|Year : 2018 | Volume
| Issue : 3 | Page : 73-85
The role of adrenomedulin and leptin in type 2 diabetes mellitus: can be used as early predictors for its microvascular complications?
Effat A.E Tony1, Manal El Eldeen1, Abeer A Tony2, Tahra El-Shereif3, Madleen A.A Abdou3
1 Department of Internal Medicine, Faculty of Medicine, Assiut University, Assuit, Egypt
2 Department of Neuropsychiatry, Aswan University, Aswan, Egypt
3 Department of Clinical Pathology, Faculty of Medicine, Assiut University, Assuit, Egypt
|Date of Submission||25-Jan-2018|
|Date of Acceptance||27-May-2018|
|Date of Web Publication||09-Nov-2018|
Effat A.E Tony
Nephrology Unit, Internal Medicine and Nephrology Department, Faculty of Medicine, Assuit University, Assuit 71515
Source of Support: None, Conflict of Interest: None
Background Microvascular vasodegeneration is the major factor in progression of diabetic complications. Adipocytokines secrete a variety of hormones and cytokines, which contribute to the development of vascular and renal diseases. Elevated levels of leptin are observed in chronic renal failure and hypertension. Adrenomedulin (AM), with its antiproliferative effects, is considered as an associated factor in the course of vascular and diabetic insults. However, there is lack of knowledge about the precise role, regulation, production and release at the systemic level of AM, and its correlation with the peripheral blood flow in diabetic vascular insult.
Aim We aimed to assess the levels of AM and leptin in type 2 diabetes mellitus (T2DM) patients, to assess their correlations with glycemic control and microvascular complications, and to assess whether these levels vary with the stage of diabetic nephropathy (DN).
Patients and methods This is a prospective study including 100 T2DM patients, aged 32–48 years old. Patients were classified into two groups according to albuminuria (group A) and according to estimated glomerular filtration rate (group B). Participants were subjected to history taking, and clinical and fundus examinations. Peripheral hemogram, liver and kidney function tests, lipogram, glycosylated hemoglobin, urine albumin/creatinine ratio, serum leptin and AM were performed. They also underwent ECG and transthoracic echocardiogram.
Results The levels of leptin and AM were significantly higher in T2DM patients with microvascular complications than in those without (P<0.001 for each). Leptin and AM levels were progressively elevated in all stages of DN, and the increment was dependent on the severity of DN (P<0.001, for each). There was a significant correlation between AM levels and glycosylated hemoglobin among diabetic patients with microvascular complications. Multivariate logistic regression analysis showed that the odds ratio for the presence of DN in the highest leptin was 4.1 (95% confidence interval: 3.88–5.03, P=0.001); therefore, leptin was an independent risk factor for DN.
Conclusion AM and leptin play a role in the pathogenesis of microvasculopathy in T2DM patients. An increased AM and leptin level correlates with poor metabolic control.
Keywords: adrenomedullin, diabetic nephropathy, leptin, microvascular complications, type 2 diabetes mellitus
|How to cite this article:|
Tony EA, El Eldeen M, Tony AA, El-Shereif T, Abdou MA. The role of adrenomedulin and leptin in type 2 diabetes mellitus: can be used as early predictors for its microvascular complications?. J Egypt Soc Nephrol Transplant 2018;18:73-85
|How to cite this URL:|
Tony EA, El Eldeen M, Tony AA, El-Shereif T, Abdou MA. The role of adrenomedulin and leptin in type 2 diabetes mellitus: can be used as early predictors for its microvascular complications?. J Egypt Soc Nephrol Transplant [serial online] 2018 [cited 2019 May 26];18:73-85. Available from: http://www.jesnt.eg.net/text.asp?2018/18/3/73/245127
| Introduction|| |
The prolonged hyperglycemia, altered metabolic pathways and nonenzymatic ,,,, glycation of proteins have a stronger relationship with the complications of diabetes mellitus (DM) . Progressive microvascular vasodegeneration is the major factor in progression of diabetic complications . Hemodynamic-mediated vascular injury was identified as one mechanism in the pathogenesis of diabetic nephropathy (DN). Sustained increase in glomerular capillary pressure driven by increase in plasma flow has been observed in early stages of nephropathy. The elevation in glomerular capillary pressure might be damaging to glomerular endothelial, epithelial, and mesangial cells, thereby initiating and contributing to the progression of nephropathy. Although numerous mediators of diabetic hyperfiltration had been proposed, the exact mechanism remained unclear . It is therefore tempting to speculate that endothelial-derived vasodilator substances like adrenomedullin (AM) could be involved, as plasma midregional proadrenomedullin (MR-pro AM) was increasingly elevated from healthy to renal impaired patients and well correlated to the magnitude of microcirculatory perfusion. AM, which is recognized as an adipokine , is a 52-amino acid peptide, deeply involved in insulin secretion, and its receptors are expressed in the kidneys, especially in the glomerulus and distal nephron . In healthy states, AM circulates at low concentration, which increases significantly in a number of disease states including congestive heart failure, sepsis, essential hypertension, and renal impairment . AM is produced by several cardiovascular tissues including the myocardium, vascular endothelium and vascular smooth muscle, exerting vasodilator, natriuretic, diuretic, angiogenic, antifibrotic and antioxidant actions . Wong et al.  stated that AM might play a role in the pathogenesis of diabetic vasculopathy in type 1 and type 2 diabetes mellitus (T2DM), and it plays a critical role in several other diseases such as cardiovascular and renal diseases. Although a few studies have investigated the relationship between AM and type 1 diabetes , the relationship between AM and T2DM has not been well elucidated. Preliminary studies on small numbers of T2DM patients reported inconsistent results . Adipocytokines are adipose tissue-derived molecules with hormone-like actions that are produced exclusively by adipocytes. They are established metabolic regulators with functions in several other systems including inflammation . Leptin is one of the most abundant adipocytokines. Leptin is essential for normal body weight balance, but the exact mechanisms by which leptin activates hypothalamic neuronal circuit are only known to a limited extent. Leptin most probably inhibits food intake and increases energy expenditure by an interaction with specific leptin receptors located in the hypothalamus . Leptin has been suggested as a sensitive marker for the diagnosis of obesity-related disease. Moreover, leptin exerts atherogenic and angiogenetic effects, and is associated with the development of T2DM and cardiovascular disease. Leptin has been shown to be associated with insulin resistance and inflammatory factors . The kidneys play a substantial role in leptin removal from the plasma by absorbing and degrading the peptide. Some authors suggested that renal leptin degradation is already impaired in patients with mild to moderate renal insufficiency . However, only a few studies have addressed the relationship between plasma leptin levels and diabetic microvascular complications, and showed contradictory results .
| Patients and methods|| |
The present study was conducted on 100 patients with T2DM. The study was approved by the Ethical Committee of Faculty of Medicine, Assiut University, and a written informed consent was obtained from each participant. The T2DM patients (diagnosed according to ADA2010) were classified according to their albuminuria levels (group A) and according to their estimated glomerular filtration rate (eGFR) (group B) into two groups. Group A was then subdivided into group A1 patients with normoalbuminuria (defined as <30 mg/24 h), group A2 patients with microalbuminuria (defined as 30–299 mg/24 h) and group A3 patients with macroalbuminuria (defined as >300 mg/24 h), and the group B was subclassified into five subgroups according to eGFR stages: G1 (≥90 ml/min/1.73 m2), G2 (60–89 ml/min/1.73 m2), G3 (30–59 ml/min/1.73 m2), G4 (15–29 ml/min/1.73 m2) and G5 (≤15 ml/min/1.73 m2). Patients with albuminuria (rather than that caused by DM) had past history of cardiovascular events (heart failure or history of coronary artery disease), infections, apparent autoimmune disease, liver cell failure, respiratory failure and acute diabetic complications; hypertension and diabetic patients on regular hemodialysis were excluded. The eGFR was calculated by the modification of diet in renal disease equation . Patient groups were matched for sex and age. All patients were submitted to full history taking, thorough clinical examination, and anthropometric measures to determine the BMI. Abdominal ultrasound was carried out to exclude patients with obstructive uropathy. ECG and transthoracic echocardiography were performed for all participants. Fundus examination was performed by an ophthalmologist after maximum pupillary dilatation using an ophthalmoscope to identify diabetic retinopathy. After centrifugation to yield platelet-poor plasma from samples on anticoagulants (3.8% sodium citrate) and serum from clotted blood samples, serum and plasma samples were stored in aliquots at −20°C until assay. The following routine laboratory investigations were performed in all patient groups: peripheral hemogram was performed on whole blood samples on EDTA using Beckman Coulter Hmx (Brea, CA, USA), and glycosylated hemoglobin (HbA1c%) will be measured by high-performance liquid chromatography. Liver function tests, kidney function tests and lipid profile were measured by standard laboratory methods using Hitachi 911 autoanalyzer (Roche). 24 h urinary albumin excretion was measured by the immulite analyzer. Serum levels of AM were assessed by ELISA technique using AM (human) (EIA-3418 kit; DRG International Inc., Boehringer Mannheim, Germany). Fasting serum leptin, was measured by RIA using kits supplied by Linco Research (1 and 9), CABIOTECH (CA, USA) Catalog No.: VD220. Urine creatinine and albumin were measured with spectrophotometric analysis. Urinary protein by dip stick method was performed, and the quantitative urine albumin/creatinine ratio in morning spot urine samples was used for standard microalbuminuria determination.
Statistical analyses is carried out using the statistical package for the social sciences (SPSS) (Statistical Package for the Social Sciences Software Program; SPSS Inc., Chicago, Illinois) version 21. Descriptive statistics for each variable is determined. Normally distributed data are expressed as mean±SD. Median and minimum–maximum values are used for variables without a normal distribution. Data with a normal distribution are compared by Student t-test and analysis of variance test. Comparisons of continuous variables with an asymmetric distribution are carried out by using the Mann–Whitney U-test and Kruskal–Wallis test. Associations between the variables are explored using the Pearson correlation and Spearman’s ρ (for data that will not be normally distributed). Binary logistic regression analysis is performed to define variables associated with albuminuria. Receiver-operating characteristic analyses are used to compare the performance and prognostic power of AM, and leptin for albuminuria and diabetic microvascular complications. The predictive validities are quantified as the area under the receiver-operating characteristic curves (c statistics), and the comparisons of c statistics are performed by MedCalc statistic software; Microsoft Office Excel Software program (2010) for Windows (Microsoft Corporation). A P value less than 0.05 is considered significant.
| Results|| |
The demographic data of all our studied T2DM patients is as follows: 64 (64%) patients were male individuals. Their age ranged from 32 to 48 years with a mean±SD of 40.55±7.33 years. The mean±SD of disease duration was 7.61±2.86 years. The mean±SD of MAP was 52.55±5.89. Most of the patients (72%) were overweight; their BMI ranged from 21 to 33 (kg/m2) with mean±SD of 27.09±5.55 (kg/m2). Half of the patients (50%) received oral hypoglycemic agents, and 92% were on conservative renal replacement therapy, while only eight (8%) patients were on hemodialysis on demand (secondary to the occurrence of acute kidney injury, whatever the cause, during the study).
The frequency of clinical main vascular complications in the studied patient groups is as described below. The frequency of microvascular complications was present in 100% of our cases and manifested as follows: retinopathy in 70% of patients; 28.6% of them had proliferative changes while 71.4% of them had nonproliferative changes, 82% of our patients had neuropathy, motor in 15.9%, sensory in 50%, sensorimotor in 46.3% and autonomic features in 34.1%. All studied patients had DN. Meanwhile, the macrovascular complications were present in 55% (of our patients who had microvascular complications) and manifested as follows: angina in 41.8% of patients, peripheral vascular disease in 36.4% and only 21.8% of them had cerebrovascular stroke as shown in [Table 1]. [Table 2] shows that our studied patients were classified according to creatinine clearance into five stages from I to V, wherein most of them (47%) had stage III while none of the patients had stage V. Our patients were classified according to albuminuria as follows: 18 (18%) patients had normoalbuminria, and 31 (31%) of them had microalbuminuria, while 51 (51%) patients had macroalbuminuria. Stage I DN was manifested in 33% of our patients with variable degree of albuminuria, mainly microalbuminuria (16%); these differences were of high statistical significance with a P value of up to 0.001. Stage III DN was manifested in 47% of our patients; 37% of them had an overt nephropathy. These differences were of statistical significance with P value of up to 0.02. However, there was no statistically significant difference among our patients with stage II and VI. Moreover, none of our patients was in stage V, as shown in [Table 3]. There were highly statistically significant differences between different grades of albuminuria and the basic characteristics of our studied patient groups; BMI, disease duration, glycated hemoglobin 1c (HbA1c) (24.09±4.09, 4.44±3.69 and 7.34±1.23 in A1 vs. 26.32±5.01, 5.61±3.33 and 9.91±1.0301 in A2 vs. 26.91±6.78, 8.15±3.55 and 10.78±2.2111 in A3, with P≤0.001 for each, respectively). Male sex was a characteristic feature in our T2DM patients who had an increasing degree of albuminuria with highly statistically significant difference between its different grades (11% in A1 vs. 23% in A2 vs. 36% in A3, with P≤0.001 for each, respectively). However, there were no significant statistical differences between different grades of albuminuria with respect to SBP, DBP and MAP (132.66±8.61, 83.44±3.57 and 49.22±6.25 in A1 vs. 135.09±5.31, 84.46±4.71and 50.54±3.68 in A2 vs. 132.29±7.76, 84.32±2.74 and 50.90±5.57 in A3, with P>0.05 for each, respectively). Moreover, there were highly statistically significant differences between different grades of albuminuria and the mean serum levels of AM and leptin in our patients (22988±4109.35, 55.72±19.03, 135.09±5.31). Patients with macroalbuminuria had more disease duration, HbA1c, BMI, serum levels of leptin and AM compared with those with microalbuminuria and normoalbuminuria with significant P values (P<0.05). With regard to the age of patients, the increased age, the more advanced grade of albuminuria but with no significant statistical difference between different grades of albuminuria. It was noted that patients with microalbuminuria had values in between other two groups (normal and macroalbuminuria), with regard to the significant parameters, as shown in [Table 4]. [Table 5] shows that patients with more advanced stages of DN had more serum levels of adrenomedulin (109.84±14.34, 134.69±17.98, 145.51±19.88 and 172.76±16.98, respectively) with highly significant P≤0.001, P2≤0.001 and P3≤0.03 values. Notably, patients with more advanced stages of DN had more serum levels of leptin (12.28±2.33, 18.29±5.13, 28.63±9.08 and 60.54±10.99, respectively) with highly significant P values up to 0.001 for each stage. In patients with microvascular complications, the mean levels of AM were statistically significantly higher when compared with those patients with macrovascular complications (139.34±30.98 vs. 122.23±33.03; P<0.001, respectively). Notably, the mean levels of leptin were statistically significantly higher when compared with those patients with macrovascular complications (18.69±2.99 vs. 13.01±3.19; P<0.03, respectively), as shown in [Table 6]. [Table 7] shows that 50 patients had nonproliferative retinopathy while proliferative retinopathy presented in 42 patients. The mean serum levels of AM in patients with proliferative retinopathy were statistically significantly higher than those levels in patients with nonproliferative retinopathy (167.28±46.12 vs. 130.44±33.14, with P≤0.001). Moreover, the mean serum levels of leptin in patients with proliferative retinopathy were statistically significantly higher than those levels in patients with nonproliferative retinopathy (29.02±7.02 vs. 18.40±5.09; P≤0.03). Moreover, 82 (82%) patients had different types of DN affection while 18 (18%) patients had no neuropathy. Those patients with DN had statistically significantly higher mean levels of AM compared with those patients without neuropathy (149.62±23.45 vs. 127.82±34.12; P≤0.01, respectively). Moreover, the mean serum levels of leptin in patients with DN were statistically significantly higher than those levels in patients without DN (29.28±10.09 vs. 11.93±4.12; P≤0.001). With regard to proteinuria, 63 patients had proteinuria while no proteinuria presented in 37 patients. The mean serum levels of AM in patients with proteinuria were statistically significantly higher than those levels in patients without proteinuria (169.84±29.68 vs. 105.16±18.12; P≤0.01). Moreover, the mean serum levels of leptin in patients with proteinuria were statistically significantly higher than those levels in patients without proteinuria (29.28±10.09 vs. 11.93±4.12; P≤0.001).
|Table 1 The clinical main vascular complications in all the studied groups|
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|Table 2 Classification of studied patients according to the stage of diabetic nephropathy and the degree of albuminuria|
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|Table 3 The relationship between different stages of diabetic nephropathy and the degree of albuminuria|
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|Table 4 The clinical and laboratory basics of studied patients according to degree of albuminuria|
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|Table 5 The relation between different stages of diabetic nephropathy and the levels of adrenomedulin and leptin in studied patients|
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|Table 6 The mean levels of adrenomedulin and leptin according to presence of macrovascular and microvascular complications in studied patients|
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|Table 7 The relation between microvascular complications with adrenomedulin and leptin levels in studied diabetic patients|
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Statistically significant positive correlations of the mean level of AM with duration of the disease, blood urea, serum creatinine and albuminuria (r=0.34, 0.41, 0.29 and 0.43; P≤0.02, 0.001, 0.04, 0.001, respectively) were found with statistically significant negative correlation with creatinine clearance (r=−0.5; P≤0.001); however, AM was insignificant positively correlated with BMI, HbA1c and blood glucose (r=0.13, 0.05 and 0.34; P=0.11, 0.69 and 0.84, respectively), as shown in [Table 8] and [Figure 1]a–d. Notably, statistically significant positive correlations of the mean level of leptin with duration of the disease, blood urea, serum creatinine and albuminuria (r=0.42, 0.33, 0.42 and 0.47; P=0.01, 0.001, 0.001, 0.001, respectively) were found with statistically significant negative correlation with creatinine clearance (r=−0.4; P≤0.001), as shown in [Table 8] and [Figure 2]a and b. However, leptin was insignificantly positively correlated with BMI and blood glucose (r=0.21 and 0.01; P=0.09 and 0.23, respectively) in our patients, as shown in [Table 8]. As regards the lipid profile, the mean level of low density lipoprotein (LDL) had a highly statistically significant positive correlation with AM and leptin (r=0.60 and 0.41; P=0.02 and 0.001, respectively). Moreover, the mean level of triglyceride had a highly statistically significant negative correlation with AM (r=−0.49; P=0.001), but it was insignificantly positively correlated with leptin (r=−0.1; P=0.09). Nonetheless, there were no correlations between the mean cholesterol levels in leptin or AM. However, high density lipoprotein (HDL) had statistically insignificant positive correlations with AM (r=0.23; P=0.08) and leptin (r=0.01; P=0.34), as shown in [Table 8] and [Figure 3]a and b.
|Table 8 The correlations of adrenomedulin and leptin with different parameters in the studied patients|
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|Figure 1 (a): Correlation between adrenomedulin and duration of diabetes mellitus in the studied patients. (b): Correlation between adrenomedulin and blood urea in the studied patients. (c): Correlation between level of adrenomedulin and creatinine in the studied patients. (d): Correlation between adrenomedulin and creatinine clearance in the studied patients.|
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|Figure 2 (a): Correlation between level of leptin and creatinine in the studied patients. (b): Correlation between leptin and creatinine clearance in the studied patients.|
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|Figure 3 (a): Correlation between adrenomedulin and low density lipoprotein (LDL) in the studied patients. (b): Correlation between adrenomedulin and triglycerides in the studied patients.|
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In the current study, the level of AM with a cutoff value of more than 56 nmol/l was able to detect the diagnosis and prognosis of microvascular complications in our patients with DN with sensitivity of 91% and specificity of 20%, with 87% positive predictive value (PPV) and 27% negative predictive value (NPV). Notably, the level of leptin with a cutoff value of more than 2.73 ng/ml was able to detect the diagnosis and prognosis of microvascular complications in our patients with DN with a sensitivity of 97.56% and specificity of 26.67%, with 88.3% PPV and 66.7% negative predictive value, as shown in [Table 9] and [Figure 4]. [Table 10] shows multivariate regression analysis for prediction of DN wherein duration of DM [odds ratio (OR)=2.33, 95% confidence interval (CI): 2.45–4.78, P=0.04] and level of leptin (OR=4.1, 95% CI: 3.88–5.03, P=0.00) were independent risk factors for DN.
|Table 9 The value of adrenomedulin and leptin for diagnosis and prognosis of microvascular complication in our studied patients with diabetic nephropathy|
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|Figure 4 Prediction of microvascular complications in our studied patients.|
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|Table 10 Multivariate regression analysis for prediction of diabetic nephropathy|
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| Discussion|| |
DM, a chronic progressive disease characterized by altered glucose homeostasis, is a significant cause of global morbidity and mortality. T2DM has been postulated to be a generalized inflammatory condition resulting from obesity-induced dysregulation of adipocytes, which produce an excess of inflammatory cytokines . A persistent inflammatory state further contributes to the development of the extensive vascular disease characteristic of diabetes and is implicate in the progression of chronic kidney disease ,. The disturbance of diabetic complications is based on microangiopathy. Vascular bed damage may be originated by chronically stimulated high glucose and advanced glycosylated end product, which might be mediated through cytokines, adipokines, and oxidized stress like oxidized low-density lipoprotein . It is thought that adipocytokines contribute to the increased risk of vascular complications in T2DM. However, there is still limited information on the relationship between microangiopathies and adipocytokines, such as leptin in patients with T2DM . The present study aimed to assess plasma AM and leptin levels in patients with T2DM, and their correlations with metabolic control and diabetic microvascular complications.
In the current study, most of our diabetic patients had more advanced stages of DN, which were associated with the degree of albuminuria. Moreover, in the more advanced stages of DN, the absence of albuminuria was the characteristic feature. Although albuminuria is considered a key aspect of the pathogenesis of progressive kidney dysfunction, the progressive reduction in GFR could be described in patients with T2DM in the absence of proteinuria, indicating that the associations with albuminuria and reduced eGFR are strong and independent across the range of observed values in T2DM patients. These results were in agreement with Kramer et al.  who stated that CKD with creatinine clearance (<60 ml/min/1.73 m2) occurs in the absence of increased urine microalbumin excretion in a substantial proportion of adults with T2DM. Notably, Caramori et al. , Ninomiya et al.  and MacIsaac et al.  reported that this phenomenon of reduced GFR in the absence of significant albuminuria was previously described in several epidemiologic data of patients with T2DM, although the clinical sequelae in such patients has not been previously determined. However, Kumar et al.  stated that the degree of microalbuminuria is associated with elevated serum creatinine and decreased creatinine clearance, reflecting kidney function impairment. Adipose tissue secretes adipocytokines, which influence glucose and lipid metabolism, inflammatory processes, and other bioactivities. Leptin, the most abundant adipocytokine, is essential for normal body weight balance, but the exact mechanisms by which leptin activates hypothalamic neuronal circuit are only known to a limited extent. Most probably leptin inhibits food intake and increases energy expenditure via an interaction with specific leptin receptors located in the hypothalamus . Leptin was found to be increased in conditions such as obesity, insulin resistance, T2DM, macrovascular complications and coronary artery disease . In our study, most of the diabetic patients had microvascular complications. The diabetic microvascular complications are principally driven by vascular inflammation. The potential role of adipocytokines in vascular disease is intriguing; in particular, diminishing the inflammatory state of diabetes may be central in modifying risk for progressive endothelial dysfunction and renal disease ,. Therefore, the role of leptin has been addressed.
In the current study, the statistically significant highest mean levels of leptin were found in our T2DM patients, especially those patients with more advanced stages of DN; these had proliferative retinopathy and neuropathy. Notably the mean levels of leptin were statistically significantly highest in our diabetic patients who had specifically mixed motor and sensory neuropathy. In addition, we showed the elevated serum leptin concentrations in T2DM patients with more advanced stages of DN and advanced stages of renal disease (i.e. macroalbuminuric more than microalbuminuric nephropathy); these results could be related to its impaired degradation by the affected kidney. Hyperleptinemia may play a role in the presence of anorexia, malnutrition and decreased BMI that usually accompanied chronic renal failure. It might be concluded that serum leptin levels are elevated in patients with noninsulin DN with microalbuminuria progressing to macroalbuminuria, suggesting that renal leptin degradation is impaired in the early stages of renal disease, and this impairment increases with the progression of renal disease. Our findings were in contrast with Sari et al.  who showed that leptin levels were not different between patients with and without DN, retinopathy and neuropathy. Notably, Jung et al.  reported that the kidney plays a substantial role in leptin removal from the plasma by absorbing and degrading the peptide; some authors suggested that renal leptin degradation is already impaired in patients with mild to moderate renal insufficiency. As regards retinopathy, Uckaya et al.  and Jung et al.  reported that plasma levels of leptin are elevated in T2DM patients with retinopathy, proportionate to the severity of retinopathy. Leptin-induced promotion of angiogenesis and neovascularization lends support to the possibility that leptin might play a role in the progression of diabetic retinopathy to a proliferative phase. Leptin has been shown to be associated with insulin resistance and inflammatory factors. Moreover, in agreement with Kopeisy et al. , Jung et al.  and Jung et al.  the highly significant positive correlations of leptin with blood urea, serum creatinine and albuminuria, BMI, and a significant negative correlation with creatinine clearance (mg/min) in our patients, were found suggesting that leptin levels may increase with the progression of DN. Hypertriglyceridemia is common in T2DM and is caused by overproduction of very low density lipoprotein (VLDL) in the liver and a deficiency of lipoprotein lipase, an insulin dependent enzyme. In our study, the nonsignificant positive correlations of serum leptin levels with cholesterol, triglycerides (TG) and HDL, together with a significant positive correlation between the LDL cholesterol and the leptin levels were observed. Our findings were in concordance with Nevelsteen et al.  who stated that there is no significant correlation between leptin and triglyceride. However, our result disagreed with Lucyna et al.  and Kopeisy et al.  who demonstrated that leptin and triglyceride are significantly positively correlated. As regards the degree of glycemic control in our patients, serum leptin showed an inverse correlation with HBA1c, with no statistical significance. Our results were in agreement with. Kopeisy et al. , who found no correlation between leptin and HbA1c, indicating that leptin is not affected by the degree of glycemic control. Nevertheless, our findings were in contrast with Lim et al. , who reported a significant inverse association of serum leptin with HbA1c, suggesting that HbA1c may be a factor that impacts serum leptin levels, and poorly controlled hyperglycemia may reduce leptin levels.
Secretion of vasoactive factors such as AM has been intensively investigated because of its vascular protective properties and promising potential as a therapeutic target. In the light of our study, we found that AM was significantly associated with diabetic microvascular complications. It was found, in consistence with Waked et al. , that plasma AM concentration was statistically significantly elevated in all diabetic patients with and without nephropathy, and its plasma increment was dependent on the severity of DN. This finding could be explained by the fact that kidney is an important source of AM, whereas the pulmonary vascular bed could be the main site of receptor-dependent clearance of circulating AM. In contrast, the exact site of clearance for MR-pro AM is not known at the moment. Therefore, Kato et al.  and Waked et al.  stated that the possible explanation for the elevated plasma MR-pro AM concentration among T2DM patients with nephropathy could be a reduced MR-pro ADM clearance. Moreover, the levels of AM were statistically significantly elevated in our patients with proliferative retinopathy and neuropathy.
Notably, Lim et al.  and Er et al.  stated that plasma levels of AM increased in patients with T2DM, and its levels have been found to be increased significantly in patients with microvascular complications. Waked et al.  stated that AM could exert a wide range of vascular actions (mostly protective). These include endothelium-dependent and independent vasodilatation, antioxidative stress, stimulation of endothelial nitric oxide production, antiproliferation of vascular smooth muscle cell, and adventitial fibroblast; taken together, the elevation of plasma MR-pro AM concentration in T2DM (especially in the presence of nephropathy) could be an appropriate physiological response to ongoing vascular injury. Factors that upregulate AM are incompletely understood. It is suggested that hyperglycemia might increase vascular AM expression. Katsuki et al. , and Sugo et al.  suggested other mechanisms including acute hyperinsulinemia, increased oxidative stress and proatherogenic/inflammatory factors such as angiotensin II and endothelin-1 to be involved.
In the current study, we found statistically significant highest AM levels in our diabetic patients with more advanced stages of DN and in patients with microalbuminuria and macroalbuminuria compared with those with normoalbuminuria. Moreover, we found also a positive correlation between AM and creatinine and a negative correlation between AM and creatinine clearance. These findings were in agreement with Garcia-Unzueta et al. , who reported that diabetic patients with renal insufficiency had higher levels of plasma ADM than diabetics with other complications, and plasma AM increase was proportionate to kidney function deterioration, and the higher levels of ADM and cAMP were found in patients with renal insufficiency, but their levels were normal in microalbuminuric patients. Moreover, Waked et al.  stated that plasma AM levels were increased in patients with renal impairment in microcirculatory perfusion. Therefore, AM might play a role in the pathogenesis of diabetic vasculopathy. Furthermore, we found significant increased ADM levels with longer duration of diabetes, which was consistent with Garcia-Unzueta et al. , who reported a similar relationship, suggesting that the elevation of ADM levels is a late phenomenon caused by endothelial dysfunction. Moreover, there was a significant correlation between ADM levels and HbA1c with higher HbA1c levels among diabetics with microvascular complications. This result was in agreement with Caliumi et al.  who reported that increased circulating ADM correlates with poor glucose metabolic control in T2DM patients. Lim et al.  stated that the relationship between LDL cholesterol and AM is poorly understood. It is suggested that oxidized LDL might stimulate the secretion of AM. Moreover, Iemura-Inaba et al.  found that AM and its receptor component were highly expressed in cultured adipocytes and may play a role in lipid metabolism by a different signaling pathway. In the current study, the levels of AM and leptin could be considered as good predictors [at cutoff value of >56 nmol/l with significant high sensitivity (91%) for AM and at a cutoff value of >2.73 ng/ml with significant high sensitivity (97.56%) for leptin] for the diagnosis of microvascular complications in our patients with DN. Notably, AM with significant PPV (87%) and leptin with significant PPV (88.3%) could be considered as good predictors for the prognosis and severity of microvascular complications in DN. Multivariate logistic regression analysis for prediction of DN showed that the OR for the presence of nephropathy in the highest tertile of leptin was 4.1 (95% CI: 3.88–5.03, P=0.001), and the duration of T2DM, 2.33 (95% CI: 2.45–4.78, P=0.04); therefore, they were independent risk factors for DN. In essence, based on our results, leptin and AM are supposed to play a role in the pathogenesis of microvasculopathy in T2DM patients with DN. Hence, they can be used to identify high-risk patients, and modulating their actions would have therapeutic potential in the prevention of DN. Future prospective studies with larger numbers of patients are required to establish a direct relationship between plasma adipocytokines’ concentrations and the development or severity of diabetic microangiopathies.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]