Quinacrine, an Antimalarial Drug with Strong Activity Inhibiting SARS-CoV-2 Viral Replication In Vitro.

Quinacrine (Qx), a molecule used as an antimalarial, has shown anticancer, antiprion, and antiviral activity. The most relevant antiviral activities of Qx are related to its ability to raise pH in acidic organelles, diminishing viral enzymatic activity for viral cell entry, and its ability to bind to viral DNA and RNA. Moreover, Qx has been used as an immunomodulator in cutaneous lupus erythematosus and various rheumatological diseases, by inhibiting phospholipase A2 modulating the Th1/Th2 response. The aim of this study was to evaluate the potential antiviral effect of Qx against denominated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in Vero E6 cells. The cytotoxicity of Qx in Vero E6 cells was determined by the MTT assay. Afterwards, Vero E6 cells were infected with SARS-CoV-2 at different multiplicities of infections (MOIs) of 0.1 and 0.01 in the presence of Qx (0-30 µM) to determinate the half maximal effective concentration (EC50). After 48 h, the effect of Qx against SARS-CoV-2 was assessed by viral cytotoxicity and viral copy numbers, the last were determined by digital real-time RT-PCR (ddRT-PCR). Additionally, electron and confocal microscopy of Vero E6 cells infected and treated with Qx was studied. Our data show that Qx reduces SARS-CoV-2 virus replication and virus cytotoxicity, apparently by inhibition of viral ensemble, as observed by ultrastructural images, suggesting that Qx could be a potential drug for further clinical studies against coronavirus disease 2019 (COVID-19) infection.

5-Nitroimidazole refractory giardiasis is common in Matanzas, Cuba and effectively treated by secnidazole plus high-dose mebendazole or quinacrine: a prospective observational cohort study.

OBJECTIVE: To evaluate the effectiveness and tolerability of secnidazole combined with high-dose mebendazole for treatment of 5-nitroimidazole-resistant giardiasis. METHOD: Adults with microscopically verified Giardia intestinalis monoinfection attending a secondary level hospital in Matanzas City, Cuba were prospectively included in a cohort. A recently introduced treatment ladder consisting of metronidazole as first-line treatment, followed by secnidazole, tinidazole, secnidazole plus mebendazole and quinacrine as second-to fifth-line treatments, respectively, was used. Adverse events and treatment success were determined by questioning and microscopy on concentrated stool samples, respectively on days 3, 5 and 7 after the end of treatment. If G. intestinalis was detected on day 3, 5 or 7, then the infection was classified as refractory and no further microscopy was performed. RESULTS: A total of 456 individuals were included. Metronidazole, 500 mg three times daily for 5 days, cured 248/456 (54%) patients. A single 2-g secnidazole dose as second-line treatment cured 50/208 (24%) patients. A single 2-g tinidazole dose as third-line treatment cured 43/158 (27%) patients. Three rounds of 5-nitroimidazole therapy therefore cured 341/456 (75%) patients. Secnidazole plus mebendazole (200 mg every 8 hours for 3 days) cured 100/115 (87%) of nitroimidazole refractory infections. Quinacrine cured the remaining 15 patients. All treatments were well tolerated. CONCLUSIONS: 5-Nitroimidazole refractory giardiasis was common, indicating that an alternative first-line treatment may be needed. Retreatment of metronidazole refractory giardiasis with an alternative 5-nitroimidazole was suboptimal, indicating cross-resistance. Mebendazole plus secnidazole were well tolerated and effective for the treatment of 5-nitroimidazole refractory G. intestinalis infection in this setting.

Inhibition of Kir4.1 potassium channels by quinacrine.

Inwardly rectifying potassium (Kir) channels are expressed in many cell types and contribute to a wide range of physiological processes. Particularly, Kir4.1 channels are involved in the astroglial spatial potassium buffering. In this work, we examined the effects of the cationic amphiphilic drug quinacrine on Kir4.1 channels heterologously expressed in HEK293 cells, employing the patch clamp technique. Quinacrine inhibited the currents of Kir4.1 channels in a concentration and voltage dependent manner. In inside-out patches, quinacrine inhibited Kir4.1 channels with an IC50 value of 1.8±0.3µM and with extremely slow blocking and unblocking kinetics. Molecular modeling combined with mutagenesis studies suggested that quinacrine blocks Kir4.1 by plugging the central cavity of the channels, stabilized by the residues E158 and T128. Overall, this study shows that quinacrine blocks Kir4.1 channels, which would be expected to impact the potassium transport in several tissues.

Participation of PLA2 and PLC in DhL-induced activation of Rhinella arenarum oocytes.

Rhinella arenarum oocytes can be artificially activated, a process known as parthenogenesis, by a sesquiterpenic lactone of the guaianolide group, dehydroleucodine (DhL). Transient increases in the concentration of cytosolic Ca2+ are essential to trigger egg activation events. In this sense, the 1-4-5 inositol triphosphate receptors (IP3R) seem to be involved in the Ca2+ transient release induced by DhL in this species. We analyzed the involvement of phosphoinositide metabolism, especially the participation of phospholipase A2 (PLA2) and phospholipase C (PLC) in DhL-induced activation. Different doses of quinacrine, aristolochic acid (ATA) (PLA2 inhibitors) or neomycin, an antibiotic that binds to PIP2, thus preventing its hydrolysis, were used in mature Rhinella arenarum oocytes. In order to assay the participation of PI-PLC and PC- PLC we used U73122, a competitive inhibitor of PI-PLC dependent events and D609, an inhibitor of PC-PLC. We found that PLA2 inhibits quinacrine more effectively than ATA. This difference could be explained by the fact that quinacrine is not a specific inhibitor for PLA2 while ATA is specific for this enzyme. With respect to the participation of PLC, a higher decrease in oocyte activation was detected when cells were exposed to neomycin. Inhibition of PC-PLC with D609 and IP-PLC with U73122 indicated that the last PLC has a significant participation in the effect of DhL-induced activation. Results would indicate that DhL induces activation of in vitro matured oocytes of Rhinella arenarum by activation of IP-PLC, which in turn may induce IP3 formation which produces Ca2+ release.

Mechanisms for Kir channel inhibition by quinacrine: acute pore block of Kir2.x channels and interference in PIP2 interaction with Kir2.x and Kir6.2 channels.

Cardiac inward rectifier potassium currents determine the resting membrane potential and contribute repolarization capacity during phase 3 repolarization. Quinacrine is a cationic amphiphilic drug. In this work, the effects of quinacrine were studied on cardiac Kir channels expressed in HEK 293 cells and on the inward rectifier potassium currents, I(K1) and I(KATP), in cardiac myocytes. We found that quinacrine differentially inhibited Kir channels, Kir6.2 ∼ Kir2.3 > Kir2.1. In addition, we found in cardiac myocytes that quinacrine inhibited I(KATP) > I(K1). We presented evidence that quinacrine displays a double action towards strong inward rectifier Kir2.x channels, i.e., direct pore block and interference in phosphatidylinositol 4,5-bisphosphate, PIP(2)-Kir channel interaction. Pore block is evident in Kir2.1 and 2.3 channels as rapid block; channel block involves residues E224 and E299 facing the cytoplasmic pore of Kir2.1. The interference of the drug with the interaction of Kir2.x and Kir6.2/SUR2A channels and PIP(2) is suggested from four sources of evidence: (1) Slow onset of current block when quinacrine is applied from either the inside or the outside of the channel. (2) Mutation of Kir2.3(I213L) and mutation of Kir6.2(C166S) increase their affinity for PIP(2) and lowers its sensitivity for quinacrine. (3) Mutations of Kir2.1(L222I and K182Q) which decreased its affinity for PIP(2) increased its sensitivity for quinacrine. (4) Co-application of quinacrine with PIP(2) lowers quinacrine-mediated current inhibition. In conclusion, our data demonstrate how an old drug provides insight into a dual a blocking mechanism of Kir carried inward rectifier channels.

Interference with hemozoin formation represents an important mechanism of schistosomicidal action of antimalarial quinoline methanols.

BACKGROUND: The parasitic trematode Schistosoma mansoni is one of the major causative agents of human schistosomiasis, which afflicts 200 million people worldwide. Praziquantel remains the main drug used for schistosomiasis treatment, and reliance on the single therapy has been prompting the search for new therapeutic compounds against this disease. Our group has demonstrated that heme crystallization into hemozoin (Hz) within the S. mansoni gut is a major heme detoxification route with lipid droplets involved in this process and acting as a potential chemotherapeutical target. In the present work, we investigated the effects of three antimalarial compounds, quinine (QN), quinidine (QND) and quinacrine (QCR) in a murine schistosomiasis model by using a combination of biochemical, cell biology and molecular biology approaches. METHODOLOGY/PRINCIPAL FINDINGS: Treatment of S. mansoni-infected female Swiss mice with daily intraperitoneal injections of QN, and QND (75 mg/kg/day) from the 11(th) to 17(th) day after infection caused significant decreases in worm burden (39%-61%) and egg production (42%-98%). Hz formation was significantly inhibited (40%-65%) in female worms recovered from QN- and QND-treated mice and correlated with reduction in the female worm burden. We also observed that QN treatment promoted remarkable ultrastructural changes in male and female worms, particularly in the gut epithelium and reduced the granulomatous reaction to parasite eggs trapped in the liver. Microarray gene expression analysis indicated that QN treatment increased the expression of transcripts related to musculature, protein synthesis and repair mechanisms. CONCLUSIONS: The overall significant reduction in several disease burden parameters by the antimalarial quinoline methanols indicates that interference with Hz formation in S. mansoni represents an important mechanism of schistosomicidal action of these compounds and points out the heme crystallization process as a valid chemotherapeutic target to treat schistosomiasis.

Blockade of arachidonic acid pathway induces sprouting in the adult but not in the neonatal uncrossed retinotectal projection.

The uncrossed retinotectal projection of rats undergoes extensive axonal elimination and subsequent growth of axonal arbors in topographically appropriate territories within the first two/three postnatal weeks. Nitric oxide has been implicated in development and stabilization of synapses in the retinotectal pathway since blockade of nitric oxide synthesis disrupts the normal pattern of retinal innervation in subcortical nuclei. The present work investigated the role of arachidonic acid pathway in the development and maintenance of ipsilateral retinotectal axons. We also investigated the role of this retrograde messenger in the modulation of plasticity that follows retinal lesions in the opposite eye. Pigmented rats received systemic treatment with quinacrine, a phospholipase A2 inhibitor, indomethacin, a cyclooxygenase inhibitor, nordihydroguaiaretic acid, a 5-lipoxygenase inhibitor or vehicle during 4-8 days at various postnatal ages. Rats given a unilateral temporal retinal lesion were treated with either quinacrine or vehicle during the same period. For anterograde tracing of ipsilateral retinal projections, animals received intraocular injections of horseradish peroxidase. Before the third postnatal week no difference was observed in the laminar or topographic organization of the ipsilateral retinotectal projection between vehicle and treated rats in either normal or lesion conditions. After the third postnatal week, however, systemic blockade of phospholipase A2 or 5-lipoxygenase, but not cyclooxygenase induced sprouting of uncrossed axons throughout the collicular visual layers in unoperated rats. In retinal lesion groups, phospholipase A2 blockade increased the sprouting of uncrossed intact axons to the collicular surface in the same period. The results suggest that arachidonic acid or lipoxygenase metabolites play a role in the maintenance of the retinotectal synapses after the critical period and that the blockade of the arachidonic acid pathway induces reactive sprouting of retinal axons late in development.

Renal effects of supernatant from rat peritoneal macrophages activated by microcystin-LR: role protein mediators.

We have demonstrated previously that microcystin-LR promoted some renal alterations using the isolated perfused rat kidney preparation. However, these effects were not proved to be direct or indirect. The aim of the current work is to examine the renal effects promoted by supernatants from rat macrophages stimulated with microcystin-LR and the role of inflammatory mediators. Peritoneal macrophages were collected previously and were incubated for 1h in fresh medium (control) and in medium containing microcystin-LR. Dexamethasone, quinacrine, thalidomide and cycloheximide were administered 30 min before microcystin-LR. Supernatants of macrophages stimulated with or without pharmacological inhibitors were added on the perfused rat kidney model. The infusion of macrophages supernatants stimulated by microcystin-LR caused significant increases in renal vascular resistance (C: 4.93+/-0.33 vs T: 5.15+/-0.21), glomerular filtration rate (C: 0.559+/-0.008 vs T: 0.978+/-0.15) and urinary flow (C: 0.16+/-0.01 vs T: 0.23+/-0.03). Cycloheximide, quinacrine and dexamethasone blocked these effects and thalidomide blocked renal vascular resistance. Macrophages stimulated by microcystin-LR release mediators capable of promoting nephotoxicity in isolated perfused rat kidney. Phospholipase A(2), TNF-alpha and other protein mediators appear to be involved on its renal toxic mechanism.

Arachidonic acid release from rat Leydig cells: the involvement of G protein, phospholipase A2 and regulation of cAMP production.

We have previously demonstrated that the release of arachidonic acid (AA) from human chorionic gonadotropin (hCG)-stimulated Leydig cells occurs in a dose- and time-dependent manner. In addition, the amount of AA released was dependent on the hormone-receptor interaction and the concentration of LH-hCG binding sites on the cell surface. The present study was conducted to evaluate the involvement of phospholipase A(2) (PLA(2)) and G proteins in AA release from hormonally stimulated rat Leydig cells, and the possible role of this fatty acid in cAMP production. Cells were first prelabelled with [(14)C]AA to incorporate the fatty acid into cell phospholipids, and then treated in different ways to evaluate AA release. hCG (25 mIU) increased the release of AA to 180+/-12% when compared with AA released from control cells, arbitrarily set as 100%. Mepacrine and parabromophenacyl bromide (pBpB), two PLA(2) inhibitors, decreased the hormone-stimulated AA release to 85+/-9 and 70+/-24% respectively. Conversely, melittin, a PLA(2) stimulator, increased the release of AA up to 200% over control. The inhibitory effect of mepacrine on the release of AA was evident in hCG-treated Leydig cells, but not in the melittin-treated cells. To determine if the release of AA was also mediated through a G protein, cells were first permeabilized and subsequently treated with pertussis toxin or GTPgammaS, a non-hydrolyzable analog of GTP. Results demonstrate that GTPgammaS was able to induce a similar level of the release of AA as hCG. In addition, pertussis toxin completely abolished the stimulatory effect of hCG on the release of AA, indicating that a member of the G(i) family was involved in the hCG-dependent release of AA. Cells treated with PLA(2) inhibitors did not modify cAMP production, but exogenously added AA significantly reduced cAMP production from hCG-treated Leydig cells, in a manner dependent on the concentration of AA and hCG. Results presented here suggest an involvement of PLA(2) and G proteins in the release of AA from hCG-stimulated Leydig cells, and under particular conditions, regulation of cAMP production by this fatty acid in these cells.

Understanding channel blocking in the nicotinic acetylcholine receptor.

Ion-channel blockers are molecules that obstruct the path used by ions to cross the membrane through a protein channel. Many of these are local anesthetics, toxins or drugs of abuse, and the knowledge of their mechanism of action at the atomic level is an important step towards the development of new compounds on a structural basis. A molecular model of the transmembrane region of the nicotinic acetylcholine receptor, an important brain and muscle fast signaling protein, was used as a target for docking several channel blockers by means of an automatic docking method. The combination of the independent docking method and molecular models (of the receptor and blockers) reproduced or explained quite accurately experimental data (photoaffinity labeling, site-directed mutagenesis, binding assays). This represents a strong support for the validity of the predictions made for those molecules for which no experimental data is available and also for the models and methods on which are based.

Quinacrine enhances carmustine therapy of experimental rat glioma.

OBJECTIVE: The high rate of mutagenesis in malignant cells has been considered to be a primary factor in the appearance of chemotherapy-resistant cell clones in glioblastomas. Quinacrine binds strongly to deoxyribonucleic acid, preventing mutagenesis. We investigated whether quinacrine could improve carmustine therapy in C6 cell cultures and in C6 malignant gliomas implanted subcutaneously into Wistar rats. METHODS: A potential chemopreventive effect of quinacrine on acquired resistance to carmustine therapy was studied in vitro and in vivo. Deoxyribonucleic acid damage was measured in cultured C6 cells by using the micronucleus test. Wistar rats with subcutaneously implanted C6 gliomas were treated with carmustine, quinacrine, or carmustine plus quinacrine, using pharmacological schemes similar to those used for human patients. RESULTS: The addition of quinacrine to cultured C6 cells did not modify carmustine-induced cytotoxicity; however, the deoxyribonucleic acid damage in surviving cells was minor, as indicated by the frequency of micronucleated cells. The surviving cells continued to be susceptible to a second exposure to carmustine, in contrast to non-quinacrine-treated control cells, which developed resistance to carmustine in a subsequent exposure (P < 0.05). The rate of tumor remission was higher for glioma-bearing rats treated with quinacrine plus carmustine, compared with rats treated with carmustine alone (P < 0.01). CONCLUSION: The addition of quinacrine to carmustine therapy increases the antineoplastic effect of the carmustine therapy. Our results suggest that chemical inhibition of mutagenesis in malignant glial cells during chemotherapy prevents the appearance of resistant clones.

The noncompetitive inhibitor quinacrine modifies the desensitization kinetics of muscle acetylcholine receptors.

Quinacrine has been shown to act as a noncompetitive inhibitor of the nicotinic acetylcholine receptor (nAChR). However, its mechanism of action is still a matter of controversy. We analyzed in detail the action of quinacrine at both the single-channel and macroscopic current levels. The main effect of quinacrine is a profound concentration-dependent decrease in both the frequency of opening events and the duration of clusters elicited by high acetylcholine concentrations. Quinacrine also significantly increases (40-fold at 30 microM) the decay rate of macroscopic currents elicited by rapid perfusion of acetylcholine to outside-out patches. This decay is still well-described by a single exponential. Quinacrine has very little effect on the peak amplitude of the response, suggesting that it acts mainly on open channels. The recovery from desensitization after removal of acetylcholine is delayed in the presence of quinacrine. Results from both single-channel and macroscopic current recordings indicate that quinacrine increases the rate of nAChR desensitization and stabilizes the desensitized state. Interestingly, in equilibrium agonist-binding assays, quinacrine does not promote the typical high-affinity desensitized state. Thus, quinacrine seems to induce an intermediate state exhibiting the permeability but not the agonist binding properties of desensitization.

Role of arachidonic acid in leukotriene B(4)-induced guinea-pig eosinophil homotypic aggregation.

The activation of eosinophils with the lipid mediator, leukotriene B(4), induces their homotypic aggregation. Upon activation with leukotriene B(4), eosinophils release a significant amount of arachidonic acid, a process dependent on the activation of phospholipase A(2). Here, we have evaluated whether arachidonic acid could induce aggregation of eosinophils and whether the release of arachidonic acid mediated the aggregation induced by leukotriene B(4). The exogenous administration of arachidonic acid induced a concentration-dependent eosinophil homotypic aggregation. Pretreatment of eosinophils with a 5-lipoxygenase inhibitor or a leukotriene B(4) receptor antagonist abrogated arachidonic-acid-induced aggregation. Arachidonic acid induced a significant increase in leukotriene B(4) levels and desensitised leukotriene B(4)-induced aggregation in a dose-dependent manner. Moreover, this desensitisation was effectively reversed by a 5-lipoxygenase inhibitor. However, arachidonic acid failed to induce a rise in intracellular Ca(2+) in eosinophils and failed to desensitise these cells to rises in intracellular Ca(2+) induced by leukotriene B(4). Pretreatment of eosinophils with the phospholipase A(2) inhibitor, mepacrine, inhibited the aggregation responses induced by 1 nM leukotriene B(4) by approximately 50% but had no significant effect on the other concentrations of leukotriene B(4) tested (0.1 to 100 nM). In conclusion, arachidonic acid stimulates eosinophil aggregation indirectly via the release of leukotriene B(4). Although a significant amount of arachidonic acid is released in response to activation of eosinophils with leukotriene B(4), the arachidonic acid released does appear to play a major role in mediating leukotriene B(4)-induced eosinophil aggregation.

Involvement of platelet-activating factor in the modulation of vascular tone in the isolated perfused rabbit kidney.

The hypothesis that platelet-activating factor (PAF) plays a role in the modulation of the vasomotor tone and blood pressure was put forward by our group in previous in vivo studies in anaesthetised rabbits. The present study was undertaken to investigate the putative role of this lipid mediator in the vascular reactivity of the renal circulation, using the experimental model of the isolated perfused rabbit kidney. Dose-response curves to noradrenaline-induced vasoconstriction were performed before and after continuous infusions of two different PAF-receptor antagonists (WEB 2086 and yangambin) and of the phospholipase A2 inhibitor mepacrine. The increases in renal perfusion pressure elicited by noradrenaline were potentiated by all the above-mentioned treatments in a dose-dependent manner. Moreover, prostaglandin F2alpha-induced vasoconstriction was also potentiated by the administration of the PAF receptor antagonists and mepacrine. Furthermore, the administration of PAF into the renal circulation induced dose-related and long-lasting vasodilator responses, which were blocked by the PAF receptor antagonists. Nevertheless, PAF-induced renal vasodilation was also abolished by a pretreatment with mepacrine or with the cyclooxygenase inhibitor indomethacin, suggesting that it enhances the secondary formation of vasodilator arachidonic acid metabolites. The data indicate that PAF is involved in the modulation of the vasomotor tone in the renal circulation, through the release of cyclooxygenase products, constituting an additional mechanism of modulation of smooth muscle cell contractility to the ones exerted by well-known vasoactive substances of endothelial origin such as nitric oxide.

Involvement of arachidonic acid and the lipoxygenase pathway in mediating luteinizing hormone-induced testosterone synthesis in rat Leydig cells.

Evidence has been introduced linking the lipoxygenase products and steroidogenesis in Leydig cells, thereby supporting that this pathway may be a common event in the hormonal control of steroid synthesis. On the other hand, it has also been reported that lipoxygenase products of arachidonic acid (AA) may not be involved in Leydig cells steroidogenesis. In this paper, we investigated the effects of PLA2 and lipoxygenase pathway inhibitors on steroidogenesis in rat testis Leydig cells. The effects of two structurally unrelated PLA2 inhibitors (4-bromophenacyl bromide (BPB) and quinacrine) were determined. BPB blocked the LH- and Bt2cAMP-stimulated testosterone production but had no effect on 22(4)-OH-cholesterol conversion to testosterone. Quinacrine caused a dose-dependent inhibition of LH- and Bt2cAMP-induced steroidogenesis. The effects of different lipoxygenase pathway inhibitors (nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosatetraynoic acid (ETYA), caffeic acid and esculetin) have also been determined. Both NDGA and ETYA inhibited LH- and Bt2cAMP-stimulated steroid synthesis in a dose-related manner. Furthermore caffeic acid and esculetin also blocked the LH-stimulated testosterone production. Moreover, exogenous AA induced a dose-dependent increase of testosterone secretion which was inhibited by NDGA. Our results strongly support the previous concept that the lipoxygenase pathway is involved in the mechanism of action of LH on testis Leydig cells.

Pharmacological evidence of a role for platelet activating factor as a modulator of vasomotor tone and blood pressure.

The purpose of the present study was to investigate the role of platelet-activating factor (PAF, 1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine), a phospholipid mediator synthesized by endothelial and smooth muscle cells, in the modulation of vascular tone and blood pressure. In pentobarbitone-anaesthetised rabbits, unloading of the carotid sinus baroreceptors by a bilateral carotid artery occlusion elicited a reflex rise in arterial pressure which was markedly potentiated by pretreating the animals with the PAF receptor antagonists WEB 2086 [3-4-(2-chlorphenyl)-9-methyl-6H-thieno-3,2f-1,2,4-triazolo-4, 3 a-1,4-diazepin-2-yl-(4-morpholinyl)-I-propanone; 2, 5 or 10 mg kg-1, i.v.] or BN 52021 (ginkgolide B; 0.1, 0.3 or 1.0 mg kg-1, i.v.). The increases in systemic vascular resistance induced by noradrenaline (30 micrograms kg-1, i.v.) or by the central activation of the sympathetic nervous system with glutamate (1 mg kg-1, intracerebroventricular) were also significantly potentiated in animals pretreated with WEB 2086 (5 mg kg-1, i.v.). In contrast, pretreatment with the cyclooxygenase inhibitor indomethacin (3 mg kg-1, i.v.) did not affect the haemodynamic actions of noradrenaline, thus excluding the possibility that prostacyclin may modulate the potentiating effect. To further confirm that PAF is released during systemic vasoconstriction, the cardiovascular PAF receptors were desensitized by the daily administration of PAF (3 micrograms kg-1, i.v.) for seven days. This procedure significantly reduced the intensity and duration of the hypotensive response to a subsequent PAF injection (3 micrograms kg-1, i.v.). In desensitized animals, the hypertensive response to bilateral carotid artery occlusion was potentiated to the same extent as in the animals treated with PAF receptor antagonists. Inhibition of PAF biosynthesis by pretreatment of the animals with the phospholipase A2 inhibitor mepacrine (5 mg kg-1, i.v.) also enhanced the increase in blood pressure elicited by carotid artery occlusion. We conclude that PAF is involved in the acute but not basal modulation of vasomotor tone and, hence, arterial pressure, probably by a negative feedback mechanism triggered by important increases in the vascular tone.

Studies on the mechanism of PAF-induced vasopermeability in rat lungs.

The present study evaluated the effect of platelet activating factor (PAF) instilled into rat airways on vascular permeability assessed in isolated lung tissues by Evans blue (EB)-labelled plasma protein extravasation. It was found that intratracheal instillation of PAF induces a dose-dependent increase of EB extravasation in the bronchi (upper and inner) but not in the lung parenchyma. The contribution of eicosanoids to PAF-induced increase of vascular permeability was investigated by treating the animals with selected inhibitors prior to PAF administration. Mepacrine (5 mg/kg), L-663,536 (10 mg/kg), indomethacin (4 mg/kg) and dazoxiben (10 mg/kg) significantly reduced EB extravasation in the bronchi. The PAF antagonists BN-52021 (5 mg/kg), WEB-2086 (1 mg/kg), WEB-2170 (5 mg/kg) and PCA-4248 (3 mg/kg) were all effective in reducing the extravasation. These results suggest that PAF-induced increase of vascular permeability in rat bronchi is mediated by cyclooxygenase and lipoxygenase products of arachidonic acid metabolism.

Opposing effects of quinacrine and chloroquine on the development of TA3 transplanted tumors in mice.

Both quinacrine and chloroquine had been used as antimalarial agents. Furthermore, antineoplastic and antiviral effects have been described for quinacrine, while chloroquine has been described to induce viral replication and promote tumor growth. To search for differences in the growing rate of transplanted tumors, chloroquine or quinacrine were administered orally to AJ mice from 30 days previous to the inoculation of TA3 transplantable tumor cells, treatment being continued up to the end of the experiment. A control group, transplanted with tumor cells received tap drinking water. Marked differences between the three groups were found. Quinacrine had antitumoral effect, while chloroquine promoted a faster tumoral growth than controls. (p < 0.01). Results suggest caution in the use of chloroquine, because it might have a similar promoting effect on human neoplasia.