Comparison of different risk factors that result in endothelial damage leading to diabetic microangiopathy. (Original Article).

Abstract: In this study, the effect of different risk factors (hyperglycemia, hypertension, hyperlipidemia, hyperuricemia) on endothelial damage was evaluated in 61 (two of them were type 1; the other patients were type 2) diabetic patients. von Willebrand factor antigen was used as the marker of the endothelial damage. Although there was no significant decrease (P > 0.05) in von Willebrand factor level after regulation of nonregulated diabetes, a significant decrease was determined in nonregulated and hypertensive diabetic patients after improvement of risk factors (P < 0.05). As a result, nonregulated diabetes alone has less effect than nonregulated diabetes plus other risk factors (particularly hypertension) on diabetic angiopathy.

Key Words: diabetes mellitus, endothelial damage, von Willebrand factor

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Chronic endothelial damage plays an important role in the development of angiopathy in diabetes mellitus. (1) Because diabetic nephropathy is not determined in 40% of patients with nonregulated diabetes mellitus Type 1, it is believed that the role of hyperglycemia in angiopathy development is not very important. In addition to hyperglycemia, factors such as hypertension, hypercholesterolemia, hyperuricemia, and genetics accelerate the development of angiopathy. Once diabetic nephropathy is developed, its progression is not slowed down significantly by tight glucose regulation when compared with the regulation of hypertension. (2)

von Willebrand factor (vWF) is reported as n marker of endothelial damage in many recent articles. An increase in the serum level of vWF was observed in diseases that cause endothelial damage such as vasculitis, (3) systemic lupus erythematosus, rheumatoid arthritis, (4-6) scleroderma diabetes mellitus, (8-10) glomerulonephritis, (11) viral infections, toxemia of pregnancy, homocystinemia, myocardial infarction, and thromboembolic events. As microalbuminuria increases in diabetic nephropathy, vWF antigen level also increases. (9, 10, 12)

Serum vWF's synonyms are VIII R:Ag, VIII ag, VIII vWF, and antihemophilic factorlike protein. vWF is a glycoprotein that is formed from sequenced high molecular weight (200,000-240,000) subunits. It has a large multimeric structure and an average molecular weight of 1,200,000 (1-30 million). It is synthesized in the endothelium and megacaryocytes and is present in endothelial cells and platelets. It has a biologic half-life of 22 to 40 hours. vWF antigen is an antigenic expression of vWF. It is measured with the immunoassay method using n heterologous antibody. Its synonyms are factor VIII R:ag and antihemophilic factor (AHF)-like 13 antigen. Its normal serum value is 43 to 150% mg. (13)

In this study, we investigated the effect of hyperglycemia alone on the development of diabetic angiopathy among diabetic patients (type l or 2), as well as the contribution of other risk factors such as hypertension, hypercholesterolemia, and hyperuricemia together with hyperglycemia on endothelial damage and whether progression of the lesions can be stopped with correction of these factors

Materials and Methods

Sixty-one patients (two of them were type 1, the other patients were type 2) with diabetes mellitus were included in the study. Patients were being followed up at Istanbul University, Istanbul School of Medicine, Internal Medicine and Diabetes outpatient clinics. The age of the patients was more than 40 years. Their diabetes age was more than 5 years. None of them used cigarettes, alcohol, or any other drug except insulin or oral antidiabetic agents. Absence of ischemic heart disease was proved with clinical evaluation and electrocardiogram. Platelet count was more than [10.sup.5]/[mm.sup.3] in all of the patients.

Patients were divided into five different groups: group 1, 12 nonregulated diabetic patients (mean age, 51.33 [+ or -] 6.70 years) with normal blood pressure, lipidemia (cholesterol and triglyceride), and serum uric acid levels; group 2, nine regulated diabetic patients (mean age, 53.66 [+ or -] 7.05 years) with normal blood pressure and serum uric acid levels but who were hyperlipidemic (high cholesterol or triglyceride levels); group 3, 15 regulated diabetic patients (mean age, 50.00 [+ or -] 4.44 years) with normal lipidemia and serum uric acid levels but who were hypertensive (systolic and/or diastolic hypertension); group 4, 17 nonregulated diabetic patients (mean age, 60.35 [+ or -] 6.32 years) with normal lipidemia and serum uric acid levels but who were hypertensive (systolic and/or diastolic hypertension); and group 5, eight regulated diabetic patients (mean age, 53.12 [+ or -] 8.35 years) with normal blood pressure and/or lipidemia but who were hyperuricemic.

Serum samples were obtained from each subject before and after the correction of the inappropriate variable, and the samples were stored at - 20[degrees]C. All the samples collected from 61 patients were assessed by enzyme-linked immunosorbent assay at the same time. AZFE01 Malakit Factor VIII R Ag ELISA kit with a 40 to 200% mg as a normal for vWF was used. Glucose, triglyceride, cholesterol, and uric acid were measured by Bayer Diagnostic Technicon DAX-72 autoanalyzer. All of the results were evaluated statistically by the Wilcoxon paired two-sample test.

Results

The results of our study are shown in Table 1. Diabetes regulation was established after 6 months by insulin or oral antidiabetic agent. Normalized hemoglobin A1C (<7.2%) was accepted for diabetes regulation. Angiotensin-converting enzyme inhibitors and calcium-channel blockers were used for antihypertensive therapy. Hyperuricemia was controlled with allopurinol. Gemfibrozil and 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors were given for hyper-lipidemia therapy. Blood pressure and serum lipid (cholesterol and/or triglyceride) and uric acid regulation were established, respectively, after 2, 4, and 3 months. As can be seen from Table 1, the serum levels of vWF decreased significantly from the baseline values after the correction of risk factors in groups 2, 3, and 4. In Group 1, in which hyperglycemia was a risk factor, hyperglycemia and hemoglobin Al C values decreased whereas vWF levels increased significantly after the treatment. In all of the other four groups, risk factors were corrected si gnificantly after treatment. The decrease in the vWF level was more pronounced in Group 3 with hypertension and in Group 4 with both hypertension and hyperglycemia as the risk factors.

Discussion

It is well established that endothelial damage is the primary triggering pathology of the microvascular and macro-vascular complications of diabetes mellitus. However, it is not known precisely which of the risk factors among hypertension, hyperlipidemia, and hyperglycemia is more important for endothelial damage resulting in angiopathy. There are many different views about the relationship between hyperglycemia and diabetic complications. Diabetologists believe that with a good control of hyperglycemia, major complications of diabetes can be prevented. Fasting hyperglycemia persisting longer than 10 years in any diabetes type results in typical complications; (14-16) the degree of hyperglycemia correlating with the severity of microangiopathy in diabetic dogs and rats and the transplantation of a kidney from a nondiabetic donor to a diabetic recipient resulting in typical glomerulosclerosis among animals and humans (17) could be mentioned in support of this thesis. On the other hand, some authors suggest th at, as in our study group 1 in which hyperglycemia was the only risk factor, hyperglycemia cannot be associated with endothelial damage resulting in microangiopathy. For example, in support of this thesis it is shown that microangiopathy can be detected in patients who have just recently been diagnosed as having diabetes mellitus; (18) patients with a long history of diabetes have a slowly progressing vascular disease, and lowering the blood sugar level does not decrease the incidence of complications. (19) Although keeping both of these theories in mind, it is generally accepted that hyperglycemia has an untoward effect on diabetic complications. (11,20,21) Our results suggest that hyperglycemia by itself does not cause endothelial damage leading to microangiopathy.

Risk factors such as hypercholesterolemia and hypertension are more effective than isolated hyperglycemia and hyperuricemia in producing endothelial damage. Especially the significant decrease in vWF antigen level after the correction of hypertension in groups 3 and 4 was more pronounced than the decrease after the correction of hypercholesterolemia, and this finding supports the untoward effect of hypertension. In the literature it is shown that both hypercholesterolemia (22-26) and hypertension (27-30) have a role in endothelial damage. In addition, as in group 4, whenever hypertension and hyperglycemia are present together, the increase in vWF is greater than each one's separate effect (Fig. 1). It is concluded that hypertension and hyperglycemia have a synergistic effect on endothelial damage and microangiopathy.

When hypertension and hypercholesterolemia are investigated comparatively, basal vWF antigen level is higher in the hypercholesterolemic group, but after the correction of the present problem, the decrease in vWF antigen level is significantly higher in the hypertensive group (Fig. 1).

Interestingly, vWF antigen level was high among hyperuricemic patients. However, the decrease in it was not significant after the improvement of hyperuricemia. As a result, all the risk factors such as hypertension, hyperglycemia, hypercholesterolemia, and hyperuricemia, associated with endothelial damage and microangiopathy, caused an increase in vWF antigen levels. It is concluded that especially hypertension and hypercholesterolemia are important in the progression of microangiopathy, whereas isolated hyperglycemia does not have such strong negative effects. Therefore, it must once more be emphasized that in the prevention of vascular complications of diabetes mellitus, hypertension and hypercholesterolemia must be strictly controlled.

Fig. 1

Baseline vWF levels in all groups.

1   71.75
2   98.44
3   90.53
4  149.35
5  106.62

Note: Table made from bar graph

Table 1

Study results (a)

                                BT       AT   P value

Group 1  FBG (mg/dl)          280.58  150      <0.01
         [HbA.sub.1]c (%)      10.65    7.52   <0.01
         vWF Ag (mg/dl)        71.75   78.5    >0.5

Group 2  Cholesterol (mg/dl)  311.5   187.7    <0.01
         vWF Ag (mg/dl)        98.44   54.77   <0.5

Group 3  * SBP (mm Hg)        192     158.33  <0.001
         * DBP (mm Hg)        100.66   92.66  <0.001
         vWF Ag (mg/dl)        90.53   46.6    <0.05

Group 4  FBG (mg/dl)          296.35  163.29  <0.001
         [HbA.sub.1]c (%)      11.84    7.78  <0.001
         SBP (mm Hg)          194.41  157.05   <0.01
         DBP (mm Hg)          106.76   93.82   <0.01
         vWF Ag (mg/dl)       149.35   87.47   <0.05

Group 5  Uric acid (mg/dl)     10.9     7.1    <0.5
         vWF Ag (mg/dl)       106.62   81.87   >0.5

(a) BT, before therapy; AT, after therapy; FBG, fasting blood glucose;
SBP, systolic blood pressure; DBP, diastolic blood pressire; vWF ag, von
Willebrand factor antigen; Hb, hemoglobin. Normal values: FBG, 70-110
mg/dl; cholesterol, 130-200 mg/dl; triglyceride, 40-170 mg/dl; uric
acid, 2.5-7.5 mg/dl; SBP, <160 mm Hg; DBP, >95 mm Hg.

Accepted August 20, 2002.

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RELATED ARTICLE: Key Points

* In addition to hyperglycemia, factors such as hypertension, hypercholesterolemia, hyperuricemia, and genetics accelerate the development of angiopathy.

* Particularly, hypertension and hypercholesterolemia are important in the progression of microangiopathy whereas isolated hyperglycemia does not have such strong negative effects.

* Therefore, hypertension and hypercholesterolemia must be strictly controlled for prevention of vascular complications of diabetes mellitus.

From the Divisions of Nephrology and Cardiology, Department of Internal Medicine, Istanbul School of Medicine, Istanbul, Turkey.

Reprint requests to Seyit Kayacan, MD, Izzetin Calislar cad. Karaoglan sokak, Kamelya Apartment 36, D-12, Bahcelievler, Istanbul, Turkey. Email: [e-mail]

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