Novel functions of bovine milk-derived alpha-lactalbumin: anti-nociceptive and anti-inflammatory activity caused by inhibiting cyclooxygenase-2 and phospholipase A2.

Milk whey proteins contain major components of alpha-lactalbumin (alphaLA) and beta-lactoglobulin (betaLG), and a minor component of lactoferrin (LF). It has been reported that LF reduces nociception and inflammation in various animal models. However, the efficacy of alphaLA and betaLG has not been clarified. This study aimed to assess the efficacy of alphaLA and betaLG in various animal models such as acetic acid-induced writhing, carrageenan-induced paw inflammation, and adjuvant induced-arthritis. Orally administered alphaLA showed (i) inhibition of writhing induced by acetic acid in mice; (ii) suppression of nociception and inflammation in rat footpads caused by carrageenan in rat; and (iii) therapeutic effects on the development of adjuvant-induced pain and inflammation in rat. In contrast, betaLG had no effects in these animal models. To clarify the anti-nociceptive and anti-inflammatory mechanisms of alphaLA, we examined the levels of interleukin (IL)-6 and prostaglandin (PG)E(2) in carrageenan-injected paw exudates. The administration of alphaLA 1 h before carrageenan injection inhibited the increased formation of IL-6 and PGE(2) in paw exudates. Next, we demonstrated in vitro enzyme-inhibition assay; cyclooxygenase (COX), phospholipase A(2), and 5-lipoxygenase. alphaLA inhibited COX and phospholipase A(2) activities. alphaLA inhibited COX and phospholipase A(2) activities. Moreover, alphaLA showed selectivity on COX-2 as compared with COX-1. However, 5-lipoxygenase activity was not affected by alphaLA. These results suggest that alphaLA is a safe and useful natural drug for patients that require anti-inflammatory drugs, as alphaLA is contained in dairy food and is frequently ingested as daily food.