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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 3  |  Issue : 1  |  Page : 15-21

Study of advanced glycation endproducts and their receptors in Egyptian type 2 diabetic individuals with peripheral neuropathy


1 Internal Medicine, Faculty of Medicine, Mansoura University, Mansoura, Egypt
2 Clinical Pathology, Faculty of Medicine, Mansoura University, Mansoura, Egypt

Date of Submission12-Dec-2016
Date of Acceptance13-Dec-2016
Date of Web Publication27-Apr-2017

Correspondence Address:
Alaa M Wafa
Department of Internal Medicine, Diabetes and Endocrine Unit, Mansoura Faculty of Medicine, Mansoura University, Mansoura
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2356-8062.205209

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  Abstract 


Context
Diabetic neuropathy is one of the commonest long-term complications of diabetes seen in routine healthcare and considered the most common cause of peripheral neuropathy in developed world.
Aim
The aim of our work was to measure advanced glycation endproducts (AGEs) and their receptors (RAGEs) in diabetic peripheral neuropathy (DPN), both painful and painless DPN.
Patients and methods
Our study was conducted on 50 type 2 diabetes mellitus patients with peripheral neuropathy, divided into two subgroups: the first group included 25 patients with painful DPN and the second group included 25 patients with painless DPN. Moreover, a third group included 20 diabetic patients without peripheral neuropathy, and a fourth group that included 20 healthy participants. All groups were subjected to full history taking and clinical examination, anthropometric parameters, the calculation of neuropathy disability score, and nerve conduction studies (peroneal, sural, and tibial nerves). Laboratory investigations included serum AGEs and RAGEs.
Results
Our study demonstrated that hemoglobin A1c, AGE, and RAGE showed statistically significant difference between the studied groups. Hemoglobin A1c was significantly high in both neuropathic and diabetic groups in comparison with control. Regarding AGE, it was statistically higher in neuropathic group than in control (P<0.011). On the contrary, RAGE was significantly higher in both neuropathic and diabetic groups rather than control (P<0.02). Although the neuropathic group has higher levels of AGE and RAGE than diabetic group, the difference was statistically nonsignificant. Significant difference was found between studied groups regarding nerve conduction studies of sural and tibial nerves. Statistically significant difference was found in the parameters of nerve conduction studies between neuropathic group and both non-neuropathic diabetic and control groups.
Conclusion
Our study concluded that AGE and RAGE are significantly higher in diabetic patients with neuropathy versus control, with more elevation in neuropathic group than in diabetic without neuropathy.

Keywords: advanced glycation endproduct, diabetes, diabetic peripheral neuropathy, receptor for advanced glycation endproduct


How to cite this article:
Wafa AM, EL-Nahas MR, Al Biaumy AA, Mansour YM. Study of advanced glycation endproducts and their receptors in Egyptian type 2 diabetic individuals with peripheral neuropathy. Egypt J Obes Diabetes Endocrinol 2017;3:15-21

How to cite this URL:
Wafa AM, EL-Nahas MR, Al Biaumy AA, Mansour YM. Study of advanced glycation endproducts and their receptors in Egyptian type 2 diabetic individuals with peripheral neuropathy. Egypt J Obes Diabetes Endocrinol [serial online] 2017 [cited 2017 Dec 13];3:15-21. Available from: http://www.ejode.eg.net/text.asp?2017/3/1/15/205209




  Introduction Top


Diabetes has been associated with different long-term macrovascular and microvascular complications. The macrovascular involves large vessels causing peripheral vascular disease, cardiovascular disease, and cerebrovascular disease. Microvascular complications include neuropathy, retinopathy, and nephropathy [1]. Diabetic peripheral neuropathy (DPN) was recognized by the American Diabetes Association as ‘the presence of symptoms and/or signs of peripheral nerve dysfunction in people with diabetes after the exclusion of other causes’ [2]. Long-term complications of diabetes have long been believed to be the result of prolonged hyperglycemia. However, blood glucose levels alone do not reveal the whole picture. Diabetic neuropathy is one of the commonest complications of diabetes, reaching 37.4% among uncontrolled diabetic individuals. In the USA, 11.9 million adults have been diagnosed as having diabetes, and of these, 3.9 million (32.7%) have DPN [3]. Painful DPN were found in ∼11% of all diabetic individuals [4]. A diabetic complications study by Herman et al. [5] in Egypt, which used the vibration perception threshold to define DPN, demonstrated that 22 and 18% of known and newly diagnosed diabetic individuals, respectively, had DPN. One study based on clinical neuropathic symptoms and nerve conduction studies (NCSs) found that 8.3% of 86 patients with newly diagnosed type 2 diabetes mellitus (T2DM) had DPN [6]. Using the diabetic neuropathy score and diabetic neuropathy examination score to define DPN in their study in the United Arab Emirates, Saadi et al. [7] demonstrated that 34.7% among 57 diabetic individuals had DPN.

Studies have shown that those who have higher levels of advanced glycation endproducts (AGEs) experience more microvascular and cardiovascular complications [8]. AGEs are groups of compounds that result from the nonenzymatic reaction of reducing sugars with free amino groups of biological molecules. Receptors of advanced glycation endproducts (RAGEs), which are signal transduction receptors that belong to the immunoglobulin superfamily, are expressed in a variety of cell types, such as neurons, monocytes, smooth muscle cells, lymphocytes, and endothelial cells [9]. The interaction between AGE and RAGEs leads to intracellular production of reactive oxygen species through electron transport chain, xanthine oxidase, NADPH oxidase, and arachidonic acid metabolism [10],[11]. AGEs detect the modification of myelin of the peripheral nerve, which becomes susceptible to phagocytosis, and determine segmental demyelination. Also AGEs responsible for modification of major axonal cytoskeleton proteins (e.g. actin, tubulin, and neurofilament), which cause atrophy of axon and impairment of axonal transport [12]. Study of AGEs represent one of the most promising areas of research, as it is thought to have an important role in the etiology of complications of diabetes mellitus (DM), and this will provide new possible targets for the management of both type 1 DM and T2DM and related complications [13].

The aim of our work was to measure AGEs and RAGEs in DPN, both painful and painless DPN.


  Patients and methods Top


Our study is a cross-sectional study, which was carried out in outpatient clinic and inpatient ward of specialized Internal Medical Hospital, Mansoura University. The study was approved by the Mansoura Faculty of medicine, ethics committee, and then it has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. A written informed consent was obtained from all participants before inclusion in the study.

Timing of the study

The study period was of 1 year between December 2014 and December 2015.

Groups of the study

The patients were divided into the following groups: neuropathic group had 50 T2DM patients with DPN and was divided into two subgroups: the first group included 25 patients with painful DPN and the second group included 25 patients with painless DPN. The third group included 20 diabetic patients without peripheral nerve dysfunction. The fourth group included 20 healthy individuals as controls from medical staff, with matched age and sex.

Exclusion criteria

Patients who refused to participate in the study, patients who had type 1 DM, patients with serum creatinine level more than 1.5 mg/dl, patients with long-term liver disease, patients with other causes of neuropathy, patients with severe debilitating diseases, pregnant females, those with other malignancies, and patients on chemotherapy or radiotherapy.

Methodology

Clinical assessment

It included full history taking and thorough clinical examination, anthropometric parameters (BMI and waist circumference), the calculation of neuropathy disability score [14], and presence or absence of deep tendon reflexes and sensation (graded as 0, normal; 1, positive with reinforcement; 2, absent). Vibration perception threshold was tested with tuning fork 128 Hz on each malleolus, pain sensation by pin prick, temperature sensation by thermal pen, assessment of pain by visual analog pain scale.

Laboratory investigations

Laboratory investigations included urine analysis. Microalbumin level was assayed using competitive enzyme-linked immunosorbent assay (ELISA) test system for the quantitative measurement of human albumin level in urine, which was supplied by ORGENTEC Diagnostic GmbH (Mainz, Germany). Conventional laboratory tests included serum glucose and creatinine levels. Serum AGE was assayed by solid-phase sandwich ELISA assay, which was supplied by MyBiosowle (catalog number: MBS 704358), whereas RAGE was assayed by solidphase ELISA using Quanitikine RAGE ELISA Kit, which was supplied by R&D System (catalog number: DRG00). Serum of 1 ml was put into EDTA vacutainer tube for hemoglobin A1c (HbA1c) assay using fast cation exchange resin, which was supplied by Human Gesellschaft für Biochemica und Diagnostica mbH (Wiesbaden, Germany).

Nerve conduction studies

studies NCSs were performed with the use of sensory nerve to record the conduction velocity for peroneal nerve, sural nerve, and tibial nerve. DPN was diagnosed by NCSs and neuropathy disability score. Patients with DPN were divided by visual analog scale for pain into painful and painless groups.

Fundus examination

Fundus examination was done by digital retinal camera [15].


  Results Top


The results are shown in [Table 1],[Table 2],[Table 3],[Table 4],[Table 5],[Table 6],[Table 7],[Table 8],[Table 9],[Table 10],[Table 11].
Table 1 Comparison between different studied groups according to demographic characteristics

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Table 2 Comparison between painful and painless groups according to demographic characteristics

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Table 3 Comparison between painful and painless groups according to glycated products

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Table 4 Comparison between painful and painless groups according to glycated products and receptor for advanced glycation endproduct

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Table 5 Comparison between different studied groups according to nerve conduction on sural, peroneal, and tibial nerves

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Table 6 Comparison between painful and painless groups according to nerve conduction studies on sural, peroneal, and tibial

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Table 7 Correlation of advanced glycation endproduct and different studied variables in diabetic group

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Table 8 Correlation of advanced glycation endproduct and different studied variables in control group

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Table 9 Correlation of advanced glycation endproduct and different studied variables in neuropathic group

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Table 10 Correlation of receptor for advanced glycation endproduct and different studied variables in diabetic group

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Table 11 Correlation of receptor for advanced glycation endproduct and different studied variables in control and neuropathic groups

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  Discussion Top


Diabetic neuropathy is one of the commonest long-term complications seen in routine healthcare and considered the most common cause of peripheral neuropathy in developed countries [16]. It is, therefore, a major health problem with serious consequences for patients, and it results in a significant financial burden on the healthcare systems. This is especially true owing to the current global epidemic of DM. Hyperglycemia induces microvascular damage through different mechanisms: an increased flux of glucose and other sugars through the polyol pathway; an increased intracellular AGE formation; interaction between AGEs and RAGEs, leading to intracellular signaling, which disrupts cell function; a persistent activation of protein kinase C isoforms; and an increased hexosamine pathway activity. Selectively inhibiting each of these biochemical pathways has produced disappointing results [17]. Of particular interest is the accelerated formation of AGEs and their interaction with their receptors, RAGEs. The most important process responsible for AGE accumulation in diabetic patients is the nonenzymatic glycation reaction, or Maillard reaction. This can be globally seen as a different process; the final stage of which comprises a complex series of oxidation, dehydration, and cyclization reactions, which give rise to endogenous AGEs, that is, thermodynamically unstable compounds that typically accumulate on proteins with a long half-life, though they have been shown to form on proteins with a short half-life too, such as plasma proteins, lipoproteins, and intracellular proteins [18].

The other way in which these compounds accumulate in diabetic patients is through a defective renal excretion of AGEs, typical of diabetic nephropathy, because renal clearance is inversely related to plasma levels of AGEs. This gradually creates a vicious circle as the greater circulating pool of plasma AGEs in turn changes the shape and structure of many proteins at glomerular level (particularly type IV collagen and the mesangium), as well as interacting with specific receptors. These interactions are associated with a worsening chronic kidney disease and further impairment of glycoxidation product clearance [19]. Much attention has recently been paid to exogenous AGEs, harmful products of ‘browning’ (or the Maillard reaction) in different foods. Together with endogenous AGEs, these compounds form the majority of glycation free adducts, the greater proportion of circulating AGEs in diabetic and nondiabetic individuals. Among the various food processing methods, heating, sterilizing, and microwaves contribute to the generation of exogenous AGEs. Binding of AGEs to RAGEs has been suggested to contribute to the pathogenesis of diabetic vascular complications. Interaction of AGE with its receptor RAGE transduces multiple signals such as NADPH oxidase, mitogen-activated protein kinases, extracellular signal regulated kinases, and GTPase [20]. Activation of NADPH oxidase causes enhanced (reactive oxygen species) generation, which may lead to peroxidation and glycoxidation reactions that result in protein carbonyl formation, advanced oxidation protein product generation, and lipid peroxidation. These oxidative stress markers have been shown to be enhanced significantly in diabetic patients. Using pharmacological agents that are able to inhibit AGE formation and disrupt the RAGE-ligand axis either through downregulating membrane-bound RAGE or inducing the production of circulating RAGEs may be a possible means to decrease diabetic vascular complications [21].

This cross-sectional study was conducted at the inpatient and outpatient clinics of specialized medical hospital, Mansoura University, to asses AGEs and their receptors in both painful and painless DPN. The study comprised 50 patients with diabetic neuropathy (proved by NCSs); 25 patients had painful neuropathy, with 8% of patients showing marked degree of pain, whereas 8% showing least degree of pain. The other 25 patients had painless neuropathy. Moreover, there were 20 diabetic patients without neuropathy and 20 healthy individuals. All were enrolled by simple randomization.

Clinical data of our study revealed that there was no statistically significant difference between the different groups regarding age and sex. However, in all studied groups, the proportion of males was more than females (66 and 34%, respectively); this could be explained simply by refusal of females to do NCSs rather than increase prevalence of neuropathy in males. Hypertension and ischemic heart disease were significantly higher in the neuropathic group in comparison with the control group. This is shown in the study of comorbidity, with a significance of P value equal to 0.02. This may be because of high prevalence of dyslipidemia, hypertension, obesity, and other cardiovascular risk factors in diabetic patients. Ischemic heart disease is considered one of the most common causes of death in diabetic patients with peripheral neuropathy [22]. Painful and painless groups showed no statistically significant difference in age, sex, medication, and comorbidity.

The study of glycated products demonstrated that HbA1c was found to be significantly high in both neuropathic and diabetic groups versus control. Regarding AGE, it was statistically higher in neuropathic group compared with control (P<0.011). On the contrary, RAGE was significantly higher in both neuropathic and diabetic groups compared with the control group (P<0.02). Although the neuropathic group has higher level of AGE and RAGE than diabetic group, the difference was statistically nonsignificant. Our results are consistent with a study that showed a significant higher level of serum AGE level by ELISA in T2DM patients having microvascular complications. It showed that AGEs were ∼23% higher in diabetic patients compared with healthy participants and concluded that AGE level has been suggested to act as a predictor of cardiovascular disease mortality and diabetic nephropathy [22]. This also correlates with another study that stated that presence of RAGE in blood was significantly higher in diabetic individuals than controls (P<0.01) [23]. Another research work obtained the same results with a significance of P value equal to 0.028. It concluded that RAGE was independently associated with DPN in individuals with T2DM in a study conducted on 198 T2DM individuals, confirming the relationship between advanced glycoxidation and DPN, independently of other risk factors [24]. Interference of exogenous AGE with the sensitivity of the assay could be the cause of making the difference nonsignificant between neuropathic and diabetic groups in our study, so further studies should consider assessment of exogenous AGE. Correlations between AGE and RAGE and all other variables including age, sex, comorbidity, HbA1c, and parameters of NCS were done for our studied groups, but no statistically significant correlation was found. NCSs can diagnose diabetic neuropathy at a very early stage even before symptoms and signs set in, as demonstrated from a study conducted on 50 diabetic patients and 50 nondiabetic controls of comparable age and BMI [25]. This goes with our study where there was a statistically significant difference in all categories of nerve conduction regarding sural, tibial, and peroneal nerves between neuropathic group and both diabetic and control groups. Painful and painless groups did not show statistically significant difference regarding glycation endproducts and all parameters of NCS. The distinction between painful and painless neuropathy is not clear in the literature. In this study, we tried to study some of the pathogenetic mechanisms of diabetic neuropathy to accuse AGEs and their receptors as one of these mechanisms.


  Conclusion Top


Our study concluded that AGE and RAGE are significantly higher in diabetic patients with neuropathy versus control. Although the neuropathic group has higher level of AGE and RAGE than diabetic group, the difference was statistically nonsignificant, so further studies are suggested to exclude conflicting agents.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11]



 

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