The relationship between chronic glycaemic control and oxidative stress in type 2 diabetes mellitus.

This study compares the lipid peroxidation marker urinary thiobarbituric acid reactive substances (TBARS) and antioxidants including plasma alpha-tocopherol (vitamin E), plasma (P-GSH-Px) and erythrocyte glutathione peroxidase (E-GSH-Px) activities, and plasma selenium levels in two groups of type 2 diabetic subjects (both n=20) with a disease duration of < or =2 (GP1) and 4-6 years (GP2), and non-diabetic age and gender-matched control subjects (CG, n=20). The mean (standard deviation [SD]) age of the groups was similar at 41(10) years. Fasting blood and midstream urine samples were obtained from diabetic and non-diabetic subjects attending the diabetic clinic and HbAlc, fructosamine, urine TBARS, total antioxidant (TAS) levels, P-GSH-Px, E-GSHPx and plasma selenium and vitamin E concentrations were measured. HbA1c (%) and fructosamine levels in the GP1 and GP2 diabetic subjects and the controls were 5.75 (0.67), 11.43 (2.01) and 4.33 (0.47), and 3.09 (0.57), 6.09 (1.15) and 1.67 (0.31), respectively (GP1 vs. GP2, GP1 vs. GC and GP2 vs. CG, all P < 0.001). Elevated urinary TBARS (micromol/mmol urinary creatinine) in the GP1, GP2 and GC groups were 2.47 (0.37), 3.73 (0.93) and 1.18 (0.24), respectively (GP1 vs. GP2, GP1 vs. GC and GP2 vs. CG, all P < 0.001). A significant correlation between HbA1c and TBARS was also noted (r2 = 0.894, P < 0.001) but only in the GP2 subjects. TAS levels were only decreased in the GP2 group compared to control values (0.59 [0.18] vs. 1.74 [0.21], P < 0.001). Plasma vitamin E concentrations (micromol/L) of 34.11 (3.31), 9.57 (2.20) and 39.01 (2.91) were observed in the GP1, GP2 and GC groups, respectively (GP1 vs. CG, P < 0.05 and GP1 vs. GP2 and GP vs. CG, both P < 0.001). E-GSH-Px (U/g Hb) and P-GSH-Px (U/L) activities in GP1, GP2 and CG groups were also decreased at 57.04 (4.31), 24.0 (8.94) and 67.6 (4.29), and 6.16 (1.56), 2.67 (0.47) and 8.72 (0.31), respectively (E-GSH-Px: CG vs. GP1, P < 0.01, CG vs. GP2 and GP1 vs. GP2, both P < 0.001; P-GSH-Px: CG vs. GP1, CG vs. GP2 and GP1 vs. GP2, all P < 0.001). Plasma selenium levels (miromol/L) were only significantly decreased in GP2 compared to both GP1 and CG values (0.49 [0.29] vs. 1.67 [0.80] vs. 1.79 [0.26], both P < 0.001). These observations support the suggestion that chronic hyperglycaemia can influence the generation of free radicals, which may lead ultimately to increased lipid peroxidation and depletion of antioxidants, and thereby enhanced oxidative stress in subjects with type 2 diabetes mellitus.

Serum cystatin C, enzymuria, tubular proteinuria and early renal insult in type 2 diabetes.

This study investigates the association between serum cystatin C, serum creatinine concentrations, N-acetyl-beta-D-glucosaminidase (NAG enzymuria), urine alpha1-microglobulin (alpha1-MG) and beta2-microglobulin (beta2-MG) levels in subjects with type 2 diabetes (n=40, 20M/20F, age range 25-65 years; duration of diabetes 8-10 years) and age- and gender-matched healthy controls (n= 20). Exclusion criteria were absence of gross proteinuria, hypertension, dyslipidaemia or cardiovascular disease. Fasting blood samples and mid-stream specimen of urine (MSSU) were collected and serum creatinine, cystatin C, urine creatinine, NAG enzymuria, alpha1-MG and beta2-MG were measured. Diabetic subjects were separated into two groups based on albumin:creatinine concentration ratio. Group A: <3.5 (mg/mmol creatinine), group B: 3.5-35 (mg/mmol creatinine). While serum creatinine concentrations remained within the laboratory reference range for all groups, serum cystatin C concentration (mg/L) was significantly increased in group B (1.79 +/- 0.42 [mean +/- SD] compared to both control [0.81 +/- 0.10] and group A values [0.95 +/- 0.10]; both P<0.001). NAG enzymuria (units/mmol creatinine) was increased in both diabetic groups compared to control values (group B: 122 +/- 7, group A: 70 +/- 5, controls 27 +/- 2, all P<0.001). alpha1-microglobulin (microg/mmol creatinine) concentrations, similar in both the control group and group A diabetics at 1.10 +/- 0.10 and 1.11 +/- 0.21, respectively, were significantly elevated in group B at 2.10 +/- 0.41 (both P<0.01). Similarly, elevated beta2-MG (microg/mmol creatinine) levels were also observed in group B compared to both group A and control values (3.20 +/- 0.21 vs. 1.80 +/- 0.51 and 0.91 +/- 0.11, respectively; both P<0.001). In addition, group B levels were significantly higher than group A (P<0.001). These observations suggest that serum cystatin C is a more appropriate and effective biomarker for the overall estimation of GFR than serum creatinine values. In addition, increased serum cystatin C values were also associated with early renal tubular insult in subjects with type 2 diabetes, as characterised by increased NAG enzymuria, alpha1- and beta2-microglobulin excretion.

Urinary enzyme measurements as early indicators of renal insult in type 2 diabetes.

The association between urine microalbumin, alpha1-microglobulin concentration (alpha1MG) and the urinary enzyme activities of alanine aminopeptidase (AAP), N-acetyl-beta-D-glucosaminidase (NAG), alpha-glutathione-S-transferase (alphaGST) and pi-glutathione-S-transferase (piGST) is investigated in 36 type 2 diabetic and 15 age- and sex-matched non-diabetic subjects. Diabetic subjects were grouped into those with microalbuminuria <3 mg/L (group A: 7M/5F), 3-30 mg/L (group B: 5M/7F) and 30-300 mg/L (group C: 6M/6F). While serum creatinine concentration remained within the laboratory reference range (<115 mmol/L) in all experimental groups, alpha1MG excretion increased with the severity of microalbuminuria (control group and groups A, B and C mean [SD] values were 1.3 [0.21], 1.6 [0.11], 2.18 [0.42] and 2.8 [0.51] mg/mmol urinary creatinine, respectively). Activities of NAG (U/mmol creatinine) were significantly elevated in groups A, B and C at 98.7 (8.6), 112.8 (12.9) and 147.4(16.2), respectively, compared with the reference range <35 U/mmol creatinine (group C vs. groups A and B: P < 0.01). Activity of AAP (U/mmol creatinine) was significantly elevated in groups B and C at 7.6 (0.5) and 7.9 (0.6), respectively (both P < 0.001), compared to the control and group A values (2.5 [0.2]). Activity of piGST (U/mmol creatinine) was elevated in groups B and C at 2.6 (0.4) and 2.8 (0.5), respectively (both P < 0.001), compared to the control and group A values (1.1 [0.1]). Similarly, urine piGST activity was also elevated in groups B and C at 2.9 (0.6) and 3.1 (0.5), respectively (both P < 0.001), compared to control and group A values (1.3 [0.1] and 1.4 [0.2]). These results suggests that site-specific urinary biochemical markers provide valuable information about early renal proximal and distal tubular insult that ultimately may precede enhanced glomerular permeability in subjects with type 2 diabetes.