Versatile lysine dendrigrafts and polyethylene glycol hydrogels with inherent biological properties: in vitro cell behavior modulation and in vivo biocompatibility.

Poly(ethylene glycol) (PEG) hydrogels have been extensively used as scaffolds for tissue engineering applications, owing to their biocompatibility, chemical versatility, and tunable mechanical properties. However, their bio-inert properties require them to be associated with additional functional moieties to interact with cells. To circumvent this need, we propose here to reticulate PEG molecules with poly(L-lysine) dendrigrafts (DGL) to provide intrinsic cell functionalities to PEG-based hydrogels. The physico-chemical characteristics of the resulting hydrogels were studied in regard of the concentration of each component. With increasing amounts of DGL, the cross-linking time and swelling ratio could be decreased, conversely to mechanical properties, which could be tailored from 7.7 ± 0.7 to 90 ± 28.8 kPa. Furthermore, fibroblasts adhesion, viability, and morphology on hydrogels were then assessed. While cell adhesion significantly increased with the concentration of DGL, cell viability was dependant of the ratio of DGL and PEG. Cell morphology and proliferation; however, appeared mainly related to the overall hydrogel rigidity. To allow cell infiltration and cell growth in 3D, the hydrogels were rendered porous. The biocompatibility of resulting hydrogels of different compositions and porosities was evaluated by 3 week subcutaneous implantations in mice. Hydrogels allowed an extensive cellular infiltration with a mild foreign body reaction, histological evidence of hydrogel degradation, and neovascularization.

In vitro epidermis model mimicking IGF-1-specific age-related decline.

Ageing is a complex multifaceted process affecting skin functionality and structure. Several 3D organotypic skin culture models have reproduced ageing by inducing replicative senescence, glycation or oxidative stress. Yet, very few models have focused on hormonal ageing and especially the insulin-like growth factor 1 (IGF-1) signalling pathway, which has been associated with longevity in animal studies and is necessary for the early stages of skin development. In this study, we built an organotypic epidermis model with targeted IGF-1 receptor knockdown to reproduce some aspects of hormonal ageing on skin. Our model displayed morphological and functional features of aged epidermis, which were mostly attributed to a loss of function of the Stratum basale. IGF-1 receptor knockdown keratinocytes depicted an extended cell cycle, reduced proliferation potential and reduced adhesion capacities and greater sensitivity to oxidative stress than control cells. Altogether, this model represents an essential tool for further investigations into the mechanisms linked to some aspects of hormonal decline or when screening for potent anti-ageing compounds.

Analysis of epidermal lipids in normal and atopic dogs, before and after administration of an oral omega-6/omega-3 fatty acid feed supplement. A pilot study.

Alterations of the lipid expression in the skin of human and canine atopic subjects may be one of the key factors in the disease development. We have analyzed the ultrastructure of the clinically uninvolved skin of atopic dogs and compared it with the lipid composition of their tape-stripped stratum corneum (SC). The effect of a 2 month treatment of atopic dogs by food supplementation with a mixture of essential fatty acids was evaluated on skin samples taken before and after the treatment period. Electron microscopy revealed that the non-lesional skin of atopic dogs exhibited an abnormal and largely incomplete structure of the lamellar lipids with little cohesion between the corneocyte strata. The SC of atopic dogs was characterized by a significant decrease in the lipid content when compared to the healthy controls. Following oral supplementation with the mixture of essential fatty acids, the overall lipid content of the SC markedly increased. This feature was observed both with the free and, most importantly, with the protein-bound lipids (cholesterol, fatty acids and ceramides), the latter constituting the corneocyte-bound scaffold for ordinate organisation of the extracellular lipid bi-layers. Indeed, the semi-quantitative electron microscopy study revealed that the treatment resulted in a significantly improved organization of the lamellar lipids in the lower SC, comparable to that of the healthy dogs. Our results indicate the potential interest of long-term alimentary supplementation with omega-6 and omega-3 essential fatty acids in canine atopic dermatitis.

Atopic dermatitis in dogs is associated with a high heterogeneity in the distribution of protein-bound lipids within the stratum corneum.

The stratum corneum (SC) was taken from five atopic dogs by tape stripping (12 strips) of non-lesional areas of the abdomen. The free and protein-bound lipids were extracted and analyzed by thin-layer chromatography after fractionation on aminopropyl-bonded silica gel columns. A very frequent feature was the heterogeneity in the lipid content of consecutive layers. This was even more accentuated for the covalently bound lipids, with variations from one layer to another in the concentrations of cholesterol, omega hydroxylated ceramides and omega hydroxylated long-chain fatty acids. Among the free lipids, large amounts of glucosylceramides were present in canine atopic SC although they are nearly absent from the SC of normal dogs. A heterogeneous distribution of lipids was seen in canine atopic SC. These results suggest that strikingly deep variations occur in the lipid metabolism of keratinocytes in the skin of atopic dogs. In order to gain insight into this phenomenon, further studies should be focused on the activity of enzymes involved in both biosynthetic and catabolic processes.