Toxicology Program


Date of this Version

Spring 5-2011


A Thesis Presented to the Faculty of The Graduate College at University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Toxicology, Under the Supervision of Professor Patrick J. Shea. Lincoln, Nebraska: May 2011

Copyright 2011 Nikita Joshi


Nitrosamines comprise a large group of potentially toxic compounds occurring in the environment as by-products of various manufacturing, agricultural and natural processes. Nitrosamines are produced from reaction of nitrite with a suitable secondary amine in an acidic matrix; these acidic conditions can occur in environmental media and in the mammalian gastrointestinal (GI) tract. This research focused on the stability, transfer, and impacts of the environmentally relevant nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosmorpholine (NMOR), and N-nitrosoatrazine (NNAT) (formed from reaction of nitrite with dimethylamine, morpholine, and atrazine), using the chicken egg and embryo model systems. Chicken eggs were used to determine nitrosamine transfer between a hydrophilic medium (egg white or albumin) and a lipophilic medium (yolk) via a biomembrane (vitelline membrane). Results from these studies with unfertilized chicken eggs showed that the selected nitrosamines transferred from the egg white to yolk where they were relatively stable. NNAT has a relatively higher affinity for the lipophilic yolk fraction, which suggests that it may have a greater potential to bioconcentrate than NDMA and NMOR. An understanding of the transfer behavior of nitrosamines can be used to assess bioavailability and fate, as well as potential environmental and biological impacts. An observed decrease in total nitrosamine in the yolk with time may indicate denitrosation, releasing nitrous acid, which can decompose to nitrite and nitric oxide (NO), an important biological messenger during embryonic and fetal development. Thus teratogenicity of these compounds was assessed using chicken embryos. Major defects observed after exposure to these selected compounds included ectopic heart, gastroschisis, caudal regression, craniofacial hypoplasia, and neural tube defects. A significant relationship was observed between malformed embryos and NNAT (0.46 µg). Additionally nitrotyrosine concentrations (a marker of NO-mediated stress) in NNAT treated, malformed embryos were greater than those observed in treated, normal-appearing embryos. Results indicate that NNAT may be teratogenic and that nitrotyrosine, a marker of NO-dependent oxidative stress, maybe reflective of one biochemical pathway through which nitrosamines exert teratogenic effects.