ABSTRACT
Nicotinic acid as a hypolipidemic agent appears unique due to its potential to increase HDL cholesterol levels to a greater extent than other drugs. However, it has some side effects, among which severe skin flushing is the most frequent and often limits patients' compliance. In a search for novel agonists for the recently identified and cloned G protein-coupled nicotinic acid receptor, we synthesized a series of substituted pyrazole-3-carboxylic acids that proved to have substantial affinity for this receptor. The affinities were measured by inhibition of [(3)H]nicotinic acid binding to rat spleen membranes. Potencies and intrinsic activities relative to nicotinic acid were determined by their effects on [(35)S]GTPgammaS binding to rat adipocyte and spleen membranes. Interestingly, most compounds were partial agonists. In particular, 2-diazabicyclo[3,3,0(4,8)]octa-3,8-diene-3-carboxylic acid (4c) and 5-propylpyrazole-3-carboxylic acid (4f) proved active with K(i) values of approximately 0.15 microM and EC(50) values of approximately 6 microM, while their intrinsic activity was only approximately 50% when compared to nicotinic acid. Even slightly more active was 5-butylpyrazole-3-carboxylic acid (4g) with a K(i) value of 0.072 microM, an EC(50) value of 4.12 microM, and a relative intrinsic activity of 75%. Of the aralkyl derivatives, 4q (5-(3-chlorobenzyl)pyrazole-3-carboxylic acid) was the most active with a relatively low intrinsic activity of 39%. Partial agonism of the pyrazole derivatives was confirmed by inhibition of G protein activation in response to nicotinic acid by these compounds. The pyrazoles both inhibited the maximum effect elicited by 100 microM nicotinic acid and concentration dependently shifted nicotinic acid concentration-response curves to the right, pointing to a competitive mechanism of action.
Subject(s)
Nicotinic Agonists/chemical synthesis , Pyrazoles/chemical synthesis , Receptors, Nicotinic/drug effects , Adipocytes/metabolism , Animals , Cell Membrane/metabolism , GTP-Binding Proteins/agonists , In Vitro Techniques , Niacin/pharmacology , Nicotinic Agonists/chemistry , Nicotinic Agonists/pharmacology , Nicotinic Antagonists/chemical synthesis , Nicotinic Antagonists/chemistry , Nicotinic Antagonists/pharmacology , Pyrazoles/chemistry , Pyrazoles/pharmacology , Radioligand Assay , Rats , Spleen/metabolism , Structure-Activity RelationshipABSTRACT
On the basis of their antigenic properties, influenza virus strains are classified into types and subtypes, which are further subdivided into variants that differ to various degrees in haemagglutination-inhibition assays. Evidence is presented that during infection with an influenza A(H3N2) virus the respiratory tract of a human patient often harbours more than one antigenic virus variant. These variants are frequently propagated by embryonated fowl eggs and monkey cells with different efficiencies, and this may lead to the selection of different variants by either of these host systems. Also, passage of virus by a given host is sometimes attended by changes in reactivity in haemagglutination-inhibition tests. In some cases the heterogeneity described also affects the specific immunogenicity of the virus in ferrets. Virus strains cloned in monkey kidney cell cultures gave variants that were stable upon further passage. These results may have implications for antigenic and biochemical investigations of epidemiologically relevant virus variants. It is argued that the antigenic drift of influenza A(H3N2) viruses is best characterized by analyses, both with post-infection ferret antisera and with panels of monoclonal antibodies, of virus strains isolated and passaged in monkey kidney cell cultures only.
