Evidence for the Maillard reaction in rat lung collagen and its relationship with solubility and age

Peptide location fingerprinting identifies species- and tissue-conserved structural remodelling of proteins as a consequence of ageing and disease

Extracellular matrices (ECMs) in the intervertebral disc (IVD), lung and artery are thought to undergo age-dependant accumulation of damage by chronic exposure to mechanisms such as reactive oxygen species, proteases and glycation. It is unknown whether this damage accumulation is species-dependant (via differing lifespans and hence cumulative exposures) or whether it can influence the progression of age-related diseases such as atherosclerosis. Peptide location fingerprinting (PLF) is a new proteomic analysis method, capable of the non-targeted identification of structure-associated changes within proteins. Here we applied PLF to publicly available ageing human IVD (outer annulus fibrosus), ageing mouse lung and human arterial atherosclerosis datasets and bioinformatically identified novel target proteins alongside common age-associated differences within protein structures which were conserved between three ECM-rich organs, two species, three IVD tissue regions, sexes and in an age-related disease. We identify peptide yield differences across protein structures which coincide with biological regions, potentially reflecting the functional consequences of ageing or atherosclerosis for macromolecular assemblies (collagen VI), enzyme/inhibitor activity (alpha-2 macroglobulin), activation states (complement C3) and interaction states (laminins, perlecan, fibronectin, filamin-A, collagen XIV and apolipoprotein-B). Furthermore, we show that alpha-2 macroglobulin and collagen XIV exhibit possible shared structural consequences in IVD ageing and arterial atherosclerosis, providing novel links between an age-related disease and intrinsic ageing. Crucially, we also demonstrate that fibronectin, laminin beta chains and filamin-A all exhibit conserved age-associated structural differences between mouse lung and human IVD, providing evidence that ECM, and their associating proteins, may be subjected to potentially similar mechanisms or consequences of ageing across both species, irrespective of differences in lifespan and tissue function.

Extracellular Matrix Stiffness in Lung Health and Disease

The extracellular matrix (ECM) provides structural support and imparts a wide variety of environmental cues to cells. In the past decade, a growing body of work revealed that the mechanical properties of the ECM, commonly known as matrix stiffness, regulate the fundamental cellular processes of the lung. There is growing appreciation that mechanical interplays between cells and associated ECM are essential to maintain lung homeostasis. Dysregulation of ECM-derived mechanical signaling via altered mechanosensing and mechanotransduction pathways is associated with many common lung diseases. Matrix stiffening is a hallmark of lung fibrosis. The stiffened ECM is not merely a sequelae of lung fibrosis but can actively drive the progression of fibrotic lung disease. In this article, we provide a comprehensive view on the role of matrix stiffness in lung health and disease. We begin by summarizing the effects of matrix stiffness on the function and behavior of various lung cell types and on regulation of biomolecule activity and key physiological processes, including host immune response and cellular metabolism. We discuss the potential mechanisms by which cells probe matrix stiffness and convert mechanical signals to regulate gene expression. We highlight the factors that govern matrix stiffness and outline the role of matrix stiffness in lung development and the pathogenesis of pulmonary fibrosis, pulmonary hypertension, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. We envision targeting of deleterious matrix mechanical cues for treatment of fibrotic lung disease. Advances in technologies for matrix stiffness measurements and design of stiffness-tunable matrix substrates are also explored. © 2022 American Physiological Society. Compr Physiol 12:3523-3558, 2022.

Stochastic non-enzymatic modification of long-lived macromolecules - A missing hallmark of aging

Damage accumulation in long-living macromolecules (especially extracellular matrix (ECM) proteins, nuclear pore complex (NPC) proteins, and histones) is a missing hallmark of aging. Stochastic non-enzymatic modifications of ECM trigger cellular senescence as well as many other hallmarks of aging affect organ barriers integrity and drive tissue fibrosis. The importance of it for aging makes it a key target for interventions. The most promising of them can be AGE inhibitors (chelators, O-acetyl group or transglycating activity compounds, amadorins and amadoriases), glucosepane breakers, stimulators of elastogenesis, and RAGE antagonists.

Lung function measurements in the prediabetes stage: data from the ILERVAS Project

AIMS

Patients with type 2 diabetes have been considered a susceptible group for pulmonary dysfunction. Our aim was to assess pulmonary function on the prediabetes stage.

METHODS

Pulmonary function was assessed in 4,459 non-diabetic subjects, aged between 45 and 70 years, without cardiovascular disease or chronic pulmonary obstructive disease from the ongoing study ILERVAS. A "restrictive spirometric pattern", an "abnormal FEV1" and an "obstructive ventilatory defect" were assessed. Prediabetes was defined by glycosylated hemoglobin (HbA1c) between 5.7 and 6.4% according to the American Diabetes Association criteria.

RESULTS

Population was composed of 52.1% women, aged 57 [53;63] years, a BMI of 28.6 [25.8;31.8] kg/m², and with a prevalence of prediabetes of 29.9% (n = 1392). Subjects with prediabetes had lower forced vital capacity (FVC: 93 [82;105] vs. 96 [84;106], p < 0.001) and lower forced expired volume in the first second (FEV1: 94 [82;107] vs. 96 [84;108], p = 0.011), as well as a higher percentage of the restrictive spirometric pattern (16.5% vs. 13.6%, p = 0.015) and FEV1 < 80% (20.3% vs. 17.2%, p = 0.017) compared to non-prediabetes group. In the prediabetes group, HbA1c was negatively correlated with both pulmonary parameters (FVC: r = - 0.113, p < 0.001; FEV1: r = - 0.079, p = 0.003). The multivariable logistic regression model in the whole population showed that there was a significant and independent association between HbA1c with both restrictive spirometric pattern [OR = 1.42 (1.10-1.83), p = 0.008] and FEV1 < 80% [OR = 1.50 (1.19-1.90), p = 0.001].

CONCLUSIONS

The deleterious effect of type 2 diabetes on pulmonary function appears to be initiated in prediabetes, and it is related to metabolic control. TRIAL REGISTRATION CLINICALTRIALS.GOV: NCT03228459.

Evaluation of the severity of small airways obstruction and alveolar destruction in chronic obstructive pulmonary disease

BACKGROUND

Airflow limitation in COPD is caused by a mixture of small airways obstruction and alveolar destruction.

OBJECTIVE

To evaluate the contributions of these factors to airflow limitation through measurement of two biomarkers, pentosidine and vascular endothelial growth factor (VEGF), which reflect pathology or function of the lower respiratory tract of COPD.

METHODS

We measured pentosidine and VEGF levels in induced sputum from 23 non-smokers, 26 smokers without COPD, and 43 smokers with COPD. We evaluated the correlations of two biomarkers levels with the grade of low attenuation area (LAA) in high-resolution computed tomographic scans and the Δ N₂ from the nitrogen washout curve.

RESULTS

Pentosidine levels were significantly higher in smokers with COPD than in non-smokers and smokers without COPD. In contrast, VEGF levels were significantly lower in smokers without COPD than in non-smokers, and further decreased in smokers with COPD. In the four-stage classification of LAA grading, pentosidine levels steeply increased from grade I to Ⅳ, while VEGF levels decreased with increasing severity of LAA grade. Pentosidine levels were positively correlated with Δ N₂ in COPD patients with mild emphysema. In contrast, VEGF levels were inversely correlated with Δ N₂ in COPD patients with severe emphysema.

CONCLUSION

Pentosidine level is responsible for the severity of small airways obstruction, while VEGF level reflects the magnitude of alveolar destruction. Thus, simultaneous measurement of pentosidine and VEGF levels may be a promising approach to discriminate the severity of small airways obstruction and alveolar destruction in the lower respiratory tract of COPD.

The role of glycation in the pathogenesis of aging and its prevention through herbal products and physical exercise

[Purpose]

Advanced glycation end products (AGEs) are non-enzymatic modifications of proteins or lipids after exposure to sugars. In this review, the glycation process and AGEs are introduced, and the harmful effects of AGEs in the aging process are discussed.

[Methods]

Results from human and animal studies examining the mechanisms and effects of AGEs are considered. In addition, publications addressing means to attenuate glycation stress through AGE inhibitors or physical exercise are reviewed.

[Results]

AGEs form in hyperglycemic conditions and/or the natural process of aging. Numerous publications have demonstrated acceleration of the aging process by AGEs. Exogenous AGEs in dietary foods also trigger organ dysfunction and tissue aging. Various herbal supplements or regular physical exercise have beneficial effects on glycemic control and oxidative stress with a consequent reduction of AGE accumulation during aging.

[Conclusion]

The inhibition of AGE formation and accumulation in tissues can lead to an increase in lifespan.

Effect of glycation inhibitors on aging and age-related diseases

Vast evidence supports the view that glycation of proteins is one of the main factors contributing to aging and is an important element of etiopathology of age-related diseases, especially type 2 diabetes mellitus, cataract and neurodegenerative diseases. Counteracting glycation can therefore be a means of increasing both the lifespan and healthspan. In this review, accumulation of glycation products during aging is presented, pathophysiological effects of glycation are discussed and ways of attenuation of the effects of glycation are described, concentrating on prevention of glycation. The effects of glycation and glycation inhibitors on the course of selected age-related diseases, such as Alzheimer's disease, Parkinson's disease and cataract are also reviewed.

Quantitative and Qualitative Change of Collagen of Achilles Tendons in Rats With Systemic Administration of Glucocorticoids

BACKGROUND

It is unclear whether glucocorticoid (GC) therapy is directly related to Achilles tendon rupture (ATR), because many of the reported patients were receiving long-term GC therapy for underlying diseases. This study aimed to elucidate the mechanism by which systemic GC administration causes weakening of the Achilles tendon by biochemically, mechanically, and morphologically evaluating quantitative and qualitative changes in collagen.

METHODS

Male 8-week-old mice were subcutaneously treated with either prednisolone (10 mg/mL/kg; GC group) or saline (1 mL/kg; control group) for 8 weeks and then subjected to the following experiments: (1) a tensile strength test; (2) quantification of the gene expressions of type 1 collagen and lysyl oxidase; (3) quantification of collagen content, enzymatic crosslinks (immature + mature), and senescent crosslinks; and (4) measurement of collagen fiber diameter by electron microscopy.

RESULTS

The maximum tensile load and gene expressions of type 1 collagen and lysyl oxidase were decreased in the GC group. Collagen content was significantly decreased in the GC group compared with the control group. The content of enzymatic crosslinks was significantly lower in the GC group than in the control group. The corresponding amount of senescent crosslinks was not significantly different. The mean collagen fiber diameter was significantly smaller in the GC group than in the control group. Histogram analysis showed a decreased number of thick fibers and an increased number of thin fibers in the GC group.

CONCLUSION

These observations suggest that systemic GC administration causes decreased strength of the Achilles tendon by decreasing its collagen content, hindering the formation of enzymatic crosslinks and thereby keeping collagen fibers in an immature state with smaller diameters.

CLINICAL RELEVANCE

This animal study showed that systemic GC administration directly prevents maturation of tendon collagen fibers and decreases tendon strength, regardless of the presence or absence of underlying disease.

Fibroblast viability and phenotypic changes within glycated stiffened three-dimensional collagen matrices

Background

There is growing interest in the development of cell culture assays that enable the rigidity of the extracellular matrix to be increased. A promising approach is based on three-dimensional collagen type I matrices that are stiffened by cross-linking through non-enzymatic glycation with reducing sugars.

Methods

The present study evaluated the biomechanical changes in the non-enzymatically glycated type I collagen matrices, including collagen organization, the advanced glycation end products formation and stiffness achievement. Gels were glycated with ribose at different concentrations (0, 5, 15, 30 and 240 mM). The viability and the phenotypic changes of primary human lung fibroblasts cultured within the non-enzymatically glycated gels were also evaluated along three consecutive weeks. Statistical tests used for data analyze were Mann–Whitney U, Kruskal Wallis, Student’s t-test, two-way ANOVA, multivariate ANOVA, linear regression test and mixed linear model.

Results

Our findings indicated that the process of collagen glycation increases the stiffness of the matrices and generates advanced glycation end products in a ribose concentration-dependent manner. Furthermore, we identified optimal ribose concentrations and media conditions for cell viability and growth within the glycated matrices. The microenvironment of this collagen based three-dimensional culture induces α-smooth muscle actin and tenascin-C fibroblast protein expression. Finally, a progressive contractile phenotype cell differentiation was associated with the contraction of these gels.

Conclusions

The use of non-enzymatic glycation with a low ribose concentration may provide a suitable model with a mechanic and oxidative modified environment with cells embedded in it, which allowed cell proliferation and induced fibroblast phenotypic changes. Such culture model could be appropriate for investigations of the behavior and phenotypic changes in cells that occur during lung fibrosis as well as for testing different antifibrotic therapies in vitro.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0237-z) contains supplementary material, which is available to authorized users.

Potential role of pentosidine on susceptibility to small airway closure in elderly and smoking asthma

BACKGROUND

Small airway closure in asthma is determined by a complex interaction of structural and functional characteristics including lung elastic recoil. Recently, we determined that loss of elastic recoil might be attributable to pentosidine level in the airways. This study was designed to investigate the influences of aging and smoking on small airway closure in asthma.

METHODS

Sixty-one patients with asthma (20 non-smoking young adult, 23 non-smoking elderly, and 18 smoking young adult) and 36 control subjects (12 non-smoking young adult, 11 non-smoking elderly, and 13 smoking young adult) were included. We assessed airway responses during methacholine provocation and calculated the closing index. In addition, we measured pentosidine levels in induced sputum from all study subjects.

RESULTS

Pentosidine levels in induced sputum were markedly higher in asthmatic patients than in controls. In control subjects, the intergroup differences in pentosidine level among 3 subgroups were significant. Similarly, pentosidine levels were significantly higher in non-smoking elderly and smoking young adult asthmatics than in non-smoking young adult asthmatics. There was no significant difference in pentosidine levels between non-smoking elderly and smoking young adult asthmatics. The closing index was also significantly higher in non-smoking elderly and smoking young adult asthmatics than in non-smoking young adult asthmatics. Moreover, pentosidine levels in non-smoking elderly and smoking young adult asthmatics were closely correlated with closing index.

CONCLUSIONS

We determined the correlation of pentosidine level with susceptibility to small airway closure in elderly and smoking asthmatics. Our results might facilitate the understanding of elderly and smoking asthma.

A microscopic and macroscopic study of aging collagen on its molecular structure, mechanical properties, and cellular response

During aging, collagen structure changes, detrimentally affecting tissues' biophysical and biomechanical properties due to an accumulation of advanced glycation end-products (AGEs). In this investigation, we conducted a parallel study of microscopic and macroscopic properties of different-aged collagens from newborn to 2-yr-old rats, to examine the effect of aging on fibrillogenesis, mechanical and contractile properties of reconstituted hydrogels from these collagens seeded with or without fibroblasts. In addition to fibrillogenesis of collagen under the conventional conditions, some fibrillogenesis was conducted alongside a 12-T magnetic field, and gelation rate and AGE content were measured. A nondestructive indentation technique and optical coherence tomography were used to determine the elastic modulus and dimensional changes, respectively. It was revealed that in comparison to younger specimens, older collagens exhibited higher viscosity, faster gelation rates, and a higher AGE-specific fluorescence. Exceptionally, only young collagens formed highly aligned fibrils under magnetic fields. The youngest collagen demonstrated a higher elastic modulus and contraction in comparison to the older collagen. We conclude that aging changes collagen monomer structure, which considerably affects the fibrillogenesis process, the architecture of the resulting collagen fibers and the global network, and the macroscopic properties of the formed constructs.

Potential roles of pentosidine in age-related and disease-related impairment of pulmonary functions in patients with asthma

BACKGROUND

Pentosidine is well established as an intermolecular cross-linking type of advanced glycation end products, and it accumulates with aging in various connective tissues.

OBJECTIVE

To determine whether pentosidine contributes to age-related and disease-related impairment of pulmonary functions in patients with asthma.

METHODS

We measured pentosidine levels in induced sputum from young to elderly patients with asthma and assessed the slope of the nitrogen (N(2)) alveolar plateau (delta N(2)), closing volume (CV), and closing capacity (CC) from a nitrogen washout curve in a single breath.

RESULTS

Pentosidine levels in induced sputum were significantly higher in patients with asthma than in normal controls (patients with asthma: median, 20.1, interquartile range, 16.7-26.5 ng/mL; normal controls: median, 3.0, interquartile range, 0.7-7.5 ng/mL; P < .001). The levels were closely correlated with age in both normal controls and patients with asthma. However, the slope of age-related increase in pentosidine levels was markedly steeper in patients with asthma than in normal controls. CV/vital capacity, CC/total lung capacity, and delta N(2) increased with aging in both normal controls and patients with asthma. Moreover, in each range of age (21-40, 41-60, 61-80 years), CV/vital capacity, CC/total lung capacity, and delta N(2) were significantly higher in patients with asthma than in normal controls. In addition, pentosidine levels in patients with asthma were closely correlated with each of these variables.

CONCLUSION

Our results demonstrated the association between sputum levels of pentosidine and age-related small airways function in both normal controls and patients with asthma. Moreover, the age-related increase in pentosidine levels was more pronounced in patients with asthma. These findings will herald new era in the pathophysiology of elderly asthma.

[Glycation of mitochondrial proteins, oxidative stress and aging]

Mitochondrial proteins can be modified by glycation reactions from endogenous dicarbonyl compounds such as physiologically generated methylglyoxal and glyoxal. This modification could cause structural and functional changes in the proteins Consequently, dicarbonyl attack of the mitochondrial proteome may be an event leading to mitochondrial dysfunction and thus, to oxidative stress. These protein chemical modifications can play an important role in the physiological aging process and age-associated diseases, where both mitochondrial defects and increased dicarbonyl concentrations have been found. Future research should address the functional changes in mitochondrial proteins that are the targets for dicarbonyl glycation.

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.

Increased renal collagen cross-linking and lipid accumulation in nephropathy of Zucker diabetic fatty rats

BACKGROUND

Zucker diabetic fatty (ZDF) rat is a genetic model of type 2 diabetes and obesity. The mechanism underlying nephropathy in ZDF rats, however, remains unclear.

METHODS

ZDF rats were compared to age-matched Zucker lean (ZL) rats. Physiological and blood biochemical parameters, renal glomerular cross-sectional area (hematoxylin-eosin staining), fibrosis (van Giesen staining), collagen composition (Sircol Collagen Assay), lipids (enzymatic method) and mRNA expression (RT-PCR) were determined.

RESULTS

ZDF rats showed an increase in renal-insoluble collagen content and the ratio of renal-insoluble to salt-soluble collagen (2- and 1.5-fold of the control animals). There were increases in renal glomerulosclerosis and interstitial fibrosis in ZDF rats (increased to 2-fold) in the glomerular mesangium and tubulointerstitium, and increased glomerular area. Renal triglyceride accumulated to greater than 2-fold of those levels in ZL rats. These changes were accompanied by hypoalbuminemia, and elevated plasma blood urea nitrogen and uric acid levels. Gene profiling showed increased expression of transcripts encoding the glomerulosclerotic mediator collagens I and IV, plasminogen activator inhibitor-1, transforming growth factor-beta1, and angiotensin II type 1 receptor in ZDF rat kidney. Moreover, renal expression of mRNAs encoding sterol regulatory element-binding protein-1, a nuclear transcription factor that activates genes involved in fatty acid synthesis, and acetyl-CoA carboxylase, a key enzyme that mediates fatty acid synthesis, was increased in ZDF rats.

CONCLUSIONS

Our findings suggest that dysregulated gene expression may result in increased renal collagen cross-linking and lipid accumulation, that may be associated with development of nephropathy in the animal model of type 2 diabetes and obesity.

AGE-related cross-linking of collagen is associated with aortic wall matrix stiffness in the pathogenesis of drug-induced diabetes in rats

Diabetes mellitus is major risk factor for cardiovascular disease, and atherosclerosis accounts for most of the morbidity and mortality of diabetic patients. To examine the effects of diabetes on the vessel wall, we examined the association of collagen cross-linking in relation to matrix stiffness of the descending aorta in streptozotocin-induced diabetic rats. The matrix stiffness of the vessel was determined by measuring the tensile properties of the tissue. Seven weeks following the establishment of diabetes, both control and diabetic rats were killed and the descending aortas were excised and analyzed. The findings from biomechanical analysis indicated a significant increase in maximum load (26%), stress (22%), Young's modulus of elasticity (60%), and toughness (32%) in diabetic aortas compared to control. In contrast, the maximum strain of the diabetic rat aorta was significantly reduced by 20% compared to control rats, suggesting stiffening of the blood vessel. The results from biochemical analysis showed that the amount of total collagen increased by 21% in diabetic tissues compared to the control. The sequential extractions of collagen showed that the diabetic specimens yielded 34% more neutral salt-soluble collagen (NSC) than the control. The amount of pepsin-soluble collagen was 31% less in diabetic tissues than in the control group, whereas the amount of insoluble collagen (ISC) increased by 56%. A significant accumulation in advanced glycation end products (AGEs) were seen in pepsin- and collagenase-soluble collagen in diabetic vessel. Furthermore, the altered biomechanical properties of the vessel wall were strongly correlated with the biochemistry of collagen. Overall, these results provide evidence that the diabetic state is associated with the changes in collagen biochemistry and in the biomechanics of the blood vessel.

Pentosidine as a Measure of Chronological Age in Wild Birds

Birds have few reliable indicators of aging. Pentosidine is a product of nonenzymatic glycation that accumulates in tissues of an animal over its lifespan. The intent of this study was to determine if accumulation of skin pentosidine in birds of known ages changed as a function of time. Skin samples were obtained from the breast of 45 birds of various species obtained from the national aviary. In addition, foot webbing samples were obtained from 17 California Gulls (Larus callifornicus) of known ages. Collagen was measured by a hydroxypro-line spectrophotometric method and pentosidine was quantified using reverse phase high-performance liquid-chromatography. Pentosidine concentration in the skin and foot webbing increased linearly with age (P < 0.001). Hydroxyproline concentrations from the foot webbing were comparable to that measured in the skin; however, pentosidine concentrations were approximately one-fourth of that in skin. Knowledge regarding longevity of birds could provide information for species survival programs and insight into variations in longevity of an entire population.

Glycation-induced matrix stability in the rabbit achilles tendon

Connective tissue susceptibility to nonenzymatic glycation was examined following 0, 2, 4, 6, 8, and 10 weeks of incubating the rabbit Achilles tendon in phosphate-buffered saline containing ribose (glycated). The biomechanical integrity of the glycated tendons was then compared to control tendons incubated in phosphate-buffered saline (non-glycated) at each time interval, while the biochemical stability of both groups of tendons was determined by examining collagen extractability and the formation of pentosidine at 8 weeks. Whereas there were no significant biomechanical differences between control and glycated tendons at 0- and 2-week intervals (P > 0.05), moderately significant increases in maximum load, energy to yield, and toughness of glycated tendons were observed at 4 weeks. Beyond 4 weeks of incubation, the differences between glycated and non-glycated tendons became highly significant, as glycated tendons withstood more load and tensile stress (P < 0.01 for each variable), attained significantly higher modulus of elasticity (P < 0.01), absorbed more energy (P < 0.01), and became tougher (P < 0.01) than controls. These differences in the biomechanical indices of the effects of glycation were stable between the 6th and 10th week of glycation. The maximum increases in the biomechanical measurements as a result of glycation were 29% for maximum load, 125% for stress, 19% for strain, 106% for Young's modulus of elasticity, 14% for energy to yield, and 57% for toughness. Biochemical analysis showed a 61% reduction in the extractability of neutral salt-soluble collagen, a 48% decrease in acid-soluble collagen, and a 29% decline in pepsin-soluble collagen in glycated tendons (P < 0.01). In contrast, there was a 28% increase in the amount of insoluble collagen and significantly higher amounts of pentosidine (P < 0.01) in glycated tendons. Collectively, these biomechanical and biochemical results suggest that nonenzymatic glycation may explain the altered stability of connective tissue matrix induced by the processes of diabetes and aging.

Animal models for the effect of age on susceptibility to inhaled particulate matter

Epidemiological findings of associations between ambient particulate matter (PM) and respiratory and cardiovascular mortality and morbidity have fostered increased laboratory research aimed at understanding the key PM components, mechanisms, and dose-response relationships responsible for the effects. Because the health impacts are largely observed in subpopulations having characteristics known or presumed to confer increased susceptibility to PM, there is a need for identifying, developing, and using animal models of these susceptibility factors. Age, during both development and senescence of the cardiorespiratory system and its defenses, is one of the PM susceptibility factors cited frequently. This review is intended as a summary of current knowledge regarding age-related differences in the structure and function of the respiratory and pulmonary vascular systems of humans and animals. Its purpose is to facilitate the selection of appropriate animal models for research on the various facets of potential age-related susceptibility of the human respiratory tract to the effects of inhaled PM. The selection of models is a difficult challenge because no single animal species adequately models the full range of human respiratory anatomy, physiology, and age-related changes. With careful selection among the many species, strains, and comparative ages, however, animals can be selected to model most, if not all, of the individual factors hypothesized to confer increased susceptibility of humans to inhaled PM. The existing information does not provide an adequate basis for selecting models to test all of the current age-related susceptibility hypotheses. However, the information summarized in this report should facilitate the investigator's review of potential models.

Comparative differences in the composition and biomechanical properties of tibiae of seven- and seventy-two-week-old male and female broiler breeder chickens

Skeletal problems are common in both young and old poultry and are often related to bone weakness. They affect mortality on the farm and condemnations within processing plant and thus raise both welfare and economic concerns. To understand the basis of bone strength, the metaphyseal histology, composition, and the biomechanical properties of tibiae from 7- and 72-wk-old male and female broiler breeder chickens were compared. The biochemical constituents included ash, collagen, proteoglycan, transforming growth factor-beta (TGF-beta), pyridinium crosslinks, and the organic matrix-associated fluorescence. Blood variables were measured to determine the metabolic status of these birds as related to bone physiology. Although there were no differences in blood chemistry of 7-wk-old males and females, there were several differences between young and old birds. The levels of calcium, triglyceride, and iron were higher in older females than in older males. The collagen content was reduced, and the proteoglycan content increased in 72-wk-old hens. The TGF-beta content of bones from 7-wk-old females was higher than that of other groups of birds. Bone strength and stiffness, measured using loads at break and Young's modulus, respectively, were higher in older birds. The presence of medullary bones in 72-wk-old hens did not affect their bone strength, although it reduced strain values and increased Young's modulus. Compared to other groups, the 72-wk-old hens had a higher content of an inorganic matrix. The levels of hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) and the collagenase-extractable fluorescence of the organic matrix from older birds was higher. The decalcified bone matrix from older birds also showed higher susceptibility to bacterial collagenase than their younger counterparts. Bone strength showed positive correlations with its ash content, density, pyridinium crosslinks, and the fluorescence of the matrix. However, the correlation was strong with both pyridinium crosslinks and the fluorescence of the organic matrix. These results suggest that bone strength is influenced by the content of its collagen crosslinks.