Can glutathione-containing emollients inactivate methylchloroisothiazolinone/methylisothiazolinone?

Benzisothiazolinone: Pharmacokinetics, Tissue Distribution, and Mass Balance Studies in Rats

Humans are continuously exposed to benzisothiazolinone (BIT), which is used as a preservative, through multiple routes. BIT is known to be a sensitizer; in particular, dermal contact or aerosol inhalation could affect the local toxicity. In this study, we evaluated the pharmacokinetic properties of BIT in rats following various routes of administration. BIT levels were determined in rat plasma and tissues after oral inhalation and dermal application. Although the digestive system rapidly and completely absorbed orally administered BIT, it underwent severe first-pass effects that prevented high exposure. In an oral dose escalation study (5-50 mg/kg), nonlinear pharmacokinetic properties showed that C_max and the area under the curve (AUC) increased more than dose proportionality. In the inhalation study, the lungs of rats exposed to BIT aerosols had higher BIT concentrations than the plasma. Additionally, the pharmacokinetic profile of BIT after the dermal application was different; continuous skin absorption without the first-pass effect led to a 2.13-fold increase in bioavailability compared with oral exposure to BIT. The [¹⁴C]-BIT mass balance study revealed that BIT was extensively metabolized and excreted in the urine. These results can be used in risk assessments to investigate the relationship between BIT exposure and hazardous potential.

Can the Reactivity to Chromate Be Changed in Patch Testing Using a Barrier Cream?

BACKGROUND

The persistent, difficult-to-treat, allergic contact dermatitis from hexavalent chromium in European construction workers has diminished significantly since the legislative measurements that came into force in January 2005. However, sensitization to hexavalent chromium continues to be a problem. Barrier creams have been tried for various allergens with divergent results.

OBJECTIVE

The aim of the study was to investigate the protective capacity of barrier cream candidates against hexavalent chromium in a patch test situation.

METHODS

An experimental study was performed to investigate the reductive properties of glutathione and iron sulfate on the patch test reactivity in chromium-allergic individuals when exposed to hexavalent chromium. In this study, we also investigated the protective properties of a commercially available barrier cream.

CONCLUSIONS

A higher number of volunteers (16/18) showed reactions on the skin treated with the commercially available barrier cream, compared with the untreated skin (13/18) on test reading day 3/4 or day 7. The skin treated with petrolatum or Essex cream showed fewer and less prominent allergic reactions than the skin treated with the commercially available barrier cream.

Allergic contact dermatitis: From pathophysiology to development of new preventive strategies

As the body's first line of defense, the skin is the organ most frequently exposed to chemicals present in personal hygiene products, household products, or materials used in the work environment. In this context, skin disorders account for more than 40 % of all occupational and work-related diseases, constituting a significant public health burden. Among skin disorders, allergic contact dermatitis (ACD) is the most prevalent occupational disease and the most common form of immunotoxicity in humans. ACD is a T-cell-mediated skin inflammation resulting from the priming and expansion of allergen-specific CD4⁺ and CD8⁺ T cells. The clinical condition is characterized by local skin rash, itchiness, redness, swelling, and lesions, being mainly diagnosed by the patch test. Upon ACD diagnosis, avoiding the exposure to the triggering allergen is the mainstay of treatment to prevent future flares. In cases where avoidance is not possible, the use of a standard of care interim treatments such as steroid creams or ointments, barrier creams, and moisturizers are strongly recommended to alleviate symptoms. In this review, we sought to provide the reader with an overview of the pathophysiology of ACD as well as the currently available pharmacological treatment options. Furthermore, a comprehensive outline of several preventive strategies is also provided.

Experimental determination of indoor air concentration of 5-chloro-2-methylisothiazol-3(2H)-one/ 2-methylisothiazol-3(2H)-one (CMIT/MIT) emitted by the use of humidifier disinfectant

A mixture of 5-chloro-2-methylisothiazol-3(2H)-one/2-methylisothiazol-3(2H)-one (CMIT/MIT) had been used as an active ingredient in humidifier disinfectants (HDs). Owing to its high reactivity, the atmospheric concentration of CMIT/MIT, following its use in HD, would be lower than expected assuming that it is removed by ventilation only. In order to evaluate the exposure concentration of CMIT/MIT used as an HD, room-scale chamber studies were conducted under plausible use of three different HD doses at air change rates (ACR) of 0.3, 0.5, and 1.0 h-1. Atmospheric CMIT/MIT was sampled using two serial impingers containing deionized water after the attainment of steady state. Water samples in which CMIT/MIT was dissolved were concentrated using a cosolvent evaporation method with efficiencies of 35.5 and 77.9% for CMIT and MIT, respectively. The estimated air concentration, assuming that all the CMIT/MIT is absorbed in deionized water, increased linearly with increasing emission rate, but was independent of the ACR. This indicates that the removal rate of CMIT/MIT via chemical reactions is more than the removal rate by ventilation. Further investigations on homogeneous and heterogeneous chemical reactions of CMIT/MIT under ambient conditions are necessary to understand the actual exposure concentration of the mixture in HD.

Skin application of glutathione and iron sulfate can inhibit elicitation of allergic contact dermatitis from hexavalent chromium

BACKGROUND

Allergic contact dermatitis (ACD) caused by hexavalent chromium, Cr(VI), is often severe and difficult to treat. The most common source of exposure to Cr(VI) in Sweden used to be cement, and more recently leather. The contact allergy can be diminished or inhibited if the exposure is decreased or ceases. Barrier creams against different kinds of allergens have been investigated for their protective properties which may offer protection against Cr(VI) exposure.

OBJECTIVES

To investigate the capacity of formulas containing glutathione (GSH) and iron sulfate to inhibit elicitation of ACD in Cr(VI)-allergic individuals when exposed to Cr(VI).

METHODS

In 18 Cr(VI)-allergic volunteers the back was divided into eight patch test areas which were treated with preparations of possible barrier creams, prior to patch testing with a dilution series of potassium dichromate and a buffered extract of cement.

RESULTS

A significant reduction in reactivity to Cr(VI) and cement extract on skin treated with formulas containing GSH or iron sulfate was noticed, compared with untreated skin.

CONCLUSION

Formulas containing GSH or iron sulfate in barrier creams inhibit ACD in individuals allergic to Cr(VI) when applied before exposure to Cr(VI) and cement extract.

Can reducing cosmetic substances help prevent chromate contact allergy?

BACKGROUND

Allergic contact dermatitis caused by Cr(VI) is often severe and difficult to treat. Therefore, primary prevention is a main goal but, secondary prevention can be valuable to ease the symptoms or prevent relapse of Cr(VI) dermatitis when sensitization has occurred. Barrier creams have been tried for many chemical substances, but until now there is no successful barrier cream against Cr(VI).

OBJECTIVES

To investigate the ability of reducing agents to transform Cr(VI) into Cr(III) in an experimental situation, in order to find suitable chemicals to investigate for possible use in a barrier cream.

METHODS

The capacity to reduce the amount of Cr(VI) was analyzed in water solutions of acetylcysteine, cysteine, dihydroxyacetone, glutathione, and iron sulfate heptahydrate. Thereafter the reducing capacity of acetylcysteine, dihydroxyacetone, glutathione, and iron sulfate on the amount of Cr(VI) in cement extracts was investigated. The content of Cr(VI) in the test solutions and in the cement extracts was estimated by the diphenyl carbazide spot test.

RESULTS

All of the chosen chemicals reduced the amount of Cr(VI) in the test solutions and in the cement extracts to some extent. The reducing capacity was most prominent for iron sulfate.

CONCLUSION

A reducing capacity was found for all chosen chemicals.

Isothiazolinone derivatives and allergic contact dermatitis: a review and update

Allergic contact dermatitis (ACD) from isothiazolinones has frequently been described in the literature. Following an epidemic of sensitization to methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) in the 1980s, and more recently to MI, the Scientific Committee on Consumer Safety of the European Commission banned their use in leave-on products, while restricting that in rinse-off cosmetics. Despite a decreasing prevalence of ACD from MCI/MI and MI, cases caused by occupational exposure and non-cosmetic isothiazolinone sources are on the rise. Moreover, sensitization to newer and lesser known isothiazolinones has been reported. This paper reviews the epidemiology of contact allergy to different isothiazolinones, clinical presentation of isothiazolinone-induced ACD, most relevant sensitization sources and potential cross-reactions between isothiazolinone derivatives. It also provides an update on recent legislative measures.

Effects of the biocide methylisothiazolinone on Xenopus laevis wound healing and tail regeneration

The South African clawed frog, Xenopus laevis, has a strong history as a suitable model for environmental studies. Its embryos and transparent tadpoles are highly sensitive to the environment and their developmental processes are well described. It is also amenable for molecular studies. These characteristics enable its use for rapid identification and understanding of exposure-induced defects. To investigate the consequences of chemical exposure on aquatic animals, Xenopus laevis embryos and tadpoles were exposed to the biocide, methylisothiazolinone (MIT). Frog tadpoles exposed to MIT following tail amputation lost their natural regenerative ability. This inhibition of regeneration led to a failure to regrow tissues including the spinal cord, muscle, and notochord. This MIT-dependent regenerative defect is due to a failure to close the amputation wound. A wound healing assay revealed that while untreated embryos close their wounds within one day after injury, MIT-treated animals maintained open wounds that did not reduce in size and caused lethality. Concomitant exposure of MIT with chemicals containing thiol groups such as glutathione and N-acetyl cysteine restored normal wound healing and regeneration responses in tadpoles. Together these results indicate that exposure to MIT impairs developmental wound repair and tissue regeneration in Xenopus laevis. Thus, this study reveals new aspects of MIT activity and demonstrates that Xenopus laevis is a well-suited model for facilitating future research into chemical exposure effects on injury responses.

Signal transduction profile of chemical sensitisers in dendritic cells: an endpoint to be included in a cell-based in vitro alternative approach to hazard identification?

The development of non-animal testing methods for the assessment of skin sensitisation potential is an urgent challenge within the framework of existing and forthcoming legislation. Efforts have been made to replace current animal tests, but so far no alternative methods have been developed. It is widely recognised that alternatives to animal testing cannot be accomplished with a single approach, but rather will require the integration of results obtained from different in vitro and in silico assays. The argument subjacent to the development of in vitro dendritic cell (DC)-based assays is that sensitiser-induced changes in the DC phenotype can be differentiated from those induced by irritants. This assumption is derived from the unique capacity of DC to convert environmental signals encountered at the skin into a receptor expression pattern (MHC class II molecules, co-stimulatory molecules, chemokine receptors) and a soluble mediator release profile that will stimulate T lymphocytes. Since signal transduction cascades precede changes in surface marker expression and cytokine/chemokine secretion, these phenotypic modifications are a consequence of a signal transduction profile that is specifically triggered by sensitisers and not by irritants. A limited number of studies have addressed this subject and the present review attempts to summarise and highlight all of the signalling pathways modulated by skin sensitisers and irritants. Furthermore, we conclude this review by focusing on the most promising strategies suitable for inclusion into a cell-based in vitro alternative approach to hazard identification.

GSH depletion, protein S-glutathionylation and mitochondrial transmembrane potential hyperpolarization are early events in initiation of cell death induced by a mixture of isothiazolinones in HL60 cells

We recently described that brief exposure of HL60 cells to a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) induces apoptosis at low concentrations (0.001-0.01%) and necrosis at higher concentrations (0.05-0.1%). In this study, we show that glutathione (GSH) depletion, reactive oxygen species generation, hyperpolarization of mitochondrial transmembrane potential (DeltaPsim) and formation of protein-GSH mixed disulphides (S-glutathionylation) are early molecular events that precede the induction of cell death by CMI/MI. When the cells exhibit common signs of apoptosis, they show activation of caspase-9, reduction of DeltaPsim and, more importantly, decreased protein S-glutathionylation. In contrast, necrosis is associated with severe mitochondrial damage and maximal protein S-glutathionylation. CMI/MI-induced cytotoxicity is also accompanied by decreased activity of GSH-related enzymes. Pre-incubation with L-buthionine-(S,R)-sulfoximine (BSO) clearly switches the mode of cell death from apoptosis to necrosis at 0.01% CMI/MI. Collectively, these results demonstrate that CMI/MI alters the redox status of HL60 cells, and the extent and kinetics of GSH depletion and S-glutathionylation appear to determine whether cells undergo apoptosis or necrosis. We hypothesize that S-glutathionylation of certain thiol groups accompanied by GSH depletion plays a critical role in the molecular mechanism of CMI/MI cytotoxicity.

Thiol Antioxidants Block the Activation of Antigen-Presenting Cells by Contact Sensitizers

Strong contact sensitizers are able to induce signal transduction mechanisms such as tyrosine phosphorylation and activation of MAP kinases in antigen-presenting cells. We studied the capacity of different antioxidants (ascorbic acid, alpha-tocopherol, pyrrolidine dithiocarbamate, N-acetylcysteine, and glutathione) to block the increase in tyrosine phosphorylation in human monocytes seen after stimulation with strong contact sensitizers. Human peripheral blood mononuclear cells were stimulated with 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone in the presence or absence of these antioxidants. The total amount of membrane-associated phosphotyrosine in CD14+ cells was quantified using flow cytometric techniques. Complete inhibition of tyrosine phosphorylation was noticed when cells were stimulated in the presence of N-acetylcysteine or glutathione. Using N-acetylcysteine as inhibitor similar results were obtained for cells stimulated with formaldehyde, thimerosal methyldibromoglutaronitrile, diphenylcyclopropenone, p-phenylenediamine, toluene-2,5-diamine, and 2,4-dinitrofluorobenzene. By use of a trinitrophenyl-specific monoclonal antibody it was shown that N-acetylcysteine as well as cysteine prevents the binding of 2,4,6-trinitrochlorobenzene to proteins in monocytes and monocyte-derived mature dendritic cells. Furthermore, the capacity of N-acetylcysteine to block the activation of p38 and ERK1/2 MAP kinases by 2,4,6-trinitrochlorobenzene was demonstrated. The radical scavengers ascorbic acid and alpha-tocopherol as well as the nuclear factor kappaB inhibitor pyrrolidine dithiocarbamate failed to prevent the increase in tyrosine phosphorylation. Our data present evidence that reactive oxygen species as well as transcription factor nuclear factor kappaB seem to be unimportant for the induction of tyrosine phosphorylation by contact sensitizers. On the other hand, protection of thiol groups using compounds with free sulfhydryl groups is very effective to block this process. This finding may have implications for prevention of occupational sensitization to strong contact allergens.

Involvement of oxidative stress in apoptosis induced by a mixture of isothiazolinones in normal human keratinocytes

A 3:1 combination of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) is widely used to preserve cosmetic products. We show here that CMI/MI induced apoptosis in normal human keratinocytes (NHK) as at low concentrations (0.001-0.05% documented by subdiploid DNA content and phosphatidylserine exposure, while at the highest concentration (0.1% as supplied, 15 p.p.m.) the response was necrosis. Various molecular events accompanied the cytotoxic effects of CMI/MI. Generation of ROS and hyperpolarization of mitochondrial transmembrane potential (DeltaPsim) were early events, followed by increased Fas expression and activation of caspase-8, and then activation of caspase-3 and -9. The drop in DeltaPsim occurred only later in the cell death pathway, when NHK showed signs of apoptosis. Pretreatment of cells for 2 h with the redox-active agent N-acetyl-L-cysteine conferred complete protection against the CMI/MI-induced cytotoxic effects, DeltaPsim loss, and apoptosis. The pan-caspase inhibitor Z-Val-Ala-Asp(OMe)-CH2F blocked the CMI/MI-induced apoptosis without preventing ROS generation and the drop in DeltaPsim. These results indicate that the generation of ROS plays an important part in mediating apoptosis and necrosis associated with CMI/MI treatment. This new aspect of the in vitro toxicity of CMI/MI may provide important information about the relationship between the preservative's in vitro apoptotic activity and its in vivo toxicity.

Coupling of contact sensitizers to thiol groups is a key event for the activation of monocytes and monocyte-derived dendritic cells

Strong contact sensitizers are able to induce distinct signal transduction mechanisms in antigen-presenting cells by coupling to cell proteins. The predominant target structures of haptens are thought to be thiol and amino groups in cysteine and lysine residues. We studied whether coupling of small reactive chemicals to thiol or amino groups might be responsible for the activation of monocytes and mature monocyte-derived dendritic cells. Human peripheral blood mononuclear cells were stimulated in vitro with subtoxic concentrations of the strong haptens 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene, the thiol-reactive reagents N-hydroxymaleimide and N-ethylmaleimide, as well as the amino-reactive compounds sulfosuccinimidyl acetate and 2-iminothiolane. Flow cytometric quantification of tyrosine phosphorylation in CD14+ monocytes showed that 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone, 2, 4, 6-trinitrochlorobenzene, N-hydroxymaleimide, and N-ethylmaleimide but not sulfosuccinimidyl acetate and 2-iminothiolane strongly induced this process. Tyrosine phosphorylation induced by 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene was completely prevented in the presence of cysteine but not lysine, suggesting a competitive mechanism between cysteine and sulfhydryl groups of cell proteins. Using the mouse ear swelling test N-hydroxymaleimide could be classified as a significant contact allergen in comparison to 2, 4, 6-trinitrochlorobenzene, whereas no sensitizing potential became apparent for sulfosuccinimidyl acetate and 2-iminothiolane. Western blot analysis on monocytes and mature monocyte-derived dendritic cells confirmed the flow cytometric data for tyrosine phosphorylation and demonstrated a selective capacity of haptens and thiol-reactive compounds to activate ERK1/2 mitogen-activated protein kinase. Our data show that strong affinity of a small reactive chemical toward thiol groups is important for the activation of monocytes and monocyte-derived dendritic cells and can support the process of sensitization.