Permeation of topically applied caffeine through human skin – a comparison of in vivo and in vitro data

AIMS

Due to ethical reasons, in vivo penetration studies are not applicable at all stages of development of new substances. Therefore, the development of appropriate in vitro methods is essential, as well as the comparison of the obtained in vivo and in vitro data, in order to identify their transferability. The aim of the present study was to investigate the follicular penetration of caffeine in vitro and to compare the data with the in vivo results determined previously under similar conditions.

METHODS

The Follicular Closing Technique (FCT) represents a method to investigate the follicular penetration selectively. In the present study, FCT was combined with the Franz diffusion cell in order to differentiate between follicular and intercellular penetration of caffeine into the receptor medium in vitro. Subsequently, the results were compared with the data obtained in an earlier study investigating follicular and intercellular penetration of caffeine in vivo.

RESULTS

The comparison of the data revealed that the in vitro experiments were valuable for the investigation of the follicular penetration pathway, which contributed in vivo as well as in vitro to approximately 50% of the total penetration, whereas the kinetics of caffeine penetration were shown to be significantly different.

CONCLUSIONS

The combination of FCT with the Franz diffusion cell represents a valuable method to investigate follicular penetration in vitro. Nevertheless, in vivo experiments should not be abandoned as in vitro, structural changes of skin occur and blood flow and metabolism are absent, probably accounting for reduced penetration rates in vitro.     

Drug delivery to hair follicles

Introduction: The optimization of drug delivery to and via the hair follicles is gaining more and more importance as it has been recognized that the hair follicles are an interesting target site for topical applications. They are closely surrounded by capillaries and antigen-presenting cells, are associated with the sebaceous glands and are the host of stem cells in the bulge region of the hair follicle.

Areas covered: The present review shortly summarizes the complexity of the structure, biology and functions of the hair follicle and presents the models and methods suitable to investigate follicular penetration. Drug delivery to hair follicles was clearly shown to be dependent on the physicochemical properties of the applied substances and vehicles as well as on the activity status, size and density of the hair follicles. Especially particulate substances were demonstrated to be proficient drug carriers into the hair follicles, whereas dependent data for transfollicular penetration into the deeper viable skin layers could only be found for non-particulate substances which then, however, received rapid access to the circulation when the follicular pathway was accessible.

Expert opinion: Promising concepts to optimize hair follicle delivery and to beneficially utilize particulate substances for efficient follicular drug delivery are the application of external or internal stimuli for controlled drug release from the particles such as the combined application with protease or the usage of gold nanoparticles in combination with near-infrared irradiation.     

Hair follicles contribute significantly to penetration through human skin only at times soon after application as a solvent deposited solid in man

AIMS

The aim of this study was to define the underlying relative penetration of caffeine through hair follicles and through intact stratum corneum with time in vivo through pharmacokinetic modelling.

METHODS

Caffeine plasma concentration–time profiles after topical application into skin with or without hair follicle blocking were modelled using the Wagner–Nelson method or a compartmental model with first order absorption and elimination. Pharmacokinetic parameters describing absorption rate and extent of absorption through hair follicles or the stratum corneum were determined separately and compared with each other.

RESULTS

The obtained pharmacokinetic parameters from the two methods were similar. The absorption rate constant of caffeine for hair follicles was nearly 10 times higher than that for the stratum corneum and the percentage of absorption from hair follicles was more than half of that of the stratum corneum. In addition, the absorption from the stratum corneum showed an approximately 10 min delay while there was no delay for absorption from hair follicles. All caffeine absorbed by hair follicles occurs within 30 min of application and accounts for 10.5 to 33.8% of the total amount absorbed across the skin for all subjects, whereas absorption of caffeine through the stratum corneum can occur over several hours.

CONCLUSION

Hair follicles contribute significantly to percutaneous absorption of caffeine after topical application in man in vivo only at times soon after application.     

Permeant lipophilicity and vehicle composition influence accumulation of dyes in hair follicles of human skin

In skin and hair research drug targeting to the hair follicle is of great interest. Therefore the influence of permeant lipophilicity and vehicle composition on local accumulation has been examined using confocal laser scanning microscopy (CLSM). Formulations saturated with either Oregon Green^® 488, Bodipy^® FL C₅ or Bodipy^® 564/570 C₅ were prepared. The dyes were applied in citric acid buffer, 8% (w/v) surfactants in citric acid buffer or 8% (w/v) surfactants/20% (w/v) propylene glycol in citric acid buffer. Flow-through diffusion experiments were performed with fresh human scalp skin, after which the skin was imaged using CLSM. Diffusion studies showed for Oregon Green^® 488 (low lipophilicity) a higher flux when applied in citric acid buffer compared to surfactants. In contrast the fluxes of the more lipophilic dyes (Bodipy^® FL C₅ and Bodipy^® 564/570 C₅) are highest when applied in surfactants/propylene glycol. CLSM studies revealed that follicular accumulation increased with (i) a lipophilic dye and (ii) application of lipophilic dyes in surfactants–propylene glycol. Therefore we conclude that targeting to the hair follicle can be increased by the use of lipophilic drugs in combination with surfactant solutions and propylene glycol.     

Androgenetic alopecia: combing the hair follicle signaling pathways for new therapeutic targets and more effective treatment options

ABSTRACT

Introduction: In the past 30 years, only two drugs have received FDA approval for the treatment of androgenetic alopecia reflecting a lack of success in unraveling novel targets for pharmacological intervention. However, as our knowledge of hair biology improves, new signaling pathways and organogenesis processes are being uncovered which have the potential to yield more effective therapeutic modalities.

Areas covered: This review focuses on potential targets for drug development to treat hair loss. The physiological processes underlying the promise of regenerative medicine to recreate new functional hair follicles in bald scalp are also examined.

Expert opinion: The discovery of promising new targets may soon enable treatment options that modulate the hair cycle to preserve or extend the growth phase of the hair follicle. These new targets could also be leveraged to stimulate progenitor cells and morphogenic pathways to reactivate miniaturized follicles in bald scalp or to harness the potential of wound healing and embryogenic development as an emerging paradigm to generate new hair follicles in barren skin.     

The effect of caffeine on the pharmacokinetics of acetaminophen in man

The influence of caffeine (60 mg) was studied on the pharmacokinetic characteristics of acetaminophen (500 mg single dose) in ten healthy male human volunteers in a complete cross-over design. A high-performance liquid chromatography (HPLC) method was used to analyse serum drug concentrations. Caffeine caused a highly significant (p < 0.01) increase in AUC and AUMC, a significant (p < 0.05) increase in C_max, and a significant (p < 0.05) decrease in clearance (Cl/F) of acetaminophen. We conclude that caffeine taken in doses commonly available commercially or in a cup of coffee can significantly potentiate the therapeutic potential of acetaminophen in man.     

The hair follicle and its stem cells as drug delivery targets

The hair follicle is a skin appendage with a complex structure containing many cell types that produce highly specialised proteins. The hair follicle is in a continuous cycle: anagen is the hair growth phase, catogen the involution phase and telogen is the resting phase. The follicle offers many potential therapeutic targets. Hoffman and colleagues have pioneered hair-follicle-specific targeting using liposomes to deliver small and large molecules, including genes. They have also pioneered ex vivo hair-follicle targeting with continued expression of the introduced gene following transplantation. Recently, it has been discovered that hair follicle stem cells are highly pluripotent and can form neurons, glial cells and other cell types, and this has suggested that hair follicle stem cells may serve as gene therapy targets for regenerative medicine.     

Effect of caffeine on intestinal absorption of ergotamine in man

Summary Plasma and urinary radioactivity were measured in 6 normal volunteers after oral intake of³H-labelled ergotamine tartrate, either alone or combined 1:100 with caffeine. Plasma level and cumulative urinary excretion were higher after the combination than after ergotamine alone and the difference was significant at certain times. A detectable plasma level was reached 30 min after taking the combination but only 1 h after ergotamine alone. These results indicate faster and more complete intestinal absorption of ergotamine administered in combination with caffeine.     

In vivo hair growth-stimulating effect of medicinal plant extract on BALB/c nude mice

Abstract

Context: Chrysanthemum zawadskii var. latilobum (Asteraceae) (CZ) and Polygonum multiflorum Thunb. (Polygonaceae) (PM) have been used traditionally to treat different systemic diseases and acclaimed for various biological activities including hair growth.

Objective: This study investigates the hair restoration efficacy of selected medicinal plant extracts on nude mice.

Materials and methods: Nude mice genetically predisposed to pattern balding were used in this study. Topical methanol extracts of CZ and PM (10?mg/mouse/d) with standardized vehicle formulation, only vehicle (propylene glycol:ethanol:dimethyl sulfoxide, 67:30:3% v/v) and Minoxidil (2%) were applied daily for 40 consecutive days.

Results: In our study, the maximum hair score (2.5?±?0.29) was obtained in the CZ-treated group. Histological observation revealed a significant increase (p?<?0.001) in the number of hair follicles (HF) in CZ-treated mice (58.66?±?3.72) and Minoxidil-treated mice (40?±?2.71). Subsequently, immunohistochemical analysis also confirmed the follicular keratinocyte proliferation by detection of BrdU-labeling, S-phase cells in Minoxidil and CZ-treated mouse follicular bulb and outer root sheaths.

Conclusion: Our study revealed the underlying mechanism of stimulating hair growth in athymic nude mice by repair the nu/nu follicular keratin differentiation defect. Thus, the topical application of CZ may represent a novel strategy for the management and therapy of certain forms of alopecia.     

阿糖胞苷引起毛囊损伤离体模型的建立以及他克莫司对其的逆转作用

目的建立阿糖胞苷(Ara-c)诱导毛囊损伤的离体器官培养模型,并观察他克莫司(FK506)对Ara-c诱导的小鼠触须毛囊损伤的逆转作用.方法用离体器官培养的方法在倒置显微镜底下每日测量空白组、FK506 Ara-c和单纯Ara-c作用下毛囊生长长度、记录生长天数,以及液相闪烁仪测量同位素^3H-TdR的掺入率.结果 Ara-c10mg/L和25mg/L的浓度,作用2.5h能明显抑制毛囊生长和DNA合成,缩短毛囊在体外的生长时间,抑制毛囊球部细胞增殖.0.01～0.3mg/L的FK506能改善10mg/L Ara-c引起的毛囊生长和DNA合成的抑制,体外生长时间缩短以及毛囊球部细胞增殖抑制.0.1mg/L的FK506对25mg/L Ara-c引起的毛囊损伤也有相似的改善作用.结论 Ara-c诱导毛囊损伤的离体模型可以用于研究化疗脱发的机制和某些因子及药物对它的干预作用,FK506在体外对Ara-c诱导的毛囊损伤有修复作用,是治疗化疗后脱发的潜在药物.     

The absolute bioavailability of caffeine in man

Summary The absolute bioavailability of orally administered caffeine was investigated in 10 healthy adult male volunteers, aged 18.8 to 30.0 years. The subjects were administered a 5 mg/kg dose of caffeine as either an aqueous oral solution or an intravenous infusion, on separate occasions about 1 week apart, in a randomized crossover fashion. Plasma samples were collected over the 24-h period following each dose and assayed for their caffeine content using a high-performance liquid chromatographic technique. The oral absorption was very rapid, reaching a peak (T_p) plasma concentration after 29.8±8.1 min (mean±SEM). In addition, the variation in the maximum plasma concentration (C_max) was low, 10.0±1.0 µg/ml. The absolute bioavailability was assessed by comparing the areas under the plasma concentration vs. time curves for the intravenous and oral doses of caffeine. The rapid absorption resulted in essentially complete bioavailability of the oral caffeine, F(%)=108.3±3.6%. The caffeine plasma half-lives varied from 2.7 to 9.9 h, indicating substantial inter-subject variability in its elimination.     

氮酮对喃氟啶透皮吸收的影响

本文研究了喃氟啶软膏剂对小白鼠和裸鼠离体皮肤的透皮吸收。比较了小白鼠和裸鼠皮肤渗透性、药物浓度和透皮吸收促进剂对喃氟啶透皮吸收的影响。实验结果表明，小白鼠皮肤对喃氟啶渗透性大于裸鼠皮肤，采用透皮吸收促进剂和提高药物浓度可大大提高药物的透皮吸收速率。本研究为临床用药和配制喃氟啶软膏剂选择适宜药物浓度和促进剂浓度提供了依据。     

Caffeic acid skin absorption: Delivery of microparticles to hair follicles

Caffeic acid (CA) is a polyphenol that can be found in a wide range of vegetal dietary sources. It presents a remarkable antioxidant potential, but what is more interesting from the therapeutic point of view is, that it has demonstrated in vitro antimicrobial properties. Folliculitis is a common skin condition, usually caused by a bacterial or fungal infection, in which hair follicles become inflamed. A typical challenge in dermal application when the actives diffuse passively through the skin in a quick manner, as it is the case of CA, is to provide the effective concentration of the compound at the target site for the sufficient time to finalize the treatment adequately and reduce the possibility to trigger systemic side effects. To achieve this goal, it is necessary to appropriately design the drug delivery system. In this case, we leverage the ability of microparticles to accumulate into the hair follicles to design O/W-emulsions containing CA-loaded controlled-release microparticles. Two different emulsion types containing CA were prepared, one containing free CA and the other containing microencapsulated CA. Traditional and differential tape stripping techniques were performed to investigate drug distribution within the different skin layers and into the hair follicles. The Tape stripping results demonstrated that the tapes S3-S5 and S6-S10 presented a higher total amount of CA. The strips are collected and extracted in groups to assure the extraction of quantifiable amounts of drug. Samples S11-15 and S16-20 show a decrease in the amount of quantified CA, as it was expected. Thus, it can be seen that the amount of active decreases while the stratum corneum depth increases. The retention studies demonstrated that, the microparticles tend to produce a more homogeneous distribution of CA, within the stratum corneum and a higher retention into the hair follicle, which can be attributed to their size and uniformity. Besides, MPs present an additional advantage because they guarantee a continuous release of CA in the target for a prolonged period, allowing the treatment of folliculitis with a single dose until the MPs are removed from the hair follicle by its natural regeneration process or particle depletion of CA.     

Cutaneous applied nano-ZnO reduce the ability of hair follicle stem cells to differentiate

The ability of metal oxide nanoparticles to penetrate the skin has aroused a great deal of interest during the past decade due to concerns over the safety of topically applied sunscreens that contain physical UV-resistant metal particles, such as nano-Zinc oxide (nZnO). Previous studies demonstrate that metal oxide nanoparticles accumulate in skin furrows and hair follicles following topical application while little is known about the consequence of these nanoparticles on skin homeostasis. The current investigation tested the effects of nZnO (0.5?mg/day mouse) on hair follicle physiology. Topical application of Vaseline containing nZnO, bulk ZnO (bZnO), or ionized Zn to newborn mice vibrissa pad over a period of 7 consecutive days revealed that nZnO accumulated within hair follicles, and this induced the apoptosis of hair follicle stem cells (HFSCs). In vitro studies also indicated that nZnO exposure caused obvious DNA damage and induced apoptosis in HFSCs. Furthermore, it was found that nZnO exposure perturbed genes associated with HFSC apoptosis, cell communication, and differentiation. HFSCs transplantation assay demonstrated that the potential of HFSCs to differentiate was reduced. This investigation indicates a potential risk of topically applied ZnO nanoparticles on skin homeostasis.     

Distribution pattern of ethyl glucuronide and caffeine concentrations over the scalp of a single person in a forensic context

The distribution of analyte concentrations in hair across the scalp has not been thoroughly investigated. Differences in concentrations depending on sampling location are problematic, especially when measuring a second strand to confirm the result of the first measurement. Aiming at a better understanding of the concentration differences, the distribution of ethyl glucuronide (EtG) and caffeine concentrations in hair across the entire head of one test subject was investigated by dividing the scalp completely into regions of ca 2 cm × 2 cm area, yielding a total of 104 samples. For the quantification of EtG, a novel LC–MS³/MRM method was developed and validated with a limit of detection and limit of quantification of 2 and 4 pg/mg, respectively. Large variations of the concentration across the head were found, with factors of ca 3.0 and 10.6 for EtG and caffeine, respectively. These differences could not be attributed to measurement error alone. The concentrations were projected onto the subject's head, and concentration patterns were identified for EtG and caffeine. When examining multiple strands from within one 2 cm × 2 cm sampling area, the strands showed similar concentrations. Segmental analysis of selected 3 cm strands showed decreasing concentrations of EtG and caffeine from proximal to distal end, possibly due to wash‐out of the analytes. Copyright © 2017 John Wiley & Sons, Ltd.     

氮酮对丙酸氯倍他索乳膏经皮渗透和吸收的影响

目的：考察氮酮对丙酸氯倍他索乳膏经皮渗透的作用,通过比较累积通过量和皮层中量,分析在该制剂中使用氮酮的利弊。方法：采用直立式扩散池,考察氮酮在０．５％、１．０％、２．０％和５．０％浓度下０．０５％丙酸氯倍他索乳膏经皮渗透２、４、６、８、１０、２４ｈ后累积透过量和稳态流量;分别测定了经皮渗透２４ｈ后每克皮肤组织中部他索的量。结果：４个浓度氮酮均极显著促进ＣＢＴ乳膏经皮渗透（Ｐ〈０．０１）,Ｑ２４分别     

The effect of caffeine use on a visual information processing task

Past caffeine studies have shown that differences in task performance may be due to differences in habitual caffeine consumption levels of individuals. No study has yet investigated this caffeine user effect alone without confounding it with the administration of caffeine. The present study used a visual search/detection task to test whether high caffeine users have an enhanced resource capacity and therefore show higher baseline performance than low and moderate caffeine users. A three-way interaction between caffeine user (low, moderate, and high caffeine user), automaticity (automatic and non-automatic), and task difficulty (low and high) was predicted, with user effect significant for the non-automatic portion of the task. The three-way interaction was not significant, suggesting that user effect is not dependent on resource capacity. Several interpretations, based on theoretical, empirical, methodological, and statistical viewpoints, are discussed as to the non-significant caffeine user effect.     

桉油对丙酸氮倍他索乳膏经皮渗透和吸收的作用

目的：考察促进剂桉油对丙酸氯倍他索（CBT）乳膏经皮渗透的促进作用,通过比较透过量和皮层中量,分析在该制剂中是否透合使用桉油,方法：采用直立式扩散池,考察了桉油在0．5％,1．0％,5．0％浓度下0．05％CBT乳膏经皮渗透2,4,6,8,10,24h后单位面积累积透过量Q(ug.cm^-2)和稳态透皮流量J（ug.cm^-2.h^-1);HPLC法测定经皮渗透24h后每克皮肤组织中CBT的量D（ug.g^-1),结果：4种浓度的桉油均显著促进CBT乳膏透皮吸收（P＜0．01）,其J值约是对照组的3－5倍（P＜0．01）,随浓度增加,陂层量D并不随之相应增加,结论：桉油可加快CBT经皮渗透速度,也能增加皮层中CBT量,但有饱和性,建议CBT 乳膏膏以少加（＜50％）或不加桉油为好。     

经皮渗透促进剂卡必醇的应用和机制

目的　介绍卡必醇近年来国内外在经皮给药制剂中的研究和应用。方法　分析有关文献资料,对卡必醇的理化性质,以及卡必醇在经皮促渗方面的应用和机制进行总结归纳。结果和结论　卡必醇作为一种优良的渗透促进剂,具有广泛的应用前景。