The effect of heat shocks in skin rejuvenation

Abstract

The formation of wrinkles, one of the aspects of aging skin, results as a consequence of a degenerated dermis. The aged protein network, muscle contractions and gravitation result in wrinkling of the skin. Currently, in the cosmetic industry, treatments for skin rejuvenation are rapidly evolving. Only a few techniques are used to counteract the aging dermis. One of the most promising areas is non-ablative laser techniques. These techniques have clinically been tested. However, the physiological background remains to be established. It is hypothesized that laser induced heat in the skin causes a heat shock and a subsequent heat shock response by the dermal fibroblasts. This heat shock response is said to stimulate, through heat shock proteins, the collagen synthesis by these cells. Subsequently, the laser has next to the thermal effect also a photochemical effect, where the photons are absorbed by cytochrome-c proteins, located on the cell membranes of the fibroblasts, and by doing so enhance the oxidative phosphorylation process, which in turn would result in a positively stimulated metabolism of the cell resulting in synthesizing more proteins, such as collagen. The present thesis focuses on the influence of the thermal effect on the collagen production of human dermal fibroblasts in culture and in ex-vivo skin. A model was developed that describes the interaction of laser light with skin resulting in the generation of heat. This model was combined with a transport model to describe the distribution of this heat through the skin. The model was used to determine the optimal laser conditions for heating and to describe the temperature distribution in the skin as a function of time. To investigate the response of human skin to heat shocks, the initial research was performed on cell cultures. Here, human dermal fibroblasts were cultured and exposed to heat shocks of 45°C and 60°C, respectively, and with pulse duration of 2 seconds. The results of this study showed that these heat shocks enhanced the collagen type I synthesis. Subsequently, a study was performed with heat shocks of 45°C and 60°C that were applied for 2, 4, 8, 10 and 16 seconds. The conclusion from this study is that 8 to 10 second pulses at 45°C are the maximum exposure time range at which the collagen type I synthesis is optimal. In addition, viable ex-vivo human skin samples were immersed into heated PBS of 45°C and 60°C. The 45°C heat shock does not create damage at all, while the 60°C heat shock shows initial damage around the cells in the skin. It was demonstrated that procollagen type I as well as type III were upregulated by both 45°C and 60°C heat shocks. Subsequently, a pilot study of a laser induced heat shock on ex-vivo skin study was performed. The results of this research demonstrated that the 45°C laser induced heat shocked did not damage the skin samples. The 60°C laser induced heat shock, on the other hand, demonstrated the presence of hsp27 in the area of the cells, and indication of early damage. The gene expression results revealed that the 45°C heat shocks upregulated procollagen type I. In conclusion, it has been shown in this thesis that a heat shock of 45°C applied to fibroblasts or in ex-vivo skin results in upregulation of in collagen heat shock gene expression. Furthermore, the cell studies showed the relevance of the combination of time and temperature; an optimal exposure time range of 8 to 10 seconds at 45°C to achieve the highest amount of collagen type I was found. Also the harmful nature of a 60°C heat shock was revealed. Showing that collagen synthesis can be enhanced by the 45°C heat shock is another step towards understanding the physiological pathways that lead to skin rejuvenation.