Analgesic agents: comparative evaluation, mechanisms of action, prospects

A classification of analgesics based on the localization and mechanisms of their action is proposed. Opioid analgesics are compared: opioid receptor agonists, agonists-antagonists, and partial agonists. Central-action nonopioid analgesics are listed: alpha 2-adrenomimetics, Na- and K-channel blockers, reverse monoamine neuronal capture inhibitors, stimulating amino acid antagonists, etc. Peripheral-action analgesics (cycloxygenase inhibitors) are described.     

Antibiotics: mechanisms of action

Medical practice rests on the foundation of science. Clinicians are constantly making practical decisions and dealing with immediate situations that demand solutions. Time should be taken to focus on those scientific principles that underlie our diagnostic and therapeutic maneuvers. This section of Pediatrics in Review presents selected topics that are relevant to practice from the areas of physiology, pharmacology, biochemistry, and other disciplines; clarification of these will augment the pediatrician's understanding of clinical procedures.     

Infections and diabetes: mechanisms and prospects for prevention

Infections remain a serious hazard for the diabetic patient. Good metabolic control is a major factor in limiting the development and spread of infections and, most importantly, the development of diabetic complications which predispose to infections. In some patients recurrent infections can pose a problem, particularly if there is evidence of secondary immunodeficiency. In these patients adjuvant therapies, including Biological Responses Modifiers (BRMS) should be considered. Several factors could predispose diabetic patients to infections. These factors include: genetic susceptibility to infection; altered cellular and humoral immune defense mechanisms; local factors including poor blood supply and nerve damage, and alterations in metabolism associated with diabetes. In the context of a diabetic patient all or some of these factors may operate. The purpose of this review is to assess the relative contribution of these potential mechanisms in leading to infection in patients with diabetes.     

Federal research and development: Policies and prospects.

The "Office of Science and Technology was established… as a focal point for comprehensive science policies in the Executive Branch." This 1963 statement to a congressional committee indicates that "the problems of determining how to bring scientists into the formation of national scientific policies have been met in a pragmatic manner." There is substantial commitment of the federal budget to research and development and it has sharply risen during the past 5 years. Major sections are: The Federal Effort, Federal Mechanisms for Science and Technology, The Tasks Ahead, and Summary and Conclusions. Recent budget cuts "will severely arrest the capability of the NSF to meet its statutory responsibilities in research as well as in education." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

DNA topoisomerase targeting drugs: mechanisms of action and perspectives

The nuclear enzymes DNA topoisomerases I and II appeared as cellular targets for several antitumor drugs: campthotecin derivatives interacting with topoisomerase I, and actinomycin D, anthracycline derivatives, elliptinium acetate, mitoxantrone, epipodophyllotoxine derivatives, amsacrine and a new olivacine derivative, NSC-6596871 (S 16020-2), which interact with topoisomerase II. The functions of these enzymes are numerous and important since they are critical for DNA functions and cell survival. Despite the fact that they share the same target, topoisomerase II inhibitors have different mechanisms of action. Two principle types of induced alterations are involved in cellular resistance to topoisomerase II drugs: qualitative or quantitative alteration of the enzyme and/or increased drug efflux due to overexpression of P-glycoprotein. S 16020-2, a new olivacine derivative with a high antitumor activity against solid tumors, shows a potent cytotoxic effect against tumor cells expressing P-glycoprotein. This observation suggests that the comprehension of the respective effects of topoisomerase inhibitors and the precise knowledge of their mechanisms of resistance would improve the use of this therapeutic class in the clinic within rational chemotherapeutic combinations.     

Vanadium salts as insulin substitutes: mechanisms of action, a scientific and therapeutic tool in diabetes mellitus research

Vanadium and its compounds exhibit a wide variety of insulin-like effects. In this review, these effects are discussed with respect to the treatment of type I and type II diabetes in animal models, in vitro actions, antineoplastic role, treatment of IDDM and NIDDM patients, toxicity, and the possible mechanism(s) involved. Newly established CytPTK plays a major role in the bioresponses of vanadium. It has a molecular weight of approximately 53 kDa and is active in the presence of Co2+ rather than Mn2+. Among the protein-tyrosine kinase blockers, staurosporine is found to be a potent inhibitor of CytPTK but a poor inhibitor of InsRTK. Vanadium inhibits PTPase activity, and this in turn enhances the activity of protein tyrosine kinases. Our data show that inhibition of PTPase and protein tyrosine kinase activation has a major role in the therapeutic efficacy of vanadium in treating diabetes mellitus.     

Glucocorticoids: mechanisms of action and anti-inflammatory potential in asthma

The major limitations of monoclonal antibody conjugates as therapeutic agents have been their poor tumour targeting, inadequate tumour penetration and immunogenicity. More even and deeper tissue penetration has been demonstrated with smaller antibody fragments. The smaller size and absence of an Fc segment may contribute to a lowered immunogenicity with single-chain antibodies (scFv) and also permit their recombinant engineering and bacterial expression. We describe the successful engineering, expression and pre-clinical characterisation of a phosphorylatable "kemptide" (Leu-Arg-Arg-Ala-Ser-Gly) anti-carcinoembryonic antigen (anti-CEA) scFv (PKS-scFv), for use as a radioimmunotherapeutic agent. Specifically, a yield of 6 mg/l induced culture was obtained. Site-specific phosphorylation was demonstrated without loss of specificity. In vitro assays revealed a selective cytotoxicity of 32P-PKS-scFv for high-CEA-expressing LS-174T cells compared to the low-CEA-expressing HT-29 cells, with a rapid internalisation rate.     

Tetracyclines: antibiotic action, uptake, and resistance mechanisms

Tetracyclines probably penetrate bacterial cells by passive diffusion and inhibit bacterial growth by interfering with protein synthesis or by destroying the membrane. A growing number of various bacterial species acquire resistance to the bacteriostatic activity of tetracycline. The two widespread mechanisms of bacterial resistance do not destroy tetracycline: one is mediated by efflux pumps, the other involves an EF-G-like protein that confers ribosome protection. Oxidative destruction of tetracycline has been found in a few species. Several efflux transporters, including multidrug-resistance pumps and tetracycline-specific exporters, confer bacterial resistance against tetracycline. Single amino acids of these carrier proteins important for tetracycline transport and substrate specificity have been identified, allowing the mechanism of tetracycline transport to begin to emerge.     

Alcohol and free radicals: from basic research to clinical prospects

An oxidative stress occurs in the liver of rats following various conditions of ethanol administration. The ethanol-inducible cytochrome P450 2E1 plays a key role in its generation, favoured itself by an increase in the "redox-active" fraction of intracellular non-heme iron. Administration of ethanol elicits the generation of the 1-hydroxyethyl radical, which has been identified in vivo. Its reactivity contributes to alcohol-induced immunological disturbances. Liver inflammatory and fibrotic disorders can be reproduced in rats by long-term ethanol administration associated with a high fat diet. The severity of these disorders is correlated to the intensity of the oxidative stress. Some conditions of ethanol administration to rats also elicit an oxidative stress in the myocardium and central nervous system. Through its inhibitory effect on glutamine synthetase activity and resulting excitotoxicity it may contribute to neuronal death and possibly to dependence on alcohol. Disorders related to an oxidative stress were also reported in the serum and erythrocytes as well as in liver biopsies from alcoholic individuals. Their detection may be useful to follow the evolution of alcoholic liver diseases. Supplementation with antioxidants such as vitamin E may be considered in the prevention of severe cellular disorders in individuals consuming large amounts of alcoholic beverages. An increase in free radical production is likely playing a role in the induction of severe cellular damage linked to repeated withdrawals occurring as a result of heavy and sporadic ethanol intake.     

Endothelins: a role in cerebrovascular disease?

Vasoactive factors produced and released by the endothelium exert a powerful influence on vascular tone in the cerebral circulation. Impaired endothelium-dependent responses, such as decreased production of endothelium-derived relaxing factors, and/or release of endothelium-derived contractile factors may give rise to different pathophysiological conditions. Among the endothelium-derived contractile factors the endothelins have recently received particular attention. Endothelin-1 is the major isoform in the endothelin family, which also includes endothelin-2 and endothelin-3. Endothelin-1 is synthesized within the endothelium of cerebral vessels, whereas both endothelin-1 and endothelin-3 in addition have been identified in neurons and glia. Recent electrophysiological work has suggested a neuromodulatory role for these peptides, but at present the general interest is mainly focused on their vasoactive role. Physiological stimuli such as hypoxia, anoxia, and hemodynamic shear stress will stimulate the endothelial endothelin production. In the brain, at least two types of specific subreceptors have been cloned; ETA receptors, exclusively associated with blood vessels and ETB receptors also found on glial, epithelial, and ependymal cells. The endothelins seem so far to be the most potent vasoconstrictors yet identified. The circulating plasma levels of immunoreactive endothelin are low. Since more than 80% of the total amount released from endothelial cells seems to be secreted towards the underlying smooth muscle, endothelins have been ascribed a local vasoregulatory role. Endothelins are believed to be involved in several of our most common cerebrovascular diseases and the present review comments on their possible pathophysiological role in subarachnoid haemorrhage, cerebral ischemia, and migraine.     

The mechanisms of action of ketamine

The review systematizes the latest data on the main mechanisms of realization of some pharmacological properties of ketamine which are particularly valuable in the treatment of many diseases and conditions. The authors present the main aspects of the ketamine effect on the central mechanisms of anesthesia and hemodynamics and give the characteristics of its neuroprotective action. It is shown that these effects are realized also at the cost of the non-competitive blockade of the NMDA receptors in the central nervous system.     

Receptor regulatory mechanisms of antimutagenic action

Based on the data available in the literature and his own findings, the author suggests that there is a receptor regulatory mechanism of action in some antimutagens. The primary signal can be induced by an antimutagen at different stages of a regulatory cascade: a membrane, cell effectors, and cell ensembles. At the terminal stage, there is an activation of the natural system of antimutagenesis activates and an enhanced cell resistance to a mutagen.     

韶钢推行清洁生产的探索与展望

简要介绍韶钢近年来在清洁生产方面的探索和实践，并对未来进行展望．     

机电一体化研究现状及发展应用前景

讨论了机电一体化对传统的机构工程赋予的新内容，并对几种近年常见机电一体化产品进行了分析。在此基础上，简述了机电一体化研究现状、发展和应用前景，并提出了对现代机电一体化的新认识。     

Medical treatment of migraine: from mechanisms of action to contraindications

Management of migraine patients with or without aura must include appropriate medication to treat the attack and long-term preventive therapy, especially if the frequency of the attacks is greater than 2-4 per month. In both cases the choice of treatment depends on its efficacy and side effects. With regard to acute drug therapy, group studies do not suggest that ergot derivatives and sumatriptan are superior to simple analgesics and anti-inflammatory drugs, particularly if a prokinetic agent is added. These new substances are indicated for severe attacks refractory to more conventional therapy. Chronic drug abuse may induce drug-induced or rebound headaches. As regards long-term prophylaxis, group studies suggest that calcium antagonists and 5-HT-influencing drugs are superior concerning attacks frequency to beta-blocking agents, but involve very frequent side effects (weight gain and somnolence). Interesting preliminary results have also been reported with valproate and enalapril, which will confirmation by controlled studies. Finally, the choice of drug must take into account the patient's comorbidities (cardiovascular diseases, asthma, diabetes etc).