Eicosanoids & Lipoproteins

Other Lipids

• Eicosanoids are fatty acid derivatives and paracrine hormones.
• They play roles in reproduction, inflammation, fever, injury-related pain, and disease.
• There are 3 classes of eicosanoids: prostaglandins, thromboxanes, and leukotrienes.
• Prostaglandins increase body temperature.
• Thromboxanes are involved in blood clot formation.
• Leukotrienes are biological signals.
• Drugs can block the formation of prostaglandins and thromboxanes by inhibiting the enzyme involved in their conversion.

Lipoproteins

• Lipoproteins have a hydrophobic core with an amphipathic coat.
• They are spherical particles made of lipids and proteins that transport fats through the blood, which is water-based and doesn't dissolve fats.
• Chylomicrons are large, low-density lipoproteins that transport dietary triglycerides from the intestines to other tissues.
• VLDL/LDL (very low-density lipoprotein/low-density lipoprotein) are low to slightly higher density lipoproteins that transfer internally produced triglycerides and cholesterol from the liver to tissues.
• HDL (high-density lipoprotein) is a high-density lipoprotein that transports endogenous cholesterol from tissues to the liver

Lipids - General Information

• Lipids are organic molecules that are hydrophobic (low solubility in water).
• They play essential roles in energy storage, cell structure, and signaling.
• There are two categories of lipids: those that contain fatty acids and those that do not.
• Lipids that contain fatty acids are involved in storage and membrane structure.
• Lipids that do not contain fatty acids include cholesterol, vitamins, and pigments.

Fatty Acids

• Fatty acids are hydrocarbon derivatives.
• Fats and oils are used as stored forms of energy.
• They have a methyl end and a carboxylic acid end.

Storage Lipids

• TAGs (triglycerides/triacylglycerols) are energy storage molecules.
• They consist of 3 fatty acids attached to a glycerol backbone.
• They are hydrophobic and stored in anhydrous form, typically in adipose tissue.

Structural Lipids

• Structural lipids have polar head groups and nonpolar tails.
• They are structural components of membranes.
• The properties of the head group determine the surface properties of membranes.

Phospholipids

• Phospholipids consist of glycerol, 2 fatty acids, and a phosphate group.
• They can be either glycerophospholipids or sphingolipids.

Glycerophospholipids

• Glycerophospholipids are the most abundant lipids in membranes.
• They have hydrophobic and hydrophilic ends.

Sphingolipids

• Sphingolipids have a sugar group instead of a phosphate and polar group.
• They are membrane lipids with a long-chain amino alcohol called sphingosine.
• Fatty acids are joined to sphingosine via an amide linkage.
• Sugar-containing glycosphingolipids are largely found on the outer face of plasma membranes.

Ceramides

• Ceramide is the parent compound for the sphingolipid group.

Lipids that do not contain Fatty Acids

• Sterols have a nucleus of 4 fused rings.
• Cholesterol and sterols are found in membranes of eukaryotic cells but not in bacteria.
• They modulate fluidity and permeability of membranes and thicken the plasma membrane.
• Hormones are derivatives of sterols.
• Examples include bile acids, sex hormones, adrenal hormones, and vitamin D.
• Cholesterol is bound to proteins and transported to tissues via blood vessels. LDL can block arteries.

Cholesterol Esters

• Cholesterol is converted to esters for cell storage or transport in blood.
• Cholesterol esters are very water-soluble.

Cholesterol Transport

• HDL reduces cholesterol by removing it from tissues.
• LDL is considered "bad cholesterol"; when the amount needed for bile salts is surpassed, LDL accumulates in the blood vessels and causes plaques.
• HDL is considered "good cholesterol" because it picks up cholesterol from the blood and returns it to the liver; high levels are beneficial.

Diseases related to Cholesterol

• Atherosclerosis is hardening of the arteries.
• It is a progressive disease where lipids (cholesterol esters) deposit in smooth muscle cells.
• It forms lesions and calcified plaques that narrow or block arteries.
  • Coronary arteries may cause heart attack.
  • Cerebral arteries may cause stroke.
• Familial hypercholesterolemia is an inherited condition with high LDL levels.
  • There is a defect in LDL receptors, so LDL cannot be cleared from the blood.
  • Yellow skin nodules may form.
  • Leads to accumulation of fats and swelling of artery walls.
  • Treatment involves liver transplant or drugs.