Tissue-specific variation in glycation of proteins in diabetes: evidence for a functional role of amadoriase enzymes

Current research trends on the effect of diabetes mellitus on rotator cuff tendon healing/tendinopathy

Rotator cuff tendon tears are a leading cause of shoulder pain. They are challenging to treat, and tendon-bone healing has a high failure rate despite successful surgery. Tendons connect the muscles and bones, which make them important for the body's overall mobility and stability. Metabolic diseases, including diabetes or high blood pressure, can affect the healing process after repair of a damaged tendon. With a global incidence of 9.3%, diabetes is considered as a significant risk factor for rotator cuff tendon healing because it causes structural, inflammatory, and vascular changes in the tendon. However, the mechanisms of how diabetes affects tendon healing remain unknown. Several factors have been suggested, including glycation product accumulation, adipokine dysregulation, increased levels of reactive oxygen species, apoptosis, inflammatory cytokines, imbalanced matrix-metalloproteinase-to-tissue-inhibitor ratio, and impaired angiogenesis and differentiation of the tendon sheath. Despite the effects of diabetes on tendon function and healing, few treatments are available to improve recovery in these patients. This review summarizes the current literature on the pathophysiological changes of the tendon in diabetes and hyperlipidemia. Preclinical and clinical evidence regarding the association between diabetes and tendon healing is presented. Moreover, current approaches to improve tendon healing in patients with diabetes are reviewed.

Risk analysis of the association between different hemoglobin glycation index and poor prognosis in critical patients with coronary heart disease-A study based on the MIMIC-IV database

BACKGROUND

The hemoglobin glycation index (HGI) is the difference between the observed and predicted values of glycosylated hemoglobin (HbA1c), which is closely associated with a variety of poor prognoses. However, there are still no studies on the correlation between HGI and poor prognosis in patients with critical coronary artery disease. The purpose of this study was to analyze the correlation between HGI and all-cause mortality in patients with critical coronary artery disease using the MIMIC-IV database.

METHODS

The HGI was calculated by constructing a linear regression equation between HbA1c and fasting plasma glucose (FPG). A Kaplan‒Meier survival analysis model was constructed based on the HGI quartiles to clarify the differences in all-cause mortality rates between groups, and the log-rank test was used to assess the differences between groups. The hazard ratio (HR) of HGI as a risk factor for outcome events was assessed using the Cox proportional risk model and restricted cubic spline (RCS), with the Q2 group serving as the reference group.

RESULTS

A total of 5260 patients were included in this study. The 30-day mortality rate of the patients was 4.94% and the mortality rate within 365 days was 13.12%. A low HGI was significantly associated with 30-day mortality (HR, 1.96; 95% CI, (1.38, 2.78); P < 0.001) and 365-day mortality (HR, 1.48; 95% CI, (1.19, 1.85); P < 0.001) in patients with critical coronary artery disease in the completely adjusted Cox proportional risk model. In addition, high levels of HGI were associated with 365-day mortality (HR, 1.31; 95% CI, (1.02, 1.69); P < 0.05). RCS analysis revealed a U-shaped relationship between HGI and outcome events. According to the stratified analysis, the interaction test revealed that the correlation between HGI and outcome events remained stable.

CONCLUSION

There was a significant correlation between HGI and all-cause mortality in patients with critical coronary artery disease, particularly in those with low HGI. HGI can be used as a potential indicator for assessing the short- and long-term risk of mortality in such patients.

Intra-articular site-specific distribution of advanced glycation end products in the shoulder of patients with diabetes mellitus having rotator cuff tears

BACKGROUND

Advanced glycation end products (AGEs) are compounds formed due to aging and diabetes mellitus (DM). They activate NADPH oxidase (NOX) by binding to their receptors, thereby increasing the production of reactive oxygen species (ROS), which cause oxidative stress. In this study, we investigated the effects of AGEs on the tissues of the shoulder joint (such as rotator cuff synovium, and capsule) in patients with DM having rotator cuff tears.

METHODS

This study included eight patients with DM who underwent surgical treatment for rotator cuff tears with contracture. The rotator cuff, synovium, and joint capsule were harvested at the time of surgery and evaluated by hematoxylin-eosin staining. Furthermore, immunostaining was used for evaluating AGEs and receptor for AGEs (RAGE), cell activity, ROS, and apoptosis. Quantitative real-time polymerase chain reaction (qPCR) was employed for the cellular evaluation of NOX, interleukins, RAGE, and collagen.

RESULTS

The AGEs and RAGE staining as well as the ratio of ROS and apoptosis were in the following order: rotator cuff > joint capsule > synovium. In contrast, the cellular activity was significantly higher in the synovium than in the other regions. The type I collagen expression (as shown by qPCR) as well as the RAGE and NOX expressions were as follows: rotator cuff > joint capsule > synovium. Conversely, the expression of inflammatory cytokines (i.e., IL-6 and IL-1β) was higher in the synovium than in the other regions.

CONCLUSIONS

Our study is among the first to evaluate the effects of AGEs on each tissue of the shoulder joint in patients with DM having rotator cuff tears and contractures. The accumulation of AGEs in each tissue of the shoulder joint could reveal the locations affected by DM, which can lead to a better understanding of the pathophysiology of DM-related shoulder diseases.

Elicitation of Inhibitory Effects for AGE-Induced Oxidative Stress in Rotator Cuff-Derived Cells by Apocynin

Advanced glycation end-products (AGEs) play a critical supportive role during musculoskeletal disorders via glycosylation and oxidative stress. Though apocynin, identified as a potent and selective inhibitor of NADPH oxidase, has been reported to be involved in pathogen-induced reactive oxygen species (ROS), its role in age-related rotator cuff degeneration has not been well clarified. Therefore, this study aims to evaluate the in vitro effects of apocynin on human rotator cuff-derived cells. Twelve patients with rotator cuff tears (RCTs) participated in the study. Supraspinatus tendons from patients with RCTs were collected and cultured. After the preparation of RC-derived cells, they were divided into four groups (control group, control + apocynin group, AGEs group, AGEs + apocynin group), and gene marker expression, cell viability, and intracellular ROS production were evaluated. The gene expression of NOX, IL-6, and the receptor for AGEs (RAGE) was significantly decreased by apocynin. We also examined the effect of apocynin in vitro. The results showed that ROS induction and increasing apoptotic cells after treatment of AGEs were significantly decreased, and cell viability increased considerably. These results suggest that apocynin can effectively reduce AGE-induced oxidative stress by inhibiting NOX activation. Thus, apocynin is a potential prodrug in preventing degenerative changes of the rotor cuff.

Biochemical Markers of Aging (Advanced Glycation End Products) and Degeneration Are Increased in Type 3 Rotator Cuff Tendon Stumps With Increased Signal Intensity Changes on MRI

BACKGROUND

Advanced glycation end products (AGEs) are end products of protein glycation that bind to the receptor for AGEs (RAGE) and activate nicotinamide adenine dinucleotide phosphate oxidase (NOX), resulting in increased oxidative stress and rotator cuff fragility. Stump classification using the signal intensity ratio of the tendon rupture site to the deltoid muscle in the coronal view of T2-weighted fat-suppressed magnetic resonance imaging (MRI) scans is an indicator of clinical outcomes after rotator cuff repair surgery. Comparing the signal intensities of the deltoid (D) and rotator cuff tears (C), Ishitani et al. classified C/D <0.8 as type 1, 0.8 to 1.3 as type 2, and >1.3 as type 3.

HYPOTHESIS/PURPOSE

It was hypothesized that the oxidative stress and collagen degeneration that occur in the rotator cuff due to accumulation of AGEs can be assessed on MRI scans (stump classification). Therefore, this study aimed to compare AGE-related factors in the rotator cuff tear site tissues based on stump classification.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The authors included 30 patients (11 with type 1, 9 with type 2, and 10 with type 3; mean age, 62.3 years) who underwent surgery for complete rotator cuff tears at our hospital. Tendon tissue was harvested from the torn rotator cuff site during surgery for tissue and cell evaluation.

RESULTS

There was no significant difference in the mean age according to stump classification. The number of patients with diabetes was significantly larger in type 3 than in the other types (P < .05). Tissue evaluation showed significantly higher expression of AGE and RAGE staining in type 3 than in the other types (~6.7-fold; P < .01). Cell evaluation showed that the expression rates of reactive oxygen species and apoptosis were significantly higher in type 3 than in the other types (~4.3-fold; P < .01). Gene expression by real-time polymerase chain reaction showed significantly higher RAGE (~5.1-fold), NOX (~5.3-fold), and IL (~3.0-fold) in type 3 than in the other types (P < .05).

CONCLUSION

Stump classification type 3 exhibited the highest accumulation of AGEs and the highest oxidative stress and apoptosis, suggesting a high degree of degeneration and inflammation. Imaging based on stump classification reflects the degeneration and fragility of the torn rotator cuff site.

CLINICAL RELEVANCE

This study provides evidence of a relationship between stump classification, which reflects rotator cuff fragility on MRI, and pathologies related to advanced glycation end products.

Biochemical analyses for dental age estimation: a review

Background

For various legal and forensic scenarios, establishing an individual’s age, both living and dead, plays a crucial role. Various morphological, radiographic, and molecular methods can be used for age estimation. In children and adolescents, age estimation is based on the established developmental stages. However, in adults, where the development ceases into maturation, the degenerative changes play a role in determining the age.

Main body of the abstract

In the natural aging process, several molecular changes occur most commonly in the long-living proteins and hard tissues like the teeth and bone. These molecular changes gradually lead to alterations in several organs and organ systems, which can be quantified and correlated with age, including aspartic acid racemization, collagen crosslinks, advanced glycation-end products, and mitochondrial DNA mutations.

Short conclusion

Among the above methods, the racemization of aspartic acid can be considered as the most precise method. The main advantage of using aspartic acid racemization is that the sample can be collected from tissues (teeth) protected from various environmental and nutritional factors. If all the confounding factors are stable, the utilization of advanced glycation-end products can also be considered valuable. Environmental factors like lead accumulations may also help determine the age. However, further studies need to be conducted, focusing on providing a more standardized method. This review provides a concise summary of the biochemical techniques that can be used for estimation of age.

Hemoglobin glycation index, calculated from a single fasting glucose value, as a prediction tool for severe hypoglycemia and major adverse cardiovascular events in DEVOTE

INTRODUCTION

Hemoglobin glycation index (HGI) is the difference between observed and predicted glycated hemoglobin A1c (HbA1c), derived from mean or fasting plasma glucose (FPG). In this secondary, exploratory analysis of data from DEVOTE, we examined: whether insulin initiation/titration affected the HGI; the relationship between baseline HGI tertile and cardiovascular and hypoglycemia risk; and the relative strengths of HGI and HbA1c in predicting these risks.

RESEARCH DESIGN AND METHODS

In DEVOTE, a randomized, double-blind, cardiovascular outcomes trial, people with type 2 diabetes received once per day insulin degludec or insulin glargine 100 units/mL. The primary outcome was time to first occurrence of a major adverse cardiovascular event (MACE), comprising cardiovascular death, myocardial infarction or stroke; severe hypoglycemia was a secondary outcome. In these analyses, predicted HbA1c was calculated using a linear regression equation based on DEVOTE data (HbA1c=0.01313 FPG (mg/dL) (single value)+6.17514), and the population data were grouped into HGI tertiles based on the calculated HGI values. The distributions of time to first event were compared using Kaplan-Meier curves; HRs and 95% CIs were determined by Cox regression models comparing risk of MACE and severe hypoglycemia between tertiles.

RESULTS

Changes in HGI were observed at 12 months after insulin initiation and stabilized by 24 months for the whole cohort and insulin-naive patients. There were significant differences in MACE risk between baseline HGI tertiles; participants with high HGI were at highest risk (low vs high, HR: 0.73 (0.61 to 0.87)95% CI; moderate vs high, HR: 0.67 (0.56 to 0.81)95% CI; p<0.0001). No significant differences between HGI tertiles were observed in the risk of severe hypoglycemia (p=0.0911). With HbA1c included within the model, HGI no longer significantly predicted MACE.

CONCLUSIONS

High HGI was associated with a higher risk of MACE; this finding is of uncertain significance given the association of HGI with insulin initiation and HbA1c.

TRIAL REGISTRATION NUMBER

NCT01959529.

The impact of collagen protein ingestion on musculoskeletal connective tissue remodeling: a narrative review

Collagen is the central structural component of extracellular connective tissue, which provides elastic qualities to tissues. For skeletal muscle, extracellular connective tissue transmits contractile force to the tendons and bones. Connective tissue proteins are in a constant state of remodeling and have been shown to express a high level of plasticity. Dietary-protein ingestion increases muscle protein synthesis rates. High-quality, rapidly digestible proteins are generally considered the preferred protein source to maximally stimulate myofibrillar (contractile) protein synthesis rates. In contrast, recent evidence demonstrates that protein ingestion does not increase muscle connective tissue protein synthesis. The absence of an increase in muscle connective tissue protein synthesis after protein ingestion may be explained by insufficient provision of glycine and/or proline. Dietary collagen contains large amounts of glycine and proline and, therefore, has been proposed to provide the precursors required to facilitate connective tissue protein synthesis. This literature review provides a comprehensive evaluation of the current knowledge on the proposed benefits of dietary collagen consumption to stimulate connective tissue remodeling to improve health and functional performance.

Shoulder range of movement in the general population: age and gender stratified normative data using a community-based cohort

Background

An understanding of the average range of movement of the shoulder that is normally achievable is an important part of treatment for shoulder disorders. The average range of active shoulder flexion, abduction and external rotation was measured in a population cohort aged 20 years and over without shoulder pain and/or stiffness in order to provide normative shoulder range data.

Methods

Cross-sectional analysis using participants in a community-based longitudinal cohort study. There have been three stages of data collection – Stage 1 (1999–2003), Stage 2 (2004–2006) and Stage 3 (2008–2010). Each stage has consisted a of broad ranging computer assisted telephone interview, a self-complete questionnaire and a clinic assessment. Participants in this study are those who undertook assessments in Stage 2. The main outcome measures were active shoulder range of movement (flexion, abduction and external rotation) measured as part of the clinic assessment using a Plurimeter V inclinometer. Mean values were determined and analyses to examine differences between groups (sex and age) were undertaken using non-parametric tests.

Results

There were 2404 participants (51.5% male), mean age 45.8 years (SD 17.3, range 20–91). The average range of active right shoulder flexion was 161.5° for males and 158.5° for females, and active right shoulder abduction was 151.5° and 149.7° for males and females respectively. Shoulder range of movement declined with age, with mean right active shoulder flexion decreasing by 43° in males and 40.6° in females and right active shoulder abduction by 39.5° and 36.9° respectively. External rotation range also declined, particularly among females.

Conclusion

To our knowledge this is the largest community-based study providing normative data for active shoulder range of movement. This information can be used to set realistic goals for both clinical practice and clinical trials.

Influence of advanced glycation end products on rotator cuff

BACKGROUND

Most rotator cuff tears are the result of age-related degenerative changes, but the mechanisms underlying these changes have not been reported. Recently, advanced glycation end products (AGEs) have been regarded as an important factor in senescence. Therefore, we hypothesized that AGEs would have detrimental effects on rotator cuff-derived cells. In this study, we investigated the influence of AGEs on rotator cuff-derived cells in vitro and ex vivo.

METHODS

Rotator cuff-derived cells were obtained from human supraspinatus tendons. The cells were cultured in the following media: (1) regular medium with 500 μg/mL AGEs (High-AGEs), (2) regular medium with 100 μg/mL AGEs (Low-AGEs), and (3) regular medium alone (Control). Cell viability, secretion of vascular endothelial growth factor, and the expressions of hypoxia-inducible factor-1α, reactive oxygen species, and apoptosis were assessed after cultivation. An ex vivo tissue culture with AGEs was also performed to measure the tensile strength.

RESULTS

Cell viability in the High-AGEs group was significantly suppressed relative to that in the Controls. The amount of vascular endothelial growth factor secretion was significantly greater in the High- and Low-AGEs groups than in the Controls. Immunofluorescence stain demonstrated enhancement of hypoxia-inducible factor-1α and reactive oxygen species expressions and cell apoptosis in the High- and Low-AGEs groups relative to that in the Controls. In ex vivo mechanical testing, tensile strength was significantly higher in the Control group than in the AGEs groups.

DISCUSSION

These results indicated that AGEs caused age-related degenerative rotator cuff changes. The reduction of AGEs might prevent rotator cuff senescence-related degeneration.

Development of serum glycoproteomic profiling technique; simultaneous identification of glycosylation sites and site-specific quantification of glycan structure changes

Characterization and interpretation of disease-associated alterations of protein glycosylation are the central aims of the emerging glycoproteomics projects, which are expected to lead to more sensitive and specific diagnosis and improve therapeutic outcomes for various diseases. Here we report a new approach to identify carbohydrate-targeting serum biomarkers, termed isotopic glycosidase elution and labeling on lectin-column chromatography (IGEL). This technology is based on glycan structure-specific enrichment of glycopeptides by lectin-column chromatography and site-directed tagging of N-glycosylation sites by (18)O during the elution with N-glycosidase. The combination of IGEL with 8-plex isobaric tag for relative and absolute quantitation (iTRAQ) stable isotope labeling enabled us not only to identify N-glycosylation sites effectively but also to compare glycan structures on each glycosylation site quantitatively in a single LC/MS/MS analysis. We applied this method to eight sera from lung cancer patients and controls, and finally identified 107 glycopeptides in their sera, including A2GL_Asn151, A2GL_Asn290, CD14_Asn132, CO8A_Asn417, C163A_Asn64, TIMP1_Asn30, and TSP1_Asn1049 which showed the significant change of the affinity to Concanavalin A (ConA) lectin between the lung cancer samples and the controls (p < 0.05 and more than twofold change). These screening results were further confirmed by the conventional lectin-column chromatography and immunoblot analysis using additional serum samples. Our novel methodology, which should be valuable for diverse biomarker discoveries, can provide high-throughput and quantitative profiling of glycan structure alterations.

Hemoglobin glycation index: a robust measure of hemoglobin A1c bias in pediatric type 1 diabetes patients

BACKGROUND

The hemoglobin glycation index (HGI) assesses biological variation in A1c after accounting for the effect of mean blood glucose (MBG). Previous studies minimized analytical variation that could mask biological variation and showed that HGI was consistent within individuals over time and positively associated with risk for microvascular complications. We tested the hypothesis that biological variation in A1c can be assessed by HGI calculated using routine MBG and A1c data obtained from a typical diabetes clinic.

METHODS

Self-monitored MBG and A1c were collected from charts of 202 pediatric type 1 diabetes patients attending 1612 clinic visits over 6 yr. Predicted A1c was calculated from the linear regression equation of A1c on MBG in the study population. HGI was calculated by subtracting predicted A1c from observed A1c. Patients were divided into low, moderate, and high HGI tertile groups.

RESULTS

Patients used 12 models of glucose meters. Download protocols varied with clinical practice over time. A1c was measured by multiple assays and laboratories. Despite this analytical heterogeneity, HGI was significantly different between individuals and correlated within individuals. MBG (mean ± SD, mg/dL) was similar in the low (186 ± 31), moderate (195 ± 28), and high (199 ± 42) HGI groups. A1c (%) was significantly different (p < 0.0001) in the low (7.6 ± 0.7), moderate (8.4 ± 0.7), and high (9.6 ± 1.1) HGI groups.

CONCLUSION

Biological variation in A1c is a robust quantitative trait that can be assessed using HGI calculated from routine clinic data. This suggests that HGI could be used clinically for more personalized assessment of complications risk.

Diabetes mellitus impairs tendon-bone healing after rotator cuff repair

INTRODUCTION

Studies have demonstrated a significant decrease in skeletal mass, bone mineral density, and impaired fracture healing in the diabetic population. However, the effect of sustained hyperglycemia on tendon-to-bone healing is unknown.

MATERIALS AND METHODS

Forty-eight male, Lewis rats underwent unilateral detachment of the supraspinatus tendon followed by immediate anatomic repair with transosseous fixation. In the experimental group (n = 24), diabetes was induced preoperatively via intraperitoneal injection of streptozotocin (STZ, 65 mg/kg) and confirmed with both pre- and post-STZ injection intraperitoneal glucose tolerance tests (IPGTT). Animals were sacrificed at 1 and 2 weeks postoperatively for biomechanical, histomorphometric, and immunohistochemical analysis. Serum hemoglobin A1c (HbA1c) levels were measured at 2 weeks postoperatively. Statistical comparisons were performed using Student t tests with significance set at P < .05.

RESULTS

IPGTT analysis demonstrated a significant impairment of glycemic control in the diabetic compared to control animals (P < .05). Mean HbA1c level at 2 weeks postoperatively was 10.6 ± 2.7% and 6.0 ± 1.0% for the diabetic and control groups, respectively (P < .05). Diabetic animals demonstrated significantly less fibrocartilage and organized collagen, and increased AGE deposition at the tendon-bone interface (P < .05). The healing enthesis of diabetic animals demonstrated a significantly reduced ultimate load-to-failure (4.79 ± 1.33 N vs 1.60 ± 1.67 N and 13.63 ± 2.33 N vs 6.0 ± 3.24 N for control versus diabetic animals at 1 and 2 weeks, respectively) and stiffness compared to control animals (P < .05).

DISCUSSION

Sustained hyperglycemia impairs tendon-bone healing after rotator cuff repair in this rodent model. These findings have significant clinical implications for the expected outcomes of soft tissue repair or reconstructive procedures in diabetic patients with poor glycemic control.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

The Maillard reaction in the human body. The main discoveries and factors that affect glycation

Ever since the discovery of the Maillard reaction in 1912 and the discovery of the interaction between advanced glycation end-products and cellular receptors, impressive progress has been made in the knowledge of nonenzymatic browning of proteins in vivo. This reaction which leads to the accumulation of random damage in extracellular proteins is known to have deleterious effects on biological function, and is associated with aging and complication in chronic diseases. Despite a controlled membrane permeability and a protective regulation of the cells, intracellular proteins are also altered by the Maillard reaction. Two main factors, protein turnover and the concentration of carbonyls, are involved in the rate of formation of the Maillard products. This paper reviews the key milestones of the discovery of the Maillard reaction in vivo, better known as glycation, and the factors which are likely to affect it.

"Blinding" of AMP-dependent kinase by methylglyoxal: a mechanism that allows perpetuation of hepatic insulin resistance?

AMP-dependent kinase (AMPK) is a regulatory carrefour and a key target for therapeutics. The role of AMPK in regulating cellular energy status (by sensing low energy using [AMP] as its signal) and activating catabolic pathways while inhibiting anabolic routes, places this enzyme at a central control point in maintaining energy homeostasis. The exquisite allosteric sensing of AMP is done by a domain with three arginine residues, which make it very vulnerable to glycation, especially by the alpha-dicarbonyl methylglyoxal (MG). MG accumulates in hyperglycemia, insulin resistance, diabetes and when there is excess flux of reactive oxygen species coming from the mitochondria. We hypothesize that excess MG in the above-mentioned conditions blocks the sensing of AMP by AMPK, thereby favoring gluconeogenesis (thus hepatic glucose output and hyperglycemia) and lipogenesis (hepatic steatosis and high VLDL), hallmarks of insulin resistance and diabetes. Our hypothesis may explain, for instance, the perpetuation of hepatic insulin resistance, as well as part of the action of metformin, which is a potent anti-glycation agent. Future targets for type 2 diabetes treatments will likely be those that can effect beneficial changes in the activity of AMPK, and our theory predicts that anti-glycation agents may become part of that armamentarium.

Glycation of wood frog (Rana sylvatica) hemoglobin and blood proteins: in vivo and in vitro studies

The effects of in vivo freezing and glucose cryoprotectant on protein glycation were investigated in the wood frog, Rana sylvatica. Our studies revealed no difference in the fructoselysine content of blood plasma sampled from control, 27 h frozen and 18 h thawed wood frogs. Glycated hemoglobin (GHb) decreased slightly with 48 h freezing exposure and was below control levels after 7d recovery, while glycated serum albumin was unchanged by 48 h freezing but did increase after 7d of recovery. In vitro exposure of blood lysates to glucose revealed that the GHb production in wood frogs was similar to that of the rat but was lower than in leopard frogs. We conclude that wood frog hemoglobin was glycated in vitro; however, GHb production was not apparent during freezing and recovery when in vivo glucose is highly elevated. It is possible that wood frog blood proteins have different in vivo susceptibilities to glycation.

Age-related muscle dysfunction

Aging is associated with a progressive decline of muscle mass, strength, and quality, a condition described as sarcopenia of aging. Despite the significance of skeletal muscle atrophy, the mechanisms responsible for the deterioration of muscle performance are only partially understood. The purpose of this review is to highlight cellular, molecular, and biochemical changes that contribute to age-related muscle dysfunction.

Collagen, cross-linking, and advanced glycation end products in aging human skeletal muscle

We examined intramuscular endomysial collagen, cross-linking, and advanced glycation end products, as well as the general and contractile protein concentration of 20 young (25 +/- 3 yr) and 22 old (78 +/- 6 yr, range: 70-93 yr) sedentary men and women to better understand the underlying basis of changes in skeletal muscle mass and function that occur with aging. The old individuals had an impaired ability (increased time) (P < 0.05) to climb stairs (80%), rise from a chair (56%), and walk (44%), as well as lower (P < 0.05) quadriceps muscle volume (-29%), muscle strength (-35%), muscle power (-48%), and strength (-17%) and power (-33%) normalized to muscle size. Vastus lateralis muscle biopsies revealed that intramuscular endomysial collagen (young: 9.6 +/- 1.1, old: 10.2 +/- 1.2 microg/mg muscle wet wt) and collagen cross-linking (hydroxylysylpyridinoline) (young: 395 +/- 65, old: 351 +/- 45 mmol hydroxylysylpyridinoline/mol collagen) were unchanged (P > 0.05) with aging. The advanced glycation end product, pentosidine, was increased (P < 0.05) by approximately 200% (young: 5.2 +/- 1.3, old: 15.9 +/- 4.5 mmol pentosidine/mol collagen) with aging. While myofibrillar protein concentration was lower (-5%, P < 0.05), the concentration of the main contractile proteins myosin and actin were unchanged (P > 0.05) with aging. These data suggest that the synthesis and degradation of proteins responsible for the generation (myosin and actin) and transfer (collagen and pyridinoline cross-links) of muscle force are tightly regulated in aging muscle. Glycation-related cross-linking of intramuscular connective tissue may contribute to altered muscle force transmission and muscle function with healthy aging.

Genomic Damage and Malignancy in End-Stage Renal Failure: Do Advanced Glycation End Products Contribute?

In end-stage renal disease (ESRD) there is not only excessive morbidity and mortality due to cardiovascular disease but also an enhanced occurrence of various types of cancer. Both are characterized by oxidative stress and inflammation as two of the central underlying causes of the disease states. In cancer, genomic damage has been demonstrated to be of high pathogenetic relevance. DNA lesions may induce mutations of oncogenes and tumor-suppressor genes which, in the long-run, may lead to malignancies if mutagenicity is not mitigated by repair mechanisms. A high incidence of genomic damage in ESRD patients has been validated by various biomarkers of DNA lesions. We reviewed the mechanisms of DNA damage, focusing in particular on the role of advanced glycation end products (AGEs) which accumulate markedly in renal insufficiency. Considering the in vitro and in vivo findings to date, one has to assume a significant role of AGEs in DNA damage and the potential development of cancer.

The effects of the Maillard reaction on the physical properties and cell interactions of collagen

The non-enzymic glycation of collagen occurs as its turnover decreases during maturation, with complex carbohydrates accumulating slowly and the end-products of these reactions being permanent. The nature of these advanced glycation end-reaction products (AGEs) can be categorised as: 1) cross-linking: intermolecular cross-linking may occur between two adjacent molecules and involve lysine to lysine or lysine to arginine residues. Several compounds have been characterised. They are believed to be located between the triple helical domains of adjacent molecules in the fibre resulting in major changes of the physical properties, primarily, fibre stiffness, thermal denaturation temperature and enzyme resistance, all of which increase slowly with age but the rate is accelerated in diabetes mellitus due to high glucose levels: 2) side-chain modifications: these changes alter the charge profile of the molecule affecting the interactions within the fibre and if they occur at specific sites can affect the cell-collagen interaction. Modification of arginine within the sites RGD and GFOGER recognised by the two specific integrins (alpha1beta2 and alpha2beta1) for collagen reduce cell interactions during turnover and for platelet interactions (alpha1beta2). These changes can ultimately affect repair of, for example, vascular damage and dermal wound healing in diabetes mellitus. Both types of modification are deleterious to the optimal properties of collagen as a supporting framework structure and as a controlling factor in cell matrix interactions. Glycation during ageing and diabetes is therefore responsible for malfunctioning of the diverse collagenous tissues throughout the body.