Aβ peptide interactions with isoflurane, propofol, thiopental and combined thiopental with halothane: A NMR study☆
Pravat K. Mandal ⁎, Jay W. Pettegrew
Western Psychiatric Institute and Clinic, Department of Psychiatry, University of Pittsburgh Medical School, Pittsburgh, PA 15213, USA
A r t i c l e I n f o
Received 23 April 2008
Received in revised form 30 June 2008
Accepted 1 July 2008 Available online xxxx
a b s t r a c t
Aβ peptide is the major component of senile plaques (SP) which accumulates in AD (Alzheimer’s disease) brain. Reports from different laboratories indicate that anesthetics interact with Aβ peptide and induce Aβ oligomerization. The molecular mechanism of Aβ peptide interactions with these anesthetics was not determined. We report molecular details for the interactions of uniformly 15N labeled Aβ40 with different anesthetics using 2D nuclear magnetic resonance (NMR) experiments. At high concentrations both isoflurane and propofol perturb critical amino acid residues (G29, A30 and I31) of Aβ peptide located in the hinge region leading to Aβ oligomerization. In contrast, these three specific residues do not interact with thiopental and subsequently no Aβ oligomerization was observed. However, studies with combined anesthetics (thiopental and halothane), showed perturbation of these residues (G29, A30 and I31) and subsequently Aβ oligomerization was found. Perturbation of these specific Aβ residues (G29, A30 and I31) by different anesthetics could play an important role to induce Aβ oligomerization.
© 2008 Elsevier B.V. All rights reserved.
Alzheimer’s disease (AD) is a neurodegenerative disease affecting millions of elderly people worldwide and AD is characterized by amyloid deposits in the brain. Although AD was discovered one century ago, the molecular cause of AD is not yet known. Researchers have discovered several risk factors associated with AD, but at present there is no cure. Amyloid deposits consist of either the 40-residue containing Aβ40 and/or the 42-residue containing Aβ42 peptide. Aβ42 has a higher aggregation tendency compared to Aβ40  and Aβ42 peptide is more pathogenic than Aβ40 [1,2]. The structural alteration of Aβ leading to oligomerization is believed to play an important role in AD .
At clinically relevant concentrations of halothane and isoflurane, Aβ peptide oligomerization and cytotoxicity was reported in rat pheochromocytoma cells . Biophysical studies involving sizeexclusion chromatography, analytical ultracentrifugation and photo-induced cross-linking experiments indicated the inhaled anesthetics halothane and isoflurane facilitate intermediate Aβ oligomer formation . Halothane induced more amyloid plaque in transgenic mice with AD pathology . It is also reported that Aβ oligomers generate in situ altered neuronal function . However, the specific binding site of these anesthetics as well as molecular mechanism of anesthetic-induced Aβ oligomerization is unknown.
☆ Part of the results was presented at Biophysical Society meeting, 2007.
⁎ Corresponding author.
E-mail addresses: Pravat.email@example.com, firstname.lastname@example.org (P.K. Mandal).
0005-2736/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
We previously reported that halothane interacts with amino acid residues (G29, A30 and I31) in the critical hinge region of Aβ40 and Aβ42 using nuclear magnetic resonance (NMR) spectroscopic studies conducted in a membrane mimic environment consisting of sodium dodecyl sulphate (SDS) . The oligomerization propensity of Aβ42 is much higher than Aβ40. Hence Aβ40 is better suitable than Aβ42 for time dependence NMR studies.
In this report we investigate the specificity of other anesthetics (both inhaled and intravenous) to interact with Aβ40 peptide in a membrane mimic environment. We also want to investigate whether the halothane–Aβ interaction is affected by the presence of other anesthetic with different physiochemical characteristics. We wish to address the following questions:
- Does the popularly used inhaled anesthetic, isoflurane, interact with Aβ40?
- Do intravenous anesthetics, propofol and thiopental interactwith Aβ40?
- Does thiopental influence Aβ–halothane interactions?
- Can we derive a molecular mechanism of Aβ peptide oligomerization due to the influence of these popularly used anesthetics? 2. Materials and methods
To understand these important questions, we have conducted a
series of NMR experiments to investigate Aβ40 peptide interactions with isoflurane, propofol, thiopental and thiopental combined with halothane.
This report reveals the molecular details of Aβ peptide interactions with several anesthetics that differ in physiochemical properties and molecular volumes. Existing literature indicates that amyloid load is increased in transgenic mice with halothane exposure . These animal model studies need to be extended to intravenous as well as combination of different types of anesthetics. The NMR experimental approach utilized in this study can be extended to other amyloid peptides including the islet amyloid polypeptides [46–51].
The anesthetic concentrations used in our NMR studies were higher than anesthetic concentrations used in clinical settings. Clinically relevant concentrations of halothane and isoflurane are approximately 0.3 mM [52–54]. In our NMR studies the Aβ peptide concentration was 0.45 mM, much higher than in vivo (21±7 μM) concentrations . However, Aβ peptide concentrations used in in vitro studies are usually ∼22 fold higher than in vivo concentrations, in keeping with the higher anesthetic concentrations used in our biophysical studies. Our NMR studies of Aβ peptide with different anesthetics are being extended at clinically relevant concentrations. Future studies with Aβ-anesthetic interactions in lipid bilayers environment will be performed.
Professor Vincenzo Fodale, MD, (Department of Neurosciences, Psychiatric and Anesthesiological Sciences, University of Messina, Italy) is highly appreciated for helpful discussion.
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