Stimulatory effect of nobiletin, a citrus polymethoxy flavone, on catecholamine synthesis through Ser^sup 19^ and Ser^sup 40^ phosphorylation of tyrosine hydroxylase in cultured bovine adrenal medullary cells

Naunyn-Schmiedeberg's Arch Pharmacol (2014) 387:1522 DOI 10.1007/s00210-013-0916-6

ORIGINAL ARTICLE

Stimulatory effect of nobiletin, a citrus polymethoxy flavone, on catecholamine synthesis through Ser19 and Ser40 phosphorylation of tyrosine hydroxylase in cultured bovine adrenal medullary cells

Han Zhang & Nobuyuki Yanagihara & Yumiko Toyohira & Keita Takahashi &

Hirohide Inagaki & Noriaki Satoh & Xiaoja Li & Xiumei Goa & Masato Tsutsui &

Kojiro Takahaishi

Received: 13 April 2013 /Accepted: 4 September 2013 /Published online: 17 September 2013 # Springer-Verlag Berlin Heidelberg 2013

Abstract We previously reported the dual effects of nobiletin, a compound of polymethoxy flavones found in citrus fruits, on catecholamine secretion in cultured bovine adrenal medullary cells. Here, we report the effects of nobiletin on catecholamine synthesis in the cells. Nobiletin increased the synthesis of 14C-

catecholamines from [14C]tyrosine in a time (2030 min)- and concentration (1.0100 M)-dependent manner. Nobiletin (10100 M) also activated tyrosine hydroxylase activity. The stimulatory effect of nobiletin on 14C-catecholamine synthesis was not observed when extracellular Ca2+ was not

present in the incubation medium. Protein kinase inhibitors including H-89, an inhibitor of cyclic AMP-dependent protein kinase, and KN-93, an inhibitor of Ca2+/calmodulin-dependent

protein kinase II, suppressed the stimulatory effects of nobiletin on catecholamine synthesis as well as tyrosine hydroxylase activity. Nobiletin also induced the phosphorylation of tyrosine hydroxylase at Ser19 and Ser40. Nobiletin (1.0 100 M) inhibited 14C-catecholamine synthesis induced by acetylcholine. The present findings suggest that nobiletin, by itself, stimulates catecholamine synthesis through tyrosine hydroxylase phosphorylation at Ser19 and Ser40, whereas it inhibits catecholamine synthesis induced by acetylcholine in bovine adrenal medulla.

Keywords Adrenal medulla . Catecholamine synthesis . Citrus flavonoid . Nobiletin . Phosphorylation . Tyrosine hydroxylase

Introduction

Nobiletin (5,6,7,8,3,4-hexamethoxyflavone) is a major component of polymethoxylated flavones found in the peel of citrus fruits (Bocco et al. 1998) which is used in a Chinese traditional herbal medicine to treat a poor appetite, cough, vomiting, and hypertension. Nobiletin exhibits many favorite pharmacological activities, including antiatherogenic (Whitman et al. 2005), cardiovascular protective effects (Middleton et al. 2000), neuronal effects such as neurotrophic effects in vitro (Nagase et al. 2005a), and antidementia activities in vivo (Nakajima et al. 2007; Onozuka et al. 2008). The precise mechanisms underlying nobiletins effects, however, remain to be determined.

Adrenal medullary cells derived from the embryonic...