anew method of restoring hair growth - using drugs that are already approved for safety - may be on the way, according to research published in Science Advances.
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Researchers at Columbia University Medical Center in New York have found that when hair follicles are suspended in a resting state, rapid and robust growth can be restored by inhibiting a family of enzymes inside the follicles.
Hair follicles do not produce hair constantly but rather cycle between four resting and growing phases.
More than 90% of the hair is normally in the growing phase, "anagen," which can last from 2-6 years.
The relatively short catagen phase follows, when the follicle regresses and moves toward the surface. "Telogen" is the resting phase, and "exogen" is when the hair falls out before the follicle resumes growth.
Generally, the longer the hair, the longer the phases are; long hair tends to grow more slowly.
Enzyme inhibitors promote growth
aIn experiments with normal mouse and human hair follicles, Dr. Angela Christiano, PhD, and colleagues found that drugs that inhibit the Janus kinase (JAK) family of enzymes promote rapid and robust hair growth when directly applied to the skin.
This suggests that JAK inhibitors could be used to restore hair growth in various forms of hair loss, such as that induced by male pattern baldness - also called androgenetic alopecia - and other types of hair loss that occur when hair follicles are trapped in a resting state.
Two JAK inhibitors have already been approved by the US Food and Drug Administration (FDA), one for treatment of blood diseases (ruxolitinib) and the other for rheumatoid arthritis (tofacitinib).
Both are being tested in clinical trials for the treatment of plaque psoriasis and alopecia areata, an autoimmune disease that attacks the follicles, causing hair loss.
It was while studying alopecia areata that the researchers chanced upon the effect of JAK inhibitors on hair follicles.
They had already found that JAK inhibitors shut off the signal that causes the autoimmune attack, and that oral forms of the drug restore hair growth in some people with the disorder.
Enzyme inhibitors promote strong, rapid hair growth
In experiments, the team noticed that mice grew more hair when the drug was applied topically to the skin than when given internally. This suggested JAK inhibitors might have a direct effect on hair follicles, in addition to inhibiting the immune attack.
Looking more closely at normal mouse hair follicles, they found that JAK inhibitors rapidly awakened resting follicles out of dormancy.
JAK inhibitors appear to trigger the follicles' normal reawakening process. Mice treated for 5 days with one of two JAK inhibitors sprouted new hair within 10 days, greatly accelerating the hair follicle growth phase. No hair grew on untreated control mice in the same time period.
The inhibitors also produce longer hair from human hair follicles grown in culture and on skin grafted onto mice.
In light of these findings, the researchers hope the drugs could induce new hair growth and extend the growth of existing hairs in humans.
Dr. Christiano says:
"What we've found is promising, though we haven't yet shown it is effective for male pattern baldness. More work needs to be done to test formulations of JAK inhibitors specially made for the scalp to determine whether they can induce hair growth in humans."
