Age-related increase in an advanced glycation end product in penile tissue

Summary Nonenzymatic glycosylation (glycation) of proteins, often referred to as the Maillard reaction, has been proposed to play a role in age and diabetes-related processes by forming protein and DNA adducts and cross-links. These cross-links may contribute to erectile dysfunction by scavenging nitric oxide, which is needed for erection. As the basis for a possible role of the advanced Maillard reaction in age-related erectile dysfunction, we investigated the presence of the specific advanced glycation endproduct (AGE) pentosidine in penile corpus cavernosum tissue and penile tunica albuginea tissue as a function of age. A total of 23 penile tissue specimens were obtained at autopsy, from which 19 samples of tunica albuginea and 21 samples of corpus cavernosum were derived. In addition, 13 penile corporal and tunical specimens were procured at the time of insertion of a penile prosthesis, from which 12 tunica albugineal specimens and 10 samples of corpus cavernosum were derived. Collagen was extracted withacetic acid and pepsin digestion, and the final insoluble collagen product was acid-hydrolyzed with 6 N HCL for 24 h at 110°C. Pentosidine was quantified by high-performance liquid chromatography using a reverse-phase column. The level of pentosidine (expressed in picomoles per milligram of insoluble collagen) was found to increase with age in cadaver as well as living penile corporal and tunical albugineal tissues. Best-fit analysis revealed an exponential increase in both types of cadaver penile tissue, with regression equations of y=15.29×10^(9.9e–3x), R ²=0.79, being obtained in the tunica and y=13.2×10^(7.63e–3x), R ²=0.56, in the corpora. These correspond to 6- and 4-fold increases in pentosidine levels from puberty to the age of 100 years (P<0.05), respectively. Mean pentosidine levels were higher in the tunica than in the corpora. Comparison of pentosidine levels in the tunica versus the corpora revealed a weakly linear correlation (y=24.88+1.08x, R ²=0.32). Levels in the tunical and corporal specimens from the living human specimens fell with the predicted confidence intervals of the cadaveric tissue. Tunical specimens from patients who underwent repair or revision of a previously inserted penile prosthesis had very low levels of pentosidine. The exponential age-related increase in pentosidine observed in both types of penile tissue suggests and impairment of collagen turnover, which could be related to the advanced glycation reaction in aging. It is not known whether pentosidine itself is directly associated with erectile dysfunction, but its formation is usually accompanied by extensive tissue modification. Formation of advanced Maillard reaction products, which is greatly accelerated in aging, diabetes, and uremia, could contribute to erectile dysfunction in these syndromes.     

Contribution of the advanced glycation end product pentosidine and of maturation of type I collagen to compressive biomechanical properties of human lumbar vertebrae

Collagen characteristics contribute to bone biomechanical properties. Yet, few studies have analyzed the independent contributions of bone mineral density (BMD) and post-translational modifications of type I collagen to whole bone strength. Thus, the aim of this study was to determine the relative contributions of BMD and both enzymatic and non-enzymatic collagen crosslink concentration to the biomechanical properties of human vertebrae. Nineteen L3 vertebrae were collected after necropsy (age 26-93; 10 males, 9 females). BMD of the vertebral body was measured by DXA, and the vertebrae were compressed to failure to assess the stiffness, failure load and work to fracture. After mechanical testing, the concentration of both enzymatic crosslinks pyridinoline (PYD), and deoxypyridinoline (DPD) as well as, and the non-enzymatic crosslinks pentosidine (PEN) were analyzed in trabecular and cortical bone by reversed-phase HPLC. The extent of aspartic acid isomerization of type I collagen C telopeptide (CTX) was evaluated by ELISA of native (alpha CTX) and isomerized (beta CTX) forms. BMD was significantly positively related with stiffness (R(2) = 0.74; P < 0.0001), failure load (R(2) = 0.69; P < 0.0001) and work to fracture (R(2) = 0.44; P = 0.002). Bivariate regression analysis showed no association between collagen traits and biomechanical properties. However, in a multiple regression model, BMD and trabecular PEN were both significantly associated with failure load and work to fracture (multiple R(2) = 0.83, P = 0.001 and R(2) = 0.67, P = 0.001, respectively). Similarly, BMD and trabecular alpha/beta CTX ratio were both associated with stiffness (multiple R(2) = 0.83, P = 0.015). These findings indicate that post-translational modifications of type I collagen have an impact on skeletal fragility.     

Impact of extracted urinary proteins and advanced glycation end product on autophagy pathway in renal tubular epithelial cells

Objective To investigate the effect of urinary proteins extracted from minimal change nephritic syndrome (MCNS) and advanced glycation end products (AGEs) on autophagy activity in renal tubular epithelial cells (TECs). Methods Kidney tissue specimens of patients with MCNS and DN were obtained from the kidney pathology library of the Affiliated Hospital of Guangdong Medical College. The kidney tissue from patients with hematuria and proven to be minimal change by pathology examination were used as control. The expression of LC3-Ⅱ in kidney was examined by immune histochemistry in vivo. Expression of LC3-Ⅱ was also studied after exposing HK-2 cells to 8 g/L urinary proteins and 100 mg/L AGE-BSA respectively. LC3-Ⅱ turnover was examined after exposure to urinary proteins in presence of Lysosomal inhibitors leupeptin (200 mg/L) or chloroquine(10μmol/L) by western blot assay. In addition, the autophagosome or autolysosome formation was assessed after transfecting a tandem mRFP-GFP tagged LC3 (tfLC3) plasmid into HK-2 cells. Finally, the production of neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were measured by ELISA after exposure of cells to autophagy enhancer rapamycin (10 μmol/L) and autophagy inhibitor chloroquine (10 μmol/L) in addition to urinary proteins. Results (1)In comparison with the control group, the expression of LC3-Ⅱ was significantly increased in TECs from patients with MCNS and DN(P＜0.01). (2)The expression of LC3-Ⅱwas enlarged after exposed to urinary proteins(P＜0.01), and further increased after leupeptin (autophagy inhibitor) addition. (3) Exposure to urinary proteins increased the autophogosomes and autolysosomes when observed by transfection of tfLC3 plasmid(P＜0.01). (4)The expression of LC3-Ⅱ was also elevated after treatment with AGE-BSA(P＜0.01), but no further increase after chloroquine (autophagy inhibitor) addition. (5) Only the autophogosome formation(P＜0.01), but not autolysosome formation, was found increased by transfection of tfLC3 plasmid after exposure to AGE-BSA. (6) Pre-treatment of HK-2 cells with autophagy enhancer rapamycin reduced the productions of neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), while blocking autophagy with autophagy inhibitor chloroquine exerted an opposite effect. Conclusions Autophagy was activated by urinary proteins, but inactivated by AGE-BSA. Autophagy activation may play a key role in protecting TECs in the progression of primary and secondary kidney diseases.     

Oxidative stress, advanced glycation end product, and coronary artery calcification in hemodialysis patients

Coronary artery calcification is an index of the severity of atherosclerotic vascular disease, and may predict future adverse cardiovascular events in uremic patients undergoing hemodialysis (HD). HD patients are exposed to oxidative stress, and show high plasma levels of advanced glycation end products (AGEs). The association between oxidative stress, AGEs, established cardiovascular risk factors, and coronary artery calcification score (CACS) was studied in 225 HD patients (123 male, 102 female patients). CACS was measured by using multi-detector row computed tomography. Age, systolic blood pressure, calcium, calcium x phosphate, malondialdehyde, lipid peroxides, and pentosidine were significantly and positively correlated with CACS. Duration on HD tended to be positively correlated with CACS. From the independent variables included in the forward stepwise multiple linear regression analysis, only age, systolic blood pressure, lipid peroxides, calcium, and pentosidine were independently associated with CACS. The odds ratios for past history of coronary artery disease and the presence of diabetes mellitus for high CACS (> or =100) were 6.25 (95% confidence interval; 1.83-21.4) and 2.03 (95% confidence interval; 1.02-4.05), respectively. The plasma pentosidine was significantly and positively correlated with indoxyl sulfate. In conclusion, in addition to such traditional cardiovascular risk factors as past history, diabetes mellitus, aging, systolic blood pressure and calcium overload, oxidative stress (lipid peroxides), and AGE (pentosidine) are associated with extensive coronary artery calcification in HD patients. Lipid peroxidation and glycoxidation may be involved in the pathogenesis of coronary artery calcification.     

晚期糖基化终末产物与其受体相互作用对足细胞凋亡的影响

目的 探讨可溶性与复合型晚期糖基化终末产物(AGE)与晚期糖基化终末产物受体（RAGE）的相互作用对足细胞凋亡的影响。 方法 以可溶性（CML-BSA、AGE-BSA）和复合型（AGE修正胶原Ⅳ）AGE刺激小鼠足细胞，并用浓度分别为10、50、100 mg/L的AGE刺激细胞，应用TUNEL染色和荧光激活细胞分类（FACS）法来计数凋亡和坏死的足细胞。用RAGE iRNA转染足细胞后，以同样剂量的可溶性和复合型AGE刺激足细胞，观察凋亡情况的改变。 结果 可溶性和复合型AGE均可诱导小鼠足细胞凋亡，复合型AGE引起的足细胞凋亡是可溶性AGE的2~3倍（均P < 0.01）。AGE呈剂量依赖性引起足细胞凋亡。用RAGE iRNA转染足细胞，降低60%~70%RAGE基因活性后，可溶性AGE引起的凋亡率明显下降，复合型AGE诱导的凋亡有下降趋势，但不明显。只有在AGE 100 mg/L刺激后才发生细胞坏死。结论 可溶性AGE主要通过与RAGE相互作用引起足细胞凋亡，复合型AGE部分通过与RAGE相互作用诱导足细胞凋亡。减少AGE生成和RAGE表达可能是预防肾脏病进展的重要途径。     

Advanced glycation end product interventions reduce diabetes-accelerated atherosclerosis

Advanced glycation end product (AGE) formation may contribute to the progression of atherosclerosis, particularly in diabetes. The present study explored atherosclerosis in streptozotocin-induced diabetic apolipoprotein E-deficient (apoE-/-) mice that were randomized (n = 20) to receive for 20 weeks no treatment, the AGE cross-link breaker ALT-711, or the inhibitor of AGE formation aminoguanidine (AG). A sixfold increase in plaque area with diabetes was attenuated by 30% with ALT-711 and by 40% in AG-treated mice. Regional distribution of plaque demonstrated no reduction in plaque area or complexity within the aortic arch with treatment, in contrast to the thoracic and abdominal aortas, where significant attenuation was seen. Diabetes-associated accumulation of AGEs in aortas and plasma and decreases in skin collagen solubility were ameliorated by both treatments, in addition to reductions in the vascular receptor for AGE. Collagen-associated reductions in the AGEs carboxymethyllysine and carboxyethyllysine were identified with both treatments. Diabetes was also accompanied by aortic accumulation of total collagen, specifically collagens I, III, and IV, as well as increases in the profibrotic cytokines transforming growth factor-beta and connective tissue growth factor and in cellular alpha-smooth muscle actin. Attenuation of these changes was seen in both treated diabetic groups. ALT-711 and AG demonstrated the ability to reduce vascular AGE accumulation in addition to attenuating atherosclerosis in these diabetic mice.     

Food restriction prevents advanced glycation end product accumulation and retards kidney aging in lean rats

ABSTRACT.: Tissue content of advanced glycation end products (AGE) increases with age and contributes to the changes in structure and function of the renal and cardiovascular systems. The effect of chronic food restriction on this AGE accumulation was investigated in lean WAG/Rij rats. A 30% food restriction performed from 10 to 30 mo in female rats reduced their mean body weight from 240 +/- 7 to 160 +/- 12 g, but did not modify their survival. AGE collagen content increased from 14.3 +/- 5.5 to 104.7 +/- 13.0 arbitrary units per microgram (AU/microg) of hydroxyproline (OHPro) in kidney between 10 and 30 mo, and from 9.7 +/- 1.2 to 310.6 +/- 34.6 AU/microg OHPro in the abdominal aorta. Food restriction reduced AGE accumulation to 21.4 +/- 3.3 and 74.6 +/- 16.5 AU/microg OHPro in kidney and aorta of 30-mo-old animals. Similar results were found for collagen prepared from isolated glomeruli (7.8 +/- 1.2, 81.2 +/- 16.1, and 10.3 +/- 4.3 AU/microg OHPro in 10-mo, 30-mo, and restricted 30-mo-old rats). Reduction of intrarenal and arterial AGE accumulation by food restriction was confirmed by immunostaining in optical microscopy. Age-related changes in arterial and kidney structures as polyuria and proteinuria were mainly prevented by food restriction. These data indicate that chronic food restriction reduces the accumulation of AGE and preserves the structure and function of the renal and cardiovascular systems in learn rats, although it did not affect survival of the animals between 10 and 30 mo.     

Marked increases in macrophage colony-stimulating factor and interleukin-18 in maintenance hemodialysis patients: comparative study of advanced glycation end products, carboxymethyllysine and pentosidine

BACKGROUND: Recent studies have demonstrated the crucial involvement of advanced glycation end products (AGEs) in major complications of long-term hemodialysis (HD) patients. HD, in a clinical setting, is characterized by increased production of proinflammatory cytokines. AGEs and cytokines are presumed to be responsible for the development of major complications in long-term HD. We therefore investigate here the relationship between a newly identified cytokine, interleukin-18 (IL-18), and two AGEs, carboxymethyllysine-hemoglobin (CML-Hb) and pentosidine. METHODS: CML-Hb, pentosidine macrophage colony-stimulating factor (M-CSF), and IL-18 were evaluated in 35 patients undergoing stable maintenance HD. CML-Hb and pentosidine were measured by a dot blot and competitive ELISA. Cytokines were measured with a cytokine-specific ELISA. RESULTS: Circulating levels of CML-Hb and pentosidine were elevated in HD patients as compared to controls. The serum values of M-CSF and IL-18 were significantly increased in the HD patients in comparison to controls. Moreover, these two AGEs and serum values of M-CSF, M-CSF and IL-18 showed significant correlation by simple and multiple regression analysis. CONCLUSION: Elevation of circulating IL-18 levels was demonstrated in maintenance HD patients relative to controls. A correlative increase in M-CSF and IL-18 suggests the presence of a primed state of monocytes/macrophages in HD patients.