Processed food toxicants part 2 Flashcards
Post midterm
What is acrylamide?
- Industrially produced vinyl compound, commonly polymerized (e.g., during use for gel formation for SDS-Page analysis)
What are the industrial uses for acrylamide? [4]
- Flocculant for wastewater treatment
- Cosmetics, paper & textiles
- Soil conditioner
- SDS-Page gel
Describe the evidence of risk of acrylamide.
- 1997 - evidence of acrylamide exposure in control group
- 2002 - Swedish study links acrylamide exposure to fried food (animal study)
- 2002 - present - many studies on formation, sources, metabolism, toxicokinetics, and risk assessment
One of the most studied food toxicants for risk assessment.
What is the mechanism of formation of acrylamide in food?
- Amino acid asparagine and D-glucose (reducing sugar) react in multi-step pathway
One of the strategies to reduce this would be to replace asparagine.
What factors affect formation of acrylamide in food?
- Asparagine and reducing sugar content
- Cooking method (deep frying; pan frying; microwaving)
- Cooking temperature (formation increases with temperature)
- Time dependent (concentration increases with time)
Potatoes do not have a lot of protein, but the protein they do have is very rich in asparagine. Additionally - potatoes contain lots of reducing sugar.
Discuss the levels of acrylamide in food.
Discuss the levels of acrylamide in selected coffees.
Brewed coffee contains relatively less because of filtration
Describe the toxicokinetics of acrylamide.
- May be bound (e.g., to zinc), which prevents it from undergoing metabolism
- Acrylamide is a typical toxicant as far as toxicokinetics goes
- The rates of absorption, metabolism, and excretion of acryalmide and its metabolites are very well quantified in the research.
What are the routes of exposure for acrylamide?
Oral
Inhalation
How is acrylamide absorbed?
- GI tract → bloodstream
- Small vinyl monomer; readily passes through mucosal membranes
- Biological barriers are ineffective
- Small vinyl monomer; readily passes through mucosal membranes
Small MW with high bioavailability that is available for biotransformation by phase I and II enzymes.
Describe the metabolism of acrylamide.
Phase I reaction
* Oxidation of acrylamide catalyzed by cytochrome P450 2E1 to yield glycidamide & further glyceramide
Phase II reaction
* Conjugation of acrylamide and glycidamide with glutathione by glutathione-S-transferase to yield AAMA and GAMA
AAMA - acrylamide mercapturic acid conjugates
GAMA - glycidamide mercapturic acid conjugates
What occurs in the phase I reaction of acrylamide metabolism?
- Acrylamide is oxidized
- Catalyzed by cytochrome P450 2E1
- Yields: glycidamide & further glyceramide
What happens in the phase II reaction of acrylamide metabolism?
- Conjugation of acrylamide and glycidamide with glutathione
- Catalyzed by glutathione-S-transferase
- Yields acrylamide and glycidamide mercapturic acid conjugates (AAMA and GAMA)
Which types of adducts contribute to accumulation of acrylamide toxicity?
- Hemoglobin adducts
- DNA adducts
What is the major depot of acrylamide in tissues?
Red blood cells
Describe the accumulation of acrylamide.
- Widely distributed in tissues after absorption
- Short half-life (1.4-3 hours)
- Major depot: red blood cells
- Small amount detect in tissues after weeks
- Two types of adducts contribute to accumulation
- Hemoglobin adducts
- DNA adducts
How does acrylamide adduct with hemoglobin?
- With cysteine and valine residues
What is the internal dose biomarker for neurotoxicity of acrylamide?
- 14C-acrylamide
Similar to how Hb-A1c is measured to assess diabetes.
Acrylamide adduct with cysteine in hemoglobin
How are acrylamide cysteine adducts detected?
- Acid hydrolysis of protein → isolate cysteine adducts
- GC/MS analysis
How are acrylamide valine adducts detected?
- Adduct to N-terminal valine in hemoglobin
- GC/MS-MS analysis
Describe the excretion of acrylamide.
- First order removal from tissues (half life = 1.4-3 hours)
- Parental compound and metabolites detected in urine
- Acrylamide: 2% in rat
- N-acetyl-s-(2-carbamoyl-ethyl)cysteine
- Glycidamide
- Readily detected in rat
- Reported in some human studies
The nervous system is a principal site for […]
amino acid acute toxic actions
Inhalation of acrylamide is more dangerous than ingestion.
Neurotoxicity
What are the symptoms of airborne acrylamide exposure?
- Tingling or numbness in hands or feet
- Weak legs, loss of toe reflexes and sensations, and numbness preceded by skin peeling
- Cerebral dysfunction
The nervous system is a principal site for amino acid acute toxic action
Neurotoxicity
What is the acute dose-response for acrylamide exposure?
- 100 mg/kg bw: single oral dose for acute neurotoxic effects
- 150 mg/kg bw: reported LD50
What is the chronic dose response of acrylamide?
<0.2 mg/kg/bw/d, 90 d: NOEL in morphological change in nerves
What is the lowest observable effect level of acrylamide exposure for degenerative changes in nerves?
Accumulative effects
LOEL: for degenerative changes in nerves
20 mg/kg/bw, 90 days = 2mg/kg bw, 2 years
What is the average intake of acrylamide?
- General population is 0.001 mg acrylamide/kg/bw/d
- High intake consumers 0.004 mg acrylamide/kg/bw/d
- Overall exposure from food cooked at home is unavailable
- Difficult to estimate overall acylamide daily intake worldwide
What is the proposed mechanism of toxicity for acrylamide? [2]
- Causes changes in the expression of neurotransmitter receptors
- Alter the expression of genes governing the synthesis of brain proteins
- Formation between acrylamide and cysteine-rich terminal proteins that mediate fusion of membranes
- Inhibits the action of brain Glutathione-S-transferase and reduce levels of glutathione in the brain
A possible explanation for the neurotoxicity of acrylamide
is that it is a bipolar moleculea, hydrogen-bonding interactions with cell components. This property may enhance its ability to alter cell membrane structures and accelerate its diffusion and penetration to nerve terminal sites associated with normal function of the nervous system.
Acrylamide can act as a reproductive toxicant at specified exposures.
What are the symptoms? [5]
- Reduced fertility rates
- Increased resorptions of fetuses
- Reduced litter size in pregnant females
- Formation of abnormal sperm
- Impacted survival and health of offsprings
What is the evidence of the toxicity potential of acrylamide?
- DNA-bonding: GA 100-1000X more reactive than AA
- Ames Salmonella Assay: only GA showed mutation
- Both GA and AA had more A-G transitions and G-C transitions than control (i.e., the metabolites were more toxic than the toxin)
- Brain and reproductive system tumors
- Genotoxicity: alkylation (adducts) of DNA with AA/GA
- Lower glutathione concentration (weakens detoxification system)
Ames Salmonella Assay is used because Salmonella easily mutates. It is used as a proxy (‘quick & dirty’) method to show mutagenicity. The control will use the toxin, other samples will use S9 (sediment of mouse liver homogenate after 9000 rpm centrifugation - i.e., contains metabolites of toxin).
Two problems with this test:
(1) Bacteria do not have a DNA repair mechanism as eukaryotic organisms do, and
(2) Bacteria do not have livers, so they do not have the capacity to metabolize.
A lower glutathione concentration […]
weakens detoxification system
What are the approaches for neutralization of acrylamide in food. [5]
- Removal of asparagine by asparaginase (effective in potato chips and french fries)
- Control the food supplies: selection of cultivars, storage temp, blanching to remove reducing sugars
- Addition of lysine (it has two amino groups so it is very efficient in the Maillard reaction and will out-compete asparagine)
- Lowering frying temperature (<175 C)
- Oil type and additives (e.g., stabilizers to slow down lipid oxidation - like antioxidants or sequestering agents) - corn oil better than olive oil or rosemary oil - oxidized lipids will act like a reducing sugar in the Maillard reaction, and different oils have different susceptibilities to auto-oxidation.
What is the negative impact of frying fries at a lower temperature to reduce acrylamide formation?
Higher fat content
What is the negative impact of reducing acrylamide in cereals in this manner?
Elevated sodium levels
What is the negative impact of reducing acrylamide in coffee by increasing roasing degree?
Decrease flavour and antioxidant activity
What is excreted in urine during the detoxification of acrylamide exposure?
- Unchanged AA - short half-life (1.4-3 hours)
- Glycidamide - (2.3-3.9 hours)
- Mercapturic conjugates - longer half lives
- AAMA ~18 hours
- GAMA ~ 25 hours
Discuss the correlation between urinary acrylamide metabolites and other biomarkers.
- Inconsistent data for mice and rats regarding Hb-adducts
- Significant linear correlation in mice and rates regarding DNA-adducts
Why are nitrates and nitrites used in foods?
To preserve meats and prevent growth of Clostridium botulinum
What is the role of bacteria in the gastrointestinal tract regarding nitrate?
Reduction of nitrate to nitrite is a common reaction for bacteria in the GI tract.
How are nitrites involved in the curing process?
Nitrites are rapidly converted to nitric oxide during the curing process and by reduction reaction by dehydroascorbic acid or erythrobic acid
How do nitrites react with secondary amines (e.g., proline), and under what conditions can nitrosamine formation occur?
- Nitrites react with secondary amines to form nitrosamines.
- Nitrosamine formation can occur under the acidic conditions of the gastrointestinal tract.
- In addition, nitrosamines formed by nitrosation reaction can occur during frying.
Nitrosamines are precursors to carcinogens.
Nitric oxide in small doses is beneficial, but in high concentrations, potent free radicals can be generated.
What are food sources of nitrates, nitrites and nitrosamines?
- Consumption of nitrates from vegetables sources are higher than from cured meat products.
- Spinach, celery, beets, radishes, and cabbages contain high concentrations of nitrates (that’s why celery extract is added sometimes in place of nitrates, since they look better on a ‘clean label’ but provide the same preservative effect)
- Nitrosamines are found very infrequently in all cured products except overcooked bacon.
Nitrosamines are not found in the vegetables because they are formed endogenously.
What is the Nitrogen cycle?
- Drinking water
- Food
- Food additives
Complete protection from exposure to nitrites is impossible; in fact, our gut microbiome can even produce them. Concern about them is overstated, given that we are nitrite sources ourselves.
What are the adverse health effects caused by nitrites and nitrosamines?
- Nitrites can oxidize hemoglobin to methemoglobin, resulting in the loss of oxygen-binding ability.
- Nitrosamines are activated through cytochrome P450, involving oxidative N-dealkylation, which forms diethylnitrosamine and dimethylnitrosamine.
- Akylation of DNA bases (impact gene expression)
- Generation of ROS (oxidative stress)
- Induction of DNA cross-links (unravel and replicate)
How do nitrosamines, chronic inflammation, and altered gut microbiota contribute to the development of colorectal cancer?
Chronic inflammation, particularly in the gastrointestinal tract, can lead to colorectal cancer. Nitrosamines, formed by the reaction of nitrites and amines, have carcinogenic potential and may alter gut microbiota, which can trigger inflammatory responses and affect metabolic processes.
Nitrosamines can induce cancers in the: [6]
- Liver
- Kidney
- Bladder
- GI tract
- Pancreas
- Respiratory tract
- Fatal dose of potassium nitrate for adults = 30-35g consumed as a single dose.
- Fatal dose of sodium nitrite is 22-23mg/kg body weight.
What are the positive effects of nitrate, nitrite and nitric oxide?
Nitrate, nitrite, and nitric oxide play crucial roles in regulating blood pressure, promoting blood flow, reducing inflammation, and potentially impacting tumor progression. They offer cardiovascular benefits, tissue protection, and help prevent Clostridium botulinum while also enhancing food quality and alleviating conditions like metabolic syndrome.
Why are toxicity equivalency factors and mutagenicity factors used to establish a risk profile for PAHs?
- PAH contamination is rarely due to a single compound but instead - PAH mixtures.
