An oxidized metabolite of linoleic acid increases intracellular calcium in rat adrenal glomerulosa cells

Is hydrogen ion (H(+)) the real second messenger in calcium signalling?

Most second messengers have the acknowledged ability to mobilize the segregated Ca(2+) from intracellular stores, although the mechanisms of mobilization are unclear. To study this problem, the fact that inositol 1,4,5-trisphosphate, and six other known endogenous Ca(2+) mobilizers are acids, or acid-generating compounds, is highlighted. In physiological conditions, a newly generated acid releases H(+). The transient rise of H(+) in the cytosol may induce the lowering of pH, mobilization of bound Ca(2+), protein conformational rearrangement, store depletion, and Ca(2+) influx. Accordingly, a new description of the basic mechanism for signal transduction in non-excitable cells and the related consequences is put forward.

Effects of nonylphenol on aldosterone release from rat zona glomerulosa cells

Alkylphenol ethoxylate, which consists of approximately 80% nonylphenol ethoxylate (NPE), is a major nonionic surfactant. Nonylphenol (NP), the primary degradation product of NPE, has been reported to interfere with reproduction in fish, reptiles, and mammals by inducing cell death in the gonads and by affecting other reproductive parameters. However, the effects of NP on rat adrenal zona glomerulosa cells (ZG) and the underlying mechanisms remain unclear. In this study, we explored the effects of NP on aldosterone release. ZG cells were incubated with NP in the presence or absence of the secretagogues angiotensin II (ANG II), potassium, 8-Br-cAMP, 25-OH-cholesterol, corticosterone or cyclopiazonic acid (CPA). After performing radioimmunoassay (RIA) and Western blot analysis, we found that (1) NP stimulated aldosterone release in cells induced by ANG II, KCl, 8-Br-cAMP, 25-OH-cholesterol, corticosterone, and CPA; (2) NP triggered the release of higher amounts of pregnenolone in cells treated with vehicle and 25-OH-cholesterol+trilostane than in cells treated with other compounds; and (3) the stimulatory effect of NP seemed to be mediated through steroidogenic acute regulatory protein (StAR) and aldosterone synthase activity. These observations suggest that the effects of NP are mediated via increased free Ca(2+) in the cytoplasm.

Synthesis of six epoxyketooctadecenoic acid (EKODE) isomers, their generation from nonenzymatic oxidation of linoleic acid, and their reactivity with imidazole nucleophiles

As a class of linoleic acid oxidation products, epoxyketooctadecenoic acids (EKODEs), are formed in vivo and in vitro by a free radical mechanism initiated by either enzymatic or nonenzymatic pathways. They have so far been made available in small-scale quantities, often as isomeric mixtures, from reductive decomposition of linoleic acid-derived hydroperoxides. There is major interest in these compounds owing to their highly potent biological activities and their ability to covalently modify proteins. The synthesis of six EKODE regio- and stereoisomers, two trans alpha',beta'-epoxy-alpha,beta-enones, and two trans and the two cis gamma,delta,-epoxy-alpha,beta-enones was accomplished, with the key steps being Wittig-type reactions and aldol condensations. All six EKODE isomers were confirmed by HPLC to be generated in the autoxidation of linoleic acid promoted by Fe(II)/ascorbic acid through spiking in of authentic samples. On the basis of evidence for EKODE modification of protein His residues, the reactions of Nalpha-benzoyl-L-histidine with autoxidizing linoleic acid and with the individual EKODE isomers were compared, as were the kinetics of the various EKODE reactions with imidazole nucleophiles. The structures of His-EKODE-(E)-I adducts were confirmed to reflect conjugate addition (epoxide ring remains intact) through an NMR study of the reaction of imidazole with a generic EKODE-(E)-I analog. The synthesis of the EKODE isomers makes these important molecules available for further chemical and biological evaluation.

Comprehensive suppression of the renin-angiotensin-aldosterone system in chronic kidney disease: covering all of the bases

Reducing proteinuria and blood pressure in chronic kidney disease (CKD) decreases rate of progression. Inhibition of the renin-angiotensin system by angiotensin-converting enzyme inhibitors and/or angiotensin receptor blockers is beneficial in reducing proteinuria but incomplete in suppressing aldosterone production and its renal effects. Adding aldosterone receptor blockers to these other agents may further halt the progression of CKD.