I was trying to upload the study to gourmetstylewellness.com but 200K is the max file size limit. Here is the Discussion portion.. btw, the only mention of a vehicle consisted of RK being dissolved in 10% Tween 20/10% ethanol (10%) and diluted with normal saline. Also, 0.01% had the most positive effects on IGF-I levels so that's the ideal concentration. (Polysorbate 20 = Tween 20)
Discussion
In the present study, we examined whether RK activates sensory neurons, thereby increasing CGRP release from sensory neurons isolated from WT mice. Since the structure of RK is quite similar to that of capsaicin, it is possible that RK activates sensory neurons by activating VR-1. Consistent with this hypothesis are observations
in the present study demonstrating that RK, at concentrations higher than 1lM, increased CGRP release from DRG isolated from WT mice and that this increase was completely reversed by CPZ, an inhibitor of VR-1 activation.
We previously reported that activation of sensory neurons by topical application of capsaicin increases dermal IGF-I production in WT mice [15], suggesting that topical application of RK might increase dermal
IGF-I levels by activating sensory neurons in WT mice. Consistent with this hypothesis are observations in the present study showing that topical application of 0.005% and 0.01% RK increased dermal IGF-I levels in WT mice, but not in CGRP/mice at 30 min after
topical application. Since skin fibroblasts have been shown to express the CGRP receptor [24] and are capable of producing IGF-I [8], our present observations suggest that topical application of 0.01% RK might increase dermal IGF-I levels in skin fibroblasts through activation of sensory neurons.
Although RK increased CGRP release from DRG isolated from WT mice in a concentration dependent manner in vitro, RK, at concentrations higher than 0.05%, did not increase dermal IGF-I levels in these
mice at 30 min after topical application. We previously
reported that dermal IGF-I levels increased transiently after topical application of 0.01% capsaicin in WT mice [15]. Preliminary experiments showed that, although dermal IGF-I levels at 30 min after topical application of 0.05% and 0.1% capsaicin were significantly lower than those after topical application of 0.01% capsaicin, at 15 min after 0.05% and 0.1% capsaicin application,
these levels were significantly higher than those after 0.01% capsaicin. These observations suggest that 0.05% and 0.1% RK might more strongly stimulate sensory neurons than 0.005% and 0.01% RK, thereby rapidly increasing dermal IGF-I levels with peak time points earlier than 30 min after topical application and
that these increases might be followed by a rapid decrease due to depletion of CGRP from sensory neurons. Consistent with this hypothesis are observations made in the present study demonstrating that RK concentrations in the skin at 30 min after topical application of 0.1% RK were 10 times higher than thoseafter 0.01% RK application. Thus, excessive stimulation of sensory
neurons by high concentrations of RK might explain why 0.01% RK increased dermal IGF-I levels, while neither 0.05% nor 0.1% RK had this effect 30 min after topical application as shown in the present study. This possibility should be further investigated.
Topical application of 0.01% RK increased dermal IGF-I levels at 30min after application as shown in the present study. Production of IGF-I via capsaicin in vivo is more rapid than that occurring in response to CGRP in vitro [25], indicating that the former might
not be mediated by the increase in transcription as in the latter, but rather by other unknown mechanism(s). Our previous report demonstrated that subcutaneous administration of capsaicin increased tissue levels of IGF-I and IGF-I mRNA in various organs including the skin at 30 min after administration in mice [14], raising the possibility that stimulation of sensory neurons by topical
application of 0.01% RK might increase IGF-I production by increasing its transcription. This possibility should be examined in future experiments.
In the present study, immunohistochemical expresion of IGF-I at dermal papillae in hair follicles is clearly increased in WT mice to which 0.01% RK had been topically applied for 4 weeks as shown in the present study. Consistent with these observations is a previous report demonstrating that IGF-I is produced by dermal papilla cells [7]. IGF-I is known to be an important growth factor in many biological systems [26] and it has also been shown to play a critical
role in promoting hair growth [4]. Since IGF-I receptor mRNA was detected in keratinocytes [8], it is possible that IGF-I produced by dermal papilla cells acts on keratinocytes, thereby promoting hair growth through stimulation of the proliferation of keratinocytes in hair follicles [4]. Thus, it is possible that increase in IGF-I levels in hair follicles with topical application of 0.01% RK promotes hair growth in WT mice. Consistent with this hypothesis are our present observations demonstrating that hair re-growth was more marked
in WT mice to which 0.01% RK had been topically applied for 4 weeks than in those receiving vehicles for 4 weeks.
In contrast to our results, capsaicin has been shown to inhibit hair shaft elongation by inducing premature hair follicle regression via VR-1 stimulation of the outer root sheath keratinocytes in organ-cultured human scalp hair follicles [27]. However, in the present study, RK significantly increased IGF-I expression and promoted hair re-growth in mice. These observations suggest that RK might interact mainly with VR-1 on sensory neurons, thereby increasing IGF-I production in dermal papillae through an increase in CGRP release from sensory neurons in vivo.
Topical application of 0.01% RK to the scalp for 5 months promoted hair growth in 5 of the 10 volunteers with alopecia in the present study. Consistent with these observations is our recent report demonstrating that administration of capsaicin and isoflavone promoted hair growth by increasing IGF-I production in humans with alopecia [19]. These observations raised the possibility that topical application of 0.01% RK to the scalp increases IGF-I production
in hair follicles through activation of sensory neurons, thereby promoting hair growth in humans suffering from alopecia. These possibilities should be further examined in a large controlled study of human subjects with alopecia.
We previously demonstrated that stimulation of sensory neurons increases tissue blood flow by increasing endothelial productions of nitric oxide and prostacyclin through activation of endothelial nitric oxide synthase and cyclooxygenase-1, respectively [28]. Thus,it is possible that stimulation of sensory neurons by RK increases
dermal blood flow, thereby contributing to the promotion of hair growth. Furthermore, capsaicin has been shown to down-regulate androgen receptor expression by prostate cancer cells [29]. Since androgen plays a critical role in the development of alopecia [30] and balding hair follicle dermal papilla cells contain higher levels of
androgen receptors than those from non-balding scalp
[31], RK, like capsaicin, might promote hair growth by decreasing androgen action through androgen receptor down-regulation on dermal papilla cells.
CGRP has been shown to promote proliferation of human keratinocytes by increasing intracellular cAMP levels in vitro [32], suggesting that topical application of 0.01% RK might promote hair growth not only by increasing IGF-I production, but also by increasing CGRP release from sensory neurons in mice and
humans with alopecia.
IGF-I increases the production of collagen [10] and
elastin [33] by skin fibroblasts and promotes proliferation of keratinocytes [34], suggesting that IGF-I produced by fibroblasts might act on these fibroblasts themselves as well as on keratinocytes, thereby promoting the productions of both collagen and elastin as well as proliferation, respectively. Patients with Laron syndrome showed skin morphological changes such as decreased thickness with decreased elastin contents [35]. The IGF-I receptor has been demonstrated in human skin biopsies [8]. These observations suggest that detrimental skin morphological changes observed in patients with Laron syndrome might be attributable to
reduced production of IGF-I.
Topical application of 0.01% RK to facial skin significantly increased cheek skin elasticity in5healthy female volunteers after 14 days of application(p< 0.04). Consistent with these observations is our previous report [15] demonstrating that topical application of 0.01% capsaicinto facial skin increased cheek skin elasticity in female
volunteers. The important mechanical property that primarily maintains skin elasticity is attributable to the content andmolecular structure of collagen fibers embedded in the ground substance [36]. The sweat secretion rate has been found to be decreased in patients with GH deficiency who have low serum IGF-I levels [37]. Decreased ability to sweat results from the atrophy of eccrine sweat
glands due to lack of stimulation by either GH or IGF-I, or both [38]. Since intra-epidermal elasticity is known to be associated with the presence of sweat [39], topical application of 0.01% RK might have increased sweat in the facial skin epidermis of the volunteers, thereby contributing to the increase in facial skin elasticity.
Detrimental skin morphological changes such as decreases in skin thickness and collagen contents are observed in postmenopausal women [40] as well as in patients with Laron syndrome [35], raising the possibility that topical application of 0.01% RK might increase
skin elasticity, probably by increasing dermal IGF-I contents in aged women.
