A phosphodiesterase inhibitor is a drug that blocks one or more of the five subtypes of the enzyme phosphodiesterase (PDE), thereby preventing the inactivation of the intracellular second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) by the respective PDE subtype(s). The ubiquitous presence of this enzyme means that non-specific inhibitors have a wide range of actions, the actions in the heart, and lungs being some of the first to find a therapeutic use.
A cyclic nucleotide (cNMP) is a single-phosphate nucleotide with a cyclic bond arrangement between the sugar and phosphate groups. Like other nucleotides, cyclic nucleotides are composed of three functional groups: a sugar, a nitrogenous base, and a single phosphate group. As can be seen in the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) images, the 'cyclic' portion consists of two bonds between the phosphate group and the 3' and 5' hydroxyl groups of the sugar, very often a ribose.
A phosphodiesterase (PDE) is an enzyme that breaks a phosphodiester bond. Usually, phosphodiesterase refers to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below. However, there are many other families of phosphodiesterases, including phospholipases C and D, autotaxin, sphingomyelin phosphodiesterase, DNases, RNases, and restriction endonucleases, as well as numerous less-well-characterized small-molecule phosphodiesterases.
Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP. Its most likely mechanism of action is activation of intracellular protein kinases in response to the binding of membrane-impermeable peptide hormones to the external cell surface.
Transducin (Gt) is a protein naturally expressed in vertebrate retina rods and cones and it is very important in vertebrate phototransduction. It is a type of heterotrimeric G-protein with different α subunits in rod and cone photoreceptors.
A phosphodiesterase type 5 inhibitor is a drug used to block the degradative action of cGMP-specific phosphodiesterase type 5 (PDE5) on cyclic GMP in the smooth muscle cells lining the blood vessels supplying various tissues. These drugs dilate the corpora cavernosa of the penis, facilitating erection with sexual stimulation, and are used in the treatment of erectile dysfunction (ED). Sildenafil was the first effective oral treatment available for ED. Because PDE5 is also present in the smooth muscle of the walls of the arterioles within the lungs, sildenafil and tadalafil dilates those vessels, and are FDA-approved for the treatment of pulmonary hypertension. Increasingly, the wider cardiovascular benefits of PDE5 inhibitors are being appreciated.
cGMP-specific phosphodiesterase type 5 is an enzyme from the phosphodiesterase class. It is found in various tissues, most prominently the corpus cavernosum and the retina. It has also been recently discovered to play a vital role in the cardiovascular system.
3'5'-cyclic nucleotide phosphodiesterases are a family of phosphodiesterases. Generally, these enzymes hydrolyze some nucleoside 3',5'-cyclic phosphate to some nucleoside 5'-phosphate thus controlling the cellular levels of the cyclic second messengers and the rates of their degradation. Some examples of nucleoside 3',5'-cyclic phosphate include:
EHNA is a potent adenosine deaminase inhibitor, which also acts as a phosphodiesterase inhibitor that selectively inhibits phosphodiesterase type 2 (PDE2).
PDE3 is a phosphodiesterase. The PDEs belong to at least eleven related gene families, which are different in their primary structure, substrate affinity, responses to effectors, and regulation mechanism. Most of the PDE families are composed of more than one gene. PDE3 is clinically significant because of its role in regulating heart muscle, vascular smooth muscle and platelet aggregation. PDE3 inhibitors have been developed as pharmaceuticals, but their use is limited by arrhythmic effects and they can increase mortality in some applications.
PDE1 is a phosphodiesterase enzyme also known as calcium- and calmodulin-dependent phosphodiesterase. It is one of the 11 families of phosphodiesterase (PDE1-PDE11). PDE1 has three subtypes, PDE1A, PDE1B and PDE1C which divide further into various isoforms. The various isoforms exhibit different affinities for cAMP and cGMP.
The PDE2 enzyme is one of 21 different phosphodiesterases (PDE) found in mammals. These different PDEs can be subdivided to 11 families. The different PDEs of the same family are functionally related despite the fact that their amino acid sequences show considerable divergence. The PDEs have different substrate specificities. Some are cAMP selective hydrolases, others are cGMP selective hydrolases and the rest can hydrolyse both cAMP and cGMP.
IBMX (3-isobutyl-1-methylxanthine), like other methylated xanthine derivatives, is both a:
- competitive non-selective phosphodiesterase inhibitor which raises intracellular cAMP, activates PKA, inhibits TNFα and leukotriene synthesis, and reduces inflammation and innate immunity, and
- nonselective adenosine receptor antagonist.
G protein-coupled receptor 35 also known as GPR35 is a G protein-coupled receptor which in humans is encoded by the GPR35 gene. Heightened expression of GPR35 is found in immune and gastrointestinal tissues, including the crypts of Lieberkühn.
In enzymology, a 3',5'-cyclic-GMP phosphodiesterase (EC 3.1.4.35) is an enzyme that catalyzes the chemical reaction
Retinal rod rhodopsin-sensitive cGMP 3',5'-cyclic phosphodiesterase subunit gamma is an enzyme that in humans is encoded by the PDE6G gene.
High affinity cAMP-specific 3',5'-cyclic phosphodiesterase 7A is an enzyme that in humans is encoded by the PDE7A gene. Mammals possess 21 cyclic nucleotide phosphodiesterase (PDE) genes that are pharmacologically grouped into 11 families. PDE7A is one of two genes in the PDE7 family, the other being PDE7B. The PDE7 family, along with the PDE4 and PDE8 families, are cAMP-specific, showing little to no activity against 3', 5'-cyclic guanosine monophosphate (cGMP).
High affinity cGMP-specific 3',5'-cyclic phosphodiesterase 9A is an enzyme that in humans is encoded by the PDE9A gene.
cAMP and cAMP-inhibited cGMP 3',5'-cyclic phosphodiesterase 10A is an enzyme that in humans is encoded by the PDE10A gene.
Phosphodiesterases (PDEs) are a superfamily of enzymes. This superfamily is further classified into 11 families, PDE1 - PDE11, on the basis of regulatory properties, amino acid sequences, substrate specificities, pharmacological properties and tissue distribution. Their function is to degrade intracellular second messengers such as cyclic adenine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which leads to several biological processes like effect on intracellular calcium level by the Ca2+ pathway.
