Kinetics of aluminum-induced inhibition of delta-aminolevulinic acid dehydratase in vitro

Both aluminum and polyphenols in green tea decoction (Camellia sinensis) affect iron status and hematological parameters in rats

BACKGROUND

Green tea leaves naturally contain high levels of polyphenols and aluminum (Al). Polyphenols in green tea decoction are considered to be one of the major factors responsible of low iron status. However, the effects of Al from green tea decoction on iron status and hematological parameters remained unclear.

AIM OF THE STUDY

The objective was to investigate the Al absorption from green tea decoction and studied its influence on iron status and hematological parameters in rats.

METHODS

During the experiment period, rats were given the experimental diet + a simple dose of Al sulfate with or without graded doses of green tea decoction (25, 50 and 100 g/l). The Al absorption was evaluated in the serum; however, iron status was evaluated by the iron concentration in the liver, kidney, spleen and femur. In addition, the hemoglobin and hematocrit were evaluated.

RESULTS

Our results showed that the serum Al significantly increased between 61.5 and 342%, as tea doses-dependant. The Al sulfate significantly decreased the reserve of iron in all studied organs between 21.7 and 17% (P < 0.05). In groups receiving green tea decoction alone or Al + graded doses of tea, the reserve of iron significantly decreased in all studied organs between 59.4 and 18.5% (P < 0.01). Al alone or associated with drinking doses of tea significantly decreased hemoglobin concentration between 23.6 and 9% (P < 0.05) and hematocrit between 12.7 and 7% (P < 0.01).

CONCLUSION

Our data showed that Al from green tea decoction was more absorbed in the serum than Al sulfate. Al absorption was associated with low iron status and reduction of hemoglobin and hematocrit. Considering that Al competes with iron in different stage of erythropoiesis including transferrin binding, so we could assume that the negative effect of tea on iron status arises not only from polyphenols iron complexes but also from Al released in tea decoction.

The inhibition kinetics of yeast glutathione reductase by some metal ions

Glutathione reductase (GR, type IV, Baker's yeast, E.C 1.6.4.2) is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH). In this study some metal ions have been tested on GR; lithium, manganese, molybdate, aluminium, barium, zinc, calcium, cadmium and nickel. Cadmium, nickel and calcium showed a good to moderate inhibitory effect on yeast GR. GR is inhibited non-competitively by Zn2+ (up to 2 mM) and activated above this concentration. Ca2+ inhibition was non-competitive with respect to GSSG and uncompetitive with respect to NADPH. Nickel inhibition was competitive with respect to GSSG and uncompetitive with respect to NADPH. The inhibition constants for these metals on GR were determined. The chelating agent EDTA recovered 90% of the GR activity inhibited by these metals.

Hematological changes in rats chronically exposed to oral aluminum

This study was aimed to investigate the effects of the long-term oral exposure to aluminum sulfate on hematological parameters in rats. For this purpose, 24 adult female Wistar rats were divided in three groups with 8 animals each (control, citrate, and citrate plus aluminum groups). Rats from control and citrate groups had free access to tap water and to a sodium citrate solution (35 mM), respectively. Rats from citrate plus aluminum group received, as unique source of liquid, an aluminum sulfate solution (30 mM) diluted in the above-mentioned sodium citrate solution, ad libitum. After the treatment period (18 months), aluminum-exposed rats showed a significant decrease in the number of red blood cells, blood hemoglobin concentration and hematocrit when compared to rats from the control group. Serum iron levels were also significantly lower in citrate plus aluminum group, whereas total iron binding capacity did not change after citrate plus aluminum exposure. Erythrocyte thiobarbituric acid-reactive substances (TBARS) and nonprotein thiols (NPSH) levels, erythrocyte osmotic fragility and hepatic delta-aminolevulinic acid dehydratase (delta-ALA-D) activity did not change after treatment with citrate plus aluminum. Conversely, aluminum exposure increased delta-ALA-D activity in bone marrow. The present results indicate that long-term oral exposure to low doses of aluminum sulfate promotes alterations on erythrocyte parameters in rats, probably as a consequence of alterations in the iron status. In addition, although the details of the underlying mechanism remain unclear, our study reports, for the first time, a stimulatory effect of chronic aluminum exposure on bone marrow delta-ALA-D activity.

Aluminum-induced oxidative stress in rat brain: response to combined administration of citric acid and HEDTA

Aluminum, a known neurotoxic substance, has been suggested as a contributing factor in the pathogenesis of Alzheimer's disease. Therapeutic efficacy of combined administration of citric acid (CA) and N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) was evaluated in decreasing blood and brain aluminum concentration and parameters indicative of hematological disorders and brain oxidative stress. Adult male wistar rats were exposed to drinking water containing 0.2% aluminum nitrate for 8 months and treated once daily for 5 consecutive days with CA (50 mg/kg, orally) or HEDTA (50 mg/kg, intraperitoneally) either individually or in combination. Aluminum exposure significantly inhibited blood delta-aminolevulinic acid dehydratase while increased zinc protoporphyrin confirming changed heme biosynthesis. Significant decrease in the level of glutathione S-transferase in various brain regions and an increase in whole brain thiobarbituric acid reactive substance, and oxidized glutathione (GSSG) levels were also observed. Glutathione peroxidase activity showed a significant increase in cerebellum of aluminum exposed rats. Most of the above parameters responded moderately to the individual treatment with CA and HEDTA, but significantly reduced blood and brain aluminum burden. However, more pronounced beneficial effects on some of the above described parameters were observed when CA and HEDTA were administered concomitantly. Blood and brain aluminum concentration however, showed no further decline on combined treatment over the individual effect with HEDTA or CA. We conclude that in order to achieve an optimum effect of chelation, combined administration of CA and HEDTA might be preferred. However, further work is needed before a final recommendation could be made.

Effects of aluminum sulfate on erythropoiesis in rats

The aim of this study was to investigate the effects of chronically administered aluminum on erythropoiesis in rats. After treatment (i.p. injections of Al(2)(SO(4))(3), 50 micromol/kg body weight, five times a week) for 3 months, the treated (Al) group showed significantly decreased hemoglobin concentration (32%) and hematocrit (24%) compared with the control group. Serum iron decreased significantly in the Al group, whereas total iron binding capacity did not change. Treatment did not alter the activity of hepatic, renal or cerebral delta-ALA-D. Biochemical measurements related to 2-thiobarbituric acid-reactive substance (TBARS) levels from serum and hepatic, renal and cerebral homogenates also did not change after treatment. Hepatic concentrations of aluminum were higher in the Al group than in the control group. Renal and cerebral aluminum concentrations did not vary between groups. The present results indicate that exposure to aluminum sulfate promotes signs of anemia in rats as a consequence of alterations in iron status.

Aluminum: impacts and disease

Aluminum is the most widely distributed metal in the environment and is extensively used in modern daily life. Aluminum enters into the body from the environment and from diet and medication. However, there is no known physiological role for aluminum within the body and hence this metal may produce adverse physiological effects. The impact of aluminum on neural tissues is well reported but studies on extraneural tissues are not well summarized. In this review, the impacts of aluminum on humans and its impact on major physiological systems are summarized and discussed. The neuropathologies associated with high brain aluminum levels, including structural, biochemical, and neurobehavioral changes, have been summarized. In addition, the impact of aluminum on the musculoskeletal system, respiratory system, cardiovascular system, hepatobiliary system, endocrine system, urinary system, and reproductive system are discussed.

Chronic exposure to aluminium impairs the glutamate-nitric oxide-cyclic GMP pathway in the rat in vivo

Aluminium is neurotoxic and is considered a possible etiologic factor in Alzheimer's disease, dialysis syndrome and other neurological disorders. The molecular mechanism of aluminium-induced impairment of neurological functions remains unclear. We showed that aluminium impairs the glutamate-nitric oxide-cGMP pathway in cultured neurons. The aim of this work was to assess by in vivo brain microdialysis whether chronic administration of aluminium in the drinking water (2.5% aluminium sulfate) also impairs the glutamate-nitric oxide-cGMP pathway in the cerebellum of rats in vivo. Chronic exposure to aluminium reduced NMDA-induced increase of extracellular cGMP by ca 50%. The increase in extracellular cGMP induced by the nitric oxide generating agent S-nitroso-N-acetylpenicillamine was higher (240%) in rats treated with aluminium than in controls. Immunoblotting experiments showed that aluminium reduced the cerebellar content of calmodulin and nitric oxide synthase by 34 and 15%, respectively. Basal activity of soluble guanylate cyclase was decreased by 66% in aluminium-treated rats, while the activity after stimulation with S-nitroso-N-acetylpenicillamine was similar to controls. Basal cGMP in the cerebellar extracellular space was decreased by 50% in aluminium-treated rats. These results indicate that chronic exposure to aluminium reduces the basal activity of guanylate cyclase and impairs the glutamate-nitric oxide-cGMP pathway in the animal in vivo.