Interaction of Hoechst 33342 with POPC Membranes at Different pH Values.

Hoechst 33342 (H33342) is a fluorescent probe that is commonly used to stain the DNA of living cells. To do so, it needs to interact with and permeate through cell membranes, despite its high overall charge at physiological pH values. In this work, we address the effect of pH in the association of H33342 with lipid bilayers using a combined experimental and computational approach. The partition of H33342 to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid membranes was experimentally quantified using fluorescence spectroscopy and isothermal titration calorimetry (ITC) measurements. Quantum chemical calculations were performed to select the most stable isomer of H33342 for the overall charges 0, +1, and +2, expected to predominate across the 5 < pH < 10 range. The interaction of these isomers with POPC bilayers was then studied by both unrestrained and umbrella sampling molecular dynamics (MD) simulations. Both experimental results and computational free energy profiles indicate that the partition coefficient of H33342 displays a small variation over a wide pH range, not exceeding one order of magnitude. The enthalpy variation upon partition to the membrane suggests efficient hydrogen bonding between the probe and the lipid, namely, for the protonated +2 form, which was confirmed in the MD simulation studies. The relatively high lipophilicity obtained for the charged species contrasts with the decrease in their general hydrophobicity as estimated from octanol/water partition. This highlights the distinction between lipophilicity and hydrophobicity, as well as the importance of considering the association with lipid bilayers when predicting the affinity for biomembranes.

Calculation of Permeability Coefficients from Solute Equilibration Dynamics: An Assessment of Various Methods.

Predicting the rate at which substances permeate membrane barriers in vivo is crucial for drug development. Permeability coefficients obtained from in vitro studies are valuable for this goal. These are normally determined by following the dynamics of solute equilibration between two membrane-separated compartments. However, the correct calculation of permeability coefficients from such data is not always straightforward. To address these problems, here we develop a kinetic model for solute permeation through lipid membrane barriers that includes the two membrane leaflets as compartments in a four-compartment model. Accounting for solute association with the membrane allows assessing various methods in a wide variety of conditions. The results showed that the often-used expression Papp = ß × r/3 is inapplicable to very large or very small vesicles, to moderately or highly lipophilic solutes, or when the development of a significant pH gradient opposes the solute's flux. We establish useful relationships that overcome these limitations and allow predicting permeability in compartmentalised in vitro or in vivo systems with specific properties. Finally, from the parameters for the interaction of the solute with the membrane barrier, we defined an intrinsic permeability coefficient that facilitates quantitative comparisons between solutes.

Effect of dipole moment on amphiphile solubility and partition into liquid ordered and liquid disordered phases in lipid bilayers.

Association of amphiphiles with biomembranes is important for their availability at specific locations in organisms and cells, being critical for their biological function. A prominent role is usually attributed to the hydrophobic effect, and to electrostatic interactions between charged amphiphiles and lipids. This work explores a closely related and complementary aspect, namely the contribution made by dipole moments to the strength of the interactions established. Two xanthene amphiphiles with opposite relative orientations of their dipole and amphiphilic moments have been selected (Rhodamine-C14 and Carboxyfluorescein-C14). The membranes studied have distinct lipid compositions, representing typical cell membrane pools, ranging from internal membranes to the outer and inner leaflet of the plasma membrane. A comprehensive study is reported, including the affinity of the amphiphiles for the different membranes, the stability of the amphiphiles as monomers and their tendency to form small clusters, as well as their transverse location in the membrane. The orientation of the amphiphile dipole moment, which determines whether its interaction with the membrane dipole potential is repulsive or attractive, is found to exert a large influence on the association of the amphiphile with ordered lipid membranes. These interactions are also responsible for the formation of small clusters or stabilization of amphiphile monomers in the membrane. The results obtained allow understanding the prevalence of protein lipidation at the N-terminal for efficient targeting to the plasma membrane, as well as the tendency of GPI-anchored proteins (usually lipidated at the C-terminal) to form small clusters in the membrane ordered domains.

Frontal cutaneous meningioma--Case report.

Cutaneous meningiomas are rare tumors most commonly located on the scalp. We report the case of a 55-year-old male who presented with a 2 x 3 cm tumoral lesion on the forehead. The lesion was hard, adherent and covered by normal skin. Incisional biopsy revealed a proliferation of monomorphic round cells, organized in nests and focally forming pseudovascular spaces. Immunohistochemical study revealed positivity for epithelial antigen membrane and vimentin. Vascular markers, cytokeratins and S100 protein were negative. A brain CT scan did not show any evidence of intracranial meningioma. The authors describe the case of a cutaneous frontal meningioma in probable relation with previous cranioencephalic trauma.

Frontal cutaneous meningioma - Case report

Cutaneous meningiomas are rare tumors most commonly located on the scalp. We report the case of a 55-year-old male who presented with a 2x3 cm tumoral lesion on the forehead. The lesion was hard, adherent and covered by normal skin. Incisional biopsy revelead a proliferation of monomorphic round cells, organized in nests and focally forming pseudovascular spaces. Immunohistochemical study revealed positivity for epithelial antigen membrane and vimentin. Vascular markers, cytokeratins and S100 protein were negative. A brain CT scan did not show any evidence of intracranial meningioma. The authors describe the case of a cutaneous frontal meningioma in probable relation with previous cranioencephalic trauma.

[Cutaneous loxoscelism in Portugal: a rare cause of dermonecrosis]. / Loxoscelismo Cutâneo em Portugal: Causa Rara de Dermonecrose.

Cutaneous loxoscelism is an exceptional diagnosis in Portugal, regardless of the documented presence of Loxosceles rufescens.We report a 33-year old female patient presenting to our clinic after having visualized a bite from a spider in the inner aspect of the right thigh. Afterwards, she developed a warm, painful erythematous plaque, progressing to skin necrosis and torpid ulcer formation. Considering the failure of conservative measures, surgical debridement of the ulcer followed by repair using an O-Z plasty achieved good functional outcome. Definite diagnosis of cutaneous loxoscelism may be difficult since it relies on the visualization of the bite, capture of the spider for identification and typical clinical features. This case meets several criteria that allow the establishment of a causative link between spider bite and dermonecrosis. It is, to the best of our knowledge, the first diagnosis of loxoscelism reported in Portugal.

O loxoscelismo cutâneo é um diagnóstico excecional em Portugal, apesar da presença reconhecida da espécie Loxosceles rufescens. Apresentamos uma doente de 33 anos que desenvolveu placa eritematosa quente, dolorosa, com progressão para necrose cutânea e ulceração tórpida na face interna da coxa direita, em relação com mordedura visualizada de aranha. Em virtude da ausência de cicatrização adequada após tratamento conservador, recorreu-se ao desbridamento cirúrgico da úlcera, tendo-se realizado plastia em O-Z para a sua reconstrução, com bom resultado funcional. O diagnóstico de loxoscelismo cutâneo é difícil e obriga idealmente à observação da mordedura, verificação de sinais clínicos compatíveis e captura da aranha para identificação por taxonomista. Estecaso clínico reúne critérios que relacionam uma mordedura de aranha com a necrose cutânea resultante, sendo este, no nossoconhecimento, o primeiro caso relatado em Portugal.

Trichilemmal cyst nevus of the scalp.

We report the observation of a 24-year-old woman presenting a plaque-like lesion of the occipital scalp with hair rarefaction. This lesion was congenital and consisted of numerous, agminated, very small, trichilemmal cysts. It remained stable since birth, slowly growing in proportion with the patient during childhood. We discuss the nosological status of this intriguing lesion and its relationship with the recently described trichilemmal cyst nevus.

Unilateral progressive osseous heteroplasia.

A 50-year-old male patient presented with firm subcutaneous nodules and plaques with a gritty texture, unilaterally affecting the left side of the trunk and the left limbs. These lesions had had a progressive course since early childhood and caused functional impairment. There was no family history of similar disorders. No phospho-calcium metabolism abnormalities were observed. Biopsies of the affected areas demonstrated osteoma cutis. Analysis of DNA showed no mutation of the GNAS gene. The clinical features were consistent with progressive osseous heteroplasia, atypically presented in a unilateral form, probably revealing a mosaic distribution.

Neutrophilic dermatosis of the dorsal hands associated with hypopharyngeal carcinoma.

Neutrophilic dermatosis of the dorsal hands (NDDH) is a rare and recently described disorder regarded as a subset of neutrophilic dermatosis, similar to superficial pyoderma gangrenosum and pustular vasculitis. Many currently consider it to be a localized variant of Sweet Syndrome. We describe the case of a 63-year-old male patient with NDDH associated with hypopharyngeal carcinoma. A biopsy demonstrated changes consistent with those seen in Sweet Syndrome, with leukocytoclasia but no signs of true vasculitis. Treatment with oral prednisolone resulted in complete resolution of the lesions in 1 month, with no recurrences. The clinical presentation, the histological features, and the excellent response to oral corticosteroid therapy allowed us to classify this case as NDDH. We emphasize the rare association of this entity with a solid tumor.

Dermatite de contacto alérgica a desinfectantes na indústria alimentar / Allergic contact dermatitis from disinfectants in the alimentary industry

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The authors report a case of allergic contact dermatitis in the alimentary industry due to contact with disinfectants containing glutaraldehyde and chloroxylenol. In our study, testing these allergens over fragments of different types of gloves, showed that only nitrile latex gloves conferred protection against chloroxylenol and a partial protection against glutaraldehyde. The authors stress the importance of testing these disinfectants in the alimentary industry where care about bacterial contamination needs to be taken care of

Multiple cutaneous reticulohistiocytomas in a patient with rheumatoid arthritis.

A 64-year-old woman with a long-standing peripheral symmetric polyarthritis with positive rheumatoid serology was evaluated for multiple asymptotic papulonodules of fingers, mentum, lower lip, ears, and eyelids. Histopathologic examination showed a dermal infiltrate composed of histiocytes, multinucleate giant cells with ground-glass cytoplasm, and lymphocytes, suggestive of reticulohistiocytoma. The possibilities of multicentric reticulohistiocytosis with positive rheumatoid serology or coexistence of multiple cutaneous reticulohistiocytomas and rheumatoid arthritis are discussed.