Human fibronectin metabolism.

Area of Science:

• Biochemistry
• Physiology
• Critical Care Medicine

Background:

• Fibronectin (Fn) is a crucial adhesive glycoprotein involved in cell adhesion and matrix formation.
• Understanding Fn's metabolic behavior is vital for comprehending its role in health and disease, particularly in critical illness.

Purpose of the Study:

• To investigate the metabolic fate of fibronectin (Fn) in healthy individuals and critically ill patients.
• To determine the factors contributing to low plasma Fn levels observed in critical illness.

Main Methods:

• Human plasma fibronectin (Fn) was purified and radiolabeled.
• Metabolic parameters including fractional catabolic rate (FCR), half-life (t1/2), extravascular/intravascular diffusion ratio (EV/IV), and synthesis rate (SR) were measured in eight healthy controls and 11 patients (six critically ill).

Main Results:

• In healthy controls, Fn exhibited rapid catabolism with a fractional catabolic rate (FCR) of 4.81%/h and a half-life (t1/2) of 25 hours.
• Critically ill patients showed a lower EV/IV ratio, and those with low plasma Fn had markedly depressed synthesis rates (SR).
• Plasma Fn levels correlated with SR but not with t1/2 or FCR.

Conclusions:

• Reduced synthesis of fibronectin (Fn), not increased catabolism or distribution, is the primary cause of Fn deficiency in critically ill patients.
• These findings highlight the importance of synthesis in maintaining adequate Fn levels during critical illness.