Pathways

Tolpropamine is an alkylamine 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.

Tolterodine is a muscarinic receptor antagonist used to treat overactive bladder with urinary incontinence, urgency, and frequency. It can be found under the brand names Detrol and Detrusitol. Tolterodine is a competitive muscarinic receptor antagonist. Both urinary bladder contraction and salivation are mediated via cholinergic muscarinic receptors. After oral administration, tolterodine is metabolized in the liver, resulting in the formation of the 5-hydroxymethyl derivative, a major pharmacologically active metabolite. The 5-hydroxymethyl metabolite, which exhibits an antimuscarinic activity similar to that of tolterodine, contributes significantly to the therapeutic effect. Both tolterodine and the 5-hydroxymethyl metabolite exhibit a high specificity for muscarinic receptors, since both show negligible activity or affinity for other neurotransmitter receptors and other potential cellular targets, such as calcium channels. Tolterodine has a pronounced effect on bladder function. The main effects of tolterodine are an increase in residual urine, reflecting an incomplete emptying of the bladder, and a decrease in detrusor pressure, consistent with an antimuscarinic action on the lower urinary tract. Tolterodine is an antimuscarinic medication that selectively and competitively binds to muscarinic M3 receptors in the bladder, thereby decreasing bladder contraction by decreasing detrusor muscle tone and increasing internal urethral sphincter tone. Possible side effects of using tolterodine may include dry mouth, headache, vertigo, and vomiting. Tolterodine can be administered as an oral capsule or tablet.

Toluene degradation allows bacteria to use toluene, a common environmental pollutant, as both a carbon and energy source. Toluene enters the bacterial cell by passive diffusion due to its hydrophobic nature. Once within the cell, toluene undergoes a variety of enzymatic reactions. The first step is for the Gamma-Subunit of benzylsuccinate synthase to convert it into benzylsuccinate. This intermediate is then converted to Benzylsuccinyl-CoA by subunit of Benzylsuccinate CoA-transferases. Subsequently, Benzylsuccinyl-CoA undergoes a series of enzymatic reactions to form Benzoylsuccinyl-CoA, and finally benzoyl-CoA, which enters the benzoate degradation pathway, providing the bacteria with energy and carbon for growth and survival.

Metabolites of Tolvaptan are predicted with biotransformer.

Topiramate is an anticonvulsant drug used in the control of epilepsy and in the prophylaxis and treatment of migraines. Topiramate is indicated for the following conditions: 1)Monotherapy for partial onset or primary generalized tonic-clonic seizures for patients 2 years of age and above 2)Adjunctive therapy for partial onset seizures or primary generalized tonic-clonic seizures for both adult and pediatric patients above 2 years old 3)Adjunctive therapy for seizures associated with Lennox-Gastaut syndrome in patients above 2 years of age 4)Prophylaxis of migraine in children 12 years of age and older and adults. Topiramate is also used off-label as an adjunct therapy for weight management21 and for mood disorders. A seizure is an abnormal and unregulated electrical discharge occurring in the brain. This leads to transient interruption in brain function, manifested by reduced alertness, abnormal sensations, and focal involuntary movements or convulsions. Topiramate inhibits excitatory neurotransmitter activity by antagonizing AMPA and kainate glutamate receptors on the post synaptic membrane. These receptors are ligand gated ion channels, once bound to glutamate, the allow the influx of sodium ions into the post-synaptic neuron leading to depolarization and neuronal excitation. By antagonizing these glutamate receptors, topiramate prevents depolarization of the post-synaptic receptors. Topiramate may also prevent glutamate release from pre-synaptic neurons. This occurs by topiramate inhibiting voltage gated sodium channels in the presynaptic neuron, these sodium channels are responsible for allow sodium ion influx into the presynaptic neuron and depolarization. Depolarization leads to the opening of L-type voltage gated calcium channels at the neuronal terminal. This leads to the influx of calcium ions which stimulate the release of glutmate via exocytosis. By inhibiting the voltage gates sodium channels, depolarization in the presynaptic neurons is prevented, thus preventing calcium channel activation, calcium influx and glutamate release. Topiramate may also enhance the activity of GABA-A receptors on post synaptic neurons. GABA-A receptors, when activated, lead to the influx of negative chloride ions causing hyperpolarization and neuronal inhibition. Topiramate is a weak inhibitor of carbonic anhydrase; acidosis in the brain has partial protection against seizures by downregulating NMDA receptor activity. NMDA receptor are excitatory since they are ion channels that cause the influx of calcium ions into the neuron. By downregulating NMDA receptors, excitatory activity is reduced. Overall, topiramate functions are to reduce excitatory activity in neurons and enhance inhibitory activity. Most common adverse effects in epilepsy trials included the involvement of the central nervous system (paresthesia, fatigue, cognitive problems, dizziness, somnolence, psychomotor slowing, memory/concentration difficulties, nervousness, confusion), endocrine/metabolism (weight loss, anorexia), respiratory (infection), miscellaneous (fever, flushing).

Metabolites of Topiramate are predicted with biotransformer.

Topotecan, also known as Hycamtin, is an antineoplastic agent used to treat ovarian cancer, small cell lung cancer, or cervical cancer. It is a semi-synthetic derivative of camptothecin (obtained from the plant Camptotheca acuminata). This molecule is an anti-tumor drug with topoisomerase I-inhibitory activity. DNA topoisomerases are enzymes in the cell nucleus that regulate DNA topology (3-dimensional conformation) and DNA repairs. During these processes, DNA topoisomerase I creates reversible single-stranded breaks in DNA, allowing intact single DNA strands to pass through the break and relieve the topologic constraints. After DNA is sufficiently relaxed and the strand passage reaction is complete, DNA topoisomerase reattaches the broken DNA strands to form the unaltered topoisomers. Topotecan is believed to exert its cytotoxic effects during the S-phase of the cell cycle replication. Topotecan binds to the topoisomerase I-DNA complex and prevents the religation of the single strand breaks and of any breaks in the DNA. This ternary complex interferes with the moving replication fork, which leads to the induction of replication arrest. In consequence, this causes lethal double-stranded breaks in the DNA. The formation of this ternary complex eventually leads to apoptosis. Moreover, topotecan mimics a DNA base pair and binds at the site of DNA cleavage. Intercalation displaces the downstream DNA, thus preventing the religation of the cleaved strand.