Inhibition of adenylate cyclase activity by 5-aminolevulinic acid in rat and human brain

Mechanisms of Neuronal Damage in Acute Hepatic Porphyrias

Porphyrias are a group of congenital and acquired diseases caused by an enzymatic impairment in the biosynthesis of heme. Depending on the specific enzyme involved, different types of porphyrias (i.e., chronic vs. acute, cutaneous vs. neurovisceral, hepatic vs. erythropoietic) are described, with different clinical presentations. Acute hepatic porphyrias (AHPs) are characterized by life-threatening acute neuro-visceral crises (acute porphyric attacks, APAs), featuring a wide range of neuropathic (central, peripheral, autonomic) manifestations. APAs are usually unleashed by external "porphyrinogenic" triggers, which are thought to cause an increased metabolic demand for heme. During APAs, the heme precursors δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) accumulate in the bloodstream and urine. Even though several hypotheses have been developed to explain the protean clinical picture of APAs, the exact mechanism of neuronal damage in AHPs is still a matter of debate. In recent decades, a role has been proposed for oxidative damage caused by ALA, mitochondrial and synaptic ALA toxicity, dysfunction induced by relative heme deficiency on cytochromes and other hemeproteins (i.e., nitric oxide synthases), pyridoxal phosphate functional deficiency, derangements in the metabolic pathways of tryptophan, and other factors. Since the pathway leading to the biosynthesis of heme is inscribed into a complex network of interactions, which also includes some fundamental processes of basal metabolism, a disruption in any of the steps of this pathway is likely to have multiple pathogenic effects. Here, we aim to provide a comprehensive review of the current evidence regarding the mechanisms of neuronal damage in AHPs.

Liver δ-aminolevulinate dehydratase activity is inhibited by neonicotinoids and restored by antioxidant agents

Neonicotinoids represent the most used class of insecticides worldwide, and their precursor, imidacloprid, is the most widely marketed. The aim of this study was to evaluate the effect of imidacloprid on the activity of hepatic δ-aminolevulinate dehydratase (δ-ALA-D), protective effect of potential antioxidants against this potential effect and presence of chemical elements in the constitution of this pesticide. We observed that δ-ALA-D activity was significantly inhibited by imidacloprid at all concentrations tested in a dose-dependent manner. The IC₅₀ value was obtained and used to evaluate the restoration of the enzymatic activity. δ-ALA-D inhibition was completely restored by addition of dithiotreitol (DTT) and partly by ZnCl_2, demonstrating that the inhibition occurs by oxidation of thiol groups and by displacement of the Zn (II), which can be explained by the presence of chemical elements found in the constitution of pesticides. Reduced glutathione (GSH) had the best antioxidant effect against to δ-ALA-D inhibition caused by imidacloprid, followed by curcumin and resveratrol. It is well known that inhibition of the enzyme δ-ALA-D may result in accumulation of its neurotoxic substrate (δ-ALA), in this line, our results suggest that further studies are needed to investigate the possible neurotoxicity induced by neonicotinoids and the involvement of antioxidants in cases of poisoning by neonicotinoids.

Are delta-aminolevulinate dehydratase inhibition and metal concentrations additional factors for the age-related cognitive decline?

Aging is often accompanied by cognitive impairments and influenced by oxidative status and chemical imbalances. Thus, this study was conducted to examine whether age-related cognitive deficit is associated with oxidative damage, especially with inhibition of the enzyme delta-aminolevulinate dehydratase (ALA-D), as well as to verify the influence of some metals in the enzyme activity and cognitive performance. Blood ALA-D activity, essential (Fe, Zn, Cu, Se) and non-essential metals (Pb, Cd, Hg, As, Cr, Ni, V) were measured in 50 elderly and 20 healthy young subjects. Cognitive function was assessed by tests from Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) battery and other. The elderly group presented decreased ALA-D activity compared to the young group. The index of ALA-D reactivation was similar to both study groups, but negatively associated with metals. The mean levels of essential metals were within the reference values, while the most toxic metals were above them in both groups. Cognitive function impairments were observed in elderly group and were associated with decreased ALA-D activity, with lower levels of Se and higher levels of toxic metals (Hg and V). Results suggest that the reduced ALA-D activity in elderly can be an additional factor involved in cognitive decline, since its inhibition throughout life could lead to accumulation of the neurotoxic compound ALA. Toxic metals were found to contribute to cognitive decline and also to influence ALA-D reactivation.

Effect of chronic administration of the vinyl chalcogenide 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one on oxidative stress in different brain areas of rats

Selenium (Se) is an essential mineral for mammals. It is a nutrient related to the complex metabolic and enzymatic functions. Although Se has important physiological functions in the cells, organic compounds of Se can be extremely toxic, and may affect the central nervous system. This study aims to investigate the effect of the chronic treatment with the vinyl chalcogenide 3-methyl-1-phenyl-2-(phenylseleno)oct-2-en-1-one on some parameters of oxidative stress in the brain of rats. Animals received the vinyl chalcogenide (125, 250 or 500 μg/kg body weight) intraperitoneally once a day during 30 days. The cerebral cortex, the hippocampus, and the cerebellum were dissected and homogenized in KCl. Afterward, thiobarbituric acid reactive substances (TBARS), carbonyl, sulfhydryl, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were measured in the brain. Results showed that the organoselenium enhanced TBARS in the cerebral cortex of rats but the compound was not able to change carbonyl levels. Furthermore, the organoselenium reduced thiol groups measured by the sulfhydryl assay in all tissues studied. The activity of the antioxidant enzyme CAT was increased by the organochalcogen in the cerebral cortex and in the cerebellum, and the activity of SOD was increased in the hippocampus. On the other hand, the activity of the antioxidant enzyme GPx was reduced in all brain structures. Our findings indicate that this organoselenium compound induces oxidative stress in different brain regions of rats, corroborating to the fact that this tissue is a potential target for organochalcogen action.

Effect of in vitro exposure of human serum to 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on oxidative stress

The objective of this study was to verify the effect of the organochalcogen 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on some parameters of oxidative stress in human serum. Serum of volunteers were incubated for 30 min in the presence or absence of 1, 10, or 30 microM of 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one and oxidative stress was measured. First, we tested the influence of the compound on 1,1-diphenyl-2-picrylhydrazyl (DPPH(*)) radical-scavenging and verified that the organotellurium did not have any antioxidant properties. The organochalcogen was capable to enhance TBARS but the compound was not able to alter carbonyl assay. Furthermore, the organochalcogen provoked a reduction of protein thiol groups measured by the sulfhydryl assay. Moreover, the organotellurium enhanced the activity of catalase and superoxide dismutase, inhibited the activity of glutathione peroxidase and did not modify the glutathione S-transferase activity. Furthermore, nitric oxide production and hydroxyl radical activity were not affected by the compound. Our findings showed that this organochalcogen induces oxidative stress in human serum, indicating that this compound is potentially toxic to human beings.

Delta-ALA-D activity is a reliable marker for oxidative stress in bone marrow transplant patients

Background

Bone marrow transplantation (BMT) is often used in the treatment of various diseases. Before BMT, patients are submitted to a conditioning regimen (CR), which consists of the administration of high doses of chemotherapy. The action of many cytostatic drugs involves the overproduction of reactive oxygen species, which together with inadequate antioxidant protection can lead to oxidative stress and this has been implicated in the etiology of various diseases. The objectives of this study were to look for evidence of oxidative stress and also to analyze δ-Aminolevulinato dehydratase (δ-ALA-D) activity as a possible marker of oxidative stress in autologous and allogeneic BMT patients.

Methods

Lipid peroxidation, vitamin C and thiol group levels as well as catalase, superoxide dismutase and δ-ALA-D activity were determined in 37 healthy controls, 13 patients undergoing autologous peripheral blood stem cell transplantation and 24 patients undergoing allogeneic BMT.

Results

We found that patients presented signs of oxidative stress before they were submitted to BMT, during CR and up to 20 days after BMT. There was a decrease in enzymatic and non enzymatic antioxidant defenses, in δ-ALA-D activity, and an increase in lipoperoxidation in the blood of both patient groups.

Conclusion

This study has indicated that autologous and allogeneic BMT are associated with oxidative stress. Moreover, blood δ-ALA-D activity seems to be an additional biomarker of oxidative stress in BMT patients.

Oxidative stress and delta-ALA-D activity in different conditioning regimens in allogeneic bone marrow transplantation patients

OBJECTIVES

To compare different conditioning regimens (CR), in order to determine whether either of them could be less toxic to allogeneic bone marrow transplantation (BMT) patients in terms of oxidative stress and also analyze delta-ALA-D activity as a possible marker of oxidative stress.

DESIGN AND METHODS

Lipid peroxidation, vitamin C, thiol groups levels and catalase, superoxide dismutase and delta-ALA-D activity were determined in 21 healthy controls, 5 patients with fludarabine+cyclophosphamide (FluCy) CR, 12 with busulfan+cyclophosphamide (BuCy) and 4 with cyclophosphamide+total body irradiation (CyTBI).

RESULTS

There were a decrease in enzymatic and non enzymatic antioxidants, in delta-ALA-D activity, and in all CRs and an increase in lipid peroxidation more pronounced in CyTBI CR.

CONCLUSIONS

All CRs promoted oxidative stress in allogeneic BMT patients, but this was more pronounced with CyTBI and delta-ALA-D activity seemed to be an additional biomarker of oxidative stress in these patients.

Potentially adverse interactions between haloperidol and valerian

This study was designed to determine whether the treatment with haloperidol (HP), valerian or both in association impairs the liver or kidney functions. Valerian alone did not affect oxidative stress parameters in the liver or kidney of rats. HP alone only increased glutathione (GSH) depletion in liver, but not in kidney. However, when HP was associated with valerian, an increase in lipid peroxidation levels and dichlorofluorescein (DCFH) reactive species production was observed in the hepatic tissue. Superoxide dismutase (SOD) and Catalase (CAT) activities were not affected by the HP plus valerian treatment in the liver and kidney of rats. HP and valerian when administered independently did not affect the activity of hepatic and renal delta-aminolevulinate dehydratase (delta-ALA-D), however, these drugs administered concomitantly provoked an inhibition of hepatic delta-ALA-D activity. The delta-ALA-D reactivation index was higher in rats treated with HP plus valerian than other treated groups. These results strengthen the view that delta-ALA-D can be considered a marker for oxidative stress. Serum aspartate aminotransferase (AST) activity was not altered by any treatment. However, serum alanine aminotransferase (ALT) activity was higher in the HP group and HP plus valerian group. Our findings suggest adverse interactions between haloperidol and valerian.

1,1,2-Tris-organoselenide alkene derivatives, but not 1,2-bis-organoselenide alkene derivatives, inhibited δ-aminolevulinate dehydratase activity from human erythrocytic cells in vitro

Organochalcogens are important intermediates and useful reagents in organic synthesis. Recent data from our laboratory demonstrated that bis and tris-selenide alkene derivatives are attractive synthetic targets because of their chemio-, regio- and stereo-selective reactions. Since the erythrocytic delta-aminolevulinate dehydratase (delta-ALA-D) activity could be an important indicator of toxicity, this report investigated bis and tris-selenide alkene derivatives effects on blood delta-ALA-D in vitro. To investigate the mechanisms by which these compounds inhibit human blood delta-ALA-D activity, a thiol reducing agent or zinc chloride were used. 1,2-Bis-selenide alkene derivatives 1a (R=4-MeOC(6)H(4)), 1b (R=4-ClC(6)H(4)) and 1c (R=2,4,6-Me(3)C(6)H(2)) did not inhibit human blood delta-ALA-D activity. 1,1,2-Tris-selenide alkene derivative 2a (R=C(6)H(5)) was the most potent delta-ALA-D inhibitor. Compounds 2b (R=4-MeOC(6)H(4)) and 2c (R=4-ClC(6)H(4)) displayed similar inhibitory potency towards delta-ALA-D activity. Dithiothreitol, a hydrophobic SH-reducing agent, was able to restore and to protect delta-ALA-D activity inhibited by tris-selenide alkene derivatives. Conversely, ZnCl(2) did not alter the enzyme inhibition induced by tris-selenide alkene derivatives. From these findings we suggest that 1,1,2-tris-selenide alkene derivatives inhibited delta-ALA-D activity by an interaction with essential sulfhydryl groups for the enzyme activity.

A biochemical and toxicological study with diethyl 2-phenyl-2-tellurophenyl vinylphosphonate in a sub-chronic intraperitoneal treatment in mice

Diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP) is an organotellurium compound with low toxicity after subcutaneous administration in mice. This study evaluated possible in vivo and ex vivo toxicological effects of daily injections of DPTVP for 12 days in mice, using the intraperitoneal administration. This route potentially increases the pharmacokinetics of absorption, distribution, metabolism and toxicity of DPTVP. Treatment with DPTVP (0, 30, 50, 75, 100, 250, 350 or 500 micromol/kg) were not associated with mortality or body weight loss. Nevertheless, the liver and liver-to-body weight ratio increased in groups treated with 350 and 500 micromol/kg of DPTVP. However, plasmatic aspartate and alanine aminotransferase activities (classical markers of hepatotoxicity) were not increased after diethyl-2-phenyl-2-tellurophenyl vinylphosphonate administration. Hepatic, renal and cerebral thiobarbituric acid reactive substances (TBARS), delta-ALA-D activity and Vitamin C levels were not modified after DPTVP treatment. Renal and hepatic superoxide dismutase (SOD) and catalase (CAT) were unchanged after DPTVP treatment. Conversely, SOD activity significantly increased in brain in groups treated with 50, 75, 100 and 500 micromol/kg of DPTVP treated groups. Our findings corroborates that brain is a potential target for organochalcogen action. The absence of severe overt signs of toxicity after sub-chronic exposure to DPTVP reinforces the necessity for more detailed pharmacological studies concerning this new organotellurium compound.

Oxidative stress and δ-ALA-D activity in chronic renal failure patients

In this paper, we studied the influence of uremia and hemodialysis on oxidative parameters and delta-aminolevulinic acid dehydratase (delta-ALA-D) activity in control subjects, patients with chronic renal failure (CRF) on hemodialysis treatment (HD) and in patients not undergoing hemodialysis (ND). An increased lipid peroxidation was observed in the serum of HD and ND patients, as measured by the MDA serum levels. However, the level of MDA from erythrocytes was only elevated in HD patients. Blood catalase activity was increased in HD and ND groups. This study also showed a decreased activity of blood delta-aminolevulinic acid dehydratase (delta-ALA-D) in both groups of patients. This study demonstrated a positive correlation between ALA-D activity and hemoglobin, suggesting that inhibition of this enzyme might enhance anemia in CRF. A negative correlation was found between the alteration in delta-ALA-D activity and oxidative stress, which may indicate that the inhibition of ALA-D can be used as an index of oxidative stress.

Decrease of hepatic δ-aminolevulinate dehydratase activity in an animal model of fatigue

Fatigue can be defined physiologically as inability to maintain the expected power output. At present, no standard of fatigue are yet available. In order to find biomarkers of fatigue, we investigated the level of delta-aminolevulinic acid (ALA), the first intermediate metabolite in the heme biosynthetic pathway, in the plasma and urine of an animal model of fatigue. To prepare fatigued animals, we kept rats for 5 days in a cage filled with water to a height of 1.5 cm. As a result, the plasma and urinary ALA levels were increased in the fatigued animals as compared with those in the control animals. One day after the rats had been returned to their normal cages, these increased levels were restored to the control ones. We also examined the activity of the enzyme ALA dehydratase (ALAD), which is the second enzyme in the heme biosynthetic pathway, and ALAD gene expression during the fatigue and its recovery sessions. The ALAD activity, as well as its gene expression, in the liver of the fatigued animals was decreased as compared with those of the control animals. Both activity and gene expression of ALAD were recovered to their respective control levels after the rats had been allowed to rest in their normal cages for 1 day. Furthermore, the activity of ALA synthase (ALAS), the rate-limiting enzyme in the heme biosynthesis, in the liver was increased after the fatigue session for 5 days. Although this level of increase in the plasma concentration of ALA may not induce fatigue, increase in plasma and urinary ALA levels can be biomarkers of fatigue.

Griseofulvin enhances the effect of aminolevulinic acid-based photodynamic therapy in vitro

OBJECTIVE

In this study, we investigated whether or not griseofulvin (GF), which is an antimycotic widely used for the oral treatment of skin fungal infections, enhanced the effect of aminolevulinic acid-based photodynamic therapy (ALA-PDT) in vitro, using several tumor cell lines.

METHODS

A human squamous cell carcinoma line (KB), two human osteosarcoma cell lines from mandible (HOSM-1, HOSM-2), and the human gingiva-derived fibroblast line (HF), representing normal cells, were used. GF enhancement of ALA-PDT was evaluated by comparing the effect of ALAin combination with GF to the effect of ALAalone (GF enhancement rate of ALA-PDT). Also, the effect of GF on intracellular accumulation of protoporphyrin IX (PpIX) was evaluated by comparing the intracellular accumulation of PpIX in the ALA and GF combined treatment with that of ALA treatment alone (pGF enhancement rate of intracellular PpIX).

RESULTS

GFenhancement rate of ALA-PDT was 2.51 in KB cells, and 1.65 and 1.27 in HOSM-1 and HOSM-2 cells, respectively. GF enhancement rates of intracellular PpIX were 1.94 in KB cells, 1.53 in HOSM-1 cells, and 1.19 in HOSM-2 cells. GF enhancement rate of intracellular PpIX followed the same trends as the levels of GF enhancement rate of ALA-PDT in the different cell types. For HF, a large effect was not revealed in this study.

CONCLUSION

The present study, although preliminary, strongly suggests that concomitant treatment with ALAand GF may be very useful to enhance the effect of ALA-PDT.

Diethyl 2-phenyl-2 tellurophenyl vinylphosphonate: An organotellurium compound with low toxicity

It is well-known that organotellurium compounds can have antioxidant activity in vitro, but in vivo these compounds can be potentially toxic to rodents. Here we investigated the potential in vitro and ex vivo toxicity of a new beta-organochalcogenyl vinylphosphonate, the diethyl 2-phenyl-2 tellurophenyl vinylphosphonate. The in vitro antioxidant activity of this organotellurium compound was also investigated. In vitro, the rate of dithiotreitol (DTT) oxidation was increased and the activity of cerebral, renal and hepatic delta-aminolevulinate dehydratase (delta-ALA-D) was decreased by diethyl 2-phenyl-2-tellurophenyl vinylphosphonate (120-1200 microM), indicating that this compound oxidize-SH groups. The antioxidant activity was also observed in brain, liver and kidney, in very low concentrations (0.4, 1.0, 4.0, 10.0 and 40.0 microM), and this capacity was comparable to the antioxidant standard organotellurium compound, diphenyl ditelluride. In vivo, delta-ALA-D activity in liver, kidney and brain of mice treated for 12 days with dimethylsulfoxide (DMSO) as vehicle, 25, 75 or 250 micromol/kg of diethyl 2-phenyl-2-tellurophenyl vinylphosphonate was not affected. Furthermore, only one animal treated with the highest dose died, whereas all animals treated with diphenyl ditteluride died in the fourth day. These results suggest that this novel organotellurium compound interacts with the sulfhydryl groups, however only at higher doses when compared with diphenyl ditelluride. Since diethyl 2-phenyl-2 tellurophenyl vinylphosphonate had low toxicity to mice after sub-chronic exposure, it becomes important to investigate its possible pharmacological properties.

Effects of extracellular δ-aminolaevulinic acid on sodium currents in acutely isolated rat hippocampal CA1 neurons

The effects of delta-aminolaevulinic acid (ALA) on voltage-gated sodium channel (VGSC) currents (I(Na)) in acutely isolated hippocampal CA1 neurons from 10- to 12-day-old Wistar rats were examined by using the whole-cell patch-clamp technique under voltage-clamp conditions. ALA from 0.01 microm to 20 microm was applied to the recorded neurons. Low concentrations of ALA (0.01-1.0 microM) increased I(Na) amplitude, whereas high concentrations of ALA (5.0-20.0 microM) decreased it. The average I(Na) amplitude reached a maximum of 117.4 +/- 3.9% (n = 9, P < 0.05) with 0.1 microM ALA, and decreased to 78.1 +/- 3.8% (n = 13, P < 0.05) with 10 microm ALA. ALA shifted the steady-state activation and inactivation curves of I(Na) in the hyperpolarizing direction with different V0.5, suggesting that ALA could depress the opening threshold of the voltage-gated sodium channel (VGSC) and thus increase the excitability of neurons through facilitating the opening of VGSC. The time course of recovery from inactivation was significantly prolonged at both low and high concentrations of ALA, whereas either low or high concentrations of ALA had no significant effect on the attenuation of I(Na) during stimulation at 5 Hz, indicating that the effect of ALA on VGSC is state-independent. Furthermore, we found that application of ascorbic acid, which blocks pro-oxidative effects in neurons, could prevent the increase of I(Na) amplitude at low concentrations of ALA. Baclofen, an agonist of GABAb receptors, induced some similar effects to ALA on VGSC, whereas bicuculline, an antagonist of GABAa receptors, could not prevent ALA-induced effects on VGSC. These results suggested that ALA regulated VGSC mainly through its pro-oxidative effects and GABAb receptor-mediated effects.

Effect of thuringiensin on adenylate cyclase in rat cerebral cortex

The purpose of this work is to evaluate the effect of thuringiensin on the adenylate cyclase activity in rat cerebral cortex. The cyclic adenosine 3'5'-monophosphate (cAMP) levels were shown to be dose-dependently elevated 17-450% or 54-377% by thuringiensin at concentrations of 10 microM-100 mM or 0.5-4 mM, due to the activation of basal adenylate cyclase activity of rat cerebral cortical membrane preparation. Thuringiensin also activated basal activity of a commercial adenylate cyclase from Escherichia coli. However, the forskolin-stimulated adenylate cyclase activity in rat cerebral cortex was inhibited by thuringiensin at concentrations of 1-100 microM, thus cAMP production decreased. Furthermore, thuringiensin or adenylate cyclase inhibitor (MDL-12330A) reduced the forskolin (10 microM)-stimulated adenylate cyclase activity at concentrations of 10 microM, 49% or 43% inhibition, respectively. In conclusion, this study demonstrated that thuringiensin could activate basal adenylate cyclase activity and increase cAMP concentrations in rat cerebral cortex or in a commercial adenylate cyclase. Comparing the dose-dependent effects of thuringiensin on the basal and forskolin-stimulated adenylate cyclase activity, thuringiensin can be regarded as a weak activator of adenylate cyclase or an inhibitor of forskolin-stimulated adenylate cyclase.

2,3-Dimercaptopropanol, 2,3-dimercaptopropane-1-sulfonic acid, and meso-2,3-dimercaptosuccinic acid inhibit delta-aminolevulinate dehydratase from human erythrocytes in vitro

The effects of dithiol chelating agents meso-2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropane-1-sulfonic acid (DMPS), and 2,3-dimercaptopropanol (BAL) on delta-aminolevulinate dehydratase (delta-ALA-D) from human erythrocytes were evaluated. Furthermore, possible protective effects of zinc chloride (ZnCl(2)), dithiothreitol (DTT), and cysteine were studied. delta-ALA-D activity from human erythrocytes was inhibited by dithiol chelating agents in a concentration-dependent manner. Cysteine, at all concentrations tested, did not protect the inhibitory effect of 1 and 4 mM DMPS and DMSA, but protected 1 mM BAL inhibition. Dithiotreitol was able to protect the inhibition caused by 1 mM BAL (28%), DMPS (56%), and DMSA (40%) in a concentration-dependent manner. Zinc chloride protected and restored 1 mM BAL inhibitory effect on delta-ALA-D. Zinc chloride at 500 microM and 1 mM, respectively, protected inhibitory effects of DMPS and DMSA (1 and 4 mM), but did not reverse its effects. The preincubation of dithiol chelating agents with enzyme demonstrated that DMSA was the most potent delta-ALA-D inhibitor of human erythrocytes. These data are in agreement with delta-ALA-D activity from purified enzyme. ZnCl(2) (1 microM) added, in the reaction mixture, increased enzyme activity and DTT (100 microM) totally restored the enzyme activity for all chelating agents tested.

Organochalcogens effects on delta-aminolevulinate dehydratase activity from human erythrocytic cells in vitro

Organochalcogens are important intermediates and useful reagents in organic synthesis, which can increase human exposure risk to these chemicals in the workplace. As well, there are a number of reported cases of acute toxicity following organochalcogen ingestion of vitamins and dietary supplements. Since, the erythrocytic delta-ALA-D activity could be an important indicator of toxicity this report investigated the organochalcogens effects on blood delta-ALA-D in vitro. To investigate a possible involvement of cysteinyl groups in the inhibitory actions of diphenyl diselenide, diphenyl ditelluride and Ebselen (4-100 micro M), the effects of thiol reducing agents (0-3 mM) or zinc chloride (0-2 mM) were examined. Diphenyl ditelluride, diphenyl diselenide and Ebselen inhibited in a concentration-dependent manner delta-ALA-D activity from human erythrocytes. Ebselen was lesser delta-ALA-D inhibitor than (PhSe)(2) and (PhTe)(2), whereas the diorganoyldichalcogenides displayed similar inhibitory potency towards delta-ALA-D. Dithiothreitol, a hydrophobic SH-reducing agent, was able to reactivate and to protect inhibited delta-ALA-D. The pre-incubation of blood with the inhibitors changed considerably the reversing potency of thiols. From these findings we suggest that organochalcogens inactivate in vitro human erythrocyte delta-ALA-D by an interaction with the sulfhydryl group essential of the enzyme activity.

Protoporphyrin-IX accumulation and cutaneous tumor regression in mice using a ferrochelatase inhibitor

The use of endogenously created porphyrins as an alternative to photosensitizer injection for photodynamic therapy (PDT) of cancer is a rapidly evolving area of study. In-situ accumulation of protoporphyrin-IX (PpIX) by hemebiosynthesis inhibition represents a novel method for PDT of cancer cells. The kinetics of PpIX accumulation and cutaneous tumor regression in mice was studied using lead (a known and effective inhibitor of ferrochelatase). Cutaneous tumors were exposed to various doses of ferrochelatase enzyme inhibitor (lead) and to different durations and doses of visible light. The maximum increase in PpIX levels (blood, skin and tumor) was observed 48 h after the parenteral administration of second injection of lead within a period of 1 month. The maximum tumor regression was observed in mice that were exposed to visible light at a light dose of 648J/cm(2) (1h exposure in four sessions of 15 min, with a gap of 10 min between each exposure). Continuous treatment for 6 consecutive days resulted in almost complete regression of the tumors in most of the animals. Histopathological sections of tumors after light exposure showed necrotic tissue with degenerated lymphocytes, monocytes, and neutrophils. Since the ferrochelatase inhibitor (lead) used in the present study is toxic, the search must continue for a safe, non-toxic inhibitor to enhance sensitizer-mediated PDT.

Topical application of 5-aminolevulinic acid and its methylester, hexylester and octylester derivatives: considerations for dosimetry in mouse skin model

Ester derivatives of 5-aminolevulinic acid (ALA-esters) have been proposed as alternative drugs for ALA in photodynamic therapy. After topical application of creams containing ALA, ALA methylester (ALA-Me), ALA hexylester (ALA-Hex) and ALA octylester (ALA-Oct) on mouse skin, typical fluorescence excitation and emission spectra of protoporphyrin IX (PpIX) were recorded, exhibiting a similar spectral shape for all the drugs in the range of concentrations (0.5-20%) studied. The accumulation kinetics of PpIX followed nearly a similar profile for all the drug formulations. The fluorescence of PpIX peaked at around 6-12 h of continuous cream application. Nevertheless, some differences in pharmacokinetics were noticed. For ALA cream, the highest PpIX fluorescence was achieved using 20% of ALA in an ointment. Conversely, 10% of ALA-Me and ALA-Hex, but not of ALA-Oct, in the cream was more efficient (P < 0.05) than was 20%. The cream becomes rather fluid when 20% of any of these ALA-esters is used in ointment, whereas 10% and lower concentrations of ALA-esters do not significantly increase fluidity of the cream. The dependence of PpIX accumulation on the concentration of ALA and ALA-ester in the applied cream followed (P < 0.002) kinetics as described by a mathematical model based on the Michaelis-Menten equation for enzymatic processes. Under the present conditions, the PpIX amount in the skin increased by around 50% by the application of ALA-Me, ALA-Hex or ALA-Oct for 4-12 h as compared with ALA for the same period. Observations of the mice under exposure to blue light showed that after 8-24 h of continuous application of ALA, the whole mouse was fluorescent, whereas in the case of ALA-Me, ALA-Hex and ALA-Oct the fluorescence of PpIX was located only at the area of initial cream application. The amount of the active compound in the applied cream necessary to induce 90% of the maximal amount of PpIX was determined for normal mouse skin. Optimal PpIX fluorescence can be attained using around 5% ALA, 10% ALA-Me and 5% ALA-Hex creams during short application times (2-4 h). Topical application of ALA-Oct may not gain optimal PpIX accumulation for short applications (<5 h). For long application times (8-12 h), it seems that around 1% ALA, 4% ALA-Me, 6% ALA-Hex and 16% ALA-Oct can give optimal PpIX fluorescence. But for long application times and high concentrations, systemic effect of ALA applied topically on relatively large areas should be considered.

Delta-aminolevulinate dehydratase inhibition by phenyl selenoacetylene: effect of reaction with hydrogen peroxide

The effect of phenyl selenoacetylene and its selenoxide on delta-aminolevulinate dehydratase from liver of adult rats (mammalian source) and from cucumber leaves (plant source) was investigated. In vivo, selenides can be oxidized to selenoxides by flavin-containing monooxygenases and selenoxides can regenerate selenides by thiol oxidation. The compound phenyl selenoacetylene was converted to selenoxides by reaction with hydrogen peroxide. Phenyl selenoacetylene inhibited mammalian and plant delta-aminolevulinate dehydratase with an IC50 about 250 microM and >400 microM, respectively. Its selenoxide inhibited the enzyme more strongly, with IC50 values of 45 microM and 100 microM for the mammalian and plant source, respectively. The selenoxide inhibitory action was antagonized by dithiothreitol suggesting the involvement of -SH groups. Moreover, delta-aminolevulinate dehydratase from a plant source was inhibited by the selenoxide, suggesting a possible involvement of -SH groups located at a site distinct from the region implicated in Zn2+ binding in mammalian delta-aminolevulinate dehydratase. The results of the present study suggest that (i) delta-aminolevulinate dehydratase is a potential molecular target for phenyl selenoacetylene, due to the oxidation of enzyme sulfhydryl groups, and that (ii) the monooxygenation of this selenocompound, which in vivo could be possibly mediated by flavin-containing monooxigenases, increases its inhibitory effect.

5-Aminolevulinic acid inhibits [3H]muscimol binding to human and rat brain synaptic membranes

The interaction of 5-aminolevulinic acid (ALA) with GABA(A) receptors has been proposed to underlie the neurological dysfunctions of ALA-accumulating disorders, such as acute intermittent porphyria. The effects of ALA on [3H]muscimol binding to human and rat cerebral cortical membranes were compared. ALA (0.1-10 mM) significantly inhibited the binding of [3H]muscimol (12 nM), with a similar potency in rat and human membranes (IC50 = 199 vs. 228 microM, respectively). Kinetical analysis revealed that ALA (1 mM) significantly increased the Kd and decreased the Bmax of [3H]muscimol to both rat (100 and 50%, respectively) and human (200 and 40%, respectively) membranes, indicating a mixed-type inhibition. The similarity in the potency and mechanism of the ALA-induced inhibition of muscimol binding in rat and human membranes indicate that rat studies are useful to evaluate the neurotoxic properties of ALA towards the human GABAergic system, and may help to understand the pathophysiology of porphyria.