Melatonin high-affinity binding to alpha-1-acid glycoprotein in human serum

Area of Science:

• Pharmacology
• Biochemistry
• Clinical Chemistry

Background:

• Melatonin is a crucial hormone regulating circadian rhythms.
• Understanding melatonin's interaction with serum proteins is vital for its pharmacokinetic studies.

Purpose of the Study:

• To investigate the binding characteristics of melatonin to human serum proteins.
• To identify the specific serum proteins involved in melatonin binding and their affinities.

Main Methods:

• Equilibrium dialysis was employed to study 3H-melatonin binding to human serum proteins at 37°C and pH 7.4.
• Binding affinities and capacities were determined for individual proteins and serum mixtures.

Main Results:

• Melatonin binding to human serum was moderate (53%) at physiological concentrations (<1 nmol/L).
• Alpha 1-acid glycoprotein demonstrated high-affinity binding (27 ± 3 (mmol/l)⁻¹), while albumin showed low-affinity binding (1.5 ± 0.1 (mmol/l)⁻¹).
• Binding exhibited both saturable (alpha 1-acid glycoprotein) and nonsaturable (albumin) components, with albumin potentially potentiating binding to alpha 1-acid glycoprotein.

Conclusions:

• Melatonin's serum protein binding is primarily mediated by alpha 1-acid glycoprotein and albumin.
• The concentration of alpha 1-acid glycoprotein may influence the total amount of melatonin bound in plasma.
• Albumin's presence can modulate the high-affinity binding of melatonin to alpha 1-acid glycoprotein.