Novel qualitative structure-activity relationships for the antinociceptive actions of H2 antagonists, H3 antagonists and derivatives

Recent studies have shown that cimetidine, burimamide and improgan (also known as SKF92374, a cimetidine congener lacking H2 antagonist activity) induce antinociception after intracerebroventricular administration in rodents. Because these substances closely resemble the structure of histamine (a known mediator of some endogenous analgesic responses), yet no role for known histamine receptors has been found in the analgesic actions of these agents, the structure-activity relationships for the antinociceptive effects of 21 compounds chemically related to H2 and H3 antagonists were investigated in this study. Antinociceptive activity was assessed on the hot-plate and tail-flick tests after intracerebroventricular administration in rats. Eleven compounds induced time-dependent (10-min peak) and dose-dependent antinociceptive activity with no observable behavioral impairment. ED50 values, estimated by nonlinear regression, were highly correlated across nociceptive assays (r2 = 0.98, n = 11). Antinociceptive potencies varied more than 6-fold (80-464 nmol), but were not correlated with activity on H1, H2 or H3 receptors. Although highly potent H3 antagonists such as thioperamide lacked antinociceptive activity, homologs of burimamide and thioperamide containing N-aromatic substituents retained H3 antagonist activity and also showed potent, effective analgesia. A literature review of the pharmacology of these agents did not find a basis for their antinociceptive effects. Taken with previous findings, the present results suggest: 1) these compounds act on the brain to activate powerful analgesic responses that are independent of known histamine receptors, 2) the structure-activity profile of these agents is novel and 3) brain-penetrating derivatives of these compounds could be clinically useful analgesics.     

Production of platelet-derived growth factor in aseptic loosening of total hip replacement

Aseptic loosening is the predominant cause of total hip implant failure. It has been assumed that a layer or membrane, containing macrophages, fibroblasts and vascular endothelial cells, of synovial-like tissue develops at the implant-to-bone interface almost invariably and, with time, somehow leads to loosening of the components from the surrounding bone. These cells produce a variety of cytokines and proteolytic enzymes which stimulate bone resorption. Platelet derived growth factor (PDGF) may be one of the cytokines which stimulate bone resorption and contribute to aseptic loosening in total hip replacement (THR). Synovial-like membrane from the implant or cement-to-bone interface (n = 10) and pseudocapsule (n = 10) were obtained from ten patients operated on for aseptic loosening of THR. As a control, nine samples of connective tissues were obtained from patients who had mandibular or maxillary fractures fixed with bone implant. The avidin-biotin-peroxidase complex (ABC) method with polyclonal rabbit anti-human IgG against the A-chain and B-chain of PDGF was used for staining. ABC-alkaline phosphatase-anti-alkaline-phosphatase double staining with monoclonal mouse anti-human fibroblast IgG1 and CD68 antibodies was used to ascertain the cellular origin of PDGF. Results of the PDGF staining were quantitated by a semi-automatic VIDAS image analysis system. The PDGF-A and PDGF-B chain containing cells were found in all periprosthetic tissues, in particular in macrophages with phagocytosed particulate debris, but to some extent also in fibroblasts and in endothelial cells. The numbers of PDGF-A and PDGF-B chain positive cells per mm 2 in synovial-like interface membrane (1881 +/- 486 and 1877 +/- 214) and pseudocapsule (1786 +/- 236 and 1676 +/- 152) were higher (P < 0.01) around loose THR than in control tissue (821 +/- 112 and 467 +/- 150), respectively. The results of the present study suggest that PDGF is preferably expressed by macrophages, which to an increased extent produce it in the synovial-like interface membrane and pseudocapsular synovial-like membrane. Because of its role in bone resorption, it may well play a role in periprosthetic bone loss and aseptic loosening and deserves more detailed study as a mediator and potential target in the modulation or prevention of loosening of THR.     

Age-dependent increase in ortho-tyrosine and methionine sulfoxide in human skin collagen is not accelerated in diabetes. Evidence against a generalized increase in oxidative stress in diabetes

The glycoxidation products Nepsilon-(carboxymethyl)lysine and pentosidine increase in skin collagen with age and at an accelerated rate in diabetes. Their age-adjusted concentrations in skin collagen are correlated with the severity of diabetic complications. To determine the relative roles of increased glycation and/or oxidation in the accelerated formation of glycoxidation products in diabetes, we measured levels of amino acid oxidation products, distinct from glycoxidative modifications of amino acids, as independent indicators of oxidative stress and damage to collagen in aging and diabetes. We show that ortho-tyrosine and methionine sulfoxide are formed in concert with Nepsilon-(carboxymethyl)lysine and pentosidine during glycoxidation of collagen in vitro, and that they also increase with age in human skin collagen. The age-adjusted levels of these oxidized amino acids in collagen was the same in diabetic and nondiabetic subjects, arguing that diabetes per se does not cause an increase in oxidative stress or damage to extracellular matrix proteins. These results provide evidence for an age-dependent increase in oxidative damage to collagen and support previous conclusions that the increase in glycoxidation products in skin collagen in diabetes can be explained by the increase in glycemia alone, without invoking a generalized, diabetes-dependent increase in oxidative stress.     

Altered visual field asymmetry for lexical decision as a result of concurrent presentation of music fragments of different emotional valences

OBJECTIVES: To investigate the effect of membrane lipid composition on the susceptibility to bile salt damage and protection. DESIGN: Artificial model cholesterol/phospholipid (c/p) membranes (vesicles) with a varying cholesterol (0-15 mM) and phospholipid content (3-30 mM), and with a c/p ratio ranging up to 1.70, were prepared by sonication. We examined the effect of incubation with increasing concentrations of either tauroursodeoxycholate (TUDC), taurocholate (TC) or taurodeoxycholate (TDC) alone, or with proportionally varying mixtures of TUDC and TDC. METHOD: Vesicle integrity was assessed by the change in optical absorbance at 340 nm. RESULTS: Absorption of the bile salt-vesicle mixture decreased, with increasing bile salt concentration and hydrophobicity: TUDC less than TC less than TDC. Moreover, bile salt-induced damage also depended on membrane composition: vesicles containing more than 5 mM cholesterol and with a c/p ratio greater than 0.8 were less likely to be solubilized by 30 mM bile salt. Similarly, only in cholesterol-rich vesicles (c/p > 0.5) was a protective effect of TUDC against membrane disruption by TDC revealed upon incubation with various TUDC/TDC mixtures. CONCLUSION: Apart from the bile salt concentration and hydrophobicity, the cholesterol content of vesicles is pivotal, both in the bile salt-induced solubilization of cholesterol/phospholipid vesicles and in the potency of TUDC to prevent this.     

Regulation of hippocampal synaptic plasticity by the tyrosine kinase receptor, REK7/EphA5, and its ligand, AL-1/Ephrin-A5

The Eph-related tyrosine kinase receptor, REK7/EphA5, mediates the effects of AL-1/Ephrin-A5 and related ligands and is involved in the guidance of retinal, cortical, and hippocampal axons during development. The continued expression of REK7/EphA5 in the adult brain, in particular in areas associated with a high degree of synaptic plasticity such as the hippocampus, raises the question of its function in the mature nervous system. In this report we examined the role of REK7/EphA5 in synaptic remodeling by asking if agents that either block or activate REK7/EphA5 affect synaptic strength in hippocampal slices from adult mouse brain. We show that a REK7/EphA5 antagonist, soluble REK7/EphA5-IgG, impairs the induction of long-term potentiation (LTP) without affecting other synaptic parameters such as normal synaptic transmission or paired-pulse facilitation. In contrast, perfusion with AL-1/Ephrin-A5-IgG, an activator of REK7/EphA5, induces a sustained increase in normal synaptic transmission that partially mimics LTP. The sustained elevation of normal synaptic transmission could be attributable to a long-lasting binding of the AL-1/Ephrin-A5-IgG to the endogenous REK7/EphA5 receptor, as revealed by immunohistochemistry. Furthermore, maximal electrical induction of LTP occludes the potentiating effects of subsequent treatment with AL-1/Ephrin-A5-IgG. Taken together these results implicate REK7/EphA5 in the regulation of synaptic plasticity in the mature hippocampus and suggest that REK7/EphA5 activation is recruited in the LTP induced by tetanization.