In vivo multiphoton multiparametric 3D quantification of human skin aging on forearm and face

Quantifying skin aging changes and characterizing its 3D structure and function in a non-invasive way is still a challenging area of research, constantly evolving with the development of imaging methods and image analysis tools. In vivo multiphoton imaging offers means to assess skin constituents in 3D, however prior skin aging studies mostly focused on 2D analyses of dermal fibers through their signals’ intensities or densities. In this work, we designed and implemented multiphoton multiparametric 3D quantification tools for in vivo human skin pigmentation and aging characterization. We first demonstrated that despite the limited field of view of the technic, investigation of 2 regions of interest (ROIs) per zone per volunteer is a good compromise in assessing 3D skin constituents in both epidermis and superficial dermis. We then characterized skin aging on different UV exposed areas—ventral and dorsal forearms, face. The three major facts of aging that are epidermal atrophy, the dermal–epidermal junction (DEJ) flattening and dermal elastosis can be non-invasively quantified and compared. Epidermal morphological changes occur late and were only objectified between extreme age groups. Melanin accumulation in suprabasal layers with age and chronic exposure on ventral and dorsal forearms is less known and appears earlier. Superficial dermal aging changes are mainly elastin density increase, with no obvious change in collagen density, reflected by SHGto2PEF ratio and SAAID index decrease and ImbrN index increase on all skin areas. Analysis of the z-dermal distribution of these parameters highlighted the 2nd 20 µm thickness normalized dermal sub-layer, that follows the DEJ shape, as exhibiting the highest aging differences. Moreover, the 3D ImbrN index allows refining the share of photoaging in global aging on face and the 3D SAAID index on forearm, which elastin or fibrillar collagens densities alone do not allow. Photoaging of the temple area evolves as a function of chronic exposure with a more pronounced increase in elastin density, also structurally modified from thin and straight elastic fibers in young volunteers to dense and compact pattern in older ones. More generally, multiphoton multiparametric 3D skin quantification offers rich spatial information of interest in assessing normal human skin condition and its pathological, external environment or product induced changes.

Non-Invasive Skin Imaging Assessment of Human Stress During Head-Down Bed Rest Using a Portable Handheld Two-Photon Microscope

Spaceflight presents a series of physiological and pathological challenges to astronauts resulting from ionizing radiation, microgravity, isolation, and other spaceflight hazards. These risks cause a series of aging-related diseases associated with increased oxidative stress and mitochondria dysfunction. The skin contains many autofluorescent substances, such as nicotinamide adenine dinucleotide phosphate (NAD(P)H), keratin, melanin, elastin, and collagen, which reflect physiological and pathological changes in vivo. In this study, we used a portable handheld two-photon microscope to conduct high-resolution in vivo skin imaging on volunteers during 15 days of head-down bed rest. The two-photon microscope, equipped with a flexible handheld scanning head, was used to measure two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) images of the left forearm, left front chest, and forehead of volunteers. Changes in TPEF, SHG, and the extended SHG-to-AF(TPEF) aging index of the dermis (SAAID) were measured. It was found that TPEF intensity increased during bed rest and was restored to normal levels after recovery. Meanwhile, SHG increased slightly during bed rest, and the skin aging index increased. Moreover, we found the skin TPEF signals of the left forearm were significantly negatively associated with the oxidative stress marker malondialdehyde (MDA) and DNA damage marker 8-hydroxy-2′-desoxyguanosine (8-OHdG) values of subjects during head-down bed rest. Meanwhile, the SHG signals were also significantly negatively correlated with MDA and 8-OHDG. A significant negative correlation between the extended SAAID of the left chest and serum antioxidant superoxide dismutase (SOD) levels was also found. These results demonstrate that skin autofluorescence signals can reflect changes in human oxidant status. This study provides evidence for in-orbit monitoring of changes in human stress using a portable handheld two-photon microscope for skin imaging.

Recent Advances and the Potential for Clinical Use of Autofluorescence Detection of Extra-Ophthalmic Tissues

The autofluorescence (AF) characteristics of endogenous fluorophores allow the label-free assessment and visualization of cells and tissues of the human body. While AF imaging (AFI) is well-established in ophthalmology, its clinical applications are steadily expanding to other disciplines. This review summarizes clinical advances of AF techniques published during the past decade. A systematic search of the MEDLINE database and Cochrane Library databases was performed to identify clinical AF studies in extra-ophthalmic tissues. In total, 1097 articles were identified, of which 113 from internal medicine, surgery, oral medicine, and dermatology were reviewed. While comparable technological standards exist in diabetology and cardiology, in all other disciplines, comparability between studies is limited due to the number of differing AF techniques and non-standardized imaging and data analysis. Clear evidence was found for skin AF as a surrogate for blood glucose homeostasis or cardiovascular risk grading. In thyroid surgery, foremost, less experienced surgeons may benefit from the AF-guided intraoperative separation of parathyroid from thyroid tissue. There is a growing interest in AF techniques in clinical disciplines, and promising advances have been made during the past decade. However, further research and development are mandatory to overcome the existing limitations and to maximize the clinical benefits.

Imaging and quantifying drug delivery in skin - Part 2: Fluorescence andvibrational spectroscopic imaging methods

Understanding the delivery and diffusion of topically-applied drugs on human skin is of paramount importance in both pharmaceutical and cosmetics research. This information is critical in early stages of drug development and allows the identification of the most promising ingredients delivered at optimal concentrations to their target skin compartments. Different skin imaging methods, invasive and non-invasive, are available to characterize and quantify the spatiotemporal distribution of a drug within ex vivo and in vivo human skin. The first part of this review detailed invasive imaging methods (autoradiography, MALDI and SIMS). This second part reviews non-invasive imaging methods that can be applied in vivo: i) fluorescence (conventional, confocal, and multiphoton) and second harmonic generation microscopies and ii) vibrational spectroscopic imaging methods (infrared, confocal Raman, and coherent Raman scattering microscopies). Finally, a flow chart for the selection of imaging methods is presented to guide human skin ex vivo and in vivo drug delivery studies.

Multiphoton Microscopy for Noninvasive and Label-Free Imaging of Human Skin and Oral Mucosa Equivalents

Multiphoton microscopy has emerged as a powerful modality for noninvasive, spatial, and temporal imaging of biological tissues without the use of labels and/or dyes. It provides complimentary imaging modalities, which include two-photon excited fluorescence (2PEF) and second harmonic generation (SHG). 2PEF from endogenous chromophores such as nicotinamide adenine dinucleotides (NADH), flavins and keratin enable visualization of cellular and subcellular structures. SHG provides visualization of asymmetric macromolecular structures such as collagen. These modalities enable the visualization of biochemical and biological alterations within live tissues in their native state.Organotypic cultures of the skin and oral mucosa equivalents have been increasingly used across basic and translational research. However, assessment of the skin and oral mucosa equivalents is predominantly based on histological techniques which are not suited for real-time imaging and longitudinal studies of the tissues in their native state. 2PEF from endogenous chromophores and SHG from collagen can be effectively used as an imaging tool for noninvasive and label-free acquisition of cellular and matrix structures of live skin and oral mucosa cultures.In this chapter, the methods for noninvasive and label-free imaging of monolayer and organotypic cultures of the skin and oral mucosa using multiphoton microscopy are described.

The skin-depigmenting potential of Paeonia lactiflora root extract and paeoniflorin: in vitro evaluation using reconstructed pigmented human epidermis

OBJECTIVE

The roots of the herb Paeonia lactiflora ('White Peony') are used in association with other herbs in traditional clinical cosmetic practice in China as oral treatment for skin pigmentary disorders, such as brown or dark pigmentary spots. However, the skin-depigmenting potential of Paeonia lactiflora root extract and its main ingredient paeoniflorin has been scarcely investigated by topical application. The purpose of this study was to evaluate the efficacy of Paeonia lactiflora root extract and paeoniflorin as skin whitening agent in cosmetic application.

METHODS

Paeonia lactiflora root extract (containing 53.25% of paeoniflorin) and paeoniflorin (97% purity) were applied topically on reconstructed pigmented human epidermis model, a three-dimensional (3D) human skin equivalent, showing morphological and functional characteristics similar to those of in vivo human skin. Two specific methods were used for quantifying melanin inside the reconstructed pigmented epidermis: Fontana-Masson staining (2D quantification) and multiphoton microscopy (3D quantification).

RESULTS

Compared to vehicle (dimethyl sulfoxide DMSO), a significant decrease in 2D and 3D melanin content was observed after topical application on reconstructed pigmented epidermis of Paeonia lactiflora extract at 300 μg mL(-1) (-28% and -27%, respectively) and paeoniflorin at 120 μg mL(-1) /250 μM (-30% and -23%, respectively), which is in the same order of magnitude as the positive reference 4-n-butylresorcinol at 83 μg mL(-1) /500 μM (-26% and -40%, respectively).

CONCLUSION

These results demonstrate, for the first time, the depigmenting potential of paeoniflorin and thus the potential interest of using Paeonia lactiflora root extracts containing paeoniflorin in cosmetic or dermatological applications for reducing the severity of some hyperpigmented skin disorders.

Epidermal changes during UVB phototherapy assessed by multiphoton laser tomography

BACKGROUND

Multiphoton laser tomography (MPT) is a non-invasive technique that allows imaging of skin in vivo with very high spatial resolution and contrast. Previous work of our group has demonstrated that known morphological changes due to erythematogenic ultraviolet B (UVB) irradiation may be imaged in vivo by MPT. The present work investigated if morphological skin changes known from experimental erythematogenic UVB irradiation are also demonstrable in the course of a standard phototherapy regime that implies suberythematogenic doses of narrow band UVB.

METHODS

Sixteen patients with psoriasis vulgaris receiving a narrow band phototherapy were included. A test field and a light-protected control field were measured with the multiphoton tomograph DermaInspect^® at four time points: at baseline, the next day, after 3 days and at the day of the last exposure.

RESULTS

In the course of the UVB phototherapy, spongiosis and pleomorphy as parameters of inflammation and cellular damage did not show significant changes. By contrast, an adaptive skin reaction with significant changes of keratosis and pigmentation was observed.

CONCLUSION

MPT is a suitable technique for the investigation of qualitative and quantitative skin changes after UVB irradiation. After suberythematogenic UVB irradiation, photoadaptive skin changes, but no cellular damage can be observed with MPT.

[Methods for measuring skin aging]

Aging affects human skin and is becoming increasingly important with regard to medical, social and aesthetic issues. Detection of intrinsic and extrinsic components of skin aging requires reliable measurement methods. Modern techniques, e.g., based on direct imaging, spectroscopy or skin physiological measurements, provide a broad spectrum of parameters for different applications.

Phase and Texture Characterizations of Scar Collagen Second-Harmonic Generation Images Varied with Scar Duration

This work developed a phase congruency algorithm combined with texture analysis to quantitatively characterize collagen morphology in second-harmonic generation (SHG) images from human scars. The extracted phase and texture parameters of the SHG images quantified collagen directionality, homogeneity, and coarseness in scars and varied with scar duration. Phase parameters showed an increasing tendency of the mean of phase congruency with scar duration, indicating that collagen fibers are better oriented over time. Texture parameters calculated from local difference local binary pattern (LD-LBP) and Haar wavelet transform, demonstrated that the LD-LBP variance decreased and the energy of all subimages increased with scar duration. It implied that collagen has a more regular pattern and becomes coarser with scar duration. In addition, the random forest regression was used to predict scar duration, demonstrating reliable performance of the extracted phase and texture parameters in characterizing collagen morphology in scar SHG images. Results indicate that the extracted parameters using the proposed method can be used as quantitative indicators to monitor scar progression with time and can help understand the mechanism of scar progression.

High-definition optical coherence tomography intrinsic skin ageing assessment in women: a pilot study

Several non-invasive two-dimensional techniques with different lateral resolution and measurable depth range have proved to be useful in assessing and quantifying morphological changes in skin ageing. Among these, only in vivo microscopy techniques permit histometric measurements in vivo. Qualitative and quantitative assessment of chronological (intrinsic) age-related (IAR) morphological changes of epidermis, dermo-epidermal junction (DEJ), papillary dermis (PD), papillary-reticular dermis junction and reticular dermis (RD) have been performed by high-definition optical coherence tomography in real time 3-D. HD-OCT images were taken at the internal site of the right upper arm. Qualitative HD-OCT IAR descriptors were reported at skin surface, at epidermal layer, DEJ, PD and upper RD. Quantitative evaluation of age-related compaction and backscattered intensity or brightness of different skin layers was performed by using the plugin plot z-axis profile of ImageJ^® software permitting intensity assessment of HD-OCT (DICOM) images (3-D images). Analysis was in blind from all clinical information. Sixty, fair-skinned (Fitzpatrick types I–III) healthy females were analysed retrospectively in this study. The subjects belonged to three age groups: twenty in group I aged 20–39, twenty in group II aged 40–59 and twenty in group III aged 60–79. Only intrinsic ageing in women has been studied. Significant age-related qualitative and quantitative differences could be noticed. IAR changes in dermal matrix fibers morphology/organisation and in microvasculature were observed. The brightness and compaction of the different skin layers increased significantly with intrinsic skin ageing. The depth of visibility of fibers in RD increased significantly in the older age group. In conclusion, HD-OCT allows 3-D in vivo and real time qualitative and quantitative assessment of chronological (intrinsic) age-related morphological skin changes at high resolution from skin surface to a depth of the superficial reticular dermis.

In vivo non-invasive monitoring of collagen remodelling by two-photon microscopy after micro-ablative fractional laser resurfacing

Non-linear optical microscopy is becoming popular as a non-invasive in vivo imaging modality in dermatology. In this study, combined TPF and SHG microscopy were used to monitor collagen remodelling in vivo after micro-ablative fractional laser resurfacing. Papillary dermis of living subjects, covering a wide age range, was imaged immediately before and forty days after treatment. A qualitative visual examination of acquired images demonstrated an age-dependent remodelling effect on collagen. Additional quantitative analysis of new collagen production was performed by means of two image analysis methods. A higher increase in SHG to TPF ratio, corresponding to a stronger treatment effectiveness, was found in older subjects, whereas the effect was found to be negligible in young, and minimal in middle age subjects. Analysis of collagen images also showed a dependence of the treatment effectiveness with age but with controversial results. While the diagnostic potential of in vivo multiphoton microscopy has already been demonstrated for skin cancer and other skin diseases, here we first successfully explore its potential use for a non-invasive follow-up of a laser-based treatment.

Influence of sun exposure on the cutaneous collagen/elastin fibers and carotenoids: negative effects can be reduced by application of sunscreen

Resonance Raman spectroscopy and multi-photon tomography were used in vivo to analyse the influence of sun exposure on the cutaneous carotenoids and collagen/elastin fibers. Comparing Berlin (low sun exposure) and Monegasque (high sun exposure) volunteers, it could be demonstrated that extended sun exposure significantly reduces the cutaneous carotenoids and collagen/elastin concentration (p < 0.05). The tendency towards correlation (R(2) = 0.41) between the dermal collagen/elastin (SAAID) and carotenoids confirms the important role of antioxidants in the protection against sun-induced negative effects. The application of sunscreen was shown to be effective, protecting cutaneous carotenoids and collagen/elastin from being damaged subsequent to sun exposure.

Acute UVB-induced epidermal changes assessed by multiphoton laser tomography

BACKGROUND

In vivo multiphoton tomography (MPT) of human skin has become a valuable tool for non-invasive examination of morphological and biophysical skin properties and their alterations. So far, skin changes after UVB irradiation were mainly evaluated clinically and histologically. The present study aimed at non-invasive imaging of histological changes during acute UVB irradiation by multiphoton laser tomography.

METHODS

In 10 volunteers, five areas were irradiated once with an erythematous UVB dose. Multiphoton measurements were performed four times, i.e. before irradiation (baseline), and 24, 48 and 72 h after irradiation, respectively. The data were evaluated for changes of epidermal pleomorphy, spongiosis, pigmentation and thickness.

RESULTS

The four parameters were altered significantly by acute UVB irradiation, i.e. epidermal pleomorphy, spongiosis, pigmentation and thickness increased within 72 h after irradiation.

CONCLUSION

Thus, the study has shown that typical epidermal changes induced by acute UVB irradiation can be evaluated by MPT.

A quantitative approach to histopathological dissection of elastin-related disorders using multiphoton microscopy

BACKGROUND

Multiphoton microscopy (MPM) is a novel imaging technology that has recently become applicable for diagnostic purposes. The use of (near) infrared light in MPM allows for deep tissue imaging. In addition, this modality exploits the autofluorescent nature of extracellular matrix fibres within the skin.

OBJECTIVES

To quantitate the structure and abundance of elastic fibres in human dermis in three dimensions utilizing autofluorescent signals generated by MPM for the objective examination of elastin-related skin disorders.

METHODS

Cross-sections of skin samples from elastin-related disorders were analysed by MPM and correlated to histopathology. In situ visualization of elastic fibres by MPM was conducted by en face imaging of ex vivo skin samples through the intact epidermis. Image analysis software was used to quantify elastic fibres in three dimensions.

RESULTS

Based on the MPM-detected elastin-specific autofluorescence, we developed the Dermal Elastin Morphology Index (DEMI), calculated as the ratio of elastic fibre surface area and volume. This enabled objective three-dimensional quantification of elastic fibres. Quantitative scoring of sun-damaged skin using DEMI correlated with qualitative histopathological grading of the severity of solar elastosis. Furthermore, this approach was applied to changes in elastic fibre architecture in other disorders, such as pseudoxanthoma elasticum (PXE), PXE-like syndrome, elastofibroma, focal dermal elastosis, anetoderma, mid-dermal elastolysis and striae distensae. We imaged elastic fibres in intact ex vivo skin imaged en face through the epidermis, indicating that this approach could be used in vivo.

CONCLUSIONS

MPM has the potential for noninvasive in vivo visualization of elastic fibres in the dermis with near histological resolution. DEMI allows objective assessment of elastic fibres to support diagnosis and monitoring of disease progress or therapy of elastin-related skin disorders.

Application of Multiphoton Microscopy in Dermatological Studies: a Mini-Review

This review summarizes the historical and more recent developments of multiphoton microscopy, as applied to dermatology. Multiphoton microscopy offers several advantages over competing microscopy techniques: there is an inherent axial sectioning, penetration depths that compete well with confocal microscopy on account of the use of near-infrared light, and many two-photon contrast mechanisms, such as second-harmonic generation, have no analogue in one-photon microscopy. While the penetration depths of photons into tissue are typically limited on the order of hundreds of microns, this is of less concern in dermatology, as the skin is thin and readily accessible. As a result, multiphoton microscopy in dermatology has generated a great deal of interest, much of which is summarized here. The review covers the interaction of light and tissue, as well as the various considerations that must be made when designing an instrument. The state of multiphoton microscopy in imaging skin cancer and various other diseases is also discussed, along with the investigation of aging and regeneration phenomena, and finally, the use of multiphoton microscopy to analyze the transdermal transport of drugs, cosmetics and other agents is summarized. The review concludes with a look at potential future research directions, especially those that are necessary to push these techniques into widespread clinical acceptance.

Automatic 3D segmentation of multiphoton images: a key step for the quantification of human skin

BACKGROUND/PURPOSE

Multiphoton microscopy has emerged in the past decade as a useful noninvasive imaging technique for in vivo human skin characterization. However, it has not been used until now in evaluation clinical trials, mainly because of the lack of specific image processing tools that would allow the investigator to extract pertinent quantitative three-dimensional (3D) information from the different skin components.

METHODS

We propose a 3D automatic segmentation method of multiphoton images which is a key step for epidermis and dermis quantification. This method, based on the morphological watershed and graph cuts algorithms, takes into account the real shape of the skin surface and of the dermal-epidermal junction, and allows separating in 3D the epidermis and the superficial dermis.

RESULTS

The automatic segmentation method and the associated quantitative measurements have been developed and validated on a clinical database designed for aging characterization. The segmentation achieves its goals for epidermis-dermis separation and allows quantitative measurements inside the different skin compartments with sufficient relevance.

CONCLUSIONS

This study shows that multiphoton microscopy associated with specific image processing tools provides access to new quantitative measurements on the various skin components. The proposed 3D automatic segmentation method will contribute to build a powerful tool for characterizing human skin condition. To our knowledge, this is the first 3D approach to the segmentation and quantification of these original images.

3D resolved mapping of optical aberrations in thick tissues

We demonstrate a simple method for mapping optical aberrations with 3D resolution within thick samples. The method relies on the local measurement of the variation in image quality with externally applied aberrations. We discuss the accuracy of the method as a function of the signal strength and of the aberration amplitude and we derive the achievable resolution for the resulting measurements. We then report on measured 3D aberration maps in human skin biopsies and mouse brain slices. From these data, we analyse the consequences of tissue structure and refractive index distribution on aberrations and imaging depth in normal and cleared tissue samples. The aberration maps allow the estimation of the typical aplanetism region size over which aberrations can be uniformly corrected. This method and data pave the way towards efficient correction strategies for tissue imaging applications.

Non-invasive evaluation of dermal elastosis by in vivo multiphoton tomography with autofluorescence lifetime measurements

The non-invasive differentiation of dermal elastic fibres from solar elastosis in vivo is of great interest in dermatologic research, especially for efficacy testing of anti-ageing products. To date, no studies on multiphoton excited fluorescence lifetime characteristics of human elastic fibres and solar elastosis are reported. The goal of the present work was the identification of differential criteria for elastic fibres and solar elastosis by the analysis of fluorescence decay curves acquired by time-correlated single photon counting in vivo multiphoton tomography. For this purpose, fluorescence lifetime measurements (FLIM) were performed with 47 volunteers of different age groups at sun-protected and sun-exposed localizations. Bi-exponential curve fitting was applied to the FLIM data, and characteristic differences between age groups and localizations were found in both relevant fit parameters describing the decay slope. The FLIM analyses have shown that dermal autofluorescence has different lifetimes depending on age and in part on localization.

Applications of multiphoton tomographs and femtosecond laser nanoprocessing microscopes in drug delivery research

Multiphoton tomography for in vivo high-resolution multidimensional imaging has been used in clinical investigations and small animal studies. The novel femtosecond laser tomographs have been employed to detect cosmetics and pharmaceutical components in situ as well as to study the interaction of drugs with intratissue cells and the extracellular matrix under physiological conditions. Applications include the intra-tissue accumulation of sunscreen nanoparticles in humans, the monitoring the metabolic status of patients with dermatitis, the biosynthesis of collagen after administration of anti-aging products, and the detection of porphyrins after application of 5-aminolevulinic acid. More than 2000 patients and volunteers in Europe, Australia, and Asia have been investigated with these unique tomographs. In addition, femtosecond laser nanoprocessing microscopes have been employed for targeted delivery and deposition in body organs, optical transfection and optical cleaning of stem cells, as well as for the optical transfer of molecular beacons to track microRNAs. These diverse applications highlight the capacity for multiphoton tomography and femtosecond laser nanoprocessing tools to advance drug delivery research.