Insulin enhances macrophage scavenger receptor-mediated endocytic uptake of advanced glycation end products

Anti-glycating and anti-cytotoxic effect of silibinin on albumin at early glycation: A physiochemical study

During persistent hyperglycaemia, albumin, one of the major blood proteins, can undergo fast glycation. It can be expected that timely inhibition of protein glycation might be add quality years to diabetic patients' life. Therefore, this study was designed to analyse the role of silibinin to reduced or delay amadori adduct formation at early glycation and its beneficial effect to improve the glycated albumin structure and conformation. We also analysed cytotoxic effect of amadori-albumin in the presence of silibinin on murine macrophage cell line RAW cells by MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) assay. Formation of early glycated product (furosine) in all samples was confirmed by LCMS. Albumin incubated with glucose only showed presence of furosine like structure. Albumin treated with silibinin in the presence of glucose did not show such furosine like peak. This LCMS result showed the silibinin play a protective role in the formation of early glycated product. HMF contents were also reduced in the presence of silibinin, when albumin was incubated with increasing concentrations of silibinin (100 and 200 μM) in the presence of glucose. ANS binding fluorescence decrease by increasing silibinin concentrations with amadori-albumin. SDS-PAGE was also showed that no significant difference in the band mobility of albumin treated with silibinin as compared to native albumin. The secondary conformational alteration in amadori-albumin due to silibinin were confirmed by FTIR. This spectrum showed slight shift in amide I and Amide II band in albumin co-incubated with glucose and silibinin as compared to albumin incubated with glucose only. We further discussed about cytotoxic effect of amadori albumin and its prevention by silibinin. MTT assay results demonstrated that amadori-albumin showed cytotoxic effect on RAW cells but silibinin showed protective role and increased the cell viability. Moreover, the results showed that silibinin has anti-glycating potential and playing a role to prevent the formation of Amadori-albumin in-vitro. Silibinin possesses strong anti-glycating capacity and can improve albumin structure and function at early stage. It might be useful in delaying the progression of diabetes mellitus and its secondary complications at early stage.

Differences in kinetics and dynamics of endogenous versus exogenous advanced glycation end products (AGEs) and their precursors

Advanced glycation end products (AGEs) and their precursors, referred to as glycation products, are a heterogenous group of compounds being associated with adverse health effects. They are formed endogenously and in exogenous sources including food. This review investigates the roles of endogenously versus exogenously formed glycation products in the potential induction of adverse health effects, focusing on differences in toxicokinetics and toxicodynamics, which appeared to differ depending on the molecular mass of the glycation product. Based on the available data, exogenous low molecular mass (LMM) glycation products seem to be bioavailable and to contribute to dicarbonyl stress and protein cross-linking resulting in formation of endogenous AGEs. Bioavailability of exogenous high molecular mass (HMM) glycation products appears limited, while these bind to the AGE receptor (RAGE), initiating adverse health effects. Together, this suggests that RAGE-binding in relevant tissues will more likely result from endogenously formed glycation products. Effects on gut microbiota induced by glycation products is proposed as a third mode of action. Overall, studies which better discriminate between LMM and HMM glycation products and between endogenous and exogenous formation are needed to further elucidate the contributions of these different types and sources of glycation products to the ultimate biological effects.

Assessment of Early Markers of Cardiovascular Risk in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous syndrome, with long-term sequelae from birth to senescence. The long-term effects of PCOS are attributed to several metabolic aberrations ensuing the syndrome. In a systematic review of literature regarding the cardiovascular risk factors that accompany PCOS, we found that macrovascular function has been assessed by flow-mediated dilatation (FMD), microvascular function by venous occlusion plethysmography (VOP), and arterial structure by ultrasonographic assessment of intima-media thickness (IMT) usually of the carotid artery. Contradictory results have been reported; however, in most studies, endothelial dysfunction, an early marker of atherosclerosis assessed either by haemodynamic methods such as FMD or by biochemical methods such as endothelin-1 levels, was found to be impaired. VOP is a less-studied method, with few indices altered. IMT was found to be altered in most of the included studies, but the population was more heterogeneous. Inflammatory markers, including C-reactive protein, were also found to be altered in most studies. On the other hand, a number of interventions have been shown beneficial for the markers of cardiovascular risk, in the context of insulin-sensitizers. However, other interventions such as oral contraceptive pills or statins did not consistently show a similar beneficial effect. In summary, the early identification and eventual treatment of cardiovascular clinical and biochemical risk factors may be used in clinical practice to prevent potential 'silent' triggers of cardiovascular disease.

Assessment of Early Markers of Cardiovascular Risk in Polycystic Ovary Syndrome

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The role of advanced glycation end products in human infertility

Advanced glycation end products (AGEs) are heterogeneous products of the non-enzymatic interaction between proteins and reducing sugars. Numerous studies have shown that AGEs are associated with senescence, diabetes, vascular disease, aging and kidney disease. Infertility has been affected approximately 10 to15% of couples of reproductive ages. AGEs accumulation has been shown to play a crucial role in pathogenesis of infertility-related diseases. The present review provides the generation process, mechanism and pathological significance of AGEs and the novel treatment targeting AGEs for infertility.

Evaluation of the innate immunostimulatory potential of originator and non-originator copies of insulin glargine in an in vitro human immune model

BACKGROUND

The manufacture of insulin analogs requires sophisticated production procedures which can lead to differences in the structure, purity, and/or other physiochemical properties of resultant products that can affect their biologic activity. Here, we sought to compare originator and non-originator copies of insulin glargine for innate immune activity and mechanisms leading to differences in these response profiles in an in vitro model of human immunity.

METHODS

An endothelial/dendritic cell-based innate immune model was used to study antigen-presenting cell activation, cytokine secretion, and insulin receptor signalling pathways induced by originator and non-originator insulin glargine products. Mechanistic studies included signalling pathway blockade with specific inhibitors, analysis of the products in a Toll-like receptor reporter cell line assay, and natural insulin removal from the products by immunopurification.

FINDINGS

All insulin glargine products elicited at least a minor innate immune response comparable to natural human insulin, but some lots of a non-originator copy product induced the elevated secretion of the cytokines, IL-8 and IL-6. In studies aimed at addressing the mechanisms leading to differential cytokine production by these products, we found (1) the inflammatory response was not mediated by bacterial contaminants, (2) the innate response was driven by the native insulin receptor through the MAPK pathway, and (3) the removal of insulin glargine significantly reduced their capacity to induce innate activity. No evidence of product aggregates was detected, though the presence of some high molecular weight proteins argues for the presence of insulin glargine dimers or others contaminants in these products.

CONCLUSION

The data presented here suggests some non-originator insulin glargine product lots drive heightened in vitro human innate activity and provides preliminary evidence that changes in the biochemical composition of non-originator insulin glargine products (dimers, impurities) might be responsible for their greater immunostimulatory potential.

Advanced glycation end products: A link between metabolic and endothelial dysfunction in polycystic ovary syndrome?

Polycystic ovary syndrome (PCOS), a heterogeneous syndrome of reproductive and metabolic alterations, is associated with increased long-term risk of cardiovascular complications. This phenomenon has been linked to an increase in oxidative stress and inflammatory markers. Advanced glycation end products (AGEs) are pro-inflammatory molecules that trigger a state of intracellular oxidative stress and inflammation after binding to their cell membrane receptors RAGE. The activation of the AGE-RAGE axis has been well known to play a role in atherosclerosis in both men and women. Women with PCOS have systemic chronic inflammatory condition even at the ovarian level as represented by elevated levels of serum/ovarian AGEs and increased expression of the pro-inflammatory RAGE in ovarian tissue. Data also showed the presence of sRAGE in the follicular fluid and its potential protective role against the harmful effect of AGEs on ovarian function. Thus, whether AGE-RAGE axis constitutes a link between metabolic and endothelial dysfunction in women with PCOS is addressed in this review. Additionally, we discuss the role of hormonal changes observed in PCOS and how they are linked with the AGE-RAGE axis in order to better understand the nature of this complex syndrome whose consequences extend well beyond reproduction.

Relationship among Short and Long Term of Hypoinsulinemia-Hyperglycemia, Dermatophytosis, and Immunobiology of Mononuclear Phagocytes

Dermatophytes are fungi responsible for causing superficial infections. In patients with diabetes mellitus (DM), dermatophytosis is usually more severe and recurrent. In the present study, we aimed to investigate the influence of short and long term hypoinsulinemia-hyperglycemia (HH) during experimental infection by Trichophyton mentagrophytes as well as alterations in the mononuclear phagocytes. Our results showed two distinct profiles of fungal outcome and immune response. Short term HH induced a discrete impaired proinflammatory response by peritoneal adherent cells (PAC) and a delayed fungal clearance. Moreover, long term HH mice showed low and persistent fungal load and a marked reduction in the production of TNF-α by PAC. Furthermore, while the inoculation of TM in non-HH mice triggered high influx of Gr1⁺ monocytes into the peripheral blood, long term HH mice showed low percentage of these cells. Thus, our results demonstrate that the time of exposure of HH interferes with the TM infection outcome as well as the immunobiology of mononuclear phagocytes, including fresh monocyte recruitment from bone marrow and PAC activity.

Advanced glycation End-products (AGEs): an emerging concern for processed food industries

The global food industry is expected to increase more than US $ 7 trillion by 2014. This rise in processed food sector shows that more and more people are diverging towards modern processed foods. As modern diets are largely heat processed, they are more prone to contain high levels of advanced glycation end products (AGEs). AGEs are a group of complex and heterogeneous compounds which are known as brown and fluorescent cross-linking substances such as pentosidine, non-fluorescent cross-linking products such as methylglyoxal-lysine dimers (MOLD), or non-fluorescent, non-cross linking adducts such as carboxymethyllysine (CML) and pyrraline (a pyrrole aldehyde). The chemistry of the AGEs formation, absorption and bioavailability and their patho-biochemistry particularly in relation to different complications like diabetes and ageing discussed. The concept of AGEs receptor - RAGE is mentioned. AGEs contribute to a variety of microvascular and macrovascular complications through the formation of cross-links between molecules in the basement membrane of the extracellular matrix and by engaging the receptor for advanced glycation end products (RAGE). Different methods of detection and quantification along with types of agents used for the treatment of AGEs are reviewed. Generally, ELISA or LC-MS methods are used for analysis of foods and body fluids, however lack of universally established method highlighted. The inhibitory effect of bioactive components on AGEs by trapping variety of chemical moieties discussed. The emerging evidence about the adverse effects of AGEs makes it necessary to investigate the different therapies to inhibit AGEs.

Role of advanced glycation end products in cellular signaling

Improvements in health care and lifestyle have led to an elevated lifespan and increased focus on age-associated diseases, such as neurodegeneration, cardiovascular disease, frailty and arteriosclerosis. In all these chronic diseases protein, lipid or nucleic acid modifications are involved, including cross-linked and non-degradable aggregates, such as advanced glycation end products (AGEs). Formation of endogenous or uptake of dietary AGEs can lead to further protein modifications and activation of several inflammatory signaling pathways. This review will give an overview of the most prominent AGE-mediated signaling cascades, AGE receptor interactions, prevention of AGE formation and the impact of AGEs during pathophysiological processes.

Stress hyperglycemia, insulin treatment, and innate immune cells

Hyperglycemia (HG) and insulin resistance are the hallmarks of a profoundly altered metabolism in critical illness resulting from the release of cortisol, catecholamines, and cytokines, as well as glucagon and growth hormone. Recent studies have proposed a fundamental role of the immune system towards the development of insulin resistance in traumatic patients. A comprehensive review of published literatures on the effects of hyperglycemia and insulin on innate immunity in critical illness was conducted. This review explored the interaction between the innate immune system and trauma-induced hypermetabolism, while providing greater insight into unraveling the relationship between innate immune cells and hyperglycemia. Critical illness substantially disturbs glucose metabolism resulting in a state of hyperglycemia. Alterations in glucose and insulin regulation affect the immune function of cellular components comprising the innate immunity system. Innate immune system dysfunction via hyperglycemia is associated with a higher morbidity and mortality in critical illness. Along with others, we hypothesize that reduction in morbidity and mortality observed in patients receiving insulin treatment is partially due to its effect on the attenuation of the immune response. However, there still remains substantial controversy regarding moderate versus intensive insulin treatment. Future studies need to determine the integrated effects of HG and insulin on the regulation of innate immunity in order to provide more effective insulin treatment regimen for these patients.

Increased serum levels of advanced glycation end-products is associated with severity of sleep disordered breathing but not insulin sensitivity in non-diabetic men with obstructive sleep apnoea

BACKGROUND

Patients with diabetes mellitus are known to have increased serum levels of advanced glycation end-products (AGEs), and this is also associated with insulin resistance. This study aimed to investigate the relationship between serum AGEs and insulin sensitivity in non-diabetic subjects with obstructive sleep apnoea (OSA).

METHODS

Adult males with no known comorbidities were recruited from the sleep clinic of a university teaching hospital. They underwent overnight in-laboratory polysomnography. Fasting blood was taken to measure serum AGE and plasma glucose levels. Insulin sensitivity was estimated using the short insulin tolerance test.

RESULTS

In total, 105 subjects with a mean age of 43.5 (standard deviation [SD] 9.2)years, mean body mass index of 27.1 (SD 4.0)kg/m(2), and median apnoea-hypopnoea index (AHI) of 17 (interquartile range 5-46) were analysed. Serum AGE levels were significantly higher in subjects with OSA (AHI ≥5), compared with those without OSA (AHI <5) (3.9 [SD 1.2] vs. 3.2 [SD 0.8]μg/ml, respectively; P=0.037) after adjusting for confounders. AGE levels were positively correlated with AHI (r=0.318, P=0.001), but not with insulin sensitivity. AGE levels decreased in subjects with moderate-to-severe OSA who received continuous positive airway pressure (CPAP) treatment for three months (n=18, P=0.017).

CONCLUSIONS

Serum AGE levels correlate with AHI in non-diabetic adult males. This relationship cannot be explained by insulin sensitivity. Supporting the hypothesis of a direct relationship between AHI and AGEs, AGE levels were found to decline with CPAP therapy.

[The role of AGEs and ROS in atherosclerosis]

Advanced glycation end products (AGEs) are among the "newcomers" of metabolic research during the last 2-3 decades. Also known as Maillard products, they have belonged to the everyday life of food research for a long time, but their role in the development of diabetes and cardiovascular complications has been suggested only recently. Even though multiple studies have recently dealt with the role of AGEs and their receptors in mediating pathomechanisms, we are still far from understanding them completely and maybe even farther from developing effective therapeutic approaches. Nevertheless, the present article attempts to offer an overview of known associations between AGEs and vascular complications, in order to draw attention to a less known subject--the AGEs--and, maybe, to stimulate further research in this very exciting field.

Increased serum advanced glycation end-products is a distinct finding in lean women with polycystic ovary syndrome (PCOS)

BACKGROUND

Nonenzymatic advanced glycation and oxidation end-products, advanced glycation end-products (AGEs), impart a potent impact on vessels and other tissues in diabetic state and in euglycaemic conditions with increased oxidative stress. Insulin resistant (IR) polycystic ovary syndrome (PCOS) women, have elevated serum AGEs, increased receptor (RAGE) expression, and increased deposition with differential localization in the polycystic ovarian tissue (theca and granulosa) compared to normal.

OBJECTIVE

To determine whether the raised AGE levels in noninsulin resistant women with PCOS is a distinct finding compared with those presenting the isolated components of the syndrome and among PCOS subphenotypes. Noninsulin resistant women were selected in order to show that serum AGEs are elevated in PCOS independently of the presence of IR.

DESIGN

Clinical trial.

PATIENTS

One hundred and ninety-three age- and BMI-matched young lean noninsulin resistant women were studied. Among them, 100 women were diagnosed with PCOS according to Rotterdam criteria, and divided to subphenotypes (hyperandrogenaemia with or without PCO morphology and with or without anovulation). Sixty-eight women with the isolated components of the PCOS phenotype were also studied along with 25 healthy women.

MEASUREMENTS

Serum AGE levels, metabolic, hormonal profiles and intravaginal ultrasound were determined in all subjects.

RESULTS

The studied population did not differ in BMI, fasting insulin concentration, waist : hip and glucose : insulin ratios. PCOS women exhibited statistically higher AGEs levels (7.96 +/- 1.87 U/ml, P < 0.001) compared with those with isolated hyperandrogenaemia (5.61 +/- 0.61 U/ml), anovulation (5.53 +/- 1.06 U/ml), US-PCO morphology (5.26 +/- 0.25 U/ml) and controls (5.86 +/- 0.89 U/ml).

CONCLUSIONS

In PCOS, serum AGEs are distinctly elevated compared with women having the isolated characteristics of the syndrome. No difference was observed between PCOS subphenotypes. As chronic inflammation and increased oxidant stress have been incriminated in the pathophysiology of PCOS, the role of AGEs as inflammatory and oxidant mediators, may be linked with the metabolic and reproductive abnormalities of the syndrome.

Immunohistochemical localization of advanced glycation end-products (AGEs) and their receptor (RAGE) in polycystic and normal ovaries

The aim of the present study was to investigate the localization/immunohistochemical distribution of AGEs and RAGE, as well as their putative signalling mediator NF-kappaB in ovaries of women with polycystic ovary syndrome (PCOS) compared to normal. Archival ovarian-tissue samples from biopsies of six women with PCOS and from six healthy of similar age women, were examined immunohistochemically with monoclonal anti-AGEs, anti-RAGE and anti-NF-kappaB(p50/p65) specific antibodies. In healthy women, AGE immunoreactivity was observed in follicular cell layers (granulosa and theca) and luteinized cells, but not in endothelial cells. PCOS specimens displayed AGE immunoexpression in theca interna and granulosa cells as well as in endothelial cells, but staining of granulosa cells was stronger than in that of normal ovaries. RAGE was highly expressed in normal and PCOS tissues. Normal tissue exhibited no staining differences between granulosa cell layer and theca interna. However, in PCOS ovaries, granulosa cells displayed stronger RAGE expression compared to theca interna cells in comparison to controls. NF-kappaB(p50/p65) was expressed in the cytoplasm of theca interna and granulosa cells of both normal and PCOS ovaries; whereas the NF-kappaB p65 subunit was only observed in granulosa cells nuclei in PCOS tissue. In conclusion, these findings demonstrate for the first time that RAGE and AGE-modified proteins with activated NF-kappaB are expressed in human ovarian tissue. Furthermore, a differential qualitative distribution of AGE, RAGE and NF-kappaB p65 subunit was observed in women with PCOS compared to healthy controls, where a stronger localization of both AGE and RAGE was observed in the granulosa cell layer of PCOS ovaries.

Effect of metformin administration on plasma advanced glycation end product levels in women with polycystic ovary syndrome

Metformin therapy in polycystic ovary syndrome (PCOS) improves metabolic and hormonal profiles. Its therapeutic effect on cardiovascular risk factors is under investigation. Advanced glycation end products (AGEs), well-known atherogenic molecules, were recently found to be elevated in plasma of women with PCOS. The purpose of the study was to investigate the effect of metformin treatment in plasma AGE levels of women with PCOS. This was a descriptive clinical trial. The study involved 22 patients with PCOS (age, 25.09 +/- 1.05 years; body mass index [BMI], 28.44 +/- 1.51 kg/m(2)) and 22 healthy women (age, 26.50 +/- 0.85 years; BMI, 25.62 +/- 1.30 kg/m(2)). Measurements of plasma AGE levels (U/mL) were performed, and the metabolic and hormonal profiles were determined in all subjects. All women with PCOS received a dose of 1700 mg metformin daily for 6 months. AGEs levels were reduced after metformin administration in 22 women with PCOS (9.98 +/- 0.13 [before metformin] vs 9.86 +/- 0.11 [after metformin], P = .05). In a subgroup analysis, of 16 women with PCOS and normal glucose tolerance, the drop of AGE levels was potentiated (9.98 +/- 0.19 [before] vs 9.81 +/- 0.15 [after], P = .02). Body mass index as well as the other parameters studied remained unchanged after metformin therapy apart from a drop of testosterone levels (P = .01) and free androgen index (P = .009). In conclusion, after metformin therapy, the atherogenic AGE molecules were reduced in the serum of women with PCOS . The clinical relevance of this finding in PCOS, a high-risk group for type 2 diabetes mellitus and cardiovascular disease, remains to be seen. Future studies are required to confirm the need of therapeutic intervention for short-term abnormalities and for prevention of long-term sequelae characterizing this syndrome.

Increased levels of serum advanced glycation end-products in women with polycystic ovary syndrome

OBJECTIVE

Women with polycystic ovary syndrome (PCOS) carry a number of cardiovascular risk factors and are considered to be at increased risk for atherosclerosis. Elevated concentrations of advanced glycation end-products (AGE), which exert their effects through interaction with specific receptors (RAGE), have been implicated in the cellular and tissue damage during atherosclerotic processes.

DESIGN/PATIENTS

We investigated serum AGE levels in 29 young women with PCOS as well as the expression of their receptor, RAGE, in circulating monocytes and compared them levels with 22 healthy control women.

MEASUREMENTS/RESULTS

Women with PCOS had higher levels of serum AGE proteins compared to healthy individuals (9.81 +/- 0.16 vs. 5.11 +/- 0.16, P < 0.0001), and increased RAGE expression was observed in monocytes of PCOS women compared to controls (30.91 +/- 10.11 vs. 7.97 +/- 2.61, P < 0.02). A positive correlation was observed between AGE proteins and testosterone (T) levels (r = 0.73, P < 0.0001). The correlation between AGE proteins and T levels remained high (partial correlation coefficient = 0.61, P = 0.0001) after controlling for body mass index (BMI), insulin levels and the area under the curve for glucose (AUCGLU) during an oral glucose tolerance test (OGTT). A positive correlation was also observed between AGE proteins and the free androgen index (FAI) (r = 0.58, P < 0.0001), waist-to-hip ratio (WHR) (r = 0.31, P < 0.02), insulin (r = 0.46, P < 0.001), homeostasis model assessment (HOMA) (r = 0.47, P < 0.0001), AUCGLU (r = 0.52, P < 0.002) and RAGE (r = 0.59, P < 0.01). A negative correlation was observed between AGE proteins and glucose/insulin ratio (GLU/INS) (r = -0.35, P < 0.01), and the quantitative insulin sensitivity check index (QUICKI) (r =-0.50, P < 0.01). In multiple regression analysis T was the only independent predictor of AGE levels (P < 0.0001, b = 0.044) between BMI, insulin, SHBG and AUCGLU (adjusted R2 = 0.59, F = 44.41, P < 0.0001).

CONCLUSION

These data clearly demonstrate, for the first time, that PCOS women without overt hyperglycaemia have increased AGE levels and elevated RAGE expression when compared with controls.

Nobiletin, a citrus flavonoid isolated from tangerines, selectively inhibits class A scavenger receptor-mediated metabolism of acetylated LDL by mouse macrophages

Flavonoids are a class of chemically related polyphenols that are nearly ubiquitous in nature. Of the more-than 4000 flavonoids thus identified, citrus fruit-derived flavonoids are suggested to have an inverse association with the occurrence of coronary heart disease via their ability to reduce plasma cholesterol concentrations. Our current studies examined whether citrus flavonoids possess an additional antiatherogenic effect by modulating macrophage metabolism of the specific class A scavenger receptor (SR-A) ligand, acetylated LDL (acLDL). In this study, both acLDL-metabolism and SR-A expression by cultured murine J774A.1 macrophages was examined following 24 h pretreatment (100 microM) with the flavonoids: naringenin (from grapefruit), hesperetin (from oranges), and tangeretin and nobiletin (from tangerines). Of these flavonoids, only nobiletin inhibited (50-72%) acLDL metabolism as measured by both cellular cholesterol ester mass and [3H]oleate incorporation into cholesterol esters. This nobiletin-mediated effect was specific for SR-A and not a global effect on lipoprotein metabolism by the macrophage, as all four citrus flavonoids significantly reduce the metabolism of beta-VLDL, which is primarily taken up by macrophages via the LDL receptor. Nevertheless, nobiletin did not affect SR-A protein expression, as measured by Western blot analysis, nor was cell surface expression of SR-A affected as measured by 4 degrees C binding studies using [125I]acLDL. In conclusion, our findings suggest that in addition to reducing plasma cholesterol concentrations, nobiletin may prevent atherosclerosis at the level of the vascular wall by inhibiting macrophage foam-cell formation.

Mechanisms involved in the stimulatory effect of advanced glycation end products on growth of rat aortic smooth muscle cells

Hyperglycemia is an important cause of accelerated atherosclerosis in diabetic patients. We examined the effect of hyperglycemia and advanced glycation end products (AGE) on proliferation of rat aortic smooth muscle cells (SMC) in culture; in vivo, this event is believed to contribute importantly to atherogenesis in diabetes mellitus. Glucose itself dose-dependently inhibited thymidine uptake by SMC, but AGE increased thymidine uptake, suggesting that SMC proliferation is accelerated by AGE. To examine possible mechanisms for this effect, we studied nuclear factor-kappa B (NF-kappaB) activation and the tyrosine phosphorylation pathway; AGE stimulated NF-kappaB activity, but phosphorylation of the platelet-derived growth factor (PDGF) receptor was unchanged. In Chinese hamster ovary (CHO) cells overexpressing galectin-3, an AGE receptor related to atherosclerosis, AGE increased thymidine uptake. This suggests SMC proliferation is enhanced by AGE via galectin-3. As pathways involving AGE-galectin-3 interaction thus may be involved in macroangiopathy, AGE appears to be important to the role of SMC in accelerated atherosclerosis associated with diabetes mellitus.

Lack of recognition of Nε-(carboxymethyl)lysine by the mouse liver reticulo-endothelial system: implications for pathophysiology

Advanced glycation end products (AGEs) are known to be associated with a number of pathological conditions, such as diabetes mellitus, Alzheimer's disease, uremia, as well as with normal aging. This study was undertaken to investigate whether Nepsilon-(carboxymethyl)lysine (CML), a major structure among numerous AGEs, engenders hepatic AGE clearance. For this purpose uptake of BSA substituted with heterogeneous AGEs or with CML only was monitored in vivo and in cultured hepatic scavenger cells. Here, we show that following intravenous administration of 125I-AGE-BSA and 125I-CML-BSA, blood radioactivity was reduced by 50% after 50s and >100 min, respectively. Recoveries from the circulation at 6 min after injection were: 5% for AGE-BSA, 95% for CML-BSA. More than 80% of the injected AGE-BSA was recovered from the liver. AGE-BSA, but not CML-BSA, was avidly endocytosed by cultured liver scavenger cells. Our results suggest that CML does not engender AGE-BSA clearance. Macromolecules substituted with CML only may escape elimination and cause pathological effects.

Interactions of integrins with their partner proteins in leukocyte membranes

Integrins participate in many aspects of immunologic and inflammatory responses, especially those involving cell migration, adherence, and activation. Although leukocyte integrins such as complement receptor type 3 (CR3) are known to carry out certain functions without the intervention of other plasma membrane receptors, many plasma membrane proteins are now known to physically interact and functionally cooperate with integrins. Several of these interactions are highly dynamic within cell membranes; thus integrin-partner protein interactions change during certain physiological processes. This allows an extraordinary adaptability of the system to prime and promote proinflammatory signaling. Since our discovery of the CR3-FcgammaRIIIB interaction, the plasma membrane protein repertoire of beta1, beta2, and beta3 integrins has grown to include: FcgammaRIIA (CD32), uPAR (urokinase-type plasminogen activator receptor; CD87), CD14, voltage-gated K+channels (Kv1.3), integrin-associated protein (IAP), CD98, tetraspans (TM4SF), insulin receptors, and PDGFbeta receptors. In this article we will highlight certain features of this growing field of research, especially with regard to their relevance in immunology and inflammation.

Vascular signaling pathways in the metabolic syndrome

There are several potential cellular and molecular pathways whereby cardiovascular risk factors act through very specific signal transduction pathways in the formation of atherosclerosis, as seen often in the metabolic syndrome. Many examples point to multiple postreceptor defects in the insulin signaling pathway in vascular tissue, however, there are differences in the insulin receptor pathway in vascular tissue compared with skeletal muscle or fat. In addition to insulin receptors, insulin may affect atherosclerotic changes in the vascular cells via stimulation of insulin-like growth factor-1 receptors and their signaling pathway. Insulin also causes activation of the vascular renin-angiotensin system in both vascular smooth muscle cells and endothelial cells. Insulin-activated tissue renin-angiotensin system leads to increased cell growth and contributes to the cause of atherosclerosis. The fact that agents that inhibit the renin-angiotensin system also block insulin-mediated renin-angiotensin system expression and cell growth reinforces the potential implication of a vascular insulin-renin-angiotensin system pathway. Finally, novel substances such as the adipokines, factors produced from fat cells, reveal new risk factors in the metabolic syndrome and offer further evidence for a link between insulin resistance and accelerated atherosclerosis.

Diabetes and advanced glycation endproducts

Bio-reactive advanced glycation endproducts (AGE) alter the structure and function of molecules in biological systems and increase oxidative stress. These adverse effects of both exogenous and endogenously derived AGE have been implicated in the pathogenesis of diabetic complications and changes associated with ageing including atherosclerosis, renal, eye and neurological disease. Specific AGE receptors and nonreceptor mechanisms contribute to these processes but also assist in the removal and degradation of AGE. The final disposal of AGE depends on renal clearance. Promising pharmacologic strategies to prevent AGE formation, reduce AGE toxicity, and/or inactivate AGE are under investigation.

Markedly elevated levels of plasma advanced glycation end products in patients with liver cirrhosis - amelioration by liver transplantation

BACKGROUND/AIMS

Modification by advanced glycation renders macromolecules susceptible to elimination in the liver via scavenger receptors. Thus, in advanced liver disease an accumulation of advanced glycation end products (AGEs) in circulation might occur, due to the reduction of effective liver mass.

METHODS

Plasma AGE levels (fluorescent AGEs-AGE-Fl and N(epsilon)-carboxymethyllysine - CML) were determined in 51 patients with liver cirrhosis (Ci) and 19 healthy controls. Five patients were followed 36 months after liver transplantation.

RESULTS

In cirrhotic patients, markedly elevated concentrations of AGEs were revealed (AGE-Fl: control, 0.3+/-0.01 x 10(5) AU, Ci: 1.06+/-0.06 x 10(5) AU, P<0.01; CML, control: 431.7+/-16.3 ng/ml, Ci: 647.6+/-258.5, P<0.01). CML levels correlated with the severity of liver disease, as determined by clinical score (r=0.663, P<0.001), albumin level (r=0.704, P<0.001) and monoethylglycinexylide test (r=0.852, P<0.01). Reduced renal function contributed to the rise of CML in proportion to the degree of renal impairment. Liver transplantation resulted in about 50% decline of CML levels within 3 months, while impairment of renal function still persisted, underlying the central role of the liver for AGE removal.

CONCLUSIONS

In liver Ci, hepatic removal of AGEs is impaired. With regard to the toxicity of AGEs, their accumulation could be of pathophysiological relevance.

The AGE-receptor in the pathogenesis of diabetic complications

Native glucose-derived glycation derivatives (advanced glycation end products, AGE) in vascular, renal and neuronal tissues contribute to organ damage. Glycation derivatives include a number of chemically and cell-reactive substances, also termed glycoxidation products or glycotoxins (GT). Cell-associated AGE-specific receptors (AGE-Rs), AGE-R1-3, RAGE, as well as the scavenger receptors ScR-II and CD-36 that are present on vascular, renal, hemopoietic, and neuronal/glial cells, serve in the regulation of AGE uptake and removal. AGE-Rs also modulate cell activation, growth-related mediators, and cell proliferation, consequently influencing organ structure/function. This occurs via oxidant stress triggered via receptor-dependent or -independent pathways, and leads to signal activation pathways, resulting in pro-inflammatory responses. In susceptible individuals, the AGE-R expression/function may be subject to environmental or gene-related modulation, which in turn may influence tissue-specific gene functions. In this context, altered expression and activity of AGE-R components has recently been found in both mouse diabetes models and humans with diabetic complications. Although several gene polymorphisms are detected in most AGE-R components, no significant correlation to diabetic complications has as yet been found. Further investigation is underway to define whether primary or secondary genetic links of pathogenic significance exist in this system. Various AGE-binding peptides or soluble receptors have emerged as potential sequestering agents for toxic AGEs as potential therapies for diabetic complications.

Macrophage colony-stimulating factor rapidly enhances beta-migrating very low density lipoprotein metabolism in macrophages through activation of a Gi/o protein signaling pathway

Previous studies have examined lipoprotein metabolism by macrophages following prolonged exposure (>24 h) to macrophage colony-stimulating factor (M-CSF). Because M-CSF activates several signaling pathways that could rapidly affect lipoprotein metabolism, we examined whether acute exposure of macrophages to M-CSF alters the metabolism of either native or modified lipoproteins. Acute incubation of cultured J774 macrophages and resident mouse peritoneal macrophages with M-CSF markedly enhanced low density lipoproteins (LDL) and beta-migrating very low density lipoproteins (beta-VLDL) stimulated cholesteryl [(3)H]oleate deposition. In parallel, M-CSF treatment increased the association and degradation of (125)I-labeled LDL or beta-VLDL without altering the amount of lipoprotein bound to the cell surface. The increase in LDL and beta-VLDL metabolism did not reflect a generalized effect on lipoprotein endocytosis and metabolism because M-CSF did not alter cholesterol deposition during incubation with acetylated LDL. Moreover, M-CSF did not augment beta-VLDL cholesterol deposition in macrophages from LDL receptor (-/-) mice, indicating that the effect of M-CSF was mediated by the LDL receptor. Incubation of macrophages with pertussis toxin, a specific inhibitor of G(i/o) protein signaling, had no effect on cholesterol deposition during incubation with beta-VLDL alone, but completely blocked the augmented response promoted by M-CSF. In addition, incubation of macrophages with the direct G(i/o) protein activator, mastoparan, mimicked the effect of M-CSF by enhancing cholesterol deposition in cells incubated with beta-VLDL, but not acetylated LDL. In summary, M-CSF rapidly enhances LDL receptor-mediated metabolism of native lipoproteins by macrophages through activation of a G(i/o) protein signaling pathway. Together, these findings describe a novel pathway for regulating lipoprotein metabolism.

LY-294002-inhibitable PI 3-kinase and regulation of baseline rates of Na(+) transport in A6 epithelia

Blocker-induced noise analysis of epithelial Na(+) channels (ENaCs) was used to investigate how inhibition of an LY-294002-sensitive phosphatidylinositol 3-kinase (PI 3-kinase) alters Na(+) transport in unstimulated and aldosterone-prestimulated A6 epithelia. From baseline Na(+) transport rates (I(Na)) of 4.0 +/- 0.1 (unstimulated) and 9.1 +/- 0.9 microA/cm(2) (aldosterone), 10 microM LY-294002 caused, following a relatively small initial increase of transport, a completely reversible inhibition of transport within 90 min to 33 +/- 6% and 38 +/- 2% of respective baseline values. Initial increases of transport could be attributed to increases of channel open probability (P(o)) within 5 min to 143 +/- 17% (unstimulated) and 142 +/- 10% of control (aldosterone) from baseline P(o) averaging near 0.5. Inhibition of transport was due to much slower decreases of functional channel densities (N(T)) to 28 +/- 4% (unstimulated) and 35 +/- 3% (aldosterone) of control at 90 min. LY-294002 (50 microM) caused larger but completely reversible increases of P(o) (215 +/- 38% of control at 5 min) and more rapid but only slightly larger decreases of N(T). Basolateral exposure to LY-294002 induced no detectable effect on transport, P(o) or N(T). We conclude that an LY-294002-sensitive PI 3-kinase plays an important role in regulation of transport by modulating N(T) and P(o) of ENaCs, but only when presented to apical surfaces of the cells.

Macrophage class A scavenger receptor-mediated phagocytosis of Escherichia coli: role of cell heterogeneity, microbial strain, and culture conditions in vitro

Macrophage class A scavenger receptors (SR-AI and SR-AII) contribute to host defense by binding polyanionic ligands such as lipopolysaccharide and lipoteichoic acid. SR-A knockout (SR-A(-/-)) mice are more susceptible to endotoxic shock and Listeria monocytogenes infection in vivo, possibly due to decreased clearance of lipopolysaccharide and microorganisms, respectively. We have used flow cytometry to analyze the role of SR-A and other scavenger-like receptors in phagocytosis of bacteria in vitro. Chinese hamster ovary cells stably transfected with human SR-A bound Escherichia coli and Staphylococcus aureus but ingested few organisms. Primary human monocyte-derived macrophages (Mphi) bound and ingested E. coli more efficiently, and this was partially but selectively blocked by the general SR inhibitor, poly(I). A specific and selective role for SR-A was shown, since bone marrow culture-derived Mphi from SR-A(-/-) mice ingested fewer E. coli organisms than did wild-type cells, while uptake of antibody-opsonized E. coli was unaffected. SR-A-dependent uptake of E. coli varied with the bacterial strain; ingestion of DH5alpha and K1 by SR-A(-/-) Mphi was reduced by 30 to 60% and 70 to 75%, respectively. Phagocytosis and endocytosis via SR-A were markedly down-modulated when Mphi were plated on serum-coated tissue culture plastic compared to bacteriologic plastic, where cell adhesion is mediated by SR-A and CR3, respectively. This paper demonstrates that SR-A can bind and ingest bacteria directly, consistent with a role in host defense in vivo, and highlights the importance of the source of the Mphi, bacterial strain, and culture conditions on receptor function in vitro.

Advanced glycation end products: a Nephrologist's perspective

Advanced glycation end products (AGEs) are a heterogeneous group of molecules that accumulate in plasma and tissues with advancing age, diabetes, and renal failure. There is emerging evidence that AGEs are potential uremic toxins and may have a role in the pathogenesis of vascular and renal complications associated with diabetes and aging. AGEs are formed when a carbonyl of a reducing sugar condenses with a reactive amino group in target protein. These toxic molecules interact with specific receptors and elicit pleiotropic responses. AGEs accelerate atherosclerosis through cross-linking of proteins, modification of matrix components, platelet aggregation, defective vascular relaxation, and abnormal lipoprotein metabolism. In vivo and in vitro studies indicate that AGEs have a vital role in the pathogenesis of diabetic nephropathy and the progression of renal failure. The complications of normal aging, such as loss of renal function, Alzheimer's disease, skin changes, and cataracts, may also be mediated by progressive glycation of long-lived proteins. AGEs accumulate in renal failure as a result of decreased excretion and increased generation resulting from oxidative and carbonyl stress of uremia. AGE-modified beta(2)-microglobulin is the principal pathogenic component of dialysis-related amyloidosis in patients undergoing dialysis. Available dialytic modalities are not capable of normalizing AGE levels in patients with end-stage renal disease. A number of reports indicated that restoration of euglycemia with islet-cell transplantation normalized and prevented further glycosylation of proteins. Aminoguanidine (AGN), a nucleophilic compound, not only decreases the formation of AGEs but also inhibits their action. A number of studies have shown that treatment with AGN improves neuropathy and delays the onset of retinopathy and nephropathy. N-Phenacylthiazolium bromide is a prototype AGE cross-link breaker that reacts with and can cleave covalent AGE-derived protein cross-links. Thus, there is an exciting possibility that the complications of diabetes, uremia, and aging may be prevented with these novel agents.

Coordinate regulation of the alpha(2)-macroglobulin signaling receptor and the low density lipoprotein receptor-related protein/alpha(2)-macroglobulin receptor by insulin

We have studied insulin-dependent regulation of macrophage alpha(2)-macroglobulin signaling receptors (alpha(2)MSR) and low density lipoprotein receptor-related protein/alpha(2)M receptors (LRP/alpha(2)MR) employing cell binding of (125)I-alpha(2)M*, inhibition of binding by receptor-associated protein (RAP) or Ni(2+), LRP/alpha(2)MR mRNA levels, and generation of second messengers. Insulin treatment increased the number of alpha(2)M* high (alpha(2)MSR) and low (LRP/alpha(2)MR) affinity binding sites from 1, 600 and 67,000 to 2,900 and 115,200 sites per cell, respectively. Neither RAP nor Ni(2+) blocked the binding of (125)I-alpha(2)M* to alpha(2)MSR on insulin- or buffer-treated cells, but they both blocked binding to LRP/alpha(2)MR. Insulin significantly increased LRP/alpha(2)MR mRNA levels in a dose- and time-dependent manner. Insulin-augmented (125)I-alpha(2)M* binding to macrophages was severely reduced by wortmannin, LY294002, PD98059, SB203580, or rapamycin. The increase in alpha(2)MSR receptor synthesis was reflected by augmented generation of IP(3) and increased [Ca(2+)](i) levels upon receptor ligation. Incubation of macrophages with wortmannin, LY294002, PD98059, SB203580, rapamycin, or antibodies against insulin receptors before insulin treatment and alpha(2)M* stimulation significantly reduced the insulin-augmented increase in IP(3) and [Ca(2+)](i) levels. Pretreatment of cells with actinomycin D or cycloheximide blocked the synthesis of new alpha(2)MSR. In conclusion, we show here that insulin coordinately regulates macrophage alpha(2)MSR and LRP/alpha(2)MR, utilizing both the PI 3-kinase and Ras signaling pathways to induce new synthesis of these receptors.

Metabolism of modified LDL and foam cell formation in murine macrophage-like RAW 264 cells

The uptake of modified low density lipoprotein (LDL) by arterial macrophages is a key event in the atherogenesis. We studied 1) the uptake and degradation of modified LDL, 2) LDL recognition by specific receptors, and 3) the foam cell formation with murine macrophage-like RAW 264 cells in vitro. The cells took up and degraded effectively 125I-labeled acetylated LDL (Ac-LDL) and aggregated LDL (Aggr-LDL). Also oxidized LDL (Ox-LDL) was taken up but it was degraded poorly. The degradation of 125I-Ac-LDL was efficiently competed by both unlabeled Ac-LDL and Ox-LDL, whereas the degradation of 125I-Ox-LDL was partially competed by unlabeled Ox-LDL and Aggr-LDL but not at all by unlabeled Ac-LDL. The incubation with increasing concentrations of Ac-LDL, Aggr-LDL or Ox-LDL resulted in marked foam cell formation in the RAW 264 cells. Ox-LDL was cytotoxic at 500 to 1000 microg/ml concentrations. The results show that RAW 264 cells have at least two classes of receptors for modified lipoproteins: one that recognizes both Ox-LDL and Ac-LDL, and is similar to the scavenger receptors, and another that recognizes Ox-LDL but not Ac-LDL. RAW 264 cells are a convenient model cell line for examining the metabolism of modified lipoproteins, not only that of Ac-LDL but also that of Ox-LDL and Aggr-LDL, and cellular accumulation of lipids derived from modified LDL.

Receptors for proteins modified by advanced glycation endproducts (AGE)--their functional role in atherosclerosis

Long-term incubation of proteins with glucose leads, through the formation of early stage products such as Schiff base and Amadori rearrangement products, to the formation of advanced glycation end products (AGE). Recent studies of AGE-structures as well as the receptor for AGE-proteins (AGE-receptors) have emphasized the involvement of protein modification by AGE in aging and age-enhanced disease processes. Immunohistochemical analyses of human atherosclerotic lesions using a monoclonal anti-AGE antibody have demonstrated diffuse extracellular AGE-deposition as well as dense intracellular AGE-deposition in macrophage- and vascular smooth muscle cell (SMC)-derived foam cells. In vitro experiments using both CHO cells overexpressing macrophage scavenger receptor-A (MSR-A) and peritoneal macrophages from MSR-A-knockout mice have shown that the MSR-A plays a major role in endocytic uptake of AGE-proteins by macrophages. Furthermore, in vitro experiments with rabbit arterial SMCs demonstrated a novel AGE-receptor mediating endocytosis of AGE-proteins. These in vivo and in vitro experiments suggest that AGE-proteins formed extracellularly in atherosclerotic lesions are endocytosed by macrophages through MSR-A in the early stage, and by SMCs through the novel AGE-receptor in the advanced stage, implicating functional contribution of the AGE-receptor-mediated interaction of AGE-proteins with these cells to atherosclerotic processes in arterial walls.

Role of macrophage scavenger receptors in hepatic granuloma formation in mice

In mice homozygous for the gene mutation for type I and type II macrophage scavenger receptors (MSR-A), MSR-A-/-, the formation of hepatic granulomas caused by a single intravenous injection of heat-killed Corynebacterium parvum was delayed significantly for 10 days after injection, compared with granuloma formation in wild-type (MSR-A+/+) mice. In the early stage of granuloma formation, numbers of macrophages and their precursor cells were significantly reduced in MSR-A-/- mice compared with MSR-A+/+ mice. In contrast to MSR-A+/+ mice, no expression of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and interferon-gamma mRNA was observed in MSR-A-/- mice by 3 days after injection. Also in MSR-A-/- mice, uptake of C. parvum by Kupffer cells and monocyte-derived macrophages in the early stage of granuloma formation was lower and elimination of C. parvum from the liver was slower than in MSR-A+/+ mice. In the livers of MSR-A+/+ mice, macrophages and sinusoidal endothelial cells possessed MSR-A, but this was not seen in the livers of MSR-A-/- mice. In both MSR-A-/- and MSR-A+/+ mice, expression of other scavenger receptors was demonstrated. These data suggest that MSR-A deficiency impairs the uptake and elimination of C. parvum by macrophages and delays hepatic granuloma formation, particularly in the early stage.