Isolation and partial characterization of collagen chains dimerized by sugar-derived cross-links

Age-dependent changes in collagen crosslinks reduce the mechanical toughness of human meniscus

The mechanical resilience of the knee meniscus is provided by a group of structural proteins in the extracellular matrix. Aging can alter the quantity and molecular structure of these proteins making the meniscus more susceptible to debilitating tears. In this study, we determined the effect of aging on the quantity of structural proteins and collagen crosslinks in human lateral meniscus, and examined whether the quantity of these molecules was predictive of tensile toughness (area under the stress-strain curve). Two age groups were tested: a young group under 40 and an older group over 65 years old. Using mass spectrometry, we quantified the abundance of proteins and collagen crosslinks in meniscal tissue that was adjacent to the dumbbell-shaped specimens used to measure uniaxial tensile toughness parallel or perpendicular to the circumferential fiber orientation. We found that the enzymatic collagen crosslink deoxypyridinoline had a significant positive correlation with toughness, and reductions in the quantity of this crosslink with aging were associated with a loss of toughness in the ground substance and fibers. The non-enzymatic collagen crosslink carboxymethyl-lysine increased in quantity with aging, and these increases corresponded to reductions in ground substance toughness. For the collagenous (Types I, II, IV, VI, VIII) and non-collagenous structural proteins (elastin, decorin, biglycan, prolargin) analyzed in this study, only the quantity of collagen VIII was predictive of toughness. This study provides valuable insights on the structure-function relationships of the human meniscus, and how aging causes structural adaptations that weaken the tissue's mechanical integrity.

Membrane barriers for guided bone regeneration: An overview of available biomaterials

Dental implants revolutionized the treatment options for restoring form, function, and esthetics when one or more teeth are missing. At sites of insufficient bone, guided bone regeneration (GBR) is performed either prior to or in conjunction with implant placement to achieve a three-dimensional prosthetic-driven implant position. To date, GBR is well documented, widely used, and constitutes a predictable and successful approach for lateral and vertical bone augmentation of atrophic ridges. Evidence suggests that the use of barrier membranes maintains the major biological principles of GBR. Since the material used to construct barrier membranes ultimately dictates its characteristics and its ability to maintain the biological principles of GBR, several materials have been used over time. This review, summarizes the evolution of barrier membranes, focusing on the characteristics, advantages, and disadvantages of available occlusive barrier membranes and presents results of updated meta-analyses focusing on the effects of these membranes on the overall outcome.

AGE-breaker ALT711 reverses glycation-mediated cancer cell migration

Diabetes is associated with increased risk of breast cancer and worse prognoses for cancer patients. Hyperglycemia can result in increased glycation, the process wherein crosslinkages are formed between sugars and extracellular matrix (ECM) proteins through the formation of advanced glycation endproducts (AGEs). Although accumulation of AGEs occurs naturally in vivo over time, it is greatly accelerated by the hyperglycemic environment of diabetic patients. AGE accumulation has been linked to stiffening-related diseases such as hypertension, cancer metastasis, and neurodegenerative disorders. In response, several AGE-inhibiting and AGE-breaking drugs have received significant attention for their ability to reduce AGE accumulation. The resulting effects of these drugs on cell behavior is not well understood. In this study, we measured cancer cell migration in glycated collagen with and without the AGE-breaking drug alagebrium chloride (ALT711) to investigate the drug's ability to disrupt ECM crosslinks and reduce tumor cell spreading, contractility, and migration. The mechanical properties and chemical composition of collagen glycated with increasing concentrations of glucose with and without ALT711 treatment were measured. Increasing glucose concentration resulted in increased AGE accumulation and matrix stiffness as well as increased cancer cell contractility, elongation, and migration. Treatment with ALT711 significantly lowered AGE accumulation within the collagen, decreased collagen stiffness, and reduced cell migration. These findings suggest that while hyperglycemia can increase collagen matrix stiffness, resulting in increased breast cancer cell migration, an AGE-breaker can reverse this phenotype and may be a viable treatment option for reducing cancer cell migration due to glycation.

Intramuscular connective tissue content and mechanical properties: Influence of aging and physical activity in mice

Aging is accompanied by morphological and mechanical changes to the intramuscular connective tissue (IMCT) of skeletal muscles, but whether physical exercise can influence these changes is debated. We investigated the effects of aging and exercise with high or low resistance on composition and mechanical properties of the IMCT, including direct measurements on isolated IMCT which has rarely been reported. Middle-aged (11 months, n = 24) and old (22 months, n = 18) C57BL/6 mice completed either high (HR) or low (LR) resistance voluntary wheel running or were sedentary (SED) for 10 weeks. Passive mechanical properties of the intact soleus and plantaris muscles and the isolated IMCT of the plantaris muscle were measured in vitro. IMCT thickness was measured on picrosirius red stained cross sections of the gastrocnemius and soleus muscle and for the gastrocnemius hydroxyproline content was quantified biochemically and advanced glycation end-products (AGEs) estimated by fluorometry. Mechanical stiffness, IMCT content and total AGEs were all elevated with aging in agreement with previous findings but were largely unaffected by training. Conclusion: IMCT accumulated with aging with a proportional increase in mechanical stiffness, but even the relatively high exercise volume achieved with voluntary wheel-running with or without resistance did not significantly influence these changes.

Covalently Crosslinked Hydrogels via Step-Growth Reactions: Crosslinking Chemistries, Polymers, and Clinical Impact

Hydrogels are an important class of biomaterials with the unique property of high-water content in a crosslinked polymer network. In particular, chemically crosslinked hydrogels have made a great clinical impact in past years because of their desirable mechanical properties and tunability of structural and chemical properties. Various polymers and step-growth crosslinking chemistries are harnessed for fabricating such covalently crosslinked hydrogels for translational research. However, selecting appropriate crosslinking chemistries and polymers for the intended clinical application is time-consuming and challenging. It requires the integration of polymer chemistry knowledge with thoughtful crosslinking reaction design. This task becomes even more challenging when other factors such as the biological mechanisms of the pathology, practical administration routes, and regulatory requirements add additional constraints. In this review, key features of crosslinking chemistries and polymers commonly used for preparing translatable hydrogels are outlined and their performance in biological systems is summarized. The examples of effective polymer/crosslinking chemistry combinations that have yielded clinically approved hydrogel products are specifically highlighted. These hydrogel design parameters in the context of the regulatory process and clinical translation barriers, providing a guideline for the rational selection of polymer/crosslinking chemistry combinations to construct hydrogels with high translational potential are further considered.

Tensile Properties of Three Selected Collagen Membranes

BACKGROUND

Biological barriers are commonly used to treat alveolar bone defects and guide tissue regeneration. Understanding the biological and mechanical properties of the available membranes is crucial for selecting the one that is optimal for enhancing clinical outcomes.

PURPOSE

To evaluate the mechanical behavior of three different collagen membranes to increasing tensile force in dry and wet conditions.

MATERIALS AND METHODS

Three commercially collagen membranes were selected for analysis: Bio-Gide® (Geistlich Biomaterials, Baden-Baden, Germany), Remaix™ (RX; Matricel GmbH, Herzogenrath, Germany), and Ossix Plus® (Datum Dental Biotech, Lod, Israel). Increasing tensile forces were applied on 10 dry and wet membranes of standard size via a loading machine. Force and extension values were acquired up to maximum load before failure, and maximum stress, maximum extension, and amount of energy needed for membrane tearing were analyzed. Membranes' densities were also calculated.

RESULTS

The Remaix membrane exhibited the highest values of maximum load tensile strength, maximum extension, and maximum energy required for membrane tearing, followed by Bio-Gide. Ossix Plus had the lowest scores in all these parameters. Dry membranes had the highest scores for all parameters except extension. Membrane density was directly and significantly correlated with all tested parameters.

CONCLUSIONS

The study was undertaken to provide clinicians with data upon which to base the selection of collagen membranes in order to achieve optimal clinical results. It emerged that the mechanical properties of dry and wet collagen membranes were significantly different from one another. Among the 3 tested membranes, Remaix exhibited higher performance results in all the mechanical tests. Collagen membrane density seems to have a significant influence upon mechanical resistance. These findings may also guide manufacturers in improving the quality of their product.

Advanced glycation end-product cross-linking inhibits biomechanical plasticity and characteristic failure morphology of native tendon

Advanced glycation end-products (AGEs) are formed in vivo from the nonenzymatic reaction between sugars and proteins. AGEs accumulate in long-lived tissues like tendons, cross-linking neighboring collagen molecules, and are in part complicit in connective tissue pathologies experienced in aging and with diabetes. We have previously described discrete plasticity: a characteristic form of nanoscale collagen fibril damage consisting of serial fibril kinking and collagen denaturation that occurs in some mechanically overloaded tendons. We suspect that this failure mechanism may be an adaptive trait of collagen fibrils and have published evidence that inflammatory cells may be able to recognize and digest the denatured collagen produced by overload. In this study, we treated bovine tail tendons with ribose to simulate long-term AGE cross-linking in vitro. We hypothesized that a high degree of cross-linking would inhibit the intermolecular sliding thought to be necessary for discrete plasticity to occur. Tendons were mechanically overloaded, and properties were investigated by differential scanning calorimetry and scanning election microscopy. Ribose cross-linking treatment altered the mechanical response of tendons after the yield point, significantly decreasing postyield extensibility and strain energy capacity before rupture. Coincident with altered mechanics, ribose cross-linking completely inhibited the discrete plasticity failure mechanism of tendon. Our results suggest that discrete plasticity, which may be an important physiological mechanism, becomes pathologically disabled by the formation of AGE cross-links in aging and diabetes. NEW & NOTEWORTHY We have previously shown that mechanically overloaded collagen fibrils in mammalian tendons accrue nanoscaled damage. This includes development of a characteristic kinking morphology within a shell of denatured collagen: discrete plasticity. Here, using a ribose-incubation model, we show that advanced glycation end-product cross-linking associated with aging and diabetes completely inhibits this mechanism. Since discrete plasticity appears to cue cellular remodeling, this result has important implications for diabetic tendinopathy.

Collagen-silica bio-composite enriched with Cynodon dactylon extract for tissue repair and regeneration

Development of biomaterials for tissue engineering applications is of great interest to meet the demand of different clinical requirements. The wound heal dressing biomaterials should necessarily contain well-defined therapeutic components and desirable physical, chemical and biological properties to support optimal delivery of therapeutics at the site of the wound. In this study, we developed collagen-silica wound heal scaffold incorporated with the extract of Cynodon dactylon, characterized and evaluated for its wound heal potential in vitro and in vivo against collagen (Col) and Collagen-silica (CS) scaffolds that served as controls. The prepared Collagen-Silica-Cynodon extract (CSCE) scaffold exhibits porous morphology with preferable biophysical, chemical, mechanical and mass transfer properties besides its controlled biodegradation at the wound site. Stability of CSCE was found to be better than that of native collagen due to intermolecular interactions between collagen and constituents of C. dactylon as confirmed by FTIR analysis. Notably, in vitro biocompatibility assay using DAPI and Rhodamine 123 staining demonstrated that the proliferation of NIH3T3 fibroblast cells was better for CSCE when compared to the Col and CS scaffolds. In vivo wound healing experiments with full-thickness excision wounds in wistar rat model demonstrated that the wounds treated with CSCE showed accelerated healing with enhanced collagen deposition when compared to wounds treated with Col and CS scaffolds, and these studies substantiated the efficacy of CSCE scaffold for treating wounds.

Role of advanced glycation end products in mobility and considerations in possible dietary and nutritional intervention strategies

Advanced glycation end products (AGEs), a group of compounds that are formed by non-enzymatic reactions between carbonyl groups of reducing sugars and free amino groups of proteins, lipids or nucleic acids, can be obtained exogenously from diet or formed endogenously within the body. AGEs accumulate intracellularly and extracellularly in all tissues and body fluids and can cross-link with other proteins and thus affect their normal functions. Furthermore, AGEs can interact with specific cell surface receptors and hence alter cell intracellular signaling, gene expression, the production of reactive oxygen species and the activation of several inflammatory pathways. High levels of AGEs in diet as well as in tissues and the circulation are pathogenic to a wide range of diseases. With respect to mobility, AGEs accumulate in bones, joints and skeletal muscles, playing important roles in the development of osteoporosis, osteoarthritis, and sarcopenia with aging. This report covered the related pathological mechanisms and the potential pharmaceutical and dietary intervention strategies in reducing systemic AGEs. More prospective studies are needed to determine whether elevated serum AGEs and/or skin autofluorescence predict a decline in measures of mobility. In addition, human intervention studies are required to investigate the beneficial effects of exogenous AGEs inhibitors on mobility outcomes.

Multiscale mechanical effects of native collagen cross-linking in tendon

The hierarchical structure of tendon allows for attenuation of mechanical strain down decreasing length scales. While reorganization of collagen fibers accounts for microscale strain attenuation, cross-linking between collagen molecules contributes to deformation mechanisms at the fibrillar and molecular scales. Divalent and trivalent enzymatic cross-links form during the development of collagen fibrils through the enzymatic activity of lysyl oxidase (LOX). By establishing connections between telopeptidyl and triple-helical domains of adjacent molecules within collagen fibrils, these cross-links stiffen the fibrils by resisting intermolecular sliding. Ultimately, greater enzymatic cross-linking leads to less compliant and stronger tendon as a result of stiffer fibrils. In contrast, nonenzymatic cross-links such as glucosepane and pentosidine are not produced during development but slowly accumulate through glycation of collagen. Therefore, these cross-links are only expected to be present in significant quantities in advanced age, where there has been sufficient time for glycation to occur, and in diabetes, where the presence of more free sugar in the extracellular matrix increases the rate of glycation. Unlike enzymatic cross-links, current evidence suggests that nonenzymatic cross-links are at least partially isolated to the surface of collagen fibers. As a result, glycation has been proposed to primarily impact tendon mechanics by altering molecular interactions at the fiber interface, thereby diminishing sliding between fibers. Thus, increased nonenzymatic cross-linking decreases microscale strain attenuation and the viscous response of tendon. In conclusion, enzymatic and nonenzymatic collagen cross-links have demonstrable and distinct effects on the mechanical properties of tendon across different length scales.

Age-related changes in the knee meniscus

BACKGROUND

Aging is the most prominent risk factor for the development of osteoarthritis (OA), which affects knees and causes major health burdens. Meniscal dysfunction mostly based on degeneration contributes to the development and progression of knee OA. Meniscal degeneration is caused by various extrinsic factors, such as repetitive trauma or leg malalignment, while meniscal aging is considered as internal changes, such as molecular or cellular changes. Little is known about age-related changes in the meniscus. Therefore, this review aimed to summarize and clarify the understanding of the aged meniscus.

METHODS

There are few articles about natural aging in the meniscus, because most reports only demonstrate the effects of OA on the meniscus. We searched PubMed (1948 to November 2016) to identify and summarize all English-language articles evaluating natural aging in the meniscus.

RESULTS

There is evidence of compositional change in the meniscus with aging, involving cells, collagens, and proteoglycans. In addition, as recent reports on the natural aging of cartilage have indicated, senescence of the meniscal cells may also lead to disruption of meniscal cells and tissue homeostasis. Due to the low turnover rate of collagen, accumulation of advanced glycation end-products largely contributes to tissue stiffness and vulnerability, and finally results in degenerative changes or tears. Furthermore, environmental factors such as joint fluid secreted by inflamed synovium could also contribute to meniscal tissue deterioration.

CONCLUSIONS

Age-related changes induce meniscal tissue vulnerability and finally lead to meniscal dysfunction.

Detection of Pentosidine Cross-Links in Cell-Secreted Decellularized Matrices Using Time Resolved Fluorescence Spectroscopy

Hyperglycemia-mediated, nonenzymatic collagen cross-links such as pentosidine (PENT) can have deleterious effects on cellular interactions with the extracellular matrix (ECM). Present techniques to quantify PENT are limited, motivating the need for improved methods to study the accumulation and contribution of PENT toward diabetic clinical challenges such as impaired bone healing. Current methods for studying PENT are destructive, laborious, and frequently employ oversimplified collagen films that lack the complexity of the native ECM. The primary goal of this study was to evaluate the capacity of time-resolved fluorescence spectroscopy (TRFS) to detect PENT in cell-secreted ECMs possessing enhanced compositional complexity. To demonstrate an application of this method, we assessed the response of human mesenchymal stem cells (MSCs) to cross-linked substrates to explore the role of detected PENT on osteogenic differentiation. We exposed MSC-secreted decellularized matrices (DMs) to 0.66 M ribose for 2 weeks and used TRFS to detect the accumulation of PENT. Ribose treatment resulted in a 30 nm blue shift in peak fluorescence emission and a significant decrease in average lifetime compared to that of control DMs (4.4 ± 0.3 ns vs 3.5 ± 0.09 ns). Evaluation of samples with high performance liquid chromatography (HPLC) confirmed that changes in observed fluorescence were due to PENT accumulation. A strong correlation was found between TRFS parameters and the HPLC measurement of PENT, validating the use of TRFS as an alternative method of PENT detection. Osteoblastic gene expression was significantly reduced in MSCs seeded on ribose DMs at days 7 and 14. However, no significant differences in calcium deposition were detected between control and ribose DMs. These data demonstrate the efficacy of nondestructive fluorescence spectroscopy to examine the formation of nonenzymatic collagen cross-links within biomimetic culture platforms and showcase one example where an improved biomimetic substrate can be used to probe cell-ECM interactions in the presence of collagen cross-links.

Nanophase bone substitute for craniofacial load bearing application: Pilot study in the rodent

An exploratory pilot study shows that a rodent mandibular defect model is useful in determining the biological response to a nanophase collagen/apatite composite designed as a biomimetic load-bearing bone substitute. Using a critical size defect, eight groups of rats (n = 3) were implanted with four renditions of the nanophase bone substitute (NBS) biomaterial. Each rendition was tested with and without recombinant human bone morphogenetic protein 2 (BMP2). NBS biomaterial renditions were: baseline, hyper-densified, d-ribose crosslinked, and d-ribose crosslinked and hyper-densified. Biological outcomes were assessed surgically, radiologically, and histologically. With the limited power available due to the small N's involved, some interesting hypotheses were generated that will be more fully investigated in future studies. BMP2 loaded NBS, when uncrosslinked, resulted in robust bone formation in the entire defect volume (regardless of porosity). Unloaded NBS were well tolerated but did not cause significant new bone formation in the defect volume. Densification alone had little effect on in vivo performance. Crosslinking thwarted implant uptake of BMP2 and resulted in fibrous encapsulation. It is concluded that the nanophase bone substitute is well tolerated in this bone defect model. When loaded with BMP2, implantation resulted in complete bony healing and defect closure with implant density (porosity) having little effect on bone healing or remodeling. Without BMP2 the biomaterial did not result in defect closure. Crosslinking, necessary to increase mechanical properties in an aqueous environment, disrupts osteointegration and BMP2 uptake. Alternate implant fabrication strategies will be necessary to achieve an improved balance between material strength and osteointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 520-532, 2018.

Tetracycline impregnation affects degradation of porcine collagen matrix in healthy and diabetic rats

OBJECTIVES

The present study evaluated the degradation of collagen matrix (CM) immersed in tetracycline (TTC) or phosphate-buffered saline (PBS) in diabetic and normoglycemic rats.

MATERIALS AND METHODS

Diabetes was induced in 15 rats by systemic streptozotocin (STZ) (experimental); 15 healthy rats served as controls. One day before implantation 60 CM disks, 5 mm in diameter, were labeled with biotin: 30 were immersed in tetracycline (TTC) and 30 in PBS. One disk of each type was implanted subdermally in each rat. Animals were euthanized after 3 weeks, and tissue specimens containing the disks were prepared for histologic analysis. Horseradish peroxidase (HRP)-conjugated streptavidin was used to detect the remaining biotinylated collagen. Residual collagen area within the CM disks was analyzed and compared to baseline.

RESULTS

Diabetes significantly increased the CM degradation. Immersion of the CM disks in a 50-mg/mL TTC solution before implantation decreased its degradation both in diabetic and normoglycemic rats.

CONCLUSIONS

Diabetes significantly increases collagen matrix degradation; immersion of collagen matrix in TTC before implantation decreases its degradation in both diabetic and normoglycemic conditions.

CLINICAL RELEVANCE

Immersion of medical collagen devices in TTC may be an effective means to decrease their resorption rate and increase their effectiveness, especially in situations with increased degradation such as diabetes.

Paclitaxel/epigallocatechin gallate coloaded liposome: a synergistic delivery to control the invasiveness of MDA-MB-231 breast cancer cells

Matrix metalloproteinases (MMPs) have been investigated as a potential target for treating invasive breast cancers. The chemotherapy for breast cancer is often prescribed as a combination of drugs. The present study investigates a novel strategy of combining a MMP inhibitor, Epigallocatechin gallate (EGCG), along with an anticancer drug, Paclitaxel (PTX), in the form of a liposomal co-delivery system. The developed PTX/EGCG co-loaded liposomes showed an entrapment of 77.11±2.30% and 59.11±3.51% for PTX and EGCG, respectively. The in vitro efficacy of the liposomes was assessed by their ability to promote apoptosis and curtail cell invasion. On all parameters, namely cytotoxicity and caspase-3 activity that are indicators of apoptosis, and MMP-2 and - 9 inhibition and invasion assays that are indicators of cell invasion, the PTX/EGCG co-loaded liposomes showed better results than each of the individual drug loaded liposomes. These findings demonstrate the synergistic outcome of PTX/EGCG combination and indicate the suitability of PTX/EGCG co-loaded liposomes for the treatment of invasive breast cancer.

Sol-gel assisted fabrication of collagen hydrolysate composite scaffold: a novel therapeutic alternative to the traditional collagen scaffold

Collagen is one of the most widely used biomaterial for various biomedical applications. In this Research Article, we present a novel approach of using collagen hydrolysate, smaller fragments of collagen, as an alternative to traditionally used collagen scaffold. Collagen hydrolysate composite scaffold (CHCS) was fabricated with sol-gel transition procedure using tetraethoxysilane as the silica precursor. CHCS exhibits porous morphology with pore sizes varying between 380 and 780 μm. Incorporation of silica conferred CHCS with controlled biodegradation and better water uptake capacity. Notably, 3T3 fibroblast proliferation was seen to be significantly better under CHCS treatment when compared to treatment with collagen scaffold. Additionally, CHCS showed excellent antimicrobial activity against the wound pathogens Staphylococcus aureus, Bacillus subtilis, and Escherichia coli due to the inherited antimicrobial activity of collagen hydrolysate. In vivo wound healing experiments with full thickness excision wounds in rat model demonstrated that wounds treated with CHCS showed accelerated healing when compared to wounds treated with collagen scaffold. These findings indicate that the CHCS scaffold from collagen fragments would be an effective and affordable alternative to the traditionally used collagen structural biomaterials.

Glycation cross-linking induced mechanical-enzymatic cleavage of microscale tendon fibers

Recent molecular modeling data using collagen peptides predicted that mechanical force transmitted through intermolecular cross-links resulted in collagen triple helix unwinding. These simulations further predicted that this unwinding, referred to as triple helical microunfolding, occurred at forces well below canonical collagen damage mechanisms. Based in large part on these data, we hypothesized that mechanical loading of glycation cross-linked tendon microfibers would result in accelerated collagenolytic enzyme damage. This hypothesis is in stark contrast to reports in literature that indicated that individually mechanical loading or cross-linking each retards enzymatic degradation of collagen substrates. Using our Collagen Enzyme Mechano-Kinetic Automated Testing (CEMKAT) System we mechanically loaded collagen-rich tendon microfibers that had been chemically cross-linked with sugar and tested for degrading enzyme susceptibility. Our results indicated that cross-linked fibers were >5 times more resistant to enzymatic degradation while unloaded but became highly susceptible to enzyme cleavage when they were stretched by an applied mechanical deformation.

Preparation and evaluation of mesalamine collagen in situ rectal gel: a novel therapeutic approach for treating ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory disease that primarily affects the colonic mucosa. Mesalamine had been established as a first line drug for treating mild to moderate UC. A continued availability of the drug for treatment of damaged tissues remains a great challenge today. In the present study, a novel mesalamine collagen in situ gel has been prepared using type I collagen, which is pH/temperature sensitive. This hydrogel undergoes sol-gel transition under physiological pH and temperature which was confirmed by rheological studies. The in vitro release profile demonstrated sustained release of mesalamine over a period of 12h. The in vivo efficacy of the in situ gel was performed using dextran sodium sulphate induced ulcerative colitis model in BALB/c mice. The clinical parameters such as, body weight changes, rectal bleeding and stool consistency were evaluated. In addition, the histopathological investigation was conducted to assess severity of mucosal damage and inflammation infiltrate. There was a significant reduction in rectal bleeding and mucosal damage score for collagen-mesalamine in situ gel group compared to the reference group. Apart from releasing mesalamine in controlled manner, the strategy of administering mesalamine through collagen in situ gel facilitates regeneration of damaged mucosa resulting in a synergistic effect for the treatment of ulcerative colitis.

Nanophase bone substitute in vivo response to subcutaneous implantation

A collagen-apatite composite designed as a load-bearing bone substitute implant is used to characterize the relationship between implant morphology and in vivo behavior. This nanophase bone substitute (NBS) is studied morphologically using a nondestructive imaging technique and biologically using the rodent subcutaneous model. Porosity and pore interconnectivity are correlated with histological outcomes showing cellular invasion occurs with average pore sizes below 100 μm. Crosslinking with D-ribose is shown to affect cellular infiltration in a dose-response manner. These data suggest that collagen-apatite bone substitutes can support cellular infiltration with pore size significantly smaller than 100 μm, an encouraging result regarding development of the NBS into a platform of biomaterials with enhanced mechanical properties. The data also indicate that increasing crosslinking density decreases cellular infiltration of NBS. Thus, modulating mechanical properties of the material by altering crosslink density is likely to produce decreased biological response within the material.

A novel anti-ageing mechanism for retinol: induction of dermal elastin synthesis and elastin fibre formation

Dermal elastic fibres are extracellular matrix protein complexes produced by fibroblasts and involved in skin elasticity. Elastin fibres decrease with age as a result of reduced synthesis and increased degradation, resulting in skin sagging and reduced skin elasticity. In this study, we show that retinol (ROL), known to enhance dermal collagen production, is also enhancing elastin fibre formation. ROL induced elastin gene expression and elastin fibre formation in cultured human dermal fibroblasts. Topical treatment of cultured human skin explants with a low dose (0.04%) of ROL increased mRNA and protein levels of tropoelastin and of fibrillin-1, an elastin accessory protein, as documented by QPCR and immunohistochemistry staining. Luna staining confirmed the increased elastin fibre network in the ROL-treated skin explants, as compared with untreated controls. These data demonstrate that ROL exerts its anti-ageing benefits not only via enhanced epidermal proliferation and increased collagen production, but also through an increase in elastin production and assembly.

Ossification of a collagen membrane cross-linked by sugar: a human case series

BACKGROUND

Collagen membranes cross-linked by glycation (GLYM) for guided bone regeneration (GBR) and guided tissue regeneration (GTR) are used extensively with proven safety and efficacy. Complete GLYM ossification, when placed in contact with bone, was described in a canine jaw model, suggesting that GLYM may serve as an ossification substrate. The purpose of this case series was to histologically evaluate GLYM in GBR procedures in humans.

METHODS

We retrospectively selected seven consecutive patients with implant-related bony defects who underwent GBR with GLYM. Six defects had bone grafts, and one had a barrier alone. Selection criteria were primary closure upon post-surgical examination and tissue that was 2- to 3-mm thick over the implant's cover screw. Tissue was removed when the implants were uncovered after 20 to 29 weeks. Decalcified sections were stained and analyzed under light microscopy.

RESULTS

In five of seven specimens, GLYM was identified and preserved its barrier effect. The mean membrane thickness was 0.17 +/- 0.054 mm. In two cases, the bone grafts under the membrane were embedded in new bone, whereas in five cases, they were embedded in fibrous connective tissue. Formation of new dense bone was observed along the side of the membrane facing the original bone, and various degrees of membrane ossification were evident in all five cases.

CONCLUSIONS

GLYM maintained its barrier effect in five of seven cases for 25 weeks and induced dense new bone along its interface with underlying tissues. To the best of our knowledge, this is the first report on GLYM ossification in humans with direct mineral apposition on glycated collagen and suggests a new concept of tissue-integrated active barriers.

Long-term efficacy of a novel ribose-cross-linked collagen dermal filler: a histologic and histomorphometric study in an animal model

BACKGROUND

Degradation and loss of the three-dimensional shape are the major causes of limited functional longevity of dermal fillers made of natural polymers as collagen and hyaluronic acid.

OBJECTIVE

This study assessed the functional longevity of a new ribose-cross-linked collagen filler during 24 months in an animal model.

METHODS

Ribose-cross-linked collagen (Evolence, Colbar Life Sciences Ltd), glutaraldehyde-cross-linked collagen (Zyplast, Inamed Inc.), and non-cross-linked collagen (Zyderm, Inamed Inc.) were injected in the rabbit ear dermis. Biopsies obtained at 1, 6, 12, and 24 months were histomorphometrically assessed for shape preservation and cell repopulation.

RESULT

The three-dimensional shape of Evolence remained stable during 24 months. Zyderm and Zyplast lost their three-dimensional shape after 6 months. Although the cell density in Evolence remained stable over time, that in Zyplast and Zyderm decreased significantly at 12 and 24 months.

CONCLUSION

Ribose-cross-linked collagen is endowed with a higher functional longevity as assessed in an animal model when compared with the most used collagen-based dermal fillers.

Ossification of a novel cross-linked porcine collagen barrier in guided bone regeneration in dogs

BACKGROUND

Collagen membranes for guided bone regeneration (GBR) and guided tissue regeneration (GTR) are used extensively as bioabsorbable barriers. Cross-linking of collagen increases its biodurability and enables the control of its degradation kinetics and barrier function. A novel cross-linking technology was used to produce a porcine type I collagen membrane (GLYM). The purpose of this study was to evaluate the safety, efficacy, and degradation kinetics of GLYM compared to a non-cross-linked bilayer type I and III porcine collagen membrane (BCM) in surgically created defects in dogs.

METHODS

After tooth extraction, two mandibular bilateral critical size defects were created in 12 beagle dogs that were randomly assigned to one of five groups: GLYM + bovine bone mineral (BBM), BCM + BBM, BBM alone, sham-operated, or GLYM alone. Dogs were euthanized after 8, 16, and 24 weeks, and sites were prepared for qualitative, semiquantitative, and quantitative light microscopy analyses.

RESULTS

Membrane-protected sites displayed bone filling between the BBM particles with almost complete restoration of the original ridge morphology that increased with time up to 16 weeks and remained unchanged at 24 weeks. Both membranes showed marked degradation within 16 to 24 weeks, with BCM inconsistency that was undetectable in one of four sites at 8, 16, and 24 weeks. Membrane ossification was observed in all GLYM sites and in only one BCM site, which progressed with time to 24 weeks. Bone increased by approximately 1 mm on the lingual side, where the GLYM membrane was in direct contact with bone.

CONCLUSIONS

Both membranes were safe and effective in supporting bone regeneration in critical size alveolar ridge defects in dogs and completely degraded within 24 weeks with marked BCM inconsistency. In areas of direct contact with bone, all GLYM sites were progressively ossified with time and augmented the original alveolar ridge. To the best of our knowledge, this is the first report of complete ossification of a collagen barrier membrane in GBR procedures.

Advanced glycation endproducts interfere with integrin-mediated osteoblastic attachment to a type-I collagen matrix

The adhesion of osteoblasts to bone extracellular matrix, of which type-I collagen constitutes >85%, can modulate diverse aspects of their physiology such as growth, differentiation and mineralisation. In this study we examined the adhesion of UMR106 rat osteoblast-like cells either to a control (Col) or advanced-glycation-endproduct-modified (AGEs-Col) type I collagen matrix. We investigated the possible role of different integrin receptors in osteoblastic adhesion, by co-incubating these cells either with beta-peptide (conserved sequence 113-125 of the beta subunit of integrins) or with two other peptides, RGD (Arg-Gly-Asp) and DGEA (Asp-Gly-Glu-Ala), which are recognition sequences for the alpha-subunits of alpha(1,5)beta(1) and alpha(2)beta(1) integrins. Collagen glycation inhibited the adhesion of UMR106 osteoblasts to the matrix (40% reduction versus Col, P > 0.001). beta-Peptide showed a dose- and glycation-dependent inhibitory effect on adhesion, and at a concentration of 100 microM decreased the attachment of UMR106 cells to both matrices (42% to Col, P<0.001and 25% to AGEs-Col, P<0.01). The synthetic peptides RGD (1mM) and DGEA (5mM) inhibited the attachment of UMR106 cells to Col (30 and 20%, P > 0.01 and P< 0.001, respectively), but not to AGEs-Col. beta-Peptide induced an increase in UMR106 cell clumping and a decrease in cellular spreading, while DGEA increased spreading with cellular extensions in multiple directions. These results indicate that both alpha and beta integrin subunits participate in osteoblastic attachment to type-I collagen, probably through the alpha(1,5)beta(1) and alpha(2)beta(1) integrins. AGEs-modification of type-I collagen impairs the integrin-mediated adhesion of osteoblastic cells to the matrix, and could thus contribute to the pathogenesis of diabetic osteopenia.

Evaluation of peptide electropherograms by multivariate mathematical-statistical methods. I. Principal component analysis

Depository effects in slowly metabolised proteins, typically glycation or the estimation of products arising from the reaction of unsaturated long-chain-fatty acid metabolites (possessing aldehydic groups) are very difficult to assess owing to their extremely low concentration in the protein matrix. In order to reveal such alterations we applied deep enzymatic fragmentation resulting in a set of small peptides, which, if modified, are likely to change their electrophoretic properties and can be visualised on the resulting profile. Peptide maps of collagen (a mixture of collagen types I and III digested by bacterial collagenase) were applied as the model protein structure for detecting the nonenzymatic posttranslational changes originating during various physiological conditions like high fructose diet and hypertriglyceridemic state. Capillary electrophoresis in acidic media (sodium phosphate buffer, pH 2.5) was used as the separation method capable of (partial) separation of over 60 peptide peaks. Two to 13 changes were revealed in the profiles obtained reflecting the physiological conditions of the animals tested. Combination of peptide profiling with subsequent t-test evaluation of individual peak areas and principal component analysis based on cumulative peak areas of individual sections of the electropherograms allowed to determine in which section (part) of the electropherogram the physiological state indicating changes occurred. Simultaneously it was possible to reveal the qualitative differences between the four physiological regimes investigated (i.e., which regime affects the collagen molecules most and which affects them least). The approach can be used as guidance for targeted preseparation of the very complex peptide mixture.

Advanced separation methods for collagen parent alpha-chains, their polymers and fragments

Current techniques used for collagen alpha-chains and their CNBr fragments are reviewed. Ion exchange, gel permeation, reversed-phase and affinity chromatography are discussed mainly from the preparative aspects as these are both the techniques of choice to remove biological matrix contaminants always present in collagen preparations and techniques routinely used for preparative purposes. Among electromigration procedures gel electrophoresis is widely used both for intact collagen alpha-chains and their fragments. Recently this technique was applied also for miniaturised preparations. Immunoblotting techniques serve more specific detection of otherwise hard to distinguish different collagen polypeptide chains. Capillary electromigration techniques brought recently new aspects of understanding the behaviour of collagen proteins upon different separation modes and seem to represent a smart perspective for better quantitation of individual collagen species.

Multicomponent analysis by off-line combination of synchronous fluorescence spectroscopy and capillary electrophoresis of collagen glycation adducts

Capillary electrophoresis separation and synchronous fluorescence spectral detection was used off-line to reveal the nature of fluorescent adducts formed in vivo in the collagen molecule and their distribution in the molecule. It was shown that by using the delta lamda in the area of the Stokes shift for the analyzed entities (approximately 10 nm for pentosidine, 4,5(E)-epoxy-2(E)-heptenal and 4,5(E)-epoxy-2(E)-decenal lysine adducts) a distinct profile of spectral bands can be obtained allowing for differentiation of the several entities involved. In combination with capillary electrophoretic separation of the CNBr peptides the location of individual adducts was possible: while pentosidine (and, perhaps, pentosidine related compounds K1-K4) is found in the large alpha 1(I)CB6 and alpha 2(I)CB3.5 peptides along with a complete set of the other fluorescent adducts, low-molecular-mass peptides originating from the terminal region of the molecule are devoid of any fluorescence. All other parts of the molecule possess synchronous fluorescence profiles corresponding to the intact molecule except that they are devoid of pentosidine. The results indicate random distribution of fluorescent adducts in the collagen molecule and, in a broader context, indicate the usefulness of multicomponent analysis by means of combining synchronous luminescence spectra and capillary electrophoresis.

Mechanisms of maturation and ageing of collagen

The deleterious age-related changes in collagen that manifest in the stiffening of the joints, the vascular system and the renal and retinal capillaries are primarily due to the intermolecular cross-linking of the collagen molecules within the tissues. The formation of cross-links was elegantly demonstrated by Verzar over 40 years ago but the nature and mechanisms are only now being unravelled. Cross-linking involves two different mechanisms, one a precise enzymically controlled cross-linking during development and maturation and the other an adventitious non-enzymic mechanism following maturation of the tissue. It is this additional non-enzymic cross-linking, known as glycation, involving reaction with glucose and subsequent oxidation products of the complex, that is the major cause of dysfunction of collagenous tissues in old age. The process is accelerated in diabetic subjects due to the higher levels of glucose. The effect of glycation on cell-matrix interactions is now being studied and may be shown to be an equally important aspect of ageing of collagen. An understanding of these mechanisms is now leading to the development of inhibitors of glycation and compounds capable of cleaving the cross-links, thus alleviating the devastating effects of ageing.

The nitrite/elastin reaction: implications for in vivo degenerative effects

Nitrite ion is a by-product of nitrogen oxides (nitric oxide and nitrogen dioxide) from cigarette smoke and is used as a preservative for curing meats. Therefore, study of the reaction of nitrite with elastin in vitro was undertaken. By colorimetric assay, reactivity of nitrite with insoluble elastin at neutral pH, 37 degrees C, and physiologic concentration was confirmed. In histochemical studies on in situ human aortic elastin, nitrite-treated sections displayed marked structural disruptions. Determinations of fluorescence and absorbance on nitrite-treated soluble bovine elastin revealed marked alterations of fluorescence, and increased UV and visible absorbance. Amino acid analysis confirmed that it reacted with tyrosine. The findings indicate that non-enzymatic nitration by nitrite may have deleterious effects on elastin in vivo and may provide insights into the pathogenesis of chronic elastin degenerative processes, including aortic aneurysms, pulmonary emphysema, and premature skin wrinkling, all of which have been well known to have associations with cigarette smoking.

Post-translational non-enzymatic modification of proteins. II. Separation of selected protein species after glycation and other carbonyl-mediated modifications

There are two strategies applicable to revealing non-enzymatic post-translational modifications of proteins; while assaying of the hydrolytically stable adducts was the subject of our previous communication [1], here we attempted to review separation technologies for the unfragmented modified proteins. There are a few standard procedures used for this purpose, namely Laemmli gel electrophoresis, different modes of gel permeation chromatography and boronate affinity chromatography. The latter approach makes use of the vicinal hydroxy groups present in glycated proteins. Some (but not all) arising adducts exhibit typical fluorescence which can be exploited for detection. In most cases fluorescence is measured at 370/440 nm for the so-called advanced glycation products or at 335/385 nm for the only so far well characterized glycation marker (pentosidine). Some indication exists that, e.g., synchronous fluorescence detection will probably in the future add to the selectivity and allow the distinction of the different adducts arising during non-enzymatic post-translational modifications (glycation). The proteins reviewed are serum albumin, collagen and lens proteins while glycation of hemoglobin is the subject of another review within the present volume.

Glycation of collagen in hypertriglyceridemic rats

Nonenzymatic collagen glycation and modification with lipid derived metabolites was studied in rat skin and tail tendon collagen of control and hypertriglyceridemic (HTG) rats. Age-dependent changes typical for lipid and sugar derived adducts were evaluated by measuring fluorescence of these collagens at wavelengths typical for sugar (335/385 and 370/440 nm) and lipid derived adducts (356/460 and 390/460 nm). In addition pentosidine assay (corresponding to the fluorescence parameters 335/385 nm) was performed as well. It was found that pentosidine concentration as well as fluorescence intensities in skin collagen was the same for control and HTG rats and significantly increased with age. On the other hand, no significant age-dependent changes in fluorescence intensities were observed in tail tendon collagen. Pentosidine concentration in tail tendon collagen was much lower than that in skin and it was decreased in young HTG rats compared to control ones. It increased with age, more distinctly in HTG rats than in their control counterparts, in such a way that at the age of 19 months the pentosidine levels were undistinguishible in both rat strains. Possible mechanisms underlying these results are discussed.

Glycation of collagen: the basis of its central role in the late complications of ageing and diabetes

The most serious late complication of ageing and diabetes mellitus follow similar patterns in the dysfunction of retinal capillaries, renal tissue, and the cardiovascular system. The changes are accelerated in diabetic patients owing to hyerglycaemia and are the major cause of premature morbidity and mortality. These tissues and their optimal functioning are dependent on the integrity of their supporting framework of collagen. It is the modification of the properties by glycation that results in many of the damaging late complications. Initially glycation affects the interactions of collagen with cells and other matrix components, but the most damaging effects are caused by the formation of glucose-mediated intermolecular cross-links. These cross-links decrease the critical flexibility and permeability of the tissues and reduce turnover. In contrast to the renal and retinal tissue, the cardiovascular system also contains a significant proportion of other fibrous connective tissue protein elastin, and its properties are similarly modified by glycation. The nature of these glycation cross-links is now being unravelled and this knowledge is crucial in any attempt to inhibit these deleterious glycation reactions.