Inhibition of collagen fibril formation in vitro and subsequent cross-linking by glucose

Association between Endodontic Infection, Its Treatment and Systemic Health: A Narrative Review

The 'Focal Infection Era in Dentistry' in the late 19th and early 20th century resulted in widespread implementation of tooth extraction and limited the progress of endodontics. The theory proposed that bacteria and toxins entrapped in dentinal tubules could disseminate systemically to remote body parts, resulting in many types of degenerative systemic diseases. This theory was eventually refuted due to anecdotal evidence. However, lately there has been increased interest in investigating whether endodontic disease could have an impact on general health. There are reviews that have previously been carried out on this subject, but as new data have emerged since then, this review aims to appraise the available literature investigating the dynamic associations between apical periodontitis, endodontic treatment, and systemic health. The available evidence regarding focal infection theory, bacteraemia and inflammatory markers was appraised. The review also collated the available research arguing the associations of apical periodontitis with cardiovascular diseases, diabetes mellitus, adverse pregnancy outcome and autoimmune disorders, along with the effect of statins and immunomodulators on apical periodontitis prevalence and endodontic treatment prognosis. There is emerging evidence that bacteraemia and low-grade systemic inflammation associated with apical periodontitis may negatively impact systemic health, e.g., development of cardiovascular diseases, adverse pregnancy outcomes, and diabetic metabolic dyscontrol. However, there is limited information supporting the effect of diabetes mellitus or autoimmune disorders on the prevalence and prognosis post endodontic treatment. Furthermore, convincing evidence supports that successful root canal treatment has a beneficial impact on systemic health by reducing the inflammatory burden, thereby dismissing the misconceptions of focal infection theory. Although compelling evidence regarding the association between apical periodontitis and systemic health is present, further high-quality research is required to support and establish the benefits of endodontic treatment on systemic health.

Insights into the effect of artificial sweeteners on the structure, stability, and fibrillation of type I collagen

Artificial sweeteners (AS) are widely used as sugar substitutes because natural sweetener (sugar) leads to a number of health issues, including diabetes, obesity, and tooth decay. Since natural sugar (sucrose), diabetes and skin are highly interlinked, and also sucrose is known to inhibit the fibrillation of collagen, the major protein of the skin, a study on the impact of AS on collagen is important and essential. Herein, we have studied the influence of commonly used AS such as Sucralose (SUC), Aspartame (APM), and Saccharin (SAC) on the structure, stability, and fibrillation of collagen using various spectroscopic methods. The circular dichroism and turbidity results suggest that the AS does not disrupt the triple helix structure and also the fibrillar property of collagen, respectively. The fibrillar morphology was sustained, although there was a trivial difference in the entanglement of fibrils in the presence of SAC, compared to native collagen fibrils. The thermal stability of collagen is maintained in the presence of AS. Fluorescence and STD-NMR results indicate that the interaction between AS and collagen was weak, which supports the intact structure, stability, and fibrillation property of collagen. The current study thus suggests that the chosen AS does not influence collagen properties.

A novel chemically modified curcumin reduces inflammation-mediated connective tissue breakdown in a rat model of diabetes: periodontal and systemic effects

BACKGROUND AND OBJECTIVE

Periodontal disease is the most common chronic inflammatory disease known to mankind (and the major cause of tooth loss in the adult population) and has also been linked to various systemic diseases, particularly diabetes mellitus. Based on the literature linking periodontal disease with diabetes in a "bidirectional manner", the objectives of the current study were to determine: (i) the effect of a model of periodontitis, complicated by diabetes, on mechanisms of tissue breakdown including bone loss; and (ii) the response of the combination of this local and systemic phenotype to a novel pleiotropic matrix metalloproteinase inhibitor, chemically modified curcumin (CMC) 2.24.

MATERIAL AND METHODS

Diabetes was induced in adult male rats by intravenous injection of streptozotocin (nondiabetic rats served as controls), and Escherichia coli endotoxin (lipopolysaccharide) was repeatedly injected into the gingiva to induce periodontitis. CMC 2.24 was administered by oral gavage (30 mg/kg) daily; untreated diabetic rats received vehicle alone. After 3 wk of treatment, the rats were killed, and gingiva, jaws, tibia and skin were collected. The maxillary jaws and tibia were dissected and radiographed. The gingival tissues of each experimental group (n = 6 rats/group) were pooled, extracted, partially purified and, together with individual skin samples, analyzed for matrix metalloproteinase (MMP)-2 and MMP-9 by gelatin zymography; MMP-8 was analyzed in gingival and skin tissue extracts, and in serum, by western blotting. The levels of three bone-resorptive cytokines [interleukin (IL)-1β, IL-6 and tumor necrosis factor-α], were measured in gingival tissue extracts and serum by ELISA.

RESULTS

Systemic administration of CMC 2.24 to diabetic rats with endotoxin-induced periodontitis significantly inhibited alveolar bone loss and attenuated the severity of local and systemic inflammation. Moreover, this novel tri-ketonic phenylaminocarbonyl curcumin (CMC 2.24) appeared to reduce the pathologically excessive levels of inducible MMPs to near-normal levels, but appeared to have no significant effect on the constitutive MMPs required for physiologic connective tissue turnover. In addition to the beneficial effects on periodontal disease, induced both locally and systemically, CMC 2.24 also favorably affected extra-oral connective tissues, skin and skeletal bone.

CONCLUSION

This study supports our hypothesis that CMC 2.24 is a potential therapeutic pleiotropic MMP inhibitor, with both intracellular and extracellular effects, which reduces local and systemic inflammation and prevents hyperglycemia- and bacteria-induced connective tissue destruction.

O-GlcNAcylation: a bridge between glucose and cell differentiation

Glucose is the major energy supply and a critical metabolite for most cells and is especially important when cell is differentiating. High or low concentrations of glucose enhances or inhibits the osteogenic, chondrogenic and adipogenic differentiation of cell via the insulin, transforming growth factor‐β and peroxisome proliferator‐activated receptor γ pathways, among others. New evidence implicates the hexosamine biosynthetic pathway as a mediator of crosstalk between glucose flux, cellular signalling and epigenetic regulation of cell differentiation. Extracellular glucose flux alters intracellular O‐GlcNAcylation levels through the hexosamine biosynthetic pathway. Signalling molecules that are important for cell differentiation, including protein kinase C, extracellular signal‐regulated kinase, Runx2, CCAAT/enhancer‐binding proteins, are modified by O‐GlcNAcylation. Thus, O‐GlcNAcylation markedly alters cell fate during differentiation via the post‐transcriptional modification of proteins. Furthermore, O‐GlcNAcylation and phosphorylation show complex interactions during cell differentiation: they can either non‐competitively occupy different sites on a substrate or competitively occupy a single site or proximal sites. Therefore, the influence of glucose on cell differentiation via O‐GlcNAcylation offers a potential target for controlling tissue homoeostasis and regeneration in ageing and disease. Here, we review recent progress establishing an emerging relationship among glucose concentration, O‐GlcNAcylation levels and cell differentiation.

Interrelationship Between Periapical Lesion and Systemic Metabolic Disorders

BACKGROUND

Periapical periodontitis, also known as periapical lesion, is a common dental disease, along with periodontitis (gum disease). Periapical periodontitis is a chronic inflammatory disease, caused by endodontic infection, and its development is regulated by the host immune/inflammatory response. Metabolic disorders, which are largely dependent on life style such as eating habits, have been interpreted as a "metabolically-triggered" low-grade systemic inflammation and may interact with periapical periodontitis by triggering immune modulation. The host immune system is therefore considered the common fundamental mechanism of both disease conditions.

METHOD

We have reviewed >200 articles to discuss the interrelationship between periapical lesions and metabolic disorders including type 2 diabetes mellitus, hypertension, and non-alcoholic fatty liver diseases (NAFLD), and their common pathological background in immunology/osteoimmunology and cytokine biology.

RESULTS

An elevated inflammatory state caused by metabolic disorders can impact the clinical outcome of periapical lesions and interfere with wound healing after endodontic treatment. Although additional well-designed clinical studies are needed, periapical lesions appear to affect insulin sensitivity and exacerbate non-alcoholic steatohepatitis.

CONCLUSION

Immune regulatory cytokines produced by various cell types, including immune cells and adipose tissue, play an important role in this interrelationship.

Hyaluronan in wound healing: rediscovering a major player

Wound healing involves a series of carefully modulated steps, from initial injury and blood clot to the final reconstituted tissue or scar. A dynamic reciprocity exists throughout between the wound, blood elements, extracellular matrix, and cells that participate in healing. Multiple cytokines and signal transduction pathways regulate these reactions. A major component throughout most of the process is hyaluronan, a straight-chain carbohydrate extracellular matrix polymer. Hyaluronan occurs in multiple forms, chain length being the only distinguishing characteristic between them. Levels of hyaluronan in its high-molecular-weight form are prominent in the earliest stages of wound repair. Progressively more fragmented forms occur in a manner not previously appreciated. We outline here steps in the wound healing cascade in which hyaluronan participates, as well as providing a review of its metabolism. Although described by necessity in a series of quantum steps, the healing process is constituted by a smooth continuum of overlapping reactions. The prevalence of hyaluronan in the wound (initially termed "hexosamine-containing mucopolysaccharide"), particularly in its early stages, was pointed out over half a century ago by the Harvard surgeon J. Engelbert Dunphy. It appears we are now returning to where we started.

High glucose induced differential expression of lysyl oxidase and its isoform in ARPE-19 cells

PURPOSE

Lysyl oxidase (LOX) stabilizes the extracellular matrix (ECM) by cross-linking collagen and elastin molecules. In proliferative diabetic retinopathy (PDR), there is ECM remodeling with neovascularization and basement membrane changes. While protease activities are well reported, the role of LOX in the pathogenesis of diabetic retinopathy is less studied. This study was done to see the effect of high glucose on the activity and expression of LOX and its isoforms in ARPE-19 cells.

MATERIALS AND METHODS

ARPE-19 cells were exposed to high glucose up to 48 h, and LOX activity was determined by N-acetyl-3,7-dihydroxyphenoxazine assay. The mRNA expression of LOX and its isoforms was done by real-time PCR and the protein expression by ELISA. Immunohistochemistry for LOX was done in epiretinal membrane from PDR.

RESULTS

With an increase in glucose concentration LOX activity and protein was reduced significantly at 30 mM glucose at 48 h. mRNA expression of LOX, LOXL1, and LOXL2 varied with time and concentration of glucose. Vascular endothelial growth factor (VEGF) increased the LOX activity as well as the mRNA expression. Pigment epithelium-derived factor (PEDF) downregulated the mRNA expression of LOX, LOXL1, and LOXL2. The matrix metalloprotease (MMP) activity increased significantly with the increase in glucose concentration. The diabetic neovascular membrane showed increased immunostaining of LOX.

CONCLUSIONS

This study suggests that although the LOX activity, which is composite of all the isoforms, was reduced under high glucose conditions, there was a differential mRNA expression with increased LOX and LOXL1 and decreased LOXL2 expression.

Review: The diabetic bone: a cellular and molecular perspective

With the increasing worldwide prevalence of diabetes the resulting complications, their consequences and treatment will lead to a greater social and financial burden on society. One of the many organs to be affected is bone. Loss of bone is observed in type 1 diabetes, in extreme cases mirroring osteoporosis, thus a greater risk of fracture. In the case of type 2 diabetes, both a loss and an increase of bone has been observed, although in both cases the quality of the bone overall was poorer, again leading to a greater risk of fracture. Once a fracture has occurred, healing is delayed in diabetes, including nonunion. The reasons leading to such changes in the state of the bone and fracture healing in diabetes is under investigation, including at the cellular and the molecular levels. In comparison with our knowledge of events in normal bone homeostasis and fracture healing, that for diabetes is much more limited, particularly in patients. However, progress is being made, especially with the use of animal models for both diabetes types. Identifying the molecular and cellular changes in the bone in diabetes and understanding how they arise will allow for targeted intervention to improve diabetic bone, thus helping to counter conditions such as Charcot foot as well as preventing fracture and accelerating healing when a fracture does occur.

Tight glycaemic control is a key factor in wound healing enhancement strategies in an experimental diabetes mellitus model

BACKGROUND

Diabetes mellitus is a leading cause of impaired wound healing. The aim of this study was to establish a glucose-controlled diabetic wound healing model.

METHOD

Sprague-Dawley rats were divided into three groups: Control group (C), Diabetic Non-glucose Controlled group (DNC) and Diabetic glucose Controlled group (DC).

RESULTS

Glucose control was achieved using Insulman Rapid (average daily glucose level <10 mmol/L). 18 Sprague-Dawley rats underwent a dorsal skin wound incision and 10 days later were killed. Fresh and fixed wound tensile strength, hydroxyproline and transforming growth factor beta-1 levels were improved in the DC group when compared to the DNC group. The quantity of fibroblasts present was similar in each group.

CONCLUSION

This study demonstrates the impact that diabetes has on acute wound healing and suggests that wound modulating agents must be tested in both the tightly glucose-controlled as well as the poorly glucose-controlled diabetic animal models prior to proceeding with translational clinical studies.

Suppression of allergic inflammatory response in the skin of alloxan-diabetic rats: relationship with reduced local mast cell numbers

BACKGROUND

Diabetic patients are refractory to allergic inflammatory diseases. In this study, the influence of alloxan-induced diabetes on allergic skin inflammation was investigated.

METHODS

Diabetes was induced by intravenous injection of alloxan into male Wistar rats, and the analyses were performed 21 days later. Animals were actively sensitized with a mixture of aluminium hydroxide plus ovalbumin and challenged intradermally with ovalbumin on day 14.

RESULTS

Diabetic sensitized rats exhibited a less pronounced antigen-induced protein extravasation in the dorsal skin when compared with normal animals. Also, fragments of the dorsal subcutaneous tissue from diabetic sensitized rats showed a reduction in histamine release after stimulation with antigen in vitrowhen compared with fragments obtained from nondiabetic sensitized rats. Optical microscopy analysis revealed that the dorsal skin of diabetic rats showed a marked reduction in dermis thickness, as compared with that seen in normal animals. A significant decrease in the number of skin mast cells was also noted, a phenomenon that paralleled with the reduction in the expression of extracellular matrix components laminin, fibronectin and collagen. Administration of insulin into diabetic rats restored basal mast cell numbers as well as the levels of laminin, fibronectin and collagen.

CONCLUSIONS

Our findings show that alloxan diabetes induces downregulation of the skin allergic inflammatory response in rats, and this was correlated with reduction in local mast cell numbers and expression of extracellular matrix components. Lastly, these alterations were reversed with insulin treatment.

Intermolecular cross-linking in fibrotic collagen

The extent, nature and location of the cross-links involved in the stabilization of collagen in fibrotic lesions are crucial to its subsequent removal, naturally or induced by treatment. Stabilization is achieved initially by divalent aldimine and keto-imine intermolecular cross-links located at the end-overlap region in the quarter-stagger alignment of the molecules in the fibre. Elucidation of the location of the cross-links also provides chemical evidence for the organization of the collagen molecule in the fibre. All the fibrous collagens are stabilized by these cross-links, the more stable keto-imine cross-link predominating in the types I and II collagens present in the initial stages of fibrosis. Further stabilization of the lesion usually follows, increasing the resistance to degradative enzymes, thus rendering the fibrosis irreversible. This maturation process, which also occurs in normal ageing, involves the formation of multivalent cross-links derived from the initial aldimine and keto-imine cross-links to form a three-dimensional network through a polymeric peptide (poly-alpha 1CB6 in type I collagen). The nature of these cross-links has not yet been elucidated. The so-called mature cross-link, 3-hydroxypyridinoline, could not be identified in this polymeric network. A secondary process involving non-enzymic glycosylation of lysine residues and subsequent intermolecular cross-linking has also been demonstrated, although the nature and extent of this type of cross-link remain to be determined.

Optimizing the patient for surgical treatment of the wound

Plastic surgeons are consulted often to close wounds that fail or are difficult to heal. Optimizing the patient's medical condition before surgical closure of a wound can mean the difference between a successful outcome and an undesirable one. It is imperative that plastic surgeons have an extensive knowledge of the modifiable risk factors affecting the wound-healing process and their subsequent complications. This knowledge allows the surgeon to tailor the treatment options and intervene when appropriate to optimize outcomes for successful surgical closure of a wound. Whether the impairments to wound healing and closure are local or systemic, they must be addressed appropriately.

Hesperetin attenuates the highly reducing sugar-triggered inhibition of osteoblast differentiation

Diabetic bone disease is associated with increased oxidative damage and 2-deoxy-D: -ribose (dRib) is used to induce oxidative damage similar to that observed in diabetics. To determine if hesperetin (3',5,7-trihydroxy-4-methoxyflavanone) could influence osteoblast dysfunction induced by dRib, osteoblastic MC3T3-E1 cells were treated with dRib and hesperetin. Then, markers of osteoblast function and oxidative damage were examined. Hesperetin (10(-7)-10(-5) M) caused a significant elevation of alkaline phosphatase (ALP) activity, collagen content, and total antioxidant potential of MC3T3-E1 cells in the presence of 20 mM dRib (p < 0.05). Moreover, hesperetin (10(-7) M) decreased cellular protein carbonyl (PCO), advanced oxidation protein products (AOPP), and malondialdehyde (MDA) contents of osteoblastic MC3T3-E1 cells in the presence of 20 mM dRib. These results demonstrate that hesperetin attenuates dRib-induced damage, suggesting that hesperetin may be a useful dietary supplement for minimizing oxidative injury in diabetes related bone diseases.

Biological fate and clinical implications of arginine metabolism in tissue healing

Since its discovery in 1987, many biological roles (including wound healing) have been identified for nitric oxide (NO). The gas is produced by NO synthase using the dibasic amino acid L-arginine as a substrate. It has been established that a lack of dietary L-arginine delays experimental wound healing. Arginine can also be metabolized to urea and ornithine by arginase-1, a pathway that generates L-proline, a substrate for collagen synthesis, and polyamines, which stimulate cellular proliferation. Herein, we review subjects of interest in arginine metabolism, with emphasis on the biochemistry of wound NO production, relative NO synthase isoform activity in healing wounds, cellular contributions to NO production, and NO effects and mechanisms of action in wound healing.

Lysyl oxidase in development, aging and pathologies of the skin

Lysyl oxidase (LOX) is a copper- and lysyl-tyrosyl cofactor containing amine oxidase that has been known to play a critical role in the catalysis of lysine-derived crosslinks in extracellular matrix (ECM) proteins in the dermis. Changes in the composition and crosslinked state of the ECM and alterations in LOX synthesis and activity are known to be associated with aging and a range of acquired and heritable skin disorders. It has been assumed until recently that the LOX-related changes in the skin are mediated through the catalytic activity of LOX. However, work by several laboratories over the last few years has shown that LOX is a multifunctional protein. In this review we discuss the regulation of expression, localization and activation of LOX in the normal developing and adult skin, and alterations in LOX expression and activity associated with skin aging and senescence, and in pathological conditions, including wound healing, fibrosis, hypertrophic scarring, keloids, scleroderma, and diabetic skin. We further evaluate the role of LOX in skin ECM changes associated with the normal aging process and with these pathological states. In addition to collagen and elastin cross-linkages, regulatory and activation mechanisms and cell type specific LOX interactions may contribute to a range of novel intra- and extracellular LOX functions that appear critical determinants of the cellular microenvironment in the normal skin and in these skin disorders.

Systemic effects of periodontal diseases

A number of studies suggest an association between periodontal disease and cardiovascular disease, pulmonary disease, diabetes,and pregnancy complications. Presently, the data must be regarded as preliminary. Additional large-scale longitudinal epidemiologic and interventional studies are necessary to validate these associations and to determine whether the associations are causal. The goal of this article is to review the history of this concept, describe the biologically plausible circumstances that may underlie these potential associations, and provide a summary of the published literature that supports or refutes them.

Update on diabetes mellitus and related oral diseases

Diabetes mellitus (DM) is a group of complex multisystem metabolic disorders characterized by a relative or absolute insufficiency of insulin secretion and/or concomitant resistance to the metabolic action of insulin on target tissues. The chronic hyperglycaemia of diabetes is associated with long-term systemic dysfunction. The present article summarizes current knowledge of DM and details the oral and dental implications of this common endocrine disorder.

Diabetes mellitus and the dental pulp

This study attempts to evaluate the oral manifestations of and the limited available dental pulp information on diabetes mellitus, a common metabolic disorder of carbohydrate and lipid metabolism affecting over 16 million Americans. Diabetics are particularly prone to bacterial or opportunistic infections. This vulnerability is caused by a generalized circulatory disorder whereby the blood vessels are damaged by the accumulation of atheromatous deposits in the tissues of the blood vessels lumen. In addition, blood vessels, particularly capillaries, develop a thickened basement membrane, which impairs a leukotactic response, and there is a decrease in the polymorphonuclear leucocyte microbicidal ability and failure to deliver the humoral and cellular components of the immune system. Because the dental pulp has limited or no collateral circulation, it is more prone to be at risk for infection. Clinical and radiographic studies by other investigators have shown that there is a greater prevalence of periapical lesions in diabetics than in nondiabetics. In a study of 252 diabetics with poor glycemic control, a high rate of asymptomatic tooth infection was found. Inflammatory reactions are greater in diabetic states, and the increased local inflammation causes an intensification of diabetes with a rise in blood glucose, placing the patient in an uncontrolled diabetic state. This often requires an increase in insulin dosage or therapeutic adjustment. Removal of the inflammatory state in the periodontium created a need for a lesser amount of insulin for glycemic control. Thus, it is essential to remove all infections including those of the dental pulp. When diabetes mellitus is under therapeutic control, periapical and other lesions heal as readily as in nondiabetics.

Extracellular matrix maturation in the left ventricle of normal and diabetic swine

The main objective of this study is to determine the transmural distribution of extracellular matrix (ECM) collagen and maturation in non-diabetic and diabetic hearts. The Yucatan miniature swine heart ECM was analyzed in eight streptozotocin (STZ) induced diabetic pigs (Diabetic-Swine) and age matched normal control pigs (Nondiabetic-Swine). After 12 weeks of STZ induced diabetes, transmural biopsies were obtained from the left ventricular free wall divided into subendocardial, mid- and subepicardial layers. Collagen concentration and maturation were measured by RP-HPLC determination of hydroxyproline (Hyp) and content of hydroxylysylpyridinoline (HP) cross-links, respectively. Results showed a significant elevation in arterial glucose (P<0.05) and reduction in arterial plasma insulin levels in the Diabetic-Swine. Hyp concentration was significantly greater (P<0.05) in the subendocardial layers in both the Diabetic and Nondiabetic animals. The HP cross-link content was significantly greater (17%) in the Diabetic-swine subendocardial layer compared to Nondiabetic-Swine (P<0.05), but not in other layers. In summary, the accumulation and/or increase in HP cross-link content in the Diabetic-Swine subendocardial layer suggests that myocardial fibrosis may be greater in this specific region.

Nitric oxide enhances experimental wound healing in diabetes

BACKGROUND

Diabetes is characterized by a nitric oxide deficiency at the wound site. This study investigated whether exogenous nitric oxide supplementation with the nitric oxide donor molsidomine (N-ethoxycarbomyl-3-morpholinyl-sidnonimine) could reverse the impaired healing in diabetes.

METHODS

Wound healing was studied by creating a dorsal skin incision with subcutaneous polyvinyl alcohol sponge implantation in diabetic and non-diabetic rats. Half of each group was treated with molsidomine. Collagen metabolism was assessed by wound breaking strength, hydroxyproline (OHP) content, RNA expression for collagen type I and III, and matrix metalloproteinase (MMP) 2 activity in wound sponges. Wound fluid, plasma and urinary nitric oxide metabolite levels, and the number of inflammatory cells were assessed.

RESULTS

OHP content and wound breaking strength were significantly increased by molsidomine. MMP-2 activity in wound fluid was decreased in diabetes and upregulated by nitric oxide donors. The impaired inflammatory reaction in diabetes was unaffected by nitric oxide donor treatment and ex vivo nitric oxide synthesis was no different between wound macrophages from control and diabetic animals, suggesting that the nitric oxide deficiency in the wound is due to a smaller inflammatory reaction in diabetes.

CONCLUSION

The nitric oxide donor molsidomine can at least partially reverse impaired healing associated with diabetes.

The effects of high levels of glucose and insulin on type I collagen synthesis in mature human odontoblasts and pulp tissue in vitro

High levels of dietary sucrose affect the metabolism of the pulp-dentin complex and enhance the caries process in dentin. The high-sucrose diet reduces dentin formation in young rats (Tjäderhane et al., 1994; Hietala and Larmas, 1995; Tjäderhane, 1996) and in pups of rat dams fed high-sucrose diet during lactation (Pekkala et al., 2000a). However, the mechanisms behind the effects are unknown. A direct effect of elevated blood glucose or an indirect effect via insulin has been suggested. We investigated the effects of high glucose and insulin on type I collagen synthesis in human odontoblasts and pulp tissue in vitro, using an organ culture method for functional post-mitotic odontoblasts. Odontoblasts and pulp tissue were cultured separately for 10 days in DMEM with 15% FBS containing additional glucose (G) (4.45 g/L) or insulin (I) (0.6 microgram/mL) or both together (GI). We evaluated type I collagen synthesis with RIA, measuring the level of N-terminal propeptide of type I collagen (PINP) secreted into the culture media. PINP secretion decreased in odontoblasts and pulp tissue in G and GI groups when compared with the control and insulin samples (p = 0.001 in both groups in the pulp samples). Insulin alone did not affect PINP secretion distinctly. The results indicate that high levels of glucose, but not insulin, directly down-regulate the type I collagen synthesis in young, differentiated human odontoblasts and pulp tissue. Insulin does not affect the inhibitory effect of high sucrose. These in vitro findings indicate that the high-sucrose diet may alter odontoblast function independently of insulin.

Diabetes and periodontal diseases. Committee on Research, Science and Therapy. American Academy of Periodontology

This position paper on diabetes mellitus was prepared by the Research, Science and Therapy Committee of The American Academy of Periodontology. It is intended to: 1) update members of the dental profession on the diagnosis and medical management of patients with diabetes mellitus; 2) summarize current knowledge on the relation between diabetes mellitus and periodontal diseases; 3) provide an overview of factors in diabetic patients relevant to understanding the pathogenesis of periodontal diseases in these subjects; 4) outline special considerations associated with treatment of periodontal diseases in diabetic patients; and 5) discuss possible approaches to the management of diabetic emergencies in the dental office.

Diabetes and periodontal diseases

This position paper on diabetes mellitus was prepared by the Research, Science and Therapy Committee of The American Academy of Periodontology. It is intended to: 1) update members of the dental profession on the diagnosis and medical management of patients with diabetes mellitus; 2) summarize current knowledge on the relation between diabetes mellitus and periodontal diseases; 3) provide an overview of factors in diabetic patients relevant to understanding the pathogenesis of periodontal diseases in these subjects; 4) outline special considerations associated with treatment of periodontal diseases in diabetic patients; and 5) discuss possible approaches to the management of diabetic emergencies in the dental office.

Glucocorticoid-dependent impairment of wound healing in experimental diabetes: amelioration by adrenalectomy and RU 486

BACKGROUND

Failure of wounds to heal represents one of the major diabetic complications. Emerging evidence favors the involvement of glucocorticoids (GCs) in the pathogenesis of impaired wound healing in diabetes mellitus.

OBJECTIVE

The purpose of this study was to examine wound healing potential in diabetics under conditions in which the hypercortisolemic state is normalized.

DESIGN AND INTERVENTION

Linear skin incision and polyvinyl alcohol (PVA) sponge were used as wound healing models. Six groups of rats matched with respect to age, sex, and strain were included in this study. Animals in groups 1 and 6 were injected with citrate buffer, whereas rats in groups 2,3,4, and 5 received streptozotocin (STZ, 55 mg/kg iv in citrate buffer). Five days later animals in groups 4,5, and 6 received insulin (group 4) and subcutaneous implantation of slow-releasing pellets containing either the GC receptor blocker RU 486 (group 5) or a high dose of GC (group 6).

MAIN OUTCOME MEASUREMENTS

Skin wound tensile strength and PVA sponge collagen metabolism were determined using tensiometric, spectrosphotometric, and polymerase chain reaction-based assays. In addition, cell infiltration and granulation tissue growth were assessed using a well-established histochemical technique.

RESULTS

Wound-related parameters including fibroplasia, neovascularization, and inflammatory cell numbers were reduced as a function of diabetes. Similarly, skin wound tensile strength, PVA sponge hydroxyproline content, and the levels of mRNA transcripts for type I and III collagen were also decreased in this disease state. This diabetes-related deficit in wound healing potential was ameliorated by subjecting diabetic animals to insulin treatment or by counteracting the excessive actions of GCs using both pharmacological (RU 486) and endocrinological (ADX) paradigms.

CONCLUSION

The current study supports the notion that GCs are implicated in the wound healing deficit of diabetics. Moreover, it illuminates the therapeutic potential of the GC receptor blocker (e. g., RU 486) in promoting wound repair under hypercortisolemic conditions including diabetes and Cushing's syndrome.

Collagen in tissue-engineered cartilage: types, structure, and crosslinks

The function of articular cartilage as a weight-bearing tissue depends on the specific arrangement of collagen types II and IX into a three-dimensional organized collagen network that can balance the swelling pressure of the proteoglycan/water gel. To determine whether cartilage engineered in vitro contains a functional collagen network, chondrocyte-polymer constructs were cultured for up to 6 weeks and analyzed with respect to the composition and ultrastructure of collagen by using biochemical and immunochemical methods and scanning electron microscopy. Total collagen content and the concentration of pyridinium crosslinks were significantly (57% and 70%, respectively) lower in tissue-engineered cartilage that in bovine calf articular cartilage. However, the fractions of collagen types II, IX, and X and the collagen network organization, density, and fibril diameter in engineered cartilage were not significantly different from those in natural articular cartilage. The implications of these findings for the field of tissue engineering are that differentiated chondrocytes are capable of forming a complex structure of collagen matrix in vitro, producing a tissue similar to natural articular cartilage on an ultrastructural scale.

Periodontal disease as a complication of diabetes mellitus

Based on our clinical observations that patients with insulin-dependent diabetes mellitus (IDDM) are subject to periodontal disease, we developed the hypothesis that hyper- or hypoglycemia might contribute to the pathogenesis of diabetic periodontitis. In this article, experimental facts that substantiate this hypothesis are presented on the basis of our studies and then discussed. Hyperglycemia progressively glycates body proteins, forming advanced glycation end products (AGE), which stimulate phagocytes to release inflammatory cytokines such as TNF-alpha and IL-6. In this context, to understand the effects of hyperglycemic episodes on periodontal health, 24 adolescent IDDM patients were examined for their periodontal status, and 3 of them were found to have periodontitis. Laboratory analyses on these 3 patients revealed that 2 had elevated serum TNF-alpha levels. These results may partly support the current hypothesis of a mechanism of diabetic complications in which abnormal cytokine levels induced by AGE could exacerbate inflammatory responses. In IDDM patients, the diabetes is often accompanied not only by hyperglycemic episodes but also by iatrogenic hypoglycemia. Periodontal ligament cells (PDL) cultured under hyperglycemic conditions were impaired in such biological functions as adhesion and motility, while cells cultured under hypoglycemic conditions (10 mg/dL) gradually dissociated from their anchor and underwent cell death. These phenomena correlated well with the expression profile of fibronectin receptor. Interestingly, these changes due to the different glucose levels were observed more intensively in PDL than in other fibroblastic cells, suggesting that the biological functions of PDL are easily led to impairment by variation or rapid fluctuation of glucose levels. These observations suggest that hyperglycemia could indirectly exacerbate inflammatory tissue destruction through the body's scavenger system against AGE, and that both hyper- and hypoglycemia might directly impair the biological functions of periodontal connective tissues through cell-matrix interactions.

Diabetes--a risk factor for periodontitis in adults?

With the increasing number of diabetics in an aging population and controversial research reports on the relationship of diabetes to periodontitis, clarification of diabetes as a risk factor for periodontitis would be helpful. This review notes variations in type, metabolic control, and duration of diabetes and highlights the results of studies that have considered these variations. Diabetics who maintained reasonably good metabolic control had not lost more teeth or experienced more periodontal attachment loss than non-diabetics, although they had more periodontal pockets. Poorly-controlled diabetics with extensive calculus on their teeth had more periodontitis and tooth loss than well-controlled diabetics or non-diabetics. Long-duration diabetics were also at greater risk for periodontitis. Mechanisms by which diabetes may contribute to periodontitis include vascular changes, neutrophil dysfunction, altered collagen synthesis, and genetic predisposition. Minimizing plaque and calculus in the oral cavity through careful self-care and regular professional care is important to reduce the risk of periodontitis in diabetics.

Non-enzymic glycation of collagen inhibits binding of oxidized low-density lipoprotein

We have examined the effect of non-enzymic glycation of native soluble collagen, in solution or in gels, on binding of oxidized low-density lipoprotein (LDL). We found the following. (1) Glycation markedly inhibited binding of LDL. This is contrary to results previously reported; the difference may be attributable to the use of detergent- and heat-denatured collagen, covalently bound to agarose beads, in the earlier study. (2) With increased duration of glycation, collagen solution would not gel, and preformed gels dissolved. (3) [14C]Glucose bound to collagen gels dissociated slowly, even at pH 5, suggesting that it was not present as a Schiff's base; in addition, ketoamines, pentosidine and fluorescent advanced glycation products were not detectable in glycated collagen gels, although they accumulated in tendon collagen glycated under the same conditions. It is hypothesized that the difference in glycation effects between gel and tendon may be due to the strength of cross-linking before glycation: the increase in intermolecular distance in collagen fibrils which results from glycation disrupts the fibrils in gels, preventing binding of LDL and formation of glycation-dependent cross-links, whereas the extensive cross-linking in tendon maintains the intermolecular distances within a range which permits formation of glycation cross-links.

Glucose and glucose analogs modulate collagen metabolism

Patients with diabetes often develop complications involving collagen-containing connective tissues. Previous in vitro studies have demonstrated that glucose inhibits collagen fibril formation and subsequent cross-linking. Collagen with diminished cross-linking is more susceptible to collagenolytic degradation. This may underlie the decreased collagen levels. To test this hypothesis, D-glucose and its two analogs, L-glucose and 2-deoxy-D-glucose, were used in chick calvaria organ cultures to examine parameters of collagen metabolism. L-Glucose is not used by the cell and functions as an extracellular glucose-like molecule, while 2-deoxy-D-glucose inhibits normal D-glucose uptake by blockading the glucose transport mechanism. Each of these three sugars had the ability to inhibit collagen fibril formation. D-Glucose stimulated collagen synthesis; L-glucose had no effect; and deoxyglucose inhibited collagen synthesis. D-Glucose was able to reverse the inhibitory effect of deoxyglucose. D-Glucose did not change levels of degradation of newly synthesized collagen while both L-glucose and deoxyglucose stimulated collagen degradation. When glucose transport was inhibited by deoxyglucose, collagen degradation was further enhanced. We suggest that decreased collagen levels in the connective tissues of diabetics may result from a combination of inhibition of collagen fibril formation and subsequent cross-linking, as well as increased collagen degradation.

Aminoguanidine treatment reduces the increase in collagen stability of rats with experimental diabetes mellitus

Alterations in the biophysical properties of connective tissues in diabetes mellitus have been attributed to the nonenzymatic glycation of the collagens and the subsequent formation of browning products, cross-linking the proteins. Aminoguanidine may bind to carbonyl groups of these nonenzymatic glycation products and thereby block the process. Rats with streptozotocin-induced diabetes were treated with aminoguanidine, 25 mg.kg-1.day-1, for 120 days. The aminoguanidine treatment did not counteract the increase in blood glucose concentrations, nor did it prevent the arrest in weight gain of diabetic rats. The increased stability in 7 mol/l urea and increased tensile strength of tail tendons from the diabetic rats, however, were prevented by the aminoguanidine treatment. Aminoguanidine did not reduce the formation of early nonenzymatic glycation products (aldimine and Amadori rearrangement products), whereas the amount of browning products (fluorescent compounds) was reduced in the tail tendon collagen of the diabetic rats. Aminoguanidine treatment of intact rats did not influence these parameters. These findings indicate that the biophysical alterations of collagens induced by experimental diabetes are caused by cross-links derived from the nonenzymatic glycation, and furthermore, that aminoguanidine treatment may prevent the concomitant changes in biophysical properties of connective tissues.

Effect of alpha-glucosidase inhibition on the nonenzymatic glycation of glomerular basement membrane

1. The effect of the alpha-glucosidase inhibitor Acarbose on integrated glycemic control and on nonenzymatic glycation of glomerular basement membrane was examined in streptozotocin diabetic rats. 2. Treatment with Acarbose for 8 weeks after induction of diabetes significantly reduced the level of HbA1c and of glomerular basement membrane glycation. 3. Acarbose exerts a significant antihyperglycemic effect and has a salutary influence on the nephropathic process in experimental diabetes.

Relationship between the content of lysyl oxidase-dependent cross-links in skin collagen, nonenzymatic glycosylation, and long-term complications in type I diabetes mellitus

Many abnormalities in collagen have been reported in insulin-dependent diabetes mellitus, some or all of which have been attributed to increased cross-linking. Although recent work has focused on the role of glucose-derived collagen cross-links in the pathogenesis of diabetic complications, relatively few studies have investigated the role of lysyl oxidase-dependent (LOX) cross-links. In the present study, LOX cross-links and nonenzymatic glycosylation were quantified in skin collagen from diabetic subjects. There was an increase in the difunctional cross-link dihydroxylysinonorleucine (DHLNL) as well as in one of its trifunctional maturation products, hydroxypyridinium. All other LOX crosslinks were normal. Nonenzymatic glycosylation was increased in diabetic skin collagen, and this increase was correlated with increases in DHLNL (P less than 0.001). The biochemical results were examined for correlations with clinical data from the same subjects. Increases in DHLNL content were associated with duration of diabetes (P less than 0.003), glycohemoglobin levels (P less than 0.001), hand contractures (P less than 0.05), skin changes (P less than 0.005), and microalbuminuria (P less than 0.01). In nondiabetic subjects age was not correlated with collagen cross-link content with the exception that his-HLNL increased with age (r = 0.79, P less than 0.02). In diabetic subjects, PA levels decreased with age (r = 0.51, P less than 0.02). With increased duration of diabetes, DHLNL content was increased (r = 0.55, P less than 0.003) and OHP was increased (r = 0.59, P less than 0.01), whereas PA levels were decreased (r = -0.48, P less than 0.04). Nonenzymatic glycosylation of collagen was also increased with increased duration of diabetes (hex-lys, r = 0.47, P less than 0.02; hex-hyl, r = 0.39, P less than 0.05). We conclude that: (a) lysyl oxidase-dependent cross-linking is increased in skin collagen in diabetes and (b) that these changes in skin collagen are correlated with duration of diabetes, glycemic control, and long-term complications.

Levels of [3H]glucosamine incorporation into hyaluronic acid by fibroblasts is modulated by culture conditions

Tissue culture conditions can modulate apparent levels of incorporation of the radiolabeled precursor [3H]glucosamine into hyaluronic acid in cells. A careful study was made on the effects of culture conditions on human skin fibroblasts. A newly described technique to measure hyaluronic acid was utilized based on incorporation of [3H]glucosamine into cetylpyridinium chloride-precipitable hyaluronidase-digestible material. The precipitate was collected on glass fiber filters using a manifold suction apparatus. A six-fold greater level of incorporation occurred in rapidly growing preconfluent than in confluent fibroblasts. Ascorbic acid stimulated incorporation with a maximum at 25 micrograms/ml. The same ascorbic acid optimum was observed for collagen prolylhydroxylation. When beta-hydroxybutyrate was used as an energy source instead of D-glucose, a 3.5-fold increase in levels was observed. All tissue-culture media examined supported comparable levels of incorporation, except for Roswell Park Memorial Institute Media-1640, in which cells had only half the level. Fetal calf serum supported high levels of incorporation in a dose-dependent manner, while newborn calf and calf sera supported much lower levels of incorporation. Under serum-free conditions, lactalbumin hydrolysate was best able to support incorporation of hyaluronic acid. In the search for mechanisms that modulate hyaluronic acid, it is critical to consider the tissue culture conditions under which incorporation of radiolabeled precursors are being examined.

The mineral and mechanical properties of bone in chronic experimental diabetes

The long-term effects of experimentally induced diabetes on bone were studied in eight male Lewis rats, intravenously (i.v.) injected with 65 mg/kg of streptozocin (STZ) and maintained for 12 months. Eight untreated age-matched rats served as controls. In the STZ-treated rats, experimentally induced diabetes was documented by the presence of hyperglycemia at 24 h and at 3 and 12 months. Significantly less weight was gained and less growth occurred in the STZ-treated rats despite careful attention to feeding and hydration. Mineral alterations were detected in the bones of the animals with experimental diabetes. Decreased hydroxyapatite crystal perfection, decreased Ca/P of the ash, and decreased ash content in the tibial metaphyses with increased ash content in the tibial diaphyses, was noted relative to controls. Bone osteocalcin content was increased in the metaphyses of the STZ-treated rats. While absolute measures of stiffness, torsional strength and energy absorption were decreased in the bones of the STZ-treated animals, when torsional strength and stiffness were normalized for differences in both growth and geometry, the normalized stiffness values for the diabetic bones were increased. The results suggest that in experimental diabetes certain aspects of bone mineralization are adversely affected and lead to reduced strength-related properties. However, a compensatory increase in stiffness occurs. The reason for this increase, although not known, may be related to changes in bone crystal structure.

Nonenzymatically glycosylated proteins

Nonenzymatic glycosylation takes place in all proteins with a free-reacting lysine or valine in the presence of glucose. The formation of glycosylated plasma albumin, hemoglobin (Hb A1c), and skin collagen provides a diagnostic index of short- to long-term time-concentration of glucose in vivo. A wide range of assay methods are available, with affinity chromatographic, isoelectric focusing, and spectrophotometric methods providing the best accuracy and versatility. Glycosylated hemoglobin assays indicate glucose pressure over the previous 2 to 3 months and are of diagnostic value in general diabetic control, while glycosylated plasma albumin determinations are preferable in acute episodes in the life of a diabetic (e.g., pregnancy, infection, stress, trauma, surgery), since they provide an overview of changing blood glucose values of the previous 2 to 4 weeks. Glycosylated collagen estimations reflect tissue aging and are relevant in healing processes. Glycosylation alters the biologic activity of proteins, and these may relate to the manifold complications concomitant on the lifelong elevation of blood and tissue glucose in the diabetic (C6a). Assays for glycosylated hemoglobin have been routinely performed in clinical chemistry laboratories for a decade, and convenient determination for other nonenzymatically glycosylated proteins is proceeding apace.

Hyperchromic effect of collagen induced by human collagenase

Loss of the highly ordered triple-helix structure of native collagen on denaturation or enzymatic degradation involves a helix-to-coil transition, which can be seen as an increase at 227 nm in its ultraviolet difference absorption spectrum. We report here the successful use of this hyperchromic effect to quantify collagen in solution and to follow up the time-course of collagen degradation catalyzed by collagenase. Using 14C-labelled collagen substrate we show the excellent correlation between enzyme-induced increase in ultraviolet difference absorption and formation of specific cleavage products. The novel method was found to be suitable to characterize the enzymatic properties of human leukocyte collagenase. Activation of latent collagenase to the active enzyme could be followed continuously and an activation lag estimated.

Collagen and elastin synthesis in human stroma and breast carcinoma cell lines: modulation by the extracellular matrix

The desmoplastic response to breast carcinoma is being studied. The stimulation of stromal cell proliferation by a preformed breast tumor matrix was shown. An additional mechanism for stimulating scleroprotein deposition is described here. On a per-cell basis, the synthesis of collagen and elastin was increased by 50% and 70%, respectively, in fibroblasts grown on the preformed breast tumor matrix compared to the same cells grown on plastic or on their own preformed matrix. Breast tumor cells themselves synthesized small amounts of collagen and elastin compared to fibroblasts. These levels were unchanged when breast tumor cells were grown on the preformed matrix of fibroblasts. Addition of steroid hormones to cultured cells grown on plastic or on preformed matrices in various combinations, did not change the levels of either collagen or elastin synthesis. The matrix of human breast tumor cells exerts a dual effect; it is mitogenic for fibroblasts, and also stimulates the level of collagen and elastin synthesis, events that could contribute to the formation of the desmoplastic response to human breast cancer in situ.

Depressor effect of diabetes in spontaneously hypertensive rat: role of vascular reactivity and prolyl hydroxylase and lysyl oxidase activities

Streptozotocin (STZ)-induced diabetes (8 weeks) produced a marked depressor effect in the spontaneously hypertensive rat (SHR), confirming earlier studies, but had no effect on arterial pressure of normotensive controls (WKY). We investigated the phenomenon further by examining the effects of diabetes on the activities of aortic prolyl hydroxylase (PH) and lysyl oxidase (LO), marker enzymes for collagen biosynthesis, and on the reactivity of isolated mesenteric arteries to vasoactive agents. PH and LO activities of nondiabetic SHR were greater than those of the WKY controls. Diabetes markedly reduced PH and LO activities of SHR aortae, but had no significant effect on PH and LO activities of the WKY strain. The effects of diabetes on vascular collagen biosynthetic enzymes of SHR were not associated with reductions in mesenteric arterial responsiveness or sensitivity to norepinephrine, methoxamine, serotonin or KC1. These results suggest that the depressor effect of diabetes in SHR is associated with a reduction in vascular collagen biosynthesis but not a reduction in vascular reactivity.

Dietary ascorbic acid normalizes diabetes-induced underhydroxylation of nascent type I collagen molecules

Nascent collagen alpha chains (types I and III) isolated from diabetic rat skin were shown to be underhydroxylated, an underhydroxylation normalized (type I) or partially corrected (Type III) by dietary ascorbic acid. Increased hydroxylation occurred concomitantly with reduced intracellular procollagen degradation and increased production of nascent collagen molecules, both contributing to an increased total skin collagen mass. Overall, by correcting a defect (underhydroxylation) in a posttranslational event and by increasing collagen production, dietary ascorbic acid improved the collagen status of a diabetes-perturbed connective tissue.