Studied by 13 people
BIOL 4316
How do you know if the toxixcity of a chemical is low?
Low rate of absorption, accumulates in organs other than the target, is bio transformed into less toxic metabolites, is rapidly eliminated.
Barriers Toxicants must pass through:
Skin, lungs, Alimentary canal
Target of Hg, Pb
CNS, Kidney, hemetopoietic organs.
Benzene target
Hemtopoetic organs
CCl4 (carbon terachloride) target
liver damage
Toxicants are eliminated by the body by:
Bio-transformation → liver, Excretion → kidney, lungs and biliary, Storage → fat
Thickness
number of layers and kinds of cells.
Eg: statified epithelium →skin, simple epithelium → lungs, endothelium → blood vessles.
Structure of plasma membrane
Thickness = 7nm, bilayer of non-ridgid phospolipids and cholesterol (fluid mosaic model), protiens embedded in lipids → serve as transport protiens, channels, receptors, enzymes and form structures.
Rate of transport of toxicangt is dependant on:
partition coefficient (PC) and concentration graident across PM
How do small hydrophobic molecules diffisue through PM?
aqueous channels
large organic molecules difuse through PM through:
hydropbobic domains
Ethanol absorbtion:
lipid soluble, easily absorbed through the stomach.
How do toxicants ina solution exist?
either as ionized or unionized
Why are polar molecules unablt tocross PM?
they are ionized/ionic
why do non-polar molecules rapidly cross PM?
they are non-ionized/non-ionic
Diffusion of toxicanyts depends on:
lipid solubiblty
Fick’s law
the movement (flux) of mass (molecules) due to diffusion is based on the concentration of the substances and the area that the substance has to pass through.
Acorrding to Fick’s law, rate of diffucion is dependent on:
concentration of gradient across PM, thickness of PM, diffucion constant of toxicants, molecular weight of toxicants, surface area of PM.
many toxicants are (related to pH):
Weak acids/bases.
what is the amount of weak organic acids or bases in a solution dependent on?
their disassociation contant (K).
HA (acid) → H+ (disassociated proton) + A- (conjugate base); process is reversable and dependent on pH.
Toxiants which go through PM with simple difusion
TCDD (2,3,7,8-Tetrachlorodibenzodioxin) and DTT (Dithiothreitol)
Toxicant which go through PM with mediated channel transport
Terodotoxin → neurotoxin found in pufferfish which can cause rapid weakening and paralysis of muscles, including those of the respiratory tract, which can lead to respiratory arrest and death.
Toxins which cross PM with carrier mediated transport
Fe (Iron), 5-flurouracil (5-FU), paraquat, α-amantin, Ca (calcium), Pb (lead).
Toxins which cross PM with active transport
Penicillin (β-lactam antibiotics)
pH
-log[H+]
pKa
pH at which 50% of acid/base has been disassociated
Henderson-Hasselbalch equation weak acids
log[non-ionized form]/[ionized form] = pKa - pH
Henderson-Hasselbalch equation weak base
log [ionized form]/[non-ionized form] = pKa-pH
Acids with low pKa; acids with high pKa
strong; weak
Bases with low pKa; bases with high pka
weak; strong
pH formula
pH = pKa + log [A-]/[HA]
pKa alone cannot say whether compund is acidic/basic.
What greatly influences penetration of toxicants across PM?
partition coefficent (PC)
PC is related to solubiltiy of toxicants in lipids. What is the formula for calculating PC?
PC = concentration of toxicant in lipid/concentration of water
PC relation to lipid solubility
postitive correlation; higher PC = higher lipid solubility
solvent commenly used for PC determination
Octanol because it best mimics phospolipids of the PM
other solvents used for PC determination
chlorofom, ether, and organic olive oil
Filtration
movement of molecules through membranes of region with high hydrostatic pressure to region with low hydrostatic pressure. Includes speeration of solis from fluids; generally applies only to capillary walls.
example of filtration
renal golmeruli where molecules of 60,000 Da pass through
Glumerular cappilary filtation barriers
Endothelium, basement membrane, epithelial cells. (order from inside to outside)
Endothelium glomerular cappilary filtration barrier
fenestrated ( has multiple tiny holes)
basement membrane glomerular cappilary filtration barrier
negatively charged restriction site for protiens
Epithelial cells glomerular cappilary filtration barrier
restriction site for [pprotiens too, chracterized by foot-like processes called podocytes.
Active trasnport example
Na+ transport
facilitated difusion example
glucose from GI → plasma →RBCs
example of phagocytosis and pinocytosis
removal of perticulate material by macrophages
3 routes of absorbtion of toxicants
absorbtion by GI tract, lungs, and/or skin.
why is GI route absorbtion (genrally aclled absorbtion) important for toxicalogists
suicidial situaltion and children exposure
Examples of toxicants which are absorbed by GI
Nitorglycerin (sublingual), rectal supositories, most entry of tocicants (oral)
what is GI absorption if toxicant dependant on?
ionic species of the toxicant (wheher ionized or unionized)
Stomach pH in relation to intestinal pH
Stomach pH = highly acidic ( pH = 2); intesinal pH = near neutral (pH = 6)
What can help detremine posibility of absorbtion of toxicants through GI?
pKa value
3 specific transport systems of mamalia Gi for absorbtion of substances
2-step absorbtion, active transport, facillitated difusion
2 step absorbtion example
Fe2+ which is rapid through mucosa and slow into blood
Active transport GI absorption example
very few substances n/a
Facilitated difusion GI absorbtion example
azo dyes
where does most absorbtion of aspirin occur? stomach or intenstine?
The pKa of aspirin = 3.5. So, most aspirin is mostly absorbed in the stomach
Steps to find if ratio favors absorbtion (with benezoic acid pH = 4 in stomach)
pka-pH = log10 [non-ionized]/[ionized]
4 (pH of toxicant) - 2 (pH of stomach) = log10 [non-ionized]/[ionized]
2 (difference of 2 from 4) = log10 [non-ionized]/[ionized]
10² (10 is put to power of 2 or diffence of pHs to cencel out log) = [non-ionized]/[ionized]
100 (10 squared equals to 100) = [non-ionized]/[ionized]
100/1 (100 is non-ionized and 1 is ionized) = [non-ionized]/[ionized]
Ratio favors absorbtion in Stomach!
Steps to find if ratio favors absorbtion (with benezoic acid pH = 4 in stomach)
pka-pH = log10 [non-ionized]/[ionized]
4 (pH of toxicant) - 6 (pH of small intestine) = log10 [non-ionized]/[ionized]
-2 (difference of 6 from 4) = log10 [non-ionized]/[ionized]
10^-2 (10 is put to power of -2 or diffence of pHs to cencel out log) = [non-ionized]/[ionized]
1/100 (10 negatively squared equals to 1/100) = [non-ionized]/[ionized]
1/100 (1 is non-ionized and 100 is ionized) = [non-ionized]/[ionized]
Ratio does not favor absorbtion in small intestine.
Restisatnce of toxicants to what things affect absorption through GI
pH, enzymes, mircoflora.
Eg: sname venome is least toxic through oral route but fatal through IV and DDT is converted to DDE (safer metabolite) when consumed orally by gut bacteria.
Chleating agents
Ethalene diamine tetracetic acid (EDTA) increased membrane permeability increasing absorbtion
How does GI mobility ag=fect absorbtion?
higher GI motility higher absorbtion
How do other metals affect other metal absorbtion?
Cadmium (Cd) decreases absorbtion of Zinc (Zn)
Zn decreases absorbtion of Copper (Cu)
How does old age affect absorbtion
old age decreases absorbtion
How does starvation affect absorbtion
starvation increases absorbtion
Toxicants absorbed by lungs are usually:
gases and vapors such as CO, NO2 and SO2
Gasses and vapors in the atmostpher are in ________ with blood.
direct equilibrium
If gas is more soluble in blood it has a high absorbtiion rate. What is the exception to this rule?
Chlorofom gas
where in lungs are particles 2-5 µM deposoted?
tracheo-brochiolar region where later they are cleared by mucosa
Where are particles 1µM or smaller in lungs?
these are penetrate into aveolar sacs where overal removal of particles from aveoli is inefficent.
where are particles 5-30µM deposoted in lungs?
NOT deposited in lungs instead they hand arround in nose, mouth and/or pharynx
What examples of chemicals enter through skin?
nerva gas like sarin and CCL4
what is the major mechnsism of difucion through skin?
percutaneous absorbtion
Skin absorbtion phase 1
epthelium
skin absorbtion phase 2
dermis
skin absorbtion phase 3
blood and internal fluids
What example of chemical agent increases rate of penetration of chemicals through skin?
Dimethyl sulferoxide (DMSO) is belived to remove fat d=from skin and increase absorbtion.
Disrtibution of toxicants is very rapid. What factors does distribution depend on?
extent of blood supply or an organ, rate of diffiution or speacial stransport, PC
the site of accumulation may not be the sute of action so:
the toxin is inert till it reaches its target.
total body water is divided in3 compartments
plasma water, intersitital water, intracellular water
volume of distribution (VD)
porportion of a chemical in the body that is found in plasma
How is VD determined
disolving known amount of dye in an unknown volume of water and then calculating for VD.
VD formula
VD = amountof dye added/ concentration in water
VD formula in vivo
amounto fchemical administered /concentration in plasma
Toxicants stored in tissues have what volume of diribution?
restricted
toxicants are often ______ in tissues
concntrated; some can achieve a high concemtration at the site of action like CO in the hemoglobin (Hb) and paraquat in the lungs.
Storage sites of toxicants in the bosy are called ______
storage deposists which are protective mechanisms. Concentration in storage deposits are in equilibrium with those in the plasma and the biological half life (t 1/2) of stored toxicants is very long.
What are the storage deposits of the body?
plasma protiens, liver, kidney, fat, and bone.
Albumin (plasma protien stoage depot)
binds to Ca2+, Cu2+, Zn2+, bilirubin, uric acid, penicillin, salicylates, histamine, and barbituates.
trasnferrin (Plasam protien storgae depot)
transfers Fe2+
Lipoprotiens (plasma protien storage depot)
binds to lipid soluble compounds
Are protien bound toxicants available for distribution?
No.
How can a substance perviously bound to a plasma protien be diplaced?
If another substance competed with binding to the plasma protien and displaces the previous substance.
Eg: Strong dose of sulfonamide (an antibiotic) can displace an antidiabetic drug which was bound b=perviously. When this happens the antidiabetic drug is able to be dirtbuted via the blood and can result in hypoglycemia.
Xenobiotic
a compound not originally in the human body. Can distplace normal physiological compounds bound to plasma protiens.
Examples: dieldrin, acrylonitrile
How does the liver and kidney work together as storage depots?
Both have high capacity to elimate toxins. The liver biotransforms toxicants while the kidney eliminates those toxins trhough the urine.
Ligandin
protien in the lievr cytoplasm; has high affinity for organic acids, carcinogens, and corticosteriods.
Metallothionein
protin on both the liver and kidney; binds to metal ions like Cd2+ and Zn2+. Also enables liver to store Pb2+.
Why is fat a great storage depot?
Many xenobiotics are fat solible (chloroform, DDT, and PCB) and alos are able to enter the fat through simple diffusion. A substance with high partition coefficent (PC) will accumulate in the fat. This is a reason why obese people are at risk for too much toxin storgage.
Eg: during WWII mnay solders were found to have DDT in thier fat because the fat was able to store DDT which had a high PC.
Bone as a storage depot
great for F, Pb, and Sr. Additionally, F- and OH- are redeily exchangeable so there is an equilibrium between the bone and blood.
Bone seeker
Ra2+, includes such metals which actively seeks the bone out and behaves like Ca2+. This makes it so that Ra2+ can actually be made into bone tissue which can cause severe bone diseases later on.
Blood brain barrier (BBB)
A selective semi-permeable membrane between the blood and the interstitium of the brain.
