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Nitrites and Nitrosamines

by Kevin Ahern, PhD
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    00:03 Now, nitrogen compounds are very important for making amino acids and all the other molecules that I've talked about.

    00:10 But there are some very hazardous components of nitrogen metabolism that I need to discuss and we need to understand.

    00:18 These components I'll describe in the next couple of slides.

    00:21 And the first of these involves a fairly reactive molecule known as nitrites.

    00:25 Nitrites appear in our food and our made in our body from nitrites.

    00:30 So let's see what happens with them.

    00:33 Nitrite can be formed by the ionization of nitrous acid, HNO2, or by the reduction of nitrites.

    00:40 Nitrite is used to cure meats.

    00:43 Bacon for example is a preserved by treating it with nitrite.

    00:47 This is done to prevent botulism and it’s an acceptable use of nitrite.

    00:52 When it’s reduced to nitric oxide, it happens in hypoxic conditions.

    00:57 Production of nitric oxide is good if the cell is trying to signal it and it is bad if the cell is not trying to use to signal it.

    01:05 In the human diet, the most common source of nitrites is not from consuming them in meats but rather from the reduction of nitrites that appear in vegetables.

    01:14 And how did the nitrites get in to the vegetables? Well, two ways.

    01:18 One by fertilizer and one by plant stress.

    01:23 The hazards with nitrites are associated with its ability to form cancer causing nitrosamines.

    01:29 This happens in acidic conditions such as we have in our stomach.

    01:33 Nitrites can oxidize hemoglobin's iron and convert it from a plus two form, the ferrous form to a plus three form the ferric form.

    01:42 Well, when that happens within hemoglobin, that hemoglobin is nonfunctional.

    01:46 It will no longer be able to carry oxygen.

    01:49 So, consumption of a lot of nitrites or creation of a lot of nitrites can be a very serious problem.

    01:55 So nitrosamines are produced from nitrites by a couple of reactions that I'm going to show you here that involve water, acid and secondary amines.

    02:03 So, here’s the reaction process.

    02:05 A nitrite that's in our body is shown on the left there or actually in the center of the slide.

    02:10 In an acid environment as indicated by the two protons there, nitrous acid ion is created H2NO2+ and that will spontaneously come apart to form water and nitrosonium ion.

    02:24 The nitrosonium ion in the next step of the process combines with the secondary amines such as proline and that produces the very hazardous nitrosamine that you can see on the right.

    02:33 Now nitrosamines, because the R groups are there, are classes of compounds.

    02:37 It’s not one structure because those R-groups can have various [INAUDIBLE 00:02:40] associated with them.

    02:43 Strong acids, as we've seen here, are high temperatures such as frying favor the production of nitrites.

    02:50 These compounds, as I said, are found in processed meats.

    02:53 They are also found in beer.

    02:54 They're found in cigarette smoke and in chewing tobacco.

    02:58 The formation of nitrosamines is actually inhibited by vitamin C and is on reason that people think vitamin C is something that has a very protective mechanism for our body.

    03:08 Now, nitrosamines are problems in the body because they can react with DNA to form what are called DNA adducts.

    03:14 In these reactions, nitrosamines are covalently joined to basis of DNA.

    03:19 In joining those bases to the DNA, means that when the DNA has copied, it's much more likely to form a mutation.

    03:25 Well, this means that nitrosamines are very likely carcinogens.

    03:29 Meaning they cause cancer in humans.

    03:31 And there is pretty good evidence that nitrosamines are associated with gastric and esophageal risks of cancer.

    03:38 Now, how do we get nitrosamines in other ways? Well, a very good way of getting them besides the way that I’ve described so far is through tobacco.

    03:46 Nicotine and its metabolites that are made from it can form nitrosamines quite readily.

    03:51 One nitrosamine called NNK is nicotine derived and it is very important in carcinogenesis.

    03:57 We can see NNK in the figure on the right part of the screen.

    04:01 NNK is found in tobacco and it's also found in e-cigarettes.

    04:05 So you don't escape it by smoking e-cigarettes.

    04:07 NNK activation by P-450 system of your liver is important in activating signaling cascades and uncontrolled growth.

    04:15 And we've seen in other lectures how losing control of signaling cascades is a big problem.


    About the Lecture

    The lecture Nitrites and Nitrosamines by Kevin Ahern, PhD is from the course Amino Acid Metabolism.


    Included Quiz Questions

    1. They form nitrosamines in stomach acid.
    2. They are oxidized to nitric oxide in oxygen abundance.
    3. They oxidize hemoglobin’s iron to Fe++.
    4. All of the answers are true.
    5. None of the answers are true.
    1. All of the answers are true.
    2. None of the answers are true.
    3. They are produced from secondary amines.
    4. They arise from a nitrosonium ion.
    5. They are likely carcinogens in humans.

    Author of lecture Nitrites and Nitrosamines

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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