Pathways

The sulfur metabolism pathway starts in three possible ways. The first is the uptake of sulfate through an active transport reaction via a sulfate transport system containing an ATP-binding protein which hydrolyses ATP. Sulfate is converted by the sulfate adenylyltransferase enzymatic complex to adenosine phosphosulfate through the addition of adenine from a molecule of ATP, along with one phosphate group. Adenosine phosphosulfate is further converted to phoaphoadenosine phosphosulfate through an ATP hydrolysis and dehydrogenation reaction by the adenylyl-sulfate kinase. Phoaphoadenosine phosphosulfate is finally dehydrogenated and converted to sulfite by phosphoadenosine phosphosulfate reductase. This reaction requires magnesium, and adenosine 3',5'-diphosphate is the bi-product. A thioredoxin is also oxidized. Sulfite can also be produced from the dehydrogenation of cyanide along with the conversion of thiosulfate to thiocyanate by the thiosulfate sulfurtransferase enzymatic complex. Sulfite next undergoes a series of reactions that lead to the production of pyruvic acid, which is a precursor for pathways such as gluconeogenesis. The first reaction in this series is the conversion of sulfite to hydrogen sulfide through hygrogenation and the deoxygenation of sulfite to form a water molecule. The reaction is catalyzed by the sulfite reductase [NADPH] flavoprotein alpha and beta components. Siroheme, 4Fe-4S, flavin mononucleotide, and FAD function as cofactors or prosthetic groups. Hydrogen sulfide next undergoes dehydrogenation in a reversible reaction to form L-Cysteine and acetic acid, via the cysteine synthase complex and the coenzyme pyridoxal 5'-phosphate. L-Cysteine is dehydrogenated and converted to 2-aminoacrylic acid (a bronsted acid) and hydrogen sulfide(which may be reused) by a larger enzymatic complex composed of cysteine synthase A/B, protein malY, cystathionine-β-lyase, and tryptophanase, along with the coenzyme pyridoxal 5'-phosphate. 2-aminoacrylic acid isomerizes to 2-iminopropanoate, which along with a water molecule and a hydrogen ion is lastly converted to pyruvic acid and ammonium in a spontaneous fashion. The second possible initial starting point for sulfur metabolism is the import of taurine(an alternate sulfur source) into the cytoplasm via the taurine ABC transporter complex. Taurine, oxoglutaric acid, and oxygen are converted to sulfite by the alpha-ketoglutarate-dependent taurine dioxygenase. Carbon dioxide, succinic acid, and aminoacetaldehyde are bi-products of this reaction. Sulfite next enters pyruvic acid synthesis as already described. The third variant of sulfur metabolism starts with the import of an alkyl sulfate, in this case 1-butanesulfonate, into the cytoplasm via an aliphatic sulfonate ABC transporter complex which hydrolyses ATP. 1-butanesulfonate is dehydrogenated and along with oxygen is converted to sulfite and betaine aldehyde by the FMNH2-dependent alkanesulfonate monooxygenase enzyme. Water and flavin mononucleotide(which is used in a subsequent reaction as a prosthetic group) are also produced. Sulfite is next converted to pyruvic acid by the process already described.

Sulindac, sold as Clinoril, is a non-steroidal anti-inflammatory drug (NSAID). These drugs are typically used to treat conditions associated with pain and inflammation, such as rheumatoid arthritis, headaches or migraines, and dysmenorrhoea. Sulindac is believed to be a non-selective NSAID, meaning that it inhibits both prostaglandin G/H synthase 1 and 2 (COX-1 and COX-2). In this pathway, sulindac, a prodrug, is administered orally. Once in the body, it is metabolized to form the active form of sulindac, which then inhibits the COX-1 and COX-2 enzymes. These enzymes are normally responsible for the formation of prostaglandin G2 from arachidonic acid, well as the formation of prostaglandin H2 from prostaglandin G2. These prostaglandins are responsible for inflammation and fever, as well as muscle contractions in labour and menstruation. With the COX-1 and COX-2 enzymes being inhibited by sulindac, prostaglandins cannot be produced, and inflammation and fever can be reduced. Compared to other NSAIDs, sulindac is less likely to damage the kidneys and cause gastrointestinal effects such as ulcers, but is more likely to damage the liver and pancreas.

Sulindac is a nonsteroidal anti-inflammatory drug (NSAID) used to treat ankylosing spondylitis (AS), colorectal adenomas, gouty arthritis, osteoarthritis (OA), and rheumatoid arthritis, among others. This drug possesses analgesic and antipyretic activities. This drug is a prodrug, its active metabolite is the sulfide form of the molecule. It acts by binding as an inhibitor to the prostaglandin G/H synthase 2. This results in the inhibition of the cyclooxygenase pathway. The cyclooxygenase pathway begins in the cytosol with phospholipids being converted into arachidonic acid by the action of phospholipase A2. The rest of the pathway occurs on the endoplasmic reticulum membrane, where prostaglandin G/H synthase 1 & 2 convert arachidonic acid into prostaglandin H2. Prostaglandin H2 can either be converted into thromboxane A2 via thromboxane A synthase, prostacyclin/prostaglandin I2 via prostacyclin synthase, or prostaglandin E2 via prostaglandin E synthase. COX-2 is an inducible enzyme, and during inflammation, it is responsible for prostaglandin synthesis. It leads to the formation of prostaglandin E2 which is responsible for contributing to the inflammatory response by activating immune cells and for increasing pain sensation by acting on pain fibers. Sulindac (its sulfide metabolite) inhibits the action of COX-1 and COX-2 on the endoplasmic reticulum membrane. This reduces the formation of prostaglandin H2 and therefore, prostaglandin E2 (PGE2). The low concentration of prostaglandin E2 attenuates the effect it has on stimulating immune cells and pain fibers, consequently reducing inflammation and pain. This drug is administered as an oral tablet.

Metabolites of Sulindac are predicted with biotransformer.

Sulodexide mixture of glycosaminoglycans (GAGs), dermatan sulfate (DS) and fast-moving heparin. Its mechanism of action inhibits coagulation by inhibiting antithrombin III thus stopping the conversion of prothrombin and thrombin. Doing that also inhibits the conversion of fibrinogen to fibrin halting the clotting factor. Sulodexide is administered via oral, intravenous or intramuscular, it is mainly metabolized by the liver. It is eliminated through renal, fecal and bile routes, and sometimes adverse effects occur that relate to the gastrointestinal system. Some other adverse reaction to sulodexide despite being fairly well tolerated includes diarrhea, epigastralgia, dyspepsia, heartburn and dizziness. Some allergic reactions can cause skin rash but these occurrences are rare.

Sulpiride is a substituted benzamide derivative and a selective dopamine D2 antagonist indicated to treat acute and chronic schizophrenia. Sulpiride is a selective dopamine D2 and D3 receptor antagonist.