Browsing Pathways

Quetiapine is a tricyclic H1-antihistamine. H1-antihistamines interfere with the agonist action of histamine at the H1 receptor and are administered to attenuate inflammatory process in order to treat conditions such as allergic rhinitis, allergic conjunctivitis, and urticaria. Reducing the activity of the NF-κB immune response transcription factor through the phospholipase C and the phosphatidylinositol (PIP2) signalling pathways also decreases antigen presentation and the expression of pro-inflammatory cytokines, cell adhesion molecules, and chemotactic factors. Furthermore, lowering calcium ion concentration leads to increased mast cell stability which reduces further histamine release. First-generation antihistamines readily cross the blood-brain barrier and cause sedation and other adverse central nervous system (CNS) effects (e.g. nervousness and insomnia). Second-generation antihistamines are more selective for H1-receptors of the peripheral nervous system (PNS) and do not cross the blood-brain barrier. Consequently, these newer drugs elicit fewer adverse drug reactions.

Phenindamine is a first-generation tricyclic H1-antihistamine. H1-antihistamines interfere with the agonist action of histamine at the H1 receptor and are administered to attenuate inflammatory process in order to treat conditions such as allergic rhinitis, allergic conjunctivitis, and urticaria. Reducing the activity of the NF-κB immune response transcription factor through the phospholipase C and the phosphatidylinositol (PIP2) signalling pathways also decreases antigen presentation and the expression of pro-inflammatory cytokines, cell adhesion molecules, and chemotactic factors. Furthermore, lowering calcium ion concentration leads to increased mast cell stability which reduces further histamine release. First-generation antihistamines readily cross the blood-brain barrier and cause sedation and other adverse central nervous system (CNS) effects (e.g. nervousness and insomnia). Second-generation antihistamines are more selective for H1-receptors of the peripheral nervous system (PNS) and do not cross the blood-brain barrier. Consequently, these newer drugs elicit fewer adverse drug reactions.

Repaglinide is a non-sulfonylurea insulin secretagogue used in the treatment of type 2 diabetes. As the name of the drug class suggests, repaglinide acts on pancreatic beta-cells to stimulate insulin secretion. Under physiological conditions, insulin secretion from beta-cells is mediated by elevated glucose concentration in the blood. Glucose enters the cell via GLUT2 (SLC2A2) transporters. Once inside the cell, glucose is metabolized to produce ATP. High concentration of ATP will inhibit ATP-dependent potassium channels (ABCC8), which depolarizes the cell. Depolarization causes opening of voltage-gated calcium channels, allowing calcium to enter cell. High intracellular calcium subsequently stimulate vesicle exocytosis and insulin secretion. Repaglinide stimulate insulin secretion in a glucose-sensitive manner by inhibiting ATP-dependent potassium channels. As a result, there tends to be a lesser likelihood of hypoglycemia with repaglinide therapy compared to sulfonylureas.

5-Oxoprolinase deficiency, also called OPLAHD, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of glutathione metabolism caused by a defective 5-oxoprolinase. 5-Oxoprolinase catalyzes the conversion of 5-oxoproline into glutamate which is an important neurotransmitter. This disorder is characterized by a large accumulation of 5-oxoproline in the urine. Symptoms of the disorder include enterocolitis, mental retardation, kidney stone formation, and hypoglycemia. 5-Oxoprolinase deficiency has been reported in approximately 8 people.

Sulfite oxidase deficiency (SOD) is a disorder, an autosomal recessive disease. In classic SOD, it is usually identified a few days after the birth of an affected individual, and is recognizable through characteristic dysmorphic features, seizures, and other signs of progressive encephalopathy. Patients also have ocular lenses that are dislocated, and usually die within a few months of being born. In late- onset SOD, the disorder is identified only in the later months, usually 6-18 months, of the child’s life by a delay or regression of neurological progress. This disorder is very rare, but the actual prevalence is not known. It can be diagnosed through a sulfite test strip in urine or by a skin fibroblast culture, which will indicate an absence of sulfite oxidase.

Thioguanine is a purine antimetabolite prodrug closely related to mercaptopurine and similarly inhibits purine metabolism. The thioguanine pathway is shown as a part of the mercaptopurine pathway. Thioguanine exerts cytotoxic effects via incorporation of thiodeoxyguanosine triphosphate into DNA and thioguanosine triphosphate into RNA and inhibition of Ras-related C3 botulinum toxin substrate 1, which induces apoptosis of activated T cells. Once in a cell, thioguanine is converted to thioguanosine monophosphate by hypoxanthine-guanine phosphoribosyltransferase. Thioguanosine monophosphate is then phosphorylated to thioguanosine diphosphate, which is converted via a thiodeoxyguanosine diphosphate intermediate to thiodeoxyguanosine triphosphate. Thiodeoxyguanosine triphosphate is incorporated into DNA causing cytotoxicity. Thioguanosine diphosphate is also converted to thioguanosine triphosphate which is incorporated into RNA. The thioguanosine triphosphate metabolite also inhibits Ras-related C3 botulinum toxin substrate 1, a plasma membrane-associated small GTPase that regulates cellular processes, inducing apoptosis in activated T cells.

Mycophenolic Acid (MPA) is an immunosuppressive agent that acts as a noncompetitive, selective and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH). It is available as a prodrug, Mycophenolate mofetil (MMF), which is a 2-morpholinoethyl ester with improved bioavailability. After absorption, MMF is hydrolyzed to MPA and N-(2-carboxymethyl)- morpholine, N-(2-hydroxyethyl)-morpholine, and the N-oxide of N-(2-hydroxyethyl)-morpholine by the carboxylesterases CES-1 (in the liver only) and CES-2 (in the liver and intestine). The morpholine metabolites are excreted in the urine. MPA is glucuronidated by UDP glucuronosyl transferases (UGTs) UGT1A7, UGT1A8, UGT1A9 and UGT1A10 to MPA-7-O-glucuronide, which is excreted in the urine. Other metabolites of MPA include MPA-acyl glucoronide, which is formed by UGT2B7, and 6-O-desmethyl-MPA, which is formed by the CYP enzymes CYP3A4, CYP3A5 and CYP2C8. MPA enters hepatocytes by the organic anion transport proteins (OATPs) SLCO1B1 and SLCO1B3. MPA and its metabolites are excreted in the bile via the ABCC2, ABCG2, and ABCB1 proteins.

Gamma-cystathionase deficiency, also called cystathionase deficiency, is an autosomal recessive metabolic disorder caused by a defective cystathionine gamma-lyase. Cystathionine gamma-lyase catalyzes the conversion of L-Serine and homocysteine into L-Cystathionine which is the substrate of cystathionine gamma-lyase. This disorder is characterized by a large accumulation of L-Cystathionine in the cell. Symptoms of the disorder include mental deficiency and seizure. Since there is currently no cure forGamma-cystathionase deficiency, treatment involves managing the disorder's symptoms.

Citrullinemia Type 1, also called argininosuccinate synthetase deficiency, argininosuccinic acid synthetase deficiency or ASS deficiency, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of the urea cycle caused by a deficiency of argininosuccinate synthetase. Argininosuccinate synthetase is an important enzyme in the process of removing nitrogen from the body. This disorder is characterized by a large accumulation of ammonia in the blood as well as other bodily fluids . Symptoms of the disorder include vomiting, lethargy and intracranial pressure. Treatment with protein restriction and intravenous administration of arginine can help manage symptoms, and diet management throughout the patient’s life can also show improvement. It is estimated that citrullinemia type 1 affects 1 in 57,000 individuals.

Pyruvate carboxylase deficiency is caused by mutation in the pyruvate carboxylase gene. Serine—pyruvate aminotransferase catalyzes the reaction of serine and pyruvate to produce 3-hydroxypyruvate and L-alanine, as well as the reaction from L-alanine and glyodxylate to pyruvate and glycine. A defect in this results in accumulation of ammonia, glucose and pyruvate in blood; proline, lysine, citrulline, and alanine in plasma; and 2-oxoglutaric acid, fumaric acid, ketone bodies and succinate in urine. Symptoms include ataxia, lactic acidosis, mental retardation, metabolic acidosis, siezures, and dyspnea.