A COMBINED USE OF C-13-CROSS POLARIZATION MAGIC ANGLE SPINNING, C-13-MAGIC ANGLE SPINNING AND P-31-NUCLEAR MAGNETIC-RESONANCE SPECTROSCOPY WITH DIFFERENTIAL SCANNING CALORIMETRY TO STUDY CANNABINOID-MEMBRANE INTERACTIONS/

We have examined and compared the thermotropic and dynamic properties of cannabimimetic (-)-Delta(8)-tetrahydrocannabinol (Delta(8)-THC) and its biologically almost inactive analog (-)-O-methyl-Delta(8)-tetrahy drocannabinol (Me-Delta(8)-THC) using non spinning P-31 and high resol ution C-13 solid state NMR spectroscopy in combination with DSC (Diffe rential Scanning Calorimetry) in dipalmitoylphosphatidylcholine (DPPC) bilayers. DSC traces showed that cannabinoids broaden the phase trans ition and shift the phase transition temperature of DPPC bilayers to l ower temperatures and the active one produces more significant lowerin g and broadening. The DSC results also showed that Me-Delta(8)-THC low ers and broadens the pretransition area. However, the severe broadenin g of the phase transition in the thermogram of DPPC/Delta(8)-THC did n ot allow any conclusive results for its effect in the pretransition ar ea. C-13 and P-31-NMR data were used to complement this information. C -13-NMR spectroscopy appeared very sensitive to detect conformational changes in the pretransition area when the chemical shift changes of t he observed peaks in the hydrophobic region were studied versus temper ature increase. The obtained results confirmed DSC data for DPPC/Me-De lta(8)-THC preparation and showed no visible pretransition for DPPC/De lta(8)-THC sample. C-13-NMR spectroscopy gave direct evidence of the i ntercalation of both molecules into the membrane bilayers due to the s pecific additional peaks appeared in the DPPC/Delta(8)-THC and DPPC/Me -Delta(8)-THC preparations. The specific additional peaks appeared in the C-13-CP/MAS and MAS spectra when each of the cannabinoids was pres ent in the preparation indicates a different mobility of the correspon ding molecular moiety in the phospholipid bilayer environment. P-31-NM R spectroscopy revealed that the presence of the active analog causes significant conformational changes in the vicinity of the headgroup wh ile the almost inactive analog only minor changes. These data suggest that the almost inactive cannabinoid intercalates in the hydrophobic r egion of the membrane bilayer while the active one in the backbone and polar region. In conclusion, the obtained results show that phospholi pid-cannabinoid interactions of the studied pair of analogs differ and therefore may related to their different biological activities. (C) 1 998 Elsevier Science Ireland Ltd. All rights reserved.