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Among the many known health benefits of tea catechins count anti-inflammatory and neuroprotective activities, as well as effects on the regulation of food intake. Here we address cannabimimetic bioactivity of catechin derivatives occurring in tea leaves as a possible cellular effector of these functionalities. Competitive radioligand binding assays using recombinant human cannabinoid receptors expressed in Chem-1 and CHO cells identified (-)-epigallocatechin-3-O-gallate, EGCG (K(i)=33.6 microM), (-)-epigallocatechin, EGC (K(i)=35.7 microM), and (-)-epicatechin-3-O-gallate, ECG (K(i)=47.3 microM) as ligands with moderate affinity for type 1 cannabinoid receptors, CB1. Binding to CB2 was weaker with inhibition constants exceeding 50 microM for EGC and ECG. The epimers (+)-catechin and (-)-epicatechin exhibited negligible affinities for both CB1 and CB2. It can be concluded that central nervous cannabinoid receptors may be targeted by selected tea catechins but signaling via peripheral type receptors is less likely to play a major role in vivo.

Human cannabinoid receptors 1 (hCB 1 R) and 2 (hCB 2 R) are expressed in the CNS and couple to G i /G o -proteins. The aim of this study was to compare coupling of hCB 1 R and hCB 2 R to Gα i2 β 1 γ 2 in Sf9 insect cells. High-affinity agonist binding at hCB 1 R, but not at hCB 2 R, was resistant to guanine nucleotides. hCB 1 R activated Gα i2 β 1 γ 2 much more rapidly than hCB 2 R in the [ 35 S]guanosine 5′-[γ-thio]triphosphate ([ 35 S]GTPγS) binding assay. Moreover, hCB 1 R exhibited a higher constitutive activity than hCB 2 R as assessed by the relative inhibitory effects of inverse agonists on [ 35 S]GTPγS binding and steady-state high-affinity GTPase activity compared to the stimulatory effects of the hCB 1/2 R agonist CP 55,940 [(-)- cis -3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]- trans -4-(3-hydroxypropyl)cyclohexanol]. Gα i2 β 1 γ 2 coupled to hCB 2 R exhibited higher GDP- and GTPγS-affinities than Gα i2 β 1 γ 2 coupled to hCB 1 R. NaCl effectively reduced constitutive activity of hCB 1 R but not of hCB 2 R. Collectively, hCB 1 R and hCB 2 R couple differentially to Gα i2 β 1 γ 2 . Moreover, hCB 1 R exhibits higher constitutive activity than hCB 2 R. These differences point to distinct functions of hCB 1 R and hCB 2 R in the CNS.