Linagliptin, when compared to placebo, improves CD34+ve endothelial progenitor cells in type 2 diabetes subjects with chronic kidney disease taking metformin and/or insulin: a randomized controlled trial.

BACKGROUND: Endothelial Progenitor cells (EPCs) has been shown to be dysfunctional in both type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD) leading to poor regeneration of endothelium and renal perfusion. EPCs have been shown to be a robust cardiovascular disease (CVD) risk indicator. Cellular mechanisms of DPP4 inhibitors such as linagliptin (LG) on CVD risk, in patients with T2DM with established CKD has not been established. Linagliptin, a DPP4 inhibitor when added to insulin, metformin or both may improve endothelial dysfunction in a diabetic kidney disease (DKD) population. METHODS: 31 subjects taking metformin and/or Insulin were enrolled in this 12 weeks, double blind, randomized placebo matched trial, with 5 mg LG compared to placebo. Type 2 diabetes subjects (30-70 years old), HbA1c of 6.5-10%, CKD Stage 1-3 were included. CD34+ cell number, migratory function, gene expression along with vascular parameters such as arterial stiffness, biochemistry, resting energy expenditure and body composition were measured. Data were collected at week 0, 6 and 12. A mixed model regression analysis was done with p value < 0.05 considered significant. RESULTS: A double positive CD34/CD184 cell count had a statistically significant increase (p < 0.02) as determined by flow cytometry in LG group where CD184 is SDF1a cell surface receptor. Though mRNA differences in CD34+ve was more pronounced CD34- cell mRNA analysis showed increase in antioxidants (superoxide dismutase 2 or SOD2, Catalase and Glutathione Peroxidase or GPX) and prominent endothelial markers (PECAM1, VEGF-A, vWF and NOS3). Arterial stiffness measures such as augmentation Index (AI) (p < 0.04) and pulse wave analysis (PWV) were improved (reduced in stiffness) in LG group. A reduction in LDL: HDL ratio was noted in treatment group (p < 0.04). Urinary exosome protein examining podocyte health (podocalyxin, Wilms tumor and nephrin) showed reduction or improvement. CONCLUSIONS: In DKD subjects, Linagliptin promotes an increase in CXCR4 expression on CD34 + progenitor cells with a concomitant improvement in vascular and renal parameters at 12 weeks. Trial Registration Number NCT02467478 Date of Registration: 06/08/2015.

Sucralose promotes accumulation of reactive oxygen species (ROS) and adipogenesis in mesenchymal stromal cells.

Consumption of non-nutritive sweeteners (NNS) has been consistently associated with obesity and cardiometabolic disease in epidemiologic studies. Herein, we investigated effects of sucralose, a widely used NNS, at a cellular level. We wanted to investigate effect of sucralose on reactive oxygen species accumulation and adipogenesis in a human adipocyte tissue-derived mesenchymal stromal cells (MSCs) in a controlled fashion. METHODS: In vitro experiments were conducted on commercially available MSCs obtained from human adipose tissue. hMSCs were exposed with sucralose at 0.2 mM (a concentration which could plausibly be observed in the circulatory system of high NNS consumers) up to 1.0 mM (supra-physiologic concentration) in the presence of both normal and high glucose media to detect a dose response based on the outcome measures. Reactive oxygen species (ROS) were detected using Mitosox Red staining and further analyzed by ImageJ and gene expression analysis. Effect of sucralose on adipogenic differentiation was observed in different concentrations of sucralose followed by gene expression analysis and Oil Red O staining. RESULTS: Increased ROS accumulation was observed within 72 h of exposure. Increased adipogenesis was also noted when exposed to higher dose of sucralose. CONCLUSION: Sucralose promotes ROS accumulation and adipogenesis in human adipose tissue derived mesenchymal stromal cells.

Antioxidant-upregulated mesenchymal stem cells reduce inflammation and improve fatty liver disease in diet-induced obesity.

BACKGROUND: The incidence of obesity and diabetes is increasing rapidly. Optimal management is still elusive. Obesity associated with type 2 diabetes is known to cause adipose tissue inflammation, increase oxidative stress, and cause white fat hyperplasia and mitochondrial dysfunction. In this study, we investigated whether mitochondrial and cytosolic antioxidant-upregulated mesenchymal stem cell (MSC) delivery reduces oxidative stress and subsequently improves glucose tolerance, reduce systemic inflammation, and improves fatty liver disease in diet-induced obese (DIO) mouse models. METHODS: Antioxidant genes Sod2 (mitochondrial) and catalase (cytosolic) or null (control) were upregulated in human adipose tissue-derived MSCs using adenoviral constructs. Modified MSCs were then delivered intraperitoneally into mice that were fed a 45% or 60% high-fat diet (HFD), and animals were followed for 4 weeks. RESULTS: Over 4 weeks, body weight remained stable; however, we noted a significant reduction in liver fat content by histological analysis and liver triglyceride assay. Triglyceride assay (p < 0.01) confirmed reduced liver fat accumulation in animals that received either Sod2- or Cat-MSCs. There was a lower plasma level of inflammatory marker TNFα, measured in mice that were fed either 45% or 60% HFD and received Sod2- or Cat-MSCs, indicating reduced systemic inflammation. Ucp1 mRNA was upregulated approximately 100-1000-fold for omental fat and 10-100-fold for pericardial fat compared to the Null-MSC-receiving group. Pcgc1a and Prdm16 mRNA upregulation was also noted particularly for pericardial fat. Glucose tolerance showed a positive improvement trend with a lower area under the curve (AUC) values for both Sod2- and Cat-MSCs groups in comparison to control. For mice fed with 60% HFD and that received Sod2-MSCs, glucose levels were significantly lower than control (*p < 0.05) at a time point of 60 min in the glycemic curve during glucose tolerance test. CONCLUSION: Reduction of oxidative stress post-antioxidant-upregulated MSC delivery, intraperitoneally, reduces systemic inflammation and fat accumulation in the liver. There is evidence of an increase in browning of white adipose tissue depots with concomitant improvement of glucose tolerance in a weight-independent fashion. Antioxidant-upregulated MSC delivery may be a safe yet effective therapy for obesity and prediabetes and improves related complication such as non-alcoholic fatty liver disease.

Reassessing the effects of continuous positive airway pressure (CPAP) on arterial stiffness and peripheral blood derived CD34+ progenitor cells in subjects with sleep apnea.

BACKGROUND: Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular diseases (CVD) and vascular health. Peripheral blood-derived CD34+ progenitor cells have been used as biomarker for CVD risk and may play a similar role in OSA and CVD risk assessment. Although there are some controversial results in the literature, OSA patients may have a reduction in the number and function of CD34+ cells. The damages promoted by OSA in CD34+ cells may lead to an increase in endothelial oxidative stress and endothelial inflammation which may lead to a reduced endothelial repair capacity. In this study, we explored the effect of continuous positive airway pressure (CPAP) on peripheral blood-derived CD34+ cells and arterial stiffness (another predictor of endothelial health and CVD risk) in OSA patients. METHODS AND RESULTS: Nine overweight and obese subjects without prediabetes or diabetes were recruited. Eight out of nine subjects had moderate to severe degree of OSA. CD34+ cells were isolated from peripheral blood. Number and function of these cells were monitored before and after 3 months of treatment with CPAP. No significant changes were observed in the number of CD34+ cells, CFU-Hill's colony formation unit (CFU) count or migratory response to the chemotactic factor SDF-1a after CPAP use. However, CXCR4 mRNA expression significantly increased by 2.2-fold indicating that CPAP may have a positive effect on SDF1a receptor (CXCR4), thereby improving migration of CD34+ cells mediated by SDF1a after the 3 month period. Interestingly, in clinical arena our results showed a reduction of pulse wave velocity (an established parameter of arterial stiffness) following CPAP therapy. CONCLUSIONS: Our findings suggest that 3-month CPAP intervention does not show statistical significant increase in CD34+ cell number and function, in mostly moderate to severe OSA subjects; however, it did demonstrate a positive trend. CPAP therapy, did help improve arterial stiffness parameter.

Endothelium-Derived Factors Influence Differentiation of Fat-Derived Stromal Cells Post-Exercise in Subjects with Prediabetes.

Purpose: We investigated the effect of aerobic and resistance exercise on abdominal subcutaneous fat-derived stromal cells in middle-aged subjects with prediabetes, pre- and post-exercise to establish molecular mechanisms that drive the effect of exercise. Methods: Five subjects, aged between 40 and 60 years with a body mass index between 25 and 39.9 kg/m2 and with prediabetes, were enrolled in a 12-week exercise intervention program. Biophysical parameters were assessed pre- and post-exercise. Stromal cells were obtained from subcutaneous abdominal fat and cultured for 2-3 weeks. The stromal cells were then analyzed for mRNA analysis pre- and post-exercise. This was followed up with in vitro experiments where commercially obtained human fat-derived mesenchymal stromal cells (MSCs) were exposed to adipogenic media, and conditioned media from human endothelial conditioned media (ECM) cells were added to note if ECM addition altered adipogenesis. Subsequently, MSC differentiation was monitored by reverse transcription-polymerase chain reaction (RT-PCR). Results: Post-exercise, subjects' cardiometabolic parameters improved. MSC obtained at post-exercise phase, from subcutaneous fat biopsies, on RT-PCR analysis, showed upregulation of antioxidant, mitochondrial, glucose transporter, and genes associated with osteogenesis compared with pre-exercise MSC mRNA. A concomitant increase in plasma osteocalcin levels was also noted post-exercise. In vitro, MSCs exposed to adipogenic differentiation media with the addition of ECM showed a significant reduction in expression of adipogenic marker genes and instead showed upregulation of genes associated with osteogenic differentiation. Conclusions: Exercise appears to prevent adipogenic differentiation of fat-derived stromal cells and promote osteogenic differentiation, in prediabetic middle-aged subjects. Interestingly, the addition of endothelium-derived factors to adipogenic media also appears to prevent adipogenic differentiation of commercially obtained fat-derived stromal cells and promotes osteogenic differentiation. Both in vivo and in vitro findings emphasize the paracrine effect of endothelium-derived factors on fat differentiation.

The synergistic effects of saxagliptin and metformin on CD34+ endothelial progenitor cells in early type 2 diabetes patients: a randomized clinical trial.

AIMS: Type 2 diabetes is associated with endothelial dysfunction leading to cardiovascular disease. CD34+ endothelial Progenitor Cells (EPCs) are responsible for endothelial repair and neo-angiogenesis and can be used as a cardiovascular disease risk biomarker. This study investigated whether the addition of saxagliptin, a DPP-IV inhibitor, to metformin, may reduce cardiovascular disease risk in addition to improving glycemic control in Type 2 diabetes patients. METHODS: In 12 week, double-blind, randomized placebo-controlled trial, 42 subjects already taking metformin 1-2 grams/day were randomized to placebo or saxagliptin 5 mg. Subjects aged 40-70 years with diabetes for < 10 years, with no known cardiovascular disease, BMI 25-39.9, HbA1C 6-9% were included. We evaluated EPCs number, function, surface markers and gene expression, in addition to arterial stiffness, blood biochemistries, resting energy expenditure, and body composition parameters. A mixed model regression to examine saxagliptin vs placebo, accounting for within-subject autocorrelation, was done with SAS (p < 0.05). RESULTS: Although there was no significant increase in CD34+ cell number, CD31+ cells percentage increased. Saxagliptin increased migration (in response to SDF1α) with a trend of higher colony formation count. MNCs cytometry showed higher percentage of CXCR4 double positivity for both CD34 and CD31 positive cells, indicating a functional improvement. Gene expression analysis showed an upregulation in CD34+ cells for antioxidant SOD1 (p < 0.05) and a downregulation in CD34- cells for IL-6 (p < 0.01). For arterial stiffness, both augmentation index and systolic blood pressure measures went down in saxagliptin subjects (p < 0.05). CONCLUSION: Saxagliptin, in combination with metformin, can help improve endothelial dysfunction in early diabetes before macrovascular complications appear. Trial registration Trial is registered under clinicaltrials.gov, NCT02024477.

Biophysical approaches in the study of biomembrane solubilization: quantitative assessment and the role of lateral inhomogeneity.

Detergents are amphiphilic molecules widely used to solubilize biological membranes and/or extract their components. Nevertheless, because of the complex composition of biomembranes, their solubilization by detergents has not been systematically studied. In this review, we address the solubilization of erythrocytes, which provide a relatively simple, robust and easy to handle biomembrane, and of biomimetic models, to stress the role of the lipid composition on the solubilization process. First, results of a systematic study on the solubilization of human erythrocyte membranes by different series of non-ionic (Triton, CxEy, Brij, Renex, Tween), anionic (bile salts) and zwitterionic (ASB, CHAPS) detergents are shown. Such quantitative approach allowed us to propose Resat-the effective detergent/lipid molar ratio in the membrane for the onset of hemolysis as a new parameter to classify the solubilization efficiency of detergents. Second, detergent-resistant membranes (DRMs) obtained as a result of the partial solubilization of erythrocytes by TX-100, C12E8 and Brij detergents are examined. DRMs were characterized by their cholesterol, sphingolipid and specific proteins content, as well as lipid packing. Finally, lipid bilayers of tuned lipid composition forming liposomes were used to investigate the solubilization process of membranes of different compositions/phases induced by Triton X-100. Optical microscopy of giant unilamellar vesicles revealed that pure phospholipid membranes are fully solubilized, whereas the presence of cholesterol renders the mixture partially or even fully insoluble, depending on the composition. Additionally, Triton X-100 induced phase separation in raft-like mixtures, and selective solubilization of the fluid phase only.

Effect of Triton X-100 on Raft-Like Lipid Mixtures: Phase Separation and Selective Solubilization.

Under certain conditions, biological membranes exhibit resistance to solubilization, even at high detergent concentration. These insoluble fragments are enriched in sphingolipids, cholesterol, and certain proteins having a preference for more organized environments. Here we investigated the effect of detergent Triton X-100 (TX-100) on raft-like lipid mixtures composed of POPC (palmitoyl oleoyl phosphatidylcholine, an unsaturated lipid), SM (sphingomyelin, a saturated lipid), and cholesterol, focusing on the detergent-induced phase separation at subsolubilizing concentration and the extent of solubilization at higher concentration. Giant unilamellar vesicles (GUVs) of POPC/SM/chol containing a fluorescent probe known to prefer the liquid-disordered phase were prepared and observed with fluorescence microscopy. A phase diagram constructed in the presence and absence of 0.1 mM TX-100 showed that the detergent induces macroscopic liquid-ordered/liquid-disordered (Lo/Ld) phase separation over a wide range of membrane composition, indicating that TX-100 has the ability to rearrange the lateral heterogeneity of the lipid mixture. The extent of solubilization of the POPC/SM/chol GUVs was quantified by measuring the vesicle size before and after the injection of a high concentration of TX-100. In parallel, the solubilization extent of large unilamellar vesicles (LUVs) was assessed by turbidity measurements. The extent of solubilization decreases significantly as the fractions of SM and cholesterol in the mixture increase. The origin of the detergent resistance is the low partitioning of TX-100 in cholesterol-rich membranes, especially in SM-containing ones, as evidenced by isothermal titration calorimetry experiments on LUVs. Our results provide a guide to future research on the effects of TX-100 on raft-like lipid mixtures.

Use of p53-Silenced Endothelial Progenitor Cells to Treat Ischemia in Diabetic Peripheral Vascular Disease.

BACKGROUND: Peripheral vascular disease is a major diabetes mellitus-related complication. In this study, we noted that expressions of proapoptotic p53 gene and its downstream cascade gene such as p21 are upregulated in hyperglycemia. Therefore, we investigated whether p53- and p21-silenced endothelial progenitor cells (EPCs) were able to survive in hyperglycemic milieu, and whether transplantation of either p53 knockout (KO) or p21KO or p53- and p21-silenced EPCs could improve collateral vessel formation and blood flow in diabetic vaso-occlusive peripheral vascular disease mouse models. METHODS AND RESULTS: We transplanted p53 and p21KO mouse EPCs (mEPCs) into streptozotocin-induced diabetic (type 1 diabetes mellitus model) C57BL/6J and db/db (B6.BKS(D)-Leprdb/J) (type 2 model) post-femoral artery occlusion. Similarly, Ad-p53-silenced and Ad-p21-silenced human EPCs (CD34+) cells were transplanted into streptozotocin-induced diabetic NOD.CB17-Prkdcscid/J mice. We measured blood flow at 3, 7, and 10 days and hindlimb muscles were obtained postsacrifice for mRNA estimation and CD31 staining. Enhanced blood flow was noted with delivery of p53 and p21KO mEPCs in streptozotocin-induced diabetic C57BL/6J mice. Similar results were obtained when human Ad-p53shEPCs(CD34+) and Ad-p21shEPCs(CD34+) were transplanted into streptozotocin-induced nonobese diabetic severe combined immunodeficiency mice. Gene expression analysis of p53 and p21KO EPCs transplanted hindlimb muscles showed increased expression of endothelial markers such as endothelial nitric oxide synthase, vascular endothelial growth factor A, and platelet endothelial cell adhesion molecule 1. Similarly, quantitative reverse transcriptase polymerase chain reaction of human Ad-p53shEPCs (CD34+)- and Ad-p21shEPCs (CD34+)-transplanted hindlimb muscles also showed increased expression of endothelial markers such as vascular endothelial growth factor A, noted primarily in the p53-silenced EPCs group. However, such beneficial effect was not noted in the db/db type 2 diabetic mouse models. CONCLUSIONS: Transient silencing of p53 using adenoviral vector in EPCs may have a therapeutic role in diabetic peripheral vascular disease.

Genetic modification of human mesenchymal stem cells helps to reduce adiposity and improve glucose tolerance in an obese diabetic mouse model.

INTRODUCTION: Human mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into fat, muscle, bone and cartilage cells. Exposure of subcutaneous abdominal adipose tissue derived AD-MSCs to high glucose (HG) leads to superoxide accumulation and up-regulation of inflammatory molecules. Our aim was to inquire how HG exposure affects MSCs differentiation and whether the mechanism is reversible. METHODS: We exposed human adipose tissue derived MSCs to HG (25 mM) and compared it to normal glucose (NG, 5.5 mM) exposed cells at 7, 10 and 14 days. We examined mitochondrial superoxide accumulation (Mitosox-Red), cellular oxygen consumption rate (OCR, Seahorse) and gene expression. RESULTS: HG increased reactive superoxide (ROS) accumulation noted by day 7 both in cytosol and mitochondria. The OCR between the NG and HG exposed groups however did not change until 10 days at which point OCR of HG exposed cells were reduced significantly. We noted that HG exposure upregulated mRNA expression of adipogenic (PPARG, FABP-4, CREBP alpha and beta), inflammatory (IL-6 and TNF alpha) and antioxidant (SOD2 and Catalase) genes. Next, we used AdSOD2 to upregulate SOD2 prior to HG exposure and thereby noted reduction in superoxide generation. SOD2 upregulation helped reduce mRNA over-expression of PPARG, FABP-4, IL-6 and TNFα. In a series of separate experiments, we delivered the eGFP and SOD2 upregulated MSCs (5 days post ex-vivo transduction) and saline intra-peritoneally (IP) to obese diabetic (db/db) mice. We confirmed homing-in of eGFP labeled MSCs, delivered IP, to different inflamed fat pockets, particularly omental fat. Mice receiving SOD2-MSCs showed progressive reduction in body weight and improved glucose tolerance (GTT) at 4 weeks, post MSCs transplantation compared to the GFP-MSC group (control). CONCLUSIONS: High glucose evokes superoxide generation, OCR reduction and adipogenic differentiation. Mitochondrial superoxide dismutase upregulation quenches excess superoxide and reduces adipocyte inflammation. Delivery of superoxide dismutase (SOD2) using MSCs as a gene delivery vehicle reduces inflammation and improves glucose tolerance in vivo. Suppression of superoxide production and adipocyte inflammation using mitochondrial superoxide dismutase may be a novel and safe therapeutic tool to combat hyperglycemia mediated effects.

Direct visualization of the action of Triton X-100 on giant vesicles of erythrocyte membrane lipids.

The raft hypothesis proposes that microdomains enriched in sphingolipids, cholesterol, and specific proteins are transiently formed to accomplish important cellular tasks. Equivocally, detergent-resistant membranes were initially assumed to be identical to membrane rafts, because of similarities between their compositions. In fact, the impact of detergents in membrane organization is still controversial. Here, we use phase contrast and fluorescence microscopy to observe giant unilamellar vesicles (GUVs) made of erythrocyte membrane lipids (erythro-GUVs) when exposed to the detergent Triton X-100 (TX-100). We clearly show that TX-100 has a restructuring action on biomembranes. Contact with TX-100 readily induces domain formation on the previously homogeneous membrane of erythro-GUVs at physiological and room temperatures. The shape and dynamics of the formed domains point to liquid-ordered/liquid-disordered (Lo/Ld) phase separation, typically found in raft-like ternary lipid mixtures. The Ld domains are then separated from the original vesicle and completely solubilized by TX-100. The insoluble vesicle left, in the Lo phase, represents around 2/3 of the original vesicle surface at room temperature and decreases to almost 1/2 at physiological temperature. This chain of events could be entirely reproduced with biomimetic GUVs of a simple ternary lipid mixture, 2:1:2 POPC/SM/chol (phosphatidylcholine/sphyngomyelin/cholesterol), showing that this behavior will arise because of fundamental physicochemical properties of simple lipid mixtures. This work provides direct visualization of TX-100-induced domain formation followed by selective (Ld phase) solubilization in a model system with a complex biological lipid composition.

Thermodynamic and structural characterization of zwitterionic micelles of the membrane protein solubilizing amidosulfobetaine surfactants ASB-14 and ASB-16.

Surface tension and isothermal titration calorimetry (ITC) were used to determine the critical micelle concentration (cmc) of the zwitterionic amidosulfobetaine surfactants ASB-14 and ASB-16 (linear-alkylamidopropyldimethylammoniopropanosulfonates) at 25 °C. The cmc and the heat of micellization were determined from 15 to 75 °C by ITC for both surfactants. The increase in temperature caused significant changes in the enthalpy and in the entropy of micellization, with small changes in the standard Gibbs energy (ΔG(mic)), which is consistent to an enthalpy−entropy compensation with a compensatory temperature of 311 K (ASB-14) and 314 K (ASB-16). In the studied temperature range, the heat capacity of micellization (ΔC(p)(mic)) was essentially constant. The experimental ΔC(p)(mic) was lower than that expected if only hydrophobic interactions were considered, suggesting that polar interactions at the head groups are of significant importance in the thermodynamics of micelle formation by these surfactants. Indeed, a NMR NOESY spectrum showed NOEs that are improbable to occur within the same monomer, resulting from interactions at the polar head groups involving more than one monomer. The ITC and NMR results indicate a tilt in the polar headgroup favoring the polar interactions. We have also observed COSY correlations typical of dipolar interactions that could be recovered with the partial alignment of the molecule in solution, which results in an anisotropic tumbling. The anisotropy suggested an ellipsoidal shape of the micelles, which results in a positive magnetic susceptibility, and ultimately in orientation induced by the magnetic field. Such an ellipsoidal shape was confirmed from results obtained by SAXS experiments that revealed aggregation numbers of 108 and 168 for ASB-14 and ASB-16 micelles, respectively. This study characterizes an interesting micelle system that can be used in the study of membrane proteins by solution NMR spectroscopy.

Multiple stages of detergent-erythrocyte membrane interaction--a spin label study.

The various stages of the interaction between the detergent Triton X-100 (TTX-100) and membranes of whole red blood cells (RBC) were investigated in a broad range of detergent concentrations. The interaction was monitored by RBC hemolysis-assessed by release of intracellular hemoglobin (Hb) and inorganic phosphate-and by analysis of EPR spectra of a fatty acid spin probe intercalated in whole RBC suspensions, as well as pellets and supernatants obtained upon centrifugation of detergent-treated cells. Hemolysis finished at ca. 0.9mM TTX-100. Spectral analysis and calculation of order parameters (S) indicated that a complex sequence of events takes place, and allowed the characterization of various structures formed in the different stages of detergent-membrane interaction. Upon reaching the end of cell lysis, essentially no pellet was detected, the remaining EPR signal being found almost entirely in the supernatants. Calculated order parameters revealed that whole RBC suspensions, pellets, and supernatants possessed a similar degree of molecular packing, which decreased to a small extent up to 2.5mM detergent. Between 3.2 and 10mM TTX-100, a steep decrease in S was observed for both whole RBC suspensions and supernatants. Above 10mM detergent, S decreased in a less pronounced manner and the EPR spectra approached that of pure TTX-100 micelles. The data were interpreted in terms of the following events: at the lower detergent concentrations, an increase in membrane permeability occurs; the end of hemolysis coincides with the lack of pellet upon centrifugation. Up to 2.5mM TTX-100 the supernatants consist of a (very likely) heterogeneous population of membrane fragments with molecular packing similar to that of whole cells. As the detergent concentration increases, mixed micelles are formed containing lipid and/or protein, approaching the packing found in pure TTX-100 micelles. This analysis is in agreement with the models proposed by Lasch (Biochim. Biophys Acta 1241 (1995) 269-292) and by Le Maire and coworkers (Biochim. Biophys. Acta 1508 (2000) 86-111).

Effect of cholesterol depletion and temperature on the isolation of detergent-resistant membranes from human erythrocytes.

Transient lateral microdomains or lipid rafts play important roles in many physiological membrane-mediated cell processes. Detergent-resistant membranes (DRMs) are good models for the study of lipid rafts. Here we report that DRMs can be obtained by treating human erythrocytes with the nonionic detergents Triton X-100 or octaethylene glycol monododecyl ether (C(12)E(8)) at 37 degrees C, and by treatment at 4 degrees C of cholesterol-depleted erythrocytes. Electron paramagnetic resonance with spin labels inserted at different membrane depths (5- and 16-doxyl stearic acids, 5-SASL and 16-SASL) were used to measure the order parameter (S) of the cell membranes and DRMs. We previously reported significantly higher S values in DRMs with respect to intact erythrocyte membranes. Here we show that higher S values were still measurable in DRMs prepared from intact erythrocytes at 37 degrees C, or from cholesterol-depleted cells at 4 degrees C, for both detergents. For 5-SASL only, increased S values were measured in 4 degrees C DRMs obtained from cholesterol-depleted versus intact erythrocytes. Flotillin-2, a protein marker of lipid rafts, was found in DRMs from intact cells in trace amounts but it was sensitively increased in C(12)E(8) DRMs prepared at 4 degrees C from cholesterol-depleted erythrocytes, while the membrane-skeletal proteins spectrin and actin were excluded from both Triton X-100 and C(12)E(8) DRMs. However, contrary to the 4 degrees C treatment results, flotillin-2 and stomatin were not resistant to Triton X-100 and C(12)E(8) treatment at physiological temperature. The role of cholesterol in DRMs formation is discussed and the results presented provide further support for the use of C(12)E(8) to the study of DRMs.