Effects of metformin and pioglitazone on serum pentosidine levels in type 2 diabetes mellitus

Bone effects of metformin monotherapy and its combination with teneligliptin: A 12-week follow-up study in patients with type 2 diabetes mellitus

AIMS

The skeletal effects of metformin monotherapy and in combination with teneligliptin are not well illustrated in patients with T2DM. To address this, we conducted an observational study to evaluate the effect of these oral hypoglycemic agents on bone turnover markers.

METHODS

We recruited patients with T2DM and first-ever prescribed metformin monotherapy or metformin combined with teneligliptin from a tertiary care teaching hospital in New Delhi, North India. Both bone formation and resorption markers, IL-6 and PTD, were estimated along with glycated hemoglobin at baseline and 12 weeks.

RESULTS

In both groups, hbA1c levels decreased significantly from baseline to 12 weeks. In the metformin-treated group, β-CTX, sRANKL, IL-6, and PTD decreased significantly, and no significant changes were observed in P1NP, OC, BAP, or OPG at 12 weeks from baseline. In the metformin + teneligliptin group, BAP, β-CTX, sRANKL, IL-6, and PTD decreased significantly, and no significant changes were observed in P1NP, OC, or OPG after 12 weeks from baseline.

CONCLUSIONS

The positive bone outcome of metformin or teneligliptin was linked to bone resorption rather than bone formation and was independent of changes in HbA1c or PTD. However, these results must be confirmed with well-designed RCTs with more extended follow-up periods.

Glucose transport, transporters and metabolism in diabetic retinopathy

Diabetic retinopathy (DR) is the most common reason for blindness in working-age individuals globally. Prolonged high blood glucose is a main causative factor for DR development, and glucose transport is prerequisite for the disturbances in DR caused by hyperglycemia. Glucose transport is mediated by its transporters, including the facilitated transporters (glucose transporter, GLUTs), the "active" glucose transporters (sodium-dependent glucose transporters, SGLTs), and the SLC50 family of uniporters (sugars will eventually be exported transporters, SWEETs). Glucose transport across the blood-retinal barrier (BRB) is crucial for nourishing the neuronal retina in the context of retinal physiology. This physiological process primarily relies on GLUTs and SGLTs, which mediate the glucose transportation across both the cell membrane of retinal capillary endothelial cells and the retinal pigment epithelium (RPE). Under diabetic conditions, increased accumulation of extracellular glucose enhances the retinal cellular glucose uptake and metabolism via both glycolysis and glycolytic side branches, which activates several biochemical pathways, including the protein kinase C (PKC), advanced glycation end-products (AGEs), polyol pathway and hexosamine biosynthetic pathway (HBP). These activated biochemical pathways further increase the production of reactive oxygen species (ROS), leading to oxidative stress and activation of Poly (ADP-ribose) polymerase (PARP). The activated PARP further affects all the cellular components in the retina, and finally resulting in microangiopathy, neurodegeneration and low-to-moderate grade inflammation in DR. This review aims to discuss the changes of glucose transport, glucose transporters, as well as its metabolism in DR, which influences the retinal neurovascular unit (NVU) and implies the possible therapeutic strategies for treating DR.

Methylglyoxal in the Brain: From Glycolytic Metabolite to Signalling Molecule

Advances in molecular biology technology have piqued tremendous interest in glycometabolism and bioenergetics in homeostasis and neural development linked to ageing and age-related diseases. Methylglyoxal (MGO) is a by-product of glycolysis, and it can covalently modify proteins, nucleic acids, and lipids, leading to cell growth inhibition and, eventually, cell death. MGO can alter intracellular calcium homeostasis, which is a major cell-permeant precursor to advanced glycation end-products (AGEs). As side-products or signalling molecules, MGO is involved in several pathologies, including neurodevelopmental disorders, ageing, and neurodegenerative diseases. In this review, we demonstrate that MGO (the metabolic side-product of glycolysis), the GLO system, and their analogous relationship with behavioural phenotypes, epigenetics, ageing, pain, and CNS degeneration. Furthermore, we summarise several therapeutic approaches that target MGO and the glyoxalase (GLO) system in neurodegenerative diseases.

Urinary sulphated glycosaminoglycans excretion in obese patients with type 2 diabetes mellitus treated with metformin

OBJECTIVE

The pattern of urinary excretion of total sulphated glycosaminoglycans (GAGs) and their particular types: chondroitin sulphate/dermatan sulphate (CS/DS) and heparan sulphate (HS) was analysed in obese patients with type 2 diabetes mellitus (T2DM) treated with metformin in monotherapy for the period of six months.

METHODS

The urinary sulphated glycosaminoglycans were quantitated using standardised dye (1.9-dimethylmethylene blue)-binding method and normalised to creatinine level.

RESULTS

Urinary total GAGs, CS/DS and HS levels were significantly higher in untreated diabetic patients in comparison to healthy subjects. Moreover, it was observed that urinary total GAGs, CS/DS and HS levels in diabetic patients after six-month metformin therapy were significantly decreased versus pre-treatment situation.

CONCLUSIONS

The obtained results suggest that the six-month treatment with metformin in obese patients with T2DM has a regulating influence on the systemic changes in proteoglycans/glycosaminoglycans, resulting in a decrease in the urinary excretion of total GAGs, CS/DS and HS.

Prediction of Femoral Strength Based on Bone Density and Biochemical Markers in Elderly Men With Type 2 Diabetes Mellitus

Purpose: Effects of bone density, bone turnover and advanced glycation end products (AGEs) on femoral strength (FS) are still unclear in patients with type 2 diabetes mellitus (T2DM). This study aims to assess and predict femoral strength and its influencing factors in elderly men with T2DM. Methods: T2DM patients (n = 10, mean age, 66.98 years) and age-matched controls (n = 8, mean age, 60.38 years) were recruited. Femoral bone mineral density (BMD) and serum biochemical indices of all subjects were measured. FS was evaluated through finite element analysis based on quantitative computed tomography. Multiple linear regression was performed to obtain the best predictive models of FS and to analyze the ability of predictors of FS in both groups. Results: FS (p = 0.034), HbA1c (p = 0.000) and fasting blood glucose (p = 0.000) levels of T2DM group were significantly higher than those of control group; however, the P1NP level (p = 0.034) was significantly lower. FS was positively correlated with femoral neck T score (FNTS) (r = 0.794, p < 0.01; r = 0.881, p < 0.01) in both groups. FS was correlated with age (r = -0.750, p < 0.05) and pentosidine (r = -0.673, p < 0.05) in T2DM group. According to multiple linear regression, FNTS and P1NP both contributed to FS in two groups. P1NP significantly improved the prediction of FS in both groups, but significant effect of FNTS on predicting FS was only presented in control group. Furthermore, pentosidine, age and HbA1c all played significant roles in predicting FS of T2DM. Conclusion: Femoral strength was higher in elderly men with T2DM, which might be caused by higher BMD and lower bone turnover rate. Moreover, besides BMD and bone formation level, AGEs, blood glucose and age might significantly impact the prediction of femoral strength in T2DM.

Glucose Metabolism in Osteoblasts in Healthy and Pathophysiological Conditions

Bone tissue in vertebrates is essential to performing movements, to protecting internal organs and to regulating calcium homeostasis. Moreover, bone has also been suggested to contribute to whole-body physiology as an endocrine organ, affecting male fertility; brain development and cognition; and glucose metabolism. A main determinant of bone quality is the constant remodeling carried out by osteoblasts and osteoclasts, a process consuming vast amounts of energy. In turn, clinical conditions associated with impaired glucose metabolism, including type I and type II diabetes and anorexia nervosa, are associated with impaired bone turnover. As osteoblasts are required for collagen synthesis and matrix mineralization, they represent one of the most important targets for pharmacological augmentation of bone mass. To fulfill their function, osteoblasts primarily utilize glucose through aerobic glycolysis, a process which is regulated by various molecular switches and generates adenosine triphosphate rapidly. In this regard, researchers have been investigating the complex processes of energy utilization in osteoblasts in recent years, not only to improve bone turnover in metabolic disease, but also to identify novel treatment options for primary bone diseases. This review focuses on the metabolism of glucose in osteoblasts in physiological and pathophysiological conditions.

Which Is a Better Skeletal Muscle Mass Index for the Evaluation of Physical Abilities: The Present Height or Maximum Height?

Objective Sarcopenia and osteoporosis often coexist in older adults. Sarcopenia is diagnosed using the skeletal muscle mass index (SMI), which is calculated as the appendicular skeletal muscle mass (ASM)/(present height)², although patients with osteoporosis frequently have a loss of body height. We therefore investigated whether the present height or maximum height is more useful for calculating the SMI in the evaluation of physical abilities. Methods We conducted a cross-sectional study to investigate the association of the SMI with physical abilities, such as the grip strength and gait speed, in 587 postmenopausal women. The SMI was evaluated using whole-body dual-energy X-ray absorptiometry (DXA). The SMI [(ASM)/(present height)²], modified SMI (mSMI) [(ASM)/(maximum height)²], and SMI difference (ΔSMI) (mSMI-SMI) were calculated. Results Age and body mass index (BMI)-adjusted regression analyses showed that the SMI (β=0.30, p<0.001 and β=0.14, p=0.034) and mSMI (β=0.40, p<0.001 and β=0.29, p<0.001) were positively associated while the ΔSMI was negatively associated with the grip strength and gait speed (β=-0.15, p<0.001 and β=-0.24, p<0.001, respectively). Furthermore, the age, BMI, and presence of osteoporotic fractures-adjusted logistic regression analyses showed that a low mSMI (<5.4 kg/m²) was significantly associated with a low grip strength (<18 kg) and slow gait speed (1.0 m/s) [odds ratio (OR) =2.45, 95% confidence interval (CI) =1.52-3.95 per SD increase, p<0.001; and OR=1.73, 95% CI=1.01-2.96, p=0.042, respectively], although a low SMI showed no such relationship (p=0.052 and p=0.813, respectively). Conclusion The mSMI using the maximum height is more useful for evaluating physical abilities than conventional SMI estimation in postmenopausal women.

A scoring assessment tool for the risk of vertebral fractures in patients with type 2 diabetes mellitus

BACKGROUND

Development of assessment tool for fracture risk is an urgent task, because bone mineral density (BMD) is less useful for evaluating fracture risk in type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

In total, 808 T2DM patients were enrolled in this cross-sectional study. To develop a scoring assessment tool using clinical risks for vertebral fracture (VF), we evaluated which variables were associated with VF by logistic regression analysis, and categorized these variables based on cut-off values obtained by using receiver operating characteristic (ROC) curves. For calculation of the score, the relative weight of the factors was determined, and a tentative score was assigned. Then, cut-off point of the score was examined to predict VF.

RESULTS

Logistic regression analyses showed that age, diabetes duration, body mass index (BMI), serum albumin, and T score at femoral neck (FN-T score) were associated with VF risk. Parameter estimates for each risk factor obtained by logistic analyses were converted to risk scores (maximum score 23). ROC analysis showed that 8.5 was the cut-off value for detecting VF. Multiple logistic regression analysis adjusted for confounding factors showed that score ≥9 was significantly associated with an increased risk of prevalent VF (odds ratio 1.99, 95% confidence interval 1.22-3.24, p = 0.006).

CONCLUSIONS

This is the first study to show that a scoring assessment tool using age, duration of diabetes, BMI, serum albumin, and FN-T score is useful to estimate VF risk in patients with T2DM, being more sensitive than BMD alone in detecting bone fragility.

Higher Serum Uric Acid is a Risk Factor of Reduced Muscle Mass in Men with Type 2 Diabetes Mellitus

OBJECTIVE

Sarcopenia has been recognized as a diabetic complication, and hyperuricemia is often accompanied by type 2 diabetes mellitus (T2DM). However, it is unknown whether serum uric acid (UA) levels are associated with reduced muscle mass in T2DM.

METHODS

We conducted a cross-sectional study to investigate the association of serum UA with muscle mass in 401 subjects with T2DM (209 men and 192 postmenopausal women). The relative skeletal muscle mass index (RSMI) was evaluated using whole-body dual-energy x-ray absorptiometry.

RESULTS

Multiple regression analyses adjusted for body weight, age, serum creatinine, hemoglobin A1c (HbA1c), and duration of T2DM showed that serum UA was negatively associated with RSMI in all subjects and men with T2DM (β=-0.13, p=0.001 and β=-0.17, p=0.003, respectively). Moreover, logistic regression analyses adjusted for these confounding factors showed that a higher serum UA level was significantly associated with low RSMI in men with T2DM [odds ratio (OR)=1.94, 95% confidence interval (CI)=1.10-3.45 per SD increase, p=0.023]. In addition, higher serum UA levels were significantly associated with low RSMI after additional adjustment for age, duration of T2DM, HbA1c level, serum creatinine level, and sex in all subjects with T2DM [OR=1.80, 95% CI=1.20-2.72 per SD increase, p=0.005].

CONCLUSIONS

The present study showed for the first time that higher serum UA is an independent risk factor of reduced muscle mass in men with T2DM.

The clinical usefulness of glycated albumin in patients with diabetes and chronic kidney disease: Progress and challenges

Prolonged hyperglycemia leads to a non-enzymatic glycation of proteins, and produces Amadori products, such as glycated albumin (GA) and glycated hemoglobin (HbA1c). The utility of HbA1c in the setting of chronic kidney disease (CKD) may be problematic since altered lifespan of red blood cells, use of iron and/or erythropoietin therapy, uremia and so on. Therefore, as an alternative marker, GA has been suggested as a more reliable and sensitive glycemic index in patients with CKD. In addition to the mean plasma glucose concentration, GA also reflects postprandial plasma glucose and glycemic excursion. Besides, with a half-life of approximately 2-3 weeks, GA may reflect the status of blood glucose more rapidly than HbA1c. GA is also an early precursor of advanced glycation end products (AGEs), which cause alterations in various cellular proteins and organelles. Thus, high GA levels may correlate with adverse outcomes of patients with CKD. In this review, the clinical usefulness of GA was discussed, including a comparison of GA with HbA1c, the utility and limitations of GA as a glycemic index, its potential role in pathogenesis of diabetic nephropathy and the correlations between GA levels and outcomes, specifically in patients with diabetes and CKD.

Mechanistic targeting of advanced glycation end-products in age-related diseases

Glycative stress, caused by the accumulation of cytotoxic and irreversibly-formed sugar-derived advanced glycation end-products (AGEs), contributes to morbidity associated with aging, age-related diseases, and metabolic diseases. In this review, we summarize pathways leading to formation of AGEs, largely from sugars and glycolytic intermediates, and discuss detoxification of AGE precursors, including the glyoxalase system and DJ-1/Park7 deglycase. Disease pathogenesis downstream of AGE accumulation can be cell autonomous due to aggregation of glycated proteins and impaired protein function, which occurs in ocular cataracts. Extracellular AGEs also activate RAGE signaling, leading to oxidative stress, inflammation, and leukostasis in diabetic complications such as diabetic retinopathy. Pharmaceutical agents have been tested in animal models and clinically to diminish glycative burden. We summarize existing strategies and point out several new directions to diminish glycative stress including: plant-derived polyphenols as AGE inhibitors and glyoxalase inducers; improved dietary patterns, particularly Mediterranean and low glycemic diets; and enhancing proteolytic capacities of the ubiquitin-proteasome and autophagy pathways that are involved in cellular clearing of AGEs.

Pioglitazone inhibits advanced glycation induced protein modifications and down-regulates expression of RAGE and NF-κB in renal cells

The present work aims to determine the effect of pioglitazone on in-vitro albumin glycation and AGE-RAGE induced oxidative stress and inflammation. Bovine serum albumin was glycated by methylglyoxal in absence or presence of pioglitazone. Glycation markers (fructosamine, carbonyl groups, β-amyloid aggregation, thiol groups, bilirubin binding capacity and AOPP); protein conformational changes (native-PAGE and HPLC analysis) were determined. Cellular study was done by estimating antioxidants, ROS levels, expression profile of membrane RAGE, NF-κB and levels of inflammatory cytokines (IL-6, TNF-α) using HEK-293 cell line. We observed that levels of glycation markers were reduced at higher concentration of pioglitazone as compared to glycated albumin. Structural analysis of glycated albumin showed inhibition of protein migration and structural changes when treated with pioglitazone. Pioglitazone has potentially restored cellular antioxidants and reduced levels of IL-6 and TNF-α by declining expression of membrane RAGE and NF-κB. In conclusion, pioglitazone preferentially binds to protein and alleviates protein structural changes by maintaining its integrity. Additionally, it suppresses RAGE and NF-κB levels hence alleviate cellular oxidative stress and inflammation.

Does a Treadmill Running Exercise Contribute to Preventing Deterioration of Bone Mineral Density and Bone Quality of the Femur in KK-Ay Mice, a Type 2 Diabetic Animal Model?

Although it has been recently shown that type 2 diabetics have an increased risk of hip fracture, the effects of exercise therapy to prevent this have not been clarified. We examined whether a treadmill running exercise contributes to the bone mineral density (BMD) and bone microarchitecture of the femur and what kind of exercise intensity and duration are optimum in type 2 diabetes mellitus using KK-Ay diabetic mice. The mice were divided into two running groups, one fast speed and short duration (FS), the other slow speed and long duration (SL), and a group of controls with no running (CO). The running exercise was started when the mice were 8 weeks of age, and continued once a day 5 days per week for 10 weeks. Ten weeks after the start of the running exercise, the BMD of the proximal region and mid-diaphysis in the SL were significantly higher in comparison with that in the CO, whereas there was no difference in bone microarchitecture among the three groups. Blood glucose, insulin levels, and visceral fat contents in the SL were significantly lower than those in the CO and FS. Bone resorption protein and C-reactive protein levels in the SL were significantly lower than those in the CO. These results suggest that slow, long duration loading is better for both bone and glycemic control than fast, short duration loading in type 2 diabetes.

Association of osteoglycin and FAM5C with bone turnover markers, bone mineral density, and vertebral fractures in postmenopausal women with type 2 diabetes mellitus

OBJECTIVE

Accumulating evidence suggests a reciprocal relationship between muscle and bone. Previous in vitro studies showed that the muscle-derived factors, osteoglycin (OGN) and family with sequence similarity 5, member C (FAM5C), regulate osteoblastic differentiation. However, there are no reports investigating the association between circulating OGN and FAM5C and bone metabolism in humans.

DESIGN

We conducted a cross-sectional study and investigated the association of serum OGN and FAM5C levels and muscle mass examined by whole-body dual-energy x-ray absorptiometry with bone mineral density (BMD), bone turnover markers, and the presence of vertebral fractures (VFs) in 156 postmenopausal women with type 2 diabetes mellitus (T2DM).

RESULTS

Multiple regression analysis adjusted for age, duration of T2DM, body mass index, serum creatinine, and log(hemoglobin A1c) showed that log(OGN) was negatively associated with BMD at the femoral neck (β=-0.17, p=0.014). Serum OGN levels were higher in subjects with VFs than in those without VFs [mean±standard deviation (SD): 100.2±84.7 vs. 74.4±31.7pg/mL, p=0.013]. Moreover, logistic regression analysis adjusted for the confounding factors described above showed that the serum OGN level was positively associated with the presence of VFs (odds ratio=1.84, 95% confidence interval=1.03-3.29 per SD increase, p=0.039). In contrast, neither the serum FAM5C level nor muscle mass indices were associated with bone turnover markers and the presence of VFs.

CONCLUSIONS

The present study showed for the first time that higher serum OGN levels were associated with decreased BMD and increased risk of vertebral fractures in postmenopausal women with T2DM.

Reduced muscle mass and accumulation of visceral fat are independently associated with increased arterial stiffness in postmenopausal women with type 2 diabetes mellitus

BACKGROUND

Several studies showed that sarcopenia and visceral obesity are associated with arterial stiffness. Thus, their coexistence may be a crucial risk factor of arteriosclerosis. However, little is known about the cross relationships among muscle mass, visceral fat mass, and arterial stiffness in type 2 diabetes mellitus (T2DM).

METHODS

We recruited 97 postmenopausal women with T2DM and examine the association of muscle mass and visceral fat mass with brachial-ankle pulse wave velocity (baPWV). Relative skeletal muscle mass index (RSMI) and %trunk fat were evaluated by whole body dual-energy X-ray absorptiometry. Subcutaneous and visceral fat areas were measured by computed tomography.

RESULTS

Multiple regression analyses adjusted for age, duration of T2DM, systolic blood pressure, body mass index, HbA1c, serum creatinine, low-density lipoprotein-cholesterol, uric acid, and the usage of anti-hypertensive drug showed that RSMI was negatively associated with baPWV (β=-0.40, p=0.027), while %trunk fat and visceral fat area were positively associated with it (β=0.29, p=0.004 and β=0.51, p=0.001, respectively). Moreover, after additional adjustment for RSMI, %trunk fat and visceral fat area were positively associated with baPWV (β=0.26, p=0.010 and β=0.46, p=0.003, respectively) although the association between RSMI and baPWV became marginal after additional adjustment for %trunk fat or visceral fat area (β=-0.30, p=0.146 and β=-0.30, p=0.085, respectively).

CONCLUSIONS

Reduced muscle mass and increased visceral fat are independently associated with increased arterial stiffness in postmenopausal women with T2DM.

Reduction in Endogenous Insulin Secretion is a Risk Factor of Sarcopenia in Men with Type 2 Diabetes Mellitus

Sarcopenia has recently attracted widespread attention, because it increases risks of fall and bedridden. Although patients with type 2 diabetes mellitus (T2DM) are known to have lower muscle mass of limbs than healthy people, the mechanism is still unclear. We thus examined the association of muscle mass with parameters of endogenous insulin secretion such as fasting immunoreactive insulin, fasting C-peptide immunoreactivity (CPR), and daily urine CPR in 191 men with T2DM. Muscle mass of arms and legs was evaluated by dual-energy X-ray absorptiometry, and we calculated relative skeletal muscle index (RSMI), which is useful for the diagnosis of sarcopenia. Multiple regression analyses adjusted for age, duration of T2DM, serum creatinine, HbA1c, and insulin-like growth factor-I showed that each parameter of endogenous insulin was significantly and positively correlated with muscle mass of arms and legs as well as RSMI (p < 0.05). Moreover, logistic regression analyses adjusted for confounding factors mentioned above showed that each parameter of endogenous insulin was significantly lower in subjects with sarcopenia than those without it (p < 0.05). In conclusion, reduction in endogenous insulin secretion is an independent risk factor of sarcopenia in men with T2DM.

Uremic Toxicity of Advanced Glycation End Products in CKD

Advanced glycation end products (AGEs), a heterogeneous group of compounds formed by nonenzymatic glycation reactions between reducing sugars and amino acids, lipids, or DNA, are formed not only in the presence of hyperglycemia, but also in diseases associated with high levels of oxidative stress, such as CKD. In chronic renal failure, higher circulating AGE levels result from increased formation and decreased renal clearance. Interactions between AGEs and their receptors, including advanced glycation end product-specific receptor (RAGE), trigger various intracellular events, such as oxidative stress and inflammation, leading to cardiovascular complications. Although patients with CKD have a higher burden of cardiovascular disease, the relationship between AGEs and cardiovascular disease in patients with CKD is not fully characterized. In this paper, we review the various deleterious effects of AGEs in CKD that lead to cardiovascular complications and the role of these AGEs in diabetic nephropathy. We also discuss potential pharmacologic approaches to circumvent these deleterious effects by reducing exogenous and endogenous sources of AGEs, increasing the breakdown of existing AGEs, or inhibiting AGE-induced inflammation. Finally, we speculate on preventive and therapeutic strategies that focus on the AGE-RAGE axis to prevent vascular complications in patients with CKD.

Advanced glycation end product accumulation: a new enemy to target in chronic kidney disease?

PURPOSE OF REVIEW

The critical role of advanced glycation end products (AGEs) in the progression of chronic diseases and their complications has recently become more apparent. This review summarizes the recent contributions to the field of AGEs in chronic kidney disease (CKD).

RECENT FINDINGS

Over the past 3 decades, AGEs have been implicated in the progression of CKD, and specifically diabetic nephropathy. Although numerous in-vitro and in-vivo studies highlight the detrimental role of AGEs accumulation in tissue injury, few prospective human studies or clinical trials show that inhibiting this process ameliorates disease. Nonetheless, recent studies have focused on the novel mechanisms that contribute to end-organ injury as a result of AGEs accumulation, as well as novel targets of therapy in kidney disease.

SUMMARY

As the prevalence and the incidence of CKD rises in the United States, it is essential to identify therapeutic strategies that either delay the progression of CKD or improve mortality in this population. The focus of this review is on highlighting the recent studies that advance our current understanding of the mechanisms mediating AGEs-induced CKD progression, as well as novel treatment strategies that have the potential to abrogate this disease process.

VIDEO ABSTRACT

http://links.lww.com/CONH/A12.

Inhibitory effect of metformin and pyridoxamine in the formation of early, intermediate and advanced glycation end-products

Background

Non-enzymatic glycation is the addition of free carbonyl group of reducing sugar to the free amino groups of proteins, resulting in the formation of a Schiff base and an Amadori product. Dihydroxyacetone (DHA) is one of the carbonyl species which reacts rapidly with the free amino groups of proteins to form advanced glycation end products (AGEs). The highly reactive dihydroxyacetone phosphate is a derivative of dihydroxyacetone (DHA), and a product of glycolysis, having potential glycating effects to form AGEs. The formation of AGEs results in the generation of free radicals which play an important role in the pathophysiology of aging and diabetic complications. While the formation of DHA-AGEs has been demonstrated previously, no extensive studies have been performed to assess the inhibition of AGE inhibitors at all the three stages of glycation (early, intermediate and late) using metformin (MF) and pyridoxamine (PM) as a novel inhibitor.

Methodology/Principal Findings

In this study we report glycation of human serum albumin (HSA) & its characterization by various spectroscopic techniques. Furthermore, inhibition of glycation products at all the stages of glycation was also studied. Spectroscopic analysis suggests structural perturbations in the HSA as a result of modification which might be due to generation of free radicals and formation of AGEs.

Conclusion

The inhibition in the formation of glycation reaction reveals that Pyridoxamine is a better antiglycating agent than Metformin at all stages of the glycation (early, intermediate and late stages).

Comparative effects of pioglitazone and metformin on oxidative stress markers in newly diagnosed type 2 diabetes patients: a randomized clinical trial

AIMS

Recent studies have suggested that pioglitazone exerts anti-oxidant properties which may countervail oxidative stress (OS). We aimed to elucidate the effects of pioglitazone on OS modulation and to compare its effects with metformin.

METHODS

Data from the randomized clinical trial (registration no.NCT01521624) were used. Newly diagnosed type 2 diabetes patients were assigned to pioglitazone 30mg daily (n=30), metformin 1000mg daily (n=50), or no medication (n=49). Recommendations for exercise and dietary modifications were provided for three groups. Serum concentrations of advanced oxidation protein products(AOPP), advanced glycation end products(AGE), ferritin reducing ability of plasma(FRAP), and enzymatic activities of paraoxonase(PON), lecithin-cholesterol asyltransferase(LCAT), and lipoprotein lipase(LPL) were measured at baseline and after three months.

RESULTS

In comparison with no medication, pioglitazone proved to be superior in OS amelioration (p<0.05 in all analyses). Compared with metformin, both medications were equally effective in decrement of AOPP and AGE, along with increment of PON (p=0.688, 0.140, and 0.273, respectively). FRAP concentrations increased significantly with metformin (p=0.012). On the other hand, pioglitazone yielded better efficacy in restoration of LCAT and LPL enzymatic activities (p=0.037, and <0.001, respectively).

CONCLUSIONS

Similar to metformin, three months treatment with Pioglitazone is beneficial in terms of OS alleviation and anti-oxidant capacity restoration.

Current therapeutic interventions in the glycation pathway: evidence from clinical studies

The increased formation of advanced glycation endproducts (AGEs) constitutes a potential mechanism of hyperglycaemia-induced micro- and macrovascular disease in diabetes. In vitro and animal experiments have shown that various interventions can inhibit formation and/or actions of AGEs, in particular the specific AGE inhibitor aminoguanidine and the AGEs crosslink breaker alagebrium, and the B vitamins pyridoxamine and thiamine, and the latter's synthetic derivative, benfotiamine. The potential clinical value of these interventions, however, remains to be established. The present review provides, from the clinical point of view, an overview of current evidence on interventions in the glycation pathway relating to (i) the clinical benefits of specific AGE inhibitors and AGE breakers and (ii) the potential AGE-inhibiting effects of therapies developed for purposes unrelated to the glycation pathway. We found that safety and/or efficacy in clinical studies with the specific AGE inhibitor, aminoguanidine and the AGE breaker, alagebrium, appeared to be a concern. The clinical evidence on the potential AGE-inhibiting effects of B vitamins is still limited. Finally, current evidence for AGE inhibition by therapies developed for purposes unrelated to glycation is limited due to a large heterogeneity in study designs and/or measurement techniques, which have often been sub-optimal. We conclude that, clinical evidence on interventions to inhibit formation and/or action of AGEs is currently weak and unconvincing.

Redox proteomics in study of kidney-associated hypertension: new insights to old diseases

SIGNIFICANCE

The kidney helps to maintain low blood pressure in the human body, and impaired kidney function is a common attribute of aging that is often associated with high blood pressure (hypertension). Kidney-related pathologies are important contributors (either directly or indirectly) to overall human mortality. In comparison with other organs, kidney has an unusually wide range of oxidative status, ranging from the well-perfused cortex to near-anoxic medulla.

RECENT ADVANCES

Oxidative stress has been implicated in many kidney pathologies, especially chronic kidney disease, and there is considerable research interest in oxidative stress biomarkers for earlier prediction of disease onset. Proteomics approaches have been taken to study of human kidney tissue, serum/plasma, urine, and animal models of hypertension.

CRITICAL ISSUES

Redox proteomics, in which oxidative post-translational modifications can be identified in protein targets of oxidative or nitrosative stress, has not been very extensively pursued in this set of pathologies.

FUTURE DIRECTIONS

Proteomics studies of kidney and related tissues have relevance to chronic kidney disease, and redox proteomics, in particular, represents an under-exploited toolkit for identification of novel biomarkers in this commonly occurring pathology.

Effects of metformin on markers of oxidative stress and antioxidant reserve in patients with newly diagnosed type 2 diabetes: a randomized clinical trial

BACKGROUND & AIMS

Given the long term benefits observed with metformin use in diabetes patients, a role in modulating oxidative stress is imputable. Effects of metformin on markers of oxidative stress, antioxidant reserve, and HDL-c associated antioxidant enzymes were investigated.

METHODS

In a clinical trial setting (Registered under Clinical Trials.gov Identifier no. NCT01521624) 99 medication-naïve, newly diagnosed type 2 diabetes patients were randomly assigned to either metformin or lifestyle modification. AOPP, AGE, FRAP, activities of LCAT, and PON were measured at baseline and after 12-weeks.

RESULTS

Baseline values of the oxidative stress markers did not differ significantly between the two groups. In cases, after three months treatment, there was a significant reduction in AOPP (137.52 ± 25.59, 118.45 ± 38.42, p < 0.001), and AGE (69.28 ± 4.58, 64.31 ± 8.64, p = 0.002). FRAP and PON increased significantly (1060.67 ± 226.69, 1347.80 ± 251.40, p < 0.001 and 29.85 ± 23.18, 37.86 ± 27.60, p = 0.012 respectively). LCAT levels remained unchanged (45.23 ± 4.95, 46.15 ± 6.28, p = 0.439). Comparing the two groups in a final multivariate model, AOPP, FRAP, and AGE levels changed more significantly in metformin compared with lifestyle modification alone (p = 0.007, p < 0.001 and p < 0.001 respectively). Escalation in LCAT or PON activities did not differ between the two groups (p = 0.199 and 0.843 respectively).

CONCLUSIONS

Use of metformin is more effective in reducing oxidative stress compared with lifestyle modification alone.

Pioglitazone attenuates the detrimental effects of advanced glycation end-products in the pancreatic beta cell line HIT-T15

Pioglitazone is an anti-diabetic agent that preserves pancreatic beta cell mass and improves their function. Advanced Glycation End-Products (AGEs) are implicated in diabetic complications. We previously demonstrated that exposure of the pancreatic islet cell line HIT-T15 to high concentrations of AGEs significantly decreases cell proliferation and insulin secretion, and affects transcription factors regulating insulin gene transcription. The aim of this work was to investigate the effects of Pioglitazone on the function and viability of HIT-T15 cells cultured with AGEs. HIT-T15 cells were cultured for 5 days in the presence of AGEs alone, or supplemented with 1 μmol/l Pioglitazone. Cell viability, insulin secretion and insulin content, redox balance, expression of the AGE receptor (RAGE), and NF-kB activation were then determined. The results showed that Pioglitazone protected beta cells against AGEs-induced apoptosis and necrosis. Moreover, Pioglitazone restored the redox balance and improved the responsiveness to low glucose concentration. Adding Pioglitazone to the AGEs culture attenuated NF-kB phosphorylation, and prevented AGEs to down-regulate IkBα expression. These findings suggest that Pioglitazone protects beta cells from the dangerous effects of AGEs.

Role of advanced glycation endproducts and glyoxalase I in diabetic peripheral sensory neuropathy

Diabetic neuropathy is the most common and debilitating complication of diabetes mellitus with more than half of all patients developing altered sensation as a result of damage to peripheral sensory neurons. Hyperglycemia results in altered nerve conduction velocities, loss of epidermal innervation, and development of painful or painless signs and symptoms in the feet and hands. Current research has been unable to determine whether a patient will develop insensate or painful neuropathy or be protected from peripheral nerve damage all together. One mechanism that has been recognized to have a role in the pathogenesis of sensory neuron damage is the process of reactive dicarbonyls forming advanced glycation endproducts (AGEs) as a direct result of hyperglycemia. The glyoxalase system, composed of the enzymes glyoxalase I (GLO1) and glyoxalase II, is the main detoxification pathway involved in breaking down toxic reactive dicarbonyls before producing carbonyl stress and forming AGEs on proteins, lipids, or nucleic acids. This review discusses AGEs, GLO1, their role in diabetic neuropathy, and potential therapeutic targets of the AGE pathway.

Role of advanced glycation endproducts and potential therapeutic interventions in dialysis patients

It has been nearly 100 years since the first published report of advanced glycation end products (AGEs) by the French chemist Maillard. Since then, our understanding of AGEs in diseased states has dramatically changed. Especially in the last 25 years, AGEs have been implicated in complications related to aging, neurodegenerative diseases, diabetes, and chronic kidney disease. Although AGE formation has been well characterized by both in vitro and in vivo studies, few prospective human studies exist demonstrating the role of AGEs in patients on chronic renal replacement therapy. As the prevalence of end-stage renal disease (ESRD) in the United States rises, it is essential to identify therapeutic strategies that either delay progression to ESRD or improve morbidity and mortality in this population. This article reviews the role of AGEs, especially those of dietary origin, in ESRD patients as well as potential therapeutic anti-AGE strategies in this population.