Characterization of acetyl-CoA: lyso-PAF acetyltransferase of human mesangial cells

Platelet activating factor (PAF) is a potent inflammatory mediator produced by various renal cells and it is implicated in renal pathology. The aim of this study is the characterization of remodeling lyso-PAF acetyltransferase, which is activated under inflammatory conditions, in human mesangial cell. Total membranes of mesangial cells were isolated and enzymatic activity and kinetic parameters were determined by trichloroacetic acid precipitation method. The effect of BSA, divalent cations, EDTA, and various chemicals on the activity of lyso-PAF acetyltransferase was also studied. Various detergents were also tested for the solubilization of the enzyme and only glycerol did not affect its activity. Partial purification of solubilized enzyme preparations of human kidney tissue and mesangial cells was performed on anion exchange column chromatography and native-PAGE electrophoresis and two active fractions were detected.     

Acetyl-CoA:1-O-alkyl-sn-glycero-3-phosphocholine acetyltransferase (lyso-PAF AT) activity in cortical and medullary human renal tissue.

Platelet-activating factor (PAF) is one of the most potent inflammatory mediators. It is biosynthesized by either the de novo biosynthesis of glyceryl ether lipids or by remodeling of membrane phospholipids. PAF is synthesized and catabolized by various renal cells and tissues and exerts a wide range of biological activities on renal tissue suggesting a potential role during renal injury. The aim of this study was to identify whether cortex and medulla of human kidney contain the acetyl-CoA:1-O-alkyl-sn-glycero-3-phosphocholine acetyltransferase (lyso-PAF AT) activity which catalyses the last step of the remodeling biosynthetic route of PAF and is activated in inflammatory conditions. Cortex and medulla were obtained from nephrectomized patients with adenocarcinoma and the enzymatic activity was determined by a trichloroacetic acid precipitation method. Lyso-PAF AT activity was detected in both cortex and medulla and distributed among the membrane subcellular fractions. No statistical differences between the specific activity of cortical and medullary lyso-PAF AT was found. Both cortical and medullary microsomal lyso-PAF ATs share similar biochemical properties indicating common cellular sources.     

Quantification of kininogen in human renal medulla

Renal kininogen was detected in human medullary tissue as well as human medullary tubule suspensions. After treatment with pig pancreatic kallikrein or human renal cortical homogenate liberated kinin was measured by bradykinin radioimmunoassay. In the absence of inhibitors kinins were degraded by kininases located in the same part of the kidney. Several known inhibitors of kininase I and II did not inhibit this activity. Endogenous medullary kininase was inhibited by preincubation of homogenates at 56 degrees C for one hour or by addition of 0.25 mmol/l HgCl2. Under these conditions endogenous medullary kinin release amounted to 9-26 nmol/g protein. The action of renal cortical kininogenase on kinin formation from papillary kininogen was completely inhibited by addition of 1 mumol/l aprotinin. Kininogen examined in renal tubule suspensions revealed an increase in amount per g protein compared to homogenates, confirming the tubular localization of renal kininogen.     

Regulation of renal Na(+),K(+)-ATPase and ouabain-sensitive H(+),K(+)-ATPase by the cyclic AMP-protein kinase A signal transduction pathway

We investigated the effect of the cyclic AMP-protein kinase A (PKA) signalling pathway on renal Na(+),K(+)-ATPase and ouabain-sensitive H(+),K(+)-ATPase. Male Wistar rats were anaesthetized and catheter was inserted through the femoral artery into the abdominal aorta proximally to the renal arteries for infusion of the investigated substances. Na(+),K(+)-ATPase activity was measured in the presence of Sch 28080 to block ouabain-sensitive H(+),K(+)-ATPase and improve specificity of the assay. Dibutyryl-cyclic AMP (db-cAMP) administered at a dose of 10(-7) mol/kg per min and 10(-6) mol/kg per min increased Na(+),K(+)-ATPase activity in the renal cortex by 34% and 42%, respectively, and decreased it in the renal medulla by 30% and 44%, respectively. db-cAMP infused at 10(-6) mol/kg per min increased the activity of cortical ouabain-sensitive H(+),K(+)-ATPase by 33%, and medullary ouabain-sensitive H(+),K(+)-ATPase by 30%. All the effects of db-cAMP were abolished by a specific inhibitor of protein kinase A, KT 5720. The stimulatory effect on ouabain-sensitive H(+),K(+)-ATPase and on cortical Na(+),K(+)-ATPase was also abolished by brefeldin A which inhibits the insertion of proteins into the plasma membranes, whereas the inhibitory effect on medullary Na(+),K(+)-ATPase was partially attenuated by 17-octadecynoic acid, an inhibitor of cytochrome p450-dependent arachidonate metabolism. We conclude that the cAMP-PKA pathway stimulates Na(+),K(+)-ATPase in the renal cortex as well as ouabain-sensitive H(+),K(+)-ATPase in the cortex and medulla by a mechanism requiring insertion of proteins into the plasma membrane. In contrast, medullary Na(+),K(+)-ATPase is inhibited by cAMP through a mechanism involving cytochrome p450-dependent arachidonate metabolites.     

Studies on in vitro polymerization of tubulin from renal medullary extracts.

Previous in vivo studies showed that microtubules are involved in the cellular action of vasopressin. In order to analyze the role of renal medullary microtubules, a system was developed which would allow the study of the assembly of tubulin in renal medulla extracts into microtubules in vitro. The assembly of tubulin into microtubules occurred in renal medullary cytosol (100 000 times g supernatant) under specific conditions which include pre-concentration of cytosol by ultrafiltration, the presence of ethylene glycol bis(2-aminoethyl)ether tetraacetic acid (EGTA) and 4 M glycerol, and warming at 37 degrees C. Formation of microtubules, which sedimented at 100 000 times g, was proved by (a) an increase in the apparent [3H]colchicine-binding activity of depolymerized pellets, (b) appearance of typical microtubules as shown by electron microscopy, and (c) by the increase in the quantity of microtubular protein analyzed by polyacrylamide gel electrophoresis. Vinblastine at a concentrationof 10(-6) M completely blocked formation of microtubules. A slight increase of ionized calcium in the polymerization mixture also prevented microtubule assembly; this inhibitory effect of ionized calcium was present at concentrations as low as 10(-4) M. Blockade of microtubule assembly by the increase in concentration of ionized calcium or by vinblastine may be the basis of known inhibitory effect of these two agents upon the hydroosmotic effect of vasopressin in vivo.     

Interaction of ethacrynic acid and cysteine with renal medullary adenylate cyclase

Results of the present study indicate that (1) ethacrynic acid, dihydroethacrynic acid, and the cysteine adduct of ethacrynic acid inhibit plasma membrane-bound adenylate cyclase from canine renal medulla; (2) reaction with a sulfhydryl group is not essential for inhibition by ethacrynic acid and its derivatives, but may contribute quantitatively to the inhibition; and (3) cysteine enhances the activity of renal medullary adenylate cyclase in the presence of a vasopressin analog or sodium fluoride.Observations support the view that ethacrynic acid and its cysteine adduct interfere with the action of vasopressin on the distal nephron at the site of renal medullary adenylate cyclase.     

Modulation of lyso-platelet-activating factor: acetyl-CoA acetyltransferase from rat splenic microsomes. The role of calcium ions

The enzyme lyso-platelet-activating factor: acetyl-CoA acetyltransferase (EC 2.3.1.67) was assayed in microsomal fractions from rat spleens. The addition of micromolar Ca2+ rapidly enhanced acetyltransferase activity and this activation was reversed by the addition of EGTA in excess of Ca2+. The effect of Ca2+ was on the apparent Km of the enzyme for the substrate acetyl-CoA without showing any significant effect on the Vmax of the acetylation reaction. When microsomes were isolated in the presence of 5 mM EGTA, to remove endogenous calmodulin, the same enhancing effect of Ca2+ on the acetylation reaction was observed. The addition of exogenous calmodulin to this preparation had no effect on the enzyme activity. Preincubation of spleen microsomes with the calmodulin inhibitor trifluoperazine decreased acetyltransferase in both the presence and the absence of Ca2+, indicating an effect of this drug independently of calmodulin. The addition of Mg-ATP to the assay mixture also had no effect on the acetylation reaction. These data suggest that Ca2+ modulates acetyltransferase activity from rat spleen microsomes by a mechanism that seems to be independent of calmodulin or protein phosphorylation.     

Nitric oxide decreases renal medullary Na+, K+-ATPase activity through cyclic GMP-protein kinase G dependent mechanism.

The aim of this study was to investigate the effect of nitric oxide on renal Na+,K(+)-ATPase and ouabain-sensitive H+,K(+)-ATPase activities. The study was performed in male Wistar rats. The investigated substances were infused under general anaesthesia into abdominal aorta proximally to the renal arteries. The activity of ATPases was assayed in isolated microsomal fraction. NO donor, S-nitroso-N-acetylpenicillamine (SNAP), infused at doses of 10(-7) and 10(-6)mol/kg/min decreased medullary Na+,K(+)-ATPase activity by 29.4% and 45.2%, respectively. Another NO donor, spermine NONOate, administered at the same doses reduced Na+,K(+)-ATPase activity in the renal medulla by 31.7% and 46.5%, respectively. Neither of NO releasers had any effect on Na+,K(+)-ATPase in the renal cortex and on either cortical or medullary ouabain-sensitive H+,K(+)-ATPase. Infusion of NO precursor, L-arginine (100 micromol/kg/min), decreased medullary Na+,K(+)-ATPase activity by 32.2%, whereas inhibitor of nitric oxide synthase, L-NAME (10 nmol/kg/min), increased this activity by 20.7%. The effect of synthetic NO donors was mimicked by 8-bromo-cGMP and blocked by inhibitors of soluble guanylate cyclase, ODQ or methylene blue, as well as by specific inhibitor of protein kinase G, KT5823. In addition, inhibitory effect of either SNAP or 8-bromo-cGMP on medullary Na+,K(+)-ATPase was abolished by 17-octadecynoic acid (17-ODYA), which inhibits cytochrome P450-dependent metabolism of arachidonic acid. These data suggest that NO decreases Na+,K(+)-ATPase activity in the renal medulla through the mechanism involving cGMP, protein kinase G, and cytochrome P450-dependent arachidonate metabolites. In contrast, NO has no effect on Na+,K(+)-ATPase in the renal cortex and on either cortical or medullary ouabain-sensitive H+,K(+)-ATPase.     

Iodinated neurohypophyseal hormones as potential ligands for receptor binding and intermediates in synthesis of tritiated hormones.

[3-Iodo-Tyr2]oxytocin (MIOT), [3,5-diiodo-Tyr2]oxytocin (DIOT), [3-iodo-Tyr2,Lys8]vasopressin (MILVP), [3,5-diiodo-Tyr2,Lys8]vasopressin (DILVP), [3-iodo-Tyr2,Arg8]vasopressin (MIAVP), and [3,5-diiodo-Tyr2,Arg8]vasopressin (DIAVP) were synthesized by iodination of the respective hormones, pruified, and characterized. All the monoiodo hormones had to be freshly prepared prior to bioassays, since on storage they gave rise to hormonal-like biological activity. The biological activities of these iodo analogues were measured in an adenylate cyclase assay employing neurohypophyseal hormone (NHH) sensitive bovine renal medullary membranes, and/or the rat oxytocic assay. In the cyclase assay, DIOT, DILVP, and DIAVP were inactive as agonists or antagonists. MIOT shows no agonistic activity in the renal cyclase system and uterus, but is a weak reversible inhibitor of oxytocin (OT) in both systems. When MIOT (10(-4) M) was preincubated with renal membranes for 10 min at 37 degrees C before addition of OT, it behaved as a noncompetitive inhibitor of NHH-stimulated adenylate cyclase. MILVP and MIAVP appear to be partial agonists with Km (half maximal response) 3 X 10(-6) and 3 X 10(-7) M, respectively, as determined in the cyclase assay. Upon preincubation with renal medullary membranes, MILVP (10(-6) M) behaves as a more potent noncompetitive inhibitor of OT than MIOT. Accordingly, iodo derivatives of NHH do not exhibit sufficient affinity to serve an specific ligands to measure OT, LVP, or AVP receptors in the uterus and kidney. Study of the specificity of inhibition produced by MIOT revealed that this analogue does not act selectively upon NHH receptors. Thus, MIOT modified adenylate cyclase systems which do not have NHH receptors, e.g., the PTH-sensitive adenylate cyclase in bovine renal cortex and the glucagon-sensitive adenylate cyclase in rat liver. DIOT, DILVP, and DIAVP were subjected to catalytic tritiation (employing carrier free tritium) and were converted to [3H]OT (25, 31, and 25 Ci/mmol), [3H]LVP (26 and 23 Ci/mmol), and [3H]AVP (17 Ci/mmol), respectively. These tritiated ligands have been successfully used to measure NHH receptor sites both in kidney and uterine membranes as described in other studies.     

Enzymatic determination of choline acetyltransferase by coenzyme A cycling and its application to analysis of single mammalian neurons

Abstract: An enzymatic assay for choline acetyltrans-ferase was developed by measuring acetyl-coenzyme A (acetyl-CoA) formed from CoASH and acetylcholine (ACh). This method is extremely sensitive and may be applied to the analysis of microgram to nanogram crude samples. The method is, however, not useful when choline acetyltransferase is present in very low concentrations. The basis of this method is to amplify a small amount of synthesized acetyl-CoA in the assay mixture by using an enzymatic amplification reaction, CoA cycling. This amplification mechanism made it possible to perform microassays (13 nl-2.2 μl of assay volume) of freeze-dried sections prepared from cerebral cortex, striatum, and hippocampus of mice and single cell bodies isolated from freeze-dried sections of rabbit spinal cords. These samples were weighed and added directly to the reaction mixture. The activities of the above cerebral regions, assayed with 1,500–2,000-fold amplification, corresponded well to the results previously reported by other workers. The average activity of single anterior horn cells, determined with 64,000–420,000-fold amplification, was 40-fold higher than that of rabbit cerebral cortex, and the specific activities on a dry weight basis were widely distributed among individual neurons. No activity was detected in the noncholinergic dorsal root ganglion cells or in cerebellar cortex.     

Renal tubular acidosis: developments in our understanding of the molecular basis

Renal tubular acidosis is a metabolic acidosis due to impaired acid excretion by the kidney. Hyperchloraemic acidosis with a normal anion gap and normal (or near normal) glomerular filtration rate, and in the absence of diarrhoea, defines this disorder. However, systemic acidosis is not always evident and renal tubular acidosis can present with hypokalaemia, medullary nephrocalcinosis and recurrent calcium phosphate stone disease, as well as growth retardation and rickets in children, or short stature and osteomalacia in adults. Renal dysfunction in renal tubular acidosis is not always confined to acid excretion and can be part of a more generalised renal tubule defect, as in the renal Fanconi syndrome. Isolated renal tubular acidosis is more usually acquired, due to drugs, autoimmune disease, post-obstructive uropathy or any cause of medullary nephrocalcinosis. Less commonly, it is inherited and may be associated with deafness, osteopetrosis or ocular abnormalities. The clinical classification of renal tubular acidosis has been correlated with our current physiological model of how the nephron excretes acid, and this has facilitated genetic studies that have identified mutations in several genes encoding acid and base ion transporters. In vitro functional studies of these mutant proteins in cell expression systems have helped to elucidate the molecular mechanisms underlying renal tubular acidosis, which ultimately may lead to new therapeutic options in what is still treatment only by giving an oral alkali.     

Renal sodium handling and stimulation of medullary Na-K-ATPase during blockade of prostaglandin synthesis

The effect of suppression of prostaglandin synthesis on renal sodium handling and microsomal Na-K ATPase was studied in control and indomethacin treated intact rats maintained on a normal sodium diet (series A) and chronically salt loaded (series B). Indomethacin administration resulted in a decreased GFR and a significantly depressed urinary excretion and an increased fractional reabsorption of sodium in animals fed the normal sodium diet or chronically salt loaded. In rats maintained on a normal Na diet, the activity of the renal medullary Na-K ATPase after indomethacin was 206.3 +/- 6.4 ug Pi/mg protein, i.e. significantly higher as compared with the enzyme activity in the medullary renal fraction from control animals in which it averaged 148 +/- 7.79 ug Pi/mg protein (p less than 0.001). While after chronic salt load a similar increment in the activity of renal medullary Na-K ATPase was observed, no additional stimulation was elicited by subsequent indomethacin administration. The addition of exogenous PGE2, 0.1 mM to microsomal fractions obtained from kidneys of normal rats, was associated with a moderate suppression of the medullary Na-K-ATPase activity, from a basal level of 170 +/- 16 to 151.3 +/- 13 umol Pi/mg protein/hr (p less than 0.005). In isolated segments of medullary thick ascending limb of Henle's loop (MTAL) addition of PGE2 to the incubation medium resulted in a significant inhibition of Na-K ATPase from 37.2 +/- 2 to 21.25 +/- 1.17 x 10(-11) mol/mm/min (p less than 0.0001). These findings suggest that the increased renal Na reabsorption after inhibition of PG synthesis might be related, at least partly, to stimulation of medullary Na-K ATPase. In parallel, the reported natriuretic effect of prostaglandins might imply a direct inhibitory effect of these mediators on renal Na-K ATPase.     

Interferon induces astrocyte maturation causing an increase in cholinergic properties of cultured human spinal cord cells

It has been well established that interferon-gamma (IFN-gamma) can modify the immune status of cells in the central nervous system (CNS) by inducing major histocompatibility antigens. Furthermore, it has been shown that endogenous IFN can be produced in the brain following viral infection and a form of IFN-alpha/beta can be produced by astrocytes in culture. Here we show that IFN can induce astrocyte maturation and alter neurotransmitter properties in cultured CNS neurons at a given developmental stage. IFN causes a dose-dependent increase in choline acetyltransferase activity and glial fibrillary acidic protein (GFAP) immunoreactivity in cultures of human embryonic spinal cord neurons. The GABAergic activity and the Thy1 immunoreactivity remain unchanged. IFN-gamma does not act directly on the neurons but via the nonneuronal cells, probably the astrocytes, which in turn stimulate the cholinergic traits. These studies could be important for demonstrating an action of the immune system on glial cell maturation and on the neurotransmitter phenotype expression in CNS neurons.     

Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.     

N-demethylation activity of renal and hepatic subcellular fractions: an interspecies comparison.

The enzymatic activity of the mixed-function oxidase system in the kidney and liver was evaluated by means of an in vitro N-demethylation activity assay with aminopyrine as the substrate. Renal and hepatic demethylation activity of 9000 x g supernatant fraction was determined in the rat, rabbit, and guinea-pig. In terms of interspecies comparison, the renal tissue demethylation activities were on a similar level with a slight increase in the order guinea-pig, rabbit and rat. In relation to hepatic activity, these relative demethylation activities of renal tissue had the same values in the rat and rabbit, whereas that in the guinea pig was significantly lower. The distribution of demethylation activity in the kidney was determined by comparing the cortex and medullary activity in relation to the total kidney tissue activity in the rabbit and guinea-pig. Although the higher demethylation activities were obtained in rabbit renal preparations and low demethylation activity was detected in the guinea-pig renal medulla only, no significant interspecies differences were found by the statistical evaluation. It may be concluded that the mixed-function oxidase system responsible for renal demethylation activity seems to be concentrated in the renal cortex and its distribution coincides in the rabbit and guinea-pig kidney.     

A fluorometric assay for the determination of 1-deoxy-D-xylulose 5-phosphate synthase activity

We report a novel fluorometric end-point assay for the determination of 1-deoxy-d-xylulose 5-phosphate synthase (DXS) activity based on the reaction of 1-deoxy-D-xylulose 5-phosphate (DX5P) with 3,5-diaminobenzoic acid in an acidic medium to form a highly fluorescent quinaldine derivative. The assay was validated in three ways: (a) for a fixed amount of DXS in the reaction mixture the emitted fluorescence increased linearly with the reaction time, (b) for a fixed reaction time fluorescence intensity increased with the concentration of DXS in the reaction mixture, and (c) the increase in fluorescence intensity correlated (r = 0.99; P < 0.002) with the amount of DX5P formed in the reaction mixture determined radiometrically. The sensitivity of the fluorometric assay is similar to that of the previously described radiometric methods. This assay can be useful for the functional characterization of DXS as well as for the screening of DXS inhibitors with potential antibiotic, herbicidal, or antimalarial action.     

Enzymatic and morphological response of the thymus to drugs in normal and zinc-deficient pregnant rats and their fetuses

In the thymus of normally fed pregnant rats the plasma membrane enzymes dipeptidyl peptidase IV (DPP IV) and alkaline phosphatase (alP) were found in cortical and medullary lymphocytes (thymocytes). Plasma membrane aminopeptidase A (APA) and adenosine monophosphate hydrolysing phosphatase (AMPP) were present in cortical reticular cells. In medullary reticular cells, aminopeptidase M (APM), gamma-glutamyl transferase (GGT), adenosine triphosphate (ATPP) and thiamine pyrophosphate (TPPP) cleaving phosphatases were detected. Medullary reticular cells did not contain APA. Lysosomal DPP I and II, acid phosphatase, acid beta-D-galactosidase, beta-D-N-acetyl-glucosaminidase, beta-D-glucuronidase and non-specific esterases occurred especially in macrophages at the corticomedullary junction. The 21-day-old fetal thymus showed a similar reaction pattern as the maternal organ except for APA which was absent before birth. After treatment of the pregnant rats with valproic acid (VPA), salicylic acid (SA), streptozotocin (ST) and retinoic acid (RA) APA showed an increase in activity in the thymic cortex. In addition, ST and RA induced AMPP, ATPP and TPPP activity in cortical reticular cells up to the same pattern as in medullary reticular cells. After ethanol (ET) administration severe damages occurred. The thymic cortex was free of DPP IV-positive lymphocytes; the medullary reticular cells showed reduced or no GGT and occasionally an increased APM activity. Dexamethasone (DEXA) given to normal or zinc-deficient rats produced the most severe lesions; thymocytes with DPP IV activity were completely absent in the cortex and medulla. In Zn-deficient pregnant rats similar alterations were observed as after ET.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potential anti-inflammatory actions of the elmiric (lipoamino) acids

A library of amino acid-fatty acid conjugates (elmiric acids) was synthesized and evaluated for activity as potential anti-inflammatory agents. The compounds were tested in vitro for their effects on cell proliferation and prostaglandin production, and compared with their effects on in vivo models of inflammation. LPS stimulated RAW 267.4 mouse macrophage cells were the in vitro model and phorbol ester-induced mouse ear edema served as the principal in vivo model. The prostaglandin responses were found to be strongly dependent on the nature of the fatty acid part of the molecule. Polyunsaturated acid conjugates produced a marked increase in media levels of i15-deoxy-PGJ(2) with minimal effects on PGE production. It is reported in the literature that prostaglandin ratios in which the J series predominates over the E series promote the resolution of inflammatory conditions. Several of the elmiric acids tested here produced such favorable ratios suggesting that their potential anti-inflammatory activity occurs via a novel mechanism of action. The ear edema assay results were generally in agreement with the prostaglandin assay findings indicating a connection between them.