Chapter 2 (exam 1) Flashcards
(73 cards)
1
Q
Absorption factors
A
Variables in Fick’s rate of diffusion
- polarity, ionization (Kow)
- surface area
- # and thickness of membranes
- Conc gradient (high - low)
2
Q
DMSO
A
Dimethyl sulfoxide
- Moves across skin barrier rapidly
- Dissolve toxicant in DMSO for rapid dermal uptake
3
Q
Partition Coefficient
A
measures polarity
- Kow = conc in the organic layer/conc in the water layer
- high Kow is highly nonpolar and crosses lipid membranes readily
- determine polarity based on structure
4
Q
Ionization
A
Neutral compounds diffuse across membranes better than charged ions
-dependent on the pH of the environment
5
Q
pKa and environment pH example
A
Aspirin pKa of -COOH = 3.49, stomach pH =2, GI pH =6
-uptake greater in stomach because at a lower pH HA will be dominant over A- and the more neutral compound will diffuse better over the nonpolar lipid membrane
6
Q
Why do pharmaceuticals come with HCL
A
- Forms a salt, which is easier to transport and package
- The toxin has little effect on the pH of the environment
7
Q
Concentration Gradient
A
- more probably that high conc molecules will hit the membrane and cross over
- based on random motion
8
Q
Passive diffusion
A
gradient dependent
- probability of hitting the membrane
- conc in blood is very close to zero, fast motion removes the substance quickly
- “hitchhiker” uptake from Pb2+ looking like Ca2+
9
Q
Active Transport
A
- burns ATP
- couple with nonspontaneous
- against the gradient
- use transport proteins and enzymes as carriers
10
Q
Filtration
A
passive diffusion of polar/charged substance through small pores
11
Q
Endocytosis/pinocytosis
A
particles into the cells by forming vesicle from membrane
-nanoparticles
12
Q
GIT
A
epithelial cells continuous with exterior high surface area pH - stomach(2) intestine(6) blood(7.4) mostly passive diffusion
13
Q
Lungs
A
- thin membrane
- facilitate exchange
- difference between upper and lower
14
Q
Particle Size in Lungs
A
Large are filtered out by the URT
Small penetrate to the LRT
15
Q
Gases and Aerosols in Lungs
A
- some particulate filtered out by URT
- permanent gases make it to the LRT
- PM2.5 - particle smaller than 2.5 um gets to LRT, less than 1 um gets to alveoli
- water soluble gases dissolve into nasal fluid
- low water solubility go to LRT
16
Q
Reactivity in Lungs
A
- highly reactive effect the URT
- low reactivity effect the LRT
- Ozone - 30% into URT even though low water solubility. High reactivity
17
Q
Brick and Mortar model of skin
A
Keratinocytes/corneocytes are polar
surrounded by nonpolar lipids
-Tortuosity describes the indirect pathway
-no active transport because cells are dead
18
Q
Solvents through dermis
A
nonpolar increase fluidity of the lipids or remove it. Less barrier to move through
19
Q
Perfusion
A
blood flow to an organ or tissue. More exposure to toxicant in the higher perfused tissue
high- brain, liver , kidneys
low- bone, adipose,
20
Q
Depots
A
accumulation of a chemical in a specific tissue based on physical or chemical properties
- nonpolar compounds in fat
- Sr2+ and Pb2+ on bone
- albumin
21
Q
Albumin
A
- blood plasma protein
- attracts nonpolar and ionic compounds to minimize the surface area exposed to water
- common for antibiotics
22
Q
Deports (reversibly bound)
A
Follow LeChatelier’s principle
- when blood conc decreases, more is released
- lead in kids, removing them from the lead environment will cause it to be released from depots
- does not apply to irreversible binding
- graphs
23
Q
Distribution barrier
A
Blood brain barrier
-blood vessels have smaller/fewer pores, more specific transporters, tighter junctions between cells
Blood placenta barrier
-not as selective as blood brain barrier
24
Q
Metabolism Goal
A
- facilitate excretion
- increase aqueous solubility
25
Nonpolar risks
- increased uptake
- increased storage in depots and accumulation
- orange baby noses from accumulation of beta-keratine in carrots and sweet potatoes
26
Pro/Con to modifying chemical structure
pro-detoxification
-decrease receptor compatability
con - metabolite more toxic than parent compound
- highly reactive metabolite
27
Membrane thickness
GIT - 30um
Respiratory - 0.4 - 1.5 um
Skin - 100-200 um
injection - 0 um
28
Phase II metabolism (general)
increase solubility by adding small polar molecule (conjugation reaction)
- sugar, polypeptides add -OH groups and some proteins can be ionized
- often occurs at the site of phase I functional group
- reliably detoxifies
- creates large polar region to increase excretion
- relies on enzyme
29
Phase I metabolism (general)
generally oxidation that increases aq solubility by adding a polar functional group
- OH, -COOH (ionizable), R=O
- single functional group
- more reactive than phase II
30
Phase I enzymes
-cytochrome P450s
Flavin containing monooxygenases (FMO)
-Dehydrogenases
31
P450 general
- enzymes for phase I
- 2000+ vary by substrate specificity and organism
- found in portals of entry (skin, nasal mucosa, lungs, GIT, liver, kidney)
- metabolize xenobiotics and endogenous materials
32
P450 as microsomal enzyme
- "small bodies" organelles in a cell
- Primarily in smooth endoplasmic reticulum
- isolate by lysing cell and centrifuge
- -s9 fraction is the percentage of microsomes and cytosolic enzymes
33
P450 general reaction
RH + O2 + NADPH + H+ = ROH + H2O + NADP+
| -NADPH to help the O2 oxidize C-H bond
34
P450 catalytic cycle
```
RH present at all times
-Fe3+ from heme and NADPH e- = Fe2+
-Fe2+ and O2 = Fe3+O2-
-NADPH e- = Fe3+[O2]2-
- 2H+ leave as water = [Fe-O]3+
-Fe3+ + ROH
(can all occur in vitro)
```
35
P450 example
benzo(a)pyrene is a polycyclic carbon
- product of incomplete combustion and cig smoke
- P450 produces an epoxide
- epoxide hydrolase produces diol
- P450 and diol make diol epoxide(toxic) that is not a substrate of P450
36
O-dealkylation
- P450 reaction
- chlorfenvinfos - organophosphate pesticide
- remove alkyl group and leave -OH
- as EN atoms, ONSP
37
Flavin-containing Monooxygenases (FMO)
- microsomal enzyme for phase I
- NADPH and O2 required
- goes between quinone(oxidized =O) and hydroquinone(reduced -OH)
- less reactive than P450
38
Alcohol dehydrogenase (ADH)
-in cytosol, of liver, kidney, lungs
-effective on primary and secondary(slower) alcohols
-Produces aldehydes and ketones, which are more toxic (activation)
RCH2OH + NAD+ = RCHO + NADH + H+
39
Fusel Oil
nonethanol alcohols
40
Aldehyde Dehydrogenase (ALDH)
- in cytosol and endoplasmic reticulum, same tissue as ADH
| - product is less toxic carboxylic acid
41
Antabuse
- treats alcoholism
- inhibits ALDH
- aldehyde accumulation and causes illness like hangover without other effects of EtOH
- resembles -COO- and ALDH is occupied. Retains high affinity
42
Phase I hydrolysis
Catalyzed by carboxylesterases in tissues and cholinesterases in plasma
- RCOOR' + H2O = RCOOH + R'OH
- Similar for S and N, replace carbonyl O, same enzyme but fastest with carboxyester
- know the arrow pushing
- nonzero rate without enzyme, can occur abiotically
43
Reductive Dehalogenation
RX = RH + HX
- decrease persistence of organochlorine/bromine
- C-Cl bonds are extremely stable
- reductive dehalogenation is extremely SLOW
- microbially mediated - anerobic (human gut, sediment under water)
44
PCBs
polychlorinated biphenyls
- used in electrical insulators
- persist for decades
- 209 congeners
- low Kow
45
Reductive dehalogenation conditions
anerobic
human gut
sediment-under water, lower rate of oxygen diffusion (consumption>supply)
Accumulation of organics in the sediment
46
PBDE
polybrominated diphenyl ethers
flame retardants
low Kow
similar to PCB in reductive dehalogenation process
47
Global Distillation
- organohalogens have a low volatility but it is not zero
- evaporate over time and circulate
- Deposit in arctic because air is cold
- high accumulation is polar bear
- high fat content in polar bear milk and gets passed to cubs
- native women are warned against breastfeeding
48
Glucuronidation facts
- glucuronosyl transferase puts glucuronic acid on a polar functional group (-OH, NH2, COOH)
- enzyme in microsomal fraction of liver, kidney, GIT
- products subject to elimination with polar waste or active transport into bile
49
Glucuronidation reaction
- glucuronic acid carrier by an energetic compound (uridine-5-diphosphoglucuronic acid (UDPGA)
- ROH + UDPGA = RO-GA + UDP
- reversed by abiotic acid hydrolysis
- beta-glucuronidase: enzyme produced by gut flora
- enterohepatic circulation (increase half life)
50
Sulfate conjugation
similar to glucuronidation
- ROH + PAPS + SULT = RO-SO3- + H+ + PAP
- PAPS - 3 phosphoadenosine-5 phosphosulfate
- SULT - sulfotransferase
- elimination with polar waste or active transport in kidney
51
Phase I to Phase II info
Phase I - powerful oxidation that produces reactive metabolites
Phase II - ready to works and is used immediately
- energized mechanism
- must work immediately because phase I metabolite is reactive
52
Gluthione conjugation
must have a reactive center on the substrate(electrophilic carbon)
gluthione is a nucleophile
53
Gluthione(GSH)
polypeptide
gamma-glutamyl-cysteinyl-glycine - high conc in liver, up to 10% of cellular protein, in cytoplasm
SH nucleophilic center
doesnt need enzyme
Rate increases with glutathione-S-transferase (GST)
54
Gluthione mechanism
RX + GSH = RSG
mercapturic acid is excreted
remove glutamate and glycine, then acetylate the N
55
Acetylation and Methyltransferases
Acetylation catalyzed by N-acetyltransferase
-adds CH3CO to N
Methyltransferases
-N, O and S methyltransferases
-Co-Substrate is S-adenosylmethionine
-HG2+ + MeHg+ = Me2Hg is nonpolar and accumulates lethal at extremely small doses
-methylate 3 amine to make 4+ amine and increase solubility
56
Ultra short lived metabolites
- bind to the enzyme that created them
- suicide substrate - piperonyl butoxide binds to P450 and decreases their activity, not toxic alone
- enzyme degradation
- new enzyme synthesis
57
Short Lived metabolites
-react close to where they are generated, dont make it beyond the cell or tissue
58
acetaminophen metabolites
- metabolism occurs by P450, sulfation, and gluceronidation
- P45O metabolite from acetaminophen is NAPQI which has toxic reaction with proteins and nucleic acids
- GSH conjugation metabolizes NAPQI
- Chronic EtOH abuse increases P450 activity and NAPQI increases, but GSH is limiting reagent and gets locally depleted
- liver cells die and release contents which can be toxic to other cells and kill them
59
Long lived metabolites
- transported systemically
- methanol CH3OH - CH2O - CHOOH (formic acid)
- formic acid travels to the eye and causes edema which causes blindness
60
Enzyme induction
increases enzyme production
- DNA-RNA-ribosome-proteins
- transcription-translation-synthesis
- inducers are often substrates for P450 and increase P450 production
- planar and nonpolar
- EtOH, benzo(a)pyrene, PCBs, PBDEs, dioxins
61
AhR
- Aryl hydrocarbon receptor
- cytosol
- complexes inducer
62
ARNT
- aryl hydrocarbon receptor nuclear translocator
| - brings complex into the nucleus
63
XRE
xenobiotic response element (drug response element)
- on the P450 gene
- binding promotes transcription
- transcription leads to more P450s
64
Ramifications of Induction
- good - facilitates excretion of nonpolar contaminants that would accumulate
- bad - produces more reactive metabolites (diol epoxides)
65
Biomarkers
measurements that indicates an exposure or effect in an organism
66
EROD assay
ethoxyresorufin-O-deethylase assay
- measure P450 activity
- ethyoxyresorufin is not fluorescent, but resorufin is
- loe fluorescent levels are detectable advantage over UV-Vis
- dealkylation of ethyoxyresorufin to resorufin
67
Bioavailability
fraction of a total exposure that can be taken up by an organism
68
How to measure toxicant in environment
- EROD assay measures effect, not just exposure, P450s are active
- integrates exposure over time
- in vitro test with a liver sample
- Blood/fat samples tell amount but not effects
69
Renal elimination
- water soluble compounds
- Phase II metabolites
- -active transporters
- -anion/acid transporters (ionized carboxylic acids)
- -cation/base transporters (ionized amine bases)
70
Liver elimination
- bile acts as a surfactant (hydrophobic and hydrophilic sides)
- active transport can remove chemcials from blood into bile, inot intestine and feces
- compounds can be subject to enterohepatic circulation
71
Respiration elimination
- relevant for permanent gases and compounds with high vapor pressure
- EtOH, solvents
72
Milk
Human - 4% (same as cow)
Polar Bear - 30-35%
Human health hazard for persistant organic pollutants (POPs)
73
Non-mammalian pathways
- skin shedding or molting
- -birds and reptiles
- leaf fall and fruit production
