynaptic inhibition, with IPTBO approximately 10 times more potent than EPTBO and equipotent with bicuculline, EPTBO equipotent with picrotoxin.The authors are grateful to Dr J. F. Collins, Department of Chemistry, Sir John Cass School of Science and Technology, 31 Jewry Street, London, for the gift of bicyclic phosphorous esters.