Distribution and Expression of Non-neuronal Transient Receptor Potential (TRPV) Ion Channels in Sensitive Skin Syndrome.

Sensitive skin syndrome is defined as the presence of burning, itching or any other unpleasant sensation on the skin, due to physical, chemical or psychological factors. It is frequently a self-diagnosed condition, and there are no accurate tests to recognize or quantify it because of the individual variations in perception and intensity of the related symptoms.

Although the pathogenesis of sensitive skin syndrome is not completely understood, the most accepted theory is the presence of an altered barrier function. Irritation results from the abnormal penetration of substances to deeper layers of the skin, where they can induce vasodilation and stimulate c-type neuronal fibers. Also, changes in the pH of the stratum corneum have been found to induce skin sensitivity through the activation of the transient potential receptor vanilloid (TRPV) neuronal receptors.

TRPV1 was first discovered in 1997, when it was identified as the specific receptor for capsaicin in a subgroup of nociceptors. It is a non-selective thermo-sensitive cationic channel that can be found in nerves from the central and peripheral nervous system, fibroblasts, smooth muscle, mast cells, endothelial cells, gastrointestinal, respiratory and urinary epithelial cells. TRPV1 can be activated by excessive heat (>42ºC), acidic pH (< 5.9), and also by endogenous substances such as N- arachidonoyl dopamine, leucotriene B, phospholipase C, and many others.

In 2001, the functional expression of TRPV1 was identified in human keratinocytes. Their physiologic role in the skin has not been completely understood, but they have been related to differentiation, proliferation, inflammation and homeostasis of the epidermal barrier. Their presence in keratinocytes and cutaneous nervous fibers suggests a role in the sensitive function of the epidermis. It has been proved that the stimulation of TRPV1 in neuronal cells can induce pruritus and burning sensation. In vitro studies have demonstrated that the exogenous stimulation of TRPV1 in keratinocytes induces the release of nitric oxide, ATP, dopamine, prostaglandins, and other pro-inflammatory substances that can act as paracrine mediators between keratinocytes and cutaneous nerve fibers. Therefore, there are scientific bases to hypothesize that an increase in the expression of these receptors can be the responsible for the sensitive skin syndrome.