Mechanism of malarial haem detoxification inhibition by chloroquine

The haem detoxification pathway of the malaria parasite Plasmodium falciparum is a potential biochemical target for drug development. Free haem, released after haemoglobin degradation, is polymerized by the parasite to form haemozoin pigment. Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2) has been implicated as the catalytic scaffold for detoxification of haem in the malaria parasite. Previously we have shown that a hexapeptide repeat sequence (Ala-His-His-Ala-Ala-Asp), which appears 33 times in Pfhrp-2, may be the major haem binding site in this protein. The haem binding studies carried out by ourselves indicate that up to 18 equivalents of haem could be bound by this protein with an observed K(d) of 0.94 microM. Absorbance spectroscopy provides evidence that chloroquine is capable of extracting haem bound to Pfhrp-2. This was supported by the K(d) value, of 37 nM, observed for the haem-chloroquine complex. The native PAGE studies reveal that the formation of the haem-Pfhrp-2 complex is disrupted by chloroquine. These results indicate that chloroquine may be acting by inhibiting haem detoxification/binding to Pfhrp-2. Moreover, the higher affinity of chloroquine for haem than Pfhrp-2 suggests a possible mechanism of action for chloroquine; it may remove the haem bound to Pfhrp-2 and form a complex that is toxic to the parasite.

The antimalarial drugs quinine, chloroquine and mefloquine are antagonists at 5-HT 3 receptors

Background and Purpose: The antimalarial compounds quinine, chloroquine and mefloquine affect the electrophysiological properties of Cys-loop receptors and have structural similarities to 5-HT3 receptor antagonists. They may therefore act at 5-HT3 receptors. Experimental Approach: The effects of quinine, chloroquine and mefloquine on electrophysiological and ligand binding properties of 5-HT3A receptors expressed in HEK 293 cells and Xenopus oocytes were examined. The compounds were also docked into models of the binding site. Key Results: 5-HT3 responses were blocked with IC50 values of 13.4 μM, 11.8 μM and 9.36 μM for quinine, chloroquine and mefloquine. Schild plots indicated quinine and chloroquine behaved competitively with pA2 values of 4.92 (KB=12.0 μM) and 4.97 (KB=16.4 μM). Mefloquine displayed weakly voltage-dependent, non-competitive inhibition consistent with channel block. On and off rates for quinine and chloroquine indicated a simple bimolecular reaction scheme. Quinine, chloroquine and mefloquine displaced [3H]granisetron with Ki values of 15.0, 24.2 and 35.7 μM. Docking of quinine into a homology model of the 5-HT3 receptor binding site located the tertiary ammonium between W183 and Y234, and the quinoline ring towards the membrane, stabilised by a hydrogen bond with E129. For chloroquine, the quinoline ring was positioned between W183 and Y234 and the tertiary ammonium stabilised by interactions with F226. Conclusions and Implications: This study shows that quinine and chloroquine competitively inhibit 5-HT3 receptors, while mefloquine inhibits predominantly non-competitively. Both quinine and chloroquine can be docked into a receptor binding site model, consistent with their structural homology to 5-HT3 receptor antagonists.

Structure-activity relationship and mechanism of action studies of manzamine analogues for the control of neuroinflammation and cerebral infections

Structure-activity relationship studies were carried out by chemical modification of manzamine A (1), 8-hydroxymanzamine A (2), manzamine F (14), and ircinal isolated from the sponge Acanthostrongylophora. The derived analogues were evaluated for antimalarial, antimicrobial, and antineuroinflammatory activities. Several modified products exhibited potent and improved in vitro antineuroinflammatory, antimicrobial, and antimalarial activity. 1 showed improved activity against malaria compared to chloroquine in both multi- and single-dose in vivo experiments. The significant antimalarial potential was revealed by a 100% cure rate of malaria in mice with one administration of 100 mg/kg of 1. The potent antineuroinflammatory activity of the manzamines will provide great benefit for the prevention and treatment of cerebral infections (e.g., Cryptococcus and Plasmodium). In addition, 1 was shown to permeate across the blood-brain barrier (BBB) in an in vitro model using a MDR-MDCK monolayer. Docking studies support that 2 binds to the ATP-noncompetitive pocket of glycogen synthesis kinase-3beta (GSK-3beta), which is a putative target of manzamines. On the basis of the results presented here, it will be possible to initiate rational drug design efforts around this natural product scaffold for the treatment of several different diseases.

Neuronal precursor cell-expressed developmentally down-regulated 4-1 (NEDD4-1) controls the sorting of newly synthesized Ca(V)1.2 calcium channels

Neuronal precursor cell-expressed developmentally down-regulated 4 (Nedd4) proteins are ubiquitin ligases, which attach ubiquitin moieties to their target proteins, a post-translational modification that is most commonly associated with protein degradation. Nedd4 ubiquitin ligases have been shown to down-regulate both potassium and sodium channels. In this study, we investigated whether Nedd4 ubiquitin ligases also regulate Ca(v) calcium channels. We expressed three Nedd4 family members, Nedd4-1, Nedd4-2, and WWP2, together with Ca(v)1.2 channels in tsA-201 cells. We found that Nedd4-1 dramatically decreased Ca(v) whole-cell currents, whereas Nedd4-2 and WWP2 failed to regulate the current. Surface biotinylation assays revealed that Nedd4-1 decreased the number of channels inserted at the plasma membrane. Western blots also showed a concomitant decrease in the total expression of the channels. Surprisingly, however, neither the Ca(v) pore-forming α1 subunit nor the associated Ca(v)β and Ca(v)α(2)δ subunits were ubiquitylated by Nedd4-1. The proteasome inhibitor MG132 prevented the degradation of Ca(v) channels, whereas monodansylcadaverine and chloroquine partially antagonized the Nedd4-1-induced regulation of Ca(v) currents. Remarkably, the effect of Nedd4-1 was fully prevented by brefeldin A. These data suggest that Nedd4-1 promotes the sorting of newly synthesized Ca(v) channels for degradation by both the proteasome and the lysosome. Most importantly, Nedd4-1-induced regulation required the co-expression of Ca(v)β subunits, known to antagonize the retention of the channels in the endoplasmic reticulum. Altogether, our results suggest that Nedd4-1 interferes with the chaperon role of Ca(v)β at the endoplasmic reticulum/Golgi level to prevent the delivery of Ca(v) channels at the plasma membrane.

Current state of evidence on 'off-label' therapeutic options for systemic lupus erythematosus, including biological immunosuppressive agents, in Germany, Austria and Switzerland--a consensus report

Systemic lupus erythematosus (SLE) can be a severe and potentially life-threatening disease that often represents a therapeutic challenge because of its heterogeneous organ manifestations. Only glucocorticoids, chloroquine and hydroxychloroquine, azathioprine, cyclophosphamide and very recently belimumab have been approved for SLE therapy in Germany, Austria and Switzerland. Dependence on glucocorticoids and resistance to the approved therapeutic agents, as well as substantial toxicity, are frequent. Therefore, treatment considerations will include 'off-label' use of medication approved for other indications. In this consensus approach, an effort has been undertaken to delineate the limits of the current evidence on therapeutic options for SLE organ disease, and to agree on common practice. This has been based on the best available evidence obtained by a rigorous literature review and the authors' own experience with available drugs derived under very similar health care conditions. Preparation of this consensus document included an initial meeting to agree upon the core agenda, a systematic literature review with subsequent formulation of a consensus and determination of the evidence level followed by collecting the level of agreement from the panel members. In addition to overarching principles, the panel have focused on the treatment of major SLE organ manifestations (lupus nephritis, arthritis, lung disease, neuropsychiatric and haematological manifestations, antiphospholipid syndrome and serositis). This consensus report is intended to support clinicians involved in the care of patients with difficult courses of SLE not responding to standard therapies by providing up-to-date information on the best available evidence.

Effects of doxorubicin cancer therapy on autophagy and the ubiquitin-proteasome system in long-term cultured adult rat cardiomyocytes

The clinical use of anthracyclines in cancer therapy is limited by dose-dependent cardiotoxicity that involves cardiomyocyte injury and death. We have tested the hypothesis that anthracyclines affect protein degradation pathways in adult cardiomyocytes. To this aim, we assessed the effects of doxorubicin (Doxo) on apoptosis, autophagy and the proteasome/ubiquitin system in long-term cultured adult rat cardiomyocytes. Accumulation of poly-ubiquitinated proteins, increase of cathepsin-D-positive lysosomes and myofibrillar degradation were observed in Doxo-treated cardiomyocytes. Chymotrypsin-like activity of the proteasome was initially increased and then inhibited by Doxo over a time-course of 48 h. Proteasome 20S proteins were down-regulated by higher doses of Doxo. The expression of MURF-1, an ubiquitin-ligase specifically targeting myofibrillar proteins, was suppressed by Doxo at all concentrations measured. Microtubule-associated protein 1 light chain 3B (LC3)-positive punctae and both LC3-I and -II proteins were induced by Doxo in a dose-dependent manner, as confirmed by using lentiviral expression of green fluorescence protein bound to LC3 and live imaging. The lysosomotropic drug chloroquine led to autophagosome accumulation, which increased with concomitant Doxo treatment indicating enhanced autophagic flux. We conclude that Doxo causes a downregulation of the protein degradation machinery of cardiomyocytes with a resulting accumulation of poly-ubiquitinated proteins and autophagosomes. Although autophagy is initially stimulated as a compensatory response to cytotoxic stress, it is followed by apoptosis and necrosis at higher doses and longer exposure times. This mechanism might contribute to the late cardiotoxicity of anthracyclines by accelerated aging of the postmitotic adult cardiomyocytes and to the susceptibility of the aging heart to anthracycline cancer therapy.

[Hypercalcemia in sarcoidosis--case report, prevalence, pathophysiology and therapeutic options]

Hypercalcemia is a highly prevalent complication of sarcoidosis. A medical history of a patient with sarcoidosis is shown as case report. Depending on the population studied about 2-63% of sarcoidosis patients show hypercalcemia. The major difference in the prevalence of hypercalcemia may be in part due to the undulating course of subacute sarcoidosis, so hypercalcemia may be missed when serum calcium is not frequently measured. Hypercalciuria appears to be twice as prevalent then hypercalcemia and should be looked for in every sarcoidosis patient. Hypercalcemia in sarcoidosis is due to the uncontrolled synthesis of 1,25-dihydroxyvitamin D3 by macrophages. 1,25-dihydroxyvitamin D3 leads to an increased absorption of calcium in the intestine and to an increased resorption of calcium in the bone. Immunoregulatory properties have been ascribed to 1,25-dihydroxyvitamin D3. It is an important inhibitor of interleukin-2 and of interferon-gamma-synthesis, two cytokines that are important in granuloma formation in sarcoidosis. It is thought that 1,25-dihydroxyvitamin D3 counterregulates uncontrolled granuloma formation. Treatment of hypercalcemia depends on the serum level of hypercalcemia and its persistence. Generally sarcoidotic patients should be advised to avoid sun exposition to reduce vitamin D3 synthesis in the skin, to omit fish oils that are rich of vitamin D and to produce more than two liters urine a day by adapting fluid intake. Although severe hypercalcemia seems to be rare, glucocorticosteroid treatment should be started if corrected total calcium level rises beyond 3 mmol/l. If hypercalcemia is symptomatic, treatment should be started even at lower levels. Glucocorticosteroids act by inhibition of the overly 1alpha-hydroxylase activity of macrophages. Alternatively, treatment with chloroquine or ketoconazole can be established. If isolated hypercalciuria without hypercalcemia is present with evidence for recurrent nephrolithiasis, patients can be treated with a thiazide diuretic.

[Juvenile chronic arthritis: therapeutic strategy 1990]

Therapeutic strategies based on experience with 119 patients with juvenile chronic arthritis are reviewed. Therapeutic goals are formulated and the means of attaining them (NSAIDs, the so-called disease modifying drugs gold, chloroquine and penicillamine, the antimetabolite methotrexate, intra-articular and systemic corticosteroids, physio- and ergotherapy, technical and orthopedic measures, as well as vocational and medicosocial aspects) are discussed. As the individual prognosis normally depends less on drugs than on preventive and rehabilitative measures, the outcome is largely determined by the quality of a well-coordinated inter-disciplinary team approach.

Hemozoin formation in malaria: a two-step process involving histidine-rich proteins and lipids

Major blood stage antimalarial drugs like chloroquine and artemisinin target the heme detoxification process of the malaria parasite. Hemozoin formation reactions in vitro using the Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2), lipids, and auto-catalysis are slow and could not explain the speed of detoxification needed for parasite survival. Here, we show that malarial hemozoin formation is a coordinated two component process involving both lipids and histidine-rich proteins. Hemozoin formation efficiency in vitro is 1-2% with Pfhrp-2 and 0.25-0.5% with lipids. We added lipids after 9h in a 12h Pfhrp-2 mediated reaction that resulted in sixfold increase in hemozoin formation. However, a lipid mediated reaction in which Pfhrp-2 was added after 9h produced only twofold increase in hemozoin production compared to the reaction with Pfhrp-2 alone. Synthetic peptides corresponding to the Pfhrp-2 heme binding sequences, based on repeats of AHHAAD, neither alone nor in combination with lipids were able to generate hemozoin in vitro. These results indicate that hemozoin formation in malaria parasite involves both the lipids and the scaffolding proteins. Histidine-rich proteins might facilitate hemozoin formation by binding with a large number of heme molecules, and facilitating the dimer formation involving iron-carboxylate bond between two heme molecules, and lipids may then subsequently assist the mechanism of long chain formation, held together by hydrogen bonds or through extensive networking of hydrogen bonds.

Artemisinin, an endoperoxide antimalarial, disrupts the hemoglobin catabolism and heme detoxification systems in malarial parasite

Endoperoxide antimalarials based on the ancient Chinese drug Qinghaosu (artemisinin) are currently our major hope in the fight against drug-resistant malaria. Rational drug design based on artemisinin and its analogues is slow as the mechanism of action of these antimalarials is not clear. Here we report that these drugs, at least in part, exert their effect by interfering with the plasmodial hemoglobin catabolic pathway and inhibition of heme polymerization. In an in vitro experiment we observed inhibition of digestive vacuole proteolytic activity of malarial parasite by artemisinin. These observations were further confirmed by ex vivo experiments showing accumulation of hemoglobin in the parasites treated with artemisinin, suggesting inhibition of hemoglobin degradation. We found artemisinin to be a potent inhibitor of heme polymerization activity mediated by Plasmodium yoelii lysates as well as Plasmodium falciparum histidine-rich protein II. Interaction of artemisinin with the purified malarial hemozoin in vitro resulted in the concentration-dependent breakdown of the malaria pigment. Our results presented here may explain the selective and rapid toxicity of these drugs on mature, hemozoin-containing, stages of malarial parasite. Since artemisinin and its analogues appear to have similar molecular targets as chloroquine despite having different structures, they can potentially bypass the quinoline resistance machinery of the malarial parasite, which causes sublethal accumulation of these drugs in resistant strains.

Synthetic peptides corresponding to a repetitive sequence of malarial histidine rich protein bind haem and inhibit haemozoin formation in vitro

Synthetic peptides containing a repetitive hexapeptide sequence (Ala-His-His-Ala-Ala-Asp) of malarial histidine-rich protein II were evaluated for binding with haem in vitro. The pattern of haem binding suggested that each repeat unit of this sequence provides one binding site for haem. Chloroquine inhibited the haem-peptide complex formation with preferential formation of a haem chloroquine complex. In vitro studies on haem polymerisation showed that none of the peptides could initiate haemozoin formation. However, they could inhibit haemozoin formation promoted by a malarial parasite extract, possibly by competitively binding free haem. These results indicate this hexapeptide sequence represents the haem binding site of the malarial histidine-rich protein and possibly the site of nucleation for haem polymerisation.

Induction of autophagy is a key component of all-trans-retinoic acid-induced differentiation in leukemia cells and a potential target for pharmacologic modulation

Acute myeloid leukemia (AML) is characterized by the accumulation of immature blood cell precursors in the bone marrow. Pharmacologically overcoming the differentiation block in this condition is an attractive therapeutic avenue, which has achieved success only in a subtype of AML, acute promyelocytic leukemia (APL). Attempts to emulate this success in other AML subtypes have thus far been unsuccessful. Autophagy is a conserved protein degradation pathway with important roles in mammalian cell differentiation, particularly within the hematopoietic system. In the study described here, we investigated the functional importance of autophagy in APL cell differentiation. We found that autophagy is increased during all-trans-retinoic acid (ATRA)-induced granulocytic differentiation of the APL cell line NB4 and that this is associated with increased expression of LC3II and GATE-16 proteins involved in autophagosome formation. Autophagy inhibition, using either drugs (chloroquine/3-methyladenine) or short-hairpin RNA targeting the essential autophagy gene ATG7, attenuates myeloid differentiation. Importantly, we found that enhancing autophagy promotes ATRA-induced granulocytic differentiation of an ATRA-resistant derivative of the non-APL AML HL60 cell line (HL60-Diff-R). These data support the development of strategies to stimulate autophagy as a novel approach to promote differentiation in AML.