Nornicotine in smokeless tobacco as a precursor for carcinogen exposure

烟草生物碱去尼古丁是N'-亚硝基索尼古丁（NNN）的前体，NNN是一种有效的烟草特异性致癌物。NNN被认为在烟草使用者中诱发食道癌和口腔癌中起重要作用。去甲尼古丁通过两种方式导致烟草使用者接触非神经网络。除了作为烟草中NNN形成的前体外，它也可能是内源性亚硝化的。烟草制品中存在的去甲尼古丁的内源性亚硝化可在烟草使用者的口腔、胃或身体其他部位发生。这与无烟烟草制品的使用尤其相关，无烟烟草制品是一种在口腔中保存较长时间的烟草，为去尼古丁亚硝化创造了有利条件。鉴于非尼古丁神经网络的高致癌性以及无烟烟草使用与口腔癌和食道癌的关联，迫切需要对无烟烟草制品中的去尼古丁含量进行监管。美国食品和药物管理局（FDA）有权根据《家庭吸烟预防和烟草控制法》对有害和潜在有害的烟草成分进行监管。关于无烟产品中去甲尼古丁的内源性亚硝化程度及其含量的函数的信息对于FDA对这一烟草成分的适当监管至关重要。本提案的目的是：(1)确定目前在美国销售的无烟产品中去甲尼古丁含量的变化。没有关于各个无烟品牌的去甲尼古丁含量的信息，目前在美国销售的产品之间的变化程度是未知的。目标1将解决这一重要差距，并将为本提案的目标2提供关键信息。(2)探讨无烟烟草使用者NNN的内源性形成。无烟烟草使用者将随机分到一种不含烟草的草药鼻烟，鼻烟中添加了不同数量的稳定同位素标记的去甲尼古丁。用液相色谱-串联质谱法测量这些受试者尿液中同位素标记的总NNN -一种暴露于NNN的生物标志物。该方法将允许对内源性去甲尼古丁亚硝化引起的尿总非神经网络与暴露于烟草制品中的非神经网络造成的尿总非神经网络进行具体鉴定。将通过逐渐减少同位素标记的去甲尼古丁添加量来研究鼻烟中去甲尼古丁的减少对内源性神经网络形成程度的影响。这项研究的结果将为致癌亚硝胺NNN的内源性形成提供极其重要的新信息，这些亚硝胺NNN是暴露于烟草使用的去甲尼古丁后形成的。了解这一过程对于充分管制烟草制品中的去甲尼古丁以尽量减少对公众的危害是绝对必要的。

DESCRIPTION: The tobacco alkaloid nornicotine is a precursor to N'-nitrosonornicotine (NNN), a potent tobacco-specific carcinogen. NNN is believed to play an important role in the induction of esophageal and oral cavity cancers in tobacco users. Nornicotine contributes to NNN exposure in tobacco users in two ways. In addition to being a precursor to NNN formation in tobacco, it may also be nitrosated endogenously. Endogenous nitrosation of nornicotine that is present in tobacco products can occur in the oral cavity, in the stomach, or elsewhere in the body of tobacco users. This is particularly relevant to the use smokeless tobacco products - a form of tobacco that is kept in the oral cavity for prolonged periods of time, creating favorable conditions for nornicotine nitrosation. Given the high carcinogenic potency of NNN and the association of smokeless tobacco use with oral and esophageal cancers, regulation of nornicotine content in smokeless tobacco products is urgently needed. The Food and Drug Administration (FDA) has authority to regulate harmful and potentially harmful tobacco constituents under the Family Smoking Prevention and Tobacco Control Act. The information on the extent of endogenous nitrosation of nornicotine as a function of its content in smokeless products is crucial for the adequate regulation of this tobacco constituent by the FDA. Aims of this proposal are: (1) to determine the variation of nornicotine content in smokeless products currently marketed in the U.S. There is no information on nornicotine content in individual smokeless brands, and the extent of variation among the currently marketed U.S. products is unknown. Aim 1 will address this important gap and will also provide critical information for Aim 2 of this proposal. (2) To investigate the endogenous formation of NNN in smokeless tobacco users. Smokeless tobacco users will be randomized to a tobacco-free herbal snuff containing various amounts of stable isotope-labeled nornicotine added to it. Isotope-labeled urinary total NNN - a biomarker of exposure to NNN - will be measured in these subjects by using liquid chromatography-tandem mass- spectrometry. This methodology will allow for specific identification of urinary total NNN from endogenous nitrosation of nornicotine, versus that resulting from exposure to NNN in tobacco products. The effect of nornicotine reduction on the extent of endogenous NNN formation will be studied by gradually decreasing the amount of isotope-labeled nornicotine added to study snuff. The results of this study will provide extremely important new information on the endogenous formation of the carcinogenic nitrosamine NNN upon exposure to nornicotine from tobacco use. An understanding of this process is absolutely necessary for the adequate regulation of nornicotine in tobacco products with the purpose of minimizing public harm.