Hyperpigmentation
An Overview of Human Pigmentation
Human skin contains specialized cells, called melanocytes, which are located at the base of the epidermis. These cells are programmed to manufacture a brown pigment, called melanin, in response to exposure of skin to sunlight. Since melanin acts as a sunscreen, the production of this pigment by melanocytes is a defense response of the skin to the damaging and potential skin cancer causing rays of the sun. In addition to UV radiation, other factors can stimulate melanocytes to make melanin. Hormones, such as those in birth control pills can cause melanocyte “activation”, and exposure of the skin to any event that causes inflammation, such as acne, dermatitis, exposure to chemicals, etc., can also result in increased melanin production by melanocytes.
Melanin production in human melanocytes is controlled primarily by the rate-limiting enzyme for melanin synthesis, tyrosinase, which catalyzes the hydroxylation of tyrosine to L-DOPA and the oxidation of L-DOPA to dopaquinone. The subsequent steps in the pathway to melanin formation can occur non-enzymatically although two additional melanocyte-specific enzymes are thought to play a role in determining what type of melanin is formed.
The chart on the left shows that the pathway can diverge to produce either a red/yellow type of melanin (pheomelanin), or brown/black melanin, called eumelanin. The type of melanin made is genetically determined, and results in some people having fair skin and red hair while others are dark-skinned and have dark hair.
The melanin produced by the action of tyrosinase is “packaged” within the melanocyte into unique vesicles called melanosomes. These organelles are then transferred from the melanocyte to surrounding keratinocytes in the skin. As keratinocytes move from the lower part of the epidermis up to the surface, they can carry the ingested melanosomes with them, and the result is a deposition of the melanin-filled melanosomes near the skin’s surface. This is what gives the skin its brownish tint. The image on the right shows a melanocyte and the production of melanosomes.
The deposition of melanin at the skin’s surface provides some sunscreen protection from the damaging effects of UV rays, although in a Caucasian, the amount of SPF that melanin provides is likely no more than an SPF of 4. Therefore, it is important to use a sunscreen regardless of how “tanned” you are!
Pigmentation Problems and Current Treatments
Uneven pigmentation occurs as a result of age, chronic sun exposure, pregnancy and even from the use of birth control pills. In addition, cosmetic procedures such as laser re-surfacing, can cause increased skin pigmentation. Lentigines (“age spots”) and other areas of hyperpigmentation resulting from years of sun exposure can occur on the face, hands, arms and chest and can be difficult to treat. The standard OTC and prescription drug treatment for hyperpigmentation is hydroquinone, either 2% for OTC products or up to 4% for prescription based products. Perhaps the most effective skin lightening drug available by prescription is Triluma which is a combination of 4% hydroquinone, tretinoin and a corticosteroid. Hydroquinone based skin lightening products have been removed from the market in many countries and the FDA is now considering banning the drug in both OTC and prescription drug products in the U.S. because of safety concerns.
Although hyperpigmentation is a very common skin problem, and one which results from a variety of factors including sun exposure, skin inflammation, and LASER re-surfacing procedures, another type of pigmentation disorder is vitiligo. This is a disease that result in a loss of melanocytes, thereby causing areas of the skin to become completely white. While the cause of the disease is largely unknown, it is commonly believed to be an autoimmune disease where the immune cells attack and destroy melanocytes. For people affected by vitiligo, this skin problem is cosmetically disfiguring and unfortunately there is very little that can be done. One approach is to simply lighten the rest of the skin so that the depigmented area is not so prominent.
Skin Lightening (Whitening) Chemicals
To reduce skin pigmentation, either for the purpose of reducing the appearance of “age spots” or for “masking” an area affected by vitiligo, a variety of “bleaching” ingredients are available. All of the commonly used skin whitening ingredients work by inhibiting the activity of tyrosinase, the enzyme responsible for melanin synthesis. As mentioned, the mainstay of skin whitening ingredients is hydroquine. This ingredient is the most effective tyrosinase inhibitor available in skin lightening products. However, because of the recent announcement by the FDA, that it is considering banning all OTC products containing hydroquinone because of safety concerns, many companies are now offering alternatives to hydroquinone in skin “whitening” products. Numerous scientific publications have presented data on the skin lightening properties of cosmetic ingredients such as arbutin, kojic acid, vitamin C, licorice extract, alpha hydroxyacids, and a plethora of plant extracts. However, finding an effective replacement for hydroquinone has proven to be difficult. Arbutin, kojic acid and vitamin C are the ingredients most often found in skin whitening products, but depending on the concentration of these skin whitening “actives” in the formulation and their ability to penetrate through the skin and down to the melanocytes, the skin lightening activity of the product may range from no effectiveness to mild skin lightening effects.
DermaMedics Skin Whitening Technology
DermaMedics scientists have discovered a plant-derived chemical that is an extremely potent inhibitor of melanin production in human melanocytes. Unlike other skin lightening ingredients, Therosol-E inhibits melanin production at 2 sites. First, the compound inhibits the synthesis of tyrosinase, so that melanocytes treated with Therosol-E have very little tyrosinase, and, therefore, simply can’t make melanin. Secondly, the compound blocks a particular step in the melanin synthesis pathway where a colorless melanin precursor is converted to a colored melanin product. Therosol-E prevents the colorless intermediate from proceeding to the next step in the melanin synthesis pathway and thus, the final brown pigment, melanin, is never produced.
Clinical Treatment of Hyperpigmentation
DermaMedics has recently discovered a novel botanically-derived chemical compound that inhibits melanin production in human melanocytes through two distinct mechanisms. First, this compound, called Therosol-E, reduces the synthesis of tyrosinase in human melanocytes by approximately 75%. Secondly, this compound blocks the melanin synthesis pathway at a unique site that prevents a colorless melanin intermediate from being converted into brown melanin. By blocking melanin production at two sites, Therosol-E is able to almost completely depigment human melanocytes. The photographs on the left show the effect of Therosol-E on melanin accumulation in human melanocyte cultures. Note the high level of melanin in the untreated melanocyte cultures and the near total absence of melanin in the Therosol-E treated cells. The cells remain viable and dendritic, dividing at the same rate as the untreated cells, but do not produce melanin.
A 2% concentration of this novel pigmentation inhibitor has been formulated into a topical lotion that also contained 2% salicylic acid to accelerate exfoliation. The formulation was subjected to clinical evaluation at several testing sites around the country. These photographs (right) show the effect of the topical lotion on hyperpigmentation in a patient that developed inflammation-induced hyperpigmentation caused by acne and rosacea. The attending physician had been treating the patient with doxycycline with limited success. After one month of applying a topical Therosol-E lotion twice a day over clean skin, the facial improvement was dramatic. Not only did the areas of hyperpigmentation disappear but the anti-inflammatory properties of Therosol-E also reduced the severity of the patient’s acne. Patents to protect this technology have been filed in both the U.S. and through the PCT.