A new ex vivo human model of osteoarthritis cartilage calcification

OBJECTIVE

Cartilage pathologic calcification is a hallmark of osteoarthritis (OA). Here, we aimed to describe a new ex vivo human model to study the progression of cartilage calcification.

METHOD

Cartilage explants (n = 11), as well as primary chondrocytes (n = 3), were obtained from OA patients undergoing knee replacement. Explants and chondrocytes were cultured in control (NT) or calcification (CM) medium (supplemented with ascorbic acid and β-glycerophosphate). Calcification was evaluated by micro-CT scan at day 0 and 21 in explants, and by Alizarin red staining in chondrocyte monolayers. Raman spectrometry allowed characterization of the crystal type. Interleukin-6 (IL-6) secretion in explant and cell supernatants was measured by ELISA. Finally, matrix degradation was evaluated by Safranin-O staining of explant sections and by glycosaminoglycans (GAG) release in supernatants.

RESULTS

Micro-CT scan showed calcifications in all explants at baseline (day 0), which in the CM group increased significantly in number and size after 21 days compared with the NT group. Raman spectrometry revealed that crystals were exclusively basic calcium phosphate crystals (carbonated hydroxyapatite) both in NT and CM. IL-6 secretion was significantly increased in calcifying conditions. Finally, CM significantly increased cartilage catabolism as assessed by decreased Safranin-O staining of tissue explants and increased GAG release in supernatants. CM effects (enhanced calcification, IL-6 secretion and proteoglycans turn-over) were recapitulated in vitro in OA chondrocytes.

CONCLUSIONS

We have described a new ex vivo human model of cartilage calcification that can summurize the triad of events seen during osteoarthritis progression, i.e. calcification, inflammation, and cartilage degradation. This model will allow the identification of new anti-calcification compounds.

The extracellular matrix of human bone marrow adipocytes and glucose concentration differentially alter mineralization quality without impairing osteoblastogenesis

Bone marrow adipocytes (BMAds) accrue in various states of osteoporosis and interfere with bone remodeling through the secretion of various factors. However, involvement of the extracellular matrix (ECM) produced by BMAds in the impairment of bone marrow mesenchymal stromal cell (BM-MSC) osteoblastogenesis has received little attention. In type 2 diabetes (T2D), skeletal fragility is associated with several changes in bone quality that are incompletely understood, and BMAd quantity increases in relationship to poor glycemic control. Considering their altered phenotype in this pathophysiological context, we aimed to determine the contribution of the ECM of mature BMAds to osteoblastogenesis and mineralization quality in the context of chronic hyperglycemia.

Human BM-MSCs were differentiated for 21 days in adipogenic medium containing either a normoglycemic (LG, 5.5 mM) or a high glucose concentration (HG, 25 mM). The ECM laid down by BMAds were devitalized through cell removal to examine their impact on the proliferation and differentiation of BM-MSCs toward osteoblastogenesis in LG and HG conditions. Compared to control plates, both adipocyte ECMs promoted cell adhesion and proliferation. As shown by the unmodified RUNX2 and osteocalcin mRNA levels, BM-MSC commitment in osteoblastogenesis was hampered by neither the hyperglycemic condition nor the adipocyte matrices. However, adipocyte ECMs or HG condition altered the mineralization phase with perturbed expression levels of type 1 collagen, MGP and osteopontin. Despite higher ALP activity, mineralization levels per cell were decreased for osteoblasts grown on adipocyte ECMs compared to controls. Raman spectrometry revealed that culturing on adipocyte matrices specifically prevents type-B carbonate substitution and favors collagen crosslinking, in contrast to exposure to HG concentration alone. Moreover, the mineral to organic ratio was disrupted according to the presence of adipocyte ECM and the glucose concentration used for adipocyte or osteoblast culture. HG concentration and adipocyte ECM lead to different defects in mineralization quality, recapitulating contradictory changes reported in T2D osteoporosis.

Our study shows that ECMs from BMAds do not impair osteoblastogenesis but alter both the quantity and quality of mineralization partly in a glucose concentration-dependent manner. This finding sheds light on the involvement of BMAds, which should be considered in the compromised bone quality of T2D and osteoporosis patients more generally.

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Glucose level alters the Extracellular Matrix composition of Bone Marrow adipocytes.

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Osteoblastogenesis on adipocyte ECMs is unaltered but produced less mineral amount.

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The quality of the mineral is altered differently by adipocyte ECMs or glucose levels.

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The presence of BM adipocytes should be valued in damaged osteoporosis bone quality.

Material and nanomechanical properties of bone structural units of cortical and trabecular iliac bone tissues from untreated postmenopausal osteoporotic women

The differences in bone nanomechanical properties between cortical (Ct) and trabecular (Tb) bone remain uncertain, whereas knowing the respective contribution of each compartment is critical to understand the origin of bone strength. Our purpose was to compare bone mechanical and intrinsic properties of Ct and Tb compartments, at the bone structural unit (BSU) level, in iliac bone taken from a homogeneous untreated human population.

Among 60 PMMA-embedded transiliac bone biopsies from untreated postmenopausal osteoporotic women (64 ± 7 year-old), >2000 BSUs were analysed by nanoindentation in physiological wet conditions [indentation modulus (elasticity), hardness, dissipated energy], by Fourier transform infrared (FTIRM) and Raman microspectroscopy (mineral and organic characteristics), and by X-ray microradiography (degree of mineralization of bone, DMB). BSUs were categorized based on tissue age, osteonal (Ost) and interstitial (Int) tissues location and bone compartments (Ct and Tb).

Indentation modulus was higher in Ct than in Tb BSUs, both in Ost and Int. dissipated energy was higher in Ct than Tb, in Int BSUs. Hardness was not different between Ct and Tb BSUs. In Ost or Int BSUs, mineral maturity (conversion of non-apatitic into apatitic phosphates) was higher in Ct than in Tb, as well as for collagen maturity (Ost). Mineral content assessed as mineral/matrix (FTIRM and Raman) or as DMB, was lower in Ct than in Tb. Crystallinity (FTIRM) was similar in BSUs from Ct and Tb, and slightly lower in Ct than in Tb when measured by Raman, indicating that the crystal size/perfection was quite similar between Ct and Tb BSUs. The differences found between Ost and Int tissues were much higher than the difference found between Ct and Tb for all those bone material properties. Multiple regression analysis showed that Indentation modulus and dissipated energy were mainly explained by mineral maturity in Ct and by collagen maturity in Tb, and hardness by mineral content in both Ct and Tb.

In conclusion, in untreated human iliac bone, Ct and Tb BSUs exhibit different characteristics. Ct BSUs have higher indentation modulus, dissipated energy (Int), mineral and organic maturities than Tb BSUs, without difference in hardness. Although those differences are relatively small compared to those found between Ost and Int BSUs, they may influence bone strength at macroscale.

Subchondral involvement in osteonecrosis of the femoral head: insight on local composition, microstructure and vascularization

OBJECTIVE

To determine changes of subchondral bone composition, micro-structure, bone marrow adiposity and micro-vascular perfusion in end-stage osteonecrosis of the femoral head (ONFH) compared to osteoarthritis (OA) using a combined in vivo and ex vivo approach.

DESIGN

Male patients up to 70 years old referred for total hip replacement surgery for end-stage ONFH were included (n = 14). Fifteen patients with OA were controls. Pre-operative MRI was used to assess bone perfusion (dynamic contrast-enhanced (DCE) sequences) and marrow fat content (chemical shift imaging). Three distinct zones of femoral head subchondral bone - necrotic, sclerotic, distant - were compared between groups. After surgery, plugs were sampled in these zones and Raman spectroscopy was applied to characterize bone mineral and organic components (old and newly-formed), and contrast-enhanced micro-computed tomography (CE-μCT) to determine bone micro-structural parameters and volume of bone marrow adipocytes, using conventional 2D histology as a reference.

RESULTS

In the necrotic zone of ONFH patients compared to OA patients: 1) the subchondral plate did not exhibit significant changes in composition nor structure; 2) the volume fraction of subchondral trabecular bone was significantly lower; 3) type-B carbonate substitution was less pronounced, 4) collagen maturity was more pronounced; and 5) bone marrow adipocytes were significantly depleted. The sclerotic zone from the ONFH group showed greater trabecular thickness, and higher DCE-MRI AUC and K_trans. Volume fraction of subchondral bone, trabecular number, and K_ep were significantly lower in the distant zone of the ONFH group.

CONCLUSIONS

This study demonstrated alterations of subchondral bone microstructure, composition, perfusion and/or adipose content in all zones of the femoral head.

Critical aspects of Raman spectroscopy as a tool for postmortem interval estimation

The estimation of the postmortem interval (PMI) from skeletal remains represents a challenging task in forensic science. PMI is often influenced by extrinsic factors (humidity, dryness, scavengers, etc.) and intrinsic factors (age, sex, pathology, way of life, medical treatments, etc.). Raman spectroscopy combined with multivariate data analysis represents a promising tool for forensic anthropologists. Despite all the advantages of the technique, Raman spectra of skeletal remains are influenced by these extrinsic and intrinsic factors, which impairs precision and reproducibility. Both parameters have to reach a high level of confidence when such spectroscopy is used as a way to predict PMI. As a consequence, advanced multivariate data analysis is necessary to quantify the effect of all factors to improve the estimation of the PMI. The objective of this work is to evaluate the effect of intrinsic and extrinsic factors on the Raman spectra of skeletal remains. We designed a protocol close to a real-world scenario. We used ANOVA-simultaneous component analysis (ASCA) to unmix and quantify the effect of 1 intrinsic (source body) and 1 extrinsic (burial time) factors on the Raman spectra. In our model, the burial time was found to generate the highest variability after the source body. ASCA showed that the variability due to the burial time has 2 mixed contributions. Seasonal variations are the first contribution. The second contribution is attributed to diagenesis. A decrease in the mineral bands and an increase in the organic bands are observed. The source body was also found to contribute to the variability in Raman spectra. ASCA showed that the source body induces variability related to the composition of bones. This quantification cannot be assessed by basic chemometrics methods such as PCA. The results of this study highlighted the need to use an advanced chemometric data analysis tool (like ASCA) combined with Raman spectroscopy to estimate the postmortem interval.

Severity Level and Duration of Energy Deficit in Mice Affect Bone Phenotype and Bone Marrow Stromal Cell Differentiation Capacity

Anorexia nervosa is known to induce changes in bone parameters and an increase in bone marrow adiposity (BMA) that depend on the duration and seriousness of the disease. Previous studies have found that bone loss is associated with BMA accumulation. Sirtuin of type 1 (Sirt1), a histone deacetylase that is partly regulated by energy balance, was shown to have pro-osteoblastogenic and anti-adipogenic effects. To study the effects of the severity and duration of energy deficits related to bone loss, a mouse model of separation-based anorexia (SBA) was established. We recently demonstrated that moderate body weight loss (18%) 8-week SBA protocol in mice resulted in an increase in BMA, bone loss, and a significant reduction in Sirt1 expression in bone marrow stromal cells (BMSCs) extracted from SBA mice. We hypothesised that Sirt1 deficit in BMSCs is associated with bone and BMA alterations and could potentially depend on the severity of weight loss and the length of SBA protocol. We studied bone parameters, BMA, BMSC differentiation capacity, and Sirt1 expression after induction of 4 different levels of body weight loss (0%,12%,18%,24%), after 4 or 10 weeks of the SBA protocol. Our results demonstrated that 10 week SBA protocols associated with body weight loss (12%, 18%, 24%) induced a significant decrease in bone parameters without any increase in BMA. BMSCs extracted from 12% and 18% SBA groups showed a significant decrease in Sirt1 mRNA levels before and after co-differentiation. For these two groups, decrease in Sirt1 was associated with a significant increase in the mRNA level of adipogenic markers and a reduction of osteoblastogenesis. Inducing an 18% body weight loss, we tested a short SBA protocol (4-week). We demonstrated that a 4-week SBA protocol caused a significant decrease in Tb.Th only, without change in other bone parameters, BMA, Sirt1 expression, or differentiation capacity of BMSCs. In conclusion, this study showed, for the first time, that the duration and severity of energy deficits are critical for changes in bone parameters, BMSC differentiation, and Sirt1 expression. Furthermore, we showed that in this context, Sirt1 expression could impact BMSC differentiation with further effects on bone phenotype.

Raman microspectroscopy reveals unsaturation heterogeneity at the lipid droplet level and validates an in vitro model of bone marrow adipocyte subtypes

Bone marrow adipocytes (BMAds) constitute the most abundant stromal component of adult human bone marrow. Two subtypes of BMAds have been described, the more labile regulated adipocytes (rBMAds) and the more stable constitutive adipocytes (cBMAds), which develop earlier in life and are more resilient to environmental and metabolic disruptions. In vivo, rBMAds are enriched in saturated fatty acids, contain smaller lipid droplets (LDs) and more readily provide hematopoietic support than their cBMAd counterparts. Mouse models have been used for BMAds research, but isolation of primary BMAds presents many challenges, and thus in vitro models remain the current standard to study nuances of adipocyte differentiation. No in vitro model has yet been described for the study of rBMAds/cBMAds. Here, we present an in vitro model of BM adipogenesis with differential rBMAd and cBMAd-like characteristics. We used OP9 BM stromal cells derived from a (C57BL/6xC3H)F2-op/op mouse, which have been extensively characterized as feeder layer for hematopoiesis research. We observed similar canonical adipogenesis transcriptional signatures for spontaneously-differentiated (sOP9) and induced (iOP9) cultures, while fatty acid composition and desaturase expression of Scd1 and Fads2 differed at the population level. To resolve differences at the single adipocyte level we tested Raman microspectroscopy and show it constitutes a high-resolution method for studying adipogenesis in vitro in a label-free manner, with resolution to individual LDs. We found sOP9 adipocytes have lower unsaturation ratios, smaller LDs and higher hematopoietic support than iOP9 adipocytes, thus functionally resembling rBMAds, while iOP9 more closely resembled cBMAds. Validation in human primary samples confirmed a higher unsaturation ratio for lipids extracted from stable cBMAd-rich sites (femoral head upon hip-replacement surgery) versus labile rBMAds (iliac crest after chemotherapy). As a result, the 16:1/16:0 fatty acid unsaturation ratio, which was already shown to discriminate BMAd subtypes in rabbit and rat marrow, was validated to discriminate cBMAds from rBMAd in both the OP9 model in vitro system and in human samples. We expect our model will be useful for cBMAd and rBMAd studies, particularly where isolation of primary BMAds is a limiting step.

Bone matrix quality in paired iliac bone biopsies from postmenopausal women treated for 12 months with strontium ranelate or alendronate

Bone quality is altered mainly by osteoporosis, which is treated with modulators of bone quality. Knowledge of their mechanisms of action is crucial to understand their effects on bone quality. The goal of our study was to compare the action of alendronate (ALN) and strontium ranelate (SrRan) on the determinants of bone quality. The investigation was performed on over 60 paired human iliac biopsies. Paired samples correspond to biopsies obtained from the same patient, one before treatment (baseline) and one after 12 months of treatment, in postmenopausal women with osteoporosis. Vibrational spectroscopy (Raman and FTIRM) and nanoindentation were used to evaluate the effect of both drugs on bone quality at the ultrastructural level. Outcomes measured by vibrational spectroscopy and nanoindentation are sensitive to bone age. New bone packets are distinguished from old bone packets. Thus, the effect of bone age is distinguished from the treatment effect. Both drugs modify the mineral and organic composition in new and old bone in different fashions after 12 months of administration. The new bone formed during ALN administration is characterized by an increased mineral content, carbonation and apatite crystal size/perfection compared to baseline. Post-translational modifications of collagen are observed through an increase in the hydroxyproline/proline ratio in new bone. The proteoglycan content is also increased in new bone. SrRan directly modulates bone quality through its physicochemical actions, independent of an effect on bone remodeling. Strontium cations are captured by the hydrated layer of the mineral matrix. The mineral matrix formed during SrRan administration has a lower carbonate content and crystallinity after 12 months than at baseline. Strontium might create bonds (crosslinks) with collagen and noncollagenous proteins in new and old bone. The nanomechanical properties of bone were not modified with either ALN or SrRan, probably due to the short duration of administration. Our results show that ALN and SrRan have differential effects on bone quality in relation to their mechanism of action.

Comparability of Raman Spectroscopic Configurations: A Large Scale Cross-Laboratory Study

The variable configuration of Raman spectroscopic platforms is one of the major obstacles in establishing Raman spectroscopy as a valuable physicochemical method within real-world scenarios such as clinical diagnostics. For such real world applications like diagnostic classification, the models should ideally be usable to predict data from different setups. Whether it is done by training a rugged model with data from many setups or by a primary-replica strategy where models are developed on a 'primary' setup and the test data are generated on 'replicate' setups, this is only possible if the Raman spectra from different setups are consistent, reproducible, and comparable. However, Raman spectra can be highly sensitive to the measurement conditions, and they change from setup to setup even if the same samples are measured. Although increasingly recognized as an issue, the dependence of the Raman spectra on the instrumental configuration is far from being fully understood and great effort is needed to address the resulting spectral variations and to correct for them. To make the severity of the situation clear, we present a round robin experiment investigating the comparability of 35 Raman spectroscopic devices with different configurations in 15 institutes within seven European countries from the COST (European Cooperation in Science and Technology) action Raman4clinics. The experiment was developed in a fashion that allows various instrumental configurations ranging from highly confocal setups to fibre-optic based systems with different excitation wavelengths. We illustrate the spectral variations caused by the instrumental configurations from the perspectives of peak shifts, intensity variations, peak widths, and noise levels. We conclude this contribution with recommendations that may help to improve the inter-laboratory studies.

Dual-energy computed-tomography-based discrimination between basic calcium phosphate and calcium pyrophosphate crystal deposition in vivo

Background:

Dual-energy computed tomography (DECT) is being considered as a non-invasive diagnostic and characterization tool in calcium crystal-associated arthropathies. Our objective was to assess the potential of DECT in distinguishing between basic calcium phosphate (BCP) and calcium pyrophosphate (CPP) crystal deposition in and around joints in vivo.

Methods:

A total of 13 patients with calcific periarthritis and 11 patients with crystal-proven CPPD were recruited prospectively to undergo DECT scans. Samples harvested from BCP and CPP calcification types were analyzed using Raman spectroscopy and validated against synthetic crystals. Regions of interest were placed in BCP and CPP calcifications, and the following DECT attenuation parameters were obtained: CT numbers (HU) at 80 and 140 kV, dual-energy index (DEI), electron density (Rho), and effective atomic number (Z_eff). These DECT attenuation parameters were compared and validated against crystal calibration phantoms at two known equal concentrations. Receiver operating characteristic (ROC) curves were plotted to determine the highest accuracy thresholds for DEI and Z_eff.

Results:

Raman spectroscopy enabled chemical fingerprinting of BCP and CPP crystals both in vitro and in vivo. DECT was able to distinguish between HA and CPP in crystal calibration phantoms at two known equal concentrations, most notably by DEI (200 mg/cm³: 0.037 ± 0 versus 0.034 ± 0, p = 0.008) and Z_eff (200 mg /cm³: 9.4 ± 0 versus 9.3 ± 0, p = 0.01) analysis. Likewise, BCP calcifications had significantly higher DEI (0.041 ± 0.005 versus 0.034 ± 0.005, p = 0.008) and Z_eff (9.5 ± 0.2 versus 9.3 ± 0.2, p = 0.03) than CPP crystal deposits with comparable CT numbers in patients. With an area under the ROC curve of 0.83 [best threshold value = 0.0 39, sensitivity = 90. 9% (81.8, 97. 7%), specificity = 64.6% (50.0, 64. 6%)], DEI was the best parameter in distinguishing between BCP and CPP crystal depositions.

Conclusion:

DECT can help distinguish between crystal-proven BCP and CPP calcification types in vivo and, thus, aid in the diagnosis of challenging clinical cases, and in the characterization of CPP and BCP crystal deposition occurring in osteoarthritis.

Short-term high-dose zoledronic acid enhances crystallinity in mandibular alveolar bone in rats

Owing to its antiresorptive properties, zoledronic acid (ZOL) is commonly used in the management of benign as well as malignant bone diseases. This molecule targets sites where bone is actively remodeling, and high concentrations have been reported in the jaw. The purpose of this study was to investigate whether treatment of male rats with ZOL, at a dosage equivalent to that used for antitumor treatment, impacts the short-term qualitative properties of mandibular bone independent of bone remodeling. Thirty rats were randomly assigned to treatment either with ZOL or with serum-vehicle (control) (weekly injections: 100 μg kg^-1 for 6 wk, n = 15 per group). Using the tetracycline double-labeling technique, remodeled bone areas, corresponding to the preferential site of bisphosphonate binding, were found in the alveolar bone along the alveolar bone proper. The composition of bone in these areas was characterized using Raman microspectroscopy and compared with adjacent, non-remodeled, older bone. The ZOL-treated group exhibited higher crystallinity in the remodeled bone areas (+2%), reflecting an early maturation of the apatite mineral after ZOL injection. Our findings highlight a direct and rapid effect of clinically relevant anti-tumoral ZOL doses on the qualitative properties of mandibular bone, especially on mineral crystallinity in the vicinity of the teeth, namely, the alveolar bone proper.

Surface Enhanced Raman Spectroscopy for Quantitative Analysis: Results of a Large-Scale European Multi-Instrument Interlaboratory Study

Surface-enhanced Raman scattering (SERS) is a powerful and sensitive technique for the detection of fingerprint signals of molecules and for the investigation of a series of surface chemical reactions. Many studies introduced quantitative applications of SERS in various fields, and several SERS methods have been implemented for each specific application, ranging in performance characteristics, analytes used, instruments, and analytical matrices. In general, very few methods have been validated according to international guidelines. As a consequence, the application of SERS in highly regulated environments is still considered risky, and the perception of a poorly reproducible and insufficiently robust analytical technique has persistently retarded its routine implementation. Collaborative trials are a type of interlaboratory study (ILS) frequently performed to ascertain the quality of a single analytical method. The idea of an ILS of quantification with SERS arose within the framework of Working Group 1 (WG1) of the EU COST Action BM1401 Raman4Clinics in an effort to overcome the problematic perception of quantitative SERS methods. Here, we report the first interlaboratory SERS study ever conducted, involving 15 laboratories and 44 researchers. In this study, we tried to define a methodology to assess the reproducibility and trueness of a quantitative SERS method and to compare different methods. In our opinion, this is a first important step toward a “standardization” process of SERS protocols, not proposed by a single laboratory but by a larger community.

Mandibular bone is protected against microarchitectural alterations and bone marrow adipose conversion in ovariectomized rats

Osteoporosis is a disease that leads to a loss of bone mass and to alterations in the bone microarchitecture that occur in a site-specific manner; however it remains controversial in the jaw. The involvement of bone marrow adipose tissue (BMAT) in the bone metabolism has been suggested in several physiopathological contexts, such as in aging and osteoporosis. To test whether the BMAT content is related to mandibular bone loss, this study aimed to investigate the potential correlations between the trabecular bone microarchitecture on one hand and BMAT content and its spatial distribution in relation to bone surface on the other hand during aging and ovariectomy (OVX) during a long-term follow-up in a mature rat model. No age-related microarchitectural or BMAT changes were observed in the mandible. The OVX-induced bone loss was three-fold lower in the mandible than in the tibia and was observed only in the alveolar bone (not in the condyle). We also report a delayed increase in the mandibular BMAT content that remained 4-6-fold lower compared to tibia. This low BMAT content in the mandible was located at a distance from the trabecular bone surface (only 5% in contact with the bone surface versus 87% in the tibia). These findings highlight a specific mandibular response to OVX, in particular fewer microarchitectural alterations compared to that in the tibia. For the latter, the trabecular bone thickness and surface were correlated with the BMAT content. Oral functions may have a protective effect on the mandibular BMAT conversion in an OVX context.

Impaired mineral quality in dentin in X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a skeletal disorder arising from mutations in the PHEX gene, transmitted in most cases as an X-linked dominant trait. PHEX deficiency leads to renal phosphate wasting and hypophosphatemia, as well as impaired mineralization of bone and dentin, resulting in severe skeletal and dental complications. Dentin mineralization defects appear as characteristic, large interglobular spaces resulting from the lack of fusion of calculospherites in the circumpulpal region during the mineralization process. Here, we examined changes in the composition and structure of dentin using Raman spectroscopy on XLH human teeth, and using transmission electron microscopy on the dentin of Hyp mice (the murine model of XLH). The dentin of patients with XLH showed changes in the quality of the apatitic mineral, with greater carbonate substitution and lower crystallinity compared to the dentin of age-matched control teeth. In addition, ultrastructural analysis by transmission electron microscopy revealed a major disorganization of the peri- and intertubular structure of the dentin, with odontoblast processes residing within an unmineralized matrix sheath in the Hyp mouse. Taken together, these results indicate that like for bone and tooth cementum, there are impaired mineral quality and matrix changes in XLH dentin reflecting high sensitivity to systemic serum phosphate levels and possibly other local changes in the dentin matrix.

Influence of collecting substrate on the Raman imaging of micron-sized particles

The influence of six common substrates on the Raman imaging of micron-sized inorganic aerosol particles was examined. Laboratory-generated single-component particles of calcite (CaCO₃) and mixed particles of calcite (CaCO₃), nitratine (NaNO₃), hematite (Fe₂O₃) and anglesite (PbSO₄) were deposited by cascade impaction on Ag, In, Si, SiO₂, microscope slide and TEM-grid substrates. The spectral contribution of substrates to Raman images of the deposited particles was evaluated by Multivariate Curve Resolution. The shape and intensity of the substrate spectra affect the effectiveness capability of the spectral deconvolution. The substrates were characterized and compared with respect to their effect on the reconstruction of Raman images of aerosol particles. The TEM-grid substrate yielded spatially stable sample measurements with a homogeneous spectral contribution, satisfactory Raman map reconstruction and the potential for application in other techniques (e.g., SEM-EDX).

Tissue-specific mineralization defects in the periodontium of the Hyp mouse model of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a dento-osseous disorder caused by inactivating mutations in the PHEX gene, leading to renal phosphate wasting and hypophosphatemia, and impaired mineralization of bones and teeth. In the oral cavity, recent reports suggest a higher susceptibility of XLH patients to periodontitis, where patients present with impaired tooth cementum - a bone-like tissue involved in tooth attachment to the jaw bones and post-eruption tooth positioning - and a higher frequency of intrabony defects. In the present study, the pathobiology of alveolar bone and tooth cementum was investigated in the Hyp mouse, the murine analog of XLH. PHEX deficiency in XLH/Hyp dramatically alters the periodontal phenotype, with hypoplasia of tooth root cementum associated with a lack of periodontal ligament attachment and the presence of an immature apatitic mineral phase of all periodontal mineralized tissues. Challenging the Hyp periodontium in two surgical experimental models - ligature-induced periodontal breakdown and repair, and a model of tooth movement adaptation inducing cementum formation - we show that bone and cementum formation, and their healing, are altered. Bone and cementum mineralization appear similarly disturbed, where hypomineralized pericellular matrix surrounds cells, and where the protein osteopontin (OPN, a mineralization inhibitor) accumulates in a tissue-specific manner, most notably in the perilacunar matrix surrounding osteocytes. Although the pathobiology is different between XLH/Hyp bone and cementum, our results show a major XLH phenotype in oral mineralized tissues consistent with variations in patient susceptibility to periodontal disorders.

Defective Mineralization in X-Linked Hypophosphatemia Dental Pulp Cell Cultures

X-linked hypophosphatemia (XLH) is a skeletal disease caused by inactivating mutations in the PHEX gene. Mutated or absent PHEX protein/enzyme leads to a decreased serum phosphate level, which cause mineralization defects in the skeleton and teeth (osteomalacia/odontomalacia). It is not yet altogether clear whether these manifestations are caused solely by insufficient circulating phosphate availability for mineralization or also by a direct, local intrinsic effect caused by impaired PHEX activity. Here, we evaluated the local role of PHEX in a 3-dimensional model of extracellular matrix (ECM) mineralization. Dense collagen hydrogels were seeded either with human dental pulp cells from patients with characterized PHEX mutations or with sex- and age-matched healthy controls and cultured up to 24 d using osteogenic medium with standard phosphate concentration. Calcium quantification, micro-computed tomography, and histology with von Kossa staining for mineral showed significantly lower mineralization in XLH cell-seeded scaffolds, using nonparametric statistical tests. While apatitic mineralization was observed along collagen fibrils by electron microscopy in both groups, Raman microspectrometry indicated that XLH cells harboring the PHEX mutation produced less mineralized scaffolds having impaired mineral quality with less carbonate substitution and lower crystallinity. In the XLH cultures, immunoblotting revealed more abundant osteopontin (OPN), dentin matrix protein 1 (DMP1), and matrix extracellular phosphoglycoprotein (MEPE) than controls, as well as the presence of fragments of these proteins not found in controls, suggesting a role for PHEX in SIBLING protein degradation. Immunohistochemistry revealed altered OPN and DMP1 associated with an increased alkaline phosphatase staining in the XLH cultures. These results are consistent with impaired PHEX activity having local ECM effects in XLH. Future treatments for XLH should target both systemic and local manifestations.

Correction: New Insights on the Composition and the Structure of the Acellular Extrinsic Fiber Cementum by Raman Analysis

[This corrects the article DOI: 10.1371/journal.pone.0167316.].

Region specific Raman spectroscopy analysis of the femoral head reveals that trabecular bone is unlikely to contribute to non-traumatic osteonecrosis

Non-traumatic osteonecrosis (ON) of the femoral head is a common disease affecting a young population as the peak age of diagnosis is in the 40 s. The natural history of non-traumatic ON leads to a collapse of the femoral head requiring prosthetic replacement in a 60% of cases. Although trabecular bone involvement in the collapse is suspected, the underlying modifications induced at a molecular level have not been explored in humans. Here, we examine changes in the molecular composition and structure of bone as evaluated by Raman spectroscopy in human end-stage ON. Comparing samples from femoral heads harvested from 11 patients and 11 cadaveric controls, we show that the mineral and organic chemical composition of trabecular bone in ON is not modified apart from age-related differences. We also show that the molecular composition in the necrotic part of the femoral head is not different from the composition of the remaining ‘healthy’ trabecular bone of the femoral head. These findings support that quality of trabecular bone is not modified during ON despite extensive bone marrow necrosis and osteocyte death observed even in the ‘healthy’ zones on histological examination.

New Insights on the Composition and the Structure of the Acellular Extrinsic Fiber Cementum by Raman Analysis

Acellular extrinsic fiber cementum is a mineralized tissue that covers the cervical half of the tooth root surface. It contains mainly extrinsic or Sharpey's fibers that run perpendicular to the root surface to anchor the tooth via the periodontal ligament. Acellular cementum is continuously and slowly produced throughout life and exhibits an alternating bright and dark pattern under light microscopy. However, although a better understanding of the structural background of acellular cementum is relevant to many fields, such as cementochronology, periodontology and tissue engineering, acellular cementum remains rarely studied and poorly understood. In this work, we studied the acellular cementum at the incremental line scale of five human mandibular canines using polarized Raman spectroscopy. We provided Raman imaging analysis and polarized acquisitions as a function of the angular orientation of the sample. The results showed that mineral crystals were always parallel to collagen fibrils, and at a larger scale, we proposed an organizational model in which we found radial collagen fibers, "orthogonal" to the cementum surface, and "non-orthogonal" fibers, which consist of branching and bending radial fibers. Concerning the alternating pattern, we observed that the dark lines corresponded to smaller, more mineralized and probably more organized bands, which is consistent with the zoological assumption that incremental lines are produced during a winter rest period of acellular cementum growth.

Doses effects of zoledronic acid on mineral apatite and collagen quality of newly-formed bone in the rat's calvaria defect

Due to their inhibitory effects on resorption, bisphosphonates are widely used in the treatment of diseases associated to an extensive bone loss. Yet, little is known about bisphosphonates effects on newly-formed bone quality. In the present study, adult male Sprague-Dawley rats (n=80) with a bone defect calvaria area were used and short-term effects of zoledronic acid (ZA) were studied on the healing bone area. Three ZA treatments were tested by using either: 1°) a low single dose (120μgZA/kg, n=10; equivalent to human osteoporosis treatment), 2°) a low fractionated doses (20μgZA/kg daily for 6days either a total of 120μg/kg, n=15), and 3°) a high fractionated doses, (100μgZA/kg weekly for 6weeks, n=15; equivalent to 6months of human bone metastasis treatment). For each treatment, a control "vehicle" treatment was performed (with an identical number of rats). After ZA administration, the intrinsic bone material properties were evaluated by quantitative backscattered electron imaging (qBEI) and Raman microspectroscopy. Neither single nor fractionated low ZA doses modify the intrinsic bone material properties of the newly-formed bone compared to their respective control animals. On the opposite, the high ZA treatment resulted in a significant decrease of the crystallinity (-25%, P< 0.05) and of the hydroxyproline-to-proline ratio (-30%, P<0.05) in newly-formed bones. Moreover, with the high ZA treatment, the crystallinity was positively correlated with the hydroxyproline-to-proline ratio (ρ=0.78, P<0.0001). The present data highlight new properties for ZA on bone formation in a craniofacial defect model. As such, ZA at high doses disrupted the apatite crystal organization. In addition, we report here for the first time that high ZA doses decreased the hydroxyproline-to-proline ratio suggesting that ZA may affect the early collagen organization during the bone healing.

Dexamethasone in osteogenic medium strongly induces adipocyte differentiation of mouse bone marrow stromal cells and increases osteoblast differentiation

BACKGROUND

Osteoblasts and adipocytes share a common mesenchymal stem cell origin. Therefore, it has been suggested that the accumulation of marrow adipocytes observed in bone loss is caused by a shift in the commitment of mesenchymal stem cells from the osteogenic pathway to the adipogenic pathway. Supporting this hypothesis the competition between adipogenic and osteogenic lineages was widely demonstrated on partially homogeneous cell populations. However, some data from mouse models showed the existence of an independent relationship between bone mineral content and bone marrow adiposity. Therefore, the combination of adipogenesis and osteogenesis in primary culture would be helpful to determine if this competition would be observed on a whole bone marrow stromal cell population in a culture medium allowing both lineages. In this aim, mouse bone marrow stromal cells were cultured in a standard osteogenic medium added with different concentrations of Dexamethasone, known to be an important regulator of mesenchymal progenitor cell differentiation.

RESULTS

Gene expression of osteoblast and adipocyte markers, biochemical and physical analyses demonstrated the presence of both cell types when Dexamethasone was used at 100 nM. Overall, our data showed that in this co-differentiation medium both differentiation lineages were enhanced compared to classical adipogenic or osteogenic culture medium. This suggests that in this model, adipocyte phenotype does not seem to increase at the expense of the osteoblast lineage.

CONCLUSION

This model appears to be a promising tool to study osteoblast and adipocyte differentiation capabilities and the interactions between these two processes.

Molecular alterations of bone quality in sequesters of bisphosphonates-related osteonecrosis of the jaws

Compared to healthy bone, the intrinsic bone materials properties in the pre-existing lamellar bone are altered in jaw bone sequesters of bisphosphonates (BP)-related osteonecrosis.

INTRODUCTION

The aim of this study was to evaluate the human jaw bone quality, especially intrinsic bone material properties among sequesters of osteonecrosis of the jaw (ONJ) induced by BP.

METHODS

Bone sequesters were obtained from 24 patients suffering from ONJ following a BP treatment. Within BP-exposed bone samples, benign-BP and malignant-BP groups were distinguished in relation to the underlying disease: osteoporosis and bone metastases or multiple myeloma, respectively. Healthy cadaveric cortical jaw bone samples were used as controls. The physicochemical parameters of bone samples - mineral/organic ratio, relative proteoglycan content, crystallinity, monohydrogen phosphate content, and type-B carbonate substitution - were evaluated by Raman microspectroscopy. Representative Raman spectral features of bones control and BP-exposed bone sequesters were identified with the Partial-Least-Square Discriminant Analysis (PLS-DA).

RESULTS

BP-exposed bone sequesters are characterized by a significant increase of mineral to organic ratio (+12 %) and a significant decrease of relative proteoglycan content (-35 %), thus regulating initial collagen matrix mineral deposition. Structural changes on mineral components are revealed by a significant decrease of both crystallinity (-2 %) and mineral maturation (-41 %) in the BP-exposed bone sequesters compared to healthy bones. These modifications were also observed distinctly in both benign-BP and malignant-BP groups. In addition, a shift of the phosphate ν1 band was highlighted by PLS-DA between bones control and BP-exposed bone sequesters, revealing a disruption of the apatitic phosphate environment in the jaw bone sequesters.

CONCLUSIONS

The present data show that jaw bone quality can be altered with an overmineralization and ultrastructural modifications of apatitic mineral in bone sequesters of BP-related ONJ.

Heterogeneous microchemistry between CdSO4 and CaCO3 particles under humidity and liquid water

Laboratory experiments using in situ Raman imaging combined with ex situ TOF-S-SIMS demonstrate the behavior of CdSO4·8/3H2O microparticles in contact with 101¯4 CaCO3 (calcite) surface under three different experimental conditions representative of unpolluted atmosphere. The contact of CdSO4·8/3H2O particles with CaCO3 surface in humid air (RH∼40-80%) does not induce any chemical reaction. In contrast, the condensation of a water drop on CdSO4·8/3H2O/CaCO3 interface causes the free dissolution of CdSO4·8/3H2O particle in the drop. A CdSO4·8/3H2O microcrystal is reformed after gentle drying with a CdSO4·H2O coating of the CaCO3 surface. The TOF-S-SIMS image of the CaCO3 surface provides evidence of a thin layer corresponding probably to insoluble coating of CdCO3 (otavite) or CdxCa1-xCO3 solid solution at the liquid-solid interface. This layer armours the CaCO3 from further dissolution and stops the reaction. The deposition of CdSO4·8/3H2O particle in water drop previously in contact with CaCO3 for a long time generates CdCO3 small rhombohedral crystals while gentle drying provokes the crystallization of bar shape crystals of CaSO4·2H2O (gypsum). These laboratory results provide valuable chemical prediction for a possible fate of cadmium rich particles emitted in the atmosphere and thus, can contribute to realistic assessment of human exposure to Cd hazard.

Comparison of two-dimensional fast Raman imaging versus point-by-point acquisition mode for human bone characterization

Recent technical developments gave rise to a new technology for two-dimensional fast Raman imaging: the DuoScan averaging mode (DS-Avg). This technology allows the acquisition of a Raman spectrum over a rastered macro spot. The aim of this study was to evaluate the interest of the DS-Avg applied on trabecular human bone. The evaluation was based on the comparison of the DS-Avg versus the point-by-point mapping mode in real usage conditions. The signal-to-noise ratio, the spectral difference, and the physicochemical parameters were estimated for comparison of the efficiency of both modes. Principal component analysis was performed to explore the capacity of both modes to detect compositional variations. Results showed that the DS-Avg spectrum was equivalent to the average spectrum of individual spectra acquired with the point-by-point mode for the same sample area. The physicochemical parameters can be also determined from DS-Avg acquisition. The DS-Avg combined with an objective ×50 allows a drastic decrease of the acquisition time, but the information about the micrometric composition is lost. The combination of the DS-Avg with an objective ×100 is a good compromise between acquisition time and resolution. The DS-Avg is a useful technology for imaging mineral and organic phases of bones and for assessing their spatial distribution on large samples. The point-by-point imaging mode is more appropriate to assess the heterogeneous composition of bone within the micrometer scale. For the first time, this study compares the DuoScan averaging mode to the point-by-point imaging mode on a trabecular human bone.

Effects of high dose of zoledronic acid on superficial vascular network of membranous bone sites: an intravital study on rat calvarium

We evaluated the impact of high dose of zoledronic acid on the superficial vascular network parameters of a membranous bone site. During a 5-day follow-up, significant reduction of the vascular density is observed only in the treated group.

INTRODUCTION

The superficial vascularization is of great importance in membranous bone-healing process. A new rat calvarium intravital model was developed to study the short-term effect of a single high dose of zoledronic acid infusion on the superficial vascularization.

METHODS

Optical bone chambers were implanted in the bone tissue surface of Sprague-Dawley rats' calvarium. Nine rats were injected i.v. with 400 µg/kg of zoledronic acid (Z group), and nine rats were injected with vehicle (PSS group). A 5-day follow-up of the vascular network was made by the use of pictures analysis method.

RESULTS

The vascular density significantly decreases only in Z group but there was no significant difference between groups at individual time points. The total length of the vascular network decreases significantly in Z group only (p=0.003) with a significant higher decrease at D3 (p=0.04) and D5 (p=0.02) compared with control. The vascular density related to the smaller vessels (width, 5-10 µm) decreases significantly between T0 and D5 in Z group only (p=0.002).

CONCLUSIONS

With the help of an original intravital animal model a significant modifications on the total length of the vascular network and the vascular density of small vessels are highlighted on a membranous bone site.

Molecular interactions between zoledronic acid and bone: An in vitro Raman microspectroscopic study

The aim of this study was to investigate molecular interactions between a bisphosphonate (BP), zoledronic acid, and bone tissue by the use of Raman microspectroscopy. In this way, samples of hydroxyapatite (HA), as a bone model, and Wistar rat femurs were soaking in zoledronic acid solutions. Sample surfaces were studied by Environmental Scanning Electron Microscopy and Raman spectroscopy. The amount of zoledronic acid incorporated onto the samples and the inorganic phosphate released in solution were determined by (31)P NMR spectroscopy. Total carbonate content in solution was evaluated by inorganic carbon analyser. After impregnation new Raman bands with frequencies close to characteristic peaks of zoledronic acid (in particular phosphate moieties and imidazole ring of the R2 side-chain) were observed on both types of samples. Physico-chemical parameters of the bone were also significantly modified (P<0.0001). The mineral to organic ratio and the carbonate to phosphate ratio decreased and the crystallinity increased. Released inorganic phosphate and carbonate were detected in the solutions. The Raman shift of the bands corresponding to the phosphate groups and the imidazole ring of the BP highlight their implication in the binding to the mineral. The detection of released inorganic phosphate and carbonate in solution, the modifications of the mineral to phosphate ratio and the carbonate to phosphate ratio reveal that BP decrease the amount of inorganic phosphate and limit the dissolution of bone mineral. The increase of the crystallinity after BP binding shows a re-organisation of the lattice with a higher symmetry. Thus, it seems that zoledronic acid has an important contribution on the increase of crystallinity. The use of Raman spectrometry brings new and complementary information on the impact of zoledronic acid on bone composition at molecular level. Raman spectrometry could help to understand by which way BPs improve bone strength and decrease fracture risk.

Laser preconditioning on cranial bone site: analysis of morphological vascular parameters

BACKGROUND AND OBJECTIVES

Bone vascularization is a key factor in the bone healing process following X-ray irradiation. Preserving the vascular network from X-ray-induced injury is a relevant approach in the promotion of bone healing. Previously, we developed a protocol of laser preconditioning (810 nm diode laser, 36 J/cm²) prior to X-ray radiation (18.75 Gy) which protects the bone vascular network from deleterious effects of X-ray radiation. The aim of this present work is to characterize the effects of laser preconditioning on the bone through a morphological analysis of vascular parameters.

MATERIALS AND METHODS

Digital images of the vascular plexus were taken through an optical bone chamber which was implanted onto the calvaria of rabbits. Bespoke software was used for the quantification of the vessels (classified in four groups according to their diameter), vessel length, and number of nodes at weeks 0, 4, and 8. Twenty rabbits were divided into four groups: control group #1 (n = 5); laser group #2 (n = 5). X-ray radiation group #3 (n = 5), laser preconditioning 24 hours prior to X-ray radiation group #4 (n = 5).

RESULTS

The bone vascular network was stable for groups #1 and #2. Statistical analysis showed a significant reduction of each observed vascular parameter for groups #3 and #4. In the laser preconditioned group #4 the loss was less marked than in the X-ray group #3, especially for large vessels (diameter >50 µm).

DISCUSSION AND CONCLUSION

We provide in vivo microcirculatory evidence to support the concept of laser preconditioning of bone. A computer-based semi-automatic system is described to quantify superficial bone vascular network parameters that had been treated by laser preconditioning prior to X-ray radiation. Laser preconditioning significantly attenuates the deletion of the superficial bone vascular network irradiated by X-ray, especially concerning large diameter vessels.

New method for Raman investigation of the orientation of collagen fibrils and crystallites in the Haversian system of bone

Knowledge of the organization of the components of bone is of primary importance in understanding how this tissue responds to stresses and provides a starting point for the design and development of biomaterials. Bone structure has been the subject of numerous studies. The mineralized fiber arrangement in cortical bone is either a twisted or orthogonal plywood structure. Both mineral models coexist in compact bone. Raman polarized spectroscopy offers definite advantages in the study of biological samples, enabling the simultaneous analysis of mineral and organic components and the determination of molecular orientation through the polarization properties of the Raman scattering. In this study, we used the Raman polarization approach to simultaneously investigate the orientation of collagen fibrils and apatite crystals in human cortical bone. Raman bands ratios were monitored as a function of sample orientation. Specific ratios were chosen--such as nu(3) PO(4)/nu(1) PO(4), amide III (1271 cm(-1))/amide III (1243 cm(-1)), and amide I/amide III (1243 cm(-1))--due to their sensitivity to apatite-crystal and collagen-fibril orientation. Based on this original approach, spatial changes were monitored as a function of distance from the Haversian canal. The results revealed simultaneous tilting in intra-lamellar collagen-fibril and mineral crystal orientations. These results are consistent with a twisted plywood organization in the Haversian bone structure at the lamellar level. But at molecular level, the co-alignment of the collagen fibrils and the apatite crystal is observed in the innermost lamellae and becomes gradually less ordered as the distance from the Haversian canal increases. This work highlights the interest of Raman spectroscopy for the multiscale investigation of bone structure.

No anti-angiogenic effect of clinical dosing regimens of a single zoledronic acid injection in an experimental bone healing site

INTRODUCTION

An anti-angiogenic effect of bisphosphonates has been reported in different experimental models. Zoledronic acid is currently administered in osteoporotic patients as a single 5 mg injection once a year and its vascular effect in bone has not been yet evaluated.

MATERIALS AND METHODS

The vascular dose effect of a single injection of zoledronic acid was evaluated on healing vascularization developed under a bone chamber implanted on the calvaria of 30 rats. After 3 weeks of healing, the rats were randomized into 3 groups receiving an injection of either physiologic saline solution (PSS) or zoledronic acid tested at 120 microg/kg, the equivalent of a 5 mg dose of zoledronic acid in humans (Z120), and 400 microg/kg, a supra-pharmacologic dose (Z400). A longitudinal follow-up of the healing vascular network was carried out at days (D) 1, 3, 6, 9, 12, 15 and 28 after injection by intravital imaging. Variations in vascular density, total length of the vascular network and mean diameter of vascular network branches were determined by image analysis (Aphelion software).

RESULTS

A decrease was observed in both vascular density and total length of the network in control and treated groups (time effect). No difference in variation in vascular density was observed between the PSS group and the Z120 group at any time point (p=NS). A trend to a higher decrease in vascular density was noted between D12 and D15 in the Z400 group. A significant decrease in total length was noted at D15 in the Z400 group (p=0.03) compared to the PSS group, whereas no change was noted in rats treated with 120 microg/kg compared to PSS rats on any of the follow-up days (p=0.2). No variation in mean diameter of vascular network branches was noted in any of the three groups at any of the follow-up days (p=0.53).

CONCLUSION

A single injection of clinically relevant dosing regimens of zoledronic acid may not have a notable impact on vascularization in bone sites. The anti-angiogenic effect of bisphosphonates seems to express itself, in our model, at higher doses than those used in patients treated for osteoporosis.

A preliminary investigation into the effects of X-ray radiation on superficial cranial vascularization

Radiation therapy (RT) is an established treatment modality for malignant neoplasms. RT induces tissue damage that may lead to osteoradionecrosis in more severe cases. Suitable animal models to study RT-induced changes in membranous craniofacial bone are currently not available. The aim of this study was therefore to quantify RT-induced changes in cranial microcirculation using a newly developed calvaria chamber model and to relate these changes to RT-induced histological damage. New Zealand white rabbits received a total radiation dose of 18.75 Gy through the calvaria chamber, and the number of vessels, the vessel length density (VLD), and angiogenic sprouting were quantified on a weekly basis during a 12-week period. At the end of 12 weeks, the RT-treated (n = 5) or control (n = 5) calvarias were biopsied for histopathological analysis. RT resulted in a steep reduction in the number of vessels and the VLD during the first 3 weeks, particularly in larger-diameter vessels, followed by a flat stabilization/remodeling phase in the subsequent 9 weeks that never restored to baseline values. Histomorphometric analysis revealed a high degree of osteocytic depletion, prominent hypocellularity in the lacunae and intraosseous vasculature, enlarged and nonconcentric Haversian systems, and a severely disorganized bone matrix in the RT-treated calvarias. Despite the prevalence of some angiogenic potential, the RT-induced effects in the early phase persisted in the intermediate to late phase, which may have contributed to the poor recovery of the RT-treated bone.

Chemistry at level of individual aerosol particle using multivariate curve resolution of confocal Raman image

Airborne particles with aerodynamic diameter in the 10-1 microm range have been collected in an industrial/urban zone by impaction and have been investigated by automated confocal Raman microspectrometry. The computer-microcontrolled XY scanning and Z focusing of Raman images provided many pixel Raman spectra which are characteristics of complex mixture at level of individual particle. The large heterogeneity was not resolved by the spatial resolution of the instrument which is limited by the optical diffraction. The severe spectral overlaps generated by heterogeneity were resolved by multivariate curve resolution (MCR) methods. The purity based method (SIMPLISMAX) was used to resolve both luminescence spectra and pure Raman spectra without prior information. The MCR-alternating least square (ALS) was used as a refined method of both spectra and spectral concentrations. The reconstructing Raman images of the respective spectral contribution supply a versatile potential to characterize the chemistry of atmospheric aerosols at the level of the individual particles.

Heterogeneous chemistry between PbSO4 and calcite microparticles using Raman microimaging

Currently, the smelting activities of lead and zinc are the loudest sources of local pollution by emission in the troposphere of dust of micrometer size containing PbSO(4). As the particles evolve in the troposphere, their chemical and physical properties - and hence their characteristics such as toxicity - change by accumulation of atmospheric heterogeneous reactions. Calcite (CaCO(3)) represents a large part of the mineral fraction in tropospheric aerosols with aerodynamic diameters less than 10 microm. The calcite particles are expected to react with PbSO(4) particles. In an effort to model the chemical behaviour of PbSO(4) individual particles in the troposphere, we present the in situ Raman imaging results during the course of the reactions in a water droplet of PbSO(4) particles with a calcite microcrystal surface. The computer-microcontrolled XY scanning and Z focusing of confocal Raman imaging combined with multivariate curve resolution (MCR) of Raman images have resolved the severe spectral overlaps of the Raman spectra which are not resolved by the spatial resolution of the instrument ( approximately 1 microm(3)). The results pointed out the identification and the mapping of Pb(3)(CO(3))(2)(OH)(2), PbCO(3) and CaSO(4).2H(2)O (gypsum) on the calcite surface.