BIOCHEM | Eicosanoids (Prostaglandins, Thromboxanes, and Leukotrienes)

Eicosanoids

signaling molecules, usually derived from arachidonic acid

Prostaglandins

Lipid compounds derived from arachindonic acid through the cyclooxygenase pathway

Structure of Prostaglandins

a 20-carhon skeleton, including a five-membered ring and two side chains with various functional groups attached

Prostaglandins Classification

based on the structure of the cyclopentane ring. Different types have different functions and effects, mediated by prostaglandin receptors

Common Types of Prostaglandins

• prostaglandin E2 (PGE2)

• prostaglandin F2 alpha (PGF2a)

• prostaglandin I2 (PGI2)

Properties of Prostaglandins

• locally acting bioactive

• not stored in cells but synthesize on demand

• highly potent and act near site of synthesis

• have short half-lived due to being synthesized incredibly quickly

Functions of Prostaglandins

• promote inflammation, pain, fever, and swelling

• sensitizes nerve endings, making the sensation more acute

• regulate blood flow in kidneys and gastrointestinal tract

• Vasodilation and vasoconstriction (dilate or constrict blood vessels, affecting blood flow)

• modulation of smooth muscle contraction

• Maintains protective lining of stomach and intestines

• regulates ovulation, menstrual cycle, and induction of labor

Thromboxane

derived from arachindonic acid; synthesized in platelets; help form blood clots; has a six-membered oxygen-containing ring

Properties of Thromboxane

• bioactive lipids with a role in hemostasis

• synthesized on demand

• have a short half life

Functions of Thromboxanes

platelet aggregation (helping platelets stick together) and vasoconstriction (makes blood vessels narrow) to form blood clots and prevent blood loss after injury

thromboxane A2 (TXA2)

it is a highly unstable and active form of thromboxanes that exerts various physiological effects through specific receptors on target cells

Thromboxane B2 (TXB2)

it is what TXA2 rapidly converts to; is more stable

Leukotrines

derived from arachindonic acid and synthesized from a lipoxygenase (LOX) pathway

Structure of Leukotrines

it does not have a ring but a linear structure with three conjugated double bonds

Properties of Leukotrines

• potent signaling molecules in chronic immune responses

• synthesized in leukocytes

• act locally with a strong influence on inflammation and allergic reactions

• have longer half-lives

Functions of Leukotrines

• inflammatory response, especially in asthma and allergic reactions

• increase vascular permeability, contributing to edema and inflammation

Leukotrine B4 (LTB4)

attracts neutrophils to site of inflammation and enhances their activity

Cysteinyl Leukotrines (LTC4, LTD4, and LTE4)

constrict the bronchial smooth muscle, leading to the bronchospasm seen in asthma