Purpose
To investigate whether plasma pentosidine, a well-defined advanced glycation end product, is associated with retinal hemodynamic abnormalities in patients with type 2 diabetes.
Design
Prospective cross-sectional study.
Methods
Forty-two eyes with type 2 diabetes mellitus were evaluated. The type 2 diabetic eyes were divided into 2 groups: 22 eyes (22 patients; mean age, 61 years) with nondiabetic retinopathy (NDR) and 20 eyes (20 patients; mean age, 61 years) with mild nonproliferative diabetic retinopathy (NPDR). We used a retinal laser Doppler system to measure the arterial diameter, velocity, and blood flow in the major temporal retinal arteries. The pulsatility ratio, a resistive index expressed as the peak systolic to the end diastolic velocity ratio, was calculated from the blood velocity traces. Plasma pentosidine was measured in 42 patients with diabetes using a commercially available competitive enzyme-linked immunosorbent assay.
Results
The pulsatility ratio significantly increased in patients with NPDR (4.8 ± 1.5) compared with patients with NDR (3.7 ± 0.8) ( P = .0061). No differences in velocity, diameter, or blood flow were seen between the 2 groups. Plasma pentosidine levels also increased significantly ( P = .0085) in patients with NPDR (0.057 ± 0.015) compared to patients with NDR (0.047 ± 0.012). The pulsatility ratio was correlated positively with the plasma pentosidine levels in patients with NPDR (Pearson correlation, r = 0.45, P = .044). Multiple regression analysis showed that the plasma pentosidine level was significantly associated with the pulsatility ratio (standardized coefficient, 0.62; P = .009).
Conclusions
The vascular rigidity of the retinal arteries may increase with increasing plasma pentosidine in patients with type 2 diabetes with retinopathy.
Diabetic retinopathy (DR), the leading cause of irreversible blindness among individuals in the work force in Western countries, includes both vascular and neural dysfunction. The earliest clinical signs of DR are microaneurysms, small outpouchings from retinal capillaries, and dot intraretinal hemorrhages. Specific morphologic and functional changes include basement membrane thickening, loss of pericytes, and increased permeability. In addition to previous studies that have reported abnormal retinal hemodynamics in patients with type 1 diabetes mellitus and DR, we recently reported that the retinal blood flow decreased in early-stage retinopathy in type 2 diabetic mellitus. Taken together, abnormal retinal circulation might play a role in the development of DR in type 1 and 2 diabetes. However, the cause of the impaired retinal microcirculation in the pathogenesis of DR in patients with type 2 diabetes is unclear.
Advanced glycation end products, which have an important role in diabetic complications in several organs, are generated by nonenzymatic glycation and oxidation of protein and reducing sugars, prevalent in the diabetic vasculature, and contribute to the development of atherosclerosis. Therefore, advanced glycation end products contribute to a variety of microvascular and macrovascular complications through formation of abnormal cross-links in collagen, which contribute to vascular stiffness. Although advanced glycation end products accumulate in the diabetic retinal microvasculature, it remains unclear whether advanced glycation end products affect the retinal hemodynamics in patients with type 2 diabetes.
Among the few advanced glycation end products characterized to date, pentosidine is chemically well defined. Plasma pentosidine was reported to be significantly higher in patients with diabetes than in subjects without diabetes and associated with an increased incidence of cardiovascular disease and increased stiffening and thickening of the large arteries in patients with type 2 diabetes. However, the effect of pentosidine on the microcirculation, including the retina, is unclear.
Although accumulated advanced glycation end products may increase the vascular stiffness in the retinal microvasculature, no study has examined the relation between the plasma advanced glycation end product levels and the retinal circulation in patients with type 2 diabetes. We investigated whether plasma pentosidine levels are associated with retinal blood flow dynamics in patients with type 2 diabetes.
Methods
Forty-two patients with type 2 diabetes were enrolled. Internal medicine specialists at Asahikawa Medical University Hospital diagnosed the type 2 diabetes. Subjects with other ocular diseases, such as glaucoma, a history of laser treatment, retinal vessel occlusion, or intraocular surgery that might affect the retinal circulation were excluded. Patients with renal impairment or rheumatoid arthritis were excluded from this study, because these conditions increase the plasma pentosidine level.
All patients underwent a baseline ophthalmic evaluation before measurement of the retinal blood flow. For each eye, the maximal grade in any of the 7 standard photographic fields was determined for each lesion and used to define the retinopathy levels. The severity of the retinopathy was categorized as none (level 10), mild nonproliferative (levels 21−37), moderate-to-severe nonproliferative (levels 43−53), or proliferative (levels 60−65). Patients were excluded who had moderate-to-severe nonproliferative DR and proliferative DR and clinically significant macular edema. The eye with the worse retinopathy that met the inclusion criteria was included. If both eyes had equal retinopathy, 1 eye was randomly assigned to the study. The patients were divided into 2 groups: patients with nondiabetic retinopathy (NDR group) (22 patients; mean age, 61 ± 12.6 years [mean ± standard deviation (SD)]) and those with mild nonproliferative DR (NPDR group) (20 patients; mean age, 61 ± 9.7 years).
Measurement of Blood Samples
On the day of the study, venous blood was obtained from all subjects. Random plasma glucose, hemoglobin A1C (HbA1C), serum creatinine, and lipid levels (total, high-density lipoprotein, and low-density lipoprotein cholesterol and triglycerides) were measured immediately using standard methods. Plasma pentosidine concentrations were measured using a commercially available competitive enzyme-linked immunosorbent assay (ELISA) (FSK pentosidine ELISA kit; Fushimi Pharmaceutical, Kagawa, Japan); the samples were stored at −80 C until analysis.
Measurement of Retinal Blood Flow
A retinal laser Doppler velocimetry system (Canon Laser Doppler Flowmeter CLBF model 100; Canon, Tokyo, Japan) estimated the blood flow in the major temporal retinal arterioles. The details of the laser Doppler velocimetry system were reported previously. Briefly, a retinal laser Doppler velocimetry system allows noninvasive measurement of absolute values of the red blood cells (RBCs) flowing in the centerline of the vessel, based on bidirectional laser Doppler velocimetry. A probing red laser light (wavelength, 675 nm) is emitted from a fundus camera-like measurement head. The red Doppler-shifted light scattered from the flowing RBCs in the retinal vessels is detected simultaneously by 2 photomultiplier tube detectors and undergoes computer-controlled spectrum analysis, and the centerline velocity of the RBCs is automatically measured sequentially over 2 seconds, which results in a velocity-time trace. This device also can measure vessel diameter and track the vessel. The green strip (wavelength, 543 nm) is oriented perpendicular to the axis of the vessel. During the session, a linear image sensor obtains 15 profiles of the target vessel illuminated by a green laser beam every 4 milliseconds just before and after each velocity measurement. The vessel diameter of the retinal artery is determined automatically by computer analysis of the signal produced by the arterial image on the array sensor using the half-height of the transmittance profile to define the vessel edge. In combination with the average velocity (V mean ) over a cardiac cycle and the diameter, the retinal blood flow through the vessel can be calculated assuming Poiseuille flow and a circular vessel profile.
In addition, the pulsatility ratio, an index of vessel rigidity, was calculated from the blood velocity traces. Pulsatility ratio is expressed as V max /V min , where V max is the peak systolic velocity during systole and V min is the end diastolic velocity.
Statistical Analysis
All data are expressed as the mean ± SD. The differences between the groups were analyzed using the Mann-Whitney U test. The χ 2 test with Yates correction was used for frequency data. Pearson correlation analysis was used to study the relation between plasma pentosidine and the circulatory parameters. Multiple regression analysis was performed to determine the relationship of the pulsatility ratio to plasma pentosidine, plasma glucose, HbA1C, blood pressure, and patient age. P < .05 was considered significant.
Results
The patient clinical characteristics and laboratory data are shown in Table 1 . No significant differences were seen between the groups in age, sex, body mass index, blood pressure, serum HbA1C, glucose, or lipid profiles. The serum creatinine values were normal in all subjects, and no patients with diabetes had nephropathy. The only significant difference between the groups was in the plasma pentosidine level, which was significantly higher in patients with NPDR compared with patients with NDR ( Figure 1 ) . The plasma pentosidine level was not correlated with HbA1C (r = −0.027) or glucose (r = −0.27) in patients with type 2 diabetes.
| Parameter | NDR | NPDR | P Value |
|---|---|---|---|
| Number of patients | 22 | 20 | |
| Age (years) | 61 ± 12 | 61 ± 10 | .89 |
| Sex (male/female) | 9/13 | 11/9 | .60 |
| BMI (kg/m 2 ) | 24.5 ± 4.6 | 22.6 ± 3.4 | .27 |
| Systolic BP (mm Hg) | 134 ± 17 | 135 ± 23 | .61 |
| Diastolic BP (mm Hg) | 72 ± 10 | 71 ± 11 | .86 |
| Heart rate (beat/min) | 72 ± 14 | 73 ± 8 | .72 |
| Pentosidine (μg/mL) | 0.047 ± 0.012 | 0.057 ± 0.015 | .0085 b |
| Plasma glucose (mg/dL) | 173.4 ± 93.2 | 138.5 ± 44.5 | .18 |
| HbA1C (%) | 7.5 ± 2.7 | 7.6 ± 1.4 | .43 |
| Total cholesterol (mg/dL) | 187 ± 41 | 177 ± 34 | .16 |
| Triglyceride (mg/dL) | 112 ± 53 | 96 ± 32 | .54 |
| HDL cholesterol (mg/dL) | 59 ± 14 | 58 ± 16 | .59 |
| LDL cholesterol (mg/dL) | 112 ± 36 | 103 ± 35 | .28 |
| Serum creatinine (mg/dL) | 0.67 ± 0.18 | 0.70 ± 0.17 | .51 |
a The data are expressed as the means ± standard deviation. Differences between groups were analyzed by Mann-Whitney U test. Categorical data were compared using the χ 2 test.
The group-averaged diameter, velocity, and retinal blood flow values were, respectively, 108.2 ± 9.8 μm, 35.2 ± 8.4 mm/s, and 10.0 ± 3.1 μL/min in patients with NDR and 105.6 ± 10.9 μm, 37.2 ± 9.1 mm/s, and 9.9 ± 3.3 μL/min in patients with NPDR. These parameters did not differ significantly between the groups.
The pulsatility ratio was 3.7 ± 0.8 in patients with NDR and 4.8 ± 1.5 in patients with NPDR, a difference that reached significance ( P = .0061) ( Figure 2 ) .
Table 2 shows the results of the Pearson correlation analysis between the plasma pentosidine level and the retinal circulation parameters in patients with type 2 diabetes with NDR and NPDR. The plasma pentosidine level in patients with NPDR was correlated positively with the pulsatility ratio (r = 0.45; P = .044) ( Figure 3 ) . Multiple regression analysis showed that the plasma pentosidine level was associated significantly (standardized coefficient, 0.62, P = .009) with the pulsatility ratio ( Table 3 ).
| NDR | NPDR | |||
|---|---|---|---|---|
| Circulatory Parameter | r | P Value | r | P Value |
| Vessel diameter (μm) | 0.01 | .94 | 0.13 | .57 |
| Velocity (mm/s) | 0.08 | .73 | 0.35 | .14 |
| V max (mm/s) | 0.10 | .65 | 0.19 | .42 |
| V min (mm/s) | −0.0002 | .99 | −0.18 | .45 |
| Retinal blood flow (μL/min) | 0.03 | .89 | 0.35 | .13 |
| Pulsatility ratio | 0.17 | .46 | 0.45 | .044 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
