Collagen structure and nonlinear susceptibility: effects of heat, glycation, and enzymatic cleavage on second harmonic signal intensity

Mice heterozygous for an osteogenesis imperfecta-linked MBTPS2 variant display a compromised subchondral osteocyte lacunocanalicular network associated with abnormal articular cartilage

Missense variants in the MBTPS2 gene, located on the X chromosome, have been associated with an X-linked recessive form of osteogenesis imperfecta (X-OI), an inherited bone dysplasia characterized by multiple and recurrent bone fractures, short stature, and various skeletal deformities in affected individuals. The role of site-2 protease, encoded by MBTPS2, and the molecular pathomechanism underlying the disease are to date elusive. This study is the first to report on the generation of two Mbtps2 mouse models, a knock-in mouse carrying one of the disease-causative MBTPS2 variants (N455S) and a Mbtps2 knock-out (ko) mouse. Because both loss-of-function variants lead to embryonic lethality in hemizygous male mutant mice, we performed a comprehensive skeletal analysis of heterozygous Mbtps2+/N455S and Mbtps2+/ko female mice. Both models displayed osteochondral abnormalities such as thinned subchondral bone, altered subchondral osteocyte interconnectivity as well as thickened articular cartilage with chondrocyte clustering, altogether resembling an early osteoarthritis (OA) phenotype. However, distant from the joints, no alterations in the bone mass and turnover could be detected in either of the mutant mice. Based on our findings we conclude that MBTPS2 haploinsufficiency results in early OA-like alterations in the articular cartilage and underlying subchondral bone, which likely precede the development of typical OI phenotype in bone. Our study provides first evidence for a potential role of site-2 protease for maintaining homeostasis of both bone and cartilage.

Pilose antler extract restores type I and III collagen to accelerate wound healing

Granulation tissue has supporting and filling functions in wound healing. The collagen produced by fibroblast acts as a cell scaffold in the granulation tissue to facilitate the formation of new blood vessels and epithelial coverage. Previously, we extracted protein components from the pilose antler that was involved in the biological process of collagen fibril organization. They were also found to contain abundant extracellular matrix(ECM) components. Therefore, in this experiment, we used a rat model of full-thickness skin excision and fibroblasts to perform an experiment for determination of the effects of pilose antler protein extract (PAE) on collagen content and fiber synthesis during wound healing. Additionally, we further analyzed its pharmacological effects on wound healing and the possible regulatory mechanisms. We found that PAE accelerated synthesis of type I and III collagen, promoted the formation of type III collagen fibers, and reduced collagen degradation by recruiting fibroblasts. Furthermore, the extract upregulated the expression of TGF β R1 and Smad2, and initiated the entry of Smad2/Smad3 into the nucleus. After adding SB431542 to inhibit TGF-β type I receptor activity, PAE's ability to promote Smad2/Smad3 nuclear localization was weakened. These data indicate that local PAE therapy can promote the proliferation of fibroblasts, dynamically regulate the expression of TGF-β, and increase the amount of collagen and the synthesis of type III collagen fibers by promoting smad2 activity in the proliferation period, thus accelerating the regenerative healing of wounds.

Electrospinning of collagen: enzymatic and spectroscopic analyses reveal solvent-independent disruption of the triple-helical structure

Electrospinning has become a well-established method for creating nanofibrous meshes for tissue-engineering applications. The incorporation of natural extracellular components, such as electrospun pure collagen nanofibers, has proven to be particularly challenging, as electrospun collagen nanofibers do not constitute native collagen fibers anymore. In this study, we show that this detrimental effect is not only limited to fluorinated solvents, as previously thought. Rat tail collagen was dissolved in acetic acid and ethanol and electrospun at various temperatures. Electrospun collagen mats were analyzed using circular dichroism, enzymatic digestion, SDS-PAGE, western blotting, and Raman spectroscopy and compared to heat-denaturated and electrospun collagen in HFIP. Our data suggest that even non-fluorinated electrospinning solvents, such as acid-based solvents, do not yield structurally intact fibers. Interestingly, neither epithelial cells nor fibroblasts displayed a different cellular response to electrospun collagen compared to collagen-coated polyurethane scaffolds in F-actin staining and metabolic analysis using fluorescent lifetime imaging. The disruption of the structural integrity of collagen might therefore be underestimated based on the cell-material interactions alone. These observations expose the larger than anticipated vulnerability of collagen in the electrospinning process. Based on these findings, the influence of the electrospinning process on the distinct biochemical properties of collagen should always be considered, when ECM-mimicking fibrous constructs are manufactured.

Electromechanical Cornea Reshaping for Refractive Vision Therapy

The corneal stroma consists of orthogonally stacked collagen-fibril lamellae that determine the shape of the cornea and provide most of the refractive power of the eye. We have applied electromechanical reshaping (EMR), an electrochemical platform for remodeling cartilage and other semirigid tissues, to change the curvature of the cornea as a potential procedure for nonsurgical vision correction. EMR relies on short electrochemical pulses to electrolyze water, with subsequent diffusion of protons into the extracellular matrix of collagenous tissues; protonation of immobilized anions within this matrix disrupts the ionic-bonding network, leaving the tissue transiently responsive to mechanical remodeling. Re-equilibration to physiological pH restores the ionic matrix, resulting in persistent shape change of the tissue. Using ex vivo rabbit eyes, we demonstrate here the controlled change of corneal curvature over a wide range of refractive powers with no loss of optical transparency. Optical coherence tomography (OCT), combined with second-harmonic generation (SHG) and confocal microscopy, establish that EMR enables extremely fine control of corneal contouring while maintaining the underlying macromolecular collagen structure and stromal cellular viability, positioning electrochemical vision therapy as a potentially simple and ultralow-cost modality for correcting routine refractive errors.

Primary radiation damage in bone evolves via collagen destruction by photoelectrons and secondary emission self-absorption

X-rays are invaluable for imaging and sterilization of bones, yet the resulting ionization and primary radiation damage mechanisms are poorly understood. Here we monitor in-situ collagen backbone degradation in dry bones using second-harmonic-generation and X-ray diffraction. Collagen breaks down by cascades of photon-electron excitations, enhanced by the presence of mineral nanoparticles. We observe protein disintegration with increasing exposure, detected as residual strain relaxation in pre-stressed apatite nanocrystals. Damage rapidly grows from the onset of irradiation, suggesting that there is no minimal 'safe' dose that bone collagen can sustain. Ionization of calcium and phosphorous in the nanocrystals yields fluorescence and high energy electrons giving rise to structural damage that spreads beyond regions directly illuminated by the incident radiation. Our findings highlight photoelectrons as major agents of damage to bone collagen with implications to all situations where bones are irradiated by hard X-rays and in particular for small-beam mineralized collagen fiber investigations.

Glass-ionomer and calcium silicate-based cements interactions with human dentine in health and disease: Two-photon fluorescence microscopy and Raman spectroscopy analysis

OBJECTIVES

To investigate the potential mineralising effects of calcium silicate-based dentine replacement material (Biodentine™) in comparison with glass-ionomer cement (GIC) (Fuji IX™) on different human dentine substrates using a multimodal non-invasive optical assessment.

METHODS

Cements were applied on artificially demineralised or naturally carious dentine and stored for 4 weeks in phosphate-rich media +/- tetracycline used for mineralisation labelling. Interfacial dentine was examined from the same sample and location before and after aging using two-photon fluorescence microscopy, fluorescence lifetime imaging (FLIM) and second harmonic generation (SHG) imaging. Additionally, Raman spectroscopy was used to detect changes in the mineral content of dentine.

RESULTS

Significant changes in the fluorescence intensity and lifetime were detected in partially demineralised dentine and caries-affected dentine underneath both tested cements, after storage (p < 0.001). This was associated with a significant increase in the mineral content as indicated by the increased intensity of the phosphate Raman peak located at 959 cm^-1 (p < 0.0001). Caries-infected dentine showed significant fluorescence changes under Biodentine™ after storage (p < 0.001), but not under GIC (p = 0.44). Tetracycline binding induced a reduction in the fluorescence lifetime with comparable increase in the fluorescence intensity in both cements' groups within the affected dentine (p < 0.001). Significance Two-photon fluorescence microscopy can be used efficiently for non-destructive in-vitro dentine caries characterisation providing a technique for studying the same dentine-cement interface over time and detect changes. Biodentine™ demonstrated comparable remineralising potential to GIC, in addition to inducing remineralisation of caries-infected dentine. This may suggest using Biodentine™ as part of minimally invasive operative dentistry (MID) in caries management.

Multiphoton microscopy assessment of the structure and variability changes of dermal connective tissue in vulvar lichen sclerosus: A pilot study

In this article, we offer a novel classification of progressive changes in the connective tissue of dermis in vulvar lichen sclerosus (VLS) relying on quantitative assessment of the second harmonic generation (SHG) signal received from formalin fixed and deparaffinized tissue sections. We formulate criteria for distinguishing four degrees of VLS development: Initial-Mild-Moderate-Severe. Five quantitative characteristics (length and thickness type I Collagen fibers, Mean SHG signal intensity, Skewness and Coherence SHG signal) are used to describe the sequential degradation of connective tissue (changes in the structure, orientation, shape and density of collagen fibers) up to the formation of specific homogeneous masses. Each of the degrees has a characteristic set of quantitatively expressed features. We focus on the identification and description of early, initial changes of the dermis as the least specific. The results obtained by us and the proposed classification of the degrees of the disease can be used to objectify the dynamics of tissue changes during treatment.

Birefringence effect studies of collagen formed by nonenzymatic glycation using dual-retarder Mueller polarimetry

SIGNIFICANCE

Nonenzymatic glycation of collagen covalently attaches an addition of sugar molecules that initially were involved in a reversibly reaction with amino groups on the protein. Due to the ultimate formation of stable irreversible advanced glycation end products, the process of glycation leads to abnormal irreversible cross-linking, which ultimately accumulates with age and/or diabetes in the extracellular matrix, altering its organization.

AIM

We report the use of dual-retarder Mueller polarimetry in conjunction with phase retardance to differentiate collagen cross-linking in a normal collagen gel matrix from that in tissues with nonenzymatic cross-linking.

APPROACH

A dual-liquid crystal-based Mueller polarimetry system that involves electronic modulation of polarization state generators (PSGs) was employed to produce all types of polarization states without moving any part and enable detection of the signal directly using a Stokes polarimeter. The linear phase retardance response was obtained for the characterization of the solution and gel forms of collagen using differential Mueller matrix analysis.

RESULTS

We found that linear phase retardance measurements via differential Mueller matrix polarimetry successfully differentiated collagen gel matrices with different degrees of cross-linking formed by a nonenzymatic glycation process and demonstrated that this technology constitutes a quick and simple modality.

CONCLUSIONS

This approach has high sensitivity for studying differences in fibrillar cross-linking in glycated collagen. Further, our work suggests that this method of structural analysis has potential clinical diagnostic value owing to its noninvasive and cost-efficient nature.

Remediating Desmoplasia with EGFR-Targeted Photoactivable Multi-Inhibitor Liposomes Doubles Overall Survival in Pancreatic Cancer

Desmoplasia is characteristic of pancreatic ductal adenocarcinoma (PDAC), which exhibits 5-year survival rates of 3%. Desmoplasia presents physical and biochemical barriers that contribute to treatment resistance, yet depleting the stroma alone is unsuccessful and even detrimental to patient outcomes. This study is the first demonstration of targeted photoactivable multi-inhibitor liposomes (TPMILs) that induce both photodynamic and chemotherapeutic tumor insult, while simultaneously remediating desmoplasia in orthotopic PDAC. TPMILs targeted with cetuximab (anti-EGFR mAb) contain lipidated benzoporphyrin derivative (BPD-PC) photosensitizer and irinotecan. The desmoplastic tumors comprise human PDAC cells and patient-derived cancer-associated fibroblasts. Upon photoactivation, the TPMILs induce 90% tumor growth inhibition at only 8.1% of the patient equivalent dose of nanoliposomal irinotecan (nal-IRI). Without EGFR targeting, PMIL photoactivation is ineffective. TPMIL photoactivation is also sixfold more effective at inhibiting tumor growth than a cocktail of Visudyne-photodynamic therapy (PDT) and nal-IRI, and also doubles survival and extends progression-free survival by greater than fivefold. Second harmonic generation imaging reveals that TPMIL photoactivation reduces collagen density by >90% and increases collagen nonalignment by >103 -fold. Collagen nonalignment correlates with a reduction in tumor burden and survival. This single-construct phototoxic, chemotherapeutic, and desmoplasia-remediating regimen offers unprecedented opportunities to substantially extend survival in patients with otherwise dismal prognoses.

Quantitative and qualitative analysis of pulmonary arterial hypertension fibrosis using wide-field second harmonic generation microscopy

We demonstrated that wide-field second harmonic generation (SHG) microscopy of lung tissue in combination with quantitative analysis of SHG images is a powerful tool for fast and label-free visualization of the fibrosis pathogenesis in pulmonary arterial hypertension (PAH). Statistical analysis of the SHG images revealed changes of the collagen content and morphology in the lung tissue during the monocrotaline-induced PAH progression in rats. First order statistics disclosed the dependence of the collagen overproduction on time, the second order statistics indicated tightening of collagen fiber network around blood vessels and their spreading into the alveolar region. Fourier analysis revealed that enhancement of the fiber orientation in the collagen network with PAH progression was followed with its subsequent reduction at the terminating phase of the disease. Proposed approach has potential for assessing pulmonary fibrosis in interstitial lung disease, after lung(s) transplantation, cancer, etc.

Assessing Collagen D-Band Periodicity with Atomic Force Microscopy

The collagen superfamily includes more than fifty collagen and/or collagen-like proteins with fibril-forming collagen type I being the most abundant protein within the extracellular matrix. Collagen type I plays a crucial role in a variety of functions, it has been associated with many pathological conditions and it is widely used due to its unique properties. One unique nano-scale characteristic of natural occurring collagen type I fibers is the so-called D-band periodicity, which has been associated with collagen natural structure and properties, while it seems to play a crucial role in the interactions between cells and collagen and in various pathological conditions. An accurate characterization of the surface and structure of collagen fibers, including D-band periodicity, on collagen-based tissues and/or (nano-)biomaterials can be achieved by Atomic Force Microscopy (AFM). AFM is a scanning probe microscope and is among the few techniques that can assess D-band periodicity. This review covers issues related to collagen and collagen D-band periodicity and the use of AFM for studying them. Through a systematic search in databases (PubMed and Scopus) relevant articles were identified. The study of these articles demonstrated that AFM can offer novel information concerning D-band periodicity. This study highlights the importance of studying collagen D-band periodicity and proves that AFM is a powerful tool for investigating a number of different properties related to collagen D-band periodicity.

A collagen I derived matricryptin increases aorta vascular wall remodeling after induced thrombosis in mouse

Matricryptins are collagen fragments proteolytically released from the extracellular matrix (ECM) with biological activity that can regulate several processes involved in ECM remodeling. Vessel wall matrix reorganization after lesion is important to the recovery of vascular function. This study aimed to analyze the effect of the peptide p1158/59 (Lindsey, 2015) on thrombosis, neointimal formation, and vascular remodeling of C57BL6 mice abdominal aorta. We used a FeCl₃ induced vascular injury mice model and analyzed thrombus size, neointima formation, gelatinase activities in situ, re-endothelization, and collagen fibers organization on the arterial wall using polarization microscopy. As result, we observed that 2 days after injury the treatment with p1158/59 increased thrombus size and gelatinase activity, vascular lesion and it did not recover the endothelium loss induced by the chemical injury. We also observed that the peptide increased neointima growth and collagen birefringence, indicating collagen fibers reorganization. It also promoted increased re-endothelization and decreased activity of gelatinases 14 days after injury. Thus, we conclude that the peptide p1158/59 impaired the initial thrombosis recovery 2 days after injury but was able to induce vascular ECM remodeling after 14 days, improving vessel re-endothelization, collagen fibers deposition, and organization.

The texture of collagen in the microenvironments of Merkel cell carcinoma

ABSTRACT

Solid tumors typically contain high levels of fibrillar collagen. The increased stromal collagen deposition usually promotes cancer progression since biochemical and biophysical cues from tumor-associated collagen fibers stimulate neoplastic cells. Few studies have investigated the relationship between Merkel cell carcinoma (MCC) and the extracellular matrix (ECM), but there are no works evaluating collagen.This is an observational, analytical, retrospective study including 11 patients with MCC. Primary tumor-stained sections were evaluated by second harmonic generation microscopy and texture analysis.Peritumoral texture features (area fraction, mean gray value, entropy, and contrast) showed much lower values than normal skin (P < .0001) revealing extensively altered structure of peritumoral collagen fibers. These differences were not significant between tumors with unfavorable and favorable known prognostic factors.Profound changes in collagen fibers present in the stroma accompanying primary MCC may contribute to the aggressive behavior of this tumor. Our results indicate that whatever MCC histological subtype, size or anatomical location, MCC promotes the same type of ECM for its development. As an outlook, therapies using ECM macromolecules or fibroblasts (the architects of ECM remodeling) as target could be useful in the treatment of MCC.

Dietary AGEs as Exogenous Boosters of Inflammation

Most chronic modern non-transmissible diseases seem to begin as the result of low-grade inflammation extending over prolonged periods of time. The importance of diet as a source of many pro-inflammatory compounds that could create and sustain such a low-grade inflammatory state cannot be ignored, particularly since we are constantly exposed to them during the day. The focus of this review is on specific components of the diet associated with inflammation, specifically advanced glycation end products (AGEs) that form during thermal processing of food. AGEs are also generated in the body in normal physiology and are widely recognized as increased in diabetes, but many people are unaware of the potential importance of exogenous AGEs ingested in food. We review experimental models, epidemiologic data, and small clinical trials that suggest an important association between dietary intake of these compounds and development of an inflammatory and pro-oxidative state that is conducive to chronic diseases. We compare dietary intake of AGEs with other widely known dietary patterns, such as the Mediterranean and the Dietary Approaches to Stop Hypertension (DASH) diets, as well as the Dietary Inflammation Index (DII). Finally, we delineate in detail the pathophysiological mechanisms induced by dietary AGEs, both direct (i.e., non-receptor-mediated) and indirect (receptor-mediated).

Second harmonic generation light quantifies the ratio of type III to total (I + III) collagen in a bundle of collagen fiber

The ratio of type III to type I collagen is important for properly maintaining functions of organs and cells. We propose a method to quantify the ratio of type III to total (type I + III) collagen (λ_III) in a given collagen fiber bundle using second harmonic generation (SHG) light. First, the relationship between SHG light intensity and the λ_III of collagen gels was examined, and the slope (k₁) and SHG light intensity at 0% type III collagen (k₂) were determined. Second, the SHG light intensity of a 100% type I collagen fiber bundle and its diameter (D) were measured, and the slope (k₃) of the relationship was determined. The λ_III in a collagen fiber bundle was estimated from these constants (k_1-3) and SHG light intensity. We applied this method to collagen fiber bundles isolated from the media and adventitia of porcine thoracic aortas, and obtained λ_III = 84.7% ± 13.8% and λ_III = 17.5% ± 15.2%, respectively. These values concurred with those obtained with a typical quantification method using sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The findings demonstrated that the method proposed is useful to quantify the ratio of type III to total collagen in a collagen fiber bundle.

Advanced glycation end products cause RAGE-dependent annulus fibrosus collagen disruption and loss identified using in situ second harmonic generation imaging in mice intervertebral disk in vivo and in organ culture models

Aging and diabetes are associated with increased low-back pain and intervertebral disk (IVD) degeneration yet causal mechanisms remain uncertain. Advanced glycation end products (AGEs), which accumulate in IVDs from aging and are implicated in diabetes-related disorders, alter collagen and induce proinflammatory conditions. A need exists for methods that assess IVD collagen quality and degradation in order to better characterize specific structural changes in IVDs due to AGE accumulation and to identify roles for the receptor for AGEs (RAGE). We used multiphoton microscopy with second harmonic generation (SHG), collagen-hybridizing peptide (CHP), and image analysis methods to characterize effects of AGEs and RAGE on collagen quality and quantity in IVD annulus fibrosus (AF). First, we used SHG imaging on thin sections with an in vivo dietary mouse model and determined that high-AGE (H-AGE) diets increased AF fibril disruption and collagen degradation resulting in decreased total collagen content, suggesting an early degenerative cascade. Next, we used in situ SHG imaging with an ex vivo IVD organ culture model of AGE challenge on wild type and RAGE-knockout (RAGE-KO) mice and determined that early degenerative changes to collagen quality and degradation were RAGE dependent. We conclude that AGE accumulation leads to RAGE-dependent collagen disruption in the AF and can initiate molecular and tissue level collagen disruption. Furthermore, SHG and CHP analyzes were sensitive to collagenous alterations at multiple hierarchical levels due to AGE and may be useful in identifying additional contributors to collagen damage in IVD degeneration processes.

Imbalanced cellular metabolism compromises cartilage homeostasis and joint function in a mouse model of mucolipidosis type III gamma

Mucolipidosis type III (MLIII) gamma is a rare inherited lysosomal storage disorder caused by mutations in GNPTG encoding the γ-subunit of GlcNAc-1-phosphotransferase, the key enzyme ensuring proper intracellular location of multiple lysosomal enzymes. Patients with MLIII gamma typically present with osteoarthritis and joint stiffness, suggesting cartilage involvement. Using Gnptg knockout (Gnptgko ) mice as a model of the human disease, we showed that missorting of a number of lysosomal enzymes is associated with intracellular accumulation of chondroitin sulfate in Gnptgko chondrocytes and their impaired differentiation, as well as with altered microstructure of the cartilage extracellular matrix (ECM). We also demonstrated distinct functional and structural properties of the Achilles tendons isolated from Gnptgko and Gnptab knock-in (Gnptabki ) mice, the latter displaying a more severe phenotype resembling mucolipidosis type II (MLII) in humans. Together with comparative analyses of joint mobility in MLII and MLIII patients, these findings provide a basis for better understanding of the molecular reasons leading to joint pathology in these patients. Our data suggest that lack of GlcNAc-1-phosphotransferase activity due to defects in the γ-subunit causes structural changes within the ECM of connective and mechanosensitive tissues, such as cartilage and tendon, and eventually results in functional joint abnormalities typically observed in MLIII gamma patients. This idea was supported by a deficit of the limb motor function in Gnptgko mice challenged on a rotarod under fatigue-associated conditions, suggesting that the impaired motor performance of Gnptgko mice was caused by fatigue and/or pain at the joint.This article has an associated First Person interview with the first author of the paper.

Hyperthermia affects collagen fiber architecture and induces apoptosis in pancreatic and fibroblast tumor hetero-spheroids in vitro

Desmoplasia, an aberrant production of extracellular matrix (ECM), is considered as one predictive marker of malignancy of pancreatic cancer. In this paper, we study the effect of mild hyperthermia on fibrillary collagen architecture in murine Achilles tendons and in a pancreatic cancer model, in vitro, i.e. 3D hetero-type tumor spheroids, consisting of pancreatic cancer (Panc-1) cells and fibroblasts (WI-38), producing collagen fibers. We clearly demonstrate that i) mild hyperthermia (40 °C, 42 °C) damages the collagen architecture in murine Achilles tendons. ii) Mild extrinsic (hot air) and iron oxide nanoparticle based magnetic hyperthermia reduce the level of collagen fiber architecture in the generated hetero-type tumor spheroids. iii) Mild magnetic hyperthermia reduces cell vitality mainly through apoptotic and necrotic processes in the generated tumor spheroids. In conclusion, hetero-type 3D tumor spheroids are suitable for studying the effect of hyperthermia on collagen fibers, in vitro.

Diabetes and Collagen: Interrelations

This review summarizes information on interrelations between diabetes development and collagen metabolism and structure. The growing global problem of diabetes requires the search for new strategies of its complications correction. Among them collagen structure violations and/or its impaired metabolism most often lead to profound disability. Even after several decades of intense studies, pathophysiological mechanisms underlying collagen changes in diabetes mellitus are still not well clear. The main complication is that not only diabetes cause changes in collagen metabolism and structure. Collagens via some mechanisms also may regulate glucose homeostasis, both directly and indirectly. The author also presented the results of own studies on bone and skin type I collagen amino acid composition changes with diabetes. Deepening our understanding of collagen metabolism and diabetes interrelations allows us to optimize approaches to overcome the collagen-mediated consequences of this disease. Recently, it has been clearly demonstrated that use of only antidiabetic agents cannot fully correct such violations. Preparations on the base of flavonoids, collagens and amino acids could be considered as perspective directions in this area of drug development.

Label-Free Multiphoton Microscopy: The Origin of Fluorophores and Capabilities for Analyzing Biochemical Processes

Multiphoton microscopy (MPM) is a method of molecular imaging and specifically of intravital imaging that is characterized by high spatial resolution in combination with a greater depth of penetration into the tissue. MPM is a multimodal method based on detection of nonlinear optical signals - multiphoton fluorescence and optical harmonics - and also allows imaging with the use of the parameters of fluorescence decay kinetics. This review describes and discusses photophysical processes within major reporter molecules used in MPM with endogenous contrasts and summarizes several modern experiments that illustrate the capabilities of label-free MPM for molecular imaging of biochemical processes in connective tissue and cells.

Multimodal Optical Diagnostics of Glycated Biological Tissues

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by the disruption of carbohydrate, lipid, and proteins metabolism and development of long-term microvascular, macrovascular, and neuropathic changes. This review presents the results of spectroscopic studies on the glycation of tissues and cell proteins in organisms with naturally developing and model diabetes and in vitro glycated samples in a wide range of electromagnetic waves, from visible light to terahertz radiation. Experiments on the refractometric measurements of glycated and oxygenated hemoglobin in broad wavelength and temperature ranges using digital holographic microscopy and diffraction tomography are discussed, as well as possible application of these methods in the diabetes diagnostics. It is shown that the development and implementation of multimodal approaches based on a combination of phase diagnostics with other methods is another promising direction in the diabetes diagnostics. The possibilities of using optical clearing agents for monitoring the diffusion of substances in the glycated tissues and blood flow dynamics in the pancreas of animals with induced diabetes have also been analyzed.

Characterization of Pancreatic Cancer Tissue Using Multiphoton Excitation Fluorescence and Polarization-Sensitive Harmonic Generation Microscopy

Thin tissue sections of normal and tumorous pancreatic tissues stained with hematoxylin and eosin were investigated using multiphoton excitation fluorescence (MPF), second harmonic generation (SHG), and third harmonic generation (THG) microscopies. The cytoplasm, connective tissue, collagen and extracellular structures are visualized with MPF due to the eosin stain, whereas collagen is imaged with endogenous SHG contrast that does not require staining. Cellular structures, including membranous interfaces and nuclear components, are seen with THG due to the aggregation of hematoxylin dye. Changes in the collagen ultrastructure in pancreatic cancer were investigated by a polarization-sensitive SHG microscopy technique, polarization-in, polarization-out (PIPO) SHG. This involves measuring the orientation of the linear polarization of the SHG signal as a function of the linear polarization orientation of the incident laser radiation. From the PIPO SHG data, the second-order non-linear optical susceptibility ratio, χ(2) zzz '/χ(2) zxx ', was obtained that serves as a structural parameter for characterizing the tissue. Furthermore, by assuming C6 symmetry, an additional second-order non-linear optical susceptibility ratio, χ(2) xyz '/χ(2) zxx ', was obtained, which is a measure of the chirality of the collagen fibers. Statistically-significant differences in the χ(2) zzz '/χ(2) zxx ' values were found between tumor and normal pancreatic tissues in periductal, lobular, and parenchymal regions, whereas statistically-significant differences in the full width at half maximum (FWHM) of χ(2) xyz '/χ(2) zxx ' occurrence histograms were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Additionally, the PIPO SHG data were used to determine the degree of linear polarization (DOLP) of the SHG signal, which indicates the relative linear depolarization of the signal. Statistically-significant differences in DOLP values were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Hence, the differences observed in the χ(2) zzz '/χ(2) zxx ' values, the FWHM of χ(2) xyz '/χ(2) zxx ' values and the DOLP values could potentially be used to aid pathologists in diagnosing pancreatic cancer.

Dietary advanced glycation end-product consumption leads to mechanical stiffening of murine intervertebral discs

Back pain is a leading cause of disability and is strongly associated with intervertebral disc (IVD) degeneration. Reducing structural disruption and catabolism in IVD degeneration remains an important clinical challenge. Pro-oxidant and structure-modifying advanced glycation end-products (AGEs) contribute to obesity and diabetes, which are associated with increased back pain, and accumulate in tissues due to hyperglycemia or ingestion of foods processed at high heat. Collagen-rich IVDs are particularly susceptible to AGE accumulation due to their slow metabolic rates, yet it is unclear whether dietary AGEs can cross the endplates to accumulate in IVDs. A dietary mouse model was used to test the hypothesis that chronic consumption of high AGE diets results in sex-specific IVD structural disruption and functional changes. High AGE diet resulted in AGE accumulation in IVDs and increased IVD compressive stiffness, torque range and failure torque, particularly for females. These biomechanical changes were likely caused by significantly increased AGE crosslinking in the annulus fibrosus, measured by multiphoton imaging. Increased collagen damage measured with collagen hybridizing peptide did not appear to influence biomechanical properties and may be a risk factor as these animals age. The greater influence of high AGE diet on females is an important area of future investigation that may involve AGE receptors known to interact with estrogen. We conclude that high AGE diets can be a source for IVD crosslinking and collagen damage known to be important in IVD degeneration. Dietary modifications and interventions that reduce AGEs warrant further investigation and may be particularly important for diabetics, in whom AGEs accumulate more rapidly.

Summary: Dietary AGEs lead to sex-specific intervertebral disc structural and functional changes and may be targeted for promoting spinal health, especially in diabetes, in which AGEs form rapidly.

Cancer Immunotherapy Getting Brainy: Visualizing the Distinctive CNS Metastatic Niche to Illuminate Therapeutic Resistance

The advent of cancer immunotherapy (CIT) and its success in treating primary and metastatic cancer may offer substantially improved outcomes for patients. Despite recent advancements, many malignancies remain resistant to CIT, among which are brain metastases, a particularly virulent disease with no apparent cure. The immunologically unique niche of the brain has prompted compelling new questions in immuno-oncology such as the effects of tissue-specific differences in immune response, heterogeneity between primary tumors and distant metastases, and the role of spatiotemporal dynamics in shaping an effective anti-tumor immune response. Current methods to examine the immunobiology of metastases in the brain are constrained by tissue processing methods that limit spatial data collection, omit dynamic information, and cannot recapitulate the heterogeneity of the tumor microenvironment. In the current review, we describe how high-resolution, live imaging tools, particularly intravital microscopy (IVM), are instrumental in answering these questions. IVM of pre-clinical cancer models enables short- and long-term observations of critical immunobiology and metastatic growth phenomena to potentially generate revolutionary insights into the spatiotemporal dynamics of brain metastasis, interactions of CIT with immune elements therein, and influence of chemo- and radiotherapy. We describe the utility of IVM to study brain metastasis in mice by tracking the migration and growth of fluorescently-labeled cells, including cancer cells and immune subsets, while monitoring the physical environment within optical windows using imaging dyes and other signal generation mechanisms to illuminate angiogenesis, hypoxia, and/or CIT drug expression within the metastatic niche. Our review summarizes the current knowledge regarding brain metastases and the immune milieu, presents the current status of CIT and its prospects in targeting brain metastases to circumvent therapeutic resistance, and proposes avenues to utilize IVM to study CIT drug delivery and therapeutic efficacy in preclinical models that will ultimately facilitate novel drug discovery and innovative combination therapies.

Quantification of collagen organization in histopathology samples using liquid crystal based polarization microscopy

A number of histopathology studies have utilized the label free microscopy method of Second Harmonic Generation (SHG) to investigate collagen organization in disease onset and progression. Here we explored an alternative label free imaging approach, LC-PolScope that is based on liquid crystal based polarized light imaging. We demonstrated that this more accessible technology has the ability to visualize all fibers of interest and has a good to excellent correlation between SHG and LC-PolScope measurements in fibrillar collagen orientation and alignment. This study supports that LC-PolScope is a viable alternative to SHG for label free collagen organization measurements in thin histology sections.

Two-photon autofluorescence lifetime imaging of human skin papillary dermis in vivo: assessment of blood capillaries and structural proteins localization

The papillary dermis of human skin is responsible for its biomechanical properties and for supply of epidermis with chemicals. Dermis is mainly composed of structural protein molecules, including collagen and elastin, and contains blood capillaries. Connective tissue diseases, as well as cardiovascular complications have manifestations on the molecular level in the papillary dermis (e.g. alteration of collagen I and III content) and in the capillary structure. In this paper we assessed the molecular structure of internal and external regions of skin capillaries using two-photon fluorescence lifetime imaging (FLIM) of endogenous compounds. It was shown that the capillaries are characterized by a fast fluorescence decay, which is originated from red blood cells and blood plasma. Using the second harmonic generation signal, FLIM segmentation was performed, which provided for spatial localization and fluorescence decay parameters distribution of collagen I and elastin in the dermal papillae. It was demonstrated that the lifetime distribution was different for the inner area of dermal papillae around the capillary loop that was suggested to be due to collagen III. Hence, we propose a generalized approach to two-photon imaging of the papillary dermis components, which extends the capabilities of this technique in skin diagnosis.

Bovine and degenerated human annulus fibrosus: a microstructural and micromechanical comparison

The complex structure of the annulus fibrosus is strongly related to its mechanical properties. Recent work showed that it is possible to observe the relative movement of fibre bundles in loaded cow tail annulus; the aim of this work was to describe and quantify annulus fibrosus micromechanics in degenerated human disc, and compare it with cow tail annulus, an animal model often used in the literature. Second harmonic generation was used to image the collagen matrix in twenty strips of annulus fibrosus harvested from intervertebral disc of seven patients undergoing surgery. Samples were loaded to 6% tensile strain in 1% steps. Elastic modulus was calculated from loading curves, and micromechanical strains were calculated from the images using custom software. The same protocol was applied to twenty strips of annulus harvested from cow tail discs. Significant morphological differences were found between human and cow tail samples, the most striking being the lack of collagen fibre crimp in the former. Fibres were also observed bending and running from one lamella to the other, forming a strong flexible interface. Interdigitation of fibre bundles was also present at this interface. Quantitative results show complex patterns of inter-bundle and inter-lamellar behaviour, with inter-bundle sliding being the main strain mechanism. Elastic modulus was similar between species, and it was not affected by the degree of degeneration. This work gives an insight into the complex structure and mechanical function of the annulus fibrosus, which should be accounted for in disc numerical modelling.

(Second) Harmonic Disharmony: Nonlinear Microscopy Shines New Light on the Pathology of Atherosclerosis

There has been increasing interest in second harmonic generation (SHG) imaging approaches for the investigation of atherosclerosis due to the deep penetration and three-dimensional sectioning capabilities of the nonlinear optical microscope. Atherosclerosis involves remodeling or alteration of the collagenous framework in affected vessels. The disease is often characterized by excessive collagen deposition and altered collagen organization. SHG has the capability to accurately characterize collagen structure, which is an essential component in understanding atherosclerotic lesion development and progression. As a structure-based imaging modality, SHG is most impactful in atherosclerosis evaluation in conjunction with other, chemically specific nonlinear optics (NLO) techniques to identify additional components of the lesion. These include the use of coherent anti-Stokes Raman scattering and two-photon excitation fluorescence for studying atherosclerosis burden, and application of stimulated Raman scattering to image cholesterol crystals. However, very few NLO studies have attempted to quantitate differences in control versus atherosclerotic states or to correlate the application to clinical situations. This review highlights the potential of SHG imaging to directly and indirectly describe atherosclerosis as a pathological condition.

Connection of Jones and Mueller Tensors in Second Harmonic Generation and Multi-Photon Fluorescence Measurements

Despite the rapidly growing use of second harmonic generation (SHG) and two-photon excited fluorescence (TPEF) microscopy, opportunities for relating polarization-dependent measurements back to local structure and molecular orientation are often confounded by losses in polarization purity. In this work, connections linking Mueller tensor and Jones tensor descriptions of polarization-dependent SHG and TPEF are shown to substantially simplify partially depolarized microscopy measurements. These connections were facilitated by the derivation of several new tensor identity relations, based on generalization of established transformations of matrices and vectors. Methods are described for integrating local-frame symmetry and azimuthal rotation angle for simplifying the Mueller tensor. Through simple expressions bridging the Mueller and Jones formalisms, mathematical models for partial depolarization can greatly simplify interpretation of SHG and TPEF measurements to reconstruct the more general Mueller tensors using the much more concise Jones descriptions for the purely polarized components. Integrating the Mueller architecture allows polarization-dependent SHG and TPEF measurements to be connected back to a relatively small set of free parameters related to local structure and orientation.

Measurement of lacunar bone strains and crack formation during tensile loading by digital volume correlation of second harmonic generation images

The maintenance of healthy bone tissue depends upon the ability of osteocytes to respond to mechanical cues on the cellular level. The combination of digital volume correlation and second harmonic generation microscopy offers the opportunity to investigate the mechanical microenvironment of intact bone on the scale of individual osteocytes. Adult human femurs were imaged under tensile loads of 5 and 15MPa and volumes of approximately 492×429×31μm(3) were analyzed, along with an image of a bone microcrack under the same loading conditions. Principal strains were significantly higher in three-dimensional digital volume correlation when compared to two-dimensional digital image correlation. The average maximum principal strain magnitude was 5.06-fold greater than the applied global strain, with peak strains of up to 23.14-fold over global strains measured at the borders of osteocyte lacunae. Finally, a microcrack that initiated at an osteocyte lacunae had its greatest tensile strain magnitudes at the crack expansion front in the direction of a second lacunae, but strain at the crack border was reduced to background strain magnitudes upon breaching the second lacunae. This serveed to demonstrate the role of lacunae in initiating, mediating and terminating microcrack growth.

Changes of skin collagen orientation associated with chronological aging as probed by polarized-FTIR micro-imaging

During chronological skin aging, alterations in dermal structural proteins cause morphological modifications. Modifications are probably due to collagen fiber (type I collagen) rearrangement and reorientation with aging that have not been researched until now. FTIR microspectroscopy appears as an interesting method to study protein structure under normal and pathological conditions. Associated with a polarizer, this vibrational technique permits us to probe collagen orientation within skin tissue sections, by computing the ratio of integrated intensities of amide I and amide II bands. In this study, we used the polarized-FTIR imaging to evaluate molecular modifications of dermal collagen during chronological aging. The data processing of polarized infrared data revealed that type I collagen fibers become parallel to the skin surface in aged skin dermis. Our approach could find innovative applications in dermatology as well as in cosmetics.

Effect of peroxide bleaching on the biaxial flexural strength and modulus of bovine dentin

Objective:

This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin.

Materials and Methods:

Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined α = 0.05).

Results:

The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching.

Conclusion:

Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.

Tissue responses to postoperative laser therapy in diabetic rats submitted to excisional wounds

In a previous study about low-level laser therapy biomodulation on a full-thickness burn model we showed that single and fractionated dose regimens increased wound healing and leukocyte influx similarly when compared with untreated control. In order to verify if this finding would be similar in an impaired wound model, we investigated the effect of single and multiple irradiations on wound closure rate, type of inflammatory infiltrate, myofibroblasts, collagen deposition, and optical retardation of collagen in diabetic rats. Female Wistar rats in the same estrous cycle had diabetes induced with streptozotocin and an 8-mm excisional wound performed with a punch. The experimental groups were: control group--untreated ulcer; single-dose group--ulcer submitted to single dose of diode laser therapy (λ = 660 ± 2 nm; P = 30 mW; energy density: 4 J/cm2) and fractionated-dose group--ulcer submitted to 1 J/cm2 laser therapy on Days 1, 3, 8, and 10. The ulcers were photographed on the experimental days and after euthanasia tissue samples were routinely processed for histological and immunohistochemistry analyses. Independently of the energy density, laser therapy accelerated wound closure by approximately 40% in the first three days in comparison to the control group. Laser therapy increased acute inflammatory infiltrate until Day 3. Both laser groups exhibited more myofibroblasts and better collagen organization than the control group. The findings demonstrate that low-level laser therapy in the immediate postoperative period can enhance the tissue repair process in a diabetes model. Similar effects were achieved with laser therapy applied a single time with an energy density of 4 J/cm2 and applied four times with an energy density of 1 J/cm2. The application of laser therapy in the inflammatory phase was the most important factor to the enhancement of the tissue repair process.

Ex vivo optical measurements of glucose diffusion kinetics in native and diabetic mouse skin

The aim of this study was to estimate the glucose diffusion coefficients ex vivo in skin of mice with diabetes induced in vivo by alloxan in comparison to non-diabetic mice. The temporal dependences of collimated transmittance of tissue samples immersed in glucose solutions were measured in the VIS-NIR spectral range to quantify the glucose diffusion/permeability coefficients and optical clearing efficiency of mouse skin. The average thickness of intact healthy and diabetic skin was 0.023 ± 0.006 cm and 0.019 ± 0.005 cm, respectively. Considerable differences in optical and kinetic properties of diabetic and non-diabetic skin were found: clearing efficiency was 1.5-fold better and glucose diffusivity was 2-fold slower for diabetic skin. Experimental Setup for measuring collimated transmittance spectra of mouse skin samples.

Second-harmonic generation imaging of cancer

The last 30 years has seen great advances in optical microscopy with the introduction of sophisticated fluorescence-based imaging methods such as confocal and multiphoton laser scanning microscopy. There is increasing interest in using these methods to quantitatively examine sources of intrinsic biological contrast including autofluorescent endogenous proteins and light interactions such as second-harmonic generation (SHG) in collagen. In particular, SHG-based microscopy has become a widely used quantitative modality for imaging noncentrosymmetric proteins such as collagen in a diverse range of tissues. Due to the underlying physical origin of the SHG signal, it is highly sensitive to collagen fibril/fiber structure and, importantly, to collagen-associated changes that occur in diseases such as cancer, fibrosis, and connective tissue disorders. An overview of SHG physics background and technologies is presented with a focused review on applications of SHG primarily as applied to cancer.

Multimodal optical characterisation of collagen photodegradation by femtosecond infrared laser ablation

Collagen is a structural component of the human body, as a connective tissue it can become altered as a result of pathophysiological conditions. Although the collagen degradation mechanism is not fully understood, it plays an important role in ageing, disease progression and applications in therapeutic laser treatments. To fully understand the mechanism of collagen alteration, in our study photo-disruptive effects were induced in collagen I matrix by point-irradiation with a femtosecond Ti-sapphire laser under controlled laser ablation settings. This was followed by multi-modal imaging of the irradiated and surrounding areas to analyse the degradation mechanism. Our multi-modal methodology was based on second harmonic generation (SHG), scanning electron microscope (SEM), autofluorescence (AF) average intensities and the average fluorescence lifetime. This allowed us to quantitatively characterise the degraded area into four distinct zones: (1) depolymerised zone in the laser focal spot as indicated by the loss of SHG signal, (2) enhanced crosslinking zone in the inner boundary of the laser induced cavity as represented by the high fluorescence ring, (3) reduced crosslinking zone formed the outer boundary of the cavity as marked by the increased SHG signal and (4) native collagen. These identified distinct zones were in good agreement with the expected photochemical changes shown using Raman spectroscopy. In addition, imaging using polarisation-resolved SHG (p-SHG) revealed both a high degree of fibre re-orientation and a SHG change in tensor ratios around the irradiation spot. Our multi-modal optical imaging approach can provide a new methodology for defining distinct zones that can be used in a clinical setting to determine suitable thresholds for applying safe laser treatments without affecting the surrounding tissues. Furthermore this technique can be extended to address challenges observed in collagen based tissue engineering and used as a minimally invasive diagnostic tool to characterise diseased and non-diseased collagen rich tissues.

Measuring strain using digital image correlation of second harmonic generation images

The micromechanical environment of bone is crucial to understanding both bone fracture and mechanobiological responses of osteocytes, yet few techniques exist that are capable of measuring strains on the micrometer scale. A method for measuring micrometer level strains has been developed based on digital image correlation (DIC) of second harmonic generation microscopy (SHGM) images. Bovine tibias milled into thin sections were imaged using SHGM under loads of 0 and 15 MPa. Strains were measured using DIC and compared to applied strain values. First and second principal strains decreased in magnitude as the analysis region area increased from 1750 µm(2) to 60,920 µm(2), converging to 1.23 ± 0.74 and -0.745 ± 0.9816 times the applied strain respectively. A representative sample histogram revealed regions of pure tensile and compressive strain, and that strains were highly heterogeneous ranging from 8410 to -8840 microstrain for an applied 2870 microstrain. Comparison with applied strain measures suggested that analysis sizes of 1750 µm(2) and greater were measuring strains on the tissue scale, and higher resolution is required for collagen fibrillar strains. Regions of low SHGM intensity ("dark" regions) were seen which are believed to be lacunar and perilacunar regions of low collagen density. However, no significant differences in strain magnitude were present in dark regions versus regions of high signal intensity. The proposed technique is effective for strains on the size order of bone microarchitecture, and would be useful for studies into the mechanical microenvironment during loading. The technique also has potential for in vivo studies in small animal models.

Thermal transitions of fibrillar collagen unveiled by second-harmonic generation microscopy of corneal stroma

The thermal transitions of fibrillar collagen are investigated with second-harmonic generation polarization anisotropy microscopy. Second-harmonic generation images and polarization anisotropy profiles of corneal stroma heated in the 35-80°C range are analyzed by means of a theoretical model that is suitable to probe principal intramolecular and interfibrillar parameters of immediate physiological interest. Our results depict the tissue modification with temperature as the interplay of three destructuration stages at different hierarchical levels of collagen assembly including its tertiary structure and interfibrillar alignment, thus supporting and extending previous findings. This method holds the promise of a quantitative inspection of fundamental biophysical and biochemical processes and may find future applications in real-time and postsurgical functional imaging of collagen-rich tissues subjected to thermal treatments.

Birefringence and second harmonic generation on tendon collagen following red linearly polarized laser irradiation

Regarding the importance of type I collagen in understanding the mechanical properties of a range of tissues, there is still a gap in our knowledge of how proteins perform such work. There is consensus in literature that the mechanical characteristics of a tissue are primarily determined by the organization of its molecules. The purpose of this study was to characterize the organization of non-irradiated and irradiated type I collagen. Irradiation was performed with a linearly polarized HeNe laser (λ = 632.8 nm) and characterization was undertaken using polarized light microscopy to investigate the birefringence and second harmonic generation to analyze nonlinear susceptibility. Rats received laser irradiation (P = 6.0 mW, I = 21.2 mW/cm(2), E ≈ 0.3 J, ED = 1.0 J/cm(2)) on their healthy Achilles tendons, which after were extracted to prepare the specimens. Our results show that irradiated samples present higher birefringence and greater non-linear susceptibility than non-irradiated samples. Under studied conditions, we propose that a red laser with polarization direction aligned in parallel to the tendon long axis promotes further alignment on the ordered healthy collagen fibrils towards the electric field incident. Thus, prospects for biomedical applications for laser polarized radiation on type I collagen are encouraging since it supports greater tissue organization.

Diabetes-mediated changes in rat type i collagen and spermatogenesis indices

Objectives: To investigate the effects of diabetes on the reproductive system andextracellular matrix proteins of diabetic rats. Materials and Methods: Wistar albinomale rats, body weight (BW) 160-200 g, were divided into two groups: I -streptozoticin diabetes, II - normal non-diabetic animals. The content of amino acidsin rat type I collagen was determined using an amino acid analyzer. Morphologicalanalyses of gonadic structures were carried out by an optic microscope. Results: Thestudy of the effects of diabetes on type I collagen amino acid content, testis cellsmorphologic and morphometric parameters and spermatogenesis demonstrated thepresence of diabetes-mediated quantitative and qualitative changes in male ratreproductive organs, spermatogenetic epithelial cells and extracellular matrixproteins in comparison with normal. Conclusions: Observed collagen moleculeschanges could hence affect the properties and correct functioning of spermatogeneticepithelium and of other tissues of reproductive organs. They could be caused bydiabetes via deficiency of insulin which is involved in collagen synthesis regulationat different stages of this process, cytochrome P450-2E1 induction and reactiveoxygen species effects on protein biosynthesis processes.

Two-photon and second harmonic microscopy in clinical and translational cancer research

Application of two-photon microscopy (TPM) to translational and clinical cancer research has burgeoned over the last several years, as several avenues of pre-clinical research have come to fruition. In this review, we focus on two forms of TPM-two-photon excitation fluorescence microscopy, and second harmonic generation microscopy-as they have been used for investigating cancer pathology in ex vivo and in vivo human tissue. We begin with discussion of two-photon theory and instrumentation particularly as applicable to cancer research, followed by an overview of some of the relevant cancer research literature in areas that include two-photon imaging of human tissue biopsies, human skin in vivo, and the rapidly developing technology of two-photon microendoscopy. We believe these and other evolving two-photon methodologies will continue to help translate cancer research from the bench to the bedside, and ultimately bring minimally invasive methods for cancer diagnosis and treatment to therapeutic reality.

Effects of zero-length and non-zero-length cross-linking reagents on the optical spectral properties and structures of collagen hydrogels

We compared the effects of zero-length cross-linkers 1-ethyl-3 (3dimethylaminopropyl) carbodiimide (EDC) and non-zero-length cross-linkers glycolaldehyde and glyceraldehyde on the optical and structural properties of three-dimensional (3D) collagen hydrogels. We evaluated these effects by multiphoton microscopy (MPM) that combined two-photon fluorescence (TPF) and second harmonic generation (SHG) contrasts and transmission electron microscopy (TEM). The collagen hydrogels were incubated separately with the above-mentioned reagents present at the concentration of 0.1 M. The incubation with glycolaldehyde and glyceraldehyde induced strong autofluorescence within the gels. We followed the formation of fluorescence with TPF signals in situ and in real time as well as characterized the micro- and nanostructures within cross-linked hydrogels by examining SHG and TEM images respectively. As detected in the SHG images, glycolaldehyde- and glyceraldehyde-modified 5-10 μm "fiberlike" collagen structures to longer, 20 μm and more, aggregated strands while EDC had minimal effect on the microstructure. TEM revealed that glycolaldehyde and glyceraldehyde either completely eliminated collagen's characteristic native fibrillar striations or generated uncharacteristic fibrils with extensions. EDC preserved the native striation patterns, decreased the fibril diameters and effectively homogenized the fibrils within hydrogels assembled at 1.8-4.68 g/L collagen concentrations and 37 °C. Our findings provide a clear understanding on how different cross-linking reagents have very different effects on the collagen hydrogels. This understanding is critical for advancing tissue engineering and wound healing applications.

3D nanometer images of biological fibers by directed motion of gold nanoparticles

Using near-infrared femtosecond pulses, we move single gold nanoparticles (AuNPs) along biological fibers, such as collagen and actin filaments. While the AuNP is sliding on the fiber, its trajectory is measured in three dimensions (3D) with nanometer resolution providing a high-resolution image of the fiber. Here, we systematically moved a single AuNP along nanometer-size collagen fibers and actin filament inside chinese hamster ovary K1 living cells, mapping their 3D topography with high fidelity.