Piperine

Piperine is the alkaloid responsible for the pungency of black pepper and long pepper, along with chavicine (an isomer of piperine). It has also been used in some forms of traditional medicine and as an insecticide. Piperine forms monoclinic needles, is slightly soluble in water and more so in alcohol, ether or chloroform: the solution in alcohol has a pepper-like taste. It yields salts only with strong acids. The platinichloride B4•H2PtCl6 forms orange-red needles. ("B" denotes one mole of the alkaloid base in this and the following formulae.) Iodine in potassium iodide added to an alcoholic solution of the base in presence of a little hydrochloric acid gives a characteristic periodide, B2•HI•I2, crystallising in steel-blue needles, mp. 145°C. Anderson first hydrolysed piperine by alkalis into a base and an acid, which were later named piperidine and piperic acid respectively. The alkaloid was synthesised by the action of piperoyl chloride on piperidine.

Preparation
Piperine is commercially available. If desired, it may be extracted from black pepper using dichloromethane. Aqueous hydrotopes can also be used in the extraction to result in high yield and selectivity. The amount of piperine varies from 1-2% in long pepper, to 5-9% in the white and the black peppers of commerce. Further, it may be prepared by treating the solvent-free residue from an alcoholic extract of black pepper, with a solution of sodium hydroxide to remove resin (said to contain chavicine, an isomer of piperine) and solution of the washed, insoluble residue in warm alcohol, from which the alkaloid crystallises on cooling.

Biological activity
The pungency of capsaicin and piperine is caused by activation of the heat and acidity sensing TRPV ion channel TRPV1 on nociceptors (pain sensing nerve cells).

Piperine has also been found to inhibit human CYP3A4 and P-glycoprotein, enzymes important for the metabolism and transport of xenobiotics and metabolites. In animal studies, piperine also inhibited other enzymes important in drug metabolism. By inhibiting drug metabolism, piperine may increase the bioavailability of various compounds and alter the effectiveness of some medications. Notably, piperine may enhance bioavailability of curcumin by 2000% in humans. The exact mechanism of piperine's bioavailability enhancing abilities is unknown. Recent evidence published in the journal Molecular Nutrition Food Research supports the idea that piperine can enhance the pharmacokinetic parameters of resveratrol via inhibiting its glucuronidation, thereby slowing its elimination.

In February 2008, researchers discovered that piperine can stimulate pigmentation in the skin, together with the exposure to UVB light.

Piperine has shown 'anti-depression like activity', and cognitive enhancing effects in rats. Piperine was discovered in 1819 by Hans Christian Ørsted, who isolated it from the fruits of Piper nigrum, the source plant of both the black and white pepper grains. Piper longum and Piper officinarum (Miq.) C. DC. (=Piper retrofractum Vahl), two species called "long pepper" also were found to contain it by Flückiger and Hanbury. West African pepper also contains it. Chemopreventive efficacy of curcumin and piperine has been shown during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis. Piperine has shown anti-inflammatory and anti-arthritic effects in human interleukin-1beta-stimulated fibroblast-like synoviocytes and in rat arthritis models.