N-nitroso compounds and human cancer: where do we stand?

Area of Science:

• Biochemistry
• Toxicology
• Oncology

Background:

• Humans encounter preformed N-nitroso compounds (NOC) and precursors that form NOC in vivo.
• Endogenous formation of NOC can occur via bacterial or macrophage-mediated reactions.
• NOC are a versatile class of carcinogens with potential links to human cancers.

Purpose of the Study:

• To assess human exposure to exogenous and endogenous NOC using the N-nitrosoproline (NPRO) test.
• To investigate factors influencing endogenous nitrosation and its role in carcinogenesis.
• To explore the impact of dietary modifiers on NOC formation and body burden.

Main Methods:

• Utilized the N-nitrosoproline (NPRO) test to estimate exposure to N-nitroso compounds (NOC).
• Studied subjects in high- and low-incidence cancer areas, with varying habits (betel quid, tobacco), infections, and infestations.
• Assessed the impact of dietary factors, specifically ascorbic acid, on endogenous NOC levels.

Main Results:

• Endogenous NOC formation is influenced by multiple factors, making nitrate/nitrite levels alone insufficient indicators.
• Higher endogenous NOC exposure was observed in high-risk subjects (e.g., specific geographic locations, tobacco users, infected individuals).
• Ascorbic acid significantly reduced the body burden of intragastrically formed NOC.

Conclusions:

• Endogenous nitrosation is complex and influenced by diet; ascorbic acid can inhibit NOC formation.
• Findings support the role of NOC in human cancer etiology, especially with prolonged early-life exposure.
• Dietary components like vitamins (found in fruits and vegetables) may offer protection against NOC-related cancers, particularly stomach cancer.