Effects of vitamin D supplementation on advanced glycation end products signaling pathway in T2DM patients: a randomized, placebo-controlled, double blind clinical trial

Serum vitamin D is substantially reduced and predicts flares in diabetic retinopathy patients

AIMS/INTRODUCTION

Research has suggested that vitamin D deficiency is associated with diabetic retinopathy (DR). Our study aimed to determine whether vitamin D deficiency is the cause of diabetic retinopathy or if diabetic retinopathy reduces vitamin D levels.

MATERIALS AND METHODS

Participants with type-2 diabetes were recruited for this prospective observational clinical study and were divided into a diabetic group without retinopathy and a diabetic group with retinopathy, with additional healthy volunteers serving as a control group. The differences in clinical characteristics among the three groups were also compared. Patients without retinopathy were then followed for 1 year to monitor the incidence of diabetic retinopathy. After follow-up, participants were divided into subgroups based on whether diabetic retinopathy occurred. The baseline data of the subgroups were compared, and the independent risk factors were analyzed.

RESULTS

Vitamin D levels were generally low. Participants with diabetic retinopathy had significantly lower vitamin D levels than did those without retinopathy (P < 0.01). A comparison of the two subgroups revealed lower baseline vitamin D concentrations in the new-DR subgroup than in the non-DR subgroup (P < 0.01). Vitamin D deficiency and elevated HbA1c levels were found to be independent risk factors for diabetic retinopathy (OR = 0.935, 95% CI: 0.867-0.981, P = 0.006; OR = 2.208, 95% CI: 1.764-2.764, P < 0.01). The limit of vitamin D intake according to the receiver-operating characteristic (ROC) curve was 26.01 ng/mL, and the area under the ROC curve was 0.603 (95% CI: 0.559-0.706, P = 0.002).

CONCLUSIONS

Vitamin D levels were significantly lower in patients diagnosed with diabetic retinopathy. More importantly, vitamin D deficiency may accelerate the onset of diabetic retinopathy.

Vitamin D supplementation modulates glycated hemoglobin (HBA1c) in diabetes mellitus

Diabetes is a metabolic illness that increases protein glycosylation in hyperglycemic conditions, which can have an impact on almost every organ system in the body. The role of vitamin D in the etiology of diabetes under RAGE (receptor for advanced glycation end products) stress has recently received some attention on a global scale. Vitamin D's other skeletal benefits have generated a great deal of research. Vitamin D's function in the development of type 1 and type 2 diabetes is supported by the discovery of 1,25 (OH)2D3 and 1-Alpha-Hydroylase expression in immune cells, pancreatic beta cells, and several other organs besides the bone system. A lower HBA1c level, metabolic syndrome, and diabetes mellitus all seems to be associated with vitamin D insufficiency. Most of the cross-sectional and prospective observational studies that were used to gather human evidence revealed an inverse relationship between vitamin D level and the prevalence or incidence of elevated HBA1c in type 2 diabetes. Several trials have reported on the impact of vitamin D supplementation for glycemia or incidence of type 2 diabetes, with varying degrees of success. The current paper examines the available data for a relationship between vitamin D supplementation and HBA1c level in diabetes and discusses the biological plausibility of such a relationship.

Glyoxal in Foods: Formation, Metabolism, Health Hazards, and Its Control Strategies

Glyoxal is a highly reactive aldehyde widely present in common diet and environment and inevitably generated through various metabolic pathways in vivo. Glyoxal is easily produced in diets high in carbohydrates and fats via the Maillard reaction, carbohydrate autoxidation, and lipid peroxidation, etc. This leads to dietary intake being a major source of exogenous exposure. Exposure to glyoxal has been positively associated with a number of metabolic diseases, such as diabetes mellitus, atherosclerosis, and Alzheimer's disease. It has been demonstrated that polyphenols, probiotics, hydrocolloids, and amino acids can reduce the content of glyoxal in foods via different mechanisms, thus reducing the risk of exogenous exposure to glyoxal and alleviating carbonyl stresses in the human body. This review discussed the formation and metabolism of glyoxal, its health hazards, and the strategies to reduce such health hazards. Future investigation of glyoxal from different perspectives is also discussed.

The Influence of Metabolic Syndrome on Potential Aging Biomarkers in Participants with Metabolic Syndrome Compared to Healthy Controls

BACKGROUND

Biological aging is a physiological process that can be altered by various factors. The presence of a chronic metabolic disease can accelerate aging and increase the risk of further chronic diseases. The aim of the study was to determine whether the presence of metabolic syndrome (MetS) affects levels of markers that are associated with, among other things, aging.

MATERIAL AND METHODS

A total of 169 subjects (58 with MetS, and 111 without metabolic syndrome, i.e., non-MetS) participated in the study. Levels of telomerase, GDF11/15, sirtuin 1, follistatin, NLRP3, AGEs, klotho, DNA/RNA damage, NAD+, vitamin D, and blood lipids were assessed from blood samples using specific enzyme-linked immunosorbent assay (ELISA) kits.

RESULTS

Telomerase (p < 0.01), DNA/RNA damage (p < 0.006) and GDF15 (p < 0.02) were higher in MetS group compared to non-MetS group. Only vitamin D levels were higher in the non-MetS group (p < 0.0002). Differences between MetS and non-MetS persons were also detected in groups divided according to age: in under 35-year-olds and those aged 35-50 years.

CONCLUSIONS

Our results show that people with MetS compared to those without MetS have higher levels of some of the measured markers of biological aging. Thus, the presence of MetS may accelerate biological aging, which may be associated with an increased risk of chronic comorbidities that accompany MetS (cardiovascular, inflammatory, autoimmune, neurodegenerative, metabolic, or cancer diseases) and risk of premature death from all causes.

What is the impact of vitamin D supplementation on glycemic control in people with type-2 diabetes: a systematic review and meta-analysis of randomized controlled trails

BACKGROUND

There is conflicting evidence on the effect of vitamin D on glycemic control. Therefore, in the current meta-analyses, we aimed to assess the effect of vitamin D supplementation on the glycemic control of type 2 diabetes (T2D) patients.

METHODS

We conducted a comprehensive search in electronic databases including; PubMed/Medline, Web of Science, Scopus, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and NIH's Clinical Trials Registry, from the inception of each database up to January first, 2021.

RESULTS

A total of 46 randomized controlled trials (RCTs) consisting of 2164 intervention subjects and 2149 placebo controls were included in this meta-analysis. Pooled analyses for HbA1c showed a significant change between the intervention and placebo group, the weighted mean difference (WMD)(95% confidence interval(CI)) was -0.20%(-0.29, -0.11) with P < 0.001. Analyses for assessing changes in FPG found a significant reduction in the intervention group after vitamin D supplementation, the WMD (95%CI) was -5.02 mg/dl (-6.75,-3.28) with P < 0.001. The result of pooled analyses for HOMA-IR revealed a significant change between the intervention and control group, the WMD (95%CI) was -0.42(-0.76, -0.07) with P = 0.019. The subgroup analyses showed the most efficacy in a higher dose and short intervention period and in subjects with deficient vitamin D status.

CONCLUSION

Vitamin D supplementation might be beneficial for the reduction of FPG, HbA1c, and HOMA-IR in type 2 diabetes patients with deficient vitamin D status. This effect was especially prominent when vitamin D was given in large doses and for a short period of time albeit with substantial heterogeneity between studies and a probability of publication bias.

Phytochemicals as Potential Inhibitors of Advanced Glycation End Products: Health Aspects and Patent Survey

BACKGROUND

The glycation of proteins and lipids synthesizes the advanced glycation end products (AGEs), i.e., substances that irreversibly damage macromolecules present in tissues and organs, which contribute to the impairment of biological functions. For instance, the accumulation of AGEs induces oxidative stress, the inflammatory responses, and consequently the on set/worsening of diseases, including obesity, asthma, cognitive impairment, and cancer. There is a current demand on natural and low-cost sources of anti-AGE agents. As a result, food phytochemicals presented promising results to inhibit glycation and consequently, the formation of AGEs.

OBJECTIVE

Here we describe how the AGEs are present in food via Maillard reaction and in organs via natural aging, as well as the effects of AGEs on the worsening of diseases. Also we described the methods used to detect AGEs in samples, and the current findings on the use of phytochemicals (phenolic compounds, phytosterols, carotenoids, terpenes and vitamins) as natural therapeuticals to inhibit health damages via inhibition of AGEs in vitro and in vivo.

METHODS

This manuscript reviewed publications available in the PubMed and Science Direct databases dated from the last 20 years on the uses of phytochemicals for the inhibition of AGEs. Recent patents on the use of anti-AGEs drugs were reviewed with the use of Google Advanced Patents database.

RESULTS AND DISCUSSION

There is no consensus about which concentration of AGEs in blood serum should not be hazardous to the health of individuals. Food phytochemicals derived from agroindustry wastes, including peanut skins, and the bagasses derived from citrus and grapes are promising anti-AGEs agents via scavenging of free radicals, metal ions, the suppression of metabolic pathways that induces inflammation, the activation of pathways that promote antioxidant defense, and the blocking of AGE connection with the receptor for advanced glycation endproducts (RAGE).

CONCLUSION

Phytochemicals derived from agroindustry are promising anti-AGEs, which can be included to replace synthetic drugs to inhibit AGE formation, and consequently to act as therapeutical strategy to prevent and treat diseases caused by AGEs, including diabetes, ovarian cancer, osteoporosis, and Alzheimer's disease.

Comparison of nutritional supplements for glycemic control in type 2 diabetes: A systematic review and network meta-analysis of randomized trials

AIMS

Direct and indirect evidence were combined in this systematic-review and network meta-analysis (NMA) to assess and compare the effect of nutritional supplements on glycemic control, and rank the supplements accordingly.

METHODS

PubMed, Scopus, and Web of Science were searched up to April 2021. We included randomized controlled trials that investigated the effect of vitamins D, C, and E, magnesium, zinc, calcium, selenium, and omega-3 on at least one glycemic marker, including glycated hemoglobin (HbA1c), fasting blood sugar (FBS), homeostasis model assessment-estimated insulin resistance (HOMA-IR), HOMA-B, and insulin, in adults with type 2 diabetes. To estimate effectiveness of supplements, a random-effects NMA in the Bayesian framework was applied. To assess risk of bias, Cochrane Collaboration Tool was used.

RESULTS

Analysis of 178 studies indicated that zinc, vitamin D, omega-3, vitamin C, and vitamin E were effective in reducing HbA1c with low certainty. For reduction of FBS, zinc, vitamin D, and vitamin C, and for HOMA-IR, vitamin D were effective with low certainty. None of the supplements were effective in the reduction of insulin and HOMA-B with low certainty. After excluding poor-quality studies, only vitamin D was significantly effective in reducing all of the markers. Consistently, when the analysis was restricted to studies with a duration of ≥12-weeks, vitamin D reduced HbA1c, FBS, and HOMA-IR.

CONCLUSIONS

Vitamin D supplementation was more effective compared to other supplements in improving HbA1c, FBS, and HOMA-IR, albeit with low certainty of evidence. This result was confirmed by low-risk of bias studies.

REGISTRATION

CRD42021240691.

Vitamin D and Ocular Diseases: A Systematic Review

The contributory roles of vitamin D in ocular and visual health have long been discussed, with numerous studies pointing to the adverse effects of vitamin D deficiency. In this paper, we provide a systematic review of recent findings on the association between vitamin D and different ocular diseases, including myopia, age-related macular degeneration (AMD), glaucoma, diabetic retinopathy (DR), dry eye syndrome (DES), thyroid eye disease (TED), uveitis, retinoblastoma (RB), cataract, and others, from epidemiological, clinical and basic studies, and briefly discuss vitamin D metabolism in the eye. We searched two research databases for articles examining the association between vitamin D deficiency and different ocular diseases. One hundred and sixty-two studies were found. There is evidence on the association between vitamin D and myopia, AMD, DR, and DES. Overall, 17 out of 27 studies reported an association between vitamin D and AMD, while 48 out of 54 studies reported that vitamin D was associated with DR, and 25 out of 27 studies reported an association between vitamin D and DES. However, the available evidence for the association with other ocular diseases, such as glaucoma, TED, and RB, remains limited.

The peculiar role of vitamin D in the pathophysiology of cardiovascular and neurodegenerative diseases

Vitamin D is a hormone with both genomic and non-genomic actions. It exerts its activity by binding vitamin D receptor (VDR), which belongs to the superfamily of nuclear receptors and ligand-activated transcription factors. Since VDR has been found in various tissues, it has been estimated that it regulates approximately 3% of the human genome. Several recent studies have shown pleiotropic effects of vitamin D in various processes such as cellular proliferation, differentiation, DNA repair and apoptosis and its involvement in different pathophysiological conditions as inflammation, diabetes mellitus, and anemia. It has been suggested that vitamin D could play an important role in neurodegenerative and cardiovascular disorders. Moderate to strong associations between lower serum vitamin D concentrations and stroke and cardiovascular events have been identified in different analytic approaches, even after controlling for traditional demographic and lifestyle covariates. The mechanisms behind the associations between vitamin D and cerebrovascular and cardiologic profiles have been widely examined both in animal and human studies. Optimization of vitamin D levels in human subjects may improve insulin sensitivity and beta-cell function and lower levels of inflammatory markers. Moreover, it has been demonstrated that altered gene expression of VDR and 1,25D3-membrane-associated rapid response steroid-binding (1,25D3-MARRS) receptor influences the role of vitamin D within neurons and allows them to be more prone to degeneration. This review summarizes the current understanding of the molecular mechanisms underlying vitamin D signaling and the consequences of vitamin D deficiency in neurodegenerative and cardiovascular disorders.

Role of vitamin D in diabetic retinopathy: Pathophysiological and clinical aspects

Epidemiological data predict a dramatic increase in the prevalence of diabetes and of diabetic retinopathy (DR) - the most common complication of diabetes-for which however we do not have so far effective tools for prevention and treatment. Since hypovitaminosis D is very frequent in patients with diabetes and vitamin D (VD) has vascular protective properties, several studies have addressed the association of VD deficiency with DR and its severity and progression, whereas the effects of VD supplementation on its natural history are largely unknown. Here we review the available evidence that supports the possible protective role of VD in DR and suggests to determine the VD levels in DR patients calling for a definitive randomized clinical trial to ascertain whether VD supplementation could protect against DR.

The Glyoxalase System in Age-Related Diseases: Nutritional Intervention as Anti-Ageing Strategy

The glyoxalase system is critical for the detoxification of advanced glycation end-products (AGEs). AGEs are toxic compounds resulting from the non-enzymatic modification of biomolecules by sugars or their metabolites through a process called glycation. AGEs have adverse effects on many tissues, playing a pathogenic role in the progression of molecular and cellular aging. Due to the age-related decline in different anti-AGE mechanisms, including detoxifying mechanisms and proteolytic capacities, glycated biomolecules are accumulated during normal aging in our body in a tissue-dependent manner. Viewed in this way, anti-AGE detoxifying systems are proposed as therapeutic targets to fight pathological dysfunction associated with AGE accumulation and cytotoxicity. Here, we summarize the current state of knowledge related to the protective mechanisms against glycative stress, with a special emphasis on the glyoxalase system as the primary mechanism for detoxifying the reactive intermediates of glycation. This review focuses on glyoxalase 1 (GLO1), the first enzyme of the glyoxalase system, and the rate-limiting enzyme of this catalytic process. Although GLO1 is ubiquitously expressed, protein levels and activities are regulated in a tissue-dependent manner. We provide a comparative analysis of GLO1 protein in different tissues. Our findings indicate a role for the glyoxalase system in homeostasis in the eye retina, a highly oxygenated tissue with rapid protein turnover. We also describe modulation of the glyoxalase system as a therapeutic target to delay the development of age-related diseases and summarize the literature that describes the current knowledge about nutritional compounds with properties to modulate the glyoxalase system.

The effects of vitamin D supplementation on inflammatory biomarkers in patients with abnormal glucose homeostasis: A systematic review and meta-analysis of randomized controlled trials

FINDINGS

on the level of inflammatory cytokines following vitamin D supplementation among individuals with abnormal glucose homeostasis (AGH) are controversial. Therefore, the present study was conducted on AGH patients to assess the impact of vitamin D on inflammatory cytokines such as CRP, TNF-α and IL-6. A systematic search up to September 2020 was performed through PubMed and Scopus databases. All clinical studies which evaluated the effect of oral vitamin D supplementation on inflammation in patients with AGH were included. The random-effects model was applied to obtain pooled results. For dose-response analysis, we used a fractional polynomial model. Overall, 38 studies, with 46 effect sizes, were included in this study. Combining effect sizes, we found that vitamin D considerably decrease serum concentrations of CRP (weight mean difference (WMD): - 0.67 mg/l; 95%CI: - 0.92, - 0.43; P < 0.001), IL-6 (WMD: -1.93 pg/mL; 95%CI: -2.80, -1.07; P < 0.001) and TNF-α (WMD: -0.81 pg/mL; 95%CI: -1.59, -0.03; P = 0.04). In the dose-response analysis, we failed to find any correlation between dosage of supplements and inflammatory biomarkers concentrations. Summarizing earlier studies, we demonstrated that circulating concentrations of inflammatory cytokines such as CRP, TNF-α, and IL-6 might be decreased following vitamin D supplementation among individuals with AGH.

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.

Vitamin D3 potentiates the nephroprotective effects of metformin in a rat model of metabolic syndrome: role of AMPK/SIRT1 activation and DPP-4 inhibition

The current study aimed to investigate the molecular mechanisms of metformin and vitamin D3-induced nephroprotection in a metabolic syndrome (MetS) rat model, evaluating the capacity of vitamin D3 to potentiate metformin action. MetS was induced by 10% fructose in drinking water and 3% salt in the diet. After 6 weeks, serum lipid profile and uric acid were measured, an oral glucose tolerance test (OGTT) was performed, and kidney function was investigated. In conjunction with the same concentrations of fructose and salt feeding, MetS rats with significant weight gain, dyslipidemia, hyperuricemia, and dysglycemia were treated orally with metformin (200 mg/kg), vitamin D3 (10 µg/kg), or both daily for 6 weeks. At the end of the study period, anthropometrical parameters were recorded, OGTT was reperformed, urine and blood samples were collected, and tissue samples were harvested at sacrifice. MetS rats showed dramatically declined renal function, enhanced intrarenal oxidative stress and inflammation, and extravagant renal histopathological damage with interstitial fibrosis. Metformin and vitamin D3 significantly reversed all the aforementioned deleterious effects in MetS rats. The study has verified the nephroprotective effects of metformin and vitamin D3 in MetS, accentuating the critical role of AMP-activated protein kinase/sirtuin-1 activation and dipeptidyl peptidase-4 inhibition. Given the synergistic effects of the combination, vitamin D3 is worth being investigated as an additional therapeutic agent for preventing MetS-induced nephropathy.

Effect of vitamin D supplementation versus placebo on essential hypertension in patients with vitamin D deficiency: a double-blind randomized clinical trial

Findings from randomized trials addressing the effect of vitamin D supplementation and blood pressure are inconsistent and have been the subject of recent debate. This study aimed to assess the effect of vitamin D supplementation on primary hypertension. This double-blind randomized clinical trial was conducted on patients aged 26-84 years with essential hypertension from March 2017 to April 2019. Patients with vitamin D insufficiency (serum vitamin D levels 20-30 ng/ml) or vitamin D deficiency (serum vitamin D levels <20 ng/ml) were enrolled in the study. Patients were randomly assigned to receive vitamin D supplementation or placebo. Systolic and diastolic blood pressure was measured before the intervention and one and two months thereafter. Of 208 patients enrolled, 171 patients remained for analysis. The effect of vitamin D supplementation on systolic blood pressure was statistically significant in the first and second months after the intervention (P=0.004 and P=0.024, respectively). The effect of vitamin D supplementation on diastolic blood pressure was statistically significant in the first month after the intervention (P=0.046), but not in the second month (P=0.885). No evidence of drug side effects was reported in the two groups. The results of this trial are suggestive of the potential benefits of vitamin D supplementation on blood pressure end points. Therefore, the use of vitamin D may be recommended as an adjuvant drug in the treatment of essential hypertension in patients with vitamin D deficiency because it is safe and well-tolerated by the patients and can significantly reduce the systolic and diastolic blood pressure. Trial registration: Iranian Registry of Clinical Trials registration number: IRCT201703129014N151.

Vitamin D and advanced glycation end products and their receptors

Advanced glycation end products (AGEs) are destructive molecules in the body that, at high levels, contribute to the progression of various chronic diseases. Numerous studies have suggested a modifying effect of vitamin D on AGEs and their receptors. This study sought to summarize the effects of vitamin D on AGEs and their receptors, including receptor for AGEs (RAGE) and soluble receptor for AGEs (sRAGE). The search method initially identified 484 articles; 331 remained after duplicate removal. Thirty-five articles were screened and identified as relevant to the study topic. After critical analysis, 27 articles were included in the final analysis. Vitamin D treatment may possibly be beneficial to reduce AGE levels and to augment sRAGE levels, particularly in vitamin D-deficient situations. Treatment with this vitamin may be effective in reducing RAGE expression in some disease conditions, but might be even harmful under normal conditions. The inhibitory or stimulatory effects of vitamin D on AGE receptors are mediated by various signaling pathways, MAPK/NF-κB, ADAM10/MMP9 and AT1R. In populations with chronic diseases and concomitant hypovitaminosis D, vitamin D supplementation can be used as a strategy to ameliorate AGE-mediated complications by modifying the AGE-RAGE and sRAGE systems.