Cysteamine is anorganosulfur compound with the formulaHSCH2CH2NH2. A white, water-soluble solid, it contains both anamine and athiol functional groups. It is often used as salts of the ammonium derivative [HSCH2CH2NH3]+[12] including thehydrochloride, phosphocysteamine, and thebitartrate.[13]The intermediatepantetheine is broken down into cysteamine andpantothenic acid.[13]
It is biosynthesized in mammals, including humans, by the degradation ofcoenzyme A. It is the biosynthetic precursor to the neurotransmitterhypotaurine.[14][13]
When applied topically it canlighten skin that's been darkened as a result of post-inflammatory hyperpigmentation, sun exposure and melasma.[18][19][20][21] Tentative evidence suggests that it may be a more effectivedepigmentation agent thanhydroquinone,retinoids and topicalcorticosteroids in individuals with chronic skin discoloration.[22][23][24] Topical application of cysteamine cream has also demonstrated similar efficacy tointradermaltranexamic acid injections for the treatment of Melasma but with much fewer adverse effects.[25]
The label for oral formulations of cysteamine carry warnings about symptoms similar toEhlers-Danlos syndrome, severe skin rashes, ulcers or bleeding in the stomach and intestines, central nervous symptoms including seizures, lethargy, somnolence, depression, and encephalopathy,low white blood cell levels,elevated alkaline phosphatase, andidiopathic intracranial hypertension that can cause headache, tinnitus, dizziness, nausea, double or blurry vision, loss of vision, and pain behind the eye or pain with eye movement.[8]
Additional adverse effects of oral cysteamine include bad breath, skin odor, vomiting, nausea, stomach pain, diarrhea, and loss of appetite.[8]
The risks of cysteamine to a fetus are not known but it harms babies in animal models at doses less than those given to people.[6][7]
For eye drops, the most common adverse effects are sensitivity to light, redness, and eye pain, headache, and visual field defects.[7]
There are no drug interactions for normal capsules or eye drops,[6][7] but the extended release capsules should not be taken with drugs that affect stomach acid likeproton pump inhibitors or with alcohol, as they can cause the drug to be released too quickly.[8] It does not inhibit anycytochrome P450 enzymes.[8]
People withcystinosis lack a functioning transporter (cystinosin) which transports cystine from the lysosome to the cytosol. This ultimately leads to buildup ofcystine in lysosomes, where it crystallizes and damages cells.[16] Cysteamine enters lysosomes and converts cystine intocysteine and cysteine-cysteamine mixed disulfide, both of which can exit the lysosome.[8]
Cysteamine also promotes the transport of L-cysteine into cells.[13]
The therapeutic effect of cysteamine on cystinosis was reported in the 1950s. Cysteamine was approved as a drug for cystinosis in the US in 1994.[8] An extended release form was approved in 2013.[26]
In 2013, the regular capsule of cysteamine cost about $8,000 per year; the extended release form that was introduced that year was priced at $250,000 per year.[26]
It was studied inin vitro and animal models forradiation protection in the 1950s, and in similar models from the 1970s onwards forsickle cell anemia, effects on growth, its ability to modulate the immune system, and as a possible inhibitor of HIV.[13]
^Reid EE (1958).Organic Chemistry of Bivalent Sulfur. Vol. 1. New York: Chemical Publishing Company, Inc. pp. 398–399.
^abcdefghiBesouw M, Masereeuw R, van den Heuvel L, Levtchenko E (August 2013). "Cysteamine: an old drug with new potential".Drug Discovery Today.18 (15–16):785–792.doi:10.1016/j.drudis.2013.02.003.PMID23416144.
^Gahl WA, Thoene JG, Schneider JA (July 2002). "Cystinosis".The New England Journal of Medicine.347 (2):111–121.doi:10.1056/NEJMra020552.PMID12110740.
^abcNesterova G, Gahl WA (6 October 2016)."Cystinosis". In Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJ, Stephens K, Amemiya A (eds.).GeneReviews. Seattle WA: University of Washington.PMID20301574.Archived from the original on 5 April 2011. Retrieved11 January 2017.
^Mansouri P, Farshi S, Hashemi Z, Kasraee B (July 2015). "Evaluation of the efficacy of cysteamine 5% cream in the treatment of epidermal melasma: a randomized double-blind placebo-controlled trial".The British Journal of Dermatology.173 (1):209–217.doi:10.1111/bjd.13424.PMID25251767.S2CID21618233.
^Mathe N, Balogun M, Yoo J (January 2021). "A case report on the use of topical cysteamine 5% cream in the management of refractory postinflammatory hyperpigmentation (PIH) resistant to triple combination cream (hydroquinone, topical corticosteroids, and retinoids)".Journal of Cosmetic Dermatology.20 (1):204–206.doi:10.1111/jocd.13755.PMID32997864.S2CID222163129.
^Kasraee B, Mansouri P, Farshi S (February 2019). "Significant therapeutic response to cysteamine cream in a melasma patient resistant to Kligman's formula".Journal of Cosmetic Dermatology.18 (1):293–295.doi:10.1111/jocd.12837.PMID30537063.S2CID54481706.
^abKarrabi M, David J, Sahebkar M (January 2021). "Clinical evaluation of efficacy, safety and tolerability of cysteamine 5% cream in comparison with modified Kligman's formula in subjects with epidermal melasma: A randomized, double-blind clinical trial study".Skin Research and Technology.27 (1):24–31.doi:10.1111/srt.12901.PMID32585079.S2CID220078010.
