Inhibition of mouse hepatic glutathione S-transferase by Δ8-tetrahydrocannabinol p-quinone and cannabidiol hydroxy-quinone

The effect of structurally related cannabinoid quinones, Δ 8 -tetrahydrocannabinol p-quinone (Δ 8 -THCPQ) and cannabidiol hydroxy-quinone (CBDHQ) on the activity of glutathione S-transferase (GST) in mouse hepatic microsomes (Ms) and 105,000 x g supernatant (SP) was studied. GST activities in Ms and SP from untreated (UT) and phenobarbital (PheB)-treated mice were measured using 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB) as substrates. In the all case, both cannabinoid quinones concentration-dependently inhibited GST activities. In the case of the GST activity with CDNB, Δ 8 -THCPQ (91.5 μM) inhibited the activity by 32 (UT-Ms), 34 (UT-SP), 59 (PheB-Ms) and 59 (PheB-SP)% of the control, respectively. The activities in the corresponding control were 147.3 ± 2.7 (UT-Ms) and 698.7 ± 9.7 (PheB-Ms) nmol/min/mg protein, 6.69 ± 0.11 (UT-SP) and 8.36 ± 0.14 (PheB-SP) μmol/min/mg protein. CBDHQ (91.5 μM) inhibited the activity by 4 (UT-Ms), 10 (UT-SP), 15 (PheB-Ms) and 14 (PheB-SP)% of the control, respectively. In the case of the GST activity with DCNB, both cannabinoid quinones also concentration-dependently inhibited. In either case, CBDHQ inhibited the GST activity to a great extent than did Δ 8 -THCPQ. The kinetic parameters for CDNB, DCNB and glutathione (GSH) on the GST activity were determined using Lineweaver-Burk reciprocal plots. For CDNB and GSH in all GST activities, the type of inhibition by CBDHQ was competitive, but that by Δ 8 -THCPQ was non-competitive in those except for UT-Ms. The inhibitory constant (K i ) values of Δ 8 -THCPQ were 30.5 μM for CDNB and 33.9 μM for GSH in UT-Ms, and those values were 57.1 μM for CDNB and 68.9 μM for GSH in UT-SP. The K i values of CBDHQ were 11.1 μM for CDNB and 25.6 μM for GSH in UT-Ms, and those values.