Reduced deformability of erythrocyte membranes from patients with Duchenne muscular dystrophy

Iron overload and impaired iron handling contribute to the dystrophic pathology in models of Duchenne muscular dystrophy

BACKGROUND

Oxidative stress is implicated in the pathophysiology of Duchenne muscular dystrophy (DMD, caused by mutations in the dystrophin gene), which is the most common and severe of the muscular dystrophies. To our knowledge, the distribution of iron, an important modulator of oxidative stress, has not been assessed in DMD. We tested the hypotheses that iron accumulation occurs in mouse models of DMD and that modulation of iron through the diet or chelation could modify disease severity.

METHODS

We assessed iron distribution and total elemental iron using LA-ICP-MS on skeletal muscle cross-sections of 8-week-old Bl10 control mice and dystrophic mdx mice (with moderate dystrophy) and dystrophin/utrophin-null mice (dko, with severe dystrophy). In addition, mdx mice (4 weeks) were treated with either an iron chelator (deferiprone 150 mg/kg/day) or iron-enriched feed (containing 1% added iron as carbonyl iron). Immunoblotting was used to determine the abundance of iron- and mitochondria-related proteins. (Immuno)histochemical and mRNA assessments of fibrosis and inflammation were also performed.

RESULTS

We observed a significant increase in total elemental iron in hindlimb muscles of dko mice (+50%, P < 0.05) and in the diaphragm of mdx mice (+80%, P < 0.05), with both tissues exhibiting severe pathology. Iron dyshomeostasis was further evidenced by an increase in the storage protein ferritin (dko: +39%, P < 0.05) and ferroportin compared with Bl10 control mice (mdx: +152% and dko: +175%, P < 0.05). Despite having features of iron overload, dystrophic muscles had lower protein expression of ALAS-1, the rate-limiting enzyme for haem synthesis (dko -44%, P < 0.05), and the haem-containing protein myoglobin (dko -54%, P < 0.05). Deferiprone treatment tended to decrease muscle iron levels in mdx mice (-30%, P < 0.1), which was associated with lower oxidative stress and fibrosis, but suppressed haem-containing proteins and mitochondrial content. Increasing iron via dietary intervention elevated total muscle iron (+25%, P < 0.05) but did not aggravate the pathology.

CONCLUSIONS

Muscles from dystrophic mice have increased iron levels and dysregulated iron-related proteins that are associated with dystrophic pathology. Muscle iron levels were manipulated by iron chelation and iron enriched feed. Iron chelation reduced fibrosis and reactive oxygen species (ROS) but also suppressed haem-containing proteins and mitochondrial activity. Conversely, iron supplementation increased ferritin and haem-containing proteins but did not alter ROS, fibrosis, or mitochondrial activity. Further studies are required to investigate the contribution of impaired ferritin breakdown in the dysregulation of iron homeostasis in DMD.

Dielectrophoretic force measurement of red blood cells exposed to oxidative stress using optical tweezers and a microfluidic chip

Red blood cell (RBC) dysfunction is often associated with a pathological intervention, and it has been proposed as a critical risk factor for certain lethal diseases. Examining the cell viability of RBCs under various physiological conditions is essential and of importance for precise diagnosis and drug discovery in the field of medicine and pharmacy. In this paper, we report a new analytical method that employs dielectrophoretic (DEP) force measurements in absolute units to assess the viability, and potentially the functionality of RBCs. We precisely quantify the frequency-dependent DEP forces of the RBCs by using a micro-electrode embedded chip combined with optical tweezers. DEP characteristics are known to be well-correlated with the viability of biological cells, and DEP forces are measured in both fresh and long-term stored RBCs to investigate the effect that the storage period has on the cell viability. Moreover, we investigate the DEP behavior of RBCs when exposed to oxidative stress and verify whether EDTA protects the RBCs from an oxidant. From the experiments, it is found that the fresh RBCs without oxidative stress display very high DEP forces over the entire frequency range, exhibiting two cutoff frequencies. However, both the RBCs stored for the long-term period and exposed to oxidative stress reveals that there exist no significant DEP forces over the frequency range. The results indicate that the DEP forces can serve as a useful parameter to verify whether the RBCs in certain blood are fresh and not exposed to oxidative stress. Therefore, it is believed that our system can be applied to a diagnostic system to monitor the cell viability of the RBCs or other types of cells.

Intracellular free calcium concentration in lymphocytes of patients with muscular dystrophies

Intracellular free calcium concentration [( Ca2+]i) of human peripheral blood lymphocytes was determined by fluorescence spectroscopic measurements with quin2 in patients with different types of muscular dystrophy and in controls. The [Ca2+]i level in lymphocytes showed a significant increase in adult type (facioscapulohumeral and limb-girdle) muscular dystrophies, while it showed a decrease in Duchenne dystrophy as compared to the values of age- and sex-matched controls. The data obtained suggest an alteration in the effectiveness of the calcium pump in lymphocytes and may represent a sign of generalized membrane damage in these hereditary muscle diseases.

Carrier detection of Duchenne dystrophy by frequency analysis of the electromyogram

A new method for Duchenne muscular dystrophy (DMD) carrier detection based on frequency analysis of electromyograms (EMG) taken from relative force contractions shows great promise in classifying possible carriers. Nine carriers were examined and compared to nineteen normals in an attempt to define a discriminant function that would be effective in classification of possible carriers of the gene responsible for DMD. EMG data were taken at 20%, 40%, and 60% of maximum effort from the biceps brachii using a specially designed dynamometer apparatus. The apparatus was able to isolate the biceps muscle group and allowed for adjustment to accommodate different body sizes. Three signal processing methods were used to find variables in the frequency domain that would provide the best discriminant function based on the jackknife classification method. Of these methods, the most promising appears to be the high-to-low ratio method at 20% maximum contraction. When combining the high and low values found with this test in conjunction with the peak cepstrum values also found at 20% maximum contraction, discrimination was found to be 83.8% accurate. Because this classification is not based solely on definite carriers, and appears to be independent of serum creatine phosphokinase (CPK) values, it would seem that classification based on a definite carrier population could be performed with greater accuracy, especially with the addition of CPK values.

4-Nitrophenylalkaline phosphatase inhibition in muscular dystrophy

The allosteric behaviour of 4-nitrophenylphosphatase from membrane erythrocytes was investigated in Duchenne muscular dystrophy (DMD) patients, in female carriers and in healthy controls. Cooperative type kinetics with a Hill coefficient of -2.19, -1.71 and -1.54 has been obtained from the inhibition by fluoride in controls, female carriers and Duchenne patients, respectively. Our observation supports the previously described membrane abnormalities in DMD erythrocytes and may extend then to female carriers.

Some biophysical properties of the erythrocyte membrane in Duchenne muscular dystrophy

Inasmuch as prior authors have suggested a 'generalized membrane defect' in patients with Duchenne muscular dystrophy, this study was undertaken to examine some biophysical properties of the erythrocytes in affected individuals. Using the micropipette technique we investigated the rheological properties of erythrocytes from 11 Duchenne muscular dystrophy patients (boys 3-14 years old) and 5 carriers (mothers 20-42 years old). The mean elastic modulus and membrane viscosity of the patient's erythrocytes were not significantly different from those of a group of 8 unaffected age-matched boys. The carrier group did not differ significantly from the adult control group in any of the rheological parameters. A significant increase in the number of stomatocytes was observed in the patient group, and a similar trend (not statistically significant) was observed in the carrier group. The membrane lipid fluidity of erythrocytes from patients, carriers, and normal controls was assessed with three different probes by fluorescence depolarization, and no significant differences were found. Our results indicate that there is a progressive elevation of the membrane elastic modulus with increasing age of the patients: the younger patients have a lower elastic modulus than their age-matched controls, while the older patients have a higher elastic modulus than their age-matched controls.

Increased concentration of spectrin is observed in avian dystrophic muscle

A significant increase in the concentration of spectrin has been observed in dystrophic chicken pectoralis major muscle when compared to normal fast-twitch muscle. In normal muscle, alpha-spectrin-specific immunofluorescence delineates each myofiber with a network pattern of staining at the sarcolemma with little staining within the cytoplasm. In dystrophic fibers, numerous intensely stained areas occur within the cytoplasm and staining at the sarcolemma is increased, thereby obscuring or eliminating the highly regular network arrangement of spectrin usually seen in this region. When immunofluorescence experiments are performed on microsomal vesicles isolated from normal and dystrophic tissues, only a small fraction of normal vesicles are stained, whereas most of the dystrophic vesicles are associated with spectrin. An increase in spectrin concentration is observed using immunoautoradiography of whole muscle and isolated microsomes, thus supporting the immunofluorescent observations described above. The early-age post-hatching when increases in spectrin concentration can be detected and the simplicity of the immunofluorescent technique make this observation useful as a new diagnostic parameter. This observation also shows that the distribution of spectrin and its concentration within nonerythroid cells can be modified by abnormal physiological states; this modification may contribute to subsequent symptoms, such as increased rigidity and abnormal calcium metabolism, that are observed in dystrophy.

Proposed treatment of Duchenne muscular dystrophy with desferrioxamine

The primary disturbance in Duchenne muscular dystrophy (DMD) appears to affect membrane function, and changes characteristic of oxidant-induced damage occur in skeletal muscle and erythrocytes. There is recent evidence that DMD is a functional tocopherol deficiency, with reduced levels of the lipoprotein required to carry tocopherol to tissues. This may explain the parallels between DMD and dietary tocopherol deficiency. Thus DMD should follow the usual experience of other examples of oxidative pathology, where the balance between tocopherol, the main antioxidant in membrane lipids, and non protein-bound iron, an important catalyst of reactions which produce oxidizing free radicals, largely determines whether or not tissue damage occurs. Desferrioxamine prevents oxidant damage in vitro and in vivo by removing this iron, and may therefore be able to reverse the muscle damage of DMD. Recent experience with this drug in long term dialysis patients is consistent with this suggestion.

Electron spin resonance spin label studies of the erythrocyte membrane in Duchenne muscular dystrophy

The membrane organisation of erythrocytes from patients with Duchenne muscular dystrophy (DMD) and from asymptomatic carriers was studied by the electron spin resonance (ESR) spin label technique. Following the work of Sato et al [1978], we used 2-(14-carboxytetradecyl)-2-ethyl-4, 4-dimethyl-3-oxazolidinyloxyl as probe. We found no significant difference in lipid fluidity at 30 degrees C, measured by the ratio of the line height at central field to that at high field ho/h-1, in DMD patients or carriers compared to appropriate control persons. Our conclusions for the dystrophic boys differ from those of Sato et al [1978], although our data are consistent with theirs within experimental error. We also studied the variation of the ratio ho/h-1 over the temperature range 5-35 degrees C in these individuals. For normal erythrocytes there is a discontinuity in this plot around 15 degrees C that is absent in the erythrocytes of DMD patients [in agreement with the findings of Sato et al, 1978] and also absent in DMD carriers. We suggest the slope of this logarithmic temperature plot over the range 15-35 degrees C is a more useful empirical parameter as the presence of these discontinuities is sometimes uncertain, and using this parameter, we find a clear separation between carriers and controls.

Deformability and cell membrane properties of erythrocytes in Duchenne muscular dystrophy

In many investigations of the hypothesis of a membrane defect in Duchenne muscular dystrophy, the erythrocyte has been the cell of choice, but reported abnormalities in the Duchenne erythrocyte are disputed. Techniques of microsieving, cell surface staining and measurement of cell water diffusion turnover rate have been used in this investigation to examine erythrocyte properties. Measurements of pressure drop-velocity relations were carried out in a capillary pore rheometer using pure erythrocyte suspensions. The study showed that Duchenne erythrocytes do not behave differently from normal, results which are in substantial agreement with similar microsieving studies. A nuclear magnetic resonance method was used to measure cell water diffusion efflux which, using our cell surface data, could be related to cell membrane permeability. Under normal conditions and conditions of chemical interference with the membrane protein, the results revealed that the membrane pathways involved in water diffusion in Duchenne erythrocytes are unaltered.

Equilibrium density gradient analysis of erythrocytes from normal humans and patients with Duchenne muscular dystrophy

Human red blood cells were fractionated by centrifugation in a continuous Ficoll/Triosil density gradient and the density distribution was determined by scanning the gradient in situ. Variation of some of the conditions used showed that erythrocyte mean cell density is very sensitive to the type of anticoagulant and washing system employed. A population study of mean cell density showed no significant difference between males and females and no correlation with age. Patients with Duchenne muscular dystrophy showed no significant difference from normals in mean cell density but an almost sevenfold increase in the variance. This may explain the disparate findings of different workers.

Erythrocyte flexibility, ATPase activities and Ca efflux in patients with Duchenne muscular dystrophy, myotonic muscular dystrophy and congenital myotonia

Erythrocyte flexibility measured by a polycarbonate membrane filtration method showed increased fragility (265 +/- 163 Hb mg/l vs. controls 86 +/- 72 Hb mg/l; mean +/- SD; P less than 0.0025) and increased rigidity (123 +/- 96 mm Hg vs. 79 +/- 19 mm Hg; P less than 0.05) in patients with congenital myotonia, while both parameters were normal in patients with Duchenne muscular dystrophy or with myotonic dystrophy. Erythrocyte ghosts obtained from patients with MyD displayed highly significant increases in both (Na+ + K+)-ATPase and (Ca2+ + Mg2+)-ATPase activities (P less than 0.005) and to a lesser extent in Mg2+-ATPase activity (P less than 0.05), while no difference was seen between patients with DMD and age-matched controls. The efflux of Ca2+ was increased from erythrocytes of patients with DMD as compared to age-matched controls (82 +/- 2% vs. 70 +/- 4%; P less than 0.005), while no difference was detected between patients with MyD and age-matched controls.

Is erythrocyte membrane phospholipid organisation abnormal in Duchenne muscular dystrophy?

Many of the abnormalities reported in erythrocytes from Duchenne muscular dystrophy (DMD) patients, including alterations in the physical state of the membrane as determined by electron spin resonance, could arise from changes in the lipid components. Although several investigators have shown there to be no compositional differences between normal and DMD erythrocytes, there still exists the hitherto unexplored possibility that the normal asymmetric organisation of the lipids may be deranged in the disease. This report is concerned with the probing of the asymmetric transbilayer distribution of the glycerophospholipids using phospholipase A2 from bee venom. Our results suggest that more phosphatidyl choline (PC) is available for attack by the enzyme in the outer leaflet of the bilayer in DMD erythrocytes than in normals. This may be due to a greater than normal proportion of the PC being present in the outer leaflet or to enhanced transbilayer movement of PC molecules from the inner leaflet. Whichever the explanation, these findings indicate an organisational abnormality in DMD erythrocyte membranes.

Erythrocyte membrane abnormalities in hypertension: a comparison between two animal models

Calcium-membrane interactions have been studied in two animal models of hypertension using the erythrocyte membrane as a model system. The Okamoto-Aoki strain of spontaneously hypertensive rats (SHR) was the first examined, and the activities of the Ca++/Mg++-ATPases in the membrane of SHR erythrocytes were found to be consistently higher than those of the normotensive controls (WKY), while other membrane enzymes such as Na+/K+-ATPase and acetylcholinesterase were not detectably altered. Erythrocyte membranes of the SHR also have a higher passive permeability to calcium as well as other functional and compositional differences when compared to those of the WKY. These findings suggest that the membrane alterations in the SHR may be related to an increased passive permeability to calcium, and a possibly compensatory increase in Ca++/Mg++-ATPase activity in these animals. The second animal model examined was the deoxycorticosterone/salt-induced hypertension (DOCA) in uninephrectomized rats. In DOCA rats with comparable degree of blood pressure elevation, none of the erythrocyte membrane abnormalities observed in the SHR were present, suggesting that the latter alterations are probably genetically determined and not a consequence of elevated arterial pressure.

Evidence against a generalized membrane defect in dystrophic mice platelets

The response of the membrane-bound enzyme AChE to changes in temperatures was investigated to test the applicability of the "generalized membrane defect" hypothesis proposed for human myotonic and Duchenne muscular dystrophies to the two forms of muscular dystrophy expressed in mice. For intact platelets from homozygous normal and dystrophic mice of both strains, a break (Tc) occurred in the Arrhenius plot of AChE activity at approximately 22 C. Solubilization of membrane-bound AChE by Triton X-100 produced a nonlinear Arrhenius plot over the temperature range (7.7 C to 37 C) in normal and dystrophic mice of both strains. However, in the presence of phospholipase A2 + C and Triton X-100, a linear Arrhenius plot was produced indicating that the membrane-bound enzyme is normally modulated by a bulk lipid domain as well as by a tightly bound (immobilized) phospholipid domain. The temperature response of platelet AChE from normal and dystrophic mice of both strains was not significantly different. These results showing normal temperature kinetics of AChE do not lend support to the theory of a membrane defect in the platelets of dystrophic mice.

Erythrocyte spectrin in Duchenne muscular dystrophy

The primary structure of erythrocyte spectrin bands I and II from controls and patients with Duchenne muscular dystrophy was compared by 2-dimensional peptide mapping. 125I-labelling was done either by the chloramine-T method or using the Bolton and Hunter reagent followed by treatment with trypsin or chymotrypsin, resulting in four different peptide maps from each band of spectrin. Although all the peptide maps of band I were considerably different to those of band II, there were no consistent differences in the maps of bands I and II from controls compared to the corresponding maps from patients with Duchenne muscular dystrophy.

Effects of inhibition of RBC HCO3-/Cl- exchange on CO2 excretion and downstream pH disequilibrium in isolated rat lungs

To determine the effects of the speed of the erythrocyte membrane chloride shift on pulmonary gas transfer, CO2 exchange and the kinetics of pH equilibration were measured with isolated rat lungs perfused with 20% suspensions of human erythrocytes. The lungs were ventilated with room air, and the inflowing perfusate blood gases were similar to those in mixed venous blood in vivo. All experiments were performed at 37 degrees C. Rates of CO2 excretion were determined by measuring the fraction of CO2 in mixed expired gas in a steady state. The time-course of extracellular pH equilibration in the effluent perfusate was measured in a downstream stopflow pH electrode apparatus. CO2 excretion was reduced by approximately 16% when the lungs were perfused with suspensions containing erythrocytes whose HCO-3/Cl- exchange rates was inhibited, compared with CO2 excretion when the lungs were perfused with normal erythrocyte suspensions. A fall of 0.06 in effluent perfusate extracellular pH was noted during perfusion with inhibited erythrocyte suspensions, in contrast to no observable downstream pH change during perfusion with normal erythrocyte suspensions. These results are in close agreement with the predictions of a theoretical model. Our observations suggest that CO2 transfer in capillary beds will be adversely affected in vivo when the rate of the erythrocyte HCO-3/Cl- exchange is abnormally low. Since a number of commonly used drugs are known to inhibit the chloride shift in human erythrocytes, these findings may have important clinical implications, especially in patients with impaired lung function.

Calcium flux of erythrocytes in Duchenne muscular dystrophy

The calcium flux of erythrocytes from patients with Duchenne muscular dystrophy (DMD) was measured. Passive influx was determined using erythrocytes incubated with lanthanum chloride as a specific inhibitor to calcium transport. There was no significant difference in calcium influx into cytosol and into membrane fractions between DMD and control age-matched boys. Influx of calcium was also determined using ATP-depleted erythrocytes incubated without the inhibitor. Again there was no significant difference between DMD and control values. Efflux of calcium was measured using erythrocytes loaded with calcium ionophore A23187. Calcium efflux speed was related to intracellular calcium concentration and the efflux reached a plateau at about 1 mM. There was no significant difference in calcium efflux rate as a function of intracellular calcium concentration between DMD and control.

Membrane elasticity of erythrocytes from normal and dystrophic mice

The membrane deformability of erythrocytes from normal and dystrophic mice was determined using a flow channel technique whereby erythrocytes attached to the floor of a parallel plate channel were deformed by fluid shear forces. A nonlinear stress-strain experimental behavior was observed for both populations of erythrocytes which was best described with a polynormal expression: tau s = a epsilon x + [b epsilon x3/2 epsilon x + 1]. A comprehensive statistical analysis of the data indicated that a large percentage of the variance of the data was due to the experimental design. Furthermore, the 2 populations of cells were different in terms of the strain-stress relationship which best fitted the data, i.e., epsilon x = alpha tau s + beta tau s2 + gamma tau s3. Up to a shear stress of 5.5 dyn/cm2, where 95% of the data points were found, the dystrophic erythrocytes were slightly but significantly more deformable than the normal erythrocytes.

Spectrin extractability from erythrocyte in Duchenne muscular dystrophies and the effect of proteases on erythrocyte ghosts

We studied the erythrocyte membrane proteins from patients with Duchenne muscular dystrophy (DMD) using SDS-polyacrylamide gel electrophoresis. Our observations were the following: (1) The electrophoretic densitogram of freshly prepared DMD-ghosts was similar to that of controls. After the extraction of spectrin from ghosts with 1 mmol/l EDTA, pH 8.0, the unextractable spectrin remained more firmly bound in the DMD ghost residues than in controls. Extractability of spectrin from DMD ghosts was decreased about 20%. In addition, several minor bands were detected between spectrin and Band 3 in the DMD ghost residues (treated ghosts). (2) Ca2+-activated, neutral protease reacted more effectively with spectrin of DMD ghosts and ATP-depleted ghosts than with that of controls. (3) Erythrocyte actin (Band 5) of DMD ghosts was more fragile than that of controls and of ATP-depleted actin in the EDTA extracts. Gradually, partial degradation of actin was observed for three weeks at 4 degrees C. (4) The intracellular ATP level and the activities of membrane-bound (Mg2+--Ca2+) ATPases in DMD erythrocytes were unchanged. We suggest that spectrin from DMD ghosts as well as actin may be subject to increased degradation.

Osmotic fragility of erythrocytes in myopathies

Erythrocytes taken from patients with myopathy have previously been reported to have increased osmotic fragility. We have examined the osmotic fragility of erythrocytes from patients with various myopathies and from carriers. The osmotic fragility was the same as in unaffected controls.

Altered erythrocyte spectrin extractability in Duchenne muscular dystrophy

Spectrin extractability was measured in the erythrocyte membranes obtained from patients with Duchenne muscular dystrophy (DMD) and normal matched controls. After the extraction of spectrin by adding deionized water, an aliquot of the pellet was applied to 6% SDS-polyacrylamide gels. Spectrin-Band 3 ratio on the gels was used as an indicator of spectrin extractability. Our data disclosed that spectrin extractability is significantly reduced in DMD patients when compared with that of controls and these results suggest that spectrin from DMD patients is more tightly bound to the membranes. Our data may also be applicable to the discussion of the relationship of spectrin to other membrane properties as well as to previously described membrane abnormalities in DMD erythrocytes.

A spin label study of the erythrocyte membranes in Duchenne muscular dystrophy

Red blood cells and freshly prepared erythrocyte membranes of 15 patients with Duchenne muscular dystrophy (DMD) as well as age-matched controls were studied by the spin label method. No significant modifications appeared for spin-labelled proteins of ghost membranes. With the two fatty acid spin labels, 5-nitroxide stearate and 16-nitroxide stearate, we have confirmed previous results of Sato et al. concerning the thermal behaviour of the erythrocyte membranes, i.e. no change near the polar part probed by 5-nitroxide stearate and a linearization of the fluidity versus temperature variation around 12 degrees C, as explored by 16-nitroxide stearate. Furthermore we studied in the whole erythrocyte the amplitude of the 5-nitroxide stearate electron spin resonance signal as a function of the microwave power. This saturation effect was observed in 12 out of 15 controls and only in 1 out of 13 DMD cases studied. In erythrocyte membranes labelled with 16-nitroxide stearate the penetration of the label inside membranes was statistically different between DMD and controls. These new findings furnish further arguments in favour of a structural alteration of the phospholipid organization of erythrocyte membranes in DMD. Associated together, these different sets of tests obtained by spin labelling permit good statistical discrimination between DMD and normal subjects.

Specificity of biophysical and biochemical alterations in erythrocyte membranes in neurological disorders--Huntington's disease, Friedreich's ataxia, Alzheimer's disease, amyotrophic lateral sclerosis, and myotonic and duchenne muscular dystrophy

Previous studies in our laboratory had demonstrated alterations in the physical state of membrane proteins in erythrocytes in Huntington's disease. In order to assess the specificity of our findings, the results of electron spin resonance studies of protein and lipid components, scanning electron-microscopic studies, enzymatic analyses of membrane-bound sodium plus potassium stimulated, magnesium-dependent adenosine triphosphatase and protein kinase, and cell deformability studies of erythrocyte membranes have been performed in the neurological disorders, Huntington's disease, Friedreich's ataxia, Alzheimer's disease, amyotrophic lateral sclerosis, and myotonic and Duchenne muscular dystrophy. Comparison of the results revealed that alterations in the biophysical and biochemical states of erythrocyte membranes in each disorder are specific to the particular disease state with the exception of those in Friedreich's ataxia and Alzheimer's disease. In the latter instance, the clinical and pathological alterations suggest that these two diseases have different primary defects. Our studies suggest that the molecular basis of each disease is different. In addition, the results suggest that biophysical and biochemical investigations of extraneural tissue in Huntington's disease and other neurological disordes have the potential of clarifying the molecular mechanisms by which these diseases arise.

Biochemistry of muscle membranes in Duchenne muscular dystrophy

In Duchenne muscular dystrophy, as in other genetic diseases, there must be a biochemical abnormality. This fundamental genetic fault has not been identified, but several indirect lines of evidence suggest that the surface membranes of skeletal muscle are affected. The biochemical evidence implies abnormal egress of soluble enzymes and other proteins from muscle, abnormal permeability, and altered properties of membrane-bound enzymes. As a result of the presumed genetic abnormality, functional properties are altered, and impaired regulation of intracellular calcium content could be responsible for the hallmarks of the disease--progressive weakness and degeneration of muscle. The evidence is by no means conclusive, however, and some of it is contradictory. Technical advances must be made before isolated membranes can be characterized biochemically. Other theories are also being evaluated.

Red cell membrane protein phosphorylation in hemolytic anemias and muscular dystrophies

We review our current understanding of membrane phosphorylation in normal and abnormal erythrocytes. The major phosphoproteins in red blood cell (RBC) membranes are spectrin (band 2), bands 3, 2.1, and 4.5, and glycophorin A. At least two protein kinases can be distinguished on the basis of their stimulation by cyclic AMP and salt; they are present both in the membrane and in the cytosol. Analysis of the conflicting data on endogenous membrane-protein phosphorylation in abnormal RBCs indicates a considerable variability of phosphorylation rates which largely depends on the manner of preparation of ghosts and enzyme assay conditions. This variability reflects differences in the partitioning of protein kinases between the membrane and cytosol, the specificity and accessibility of membrane-protein substrates, and reaction kinetics. We select examples of data from several hemolytic anemias to illustrate that precautions are needed to interpret abnormalities of membrane-protein phosphorylation properly; we discuss possible new methodological approaches.

Red blood cell alterations in muscular dystrophy: the role of lipids

Biochemical, morphologic, and biophysical studies support the concept that the red blood cell (RBC) membrane is altered in both myotonic muscular dystrophy (MyD) and Duchenne muscular dystrophy (DMD). These studies have not identified a primary metabolic defect that would explain the various alterations of membrane properties. Since the lipid milieu of the membrane affects most membrane properties, it has been extensively investigated in MyD and DMD. Although some studies have suggested specific lipid abnormalities, no reproducible alterations have been reported in the major lipid constituents of the RBC membrane in these disorders. These findings suggest that major alterations of the predominant membrane lipids are not involved in these diseases. Furthermore, studies of the RBC membrane do not provide definitive statements as to the inborn error of metabolism, whether proteins or lipid constituents are primarily affected, or even whether the described alterations are intrinsic to the membrane or are secondary to some circulating factors. Nevertheless, RBCs have proved useful in demonstrating the involvement of the plasma membrane in muscle disorders and should be important in defining how such membrane perturbations affect transport mechanisms.

Physical probes of biological membranes in studies of the muscular dystrophies

This review deals with recent physical approaches to the study of biomembranes. First, current concepts of the structure and dynamic organization of biological membranes are considered. The theoretical basis and practical application of various physical probe techniques are then discussed with specific reference to their usefulness in studies of these membranes. Particular emphasis is given to electron spin resonance and fluorescence techniques and to the potential difficulties encountered in their use and interpretation. Finally, reports applying these physical probes to various aspects of the human muscular dystrophies are reviewed and our current information in this area is summarized.

Reduced adhesiveness between skin fibroblasts from patients with Duchenne muscular dystrophy

The intercellular adhesiveness of skin fibroblasts from patients with Duchenne muscular dystrophy and normal controls has been measured by determining the collision efficencies of cells using the couette viscometer. The collision efficencies for dystrophic cells were significantly lower that those for normal cells (0.01 greater than P greater than 0.005), indicating that dystrophic cells are less adhesive than normal cells.

An evaluation of some carrier detection techniques in Duchenne muscular dystrophy

Some recently described abnormalities in the serum and red cell membranes in Duchenne dystrophy have been examined as methods of carrier detection in a single-blind controlled study. Twelve carriers (4 definite, 3 probable and 5 possible carriers previously found to have raised creatine kinase levels) and 12 normal female controls of the same age, were examined on 3 separate occasions at approximately two-weekly intervals. Analysis of age-dependent red cell shape changes, serum haemopexin levels, red cell K+ efflux rate, sensitivity of red cell ghost membrane ATPase to ouabain, membrane protein phosphorylation studies and lactate dehydrogenase isoenzyme profiles on agarose gel electrohoresis all failed to distinquish carriers from controls. The carriers suffered muscle cramps more frequently than the controls and all but one carrier and two control subjects were correctly identified by manual muscle strength testing, certain proximal muscles in paricular being consistently weaker in carriers than in the control group subjects. Scalar electrocardiography revealed higher values for the R/S ratio in Leads V1 and V2 and the sum (R-S) in V2.

Erythrocyte membrane autophosphorylation in Duchenne muscular dystrophy: effect of two methods of erythrocyte ghost preparation on results

We have compared the effects of two slightly different methods of erythrocyte ghost preparation on membrane autophosphorylation in Duchenne muscular dystrophy. Addition of 1 mmol/l EDTA to two of the washing steps altered the differences between patients and controls. These data support the known sensitive interrelationship of Ca2+ and erythrocyte membrane autophosphorylation, underline the importance of strict adherence to methodology when comparing data, and have suggested a new direction of investigation.

Lyon phenomenon in ouabain-treated erythrocytes of Duchenne muscular dystrophy carriers as revealed by cell electrophoresis

Using the cell-electrophoretic method, 0.1 mM ouabain/l Eagle MEM medium caused a moderate decrease in electrophoretic migration time (EMT) of erythrocytes in 19 out of 23 DMD-affected patients. In 8 out of 10 healthy boys, 0.1 mM ouabain induced an increase in erythrocyte EMT. Under the influence of 0.1 mM ouabain, the erythrocytes clearly showed a bimodal distribution of EMT in 9 out of 13 definite carriers and in 8 out of 17 possible carriers. In DMD patients, and in 10 healthy boys and 10 healthy women, no bimodal distribution of EMT was observed.

Erythrocyte spectrofluorometric abnormalities in Duchenne patients and carriers. A new approach to carrier detection

Duchenne muscular dystrophy (DMD) is a disorder whose pathogenesis is attributed, according to the most recent theories, to generalized membrane abnormalities, including red cell membrane. The study of erythrocyte ghosts in patients affected by DMD showed alterations in ion transport and in various enzymatic activities. Employing a spectrofluorometric method using 1-anilino-8-naphthalene sufonate (1.8-ANS) we have tried to characterize the erythrocyte ghosts of DMD patients, definite DMD carriers and normal controls, matched for age and sex. We found an increase of membrane polarity in DMD and definite DMD-carrier erythrocyte ghosts. Using this new method we were able to: - confirm by means of a different technique the previous observations of many authors on erythrocyte ghost alterations in DMD - find a new technique useful in detecting the DMD carriers. It is noteworthy that in such a way the detection rate of definite DMD carriers was higher than with the CPK test.

Fatty acid activation and transfer in blood cells of patients with muscular dystrophy

Two membrane-bound enzymes, concerned in repair of erythrocyte membranes, have been investigated in patients with muscular dystrophy. The activation of long-chain fatty acids is normal in erythrocytes from Duchenne patients, but increases two-fold in cells from myotonic dystrophy patients (congenital form). This alteration is not present in leucocytes. In all leucocytes tested palmitate was the preferred substrate while palmitoleate and linoleate were activated at a lower rate. In the erythrocytes the 3 fatty acids were activated at the same rate. Carnitine palmitoyltransferase was not significantly altered in erythrocytes of both groups of patients.

Electron spin resonance, hematological, and deformability studies of erythrocytes from patients with Huntington's disease

Electron spin resonance, hematologic, and deformability studies of erythrocytes from patients with Huntington's disease have been performed A decreased deformability of Huntington's disease erythrocytes compared to normal controls was demonstrated. No difference in erythrocyte hematologic indices, osmotic fragility, reticulocyte counts, or intracellular Na+ concentration was found. Huntington's disease serum had no demonstrable effect on electron spin resonance parameters of a protein-specific spin label attached to membrane proteins in control erythrocytes compared to the effect of control serum. This finding suggests that under the conditions employed no serum component or circulating factor is responsible for the changes in the physical state of membrane proteins in Huntington's disease erythrocytes (Butterfield, D.A., Oeswein, J.Q. and Markesbery, W.R. (1977) Nature 267, 453--455). No alteration in lipid fluidity of Huntington's disease erythrocyte membranes could be discerned suggesting that the underlying molecular defect in Huntington's disease involves a membrane protein. The results of the present studies on erythrocytes strongly support the concept that Huntington's disease is associated with a generalized membrane abnormality.

Role of intracellular calcium in promoting muscle damage: a strategy for controlling the dystrophic condition

It is suggested that various muscle diseases and examples of experimentally-induced muscle damage arise because of a high calcium level in the myoplasm. When [Ca2+]i is raised experimentally in amphibian or mammaliam muscle by treatment with A23187 or caffeine, myofilament degradation follows quickly. Such a rapid action suggests the involvement of a sequence of proteolytic activity that is stimulated by a rise in [Ca2+]i. Ca2+ might either trigger protease activity directly or indirectly, or promote the release of lysosomal enzymes. A high [Ca2+]i in dystrophic muscle is believed to be the resultant of a sequence of events that is summarized in the figure. Suggestions are presented for different ways in which the steady-state position of [Ca2+]i might ultimately be controlled for the clinical amelioration of some dystrophic conditions.

Alterations of membrane phosphorylation in erythrocyte membranes from patients with Duchenne muscular dystrophy

The phosphorylation of spectrin, band 3 protein, and the phospholipids of erythrocyte membranes (ghosts) was examined in 10 patients with Duchenne muscular dystrophy (DMD) and in healthy age- and sex-matched controls. The rates of phosphorylation of spectrin and band 3 protein were significantly higher in ghosts prepared from patient blood than from control blood at both 30 degrees C and 37 degrees C. However, the mean increases in the rate of phosphorylation of both spectrin and band 3 protein in response to a temperature change from 30 degrees C to 37 degrees C were identical in ghosts from patient and controls. Phosphorylation of phospholipid and its temperature response did not differ between patients and controls. These results complement previous observations of differences in erythrocytes from patients with DMD. The similarity of the changes in phosphorylation of both spectrin and band 3 protein indicates a common cause, possibly their lipid environment.

The fatty acid composition of various lipid fractions isolated from erythrocytes and blood plasma of patients with Duchenne and congenital myotonic muscular dystrophy

Ten lipid fractions, both neutral and phospholipids, were isolateed from erythrocytes of patients with Duchenne and congenital myotonic dystrophy. These fractions were: phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin, lysophosphatidylcholine, phosphatidic acid, glycosphingolipids, triglycerides, diglycerides and one unknown. The fatty acid compositions were compared with control values. The major deviation was a decreased level of palmitoleic acid (16 : 1omega7) in three neutral lipid fractions. It was lowered from 9.1 to 1.3% in diglycerides and from 10.6 to 2.6% in triglycerides in myotonic dystrophy. In Duchenne muscular dystrophy this percentage was decreased from 9.1 to 4.0 in diglycerides. From blood plasma were isolated phosphatidylcholine, lysophosphatidylcholine, sphingomyelin and phosphatidylethanolamine. The myristic acid (14 : 0) content was raised in lysophosphatidylcholine (from 4.4 to 8.6%) and in sphingomyelin (from 3.3 to 5.0%) in myotonic dystrophy, In the latter phospholipid the stearic acid level was decreased from 18.6 to 12.8%. In phosphatidylcholine from plasma in myotonic dystrophy the level of eicosatrienoic acid (20 : 3omega6) was lowered from 3.1 to 2.0%. Plasma fractions from Duchenne dystrophy showed no deviation. The results do not constitute an explanation for the various biochemical abnormalities found in dystrophic erythrocytes. Neither do they point to a defect in a major pathway in lipid metabolism. However, an aberration in the de novo synthesis of lipids in immature red blood cells cannot be excluded.