Melatonin stimulates release of tissue factor pathway inhibitor from the vascular endothelium

Area of Science:

• Endothelial cell biology
• Circadian rhythm research
• Hemostasis and thrombosis

Background:

• Previous studies linked circadian variations of free tissue factor pathway inhibitor (TFPI) and melatonin in males.
• The mechanism by which melatonin might influence TFPI levels, particularly in endothelial cells, remained unclear.

Purpose of the Study:

• To investigate whether melatonin modulates the production and/or secretion of TFPI in human endothelial cells.
• To determine if melatonin affects the expression of TFPI, tissue factor (TF), or plasminogen activator inhibitor type 1 (PAI-1) at the mRNA or protein level.

Main Methods:

• Primary human umbilical vein endothelial cells (HUVECs) and human coronary artery endothelial cells (HCAECs) were cultured.
• Cells were exposed to varying doses of melatonin (0-300 pg/ml) for different durations (0.5-24 h).
• Protein concentrations of free TFPI, TF, and PAI-1 in cell supernatants and lysates were measured.
• Gene expression of TFPI, TF, and PAI-1 was quantified using real-time PCR.

Main Results:

• Melatonin dose-dependently increased free TFPI protein levels in supernatants of both HUVEC and HCAEC cultures by approximately 25-30 fold.
• TFPI secretion was enhanced by melatonin independently of incubation time, while TF and PAI-1 levels remained unchanged.
• Melatonin treatment did not alter the mRNA levels of TFPI, TF, or PAI-1.
• The ratio of supernatant to cell lysate free TFPI increased significantly, indicating enhanced release from intracellular or membrane-bound stores.

Conclusions:

• Melatonin stimulates vascular endothelial cells to secrete free TFPI without affecting TFPI gene transcription.
• The findings suggest melatonin enhances the release of pre-formed TFPI from endothelial cells.
• This mechanism may have significant clinical implications for the prophylaxis and treatment of thromboembolic disorders.