Age effect on albumin and fibrinogen synthesis in humans

We determined the effect of age on synthesis rates and concentrations of albumin and fibrinogen in 12 each of young (20-30 yrs), middle age (45-55) and elderly (>65) healthy subjects. We measured fractional synthesis rates (FSR) of these proteins using L[1-¹³C]leucine and L[¹⁵N]Phenylalanine as tracers. While FSR of fibrinogen using both the tracers declined with age (Using Phenylalanine FSR for Young = 22.95 ± 3.3%/day, Middle = 17.28±1.3 and Old = 15.3 ±0.9; r²= 0.16, P<0.05) the concentrations of fibrinogen increased with age (Young = 263±33 mg/100ml, Middle =368±27 and Old = 414± 25; r² = 0.30, P<0.001). Neither the FSR nor the plasma concentrations of albumin changed with age. These results indicate that while albumin synthesis rate is not affected by age fibrinogen synthesis rate declines with age, indicating a differential age-effect on synthesis of these two liver proteins. Although synthesis rate of fibrinogen decreased with age, the concentration fibrinogen increased with age, thus, indicating that it is the decrease in fibrinogen degradation that causes an age-related increase in fibrinogen concentration. This increased fibrinogen concentration may be a factor involved in the age related increase in thromboembolic episodes.