It is now more than 50 years since the seminal report in 1956 - on the carcinogenicity of nitrosamines - that led to a major international research effort to determine whether or not these compounds were a risk to humans and to determine how they were formed and how they exerted their carcinogenic effect. For over 30 of these years, Professor Steven Tannenbaum and his colleagues in the MIT Department of Biological Engineering have contributed to this effort in a continually-evolving research program that has progressed from analysis of nitrosamines in food, through the discovery of de novo mammalian nitrate synthesis and nitric oxide production by macrophages, through the characterization and quantitation of inflammation-related DNA damage products to the current focus on chemical mechanisms and biomarkers in animal models and inflammation-related cancer in humans. This research has been supported for virtually the entire period by a Program Project Grant from the National Cancer Institute - Endogenous Nitrite Carcinogenesis in Man - and has involved well over 40 scientists in 7 research groups, many of whom are shown in the most-recent group photograph. These and previous members of the Program have contributed to research that has led to over 350 publications.
The research during the early-to-mid 1970s was carried out in the Department of Nutrition and Food science, leading naturally to analysis of nitrosamines in food, since there was evidence that the useful food preservative, sodium nitrite, could react under acidic conditions with other food constituents - secondary amines - to produce potentially carcinogenic nitrosamines. It was then discovered that a presumably harmless compound, nitrate anion, could be converted in the mouth by salivary bacteria to nitrite. This led in turn to the demonstration that nitrosamines could indeed form in saliva. Subsequent experiments concerning nitrate balance in the body led to the discovery that more nitrate was excreted in the urine than could be accounted for by dietary intake, suggesting synthesis in the body. This was subsequently shown, in collaboration with Michael Marletta (now President of Scripps Research Institute), to arise from stimulated macrophages via conversion of arginine to nitric oxide, followed by reaction with oxygen to produce nitrite that was subsequently oxidized by hemoglobin to nitrate. Concurrent with the MIT research, several groups demonstrated that an elusive vasodilator was also nitric oxide (Nobel Prize, 1998), and this was followed in turn by many reports of the detection of nitric oxide in various cell types. This compound is now recognized as an important signaling molecule that is necessary and virtually ubiquitous in living organisms. Overproduction of nitric oxide, however, which can occur, for example, during chronic inflammation, is potentially harmful, and this aspect is the focus of the MIT collaboration. The Program focuses on the overall hypothesis that DNA damage, mutation, cytotoxicity and cellular proliferation will arise from a complex reaction cascade that occurs when nitric oxide is overproduced.
Professor William Deen - now retired - and his group in Chemical Engineering developed mathematical models to predict the concentrations of nitric oxide and related compounds in aqueous solutions, cell cultures, and tissues. This information on the rates of nitric oxide synthesis and diffusion has been combined with other kinetic and morphometric data to estimate the in vivo concentrations of nitric oxide and its downstream products. Professor Tannenbaum, Professor Peter Dedon, and Dr. Pete Wishnok are developing and exploiting biomarkers for DNA and protein damage derived from the reactive species N2O3, NO2, ONOO-, and HOCl. The biomarkers can be applied to mouse models to define the relative roles of macrophages and neutrophils in the inflammatory process. Professors John Essigmann, Bevin Engelward, Gerald Wogan, and Ms. Laura Trudel, characterize the mechanisms of mutagenicity, apoptosis and homologous recombination resulting from DNA damage induced by nitric oxide with particular emphasis on how specific types of damage may contribute to tumor initiation and development. Professor James Fox, Dr. Susan Erdman, and the late Professor David Schauer, focused on the role of nitric oxide and related species in mouse models of inflammatory bowel disease and cancer, using transgenic mice. Histopathologic lesions and the pattern of macrophage and neutrophil infiltration are being correlated, in collaboration with clinical collaborators, with biomarkers for nitration, oxidation, and halogenation of DNA and proteins. To further characterize the role of nitric oxide and nitric-oxide-derived species in inflammatory bowel disease, pharmacologic inhibition of the enzyme inducible nitric oxide synthase (iNOS) is compared with genetic inactivation of the enzyme by generating enzyme-deficient knockout mice. Dr. Pete Wishnok and Professor James Fox respectively direct state-of-the-art bioanalytical and animal core facilities for the development and application of new and existing analytical methods and animal models.
The overall objective of the Program Project has been to provide a sound scientific basis for understanding the relative contributions of various classes of leukocytes to cancer via inflammatory processes. This research will lead to a better understanding of these processes and to a rational approach to their chemoprevention, and will provide biomarkers to analyze and quantitate the chemical origins of lesions, and to diagnose and characterize the progression of inflammation-related disease in human populations.
The chemical symbol for nitric oxide is NO; the T-shirts in the photograph were inspired by the song popularized by country singer Lorrie Morgan: 'What Part of NO Don't You Understand?'