A group of compounds similar to prostaglandins with immunomodulating activity. Isoprostanes are formed through free radical catalyzing non-enzymatic reactions involving peroxidation of essential fatty acids, mainly arachidonic acid or any other fatty acid with 3 or more double bonds. Isoprostanes are abundant in tissues and fluids and their concentration is dependent on the amount of oxidative stress and may be upregulated in certain diseases such as cancer, cardiovascular and neurological disorders.

A series of prostaglandin-like compounds that are produced by the attack of free-radical species on unsaturated fatty acids, especially ARACHIDONIC ACID, of cellular MEMBRANES. Once cleaved from the lipid membrane by the action of phospholipases they can circulate into various bodily fluids and eventually be excreted. Although these compounds resemble enzymatically synthesized prostaglandins their stereoisometric arrangement is usually different than the "naturally occurring" compounds.