Gowda B, Qin J, Mobarhan S, Frommel T O
Department of Medicine, Loyola University Medical Center, Maywood, IL 60153, USA.
Nutr Cancer. 1997;28(2):135-9. doi: 10.1080/01635589709514565.
Dietary supplementation with beta-carotene at 30 mg/day results in an increased serum trans-retinoic acid concentration in patients with a prior colonic polyp. In a number of human cell lines, trans-retinoic acid upregulates c-myc mRNA expression in colonic mucosa by reverse transcription polymerase chain reaction and correlated the results with serum concentrations of all-trans- (ATRA), 13-cis-(13-cRA), and total retinoic acid. Serum and colonic biopsy samples were obtained before and 90 days after administration of a placebo (n = 7) or 30 mg of beta-carotene (n = 5) daily. An increase in c-myc expression after supplementation was observed in 6 of 12 subjects, but 5 of these 6 subjects had decreased total serum retinoic acid concentration and 4 had decreased ATRA concentration. In addition, five of the six subjects with increased c-myc expression had received a placebo. Conversely, c-myc expression was increased in only two of five paired samples from subjects whose total serum retinoic acid concentration increased during the 90-day supplementation period. We conclude that c-myc expression is not correlated with ATRA, 13-cRA, or total retinoic acid concentration in vivo and that increased serum retinoic acid secondary to increased tissue beta-carotene is not sufficient to activate c-myc transcription.
对于既往有结肠息肉的患者，每天补充30毫克β-胡萝卜素可使血清反式视黄酸浓度升高。在一些人类细胞系中，反式视黄酸通过逆转录聚合酶链反应上调结肠黏膜中c-myc mRNA的表达，并将结果与全反式视黄酸（ATRA）、13-顺式视黄酸（13-cRA）和总视黄酸的血清浓度相关联。在给予安慰剂（n = 7）或每天30毫克β-胡萝卜素（n = 5）之前及给药90天后采集血清和结肠活检样本。在12名受试者中有6名在补充后观察到c-myc表达增加，但这6名受试者中有5名血清总视黄酸浓度降低，4名ATRA浓度降低。此外，c-myc表达增加的6名受试者中有5名接受了安慰剂。相反，在90天补充期内血清总视黄酸浓度升高的受试者的5对配对样本中，只有2对样本的c-myc表达增加。我们得出结论，c-myc表达与体内ATRA、13-cRA或总视黄酸浓度无关，并且组织β-胡萝卜素增加导致的血清视黄酸升高不足以激活c-myc转录。
