Evidence on the Carcinogenicity of Nitrite in Combination with

Amines or Amides

Jennifer C.Y. Hsieh, PhD Amy J. Dunn, MPH

Carcinogen Identification Committee Meeting November 15, 2016

Cancer Toxicology and Epidemiology Section Reproductive and Cancer Hazard Assessment Branch

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Overview

Chemical Identity Occurrence and Use Evidence from Studies in Humans Evidence from Studies in Animals Mechanistic Evidence and Other Relevant Data, Including Genotoxicity Studies

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Chemical Identity

Nitrite: can form salts with sodium and potassium ions

Amines Primary Secondary

Tertiary

R'''

R'' N R

R'

Quaternary

Cyclic Aromatic

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Chemical Identity (contd)

Amides Primary O Ureas (diamides)

R NH2

Secondary Carbamates (esteramides)O O

R N R' NH H

Sulfonamides (with an isosteric SO2 ) O

Tertiary S

O O N R'O

R R''

R N R' Guanidine (carbamidine, iminourea) N

R''

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Occurrence and Use

Nitrite Part of the nitrogen cycle, present in water, soil,

organisms Dynamic interchange of nitrite with nitrate Industrial Uses Nitrous acid production Chemical synthesis (e.g., saccharin, caffeine, pharmaceuticals, pesticides) Polymerization inhibitor Removal of hydrogen sulfide from natural gas

Occurrence in foods Low levels in vegetables, grains, and fish Used as a preservative (e.g., curing of meats and fish)

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Occurrence and Use (contd) Amines Widespread occurrence in biological systems All amino acids, biogenic amines (e.g., histamine, tyramine, dopamine)

Occur as food constituents (e.g., meat, fish, beer, wine, coffee, cheese, milk, ground pepper) Formed during hightemperature cooking (e.g., PhIP, MeIQ, MeIQx) Present in tobacco smoke Used In rubber, dye and nylon production As coloring/filling agents, pesticides and pharmaceuticals

(also formed as metabolites of drugs) Other industrial uses

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Occurrence and Use (contd)

Amides Widespread occurrence in biological systems The key linking moiety (peptide bond) in proteins

Occur as food constituents (e.g., beef, fish, evaporated milk) Formed during hightemperature cooking (e.g., acrylamide) Formed endogenously (methylguanidine) Used As pharmaceuticals, pesticides, research chemicals In synthetic fiber production (e.g., nylon)

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Occurrence and Use (contd)

Nitrite in combination with amines or amides Used in occupational settings, e.g., azo dye production Occurs in foods, such as plantbased foods (e.g., some vegetables, grains and fruits) and processed meats and fish Present in tobacco

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Evidence from Studies in Humans

Presented by Amy J. Dunn, MPH

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Sources of Human Evidence of Carcinogenicity

IARCs 2006 review Studies of ingested nitrite (IARC, 2010)

Other reviews Epidemiologic studies published since IARCs 2006 review

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Nitrite Exposure Evaluated in Human Studies

Majority of studies estimated dietary intake of nitrite Food frequency questionnaires Estimated levels of nitrite in foods eaten

Most drew from the literature A few measured nitrite Variation across time not always factored in

Some studies only reported nitrate + nitrite exposure levels Human diet includes amines and amides

Levels of nitrite in urine one study of gastric cancer Occupational exposure two studies

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Endpoints of Interest in Human Studies

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Endpoints of Interest in Human Studies

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Colorectal Cancer IARC 2010 IARC (2010) Two studies One casecontrol study

Increased risk of colon cancer Increased risk of rectal cancer

One cohort study No association

Did not consider studies that looked only at processed meat exposure Focused on studies that estimated nitrite exposure Because many, but not all, cured meats contain nitrite and because otherfoods can also be important sources of nitrite

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Colorectal Cancer

Other reviews IARC 2015 Working Group on Red and Processed Meats Classified consumption of processed meat as carcinogenic to humans (Group 1)

The basis was sufficient evidence for colorectal cancer (Bouvard et al. 2015)

An IARC Monograph describing the evidence has not yet been published

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Studies since IARC (2010): Colon cancer casecontrol studies

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Studies since IARC (2010): Colon cancer cohort studies

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Studies since IARC (2010): Rectal cancer casecontrol studies

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Studies since IARC (2010): Rectal cancer cohort studies

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Studies since IARC (2010): Colorectal cancer casecontrol studies

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Studies since IARC (2010): Colorectal cancer cohort studies

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Endpoints of Interest in Human Studies

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Esophageal Cancer

IARC (2010) Two casecontrol studies

Both had a positive nonsignificant association

Other reviews Jakszyn and Gonzalez (2006) examined two studies

Considered the data insufficient

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Studies since IARC (2010):

Esophageal cancer cohort studies

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Esophageal cancer casecontrol studies

Studies since IARC (2010):

Esophageal adenocarcinoma (EAC) cohort studies

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Studies since IARC (2010): Esophageal squamous cell carcinoma (ESCC) cohort studies

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Endpoints of Interest in Human Studies

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Stomach Cancer IARC (2010)

IARC (2010) Six of seven casecontrol studies found a positive association

Significant in four Two cohort studies

Finnish study no association Dutch study Significant increase in risk for highest intake

Nonsignificant after adjustment for potential confounders

Concluded: Nitrite in food is associated with increased incidence of stomach cancer

Classified the overall human evidence as limited

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Stomach Cancer Other Reviews and Metaanalyses

Other reviews and metaanalyses of ingested nitrite Jakszyn and Gonzalez (2006) Evidence supports a positive association with gastric cancer Pooled relative risks Song et al. (2015) 18 studies: RR=1.31, 95% CI, 1.131.52 Xie et al. (2016) 51 studies: RR = 1.21, 95% CI, 0.991.47 IARC 2015 Working Group on Red and Processed Meats Summarizing the findings, Bouvard et al. (2015) noted:

a positive association with the consumption of processed meat was found for stomach cancer

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http:0.99-1.47http:1.131.52

Studies since IARC (2010): Gastric cancer cohort study

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Studies since IARC (2010): Gastric cancer casecontrol studies

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Studies since IARC (2010): Gastric cardia adenocarcinoma Cohort studies

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Studies since IARC (2010): Gastric noncardia adenocarcinoma Cohort studies

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Endpoints of Interest in Human Studies

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NonHodgkin Lymphoma (NHL) IARC 2010 & Other Reviews

IARC (2010) One of two casecontrol studies found increase in risk with increasing quartiles of nitrite intake

When plant and animal sources of dietary nitrite were evaluated separately, the positive association was observed only for plant sources.

Metaanalysis: Xie et al. (2016) 4 casecontrol studies Highest vs lowest nitrite intake, RR = 1.54 (95% CI = 0.98 2.41)

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http:0.98-2.41

Studies since IARC (2010): Lymphoma casecontrol studies, Part A

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Studies since IARC (2010): Lymphoma casecontrol

studies, Part B: NHL, FL and

DLBCL

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Studies since IARC (2010): Lymphoma casecontrol

studies, Part B: CLL/SLL, MZBL

and TCL

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Endpoints of Interest in Human Studies

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Brain Cancer IARC (2010)

Childhood brain cancer 12 case control studies Maternal diet: children born to mothers who had the highest category of intake of nitrite specifically from cured meat had an almost twofold increased risk for brain tumours.

Drinkingwater Nitrite measured in homes where pregnancies occurred A twofold increase in risk for brain tumours in the offspring

Stronger among women who did not rely on bottled water

Astroglial tumors

Dietary nitrite and adult brain tumors Seven studies No significant associations over all dietary sources

The largest study (conducted in CA) observed a twofold increase in risk among men who consumed levels of nitrite above the median and levels of vitamin C below the median

Two small studies a positive association with intake of nitrite from cured meat

A larger casecontrol study A threefold increase among those with high consumption of nitrite from plant sources

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Brain Cancer Studies Since IARC (2010)

Two large cohort studies Michaud et al. (2009) Elevated but not statistically significant risks with total nitrite Dubrow et al. (2010) Significantly elevated risks with nitrite from plant sources, driven by an effect seen in men

Mens highest intake level: HR= 2.04 (1.462.87), ptrend= 0.0026 Dietary nitrate plus nitrite intake from processed meat at age 12 and 13, diet estimated retrospectively

Risks were elevated for fourth quintile, but no significant trend Metaanalysis: Xie et a