A Commonly Used Biocide 2-N-octyl-4-isothiazolin-3-oneInduces Blood-Brain Barrier Dysfunction via Cellular Thiol Modification and Mitochondrial Damage

Isothiazolinone (IT) biocides are potent antibacterial substances commonly used as preservatives or disinfectants, and 2-n-Octyl-4-isothiazolin-3-one (OIT; octhilinone) is a common IT biocide that is present in leather products, glue, paints, and cleaning products. Although humans are exposed to OIT through personal and industrial use, the potentially deleterious effects of OIT on human health are still unknown. To investigate the effects of OIT on the vascular system, which is continuously exposed to xenobiotics through systemic circulation, we treated brain endothelial cells with OIT. OIT treatment significantly activated caspase-3-mediated apoptosis and reduced the bioenergetic function of mitochondria in a bEnd.3 cell-based in vitro blood–brain barrier (BBB) model. Interestingly, OIT significantly altered the thiol redox status, as evidenced by reduced glutathione levels and protein S-nitrosylation. The endothelial barrier function of bEnd.3 cells was significantly impaired by OIT treatment. OIT affected mitochondrial dynamics through mitophagy and altered mitochondrial morphology in bEnd.3 cells. N-acetyl cysteine significantly reversed the effects of OIT on the metabolic capacity and endothelial function of bEnd.3 cells. Taken together, we demonstrated that the alteration of the thiol redox status and mitochondrial damage contributed to OIT-induced BBB dysfunction, and we hope that our findings will improve our understanding of the potential hazardous health effects of IT biocides.

Direct and Indirect Effect of Chlorhexidine on Survival of Stem Cells from the Apical Papilla and Its Neutralization

INTRODUCTION

Several irrigants have been used for disinfection in regenerative endodontic procedures including chlorhexidine (CHX). In this context, the antibacterial properties of disinfectants are mainly in focus of research even though they may have an undesirable impact on the fate of stem cells. In this study, we hypothesized that CHX has both a direct effect when applied to stem cells of the apical papilla (SCAPs) and an indirect effect when SCAPs are exposed to dentin previously conditioned with CHX.

METHODS

Cell toxicity was evaluated in vitro using the CellTox green fluorescence assay (Promega, Madison, WI) and CellTiter-Glo (Promega) after SCAPs were exposed directly to a dynamic concentration range of CHX; apical papilla explant cultures were stained with ApopTag (Merck Millipore, Billerica, MA) after culture with CHX. Furthermore, standardized slabs from human dentin were treated with CHX and consecutively rinsed in EDTA, L-α-lecithin (Sigma-Aldrich, St Louis, MO), or L-α-lecithin followed by EDTA. After that, SCAPs were cultured on the slabs for 5 days, and cellular viability was determined (indirect effect). Data were treated nonparametrically and analyzed using the Krukal-Wallis test (P ≤ .05).

RESULTS

Direct exposure of SCAPs to CHX highly affected cell viability at concentrations above 10^-3%, whereas lower concentrations had no adverse effect. During the initial 60 minutes, concentrations of 10^-2% CHX or higher resulted in early pronounced toxicity with a maximum effect within 15 minutes after exposure. Likewise, CHX-conditioned dentin slabs were detrimental to SCAP survival; however, the deleterious effects were completely reversed by neutralization with L-α-lecithin.

CONCLUSIONS

Chlorhexidine is toxic to SCAPs when applied directly or indirectly via conditioned dentin. If applied for a short time and neutralized by L-α-lecithin, it can be a gentle and cell-preserving disinfectant before endodontic regeneration.

Efficacy of some neutralizers in suspension tests determining the activity of disinfectants

The ability of six mixtures to neutralize glutaraldehyde, o-phthalaldehyde and peracetic acid was tested using four reference strains: Pseudomonas aeruginosa CIP A22, Escherichia coli CIP 54127, Staphylococcus aureus CIP 53154, and Enterococcus faecium CIP 5855. Glutaraldehyde was the hardest to neutralize, and peracetic acid the easiest. The most effective mixture was Tween 80 with sodium bisulphate, sodium thioglycolate, lecithin and cysteine, and the least effective was Tween 80, lecithin and histidine. The efficacy of the neutralizers may indicate a propensity loss of activity from interfering substances when disinfectants are used in practice.

Inhibition of bleach-induced luminol chemiluminescence

The luminol chemiluminescence presumptive test for blood is based on the mild peroxidase activity of hemoglobin in basic peroxide solution. However, this test is subject to interference by strong oxidants, certain transition metal ions, and true peroxidases. This paper reports methods for reducing the interference caused by hypochlorite-containing bleaches. Amines such as 1,2-diaminoethane react rapidly with hypochlorite without interfering significantly with the hemoglobin-catalyzed oxidation. Thus, addition of 0.1 mol/L 1,2-diaminoethane to a standard luminol-peroxide spray lead to almost complete inhibition of hypochlorite-induced chemiluminescence while satisfactory chemiluminescence was still observed from bloodstains. If time allows, an alternative method for reducing interference from hypochlorite bleach is to wait several days until the bloodstains have dried thoroughly, by which time the hypochlorite will have decomposed.

Inactivation of the antibacterial activity of iodine potassium iodide and chlorhexidine digluconate against Enterococcus faecalis by dentin, dentin matrix, type-I collagen, and heat-killed microbial whole cells

The antibacterial activity of chlorhexidine digluconate and iodine potassium iodide on Enterococcus faecalis A197A was tested in the presence of dentin, dentin matrix, dentin pretreated by EDTA and citric acid, collagen, and heat-killed cells of Enterococcus faecalis and Candida albicans. Medications were preincubated for 1 h with each of the potential inhibitors and tested for their antibacterial activity against E. faecalis, strain A197A. Surviving bacteria were sampled after 1 and 24 h of incubation. Dentin matrix and heat-killed microbial cells were the most effective inhibitors of chlorhexidine, whereas dentin pretreated by citric acid or EDTA showed only slight inhibition. Dentin and skin collagen showed some inhibition at 1 h but not after 24 h. Iodine potassium iodide was effectively inhibited by dentin, dentin matrix, and heat-killed microbial cells. Skin collagen and dentin pretreated by EDTA or by citric acid showed little or no inhibitory effect on iodine potassium iodide. Different components of dentin are responsible for the divergent patterns of inhibition of the antibacterial activity of chlorhexidine digluconate and iodine potassium iodide. Chemical treatment of dentin before applying the medication into the root canal may alter the antibacterial effect of the medication.

[The sensitivity to antibiotics and disinfecting substances of opportunistic microorganisms isolated from the oral cavity of patients with orthodontic pathology]

Antibiotic and disinfectant sensitivities of opportunistic bacteria, isolated from the oral cavity of normal subjects and orthodontic patients, were under study. The findings evidence that oral microflora of patients with orthodontic conditions is more rich in microorganisms that can induce pyoinflammatory diseases than that in health. Among the isolated opportunistic bacteria strains were found that were resistant to both: antibiotics and disinfectants. Antibiotic sensitivities of the microorganisms isolated from normal subjects and patients were found virtually the same, whereas the strains isolated from the patients have shown a higher sensitivity to disinfectants. The authors emphasize that effective prevention of pyoseptic complications in the maxillofacial area involves not only bacteriologic monitoring and studies of the microorganism sensitivity to antibiotics, but analysis of the bacterial sensitivity to disinfectants as well.

[Characteristics of gram-negative microflora on environmental objects in puerperal wards and their resistance to antibacterial preparations and disinfectants]

The species composition of gram-negative opportunistic bacteria isolated from different objects at three puerperal wards of a maternity clinic was studied. Escherichia coli and Acinetobacter were found to have a fairly wide circulation. The objects most contaminated by these bacteria were determined. The study showed that up to 33.3% of the isolated hospital strains of gram-negative bacteria were characterized by multiple resistance to antibiotics used in medical practice and to sulfathiazole. The strains showed the highest sensitivity to gentamicin and kanamycin. Most of the hospital strains were sensitive to chloramine and nirtan, but 4-13% of Klebsiella and Pseudomonas aeruginosa strains showed enhanced resistance to 0.1% chloramine solution.

[Inactivation of disinfectants by proteins and calcium ions as a function of their chemical constitution and bacterial species]

Activity of nine disinfectants was evaluated with interfering substances (albumin-yeast mixture and hard water), by two methods (NFT. 72 170, NFT. 72 171 and without interfering substance NFT. 72 150, NFT 72 151 respectively). Interference indexes were defined as the ratio of bactericidal concentration without interfering substances to bactericidal concentration with interfering substances. Five different ratings of interference effects were arbitrarily defined (no effect, moderate, average, strong, very strong). Proteins and hard water significantly inactivate aldehydes and quaternary ammonium salts : interference index is usually 25 but may reach 100-500. Inactivation of phenolic products by these two interfering substances is either lacking or inconsiderable. Conversely to Gram negative bacteria, activity of disinfectants on Gram positive bacteria is not significantly affected by proteins or hard water. P. aeruginosa can survive despite high concentrations of disinfectant in the presence of proteins and calcium ions. This finding may be a reason why this microorganism is difficult to eliminate from hospital wards.

[Bactericidal activity of various disinfectants with or without interfering protein substances]

Determination of bactericidal activity of 15 disinfectants by AFNOR standard NF T 72-151 (in distilled water) and AFNOR standard NF T 72-171 (in the presence of protein) provides practical guidelines for optimal use of the different available products. Inhibition by dirt is weak for products composed chiefly of phenol derivatives, while it is very strong for quaternary ammonium compounds as well as chlorine which therefore require prior cleansing of surfaces to be disinfected. Two strains (out of the five indicated by AFNOR standards), i.e. P. aeruginosa and M. smegmatis, are especially resistant when residual organic material is present. According to specific conditions of use, such as whether surfaces are clean or dirty, or whether a hospital or food factory is involved, appropriate AFNOR standards must be chosen to study the activity of disinfectants in various settings and on different strains.

Neutralization of the activity of eight disinfectants by organic matter

The effect of organic matter on the activity of eight disinfectants was evaluated. Three types of interfering substrates (whole milk powder, dried beef blood and fish meal) were tested according to the method of Whitmore and Miner adapted to the AOAC use-dilution method. Glutaraldehyde and to a certain extent, chlorhexidine acetate and the amphoteric surfactant kept their disinfecting activity after contact with high concentrations of organic matter. The quaternary ammonium compound as well as the quaternary ammonium-glutaraldehyde complex were more readily neutralized whereas anionic acid, iodophor and sodium hypochlorite did not tolerate the presence of organic matter. The neutralizing activity of powders was correlated to their solubility and composition.

Evaluation of glycine as an inactivator of glutaraldehyde

Glycine was evaluated as an inactivator of the sporicidal activity of glutaraldehyde. Spores from glucose depleted cultures of Bacillus stearothermophilus grown in a chemically defined medium were used. When glycine is used as an inactivator of glutaraldehyde, it lowers the pH value of the solution. Glycine 1% failed to inactivate 0.5% or higher concentrations of alkaline glutaraldehyde in sporicidal studies. If viable counts cannot be performed within the first hour after inactivation, the concentration of glycine should be at least 2% to inactivate effectively 2% alkaline glutaraldehyde.

Efficacy of inactivators against 14 disinfectant substances

More than 24 inactivators were tested for their suitability against 14 disinfectant substances by a quantitative suspension test. Even simple inactivators were found to be efficace: 0.1% cysteine and 0.5% sodium thiosulfate for mercuric chloride and the iodophor; 0.1% sodium sulfite for these two substances and for the QAC in the lower concentration; 1.0% polysorbate 80 for hexylresorcinol, o-phenylphenol and the QAC in the lower concentration; 0.5% sodium thioglycolate for mercuric chloride, the iodophor and chloramine-T. The inactivator active against most disinfectants was the combination LPHT or 0.3% lecithin / 3.0% polysorbate 80 /0.1% histidine / 0.5% sodium thiosulfate. Also active were: LPWT (0.5% lecithin / 1.0% polysorbate 80 /1.0% Lubrol W / 1.0% sodium thiosulfate), LPT (2.0% lecithin / 2.0% polysorbate 80 / 0.5% sodium thiosulfate) and PS (3.0% polysorbate 80 / 3.0% saponin).

The use of inactivators in the evaluation of disinfectants

Since the earliest days of disinfectant testing bacteriostatic effect has misled many workers in this field. This problem has long been appreciated by some and a considerable battery of neutralizers has been employed, often with great success. Other anti-bacteriostatic measures, used without control, fail to revive damaged though viable organisms.This paper sets out to describe some of the problems that are encountered in this confused field and the means whereby they may be overcome.