Differential scanning calorimetry in drug-membrane interactions

Differential Scanning Calorimetry (DSC) is a central technique in investigating drug - membrane interactions, a critical component of pharmaceutical research. DSC measures the heat difference between a sample of interest and a reference as a function of temperature or time, contributing essential knowledge on the thermally induced phase changes in lipid membranes and how these changes are affected by incorporating pharmacological substances. The manuscript discusses the use of phospholipid bilayers, which can form structures like unilamellar and multilamellar vesicles, providing a simplified yet representative membrane model to investigate the complex dynamics of how drugs interact with and penetrate cellular barriers. The manuscript consolidates data from various studies, providing a comprehensive understanding of the mechanisms underlying drug - membrane interactions, the determinants that influence these interactions, and the crucial role of DSC in elucidating these components. It further explores the interactions of specific classes of drugs with phospholipid membranes, including non-steroidal anti-inflammatory drugs, anticancer agents, natural products with antioxidant properties, and Alzheimer's disease therapeutics. The manuscript underscores the critical importance of DSC in this field and the need for continued research to improve our understanding of these interactions, acting as a valuable resource for researchers.

A rhein-huprine hybrid protects erythrocyte membrane integrity against Alzheimer's disease related Aβ(1-42) peptide

Alzheimer's disease remains largely unknown, and currently there is no complete cure for the disease. New synthetic approaches have been developed to create multi-target agents, such as RHE-HUP, a rhein-huprine hybrid which can modulate several biological targets that are relevant to the development of the disease. While RHE-HUP has shown in vitro and in vivo beneficial effects, the molecular mechanisms by which it exerts its protective effect on cell membranes have not been fully clarified. To better understand RHE-HUP interactions with cell membranes, we used synthetic membrane models and natural models of human membranes. For this purpose, human erythrocytes and molecular model of its membrane built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. The latter correspond to classes of phospholipids present in the outer and inner monolayers of the human erythrocyte membrane, respectively. X-ray diffraction and differential scanning calorimetry (DSC) results indicated that RHE-HUP was able to interact mainly with DMPC. In addition, scanning electron microscopy (SEM) analysis showed that RHE-HUP modified the normal biconcave shape of erythrocytes inducing the formation of echinocytes. Moreover, the protective effect of RHE-HUP against the disruptive effect of Aβ(1-42) on the studied membrane models was tested. X-ray diffraction experiments showed that RHE-HUP induced a recovery in the ordering of DMPC multilayers after the disruptive effect of Aβ(1-42), confirming the protective role of the hybrid.

In vitro evaluation of the protective effect of crocin on human erythrocytes

The interactions and the protective effect of the carotenoid crocin (CRO) on human erythrocytes (RBC) and molecular models of its membrane were investigated. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the RBC membrane, respectively. X-ray diffraction, differential scanning calorimetry (DSC) and electronic paramagnetic resonance spectroscopy (EPR) showed that CRO produced structural perturbations in DMPC bilayers and in isolated unsealed human erythrocyte membranes. On the other hand, scanning electron microscopy (SEM) showed that CRO induced shape changes in the RBC from their normal discoid form to echinocytes. This result indicates that the CRO molecules were mainly localized in the outer monolayer of the RBC membrane. The assessment of the protective capacity of CRO was revealed by the carotenoid inhibition of the morphological alterations caused by hypochlorous acid (HOCl) to RBC.

Protective Role of a Donepezil-Huprine Hybrid against the β-Amyloid (1-42) Effect on Human Erythrocytes

Aβ(1-42) peptide is a neurotoxic agent strongly associated with the etiology of Alzheimer's disease (AD). Current treatments are still of very low effectiveness, and deaths from AD are increasing worldwide. Huprine-derived molecules have a high affinity towards the enzyme acetylcholinesterase (AChE), act as potent Aβ(1-42) peptide aggregation inhibitors, and improve the behavior of experimental animals. AVCRI104P4 is a multitarget donepezil-huprine hybrid that improves short-term memory in a mouse model of AD and exerts protective effects in transgenic Caenorhabditis elegans that express Aβ(1-42) peptide. At present, there is no information about the effects of this compound on human erythrocytes. Thus, we considered it important to study its effects on the cell membrane and erythrocyte models, and to examine its protective effect against the toxic insult induced by Aβ(1-42) peptide in this cell and models. This research was developed using X-ray diffraction and differential scanning calorimetry (DSC) on molecular models of the human erythrocyte membrane constituted by lipid bilayers built of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE). They correspond to phospholipids representative of those present in the external and internal monolayers, respectively, of most plasma and neuronal membranes. The effect of AVCRI104P4 on human erythrocyte morphology was studied by scanning electron microscopy (SEM). The experimental results showed a protective effect of AVCRI104P4 against the toxicity induced by Aβ(1-42) peptide in human erythrocytes and molecular models.

Interaction of the antimicrobial peptide ∆M3 with the Staphylococcus aureus membrane and molecular models

Staphylococcus aureus is one of the most pathogenic bacteria; infections with it are associated with significant morbidity and mortality in health care facilities. Antimicrobial peptides are a promising next generation antibiotic with great potential against bacterial infections. In this study, evidence is presented of the biological and biophysical properties of the novel synthetic peptide ΔM3. Its antimicrobial activity against the ATCC 25923 and methicillin-resistant S. aureus strains was evaluated. The results showed that ΔM3 has activity in the same μM range as vancomycin. Biophysical studies were performed with palmitoyloleoylphosphatidylglycerol and cardiolipin liposomes loaded with calcein and used to follow the lytic activity of the peptide by fluorescence spectroscopy. On the other hand, ΔM3 was induced to interact with molecular models of the erythrocyte membrane buil-up of dimiristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, representative lipids of the outer and inner monolayers of the human erythrocyte membrane, respectively. The capacity of ΔM3 to interact with the bacteria and erythrocyte model membranes was also evaluated by X-ray diffraction and differential scanning calorimetry. The morphological changes induced by the peptide to human erythrocytes were observed by scanning electron microscopy. Results with these techniques indicated that ΔM3 interacted with the inner monolayer of the erythrocyte membrane, which is rich in anionic lipids. Additionally, the cytotoxic effects of ΔM3 on red blood cells were evaluated by monitoring the hemoglobin release from erythrocytes. The results obtained from these different approaches showed ΔM3 to be a non-cytotoxic peptide with antibacterial activity.

Phytochemical Analysis and Antioxidant and Anti-Inflammatory Capacity of the Extracts of Fruits of the Sechium Hybrid

In addition to their own antioxidants, human cells feed on external antioxidants, such as the phenolic compounds of fruits and vegetables, which work together to keep oxidative stress in check. Sechium edule, an edible species of chayote, has phenolic compounds with antioxidant activity and antineoplastic activity. A Sechium hybrid shows one thousand times greater antineoplastic activity than edible species, but its antioxidant and anti-inflammatory activities and the content of phenolic compounds are unknown. The aim of this study was to determine the antioxidant and anti-inflammatory capacity of the extract of fruits of the Sechium hybrid in vitro and in vivo. Phytochemical analysis using HPLC showed that the extract of the Sechium hybrid has at least 16 phenolic compounds; galangin, naringenin, phloretin and chlorogenic acid are the most abundant. In an in vitro assay, this extract inhibited 2,2-diphenyl-L-picrylhydrazyl (DPPH) activity and protected the dimyristoylphosphatidylethanolamine (DMPE) phospholipid model cell membrane from oxidation mediated by hypochlorous acid (HClO). In vivo, it was identified that the most abundant metabolites in the extract enter the bloodstream of the treated mice. On the other hand, the extract reduces the levels of tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin-6 (IL-6) but increases interleukin-10 (IL-10) and glutathione peroxidase levels. Our findings indicate that intake of the fruits of the Sechium hybrid leads to antioxidant and anti-inflammatory effects in a mouse model. Therefore, these results support the possibility of exploring the clinical effect of this hybrid in humans.

Toxic effects of the anticancer drug epirubicin in vitro assayed in human erythrocytes

Epirubicin is a cytotoxic drug used in the treatment of different types of cancer and increasing evidence suggests that its target is cell membranes. In order to gain insight on its toxic effects, intact red blood cells (RBC), human erythrocyte membranes and molecular models were used. The latter consisted in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipid classes found mainly in the outer and inner monolayers of the human erythrocyte membrane, respectively. The results obtained by X-ray diffraction displayed that epirubicin induced structural perturbations in multilayers of DMPC. Differential scanning calorimetry (DSC) showed that epirubicin disturbed the thermotropic behavior of both DMPC and DMPE vesicles, whereas fluorescence spectroscopy demonstrated alterations in the fluidity of DMPC vesicles and the erythrocyte membrane. Scanning electron microscopy (SEM) revealed that epirubicin changed the normal discoid form of RBC to echinocytes and stomatocytes. Electron paramagnetic resonance (EPR) disclosed that this drug induced conformational changes in the erythrocyte membrane proteins. These findings demonstrate that epirubicin interacts with lipids and proteins of the human erythrocyte membrane, effects that might compromise the integrity and function of cell membranes. This is the first time that its toxic effects on the human erythrocyte membrane have been described.

An in vitro study on the interaction of the anti-Alzheimer drug rivastigmine with human erythrocytes

The inhibition of the enzyme acetylcholinesterase (AChE) is a frequently used therapeutic option to treat Alzheimer's disease (AD). By decreasing the levels of acetylcholine degradation in the synaptic space, some cognitive functions of patients suffering from this disease are significantly improved. Rivastigmine is one of the most widely used AChE inhibitors. The objective of this work was to determine the effects of this drug on human erythrocytes, which have a type of AChE in the cell membrane. To that end, human erythrocytes and molecular models of its membrane constituted by dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. They correspond to classes of phospholipids present in the outer and inner monolayers of the human erythrocyte membrane, respectively. The experimental results obtained by X-ray diffraction and differential scanning calorimetry (DSC) indicated that rivastigmine molecules were able to interact with both phospholipids. Fluorescence spectroscopy results showed that rivastigmine produce a slight change in the acyl chain packing order and a weak displacement of the water molecules of the hydrophobic-hydrophilic membrane interface. On the other hand, observations by scanning electron microscopy (SEM) showed that the drug changed the normal biconcave shape of erythrocytes in stomatocytes (cup-shaped cells) and echinocytes (speculated shaped).

The acetylcholinesterase (AChE) inhibitor and anti-Alzheimer drug donepezil interacts with human erythrocytes

Donepezil is used to treat symptomatically the Alzheimer's disease (AD). This drug is a specific inhibitor of the enzyme acetylcholinesterase (AChE), whose main physiological function is to hydrolyze the neurotransmitter acetylcholine. The main objective of this work was to study the effect of donepezil on human erythrocytes as AChE is present in its membrane. For this purpose, human erythrocytes and molecular model of its membrane built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. The latter correspond to classes of phospholipids present in the outer and inner monolayers of the human erythrocyte membrane, respectively. Our experimental evidences obtained from X-ray diffraction and differential scanning calorimetry (DSC) analysis indicated that donepezil was capable of interacting with both phospholipids. Fluorescence spectroscopy results showed a moderate increase in the fluidity of the hydrophobic tails of DMPC and isolated unsealed human erythrocyte membranes (IUM). On the other hand, results by scanning electron microscopy (SEM) and optical defocusing microscopy (DM) showed that the drug changed the normal biconcave shape of the erythrocytes inducing the formation of stomatocytes (cup-shaped cells). This effect was explained by the incorporation of donepezil molecules into the erythrocyte membrane and interactions with AChE.

Antioxidant effect of resveratrol in single red blood cells measured by thermal fluctuation spectroscopy

The human red blood cell (RBC) membrane has significant elastic capabilities which can be described measuring typical membrane edge fluctuations and mechanical properties by optical techniques. The RBC elastic properties can be affected by changes in the surrounding media. In an attempt to elucidate the molecular mechanisms of the interaction of resveratrol with the red cell membrane and of its antioxidant capacity the changes in mechanical properties of the RBC membrane were analyzed. These studies were carried out through measurements of RBC membrane fluctuations in the presence of the oxidant agent HClO using thermal fluctuation spectroscopy (TFS). The observed results showed that the elastic capabilities of RBC changed with low concentration of hypochlorous acid but without morphological changes. However, in the presence of resveratrol the deformation and decrease of elastic capabilities induced by HClO on RBC decreased. These in vitro results demonstrated the protective effect of RV against the detrimental effects triggered by HClO upon human erythrocytes.

Protective effect of epigallocatechin gallate on human erythrocytes

The interactions and the protective effect of epigallocatechin gallate (EGCG) on human erythrocytes (RBC) and molecular models of its membrane were investigated. The latter consisted of bilayers built- up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. X-ray diffraction and differential scanning calorimetry experiments showed that EGCG induced significant structural and thermotropic perturbations in multilayers and vesicles of DMPC; however, these effects were not observed in DMPE. Fluorescence spectroscopy results revealed that EGCG produced alterations of the molecular dynamics at the level of the hydrophobic-hydrophilic interface in DMPC vesicles, and in isolated unsealed human erythrocyte membranes (IUM). EGCG also induced morphological alterations in RBC from their normal discoid form to echinocytes. These outcomes indicate that EGCG molecules were located in the outer monolayer of the erythrocyte membrane. The assessment of EGCG protective effect demonstrated that it inhibits the morphological alterations and lysis induced by HClO to human erythrocytes. The results obtained from this study suggest that the insertion of EGCG into the outer monolayer of the erythrocyte membrane might prevent the access and deleterious effects of oxidant molecules such as HClO and free radicals into the red cells, protecting them from oxidative damage.

In vitro effects of benzimidazole/thioether-copper complexes with antitumor activity on human erythrocytes

Two cytotoxic copper(II) complexes with N-H and N-methylated benzimidazole-derived ligands (Cu-L¹ and Cu-L^1Me; L¹=bis(2-methylbenzimidazolyl)(2-methylthioethyl)amine, L^1Me=bis(1-methyl-2-methylbenzimidazolyl)(2-methylthioethyl)amine) were synthesized and exposed to human erythrocytes and molecular models of its membrane. The latter were bilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), classes of lipids present in the external and internal moieties of the human red cell membrane, respectively. Scanning electron microscopy (SEM) of erythrocytes incubated with solutions of both Cu(II) complexes showed that they induced morphological changes to the normal cells to echinocytes, and hemolysis at higher concentrations. Real-time observation of the dose-dependent effects of the complexes on live erythrocytes by defocusing microscopy (DM) confirmed SEM results. The formation of echinocytes implied that complex molecules inserted into the outer moiety of the red cell membrane. X-ray diffraction studies on DMPC and DMPE showed that none of these complexes interacted with DMPE and only Cu-L¹ interacted with DMPC. This difference was explained by the fact that Cu-L^1Me complex is more voluminous than Cu-L¹ because it has two additional methyl groups; on the other hand, DMPC molecule has three methyl groups in its bulky terminal amino end. Thus, by steric hindrance Cu-L^1Me molecules cannot intercalate into DMPC bilayer, which besides is present in the gel phase. These results, together with the increased antiproliferative capacity of the N-methylated complex Cu-L^1Me over that of Cu-L¹ are rationalized mainly based on its higher lipophilicity.

Morphological Effects and Antioxidant Capacity of Solanum crispum (Natre) In Vitro Assayed on Human Erythrocytes

In order to gain insight into the molecular mechanism of the antioxidant properties of Solanum crispum, aqueous extracts of its leaves were assayed on human erythrocytes and molecular models of its membrane. Phenolics and alkaloids were detected by HPLC-MS. Scanning electron and defocusing microscopy showed that S. crispum changed erythrocytes from the normal shape to echinocytes. These results imply that molecules present in the aqueous extracts were located in the outer monolayer of the erythrocyte membrane. Dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were chosen as representative of phospholipid classes located in the outer and inner monolayers of the erythrocyte membrane, respectively. X-ray diffraction showed that S. crispum preferentially interacted with DMPC bilayers. Experiments regarding its antioxidant properties showed that S. crispum neutralized the oxidative capacity of HClO on DMPE bilayers; defocusing microscopy and hemolysis assays demonstrated the protective effect of S. crispum against the oxidant effects of HClO on human erythrocytes.

An in vitro study on the antioxidant capacity of usnic acid on human erythrocytes and molecular models of its membrane

Usnic acid (UA) has been associated with chronic diseases through its antioxidant action. Its main target is the cell membrane; however, its effect on that of human erythrocytes has been scarcely investigated. To gain insight into the molecular mechanisms of the interaction between UA and cell membranes human erythrocytes and molecular models of its membrane have been utilized. Dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were chosen as representative of phospholipid classes located in the outer and inner monolayers of the erythrocyte membrane, respectively. Results by X-ray diffraction showed that UA produced structural perturbations on DMPC and DMPE bilayers. DSC studies have indicated that thermotropic behavior of DMPE was most strongly distorted by UA than DMPC, whereas the latter is mainly affected on the pretransition. Scanning electron (SEM) and defocusing microscopy (DM) showed that UA induced alterations to erythrocytes from the normal discoid shape to echinocytes. These results imply that UA molecules were located in the outer monolayer of the erythrocyte membrane. Results of its antioxidant properties showed that UA neutralized the oxidative capacity of HClO on DMPC and DMPE bilayers; SEM, DM and hemolysis assays demonstrated the protective effect of UA against the deleterious oxidant effects of HClO upon human erythrocytes.

Antioxidant capacity of Ugni molinae fruit extract on human erythrocytes: an in vitro study

Ugni molinae is an important source of molecules with strong antioxidant activity widely used as a medicinal plant in Southern Chile-Argentina. Total phenol concentration from its fruit extract was 10.64 ± 0.04 mM gallic acid equivalents. Analysis by means of HPLC/MS indicated the presence of the anthocyanins cyanidin and peonidin, and the flavonol quercitin, all in glycosylated forms. Its antioxidant properties were assessed in human erythrocytes in vitro exposed to HClO oxidative stress. Scanning electron microscopy showed that HClO induced an alteration in erythrocytes from a normal shape to echinocytes; however, this change was highly attenuated in samples containing U. molinae extracts. It also had a tendency in order to reduce the hemolytic effect of HClO. In addition, X-ray diffraction experiments were performed in dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine bilayers, classes of lipids preferentially located in the outer and inner monolayers, respectively, of the human erythrocyte membrane. It was observed that U. molinae only interacted with DMPC. Results by fluorescence spectroscopy on DMPC large unilamellar vesicles and isolated unsealed human erythrocyte membranes also showed that it interacted with the erythrocyte membrane and DMPC. It is possible that the location of U. molinae components into the membrane outer monolayer might hinder the diffusion of HClO and of free radicals into cell membranes and the consequent decrease of the kinetics of free radical reactions.

X-Ray Studies on Phospholipid Bilayers I. Polymorphic Forms of Dimyristoyl Lecithin

A structural study of the synthetic phospholipid, L-a-dimyristoyl lecithin (DM L), has been m ade by X-ray fiber diffraction methods. Three different types of oriented specimens were prepared. They were X-ray photographed under the same conditions, including tem perature and relative humidity. T hree different types of diffraction patterns, corresponding to different confor­ mations and/or packing arrangements, were found. They are characterized by their unit cell dimensions, space groups, molecular conformations, and packing arrangements.

X-Ray Studies on Phospholipid Bilayers, in. Structure and Morphology of L-α-Dilaurylphosphatidylethanolamine (DLPE)

Phospholipid, Bilayer, X-Ray Diffraction, Morphology, Dilaurylphosphatidylethanolam ine, Membrane Powder samples and oriented films of the synthetic phospholipid L-α-dilaurylphosphatidyl-ethanolamine (DLPE) were studied by X-ray diffraction over a wide range of hydration. Only small differences were found between the unit cell dimensions of DLPE powder and oriented-film specimens. These dimensions did not vary appreciably with hydration. In the multilayer DLPE structure, the molecules pack with polar groups parallel to the bilayer plane and hydro­ carbon chains perpendicular to it. Examination of oriented films by scanning electron microscopy gave information on the surface morphology. Complementary data on the lamellar packing of the molecules and the average thickness of the bilayers was provided by thin-section and shadow-cast preparations studied by transmission electron microscopy.