Zinc pyridinethione: urinary metabolites of zinc pyridinethione in rabbits, rats, monkeys, and dogs after oral dosing

Copper pyrithione and zinc pyrithione induce cytotoxicity and neurotoxicity in neuronal/astrocytic co-cultured cells via oxidative stress

Previous studies on copper pyrithione (CPT) and zinc pyrithione (ZPT) as antifouling agents have mainly focused on marine organisms. Even though CPT and ZPT pose a risk of human exposure, their neurotoxic effects remain to be elucidated. Therefore, in this study, the cytotoxicity and neurotoxicity of CPT and ZPT were evaluated after the exposure of human SH-SY5Y/astrocytic co-cultured cells to them. The results showed that, in a co-culture model, CPT and ZPT induced cytotoxicity in a dose-dependent manner (~ 400 nM). Exposure to CPT and ZPT suppressed all parameters in the neurite outgrowth assays, including neurite length. In particular, exposure led to neurotoxicity at concentrations with low or no cytotoxicity (~ 200 nM). It also downregulated the expression of genes involved in neurodevelopment and maturation and upregulated astrocyte markers. Moreover, CPT and ZPT induced mitochondrial dysfunction and promoted the generation of reactive oxygen species. Notably, N-acetylcysteine treatment showed neuroprotective effects against CPT- and ZPT-mediated toxicity. We concluded that oxidative stress was the major mechanism underlying CPT- and ZPT-induced toxicity in the co-cultured cells.

Seborrheic dermatitis: topical therapeutics and formulation design

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

Zinc pyrithione (ZPT) -induced embryonic toxicogenomic responses reveal involvement of oxidative damage, apoptosis, endoplasmic reticulum (ER) stress and autophagy

Zinc pyrithione (ZPT) is a frequently used organometallic biocide, carrying potentially adverse consequences to multiple species in the environment. Previously we have demonstrated its embryonic, organ developmental and liver metabolic toxicity of zebrafish. However, details of ZPT toxicity during embryogenesis are still limited. The present study was designed to evaluate the effects and possible mechanisms of ZPT-induced embryonic toxicogenomic responses by morphological investigations, transcriptome and gene quantitative analysis, as well as biochemical assays. The results revealed that treatment with ZPT caused embryogenesis toxicity, specifically in irregular cell division and rearrangement, delayed differentiations of eyes and notochords, the epiboly and germ ring formation and somite segmentation defects. In addition, ZPT exposure altered gene expression during early embryonic development, especially related with morphological abnormities and metabolic dysfunctions including reduction of oxidoreductase activity. Activities of antioxidants and caspases examinations showed inductions of oxidative stress and apoptosis by ZPT and quantitative analysis of marker genes further indicated that ZPT also triggered endoplasmic reticulum (ER) stress and autophagy. Thus, we deduce here that ZPT-induced embryonic toxicogenomic responses reveal involvement of oxidative damage, apoptosis, endoplasmic reticulum (ER) stress and autophagy.

Targeted Delivery of Zinc Pyrithione to Skin Epithelia

Zinc pyrithione (ZnPT) is an anti-fungal drug delivered as a microparticle to skin epithelia. It is one of the most widely used ingredients worldwide in medicated shampoo for treating dandruff and seborrheic dermatitis (SD), a disorder with symptoms that include skin flaking, erythema and pruritus. SD is a multi-factorial disease driven by microbiol dysbiosis, primarily involving Malassezia yeast. Anti-fungal activity of ZnPT depends on the cutaneous availability of bioactive monomeric molecular species, occurring upon particle dissolution. The success of ZnPT as a topical therapeutic is underscored by the way it balances treatment efficacy with formulation safety. This review demonstrates how ZnPT achieves this balance, by integrating the current understanding of SD pathogenesis with an up-to-date analysis of ZnPT pharmacology, therapeutics and toxicology. ZnPT has anti-fungal activity with an average in vitro minimum inhibitory concentration of 10-15 ppm against the most abundant scalp skin Malassezia species (Malassezia globosa and Malassezia restrica). Efficacy is dependent on the targeted delivery of ZnPT to the skin sites where these yeasts reside, including the scalp surface and hair follicle infundibulum. Imaging and quantitative analysis tools have been fundamental for critically evaluating the therapeutic performance and safety of topical ZnPT formulations. Toxicologic investigations have focused on understanding the risk of local and systemic adverse effects following exposure from percutaneous penetration. Future research is expected to yield further advances in ZnPT formulations for SD and also include re-purposing towards a range of other dermatologic applications, which is likely to have significant clinical impact.

UHPLC-MS/HRMS method for the quantitation of pyrithione metabolites in human urine

Pyrithione glucuronide (PTG) and 2-thiopyridine glucuronide (ThPG) have been reported to be the major urinary metabolites in multiple animal species following administration of zinc pyrithione (ZnPT). However, the formation of these metabolites has never been confirmed in humans. A simple and rugged ultra-high-performance liquid chromatography high resolution mass spectrometry (UHPLC-MS/HRMS) method was developed and validated for the quantification of PTG and ThPG to investigate human metabolism of pyrithione following topical application of ZnPT as a shampoo. A UHPLC-MS/HRMS method was required due to the matrix interferences that were observed with the typical industry standard HPLC/tandem mass spectrometry (LC-MS/MS) methodology based on nominal mass triple quadrupole (QQQ) platform approach. Using UPLC-MS/HRMS, both PTG and ThPG were identified in human urine following topical application of ZnPT. The presence of these human urinary metabolites of pyrithione are consistent with findings from earlier studies in multiple animal species and suggest the metabolism of pyrithione is similar amongst those mammalian species studied.

Effect of Combined Exposure to EDTA and Zinc Pyrithione on Pyrithione Absorption in Rats

Zinc pyrithione (ZnPT) is a coordination complex of zinc and has been used widely as an anti-dandruff agent in shampoos. Many shampoos contain both ZnPT and EDTA, a chelating agent speculated to increase ZnPT absorption, thereby raising concerns about neurotoxicity. Here, we investigated the effect of EDTA on ZnPT absorption by direct comparison of ZnPT and pyrithione (PT) concentrations in shampoo formulations, and by pharmacokinetic analysis of ZnPT, PT, and 2-methanesulfonylpyridine (MSP), the main ZnPT metabolite, in rat plasma or urine following exposure to shampoo containing ZnPT alone or a combination of ZnPT and EDTA. Approximately 17.3% of ZnPT was converted to PT by the addition of EDTA in the shampoo formulation. Plasma ZnPT and PT concentrations were not measured up to 24 hr after treatment with shampoo containing 1% ZnPT or 1% ZnPT + 2% EDTA in all rats. However, PT amount in 24-hr urine sample, MSP concentration in plasma, and MSP amount in 24-hr urine sample were approximately 4-, 2.6-, and 2.7-fold higher, respectively, in the 1% ZnPT + 2% EDTA shampoo group than in the 1% ZnPT shampoo group. As confirmed by the formulation analysis and in vivo pharmacokinetic analysis, the exposure of ZnPT could be increased by the absorption of PT due to partial dissociation of ZnPT into PT.

A physiologically based pharmacokinetic model for the broad-spectrum antimicrobial zinc pyrithione: I. Development and verification

The broad-spectrum antimicrobial zinc pyrithione (ZnPT) is used in numerous products ranging from in-can preservative/mildicide in paints to antidandruff shampoo. Although products containing ZnPT have a long history of safe use, regulatory agencies routinely set limits of exposure based upon toxicological considerations. The objective of this study was to create a physiologically based pharmacokinetic (PBPK) model for ZnPT in the rat for improving dose-response analysis of ZnPT-induced toxicity, reversible hindlimb weakness, the endpoint that has been used as the basis for ZnPT risk assessments. A rat oral PBPK model was developed that includes compartments for plasma, liver, kidneys, muscle, brain, and rapidly and slowly perfused tissues. Pyrithione metabolism to 2-(methylsulfonyl)pyridine (MSP) and glucuronide conjugates was incorporated into the model. The model was parameterized and optimized based upon data from single-dose intravenous (iv) and oral gavage pharmacokinetic studies of radiolabeled pyrithione ([¹⁴C]PT) administered as zinc [¹⁴C]-pyrithione (Zn-[¹⁴C]PT) to adult female rats. It was further evaluated and refined using data from repeated, multidose oral gavage and dietary studies of Zn[¹⁴C]PT in the adult female rat that included measurements of plasma PT concentration, the putative toxic species. The model replicated the observed short-term elimination kinetics of PT in plasma and [¹⁴C]PT in whole blood following single doses and longer term temporal patterns of plasma and blood concentrations during repeated dosing schedules. The model also accounted for production and rapid elimination of S-glucuronide conjugates (SG) of 2-pyridinethiol and 2-pyridinethiol-1-oxide in urine, as well as production and slower elimination of MSP, the major [¹⁴C]PT species in blood within several hours following administration of ZnPT. The model provided internal dosimetry predictions for a benchmark dose (BMD) analysis of hindlimb weakness in rats, and was used to combine gavage and dietary studies into a single internal dose-response model with area under the curve (AUC) for plasma PT as the internal dose metric. This PBPK model has predictive validity for calculating internal doses of PT and/or [¹⁴C]PT from different routes of exposure in the rat.

Texaphyrins and water-soluble zinc(II) ionophores: development, mechanism of anticancer activity, and synergistic effects

Texaphyrins, first prepared by Sessler and coworkers in the 1980s, represent early examples of expanded porphyrins. This class of pentaaza, oligopyrrolic macrocycles demonstrates excellent tumor localization and metal-chelating properties. In biological milieus, texaphyrins act as redox mediators and are able to produce reactive oxygen species. Furthermore, texaphyrins have been shown to upregulate zinc in vivo, an important feature that inspired us to develop new zinc ionophores that might allow the same function to be elicited but via a simpler chemical means. In this review, the basic properties of texaphyrins and the zinc ionophores they helped spawn will be discussed in the cadre of developing an understanding that could lead to the preparation of new, redox-active anticancer agents.

Inhibition of acetylcholinesterase by metabolites of copper pyrithione (CuPT) and its possible involvement in vertebral deformity of a CuPT-exposed marine teleostean fish

In a previous study, we demonstrated that exposure to an antifouling biocide, copper pyrithione (CuPT), early during life induced vertebral deformity in the larvae of a marine fish, the mummichog (Fundulus heteroclitus). Skeletal deformities may be caused by inhibition by of acetylcholiensterase (AChE) activity, and to elucidate the mechanism underlying the CuPT-associated vertebral deformity, we first examined whether CuPT, zinc pyrithione (ZnPT), and their degradation products could inhibit AChE activity in the fish. Two of the degradation products, 2,2'-dipyridyldisulfide [(PS)(2)] and 2,2'-dithiobispyridine-N-oxide [(PT)(2)], but neither CuPT nor ZnPT, exhibited prominent AChE-inhibiting activity. Secondly, thin-layer chromatography revealed that mummichog hepatic microsomes metabolized CuPT to produce (PS)(2) in a microsome-dependent manner. The AChE inhibition induced in CuPT-exposed fish is likely due to (PS)(2) that was produced through metabolism of acquired CuPT. (PS)(2) may cause therefore skeletal deformity in CuPT-exposed fish by means of its neuromuscular blocking properties, through a mechanism similar to that proposed for animals exposed to organophosphorous pesticides.

Synthesis and anticancer properties of water-soluble zinc ionophores

Several water-solubilized versions of the zinc ionophore 1-hydroxypyridine-2-thione (ZnHPT), synthesized as part of the present study, have been found both to increase the intracellular concentrations of free zinc and to produce an antiproliferative activity in exponential phase A549 human lung cancer cultures. Gene expression profiles of A549 cultures treated with one of these water-soluble zinc ionophores, PCI-5002, reveal the activation of stress response pathways under the control of metal-responsive transcription factor 1 (MTF-1), hypoxia-inducible transcription factor 1 (HIF-1), and heat shock transcription factors. Additional oxidative stress response and apoptotic pathways were activated in cultures grown in zinc-supplemented media. We also show that these water-soluble zinc ionophores can be given to mice at 100 micromol/kg (300 micromol/m(2)) with no observable toxicity and inhibit the growth of A549 lung and PC3 prostate cancer cells grown in xenograft models. Gene expression profiles of tumor specimens harvested from mice 4 h after treatment confirmed the in vivo activation of MTF-1-responsive genes. Overall, we propose that water-solubilized zinc ionophores represent a potential new class of anticancer agents.

NMR characterization of an S-linked glucuronide metabolite of the potent, novel, nonsteroidal progesterone agonist tanaproget

Tanaproget is a first-in-class nonsteroidal progesterone receptor agonist that is being investigated for use in contraception. A major in vitro and in vivo metabolite of tanaproget formed in humans was initially characterized as a glucuronide of tanaproget. However, whether the glucuronide was linked to the nitrogen or sulfur of the benzoxazine-2-thione group in tanaproget could not be determined by liquid chromatography/mass spectrometry (LC/MS) and LC-tandem mass spectrometry analysis. To obtain additional structural details for this metabolite, additional quantities were generated from rat liver microsomal incubations and purified by high-performance liquid chromatography (HPLC) for NMR analysis. The NMR data for the metabolite confirmed that the glucuronide was covalently bound to either the sulfur or the nitrogen of the benzoxazine-2-thione moiety. The lack of key through-bond (scalar) and through-space (dipolar) one-dimensional (1D) and two-dimensional (2D) NMR couplings and correlations in the metabolite spectra (due primarily to low sample concentration) precluded an unambiguous structure elucidation. Subsequent synthesis of the S- and N-glucuronides of tanaproget from tanaproget facilitated the unambiguous regio- and stereochemical assignment of the metabolite by comparison of 1D NMR chemical shifts and scalar coupling constants, 2D NMR correlations, and HPLC and LC/MS characteristics between the synthetic compounds and the metabolite. From extensive comparison of the spectral and chromatographic data of the microsomally derived metabolite and the synthetic compounds, the metabolite has been determined to be the S-(beta)-D-glucuronide of tanaproget.

Chromatographic behavior of pyrithiones

Pyrithione biocides are currently viewed as a major prospect for the replacement of tributyltin antifoulants in ship paints. The chromatographic behavior of 1-hydroxy-2-pyridinethione (pyrithione, PT), bis(2-pyridinyl)disulfide 1,1'-dioxide (PT2), and the metal complexes zinc [Zn(PT)2], iron [Fe(PT)3] and copper [Cu(PT)2] pyrithione, were investigated by means of UV-vis spectroscopy, ESI-MSn, HPLC-DAD and HPLC-ESI-MSnD. This revealed transformations of the analytes, which affect the development of adequate methods for species or environmental analysis of pyrithiones. PT transforms into copper- or iron- containing complexes and/or the oxidation product PT2, depending on the type of the stationary phase used in chromatographic analysis. Speciation complicates direct chromatography of [Zn(PT)2] and [Fe(PT)3].

NMR identification of an S-linked glucuronide of a triazole thione formed in vitro

The metabolism of 3-([3-(2-Chlorophenyl)-4,5-dihydro-5-thioxo-1H-1,2,4-triazol-1-yl]methyl)benzonitrile (AR-C133611XX) was studied in isolated dog hepatocytes. The major metabolite of AR-C133611XX was characterized by high performance liquid chromatography-mass spectrometry and NMR and found to be the product of direct glucuronidation. Evidence from 1H and 13C-NMR chemical shifts and a long-range proton carbon correlation experiment was used to deduce that glucuronidation had taken place on the sulfur atom. Full NMR data on this unusual metabolite is presented. Substitution or replacement of the sulfur atom resulted in a significant decrease in the observed rate of glucuronidation.

Drug glucosidation

A number of studies have shown that drug glucosidation occurs in vertebrates. This review summarizes information on the chemical, physical and biological properties of eleven drug glucosides. Three out of two hundred individuals exhibited a complete lack of amobarbital-N-glucoside formation. The data from a pair of identical twins who were deficient in this metabolic pathway suggested the presence of a recessive trait controlled by a single pair of autosomal genes which regulate N-glucoside formation. In addition, average values seemed to be subject to interethnic variation.