Gli articoli che hai postato sono molto interessanti.
IL primo pare estendere gli effetti osservati nei roditori ai follicoli umani, ma non prende in causa l’importanza dei due differenti recettori e le eventuali relazioni fra questi e l’estradiolo sul ciclo dei capelli.
SUll’effetto induttore del catagen secondo uno degli studi che ho postato l’E2 è addirittura più Potente del DHT.
mouse skin resulted in a rapid increase in serum E2
levels that returned to low physiological levels within
12 h, indicating that E2 is rapidly absorbed through
mouse skin and rapidly cleared from the serum.
Whereas the serum levels of E2 are not sustained after
topical application, a single E2 dose every 3–4 days is
sufficient to maintain the hair follicle in telogen. Therefore,
it appears that each E2 treatment has a prolonged
local inhibitory effect on the hair follicle cycle. Perhaps
Although androgens have been extensively studied
as regulators of hair follicle growth and differentiation
(34), estrogens have received comparatively little attention.
Recently, inhibitors of 5a-reductase have hair
growth-promoting properties, indicating an inhibitory
role for DHT on hair growth (10, 21). Our current
results in mice demonstrate that among the steroids
examined, which included E2, testosterone, DHT, progesterone,
and androstenedione, E2 is the most effective
at blocking hair growth.Based on the hair growth inhibitory
action of 1 nmol E2, it appears that E2 is
>10-fold more potent than DHT. ER-binding proteins
have been identified in human skin (14, 31) and may
represent potential targets for hair growth modulation
by E2 or ICI-182780. Among the ER antagonists exam-
ined, ICI-182780 is the most potent at inducing hair
growth. All of the ER antagonists examined promoted
the telogen-anagen transition and hair growth to some
extent; however, higher doses actually inhibited hair
growth. The decreased activity of these ER antagonists,
as well as their inhibitory action at higher doses, is
consistent with the fact that these compounds are
partial agonists of ER (20).
In summary, the growth and cyclicity of a hair follicle
are controlled through complex and intricate interactions
between the epithelial cells of the follicle and
mesenchymal cells of the dermal papilla. Although it
has been suggested that diffusible factors derived from
the dermal papilla cells regulate the follicle cycle, the
exact nature of these factors is still unknown. The
identification of regulatory molecules such as estrogen
and ER antagonists that modulate the telogen-toanagen
transition could allow for the identification of
the downstream effectors of ER-a. Identification of the
effector pathways may allow for the development of
effective therapy to treat hair-related abnormalities
like alopecia and hirsutism.
http://ajpendo.physiology.org/cgi/reprint/278/2/E202
Nello studio sui gatti transgenici in pratica è stata messa a fuoco l’iportanza del recettore ER-alpha : infatti nei gatti in cui è espresso solo ER-Beta (ERKO) o non è espresso nessun recettore l’estradiolo topico non induce il telogen.
Da un altro studio che avevo scaricato
http://endo.endojournals.org/cgi/reprint/146/3/1214.pdf si apprende l’importanza del recettore ER-beta nel frenare gli effetti negativi Dell'ER-alpha
“So far, there is only indirect evidence for the significance
of endogenous E2 and ER signaling in hair growth control
Catagen progression is accelerated in mice lacking ER-beta
(Fig. 6), and BERKO mice show significant up-regulation of
apoptotic HF keratinocytes as well as a significantly reduced
dermal thickness. This supports the concept that, as in other
organs, e.g. the uterus and mammary gland (43, 57), ER-beta,
(including ER-beta ins), functions as a quencher of ER-alpha-mediated
effects. The absence of ER-alpha antagonistic signaling via
ER-beta in BERKO mice would explain uninhibited and thus
accelerated catagen induction via ER-alpha.
ER-beta stimulation by antiestrogens may mediate antioxidant
actions on activator protein-1 sites by inducing quinone
reductase (64), and the antioxidative stress enzymes glutathione
S-transferase and glutamylcysteine synthase are
up-regulated by transcriptional activity of ER-beta (65). Therefore,
one role of ER-beta may be to protect tissues from oxidative
stress by inducing a battery of antioxidative enzymes (64, 65).
Thus, the widespread and constant expression of ER-beta within
the pilosebaceous unit may also serve to protect the skin and
its appendages, which are continuously more exposed to
oxidative damage than most other organs.
If reproducible in the human system, the observations
reported here suggest that topically administered ER modulators
may be clinically exploited as powerful catagen in-
ducers (e.g. for treating hirsutism). The growing number of
selective ER modulators (66, 67) and our improved understanding
of ER signaling (39) make it increasingly attractive
to explore the use of estrogens or antiestrogens in the modulation
of hair growth. Today topical E2 administration is
traditionally employed in the treatment of female pattern
androgenetic alopecia in many countries. The limited trichogram
evidence that is currently available suggests that, in
androgen-sensitive areas of female scalp, topical E2 decreases
the telogen rate and prolongs the anagen phase of
human scalp hair follicles (17, 68, 69). Also, E2 inhibits hair
shaft elongation in human occipital scalp hair follicles in vitro
(32, 33, 70, 71). However, E2 effects on human frontotemporal
scalp HFs show significant differences between the sexes
(stimulation of hair shaft elongation in males and inhibition
in females) (32). Therefore, not only species-, but also sex-,
and location-dependent differences in the hair follicle response
to estrogens must be taken into account (32).
Curiosamente in uno studio recentissimo (dello scorso maggio)
http://www.nature.com/jid/journal/vaop/ncurrent/abs/5700344a.html gli autori indagavano gli effetti di differenti steroidi sull’espressione dei recettori per gli estrogeni e sull’espressione dell’aromatasi (quindi ER-alpha mRNA, ER-beta mRNA e Aromatase mRNA). il Desametasone riduceva ER-alpha mRNA del 38%. (Il desametasone valeerato era stato utilizzato da Gigli e Marliani per il trattamento del diradamento localizzato nella hairline, dopo segnalazione di un utente a cui l’applicazione del medicamento aveva avuto un effetto ipertricotico.)
Tutto ciò potrebbe suggerirel’utilità di inibitori specifici dellER-alpha o di agonisti dellER-Beta.
Ho scorso anche il forum del D. Proctor, in cui in effetti vengono ribadite conoscenze che già possedevo. In effetti, nei soggetti castrati, l’alopecia androgenetica si ferma allo stadio in cui è avvenuta la castrazione, ma se i capelli sono già in parte caduti la deplezione di androgeni è insufficiente di per se a farli ricrescere. Sarebbe a questo punto interessante sapere anche se nei soggetti castrati trattati con minoxidil, i capelli ricresciuti si rigenererebbero eventualmente anche dopo la sospensione del minoxidil stesso, non sussistendo più il messaggio genetico trasmesso dal DHT. E’ pur vero che gli eunuchi, non avendo praticamente steroidi androgeni in circolo non convertono nemmeno questi in estrogeni, quindi non sono un modello ideale per capire l’influenza selettiva degli androgeni o degli estrogeni sui capelli.
Lo studio “Topical estrogen accelerates hair regrowth in mice after chemotherapy-induced alopecia by favoring the dystrophic catagen response pathway to damage.” sui presunti vantaggi dell’estradiolo topico è abbastanza viziato dal fatto che i soggetti trattati avevano una alopecia indotta dalla terapia oncogena, mentre decisamente più interessante è la lettera in pdf che hai postato, che mostra come gli effetti dell’estradiolo siano rad