Mechanisms of ascorbic acid stimulation of norepinephrine synthesis in neuronal cells

Abstract

Ascorbic acid is well known to acutely stimulate norepinephrine synthesis in neurosecretory cells, but it has also been shown over several days to increase tyrosine hydroxylase mRNA and norepinephrine synthesis in cultured neurons. Since tyrosine hydroxylase is the rate-limiting step in catecholamine synthesis, an effect of ascorbate to increase tyrosine hydroxylase protein could contribute to its ability to increase or sustain catecholamine synthesis. Therefore, we evaluated whether tyrosine hydroxylase protein expression and function is increased in SH-SY5Y neuroblastoma cells by physiologically relevant intracellular ascorbate concentrations. SH-SY5Y neuroblastoma cells did not contain ascorbate and had only very low levels of norepinephrine in culture with L-tyrosine, the substrate for tyrosine hydroxylase. However, treatment of cells with ascorbate for 6 hours or more markedly increased norepinephrine synthesis, such that intracellular ascorbate and norepinephrine increased in parallel with half maximal intracellular concentrations of about 1 mM ascorbate and 150 µM norepinephrine. This increase was enhanced by supplementing tetrahydrobiopterin, but was not mimicked by several antioxidants or by catalase or superoxide dismutase. Tyrosine hydroxylase protein expression increased at intracellular ascorbate concentrations above 1.5 mM. This contributed to norepinephrine generation, which was decreased 50–60% by inhibition of protein synthesis with cycloheximide at high intracellular ascorbate. These results suggest that expected physiologic neuronal ascorbate concentrations enhance norepinephrine synthesis both by maintaining tetrahydrobiopterin and increasing tyrosine hydroxylase expression.

Regulation of embryonic neurotransmitter and tyrosine hydroxylase protein levels by ascorbic acid

“…For example, treating AA-deficient neuroblastoma cells with AA increased tyrosine hydroxylase mRNA levels (Seitz et al, 1998). We have previously shown that AA treatment increases norepinephrine production within six hours in a neuroblastoma SH-SY5Y cell line (May et al, 2012). In addition, we showed this effect was specific for AA, since it was not mimicked by several other antioxidants.…”

A rare presentation of an ancient disease: scurvy presenting as orthostatic hypotension

“…Ascorbic acid also directly augments the synthesis of tyrosine hydroxylase by stimulating messenger RNA (mRNA) production 2. Thereafter, the conversion of dopamine to norepinephrine by dopamine β-hydroxylase (DβH) requires ascorbic acid as a cofactor 3. Our patient was able to mount a compensatory tachycardia in response to hypotension, suggesting that catecholamine synthesis was at least partially preserved.…”

“…The synthesis of epinephrine requires ascorbic acid at two steps (figure 1). In the first, ascorbic acid helps recycle the essential cofactor tetrahydrobiopterin by reduction of the trihydrobiopterin radical generated by hydroxylation of tyrosine by tyrosine hydroxylase 3. Ascorbic acid also directly augments the synthesis of tyrosine hydroxylase by stimulating messenger RNA (mRNA) production 2.…”

Parenteral vitamin C relieves chronic fatigue and pain in a patient with rheumatoid arthritis and mononeuritis multiplex secondary to CNS vasculitis

“…Vitamin C also acts as a cofactor for the biosynthesis of the neurotransmitters norepinephrine, dopamine and serotonin [16] , as well as neuropeptide hormones, such as mood enhancing oxytocin [17] . Depression is often associated with fatigue and is common in Hepatitis C patients receiving interferon-alpha treatment [7] .…”