Aluminum alters the electrophoretic properties of neurofilament proteins: role of phosphorylation state

Exposure of each of the three neurofilament proteins (NFPs) to AlCl3 resulted in their failure to migrate into sodium dodecyl sulfate (SDS)-containing gels. This effect was dependent on length of incubation (minimum, 2 h) and AlCl3 concentrations (minimum, 50 microM) and was not reversed by 20% SDS, 6 M urea, freeze-thawing, boiling, or extensive dialysis. The migration of vimentin and glial fibrillary acidic protein was not affected by AlCl3. The high-molecular-weight neurofilament subunit (NF-H) entered SDS-containing gels after exposure to aluminum lactate but migrated aberrantly as a long high-molecular-weight streak. Migration of the 160-kDa alpha-chymotryptic cleavage product of NF-H, which contains the higher phosphorylated tail domain, was also prevented from migrating into SDS-containing gels by AlCl3. Dephosphorylation of NF-H and the middle-molecular-weight neurofilament subunit (NF-M) eliminated these effects on gel migration. EDTA, EGTA, MgCl2, CaCl2, or FeCl3 had no effect on NF-H or NF-M migration; furthermore, preincubation with, or simultaneous exposure to, CaCl2 or FeCl3 did not alter the effect of AlCl3. One interpretation of these results is that Al3+ interacts with phosphate groups on extensively phosphorylated C-terminal sidearms of NFPs, resulting in intermolecular cross-linking. These findings demonstrate a direct effect of aluminum on NFPs and provide a possible mechanism for neurofilament accumulation in perikarya during aluminum intoxication.

Influx of zinc by channel catfish (Ictalurus punctatus): Uptake from external environmental solutions

1. Channel catfish (Ictalurus punctatus) take up zinc (measured with 65Zn) from external ambient solutions in a concentration dependent manner. At a concentration of 10(-6)M Zn, this uptake is equivalent to 0.4% of the total body Zn each day. 2. Zinc influx was increased by external acid conditions (decreasing pH from 7.3 to 5). 3. Elevated Ca2+ and Cd2+, but not Al3+, concentrations markedly decreased the uptake of Zn. 4. These observations may be relevant to circumstances that occur under natural conditions, and influence the zinc nutrition and toxicity of the fish.

Schistosoma mansoni: characterization of phosphoinositide response

Signal transduction pathways may have important regulatory roles in cellular events in the human parasite Schistosoma mansoni. The presence of the phosphoinositide response in S. mansoni was examined by radiolabeling intact worms with 20 muCi of [3H]myoinositol for 24 hr and stimulating parasites with 25 mM NaF and 10 microM AlCl3 in the presence of 10 mM LiCl. Total inositol phosphates were increased within 2 min and maximal accumulation was achieved after 30 min. Similar results were seen with the non-hydrolyzable GTP analogues GTP gamma S and GppNHp while only minimal changes were detected with GMP. Neomycin inhibited NaF-induced inositol phosphate production. NaF stimulated a significant 3.6-fold increase of inositol phosphates in females compared to males. These data suggest that stimulation of guanine nucleotide-binding regulatory proteins activates phospholipase C resulting in production of inositol phosphates in S. mansoni.

Effects of aluminum speciation on murine neuroblastoma cells

Murine neuroblastoma cells behave differently in the presence of Al(acac)3 [acac = 2,4-pentanedionate; acetylacetonate] or Al(malt)3 [malt = 3-hydroxy, 2-methyl, 4-pyronate; maltolate] with respect to Al(lac)3 [lac = 2-hydroxypropionate; lactate]. Thus, a remarkable cytotoxic effect was observed in the first case; on the contrary, an evident cytostatic and neuritogenic effect was produced by aqueous Al(lac)3. The hydrolytically stable complexes Al(acac)3 and Al(malt)3 were both toxic in the concentration range of 0.10-0.30 and 0.10-0.50 mM, respectively, over 24 h. In contrast with this behavior Al(lac)3 displayed a potent cytostatic activity with induction of neurites at 0.2-10 mM. Al(OH)3 manifested biological effects comparable to those exhibited by Al(lac)3. AlPO4 was also cytostatic and led to a morphological differentiation of the neuroblastoma cells, qualitatively different from that elicited by Al(lac)3. The morphological effects induced by Al(lac)3, Al(OH)3, and AlPO4 were irreversible.

Aluminum(III) influences the permeability of the blood-brain barrier to [14C]sucrose in rats

To determine the influence of the metal coordination sphere on the permeability of the blood-brain barrier (BBB), rats were injected intraperitoneally with aluminum lactate (Al(lact)3), aluminum acetylacetonate (Al(acac)3), aluminum maltolate (Al(malt)3) at pH 7.5, or with physiological saline. Two h after each treatment, [14C]sucrose physiological saline solution was injected in animals, and the radioactivity was measured in 5 brain regions (cerebral cortex, mesencephalon, diencephalon, medulla-pons, cerebellum). Radioactivity was significantly elevated in brains from animals treated with Al(malt)3 (hydrolytically stable and hydrophilic), and with Al(acac)3 (hydrolytically stable and lipophilic) but not with Al(lact)3. Time-course study carried out at 2, 4 and 24 h with different aluminum compounds showed a persistent radioactivity 24 h after treatment only in the brain from animals treated with Al(acac)3. Morin stain localized AlIII only in neurons from animals treated with Al(acac)3. These findings indicate that AlIII alters the BBB function in the rat either permanently or transiently depending on the physiochemical properties of the metal coordination sphere. Implications of these results, in terms of AlIII as a potential toxic factor in humans, are considered and discussed.

Mitosis and inhibition of intracellular transport stimulate palmitoylation of a 62-kD protein

Recent studies suggest that a cycle of acylation/deacylation is involved in the vesicular transport of proteins between intracellular compartments at both the budding and the fusion stage (Glick, B. S., and J. E. Rothman. 1987. Nature (Lond.). 326:309-312). Since a number of cellular processes requiring vesicular transport are inhibited during mitosis, we examined the fatty acylation of proteins in interphase and mitotic cells. We have identified a major palmitoylated protein with an apparent molecular weight of 62,000 (p62), whose level of acylation increases 5-10-fold during mitosis. Acylation was reversible and p62 was no longer palmitoylated in cells that have exited mitosis and entered G1. p62 is tightly bound to the cytoplasmic side of membranes, since it was sensitive to digestion with proteases in the absence of detergent and was not removed by treatment with 1 M KCl. p62 is removed from membranes by nonionic detergents or concentrations of urea greater than 4 M. The localization of p62 by subcellular fractionation is consistent with it being in the cis-Golgi or the cis-Golgi network. A palmitoylated protein of the same molecular weight was also observed in interphase cells treated with inhibitors of intracellular transport, such as brefeldin A, monensin, carbonylcyanide m-chlorophenylhydrazone, or aluminum fluoride. The protein palmitoylated in the presence of brefeldin A was shown to be the same as that palmitoylated during mitosis using partial proteolysis. Digestion with two enzymes, alkaline protease and endoprotease lys-C, generated the same 3H-palmitate-labeled peptide fragments from p62 from mitotic or brefeldin A-treated cells. We suggest that the acylation and deacylation of p62 may be important in vesicular transport and that this process may be regulated during mitosis.

Aluminum: a pH-dependent inhibitor of NADP-isocitrate dehydrogenase from porcine heart

Aluminum showed a pH-dependent inhibitory effect on NADP-isocitrate dehydrogenase from porcine heart. Aluminum ions (Al3+) acted as a partial competitive inhibitor of the enzyme with respect to the substrate threo-Ds-isocitrate and inhibited the enzyme non-competitively with respect to NADP at pH 6.85. Fractional velocity plot analysis showed the Ki of the enzyme for aluminum ions to be 0.88 microM. When pH was elevated to 8.0, aluminum ions, which occur as a form of the Al(OH)4- anion, acted as partial uncompetitive and non-competitive inhibitors of the enzyme with respect to the substrates isocitrate and NADP, respectively. The Kí of the enzyme was determined to be 5.64 microM at pH 8.0 by fractional velocity plot analysis. The inhibition of NADP-isocitrate dehydrogenase by two forms of aluminum ions may explain aluminum toxicity in various tissues and organs.

Characterization of GTP binding and hydrolysis in plasma membranes of zucchini

We have investigated the possibility that G-protein-like entities may be present in the plasma membrane (PM) of zucchini (Cucurbita pepo L.) hypocotyls by examining a number of criteria common to animal and yeast G-proteins. The GTP binding and hydrolysis characteristics of purified zucchini PM are similar to the characteristics of a number of known G-proteins. Our results demonstrate GTP binding to a single PM site having a Kd value between 16-31 nM. This binding has a high specificity for guanine nucleotides, and is stimulated by Mg2+, detergents, and fluoride or aluminium ions. The GTPase activity (Km = 0.49 micromole) of zucchini PM shows a sensitivity to NaF similar to that seen for other G-proteins. Localization of GTP mu 35S binding to nitrocellulose blots of proteins separated by SDS-PAGE indicates a 30-kDa protein as the predominant GTP-binding species in zucchini PM. Taken together, these data indicate that plant PM contains proteins which are biochemically similar to previously characterized G-proteins.

Effects of isoproterenol and forskolin on carbachol- and fluoroaluminate-induced polyphosphoinositide hydrolysis, inositol trisphosphate production, and contraction in bovine iris sphincter smooth muscle: interaction between cAMP and IP3 second messenger systems

We have investigated the effects of isoproterenol (ISO) and forskolin on carbachol(CCh)- and fluoroaluminate (AlF4-)-induced phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, myo-inositol 1,4,5-trisphosphate (IP3) production, 1,2-diacylglycerol, measured as phosphatidic acid (PA) formation, and contraction in the bovine iris sphincter smooth muscle. The data from these studies can be summarized as follows. (1) CCh (20 microM) stimulated significantly PIP2 hydrolysis, IP3 production, PA formation, and contraction. (2) Addition of ISO (0.1-25 microM), which raises the tissue cAMP level, to muscle precontracted with CCh attenuated PIP2 hydrolysis, IP3 production, PA formation and contraction in a time- and dose-dependent manner. (3) AlF4- (10 microM) induced a slow but progressive hydrolysis of PIP2, accompanied by parallel production of IP3, formation of PA, and contraction of the smooth muscle. The effects of AlF4- were dose-dependent and inhibited by deferoxamine, an Al3+ ion chelator. (4) Both forskolin (1-25 microM), which directly stimulates adenylate cyclase, and ISO inhibited the responses induced by AlF4- (10 microM) in a dose-dependent manner. (5) NaF (1-5 mM) had no effect on the activity of phospholipase C (PLC), purified from bovine iris sphincter. Furthermore, phosphorylation of the enzyme by catalytic subunit of protein kinase A had no inhibitory effect on PLC activity against PIP2. In conclusion, neither the muscarinic receptor nor PLC are the target sites for cAMP inhibition; instead the putative G-protein, which couples the activated muscarinic receptor to PLC, may be phosphorylated by cAMP-dependent protein kinase. This could attenuate the stimulation of PLC by the G-protein, thus resulting in inhibition of PIP2 hydrolysis and consequently leading to muscle relaxation. These results demonstrate cross-talk between the cAMP and IP3-Ca2+ second messenger systems and suggest that this could constitute a regulatory mechanism for the process of contraction-relaxation in smooth muscle.

Irregular opacities in the lung, occupational asthma, and airways dysfunction in aluminum workers

We examined chest X-rays, measured expiratory flows and FVC by spirometry and TLC by projected lung area, ascertained respiratory data by questionnaires, and performed chest examinations in 670 Southeastern aluminum workers and 659 unexposed regional controls. Both groups were asbestos exposed. More aluminum workers had irregular opacities and fewer had pleural abnormalities than did regional pipefitter referents. The pulmonary function tests were expressed as percentage of predicted to adjust for height, age and duration of smoking based on a randomly selected U.S. reference population. Data from aluminum workers were compared to regional controls with students "t" tests run for unequal size groups. Aluminum workers had significant reductions in FEV1 of 3.2% predicted (p less than .003), FEF25-75 of 11.3% predicted (p less than .0001), FEF75-85 of 22.5% predicted (p less than .0001), and an increased TLC of 2.0% predicted (p less than .005). The 145 who had never smoked (NS) were compared with 124 NS controls and showed this same pattern of differences; but in smokers, the differences were significant for mid and terminal flows, but not for FEV1. In aluminum workers who never smoked, asthma prevalence by history was 7.6% vs. 4.0% in controls, and wheezes were heard in 21.4% vs. 2.4% in controls. In aluminum workers who were current smokers, asthma prevalence was 16.4% vs. 9.4% in controls, and wheezes were heard in 43.7% vs. 21.1% in controls. Aluminum workers had significantly more asthma, wheezing, airways obstruction, and pulmonary parenchymal abnormalities similar to asbestosis than did regional blue collar controls not melting and casting aluminum.

Antibacterial activity of dental implant metals

This study was conducted to investigate the specific in vitro antibacterial effect of seven dental implant metals on oral bacteria which have often been identified in failing implants. The metals chosen for evaluation were titanium, chromium, cobalt, aluminum, iron, gold, and vanadium. These metals were selected because they are contained in many commonly used dental implants. The bacteria selected for this study included isolates of Porphyromonas endodontalis, Porphyromonas gingivalis, Prevotella intermedia, Prevotella melaniogenica, Actinobacillus actinomycetemcomitans, Actinomyces naeslundii, and Actinomyces viscosus. Sets of tubes containing either supplemented trypticase soy broth, brain-heart infusion-yeast extract, or brain-heart infusion-yeast extract with 5 percent defibrinated rabbit blood were aseptically prepared with doubling dilutions of the seven metals starting at an initial concentration of 500 micrograms/ml and terminating at 0 microgram/ml. Cultures of each organism were inoculated into each set of broth tubes containing all concentrations of metals. Tubes were incubated either anaerobically or in an atmosphere of 5 percent carbon dioxide for 48 hours at 35 degrees C and then assayed for ATP content which was proportional to the viable cellular biomass. The results showed that, although being bacteria and concentration dependent, all seven metals suppressed the growth of each organism. The rank order of antibacterial activity expressed by dental implant metals was gold > titanium > cobalt > vanadium > aluminum > chromium > iron.

Trimeric G-proteins of the trans-Golgi network are involved in the formation of constitutive secretory vesicles and immature secretory granules

Non-hydrolysable analogues of GTP, such as GTP gamma S and GMP-PNP, have previously been shown to inhibit the formation of constitutive secretory vesicles (CSVs) and immature secretory granules (ISGs) from the trans-Golgi network (TGN). Using a cell-free system, we show here that the formation of these vesicles is also inhibited by [A1F4]-, a compound known to act on trimeric G-proteins. Addition of highly purified G-protein beta gamma subunits stimulated, in a differential manner, the cell-free formation of both CSVs and ISGs. ADP-ribosylation experiments revealed the presence of a pertussis toxin-sensitive G-protein alpha subunit in the TGN. We conclude that trimeric G-proteins regulate the formation of secretory vesicles from the TGN.

Mechanism of fluoride activation of G protein-gated muscarinic atrial K+ channels

Aluminum fluoride (AlF4-) activates the heterotrimeric G protein Gs (stimulatory G protein of adenylylcyclase) (Sternweis, P. C., and Gilman, A. G. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 4888-4891) and GT (transducin), and for GT, Bigay et al. (Bigay, J., Deterre, P., Pfister, C., and Chabre, M. (1985) FEBS Lett. 191, 181-185) have made the intriguing proposal that AlF4- acts by mimicking the gamma-phosphate of GTP. The endogenous G protein (probably G alpha i-2 or G alpha i-3 (Yatani, A., Mattera, R., Codina, J., Graf, R., Okabe, K., Padrell, E., Iyengar, R., Brown, A. M., and Birnbaumer, L. (1988) Nature 336, 680-682) that stimulates the muscarinic atrial K+ (K+[ACh]) channel is also thought to be activated by AlF4- (Kurachi, Y., Nakajima, T., and Ito, H. (1987) Circulation 76, 105P). To investigate the AlF4- mechanism, we applied potassium fluoride (KF) to the cytoplasmic face of inside-out membrane patches excised from guinea pig atria. We found that KF activated single K+[ACh] channel currents in both a concentration- and a Mg(2+)-dependent manner. Activation persisted following removal of KF, but unlike activation by guanosine 5'-(3-thiotriphosphate) (GTP gamma S), was fully reversed by removal of Mg2+. Evidence for Al3+ involvement was that the Al3+ chelator deferoxamine (500 microM) inhibited KF activation and that at low concentrations of KF (less than 1 mM), micromolar AlCl3 concentrations potentiated KF stimulation. The rate of activation produced by KF was far slower than the rate produced by GTP or GTP gamma S, and unlike these guanine nucleotides, the rate was unchanged in the presence of agonist. To test the gamma-phosphate-mimicking hypothesis, we evaluated the requirement for GDP; and to accomplish this, it was necessary to establish a condition that ensured exchange of guanine nucleotides. This condition was satisfied by using the muscarinic agonist carbachol because both the rate and the extent of activation of the K+[ACh] channels produced by GTP were much faster in carbachol, and both were greatly slowed when GDP was added along with GTP. By contrast, the effects of KF were unchanged by carbachol in the presence or absence of GDP. Further evidence that GDP is not essential for activation by AlF4- was provided by the observation that during carbachol activation and following extensive washing with GMP, guanosine 5'-O-(2-thiodiphosphate) at blocking concentrations had no effect on activation produced by KF.(ABSTRACT TRUNCATED AT 400 WORDS)

Aluminum decreases the zinc concentration of soft tissues and bones of rats fed a low calcium-magnesium diet

The relationship between magnesium (Mg) and zinc (Zn) in soft tissues and bone of rats was studied after administration of unbalanced mineral diets. Minerals and metals in soft tissues and bone were determined using inductively coupled plasma emission spectrometry (ICP). There were significant positive correlations between serum Zn and Mg levels, between serum Zn and Zn content of soft tissues and bone, and between serum Mg levels and Zn content of bone and soft tissues in rats fed unbalanced mineral diets. A significant positive correlation was also found between Zn and Mg content in the lumbar spine and femoral bone of rats. It appears that altered bone mineralization induced by unbalanced mineral diets leads to mobilization of Mg and Zn from rat bones in similar ways.

Fluoroaluminate treatment of rat liver microsomes inhibits GTP-dependent vesicle fusion

1. Inhibition of GTP-dependent membrane fusion of rat liver microsomes requires preincubation of the membranes with GDP (17 microM) and relatively high Mg2+ concentration (0.5 mM) as well as AlCl3 (30 microM) and KF (5 mM). Preincubation is required for maximal inhibition (75%). 2. Vesicle fusion in rat liver microsomes has been demonstrated in the absence of polyethylene glycol (PEG). Further, inhibition by AlF4- of GTP-dependent vesicle fusion in the absence of PEG has been demonstrated. 3. Under similar preincubation conditions AlF4- can bring about inhibition (80%) of the high-affinity PEG-stimulated GTPase activity in rat liver microsomes, previously described by Nicchitta, Joseph & Williamson [(1986) FEBS Lett. 209, 243-248]. 4. Preincubation of small-Mr GTP-binding proteins (Gn proteins) on nitrocellulose strips with GDP (20 pM), AlCl3 (30 microM) and KF (5 mM) results in inhibition of binding of guanosine 5'-[gamma-[35S]thio]triphosphate to Gn proteins. The extent of inhibition of this binding differs for different Gn proteins.

Time-gated fluorescence spectroscopy of porphyrin derivatives and aluminium phthalocyanine incorporated in vivo in a murine ascitic tumour model

The effect of systemic administration on drug uptake at cellular level was evaluated using time-gated fluorescence spectroscopy performed on a murine ascitic tumour model. Mice bearing L1210 leukaemia were injected intraperitoneally or intravenously with 25 mg per kg body weight hematoporphyrin derivative (HpD), 12.5 mg per kg body weight photofrin II (PII), 25 or 5 mg per kg body weight disulphonated aluminium phthalocyanine (AlS2Pc). Every 2 h and for up to 22 or 30 h, mice were sacrificed, leukaemic cells extracted from the peritoneum, washed, and resuspended in buffer for fluorescence measurements. HpD and PII emission spectra were almost identical 12 h after intraperitoneal injection with main peaks at 630 nm and no appreciable changes afterwards. In the first 12 h, the PII fluorescence spectrum was constant, while in the case of HpD a shoulder at 615 nm was detectable. Similar fluorescence behaviour was observed after intravenous administration of porphyrin derivatives. These results seem to confirm that the tumour localizing fraction is the part actually retained by the cells. The AlS2Pc spectrum peaked at 685 nm and did not change in any of our experiments. AlS2Pc is incorporated more rapidly with respect to porphyrins, as was clearly observed in the case of intravenous administration, where the AlS2Pc fluorescence was readily detectable after 2 h, whereas the PII emission became apparent only after 4-6 h.

Binding of ARF and beta-COP to Golgi membranes: possible regulation by a trimeric G protein

The binding of cytosolic coat proteins to organelles may regulate membrane structure and traffic. Evidence is presented that a small guanosine triphosphate (GTP)-binding protein, the adenosine diphosphate ribosylation factor (ARF), reversibly associates with the Golgi apparatus in an energy, GTP, and fungal metabolite brefeldin A (BFA)-sensitive manner similar to, but distinguishable from, the 110-kilodalton cytosolic coat protein beta-COP. Addition of beta gamma subunits of G proteins inhibited the association of both ARF and beta-COP with Golgi membranes that occurred upon incubation with guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S). Thus, heterotrimeric G proteins may function to regulate the assembly of coat proteins onto the Golgi membrane.

Aluminum interrupts the formation of alkaline-ribonuclease-inhibitor complex from bovine brain

The effect of aluminum on alkaline ribonuclease (RNase) and RNase inhibitor, purified from bovine brain, was investigated. Incubation of alkaline RNase with aluminum interrupted binding of RNase inhibitor to alkaline RNase. A stoichiometry of 1:1 for the binding of aluminum to brain alkaline RNase was estimated, whereas no aluminum was found to be bound to the RNase inhibitor. Aluminum-bound alkaline RNase, however, retained a full alkaline RNase activity. None of the enzyme-bound aluminum was dissociated by dialysis against 50 mM Hepes, pH 7.0, at 4 degrees C for 24 h. Citrate, EDTA, NaF and apotransferrin protected the alkaline RNase against aluminum binding. Aluminum did not bind to the incubated alkaline RNase-inhibitor complex, suggesting that aluminum might compete with RNase inhibitor for the binding site. However, the data from chemical modification and spectroscopic studies indicate that it is also highly possible that aluminum binding to the enzyme induces conformational changes at or near the inhibitor-binding site, which subsequently interrupt binding of RNase inhibitor to alkaline RNase. These results suggest that accumulation of aluminum in brain might affect the regulation of RNA metabolism.

Modulation of [3H]dihydropyridine binding by activation of protein kinase C in vascular smooth muscle

The influence of noradrenaline and protein kinase C modulators on (+)-[3H]isradipine binding to voltage-dependent calcium channels has been studied in membranes of equine portal vein smooth muscle and intact strips isolated from rat portal vein. Specific (+)-[3H]isradipine binding to intact strips was increased by noradrenaline, a combination of aluminium and fluoride, and phorbol esters. The increase in isradipine binding induced by noradrenaline was inhibited by 1 microM prazosin while that induced by phorbol esters was inhibited by H7 (a protein kinase C inhibitor). In strips pretreated 6 h with 10 micrograms.ml-1 pertussis toxin, the noradrenaline-induced increase in isradipine binding was unchanged. In contrast, isradipine binding to membranes was unaffected by noradrenaline or GTP-gamma-S. Only phorbol esters had a stimulatory effect on isradipine binding when membranes were incubated in a medium containing 10 microM ATP and 5 mM Mg2+. Scatchard plot analysis reveals that the stimulation of isradipine binding by both noradrenaline and phorbol esters appears to result from a decrease in KD rather than an effect on the maximal binding capacity. Contractions evoked by noradrenaline were concentration-dependently depressed by isradipine. About 30% of the response was resistant to inhibition, while KCl-induced contractions were completely blocked. However, noradrenaline-induced contractions were more sensitive to isradipine inhibition than were KCl-induced contractions. These results suggest that activation of protein kinase C modulates isradipine binding to voltage-dependent Ca2+ channels independently of a separate modulation by membrane depolarization.

Different mechanisms of homologous and heterologous desensitization of thrombin-induced endothelial prostacyclin production

Several workers have described desensitization of endothelial prostacyclin production but conflicting evidence has been published regarding the mechanism of desensitization, whether it is homologous (agonist specific) or heterologous, and whether inactivation of cyclooxygenase is involved. The purpose of the present study was to determine the relation between the intensity of a first thrombin stimulus and the subsequent response to a repeat thrombin, histamine, ionophore A23187 or aluminium fluoride (AlF4) stimulation and to determine possible targets of desensitization. Following thrombin stimulation of confluent cultured human umbilical vein endothelial cells (HUVEC) only homologous desensitization of inositol phosphate production was observed. Both homologous and heterologous desensitization of arachidonic acid release and prostacyclin production occurred, the latter towards both histamine and the ionophore A23187. For any given dose of the first stimulant there was a much greater effect on the homologous response than on the heterologous response. These differences suggest different mechanisms. The homologous desensitization probably involves the receptor whereas the present results suggest that the target of heterologous desensitization is distal to calcium mobilization in the signal transduction pathway. The possibilities include decreased activity of phospholipase A2 or a decreased pool of accessible arachidonic acid.

Interaction of aluminium and gallium with human lymphocytes: the role of transferrin

Aluminium-transferrin (Al-Tf) and gallium-transferrin caused a dose-dependent decrease in proliferation of human peripheral blood lymphocytes cultured for 3 days with phytohaemagglutinin (PHA). Addition of apotransferrin reduced the inhibitory effect. Al added as AlCl3 or aluminium citrate had no effect, and there was no significant difference in the response of cells from renal failure patients with or without high serum Al levels or controls. Lymphocytes cultured in the presence of Al-Tf showed a dose-dependent uptake of Al, whereas uptake from aluminium citrate was low and not dose-dependent. Uptake from AlCl3 was very high but probably involved a nonspecific uptake mechanism. Levels of Al in freshly isolated lymphocytes were approximately 1.6 ng/10(6) cells, there being no difference between cells from patients and controls. It is concluded that Al, when bound to transferrin, may have a detrimental effect on lymphocyte function and might contribute to the decreased immune responsiveness of renal failure patients on haemodialysis. However, lymphocyte Al levels are probably not useful as a marker of Al overload in such patients.

Interference of AlF4- with nucleotide and DNA binding of rat histone H1 in vitro. Implications for the pathogenesis of Alzheimer's disease

We demonstrate here that the H2PO4- analogue AlF4- binds to the nucleotide-binding site of rat liver histone H1 in vitro, and interferes with nucleotide recognition and H1 DNA binding. AlF4- may thus compromise the genetically determined pattern of protein synthesis through binding to H1, the general repressor. The present findings are of interest as a number of studies have implicated aluminium as a factor in the pathogenesis of Alzheimer's disease.

Activation of acid ribonuclease from bovine brain by aluminum

An acid ribonuclease (optimum pH 6.0) has been purified from bovine brain in a five-step procedure. The preparation appeared homogeneous on SDS-polyacrylamide gel electrophoresis. The molecular size of the acid ribonuclease is 70 kDa and it is a dimeric protein with a subunit molecular size of 35 kDa. The acid RNase was activated by aluminum at low concentration. Preincubation of the acid RNase with 10 microM increased the specific activity of the enzyme 2.3-fold at acid pH, while the effect of aluminum was much weaker at alkaline pH under otherwise the same conditions. A stoichiometry of 1: 1 for the binding aluminum to brain acid RNase was estimated. None of the enzyme-bound aluminum was dissociated by dialysis against 50 mM HEPES, pH 7.0 at 4 degrees C for 24 h. Citrate, EDTA, NaF, and apotransferrin abolished the effects of aluminum on the enzyme. Ribonucleic acid also protected the enzyme against the activation caused by aluminum. These results suggest that accumulation of aluminum in brain may change the regulation of ribonucleic acid metabolism.

Photodynamic therapy induces rapid cell death by apoptosis in L5178Y mouse lymphoma cells

The mode of cell death of two strains of mouse lymphoma L5178Y cells was studied following photodynamic therapy (PDT) sensitized by chloroaluminum phthalocyanine. Strains LY-R and LY-S differ in their relative sensitivities to UVC radiation, X-radiation, and PDT; both responded to PDT by undergoing apoptosis. The DNA was degraded into fragments with lengths which are multiples of approximately 180-190 base pairs (i.e., oligonucleosome size), a biochemical marker of apoptosis. The DNA fragmentation was dose and time dependent which indicates this response to be an enzymic process related to cell killing. Cycloheximide, a protein synthesis inhibitor, and actinomycin D, an RNA synthesis inhibitor, enhanced the endonucleolytic DNA fragmentation. Transmission electron microscopy revealed chromatin condensation around the periphery of the nucleus, which is also characteristic of apoptosis. The induction of apoptosis in L5178Y cells by PDT was rapid, with marked degradation of DNA occurring in as little as 30 min. The rapidity of the response to PDT suggests that cellular damage produced by PDT can directly activate endonucleolysis and chromatin condensation, thereby by-passing many of the early steps in the signal transduction program which are acted upon by other agents causing apoptosis.