Accelerated age-related browning of human collagen in diabetes mellitus

Bone turnover markers in the preoperative assessment of bone quality - A prospective investigation of bone microstructure and advanced glycation endproducts in lumbar fusion patients

INTRODUCTION

Effective tools to evaluate bone quality preoperatively are scarce and the standard method to determine bone quality requires an invasive biopsy. A non-invasive, and preoperatively available method for bone quality assessment would be of clinical value. The purpose of this study is to investigate the associations of bone formation marker, serum bone alkaline phosphatase (BAP), and bone resorption marker, urine collagen cross-linked N-telopeptide (uNTX) to volumetric bone mineral density (vBMD), fluorescent advanced glycation endproducts (fAGEs) and bone microstructure.

MATERIALS AND METHODS

A cross-secional analysis using prospective data of patients undergoing lumbar spinal fusion was performed. BAP and uNTX were preoperatively collected. Quantitative computed tomography (QCT) was performed at the lumbar spine (vBMD ≤ 120 mg/cm3 osteopenic/osteoporotic). Bone biopsies from the posterior superior iliac spine were obtained and evaluated with multiphoton fluorescence microscopy for fAGEs and microcomputed tomography (µCT) for bone microarchitecture. Correlations between BAP/uNTX to vBMD, fAGEs and µCT parameters were assessed with Spearman's ρ. Receiver operating characteristic (ROC) analysis evaluated BAP and uNTX as predictors for osteopenia/osteoporosis. Multivariable linear regression models adjusting for age, sex, BMI, race and diabetes mellitus determined associations between BAP/uNTX and fAGEs.

RESULTS

127 prospectively enrolled patients (50.4% female, 62.5 years, BMI 28.7 kg/m2) were analyzed. uNTX (ρ=-0.331,p < 0.005) and BAP (ρ=-0.245,p < 0.025) decreased with cortical fAGEs, and uNTX (ρ=-0.380,p < 0.001) decreased with trabecular fAGEs. BAP and uNTX revealed no significant correlation with vBMD. ROC analysis for BAP and uNTX discriminated osteopenia/osteoporosis with AUC of 0.477 and 0.561, respectively. In the multivariable analysis, uNTX decreased with increasing trabecular fAGEs after adjusting for covariates (β = 0.923;p = 0.031).

CONCLUSION

This study demonstrated an inverse association of bone turnover markers and fAGEs. Both uNTX and BAP could not predict osteopenia/osteoporosis in the spine. uNTX reflects collagen characteristics and might have a complementary role to vBMD, as a non-invasive tool for bone quality assessment in spine surgery.

Role of advanced glycation endproducts in bone fragility in type 1 diabetes

The excess fracture risk observed in adults with type 1 diabetes (T1D) is inexplicable in the presence of only modest reductions in areal bone mineral density (BMD). Accumulation of advanced glycation endproducts (AGEs) in bone has been invoked as one explanation for the increased bone fragility in diabetes. The evidence linking AGEs and fractures in individuals with T1D is sparse, although the association has been observed in individuals with type 2 diabetes. Recent data show that in T1D, AGEs as measured by skin intrinsic fluorescence, are a risk factor for lower BMD. Further research in T1D is needed to ascertain whether there is a causal relationship between fractures and AGEs. If confirmed, this would pave the way for finding interventions that can slow AGE accumulation and thus reduce fractures in T1D.

Effect of in vitro ribosylation on the dynamic fracture behavior of mature bovine cortical bone

In this study, the fracture behavior of ribosylated bovine cortical bone is investigated under loading conditions simulating a fall event. Single edge notched specimens, separated into a control group (n = 11) and a ribosylated group (n = 8), were extracted from the mid-diaphysis of a single bovine femur harvested from a mature cow. A seven-day ribosylation process results in the accumulation of Advanced-Glycation End Products (AGEs) cross-links and AGE adducts. Specimens were subjected to symmetric three point bending (opening mode) and an impact velocity of 1.6 m/s using a drop tower. Near-crack displacement fields up to fracture initiation are determined from high-speed images post-processed using digital image correlation. A constrained over-deterministic least squares regression and orthotropic material linear elastic fracture mechanics theory are used to extract the in-plane critical stress intensity factors at fracture initiation (i.e., fracture initiation toughness values). Statistically significant differences were not observed when comparing the in-plane fracture initiation toughness values (p≥0.96) or energy release rate (p=0.90) between the control and seven-day ribosylated groups. The intrinsic variability of bone may require high sample numbers in order to achieve an adequately powered experiment when assessing dynamic fracture behavior. While there are no detectable differences due to the ribosylation treatment investigated, this is likely due to the limited sample sizes utilized.

Methylglyoxal-derived hydroimidazolone, MG-H1, increases food intake by altering tyramine signaling via the GATA transcription factor ELT-3 in Caenorhabditis elegans

The Maillard reaction, a chemical reaction between amino acids and sugars, is exploited to produce flavorful food ubiquitously, from the baking industry to our everyday lives. However, the Maillard reaction also occurs in all cells, from prokaryotes to eukaryotes, forming advanced glycation end-products (AGEs). AGEs are a heterogeneous group of compounds resulting from the irreversible reaction between biomolecules and α-dicarbonyls (α-DCs), including methylglyoxal (MGO), an unavoidable byproduct of anaerobic glycolysis and lipid peroxidation. We previously demonstrated that Caenorhabditis elegans mutants lacking the glod-4 glyoxalase enzyme displayed enhanced accumulation of α-DCs, reduced lifespan, increased neuronal damage, and touch hypersensitivity. Here, we demonstrate that glod-4 mutation increased food intake and identify that MGO-derived hydroimidazolone, MG-H1, is a mediator of the observed increase in food intake. RNAseq analysis in glod-4 knockdown worms identified upregulation of several neurotransmitters and feeding genes. Suppressor screening of the overfeeding phenotype identified the tdc-1-tyramine-tyra-2/ser-2 signaling as an essential pathway mediating AGE (MG-H1)-induced feeding in glod-4 mutants. We also identified the elt-3 GATA transcription factor as an essential upstream regulator for increased feeding upon accumulation of AGEs by partially controlling the expression of tdc-1 gene. Furthermore, the lack of either tdc-1 or tyra-2/ser-2 receptors suppresses the reduced lifespan and rescues neuronal damage observed in glod-4 mutants. Thus, in C. elegans, we identified an elt-3 regulated tyramine-dependent pathway mediating the toxic effects of MG-H1 AGE. Understanding this signaling pathway may help understand hedonistic overfeeding behavior observed due to modern AGE-rich diets.

Plasma AGE and Oxidation Products, Renal Function, and Preeclampsia in Pregnant Women with Type 1 Diabetes: A Prospective Observational Study

Aims

We aimed to determine whether plasma advanced glycation end products or oxidation products (AGE/oxidation-P) predict altered renal function and/or preeclampsia (PE) in pregnant women with type 1 diabetes.

Methods

Prospectively, using a nested case-control design, we studied 47 pregnant women with type 1 diabetes, of whom 23 developed PE and 24 did not. Nineteen nondiabetic, normotensive pregnant women provided reference values. In plasma obtained at ~12, 22, and 32 weeks' gestation (visits 1, 2, and 3; V1-V3), we measured five AGE products (carboxymethyllysine (CML), carboxyethyl-lysine (CEL), methylglyoxal-hydroimidazolone (MGH1), 3-deoxyglucosone hydroimidazolone (3DGH), and glyoxal-hydroimidazolone (GH1)) and four oxidation products (methionine sulfoxide (MetSO), 2-aminoadipic acid (2-AAA), 3-nitrotyrosine (3NT), and dityrosine (DT)), by liquid chromatography/mass spectroscopy. Clinical outcomes were "estimated glomerular filtration rate" (eGFR) at each visit and onset of PE.

Results

In diabetic women, associations between AGE/oxidation-P and eGFR were found only in those who developed PE. In this group, CEL, MGH1, and GH1 at V2 and CML, CEL, MGH1, and GH1 at V3 were inversely associated with contemporaneous eGFR, while CEL, MGH1, 3DGH, and GH1 at V2 were inversely associated with eGFR at V3 (all p < 0.05). There were no associations of plasma AGE or oxidation-P with pregnancy-related development of proteinuria or PE.

Conclusions

Inverse associations of second and early third trimester plasma AGE with eGFR among type 1 diabetic women who developed PE suggest that these patients constitute a subset susceptible to AGE-mediated injury and thus to cardiorenal complications later in life. However, AGE/oxidation-P did not predict PE in type 1 diabetic women.

Osteosarcopenia in the Spine Beyond Bone Mineral Density: Association Between Paraspinal Muscle Impairment and Advanced Glycation Endproducts

STUDY DESIGN

Prospective cross-sectional study.

OBJECTIVE

To determine if an accumulation of advanced glycation endproducts (AGEs) is associated with impaired paraspinal muscle composition.

BACKGROUND

Impaired bone integrity and muscle function are described as osteosarcopenia. Osteosarcopenia is associated with falls, fragility fractures, and reduced quality of life. Bone integrity is influenced by bone quantity (bone mineral density) and quality (microarchitecture and collagen). The accumulation of AGEs stiffens collagen fibers and increases bone fragility. The relationship between paraspinal muscle composition and bone collagen properties has not been evaluated.

METHODS

Intraoperative bone biopsies from the posterior superior iliac spine were obtained and evaluated with multiphoton microscopy for fluorescent AGE cross-link density (fAGEs). Preoperative magnetic resonance imaging measurements at level L4 included the musculus (m.) psoas and combined m. multifidus and m. erector spinae (posterior paraspinal musculature, PPM). Muscle segmentation on axial images (cross-sectional area, CSA) and calculation of a pixel intensity threshold method to differentiate muscle (functional cross-sectional area, fCSA) and intramuscular fat (FAT). Quantitative computed tomography was performed at the lumbar spine. Univariate and multivariable regression models were used to investigate associations between fAGEs and paraspinal musculature.

RESULTS

One hundred seven prospectively enrolled patients (50.5% female, age 60.7 y, BMI 28.9 kg/m 2 ) were analyzed. In all, 41.1% and 15.0% of the patients demonstrated osteopenia and osteoporosis, respectively. Univariate linear regression analysis demonstrated a significant association between cortical fAGEs and CSA in the psoas (ρ=0.220, P =0.039) but not in the PPM. Trabecular fAGEs revealed no significant associations to PPM or psoas musculature. In the multivariable analysis, higher cortical fAGEs were associated with increased FAT (β=1.556; P =0.002) and CSA (β=1.305; P =0.005) in the PPM after adjusting for covariates.

CONCLUSION

This is the first investigation demonstrating that an accumulation of nonenzymatic collagen cross-linking product fAGEs in cortical bone is associated with increased intramuscular fat in the lumbar paraspinal musculature.

Effect of non-enzymatic glycation on collagen nanoscale mechanisms in diabetic and age-related bone fragility

Age and diabetes have long been known to induce an oxidative reaction between glucose and collagen, leading to the accumulation of advanced glycation end-products (AGEs) cross-links in collagenous tissues. More recently, AGEs content has been related to loss of bone quality, independent of bone mass, and increased fracture risk with aging and diabetes. Loss of bone quality is mostly attributed to changes in material properties, structural organization, or cellular remodeling. Though all these factors play a role in bone fragility disease, some common recurring patterns can be found between diabetic and age-related bone fragility. The main pattern we will discuss in this viewpoint is the increase of fibrillar collagen stiffness and loss of collagen-induced plasticity with AGE accumulation. This study focused on recent related experimental studies and discusses the correlation between fluorescent AGEs content at the molecular and fibrillar scales, collagen deformation mechanisms at the nanoscale, and resistance to bone fracture at the macroscale.

Changes in the AGE/Macrophage/TNF-α Pathway Affect Skin Dryness during KK-Ay/Tajcl Mice Aging

Skin dryness associated with type 2 diabetes worsens with age; however, the underlying mechanisms remain unclear. Herein, we investigated the effects of aging on skin dryness using a type 2 diabetes mice model. Specific pathogen-free KK-Ay/TaJcl mice of different ages (10, 27, 40, and 50 weeks) were used in this study. The results confirmed that skin dryness worsens with age. Furthermore, increased levels of advanced glycation end products (AGE), prostaglandin E2 (PGE2), and tumor necrosis factor (TNF)-α, along with an increased expression of the major AGE receptor (RAGE), an increased macrophage number, and decreased collagen expression were observed in the skin of aged KK-Ay/TaJcl mice. In conclusion, dry skin conditions worsen with age in diabetic mice, and the AGE/RAGE/PGE2 and TNF-α pathways play an important role in exacerbating skin dryness during aging in these mice.

On the Nature of Stationary and Time-Resolved Fluorescence Spectroscopy of Collagen Powder from Bovine Achilles Tendon

This paper presents a more systematic study of steady-state and time-resolved autofluorescence spectroscopy of collagen isolated from bovine Achilles tendon. In steady-state fluorescence measurements, the excitation and emission spectra of collagen powder, recorded at different fluorescence excitation and detection wavelengths, were compared with the fluorescence excitation and emission spectra of the amino acids phenylalanine, tyrosine, and tryptophan, as well as with similar spectra for 13 autofluorescent collagen cross-links, which have been identified and described in the literature so far. In time-resolved studies, fluorescence was excited by the pulsed light of different wavelengths, and for each excitation wavelength, fluorescence decay was recorded for several detection wavelengths. Data analysis allowed recovery of the fluorescence decay times for each experimental excitation detection event. The obtained information on the decay times of the measured fluorescent signals was discussed, taking into account the available literature data from similar studies of isolated collagen and collagen-rich tissues. Based on the obtained results, it was found that the shape and position of the measured fluorescence excitation and emission spectra of collagen strongly depend on the emission and excitation wavelengths selected in the measurements. From the recorded excitation and emission bands of collagen, it can be concluded with high probability that there are additional, so far unidentified, collagen cross-links, which can be excited at longer excitation wavelengths. In addition, the collagen excitation spectra were measured at longer emission wavelengths at which the collagen cross-links emit fluorescent light. In addition to the emission spectra obtained for excitation in the deep-UV region, the results of time-resolved fluorescence studies with excitation in the deep-UV region and detection at longer wavelengths suggest that fluorescence excitation energy transfer processes occur from the amino acids to the collagen cross-links, and also between the cross-links themselves.

Impact of elevated serum advanced glycation end products and exercise on intact and injured murine tendons

OVERVIEW

Delayed tendon healing is a significant clinical challenge for those with diabetes. We explored the role of advanced glycation end-products (AGEs), a protein modification present at elevated levels in serum of individuals with diabetes, on injured and intact tendons using a mouse model. Cell proliferation following tissue injury is a vital component of healing. Based on our previous work demonstrating that AGEs limit cell proliferation, we proposed that AGEs are responsible for the delayed healing process commonly observed in diabetic patients. Further, in pursuit of interventional strategies, we suggested that moderate treadmill exercise may support a healing environment in the presence of AGEs as exercise has been shown to stimulate cell proliferation in tendon tissue.

MATERIALS AND METHODS

Mice began receiving daily intraperitoneal injections of bovine serum albumin (BSA)-Control or AGE-BSA injections (200μg/ml) at 16-weeks of age. A tendon injury was created in the central third of both patellar tendons. Animals assigned to an exercise group began a moderate treadmill protocol one week following injury. The intact Achilles tendon and soleus muscle were also evaluated to assess the effect of BSA and AGE-BSA on un-injured muscle and tendon.

RESULTS

We demonstrate that our injection dosing and schedule lead to an increase in serum AGEs. Our findings imply that AGEs indeed modulate gene expression following a patellar tendon injury and have modest effects on gene expression in intact muscle and tendon.

CONCLUSIONS

While additional biomechanical analysis is warranted, these data suggest that elevated serum AGEs in persons with diabetes may impact tendon health.

Glycation Interferes with the Activity of the Bi-Functional UDP-N-Acetylglucosamine 2-Epimerase/N-Acetyl-mannosamine Kinase (GNE)

Mutations in the gene coding for the bi-functional UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE), the key enzyme of the sialic acid biosynthesis, are responsible for autosomal-recessive GNE myopathy (GNEM). GNEM is an adult-onset disease with a yet unknown exact pathophysiology. Since the protein appears to work adequately for a certain period of time even though the mutation is already present, other effects appear to influence the onset and progression of the disease. In this study, we want to investigate whether the late onset of GNEM is based on an age-related effect, e.g., the accumulation of post-translational modifications (PTMs). Furthermore, we also want to investigate what effect on the enzyme activity such an accumulation would have. We will particularly focus on glycation, which is a PTM through non-enzymatic reactions between the carbonyl groups (e.g., of methylglyoxal (MGO) or glyoxal (GO)) with amino groups of proteins or other biomolecules. It is already known that the levels of both MGO and GO increase with age. For our investigations, we express each domain of the GNE separately, treat them with one of the glycation agents, and determine their activity. We demonstrate that the enzymatic activity of the N-acetylmannosamine kinase (GNE-kinase domain) decreases dramatically after glycation with MGO or GO-with a remaining activity of 13% ± 5% (5 mM MGO) and 22% ± 4% (5 mM GO). Whereas the activity of the UDP-N-acetylglucosamine 2-epimerase (GNE-epimerase domain) is only slightly reduced after glycation-with a remaining activity of 60% ± 8% (5 mM MGO) and 63% ± 5% (5 mM GO).

Increased Advanced Glycation Endproducts, Stiffness, and Hardness in Iliac Crest Bone From Postmenopausal Women With Type 2 Diabetes Mellitus on Insulin

Individuals with type 2 diabetes mellitus (T2DM) have a greater risk of bone fracture compared with those with normal glucose tolerance (NGT). In contrast, individuals with impaired glucose tolerance (IGT) have a lower or similar risk of fracture. Our objective was to understand how progressive glycemic derangement affects advanced glycation endproduct (AGE) content, composition, and mechanical properties of iliac bone from postmenopausal women with NGT (n = 35, age = 65 ± 7 years, HbA1c = 5.8% ± 0.3%), IGT (n = 26, age = 64 ± 5 years, HbA1c = 6.0% ± 0.4%), and T2DM on insulin (n = 25, age = 64 ± 6 years, HbA1c = 9.1% ± 2.2%). AGEs were assessed in all samples using high-performance liquid chromatography to measure pentosidine and in NGT/T2DM samples using multiphoton microscopy to spatially resolve the density of fluorescent AGEs (fAGEs). A subset of samples (n = 14 NGT, n = 14 T2DM) was analyzed with nanoindentation and Raman microscopy. Bone tissue from the T2DM group had greater concentrations of (i) pentosidine versus IGT (cortical +24%, p = 0.087; trabecular +35%, p = 0.007) and versus NGT (cortical +40%, p = 0.003; trabecular +35%, p = 0.004) and (ii) fAGE cross-link density versus NGT (cortical +71%, p < 0.001; trabecular +44%, p < 0.001). Bone pentosidine content in the IGT group was lower than in the T2DM group and did not differ from the NGT group, indicating that the greater AGE content observed in T2DM occurs with progressive diabetes. Individuals with T2DM on metformin had lower cortical bone pentosidine compared with individuals not on metformin (-35%, p = 0.017). Cortical bone from the T2DM group was stiffer (+9%, p = 0.021) and harder (+8%, p = 0.039) versus the NGT group. Bone tissue AGEs, which embrittle bone, increased with worsening glycemic control assessed by HbA1c (Pen: R2  = 0.28, p < 0.001; fAGE density: R2  = 0.30, p < 0.001). These relationships suggest a potential mechanism by which bone fragility may increase despite greater tissue stiffness and hardness in individuals with T2DM; our results suggest that it occurs in the transition from IGT to overt T2DM. © 2022 American Society for Bone and Mineral Research (ASBMR).

Association between Urinary Advanced Glycation End Products and Subclinical Inflammation in Children and Adolescents: Results from the Italian I.Family Cohort

Advanced Glycation End Products (AGEs) have been positively correlated with inflammation in adults, while inconsistent evidence is available in children. We evaluated the association between urinary AGEs, measured by fluorescence spectroscopy, and biomarkers of subclinical inflammation in 676 healthy children/adolescents (age 11.8 ± 1.6 years, M ± SD) from the Italian cohort of the I.Family project. Urinary fluorescent AGEs were used as independent variable and high-sensitivity C-reactive protein (hs-CRP) was the primary outcome, while other biomarkers of inflammation were investigated as secondary outcomes. Participants with urinary AGEs above the median of the study population showed statistically significantly higher hs-CRP levels as compared to those below the median (hs-CRP 0.44 ± 1.1 vs. 0.24 ± 0.6 mg/dL, M ± SD p = 0.002). We found significant positive correlations between urinary AGEs and hs-CRP (p = 0.0001), IL-15 (p = 0.001), IP-10 (p = 0.006), and IL-1Ra (p = 0.001). At multiple regression analysis, urinary AGEs, age, and BMI Z-score were independent variables predicting hs-CRP levels. We demonstrated for the first time, in a large cohort of children and adolescents, that the measurement of fluorescent urinary AGEs may represent a simple, noninvasive, and rapid technique to evaluate the association between AGEs and biomarkers of inflammation. Our data support a role of AGEs as biomarkers of subclinical inflammation in otherwise healthy children and adolescents.

A Prospective Analysis of Skin and Fingertip Advanced Glycation End-Product Devices in Healthy Volunteers

Background: Advanced glycation end products (AGEs) have been shown to accumulate in bone and are gaining interest in connective tissue research. Aims: To investigate the intrarater reliability, two-timepoint agreement and correlations within and between two commercially available skin autofluorescence (SAF) AGE devices. Methods: Healthy volunteers were enrolled in a prospective study at a single academic institution. Each participant underwent SAF analysis by two different, commercially available devices on two occasions, 14 days apart. Upon enrollment, a general survey about the participant’s lifestyle and health status was completed and followed up on for any changes at timepoint two. Results: In total, 40 participants (F:M ratio 5:3) with an average age of 39.0 ± 12.5 years were analyzed. For the AGE reader (skin) and AGE sensor (fingertip), both intrarater reliability and two-timepoint agreement were excellent with an interclass correlation coefficient (ICC) > 0.90 and a strong correlation within both machines. However, there was no correlation between both machines for either timepoint. In total, 4 participants were identified as outliers above the +2SD. Additionally, 5 participants with dark-colored skin could not be measured with the AGE reader at timepoint one and 4 at timepoint two. In contrast, all participants were able to undergo SAF analysis with the AGE sensor, irrespective of their skin type. Conclusions: Both machines showed excellent intrarater reliability and two-timepoint agreement, but the skin AGE reader might have limited applicability in individuals with dark-colored skin. Future research on AGEs might take our findings into consideration.

Descriptive transcriptome analysis of tendon derived fibroblasts following in-vitro exposure to advanced glycation end products

BACKGROUND

Tendon pathologies affect a large portion of people with diabetes. This high rate of tendon pain, injury, and disease appears to manifest independent of well-controlled HbA1c and fasting blood glucose. Advanced glycation end products (AGEs) are elevated in the serum of those with diabetes. In vitro, AGEs severely impact tendon fibroblast proliferation and mitochondrial function. However, the extent that AGEs impact the tendon cell transcriptome has not been evaluated.

OBJECTIVE

The purpose of this study was to investigate transcriptome-wide changes that occur to tendon-derived fibroblasts following treatment with AGEs. We propose to complete a descriptive approach to pathway profiling to broaden our mechanistic understanding of cell signaling events that may contribute to the development of tendon pathology.

METHODS

Rat Achilles tendon fibroblasts were treated with glycolaldehyde-derived AGEs (200μg/ml) for 48 hours in normal glucose (5.5mM) conditions. In addition, total RNA was isolated, and the PolyA+ library was sequenced.

RESULTS

We demonstrate that tendon fibroblasts treated with 200μg/ml of AGEs differentially express 2,159 gene targets compared to fibroblasts treated with an equal amount of BSA-Control. Additionally, we report in a descriptive and ranked fashion 21 implicated cell-signaling pathways.

CONCLUSION

Our findings suggest that AGEs disrupt the tendon fibroblast transcriptome on a large scale and that these pathways may contribute to the development and progression of diabetic tendinopathy. Specifically, pathways related to cell cycle progression and extracellular matrix remodeling were affected in our data set and may play a contributing role in the development of diabetic tendon complications.

An inducible model for unraveling the effects of advanced glycation end-product accumulation in aging connective tissues

PURPOSE

In connective tissues there is a clear link between increasing age and degeneration. Advanced glycation end-products (AGEs) are believed to play a central role. AGEs are sugar-induced non-enzymatic crosslinks which accumulate in collagen with age and diabetes, altering tissue mechanics and cellular function. Despite ample correlative evidence linking collagen glycation to tissue degeneration, little is known how AGEs impact cell-matrix interactions, limiting therapeutic options. One reason for this limited understanding is that AGEs are typically induced using high concentrations of ribose which decrease cell viability, making it impossible to investigate cell-matrix interactions. The objective of this study was to develop a system to trigger AGE accumulation while maintaining cell viability.

MATERIALS AND METHODS

Using cell-seeded high density collagen gels, we investigated the effect of two systems for AGE induction, ribose at low concentrations (30, 100, and 200 mM) over 15 days of culture and riboflavin (0.25 and 0.75 mM) induced with blue light for 40 seconds (riboflavin-465 nm).

RESULTS

We found ribose and riboflavin-465 nm treatment produces fluorescent AGE quantities which match and/or exceed human fluorescent AGE levels for various tissues, ages, and diseases, without affecting cell viability or metabolism. Interestingly, a 40 second treatment of riboflavin-465 nm produced similar levels of fluorescent AGEs as 3 days of 100 mM ribose treatment.

CONCLUSIONS

Riboflavin-465 nm is a promising method to trigger AGEs on demand in vivo or in vitro without impacting cell viability and offers potential for unraveling the mechanism of AGEs in age and diabetes related tissue damage.

Skin-Beautifying Effects of Magnolol and Honokiol Glycosides

Glycosides have been synthesized using the starting materials magnolol (1) and honokiol (4), isolated from the Japanese white-bark magnolia, and their anti-aging effects on the skin (skin-beautifying effects) have been examined. The advanced glycation end-product (AGE) inhibitory activity test (anti-glycation test) and glycation induction model test, using human-derived dermal fibroblasts, TIG-110 cells, have been conducted to evaluate the anti-aging effects. The synthesized glycoside compounds, 5,5′-di(prop-2-en-1-yl)[1,1′-biphenyl]-2-hydroxy-2′-glucopyranoside (3a), 5,5′-di(prop-2-en-1-yl)[1,1′-biphenyl]-2,2′-diglucopyranoside (3b), 3′,5-di(prop-2-en-1-yl)[1,1′-biphenyl]-4′-hydroxy-2-glucopyranoside (6a) and 3′,5-di(prop-2-en-1-yl)[1,1′-biphenyl]-2,4′-diglucopyranoside (6b), have shown significant anti-glycation activities of less than 0.10 mM in IC50. The glycation induction model test with the fibroblasts, TIG-110 cells, demonstrates that the aforementioned glycosides significantly inhibit the decrease in cell viability. These newly synthesized glycoside compounds are expected to be used as cosmetic ingredients, health foods, and pharmaceutical ingredients, which have inhibitory effects against AGE formation.

Biochemical Markers of Bone Turnover in Older Adults With Type 1 Diabetes

CONTEXT

Type 1 diabetes (T1D) is characterized by high fracture risk, yet little is known regarding diabetes-related mechanisms or risk factors.

OBJECTIVE

Determine whether glycemic control, advanced glycation end products (AGEs), and microvascular complications are associated with bone turnover markers among older T1D adults.

DESIGN

Cross-sectional.

SETTING

Epidemiology of Diabetes Interventions and Complications study (6 of 27 clinical centers).

PARTICIPANTS

232 T1D participants followed for >30 years.

EXPOSURES

Glycemic control ascertained as concurrent and cumulative hemoglobin A1c (HbA1c); kidney function, by estimated glomerular filtration rates (eGFR); and AGEs, by skin intrinsic fluorescence.

MAIN OUTCOME MEASURES

Serum procollagen 1 intact N-terminal propeptide (PINP), bone-specific alkaline phosphatase (bone ALP), serum C-telopeptide (sCTX), tartrate-resistant acid phosphatase 5b (TRACP5b), and sclerostin.

RESULTS

Mean age was 59.6 ± 6.8 years, and 48% were female. In models with HbA1c, eGFR, and AGEs, adjusted for age and sex, higher concurrent HbA1c was associated with lower PINP [β -3.4 pg/mL (95% CI -6.1, -0.7), P = 0.015 for each 1% higher HbA1c]. Lower eGFR was associated with higher PINP [6.9 pg/mL (95% CI 3.8, 10.0), P < 0.0001 for each -20 mL/min/1.73 m2 eGFR], bone ALP [1.0 U/L (95% CI 0.2, 1.9), P = 0.011], sCTX [53.6 pg/mL (95% CI 32.6, 74.6), P < 0.0001], and TRACP5b [0.3 U/L (95% CI 0.1, 0.4), P = 0.002]. However, AGEs were not associated with any bone turnover markers in adjusted models. HbA1c, eGFR, and AGEs were not associated with sclerostin levels.

CONCLUSIONS

Among older adults with T1D, poor glycemic control is a risk factor for reduced bone formation, while reduced kidney function is a risk factor for increased bone resorption and formation.

In Vitro Reactivity of the Glucose Degradation Product 3,4-Dideoxyglucosone-3-ene (3,4-DGE) towards Abundant Components of the Human Blood Circulatory System

3,4-Dideoxyglucosone-3-ene (3,4-DGE) is a glucose degradation product present in processed foods and medicinal products. Additionally, its constant formation from 3-deoxyglucosone in plasma has been suggested. Due to its α,β-unsaturated dicarbonyl moiety, 3,4-DGE is highly reactive and has shown harmful effects in vitro. Here, we investigated the impact of major components of the human blood circulatory system on 3,4-DGE in vitro. Under physiological conditions, plasma concentrations of human serum albumin (HSA) reacted efficiently with 3,4-DGE, resulting in only 8.5% of the initial 3,4-DGE concentration after seven hours (vs. 83.4% without HSA, p < 0.001). Thereby, accessible thiol groups were reduced from 0.121 to 0.064 mol/mol HSA, whereas ketoprofen binding and esterase-like activity of HSA were not affected. Plasma concentrations of glutathione (GSH) reacted immediately and completely with 3,4-DGE, leading to two stereoisomeric adducts. Plasma concentrations of immunoglobulin G (IgG) bound to 3,4-DGE to a lower extent, resulting in 62.6% 3,4-DGE after seven hours (vs. 82.2% in the control, p < 0.01). Immobilized human collagen type IV did not alter 3,4-DGE concentrations. The results indicated that particularly HSA, GSH, and IgG readily scavenge 3,4-DGE after its appearance in the blood stream, which may be associated with a reduced antioxidative and cytoprotective activity for the living cells and, thus, the human organism by blocking free thiol groups.

Sodium Cholate-Based Active Delipidation for Rapid and Efficient Clearing and Immunostaining of Deep Biological Samples

Recent surges of optical clearing provided anatomical maps to understand structure-function relationships at organ scale. Detergent-mediated lipid removal enhances optical clearing and allows efficient penetration of antibodies inside tissues, and sodium dodecyl sulfate (SDS) is the most common choice for this purpose. SDS, however, forms large micelles and has a low critical micelle concentration (CMC). Theoretically, detergents that form smaller micelles and higher CMC should perform better but these have remained mostly unexplored. Here, SCARF, a sodium cholate (SC)-based active delipidation method, is developed for better clearing and immunolabeling of thick tissues or whole organs. It is found that SC has superior properties to SDS as a detergent but has serious problems; precipitation and browning. These limitations are overcome by using the ion-conductive film to confine SC while enabling high conductivity. SCARF renders orders of magnitude faster tissue transparency than the SDS-based method, while excellently preserving the endogenous fluorescence, and enables much efficient penetration of a range of antibodies, thus revealing structural details of various organs including sturdy post-mortem human brain tissues at the cellular resolution. Thus, SCARF represents a robust and superior alternative to the SDS-based clearing methods and is expected to facilitate the 3D morphological mapping of various organs.

Resveratrol and Curcumin Attenuate Ex Vivo Sugar-Induced Cartilage Glycation, Stiffening, Senescence, and Degeneration

OBJECTIVE

Advanced glycation end-product (AGE) accumulation is implicated in osteoarthritis (OA) pathogenesis in aging and diabetic populations. Here, we develop a representative nonenzymatic glycation-induced OA cartilage explant culture model and investigate the effectiveness of resveratrol, curcumin, and eugenol in inhibiting AGEs and the structural and biological hallmarks of cartilage degeneration.

DESIGN

Bovine cartilage explants were treated with AGE-bovine serum albumin, threose, and ribose to determine the optimal conditions that induce physiological levels of AGEs while maintaining chondrocyte viability. AGE crosslinks, tissue stiffness, cell viability, metabolism and senescence, nitrite release and loss of glycosaminoglycans were assessed. Explants were cotreated with resveratrol, curcumin, or eugenol to evaluate their anti-AGE properties. Blind docking analysis was conducted to estimate binding energies of drugs with collagen II.

RESULTS

Treatment with 100 mM ribose significantly increased AGE crosslink formation and tissue stiffness, resulting in reduced chondrocyte metabolism and enhanced senescence. Blind docking analysis revealed stronger binding energies of both resveratrol and curcumin than ribose, with glycation sites along a human collagen II fragment, indicating their increased likelihood of competitively inhibiting ribose activity. Resveratrol and curcumin, but not eugenol, successfully inhibited AGE crosslink formation and its associated downstream biological response.

CONCLUSIONS

We establish a cartilage explant model of OA that recapitulates several aspects of aged human cartilage. We find that resveratrol and curcumin are effective anti-AGE therapeutics with the potential to decelerate age-related and diabetes-induced OA. This in vitro nonenzymatic glycation-induced model provides a tool for screening OA drugs, to simultaneously evaluate AGE-induced biological and mechanical changes.

Comparison of Different Tissue Clearing Methods for Three-Dimensional Reconstruction of Human Brain Cellular Anatomy Using Advanced Imaging Techniques

The combination of tissue clearing techniques with advanced optical microscopy facilitates the achievement of three-dimensional (3D) reconstruction of macroscopic specimens at high resolution. Whole mouse organs or even bodies have been analyzed, while the reconstruction of the human nervous system remains a challenge. Although several tissue protocols have been proposed, the high autofluorescence and variable post-mortem conditions of human specimens negatively affect the quality of the images in terms of achievable transparency and staining contrast. Moreover, homogeneous staining of high-density epitopes, such as neuronal nuclear antigen (NeuN), creates an additional challenge. Here, we evaluated different tissue transformation approaches to find the best solution to uniformly clear and label all neurons in the human cerebral cortex using anti-NeuN antibodies in combination with confocal and light-sheet fluorescence microscopy (LSFM). Finally, we performed mesoscopic high-resolution 3D reconstruction of the successfully clarified and stained samples with LSFM.

Accumulation of Nε-(carboxyethyl) lysine in Caenorhabditis elegans is correlated with the formation of ketone body

Advanced glycation end-products (AGEs) are formed when proteins react with carbonyl compounds, and they gradually accumulate with age. However, AGE accumulation with aging is not fully understood because longevity studies in mammals are time-consuming. Therefore, we used Caenorhabditis elegans to evaluate the correlation between aging and AGE accumulation. Age-synchronized C. elegans nematodes were cultured for 3 and 12 days. The levels of Nε-(carboxymethyl) lysine, Nω-(carboxymethyl) arginine, Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl) ornithine, and Nε-(carboxyethyl) lysine (CEL) were compared. Glucose, methylglyoxal, and acetol were incubated with human serum albumin, and CEL formation was evaluated. The levels of methylglyoxal and ketone bodies in C. elegans were quantified. CEL accumulation increased significantly with culture duration. Methylglyoxal and ketone bodies-possible forerunners of AGE accumulation-were also quantified with respect to culture duration. The levels of ketone bodies increased significantly during culture, and correlated closely with CEL accumulation (R2 = 0.72, p = 0.0008), whereas the levels of methylglyoxal did not increase over time. CEL was formed in vitro in a time-dependent manner from methylglyoxal and acetol when incubated with human serum albumin at the same temperature as C. elegans culture, suggesting that increased levels of CEL in C. elegans are attributable to ketone bodies.

Protein oxidation - Formation mechanisms, detection and relevance as biomarkers in human diseases

Generation of reactive oxygen species and related oxidants is an inevitable consequence of life. Proteins are major targets for oxidation reactions, because of their rapid reaction rates with oxidants and their high abundance in cells, extracellular tissues, and body fluids. Additionally, oxidative stress is able to degrade lipids and carbohydrates to highly reactive intermediates, which eventually attack proteins at various functional sites. Consequently, a wide variety of distinct posttranslational protein modifications is formed by protein oxidation, glycoxidation, and lipoxidation. Reversible modifications are relevant in physiological processes and constitute signaling mechanisms ("redox signaling"), while non-reversible modifications may contribute to pathological situations and several diseases. A rising number of publications provide evidence for their involvement in the onset and progression of diseases as well as aging processes. Certain protein oxidation products are chemically stable and formed in large quantity, which makes them promising candidates to become biomarkers of oxidative damage. Moreover, progress in the development of detection and quantification methods facilitates analysis time and effort and contributes to their future applicability in clinical routine. The present review outlines the most important classes and selected examples of oxidative protein modifications, elucidates the chemistry beyond their formation and discusses available methods for detection and analysis. Furthermore, the relevance and potential of protein modifications as biomarkers in the context of disease and aging is summarized.

Protein glycation - biomarkers of metabolic dysfunction and early-stage decline in health in the era of precision medicine

Protein glycation provides a biomarker in widespread clinical use, glycated hemoglobin HbA1c (A1C). It is a biomarker for diagnosis of diabetes and prediabetes and of medium-term glycemic control in patients with established diabetes. A1C is an early-stage glycation adduct of hemoglobin with glucose; a fructosamine derivative. Glucose is an amino group-directed glycating agent, modifying N-terminal and lysine sidechain amino groups. A similar fructosamine derivative of serum albumin, glycated albumin (GA), finds use as a biomarker of glycemic control, particularly where there is interference in use of A1C. Later stage adducts, advanced glycation endproducts (AGEs), are formed by the degradation of fructosamines and by the reaction of reactive dicarbonyl metabolites, such as methylglyoxal. Dicarbonyls are arginine-directed glycating agents forming mainly hydroimidazolone AGEs. Glucosepane and pentosidine, an intense fluorophore, are AGE covalent crosslinks. Cellular proteolysis of glycated proteins forms glycated amino acids, which are released into plasma and excreted in urine. Development of diagnostic algorithms by artificial intelligence machine learning is enhancing the applications of glycation biomarkers. Investigational glycation biomarkers are in development for: (i) healthy aging; (ii) risk prediction of vascular complications of diabetes; (iii) diagnosis of autism; and (iv) diagnosis and classification of early-stage arthritis. Protein glycation biomarkers are influenced by heritability, aging, decline in metabolic, vascular, renal and skeletal health, and other factors. They are applicable to populations of differing ethnicities, bridging the gap between genotype and phenotype. They are thereby likely to find continued and expanding clinical use, including in the current era of developing precision medicine, reporting on multiple pathogenic processes and supporting a precision medicine approach.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Influence of low dose naltrexone on Raman assisted bone quality, skeletal advanced glycation end-products and nano-mechanical properties in type 2 diabetic mice bone

Type 2 diabetes mellitus (T2DM) commonly affects the bone mineral phase and advanced glycation end-products (AGEs) which eventually led to changes in bone material properties on the nano and macro-scale. Several anti-diabetic compounds are widely used to control high blood sugar or glucose caused by T2DM. Low Dose Naltrexone (LDN), an opiate receptor antagonist, and a known TLR4 antagonist, treatment can improve glucose tolerance and insulin sensitivity in high-fat-diet (HFD) induced T2DM mice. However, the influences of LDN on the local bone quality, mineralization of the bone, and the skeletal AGEs levels have not been fully elucidated. The objective of this study is to understand the effect of LDN on Raman assisted bone quality, skeletal AGEs (determined by Raman spectroscopy), and nano-mechanical properties in HFD induced T2DM mice bone. In order to investigate these, mice and corresponding bones were divided into four groups (divided based on diet and treatment), (a) normal control diet treated with saline water, (b) normal control diet treated with LDN, (c) HFD treated with saline water, and (d) HFD treated with LDN. In T2DM condition (HFD treated with saline water), alteration of Raman-based compositional measures in bone quality including mineral-to-matrix ratios, carbonate substitution, mineral crystallinity, and collagen quality was observed. Our data also indicated that T2DM enhances the skeletal AGEs, and impairs the nano-mechanical properties. Interestingly, present results indicated that LDN controls the Raman-based compositional measures in bone quality in HFD induced T2DM mice bone. Additionally, LDN also protects the alteration of the skeletal AGEs levels and nano-mechanical properties in T2DM mice bone. This study concluded that LDN can control the HFD induced T2DM affected bone abnormalities at multiple hierarchical levels.

Bone tissue material composition is compromised in premenopausal women with Type 2 diabetes

Type 2 diabetes mellitus (T2DM) patients are at an increased risk of fracture despite normal to high bone mineral density (BMD) values. In this cross-sectional study we establish bone compositional properties in tetracycline labeled iliac crest biopsies from premenopausal women diagnosed with T2DM (N = 26). Within group comparisons were made as a function of tissue age (TA), presence of chronic complications (CC), glycosylated haemoglobin (HbA1c) levels, and morphometric fracture (MFx). We also compared these data at actively trabecular bone forming surfaces against sex- and age-matched healthy controls (N = 32). The bone quality indices determined by Raman microspectroscopic analysis were: mineral/matrix (MM), tissue water content (nanoporosity; NanoP), mineral maturity/crystallinity (MMC), and glycosaminoglycan (GAG), pyridinoline (Pyd), N-(carboxymethyl)lysine (CML), and pentosidine (PEN) content. Within the T2DM group, at the oldest tissue, CML and PEN contents were significantly elevated in the cancellous compared to cortical compartment. The outcomes were not dependent on MFx. On the other hand, both were significantly elevated in patients with CC, as well as those with HbA1c levels > 7%. At actively forming surfaces, the cortical compartment had higher NanoP compared to cancellous. Still within the T2DM group, patients with MFx had significantly elevated MM and GAGs compared to the ones that did not. At actively forming trabecular surfaces, compared to healthy women, T2DM patients had elevated GAGs content and MMC. The results of this study indicate increased AGEs in those with poor glycation control and chronic complications. Additionally, T2DM patients had elevated MMC and decreased GAGs content compared to healthy controls. These alterations may be contributing to the T2DM inherent elevated fracture risk and suggest a role for hyperglycemia on bone quality.

Regional differences in turnover, composition, and mechanics of the porcine flexor tendon

PURPOSE

Recent data suggest that there is a lack of turnover in the core of human tendon, but it remains unknown whether there are regional differences between core and periphery of the cross section. The purpose of this project was to investigate regional differences in turnover as estimated by the accumulation of fluorescent Advanced Glycation End-products (AGEs) and regional differences in mechanical properties.

MATERIALS AND METHODS

Tendons were obtained from lean control (n = 4) and diabetic Göttingen minipigs (streptozotocin-induced, n = 6). The deep digital flexor tendon of one hind limb was separated into a proximal, central and distal part. Autofluorescence was measured in the core and periphery of the proximal and distal parts of the tendon, and mechanical properties were tested on fascicles taken from the core and periphery of the central tendon (only diabetic animals).

RESULTS

Autofluorescence was greater in the proximal than the distal part. In the distal part of the lean control animals, autofluorescent AGE accumulation was also greater in the core than the periphery. Peak modulus in the core region (704 ± 79 MPa) was higher than the periphery (466 ± 53 MPa, p < 0.05) in diabetic tendons.

CONCLUSION

Taken together, autofluorescence varied both along the length and across the tendon cross section, indicating higher turnover in the distal and peripheral regions. In addition, mechanical properties differed across the tendon cross-section.

Reduction of visceral fat could be related to the improvement of TBS in diabetes mellitus

INTRODUCTION

Diabetes has been proposed as a risk factor for increased skeletal fragility. Visceral fat is known to yield adverse effects on bone metabolism in people with diabetes. We investigated the relationship between the change in visceral fat mass over time and TBS or BMD.

MATERIALS AND METHODS

This retrospective study enrolled 690 (male: 367; female: 323) subjects with type 2 diabetes mellitus. Visceral fat mass, lumbar and femoral neck BMD, and lumbar spine TBS were measured via dual-energy X-ray absorptiometry (DXA), including the follow-up data within a 3-year period.

RESULTS

TBS significantly increased as visceral fat mass decreased in both sexes (p < 0.001), whereas lumbar BMD and femoral neck BMD showed meaningful changes only in men. The multiple regression model with adjustment for age, weight, creatinine level, lipid profile, HbA1C, and status of osteoporosis medication use revealed that TBS and femoral neck BMD were correlated with visceral fat mass. However, regarding longitudinal changes, only the change in visceral fat mass had a significant relationship with TBS (males: β = - 0.298, p < 0.001; females: β = - 0.216, p < 0.001).

CONCLUSIONS

The results of this study may suggest the beneficial effect of controlling visceral fat mass on bone health in type 2 diabetes patients. Besides, DXA-derived TBS could be a useful diagnostic tool for evaluating the bone changes according to metabolic changes in type 2 diabetes, which are not entirely achieved with BMD.

Molecular complexities underlying the vascular complications of diabetes mellitus - A comprehensive review

Diabetes is a chronic disease, characterized by hyperglycemia, which refers to the elevated levels of glucose in the blood, due to the inability of the body to produce or use insulin effectively. Chronic hyperglycemia levels lead to macrovascular and microvascular complications. The macrovascular complications consist of peripheral artery disease (PAD), cardiovascular diseases (CVD) and cerebrovascular diseases, while the microvascular complications comprise of diabetic microangiopathy, diabetic nephropathy, diabetic retinopathy and diabetic neuropathy. Vascular endothelial dysfunction plays a crucial role in mediating both macrovascular and microvascular complications under hyperglycemic conditions. In diabetic microvasculature, the intracellular hyperglycemia causes damage to the vascular endothelium through - (i) activation of four biochemical pathways, namely the Polyol pathway, protein kinase C (PKC) pathway, advanced glycation end products (AGE) pathway and hexosamine pathway, all of which commutes glucose and its intermediates leading to overproduction of reactive oxygen species, (ii) dysregulation of growth factors and cytokines, (iii) epigenetic changes which concern the changes in DNA as a response to intracellular changes, and (iv) abnormalities in non-coding RNAs, specifically microRNAs. This review will focus on gaining an understanding of the molecular complexities underlying the vascular complications in diabetes mellitus, to increase our understanding towards the development of new mechanistic therapeutic strategies to prevent or treat diabetes-induced vascular complications.

Skin autofluorescence: early sign of lung function deterioration?

Advanced glycation end products (AGEs) comprise a heterogeneous group of stable end-products of the non-enzymatic glycation reactions described by Maillard in 1912, in which reduced sugars irreparably modify proteins, lipids and DNA. This is a slow physiological process and accumulation of AGEs is part of normal ageing. Under conditions of hyperglycaemia and oxidative stress, a much faster and more substantial generation of AGEs is induced. The myriad of pathogenic signals AGEs can induce and the fact that enhanced AGE accumulation accompanies a broad spectrum of age-associated chronic inflammatory diseases [1] form the basis of the Maillard theory of ageing [2].

The relationship between SAF and FEV₁, D_LCO and X₅, independent of COPD or diabetes. Will individuals with raised SAF and subclinical lung function alterations develop disease? What mechanisms underlie parenchymal alterations indicated by SAF?https://bit.ly/2YTtdkL

Functional imaging of mitochondria in retinal diseases using flavoprotein fluorescence

Mitochondria are critical for cellular energy production and homeostasis. Oxidative stress and associated mitochondrial dysfunction are integral components of the pathophysiology of retinal diseases, including diabetic retinopathy (DR), age-related macular degeneration, and glaucoma. Within mitochondria, flavoproteins are oxidized and reduced and emit a green autofluorescence when oxidized following blue light excitation. Recently, a noninvasive imaging device was developed to measure retinal flavoprotein fluorescence (FPF). Thus, oxidized FPF can act as a biomarker of mitochondrial dysfunction. This review article describes the literature surrounding mitochondrial FPF imaging in retinal disease. The authors describe the role of mitochondrial dysfunction in retinal diseases, experiments using FPF as a marker of mitochondrial dysfunction in vitro, the three generations of retinal FPF imaging devices, and the peer-reviewed publications that have examined FPF imaging in patients. Finally, the authors report their own study findings. Goals were to establish normative reference levels for FPF intensity and heterogeneity in healthy eyes, to compare between healthy eyes and eyes with diabetes and DR, and to compare across stages of DR. The authors present methods to calculate a patient's expected FPF values using baseline characteristics. FPF intensity and heterogeneity were elevated in diabetic eyes compared to age-matched control eyes, and in proliferative DR compared to diabetic eyes without retinopathy. In diabetic eyes, higher FPF heterogeneity was associated with poorer visual acuity. In conclusion, while current retinal imaging modalities frequently focus on structural features, functional mitochondrial imaging shows promise as a metabolically targeted tool to evaluate retinal disease.

Glycation in Huntington's Disease: A Possible Modifier and Target for Intervention

Glycation is the non-enzymatic reaction between reactive dicarbonyls and amino groups, and gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). Accumulation of AGEs on proteins is inevitable, and is associated with the aging process. Importantly, glycation is highly relevant in diabetic patients that experience periods of hyperglycemia. AGEs also play an important role in neurodegenerative diseases including Alzheimer’s (AD) and Parkinson’s disease (PD). Huntington’s disease (HD) is a hereditary neurodegenerative disease caused by an expansion of a CAG repeat in the huntingtin gene. The resulting expanded polyglutamine stretch in the huntingtin (HTT) protein induces its misfolding and aggregation, leading to neuronal dysfunction and death. HD patients exhibit chorea and psychiatric disturbances, along with abnormalities in glucose and energy homeostasis. Interestingly, an increased prevalence of diabetes mellitus has been reported in HD and in other CAG triplet repeat disorders. However, the mechanisms underlying the connection between glycation and HD progression remain unclear. In this review, we explore the possible connection between glycation and proteostasis imbalances in HD, and posit that it may contribute to disease progression, possibly by accelerating protein aggregation and deposition. Finally, we review therapeutic interventions that might be able to alleviate the negative impact of glycation in HD.

A possible role of glycation in the regulation of amyloid β precursor protein processing leading to amyloid β accumulation

Alzheimer's disease (AD) is one of the most common forms of neurodegenerative diseases amongst the aged population. The disease is multifactorial, and diabetes has been considered as one of the major risk factors for the development of AD. Chronic hyperglycemic condition in diabetes promotes non-enzymatic protein modification by glucose termed as glycation, which affects protein structure and function. Previous studies have shown that many of the enzymes, including proteases, are affected by glycation. Conversely, glycated proteins are known to become resistant to protease action. In these hypotheses, we have extended these two concepts to the regulation of amyloid-β protein precursor (AβPP) by secretases leading to amyloid-β (Aβ) accumulation. The first hypothesis deals with the glycation of α-secretases leading to its reduced activity, while in the second hypothesis, AβPP glycation may prevent α-secretases action, rendering its processing by β secretase. As diabetes is a risk factor for the development of AD, either or both these pathways may operate, leading to the manifestation of AD.

Recent Advances and the Potential for Clinical Use of Autofluorescence Detection of Extra-Ophthalmic Tissues

The autofluorescence (AF) characteristics of endogenous fluorophores allow the label-free assessment and visualization of cells and tissues of the human body. While AF imaging (AFI) is well-established in ophthalmology, its clinical applications are steadily expanding to other disciplines. This review summarizes clinical advances of AF techniques published during the past decade. A systematic search of the MEDLINE database and Cochrane Library databases was performed to identify clinical AF studies in extra-ophthalmic tissues. In total, 1097 articles were identified, of which 113 from internal medicine, surgery, oral medicine, and dermatology were reviewed. While comparable technological standards exist in diabetology and cardiology, in all other disciplines, comparability between studies is limited due to the number of differing AF techniques and non-standardized imaging and data analysis. Clear evidence was found for skin AF as a surrogate for blood glucose homeostasis or cardiovascular risk grading. In thyroid surgery, foremost, less experienced surgeons may benefit from the AF-guided intraoperative separation of parathyroid from thyroid tissue. There is a growing interest in AF techniques in clinical disciplines, and promising advances have been made during the past decade. However, further research and development are mandatory to overcome the existing limitations and to maximize the clinical benefits.

P301 L, an FTDP-17 Mutant, Exhibits Enhanced Glycation in vitro

BACKGROUND

Frontotemporal dementia and parkinsonism-linked to chromosome-17 are a group of diseases with tau mutations leading to primary tauopathies which include progressive supranuclear palsy, corticobasal syndrome, and frontotemporal lobar degeneration. Alzheimer's disease is a non-primary tauopathy, which displays tau neuropathology of excess tangle formation and accumulation. FTDP-17 mutations are responsible for early onset of AD, which can be attributed to compromised physiological functions due to the mutations. Tau is a microtubule-binding protein that secures the integrity of polymerized microtubules in neuronal cells. It malfunctions owing to various insults and stress conditions-like mutations and post-translational modifications.

OBJECTIVE

In this study, we modified the wild type and tau mutants by methyl glyoxal and thus studied whether glycation can enhance the aggregation of predisposed mutant tau.

METHODS

Tau glycation was studied by fluorescence assays, SDS-PAGE analysis, conformational evaluation, and transmission electron microscopy.

RESULTS

Our study suggests that FTDP-17 mutant P301 L leads to enhanced glycation-induced aggregation as well as advanced glycation end products formation. Glycation forms amorphous aggregates of tau and its mutants without altering its native conformation.

CONCLUSION

The metabolic anomalies and genetic predisposition have found to accelerate tau-mediated neurodegeneration and prove detrimental for the early-onset of Alzheimer's disease.

Regional collagen turnover and composition of the human patellar tendon

Tendon pathology (tendinopathy) typically occurs in specific regions of a tendon, and growth in response to exercise also appears to be more pronounced in specific regions. In a previous study in animals we found evidence of regional differences in tendon turnover, but whether the turnover of human patellar tendon differs in different regions still remains unknown. Patellar tendons were obtained from cadavers of healthy men and women (body donation program, n = 5 donors, >60 yr of age). Samples were taken from 10 different regions along the length, width, and thickness of the tendon. Turnover was measured by ¹⁴C bomb pulse dating and also estimated from the accumulation of advanced glycation end products (AGEs) by fluorescence (340/460 nm) in addition to measurement of specific AGEs by mass spectrometry. Composition in terms of collagen, glycosaminoglycans (GAGs), and DNA was also assessed in each region. ¹⁴C results showed that all tendon regions had a similar ¹⁴C concentration, which was equal to the average atmospheric ¹⁴C concentration during the first 15 yr of the person's life. Fluorescence normalized to dry weight did not differ between regions, nor did specific AGEs. Higher GAG content was observed in the proximal and near the distal insertion of the tendon. In conclusion, healthy human patellar tendon displays no regional differences in collagen turnover throughout life.NEW & NOTEWORTHY Tendon injuries and tendinopathies typically occur in specific regions of the tendon, but the reason for this specificity is not well understood. A potential factor in injury susceptibility is tissue turnover, and previous work suggests that the tendon core has practically no turnover during adult life; however, it is not known whether this is true for other regions of the tendon. Our present results on healthy human patellar tendon clearly demonstrate that turnover does not differ between regions and thereby cannot explain differences in injury susceptibility. The findings also indicate that all regions of the tendon are formed simultaneously during skeletal maturation and do not turn over appreciably during adulthood. This is an important finding because little is known about tendon growth during maturation in humans.

Suppression of Nε-(Carboxymethyl)Lysine Generation by the Antioxidant N-Acetylcysteine

Objective

Accumulated evidence suggests that Nε-(carboxymethyl)lysine (CML), which is a dominant antigen of advanced glycation end-products (AGEs), is generated in the peritoneal cavity of patients undergoing continuous ambulatory peritoneal dialysis (CAPD), and that this process may be involved in the pathophysiology of the peritoneal injury found with CAPD treatment. Since CML is a sequential product of glycation and oxidation processes, CML generation could be suppressed by antioxidants. The aim of this in vitro study was to clarify the effect of N-acetylcysteine (NAC), an antioxidant, on CML generation from proteins under high glucose settings mimicking peritoneal dialysis solutions.

Design

Test proteins (bovine serum albumin/type I collagen) were incubated continuously for 16 weeks in glucose solutions (200 mmol/L) with or without NAC (2 mmol/L), and the generation time courses (8 and 16 weeks) of CML and furosine (the biomarker of the glycation products of the early Maillard reaction) were determined.

Results

In both proteins, furosine and CML were progressively generated in accordance with the duration of the incubation period. No apparent differences were found between solutions with and without NAC in furosine levels at the 8th and 16th weeks. However, the generation of CML was lower in the solution with NAC throughout the test periods.

Conclusion

The results showed that NAC could suppress the generation of CML. This indicates the therapeutic potential of antioxidants for the glycoxidative stress-related peritoneal injury occurring during CAPD.

Cellular and Molecular Probing of Intact Human Organs

Optical tissue transparency permits scalable cellular and molecular investigation of complex tissues in 3D. Adult human organs are particularly challenging to render transparent because of the accumulation of dense and sturdy molecules in decades-aged tissues. To overcome these challenges, we developed SHANEL, a method based on a new tissue permeabilization approach to clear and label stiff human organs. We used SHANEL to render the intact adult human brain and kidney transparent and perform 3D histology with antibodies and dyes in centimeters-depth. Thereby, we revealed structural details of the intact human eye, human thyroid, human kidney, and transgenic pig pancreas at the cellular resolution. Furthermore, we developed a deep learning pipeline to analyze millions of cells in cleared human brain tissues within hours with standard lab computers. Overall, SHANEL is a robust and unbiased technology to chart the cellular and molecular architecture of large intact mammalian organs.

UV Fluorescence-Based Determination of Urinary Advanced Glycation End Products in Patients with Chronic Kidney Disease

Advanced glycation end products (AGEs) are a class of proteins or lipids that are non-enzymatically glycated and oxidized after contact with aldose sugars. The accumulation of AGEs results in carbonyl stress, which is characteristic for diabetes mellitus, uremia, atherosclerosis and vascular dysfunction. In recent decades, several innovative methods have been developed to measure the concentration of AGEs in blood or urine. In the present study, we evaluated the use of UV fluorescence as an alternative tool to detect urinary AGEs in four groups of well characterized chronic kidney disease (CKD) patients over a wide range of kidney insufficiency and in a group of healthy subjects. Using an excitation wavelength of 365 nm, the fluorescence spectra of urinary AGEs were recorded in the 400–620 nm emission range. When considering the emission peaks at 440 nm and 490 nm, a significantly higher AGE-specific fluorescence intensity was detected in CKD patients compared to healthy subjects (p < 0.0001 and p = 0.0001, respectively). The urinary creatinine adjusted fluorescence emission spectra in the group of CKD patients with diabetes mellitus were comparable with those of CKD patients without diabetes mellitus. Creatinine-adjusted fluorescence emission spectra were highest in CKD patients with proteinuria, moderate in CKD patients without proteinuria and lowest in healthy controls (p < 0.0001 at both emission wavelengths). In a multiple regression analysis, age, CRP and insulin treatment were predictors of fluorescence intensity at the emission wavelength of 440 nm. Age and insulin treatment were predictors at 490 nm. The presented method is a simple, cheap, alternative method to monitor the AGE-load in the CKD population.

Mechanisms of Collagen Crosslinking in Diabetes and Keratoconus

Collagen crosslinking provides the mechanical strength required for physiological maintenance of the extracellular matrix in most tissues in the human body, including the cornea. Aging and diabetes mellitus (DM) are processes that are both associated with increased collagen crosslinking that leads to increased corneal rigidity. By contrast, keratoconus (KC) is a corneal thinning disease associated with decreased mechanical stiffness leading to ectasia of the central cornea. Studies have suggested that crosslinking mediated by reactive advanced glycation end products during DM may protect the cornea from KC development. Parallel to this hypothesis, riboflavin-mediated photoreactive corneal crosslinking has been proposed as a therapeutic option to halt the progression of corneal thinning by inducing intra- and intermolecular crosslink formation within the collagen fibrils of the stroma, leading to stabilization of the disease. Here, we review the pathobiology of DM and KC in the context of corneal structure, the epidemiology behind the inverse correlation of DM and KC development, and the chemical mechanisms of lysyl oxidase-mediated crosslinking, advanced glycation end product-mediated crosslinking, and photoreactive riboflavin-mediated corneal crosslinking. The goal of this review is to define the biological and chemical pathways important in physiological and pathological processes related to collagen crosslinking in DM and KC.

Advanced Glycation End-Products Suppress Mitochondrial Function and Proliferative Capacity of Achilles Tendon-Derived Fibroblasts

Debilitating cases of tendon pain and degeneration affect the majority of diabetic individuals. The high rate of tendon degeneration persists even when glucose levels are well controlled, suggesting that other mechanisms may drive tendon degeneration in diabetic patients. The purpose of this study was to investigate the impact of advanced glycation end-products on tendon fibroblasts to further our mechanistic understanding of the development and progression of diabetic tendinopathy. We proposed that advanced glycation end-products would induce limitations to mitochondrial function and proliferative capacity in tendon-derived fibroblasts, restricting their ability to maintain biosynthesis of tendon extracellular matrix. Using an in-vitro cell culture system, rat Achilles tendon fibroblasts were treated with glycolaldehyde-derived advanced glycation end-products (0, 50, 100, and 200 μg/ml) for 48 hours in normal glucose (5.5 mM) and high glucose (25 mM) conditions. We demonstrate that tendon fibroblasts treated with advanced glycation end-products display reduced ATP production, electron transport efficiency, and proliferative capacity. These impairments were coupled with alterations in mitochondrial DNA content and expression of genes associated with extracellular matrix remodeling, mitochondrial energy metabolism, and apoptosis. Our findings suggest that advanced glycation end-products disrupt tendon fibroblast homeostasis and may be involved in the development and progression of diabetic tendinopathy.

Reprint of "The complex dynamics of myocardial interstitial fibrosis in heart failure. Focus on collagen cross-linking"

Myocardial interstitial fibrosis (MIF) is a common finding in heart failure (HF) patients, both with preserved and reduced ejection fraction, as well as in HF animal models. MIF is associated with impaired cardiac function and worse clinical outcome. The impact of MIF is influenced not only by the quantity but also by changes in the quality of collagen fibers and in the extracellular matrix components, such as a shift in collagen types proportion, increased fibronectin polymerization and increased degree of collagen cross-linking (CCL). In particular, CCL, a process that renders collagen fibers stiffer and more resistant to degradation, is increased both in patients and animal models of HF. Importantly, in HF patients increased cardiac CCL is directly associated with increased left ventricular stiffness and a higher risk of hospitalization for HF. The aim of this review is to address the complexity of MIF in HF, focusing on CCL.

Biocatalytic Reversal of Advanced Glycation End Product Modification

Advanced glycation end products (AGEs) are a heterogeneous group of molecules that emerge from the condensation of sugars and proteins through the Maillard reaction. Despite a significant number of studies showing strong associations between AGEs and the pathologies of aging-related illnesses, it has been a challenge to establish AGEs as causal agents primarily due to the lack of tools in reversing AGE modifications at the molecular level. Herein, we show that MnmC, an enzyme involved in a bacterial tRNA-modification pathway, is capable of reversing the AGEs carboxyethyl-lysine (CEL) and carboxymethyl-lysine (CML) back to their native lysine structure. Combining structural homology analysis, site-directed mutagenesis, and protein domain dissection studies, we generated a variant of MnmC with improved catalytic properties against CEL in its free amino acid form. We show that this enzyme variant is also active on a CEL-modified peptidomimetic and an AGE-containing peptide that has been established as an authentic ligand of the receptor for AGEs (RAGE). Our data demonstrate that MnmC variants are promising lead catalysts toward the development of AGE-reversal tools and a better understanding of AGE biology.

Label-Free Multiphoton Microscopy: The Origin of Fluorophores and Capabilities for Analyzing Biochemical Processes

Multiphoton microscopy (MPM) is a method of molecular imaging and specifically of intravital imaging that is characterized by high spatial resolution in combination with a greater depth of penetration into the tissue. MPM is a multimodal method based on detection of nonlinear optical signals - multiphoton fluorescence and optical harmonics - and also allows imaging with the use of the parameters of fluorescence decay kinetics. This review describes and discusses photophysical processes within major reporter molecules used in MPM with endogenous contrasts and summarizes several modern experiments that illustrate the capabilities of label-free MPM for molecular imaging of biochemical processes in connective tissue and cells.

The complex dynamics of myocardial interstitial fibrosis in heart failure. Focus on collagen cross-linking

Myocardial interstitial fibrosis (MIF) is a common finding in heart failure (HF) patients, both with preserved and reduced ejection fraction, as well as in HF animal models. MIF is associated with impaired cardiac function and worse clinical outcome. The impact of MIF is influenced not only by the quantity but also by changes in the quality of collagen fibers and in the extracellular matrix components, such as a shift in collagen types proportion, increased fibronectin polymerization and increased degree of collagen cross-linking (CCL). In particular, CCL, a process that renders collagen fibers stiffer and more resistant to degradation, is increased both in patients and animal models of HF. Importantly, in HF patients increased cardiac CCL is directly associated with increased left ventricular stiffness and a higher risk of hospitalization for HF. The aim of this review is to address the complexity of MIF in HF, focusing on CCL.

Advanced glycation end products as biomarkers in systemic diseases: premises and perspectives of salivary advanced glycation end products

Advanced glycation end products (AGEs) are glycated proteins associated with high dry temperature food processing, coloring and flavor modification of food products. Previous studies on diet-related disease support the role of the glycation products as biomarkers in local and general proinflammatory response. Exogenous and endogenous AGEs are involved in chronic low-level inflammation, which underlies the onset of metabolic syndrome influenced by food intake, there by demonstrating their implication in diet-related pathologies. Although studies have revealed a strong association between the accumulation of AGEs and the occurrence/worsening of metabolic diseases, their routine use for the diagnosis or monitoring of local and general disease has not yet been reported.