Toxicology 1-3 Flashcards
What is toxicology?
The study of harmful effects of chemicals on biological systems
What is a poison?
Any substance that can cause death, disease or injury, which can be just about anything in the right dose
What are the routes of exposure to poisons? Which will show the most rapid effect?
- Oral (GI tract)
- Parenteral (IV) - most rapid effect
- Dermal (skin)
- Inhalation (lungs)
What are the factors which determine the duration and intensity of poisoning?
- Dose
- Age (very young or very old more susceptible)
- Personal habits
- Genetics
What is toxicokinetics vs toxicodynamics?
Toxicokinetics - ADME of toxins
Toxicodynamics - The way that toxins interact with us and disturb vital functions
What is acute vs subacute vs chronic exposure?
Acute - single or multiple exposures in a 24 hr period
Subacute - multiple exposures in a 3 month period
Chronic - multiple exposures in a >3 month period
What are the two major categories of poisons?
- Cumulative - i.e. lead, when total exposure is critical
2. Non-cumulative - readily detoxified by body, does not cause irreversible damage except at high doses
How is a zero-order rate constant calculated? What are its units?
k = slope of zero-order elimination process.
If A = concentration of drug A in blood
k = (A1-A0)/(t1-t0)
Since it is not dependent on the concentration of the drug in the rate law, Rate = k, and thus units are mg/hr typically.
What is the “transition period” in elimination kinetics?
As enzymes for metabolization become unsaturated, but still below Km, there is a transition period where the kinetics appear to be somewhere between zero order (saturated) and first order (dose-dependent elimination)
How does alcohol exhibit zero-order elimination?
Km of alcohol dehydrogenase is below one drink, so rapidly drinking two drinks will increase the BAC disproportionately (more than double it), since ADH will become saturated
How is aspirin metabolized? When is this saturated?
- Acetylsalicylic acid -> hydrolyzed to salicylate by plasma esterases rapidly
- Salicylate -> conjugated to glycine to form salicyluric acid
Saturated completely at 1g of aspirin (3 tablets), dose not become fully dose-dependent until 300 mg.
What are the toxic heavy metals of concern? Include atomic symbol.
- Lead - Pb
- Mercury - Hg
- Arsenic - As
- Cadmium - Cd
How, in general, are heavy metals toxic?
They are not metabolized, persist for long periods of time in the body, and combine with key amino acid residues on proteins (i.e. active sites of enzymes or structural proteins)
What does acute inorganic Pb poisoning cause?
Severe GI distress, progressing to CNS abnormalities
What does chronic inorganic Pb poisoning cause?
Weakness, CNS abnormalities, GI distress
most diagnostic: wrist drop (extensor muscle weakness)
What is the source of organic Pb poisoning and how can it be distinguished from inorganic Pb poisoning?
Organic generally due to tetraethyl or tetramethyl Pb from leaded gasoline
Distinguished from inorganic because few hematological abnormalities will be noticed, only CNS effects
How is Pb poisoning diagnosed?
Hematological abnormalities typically:
Blood lead concentration >0.5 mg/mL
Elevated free erythrocyte protoporphyrin test (FEP)
What compounds are elevated in lead poisoning?
- Delta-aminolevulinate (delta-ALA) in urine
- Coproporphyrinogen elevated in urine
- Protoporphyrin 9 elevated in RBCs (without heme)
Why are these compounds elevated in lead poisoning?
Lead inhibits several SH-containing enzymes of heme biosynthesis, causing anemia by inhibiting hemoglobin synthesis (microcytic anemia).
Major enzyme blocked: Ferrochelatase -> build up of protoporphyrin 9
Secondary: delta-ALA dehydratase, and co-PPR oxidase
How are the symptoms of lead poisoning treated?
Treat seizures with diazepam
Treat cerebral edema with mannitol and dexamethasone
Maintain fluid and electrolyte balance
What chelators are used for lead poisoning?
Short-term: Dimercaprol and CaNa2EDTA
Long-term: Oral penicillamine
What are the three main forms of mercury?
- Elemental mercury - a liquid
- Inorganic mercury salts - HgCl2, previous used in healthcare
- Organic mercurials - Methyl-mercuric chloride
What form of mercury is most easily absorbed, and which poses the greatest occupational hazard?
Organic mercurials -> most easily absorbed (like organic lead)
Elemental mercury - easily inhaled as vapor, greatest risk
Where does mercury tend to concentrate?
The kidneys and brain for a long period of time -> CNS effects and acute kidney damage
What are the shared symptoms of acute and chronic mercury intoxication?
Severe gingivitis, discolored gums, and metallic taste in mouth. (stomatitis)
Kidney damage
CNS effects in longterm
How does mercury exert its biochemical effect?
The ion forms covalent bods with SH group of intracellular porteins and precipitates them.
What is the treatment for mercury poisoning, and how is it monitored? What other heavy metal is this the same as?
Acute - dimercaprol
Chronic - add oral penicillamine
Monitored by urinary Hg levels to assess removal by chelators
Pretty much the same as both arsenic and lead!
Where is Arsenic commonly found, and what is it used for medically?
Commonly found as a contaminant of coal and metal ores.
Medically: used for treatment of certain tropical diseases and certain leukemias as chemotherapy
What is Arsenic used for non-medically?
Often found in herbicides and insecticides (weed killers!)
What is the primary enzyme affected by Arsenic, and by which form?
Trivalent form (As+3) binds sulfhydryl groups. Most commonly the SH groups of the lipoamide of pyruvate dehydrogenase -> forms a stable, 6-membered ring
What is the other form of arsenic and how is it toxic?
Pentavalent form (As+5), competes with inorganic phosphate in formation of ATP to uncouple oxidative phosphorylation
Why does Cadmium have a high environmental prevalence?
Less than 5% of it is recycled, so it is a pollutant (used in batteries). Also can be inhaled via cigarette smoking.
Where does Cadmium accumulate and why?
It is a cumulative exposure from the environment, accumulates in bones (competes with calcium). Half life is 10-30 years
What is the treatment for cadmium poisoning and what is contraindicated? Why?
Maybe EDTA, but really doesn’t work well.
Contraindicated: dimercaprol, mobilizes cadmium, causing it to concentrate further in kidneys and produce nephrotoxicity
How do chelators actually chelate?
Use nitrogen, sulfur, and oxygen atoms (via electron pairs) to form coordinate-covalent bonds with the cationic metal atom. These must distribute to the sites of the body where the metal is, pick it up, and mobilize it from the body (urine)
What is one major challenge of designing a chelator?
It must chelate the heavy metals better than other divalent cations like calcium and zinc
What is BAL and what are its adverse effects? How has this been combatted?
Trade name of dimercaprol
Adverse effects: hypertension, tachycardia, nausea, vomiting, headache
How have the toxicities of dimercaprol been overcome?
More water soluble derivatives have been made which have less adverse effects: DMSA (succinate) and DMPS (propane sulfonate)
What is the primary adverse effect of edetate calcium disodium (CaNa2EDTA), and what metal can it not be used for?
Nephrotoxicity - do not use with poor renal function
CANNOT be used to treat mercury (Hg), all other heavy metals will displace the calcium just fine
What is penicillamine? Which form is less toxic?
A degradation product of penicillin, with D isomer being less toxic
What is penicillamine used for?
chelating copper (Wilson’s disease), lead, mercury, and arsenic
What is the longterm safety of penillamine?
Same adverse effects longterm of penicillin: nephrotoxicity, hypersensitivity, eosinophilia
What is Deferoxamine (Desferal) used for primarily? Why is it super juicy?
Chelation of iron in iron poisoning
Juicy: does not interfere with iron in cellular proteins like hemoglobin or cytochromes
What is the toxicity of deferoxamine?
Renally eliminated -> nephrotoxicity. Also cataracts and GI side effects