Application of Aptamer-Based Assays to the Diagnosis of Arboviruses Important for Public Health in Brazil.

Arbovirus infections represent a global public health problem, and recent epidemics of yellow fever, dengue, and Zika have shown their critical importance in Brazil and worldwide. Whilst a major effort for vaccination programs has been in the spotlight, a number of aptamer approaches have been proposed in a complementary manner, offering the possibility of differential diagnosis between these arboviruses, which often present similar clinical symptoms, as well as the potential for a treatment option when no other alternative is available. In this review, we aim to provide a background on arbovirus, with a basic description of the main viral classes and the disease they cause, using the Brazilian context to build a comprehensive understanding of their role on a global scale. Subsequently, we offer an exhaustive revision of the diagnostic and therapeutic approaches offered by aptamers against arboviruses. We demonstrate how these promising reagents could help in the clinical diagnosis of this group of viruses, their use in a range of diagnostic formats, from biosensors to serological testing, and we give a short review on the potential approaches for novel aptamer-based antiviral treatment options against different arboviral diseases.

Relevance of Hydrodynamic Effects for the Calculation of Outer Surface Potential of Biological Membrane Using Electrophoretic Data.

In this paper, we present the results of a study on the influence of hydrodynamic effects on the surface potentials of the erythrocyte membrane, comparing two different models formulated to simulate the electrophoretic movement of a biological cell: the classical Helmholtz-Smoluchowski model and a model presented by Hsu et al. (1996). This model considers hydrodynamic effects to describe the distribution of the fluid velocity. The electric potential equation was obtained from the non-linear Poisson-Boltzmann equation, considering the spatial distribution of electrical charges fixed in glycocalyx and cytoplasmic proteins, as well as electrolyte charges and ones fixed on the surfaces of lipidic bilayer. Our results show that the Helmholtz-Smoluchowski model is not able to reflect the real forces responsible to the electrophoretic behavior of cell, because it does not take account the hydrodynamic effects of glycocalyx. This charged network that covers cellular surface constitutes a complex physical system whose electromechanical characteristics cannot be neglected. Then, supporting the hypothesis of other authors, we suggest that, in electrophoretic motion analyses of cells, the classical model represents a limiting case of models that take into account hydrodynamic effects to describe the velocity distribution of fluid.

Binding of Sulpiride to Seric Albumins.

The aim of this work was to study the interaction of sulpiride with human serum albumin (HSA) and bovine serum albumin (BSA) through the fluorescence quenching technique. As sulpiride molecules emit fluorescence, we have developed a simple mathematical model to discriminate the quencher fluorescence from the albumin fluorescence in the solution where they interact. Sulpiride is an antipsychotic used in the treatment of several psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with 290 nm wavelength and observed the quenching by titrating HSA and BSA solutions with sulpiride. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that sulpiride form complexes with both albumins. Estimated association constants for the interaction sulpiride-HSA were 2.20 (±0.08) × 104 M(-1), at 37 °C, and 5.46 (±0.20) × 104 M(-1), at 25 °C. Those for the interaction sulpiride-BSA are 0.44 (±0.01) × 104 M(-1), at 37 °C and 2.17 (±0.04) × 104 M(-1), at 25 °C. The quenching intensity of BSA, which contains two tryptophan residues in the peptide chain, was found to be higher than that of HSA, what suggests that the primary binding site for sulpiride in albumin should be located next to the sub domain IB of the protein structure.

One round of SELEX for the generation of DNA aptamers directed against KLK6.

Kallikrein-related peptidase 6 (KLK6) is an active serine protease that has been implicated in common pathologies, including neurodegenerative disorders such as Parkinson and Alzheimer disease and certain types of cancer. Antibodies, either polyclonal or monoclonal, that exhibit specificity for distinct members of the extended kallikrein family, including KLK6, were developed. With the exception of KLK3/PSA, the identification and generation of aptamers, as potential new tools with improved characteristics demanded for therapeutic and diagnostic applications, has not been explored for KLKs. Here, we report for the first time the identification of novel DNA aptamers against KLK6 that were isolated using a modified systemic evolution of ligands by exponential enrichment technique. The identified aptamers were characterized using fluorescence spectroscopy, competition ELISA, and quartz crystal microbalance, and two aptamers (008 and 022) were found to exhibit high affinity (K(d) in the low nanomolar range) for KLK6. Aptamers were tested for their ability to bind to serum albumin, to demonstrate their specificity for their target, and the possible involvement of such proteins in the transport of aptamers into the bloodstream. The developed aptamers are expected to assist the development of novel diagnostic, biosensing, and therapeutic strategies.

Effects of immobilization stress on kidneys of Wistar male rats: a morphometrical and stereological analysis.

This paper verifies the morphological changes induced by immobilization stress on the kidney of rats by using stereological methods. Fifteen 4-week-old Wistar male rats were randomly assigned to control (n = 7) and stressed (n = 8) groups. Stress stimuli were performed over 5 weeks by immobilization of the rats for 2 h daily in a rigid opaque plastic cylinder that restrained their movements. Increases in the adrenal mass index (p < 0.05) and decreases in serum testosterone levels (p < 0.05) demonstrated the efficacy of the stressor stimuli. Stressed rats presented diminished body weight gain when compared to controls (p < 0.05). The mean values of kidney weight, kidney volume, kidney volume index and glomerular volume density were significantly lower in the stressed group (p < 0.05); nevertheless, no significant difference was found in the cortical/medullar ratio or in the volume-weighted mean glomerular volume. The number of glomeruli per kidney was 45% lower in the stressed group (p < 0.0001), but no change in serum creatinine levels was found. However, the morphological alterations may have serious implications predisposing individuals to renal disease and hypertension in adult life.

Study on the interaction of three classical drugs used in psychiatry in albumin through spectrofluorimetric modeling.

Comparative study of haloperidol (HPD), biperiden (BPD) and clonazepam (CNZ) interactions with human and bovine serum albumin was performed based on fluorescence quenching analysis. We used mathematical modeling comparing spectrofluorimetric data to obtain information on the possibility of competition among three drugs by sites binding. Results showed that the three drugs studied have high affinity for albumin and suggest the existence of two site classes in HSA for HPD and only one class for BPD and CNZ, in the range of concentrations tested for each drug. Among them, only HPD forms complex with HSA. Comparing normalized quenching plots suggested that the primary sites in HSA and BSA for HPD and CNZ are located at subdomain IB, whereas BPD would bind in the subdomain IIA. Considering the competition for binding sites in HSA, titrations of HPD-HSA complex by BPD and CNZ, as well as the titration of HSA solution containing CNZ titrated by BPD, show that although the three drugs do not compete with each other for binding sites, their interaction with HSA can cause conformational change in the protein, and to increase or decrease the accessibility to binding sites for other drug. This may mean alteration in the free plasma drug concentrations.

The interaction of methyl-parathion with serum and albumin of the neo-tropical fish Piaractus mesopotamicus.

The interaction of methyl-parathion with serum and albumin of pacu, Piaractus mesopotamicus, was studied, using the fluorescence quenching technique. Pacu is a neo-tropical fish specie inhabitant of rivers from western regions of Brazil. Methyl-parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous pesticide still used in agriculture and fish farming in many countries. The quenching of fluorescence can be mathematically expressed by the Stern-Volmer equation to calculate quenching constants. Stern-Volmer curves analysis is able to give important information about the pesticide-albumin interaction. Our results showed that the serum quenching reached 10% when the molar ratio of pesticide/albumin was about 7:1 for the three temperatures of the experiment. For the pure albumin quenching of 10%, methyl-parathion concentrations were 6, 7 and 9 times higher than albumin at 20, 25 and 30 degrees C, respectively. The calculated Stern-Volmer constants at 25 degrees C were 9.73x10(3)(+/-4.9x10(2))M(-1) for serum and 9.20x10(3)(+/-2.0x10(2))M(-1) for albumin. It was observed that albumin quenching is the phenomenon contributing to the quenching of the pacu serum fluorescence for methyl-parathion concentration lower than 10microM, suggesting that the protein is the most important carrier for the pesticide in serum.

Spectrofluorimetric study of the interaction of methyl-parathion with fish serum albumin.

The interaction of methyl-parathion with the albumin of Piaractus mesopotamicus (Holmberg 1887) (= pacu), a fish species typical of Brazilian rivers, was studied and the results compared with known values for human and bovine albumin obtained in an earlier investigation. Methyl-parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous pesticide still used in agriculture and fish farming in many countries. The fluorescence quenching technique with tryptophan as a natural probe was used to detect for the presence of methyl-parathion. Fluorescence can be mathematically expressed by the Stern-Volmer equation to calculate quenching constants, and changes in the behavior of Stern-Volmer curves at different temperatures indicate the nature of the mechanism causing the quenching. Our results indicate that methyl-parathion forms a complex with fish albumin. The estimated association constant is 9.73 x 103 (+/- 4.9 x 102) M(-1) at 25 degrees C.

Computational modeling of synchronization process of the circadian timing system of mammals.

This paper presents a model for the circadian temporization system of mammals which associates the synchronization dynamics of coupling oscillators to a set of equations able to reproduce the synaptic characteristics of somatodendritic membrane of neurons. The circadian timing system is organized in a way to receive information from the external and internal environments, and its function is the timing organization of physiological and behavioral processes in a circadian pattern. Circadian timing system in mammals is constituted by a group of structures which includes the suprachiasmatic nucleus, the intergeniculate leaflet and the pineal gland. In suprachiasmatic nucleus are found neuron groups working as a biological pacemaker-the so-called biological master clock. By means of numerical simulations using the Kuramoto model, we simulated the dynamics behavior of the biological pacemaker. For this we used a set of 1,000 coupled oscillators with long-range coupling, which were distributed on a 10 x 10 x 10 spherical lattice, and a new method to estimate the order parameter, which characterizes the degree of synchronization of oscillator system. Our model has been able to produce frequency responses in accordance with physiological patterns, and to reproduce two fundamental characteristics of biological rhythms: the endogenous generation and synchronization to the light-dark cycle.

Aptamers as Delivery Agents of siRNA and Chimeric Formulations for the Treatment of Cancer.

Both aptamers and siRNA technologies have now reached maturity, and both have been validated with a product in the market. However, although pegaptanib reached the market some time ago, there has been a slow process for new aptamers to follow. Today, some 40 aptamers are in the market, but many in combination with siRNAs, in the form of specific delivery agents. This combination offers the potential to explore the high affinity and specificity of aptamers, the silencing power of siRNA, and, at times, the cytotoxicity of chemotherapy molecules in powerful combinations that promise to delivery new and potent therapies. In this review, we report new developments in the field, following up from our previous work, more specifically on the use of aptamers as delivery agents of siRNA in nanoparticle formulations, alone or in combination with chemotherapy, for the treatment of cancer.

A screening test based on hematological and histological biomarkers to evaluate the environmental impacts in tambaqui (Colossoma macropomum) from a protected area in Maranhão, Brazilian Amazon.

Nowadays biomonitoring programs can benefit with mathematical models able to correlate biomarkers to monitor water pollution. The aim of this study was to develop a screening test based on hematological parameters and histological lesions in tambaqui (Colossoma macropomum), to allow the assessment of environmental impacts on fish inhabiting a protected area in Maranhão inside of Brazilian Amazon. Samples collected during three years (2012, 2013 and 2014) were grouped by season (dry and rainy) Water samples were also collected for physical chemistry analysis. Blood samples were stained with Acridine Orange to detect micronuclei and erythrocyte abnormalities. Gill tissues were stained with hematoxylin and counterstained with alcoholic eosin, and histopathological lesions were scored on a scale of 1-3, being 1 = minimal pathological importance, 2 = moderate pathological importance and 3 = marked pathological importance. A screening test for evaluating environmental impact was developed by fitting the measured data (necrosis, erythrocyte abnormalities, number of micronuclei) from tambaqui. A three-dimensional surface was fit to the empirical data. Our proposed model predicted the probability of necrosis (observed in euthanized animals) based on the numbers of micronuclei and abnormal erythrocytes (observed in blood samples from live animals) (correlation coefficient R = 0.89). The methodology could be applied for predicting contamination histories (chronic pollution that induces branchial lesions) in rivers using the micronucleus and erythrocyte abnormalities of the fishes (with a simple blood sample).

Deleterious effects of prepubertal corticosterone treatment on rat prostate.

PURPOSE: To investigate the structural and functional changes induced by corticosterone (CORT) in the ventral prostrate (VP) of rats in order to study chronic stress effects in the prepubertal phase. METHODS: Wistar rats received daily saline or CORT injections during the pubertal period from the 5th to 25th day of postnatal life. The animals were distributed into four groups: 1 - Control (n=5); 2 - Control 99mTc-P (n=5); 3 - Treated with CORT (n=14); 4 - Treated with CORT and 99mTc-P (n=10). All rats were sacrificed at two months of age. Technical tissue uptakes of 99mTc-P were used to evaluate the functional and stereological methods for morphological analysis. RESULTS: Acini distribution in the group treated with CORT differed significantly (p<0.0001) from the control. The control group's epithelial average height (10.01±0.24 microns) was statistically significant (p<0.0001) from rats treated with CORT (19.27±0.73microns). The collagen distribution was lower in the treated group (2.79%) when compared to control (3.97%). The radioactivity percentage in the groups marked with 99mTc-P (%Ati/g) did not demonstrate a statistically significant difference (p=0.285897). CONCLUSION: Chronic administration of corticosterone in prepubertal rats causes changes in their acinar structure and their ventral prostate stroma, indicating possible deleterious effects of this hormone.

Análise de percepção da insulinoterapia em diabéticos tipo 1 no Serviço de Apoio e Assistência aos Diabéticos e seus Familiares / Analysis of type 1 diabetes patients' perception of insulin therapy at the service of care and support to diabetics and their family

Objetivo: Analisar a percepção dos diabéticos tipo 1 sobre a insulinoterapia. Métodos: Trata-se de estudo epidemiológico analítico de percepção, tendo sido realizado com pacientes de um Serviço de Apoio e Assistência aos Diabéticos e seus Familiares, no período de abril a agosto de 2018. Resultados: Os 33 diabéticos tipo 1 avaliados eram predominantemente do sexo feminino (60,6%) e a média de idade foi de 21±9 anos. A maioria afirmou portar o Cartão de Identificação do Diabético (78,8%). Mais de dois terços dos pacientes afirmaram saber quando aplicar a insulina de correção. A aferição da glicemia capilar foi relatada por 78,8%. Das insulinas utilizadas no esquema basal, a glargina e a NPH foram citadas como as mais utilizadas. Do total de pacientes, 97% referiram fazer autoaplicação, e 90,9% disseram posicionar a agulha corretamente sobre a pele. Quanto aos locais de aplicação, 84,8% realizavam rodízio. A maioria dos pacientes (78,8%) que aplicavam a insulina não referiu desconforto durante ou após a aplicação, e 69,7% mostraram conhecimento sobre o significado de distrofia. Conclusão: O serviço de educação continuada desenvolvido pelo Serviço de Apoio e Assistência aos Diabéticos e seus Familiares é efetivo na aquisição de bons hábitos e dos devidos cuidados para esses pacientes. A educação do indivíduo com diabetes tipo 1 e de sua família, bem como o acompanhamento por uma equipe multidisciplinar, é essencial para o bom controle da doença,

Objective: To analyze the perception of type 1 diabetes (DM 1) patients of insulin therapy. Methods: This is an epidemiological study of analysis of perception and was performed at the service for care and support of diabetes patients and their families from April to August 2018. Results: The 33 type 1 diabetes mellitus patients evaluated were predominantly female (60.6%) and the mean age was 21 years ± 9 years. Most reported having the diabetes medical ID card (78.8%). More than two thirds of the patients reported knowing when to apply the correction insulin. The capillary glycemia measurement was reported by 78.8%. Of the insulins used in the baseline regimen, Glargine and NPH were cited as the most used. Of the total patients, 97% reported self-application and 90.9% reported positioning the needle correctly on the skin. As for the application sites, 84.8% reported rotating sites. Most patients (78.8%) who applied insulin did not report discomfort during or after application, and 69.7% showed knowledge about the meaning of dystrophy. Conclusion: The continuing education service developed by the Service for Care and Support of Diabetics and their Families is effective in promoting good habits and the proper care of these patients for their disease.The education of the individual with type 1 diabetes and of his/her family, as well as follow-up by a multidisciplinary team, is essential for good disease control.

Methyl parathion interaction with human and bovine serum albumin.

Methyl parathion (MP; O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous compound still largely used in agriculture and fish hatcheries. This pesticide is not quite selective and is potentially toxic for both vertebrates and invertebrates. Its mechanism of acute toxicity is the inhibition of the enzyme acetylcholinesterase in nervous tissue. Binding of pesticides to plasma proteins is one of many factors that influence their distribution and elimination. The free concentration available for toxic action can be effectively reduced for pesticides with high binding to plasma proteins, although the affinity of pesticides to plasma proteins is often lower than for the enzyme targets. Several different transport proteins exist in blood plasma, but albumin only is able to bind a wide diversity of xenobiotics reversibly with high affinity. It was already known that parathion (ethyl parathion) exhibits a high affinity to human and bovine serum albumins. We studied interactions of methyl parathion with these albumins by using fluorescence quenching techniques. We selectively excited the fluorescence of tryptophan residues with a 290 nm wavelength light, and observed quenching by titrating human and bovine serum albumin solutions with methyl parathion. Stern-Volmer graphs were plotted and quenching constants were estimated. Our results pointed to the formation of complexes of methyl parathion with albumins. Association constants at 25 degrees C were 3.07 x 10(4) (1.2 x 10(3))M(-1) for human serum albumin, and 1.96 x 10(4) (+/- 4.5 x 10(2))M(-1) for bovine serum albumin. At 37 degrees C, they were 1.08 x 10(4) (+/- 2.0 x 10(2))M(-1) for human serum albumin, and 8.16 x 10(3) (+/- 1.9 x 10(2))M(-1) for bovine serum albumin. Results also suggest that the primary binding site for methyl parathion on albumin is close to tryptophan residues 214 of human serum albumin and 212 of bovine serum albumin.

Chlorpromazine interactions to sera albumins. A study by the quenching of fluorescence.

Binding of chlorpromazine (CPZ) and hemin (Hmn) to human (HSA) and bovine (BSA) serum albumin was studied by fluorescence quenching technique. Intrinsic fluorescences of BSA and HSA were measured by selectively exciting their tryptophan residues. Gradual quenching was observed by titration of both proteins with CPZ and Hmn. CPZ is a widely used anti-psychosis drug that causes severe side effects and strongly interacts with biomembranes, both in its lipidic and proteic regions. CPZ also interacts with blood components, influences bioavailability, and affects the function of several biomolecules. Albumin plays an important role in the transport and storage of hormones, ions, fatty acids and others substances, including CPZ, affecting the regulation of their plasmatic concentration. Hmn is an important ferric residue of hemoglobin that binds within the hydrophobic region of albumin with great specificity. Hmn added to HSA and BSA solutions at a molar ratio of 1:1 quenched about half of their fluorescence. Stern-Volmer plots obtained from experiments carried out at 25 and 35 degrees C showed the quenching of fluorescence of HSA and BSA by CPZ to be a collisional phenomenon. Hmn quenches fluorescence by a static process, which specifically indicates the formation of a complex. Our results suggest the prime binding site for CPZ and Hmn on both HSA and BSA to be near tryptophan residues.

A simple mathematical model based on biomarkers in stress-resistant catfish species, Sciades herzbergii (Pisces, Ariidae), in São Marcos Bay, Brazil.

We present a refinement of our model describing the association between enzyme activity and histopathological lesions in the catfish, Sciades herzbergii from a polluted port. The fish were sampled from a port known to be contaminated with heavy metals and organic compounds and from a natural reserve in São Marcos Bay, Brazil. Two biomarkers, hepatic glutathione S-transferase (GST) activity and histopathological lesions, in gills and liver tissue were measured. The values for GST activity were modeled with the occurrence of branchial and hepatic lesions by fitting a third-order polynomial. Results from the mathematical model indicate that GST activity has a strong polynomial relationship with the occurrence of branchial and hepatic lesions in both wet and the dry seasons but only at the polluted port site. The model developed in this study indicates that branchial and hepatic lesions are initiated when GST activity reaches 2.17 µmol min(-1) mg protein(-1). Beyond this limit, GST activity decreased to very low levels and irreversible histopathological lesions occurred. This mathematical model based on two biomarkers (histopathological lesions and enzyme activity) in catfish provides a realistic approach to analyze stress induced by contaminants.

Effects of prepubertal corticosterone treatment on urinary bladder.

PURPOSE: The aim of this work was to analyze the bladder wall modifications after a chronic treatment with high doses of corticosterone in prepubertal rats. METHODS: This study included 26 male rats assigned into four groups: T30 was treated with corticosterone until 29 days of age and killed at day 30, while T65 group received the same treatment but was killed at day 65. Each group had its own control group (C30 and C65). For treated animals, daily intraperitoneal injections of corticosterone (20 mg/Kg) were administered between 7th and 29th day of life. Bladders were removed and collagen, smooth muscle, elastic fibers system, vascular density and epithelium were analyzed by morphometrical methods, immunofluorescence, and biochemistry. RESULTS: Vascular density in lamina propria was reduced by 40% (p<0.05) in group T65. Collagen organization was altered in T30 and T65, although total collagen concentration was unchanged. The T65 group had an increase in elastic system fibers. There was no difference in epithelial height and cell density between the groups. Concerning the smooth muscle fibers density we observed a 19% increase (p<0.05) in the T65 group. CONCLUSION: Prepubertal administration of corticosterone induces structural modifications in the bladder of rats in a medium term analysis.

Anti-heparanase aptamers as potential diagnostic and therapeutic agents for oral cancer.

Heparanase is an endoglycosidase enzyme present in activated leucocytes, mast cells, placental tissue, neutrophils and macrophages, and is involved in tumour metastasis and tissue invasion. It presents a potential target for cancer therapies and various molecules have been developed in an attempt to inhibit the enzymatic action of heparanase. In an attempt to develop a novel therapeutic with an associated diagnostic assay, we have previously described high affinity aptamers selected against heparanase. In this work, we demonstrated that these anti-heparanase aptamers are capable of inhibiting tissue invasion of tumour cells associated with oral cancer and verified that such inhibition is due to inhibition of the enzyme and not due to other potentially cytotoxic effects of the aptamers. Furthermore, we have identified a short 30 bases aptamer as a potential candidate for further studies, as this showed a higher ability to inhibit tissue invasion than its longer counterpart, as well as a reduced potential for complex formation with other non-specific serum proteins. Finally, the aptamer was found to be stable and therefore suitable for use in human models, as it showed no degradation in the presence of human serum, making it a potential candidate for both diagnostic and therapeutic use.

A fluorescent spectroscopy and modelling analysis of anti-heparanase aptamers-serum protein interactions.

Aptamers are short, single stranded oligonucleotide or peptide molecules that bind a specific target molecule and can be used for the delivery of therapeutic agents and/or for imaging and clinical diagnosis. Several works have been developed aiming at the production of aptamers and the study of their applications, but few results have been reported on plasmatic dynamics of such products. Aptamers against the heparanase enzyme have been previously described. In this work, the interactions of two constructs of the most promising anti-heparanase aptamer (molecular weights about 9200Da and 22000Da) to human and bovine serum albumins were studied by fluorescence quenching technique. Stern-Volmer graphs were plotted and quenching constants were estimated. Stern-Volmer plots obtained from experiments carried out at 25°C and 37°C showed that the quenching of fluorescence of HSA and BSA by the low molecular weight aptamer was a collisional phenomenon (estimated Stern-Volmer constant: 3.22 (±0.01)×10(5)M(-1) for HSA at 37°C and 2.47 (±0.01)×10(5)M(-1) for HSA at 25°C), while the high molecular weight aptamer quenched albumins by static process (estimated Stern-Volmer constant: 4.05 (±0.01)×10(5)M(-1) for HSA at 37°C and 6.20 (±0.01)×10(5)M(-1) for HSA at 25°C), interacting with those proteins constituting complexes. Linear Stern-Volmer plot from HSA titrated with the low MW aptamer suggested the existence of a single binding site for the quencher in this albumin. Differently, for aptamer 2, the slightly downward curvature of the Stern-Volmer plot of the titration for that albumin suggested a possible conformational change that led to the exposition of lower affinity binding sites in HSA at 25°C. Similarly, although short aptamerdoes not appear to form a stable complex (collisional interaction), the longer aptamer is found to form a stable complex with HSA. In addition, the behaviour of quenching curves for HSA and BSA and values estimated for ratio R1/R2 from model developed by Silva et al. suggest that the primary binding site in both aptamers is located closer to the tryptophan residue in sub domain IIA. It is likely that both aptamers are competing for the same primary site in albumin.

Risperidone interacts with serum albumin forming complex.

The aim of the work is to study the mechanisms of the interaction of risperidone with human and bovine serum albumins using the fluorescence quenching technique. Risperidone is an atypical antipsychotic drug used to treat many psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with a 290 nm wavelength light, and observed quenching by titrating human and bovine serum albumin solutions with risperidone. Emission spectra were recorded in the range from 300 to 450 nm for each quencher addition. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that the drug quenches the fluorescence of the human serum albumin by the formation of a complex risperidone-albumin. Association constants calculated from Stern-Volmer equation for low concentrations (lower than 1:10 ratio risperidone/albumin) were of 2.56 × 10(5)M(-1), at 25 °C, and 1.43 × 10(5)M(-1), at 37 °C. As the quenching intensity of bovine serum albumin, which contains two tryptophan residues, was found to be higher than that of human serum albumin, which contains only one tryptophan residue. Hence, we suggest that the primary binding site for risperidone in albumin should be located in sub domain IB.