A combined use of 13C-cross polarization/magic angle spinning, 13C-magic angle spinning and 31P-nuclear magnetic resonance spectroscopy with differential scanning calorimetry to study cannabinoid-membrane interactions

Abstract

We have examined and compared the thermotropic and dynamic properties of cannabimimetic (-)-Δ 8-tetrahydrocannabinol (Δ 8-THC) and its biologically almost inactive analog (-)-O-methyl-Δ 8-tetrahydrocannabinol (Me-Δ 8-THC) using non spinning 31 P and high resolution 13 C solid state NMR spectroscopy in combination with DSC (Differential Scanning Calorimetry) in dipalmitoylphosphatidylcholine (DPPC) bilayers. DSC traces showed that cannabinoids broaden the phase transition and shift the phase transition temperature of DPPC bilayers to lower temperatures and the active one produces more significant lowering and broadening. The DSC results also showed that Me-Δ 8-THC lowers and broadens the pretransition area. However, the severe broadening of the phase transition in the thermogram of DPPC/Δ 8-THC did not allow any conclusive results for its effect in the pretransition area. 13C and 31P-NMR data were used to complement this information. 13C-NMR spectroscopy appeared very sensitive to detect conformational changes in the pretransition area when the chemical shift changes of the observed peaks in the hydrophobic region were studied versus temperature increase. The obtained results confirmed DSC data for DPPC/Me-Δ 8-THC preparation and showed no visible pretransition for DPPC/Δ 8-THC sample. 13C-NMR spectroscopy gave direct evidence of the intercalation of both molecules into the membrane bilayers due to the specific additional peaks appeared in the DPPC/Δ 8-THC and DPPC/Me-Δ 8-THC preparations. The specific additional peaks appeared in the 13C-CP/MAS and MAS spectra when each of the cannabinoids was present in the preparation indicates a different mobility of the corresponding molecular moiety in the phospholipid bilayer environment. 31P-NMR spectroscopy revealed that the presence of the active analog causes significant conformational changes in the vicinity of the headgroup while the almost inactive analog only minor changes. These data suggest that the almost inactive cannabinoid intercalates in the hydrophobic region of the membrane bilayer while the active one in the backbone and polar region. In conclusion, the obtained results show that phospholipid–cannabinoid interactions of the studied pair of analogs differ and therefore may related to their different biological activities.