Porphobilinogen synthase from the butterfly, Pieris brassicae: purification and comparative characterization

Porphobilinogen represents a key building block of tetrapyrroles serving as functional ligands of many vitally important proteins. Here we report the first purification of porphobilinogen synthase (PBGS) from whole insects by sequentially employing two modes of native electrophoresis on polyacrylamide gels subsequent to more conventional procedures. Using adults of Pieris brassicae L. (Lepidoptera: Pieridae) we achieved approximately 10,000-fold purification with final yields of up to 25% of electrophoretically pure PBGS with a specific activity of approximately 160 micromol PBG h(-1) mg(-1) at 37 degrees C and an affinity of 0.36 mM to its substrate 5-aminolevulinic acid. Enzyme activity was inhibited by the substrate mimics, levulinic acid and succinylacetone, and by chelating agents. PBGS behaved as a relatively heat-stable octameric complex of 292.3 kDa composed of 36.5 kDa subunits. Most general features of this insect PBGS were comparable to those published for other animal PBGS enzymes, while remarkable differences were found to the reported recombinant Drosophila enzyme. Moreover, rabbit antiserum directed against purified Pieris PBGS revealed significant immunological differences among insect PBGS enzymes from a wide range of orders contrasting to the overall evolutionary conserved features of this enzyme.

Cadmium inhibits δ-aminolevulinate dehydratase from rat lung in vitro: Interaction with chelating and antioxidant agents

The effect of cadmium (Cd(2+)) on delta-aminolevulinate dehydratase (delta-ALA-D) activity from rat lung in vitro was investigated. delta-ALA-D activity, a parameter for metal intoxication, has been reported as a target of Cd(2+) in different tissues. The protective effect of monotherapies with dithiol chelating (meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS)) or antioxidant agents (ascorbic acid, diphenyl diselenide (PhSe)(2), and N-acetylcysteine (NAC)) was evaluated. The effect of a combined therapy (dithiol chelatingxantioxidant agent) was also studied. Zinc chloride (ZnCl(2)) and dithiothreitol (DTT) were used to investigate the mechanisms involved in cadmium, chelating and antioxidant effects on delta-ALA-D activity. Cadmium inhibited rat lung delta-ALA-D activity at low concentrations. DTT (3mM), but not ZnCl(2) (100microM), protected the inhibition of enzyme activity caused by Cd(2+). Chelating agents were not effective in restoring the enzyme activity. DMPS and DMSA presented inhibitory effect on enzyme activity. DTT restored the inhibition caused by both chelating agents, but ZnCl(2) restored only the inhibitory effect induced by DMSA. These compounds caused a marked potentiation of delta-ALA-D inhibition induced by Cd(2+). ZnCl(2) did not restore inhibition of enzyme activity caused by Cd(2+) plus chelating agents. Conversely, DTT restored the inhibition induced by Cd(2+)/DMSA, but not by Cd(2+)/DMPS. Antioxidants were not effective in ameliorating delta-ALA-D inhibition induced by Cd(2+), whereas ascorbic acid potentiated the enzyme inhibition induced by this metal. A combined effect of Cd(2+)xDMPSx(PhSe)(2) and Cd(2+)xDMPSxNAC was observed. There was no combined effect of Cd(2+)xchelatorxantioxidants when DMSA was used. This study demonstrated that Cd(2+)inhibited delta-ALA-D activity and chelating and antioxidant agents, alone or combined, did not restore the enzyme activity. In contrast, these compounds potentiated the inhibition induced by Cd(2+) in rat lung.

Gene expression profiles of homogentisate-treated Fah-/- Hpd-/-mice using DNA microarrays

Hereditary tyrosinemia I (HT I) is a genetic disorder of tyrosine metabolism caused by abnormalities of fumarylacetoacetate hydrolase. Disturbances in tyrosine metabolism lead to increased levels of succinylacetone and succinylacetoacetate. However, the mechanisms causing liver failure, cirrhosis, renal tubular dysfunction, and hepatocarcinoma are still unknown. Alterations in gene expression found in the livers of patients with HT I are responsible for the pathogenesis of this disease, for example acute liver failure. Therefore, gene expression analysis allows us to better understand its pathogenesis. We analyzed gene expressions in tyrosinemia type I model mice with liver failure using microarrays. The results were confirmed by quantitative PCR to evaluate the pathogenesis of tyrosinemia type I. We found that numerous genes, including amino acid metabolism and apoptosis related genes, were up- or down-regulated at the onset of liver failure. These findings are useful in understanding the pathogenesis of hereditary tyrosinemia.

Delta-aminolevulinic acid dehydratase inhibition and oxidative stress in relation to blood lead among urban adolescents

To explore lead-induced oxidative stress among urban adolescents, the present study, the first from India, was designed to determine the proportion of urban adolescents with blood lead >10 microg/dL and its impact on selected oxidative stress parameters and delta-aminolevulinic acid dehydratase (delta-ALAD) inhibition, which could be used as biomarkers of lead intoxication. A total of 39, urban, male adolescents, drawn from Lucknow and adjoining areas, were recruited to determine lead, delta-ALAD, malondialdehyde (MDA) and glutathione (GSH) in blood and catalase (CAT) in RBCs. Mean level of blood lead was 9.96 +/- 3.63 microg/dL (4.62-18.64); 43% of adolescents crossed the Centre for Disease Control (CDC) intervention level of 10 pg/dL blood lead. On the basis of blood lead levels (BLLs), adolescents were categorized into two groups: Group I and Group II had a blood lead <10 microg/dL (7.40 +/- 1.62) and >10 microg/dL (13.27 +/- 2.67), respectively, with significantly different mean values (P <0.001). Age, sex, body mass index (BMI), Hb level (malnutrition), and area of living as confounders of lead exposure and toxicity were not statistically different between the two groups. However, delta-ALAD activity was significantly lower (P <0.001), while CAT activity was higher in Group II than in Group I (P <0.01). MDA level was also significantly higher in Group II compared to Group I (P <0.001). There were significant negative correlation of BLL with 6-ALAD (r= -0.592, P <0.001), and positive correlations with CAT (r=0.485, P <0.01) and MDA (r=0.717, P <0.001). Interestingly, delta-ALAD, in turn, had significant negative correlations with CAT (r= -0.456, P <0.01) and MDA (r= -0.507, P <0.01). Results of the present pilot study provide clues to the possible low level of lead-induced oxidative stress in urban adolescents, suggesting that lead-induced 6-ALAD inhibition can also be an indicator of oxidative stress. The potential of oxidative stress parameters to be used as biomarkers of lead toxicity warranted further investigation.

Antioxidants and metallothionein levels in mercury-treated mice

Acute effects of mercury on mouse blood, kidneys, and liver were evaluated. Mice received a single dose of mercuric chloride (HgCl2, 4.6 mg/kg, subcutaneously) for three consecutive days. We investigated the possible beneficial effects of antioxidant therapy (N-acetylcysteine (NAC) and diphenyl diselenide (PhSe)2) compared with the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), an effective chelating agent in HgCl2 exposure in mice. We also verified whether metallothionein (MT) induction might be involved in a possible mechanism of protection against HgCl2 poisoning and whether different treatments would modify MT levels and other toxicological parameters. The results demonstrated that HgCl2 exposure significantly inhibited delta-aminolevulinate dehydratase (delta-ALA-D) activity in liver and only DMPS treatment prevented the inhibitory effect. Mercuric chloride caused an increase in renal non-protein thiol groups (NPSH) and none of the treatments modified renal NPSH levels. Urea concentration was increased after HgCl2 exposure. NAC plus (PhSe)2 was partially effective in protecting against the effects of mercury. DMPS and (PhSe)2 were effective in restoring the increment in urea concentration caused by mercury. Thiobarbituric acid-reactive substances (TBARS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities and ascorbic acid levels were not modified after mercury exposure. Mercuric chloride poisoning caused an increase in hepatic and renal MT levels and antioxidant treatments did not modify this parameter. Our data indicated a lack of therapeutic effect of the antioxidants tested.

Modern diagnosis and management of the porphyrias

Recent advances in the molecular understanding of the porphyrias now offer specific diagnosis and precise definition of the types of genetic mutations involved in the disease. Molecular diagnostic testing is powerful and very useful in kindred evaluation and genetic counselling when a disease-responsible mutation has been identified in the family. It is also the only way to properly screen asymptomatic gene carriers, facilitating correct treatment and appropriate genetic counselling of family members at risk. However, it should be noted that DNA-based testing is for the diagnosis of the gene carrier status, but not for the diagnosis of clinical syndrome or severity of the disease, e.g. an acute attack. For the diagnosis of clinically expressed porphyrias, a logical stepwise approach including the analysis of porphyrins and their precursors should not be underestimated, as it is still very useful, and is often the best from the cost-effective point of view.

Effect modification by delta-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase gene polymorphisms on associations between patella lead and renal function in lead workers

Genetic polymorphisms that affect lead toxicokinetics or toxicodynamics may be important modifiers of risk for adverse outcomes in lead-exposed populations. We recently reported associations between higher patella lead, which is hypothesized to represent a lead pool that is both bioavailable and cumulative, and adverse renal outcomes in current and former Korean lead workers. In the present study, we assessed effect modification by polymorphisms in the genes encoding for delta-aminolevulinic acid dehydratase (ALAD), the vitamin D receptor (VDR), and endothelial nitric oxide synthase on those associations. Similar analyses were conducted with three other lead biomarkers. Renal function was assessed via blood urea nitrogen, serum creatinine, measured and calculated creatinine clearances, urinary N-acetyl-beta-D-glucosaminidase, and retinol-binding protein. Mean (SD) blood, patella, tibia, and dimercaptosuccinic acid-chelatable lead values were 30.9 (16.7) microg/dl, 75.1 (101.1)and 33.6 (43.4) microg Pb/g bone mineral, and 0.63 (0.75) microg Pb/mg creatinine, respectively, in 647 lead workers. Little evidence of effect modification by genotype on associations between patella lead and renal outcomes was observed. The VDR polymorphism did modify associations between the other lead biomarkers and the serum creatinine and calculated creatinine clearance. Higher lead dose was associated with worse renal function in participants with the variant B allele. Models in two groups, dichotomized by median age, showed that this effect was present in the younger half of the population. Limited evidence of effect modification by ALAD genotype was observed; higher blood lead levels were associated with higher calculated creatinine clearance among participants with the ALAD(1-2) genotype. In conclusion, VDR and/or ALAD genotypes modified associations between all the lead biomarkers, except patella lead, and the renal outcomes.

DMPS and N-acetylcysteine induced renal toxicity in mice exposed to mercury

Acute effects of mercuric chloride (HgCl2) were evaluated on mice. Mice received a single dose of HgCl2 (4.6 mg/kg, subcutaneously) for three consecutive days. Thirty minutes after the last injection with HgCl2, mice received one single injection of 2,3-dimercapto-1-propanesulfonic acid (DMPS) or N-acetylcysteine (NAC) or diphenyl diselenide (PhSe)2. DMPS, NAC and (PhSe)2 were utilized as therapy against mercury exposure. At 24 h after the last HgCl2 injection, blood, liver and kidney samples were collected. delta-Aminolevulinate dehydratase (delta-ALA-D) and Na+, K- (+) ATPase activities, thiobarbituric acid-reactive substances (TBARS), non-protein thiols (NPSH) and ascorbic acid concentrations were evaluated. Plasma aspartate (AST) and alanine (ALT) aminotransferase activities, as well as urea and creatinine levels were determined. The group of mice exposed to Hg + (PhSe)2 presented 100% of lethality. Exposure with HgCl2 caused a decrease on the body weight gain and treatments did not modify this parameter. delta-ALA-D, AST and ALT activities, TBARS, ascorbic acid levels and NPSH (hepatic and erythrocytic) levels were not changed after HgCl2 exposure. HgCl2 caused an increase in renal NPSH content and therapies did not modify these levels. Mice treated with (PhSe)2, Hg + NAC and Hg + DMPS presented a reduction in plasma NPSH levels. Creatinine and urea levels were increased in mice exposed to Hg + NAC, while Hg + DMPS group presented an increase only in urea level. Na+, K- (+) ATPase activity was inhibited in mice exposed to Hg + DMPS and Hg + NAC. In conclusion, therapies with (PhSe)2, DMPS and NAC following mercury exposure must be better studied because the formation of more toxic complexes with mercury, which can mainly damage renal tissue.

Changes in biochemical parameters in rabbits blood after oral exposure to diphenyl diselenide for long periods

The concept that selenium-containing molecules may be better antioxidants than classical antioxidants, has led to the design of synthetic organoselenium compounds. The present study was conducted to evaluate the potential toxicity of long time oral exposure to diphenyl diselenide (PhSe)2 in rabbits. Male adult New Zealand rabbits were divided into four groups, group I served as control; groups II, III and IV received 0.3, 3.0 and 30 ppm of (PhSe)2 pulverized in the chow for 8 months. A number of parameters were examined in blood as indicators of toxicity, including delta-aminolevulinate dehydratase (delta-ALA-D), catalase, glutathione peroxidase (GPx), alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, creatinine, TBARS, non-protein-SH, ascorbic acid and selenium. The results demonstrated that 6 and 8 months of 30 ppm (PhSe)2 intake caused a significant increase in blood delta-ALA-D activity. Erythrocyte non-protein thiol levels were significantly increased after 2 months of 30 ppm (PhSe)2 intake and then return to control levels after prolonged periods of intake. Ingestion of 3.0 ppm of (PhSe)2 for 8 months significantly increased catalase activity in erythrocytes. Conversely, no alterations in GPx, ALT, AST, TBARS and selenium levels were observed in rabbit serum, conversely, selenium levels in peri-renal adipose tissue were significantly increased after 8 months of 30 ppm (PhSe)2 intake, indicating its great lipophylicity. The present results suggest that diphenyl diselenide was not hepato- or renotoxic for rabbits, but caused some biochemical alterations that can be related to some pro-oxidant activity of the compound (particularly the reduction in Vitamin C).

A biomarker approach to measure biological effects of contaminant exposure in largemouth bass from Lake Conestee, South Carolina, U.S.A

Sediments from Lake Conestee, a former reservoir now filled with pollutant-enriched sediments, located south of Greenville, South Carolina, USA, and other nearby reservoirs were collected and analyzed for lead and polycyclic aromatic hydrocarbons (PAHs). Hepatic ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), UDP-glucuronosyltransferase (UGT), sulfotransferase (SULT), and erythrocyte delta-aminolevulinic acid dehydratase (ALAD) were measured in largemouth bass (Micropterus salmoides) to characterize biological effects of these contaminants over three seasons. Results showed that total PAH concentrations in Lake Conestee sediments were significantly greater than the control during each season. An average 10-fold induction in EROD activity was observed at Lake Conestee compared with the control over all three seasons, indicating that PAHs present in sediment were bioavailable to fish. Significant gender effects were observed in EROD activity during the spring, in which activity in reproductively active female fish was significantly suppressed compared with the male fish. Sediments from Lake Conestee had elevated lead concentrations, but the lack of ALAD inhibition in bass indicated that lead was not biologically available. Total GST activity, UGT activity, and SULT activity were not significantly induced in fish from any of the affected sites compared with the reference site. Both EROD and UGT activities were highest during the winter, as were sediment PAH concentrations in Lake Conestee, possibly linked to seasonal resuspension events. The biomarkers measured in this study were useful as a first investigation into the biological effects of contaminant exposure, as well as in determining the bioavailability of contaminants in Lake Conestee.

Oxidative stress promotes degradation of the Irr protein to regulate haem biosynthesis in Bradyrhizobium japonicum

The haem proteins catalase and peroxidase are stress response proteins that detoxify reactive oxygen species. In the bacterium Bradyrhizobium japonicum, expression of the gene encoding the haem biosynthesis enzyme delta-aminolevulinic acid dehydratase (ALAD) is normally repressed by the Irr protein in iron-limited cells. Irr degrades in the presence of iron, which requires haem binding to the protein. Here, we found that ALAD levels were elevated in iron-limited cells of a catalase-deficient mutant, which corresponded with aberrantly low levels of Irr. Irr was undetectable in wild-type cells within 90 min after exposure to exogenous H2O2, but not in a haem-deficient mutant strain. In addition, Irr did not degrade in response to iron in the absence of O2. The findings indicate that reactive oxygen species promote Irr turnover mediated by haem, and are involved in iron-dependent degradation. We demonstrated Irr oxidation in vitro, which required haem, O2 and a reductant. A truncated Irr mutant unable to bind ferrous haem does not degrade in vivo, and was not oxidized in vitro. We suggest that Irr oxidation is a signal for its degradation, and that cells sense and respond to oxidative stress through Irr to regulate haem biosynthesis.

Assessment of reproductive toxicity in male rats following acute and sub-chronic exposures to diphenyl diselenide and diphenyl ditelluride

The present study was conducted to evaluate the toxicity of the exposure to diphenyl diselenide [(PhSe)2] and diphenyl ditelluride [(PhTe)2] on reproductive system in Wistar rats. Adult male rats were exposed intraperitonealy (acute) or subcutaneously (sub-chronic, during 4 or 8 weeks) to (PhSe)2 or (PhTe)2 prior to mating. A number of biochemical parameters in rat testes were examined, such as delta-aminolevulinate dehydratase (delta-ALA-D) activity, lipid peroxidation, glycogen content and components of the antioxidant defenses (superoxide dismutase (SOD) activity and ascorbic acid concentration). Furthermore, a possible effect on fertility and reproductive performance in male rats were studied. Sperm counts of caudal epididymis were also evaluated. No lethality was noted in any group. Reduction on body weight in rats which received (PhTe)2 was only evidenced in acute exposure, while (PhSe)2-exposed rats presented significant loss of body weight in acute and 4 week-exposure. Mating and fertility indexes were not affected after acute and sub-chronic exposure. Regarding other parameters studied, except for a decrease in testes glycogen content in acutely (PhSe)2-treated group, no alterations were found in treated groups. Sperm counts of rats treated acutely and sub-chronically were unaffected by drugs exposure. Histological evaluation revealed no modification on testicular tissue in rats exposed to (PhSe)2 and (PhTe)2. The results suggest the absence of the male reproductive toxicity induced by (PhSe)2 and (PhTe)2 administered intraperitonealy (acute) or subcutaneously (sub-chronical) to adult rats Wistar.

Phosphorus amendment reduces hematological effects of lead in mallards ingesting contaminated sediments

Lead poisoning of waterfowl has been reported for decades in the Coeur d'Alene River Basin (CDARB) in Idaho as a result of the ingestion of lead-contaminated sediments. This study was conducted to determine whether the addition of phosphoric acid to sediments would reduce the bioavailability and toxicity of lead to mallards (Anas platyrhynchos) as related to adverse hematological effects and altered plasma chemistries. Mallards received diets containing 12% clean sediment (controls) or 12% sediment from three different CDARB sites containing 4520, 5390, or 6990 microg/g lead (dw) with or without phosphoric acid amendment. Blood lead concentrations were significantly higher in all CDARB treatment groups and ranged from geometric mean values of 5.0 microg/g for the first two sites to 6.2 microg/g for the third site. With amendments, all blood lead concentrations became 41% to 64% lower. Red blood cell ALAD activity was depressed by 90% or more with lead-contaminated sediment from all sites and did not differ with amended diets. Free erythrocyte protoporphyrin (FEP) concentrations were elevated by contaminated sediment from all sites. Amendment decreased the elevations in FEP by as much as 80%. Hematocrit values and hemoglobin concentrations were lower for all lead site sediments by as much as 30% for site 3. Plasma enzyme activities for ALT, CK, and LDH-L were elevated by as much as 2.2-fold, and plasma creatinine concentration was 1.7-fold higher for site 3 sediment. Amendments restored hematocrit, hemoglobin, and plasma enzyme activities so that they did not differ from controls. Although amendments of phosphorus substantially reduced the bioavailability of lead and alleviated many of the adverse hematological effects, lead concentrations in the blood of mallards fed the amended sediments were still above those believed to be harmful to waterfowl under the present conditions.

Involvement of some low-molecular thiols in the peroxidative mechanisms of lead and ethanol action on rat liver and kidney

The involvement of low-molecular thiols, such as reduced glutathione (GSH) and metallothionein (Mt), in the mechanisms of the peroxidative action of lead (Pb) and ethanol (EtOH) in liver and kidney was investigated on rats treated with 500 mg Pb/l (in drinking water) and 5 g EtOH/kg body wt./24h (p.o.), alone and in conjunction with each other for 12 weeks. Beside of GSH and Mt, concentration of total and non-protein SH groups (TSH and NPSH, respectively) in these organs as well as the blood activity of dehydratase of delta-aminolevulinic acid (delta-ALAD) and the urinary concentration of delta-aminolevulinic acid (delta-ALA) were determined. The exposure to Pb and EtOH alone and in conjunction with each other led to a decrease in the blood delta-ALAD activity and an increase in the urinary delta-ALA concentration, and these effects were more markedly advanced at co-exposure. In the liver and kidney of rats treated with Pb and/or EtOH, a decrease in concentrations of GSH and NPSH was noted, compared to control. However, in the Pb+EtOH group, only the liver concentrations of NPSH and GSH were lower also compared to the Pb and EtOH groups. The liver concentration of TSH decreased in the rats exposed to EtOH alone and in conjunction with Pb, whereas the kidney concentration of TSH decreased only at co-exposure to Pb and EtOH. Mt concentration was unchanged except for an increase in the liver in the Pb and Pb+EtOH groups. Two-way analysis of variance (ANOVA/MANOVA) revealed that the changes noted at the co-exposure to Pb and EtOH resulted from an independent action of the two xenobiotics as well as from their interactive action. Negative correlations noted between the liver and kidney concentrations of GSH and/or NPSH and recently reported malondialdehyde (MDA, an indicator of lipid peroxidation) concentration in both organs of those rats indicate the relationship between the content of SH groups and the intensity of the Pb and/or EtOH-induced lipid peroxidation. The results allow for the conclusion that the decrease in the liver and kidney concentrations of GSH and NPSH are involved in the mechanisms of the peroxidative action of Pb and EtOH alone and at co-exposure in these organs.

Health effects in children aged 3-6 years induced by environmental lead exposure

OBJECTIVES

To investigate the involvement of oxidative damage in lead-induced toxicity in children aged 3-6 years and to enlighten whether oxidative stress indicators are correlated with the known indices of lead toxicity.

METHODS

Blood samples were collected from 408 subjects (217 boys and 191 girls) in the urban kindergartens. The age range of the subjects was 3-6 years. Blood lead levels (BLLs) were analyzed by flameless atomic absorption spectrophotometry. Activities of delta-aminolevulinic acid dehydratase (ALAD), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and contents of glutathione (GSH) in erythrocyte and levels of plasma malondialdehyde (MDA) were analyzed spectrophotometrically in these children.

RESULTS

Children with BLLs >or = 100 microg/L had significantly decreased erythrocyte ALAD activities and increased plasma MDA levels compared to the children with BLLs < 100 microg/L. No significant changes were observed in erythrocyte SOD and GSH-Px activities and GSH levels associated with elevated BLLs in these children.

CONCLUSION

Present data indicate that oxidative damage could be induced by lead in children with BLLs > or = 100 microg/L, and this may partly be attributed to the inhibited ALAD activities. Statistically significant changes of oxidative stress parameters in preschool children while BLLs were more than 100 microg/L could be implicated that oxidative damage might contribute to lead-induced intellectual impairment.

Regulation of Porphyrin Synthesis and Photodynamic Therapy in Heavy Metal Intoxication

Protoporphyrin IX (PpIX) synthesis by malignant cells is successfully exploited for photodynamic therapy (PDT) following administration of 5-aminolevulinic acid (ALA) and light irradiation. The influence of two environmental heavy metal poisons, lead and gallium, on PpIX-synthesis and ALA-PDT was studied in two neu-ronal cell lines, SH-SY5Y neuroblastoma and PC12 pheochromocytoma. The heavy metal intoxication affected two of the heme-synthesis enzymes, ALA-dehydratase (ALAD) and porphobilinogen deaminase (PBGD). The present results show that lead poisoning significantly decreased the PBGD cellular level and inhibited its enzymatic activity, whereas the effects of gallium were less prominent. Although, the protein levels were reduced, the mRNA levels of PBGD remained unchanged during metal intoxication. These findings show additional inhibitory activity of lead on top of its classical effect on ALAD. Proteasome activity was enhanced during lead treatment, as measured by the AMC fluorigenic proteasome assay. The reduction in PBGD levels was not a consequence of PBGD mRNA reduced synthesis, which remained unchanged as shown by RT-PCR analysis. As a result of the lead poisoning, marked alterations in the cell cycle were observed, including a decreased G1 phase and an increased number of S phase cells. The efficacy of ALA-PDT was reduced in correlation with decreased activities of the enzymes during lead intoxication. We may conclude that lead poisoning adversely affects the outcome of ALA photodynamic therapy of cancer.

Oxidation of delta-ALA-D and DTT mediated by ascorbic acid: modulation by buffers depends on free iron

Ascorbic acid (AA) is one of the most important endogenous reducing agents and can participate in a variety of cellular events. In vitro, AA can act as a potent oxidant agent in the presence of free metals, promote modifications in protein structures and form reactive oxygen species during its oxidation. We have observed that AA (above 6 mmol/l) inactivates delta-aminolevulinate dehidratase (delta-ALA-D), a sulfhydryl-containing enzyme and that the inhibitory action was considerably decreased when 3-morpholinepropanesulfonic acid buffer (MOPS - pH: 6.8; 100 mmol/l) was used in the delta-ALA-D activity assay instead of potassium phosphate buffer (PB - pH: 6.8; 100 mmol/l). delta-ALA-D inhibition, probably, is mediated by the oxidation of -SH groups caused by the auto-oxidation of AA promoted by metals or another oxidizing system present in liver supernatants. This hypothesis was confirmed by studying dithiothreitol (DTT - 400 micromol/l) oxidation, as a model of enzyme thiols, where we observed that the mechanism underlying DTT and delta-ALA-D oxidation caused by ascorbate is the same. The difference observed between different buffers may be related to the oxidation of Fe(II) to Fe(III) that was more accentuated in PB than in MOPS buffer. The presence of ethilenediamintetraacetic acid (EDTA - 100 micromol/l) and Fe(III) (5 micromol/l) stimulated DTT oxidation more in PB than in MOPS buffer. Deferroxamine (DF - 100 micromol/l) considerably decreased DTT oxidation. Catalase (0.4 mg/ml) and Superoxide dismutase (SOD - 300 U/ml) had only a modest effect on DTT oxidation. The present results suggest that delta-ALA-D inhibition by AA is mediated primarily by the oxidized form of AA and reactive oxygen species play only a modest role in the process.

Morpheeins--a new structural paradigm for allosteric regulation

Classic models for the allosteric regulation of protein function consider an equilibrium among protein structures of constant oligomeric multiplicity. The morpheein (mor-phee'-in) concept expands this model to include a dynamic equilibrium of protein structures wherein a protein monomer can exist in more than one conformation and each monomer conformation dictates a different quaternary structure of finite multiplicity and different functionality. The morpheein concept provides a new framework for understanding allosteric regulation, kinetic cooperativity and hysteresis. Porphobilinogen synthase constitutes a prototype morpheein ensemble comprising several interconverting quaternary structure isoforms; one monomer conformation dictates assembly of a high-activity octamer, whereas an alternative monomer conformation dictates assembly of a low-activity hexamer. It is proposed here that the behavior of some other allosteric enzymes reflect dynamic morpheein equilibrium systems and six candidate proteins are enumerated.

Beneficial role of monoesters of meso-2,3-dimercaptosuccinic acid in the mobilization of lead and recovery of tissue oxidative injury in rats

We investigated the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) and two of its analogues, monomethyl dimercaptosuccinic acid (MmDMSA) and mono-cyclohexyl dimercaptosuccinic acid (MchDMSA) in reducing lead concentration in blood and soft tissues, and in recovering lead induced oxidative stress in rats. Male wistar rats were exposed to lead acetate in drinking water for 20 weeks, followed by 5 days of oral treatment with DMSA (100mg/kg, oral, once daily), MmDMSA or MchDMSA (50 and 100mg/kg). Biochemical variables indicative of oxidative stress along with lead, zinc and copper concentration were evaluated in blood and other soft tissues. Exposure to lead caused a significant decrease in blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by inhibition of kidney ALAD and an increase in delta-aminolevulinic acid synthatase (ALAS) activity in liver and kidneys. Also seen were a pronounced depletion of brain GSH, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and decreased superoxide dismutase (SOD) activity and an increase in thiobarbituric acid reactive substances (TBARS) and reactive oxygen species (ROS) levels. These biochemical changes were correlated with an increased uptake of lead in blood and soft tissues. Blood and kidneys zinc concentration decreased significantly following lead exposure while, copper concentration remained unchanged. No effect of chelation on hepatic zinc concentration was noted, only liver copper concentration showed significant depletion on treatment with DMSA and MmDMSA (100mg/kg). Treatment with DMSA, MmDMSA and MchDMSA provided significant recovery in altered biochemical variables and brain DNA damage besides significant depletion of tissue lead burden. Among the chelating agents used, MchDMSA and MmDMSA provided better recovery in altered biochemical variables and depletion of lead concentration in tissues compared to DMSA. The above results suggest DMSA monoesters to be a better treatment option than DMSA in eliciting recovery to the altered biochemical variables and in the depletion of body lead burden.

Lead contamination in American woodcock (Scolopax minor) from Wisconsin

An initial survey of lead levels in American woodcock (Scolopax minor) from Wisconsin was conducted in 1998 using wing bones from hunter-donated woodcock. The results of this initial survey indicated that young-of-year woodcock were accumulating extremely high levels of lead in their bones. Similar collections were made (using steel shot) between 1999 and 2001. The combined results of this collection indicated that 43.4% of young-of-year woodcock (range 1.5-220.0 microg/g dry wt) and 70% of woodcock chicks (range 9.6-93.0 microg/g dry wt) had bone lead levels in the elevated range (>20 microg/g dry wt). Blood samples were collected from chicks at a site considered elevated based on bone lead results (Mead Wildlife Area) and a site considered background (Navarino Wildlife Area). These samples were analyzed for lead concentration and aminolevulinic acid dehydratase activity. The mean blood lead concentrations of woodcock chicks from both sites did not reach levels that are considered elevated in waterfowl (>0.200 microg/ml). However, blood lead concentrations of chicks from the Mead Wildlife Area were significantly higher than lead levels in chicks from Navarino Wildlife Area (p = 0.002). Although the ultimate sources of lead exposure for Wisconsin woodcock currently remain unidentified, anthropogenic sources cannot be ruled out. Our results indicate that elevated lead exposure in Wisconsin woodcock is common and begins shortly after hatch.

Arsenic induced blood and brain oxidative stress and its response to some thiol chelators in rats

Chronic arsenic toxicity is a widespread problem, not only in India and Bangladesh but also in various other regions of the world. Exposure to arsenic may occur from natural or industrial sources. The treatment that is in use at present employs administration of thiol chelators, such as meso 2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised with number of limitations due to their lipophobic nature, particularly for their use in cases of chronic poisoning. During chronic exposure, arsenic gains access into the cell and it becomes mandatory for a drug to cross cell membrane to chelate intracellular arsenic. To address this problem, analogs of DMSA having lipophilic character, were examined against chronic arsenic poisoning in experimental animals. In the present study, therapeutic efficacy of meso 2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), monoisoamyl DMSA (MiADMSA) were compared in terms of reducing arsenic burden, as well as recovery in the altered biochemical variables particularly suggestive of oxidative stress. Adult male Wistar rats were given 100-ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 50 mg/Kg (orally) once daily for 5 consecutive days. Arsenic exposure resulted in marked elevation in reactive oxygen species (ROS) in blood, inhibition of ALAD activity and depletion of GSH. These changes were accompanied by significant decline in blood hemoglobin level. MiADMSA was the most effective chelator in reducing ROS in red blood cells, and in restoring blood ALAD compared to two other chelators. Brain superoxide dismutase (SOD) and glutathione peroxidase (GPx) decreased, while ROS and TBARS increased significantly following arsenic exposure. There was a significant increase in the activity of glutathione-S-transferase (GST) with a corresponding decline in its substrate i.e. glutathione. Among all the three chelators, MiADMSA showed maximum reduction in the level of ROS in brain. Additionally, administration of MiADMSA was most effective in counteracting arsenic induced inhibition in brain ALAD, SOD and GPx activity. Based on these results and in particular higher metal decorporation from blood and brain, we suggest MiADMSA to be a potential drug of choice for the treatment of chronic arsenic poisoning. However, further studies are required for the choice of appropriate dose, duration of treatment and possible effects on other major organs.

Photoregulation of the greening process of wheat seedlings grown in red light*

Wheat seedling grown with their shoot bottom exposed to red light (400 micromol m(-2) s(-1)) either with constant illumination or light-dark cycles did not accumulate chlorophyll. This near-etiolation response was manifested by a critical threshold intensity of red light and did not need continuous illumination. The inhibition of the greening process resulted from reduced synthesis of glutamate-1-semialdehyde and consequent reduction in tetrapyrrole precursor 5-aminolevulinic acid. Red light perceived by the shoot bottom down regulated the protein and/or gene expression of enzymes involved in the biosynthesis of tetrapyrroles. The contents of endogenous cytokinins, i.e., isopentenyl-adenosine and dihydrozeatinriboside, were reduced in seedlings grown in red light having their shoot bottom exposed. Application of exogenous cytokinin and its analogue to roots of seedlings grown in red light reversed the down regulation of the greening process. The reversal of red-light-induced near-etiolation morphogenesis by far-red (200 micromol m(-2) s(-1)) or blue (25 mumol m(-2) s(-1)) light suggests that it could be a very high red-irradiance response of phytochrome, in the meristematic layers of the shoot bottom, that works in concert with blue light receptor(s).

Structure of yeast 5-aminolaevulinic acid dehydratase complexed with the inhibitor 5-hydroxylaevulinic acid

The X-ray structure of the enzyme 5-aminolaevulinic acid dehydratase (ALAD) from yeast complexed with the competitive inhibitor 5-hydroxylaevulinic acid has been determined at a resolution of 1.9 A. The structure shows that the inhibitor is bound by a Schiff-base link to one of the invariant active-site lysine residues (Lys263). The inhibitor appears to bind in two well defined conformations and the interactions made by it suggest that it is a very close analogue of the substrate 5-aminolaevulinic acid (ALA).

Du-zhong (Eucommia ulmoides Oliv.) cortex water extract alters heme biosynthesis and erythrocyte antioxidant defense system in lead-administered rats

This study examined the ameliorative effect of a Du-zhong (Eucommia ulmoides Oliv.) cortex water extract (DzCw) on heme biosynthesis and erythrocyte antioxidant enzyme activities in lead (Pb)-administered rats. Male rats were divided into three groups: normal control group, Pb control group (Pb), and DzCw-administered Pb group (Pb + DzCw). The Pb (25 mg/kg of body weight) was administered orally once a week for 4 weeks, while the DzCw was administered orally at a dosage of 0.139 g of DzCw/kg of body weight/day. DzCw administration significantly lowered plasma Pb concentration compared with the Pb group. Furthermore, the blood hematocrit and hemoglobin levels were significantly higher in the Pb + DzCw group than in the Pb group. Although the blood and hepatic delta-aminolevulinic acid dehydratase (ALAD) activities were significantly lower in the Pb group compared with the normal control group, both ALAD activities was normalized with the administration of DzCw. The erythrocyte superoxide dismutase and catalase activities were significantly higher in the Pb group than in the normal control group, whereas the glutathione peroxidase activity and glutathione level were lowered by Pb administration compared with the normal group. However, the administration of DzCw was found to enhance the antioxidant defense system and significantly lower lipid peroxidation levels in erythrocytes compared with the Pb group. These results indicate that the DzCw administration alleviated the Pb-induced oxidative stress in the erythrocytes through elevating the blood and hepatic ALAD activity and enhancing the antioxidant enzyme activities.