Effects of Aluminum and Calcium on Acetyl-CoA Metabolism in Rat Brain Mitochondria

Abstract: Al complexes are known to accumulate in extra- and intracellular compartments of the brain in the course of different encephalopathies. In this study possible effects of Al accumulation in the cytoplasmic compartment on mitochondrial metabolism were investigated. Al, like Ca, inhibited pyruvate utilization as well as citrate and oxoglutarate accumulation by whole brain mitochondria. Potencies of Ca²⁺_total effects were 10–20 times stronger than those of Al. Al decreased mitochondrial acetyl-CoA content in a concentration-dependent manner, along with an equivalent rise of free CoA level, whereas Ca caused loss of both intermediates from mitochondria. In the absence of P_i in the medium, Ca had no effect on mitochondrial metabolism, whereas Al lost its ability to suppress pyruvate utilization and acetyl-CoA content in Ca-free conditions. Verapamil potentiated, whereas ruthenium red reversed, Ca-evoked suppression of mitochondrial metabolism. On the other hand, in Ca-supplemented medium, Al partially overcame the inhibitory influence of verapamil. Accordingly, verapamil increased mitochondrial Ca levels much more strongly than Al. However, Al partially reversed the verapamil-evoked rise of Ca²⁺_total level. These data indicate that Al accumulated in cytoplasm in the form of the Al(PO₄)OH⁻ complex may inhibit mitochondrial functions by an increase of intramitochondrial [Ca²⁺]_total resulting from the Al-evoked rise of cytoplasmic [Ca²⁺]_free, as well as from inhibitory interference with the verapamil binding site on the Na⁺/Ca²⁺ antiporter.     

Addition of aluminum oxide microparticles to Trichoderma viride My preculture enhances cellulase production and influences fungal morphology

Morphological engineering techniques have recently become popular, since they are used to increase the production of a variety of metabolites and enzymes when fungi are grown in submerged cultures. This study aimed to facilitate cellulase production by adding aluminum oxide to Trichoderma viride My precultures.

The results showed that the highest cellulase activity was achieved when aluminum oxide at 10 g/L was used, and the activities of cellulase for filter paper and endoglucanase activity assays increased from 519.11 to 607.35 U/mL by 17.1%, and from 810.08 U/mL to 917.59 U/mL by 13.3%, compared with the control, respectively. Addition of aluminum oxide decreased the size of T. viride My pellets and increased the final pH. The changes in pellet diameter after the addition of different concentrations of aluminum oxide were fitted using a modified exponential decay model, which could precisely predict the pellet size by controlling aluminum oxide concentration.

The optimum concentration of microparticles, and therefore pellet size, could significantly improve cellulase production, which is an encouraging step towards commercial cellulase production.

     

Genotoxic and cytotoxic effects induced by aluminum in the lymphocytes of the common carp (Cyprinus carpio)

Few studies have been made in regard to the effect of aluminum on the molecular and cellular structure and function of aquatic organisms; therefore, in the present report we determined the genotoxic and cytotoxic effects induced by the metal on the lymphocytes of carp (Cyprinus carpio). Three groups of fish were exposed to 0.05, 120, and 239 mg/L of aluminum (Al), respectively, by using Al₂ (SO₄)₃·7H₂O, and another group was included as control. The cells obtained were studied with the comet assay, flow cytometry, and the TUNEL method. With the first method we found a concentration and time dependent, significant increase in the amount of DNA damage induced by Al, and a higher damage when we evaluated the level of oxidized DNA. By applying flow cytometry we established that the metal induced a DNA content increase and ploidy modifications as well as apoptosis and disturbances of the cell cycle progression. With the last method we determined a significant increase in the amount of apoptotic cells, mainly in the 72–96 h period. Our results established that Al caused deleterious DNA and cellular effects in the tested organism, and they suggested the pertinence of evaluating toxicity induced by the metal in organisms living in contaminated water bodies.     

Bacterial citrate synthase expression and soil aluminum tolerance in transgenic alfalfa

Alfalfa is very sensitive to soil acidity and its yield and stand duration are compromised due to inhibited root growth and reduced nitrogen fixation caused by Al toxicity. Soil improvement by liming is expensive and only partially effective, and conventional plant breeding for Al tolerance has had limited success. Because tobacco and papaya plants overexpressing Pseudomonas aeruginosa citrate synthase (CS) have been reported to exhibit enhanced tolerance to Al, alfalfa was engineered by introducing the CS gene controlled by the Arabidopsis Act2 constitutive promoter or the tobacco RB7 root-specific promoter. Fifteen transgenic plants were assayed for exclusion of Al from the root tip, for internal citrate content, for growth in in vitro assays, or for shoot and root growth in either hydroponics or in soil assays. Overall, only the soil assays yielded consistent results. Based on the soil assays, two transgenic events were identified that were more aluminum-tolerant than the non-transgenic control, confirming that citrate synthase overexpression can be a useful tool to help achieve aluminum tolerance. Pierluigi Barone and Daniele Rosellini contributed equally to this work.     

A novel metabolic network leads to enhanced citrate biogenesis in <Emphasis Type="Italic">Pseudomonas </Emphasis><Emphasis Type="Italic">fluorescens</Emphasis> exposed to aluminum toxicity

Aluminum (Al), an environmental toxin, is known to have a negative impact on various biological systems. However, some microbes have devised intricate mechanisms to combat the toxic influence of this trivalent metal. In this study, Pseudomonas fluorescens grown in malate invoked a unique metabolic shift to promote the synthesis of citrate, a metabolite involved in the sequestration of Al. Electrophoretic and spectrophotometric assays revealed several malate-metabolizing enzymes including malate dehydrogenase (MDH) and malic enzyme (ME) displayed increases in activity and expression in the Al-treated cells. Whereas pyruvate dehydrogenase (PDH) also showed increased activity and expression in the Al-stressed cultures, phosphoenolpyruvate carboxykinase (PEPCK) displayed a marked diminution in the Al-treated cells. The upregulation of citrate synthase (CS) coupled with the diminished activities of aconitase (ACN) and NAD-isocitrate dehydrogenase (NAD-ICDH) appeared to be instrumental in the accumulation of citrate. HPLC experiments revealed high levels of citrate in the Al-stressed cultures. Thus, an Al-enriched environment provoked a metabolic shift in P. fluorescens dedicated to the conversion of malate to citrate.     

Tissue Response to a Supplement High in Aluminum and Silicon

The objective was to determine the effects of sodium zeolite A (SZA) on mineral metabolism and tissue mineral composition in calves. Twenty calves were placed on study at 3 days of age and were placed into one of two groups: SS, which received 0.05% BW SZA added to their milk replacer, and CO, which received only milk replacer. Blood samples were taken on days 0, 30, and 60 for mineral analysis. Urine and feces were collected on day 30 for mineral metabolism, and on day 60, the calves were euthanized, and samples were taken from numerous organs for mineral analyses. Aluminum retention was increased in the SS calves (p = 0.001). Silicon concentrations were increased in the aorta, spleen, lung, muscle, and kidney of the SS calves, and aluminum was increased in all SS tissues (p < 0.05). Calcium concentrations were increased in aorta, liver, muscle, and tendon; phosphorus concentrations were increased in aorta, but decreased in plasma; magnesium concentrations were increased in aorta, heart, kidney, liver, and pancreas, but decreased in plasma; and iron concentrations were decreased in kidney and liver (p < 0.05). The accumulation of tissue aluminum and therefore potential adverse consequences may preclude any benefits of using SZA as a dietary supplement.     

Intracellular changes of metal elements by fucoidan extracted from brown seaweed (Cladosiphon okamuranus)

This study was undertaken to elucidate the intracellular changes of metal elements after the administration of fucoidan extracted from Cladosiphon okamuranus. TRL1215 cells (normal rat liver cell line) were treated with 0, 0.1, or 1.0 mg/ml fucoidan and incubated in 5% CO2 at 37 degrees C. The cellular levels of Mg, Al, Fe, and Zn were significantly increased in the 1.0 mg/ml fucoidan-treated cells compared to those of the 0.1 mg/ml fucoidan-treated cells and the control. Next, TRL1215 cells were cultured on Mylar film overnight. At 24 h after 5-bromo-2'-deoxyuridine dosing, 0, 0.1, or 1.0 mg/ml fucoidan was treated for 9 h. The cellular distribution of elements was analyzed using in-air micro-micro-particle induced X-ray emission. The X-ray spectra showed that yields of Al, Mg, and Zn were high in order of the 1.0 mg/ml fucoidan-treated sample, the 0.1 mg/ml fucoidan-treated sample, and the control. Fe yield was mildly increased by fucoidan administration. In fucoidan-treated cells, the focal accumulation of Br was correlated spatially with phosphorous-rich region, suggesting that Br was localized within the nucleus. Al distribution provided a spatial association with Br map. These data suggest that fucoidan increases the accumulations of Al, Mg, Fe, and Zn in normal rat hepatocytes, and fucoidan-binding Al is postulated to be transferred into the nucleus.     

Specific sensing of poly G by the aluminum-salophen complex

The Al(III)-salophen complex 1 exhibited strong spectroscopic changes specifically upon addition of polyG and GpG, while double stranded DNA and RNA, and single stranded polyA, polyU and polyC induced negligible spectral changes of 1. Titrations with mono-nucleotides yielded no spectroscopic changes, revealing that there must be at least two consecutive guanines in single stranded oligonucleotide structure for a measurable spectroscopic change of 1. Preliminary results show that 1 has moderate antiproliferative effect on a number of human tumour cell lines.     

A scale of metal ion binding strengths correlating with ionic charge, Pauling electronegativity, toxicity, and other physiological effects

Equilibrium constants for binding to plant plasma membranes have been reported for several metal ions, based upon adsorption studies and zeta-potential measurements. LogK values for the ions are these: Al(3+), 4.30; La(3+), 3.34; Cu(2+), 2.60; Ca(2+) and Mg(2+), 1.48; Na(+) and K(+), 0 M(-1). These values correlate well with logK values for ion binding to many organic and inorganic ligands. LogK values for metal ion binding to 12 ligands were normalized and averaged to produce a scale for the binding of 49 ions. The scale correlates well with the values presented above (R(2)=0.998) and with ion binding to cell walls and other biomass. The scale is closely related to the charge (Z) and Pauling electronegativity (PE) of 48 ions (all but Hg(2+)); R(2)=0.969 for the equation (Scale values)=-1.68+Z(1.22+0.444PE). Minimum rhizotoxicity of metal ions appears to be determined by binding strengths: log a(PM,M)=1.60-2.41exp[0.238(Scale values)] determines the value of ion activities at the plasma membrane surface (a(PM,M)) that will ensure inhibition of root elongation. Additional toxicity appears to be related to softness, accounting for the great toxicity of Ag(+), for example. These binding-strength values correlate with additional physiological effects and are suitable for the computation of cell-surface electrical potentials.     

13C heteronuclear NMR studies of the interaction of cultured neurons and astrocytes and aluminum blockade of the preferential release of citrate from astrocytes

Citrate has been identified as a major tricarboxylic acid (TCA) cycle constituent preferentially released by astrocytes. We undertook the present study to examine further the nature of metabolic compartmentation in central nervous system tissues using ¹³C-labeled glucose and to provide new information on the influence of aluminum on the metabolic interaction between neurons and astrocytes. Metabolites released into the culture medium from astrocytes and neuron-astrocyte coculture, as well as the perchloric acid extracts of the cells were analyzed using 2D ¹H and ¹³C NMR spectroscopy. Astrocytes released citrate into the culture medium and the released citrate was consumed by neurons in coculture. Citrate release by astrocytes was blocked in the presence of aluminum, with progressive accumulation of citrate within the cells. We propose citrate supply is a more efficient energy source than lactate for neurons to produce ATP, especially in the hypoglycemic state on account of it being a direct component of the TCA cycle. Astrocytes may be the cellular compartment for aluminum accumulation as a citrate complex in the brain.