Inhibition by retinol and butylated hydroxyanisole of carcinogen-mediated increases in guanylate cyclase activity and guanosine 3':5'-monophosphate accumulation. (1977)

N -Methyl- N ′-nitro- N -nitrosoguanidine (MNNG), a compound with well-established carcinogenic properties, produces marked increases in soluble guanylate cyclase activity and cyclic guanosine 3′:5′-monophosphate (cGMP) accumulation in rat liver and colonic mucosa. Preincubation of the 100,000 × g soluble fraction of liver with 1 mm retinol or butylated hydroxyanisole, dietary constituents with antioxidant properties and putative anticarcinogenic activity, inhibited by 50 to 58% the response of guanylate cyclase to a maximally effective concentration of MNNG (basal, 38 ± 4; 0.1 mm MNNG, 2193 ± 194; retinol plus MNNG, 1053 ± 131; butylated hydroxyanisole plus MNNG, 977 ± 122 pmoles cGMP per min per mg protein). Retinol and butylated hydroxyanisole similarly suppressed the actions of MNNG to increase soluble guanylate cyclase activity of colonic epithelium and accumulation of cGMP in hepatic slices or mucosal scrapings from incubated colonic segments. Optimal inhibition of MNNG-responsive soluble hepatic guanylate cyclase activity was observed after preincubation of tissue with 1 mm retinol (58% decrease), 3 mm butylated hydroxyanisole (80%), 3 mm retinoic acid (30%), and 3 mm butylated hydroxytoluene (21%). By contrast, preincubation of tissue with up to 5 mm of these agents had no effect on basal guanylate cyclase activity measured in the absence of MNNG. Prior stimulation of soluble hepatic guanylate cyclase activity with MNNG, followed by exposure to retinol or butylated hydroxyanisole, resulted in reversal of MNNG stimulation of enzyme activity. The reduction of MNNG-stimulated guanylate cyclase activity observed under these conditions was greater than (retinol) or equal to (butylated hydroxyanisole) the inhibition observed when these same agents were added to tissue prior to the addition of MNNG. Inhibitory effects of retinol or butylated hydroxyanisole could not be attributed to alterations in the divalent cation requirements of soluble hepatic guanylate cyclase activity or to direct chemical interactions leading to loss of the nitroso group from MNNG. The carcinogens N -methylnitrosourea, hydrazine, and 4-nitroquinoline 1-oxide and the test agents NaNO2, NaN3, and nitroprusside increased soluble hepatic guanylate cyclase activity 6- to 50-fold. The action of each of these compounds was significantly suppressed by retinol or butylated hydroxyanisole. By contrast the antioxidants did not alter the basal, NaF, or glucagon-responsive adenylate cyclase activities of hepatic homogenates or the basal and glucagon-stimulated cyclic adenosine 3′:5′-monophosphate accumulation of hepatic slices. Thus, the action of retinol and butylated hydroxyanisole in suppression of the responsiveness of the hepatic guanylate cyclase system to several carcinogens was selective relative to effects on the responsiveness of the adenylate cyclase system. Although the mechanisms of inhibition remain to be defined, the actions of retinol and butylated hydroxyanisole in suppression of carcinogen activation of guanylate cyclase could be involved in the expression of their anticarcinogenic properties.