Oxidative stress: Does it play a role in the genesis of early glycated proteins?

Effect of vitamin E intake on glycemic control and insulin resistance in diabetic patients: an updated systematic review and meta-analysis of randomized controlled trials

Since a 2014 meta-analysis, several randomized controlled trials (RCTs) evaluating the effect of vitamin E intake on glycemic indices and insulin resistance in adults with diabetes have reached inconsistent conclusions. Therefore, we updated the previous meta-analysis to summarize the current evidence in this regard. Online databases including PubMed, Scopus, ISI Web of Science, and Google Scholar were searched to identify relevant studies published up to September 30, 2021, using relevant keywords. Random-effects models were used to obtain overall mean difference (MD) comparing vitamin E intake with a control group. In total, 38 RCTs with a total sample size of 2171 diabetic patients (1110 in vitamin E groups and 1061 in control groups) were included. Combining the results from 28 RCTs on fasting blood glucose, 32 RCTs on HbA1c, 13 RCTs on fasting insulin, and 9 studies on homeostatic model assessment for insulin resistance (HOMA-IR) showed a summary MD of -3.35 mg/dL (95% CI: -8.10 to 1.40, P = 0.16), -0.21% (95% CI: -0.33 to -0.09, P = 0.001), -1.05 µIU/mL (95% CI: -1.53 to -0.58, P < 0.001), and -0.44 (95% CI: -0.82 to -0.05, P = 0.02), respectively. This indicates a significant lowering effect of vitamin E on HbA1c, fasting insulin and HOMA-IR, while no significant effect on fasting blood glucose in diabetic patients. However, in subgroup analyses, we found that vitamin E intake significantly reduced fasting blood glucose in studies with an intervention duration of < 10 weeks. In conclusion, vitamin E intake has a beneficial role in improving HbA1c and insulin resistance in a population with diabetes. Moreover, short-term interventions with vitamin E have resulted in lower fasting blood glucose in these patients. This meta-analysis was registered in PROSPERO with code CRD42022343118.

Research Advances on the Damage Mechanism of Skin Glycation and Related Inhibitors

Our skin is an organ with the largest contact area between the human body and the external environment. Skin aging is affected directly by both endogenous factors and exogenous factors (e.g., UV exposure). Skin saccharification, a non-enzymatic reaction between proteins, e.g., dermal collagen and naturally occurring reducing sugars, is one of the basic root causes of endogenous skin aging. During the reaction, a series of complicated glycation products produced at different reaction stages and pathways are usually collectively referred to as advanced glycation end products (AGEs). AGEs cause cellular dysfunction through the modification of intracellular molecules and accumulate in tissues with aging. AGEs are also associated with a variety of age-related diseases, such as diabetes, cardiovascular disease, renal failure (uremia), and Alzheimer's disease. AGEs accumulate in the skin with age and are amplified through exogenous factors, e.g., ultraviolet radiation, resulting in wrinkles, loss of elasticity, dull yellowing, and other skin problems. This article focuses on the damage mechanism of glucose and its glycation products on the skin by summarizing the biochemical characteristics, compositions, as well as processes of the production and elimination of AGEs. One of the important parts of this article would be to summarize the current AGEs inhibitors to gain insight into the anti-glycation mechanism of the skin and the development of promising natural products with anti-glycation effects.

Relationship between Dietary Patterns and Incidence of Type 2 Diabetes

Introduction

Increasing rate of type 2 diabetes (T2D) prevalence during the recent years has caused concern about significant risks for the public health. Dietary patterns have recently attracted great attention in the evaluation of the relationship between diet and health. In the present study, we investigated the relationship between the major identified dietary patterns and T2D.

Methods

In this matched case-control study, 315 individuals (125 newly diagnosed cases and 190 controls); 18-60 years of age were selected. A valid semiquantitative food frequency questionnaire was used to collect dietary intakes of individuals. Anthropometric characteristics and blood pressure were measured with standard instructions and body mass index and waist to hip ratio were calculated. Factor analysis was used to identify major dietary patterns. The relationship between major food patterns and T2D was assessed by logistic regression analysis.

Results

Two dietary patterns were identified: healthy and Western dietary patterns. The second tertile of the healthy dietary pattern had significantly association with decreased risk of T2D in the crude model (Odds ratios [OR]: 0.51, 95% Confidence interval [CI]: 0.29-0.9; P for trend = 0.018), Model II (OR: 0.5, 95% CI: 0.27-0.9; P for trend = 0.019), and Model III (OR: 0.56, 95% CI: 0.23-1.4 P for trend = 0.048). The inverse association of the second tertile of Western dietary pattern score with the T2D was significant in crude (OR: 9.25, 95% CI: 4.95-17.4; P for trend <0.001) and multivariable-adjusted model (OR: 16.65, 95% CI: 2.99-92.84; P for trend <0001).

Conclusions

Our study found an inverse relationship between adherence of healthy pattern and direct association with Western dietary pattern and the risk of T2D.

Modulating cell culture oxidative stress reduces protein glycation and acidic charge variant formation

Controlling acidic charge variants is critical for an industrial bioprocess due to the potential impact on therapeutic efficacy and safety. Achieving a consistent charge variant profile at manufacturing scale remains challenging and may require substantial resources to investigate effective control strategies. This is partially due to incomplete understanding of the underlying causes for charge variant formation during the cell culture process. To address this gap, we examined the effects of four process input factors (temperature, iron concentration, feed media age, and antioxidant (rosmarinic acid) concentration) on charge variant profile. These factors were found to affect the charge profile by modulating the cell culture oxidative state. Process conditions with higher acidic peaks corresponded to elevated supernatant peroxide concentration, intracellular reactive oxygen species (ROS) levels, or both. Changes in glycation level were the primary cause of the charge heterogeneity, and for the first time, supernatant peroxide was found to positively correlate with glycation levels. Based on these findings, a novel mathematical model was developed to demonstrate that the rate of acidic species formation was exponentially proportional to the concentrations of supernatant peroxide and protein product. This work provides critical insights into charge variant formation during the cell culture process and highlights the importance of modulating of cell culture oxidative stress for charge variant control.

The endothelial border to health: Mechanistic evidence of the hyperglycemic culprit of inflammatory disease acceleration

The endothelial cell (EC) layer constitutes a barrier that controls movements of fluid, solutes and cells between blood and tissue. Further, the endothelial layer regulates vascular tone and directs local humoral and cellular inflammatory processes. The strategic position makes it an important player for maintenance of health and for development of a number of diseases. Endothelial dysfunction is known to be an important component of type 2 diabetes, but is also assumed to be involved in many other diseases, for example, rheumatoid arthritis, inflammatory bowel disease, asthma, and cardiovascular diseases. We here suggest that the EC plays a pivotal role in disease pathophysiology through initiation, potentiation, and maintenance of several inflammatory mechanisms. Our contention is based on the observation that hyperglycemia-intermittent or sustained, local or systemic-is a major culprit for several endothelial dysfunctions. There is also mounting epidemiological evidence that dietary intake of refined sugars is important for the development of a number of diseases beyond obesity and type 2 diabetes. Various diseases involving inflammatory and immunological components are accelerated by hyperglycemic events because the endothelium transduces "high glucose" signaling into significant pathophysiological phenomena leading to reduced endothelial barrier function, compromised vascular tone regulation and inflammation (e.g., cytokine secretion and RAGE activation). In addition, endothelial extracellular proteins form epitopes for potential specific antibody formation upon interactions with reducing sugars. This paper reviews the endothelial metabolism, biology, inflammatory processes, physical barrier functions, and summarizes evidence that although stochastic in nature, endothelial responses to hyperglycemia are major contributors to disease pathophysiology. We present molecular and mechanistic evidence that both biological and physical barriers, protein function, specific immunity, and inflammatory processes are compromised by hyperglycemic events and thus, hyperglycemic events alone should be considered risk factors for numerous human diseases. © 2017 IUBMB Life, 69(3):148-161, 2017.

Serum glycated albumin, glycated hemoglobin, and arterial stiffness in a general Chinese population

BACKGROUND

Both glycated albumin (GA) and glycated hemoglobin (HbA1c) reflect the mean glucose levels. This study was conducted to investigate the relationships among GA, HbA1c, and arterial stiffness in the general population.

METHODS

A total of 11,014 participants were included. Serum GA; HbA1c; and arterial stiffness indices, including brachial-ankle pulse wave velocity (baPWV) and central systolic blood pressure (cSBP), were measured. Single-factor and multivariate regression analyses were performed. Receiver operating characteristic (ROC) analysis was performed to compare the predictive value of GA, HbA1c, and their combination for arterial stiffness. All analyses were stratified by sex.

RESULTS

Men had a lower GA level than women. GA, HbA1c, and plasma glucose levels were correlated. The levels of baPWV and cSBP increased across sex-specific quartiles of GA and HbA1c (P for trend<0.001 for all). Both GA and HbA1c were positively related to elevated baPWV and cSBP after adjusting for conventional factors (P<0.05 for all). These relationships remained significant when participants were divided into groups with normal glucose tolerance, prediabetes, or diabetes. Regarding screening for elevated baPWV and cSBP, the values of the area under the ROC curve (AUC) for GA were similar to those for HbA1c in men but were lower than those for HbA1c in women. The combination of GA and HbA1c did not improve the AUC compared with HbA1c alone.

CONCLUSIONS

Both GA and HbA1c were associated with arterial stiffness. The predictive value of GA for arterial stiffness was similar in men but lower in women compared with that of HbA1c.

Plasma ferritin and indices of oxidative stress in Helicobacter pylori infection among schoolchildren

OBJECTIVE

Iron deficiency is one of the most common causes for anemia in Indian children. The present study was performed to evaluate the prooxidant status and ferritin levels in Helicobacter pylori-infected schoolchildren.

METHODS

The present study included healthy controls (control group), H pylori-infected children (group I), and H pylori-uninfected children with iron deficiency (group II). Group I was further subdivided into group Ia and Ib, depending on the presence or absence of iron deficiency, respectively. Serum levels of protein carbonyls, malondialdehyde (MDA), ferritin, total protein, and albumin were evaluated and compared among study groups.

RESULTS

In H pylori-infected schoolchildren, serum MDA and protein carbonyls were significantly increased and ferritin levels were significantly decreased compared with the controls and group II. In group I, irrespective of presence and absence of iron deficiency, MDA and protein carbonyls were significantly increased compared with group II. In anemic H pylori-infected schoolchildren, levels of serum total protein were significantly decreased compared with healthy controls. In H pylori-infected patients, MDA was found to have a significant negative correlation with ferritin levels and total protein by partial correlation analysis.

CONCLUSIONS

An increased level of oxidative stress was found in H pylori-infected schoolchildren. Furthermore, the findings from the present study indicate that prolonged oxidative stress may enhance protein degradation in children.

Possible modulation of glycated protein levels in prehypertension by lipid peroxides

Glycation and lipid peroxidation are two important processes known to play a key role in complications of many pathophysiological processes. Malondialdehyde (MDA) has been reported to play a possible role in the genesis of glycated proteins. This study was undertaken to unravel the possible association of MDA with glycated hemoglobin and fructosamine in prehypertensive patients. A case-control study was performed on 42 prehypertensive and 30 control subjects. Plasma glucose, MDA, fructosamine, and glycated hemoglobin were analyzed in both the groups. Partial correlation analysis was performed to predict the independent association of MDA and fasting glucose on fructosamine and glycated hemoglobin. Plasma of prehypertensive subjects revealed significantly higher concentrations of lipid peroxides and fructosamine than in controls. Glycated hemoglobin concentrations were also found to be significantly increased in test group when compared with healthy controls. When the effects of fasting glucose on the concentrations of glycated hemoglobin and fructosamine were refuted by partial correlation analysis, MDA was found to be a significant determinant of glycated hemoglobin and fructosamine in subjects with prehypertension. These data also support the premise that lipid peroxides per se could play a role in the glycation of hemoglobin and plasma proteins in prehypertension.

Increased protein carbonylation and decreased antioxidant status in anemic H. pylori infected patients: effect of treatment

BACKGROUND/AIM

Collective evidences suggest the causal association of Helicobacter pylori infection with iron deficiency anemia. Generation of free radicals against this bacterium can lead to turbulence in oxidative-antioxidative system. This study was undertaken to evaluate the marker of oxidative protein injury, protein carbonylation, and total antioxidant status in anemic H. pylori-infected patients and to observe the alteration in them after treatment for 1 month with oral ferrous sulfate and anti-H. pylori therapy. Twenty anemic H. pylori-infected patients were randomly divided into 2 groups. The H. pylori-infected patients in Group I received both iron supplementation and anti-H pylori therapy, whereas patients in Group II received only the iron supplementation. Fifteen healthy volunteers served as controls. All the study parameters were estimated after 1 month of the treatment.

MATERIALS AND METHODS

Protein carbonylation and total antioxidant status were estimated using colorimetric method. Hematologic parameters were evaluated using Sysmex-K-100 automated cell counter.

RESULTS

In anemic H. pylori-infected patients, the protein carbonyls (PCOs) were significantly increased, whereas the total antioxidant status, iron, hemoglobin, and ferritin levels were significantly decreased compared with the controls. In Group I, while the PCOs level decreased significantly, there was a significant increase in the total antioxidant status, iron, hemoglobin, and ferritin levels after 1 month. No significant alterations were noted in the levels of PCOs, total antioxidant status, iron, hemoglobin, or ferritin in Group II patients after 1 month of the treatment.

CONCLUSIONS

The findings from this study indicate that treatment for both anemia and H. pylori infections is required for lowering the oxidative stress markers, which synergistically bring about an appropriate correction of anemia soon in these patients.

Does glucose variability influence the relationship between mean plasma glucose and HbA1c levels in type 1 and type 2 diabetic patients?

OBJECTIVE

The A1C-Derived Average Glucose (ADAG) study demonstrated a linear relationship between HbA(1c) and mean plasma glucose (MPG). As glucose variability (GV) may contribute to glycation, we examined the association of several glucose variability indices and the MPG-HbA(1c) relationship.

RESEARCH DESIGN AND METHODS

Analyses included 268 patients with type 1 diabetes and 159 with type 2 diabetes. MPG during 3 months was calculated from 7-point self-monitored plasma glucose and continuous glucose monitoring. We calculated three different measures of GV and used a multiple-step regression model to determine the contribution of the respective GV measures to the MPG-HbA(1c) relationship.

RESULTS

GV, as reflected by SD and continuous overlapping net glycemic action, had a significant effect on the MPG-HbA(1c) relationship in type 1 diabetic patients so that high GV led to a higher HbA(1c) level for the same MPG. In type 1 diabetes, the impact of confounding and effect modification of a low versus high SD at an MPG level of 160 mg/dL on the HbA(1c) level is 7.02 vs. 7.43 and 6.96 vs. 7.41. All GV measures showed the same tendency.

CONCLUSIONS

In only type 1 diabetic patients, GV shows a significant interaction with MPG in the association with HbA(1c). This effect is more pronounced at higher HbA(1c) levels. However, the impact of GV on the HbA(1c) level in type 1 diabetes is modest, particularly when HbA(1c) is close to the treatment target of 7%.

Androgens associated with advanced glycation end-products in postmenopausal women

OBJECTIVE

Higher frequency of subclinical atherosclerosis has been linked with androgen levels in postmenopausal women. Advanced glycation end-products (AGEs) are well-recognized atherogenic molecules. Therefore, we investigated the association of postmenopausal sex steroid and metabolic status with serum AGE levels.

METHODS

Serum sex hormones, fasting glucose, fasting insulin, and AGEs were assessed in 106 healthy postmenopausal women. Insulin resistance was estimated by using the homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

Women in the highest testosterone quartile (Q4) had higher serum AGE levels (Q1, 5.22 IU/mL ± 0.50; Q2, 5.08 ± 0.53 IU/mL; Q3, 5.78 ± 1.10 IU/mL vs Q4, 7.35 ± 1.23 IU/mL; P < 0.0005) compared with women in the lowest testosterone quartiles. Accordingly, women in the highest free androgen index (FAI) quartile had higher serum AGE levels (Q1, 5.36 ± 0.59 IU/mL; Q2, 5.28 ± 0.72 IU/mL vs Q4, 6.68 ± 1.48 IU/mL; P < 0.0005) compared with women in the lowest FAI quartile. These findings remained significant after adjustment for age, body mass index, HOMA-IR, and fasting glucose and fasting insulin levels. A highly significant correlation was found for testosterone and FAI with AGEs and persisted after adjustment for age, body mass index, HOMA-IR, and fasting glucose and fasting insulin levels (r = 0.67, P < 0.0005)

CONCLUSIONS

The data from the current study suggest that higher levels of AGEs are positively associated with higher androgen levels. This association, identified for the first time, may provide an additional insight into the pathophysiological mechanisms linking the described higher prevalence of cardiovascular events with higher androgen levels in postmenopausal women.

Maillard reaction, mitochondria and oxidative stress: potential role of antioxidants

Glycation and oxidative stress are two important processes known to play a key role in complications of many disease processes. Oxidative stress, either via increasing reactive oxygen species (ROS), or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo. Maillard Reactions, occur in vivo as well as in vitro and are associated with the chronic complications of diabetes, aging and age-related diseases. Hyperglycaemia causes the autoxidation of glucose, glycation of proteins, and the activation of polyol metabolism. These changes facilitate the generation of reactive oxygen species and decrease the activity of antioxidant enzymes such as Cu,Zn-superoxide dismutase, resulting in a remarkable increase of oxidative stress. A large body of evidence indicates that mitochondria alteration is involved and plays a central role in various oxidative stress-related diseases. The damaged mitochondria produce more ROS (increase oxidative stress) and less ATP (cellular energy) than normal mitochondria. As they are damaged, they cannot burn or use glucose or lipid and cannot provide cell with ATP. Further, glucose, amino acids and lipid will not be correctly used and will accumulate outside the mitochondria; they will undergo more glycation (as observed in diabetes, obesity, HIV infection and lipodystrophia). The objective of this paper is to discuss how to stop the vicious circle established between oxidative stress, Maillard Reaction and mitochondria. The potential application of some antioxidants to reduce glycation phenomenon and to increase the antioxidant defence system by targeting mitochondria will be discussed. Food and pharmaceutical companies share the same challenge, they must act now, urgently and energetically.