Toxicity Summary
IDENTIFICATION AND USE: 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) forms crystals. It is used as antimicrobial preservative in cosmetics, hygiene products, paints, emulsions, cutting oils, paper coatings, and water storage and cooling units. CMI is also used in hydraulic fracturing fluids. It is registered for pesticide use in the USA but approved pesticide uses may change periodically and so federal, state and local authorities must be consulted for currently approved uses. CMI is often used in a combination products with 2-methyl-4-isothiazolin-3-one (MI). HUMAN EXPOSURE AND TOXICITY: Kathon CG, a cosmetics preservative containing, as active ingredients, 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, appears to be a frequent cause of contact dermatitis in Europe. ANIMAL STUDIES: A mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (CMI/MIT) diluted in corn oil was administered by gavage to male and female rats at 0, 0.26, 0.78, 2.33 and 7.0 mg/kg body weight per day. Reduction of serum triglyceride levels in males and induction of hepatic phase 1 xenobiotic metabolizing enzymes in females accompanied by subtle histological changes in the liver were observed at the highest CMIT/MIT exposure. A mixture of CMI/MIT produced point mutations in the absence of a rat-liver metabolizing system in bacteria (strain TA 100) and mammalian cells in culture. In the presence of rat-liver metabolizing system a 10-fold higher concentration was required to induce point mutations in mammalian cells in culture. No mutagenic activity was observed with the metabolizing system and S. typhimurium. Negative results were obtained in the sex-linked recessive lethal assay in Drosophila, the in vivo cytogenetic assay in mice, the unscheduled DNA synthesis assay in cultured rat hepatocytes, and the in vitro cell transformation assay. In immunotoxicity studies CMI, which binds to protein, induced an auricular lymph node cell proliferation response while MI, which poorly binds to protein, neither stimulated a proliferative response nor induced an increase in lymph node size at concentrations similar to CMI.

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Interactions
Previously we reported 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) shifts the cells into a state of oxidative stress that induces apoptosis and necrosis. In this study, flow cytometric analysis showed that CMI/MI induces early perturbation of calcium homeostasis, increasing cytosolic and mitochondrial calcium and depleting the intracellular endoplasmic reticulum (ER) stores. The calcium chelator BAPTA-AM reduced necrosis and secondary necrosis, the loss of DeltaPsim and S-glutathionylation induced by necrotic doses of CMI/MI, but did not protect against CMI/MI-induced apoptosis, mitochondrial calcium uptake and mitochondrial hyperpolarization. This indicates that increased cytoplasmic calcium does not have a causal role in the induction of apoptosis, while cross-talk between the ER and mitochondria could be responsible for the induction of apoptosis. GSH-OEt pretreatment, which enhances cellular GSH content, reduced S-glutathionylation and cytosolic and mitochondrial calcium levels, thus protecting against both apoptosis and necrosis shifting to apoptosis. Therefore, the degree of GSH depletion, paralleled by the levels of protein S-glutathionylation, may have a causal role in increasing calcium levels. The mitochondrial calcium increase could be responsible for apoptosis, while necrosis is associated with cytoplasmic calcium overload. These findings suggest that S-glutathionylation of specific proteins acts as a molecular linker between calcium and redox signalling.

[1]. Methylisothiazolinone induces apoptotic cell death via matrix metalloproteinase activation in human bronchial epithelial cells. Toxicol In Vitro. 2020 Feb;62:104661.

[2]. Functional and dynamic mitochondrial damage by chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) mixture in brain endothelial cell lines and rat cerebrovascular endothelium. Toxicol Lett. 2022 Aug 1;366:45-57.

[3]. Methylisothiazolinone: dermal and respiratory immune responses in mice. Toxicol Lett. 2015 Jun 15;235(3):179-88.

[4]. Effects of chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) on Th2/Th17-related immune modulation in an atopic dermatitis mouse model. Sci Rep. 2020 Mar 5;10(1):4099.

Chloromethylisothiazolinone is a 1,2-thiazole that is 4-isothiazolin-3-one bearing a methyl group on the nitrogen atom and a chlorine at C-5. It is a powerful biocide and preservative and is the major active ingredient in the commercial product Kathon(TM). It has a role as an antimicrobial agent, a xenobiotic and an environmental contaminant. It is a member of 1,2-thiazoles and an organochlorine compound. It is functionally related to a methylisothiazolinone.
Methylchloroisothiazolinone (MCI) is an isothiazolinone commonly used as a preservative with antibacterial and antifungal properties. It is found within many commercially available cosmetics, lotions, and makeup removers. It is also a known dermatological sensitizer and allergen; some of its side effects include flaky or scaly skin, breakouts, redness or itchiness, and moderate to severe swelling in the eye area. The American Contact Dermatitis Society named Methylchloroisothiazolinone the Contact Allergen of the Year for 2013. Sensitivity to Methylchloroisothiazolinone may be identified with a clinical patch test.
Methylchloroisothiazolinone is a Standardized Chemical Allergen. The physiologic effect of methylchloroisothiazolinone is by means of Increased Histamine Release, and Cell-mediated Immunity.
See also: Magnesium Chloride (annotation moved to).

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Drug Indication
Methylchloroisothiazolinone is approved for use within allergenic epicutaneous patch tests which are indicated for use as an aid in the diagnosis of allergic contact dermatitis (ACD) in persons 6 years of age and older.

C4H5NOS

115.15

115.009

2682-20-4

Methylisothiazolinone hydrochloride;26172-54-3

33344

White to off-white solid powder

1.3±0.1 g/cm3

182.8±23.0 °C at 760 mmHg

254-256 °C(lit.)

64.3±22.6 °C

0.8±0.3 mmHg at 25°C

1.589

0.05

0

2

0

8

156

0

DHNRXBZYEKSXIM-UHFFFAOYSA-N

InChI=1S/C4H4ClNOS/c1-6-4(7)2-3(5)8-6/h2H,1H3

2-methyl-3(2H)-isothiazolone

MI N-Methylisothiazolin-3-oneMethylisothiazolinone free base KB-838

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL (~868.43 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (21.71 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (21.71 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (21.71 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)