Effects of chromium compounds on plasma membrane Mg2+-ATPase activity of BHK cells.

An ATPase activity stimulated by divalent ions (Mg²⁺, Ca²⁺, Mn²⁺, Zn²⁺) has been observed in intact hamster fibroblasts cultured in vitro (BHK line). Such activity has been determined by the incubation (30 min at 37°C) of washed cell suspensions (about 1 mg of proteins) in a medium containing 100 mM NaCl, 20 mM KCl, 15 mM Tris—HCl (pH 7.4), 10 mM NaHCO₃, 5 mM glucose and equimolar concentrations of ATP and divalent cation. Mg²⁺-ATPase activity is insensitive to ouabain and lacks specificity towards nucleoside triphosphate substrates. AMP and ADP are not hydrolyzed under these conditions. Apparent K_m of 0.76 mM and V_max of 1.46 μmol Pi · mg proteins^?1 · h^?1 have been calculated for Mg-ATP complex. This ATPase is an ectoenzyme, therefore its activity could be used as a suitable index of the action of chemicals like chromium compounds known for their cytotoxic effects on membrane functions.Salts of trivalent (CrCl₃) and hexavalent (K₂Cr₂O₇) chromium at concentrations ranging from 1 mM to 5 mM inhibit Mg²⁺-ATPase. The inhibition by K₂Cr₂O₇ is observed after pretreatment of the cells with this compound followed by its absence from the assay medium “per se” for Mg²⁺-ATPase, and it is referred to the alterations of membrane bound enzyme structures by the oxidizing hexavalent chromium. The inhibition by CrCl₃ is mainly evident when this compound is present in the incubation medium, and is referred to the interaction of trivalent chromium with Mg²⁺-ATP as it is partially reversed by increasing Mg²⁺-ATP concentration.     

The role of the sensitization to storage mites in the diagnosis of allergic respiratory diseases

Summary Numerous studies suggest the capacity of storage mites (S.M.) to induce IgE-mediated reactions but their etiopathogenetic role in allergic respiratory diseases has not yet been established. Therefore we examined 283 patients affected by rhinitis and/or bronchial asthma resident in urban and rural areas who underwent skin tests and a RAST with a group of allergens including S.M. (Acarus s., Lepidoglyphus d., Glycyphagus d., Tyrophagus p.).The incidence of patients showing a positive reaction to S.M. was evaluated according to their place of residence and work. 48 patients were selected who resulted positive to mites; 28 of them resulted positive to S.M. and pyroglyphid and 5 to S.M. only.The relationship between skin tests and RAST for S.M. positive patients resulted high forL.d. (70%),G.d. (75%),T.p. (80%) and low forA.s. (58%). In RAST positive subjects cross-reactivity withD. ptero was evaluated:A.s. (70%),L.d. (80%),T.p. (75.4%),G.d. (78.9%).Dwelling and place of work of skin and RAST positive patients revealed an equal distribution between urban and rural populations for S.M.; however, while in urban areas the association with pyroglyphid mites is constant, the rare single sensitivities are found only in rural areas and in farmers. From our data it emerges that the allergological diagnostics must use S.M. when considering respiratory diseases of professionally exposed subjects and residents of given areas. An interpretation of their etiologic role, given the frequent association with pyroglyphid mites, will demand further diagnostic data and an identification and purification of the clinically relevant allergens.     

The determination of uroporphyrinogen decarboxylase in tissues by high-performance liquid chromatography coupled to fluorescence detection

High-performance liquid chromatography coupled to fluorescence detection wsa utilized for the separation and quantitation of porphyrins as methyl esters. The method (developed for biochemical investigation of porphyrias) permitted quantitation down to 0.2 nanograms of porphyrins per sample. One of the possible applications is the study of the enzyme uroporphyrinogen decarboxylase. No significant difference was found between two methods of methylation and extraction of the samples prior to chromatography.     

The effect of trans-stilbene oxide and other structurally related inducers of drug-metabolizing enzymes on glucuronidation

Administration of trans-stilbene oxide, and new type of inducer of drug-metabolizing enzymes, to rats was found to increase hepatic microsomal UDP-glucuronyl transferase activity with both p-nitrophenol and chloramphenicol as substrate. In Triton X-100 activated microsomes the increase with p-nitrophenol as substrate was to approx. 250% of the control value, while the corresponding value for chloramphenicol was about 600%. These observations indicate that trans-stilbene oxide causes a mixed type 'induction' of UDP-glucuronyl transferase(s), i.e., changes in activity which resemble both those seen after induction with phenobarbital and after treatment with 3-methylcholanthrene. We have also shown that the activity of UDP-glucose dehydrogenase, the enzyme which produces UDP-glucuronic acid, is increased to about 300% of the control after administration of trans-stilbene oxide. The time course of this increase and of the return to control activity after cessation of treatment, the dose-response of this increase and the structural features of the trans-stilbene oxide molecule which are essential for the increase have all been examined. The other two enzymes involved in the conversion of glucose 6-phosphate to UDP-glucuronic acid, namely, phosphoglucomutase and UDP-glucose pyrophosphorylase, were found to be only slightly affected (a 30-60% increase) by treatment with trans-stilbene oxide. After induction with trans-stilbene oxide the hepatic level of UDP-glucuronic acid was unchanged.     

beta-amyloid activates the O-2 forming NADPH oxidase in microglia, monocytes, and neutrophils. A possible inflammatory mechanism of neuronal damage in Alzheimer's disease.

The deposition of beta-amyloid in the brain is the key pathogenetic event in Alzheimer's disease. Among the various mechanisms proposed to explain the neurotoxicity of beta-amyloid deposits, a new one, recently identified in our and other laboratories, suggests that beta-amyloid is indirectly neurotoxic by activating microglia to produce toxic inflammatory mediators such as cytokines, nitric oxide, and oxygen free radicals. Three findings presented here support this mechanism, showing that beta-amyloid peptides (25-35), (1-39), and (1-42) activated the classical NADPH oxidase in rat primary culture of microglial cells and human phagocytes: 1) The exposure of the cells to beta-amyloid peptides stimulates the production of reactive oxygen intermediates; 2) the stimulation is associated with the assembly of the cytosolic components of NADPH oxidase on the plasma membrane, the process that corresponds to the activation of the enzyme; 3) neutrophils and monocytes of chronic granulomatous disease patients do not respond to beta-amyloid peptides with the stimulation of reactive oxygen intermediate production. Data are also presented that the activation of NADPH oxidase requires that beta-amyloid peptides be in fibrillary state, is inhibited by inhibitors of tyrosine kinases or phosphatidylinositol 3-kinase and by dibutyryl cyclic AMP, and is potentiated by interferon-gamma or tumor necrosis factor-alpha.     

Antinociceptive activity of a 3(2H)-pyridazinone derivative in mice.

The antinociceptive activity of a 3(2H)-pyridazinone derivative (18a) was investigated in mice. 18a administered at doses which did not change either motor coordination or locomotor activity was able to induce antinociceptive effects in four nociceptive tests, the hot plate test, the tail flick test, the writhing test, and the formalin test. In the hot plate and tail flick test, 18a-induced antinociception was observed both after intraperitoneal administration and after intracerebroventricular injection thus indicating 18a has a central site of action. The pretreatment with the opioid antagonist naloxone, the alpha2-antagonist yohimbine or the GABA(B) antagonist CGP 35348 did not change 18a-induced antinociception in the hot plate test and in the tail flick test. Pretreatment with nicotinic antagonist mecamylamine did not change 18a effects either. A reversion of the 18a effects was observed after pretreatment with the muscarinic antagonists atropine and pirenzepine. Binding experiments revealed that 18a binds to muscarinic receptors, suggesting that 18a antinociception is mediated by central muscarinic receptors. The above findings together with the lack of parasympathomimetic cholinergic side effects indicate useful clinical application for this compound.     

The inositol trisphosphate receptor regulates a 50-second behavioral rhythm in C. elegans.

The C. elegans defecation cycle is characterized by the contraction of three distinct sets of muscles every 50 s. Our data indicate that this cycle is regulated by periodic calcium release mediated by the inositol trisphosphate receptor (IP3 receptor). Mutations in the IP3 receptor slow down or eliminate the cycle, while overexpression speeds up the cycle. The IP3 receptor controls these periodic muscle contractions nonautonomously from the intestine. In the intestinal cells, calcium levels oscillate with the same period as the defecation cycle and peak calcium levels immediately precede the first muscle contraction. Mutations in the IP3 receptor slow or eliminate these calcium oscillations. Thus, the IP3 receptor is an essential component of the timekeeper for this cycle and represents a novel mechanism for the control of behavioral rhythms.