Alkylation converts riboflavin into an efficient photosensitizer of phospholipid membranes

A new decyl chain [-(CH₂)₉CH₃] riboflavin conjugate has been synthesized and investigated. A nucleophilic substitution (S_N2) reaction was used for coupling the alkyl chain to riboflavin (Rf), a model natural photosensitizer. As expected, the alkylated compound (decyl-Rf) is significantly more lipophilic than its precursor and efficiently intercalates within phospholipid bilayers, increasing its fluorescence quantum yield. The oxidative damage to lipid membranes photoinduced by decyl-Rf was investigated in large and giant unilamellar vesicles (LUVs and GUVs, respectively) composed of different phospholipids. Using a fluorogenic probe, fast radical formation and singlet oxygen generation was demonstrated upon UVA irradiation in vesicles containing decyl-Rf. Photosensitized formation of conjugated dienes and hydroperoxides, and membrane leakage in LUVs rich in poly-unsaturated fatty acids were also investigated. The overall assessment of the results shows that decyl-Rf is a significantly more efficient photosensitizer of lipids than its unsubstituted precursor and that the association to lipid membranes is key to trigger phospholipid oxidation. Alkylation of hydrophilic photosensitizers as a simple and general synthetic tool to obtain efficient photosensitizers of biomembranes, with potential applications, is discussed.

Singlet Oxygen Flux, Associated Lipid Photooxidation, and Membrane Expansion Dynamics Visualized on Giant Unilamellar Vesicles

The physical properties of lipid membranes depend on their lipid composition. Photosensitized singlet oxygen (¹O₂) provides a handle to spatiotemporally control the generation of lipid hydroperoxides via the ene reaction, enabling fundamental studies on membrane dynamics in response to chemical composition changes. Critical to relating the physical properties of the lipid membrane to hydroperoxide formation is the availability of a sensitive reporter to quantify the arrival of ¹O₂. Here, we show that a fluorogenic α-tocopherol analogue, H₄BPMHC, undergoes a >360-fold emission intensity enhancement in liposomes following a reaction with ¹O₂. Rapid quenching of ¹O₂ by the probe (k_q = 4.9 × 10⁸ M^-1 s^-1) ensures zero-order kinetics of probe consumption. The remarkable intensity enhancement of H₄BPMHC upon ¹O₂ trapping, its linear temporal behavior, and its protective role in outcompeting membrane damage provide a sensitive and reliable method to quantify the ¹O₂ flux on lipid membranes. Armed with this probe, fluorescence microscopy studies were devised to enable (i) monitoring the flux of photosensitized ¹O₂ into giant unilamellar vesicles (GUVs), (ii) establishing the onset of the ene reaction with the double bonds of monounsaturated lipids, and (iii) visualizing the ensuing collective membrane expansion dynamics associated with molecular changes in the lipid structure upon hydroperoxide formation. A correlation was observed between the time for antioxidant H₄BPMHC consumption by ¹O₂ and the onset of membrane fluctuations and surface expansion. Together, our imaging studies with H₄BPMHC in GUVs provide a methodology to explore the intimate relationship between photosensitizer activity, chemical insult, membrane morphology, and its collective dynamics.

Synthesis, Characterization and Photocleavage of Bis-decyl Pteroic Acid: A Folate Derivative with Affinity to Biomembranes†

Here, we provide mechanistic insight to the photocleavage of a compound in the folate family, namely pteroic acid. A bis-decyl chain derivative of pteroic acid was synthesized, structurally characterized and photochemically investigated. We showed that, like folic acid, pteroic acid and the decylated derivative undergo a photocleavage reaction in the presence of H₂ O, while no reaction was observed in methanol solution. Furthermore, density functional theory calculations were carried out to predict relative stabilities of hypothetical mono-, bis- and tris-decylated pteroic acid derivatives to help rationalize the regioselectivity of the bis-decyl pteroic acid product. Additionally, the lipophilicity of the bis-decyl pteroic acid appears to confer a hydrophobic property enabling an interaction with biomembranes.

Evaluation of some organic compounds on bloodstream forms of Trypanosoma cruzi

Accidental transmission of Chagas' disease to man by blood transfusion is a serious problem in Latin-America. This paper describes the testing of several synthetic, semi-synthetic, and natural compounds for their activity against blood trypomastigotes in vitro at 4 degrees C. The compounds embody several types of chemical structures: benzoquinone, naphthoquinone, anthracenequinone, phenanthrenequinone, imidazole, piperazine, quinoline, xanthene, and simple benzenic and naphthalenic derivatives. Some of them are for the first time tested against Trypanosoma cruzi. The toxic effect of these compounds on this parasite was done by two quite distinct sets of experiments. In one set, the compounds were added to infected blood as ethanolic solution. In this situation the most active one was a furan-1,2-naphthoquinone, in the same range as gentian violet, a new fact to be considered in the assessment of structure-activity relationships in this class of compounds. In other set, we tentatively evaluated the biological activity of water insoluble compounds by adding them in a pure form without solvent into infected blood. In this way some appear to be very active and it was postulated that the effectiveness of such compounds must result from interactions between them and specific blood components.

Malignant fibrous histiocytoma of the aorta complicated by anuria

Tumors of the aorta have been reported infrequently in the literature. We report a case of a 63-year-old woman diagnosed with malignant aortic fibrous histiocytoma (also known as fibroxanthosarcoma). She was referred to us with suspected occlusion of the right renal artery in a single functioning kidney, with a clinical picture of anuria during the previous 48 hours. We also review 31 previously published cases in the literature.

Direct surgery on the aorto-iliac area. Prostheses--endarterectomy?

Of the 365 surgical techniques performed on the aorto-iliac area in 354 patients, 448 extremities were revascularized by means of the insertion of a prosthesis as a by-pass, and 165 by thromboendarterectomy (TEA), either global or ilio-femoral. The patency rate at five years was 83% for prostheses, and 72% for TEAs, studied as a whole, or 75% for global TEAs, and 60% for ilio-femoral, once they had been individually analysed. The analysis of these results proves that the patency of the ravascularized aorto-iliac area depends more on the associated pathology in the femoro-popliteal distal area, than on the surgical technique that has been applied. There are no significant differences in relation to the early patency or mortality between the three groups, although as regards age, younger patients with fewer risk factors were selected for global TEA operations.

Aesthetic reduction of the upper lip

The upper lip, given its surface anatomy and morphology, should be no more than 2 cm high. Therefore, to reduce the upper lip we propose an incision at its highest portion similar to the letter M which extends into the nasal vestibula. We aim at a real reduction of the height of the lip as well as restoration of its natural concavity through a scar situated obscurely, and which tends to disappear within a few months postoperatively. In patients in whom the upper lip is less than 2 cm high but the vermilion is minimal, we use Gillies' technique and make curvilinear incisions. We have also observed correction of the perioral wrinkles using this technique.

Use of pericranial flap in scalp wounds with exposed bone

We present two cases of traumatic loss of portions of the scalp, one by electrical burn and the other by avulsion. Both patients had large areas of osseous exposure, in which we made use of pericranial flaps taken from the back half of the skull in order to cover the exposed bone. At the same time, local flaps were made and skin grafted over the pericranial flap in a single surgical step using the usual surgical procedures.