Garlic can induce both GTP cyclohydrolase and nitric oxide synthase activity in choriocarcinoma cells.

Several properties of garlic (Allium sutivum L . ) can be attributed to its ability to physiologically increase nitric oxide (NO)[ 11. NO is produced from arginine by NO synthase (NOS; EC 1.14.13.39) which can exist in both constitutive (calciumdependent) and inducible (calcium-independent) isoforms [ 21. Tetrahydrobiopterin, an essential co-factor for NOS 131, is synthesized from GTP by GTP cyclohydrolase I (GTPCH-I; EC 3.5.4.16). Tetrahydrobiopterin is also a co-factor for other reactions that produce (i) tyrosine from phenylalanine, (ii) DOPA from tyrosine, (iii) 5-OH-tryptophan from tryptophan and (iv) carboxylic acid and glycerol from glyceryl esters. The enzymes NOS and GTPCH-I have both been shown to be present in the placenta 14,5[ and have also been shown to be induced by cytokines and bacterial lipopolysaccharides in several tissues 16,7]. We have used a chriocarcinoma cell line, which shows many characteristics of placental trophoblasts 181, to determine whether extracts of garlic can affect the activities of these enzymes in vitro. Garlic extracts were prepared by 1 % alcoholic extraction of garlic powder (gmlmL). This was diluted and added to cultures of BeWo cells grown to near confluence in 24-well plates. Ham's F12 medium (Sigma Chemical Co Ltd, Poole, UK) containing 100unitslmL penicillin, 100pg/mL streptomycin and 10% fetal calf serum was used for culture. After 24h incubation, nitrite (by chemiluminescence 191) and neopterin (by radioimmunoassay; ICN Pharmaceuticals, UK) concentrations were measured in the culture medium.