Lymphocyte and Plasma Vitamin C Levels in Type 2 Diabetic Patients With and Without Diabetes Complications

Abstract

Diabetes has been considered to be associated with oxidative stress. It has been suggested that increased free radicals and decline of antioxidant defense mechanisms induce diabetic micro-and macrovascular complications (1-3). Vitamin C is one of the major antioxidants and is detected in various blood components (4). However, measurements of vitamin C levels have shown inconsistent results, and the interpretation of vitamin C levels in diabetes as an antioxidant biomarker has not been clarified (5-8). In this study, we investigated the lymphocyte and plasma vitamin C levels in type 2 diabetic patients with and without diabetes complications. men and 8 women, 137 Ϯ 45 mg/dl, and 7.2 Ϯ 1.0% for diabetic patients with complications compared with 64 Ϯ 7.5 years, 7 men and 8 women, 137 Ϯ 42 mg/dl, and 6.8 Ϯ 0.8% for diabetic patients without complications, respectively). The duration of illness was longer in the diabetic patients with complications than in diabetic patients without complications (13 Ϯ 9.1 vs. 7.7 Ϯ 5.2 years, respectively, P ϭ 0.051). For the normal control subjects, 50 age-and sexmatched healthy volunteers (63 Ϯ 5.7 years, 31 men and 19 women) were recruited. The participants taking vitamin supplements were excluded from the study. All participants gave informed consent before entering the study. The study was conducted in accordance with the Declaration of Helsinki and was approved by the ethics committee at the hospital. RESEARCH DESIGN AND METHODSBlood samples were obtained by vein puncture in the morning while the patients were in the fasting state. Lymphocytes and plasma were prepared by centrifugation and the Ficoll gradients method, then immediately treated with metaphosphoric acid (final 5% wt/wt) to stabilize vitamin C (9,10). These processes were performed within 2 h under cooled conditions on ice to obtain reliable data. The vitamin C samples were stored at Ϫ80°C until analyzed, and the vitamin C (ascorbic acid, reduced form) levels were measured by high-performance liquid chromatography with the electrochemical detector method (11). All samples were handled and stored similarly in both diabetic patients and control subjects.The lymphocyte and plasma vitamin C levels in type 2 diabetic patients were compared with those of the control subjects. The differences between the vitamin C levels in type 2 diabetic patients with and without diabetes complications were also studied. Statistical analysis was performed with the unpaired Student's t test to compare the data between diabetic patients and control subjects and between type 2 diabetic patients with and without diabetes complications. A P value Ͻ0.05 was considered significant. RESULTS -The lymphocyte vitamin C level in diabetic patients was significantly lower than in control subjects (18 Ϯ 4.5 vs. 28 Ϯ 7.9 nmol/mg protein, P Ͻ 0.0001), whereas the plasma vitamin C level was not different (59 Ϯ 19 vs. 53 Ϯ 18 mol/l, P ϭ 0.17) (Fig. 1A and B). There were no significant linear correlations between the lymphocyte and plasma vitamin C levels...

Antioxidant properties of drugs used in Type 2 diabetes management: could they contribute to, confound or conceal effects of antioxidant therapy?

“…There are many reports of decreased antioxidant status in Type 2 DM patients [101][102][103][104][105][106][107]. Studies, summarized in Table 5, show also that Type 2 DM is a condition of increased oxidative stress [44,45,103,[107][108][109].…”

“…Studies, summarized in Table 5, show also that Type 2 DM is a condition of increased oxidative stress [44,45,103,[107][108][109].…”

Peripheral Vitamin C Levels in Alzheimer’s Disease: A Cross-Sectional Study

“…In terms of the vitamin C assay, sample preparation in this study was performed on ice within a 2-h time window. Prepared samples were stored at 280˚C until they were analyzed using the HPLC-ECD method, and all samples were treated in the same manner (12,21). This well-controlled procedure guaranteed the reliability and accuracy of the method.…”

“…Prepared samples were stored at 280˚C until they were analyzed. Vitamin C levels were measured by the HPLC-ECD method as the total concentrations of ascorbic acid and dehydro ascorbic acid, and all samples were treated in the same manner (12,21).…”

“…However, Bowman et al (11) also reported that plasma vitamin C levels did not independently predict cognitive decline in Alzheimer's disease. We previously reported lower lymphocyte vitamin C levels in individuals with type 2 diabetes mellitus compared with healthy controls (12) and in individuals with severe Parkinson's disease compared with those at less severe stages (13). These previous findings suggested that vitamin C levels in the peripheral blood, especially in the lymphocytes, might serve as a biomarker of oxidative stress in various diseases.…”