Alsinol, an arylamino alcohol derivative active against Plasmodium, Babesia, Trypanosoma, and Leishmania: past and new outcomes

Malaria, babesiosis, trypanosomosis, and leishmaniasis are some of the most life-threatening parasites, but the range of drugs to treat them is limited. An effective, safe, and low-cost drug with a large activity spectrum is urgently needed. For this purpose, an aryl amino alcohol derivative called Alsinol was resynthesized, screened in silico, and tested against Plasmodium, Babesia, Trypanosoma, and Leishmania. In silico Alsinol follows the Lipinski and Ghose rules. In vitro it had schizontocidal activity against Plasmodium falciparum and was able to inhibit gametocytogenesis; it was particularly active against late gametocytes. In malaria-infected mice, it showed a dose-dependent activity similar to chloroquine. It demonstrated a similar level of activity to reference compounds against Babesia divergens, and against promastigotes, and amastigotes stages of Leishmania in vitro. It inhibited the in vitro growth of two African animal strains of Trypanosoma but was ineffective in vivo in our experimental conditions. It showed moderate toxicity in J774A1 and Vero cell models. The study demonstrated that Alsinol has a large spectrum of activity and is potentially affordable to produce. Nevertheless, challenges remain in the process of scaling up synthesis, creating a suitable clinical formulation, and determining the safety margin in preclinical models.

Primaquine-quinoxaline 1,4-di-N-oxide hybrids with action on the exo-erythrocytic forms of Plasmodium induce their effect by the production of reactive oxygen species

Background

The challenge in anti-malarial chemotherapy is based on the emergence of resistance to drugs and the search for medicines against all stages of the life cycle of Plasmodium spp. as a therapeutic target. Nowadays, many molecules with anti-malarial activity are reported. However, few studies about the cellular and molecular mechanisms to understand their mode of action have been explored. Recently, new primaquine-based hybrids as new molecules with potential multi-acting anti-malarial activity were reported and two hybrids of primaquine linked to quinoxaline 1,4-di-N-oxide (PQ–QdNO) were identified as the most active against erythrocytic, exoerythrocytic and sporogonic stages.

Methods

To further understand the anti-malarial mode of action (MA) of these hybrids, hepg2-CD81 were infected with Plasmodium yoelii 17XNL and treated with PQ–QdNO hybrids during 48 h. After were evaluated the production of ROS, the mitochondrial depolarization, the total glutathione content, the DNA damage and proteins related to oxidative stress and death cell.

Results

In a preliminary analysis as tissue schizonticidals, these hybrids showed a mode of action dependent on peroxides production, but independent of the activation of transcription factor p53, mitochondrial depolarization and arrest cell cycle.

Conclusions

Primaquine–quinoxaline 1,4-di-N-oxide hybrids exert their antiplasmodial activity in the exoerythrocytic phase by generating high levels of oxidative stress which promotes the increase of total glutathione levels, through oxidation stress sensor protein DJ-1. In addition, the role of HIF1a in the mode of action of quinoxaline 1,4-di-N-oxide is independent of biological activity.

Novel antimalarial chloroquine- and primaquine-quinoxaline 1,4-di-N-oxide hybrids: Design, synthesis, Plasmodium life cycle stage profile, and preliminary toxicity studies

Emergence of drug resistance and targeting all stages of the parasite life cycle are currently the major challenges in antimalarial chemotherapy. Molecular hybridization combining two scaffolds in a single molecule is an innovative strategy for achieving these goals. In this work, a series of novel quinoxaline 1,4-di-N-oxide hybrids containing either chloroquine or primaquine pharmacophores was designed, synthesized and tested against both chloroquine sensitive and multidrug resistant strains of Plasmodium falciparum. Only chloroquine-based compounds exhibited potent blood stage activity with compounds 4b and 4e being the most active and selective hybrids at this parasite stage. Based on their intraerythrocytic activity and selectivity or their chemical nature, seven hybrids were then evaluated against the liver stage of Plasmodium yoelii, Plasmodium berghei and Plasmodium falciparum infections. Compound 4b was the only chloroquine-quinoxaline 1,4-di-N-oxide hybrid with a moderate liver activity, whereas compound 6a and 6b were identified as the most active primaquine-based hybrids against exoerythrocytic stages, displaying enhanced liver activity against P. yoelii and P. berghei, respectively, and better SI values than primaquine. Although both primaquine-quinoxaline 1,4-di-N-oxide hybrids slightly reduced the infection of mosquitoes, they inhibited sporogony of P. berghei and compound 6a showed 92% blocking of transmission. In vivo liver efficacy assays revealed that compound 6a showed causal prophylactic activity affording parasitaemia reduction of up to 95% on day 4. Absence of genotoxicity and in vivo acute toxicity were also determined. These results suggest the approach of primaquine-quinoxaline 1,4-di-N-oxide hybrids as new potential dual-acting antimalarials for further investigation.

Structure-activity relationship of new antimalarial 1-aryl-3-susbtituted propanol derivatives: Synthesis, preliminary toxicity profiling, parasite life cycle stage studies, target exploration, and targeted delivery

Design, synthesis, structure-activity relationship, cytotoxicity studies, in silico drug-likeness, genotoxicity screening, and in vivo studies of new 1-aryl-3-substituted propanol derivatives led to the identification of nine compounds with promising in vitro (55, 56, 61, 64, 66, and 70-73) and in vivo (66 and 72) antimalarial profiles against Plasmodium falciparum and Plasmodium berghei. Compounds 55, 56, 61, 64, 66 and 70-73 exhibited potent antiplasmodial activity against chloroquine-resistant strain FCR-3 (IC₅₀s < 0.28 μM), and compounds 55, 56, 64, 70, 71, and 72 showed potent biological activity in chloroquine-sensitive and multidrug-resistant strains (IC₅₀s < 0.7 μM for 3D7, D6, FCR-3 and C235). All of these compounds share appropriate drug-likeness profiles and adequate selectivity indexes (77 < SI < 184) as well as lack genotoxicity. In vivo efficacy tests in a mouse model showed compounds 66 and 72 to be promising candidates as they exhibited significant parasitemia reductions of 96.4% and 80.4%, respectively. Additional studies such as liver stage and sporogony inhibition, target exploration of heat shock protein 90 of P. falciparum, targeted delivery by immunoliposomes, and enantiomer characterization were performed and strongly reinforce the hypothesis of 1-aryl-3-substituted propanol derivatives as promising antimalarial compounds.

Trypanothione Reductase and Superoxide Dismutase as Current Drug Targets for Trypanosoma cruzi: An Overview of Compounds with Activity against Chagas Disease

It has been over a century since Carlos Chagas discovered the Trypanosoma cruzi (T. cruzi) as the causative agent of Chagas disease (CD), a neglected tropical disease with several socioeconomic, epidemiological and human health repercussions. Currently, there are only two commercialized drugs to treat CD in acute phase, nifurtimox and benznidazol, with several adverse side effects. Thus, new orally available and safe drugs for this parasitic infection are urgently required. One strategy of great importance in new drug discovery programmes is based on the search of molecules enabling to interfere with enzymes involved in T. cruzi metabolism. This review will focus on two of the most promising targets for the therapy of CD: trypanothione reductase (TR) and the iron-containing superoxide dismutase (Fe- SOD), which protect the parasite against oxidative damage by reactive oxygen species. A brief comparison of the function, mechanism of action and the active sites between T. cruzi TR and Fe-SOD with their analogues enzymes in human, glutathione reductase (GR) and the corresponding SODs, will be discussed. This review will also summarize the recent development and structure-activity relationships of novel compounds reported for their ability to selectively inhibit these targets, aiming to define molecular bases in the search for new effective treatment of CD.

ImmunoPEGliposomes for the targeted delivery of novel lipophilic drugs to red blood cells in a falciparum malaria murine model

Most drugs currently entering the clinical pipeline for severe malaria therapeutics are of lipophilic nature, with a relatively poor solubility in plasma and large biodistribution volumes. Low amounts of these compounds do consequently accumulate in circulating Plasmodium-infected red blood cells, exhibiting limited antiparasitic activity. These drawbacks can in principle be satisfactorily dealt with by stably encapsulating drugs in targeted nanocarriers. Here this approach has been adapted for its use in immunocompetent mice infected by the Plasmodium yoelii 17XL lethal strain, selected as a model for human blood infections by Plasmodium falciparum. Using immunoliposomes targeted against a surface protein characteristic of the murine erythroid lineage, the protocol has been applied to two novel antimalarial lipophilic drug candidates, an aminoquinoline and an aminoalcohol. Large encapsulation yields of >90% were obtained using a citrate-buffered pH gradient method and the resulting immunoliposomes reached in vivo erythrocyte targeting and retention efficacies of >80%. In P. yoelii-infected mice, the immunoliposomized aminoquinoline succeeded in decreasing blood parasitemia from severe to uncomplicated malaria parasite densities (i.e. from ≥25% to ca. 5%), whereas the same amount of drug encapsulated in non-targeted liposomes had no significant effect on parasite growth. Pharmacokinetic analysis indicated that this good performance was obtained with a rapid clearance of immunoliposomes from the circulation (blood half-life of ca. 2 h), suggesting a potential for improvement of the proposed model.

New hydrazine and hydrazide quinoxaline 1,4-di-N-oxide derivatives: In silico ADMET, antiplasmodial and antileishmanial activity

We report the design (in silico ADMET criteria), synthesis, cytotoxicity studies (HepG-2 cells), and biological evaluation of 15 hydrazine/hydrazide quinoxaline 1,4-di-N-oxide derivatives against the 3D7 chloroquine sensitive strain and FCR-3 multidrug resistant strain of Plasmodium falciparum and Leishmania infantum (axenic amastigotes). Fourteen of derivatives are novel quinoxaline 1,4-di-N-oxide derivatives. Compounds 18 (3D7 IC₅₀=1.40μM, FCR-3 IC₅₀=2.56μM) and 19 (3D7 IC₅₀=0.24μM, FCR-3 IC₅₀=2.8μM) were identified as the most active against P. falciparum, and they were the least cytotoxic (CC₅₀-values>241μM) and most selective (SI>86). None of the compounds tested against L. infantum were considered to be active. Additionally, the functional role of the hydrazine and hydrazide structures were studied in the quinoxaline 1,4-di-N-oxide system.

Exploring the scope of new arylamino alcohol derivatives: Synthesis, antimalarial evaluation, toxicological studies, and target exploration

Synthesis of new 1-aryl-3-substituted propanol derivatives followed by structure-activity relationship, in silico drug-likeness, cytotoxicity, genotoxicity, in silico metabolism, in silico pharmacophore modeling, and in vivo studies led to the identification of compounds 22 and 23 with significant in vitro antiplasmodial activity against drug sensitive (D6 IC₅₀ ≤ 0.19 μM) and multidrug resistant (FCR-3 IC₅₀ ≤ 0.40 μM and C235 IC₅₀ ≤ 0.28 μM) strains of Plasmodium falciparum. Adequate selectivity index and absence of genotoxicity was also observed. Notably, compound 22 displays excellent parasitemia reduction (98 ± 1%), and complete cure with all treated mice surviving through the entire period with no signs of toxicity. One important factor is the agreement between in vitro potency and in vivo studies. Target exploration was performed; this chemotype series exhibits an alternative antimalarial mechanism.

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New aryl-substituted propanol derivatives (APD) show promising antimalarial activity.

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γ-amino alcohol moiety is significant antimalarial chemotype.

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Compound 22 displays excellent in vivo parasitemia reduction (98%) and complete cure.

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APD are active against drug sensitive and multidrug resistant strains.

Synthesis, biological evaluation and structure-activity relationships of new quinoxaline derivatives as anti-Plasmodium falciparum agents

We report the synthesis and antimalarial activities of eighteen quinoxaline and quinoxaline 1,4-di-N-oxide derivatives, eight of which are completely novel. Compounds 1a and 2a were the most active against Plasmodium falciparum strains. Structure-activity relationships demonstrated the importance of an enone moiety linked to the quinoxaline ring.

Novel quinoxaline 1,4-di-N-oxide derivatives as new potential antichagasic agents

As a continuation of our research and with the aim of obtaining new agents against Chagas disease, an extremely neglected disease which threatens 100 million people, eighteen new quinoxaline 1,4-di-N-oxide derivatives have been synthesized following the Beirut reaction. The synthesis of the new derivatives was optimized through the use of a new and more efficient microwave-assisted organic synthetic method. The new derivatives showed excellent in vitro biological activity against Trypanosoma cruzi. Compound 17, which was substituted with fluoro groups at the 6- and 7-positions of the quinoxaline ring, was the most active and selective in the cytotoxicity assay. The electrochemical study showed that the most active compounds, which were substituted by electron-withdrawing groups, possessed a greater ease of reduction of the N-oxide groups.

New amide derivatives of quinoxaline 1,4-di-N-oxide with leishmanicidal and antiplasmodial activities

Malaria and leishmaniasis are two of the World's most important tropical parasitic diseases. Continuing with our efforts to identify new compounds active against malaria and leishmaniasis, twelve new 1,4-di-N-oxide quinoxaline derivatives were synthesized and evaluated for their in vitro antimalarial and antileishmanial activity against Plasmodium falciparum FCR-3 strain, Leishmania infantum and Leishmania amazonensis. Their toxicity against VERO cells (normal monkey kidney cells) was also assessed. The results obtained indicate that a cyclopentyl derivative had the best antiplasmodial activity (2.9 µM), while a cyclohexyl derivative (2.5 µM) showed the best activity against L. amazonensis, and a 3-chloropropyl derivative (0.7 µM) showed the best results against L. infantum. All these compounds also have a Cl substituent in the R⁷ position.

Novel sulfonylurea derivatives as H3 receptor antagonists. Preliminary SAR studies

The combination of antagonism at histamine H(3) receptor and the stimulation of insulin secretion have been proposed as an approach to new dual therapeutic agents for the treatment of type 2 diabetes mellitus associated with obesity. We have designed and synthesized a new series of non-imidazole derivatives, based on a basic amine ring connected through an alkyl spacer of variable length to a phenoxysulfonylurea moiety. These compounds were initially evaluated for histamine H(3) receptor binding affinities, suggesting that a propoxy chain linker between the amine and the core ring could be essential for optimal binding affinity. Compound 56, 1-(naphthalen-1-yl)-3-[(p-(3-pyrrolidin-1-ylpropoxy)benzene)]sulfonylurea exhibited the best H(3) antagonism affinity. However, since all these derivatives failed to block K(ATP) channels, the link of these two related moieties should not be considered a good pharmacophore for obtaining new dual H(3) antagonists with insulinotropic activity, suggesting the necessity to propose a new chemical hybrid prototype.

Aryl piperazine and pyrrolidine as antimalarial agents. Synthesis and investigation of structure-activity relationships

Piperazine and pyrrolidine derivatives were synthesised and evaluated for their capacity to inhibit the growth of Plasmodium falciparum chloroquine-resistant (FCR-3) strain in culture. The combined presence of a hydroxyl group, a propane chain and a fluor were shown to be crucial for the antiplasmodial activity. Five compounds of the aryl-alcohol series inhibited 50% of parasite growth at doses ≤10 μM. The most active compound 1-(4-fluoronaphthyl)-3-[4-(4-nitro-2-trifluoromethylphenyl)piperazin-1-yl] propan-1-ol was almost 20-40 times more active on P. falciparum (IC(50): 0.5 μM) than on tumorogenic and non-tumorogenic cells. In vivo it has a very weak effect; inhibiting 35% of parasite growth only, at 10 mg/kg/day against Plasmodium berghei infected mice without any impact on survival time. In silico molecular docking study and molecular electrostatic potential calculation revealed that this compound bound to the active site of Plasmodium plasmepsin II enzyme.

New 1-aryl-3-substituted propanol derivatives as antimalarial agents

This paper describes the synthesis and in vitro antimalarial activity against a P. falciparum 3D7 strain of some new 1-aryl-3-substituted propanol derivatives. Twelve of the tested compounds showed an IC₅₀ lower than 1 µM. These compounds were also tested for cytotoxicity in murine J774 macrophages. The most active compounds were evaluated for in vivo activity against P. berghei in a 4-day suppressive test. Compound 12 inhibited more than 50% of parasite growth at a dose of 50 mg/kg/day. In addition, an FBIT test was performed to measure the ability to inhibit ferriprotoporphyrin biocrystallization. This data indicates that 1-aryl-3-substituted propanol derivatives hold promise as a new therapeutic option for the treatment of malaria.

New amide derivatives as melanin-concentrating hormone receptor 1 antagonists for the treatment of obesity

Melanin-concentrating hormone (MCH) is a recently discovered central nervous system (CNS) target for treating obesity. Two novel series of amide derivatives were synthesized and evaluated biologically as MCH-R1 (melanin-concentrating hormone receptor 1) antagonists. The results showed that diphenyl substituents on the amide lead to better activity than biphenyl substituents.

Novel series of substituted biphenylmethyl urea derivatives as MCH-R1 antagonists for the treatment of obesity

We have designed and synthesized two novel series of MCH-R1 antagonists based on a substituted biphenylmethyl urea core. SAR was explored, suggesting that optimal binding with the receptor was achieved when the biphenylmethyl group and the linker were substituted on the same nitrogen of the urea moiety. Compound 1-(3'-cyano-4-biphenylmethyl)-3-(2-hydroxy-1,1-dimethylethyl)-1-{2-[1-(4-methylbenzyl)-4-piperidinyl]ethyl}urea 2t showed the best antagonist binding activity to the MCH-R1 with a 43 nM K(i).

Novel human neuropeptide Y Y5 receptor antagonists for the treatment of obesity. Synthesis and biological evaluation of pyridine hydrazide derivatives

A series of new pyridine hydrazide derivatives with high and selective antagonist activity at the human neuropeptide Y Y5 receptor were developed. Introduction of electron-withdrawing groups into the arylsulfonamide rest, together with the 3-pyridyl analogue in the hydrazide moiety, led to a significant improvement of potency and solubility, affording trans-N-(4-[N'-(pyridine-3-carbonyl)hydrazino-carbonyl]cyclohexylmethyl)-2,4-dichloro-benzenesulfonamide (14), which binds to the hY5 receptor with an IC50 value of 7.44 nmol/L.

Synthesis and evaluation of new hydrazide derivatives as neuropeptide Y Y5 receptor antagonists for the treatment of obesity

NPY is the most potent orexigenic agent known to man, with NPY Y1 and NPY Y5 being the receptor subtypes that are most likely responsible for centrally-mediated NPY-induced feeding responses. Based on the aforementioned, novel hydrazide derivatives were prepared for the purpose of searching new NPY Y5 receptor antagonists. Many of the compounds exhibited nanomolar binding affinity for this receptor, affording trans-N-(4-[N'-(3,4-dichlorophenyl)hydrazinocarbonyl]cyclohexylmethyl)-4-fluorobenzenesulfonamide, which showed the best activity (IC(50)=0.43nM).

Synthesis of new thiophene and benzo[b]thiophene hydrazide derivatives as human NPY Y5 antagonists

Neuropeptide Y is one of the most potent appetite stimulating hormones known. Novel thiophene and benzo[b]thiophene hydrazide derivatives were synthetized and evaluated biologically as NPY Y(1) and Y(5) receptor subtype antagonists. They were found to have nanomolar binding affinities for human NPY Y(5) receptor, obtaining the lead compound, trans-N-4-[N'-(thiophene-2-carbonyl)hydrazinocarbonyl]cyclohexylmethyl-4-bromobenzenesulfonamide, which binds with a 7.70 nM IC(50) to the hY(5) receptor.

Synthesis and evaluation of new arylsulfonamidomethylcyclohexyl derivatives as human neuropeptide Y Y5 receptor antagonists for the treatment of obesity

NPY is the most potent orexigenic peptide identified up to now. Stimulation of food intake is measured by the Y(1) and Y(5) receptor subtypes. In this study, the synthesis and evaluation of new arylsulfonamidomethylcyclohexyl derivatives are described as potential selective antagonists of the human NPY Y(5) receptor. The SAR of these series was examined and the amide derivatives were the compounds that showed the best activities. trans-N-(4-[(Quinolin-3-yl)aminocarbonyl]cyclohexylmethyl)-2,4-dichlorobenzenesulfonamide (42) bound to the human neuropeptide Y Y(5) receptor with a 2 nM IC(50).

A new glucose-6-phosphate dehydrogenase variant with congenital nonspherocytic hemolytic anemia (G6PD Genova). Biochemical characterization and mosaicism expression in the heterozygote

A new deficient variant of glucose-6-phosphate dehydrogenase (G6PD) causing severe congenital nonspherocytic hemolytic anemia (CNSHA) is described. The variant enzyme, characterized by slow electrophoretic mobility, extreme in vivo and in vitro lability, high Km for G6P and strongly acidic pH optimum, appears to be unique, and has been designated G6PD Genova. Investigation of an obligate heterozygote using various cytochemical, biochemical and recombinant-DNA techniques showed G6PD mosaicism in the erythrocytes and leukocytes. Therefore, the presence of a disadvantageous mutation at one Gd locus did not determine selection in favor of the normal allele in the heterozygote's hemopoietic cells.

Catalase and glutathione peroxidase are equally active in detoxification of hydrogen peroxide in human erythrocytes

Genetic deficiencies of glucose-6-phosphate dehydrogenase (G6PD) and NADPH predispose affected erythrocytes to destruction from peroxides. Conversely, genetic deficiencies of catalase do not predispose affected erythrocytes to peroxide-induced destruction. These observations have served to strengthen the assumption that the NADPH/glutathione/glutathione peroxidase pathway is the principal means for disposal of H2O2 in human erythrocytes. Recently, however, mammalian catalase was found to have tightly bound NADPH and to require NADPH for the prevention and reversal of inactivation by its toxic substrate (H2O2). Since both catalase and the glutathione pathway are dependent on NADPH for function, this finding raises the possibility that both mechanisms destroy H2O2 in human erythrocytes. A comparison of normal and acatalasemic erythrocytes in the present study indicated that catalase accounts for more than half of the destruction of H2O2 when H2O2 is generated at a rate comparable to that which leads to hemolysis in G6PD- deficient erythrocytes.

The function of catalase-bound NADPH

Catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) is of historical interest for having been the subject of some of the earliest investigations of enzymes. A feature of catalase that has been poorly understood for several decades, however, is the mechanism by which catalase remains active in the presence of its own substrate, hydrogen peroxide. We reported recently that catalase contains tightly bound NADPH. The present study with bovine and human catalase revealed that NADPH both prevents and reverses the accumulation of compound II, an inactive form of catalase that is generated slowly when catalase is exposed to hydrogen peroxide. Since the effect of NADPH occurs even at NADPH concentrations below 0.1 microM, the protective mechanism is likely to operate in vivo. This discovery of the role of catalase-bound NADPH brings a unity to the concept of two different mechanisms for disposing of hydrogen peroxide (catalase and the glutathione reductase/peroxidase pathway) by revealing that both mechanisms are dependent on NADPH.

Primary thrombocythemia: clonal origin of platelets, erythrocytes, and granulocytes in a GdB/GdMediterranean subject

A patient with primary thrombocythemia, who was heterozygous for glucose-6-phosphate dehydrogenase deficiency (GdB/GdMed), was investigated to test for the clonal origin of this myeloproliferative disorder. In order to assess somatic cell mosaicism in various tissues, we have made use of the different rate of utilization of 2-deoxyglucose-6-phosphate, an analog of glucose-6-phosphate, by normal glucose-6-phosphate dehydrogenase and by the Mediterranean variant: the results demonstrate that essential thrombocythemia is a clonal disease involving the erythrocytic, granulocytic, and megakaryocytic series, without affecting monocytes, T lymphocytes, and non-T lymphocytes.

G6PD Napoli and Ferrara II: two new glucose-6-phosphate dehydrogenase variants having similar characteristics but different intracellular lability and specific activity

Two new glucose-6-phosphate dehydrogenase (G6PD, D-glucose 6-phosphate: NADP oxido reductase, E.C. 1.1.1.49) variants, designated G6PD Napoli and G6PD Ferrara II, are described in propositi from two unrelated families. Characterization side by side of the two variants according to W.H.O. recommendations reveals minor differences which are mostly related to utilization of artificial substrates (increased in both cases as compared with normal G6PD type B). Other properties, which are not significantly distinctive between the two variants, are an enzyme activity amounting to nearly 20% of normal, a decreased electrophoretic mobility, decreased Km values for glucose-6-phosphate and NADP, normal thermostability and biphasic pH curves. However, marked differences emerged between the two variants and between either variant and G6PD B as well, when a number of microtechniques were used. These were: (1) the half-lives of G6PD Napoli and G6PD Ferrara II are 16 and 29 d, respectively, while that of G6PD B is 63 d; (2) the specific activities, measured by a method involving direct estimation of G6PD protein on sodium dodecyl sulphate polyacrylamide gel electrophoretic tracings, are 166 I.U./mg (G6PD Napoli) and 59 I.U./mg (G6PD Ferrara II), as compared with normal value of 180 I.U./mg (G6PD B). On the whole, these findings allow the conclusion that the deficiency of catalytic activity is related to an accelerated though distinctive decay of both mutant enzyme proteins within the affected erythrocytes and that a significant impairment of catalytic efficiency is also involved, as a result of the underlying structural mutation in the case of G6PD Ferrara II.

2-deoxy-glucose-6-phosphate utilization in the study of glucose-6-phosphate dehydrogenase mosaicism

The electrophoretic difference between normal glucose-6-phosphate dehydrogenase (G6PD) and two common variants (G6PD A and G6PD A-) has made the G6PD enzyme system very useful for genetic studies and for investigation on the clonal origin of tumors. This approach has not been possible for another common variant, G6PD mediterranean, which has a normal electrophoretic pattern. The different utilization of 2-deoxy-glucose-6-phosphate (2dG6P), an analog of the normal substrate, by the normal enzyme and the Mediterranean variant, allows a convenient determination of the degree of mosaicism in mononuclear cells from heterozygotes.

Favism: erythrocyte metabolism during haemolysis and reticulocytosis

The reduced activity of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate; NADP+ 1-oxidoreductase; G6PF) in Mediterranean erythrocytes explains the precarious equilibrium of the hexose monophosphate pathway (HMP) and the susceptibility of these cells to haemolytic agents. G6PD-deficient erythrocytes, in steady-state conditions, have a low NADPH/NADP+ ratio, thus allowing the HMP to operate at its maximal intracellular rate and to compensate the intrinsic erythrocyte enzyme deficiency. Studies started soon after accidental intake of fava beans by sensitive G6PD-deficient subjects demonstrate a decrease of both NADPH/NADP+ ratio and reduced glutathione. The metabolic effects induced by fava beans may be attributed to oxidative stress probably associated with an inhibitor effect of some unknown metabolite on the HMP. The availability of erythrocytes from subjects recovering from haemolysis with high reticulocyte counts and increased G6PD activity, provides new information on the rate of synthesis as well as on the in vivo decay of the mutant enzyme. Correlation of G6PD activity to reticulocyte count and extrapolation to an ideally homogenous population of reticulocytes reveal that the mutant enzyme is synthesized at a nearly normal rate. Furthermore, the present correlation allows an estimate of the in vivo half-life of Mediterranean G6PD. The rate of decline of about 8 d observed in this study well correlates to the intracellular metabolic aspects of G6PD Mediterranean erythrocytes.

Effect of haemolysis on the hexose monophosphate pathway in normal and in glucose-6-phosphate dehydrogenase-deficient erythrocytes

The hexose monophosphate pathway of human glucose-6-phosphate dehydrogenase (EC 1.1.1.49) - deficient erythrocytes is under a severe and unexplained restraint (Gaetani, G.D., Parker, J.C. and Kirkman, H.N. (1974) Proc. Natl. Acad. Sci. U.S. 71, 3584-3587). In this study the hexose monophosphate pathway activity and the NADPH level of normal and glucose-6-phosphate dehydrogenase-deficient erythrocytes were measured soon after haemolysis. The results indicate a prompt increase in 14CO2 evolution and a rise in MADPH levels. Since, in this study, the concentration of the haemolysate is comparable to that of intact erythrocytes, the relief of the restraint on glucose-6-phosphate dehydrogenase through dilution-dependent dissociation from inactivator or inhibitor is excluded. The possibility that the intracellular restraint may result from compartmentalization of glucose-6-phosphate dehydrogenase and substrates or from properties of the intact membrane of the erythrocytes is suggested.