Effect of glycosaminoglycans on calcium pyrophosphate crystal formation in collagen gels

Discerning the differential molecular pathology of proliferative middle ear lesions using Raman spectroscopy

Despite its widespread prevalence, middle ear pathology, especially the development of proliferative lesions, remains largely unexplored and poorly understood. Diagnostic evaluation is still predicated upon a high index of clinical suspicion on otoscopic examination of gross morphologic features. We report the first technique that has the potential to non-invasively identify two key lesions, namely cholesteatoma and myringosclerosis, by providing real-time information of differentially expressed molecules. In addition to revealing signatures consistent with the known pathobiology of these lesions, our observations provide the first evidence of the presence of carbonate- and silicate-substitutions in the calcium phosphate plaques found in myringosclerosis. Collectively, these results demonstrate the potential of Raman spectroscopy to not only provide new understanding of the etiology of these conditions by defining objective molecular markers but also aid in margin assessment to improve surgical outcome.

Pathophysiology of articular chondrocalcinosis--role of ANKH

Calcium pyrophosphate (CPP) crystal deposition (CPPD) is associated with ageing and osteoarthritis, and with uncommon disorders such as hyperparathyroidism, hypomagnesemia, hemochromatosis and hypophosphatasia. Elevated levels of synovial fluid pyrophosphate promote CPP crystal formation. This extracellular pyrophosphate originates either from the breakdown of nucleotide triphosphates by plasma-cell membrane glycoprotein 1 (PC-1) or from pyrophosphate transport by the transmembrane protein progressive ankylosis protein homolog (ANK). Although the etiology of apparent sporadic CPPD is not well-established, mutations in the ANK human gene (ANKH) have been shown to cause familial CPPD. In this Review, the key regulators of pyrophosphate metabolism and factors that lead to high extracellular pyrophosphate levels are described. Particular emphasis is placed on the mechanisms by which mutations in ANKH cause CPPD and the clinical phenotype of these mutations is discussed. Cartilage factors predisposing to CPPD and CPP-crystal-induced inflammation and current treatment options for the management of CPPD are also described.

Mercaptopyruvate Inhibits Tissue-Nonspecific Alkaline Phosphatase and Calcium Pyrophosphate Dihydrate Crystal Dissolution

Objective.

The enzymatic activities of tissue-nonspecific alkaline phosphatase (TNAP) including capacity to inhibit calcium pyrophosphate dihydrate (CPPD) crystal dissolution are known to be inhibited by endogenous amino acids, notably cysteine. As cysteine is recognized as a strong TNAP inhibitor, we investigated whether cysteine-related metabolites such as mercaptopyruvate (MPA) could show similar enzyme inhibition effects and, if so, whether these effects might be synergistic with cysteine at approximate physiologic concentrations of the amino acids.

Methods.

We studied the inhibitory effects of MPA as well as MPA and cysteine combined in equimolar concentrations on TNAP’s phosphatase, inorganic pyrophosphatase, and CPPD crystal dissolution activities. Kinetic parameters Vmax, KM, concentration for 50% inhibition (I50), inhibitor constant (KI), and specific activities calculated from initial velocity, Eadie-Hofstee, Simple, Dixon, and secondary plots were used to assess enzyme inhibition.

Results.

MPA significantly inhibited TNAP’s phosphatase and pyrophosphatase activities at 10× and 100× physiological concentrations. In the presence of calcium [Ca2+] and [Mg2+] = 1 mM, MPA inhibited uncompetitively TNAP’s phosphatase activity and inhibited noncompetitively its pyrophosphatase activity. CPPD crystal dissolution activity was also inhibited. Cysteine and MPA together in equimolar concentrations inhibited TNAP enzyme activities and CPPD crystal dissolution much more effectively than MPA or cysteine alone, reducing CPPD dissolution to 38% of controls at approximate physiologic inhibitor concentrations.

Conclusion.

Endogenous amino acids like cysteine and its derivative MPA have the capacity to inhibit TNAP activities at physiologic concentrations. Downregulation of their inhibiting concentration in the cartilage interstitial fluid environment may provide a therapeutic avenue to controlled dissolution of CPPD crystal deposition in tissues.

Relationship between eggshell strength and keratan sulfate of eggshell membranes

Eggshell strength is an important factor in an effort to minimize eggshell breakage, which is a significant problem in the egg production industry. In the current study, we isolated and quantified the specific glycosaminoglycans (GAGs) from the calcified eggshell and shell membranes, which are related to eggshell strength. Our data suggest that GAGs exist in calcified eggshell may influence morphology of shell but do not affect on increase of shell amount while GAGs of shell membranes are maybe highly associated with shell strength with an increase of shell weight. Shell strength showed a strong correlation with the content of GAGs (r=0.942, p<0.0005) and a weak relationship with uronic acid content (r=0.564, p=0.056) in shell membranes. Monosaccharides in shell membranes were determined by Bio-LC analysis for the identification of any specific GAGs related with shell strength. It indicates that the galactose content as a component of keratan sulfate (KS) has a significant correlation with eggshell strength (r=0.985, p<0.0005). These results suggest that eggshell strength is proportional to the KS content of eggshell membranes with an increase of eggshell weight.

Raman microspectrometry of laser-reshaped rabbit auricular cartilage: preliminary study on laser-induced cartilage mineralization

Laser-assisted cartilage reshaping (LACR) is a relatively novel technique designed to noninvasively and permanently restructure cartilaginous tissue. It is believed that heat-induced stress relaxation, in which a temperature-mediated disruption of H2O binding is associated with conformational alterations in the proteoglycan and collagen-rich matrix, constitutes the underlying mechanism of LACR. Several reports have suggested that laser-mediated cartilage mineralization may contribute to the permanent shape change of laser-reshaped cartilage. In an effort to validate these results in the context of Er:glass LACR, we performed a preliminary Raman microspectrometric study to characterize the crystal deposits in laser-irradiated chondrocytes and extracellular matrix. For the first time, we identified intracellular calcium sulfate deposits and extracellular calcium phosphate (apatite) crystals in laser-reshaped rabbit auricular cartilage. Calcium carbonate deposits are localized in both irradiated and nonirradiated samples, suggesting that this mineral plays no role in conformational retention. In our discussion, we elaborate on the possible molecular and cellular mechanisms responsible for intra- and extracellular crystallization, and propose a novel hypothesis on the formation of apatite, inasmuch as the biological function of this mineral (providing structure and rigidity in bones and dental enamel) may be extrapolated to the permanent shape change of laser-irradiated cartilage.

In vitro models of calcium crystal formation

PURPOSE OF REVIEW

Calcium pyrophosphate dihydrate crystals are common components of synovial fluids from degenerated joints and often accompany unusually severe cartilage destruction. Progress in understanding why and how calcium pyrophosphate dihydrate crystals form in articular cartilage has been hampered by the scarcity of good models in which to study this phenomenon.

RECENT FINDINGS

In this review, the author discusses various models of calcium pyrophosphate dihydrate crystal formation from early work with solutions and gels to more recent models using cells, tissues, and cell fractions. Each of these systems has advantages and disadvantages.

SUMMARY

Current models of calcium pyrophosphate dihydrate crystal formation are less than ideal for studying the major factors involved in calcium pyrophosphate dihydrate crystal formation. Borrowing from the transplantation literature, solid matrices that support cell growth and allow for easy manipulation of matrix components hold some promise for better models in the future.

Pathogenesis of cartilage calcification: mechanisms of crystal deposition in cartilage

Apatite crystals form in physiologically calcified tissues, including the hyaline cartilage of the epiphyseal growth plate. While apatite crystals appear as unwanted deposits in other cartilage sites, more frequently, crystalline materials other than or in addition to apatite develop in dystrophic cartilage deposits. These crystalline materials include calcium pyrophosphate dihydrate and other calcium phosphate and calcium carbonate phases, monosodium urate, calcium oxalate, cholesterol, and crystallized proteins. This review describes the physical chemistry of crystal deposition and the events that occur in the growth plate as a basis for understanding the pathogenesis of nonphysiologic crystal deposition in cartilage.

Inhibition of hydroxyapatite crystal growth by bone proteoglycans and proteoglycan components

The small leucine-rich proteoglycans (SLRPs) interact with hydroxyapatite (HAP) and have been demonstrated to be important modulators of mineralisation. In the present study we have examined the effect of bone SLRPs, purified bone glycosaminoglycan (GAG) chains and core proteins as well as commercial chondroitin 4-sulphate, chondroitin 6-sulphate and desulphated chondroitin on HAP crystal growth. Seeded HAP growth experiments revealed that addition of bone GAG chains resulted in almost complete inhibition of crystal growth (93%), with addition of core proteins and intact PGs resulting in 55 and 37% inhibition, respectively. In contrast, commercial chondroitin 4-sulphate was significantly less inhibitory compared with the bone SLRPs and components, yielding only a 6% reduction in HAP-induced crystal growth at the same concentration. Significantly, chondroitin 6-sulphate was found to be noninhibitory, whilst desulphated chondroitin was inhibitory to seeded HAP growth. The data indicate that direct adsorption of SLRPs to growth sites and their ability to bind calcium are significant determinants in the inhibitory process. In addition, PG/GAG chemistry and the conformation of the macromolecules in solution have also been shown to be important. This work provides new information regarding the role of bone SLRPs and their components in the regulation of the mineralisation process.

Calcium pyrophosphate dihydrate crystal deposition disease: a review of the literature and a light and electron microscopic study of a case of the temporomandibular joint with numerous intracellular crystals in the chondrocytes

The pathogenesis of calcium pyrophosphate dihydrate (CPPD) crystal deposition disease of synovial joints is still unclear, although overproduction of extracellular pyrophosphate (PPi) is thought to play a key role. We studied the light and electron microscopic appearances of a case of CPPD crystal deposition disease of the temporomandibular joint (TMJ) in search of new clues for its pathogenesis. Light microscopic examination of CPPD-containing material from the joint space revealed cartilaginous nodules with various degrees of crystallization. Transmission electron microscopic examination revealed numerous extra- as well as intracellular crystals and crystal shaped spaces in the chondrocytes. Other striking ultrastructural features of the chondrocytes included the presence of many mitochondria, frequently containing crystalline material, and the presence of highly dilated rough endoplasmic reticulum and large glycogen islands. The presence of intramitochondrial crystals may hypothetically imply a derangement in mitochondrial adenosine triphosphate or PPi metabolism. The finding of intracellular CPPD crystals in chondrocytes points to the existence of an intracellular pathway of CPPD crystal formation in CPPD crystal deposition disease of the TMJ and possibly in CPPD crystal deposition disease in general.

Alterations in glycosaminoglycan concentration and sulfation during chondrocyte maturation

We have used antibodies to chondroitin 4- and 6-sulfate and keratan sulfate along with Alcian blue staining of sulfated proteoglycans to investigate changes in content and sulfation within the avian growth plate. In normal chicks, chondroitin 4- and 6-sulfate content were similar in the proliferating and transitional zones but in the hypertrophic zone, chondroitin 4- and 6-sulfate were slightly lower (13% and 18%, respectively) and keratan sulfate was markedly lower (58%). Compared with the proliferative zone, Alcian blue staining of sulfated glycosaminoglycans was markedly lower in both the transitional (46%) and hypertrophic (22%) zones. In tibial dyschondroplasia, where chondrocyte maturation is arrested at the transitional zone, there was no difference in the chondroitin 4- and 6-sulfate or keratan sulfate staining between the proliferative and transitional zones, which were similar to normal birds. With Alcian blue staining there was no difference in the intensity of the staining within the proliferating zone compared with normal birds but staining in the transitional chondrocytes was markedly higher (39%). These results suggest that in the early steps of chondrocyte maturation there may be a decrease in the degree of glycosaminoglycan sulfation without any alteration in glycosaminoglycan concentration, and that further maturation may be accompanied by a change in the nature of the proteoglycans which may also affect the level of sulfation.

High resolution and image processing of otoconia matrix

This study was designed to investigate patterns of fibrils organization in histochemically stained otoconia. Transmission electron microscope and video imaging were used. These data indicate that otoconia of the chick (Gallus domesticus) inner ear may have central cores in vivo. The data also show that the ultrastructural organization of fibrils fixed with aldehydes and histochemical stains follows trajectories that conform to the hexagonal shape of otoconia. These changes in direction may contribute to the formation of a central core. The existence of central cores is important for the in vivo buoyancy of otoconia. Packing of fibrils is tighter after phosphotungstic acid (PTA) stained otoconia than with other histochemical stains, which usually produce looser packing of fibrils and seemingly larger central core. TEM of tilted and untilted material showed that turning of fibrils occurs at the points where the face angles of otoconia form and where central cores exist. Video image processing of the images allowed reconstructing a template which, if assumed to repeat and change trajectories, would fit the pattern of fibrils seen in fixed otoconia. Since it is highly unlikely that aldehyde primary fixation or PTA stain caused such drastic change in the direction of fibrils, the template derived from these results may closely approximate patterns of otoconia fibrils packing in vivo. However, if the above is correct, the perfect crystallographic diffraction pattern of unfixed otoconia do not correspond to patterns of fixed fibrils.

Calcium pyrophosphate dihydrate crystal deposition in synovium. Relationship to collagen fibers and chondrometaplasia

OBJECTIVE

Reasons for apparent primary deposition of calcium pyrophosphate dihydrate (CPPD) crystals in some synovial membranes have not been systematically examined. We undertook the present study to investigate for and compare possible cellular and matrix factors related to the presence of these crystals in synovium and cartilage.

METHODS

Ten synovial membrane specimens and 6 cartilage specimens were obtained at the time of joint surgery from 10 patients with CPPD crystal deposition disease, for light microscopic (LM) and electron microscopic (EM) studies.

RESULTS

In all synovial and cartilage specimens, we found many of the small CPPD crystals aligned on or in parallel to collagen fibers, as seen by EM. In 9 of the 10 crystal-containing synovia, we found foci of chondrometaplasia adjacent to CPPD, by LM. In 7 of the synovia, including the one without LM evidence of chondrometaplasia, we observed the presence of chondrocyte-like cells by EM. We did not note any predictable relationship between the crystals and matrix vesicles, either in synovium or in cartilage.

CONCLUSION

Our EM findings provide evidence of the relationship of small CPPD-like crystals, presumably early forms, to collagen fibers both in synovium and in cartilage. By LM and EM, we also demonstrate evidence of a close association between chondrometaplasia and CPPD deposits in synovium. We suggest that chondrometaplasia might be responsible for synovial CPPD formation in predisposed patients. Both the collagen fibers and chondrocyte-like cells seem to be involved in the primary formation of CPPD deposits in the synovium as well as in the cartilage.

Partial biochemical and immunochemical characterization of avian eggshell extracellular matrices

There is evidence to suggest that extracellular matrix molecules, such as proteoglycans, are involved in the regulation of mineral deposition in calcifying tissues. One mineralizing system which is characterized by extremely rapid mineralization is the hen eggshell. This eggshell consists of a pair of nonmineralized eggshell membranes subjacent to the calcified eggshell proper; the eggshell proper is organized into palisades (columns) of mineralized matrix separated by pores. Between the membranes and the shell proper are compacted foci of tissue called mammillary knobs, which are thought to be sites where mineralization is initiated. Previous work from this laboratory has shown the presence of types I, V, and X collagen in the shell membranes. To address the question of the possible role of proteoglycans and glycosaminoglycans in mineralization of the eggshell, two approaches were used. First, immunohistochemistry was performed with monoclonal antibodies to various proteoglycan and glycosaminoglycan epitopes. This analysis indicates that different glycosaminoglycans are localized to discrete regions within the eggshell. Dermatan sulfate is present within the matrix of the shell proper and, to a lesser extent, the mammillary knobs and the outer portion of the shell membranes. In contrast, keratan sulfate is found in the shell membranes and prominently in the mammillary knobs. Interestingly, different keratan sulfate antibodies immunostain distinct regions of the eggshell, which suggests that various types of keratan sulfate are distributed differently. The second approach utilized was to extract the eggshell membranes and recover anionic molecules by anion-exchange chromatography. This resulted in the extraction of material which was recognized by antibodies to keratan sulfate, but not to chondroitin sulfate. This material was very large, as evidenced by its elution in the void volume of a Sepharose CL-2B column. The large size may be due to the extensive cross-links known to occur in the eggshell. If eggshell membranes are extracted at elevated temperature, the material recovered is of much smaller size. These results indicate that molecules recognized by antibodies to glycosaminoglycans are present in the eggshell, and their localized distribution relative to the calcified matrix suggests that they may be involved in the regulation of mineral deposition.

Hydroxyapatite formation in the presence of proteoglycans of reduced sulfate content: studies in the brachymorphic mouse

Proteoglycans from the brachymorphic (bm/bm) mouse have a reduced sulfate content due to the impaired activity of adenosine phosphosulfate phosphokinase in these animals. X-ray diffraction and infrared analyses of the mineral from the calcified cartilage of the bm/bm mice demonstrate the presence of significantly larger and more perfect hydroxyapatite crystals of lower carbonate to phosphate content than crystals found in the control animals. No differences were seen in the mineral content, crystallite size, CO3:PO4 ratio, or infrared splitting factors measured in the diaphyseal bone from these animals. Electron microscopic examination similarly shows larger, more disorganized crystals in the bm/bm animals' calcified cartilage as contrasted with controls. In vitro, proteoglycan aggregates from these dwarf mice are shown in a collagen gel-growth system to be less effective inhibitors of hydroxyapatite formation and growth than similarly size sulfated proteoglycans from age-matched control animals. The proteoglycans from the control mice were comparable in inhibitory ability to proteoglycan aggregates extracted from fetal bovine epiphyses. The in vitro and in vivo mineral parameters suggest the importance of sulfate for the interaction between proteoglycans and mineral in growth plate calcification.

Proteoglycan synthesis in vitamin D-deficient cartilage: recovery from vitamin D deficiency

Vitamin D appears to be required for mineralization of skeletal elements. There is also evidence that cartilage proteoglycans may be involved in the regulation of mineralization. Previous studies have shown an alteration in the structure of the proteoglycans of the epiphyseal growth cartilage as a result of the decrease in serum calcium related to deficiency of dietary vitamin D. Vitamin D deficiency also induces a thickening of the epiphyseal growth plate presumably because of the inhibition of maturation of the growth plate chondrocytes. In order to compare the effect on proteoglycan structure with that on growth plate morphology, the proteoglycans of healing epiphyseal cartilage were characterized. The results indicate that, consistent with previous data, in vitamin D-deficient hatching chicks, the proteoglycans of the growth cartilage, but not of the articular cartilage, are smaller in monomer size with slightly smaller chondroitin sulfate chains whose sulfation pattern is unaltered. Sternal cartilage proteoglycans are unaffected. During recovery from vitamin D deficiency, the proteoglycans isolated from the growth cartilage are still not completely normal one day after supplementation with vitamin D, but are indistinguishable from normal by four days. In addition, the results conflict with those of a previous study in which only growth cartilage of hatchling chicks, not sternal or articular cartilage, was reported to synthesize large proteoglycans. Instead, all of these cartilages in the normal chicken have been found in this study to produce large proteoglycans of a size typical for mammalian cartilage and embryonic chick cartilage.