Ascorbic acid efficiently enhances neuronal synthesis of norepinephrine from dopamine

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Ascorbic acid is a cofactor for dopamine β-hydroxylase (DβH), enhancing norepinephrine synthesis from dopamine.
• Controversy exists regarding the in situ kinetics of ascorbate's effect in chromaffin cells and its applicability to neuronal cells.

Purpose of the Study:

• To evaluate the stimulation of norepinephrine synthesis from dopamine in cultured SH-SY5Y neuroblastoma cells.
• To determine the kinetics and physiological relevance of ascorbate's role in neuronal norepinephrine synthesis.

Main Methods:

• Cultured SH-SY5Y neuroblastoma cells were treated with dopamine and varying concentrations of ascorbate.
• Norepinephrine synthesis rates, intracellular ascorbate concentrations, and cellular superoxide generation were measured.
• Kinetic analysis was performed to determine the half-maximal effective ascorbate concentration.

Main Results:

• Intracellular ascorbate significantly stimulated norepinephrine synthesis from dopamine in SH-SY5Y cells.
• The ascorbate-induced stimulation was linear over 60 minutes, with half-maximal norepinephrine accumulation at 0.2-0.5 mM intracellular ascorbate.
• Ascorbate loading prevented dopamine-induced superoxide generation and protected cells at physiological concentrations.

Conclusions:

• Ascorbate promptly enhances norepinephrine synthesis from dopamine in neuronal cells at physiological intracellular concentrations.
• The kinetics observed align with the known properties of DβH, supporting ascorbate's role as a cofactor.
• Ascorbate protects neuronal cells from superoxide toxicity and facilitates DβH activity by providing electrons.