Cysteamine is an

organosulfur Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

compound with the formula . A white, water-soluble solid, it contains both an

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

and a

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

functional group. It is often used as the

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

of the ammonium derivative SCH₂CH₂NH₃sup>+, including the

hydrochloride In chemistry, a hydrochloride is an acid salt resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (e.g. an amine). An alternative name is chlorhydrate, which comes from French. An archaic alternati ...

, phosphocysteamine, and the

bitartrate , Section2 = {{Chembox Properties , C=4 , H=5 , O=6 , Formula_Charge = − , ConjugateAcid = Tartaric acid , ConjugateBase = Tartrate Bitartrate is an anion which is the conjugate base of tartaric acid. It may also refer to any salt ...

. The intermediate

pantetheine Pantetheine is the cysteamine amide analog of pantothenic acid (vitamin B5). The dimer of this compound, pantethine is more commonly known, and is considered to be the most potent form of vitamin B5. Pantetheine is an intermediate in the catabol ...

is broken down into cysteamine and

pantothenic acid Pantothenic acid (vitamin B5) is a B vitamin and an essential nutrient. All animals need pantothenic acid in order to synthesize coenzyme A (CoA), which is essential for cellular energy production and for the synthesis and degradation of prote ...

. It is biosynthesized in mammals, including humans, by the degradation of

coenzyme A Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the Fatty acid metabolism#Synthesis, synthesis and Fatty acid metabolism#.CE.B2-Oxidation, oxidation of fatty acids, and the oxidation of pyruvic acid, pyruvate in the citric ac ...

. It is the biosynthetic precursor to the

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

hypotaurine Hypotaurine is a sulfinic acid that is an intermediate in the biosynthesis of taurine. Like taurine, it also acts as an endogenous neurotransmitter via action on the glycine receptors. It is an osmolyte with antioxidant properties. Hypotaurine ...

Medical uses

As a medication sold under the brand names ''Procysbi'' or ''Cystagon'', among others, cysteamine is indicated to treat

cystinosis Cystinosis is a lysosomal storage disease characterized by the abnormal accumulation of cystine, the oxidized dimer of the amino acid cysteine. It is a genetic disorder that follows an autosomal recessive inheritance pattern. It is a rare autosom ...

, a

lysosomal storage disease Lysosomal storage diseases (LSDs; ) are a group of over 70 rare inherited metabolic disorders that result from defects in lysosomal function. Lysosomes are sacs of enzymes within cells that digest large molecules and pass the fragments on to other ...

characterized by the abnormal accumulation of

cystine Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH2CH(NH2)CO2H)2. It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mec ...

, the oxidized dimer of the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

. It removes the excessive cystine that builds up in cells of people with the disease. It is available by mouth (capsule and extended release capsule) and in

eye drop Eye drops or eyedrops are liquid drops applied directly to the surface of the eye usually in small amounts such as a single drop or a few drops. Eye drops usually contain saline to match the salinity of the eye. Drops containing only saline ...

s. When applied topically, it can lighten skin darkened by post-inflammatory

hyperpigmentation Hyperpigmentation, also known as the dark spots or circles on the skin, is the darkening of an area of Human skin, skin or nail (anatomy), nails caused by increased melanin. Causes Hyperpigmentation can be caused by sun damage, inflammation, or ...

, sun exposure or

melasma Melasma (also known as chloasma faciei,James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. . or the mask of pregnancy when present in pregnant women) is a tan or dar ...

Adverse effects

The label for oral formulations of cysteamine carry warnings about symptoms similar to Ehlers-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 Elevated alkaline phosphatase occurs when levels of alkaline phosphatase (ALP) exceed the reference range. This group of enzymes has a low substrate specificity and catalyzes the hydrolysis of phosphate esters in a basic environment. The major fun ...

, and

idiopathic intracranial hypertension Idiopathic intracranial hypertension (IIH), previously known as pseudotumor cerebri and benign intracranial hypertension, is a condition characterized by increased intracranial pressure (pressure around the brain) without a detectable cause. The m ...

that can cause headache, tinnitus, dizziness, nausea, double or blurry vision, loss of vision, and pain behind the eye or pain with eye movement. Additional adverse effects of oral cysteamine include bad breath, skin odor, vomiting, nausea, stomach pain, diarrhea, and loss of appetite. For eye drops, the most common adverse effects are sensitivity to light, redness, and eye pain, headache, and visual field defects.

Interactions

There are no drug interactions for normal capsules or eye drops, but the extended release capsules should not be taken with drugs that affect stomach acid like

proton pump inhibitors Proton-pump inhibitors (PPIs) are a class of medications that cause a profound and prolonged reduction of gastric acid, stomach acid production. They do so by irreversibly inhibiting the stomach's H+/K+ ATPase, H+/K+ ATPase proton pump. The body ...

or with alcohol, as they can cause the drug to be released too quickly. It does not inhibit any

cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...

enzymes.

Pharmacology

People with

lack a functioning transporter (cystinosin) which transports cystine from the lysosome to the cytosol. This ultimately leads to the buildup of

in lysosomes, where it crystallizes and damages cells. Cysteamine enters lysosomes and converts cystine into

and cysteine-cysteamine mixed disulfide, both of which can exit the lysosome. Cysteamine also promotes the transport of L-cysteine into cells.

History

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. An extended release form was approved in 2013.

References

{{Authority control Amines Ophthalmology drugs Orphan drugs Thiols