Pathways

Angiotensin-converting enzyme (EC 3.4.15.1), or ACE, is a central component of the renin–angiotensin system (RAS), which controls blood pressure by regulating the volume of fluids in the body. It converts the hormone angiotensin I to the active vasoconstrictor angiotensin II. Therefore, ACE indirectly increases blood pressure by causing blood vessels to constrict. ACE inhibitors are widely used as pharmaceutical drugs for treatment of cardiovascular diseases. Other lesser known functions of ACE are degradation of bradykinin, substance P, and amyloid beta-protein. Angiotensin converting enzyme (ACE) is well known for its dual actions in converting inactive Ang I to active Ang II and degrade active bradykinin (BK), which play an important role in the control of blood pressure. Since the bottle neck step is the production of pressor Ang II, this was targeted pharmacologically in 1970s and successful ACE inhibitors such as captopril were produced to treat hypertension. ACE2 was identified as the receptor for SARS (severe acute respiratory syndrome) coronavirus, which caused the outbreak of an epidemic in 2002–2003. Two isozymes of ACE are present in mammals: somatic ACE and testis ACE. Somatic ACE possesses two catalytic domains (N- and C-domains) and a C-terminal transmembrane segment (stalk). Somatic and testis ACEs in humans contain 1,306 and 665 aa residues, respectively. Testis ACE only possesses one catalytic domain. Both catalytic domains are zinc-metallopeptidase with the active motif HEMGH where the two histidine residues coordinate the zinc ion. The stalk anchors the enzyme on the membrane and is susceptible to be cleaved by shedding enzymes, resulting in plasma ACE activity. Somatic ACE is expressed in various tissues including blood vessels, kidney, intestine, adrenal gland, liver, and uterus, and is especially abundant in highly vascular organs such as retina and lung. Testis ACE is expressed by postmeiotic male germ cells and high-level expression is found in round and elongated spermatids. ACE2 is expressed in lung, liver, intestine, brain, testis, heart, and kidney. Lung possesses the highest amount of ACE. Expression of ACE is affected by steroids and thyroid hormone, but the details of the regulation are not clear. ACE is under promoter regulation by hypoxia-inducing factor 1α (HIF-1α), which upregulates the ACE expression under hypoxic conditions, resulting in an increase in Ang II concentration. The well-known function of ACE is the conversion of Ang I to Ang II and degradation of BK, which all play an important role in controlling blood pressure. ACE also acts on other natural substrates including encephalin, neurotensin, and substance P. Besides being involved in blood pressure control, ACE possesses widespread functions including renal development, male fertility, hematopoiesis, erythropoiesis, myelopoiesis, and immune responses. ACE has been the target of hypertension control since the 1970s. ACE inhibitors are prescribed as the sole or combinational treatment of high blood pressure, for the dual effects of lowering Ang II and slowing down BK degradation. Angiotensin II binds to the type 1 angiotensin II receptor (AT1), which sets off a number of actions that result in vasoconstriction and therefore increased blood pressure. The B2 (bradykinin 2) receptor is constitutively expressed and participates in bradykinin's vasodilatory role, it is a G protein coupled receptor.

Acebutolol (also known as Sectral or Prent) is a selective β1 adrenergic receptor antagonist (beta blocker), which can be used for treatment of high blood pressure (hypertension) and irregular heartbeats (arrhythmias). Acebutolol also has the ability to mild intrinsic sympathomimetic activity (ISA) with effective range of dosage. Adrenaline (also known as epinephrine) can activate β1 adrenergic receptor so that the heart rate and output will be increased. Renin is a hormone that generated from kidney, which could lead to constriction of blood vessels. Beta blockers could efficiently prohibit renin release.

Acebutolol is a cardioselective beta blocker. It can be administered orally, where it passes through hepatic portal circulation, and enters the bloodstream and travels to act on cardiomyocytes. In bronchial and vascular smooth muscle, acebutolol can compete with epinephrine for beta-2 adrenergic receptors. By competing with catecholamines for adrenergic receptors, it inhibits sympathetic stimulation of the heart. The reduction of neurotransmitters binding to beta receptor proteins in the heart inhibits adenylate cyclase type 1. Because adenylate cyclase type 1 typically activates cAMP synthesis, which in turn activates PKA production, which then activates SRC and nitric oxide synthase, its inhibition causes the inhibition of cAMP, PKA, SRC and nitric oxide synthase signaling. Following this chain of reactions, we see that the inhibition of nitric oxide synthase reduces nitric oxide production outside the cell which results in vasoconstriction. On a different end of this reaction chain, the inhibition of SRC in essence causes the activation of Caspase 3 and Caspase 9. This Caspase cascade leads to cell apoptosis. The net result of all these reactions is a decreased sympathetic effect on cardiac cells, causing the heart rate to slow and arterial blood pressure to lower; thus, acebutolol administration and binding reduces resting heart rate, cardiac output, afterload, blood pressure and orthostatic hypotension. By prolonging diastolic time, it can prevent re-infarction. Clinically, it is used to increase atrioventricular block to treat supraventricular dysrhythmias. Acebutolol also reduce sympathetic activity and is used to treat hypertension, angina, migraine headaches, and hypertrophic subaortic stenosis.

Metabolites of Acebutolol are predicted with biotransformer.

Metabolites of Aceclidine are predicted with biotransformer.

Aceclofenac is a non-steroidal anti-inflammatory drug (NSAID) with marked anti-inflammatory and analgesic properties. It is used to treat osteoarthritis, rheumatoid arthritis, and ankylosing spondylitis. Aceclofenac targets the prostaglandin G/H synthase-1 (COX-1) and prostaglandin G/H synthase-2 (COX-2) in the cyclooxygenase pathway. Aceclofenac displays more selectivity towards COX-2 (IC50 of 0.77uM) than COX-1 (IC50 of >100uM), which promotes gastric tolerance compared to the other NSAIDs. 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. Aceclofenac 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.