Broad susceptibility of Candida auris strains to 8-hydroxyquinolines and mechanisms of resistance.

The fungal pathogen Candida auris represents a severe threat to hospitalized patients. Its resistance to multiple classes of antifungal drugs and ability to spread and resist decontamination in healthcare settings make it especially dangerous. We screened 1,990 clinically approved and late-stage investigational compounds for the potential to be repurposed as antifungal drugs targeting C. auris and narrowed our focus to five Food and Drug Administration (FDA)-approved compounds with inhibitory concentrations under 10 µM for C. auris and significantly lower toxicity to three human cell lines. These compounds, some of which had been previously identified in independent screens, include three dihalogenated 8-hydroxyquinolines: broxyquinoline, chloroxine, and clioquinol. A subsequent structure-activity study of 32 quinoline derivatives found that 8-hydroxyquinolines, especially those dihalogenated at the C5 and C7 positions, were the most effective inhibitors of C. auris. To pursue these compounds further, we exposed C. auris to clioquinol in an extended experimental evolution study and found that C. auris developed only twofold to fivefold resistance to the compound. DNA sequencing of resistant strains and subsequent verification by directed mutation in naive strains revealed that resistance was due to mutations in the transcriptional regulator CAP1 (causing upregulation of the drug transporter MDR1) and in the drug transporter CDR1. These mutations had only modest effects on resistance to traditional antifungal agents, and the CDR1 mutation rendered C. auris more susceptible to posaconazole. This observation raises the possibility that a combination treatment involving an 8-hydroxyquinoline and posaconazole might prevent C. auris from developing resistance to this established antifungal agent. IMPORTANCE The rapidly emerging fungal pathogen Candida auris represents a growing threat to hospitalized patients, in part due to frequent resistance to multiple classes of antifungal drugs. We identify a class of compounds, the dihalogenated 8-hydroxyquinolines, with broad fungistatic ability against a diverse collection of 13 strains of C. auris. Although this compound has been identified in previous screens, we extended the analysis by showing that C. auris developed only modest twofold to fivefold increases in resistance to this class of compounds despite long-term exposure; a noticeable difference from the 30- to 500-fold increases in resistance reported for similar studies with commonly used antifungal drugs. We also identify the mutations underlying the resistance. These results suggest that the dihalogenated 8-hydroxyquinolines are working inside the fungal cell and should be developed further to combat C. auris and other fungal pathogens. Lohse and colleagues characterize a class of compounds that inhibit the fungal pathogen C. auris. Unlike many other antifungal drugs, C. auris does not readily develop resistance to this class of compounds.

Unravelling the interaction mechanism between clioquinol and bovine serum albumin by multi-spectroscopic and molecular docking approaches.

Clioquinol has recently been proposed for the treatment of Alzheimer's disease. It is able to diminish ß-amyloid protein aggregation and to restore cognition of Alzheimer's mice. However, its therapeutic benefits for Alzheimer's disease in human remain controversy and need further confirmation. Herein, we have explored the interaction mechanism of clioquinol toward bovine serum albumin (BSA) by means of multi-spectroscopic and docking simulation approaches. Clioquinol interacts with BSA by a combined mechanism of static and dynamic processes. Application of the Hill's equation to fluorescence quenching experiment revealed that the binding constant of the BSA-clioquinol complex is extremely high at 108 M-1 level. Competitive displacement and docking analysis consistently suggested that there are the multiple binding modes of clioquinol toward BSA. Competitive binding study showed that clioquinol shares the binding sites with ibuprofen and digitoxin on albumin, referring to be site II and site III binding compounds. Besides, partial binding in site I was also observed. Docking simulation confirmed that clioquinol favors to bind in site I, site II, site III, fatty acid binding site 5, and the protein cleft between subdomain IB and IIIB of the BSA. Due to its small size and electric dipole property, clioquinol may easily fit in multiple pockets of the BSA. Our finding suggests the potential role of BSA as a clioquinol carrier in the vascular system. Nonetheless, clioquinol-induced BSA aggregation has been observed by the three-dimensional fluorescence technique. This phenomenon may not only impair the BSA, but may also affect other endogenous proteins, which eventually causes adverse effects to human. Therefore, the redesigned or modified molecular structure of clioquinol may reduce its toxicity and improve its bioavailability.

Chemical Synergy between Ionophore PBT2 and Zinc Reverses Antibiotic Resistance.

The World Health Organization reports that antibiotic-resistant pathogens represent an imminent global health disaster for the 21st century. Gram-positive superbugs threaten to breach last-line antibiotic treatment, and the pharmaceutical industry antibiotic development pipeline is waning. Here we report the synergy between ionophore-induced physiological stress in Gram-positive bacteria and antibiotic treatment. PBT2 is a safe-for-human-use zinc ionophore that has progressed to phase 2 clinical trials for Alzheimer's and Huntington's disease treatment. In combination with zinc, PBT2 exhibits antibacterial activity and disrupts cellular homeostasis in erythromycin-resistant group A Streptococcus (GAS), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). We were unable to select for mutants resistant to PBT2-zinc treatment. While ineffective alone against resistant bacteria, several clinically relevant antibiotics act synergistically with PBT2-zinc to enhance killing of these Gram-positive pathogens. These data represent a new paradigm whereby disruption of bacterial metal homeostasis reverses antibiotic-resistant phenotypes in a number of priority human bacterial pathogens.IMPORTANCE The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, "On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you."

Clioquinol induces G2/M cell cycle arrest through the up-regulation of TDH3 in Saccharomyces cerevisiae.

Clioquinol (CQ) has been used as a classical antimicrobial agent for many years. However, its mode of action is still unclear. In our study, the growth of Candida albicans and Saccharomyces cerevisiae was inhibited by CQ. It did not kill yeast cells, but shortened G1 phase and arrested cell cycle at G2/M phase. By using two-dimensional electrophoresis based proteomic approach, six proteins were found to be significantly affected by CQ. Among them, four (PDC1, ADH1, TDH3, IPP1) were up-regulated and the other two (TDH1 and PGK1) were down-regulated. According to the Saccharomyces Genome Database (SGD), these proteins were involved in various biological processes including glycolytic fermentation, gluconeogenesis, glycolytic process, amino acid catabolism, redox reaction and reactive oxygen species metabolic process. It was noted that there was a link between TDH3 and cell cycle. The overexpression of TDH3 phenocopied CQ treatment and arrested the cell cycle at G2/M phase. RT-PCR analysis showed that the mRNA levels of CLN3 and CDC28, critical genes for passage through G1 phase, were up-regulated after the treatment of CQ as well as the overexpression of TDH3. It demonstrates that CQ inhibits the growth of yeast by up-regulating the expression of TDH3 to influence the cell cycle. It is expected to provide new insights for the antimicrobial mechanism of CQ.

Identification and Characterization of the Human Cytosolic Sulfotransferases Mediating the Sulfation of Clioquinol and Iodoquinol.

OBJECTIVE: The aim of the current study was to identify the human cytosolic sulfotransferases (SULTs) that are capable of sulfating clioquinol and iodoquinol, and to verify the presence of clioquinol/ iodoquinol-sulfating activity in human organ homogenates and cultured cells. METHOD: An established sulfotransferase assay was employed to analyze clioquinol/iodoquinolsulfating activity of thirteen known human SULTs, as well as cytosols of human kidney, liver, lung, and small intestine. Metabolic labeling with [35S]sulfate in the presence of different concentrations of clioquinol/iodoquinol was performed using cultured HepG2 human hepatoma cells and Caco-2 human colon carcinoma cells. RESULTS: A systematic analysis revealed that six of the thirteen known human SULTs, SULT1A1 SULT1A2, SULTA3, SULT1B1, SULT1C4, and SULT1E1 showed considerable clioquinol/ iodoquinol-sulfating activity. Kinetic parameters of the sulfation of clioquinol and iodoquinol by three SULTs, SULT1A1, SULT1A3, and SULT1C4, that showed the strongest clioquinol/iodoquinolsulfating activity were determined. Moreover, clioquinol/iodoquinol-sulfating activity was detected in the cytosol fractions of human liver, lung, kidney, and small intestine. Cultured HepG2 and Caco-2 cells were shown to be capable of sulfating clioquinol/iodoquinol under metabolic conditions. CONCLUSION: Collectively, these results provided a molecular basis underling the metabolism of clioquinol and iodoquinol through sulfation.

Stabilization of nontoxic Aß-oligomers: insights into the mechanism of action of hydroxyquinolines in Alzheimer's disease.

The extracellular accumulation of amyloid ß (Aß) peptides is characteristic of Alzheimer's disease (AD). However, formation of diffusible, oligomeric forms of Aß, both on and off pathways to amyloid fibrils, is thought to include neurotoxic species responsible for synaptic loss and neurodegeneration, rather than polymeric amyloid aggregates. The 8-hydroxyquinolines (8-HQ) clioquinol (CQ) and PBT2 were developed for their ability to inhibit metal-mediated generation of reactive oxygen species from Aß:Cu complexes and have both undergone preclinical and Phase II clinical development for the treatment of AD. Their respective modes of action are not fully understood and may include both inhibition of Aß fibrillar polymerization and direct depolymerization of existing Aß fibrils. In the present study, we find that CQ and PBT2 can interact directly with Aß and affect its propensity to aggregate. Using a combination of biophysical techniques, we demonstrate that, in the presence of these 8-HQs and in the absence of metal ions, Aß associates with two 8-HQ molecules and forms a dimer. Furthermore, 8-HQ bind Aß with an affinity of 1-10 µm and suppress the formation of large (>30 kDa) oligomers. The stabilized low molecular weight species are nontoxic. Treatment with 8-HQs also reduces the levels of in vivo soluble oligomers in a Caenorhabditis elegans model of Aß toxicity. We propose that 8-HQs possess an additional mechanism of action that neutralizes neurotoxic Aß oligomer formation through stabilization of small (dimeric) nontoxic Aß conformers.

Effect of substituent of terpyridines on the in vitro antioxidant, antitubercular, biocidal and fluorescence studies of copper(II) complexes with clioquinol.

An octahedral complexes of copper with clioquinol(CQ) and substituted terpyridine have been synthesized. The Cu(II) complexes have been characterized by elemental analyses, thermogravimetric analyses, magnetic moment measurements, FT-IR, electronic, (1)HNMR and FAB mass spectra. Antimycobacterial screening of ligand and its copper compound against Mycobacterium tuberculosis shows clear enhancement in the antitubercular activity upon copper complexation. Ferric-reducing anti-oxidant power of all complexes were measured. The fluorescence spectra of complexes show red shift, which may be due to the chelation by the ligands to the metal ion. It enhances ligand ability to accept electrons and decreases the electron transition energy. The antimicrobial efficiency of the complexes were tested on five different microorganisms and showed good biological activity.

Clioquinol is sulfated by human jejunum cytosol and SULT1A3, a human-specific dopamine sulfotransferase.

Clioquinol, originally marketed as an oral intestinal amebicide, was widely used for multiple intestinal disorders. Its use as an oral agent was, however, discontinued because of its possible association with subacute myelo-optico-neuropathy or SMON. Meanwhile, its use for neurodegenerative diseases has recently been suggested. The metabolic fate of clioquinol, however, is poorly described. Since clioquinol is excreted as a sulfate in animals and humans, we have sought to identify a human sulfotransferase (SULT) responsible for the sulfation. We found that sulfating activities of human jejunal cytosols to clioquinol were well correlated with those to dopamine, a typical SULT1A3 substrate. Consistently, recombinant SULT1A3 showed the highest activity to clioquinol in vitro among the human SULTs examined. The S(50) value for the clioquinol sulfation by SULT1A3 was similar to the K(m) value for that by cytosols from human jejunum, where SULT1A3 is abundantly expressed. Moreover, clioquinol inhibited both human jejunal cytosol- and SULT1A3-mediated sulfations of dopamine in a dose-dependent manner, showing similar IC(50) values. These results suggest that SULT1A3, which is highly expressed in intestine but not in liver, is responsible for the clioquinol sulfation in humans, raising a possibility that orally administered clioquinol might inhibit dopamine sulfation in human intestines.

Vibrational spectra of the Ga(III) complexes with oxine and clioquinol.

The FTIR and FT-Raman spectra of the gallium(III) complexes of 8-hydroxyquinoline (oxine) and 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), were recorded and briefly discussed by comparison with the spectra of the uncoordinated ligands and with some related species.

Hydroxyquinoline based binders: promising ligands for chelatotherapy?

We report here a thorough physico-chemical study of the coordination properties of clioquinol, an oxine-type active neurological drug in Alzheimer's disease, toward biologically relevant divalent metal ions (Cu, Zn, Ni, Co and Mn). Using a fruitful combination of electrospray mass spectrometry, absorption spectrophotometry and potentiometry, we have characterized the mono- and bis-chelated metal ion species. The determination of the stability constants showed a classical thermodynamic behavior along the studied series with the cupric complexes being by far the most stable species. Our data are discussed within the scope of Alzheimer's disease.

Tumor cellular proteasome inhibition and growth suppression by 8-hydroxyquinoline and clioquinol requires their capabilities to bind copper and transport copper into cells.

We have previously reported that when mixed with copper, 8-hydroxyquinoline (8-OHQ) and its analog clioquinol (CQ) inhibited the proteasomal activity and proliferation in cultured human cancer cells. CQ treatment of high-copper-containing human tumor xenografts also caused cancer suppression, associated with proteasome inhibition in vivo. However, the nature of the copper dependence of these events has not been elucidated experimentally. In the current study, using chemical probe molecules that mimic the structures of 8-OHQ and CQ, but have no copper-binding capability, we dissected the complex cellular processes elicited by 8-OHQ-Cu and CQ-Cu mixtures and revealed that copper binding to 8-OHQ or CQ is required for transportation of the copper complex into human breast cancer cells and the consequent proteasome-inhibitory, growth-suppressive, and apoptosis-inducing activities. In contrast, the non-copper-binding analogs of 8-OHQ or CQ blocked the very first step-copper binding-in this chain of events mediated by 8-OHQ-Cu or CQ-Cu.

Zinc-binding compounds induce cancer cell death via distinct modes of action.

Metal-binding compounds have been shown to have anticancer activity and are being evaluated clinically as anticancer agents. We have recently found that a zinc-binding compound, 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), kills cancer cells by transporting zinc into the cells. We therefore compared the action of clioquinol with two other cytotoxic zinc-binding compounds, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and pyrrolidine dithiocarbamate (PDTC). We demonstrate that metal-binding compounds can be subclassified based upon the reversibility of their cytotoxicity by metal supplementation and their modes of action. Understanding the mechanisms whereby metal-binding compounds affect cell behavior may aid in their optimization for clinical use.

Activation of epidermal growth factor receptor by metal-ligand complexes decreases levels of extracellular amyloid beta peptide.

The epidermal growth factor receptor is a receptor tyrosine kinase expressed in a range of tissues and cell-types. Activation of the epidermal growth factor receptor by a number of ligands induces downstream signalling that modulates critical cell functions including growth, survival and differentiation. Abnormal epidermal growth factor receptor expression and activation is also involved in a number of cancers. In addition to its cognate ligands, the epidermal growth factor receptor can be activated by metals such as zinc (Zn) and copper (Cu). Due to the important role of these metals in a number of diseases including neurodegenerative disorders, therapeutic approaches are being developed based on the use of lipid permeable metal-complexing molecules. While these agents are showing promising results in animal models and clinical trials, little is known about the effects of metal-ligand complexes on cell signalling pathways. In this study, we investigated the effects of clioquinol (CQ)-metal complexes on activation of epidermal growth factor receptor. We show here that CQ-Cu complexes induced potent epidermal growth factor receptor phosphorylation resulting in downstream activation of extracellular signal-regulated kinase. Similar levels of epidermal growth factor receptor activation were observed with alternative lipid permeable metal-ligands including neocuproine and pyrrolidine dithiocarbamate. We found that CQ-Cu complexes induced a significant reduction in the level of extracellular Abeta1-40 in cell culture. Inhibition of epidermal growth factor receptor activation by PD153035 blocked extracellular signal-regulated kinase phosphorylation and restored Abeta1-40 levels. Activation of the epidermal growth factor receptor by CQ-Cu was mediated through up-regulation of src kinase activity by a cognate ligand-independent process involving membrane integrins. These findings provide the first evidence that metal-ligand complexes can activate the epidermal growth factor receptor with potentially neuroprotective effects.

Clioquinol, a therapeutic agent for Alzheimer's disease, has proteasome-inhibitory, androgen receptor-suppressing, apoptosis-inducing, and antitumor activities in human prostate cancer cells and xenografts.

Tumor growth and metastasis depend on angiogenesis that requires the cofactor copper. Consistently, high levels of copper have been found in many types of human cancers, including prostate, breast, colon, and lung. Recent studies suggest that copper could be used as a novel selective target for cancer therapies. Clioquinol is capable of forming stable complexes with copper and currently used in clinics for treatment of Alzheimer's disease. Most recently, it has been reported that clioquinol possesses antitumor effects. However, the underlying molecular mechanism is unclear. We report here that after binding to copper, clioquinol can inhibit the proteasomal chymotrypsin-like activity, repress androgen receptor (AR) protein expression, and induce apoptotic cell death in human prostate cancer LNCaP and C4-2B cells. In addition, clioquinol alone exhibits similar effects in prostate cancer cell lines with elevated copper at concentrations similar to those found in patients. Addition of dihydrotestosterone did not affect clioquinol-mediated proteasome inhibition in both prostate cancer cell lines. However, dihydrotestosterone partially inhibited clioquinol-induced AR suppression and apoptosis only in androgen-dependent LNCaP cells. Animal studies show that clioquinol treatment significantly inhibits the growth of human prostate tumor C4-2B xenografts (by 66%), associated with in vivo proteasome inhibition, AR protein repression, angiogenesis suppression, and apoptosis induction. Our study provides strong evidence that clioquinol is able to target tumor proteasome in vivo in a copper-dependent manner, resulting in formation of an active AR inhibitor and apoptosis inducer that is responsible for its observed antiprostate tumor effect.

Radioiodinated clioquinol as a biomarker for beta-amyloid: Zn complexes in Alzheimer's disease.

Neocortical beta-amyloid (Abeta) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with Abeta and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([(125)I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [(125)I]CQ to synthetic Abeta precipitated by Zn(2+) (K(d)=0.45 and 1.40 nm for Abeta(1-42) and Abeta(1-40), respectively), which was fully displaced by free Zn(2+), Cu(2+), the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [(125)I]CQ concentrated in a fraction enriched for both Abeta and Zn, which was modulated by exogenous addition of Zn(2+) or DTPA. APP transgenic (Tg2576) mice injected with [(125)I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [(125)I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [(125)I]CQ. A pilot SPECT study of [(123)I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated Abeta species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology.

Alzheimer disease beta-amyloid activity mimics cholesterol oxidase.

The abnormal accumulation of amyloid beta-peptide (Abeta) in the form of senile (or amyloid) plaques is one of the main characteristics of Alzheimer disease (AD). Both cholesterol and Cu2+ have been implicated in AD pathogenesis and plaque formation. Abeta binds Cu2+ with very high affinity, forming a redox-active complex that catalyzes H2O2 production from O2 and cholesterol. Here we show that Abeta:Cu2+ complexes oxidize cholesterol selectively at the C-3 hydroxyl group, catalytically producing 4-cholesten-3-one and therefore mimicking the activity of cholesterol oxidase, which is implicated in cardiovascular disease. Abeta toxicity in neuronal cultures correlated with this activity, which was inhibited by Cu2+ chelators including clioquinol. Cell death induced by staurosporine or H2O2 did not elevate 4-cholesten-3-one levels. Brain tissue from AD subjects had 98% more 4-cholesten-3-one than tissue from age-matched control subjects. We observed a similar increase in the brains of Tg2576 transgenic mice compared with nontransgenic littermates; the increase was inhibited by in vivo treatment with clioquinol, which suggests that brain Abeta accumulation elevates 4-cholesten-3-one levels in AD. Cu2+-mediated oxidation of cholesterol may be a pathogenic mechanism common to atherosclerosis and AD.

Metal complexing agents as therapies for Alzheimer's disease.

Modern research approaches into drug development for Alzheimer's disease (AD) target beta-amyloid (Abeta) accumulation in the brain. The main approaches attempt to prevent Abeta production (secretase inhibitors) or to clear Abeta (vaccine). However, there is now compelling evidence that Abeta does not spontaneously aggregate, but that there is an age-dependent reaction with excess brain metal (copper, iron and zinc), which induces the protein to precipitate into metal-enriched masses (plaques). The abnormal combination of Abeta with Cu or Fe induces the production of hydrogen peroxide, which may mediate the conspicuous oxidative damage to the brain in AD. We have developed metal-binding compounds that inhibit the in vitro generation of hydrogen peroxide by Abeta, as well as reverse the aggregation of the peptide in vitro and from human brain post-mortem specimens. Most recently, one of the compounds, clioquinol (CQ; a USP antibiotic) was given orally for 9 weeks to amyloid-bearing transgenic mice, and succeeded in markedly inhibiting Abeta accumulation. On the basis of these results, CQ is being tested in clinical trials.

An iron-responsive element type II in the 5'-untranslated region of the Alzheimer's amyloid precursor protein transcript.

Iron-responsive elements (IREs) are the RNA stem loops that control cellular iron homeostasis by regulating ferritin translation and transferrin receptor mRNA stability. We mapped a novel iron-responsive element (IRE-Type II) within the 5'-untranslated region (5'-UTR) of the Alzheimer's amyloid precursor protein (APP) transcript (+51 to +94 from the 5'-cap site). The APP mRNA IRE is located immediately upstream of an interleukin-1 responsive acute box domain (+101 to +146). APP 5'-UTR conferred translation was selectively down-regulated in response to intracellular iron chelation using three separate reporter assays (chloramphenicol acetyltransferase, luciferase, and red fluorescent protein reflecting an inhibition of APP holoprotein translation in response to iron chelation. Iron influx reversed this inhibition. As an internal control to ensure specificity, a viral internal ribosome entry sequence was unresponsive to intracellular iron chelation with desferrioxamine. Using RNA mobility shift assays, the APP 5'-UTRs, encompassing the IRE, bind specifically to recombinant iron-regulatory proteins (IRP) and to IRP from neuroblastoma cell lysates. IRP binding to the APP 5'-UTR is reduced after treatment of cells with desferrioxamine and increased after interleukin-1 stimulation. IRP binding is abrogated when APP cRNA probe is mutated in the core IRE domain (Delta4 bases:Delta83AGAG86). Iron regulation of APP mRNA through the APP 5'-UTR points to a role for iron in the metabolism of APP and confirms that this RNA structure can be a target for the selection of small molecule drugs, such as desferrioxamine (Fe chelator) and clioquinol (Fe, Cu, and Zn chelator), which reduce Abeta peptide burden during Alzheimer's disease.

Changes in uptake of vitamin B(12) and trace metals in brains of mice treated with clioquinol.

Clioquinol is a hydroxyquinoline antibiotic that has been associated with severe side-effects in the CNS. The syndrome caused by clioquinol treatment, subacute myelo-optic neuropathy (SMON), is considered as one of the worst drug disasters of this century. The precise biochemical mechanism behind SMON is not fully understood. Clioquinol can form strong lipophilic chelates with divalent cations and therefore it has been speculated that the drug may disturb the retention of vitamin B(12) through chelation of Co(2+). In the present study, the tissue distribution and uptake capacity of [57Co]cyanocobalamin were estimated in mice treated with clioquinol or saline. The concentrations of some trace metals were also determined in brain tissue. Accumulation of vitamin B(12) in the brain and its concentration in blood were decreased by clioquinol treatment. The mean concentrations of several trace metals were also lowered in the brain while the concentration of cobalt in the brain was not affected, suggesting that clioquinol does not bind to the cobalt in vitamin B(12). Moreover, a significant decrease in the levels of S-adenosylmethionine (SAM) was observed in the brain after clioquinol treatment. This may be a consequence of decreased vitamin B(12) levels. From these results, it can be concluded that chronic treatment with clioquinol may alter the tissue homeostasis of vitamin B(12) in the brain.