Two-compartment model for rabbit skin organ culture

Polymyxins: recent advances and challenges

Antibiotic resistance is a pressing global health challenge, and polymyxins have emerged as the last line of defense against multidrug-resistant Gram-negative (MDR-GRN) bacterial infections. Despite the longstanding utility of colistin, the complexities surrounding polymyxins in terms of resistance mechanisms and pharmacological properties warrant critical attention. This review consolidates current literature, focusing on polymyxins antibacterial mechanisms, resistance pathways, and innovative strategies to mitigate resistance. We are also investigating the pharmacokinetics of polymyxins to elucidate factors that influence their in vivo behavior. A comprehensive understanding of these aspects is pivotal for developing next-generation antimicrobials and optimizing therapeutic regimens. We underscore the urgent need for advancing research on polymyxins to ensure their continued efficacy against formidable bacterial challenges.

Microporous membrane growth substrates for embryonic stem cell culture and differentiation

As the field of embryonic stem cell culture and differentiation advances, many diverse culturing techniques will ultimately be necessary in order to fully reproduce the various environments these cells normally encounter during development. Although most of the work to date has been performed on solid plastic supports, this growth support has several limitations in its representation of the in vivo environment. Impermeable substrates force the cells to exchange their gas and nutrients exclusively through the top side of the cultured cells. In contrast, cells growing in vivo are exposed from several directions to factors from the blood, other cells, soluble factors, and liquid-air interfaces. Additionally, solid plastic presents a smooth two-dimensional surface that is not experienced in vivo. Therefore, the use of traditional plastic presents limitations upon normal cellular morphology, function, and differentiation. An important alternative to growth on solid plastic is the growth of cells on microporous membranes. One of the many advantages to cell growth on porous membrane substrates is their ability to provide a surface that better mimics a three-dimensional in vivo setting. A porous membrane allows multidirectional exposure to nutrients and waste products. In addition, the membrane separation of dual chambers allows for the coculture of cells of different origin to study how cells interact through indirect signaling or through providing a conditioned niche for the proper growth and differentiation of cell types.

An explant model for the investigation of skin adaptation to mechanical stress

A test apparatus was developed to investigate the effects of mechanical stress application on collagen remodeling in skin. The system maintained a 4.5-cm x 5.5-cm skin explant at an air interface with controlled temperature, relative humidity (RH), and carbon dioxide concentration [CO2] while allowing controlled compressive and shear forces to be applied to the skin surface. For environmental control, a custom-designed flow system under Proportional-Integral-Derivative (PID) control was used. Evaluation tests demonstrated that the system maintained air above the explant at a temperature within 1 degrees C of the 37.5 degrees C set point, RH within 5% of the user-specified set point (range of 5% to 95%), and [CO2] within 1% of the 5% [CO2] set point. Least-squares errors in cyclic compressive and shear forces (0- to 20-Hz bandwidth) delivered to the explant were 0.9% and 2.8%, respectively, of user-specified values. Pig skin samples cyclically stressed for 1 hr/day for 3 days with either compressive force only or a combined compressive and shear force had significantly smaller collagen fibril densities compared with an unstressed control, a result consistent with in vivo test data. Collagen fibril diameters were significantly larger for stressed versus control for some of the samples, but the changes were not as substantial as from in vivo testing. This result may have been due to the shorter study duration in vitro (3 d versus 20 d in vivo). The system allows insight into the mechanisms of skin adaptation to mechanical stress to be investigated on a cellular and molecular level, potentially leading to therapies to encourage adaptation in at-risk patients.

Epidermal cell proliferation and terminal differentiation in skin organ culture after topical exposure to sodium dodecyl sulphate

Epidermal cell proliferation and differentiation were investigated in vitro after exposure to the anionic surfactant sodium dodecyl sulfate (SDS). Human skin organ cultures were exposed topically to various concentrations of SDS for 22 h, after which the irritant was removed. Cell proliferation was measured immunohistochemically by incorporation of bromodeoxyuridine (BrdU) into the DNA of cells during S-phase, while the expression of transglutaminase and involucrin were used as markers of differentiation. Cell proliferation was moderately increased at concentrations of SDS that did not affect the histomorphology (0.1% and 0.2% SDS). A marked increase of cell proliferation was observed 22 to 44 h after removal of SDS at a concentration (0.4%) that induced slight cellular damage. Exposure of human skin organ cultures to a toxic concentration of SDS 91.0% led to decreased cell proliferation. Transglutaminase and involucrin were expressed in the more basal layers of the epidermis after exposure to 0.4% or 1.0% SDS. Moreover, intra-epidermal sweat gland ducts were positive for transglutaminase at these irritant concentrations. These in vitro data demonstrate that SDS-induced alterations of epidermal cell kinetics, as described in vivo are at least partly due to local mechanisms and do not require the influx of infiltrate cells. However, we were unable to relate to altered cell kinetics to the release of interleukin-1 alpha or interleukin-6. Furthermore, supplementation of the culture medium with 12-hydroxyeicosantetraenoic acid did not affect epidermal cell proliferation. Rabbit skin cultures appeared more sensitive to SDS than human skin. At nontoxic doses, the irritant induced an increase of epidermal cell proliferation, similar to that observed in human skin discs.

Skin Organ Culture as an Alternative to In Vivo Dermatotoxicity Testing

Various aspects of acute cutaneous toxicity were studied in a skin organ culture model. Chemicals were applied topically for four hours, after which cytotoxicity was assessed by measuring the conversion of the tetrazolium salt, MTT. The relationship between pKa and cytotoxicity was investigated for a homologous series of benzoic acids. In this series, salicylic acid had the lowest pKa and proved to be the most toxic compound. Furthermore, the pH of the carrier solution was shown to influence the toxicity of chloroacetic acid and acetic acid in a different way. Using skin discs of both human and rabbit origin, we found that human skin was more resistant to toxicity induced by the irritants benzalkonium chloride and formaldehyde. As an additional aspect of dermal toxicology, the percutaneous absorption of testosterone was studied. After topical application to rabbit skin discs, testosterone was absorbed in a dose-dependent manner and concurrent metabolism was demonstrated.