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Biomedical subjects

J L Parra

Publications and source records attributed to J L Parra.

At least 37 records · Page 2Linked to original sources
PubMed1998

Direct formation of mixed micelles in the solubilization of phospholipid liposomes by Triton X-100.

The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.

Freeze Fracturing↗
PubMed1998

Subsolubilizing alterations caused by alkyl glucosides in phosphatidylcholine liposomes.

The subsolubilizing alterations caused by a series of alkyl glucosides (alkyl chain lengths ranging from C8 to C12) in unilamellar phosphatidylcholine (PC) liposomes were investigated. The surfactant to phospholipid molar ratios (RE) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the increase of the fluorescence intensity of liposome suspensions due to the 5(6)-carboxyfluorescein (CF) released from the interior of vesicles to the bulk aqueous phase. Given that the free surfactant concentrations was always lower than the critical micelle concentration (CMC) of the surfactant tested we may assume that the surfactant-liposome interactions were mainly ruled by the action of surfactant monomers. In general terms, the decrease in the surfactant alkyl chain length (or the rise in the surfactant CMC) resulted in an increase in the ability of these surfactants to alter the permeability of liposomes and, inversely, in an abrupt decrease in their affinity with these bilayers structures. The overall balance of these opposite tendencies shows that at the two interaction levels studied (50 and 100% of CF release) the nonyl and the octyl glucoside showed, respectively, the highest ability to alter the release of the CF trapped in bilayers (lowest RE values), whereas the dodecyl glucoside showed the highest degree of partitioning into liposomes or affinity with these bilayer structures (highest K values).

Glucosides↗
PubMed1998

Transmission electron microscopy and light scattering studies on the interaction of a nonionic/anionic surfactant mixture with phosphatidylcholine liposomes.

The interaction of an equimolecular mixture of nonylphenol polyethoxylated [NP(EO)10] and sodium dodecyl sulfate (SDS) surfactants with phosphatidylcholine (PC) liposomes was studied by means of transmission electron microscopy (TEM) and changes in the mean particle size (quasielastic light scattering; QELS) and in the static light scattering (SLS) of the system during liposome solubilization. A good correlation was found between the TEM diameter of particles and the mean hydrodynamic diameter (HD) determined by QELS. The aggregates resulting in this interaction were dependent on the surfactant concentration in the system. Thus, an initial vesicle growth occurred when the surfactant concentration was 15.98 mol%, together with the formation of a very small percentage of smaller particles. Additional surfactant amounts (28.32 mol%) led first to the formation of largest vesicles (HD 418 nm) and second to a fall in the vesicle diameter and in the SLS of the system. Thus, for 38.27 mol%, the TEM picture still showed the presence of vesicles, albeit with signs of disintegration. When additional amounts of surfactant were added to the system, the size curve started to show a bimodal distribution. Thus, for 51.81 mol% surfactant concentration, a sharp curve appeared at 51 nm, corresponding to the formation of small particles and TEM pictures clearly showed vesicle disintegration with formation of tubular structures. It is noteworthy that additional surfactant amounts (from 52 to 60 mol%) led to the formation of unclosed multilayered structures together with smaller aggregates. The gradual increase in the proportion of these smaller aggregates (mixed micelles) led to the complete solubilization of liposomes.

Anions↗
PubMed1998

Solubilization of phosphatidylcholine liposomes by the amphoteric surfactant dodecyl betaine.

The interaction of the amphoteric surfactant N-dodecyl-N,N-dimethylbetaine (C12-Bet) with phosphatidylcholine (PC) liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattering (SLS) of the system. At sublytic level a initial maximum in the bilayer/water partitioning (K) followed by an abrupt decrease of this parameter occurred as the surfactant to lipid molar ratio (Re) rose. At lytic level a direct dependence was established between both parameters. The fact that the free surfactant concentration at sublytic and lytic levels showed values lower than and similar to its critical micelle concentration indicates that permeability alterations and solubilization were determined, respectively, by the action of surfactant monomer and by the formation of mixed micelles. A direct correlation occurred in the initial interaction steps (up to 50% CF release) between the growth of vesicles their fluidity and Re. A similar direct dependence was established during solubilization (up to 30% SLS) between the fall in both the surfactant-lipid aggregate size, the SLS of the system and Re. This surfactant showed higher capacity to solubilize PC liposomes than that reported by the commonly used non-ionic surfactants octyl glucoside and Triton X-100 and by the anionic one sodium dodecyl sulfate.

Betaine↗
PubMed1998

Influence of the level of ceramides in the permeability of stratum corneum lipid liposomes caused by sodium dodecyl sulfate.

The role played by the ceramides in the sublytic interactions of sodium dodecyl sulfate (SDS) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (k) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The presence in liposomes of higher and lower ceramide proportions than that existing in the SC lipids led to a fall and to a rise in the sublytic activity of SDS on these structures. However, the SDS partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to achieve almost a constant value for a Cer proportion similar to that in the SC lipids (about 40%). Thus, at low Cer proportions the ability of SDS molecules to alter these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies. The fact that the free surfactant concentration needed to achieve the two interaction levels investigated was lower than the surfactant critical micellar concentration (CMC) indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of the liposome lipid composition.

Ceramides↗
PubMed1997

Solubilizing effects caused by the nonionic surfactant dodecylmaltoside in phosphatidylcholine liposomes.

The interaction of the nonionic surfactant dodecylmaltoside (DM) with phosphatidylcholine liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein released from the interior of vesicles and bilayer solubilization as a decrease in the static light scattered by liposome suspensions. This surfactant showed higher capacity to saturate and solubilize PC liposomes and greater affinity with these structures than those reported for the octyl glucoside. At subsolubilizing level an initial maximum in the bilayer/water partitioning (K) followed by an abrupt decrease of this parameter occurred as the effective molar ratio of surfactant to phospholipid in bilayers (Re) rose. However, at solubilizing level a direct dependence was established between both parameters. A direct correlation took place in the initial interaction steps (Re up to 0.28) between the growth of vesicles, their fluidity, and Re. A similar direct dependence was established during solubilization (Re range from 0.9 to 1.7) between the decrease in both the surfactant-PC aggregate size, the light scattering of the system, and Re (composition of aggregates). The fact that the free DM concentration at subsolubilizing and solubilizing levels showed values lower than and similar to its critical micelle concentration indicates that permeability alterations and solubilization were determined, respectively, by the action of surfactant monomer and by the formation of mixed micelles.

Fluoresceins↗
PubMed1996

Alterations in phospholipid bilayers caused by oxyethylenated nonylphenol surfactants.

The interactions of oxyethylenated nonylphenols [ethylene oxide units (EO) averaging between 5 and 30] with phosphatidylcholine liposomes were investigated. Three parameters were regarded as corresponding to the effective surfactant/lipid molar ratios at which the surfactant system (a) resulted in the transient liposome reorganization for the release of 50% of 5(6)-carboxyfluorescein (CF) trapped in the liposomes, R(50%CF); (b) saturated the liposomes, R(SAT); and (c) led to a complete liposome solubilization, R(SOL). From these parameters the surfactant partition coefficients K(50%CF), K(SAT), and K(SOL) were determined. Permeability alterations were determined as a change in CF released from the interior of vesicles and solubilization as a decrease in the static light scattering of liposome suspensions. R(SAT) and R(SOL) showed the lowest values in the critical micellar concentration (CMC) range between 0.040 and 0.087 mM and 0.050 and 0.075 mM, respectively [hydrophilic-lipophilic balance (HLB) number ranging between 13 and 16 and 14 and 15], which corresponded approximately to the nonylphenols with 10--20 and 15 EO units, respectively. However, K(50%CF), K(SAT), and K(SOL) drastically decreased as the number of EO units increased, especially in the EO range between 5 and 15. Thus, the highest surfactant affinity with bilayers (maximum K values) and its maximum ability to alter these structures (minimum R values) were governed by the CMC surfactants and their HLB numbers and, consequently, by the EO units present in the surfactant structure. The free surfactant concentrations were lower than their CMCs at sublytic level, whereas they remained similar to these values during bilayer saturation and solubilization. The nonylphenols investigated showed higher activity versus liposomes than that reported for Triton X-100, the oxyethylenated nonylphenol with an average of 10 ethylene oxide units showing low toxicity in biological tests.

Ethylene Oxide↗
PubMed1996

Changes in phosphatidylcholine liposomes caused by a mixture of Triton X-100 and sodium dodecyl sulfate.

The mechanisms governing the interaction of equimolecular mixtures of Triton X-100 (Tx-100) and sodium dodecyl sulfate (SDS) with phosphatidylcholine liposomes were investigated. Permeability alterations were determined as a change in 5(6)-carboxyfluorescein released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattered by liposome suspensions. At subsolubilizing level, a maximum bilayer/water partitioning of surfactant mixture was reached at 30% CF release, which correlated with the increased presence of SDS in the bilayers. However, transition stages between 70% CF release and 100% light-scattering corresponded to the increased presence of Tx-100 in these structures. These findings may be correlated with the reduced deleterious effects caused by this mixture in different tissues versus pure SDS, given that the presence of Tx-100 may modulate the level of SDS partitioning in the human stratum corneum. At subsolubilizing level, the mixture showed higher affinity with bilayers than those reported for single components, whereas at solubilizing level this affinity was slightly lower and higher than those reported for Tx-100 and SDS respectively. A direct relationship was established in the initial interaction steps between the growth of vesicles, the leakage of entrapped CF and the effective molar ratio of surfactant to phospholipid in bilayers (Re). This dependence was also detected during solubilization, where the decrease in the vesicle size and in the scattered light of the system depended on the Re parameter and hence on the bilayer composition. The fact that the free surfactant concentration at subsolubilizing and solubilizing levels showed respectively lower and similar values than the critical micelle concentration (c.m.c.) of the surfactant mixture indicates that permeability alterations and solubilization were determined respectively by the action of surfactant monomer and by the formation of mixed micelles. This finding supports the generally admitted assumption, for single surfactants, that the concentration of free surfactant must reach the c.m.c. for solubilization to occur and highlights the influence of the negative synergism of this surfactant mixture on the free surfactant concentration needed to saturate or solubilize liposomes.

Detergents↗
PubMed1995

Interaction of anionic/nonionic surfactant mixtures with phosphatidylcholine liposomes.

The mechanisms governing the interaction of mixtures of sodium dodecyl sulfate (SDS) and nonylphenol oxyethylenated with 10 mol of ethylene oxide (NP(EO)10) with phosphatidylcholine liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system (a) resulted in 50% of CF release (Re50%CF), (b) saturated the liposomes (ReSAT), and (c) led to a complete solubilization of these structures (ReSOL). From these parameters the corresponding surfactant partition coefficients (K50%CF, KSAT, and KSOL) were determined. Despite the fact that Re increased as the mole fraction of the SDS rose (XSDS), the K parameters showed maximum values at XSDS 0.6 and 0.2 for K50%CF and KSAT, respectively, the KSOL reaching the highest value in the absence of SDS XSDS = 0). Thus, the higher the surfactant contribution in surfactant/lipid system, the lower the XSDS at which the maximum bilayer/water partitioning of mixed surfactant systems added took place. The free surfactant concentrations SW were lower than the mixed surfactant CMCs at subsolubilizing level, whereas it remained similar to these values during saturation and solubilization of bilayers in all cases.

Chemical Phenomena↗
PubMed1995

Solubilizing effects caused by alkyl pyridinium surfactants in phosphatidylcholine liposomes.

The solubilization of neutral and electrically charged liposomes by a series of alkyl pyridinium surfactants (alkyl chain lengths C10-C14) was investigated. Solubilization was detected as a decrease in static light-scattering of liposome suspensions. Two parameters were regarded as corresponding to the effective surfactant/lipid molar ratios at which the surfactant saturated the liposomes Re(sat) and led to a complete solubilization of these structures Re(sol). From these parameters the corresponding surfactant partition coefficients were determined. The Re and K parameters fell as the surfactant alkyl chain length decreased or both the critical micellar concentration (CMC) and the hydrophilic/lipophilic balance (HLB number) increased, regardless of the bilayers electrical charge. Thus, although decyl-pyridinium bromide (DePB) showed the highest ability for saturation and solubilization of bilayers, its concentration was always higher than that needed for dodecyl-pyridinium bromide (DoPB) and tetradecyl-pyridinium bromide (TePB), the last one being the most active. These results emphasize the influence of the hydrophilic/lipophilic balance of these surfactants on liposome solubilization and the minor influence of the electrostatic factors in this process.

Amines↗
PubMed1994

Structural phase transitions involved in the interaction of phospholipid bilayers with octyl glucoside.

The transitional stages induced by the interaction of the nonionic surfactant octyl glucoside (OcOse) on phosphatidylcholine liposomes were studied by means of transmission electron microscopy (TEM), light scattering and permeability changes. A linear correlation was observed between the effective surfactant/lipid molar ratio (Re; three-stage model proposed for liposome solubilization) and the OcOse concentration in the initial and final interaction stages, despite showing almost a constant value during bilayer saturation. The bilayer/aqueous phase partition coefficient (K) decreased in the subsolubilizing interaction steps and increased during solubilization. Thus, whereas a preferential distribution of surfactant monomers in the aqueous phase with respect to the lipid bilayers took place in the initial interaction steps, a larger association of OcOse molecules with these lipids in bilayers occurred during solubilization. The initial steps of bilayer saturation (50-70% permeability) were attained for a lower free surfactant (Sw) than that for its critical micellar concentration (cmc). When Sw reached the OcOse cmc, solubilization started to occur (Resat). Large unilamellar vesicles began to form as the OcOse exceeded 60 mol/100 mol, exhibiting for 65 mol/100 mol (50% permeability) vesicles of approximately 400 nm. TEM pictures for 100% permeability (72 mol/100 mol) and Resat still showed unilamellar vesicles, albeit that the Resat TEM picture showing traces of smaller structures. Exceeding surfactant amounts led to a decrease in static light scattering; the vesicle-size curve began to show a bimodal distribution. The TEM picture showed tubular structures together with bilayer fragments. Thereafter, the open structures were gradually affected by the surfactant and the scattered intensity gradually decreased to a constant low value.

Glucosides↗
PubMed1994

Vesicle-micelle structural transition of phosphatidylcholine bilayers and Triton X-100.

The structural transition stages induced by the interaction of the non-ionic surfactant Triton X-100 on phosphatidylcholine unilamellar vesicles were studied by means of static and dynamic light-scattering, transmission-electron-microscopy (t.e.m.) and permeability changes. A linear correlation was observed between the effective surfactant/lipid molar ratios (Re) ('three-stage' model proposed for the vesicle solubilization) and the surfactant concentration throughout the process. However, this correlation was not noted for the partition coefficients of the surfactant between the bilayer and the aqueous medium (K). Thus a sharp initial K increase was observed until a maximum value was achieved for permeability alterations of 50% (initial step of bilayer saturation). Further surfactant additions resulted in a fall in the K values until 100% of bilayer permeability. Additional amounts of surfactant led to an increase in K until bilayer solubilization. Hence, a preferential incorporation of surfactant molecules into liposomes governs the initial interaction steps, leading to the initial stage of bilayer saturation with a free surfactant concentration that was lower than its critical micelle concentration (c.m.c.). Additional amounts of surfactant increased the free surfactant until the c.m.c. was reached, after which solubilization started to occur. Thus the initial step of bilayer saturation was achieved for a smaller surfactant concentration than that for the Resat, although this concentration was the minimum needed for solubilization to start. Large unilamellar vesicles began to form as the surfactant exceeded 15 mol% (50% bilayer permeability), the maximum vesicle growth being attained for 22 mol% (400 nm). Thereafter, static light-scattering started to decrease gradually, this fall being more pronounced after 40 mol%. The t.e.m. picture for 40 mol% (Resat.) showed unilamellar vesicles, although with traces of smaller structures. From 50 mol% the size distribution curves began to show a bimodal distribution. The t.e.m. pictures for 50-64 mol% revealed tubular structures, together with open bilayer fragments. Thereafter, increasing amounts of surfactant (65-69 mol%) led to planar multilayered structures which gradually tended to form concentric and helicoidal conformations. The scattered intensity decreased to a low constant value at more than 71-72 mol%. However, the surfactant concentration for the Re(sol) (72.6 mol %) still presented traces of aggregated structures, albeit with mono-modal size-distribution curves (particle size of 50 nm). This vesicle size corresponded to the liposome solubilization via mixed-micelle formation.

Light↗
PubMed1993

[Paratesticular tumor. Liposarcoma of the spermatic cord].

Liposarcoma of the spermatic cord is a rare tumour typically presenting in elderly people. It tends to grow around blood vessels. Most of them have a low level of malignancy and relapses tend to be localized. Metastasis, when present, occur through the haematological route, lymph spread being very unusual. Pre-operative diagnosis is infrequent and overall prognosis is good. The choice treatment is radical orchidectomy, while long-term follow-up of these patients is mandatory. When local relapses become evident, the choice treatment is extensive local excision, followed by optional adjuvant radiotherapy. Chemotherapy has not proven to be effective. This paper reviews the current literature and contributes one case of mixed liposarcoma of the spermatic cord.

Genital Neoplasms, Male↗
PubMed1989

Analysis of glycolipids by fast atom bombardment mass spectrometry.

The positive and negative ion fast atom bombardment (FAB) mass spectra of four glycolipids obtained from microbial cultures are reported. The spectra of the glycolipids in the positive ion mode are characterized by abundant [M + Na]+, [M + Na + matrix]+ and [M + 2Na - H]+ species. In negative FAB conditions the molecules yield [M - H]-. Our understanding of the FAB behaviour of glycolipids in both positive and negative modes has been considerably aided in the structure elucidation, without any derivatization or degradation reaction of the compounds studied. The technique allows unambiguous molecular weight determination of low-microgram amounts of these glycolipids purified from biological sources and provides useful fragmentation information.

Glycolipids↗
PubMed1987

Treatment of massive haematuria with aluminous salts.

Fifteen patients with massive vesical haematuria were treated with a 1% aluminium potassium sulphate solution in sterile distilled water, using continuous intravesical lavage with a double channel catheter. The haematuria was caused by vesical tumours in 13 patients, radiation cystitis in one and transurethral resection in one. Immediate side effects were few and none were noted in the long term, as judged by randomised biopsies from vesical mucosa. A complete response was noted in 66% of the patients, partial response in 15% and failure in 20%. This treatment is recommended for intractable bleeding from radiation cystitis and bladder tumours.

Aged↗
PubMedDate not supplied

Influence of the fluidity of liposome compositions on percutaneous absorption.

The penetration into the stratum corneum of fluorescein, as the acid form or as a sodium salt, encapsulated in liposomes formed by liquid- or gel-state phospholipids, with or without cholesterol, was investigated in humans by the stripping method. Liposomes prepared by extrusion were applied to the forearms of healthy human volunteers and 30 min later, strippings were performed. Fluorescein was extracted and determined by spectrofluorimetry. The skin penetration of sodium fluorescein was higher from fluid liposomes (phosphatidylcholine) than from rigid liposomes (hydrogenated phosphatidylcholine), but it was independent of the content of cholesterol. It seems that the liquid-crystalline state of the lipids is the main aspect involved in the fluidity of the liposome bilayer itself as well as in the interaction with the lipids of the stratum corneum. The similar enhanced penetration behavior obtained for unsaturated liposomes containing sodium or acid fluorescein seems to support the hypothesis of a previous destruction of the vesicles during its passage through the lipid intercellular pathway in the stratum corneum.

Adult↗