Does the induced membrane have antibacterial properties? An experimental rat model of a chronic infected nonunion.

INTRODUCTION: The Masquelet procedure proved its efficiency in treating infected nonunion filling bony gaps up to 25 cm. Yet the use of local antibiotics is still questionable in the daily practice with lack of evidence regarding its usefulness in controlling infection. An experimental rat model is put in place to study the antibacterial properties of the induced membrane produced during the first stage of Masquelet. METHOD: Twenty-three-month-old wistar male rats are inoculated with a 0.5 mL solution of 10^8 CFU/mL MRSA over a critical fracture done on the right femur. Six weeks later, remaining 11 rats exhibiting signs of a chronic infection with a sinus tract and oozing pus along with radiological nonunion are used for a first stage Masquelet procedure. They are randomly divided into two groups with six rats having no local antibiotic in the cement mixture and five rats having 3 g of vancomycin mixed with gentamycin loaded cement. Six weeks later (twelve weeks from baseline), all eleven rats are euthanized and blood samples for C-reactive protein are withdrawn. The induced membrane is identified and resected along with bone fragments and sent for cultures and pathology. RESULTS: MRSA is isolated in the cultures of all six rats in the first group where no local antibiotic was added. Altered polymorphonuclears with abscess and pus are noted on four of six pathology samples. However in the second group where local antibiotics were added, three out of five rats exhibited eradication of MRSA (p = 0.034) and all samples did not exhibit clear infection signs on pathology. A pyo-epithelioid over a foreign body reaction is seen predominantly in this group demonstrating a regenerative process. DISCUSSION: The induced membrane does not have antimicrobial properties capable of overcoming an infected nonunion on its own. When local antibiotics were added during the first stage of the Masquelet procedure, new bone formation occurred indicating the need to control an infection in order for bone union to occur. CONCLUSION: Local antibiotics use in adjunction to extensive debridement is advisable during the first stage of a Masquelet procedure for an infected nonunion.

Exosomes: The New Mediator of Peritoneal Membrane Function.

Fibrosis and angiogenesis are the most common processes that result in progressive peritoneal tissue remodeling and, eventually, peritoneal membrane dysfunction. The role of exosomes, which contributes to intercellular communication, in these processes has been neglected. Various biomolecules, including DNA, mRNA, proteins, lipids, and particular certain miRNAs, can be transferred by exosomes to local, neighboring and distal cells. Upon stimulation by cytokines or other microenvironment stimuli, donor cells release a mass of exosomes to peritoneal mesothelial cells, further affecting fibrosis and angiogenesis. This important exosomes-mediated intracellular communication is thought to regulate peritoneal membrane function. Understanding the molecular mechanisms of these processes, targeting changes in exosomes and regulating exosomal miRNAs will advance therapeutic methods for protecting peritoneal membrane function.

Quantification of transmembrane currents during action potential propagation in the heart.

The measurement, quantitative analysis, theory, and mathematical modeling of transmembrane potential and currents have been an integral part of the field of electrophysiology since its inception. Biophysical modeling of action potential propagation begins with detailed ionic current models for a patch of membrane within a distributed cable model. Voltage-clamp techniques have revolutionized clinical electrophysiology via the characterization of the transmembrane current gating variables; however, this kinetic information alone is insufficient to accurately represent propagation. Other factors, including channel density, membrane area, surface/volume ratio, axial conductivities, etc., are also crucial determinants of transmembrane currents in multicellular tissue but are extremely difficult to measure. Here, we provide, to our knowledge, a novel analytical approach to compute transmembrane currents directly from experimental data, which involves high-temporal (200 kHz) recordings of intra- and extracellular potential with glass microelectrodes from the epicardial surface of isolated rabbit hearts during propagation. We show for the first time, to our knowledge, that during stable planar propagation the biphasic total transmembrane current (I(m)) dipole density during depolarization was ∼0.25 ms in duration and asymmetric in amplitude (peak outward current was ∼95 µA/cm(2) and peak inward current was ∼140 µA/cm(2)), and the peak inward ionic current (I(ion)) during depolarization was ∼260 µA/cm(2) with duration of ∼1.0 ms. Simulations of stable propagation using the ionic current versus transmembrane potential relationship fit from the experimental data reproduced these values better than traditional ionic models. During ventricular fibrillation, peak I(m) was decreased by 50% and peak I(ion) was decreased by 70%. Our results provide, to our knowledge, novel quantitative information that complements voltage- and patch-clamp data.

Semi-automated quantitative analysis of the middle limiting membrane in tubercular serpiginous-like choroiditis using swept-source optical coherence tomography.

To analyze the longitudinal changes in the outer plexiform layer (OPL) in patients with tubercular serpiginous-like choroiditis (TB SLC) and compare it to the healthy control population. Clinical and imaging data of subjects with TB SLC (minimum 6-month follow-up) and healthy control subjects were reviewed. Optical coherence tomography (OCT) imaging obtained using swept-source device (DRI Triton, Topcon, Japan) from three visits (baseline, 3 months, and 6 months) were analyzed. Three OCT scans were chosen-one passing through the center of the fovea, one line above, and one line below. After random indexing to anonymize the images, they were pre-processed and fed into an automated pipeline to identify, crop, and measure the area of the OPL in the line scan. Longitudinal comparisons of OPL within the patient group were performed. The study included 32 eyes (16 patients; 11 males; mean age: 32.9 ± 7.8 years) with TB SLC. Twenty-eight eyes (14 subjects; 10 males: mean age: 31.1 ± 6.2 years) of healthy control subjects (age- and gender-matched) were also selected. The area of OPL was significantly different between the baseline and month 6 visit (6288 ± 1803 versus 5487 ± 1461; p = 0.0002) at the central scan passing through the fovea. For the scans above and below the fovea, the reduction in OPL area was significant at each visit (p < 0.0001). In comparison with healthy control subjects, OPL area values in patients with TB SLC were significantly lower at the month-3 (6116 ± 1441 versus 7136 ± 2539; p = 0.04) and the 6-month visit (5487 ± 1461 versus 7136 ± 2539; p < 0.001). The atrophied OPL at month 6 has been referred to as the "middle limiting membrane" (MLM). Subjects with TB SLC may develop progressive atrophy of the OPL resulting in formation of MLM, which is seen as a hyper-reflective line replacing the OPL. The analysis of longitudinal changes in the OPL may be useful in predicting anatomical and functional outcomes in these patients.

Postnatal development of carotid body glomus cell response to hypoxia.

This study examines developmental changes in CB glomus cell depolarization, intracellular calcium ([Ca(2+)](i)) and the magnitude of an O(2)-sensitive background ionic conductance that may play roles in the postnatal increase in oxygen sensitivity of glomus cells isolated from rats of 1-3 days and 11-14 days postnatal age. Using fura-2 and perforated patch whole cell recordings, we simultaneously measured [Ca(2+)](i) and membrane potential (E(m)) during normoxia and hypoxia. Resting E(m) in normoxia was similar at both ages. Hypoxia caused a larger E(m) depolarization and correspondingly larger [Ca(2+)](i) response in glomus cells from 11- to 14-day-old rats compared to 1-3-day-old rats. E(m) and [Ca(2+)](i) responses to 40mM K(+) were identical between the two age groups. Under normoxic conditions both age groups had similar background conductances. Under anoxic conditions (at resting membrane potential) background K(+) conductance decreased significantly more in cells from 11- to 14-day-old rats compared to cells from 1- to 3-day-old rats. Glomus cells from newborns therefore have less O(2)-sensitive background K(+) conductance. These results support the hypothesis that postnatal maturation of glomus cell O(2) sensitivity involves developmental regulation of the expression and/or O(2)-sensitivity of background ionic conductances.

Ventricular septal defect associated with aneurysm of the membranous septum.

The most common variety of ventricular septal defect, a perimembranous defect, is frequently associated with a so-called aneurysm of the membranous septum. Previous studies have suggested that ventricular septal defects associated with an aneurysm of the membranous septum tend to spontaneously decrease in size or close more than defects without such an aneurysm. To better define the natural history of this entity, clinical and catheterization data from 87 patients with ventricular septal defect and aneurysm of the membranous septum were reviewed. The initial evaluation was made at a median age of 0.3 years (range 0.1 to 11), with the final evaluation at a median age of 10 years (range 1.5 to 20) and a median duration of follow-up of 8.6 years (range 1.2 to 18.8). Approximately 75% of the ventricular septal defects had a small or no left to right shunt at last evaluation. Overall, 48 patients (55%) had no significant change in the size of the defect, and 39 (45%) showed improvement during the period of observation. Only four patients (5%) had spontaneous closure of the defect. Of the 49 patients who presented with a large left to right shunt, with or without congestive heart failure, 23 (47%) had persistence of a shunt large enough to warrant surgery. When spontaneous improvement occurred, it did so by 6 years of age in all but one patient. Therefore, a continued tendency for a ventricular septal defect associated with an aneurysm of the membranous septum to spontaneously decrease in size or close after this age may be less likely than previously suggested.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental studies of the effects of abnormal venous valves on fluid flow.

The effects of variations in the venous valve anatomy are studied experimentally using an artificial system that mimics the bicuspid valves normally found in veins in the lower extremities. The artificial valves are constructed from thin-walled, latex tubing and polyurethane film. The experimental variables in the study are the gap width between the leaflet attachments at the vein wall and the ratio of the sinus depth to vein diameter. The results show that the antegrade mass flow rate is not affected to the same degree when compared to retrograde flow by the various valve configurations examined in this study. The results also indicate that increases in the gap width, which serve to increase the degree of imperfect wall attachment, have less effect on retrograde mass flow rate in valves with deeper sinuses.

The Function of the Distal Interosseous Membrane and its Relevance to the Stability of the Distal Radioulnar Joint: An Anatomical and Biomechanical Review.

The purpose of this article is to review functional anatomy and biomechanics of the distal interosseous membrane (DIOM) and its relevance to the stability of the distal radioulnar joint. The intact DIOM constrained dorsal dislocation of the radius, but it seldom constrained palmar dislocation. A residual ulnar translation deformity of the radial shaft in distal radius fractures has the potential to cause the distal radioulnar joint instability when the triangular fibrocartilage complex injury is also present, because it may result in detensioning of DIOM. Ulnar shortening with the osteotomy performed proximal to the attachment of the DIOM had a more favorable effect on stability of the DRUJ compared with the effect of distal osteotomy, especially in the presence of the distal oblique bundle (DOB). The longitudinal resistance to ulnar shortening was significantly greater in proximal shortening than in distal shortening.

Exercise-induced membrane failure in paramyotonia congenita.

A marked decrease in the amplitude of the evoked thenar compound muscle action potential followed brief exercise at room temperature in two patients with paramyotonia congenita. This decline was more rapid and pronounced in our patient with coexistent thyrotoxicosis. The prolonged recovery period in paramyotonia congenita differs from the brief exercise-induced decreased compound muscle action potential seen in myotonia congenita and myotonic dystrophy. These findings suggest that exercise, like cold exposure, decreases membrane excitability in paramyotonia congenita.

Comparative study on age-related changes and atherosclerotic involvement of the coronary arteries of male and female subjects up to 40 years of age.

In an unselected population sample of Bucharest, including 536 subjects (284 males and 252 females) aged up to 40 years, sex appeared as one of the most important factors influencing the pattern of coronary artery growth and remodelling, as well as the pattern of atherosclerotic involvement. The internal elastic membrane of the female coronary arteries of neonates, children, juveniles and adolescents manifested a lesser tendency to fragment, to interrupt and to exhibit elastolysis than did the corresponding internal elastic membrane of male subjects. In the anterior descending and circumflex arteries, female subjects had less intima than males of similar age. Women developed the first atherosclerotic plaques a decade later than men and at a similar age showed fewer atherosclerotic plaques and atheromas. These sex differences were statistically significant for the anterior descending and circumflex arteries, but not for the right coronary artery. During adulthood, the number of women with a three vessel involvement was half that of men. In successive age groups, the degree of luminal narrowing by atherosclerotic plaques was constantly and consistently lower in female than in male subjects.

Retinal detachment prevents normal assembly of disk membranes in vitro.

The effects of retinal detachment upon disk membrane assembly in rod outer segments were assessed in Xenopus laevis retinas that had been maintained in eyecup cultures for up to 4 days. In these cultures, assembly of disk membranes occurred at a normal rate in regions of the retina that remained attached to the retinal pigment epithelium. In regions of the retina that were detached from the pigment epithelium, the assembly of new disk membranes either was abnormal or was inhibited. This result cannot be attributed to reduced access of cells in the detached retina to oxygen and metabolites. The experiments described here suggest that the apposition of the retina with the pigment epithelium is a necessary condition for normal disk membrane assembly in Xenopus retinas. This effect may be mediated by contact between the rod outer segments and the pigment epithelium, or by trophic factors in the subretinal space.

In vitro measurement of contractile force of transvitreal membranes formed after penetrating ocular injury.

We adapted a preloaded isometric microstrain gauge force transducer system to measure in vitro the contractile strength of intravitreal fibrocellular membranes formed after reproducible posterior penetrating injury to the eye. We demonstrated that these intravitreal membranes reversibly contracted to serotonin, norepinephrine bitartrate, angiotensin II, prostaglandin F1 alpha, bradykinin, and vasopressin as well as when placed in a depolarizing solution or if electrically stimulated. The membranes could be subsequently relaxed with papaverine hydrochloride, cytochalasin B, and diltiazem hydrochloride. We further demonstrated adrenergic receptor sites on these membranes. We were unable, however, to demonstrate any response to histamine or acetylcholine. Based on these findings, we postulate that the intravitreal membranes formed after perforating ocular injuries bear a functional similarity to smooth muscle and the contractile tissue formed after injury elsewhere. These membranes are of basic importance in the pathogenesis of traction retinal detachment.

Glial epiretinal membranes and contraction. Immunohistochemical and morphological studies.

It has been suggested that glial cells do not contribute substantially to the contractile forces generated by epiretinal membranes. We have established a rabbit model in which epiretinal membranes form on the inferior peripheral retina after the injection of activated macrophages into the vitreous. By two months, the membranes were extensive but without evidence of traction. At four months, however, full-thickness retinal folds were present beneath the thick epiretinal membrane. A homogeneous glial cell composition was suggested by light microscopic examination of serial sections through several membranes. Immunohistochemical staining with anti-glial fibrillary acidic protein and antivimentin and immunoelectron microscopy confirmed that these thick epiretinal membranes were composed entirely of glial cells, which may cause mild traction on the retina; this traction is associated with cell alignment and the tissue bridges connecting the membrane and the retina. The fusiform densities and indented nuclei suggested that the glial cells within the membrane may possess some characteristics of myofibroblasts.

Clinical indices of in vivo biocompatibility: the role of ex vivo cell function studies and effluent markers in peritoneal dialysis patients.

Clinical indices of in vivo biocompatibility: The role of ex vivo cell function studies and effluent markers in peritoneal dialysis patients. Over the past 20 years, studies of the biocompatibility profile of peritoneal dialysis solutions (PDF) have evolved from initial in vitro studies assessing the impact of solutions on leukocyte function to evaluations of mesothelial cell behavior. More recent biocompatibility evaluations have involved assessments of the impact of PDF on membrane integrity and cell function in peritoneal dialysis (PD) patients. The development of ex vivo systems for the evaluation of in vivo cell function, and effluent markers of membrane integrity and inflammation in patients exposed both acutely and chronically to conventional and new PDF will be interpreted in the context of our current understanding of the biology of the dialyzed peritoneum. The available data indicate that exposure of the peritoneal environment to more biocompatible PDF is associated with improvements in peritoneal cell function, alterations in markers of membrane integrity, and reduced local inflammation. These data suggest that more biocompatible PDF will have a positive impact on host defense, peritoneal homeostasis, and the long-term preservation of peritoneal membrane function in PD patients.

Myoglobin is a sensitive marker of increased muscle membrane vulnerability.

Changes in muscle proteins in serum after exercise were studied to evaluate the use of such proteins as indicators of increased muscle membrane vulnerability. Seventy-one women were asked to perform bicycle exercise for 45 min at a moderate load; four proteins (creatine kinase - CK, myoglobin - Mb, aldolase - Ald and pyruvate kinase - PK) were measured in serum up to 24 h after exercise. Twenty-one women were carriers of Duchenne's muscular dystrophy (DMD); these are known to show an elevated serum CK activity at rest, as well as increased CK response after exercise. Fifty women without a family history of neuromuscular disease were tested to obtain normal values: they showed a small peak (18%) of CK activity 8 h after exercise, and an even smaller peak of Mb (9%) 1 h after exercise. The mean post-exercise increase for both CK and Mb in the 21 DMD carriers was significantly higher than in controls; the maximum of Mb, on average 70% of baseline levels, was reached 1 h after exercise and was higher than that for CK (48%), which was reached 8 h after exercise. It is concluded that myoglobin levels after exercise are a good index of increased vulnerability of the muscle membrane.

Subretinal proliferation.

Subretinal proliferation is often present but less often identified as a component of proliferative vitreoretinopathy. Subretinal membranes form from retinal pigment epithelial cells and retinal glial cells that migrate into the subretinal space of eyes with long-standing retinal detachments. The membranes grow as sheets but break up into bands as the cells contract, with the stronger parts remaining intact.

Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses.

In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics. Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models. Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials.

The permeability of the round window membrane during otitis media.

Studies of the permeability of the round window membrane (RWM) during otitis media are important because toxins and cellular components that occur in otitis media as well as pharmacologic agents used in treating the disease have the potential to cross the RWM and pass into the inner ear. Twenty-five cats were evaluated electron microscopically as to the passage of a tracer, horseradish peroxidase, through normal RWMs and RWMs three days, one week, and two weeks following eustachian tube obstruction. Passage at three days following obstruction was similar to passage through the normal RWM. Following one to two weeks of obstruction, the permeability of the membrane was drastically reduced. The reduction in permeability was probably due to the presence of residual effusion overlying the membrane, the presence of granulation tissue within the niche, and a thickening of the RWM.

Physical properties of membranes and membrane lipids from the fiber cell of the U18666A-cataractous rat.

Steady state fluorescence anisotropy of parinaric acid probes was used to examine lipid motion in membranes and membrane lipids from U18666A-induced cataractous rat lenses. Cortical and nuclear fractions were examined separately. The drug treatment resulted in an increase in the sterol/phospholipid ratio in the nucleus and a decrease in this ratio in the cortex. Fluorescence anisotropy of trans parinaric acid (tPnA) suggested that membranes from the cortex of cataractous lenses were more ordered than the cortical membranes from control or treated-but-clear lenses. Membranes from the nucleus of control lenses were more ordered than membranes from the cortex of controls. Nuclear membranes from cataractous lenses were slightly less ordered than nuclear membrane from control or treated-but-clear lenses. Similar experiments using liposomes prepared with membrane lipid from lens cortex showed that membrane lipids from treated lenses, control lenses, and treated-but-clear lenses had similar fluorescence anisotropy profiles, suggesting that cortical lipids had similar order. Conversely, fluorescence anisotropy of parinaric acid probes in liposomes prepared from nuclear fractions showed a slight increase in lipid order from control to treated-but-clear to cataractous preparations. These results are interpreted to indicate the presence of an alteration in lipid-protein interactions in cortical membranes in the cataractous lenses; this results in more ordered membranes at the physiological temperature in these lenses. The increase in the order of cortical membranes from cataractous lenses is dependent on the presence of membrane proteins rather than lipids, since it is not seen in the liposome preparations (which are protein-free).(ABSTRACT TRUNCATED AT 250 WORDS)

Disruption of hydrophobic stability of biomembranes is the earliest event in several clinical disorders.

Hydrophobic attractive force is the major force in maintaining the stability of biomembranes, yielding coordinated functionality to the embedded proteins that they contain. This force between the composite linear hydrocarbons of the biomembranes is a function of their length and their mutual parallel distance from each other, and is extremely sensitive to this distance. Extracellular, natural linear hydrocarbons of certain length and shape can intercalate into lipid matrix of the biomembranes, reducing their innate hydrophobic net strength in a concentration-dependent manner, making them loose, leaky, and thus gaining the credence of stimulus-generating agents. In physiological circulatory concentration, these molecules may have a role for the maintenance of cellular homeostasis. However, in stagnating physiological excess, these same agents can become acutely or chronically stimulating and, therefore, disease-precipitating. Such situations do exist in the clinical disorders of acne, atherosclerosis, acute pancreatitis, diabetes, diabetic retinopathy, homocysteinemea, and stress. A systematic approach, beginning with surface film studies with the suspect linear hydrocarbons, can be followed up with in vitro and in vivo studies. This should substantiate or negate the view presented here. Isolated information, along these lines, already exist in literature. The example of acne is a suitable starting point to elaborate this view, for sebaceous gland of the human pilosebaceous unit (PSU) contains all the exemplary, stimulus-inducing linear hydrocarbons to generate surface-reaction on the pilosebaceous ductal surface.