Catalysis of nitrosation in vitro and in vivo in rats by catechin and resorcinol and inhibition by chlorogenic acid

Abstract

Measurements were made of the effects of phenolic compounds, some of which are present in the human diet, on the nitrosation of proline by nitrite to give N-nitrosoproline (NPRO). In vitro, resorcinol, catechin, p-nitrosophenol and phenol were catalysts and chlorogenic acid an inhibitor; guaiacol showed a marginal catalytic effect. Both the catalytic and the inhibiting effects were dependent on pH and on the concentration of phenolic compounds; catalysis by resorcinol and catechin was increased at optimal ratios of [nitrite]: [phenolic compound]. Endogenous nitrosation was examined in vivo by co-administration of nitrite, proline and a phenolic compound to rats and by monitoring the amount of NPRO excreted in the urine. Under similar experimental conditions, the catalytic effects observed in vivo decreased in the same order as those observed in vitro: resorcinol greater than p-nitroso-phenol greater than catechin greater than phenol greater than or equal to guaiacol; chlorogenic acid acted as an inhibitor. Catalysis and inhibition of N-nitrosation in rats in vivo appears to occur via mechanisms similar to those in vitro, although the effects in vivo were smaller. The implications of our findings for the endogenous formation of N-nitroso compounds and for variations in exposure due to different dietary constituents in humans are discussed.

Effect of Green Tea on the Formation of Nitrosamines, and Cancer Mortality

“…Nitrosation of Morpholine in Rat ---We performed and improved this method according to methods used by Pignatelli et al 27) Six-week-old Wistar male rats (Japan SLC, Hamamatsu, Japan) were housed in an air-conditioned room and given CE-2 commercial food pellets (Crea Japan, Tokyo, Japan) ad libitum. Five rats were assigned to each experimental group.…”

“…Pignatelli et al reported the catalytic action of catechins and resorcinol on the nitrosation of proline in vitro. 27) A conceivable mechanism has been thought for the catalysis of nitrosation by some of phenolic compounds. C-nitroso derivatives may be formed by further reaction with the nitrosating species to generate a more powerful nitrosating agent, which could be a nitrosoquinone oxime derivative.…”

“…Pignatelli et al determined the concentration of nitrosoproline in 24 hr urine excreted from the rats administered nitrite, proline and catechin. 27) They reported that the catalytic and inhibitory effects of catechin on the nitrosation of proline in rats depended on the concentration of catechin. Thus, the effects of brewed green tea infusion in vitro and in vivo were opposite on the nitrosation of secondary amines There are few reports about these opposite effects of brewed green tea infusion on the formation of nitrosamines in humans.…”

Green Tea and Its Extracts in Cancer Prevention and Treatment

“…In early studies catechins were investigated as potential carcinogens; Pignatelli [34] reported in 1982 the increased nitrosation of proline to the carcinogenic N-nitrosoproline, but soon antioxidant properties of catechins, interpreted as chemopreventive effects, became apparent. The first case control study of green tea extracts and cancer incidence was published in 1984 [35].…”

Phenolic Compounds in Food and Cancer Prevention

“…Chlorogenic acid also has been reported to block in vitro and in vivo nitrosation of proline by nitrite (123) and to inhibit the in vitro formation of nitrosamines from amine and nitrite (724). In addition to blocking the ultimate carcinogenic metabolites of polycyclic aromatic hydrocarbons which attack cellular DNA, caffeic acid, ferulic acid and chlorogenic acid have been shown to inhibit the mutagenicity and to accelerate the disappearance from aqueous solution of bay-region diol epoxides of polycyclic aromatic hydrocarbons which are the ultimate carcinogenic metabolites of polycyclic aromatic hydrocarbons (56).…”