The lupane triterpenoid lupeol, the ursane triterpenoid alpha-amyrin and esters of these compounds are present in the bark of roots of Alstonia boonei (Apocynaceae) and have anti-inflammatory properties. alpha-Amyrin is a competitive inhibitor of bovine trypsin and chymotrypsin (Ki values 29 microM and 18 microM, respectively). Lupeol linoleate, lupeol palmitate and alpha-amyrin linoleate are non-competitive inhibitors of trypsin (Ki values 7 microM, 10 microM and 16 microM, respectively). alpha-Amyrin linoleate is also a non-competitive inhibitor of chymotrypsin (Ki value 28 microM). Lupeol is a competitive inhibitor of both trypsin and chymotrypsin (Ki values 22 and 8 microM, respectively). alpha-Amyrin palmitate is a potent non-competitive inhibitor of chymotrypsin (Ki 6 microM). Lupeol, alpha-amyrin and the palmitic and linoleic acid esters of these compounds are ineffective or very weak as inhibitors of porcine pancreatic elastase and of Lucilia cuprina and Helicoverpa punctigera leucine aminopeptidases. These hydrophobic triterpenoids represent further examples of anti-inflammatory triterpenoids that are PKA inhibitors as well as being selective protease inhibitors.

The ursane triterpenoid alpha-amyrin and the lupane triterpenoid lupeol are potent inhibitors of the catalytic subunit (cAK) of rat liver cyclic AMP-dependent protein kinase (PKA) with IC50 values of 8 and 5 microM, respectively. The palmitate and linoleate esters of alpha-amyrin and lupeol are also potent inhibitors of cAK (IC50 values in the range of 4-9 microM). alpha-Amyrin, lupeol and lupeol linoleate are much less potent as inhibitors of rat brain Ca(2+)- and phospholipid-dependent protein kinase (PKC) (IC50 values 32, 82 and 35 microM; respectively) and alpha-amyrin linoleate and the palmitate esters of lupeol and alpha-amyrin are ineffective or very poor inhibitors of this protein kinase. These compounds are very poor or ineffective as inhibitors of chicken gizzard calmodulin-dependent myosin light chain kinase (MLCK). alpha-Amyrin inhibits plant Ca(2+)-dependent protein kinase (CDPK) (IC50 52 microM) but lupeol and the triterpenoid esters tested are ineffective. alpha-Amyrin and the linoleate and palmitate esters of alpha-amyrin and lupeol inhibit cAK in a fashion that is competitive with respect to both peptide substrate and ATP (Ki values in the range 2-6 microM). However, while lupeol is competitive with respect to ATP it is apparently non-competitive with respect to peptide substrate. alpha-Amyrin also inhibits CDPK competitively and alpha-amyrin, lupeol and lupeol linoleate are competitive inhibitors of PKC. alpha-Amyrin and the palmitate esters of lupeol and alpha-amyrin are competitive inhibitors of the potato high affinity cyclic AMP-binding phosphatase (Pase) but lupeol inhibits the Pase non-competitively. These hydrophobic triterpenoids are further examples of anti-inflammatory triterpenoids that are cAK inhibitors.

The triterpenes lupeol (L), lupeol-3-palmitate (LP), and lupeol-3-linoleate (LL) have previously been shown to reduce joint destruction in adjuvant arthritic rats. In order to explain the relative antiarthritic effectiveness (LL>LP>L), the triterpenes were tested on the release of collagenase by rat osteosarcoma (bone tumor) cells, on the release of 5 Iipoxygenase inflammatory products by human neutrophils, and on CCI,-induced hepatotoxicity in rats. The rat osteosarcoma cells released collagenase which digested type I (bone) native collagen. The collagenase release, unaffected by 50 FM lupeol, decreased in the presence of lupeol linoleate and lupeol palmitate by 97% and 78%, respectively. The 30% inhibitory concentrations (lC3,J of lupeol linoleate, lupeol palmitate, and lupeol on LTB, release by the neutrophils were 27 pM, 94 FM, and >I00 p, M, respectively. All the triterpenes equally reduced hepatic fatty degeneration in CCI, rats, but only the triterpene esters significantly reduced LDH release (34% LL; 25% LP) and accelerated hepatic cell regeneration (LL>LP). The effectiveness of the triterpenes in the models of inflammatory and arthritic processes employed here corresponded with their relative antiarthritic effectiveness in adjuvant arthritic rats. o 1995 WiIey-Liss. Inc.

No abstract

alpha-Amyrin palmitate, present in a Ghanaian antiarthritic herbal preparation of Alstonia boonei, Elaies guineensis and Rauvolfia vomitoria, was synthesised and tested on complete Freund's adjuvant-induced arthritic rats. Administered orally at 56 mg/kg body weight (BW) daily for 8 days from days 11 to 18 post adjuvant (acute) or at 66 mg/kg BW every 48 h for 5 days from days 32 to 40 (chronic), the drug returned the increases in serum hyaluronate and blood granulocytes towards non-arthritic levels and corrected the moderate anaemia of adjuvant arthritis. Histological examinations of the proximal interphalangeal foot joints showed reduced synovial proliferation and invasion of joints and reduced leucocyte infiltration of bone marrow and periarticular tissue in treated rats. The results suggest that alpha-amyrin palmitate contributes to the previously shown antiarthritic effect of the herbal preparation.