Functional inhibitors of acid sphingomyelinase, or FIASMA, is a large group of pharmacological compounds inhibiting the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

acid sphingomyelinase (ASM, EC 3.1.4.12). This enzyme is mainly located within the

lysosome A lysosome () is a membrane-bound organelle that is found in all mammalian cells, with the exception of red blood cells (erythrocytes). There are normally hundreds of lysosomes in the cytosol, where they function as the cell’s degradation cent ...

, where it cleaves

sphingomyelin Sphingomyelin (SPH, ) is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds some nerve cell axons. It usually consists of phosphocholine and ceramide, or a phosphoethanolamine hea ...

ceramide Ceramides are a family of waxy lipid molecules. A ceramide is composed of sphingosine and a fatty acid joined by an amide bond. Ceramides are found in high concentrations within the cell membrane of Eukaryote, eukaryotic cells, since they are co ...

and sphingosine, the latter of which is then phosphorylated to sphingosine-1-phosphate. These metabolites, and subsequent inhibition of the enzyme, influence the balance between cell death (

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

) and cell growth (proliferation). A lack of regulation of this sensitive equilibrium can lead to serious clinical consequences. The acronym "FIASMA" was introduced by Kornhuber and coworkers; it is derived from the term ''Functional Inhibitor of Acid SphingoMyelinAse''.

Mechanism of action of FIASMAs

FIASMAs inhibit the ASM via an indirect, functional mechanism. They insert into the inner leaf of the lysosomal membrane and subsequently cause membrane-associated enzymes, such as ASM, to detach. Upon detachment from the membrane, these enzymes are cleaved and degraded within lysosomes. Inhibition of ASM by certain drugs has been known about for a long time, but systematic studies which characterize the pharmacological group of FIASMAs are relatively recent. ASM is not completely inhibited by FIASMAs and a low residual activity remains, allowing sufficient metabolism for cellular survival to occur. Application of FIASMAs therefore do not result in a clinical condition like Niemann-Pick disease, where ASM-activity is completely lacking because of genetic mutations. In contrast to FIASMAs, a screen of over 346,000 small molecules found only 20 that were direct inhibitors of acid sphingomyelinase. These 20 included

amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia, ventricular fibrillation, and wide complex tachycardia, atrial fibrillation, and paroxys ...

and etidronic acid.

Properties of FIASMAs

FIASMAs are structurally diverse, but have common physicochemical properties. All FIASMAs identified so far share a

basic Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...

nitrogen atom and

lipophilic Lipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly") is the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such compounds are c ...

part, which characterizes them as “cationic amphiphilic drugs”. Additionally, they also violate Lipinski's Rule of Five more often than non-FIASMAs. Still, they are highly bioavailable and reabsorbed by the gastrointestinal tract. In general, they also show high

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

permeability. Ceramide and sphingomyelin have clinical relevance: * In patients with

major depressive disorder Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive depression (mood), low mood, low self-esteem, and anhedonia, loss of interest or pleasure in normally ...

, elevated ASM activity has been observed. * In

cystic fibrosis Cystic fibrosis (CF) is a genetic disorder inherited in an autosomal recessive manner that impairs the normal clearance of Sputum, mucus from the lungs, which facilitates the colonization and infection of the lungs by bacteria, notably ''Staphy ...

, accumulation of ceramide can be lowered using FIASMAs such as

amitriptyline Amitriptyline, sold under the brand name Elavil among others, is a tricyclic antidepressant primarily used to treat major depressive disorder, and a variety of pain syndromes such as neuropathic pain, fibromyalgia, migraine and tension headac ...

Known drugs acting as FIASMAs

Cell culture-based experiments identified the listed compounds as FIASMAs (

antidepressants Antidepressants are a class of medications used to treat major depressive disorder, anxiety disorders, chronic pain, and addiction. Common side effects of antidepressants include dry mouth, weight gain, dizziness, headaches, akathisia, sexu ...

are in boldface). These experiments used the human cell line H4. The ASM activity was measured using a radiolabel assay. In case of absent experimental data a chemoinformatic prediction system has been proposed, which enables identification of FIASMAs based on molecular properties. {{columns-list, colwidth=18em, *

Alverine Alverine is a drug used for functional gastrointestinal disorders. Alverine is a smooth muscle relaxant. Smooth muscle is a type of muscle that is not under voluntary control; it is the muscle present in places such as the gut and uterus. Ad ...

Amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia, ventricular fibrillation, and wide complex tachycardia, atrial fibrillation, and paroxys ...

Amitriptyline Amitriptyline, sold under the brand name Elavil among others, is a tricyclic antidepressant primarily used to treat major depressive disorder, and a variety of pain syndromes such as neuropathic pain, fibromyalgia, migraine and tension headac ...

Amlodipine Amlodipine, sold under the brand name Norvasc among others, is a calcium channel blocker medication used to treat hypertension, high blood pressure, coronary artery disease (CAD) and variant angina (also called Prinzmetal angina or coronary ar ...

* Aprindine * Astemizole * AY-9944 *

Benzatropine Benzatropine ( INN), known as benztropine in the United States and Japan, is a medication used to treat movement disorders like parkinsonism and dystonia, as well as extrapyramidal side effects of antipsychotics, including akathisia. It is n ...

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* Biperiden * Camylofin *

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* Cepharanthine *

Chlorpromazine Chlorpromazine (CPZ), marketed under the brand names Thorazine and Largactil among others, is an antipsychotic medication. It is primarily used to treat psychotic disorders such as schizophrenia. Other uses include the treatment of bipolar d ...

Chlorprothixene Chlorprothixene, sold under the brand name Truxal among others, is a typical antipsychotic of the thioxanthene group. Medical uses Chlorprothixene's principal indications are the treatment of psychotic disorders (e.g. schizophrenia) and of acut ...

* Cinnarizine * Clemastine *

Clofazimine Clofazimine, sold under the brand name Lamprene, is a medication used together with rifampicin and dapsone to treat leprosy. It is specifically used for multibacillary (MB) leprosy and erythema nodosum leprosum, and its discovery greatly impro ...

Clomiphene Clomifene, also known as clomiphene, is a medication used to treat infertility in women who anovulation, do not ovulate, including those with polycystic ovary syndrome. It is taken by mouth. Common side effects include pelvic pain and hot f ...

Clomipramine Clomipramine, sold under the brand name Anafranil among others, is a tricyclic antidepressant (TCA). It is used in the treatment of various conditions, most notably obsessive–compulsive disorder but also many other disorders, including hyper ...

* Cloperastine * Conessine *

Cyclobenzaprine Cyclobenzaprine, sold under several brand names including, historically, Flexeril, is a muscle relaxer used for muscle spasms from musculoskeletal conditions of sudden onset. It is not useful in cerebral palsy. It is taken by mouth. Common ...

Cyproheptadine Cyproheptadine, sold under the brand name Periactin among others, is a first-generation antihistamine, first-generation antihistamine with additional anticholinergic, antiserotonergic, and local anesthetic properties. It was patented in 1959 a ...

* Desipramine *

Desloratadine Desloratadine sold under the brand name Aerius among others, is a tricyclic H1 antagonist, H1 inverse agonist that is used to treat allergy, allergies. It is an active metabolite of loratadine. It was patented in 1984 and came into medical u ...

Dicycloverine Dicycloverine, also known as dicyclomine, sold under the brand name Bentyl among others, is a medication that is used to treat spasms of the intestines such as those that occur in irritable bowel syndrome (IBS). It is taken by mouth or by injec ...

Dicyclomine Dicycloverine, also known as dicyclomine, sold under the brand name Bentyl among others, is a medication that is used to treat spasms of the intestines such as those that occur in irritable bowel syndrome (IBS). It is taken by mouth or by inje ...

* Dilazep * Dimebon * Doxepin * Drofenine * Emetine * Fendiline * Flunarizine *

Fluoxetine Fluoxetine, sold under the brand name Prozac, among others, is an Antidepressant, antidepressant medication of the selective serotonin reuptake inhibitor (SSRI) class used for the treatment of major depressive disorder, Anxiety disorder, anx ...

* Flupentixol * Fluphenazine *

Fluvoxamine Fluvoxamine, sold under the brand name Luvox among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is primarily used to treat major depressive disorder and, perhaps more-especially, obsessive–compu ...

* Hydroxyzine *

Imipramine Imipramine, sold under the brand name Tofranil, among others, is a tricyclic antidepressant (TCA) mainly used in the treatment of depression. It is also effective in treating anxiety and panic disorder. Imipramine is taken by mouth. Common s ...

* Lofepramine * Loperamid * Loratadin * Maprotiline * Mebeverine * Mebhydrolin *

Mepacrine Mepacrine, also called quinacrine or by the trade names Atabrine or Atebrin, is a medication with several uses. It is related to chloroquine and mefloquine. Although available from compounding pharmacies, as of August 2020 approved formulations ...

* Mibefradil * Norfluoxetine * Nortriptyline *

Paroxetine Paroxetine ( ), sold under the brand name Paxil among others, is an Antidepressant, antidepressant medication of the selective serotonin reuptake inhibitor (SSRI) class used to treat major depressive disorder, obsessive-compulsive disorder, o ...

Penfluridol Penfluridol (Semap, Micefal, Longoperidol) is a highly potent, first generation diphenylbutylpiperidine antipsychotic. It was discovered at Janssen Pharmaceutica in 1968. Related to other diphenylbutylpiperidine antipsychotics, pimozide and flusp ...

* Perhexiline * Perphenazine * Pimethixene *

Pimozide Pimozide (sold under the brand name Orap) is a neuroleptic medication, drug of the diphenylbutylpiperidine class. It was discovered at Janssen Pharmaceutica in 1963. It has a high potency compared to chlorpromazine (ratio 50-70:1). On a weigh ...

* Profenamine * Promazine *

Promethazine Promethazine, sold under the brand name Phenergan among others, is a first-generation antihistamine, sedative, and antiemetic used to treat allergies, insomnia, and nausea. It may also help with some symptoms associated with the common cold a ...

* Protriptyline * Sertindole *

Sertraline Sertraline, sold under the brand name Zoloft among others, is an Antidepressant, antidepressant medication of the selective serotonin reuptake inhibitor (SSRI) class used to treat major depressive disorder, generalized anxiety disorder, socia ...

* Solasodine * Suloctidil *

Tamoxifen Tamoxifen, sold under the brand name Nolvadex among others, is a selective estrogen receptor modulator used to prevent breast cancer in women and men. It is also being studied for other types of cancer. It has been used for Albright syndrome ...

Terfenadine Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was brought to market by Hoechst Marion Roussel (now Sanofi) and was marketed under various brand names, including Seldane in the United States, Triluda ...

Thioridazine Thioridazine (Mellaril or Melleril) is a first generation antipsychotic drug belonging to the phenothiazine drug group and was previously widely used in the treatment of schizophrenia and psychosis. The branded product was withdrawn worldwid ...

* Tomatidine * Trifluoperazin * Triflupromazine * Trimipramine * Zolantidine

References

Enzyme inhibitors