Dynamic structure and composition of bone investigated by nanoscale infrared spectroscopy

Bone is a highly organized tissue in which each structural level influences the macroscopic and microscopic mechanical behavior. In particular, the quantity, quality, and distribution of the different bone components, i.e. collagen matrix and hydroxyapatite crystals, are associated with bone strength or fragility. Common spectroscopic techniques used to assess bone composition have resolutions limited to the micrometer range. In this study, our aims were two-fold: i) to develop and validate the AFM-IR methodology for skeletal tissues and ii) to apply the methodology to sheep cancellous bone with the objective to obtain novel findings on the composition and structure of trabecular packets.To develop the methodology, we assessed spatial and temporal reproducibility using a known homogeneous material (polymethylmethacrylate, PMMA). We verified that the major peak positions were similar and not shifted when compared to traditional Fourier Transform Infrared imaging (FTIRI). When AFM-IR was applied to sheep cancellous bone, the mineral-to-matrix ratio increased and the acid phosphate substitution ratio decreased as a function of tissue maturity. The resolution of the technique enabled visualization of different stages of the bone maturation process, particularly newly-formed osteoid prior to mineralization. We also observed alternating patterns of IR parameters in line and imaging measurements, suggesting the apposition of layers of alternating structure and / or composition that were not visible with traditional spectroscopic methods. In conclusion, nanoscale IR spectroscopy demonstrates novel compositional and structural changes within trabecular packets in cancellous bone. Based on these results, AFM-IR is a valuable tool to investigate cancellous bone at the nanoscale and, more generally, to analyze small dynamic areas that are invisible to traditional spectroscopic methods.

Post-translational modification of osteopontin: effects on in vitro hydroxyapatite formation and growth

The manuscript tests the hypothesis that posttranslational modification of the SIBLING family of proteins in general and osteopontin in particular modify the abilities of these proteins to regulate in vitro hydroxyapatite (HA) formation. Osteopontin has diverse effects on hydroxyapatite (HA) mineral crystallite formation and growth depending on the extent of phosphorylation. We hypothesized that different regions of full-length OPN would also have distinct effects on the mineralization process. Thrombin fragmentation of milk OPN (mOPN) was used to test this hypothesis. Three fragments were tested in a de novo HA formation assay; an N-terminal fragment (aa 1-147), a central fragment (aa 148-204) denoted SKK-fragment and a C-terminal fragment (aa 205-262). Compared to intact mOPN the C- and N-terminal fragments behaved comparably, promoting HA formation and growth, but the central SKK-fragment acted as a mineralization inhibitor. In a seeded growth experiment all fragments inhibited mineral proliferation, but the SKK-fragment was the most effective inhibitor. These effects, seen in HA-formation and seeded growth assays in a gelatin gel system and in a pH-stat experiment were lost when the protein or fragments were dephosphorylated. Effects of the fully phosphorylated protein and fragments were also altered in the presence of fibrillar collagen. The diverse effects can be explained in terms of the intrinsically disordered nature of OPN and its fragments which enable them to interact with their multiple partners.

Different forms of DMP1 play distinct roles in mineralization

Dentin matrix protein-1 (DMP1) is a major synthetic product of hypertrophic chondrocytes and osteocytes. Previous in vitro studies showed full-length DMP1 inhibits hydroxyapatite (HA) formation and growth, while its N-terminal fragment (37K) promotes HA formation. Since there are 3 fragments within the mineralized tissues [N-terminal, C-terminal (57K), and a chondroitin-sulfate-linked N-terminal fragment (DMP1-PG)], we predicted that each would have a distinct effect on mineralization related to its interaction with HA. In a gelatin-gel system, 37K and 57K fragments were both promoters of HA formation and growth; DMP1-PG was an inhibitor. The secondary structures of the 3 fragments and the full-length protein in the presence and absence of Ca2+ and HA determined by FTIR showed that the full-length protein undergoes slight conformational changes on binding to HA, while 37K, 57K, and DMP1-PG do not change conformation. These findings indicate that distinct forms of DMP1 may work collectively in controlling the mineralization process.

MEPE's diverse effects on mineralization

Matrix extracellular phosphoglycoprotein (MEPE) is an inhibitor of mineralization in situ and in cell cultures where altered expression is associated with oncogenic osteomalacia and hypophosphatemic rickets. The purpose of this study was to determine whether the intact protein or the peptide(s) originating from this protein was responsible for the inhibition. The ability of the intact protein and the acidic, serine- and aspartate-rich MEPE-associated motif (ASARM) peptide to promote or inhibit de novo hydroxyapatite formation and growth of hydroxyapatite seed crystals, in both phosphorylated and dephosphorylated forms, was assessed at room temperature in a dynamic gel diffusion system at 3.5 and 5 days. The most effective nucleator concentration was also examined when associated with fibrillar type I collagen. The phosphorylated intact protein was an effective promoter of mineralization in the gelatin gel diffusion system, while the ASARM peptide was an effective inhibitor. When dephosphorylated both the intact protein and the ASARM peptide had no effect on mineralization. Associated with collagen fibrils, some of the effect of the intact protein was lost. This study demonstrates the importance of posttranslational modification for the site-specific activity of MEPE and its ASARM peptide.

Assessment of the quantitative determination of paralytic shellfish poisoning toxins by pre-column derivatization and elimination of interfering compounds by solid-phase extraction

Monitoring programmes for paralytic shellfish poisoning toxins in bivalve molluscs still rely heavily on the use of mouse bioassays (MBA) for consumer protection. A high-performance liquid chromatography (HPLC) methodology (Lawrence method) was implemented in 1996 in the Portuguese monitoring programme as a complementary means of analysis. Comparison between MBA and HPLC was done at the time only by a qualitative approach due to the scarce number of positive samples tested. More quantitative data were obtained recently when studying toxin profiles in Moroccan shellfish, and the correlation found between these two methodologies is reported here for the first time. Two different matrices were studied: blue mussel and the giant cockle Acanthocardia tuberculatum. A good linear correlation was obtained for both matrices. However, a second-degree polynomial best fitted the data at both low and high extremes of toxicity. According to the HPLC quantitative results, 13% of false-negatives could be obtained by MBA due to an underestimation of toxicity near the limit of detection of the MBA. Difficulties on relying solely on HPLC for consumer protection have been aroused with uncommon matrices, such as imported clams or crustaceans, due to the presence of high concentrations of interfering compounds. The solid-phase extraction step of the Lawrence method was implemented to eliminate an unknown compound that could be mistaken for saxitoxin, and an 80% reduction of another common unknown compound eluting close to decarbamoylsaxitoxin. The implementation of the HPLC methodology achieved so far allows a high degree of consumer protection without the need to resource to animal sacrifice.

Study of paralytic shellfish poisoning toxin profile in shellfish from the Mediterranean shore of Morocco

Since 1992, a monitoring program for bivalve molluscs contaminated by algal toxins was established at different stations along the Mediterranean Moroccan shores. The monitored stations were tested every 2 weeks. The presence of toxicity was determined using the mouse bioassay method. Toxin profile was carried out by HPLC/FD in selected contaminated tissues. According to the outcomes of this surveillance from 1994 to 1999, reliable information on toxicity of shellfish was obtained. They indicate that PSP is a recurrent toxicity in molluscs along the Mediterranean shore of Morocco. It has been noted a difference of PSP accumulation among individual shellfish. The cockle (Achanthocardia tuberculatum) presents toxicity throughout the year, while other specimens from the same area such as clam (Callista chione), warty venus (Venus gallina) and marine beans (Donax trunculus) accumulate it seasonally from January to April, after which they depurate the toxin. Moreover, the study of toxin profiles among individual shellfish was undertaken. It was found that shellfish presented a complex profile pointing to contamination by Gymnodinium catenatum.

The impact of lead pollution on the environment of Rabat-Sale' (Morocco)

There are numerous possible vectors of industrial lead poisoning in unprotected work environments and the areas surrounding industrial sites. In the Rabat-Salé region, ceramics is the industry which uses most lead. Galena (PbS) is used in the fabrication of some types of pottery, and other lead-based compounds are used as glaze. A second source of lead pollution is the production of some fuels, in which lead is used as an anti detonator. In order to evaluate the impact of lead contamination on the environment, our investigation is focused on the lead concentration in the atmosphere, soil and vegetation at five stations in the Rabat-Salé region. We found concentrations of lead higher than those published for any other country in the atmosphere and vegetation near the ceramics factories of Rabat-Salé. These concentrations decreased significantly as we moved away from urban areas.

Piracetam for the treatment of sickle cell disease in children- a double blind test

Full text is available as a scanned copy of the original print version.

Okadaic acid and its interaction with sodium, potassium, magnesium and calcium ions: complex formation and transport across a liquid membrane

Okadaic acid, a macrocyclic polyether compound, was shown to mediate the transfer of Na+, K+, Mg2+ and Ca2+ ions from aqueous solution to an organic phase, with a preference for Na+ ions. A kinetic study of the transport of these ions across a liquid membrane showed that the Na+ ion was more rapidly transported than the other ions and that the Na+ ion flux was dependent on the okadaic acid concentration.