Electrochemical degradation and saponification of porcine adipose tissue.

Body contouring achieved via subcutaneous adipose tissue reduction has notably advanced over the past century, from suction assisted lipectomy to techniques with reduced degrees of invasiveness including laser, radiofrequency, high frequency focused ultrasound, cryolipolysis, and drug-based injection approaches. These costly techniques have focused on damaging adipocyte cell membranes, hydrolyzing triglycerides (TGs), or inducing apoptosis. Here, we present a simple, low-cost technique, termed electrochemical lipolysis (ECLL). During ECLL, saline is injected into the subcutaneous adipose tissue, followed by insertion of needle electrodes and application of an electrical potential. Electrolysis of saline creates localized pH gradients that drive adipocyte death and saponification of TGs. Using pH mapping, various optical imaging techniques, and biochemical assays, we demonstrate the ability of ECLL to induce acid and base injury, cell death, and the saponification of triglycerides in ex vivo porcine adipose tissue. We define ECLL's potential role as a minimally-invasive, ultra-low-cost technology for reducing and contouring adipose tissue, and present ECLL as a potential new application of an emerging electrochemical redox based treatment modality.

Dynamics of nevus development implicate cell cooperation in the growth arrest of transformed melanocytes.

Mutational activation of the BRAF proto-oncogene in melanocytes reliably produces benign nevi (pigmented 'moles'), yet the same change is the most common driver mutation in melanoma. The reason nevi stop growing, and do not progress to melanoma, is widely attributed to a cell-autonomous process of 'oncogene-induced senescence'. Using a mouse model of Braf-driven nevus formation, analyzing both proliferative dynamics and single-cell gene expression, we found no evidence that nevus cells are senescent, either compared with other skin cells, or other melanocytes. We also found that nevus size distributions could not be fit by any simple cell-autonomous model of growth arrest, yet were easily fit by models based on collective cell behavior, for example in which arresting cells release an arrest-promoting factor. We suggest that nevus growth arrest is more likely related to the cell interactions that mediate size control in normal tissues, than to any cell-autonomous, 'oncogene-induced' program of senescence.

Melanocytes are pigment-producing cells found throughout the skin. Mutations that activate a gene called BRAF cause these cells to divide and produce melanocytic nevi, also known as "moles". These mutations are oncogenic, meaning they can cause cancer. Indeed, BRAF is the most commonly mutated gene in melanoma, a deadly skin cancer that arises from melanocytes. Yet, moles hardly ever progress to melanoma. A proposed explanation for this behavior is that, once activated, BRAF initiates a process called "oncogene-induced senescence" in each melanocyte. This process, likened to premature aging, is thought to be what causes cells in a mole to quit dividing. Although this hypothesis is widely accepted, it has proved difficult to test directly. To investigate this notion, Ruiz-Vega et al. studied mice with hundreds of moles created by the same BRAF mutation found in human moles. Analyzing the activity of genes in individual cells revealed that nevus melanocytes that have stopped growing are no more senescent than other skin cells, including non-mole melanocytes. Ruiz-Vega et al. then analyzed the sizes at which moles stopped growing, estimating the number of cells in each mole. The data were then compared with the results of a simulation and mathematical modeling. This revealed that any model based on the idea of cells independently shutting down after a number of random events could not reproduce the distribution of mole sizes that had been experimentally observed. On the other hand, models based on melanocytes acting collectively to shut down each other's growth fit the observed data much better. These findings suggest that moles do not stop growing as a direct result of the activation of BRAF, but because they sense and respond to their own overgrowth. The same kind of collective sensing is observed in normal tissues that maintain a constant size. Discovering that melanocytes do this not only sheds light on why moles stop growing, it could also help researchers devise new ways to prevent melanomas from forming.

The biophysical effects of localized electrochemical therapy on porcine skin.

BACKGROUND: Minimally-invasive methods to treat scars address a common pathway of altering collagen structure, leading to collagen remodeling. OBJECTIVE: In this study, we employed in situ redox chemistry to create focal pH gradients in skin, altering dermal collagen, in a process we refer to as electrochemical therapy (ECT). The effects of ECT to induce biochemical and structural changes in ex vivo porcine skin were examined. METHODS: During ECT, two platinum electrodes were inserted into fresh porcine skin, and following saline injection, an electrical potential was applied. pH mapping, high frequency ultrasonography, and two photon excitation microscopy and second harmonic generation (SHG) microscopy were used to evaluate treatment effects. Findings were correlated with histology. RESULTS: Following ECT, pH mapping depicted acid and base production at anode and cathode sites respectively, with increasing voltage and application time. Gas formation during ECT was observed with ultrasonography. Anode sites showed significant loss of SHG signal, while cathode sites showed disorganized collagen structure with fewer fibrils emitting an attainable signal. Histologically, collagen denaturation at both sites was confirmed. CONCLUSION: We demonstrated the production of in situ acid and base in skin occurring via ECT. The effects chemically and precisely alter collagen structure through denaturation, giving insight on the potential of ECT as a simple, low-cost, and minimally-invasive means to remodel skin and treat scars.

Multiphoton Microscopy of Collagen Structure in Ex Vivo Human Skin Following Electrochemical Therapy.

OBJECTIVES: Injury to healthy dermis and the dermoepidermal junction initiates a robust healing process consisting of fibrous tissue overgrowth, collagen deposition, and scar formation. The conventional management of scars and other skin injuries has largely relied upon surgical soft tissue transfer to resurface and/or replace damaged and dysmorphic tissue with new skin. However, these strategies are invasive, expensive, and may further exacerbate integumentary injury. In this study, we examine the creation of in situ redox generated pH changes in fresh human skin. We believe this process of "electrochemical therapy" (ECT) leads to changes in collagen matrix structure. Our objective is to map local tissue pH landscapes and image changes in collagen structure of non-injured skin following ECT. STUDY DESIGN: Ex vivo human study involving ECT of human skin. METHODS: Remnant fresh ex vivo human facial skin from facelift operations was enveloped in saline-soaked gauze for a maximum of 2 hours prior to ECT and imaging. ECT was performed by inserting platinum-plated needle electrodes connected to a DC power supply. Voltage (4, 5, or 6 V) and time (3, 4, or 5 minutes) were varied systematically. High frequency ultrasound (25 MHz) was performed immediately after ECT on each sample. Treated samples were also imaged using multiphoton microscopy (MPM) with second harmonic generation (SHG) to specifically visualize collagen fibers in the dermis. The pH landscapes were mapped using indicator dyes in bisected specimens and the MPM images were compared with histologic findings. RESULTS: Above 4 V and 3 minutes, a profound reduction in dermal collagen SHG signal was observed at the anode. Although there was less blunting of SHG signal seen at the cathode, a decrease in the fluorescence of the dermoepidermal junction was observed. The pH application suggests ECT spatial selectivity and a direct relationship between voltage and application time. Ultrasound demonstrated gas formation between the anode and cathode, which is consistent with ECT's mechanism of action. Importantly, these electrochemical changes occurred without disrupting dermal and epidermal histologic architecture. CONCLUSION: ECT alters tissue pH leading to dermal collagen structural change. These results offer additional insight into the translational potential of ECT to locally remodel the soft-tissue matrix. Future directions aim to expand into a skin injury model to determine if similar collagen effects are observed in vivo. ECT is incredibly inexpensive (~$5) and may be a means to treat soft tissue injuries using simple needle-based devices and DC battery power supplies. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Brain Endothelial Erythrophagocytosis and Hemoglobin Transmigration Across Brain Endothelium: Implications for Pathogenesis of Cerebral Microbleeds.

Peripheral endothelial cells are capable of erythrophagocytosis, but data on brain endothelial erythrophagocytosis are limited. We studied the relationship between brain endothelial erythrophagocytosis and cerebral microhemorrhage, the pathological substrate of MRI-demonstrable cerebral microbleeds. To demonstrate the erythrophagocytic capability of the brain endothelium, we studied the interactions between brain endothelial cells and red blood cells exposed to oxidative stress in vitro, and developed a new in vitro cerebral microbleeds model to study the subsequent passage of hemoglobin across the brain endothelial monolayer. Using multiple approaches, our results show marked brain endothelial erythrophagocytosis of red blood cells exposed to oxidative stress compared with control red blood cells in vitro. This brain endothelial erythrophagocytosis was accompanied by passage of hemoglobin across the brain endothelial monolayer with unaltered monolayer integrity. In vivo and confocal fluorescence microscopy studies confirmed the extravasation of RBC exposed to oxidative stress across brain endothelium. These findings, demonstrating erythrophagocytosis mediated by the brain endothelial monolayer and the subsequent passage of iron-rich hemoglobin in vitro and RBC in vivo, may have implications for elucidating mechanisms involved in the development of cerebral microbleeds that are not dependent on disruption of the microvasculature.

Limiting glioma development by photodynamic therapy-generated macrophage vaccine and allo-stimulation: an in vivo histological study in rats.

Immunotherapy of brain tumors involves the stimulation of an antitumor immune response. This type of therapy can be targeted specifically to tumor cells thus sparing surrounding normal brain. Due to the presence of the blood-brain barrier, the brain is relatively isolated from the systemic circulation and, as such, the initiation of significant immune responses is more limited than other types of cancers. The purpose of this study was to show that the efficacy of tumor primed antigen presenting macrophage (MaF98) vaccines can be increased by: (1) photodynamic therapy (PDT) of the priming tumor cells and (2) intracranial injection of allogeneic glioma cells directly into the tumor site. Experiments were conducted in an in vivo brain tumor development model using Fischer rats and F98 (syngeneic) and BT4C (allogeneic) glioma cells. The results showed that immunization with Ma (acting as antigen-presenting cells), primed with PDT-treated tumor cells (MaF98), significantly slowed but did not prevent the growth of F98-induced tumors in the brain. Complete suppression of tumor development was obtained via MaF98 inoculation combined with direct intracranial injection of allogeneic glioma cells. No deleterious effects were noted in any of the animals during the 14-day observation period.

Photochemical internalization enhanced macrophage delivered chemotherapy.

BACKGROUND: Macrophage (Ma) vectorization of chemotherapeutic drugs has the advantage for cancer therapy in that it can actively target and maintain an elevated concentration of drugs at the tumor site, preventing their spread into healthy tissue. A potential drawback is the inability to deliver a sufficient number of drug-loaded Ma into the tumor, thus limiting the amount of active drug delivered. This study examined the ability of photochemical internalization (PCI) to enhance the efficacy of released drug by Ma transport. METHODS: Tumor spheroids consisting of either F98 rat glioma cells or F98 cells combined with a subpopulation of empty or doxorubicin (DOX)-loaded mouse Ma (RAW264.7) were used as in vitro tumor models. PCI was performed with the photosensitizer AlPcS2a and laser irradiation at 670 nm. RESULTS: RAW264.7 Ma pulsed with DOX released the majority of the incorporated DOX within two hours of incubation. PCI significantly increased the toxicity of DOX either as pure drug or derived from monolayers of DOX-loaded Ma. Significant growth inhibition of hybrid spheroids was also observed with PCI even at subpopulations of DOX-loaded Ma as low as 11% of the total initial hybrid spheroid cell number. CONCLUSION: Results show that RAW264.7 Ma, pulsed with DOX, could effectively incorporate and release DOX. PCI significantly increased the ability of both free and Ma-released DOX to inhibit the growth of tumor spheroids in vitro. The growth of F98 + DOX loaded Ma hybrid spheroids were synergistically reduced by PCI, compared to either photodynamic therapy or released DOX acting alone.

The RhoJ-BAD signaling network: An Achilles' heel for BRAF mutant melanomas.

Genes and pathways that allow cells to cope with oncogene-induced stress represent selective cancer therapeutic targets that remain largely undiscovered. In this study, we identify a RhoJ signaling pathway that is a selective therapeutic target for BRAF mutant cells. RhoJ deletion in BRAF mutant melanocytes modulates the expression of the pro-apoptotic protein BAD as well as genes involved in cellular metabolism, impairing nevus formation, cellular transformation, and metastasis. Short-term treatment of nascent melanoma tumors with PAK inhibitors that block RhoJ signaling halts the growth of BRAF mutant melanoma tumors in vivo and induces apoptosis in melanoma cells in vitro via a BAD-dependent mechanism. As up to 50% of BRAF mutant human melanomas express high levels of RhoJ, these studies nominate the RhoJ-BAD signaling network as a therapeutic vulnerability for fledgling BRAF mutant human tumors.

ATR Mutations Promote the Growth of Melanoma Tumors by Modulating the Immune Microenvironment.

Melanomas accumulate a high burden of mutations that could potentially generate neoantigens, yet somehow suppress the immune response to facilitate continued growth. In this study, we identify a subset of human melanomas that have loss-of-function mutations in ATR, a kinase that recognizes and repairs UV-induced DNA damage and is required for cellular proliferation. ATR mutant tumors exhibit both the accumulation of multiple mutations and the altered expression of inflammatory genes, resulting in decreased T cell recruitment and increased recruitment of macrophages known to spur tumor invasion. Taken together, these studies identify a mechanism by which melanoma cells modulate the immune microenvironment to promote continued growth.

A murine model of inflammation-induced cerebral microbleeds.

BACKGROUND: Cerebral microhemorrhages (CMH) are tiny deposits of blood degradation products in the brain and are pathological substrates of cerebral microbleeds. The existing CMH animal models are ß-amyloid-, hypoxic brain injury-, or hypertension-induced. Recent evidence shows that CMH develop independently of hypoxic brain injury, hypertension, or amyloid deposition and CMH are associated with normal aging, sepsis, and neurodegenerative conditions. One common factor among the above pathologies is inflammation, and recent clinical studies show a link between systemic inflammation and CMH. Hence, we hypothesize that inflammation induces CMH development and thus, lipopolysaccharide (LPS)-induced CMH may be an appropriate model to study cerebral microbleeds. METHODS: Adult C57BL/6 mice were injected with LPS (3 or 1 mg/kg, i.p.) or saline at 0, 6, and 24 h. At 2 or 7 days after the first injection, brains were harvested. Hematoxylin and eosin (H&E) and Prussian blue (PB) were used to stain fresh (acute) hemorrhages and hemosiderin (sub-acute) hemorrhages, respectively. Brain tissue ICAM-1, IgG, Iba1, and GFAP immunohistochemistry were used to examine endothelium activation, blood-brain barrier (BBB) disruption, and neuroinflammation. MRI and fluorescence microscopy were used to further confirm CMH development in this model. RESULTS: LPS-treated mice developed H&E-positive (at 2 days) and PB-positive (at 7 days) CMH. No surface and negligible H&E-positive CMH were observed in saline-treated mice (n = 12). LPS (3 mg/kg; n = 10) produced significantly higher number, size, and area of H&E-positive CMH at 2 days. LPS (1 mg/kg; n = 9) produced robust development of PB-positive CMH at 7 days, with significantly higher number and area compared with saline (n = 9)-treated mice. CMH showed the highest distribution in the cerebellum followed by the sub-cortex and cortex. LPS-induced CMH were predominantly adjacent to cerebral capillaries, and CMH load was associated with indices of brain endothelium activation, BBB disruption, and neuroinflammation. Fluorescence microscopy confirmed the extravasation of red blood cells into the brain parenchyma, and MRI demonstrated the presence of cerebral microbleeds. CONCLUSIONS: LPS produced rapid and robust development of H&E-positive (at 2 days) and PB-positive (at 7 days) CMH. The ease of development of both H&E- and PB-positive CMH makes the LPS-induced mouse model suitable to study inflammation-induced CMH.

Exploring Mechanisms of Biofilm Removal.

OBJECTIVE: The goal of this study was to evaluate the effects of a novel anti-plaque formulation on oral biofilm removal. Specific aim was to elucidate the role of 2 potentially complementary mechanisms on dental biofilm removal using EPIEN Dental Debriding Solution (EDDS) like desiccating action leading to denaturation and destabilization of plaque and mechanical removal of destabilized plaque through forceful rinsing action. MATERIALS AND METHODS: 25 extracted teeth, after routine debriding and cleaning, underwent standard biofilm incubation model over 4 days. Then samples were randomly divided into 5 groups of 5 teeth each, treated and stained with GUM®Red-Cote® plaque disclosing solution and imaged. Samples were subsequently treated with HYBENX® Oral Decontaminant. Group 1 samples were treated with a standardized "static" water dip exposure following biofilm incubation. Samples in Group 2 were given a standardized "dynamic" exposure to a dental high pressure air/water syringe for 20 s. Group 3 samples were exposed to a standardized "static" application of test agent (30 s dip rinse) followed by a standardized "static" water rinse (30 s dip rinse). Samples in Group 4 were given both the standardized "static" application of test formulation followed by the standardized "dynamic" exposure to a dental high pressure air/water syringe. Finally, samples in Group 5 were treated with a standardized "dynamic" application of test agent (20 s high pressure syringe at 10 ml/s) followed by the standardized "dynamic" exposure to a dental high pressure air/water syringe. RESULTS: The MPM images demonstrated that the water dip treatment resulted in the persistence of an almost continuous thick layer of biofilm coverage on the tooth surface. Similarly, test agent dip treatment followed by water dip only removed a few patches of biofilm, with the majority of the tooth surface remaining covered by an otherwise continuous layer of biofilm. Samples exposed to air/water spray alone showed some disruption of the biofilm, leaving residual patches of biofilm that varied considerably in size. Test agent dip treatment followed by air/water spray broke up the continuous layer of biofilm leaving only very small, thin scattered islands of biofilm. Finally, the dynamic test agent spray followed by air/water spray removed the biofilm almost entirely, with evidence of only very few small, thin residual biofilm islands. CONCLUSION: These studies demonstrate that test agent desiccant effect alone causes some disruption of dental biofilm. Additional dynamic rinsing is needed to achieve complete removal of dental biofilm.

Focused ultrasound-mediated sonochemical internalization: an alternative to light-based therapies.

Activation of sonosensitizers via focused ultrasound (FUS), i.e., sonodynamic therapy has been proposed as an extension to light-activated photodynamic therapy for the treatment of brain as well as other tumors. The use of FUS, as opposed to light, allows treatment to tumor sites buried deep within tissues as well as through the intact skull. We have examined ultrasonic activation of sonosensitizers together with the anticancer agent bleomycin (BLM), i.e., sonochemical internalization (SCI). SCI is a technique that utilizes FUS for the enhanced delivery of endo-lysosomal trapped macromolecules into the cell cytoplasm in a similar manner to light-based photochemical internalization. The released agent can, therefore, exert its full biological activity, in contrast to being degraded by lysosomal hydrolases. Our results indicate that, compared to drug or FUS treatment alone, FUS activation of the sonosensitizer AlPcS2a together with BLM significantly inhibits the ability of treated glioma cells to grow as three-dimensional tumor spheroids in vitro.

Measuring Redox Status of Melanoma Cells.

Redox homeostasis plays multiple roles in essentially all aspects of cellular function, and hence, reliable methods for measuring cellular or tissue redox status are key elements in understanding the redox related signal pathways. However, in the free radical biology field, there are many controversies on the methods to measure reactive oxygen species. In this chapter we describe our experience in measuring superoxide, hydrogen peroxide, and a general redox status using redox-sensitive green fluorescence proteins (roGFPs) in human melanoma cells.

Cell and brain tissue imaging of the flavonoid fisetin using label-free two-photon microscopy.

Over the last few years, we have identified an orally active, novel neuroprotective and cognition-enhancing molecule, the flavonoid fisetin. Fisetin not only has direct antioxidant activity but it can also increase the intracellular levels of glutathione, the major intracellular antioxidant. Fisetin can also activate key neurotrophic factor signaling pathways. In addition, it has anti-inflammatory activity against microglia and astrocytes and inhibits the activity of lipoxygenases, thereby reducing the production of pro-inflammatory eicosanoids and their by-products. However, key questions about its targets and brain penetration remain. In this study, we used label-free two-photon microscopy of intrinsic fisetin fluorescence to examine the localization of fisetin in living nerve cells and the brains of living mice. In cells, fisetin but not structurally related flavonols with different numbers of hydroxyl groups, localized to the nucleoli suggesting that key targets of fisetin may reside in this organelle. In the mouse brain, following intraperitoneal injection and oral administration, fisetin rapidly distributed to the blood vessels of the brain followed by a slower dispersion into the brain parenchyma. Thus, these results provide further support for the effects of fisetin on brain function. In addition, they suggest that label-free two-photon microscopy may prove useful for studying the intracellular and tissue distribution of other intrinsically-fluorescent flavonoids.

In Vivo Multiphoton Microscopy of Basal Cell Carcinoma.

IMPORTANCE: Basal cell carcinomas (BCCs) are diagnosed by clinical evaluation, which can include dermoscopic evaluation, biopsy, and histopathologic examination. Recent translation of multiphoton microscopy (MPM) to clinical practice raises the possibility of noninvasive, label-free in vivo imaging of BCCs that could reduce the time from consultation to treatment. OBJECTIVES: To demonstrate the capability of MPM to image in vivo BCC lesions in human skin, and to evaluate if histopathologic criteria can be identified in MPM images. DESIGN, SETTING, AND PARTICIPANTS: Imaging in patients with BCC was performed at the University of California-Irvine Health Beckman Laser Institute & Medical Clinic, Irvine, between September 2012 and April 2014, with a clinical MPM-based tomograph. Ten BCC lesions were imaged in vivo in 9 patients prior to biopsy. The MPM images were compared with histopathologic findings. MAIN OUTCOMES AND MEASURES: MPM imaging identified in vivo and noninvasively the main histopathologic feature of BCC lesions: nests of basaloid cells showing palisading in the peripheral cell layer at the dermoepidermal junction and/or in the dermis. RESULTS: The main MPM feature associated with the BCC lesions involved nests of basaloid cells present in the papillary and reticular dermis. This feature correlated well with histopathologic examination. Other MPM features included elongated tumor cells in the epidermis aligned in 1 direction and parallel collagen and elastin bundles surrounding the tumors. CONCLUSIONS AND RELEVANCE: This study demonstrates, in a limited patient population, that noninvasive in vivo MPM imaging can provide label-free contrast that reveals several characteristic features of BCC lesions. Future studies are needed to validate the technique and correlate MPM performance with histopathologic examination.

Distinguishing between benign and malignant melanocytic nevi by in vivo multiphoton microscopy.

Monitoring of atypical nevi is an important step in early detection of melanoma, a clinical imperative in preventing the disease progression. Current standard diagnosis is based on biopsy and histopathologic examination, a method that is invasive and highly dependent upon physician experience. In this work, we used a clinical multiphoton microscope to image in vivo and noninvasively melanocytic nevi at three different stages: common nevi without dysplastic changes, dysplastic nevi with structural and architectural atypia, and melanoma. We analyzed multiphoton microscopy (MPM) images corresponding to 15 lesions (five in each group) both qualitatively and quantitatively. For the qualitative analysis, we identified the morphologic features characteristic of each group. MPM images corresponding to dysplastic nevi and melanoma were compared with standard histopathology to determine correlations between tissue constituents and morphology and to evaluate whether standard histopathology criteria can be identified in the MPM images. Prominent qualitative correlations included the morphology of epidermal keratinocytes, the appearance of nests of nevus cells surrounded by collagen fibers, and the structure of the epidermal-dermal junction. For the quantitative analysis, we defined a numerical multiphoton melanoma index (MMI) based on three-dimensional in vivo image analysis that scores signals derived from two-photon excited fluorescence, second harmonic generation, and melanocyte morphology features on a continuous 9-point scale. Indices corresponding to common nevi (0-1), dysplastic nevi (1-4), and melanoma (5-8) were significantly different (P < 0.05), suggesting the potential of the method to distinguish between melanocytic nevi in vivo.

Evaluation of stimulated Raman scattering microscopy for identifying squamous cell carcinoma in human skin.

BACKGROUND AND SIGNIFICANCE: There is a need to develop non-invasive diagnostic tools to achieve early and accurate detection of skin cancer in a non-surgical manner. In this study, we evaluate the capability of stimulated Raman scattering (SRS) microscopy, a potentially non-invasive optical imaging technique, for identifying the pathological features of s squamous cell carcinoma (SCC) tissue. STUDY DESIGN: We studied ex vivo SCC and healthy skin tissues using SRS microscopy, and compared the SRS contrast with the contrast obtained in reflectance confocal microscopy (RCM) and standard histology. RESULTS AND CONCLUSION: SRS images obtained at the carbon-hydrogen stretching vibration at 2945 cm(-1) exhibit contrast related protein density that clearly delineates the cell nucleus from the cell cytoplasm. The morphological features of SCC tumor seen in the SRS images show excellent correlation with the diagnostic features identified by histological examination. Additionally, SRS exhibits enhanced cellular contrast in comparison to that seen in confocal microscopy. In conclusion, SRS represents an attractive approach for generating protein density maps with contrast that closely resembles histopathological contrast of SCC in human skin.

Multiscale analysis of collagen microstructure with generalized image correlation spectroscopy and the detection of tissue prestress.

Prestress in tissue is currently detected through destructive methods which obviate both in vivo and longitudinal assessment. We hypothesized that prestress could be detected and quantified by analyzing the microstructure of the extracellular matrix at different spatial scales using non-invasive and non-destructive optical imaging. A simple model of tissue prestress was created using fibroblast-mediated contraction of collagen gels around a central mandrel. Using a quantitative, multiscale, image processing technique, termed generalized image correlation spectroscopy (GICS) of second harmonic images, collagen fiber number and alignment at three different length scales characteristic of the collagen fibril, collagen fiber, and cell were analyzed. GICS fiber alignment (σ(maj/min)) was significantly different across load state, level of prestress, and length scale. The largest fiber ratio, and thus highest alignment, was seen in prestressed, externally loaded gels at a length scale equivalent to the size of the fibroblast cells. Alignment at both fiber and cell scale correlated with prestress in this model. We conclude that GICS of second harmonic images of collagen can predict prestress, and that microstructural organization at the collagen fiber and cell scale are the primary determinants of prestress in cellularized collagen gels.

In vivo multiphoton NADH fluorescence reveals depth-dependent keratinocyte metabolism in human skin.

We employ a clinical multiphoton microscope to monitor in vivo and noninvasively the changes in reduced nicotinamide adenine dinucleotide (NADH) fluorescence of human epidermal cells during arterial occlusion. We correlate these results with measurements of tissue oxy- and deoxyhemoglobin concentration during oxygen deprivation using spatial frequency domain imaging. During arterial occlusion, a decrease in oxyhemoglobin corresponds to an increase in NADH fluorescence in the basal epidermal cells, implying a reduction in basal cell oxidative phosphorylation. The ischemia-induced oxygen deprivation is associated with a strong increase in NADH fluorescence of keratinocytes in layers close to the stratum basale, whereas keratinocytes from epidermal layers closer to the skin surface are not affected. Spatial frequency domain imaging optical property measurements, combined with a multilayer Monte Carlo-based radiative transport model of multiphoton microscopy signal collection in skin, establish that localized tissue optical property changes during occlusion do not impact the observed NADH signal increase. This outcome supports the hypothesis that the vascular contribution to the basal layer oxygen supply is significant and these cells engage in oxidative metabolism. Keratinocytes in the more superficial stratum granulosum are either supplied by atmospheric oxygen or are functionally anaerobic. Based on combined hemodynamic and two-photon excited fluorescence data, the oxygen consumption rate in the stratum basale is estimated to be ∼0.035 µmoles/10(6) cells/h.