Pedro Contreiras Pinto

Bacterial cellulose membranes applied in topical and transdermal delivery of lidocaine hydrochloride and ibuprofen: In vitro diffusion studies

Bacterial cellulose (BC) is a biomaterial with unique physical and mechanical properties that triggered considerable interest, but there are few studies addressing the use of such membranes for drug loading and controlled release. This study aimed to investigate the applicability of BC membranes in topical or transdermal drug delivery systems. To assess its therapeutic feasibility, the permeation through human epidermis of two model drugs (lidocaine hydrochloride and ibuprofen) in BC and other formulation systems was compared in vitro. A uniform distribution of both drugs in the BC membranes was achieved. Diffusion studies with Franz cells showed that the incorporation of lidocaine hydrochloride in BC membranes provided lower permeation rates than those obtained with the conventional formulations. However, the results obtained with the lipophilic drug were quite different, since permeation of ibuprofen in BC was almost three times higher than that of the drug in the gel or in a PEG400 solution. These results indicate that this technology can be successfully applied to modulate the bioavailability of drugs for percutaneous administration, which could be particularly advantageous in the design of delivery systems that have, simultaneously, the ability to absorb exudates and to adhere to irregular skin surfaces.

Is there any barrier impairment in sensitive skin?: a quantitative analysis of sensitive skin by mathematical modeling of transepidermal water loss desorption curves

Background/purpose: Sensitive skin is a vague, subjective and difficult to characterize affliction. It affects a large part of the population and is accompanied with great interest by the cosmetic industry. Some studies have suggested that sensitive skin is the result of impaired barrier function, which leads to the exposure of immune system cells and sensitive nerves, resulting in marked cutaneous responses to otherwise harmless stimuli. This study aimed to investigate the cutaneous barrier integrity of individuals with sensitive skin by a novel approach: a plastic occlusion stress test followed by measurement of transepidermal water loss (TEWL) desorption curves.

Bacterial and protozoal agents of feline vector-borne diseases in domestic and stray cats from southern Portugal

BackgroundFeline vector-borne diseases (FVBD) have emerged in recent years, showing a wider geographic distribution and increased global prevalence. In addition to their veterinary importance, domestic cats play a central role in the transmission cycles of some FVBD agents by acting as reservoirs and sentinels, a circumstance that requires a One Health approach. The aim of the present work was to molecularly detect feline vector-borne bacteria and protozoa with veterinary and zoonotic importance, and to assess associated risk factors in cats from southern Portugal.MethodsSix hundred and forty-nine cats (320 domestic and 329 stray), from veterinary medical centres and animal shelters in southern Portugal, were studied. Anaplasma spp./Ehrlichia spp., Babesia spp., Bartonella spp., Borrelia burgdorferi sensu lato, Hepatozoon spp. and Leishmania spp. infections were evaluated by polymerase chain reaction (PCR) in blood samples.ResultsOne hundred and ninety-four (29.9%) cats were PCR-positive to at least one of the tested genera or complex of FVBD agents. Sixty-four (9.9%) cats were positive to Leishmania spp., 56 (8.6%) to Hepatozoon spp., 43 (6.6%) to Babesia spp., 35 (5.4%) to Anaplasma spp./Ehrlichia spp., 19 (2.9%) to Bartonella spp. and 14 (2.2%) to B. burgdorferi s.l. Thirty-three (5.1%) cats were positive to two (n = 29) or three (n = 4) genera/complex. Babesia vogeli, Bartonella clarridgeiae, Bartonella henselae, Ehrlichia canis, Hepatozoon felis and Leishmania infantum were identified by DNA sequencing.ConclusionsThe occurrence of FVBD agents in southern Portugal, some of them with zoonotic character, emphasizes the need to alert the veterinary community, owners and public health authorities for the risk of infection. Control measures should be implemented to prevent the infection of cats, other vertebrate hosts and people.

Modeling TEWL-desorption curves: a new practical approach for the quantitative in vivo assessment of skin barrier

Abstract:  The objective of the present study was to test the discriminative capacity of the mathematical modeling of the transepidermal water loss (TEWL) curves that result from a plastic occlusion stress test (POST) to variations in the skin barrier – insults inflicted to the skin or differences in two distinct anatomical regions. This study was exclusively performed in the arm. On the first part of the work, three different insults to the skin barrier were assessed: tape stripping, lipid extraction with ether : acetone, and skin‐surface biopsy. Anatomical differences were studied in the mid‐forearm and in the wrist. All sites were submitted to a POST, after which the desorption curves were recorded. The mathematical model was adjusted to the TEWL data points. Results indicate differences in the parameters obtained in the control and treated sites, which suggests differences in the water dynamics after the damage was inflicted and shows that the method is valid for the objectives proposed. There were also significant differences in the parameters obtained in the wrist and in the volar forearm, which indicates that the method is also sensitive to variations in skin histology and anatomy.

Exploring the influence of skin perfusion on transepidermal water loss

Background: Eventual relationships between the vascular function and transepidermal water loss (TEWL), in vivo, have not been entirely explored. By promoting local perfusion alterations through a well‐known challenge test, the ‘tourniquet‐cuff occlusion’ manoeuvre, the present study searches for other dynamical factors influencing the cutaneous barrier, further exploring the applicability of these flow‐related variables in dermatological research.

Transcutaneous flow related variables measured in vivo: the effects of gender

BackgoundThe identification of potential sources of error is a crucial step for any new assessment technique. This is the case for transcutaneous variables, such as flow and arterial gases, which have been applied as functional indicators of various aspects of human health. Regarding gender, a particular subject-related determinant, it is often claimed that women present higher transcutaneous oxygen pressure (tcpO2) values than men. However, the statistical significance of this finding is still uncertain.MethodsThe haemodynamical-vascular response to a local reactive hyperaemia procedure (the tourniquet cuff manoeuvre) was studied in two previously selected group of volunteers (n = 16; 8 women and 8 men). The effect of gender was assessed under standardised experimental conditions, using the transcutaneous flow-related variables tcpO2-tcpCO2 and Laser-doppler Flowmetry (LDF).ResultsRegarding tcpO2, statistically significant differences between genders were not found, although higher values were consistently found for the gases in the female group. Regarding LDF, high statistically significant differences (p < 0.005) were found, with the mens group presenting the highest values and variability. Other derived parameters used to characterise the vascular response following the cuff-deflation (t-peak) were similar in both groups.ConclusionsThe relative influence of gender was not clearly demonstrated using these experimental conditions. However the gender-related LDF differences suggest that further investigation should be done on this issue. Perhaps in the presence of certain pathological disparities involving peripheral vascular regulation, other relationships may be found between these variables.

Transepidermal water loss kinetic modeling approach for the parameterization of skin water dynamics

Background/aims: The evaluation of transepidermal water loss (TEWL) is one of the methods most frequently used in studies involving skin water dynamics. However, TEWL does not provide a direct measurement of epidermal barrier function, being rather a surrogate effect of it. In particular, when external stimuli change cutaneous water balance, these stimuli must be taken into account in order to achieve a rigorous interpretation of the results. Since TEWL is primarily attributed to the water flux from the deepest layers of the skin, through the epidermis, and towards the external environment, this whole process is reasonably compliant with Ficks first law of diffusion. Within this perspective, the aim of this work was to develop a two compartment mathematical model capable of quantitatively describing cutaneous water mass balance over time and thus to provide practical and objective comparable parameters that are particularly useful for studies critically depending on a precise evaluation of TEWL.

Comparative assessment of the performance of two generations of Tewameter: TM210 and TM300.

The measurement of transepidermal water loss (TEWL) has been established as one of the main parameters in the assessment of skin barrier function. One of the most widely employed devices to measure TEWL is the Tewameter®. Courage and Khazaka launched the TM300 in 2003 and successfully eliminated some of the limitations of the previous model. In the more recent device, the sensors inside the probe head can be pre‐heated to a temperature close to that of the skin, which considerably decreases sampling time. Additionally, the new technology of the probe does not require frequent and time‐consuming recalibration with different solutions. The main objective of this work was to perform a comparative assessment of the performance of the two different Tewameter® models. Fifteen volunteers were used in this study, which was conducted in the mid‐portion of the volar forearm. The standard measurements assessed differences in the basal values, time necessary for a stable value and coefficient of variability under normal and extreme conditions. The dynamic measurements performed were based on a plastic occlusion stress test (POST), involving the application of an occlusive patch for 24 h, after which the TEWL desorption curves were recorded. A mathematical model was adjusted to the data points using a specially modified simplex routine. Calculated parameters considered relevant to the study were t1/2evap (evaporation half‐life) and dynamic water mass (DWM). Results show slight differences in the performance the two models, which are nevertheless statistically significant. The TM300 seems to be more sensitive to differences in TEWL and presents a much quicker measurement capacity. These results confirm a marked improvement in the more recent Tewameter® model, when compared with its predecessor. The main conclusion of this work is that caution is advised when comparing results obtained with the two different models and that studies should be carried out entirely with the same device.

A Quality by design (QbD) approach on starch-based nanocapsules: A promising platform for topical drug delivery.

Exploring novel applications for approved excipients with a history of safe use in therapeutics is a smart strategy to obtain improved pharmaceutical products. The present study aimed at developing a novel starch-based nanoparticulate carrier system (StNC) for topical delivery of lipophilic bioactive molecules. The role of the different factors that affect the particle size distribution and zeta potential of StNC prepared by the emulsification-solvent evaporation method was assessed using a quality by design approach. An optimal formulation was selected and fully characterized in terms of molecular interactions (DSC and FTIR), morphology (TEM and AFM), as well as in vitro and in vivo biological properties, including biological sensitivity/irritation studies performed in human volunteers. Results show the surfactant and lipid contents play a major role in StNC particle size distribution. In addition, all tested formulations presented a zeta potential of ca. +33.6±6.7 mV, indicating a good physical stability, while revealing an excellent compromise between stability, safety and cosmeticity, evidencing that StNC are suitable nanocarriers for topical use. Finally, the design planning methodology has clearly shown its usefulness for optimizing the formulation, being also crucial for the understanding of StNC formation process. The StNC proved to be a promising formulation strategy and a potential nanocarrier for topical lipophilic bioactive molecules.

Assessment of moisturizers and barrier function restoration using dynamic methods

Background/purpose: Dynamic methods, such as the mathematical modelling of the transepidermal water loss curves that result from a plastic occlusion stress test (POST), enable the complete characterization of the dynamic water balance established between the deep and the superficial skin structures. Previous studies have indicated that this methodology was able to detect impaired barrier function and differentiate normal and dry skin. The objective of the present study is to apply the discriminative capacity of the model to the efficacy testing of moisturizing products.