Determinants of cyclooxygenase-2-mediated oxidative metabolism of the endocannabinoid, 2-arachidonoyl glycerol, in vitro and ex vivo

Prostaglandin H synthases (PGHS-1 and PGHS-2) also known as cyclooxygenases (COX-1 and COX-2) are enzymes that oxygenate fatty acid substrates (FAH) such as arachidonic acid (AA), leading to the generation of prostaglandins. Prostaglandins mediate a wide array of physiological effects, including pain, inflammation, fever, vascular homeostasis, and parturition. PGHS is the target of nonsteroidal anti-inflammatory drugs (NSAIDs), which prevent AA oxygenation and thus prostaglandin generation. The role of PGHS in mediating fever, pain and inflammation has unwittingly made PGHS perhaps the oldest documented drug target known to man. It was documented in Ebers's papyrus in 1500 BC, that the Egyptians used NSAID containing willow bark extract to treat fever (1). The importance of abating fever is evident in the convergent discovery by ancient denizens of separate continents; Romans, Native Americans, Chinese, and South African Hottentots had all established that fever could be reduced by NSAID-containing willow or myrtle leaf extracts (2-4). The first scientific record of NSAID use was by the Reverend Edward Stone, who reported to the Royal Society of London in 1763 that powdered willow bark improved the condition of fifty of his patients who were suffering from maladies manifesting fever and shivering- a condition archaically known as agues (4). Sixty-three years later, the French pharmacist Henri Leroux isolated the active ingredient in willow bark and myrtle leaves, and named it salicin based on the genus of the willow plant (Salix). Leroux further demonstrated that it was salicin that effected willow bark's antipyrexia (5). Salicin is a glycoside that is hydrolyzed to salicylic alcohol, which can be oxidized to form salicylic acid (1) (Figure 1). Thomas MacLagan, a Scottish physician, conducted the first formal clinical trial on salicin in 1874. MacLagan, having experienced no untoward effects after consuming two grams of the compound, administered it to his patient with rheumatic fever and successfully reduced the patient's fever, inflammation, and pain (6). That same year, Lautemann and Kolbe developed a chemical process by which they could generate salicylic acid at a fraction of the cost of extracting it from willow (3). It could even be argued that the rise of NSAIDs led to the birth of the pharmaceutical industry; the first drug factory was built to mass-produce salicylic acid (7). Although salicylic acid soon became the drug of choice for treating fever, pain, and inflammation, its bitterness and gastric side effects led to poor tolerance in some. In 1897, Felix Hoffman- a chemist at the Friedreich Bayer and Company- generated a more palatable form of salicylic acid by acetylating the alcohol on the phenol ring to form acetylsalicylic acid or aspirin (Figure 1) (1). The connection between the effects of NSAID use and the COX enzymes would not be made for another 70 years.