Association between Serum Zinc and Calcification Propensity (T50) in Patients with Type 2 Diabetes Mellitus and In Vitro Effect of Exogenous Zinc on T50

Zinc inhibits vascular calcification in vivo and in vitro. Patients with type 2 diabetes mellitus show hypozincemia and are at an elevated risk of cardiovascular events. Recently, an in vitro test (T₅₀-test) was developed for determination of serum calcification propensity and a shorter T₅₀ means a higher calcification propensity. This cross-sectional study investigated the association between serum zinc and T₅₀ in 132 type 2 diabetes mellitus patients with various kidney functions. Furthermore, the effect of exogenous zinc on T₅₀ was also investigated in vitro using separately pooled serum samples obtained from healthy volunteers and patients with hemodialysis. We measured T₅₀ levels using the established nephelometric method. The median (interquartile range) levels of T₅₀ and serum zinc were 306 (269 to 332) min, and 80.0 (70.1 to 89.8) µg/dL, respectively. Serum zinc level showed a weak, but positive correlation with T₅₀ (r_s = 0.219, p = 0.012). This association remained significant in multivariable-adjusted analysis, and was independent of known factors including phosphate, calcium, and magnesium. Kidney function and glycemic control were not significantly associated with T₅₀. Finally, in vitro experiments showed that addition of a physiological concentration of exogenous zinc chloride significantly increased serum T₅₀. Our results indicate that serum zinc is an independent factor with a potential role in suppressing calcification propensity in serum.

Favourable serum calcification propensity with intraperitoneal as compared with subcutaneous insulin administration in type 1 diabetes

BACKGROUND

Serum calcification propensity can be monitored using the maturation time of calciprotein particles in serum (T₅₀ test). A shorter T₅₀ indicates greater propensity to calcify; this is an independent determinant of cardiovascular disease. As the intraperitoneal (IP) route of insulin administration mimics the physiology more than the subcutaneous (SC) route in persons with type 1 diabetes (T1DM), we hypothesized that IP insulin influences determinants of calcium propensity and therefore result in a longer T₅₀ than SC insulin administration.

METHODS

Prospective, observational case-control study. Measurements were performed at baseline and at 26 weeks in age and gender matched persons with T1DM.

RESULTS

A total of 181 persons, 39 (21.5%) of which used IP and 142 (78.5%) SC insulin were analysed. Baseline T₅₀ was 356 (45) minutes. The geometric mean T₅₀ significantly differed between both treatment groups: 367 [95% confidence interval (CI) 357, 376] for the IP group and 352 (95% CI 347, 357) for the SC group with a difference of -15 (95% CI -25, -4) minutes, in favour of IP treatment. In multivariable analyses, the IP route of insulin administration had a positive relation on T₅₀ concentrations while higher age, triglycerides and phosphate concentrations had an inverse relation.

CONCLUSION

Among persons with T1DM, IP insulin administration results in a more favourable calcification propensity time then SC insulin. It has yet to be shown if this observation translates into improved cardiovascular outcomes.