Angiotensin and bradykinin interactions with phospholipids

Interactions of angiotensin II non-peptide AT(1) antagonist losartan with phospholipid membranes studied by combined use of differential scanning calorimetry and electron spin resonance spectroscopy

We used differential scanning calorimetry (DSC) and electron spin resonance (ESR) spectroscopy to investigate the interactions of Losartan, a potent, orally active Angiotensin II AT(1) receptor antagonist with phospholipid membranes. DSC results showed that Losartan sensitively affected the chain-melting behavior of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayer membranes. ESR spectroscopy showed that phosphatidylcholines spin-labeled at the 5-position of the sn-2 acyl chain (n-PCSL with n=5), incorporated either in DMPC or DPPC bilayers containing Losartan, were restricted in motion both in the gel and in the liquid-crystalline membrane phases, indicating a location of the antagonist close to the interfacial region of the phosphatidylcholine bilayer. At high drug concentrations (mole fraction >/= x=0.60), the decrease in chain mobility registered by 5-PCSL in fluid-phase membranes is smaller than that found at lower concentrations, whereas that registered by 14-PCSL is further increased. This indicates a different mode of interaction with Losartan at high concentrations, possibly arising from a location deeper within the bilayer. Additionally, Losartan reduced the spin-spin broadening of 12-PCSL spin labels in the gel-phase of DMPC and DPPC bilayers. As a conclusion, our study has shown that Losartan interacts with phospholipid membranes by affecting both their thermotropic behavior and molecular mobility.

Role of angiotensin II in brown adipose thermogenesis during cold acclimation

The role of angiotensin II (ANG II) in increased sympathetic neuroeffector mechanisms observed in cold-induced thermogenesis of brown adipose tissue (BAT) was examined. Cold exposure (4 degrees C) for 7 days resulted in an increase in interscapular fat (ISF) ANG II content expressed per gram wet weight or per lobe of ISF, without concomitant changes in plasma components of the renin-angiotensin system. Additionally, in ISF slices preloaded with [3H]norepinephrine (NE), ANG II (10 nM) resulted in an increase (3-fold) in evoked 3H overflow from ISF slices from cold-exposed rats compared with ambient temperature controls. However, although basal 3H outflow was increased (2-fold) in ISF slices from cold-exposed rats, evoked 3H overflow was not different between ISF slices from cold-exposed and control rats. Specific neuronal uptake of [3H]NE in ISF slices from cold-exposed rats was decreased by 64%. Administration of the non-peptide AT1-receptor antagonist losartan to cold-exposed rats resulted in complete inhibition of ANG II-mediated presynaptic facilitation of evoked 3H overflow from ISF slices. However, losartan administration had no effect on cold-induced increases in ANG II content, protein content, and decreases in neuronal [3H]NE uptake in ISF. Results from these studies suggest that cold-induced thermogenesis of BAT results in alterations in presynaptic ANG II facilitation of NE release and defects in removal of NE from the synaptic cleft (neuronal uptake), both of which would enhance sympathetic nervous system-mediated thermogenesis. Furthermore, these results demonstrate a role for ANG II in enhanced sympathetic activity of cold-induced thermogenesis in BAT.

Selective 1H-NMR relaxation investigations of membrane-bound drugs in vitro. 2. Angiotensin II

Binding interactions between human angiotensin II and dipalmitoylphosphatidylcholine bilayer vesicles have been detected by measuring the selective proton spin-lattice relaxation rates of aromatic protons within the peptide. Involvement of the imidazole moiety of the His-6 residue has been demonstrated by the pH dependence of the NMR observables. A lower limit of the binding constant has been evaluated at 78.12 mol-1 dm3 for the interaction involving nonionic intermolecular forces between aromatic residues and the lipid matrix.