Most
of the safe alternatives to hydroquinone impact the key enzyme, tyrosinase, that
mediates two key steps in melanogenesis. See Key Steps in Melanin
Biosynthesis.
Key ingredients. There are several ingredients that
inhibit the tyrosinase enzyme, as well as compete with the enzyme’s substrate,
L-3,4-dihydroxyphenylalanine (L-DOPA). Botanical extracts, such as Ferula
foetida (giant fennel), bearberry, licorice, Sophora angustifolia, kiwi fruit,
nasturtium, rumex (yellow dock), Phyllanthus emblica fruit and mulberry contain
bioflavonoid components similar in chemical structure to L-DOPA, the end product
of Step 1, illustrated in Key
Steps in Melanin Biosynthesis. The bioflavonoids compete with the
substrate L-DOPA, thereby preventing Step 2, also illustrated in the diagram,
from occurring.
Tyrosinase inhibitors. Tyrosinase inhibitors also exist, such
as hydroxycinnamic acid, gluconic acid, zinc glycinate, kojic acid,
aspergillus ferment, rumex extract and ergothioneine, that chelate or bind
copper, a cofactor required in Step 2 of the diagram. Binding the copper
inhibits this reaction from occurring and controls melanin formation.
Hydroxy acids. Although the use of hydroxy
acids—lactic acid, glycolic acid and salicylic acid—in skin-brightening products
has generally been utilized to accelerate desquamation and removal of
melanin-containing corneocytes, it has recently been shown that a 5%
concentration of lactic acid will inhibit the formation of the tyrosinase
enzyme, thereby slowing the process of melanin synthesis. Other exfoliating
agents used in brightening products include pumpkin enzyme, sutilains (a
protease enzyme), lactobacillus ferment and galactoarabian, a molecule that
stimulates natural desquamation in the skin.
Controlling inflammation. Controlling inflammation is another
strategy for treating hyperpigmentation. The use of anti-inflammatory
agents, such as white tea, licorice and green tea, helps address the connection
between inflammation and pigment formation. These extracts also may act as
antioxidants, slowing many of the oxidation steps involved in melanin
formation.
Melanin formation. Of particular interest are ingredients
that impact melanin formation in multiple ways. An example is zinc glycinate,
which stimulates synthesis of an antioxidant protein called metallothionein
that binds the copper and reduces tyrosinase synthesis and activity; in
addition, it suppresses melanocyte growth factors that stimulate melanin
synthesis. Niacinamide has been shown to stop the transfer of melanosomes to
neighboring keratinocytes. Glucosamine and dithiooctanediol stop the
activation of the tyrosinase enzyme, a step that involves glycosylation, or
the addition of a sugar molecule to the inactive proenzyme structure, converting
it to the activated enzyme. Obviously, if the enzyme remains inactive, melanin
formation ceases.
New
studies indicate that melanin formation can also be controlled by affecting the
signaling process involved in melanin biosynthesis. Sunscreens and
anti-inflammatory agents work by turning off the messengers that signal melanin
synthesis to commence. A brown seaweed called Ascophyllum nodosum has been shown
to inhibit endothelin-1 (ET-1), a molecule synthesized and released from the
keratinocytes after UV exposure. ET-1 stimulates the melanocyte and triggers
tyrosinase activity. When the signal molecule ET-1 is inhibited, melanin
formation is likewise inhibited. In a similar role, the use of Palmaria palmata,
a red algae, has been shown to inhibit the release of stem cell factor (SCF),
another signaling molecule released by keratinocytes upon exposure to UVB
radiation; SCF activates the melanocyte to make melanin. Palmaria palmata
inhibits the release of SCF and therefore inhibits melanocyte activation.
In
the past decade, ascorbic acid (vitamin C) has been used to control melanin
synthesis. Newer stabilized derivatives of vitamin C include magnesium ascorbyl
phosphate (MAP), ascorbyl glucoside and tetrahexyldecyl ascorbate. These
derivatives scavenge free radicals that cause erratic melanocyte activity, as
well as act as antioxidants inhibiting oxidation steps along the biosynthetic
pathway of melanin. They have also been shown to inhibit tyrosinase synthesis
and activity.
Finally,
the newest and perhaps most exciting agents to fight melanin formation are the
peptides. Oligopeptide-34 is a state-of-the-art synthesized peptide that has
been shown to decrease alpha-MSH activity and inhibit tyrosinase activity.
Although the mechanism is not clearly understood, results indicate that it
brightens skin, especially sun-induced hyperpigmentation, in half the time
when compared to other brightening complexes. The use of peptides, such as
oligopeptide-34 to control pigmentation, may very well be the newest and most
effective approach to treating hyperpigmentation. And if safety studies are
a good indicator, they are a lot safer for the end user.
The future
Dealing
with issues of pigmentation will undoubtedly continue to be a focus in the skin
care arena, and there is certainly no shortage of products designed to address
these issues. But the most important question is: Which are effective and safe
to use? Although hydroquinone continues to be the only authorized OTC whitening
agent in the United States, there are numerous studies that question its safety,
which accounts for its being banned in most countries throughout the world.
Fortunately, the pressure remains on pharmaceutical houses, cosmetic
companies and even raw material suppliers to find safe and legal alternatives to
hydroquinone. This past decade has seen a myriad of new brightening agents, all
promising to reduce hyperpigmentation while enhancing skin luminosity and,
although most have fallen short of hydroquinone’s ability to whiten skin,
new cocktails of brighteners are now available that are close in performance and
a lot safer to use.
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See more at:
http://www.skininc.com/skinscience/ingredients/41973632.html?utm_source=newsletter-html&utm_medium=email&utm_campaign=SI+E-Newsletter+12-18-2015#sthash.om5TpxYF.dpuf
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