PHAR 737 Midterm 2 Flashcards
Describe CYP P450s (structure, functions, importance)
Heme-containing superfamily of enzymes. Metabolize drugs, hormones, cholesterol and arachadonic acid. Regulate blood homestasis.
At least 80 percent are involved in phase 1 metabolism.
These are important targets for pharmacogenetics and pharmacogenomics.
Describe CYP2Cs
Most abundantly expressed enzyme in the human liver and responsible for metabolism of 15-20% of prescribed OTCs
Highly variant enzyme, and metabolizes drugs such as warfarin, tramadol, and codeine.
What is the importance of CYP2C9/2* and /3* defective variants?
Defective alleles associated with reduced S-warfarin hydroxylation, making these patients prone to bleeding events
The estimated variance in antidepressant response due to genetic variants is around _____
50 percent
Describe CYP2D6
Most polymorphic P450 with over 75 different alleles with variation in metabolism rates (5-10% whites and higher percentage of Asians are poor metabolizers)
Located in cells of instestinal wall, endothelium, liver, etc. and is missing in 7% of caucasians and 2% of non-caucasians (hyperactive in 30% of East Africans)
Deletion occurs in 3-5% worldwide, with duplications resulting in 2 pseudogenes and more than 80 possible polymorphisms in coding or promoter regions.
Describe CYP3A4
Most abundant P450 in human liver, metabolizing over 120 drugs.
Common substrates include: >Acetaminophen >Codeine >Erythromycin >Warfarin >Lovastatin
Describe UGTs
Uridine Diphosphoglucuronosyltransferases (catalyze the glucuronidation of polar aglycones)
Active on a diverse range of drugs and xenobiotics. UGT1, UGT2 and 130 structurally and functionally different variants
Describe SULTs
Sulfotransferases catalyze the transfer of the sulfonyl group from 3’-phosphoadenosine 5’-phosphosulfate (PAPS) to various compounds to make them readily excreted in urine.
There are membrane bound SULTS in golgi for sulfonation of proteins, lipids and glycosaminoglycans.
Cytosolic SULTs for sulfonation of drugs, xenobiotics, and endogenous substrates (bile, acids, steroids, neurotransmitters)
Describe NATs
Utilize the acetyl CoA to acetylate drugs and xenobiotics that contain amino and hydrazine substitutes to the corresponding amides and hydrides respectively.
NAT1 is broadly expressed
NAT2 is expressed in liver, small intestine and colon
Large allele variation globally
For 27 drugs frequently cited in adverse drug reaction studies, ____ are metabolized by at least one enzyme with a variant allele associated with decreased drug metabolism
59%
____ to _____ % of randomly selected drugs are metabolized by enzymes known to exhibit functional genetic polymorphisms
7-20
During which phase of clinical trials are genomic analyses common?
3rd (FDA recommends collection of DNA samples from all, but PK and PD outliers at the least)
How long should DNA in clinical trials be retained for postmarket analysis?
15 years at least
What main reactions make up Phase 1 metabolism? Phase 2?
Oxidation, reduction, hydrolysis
Acetylation, glucuronidation, sulfation, methylation
A SNP in CYP3A5 creates a non-functional enzyme by introduction of a _____
early stop-codon
Describe regulation of CYP3A4
Can give a drug (from cell or xenobiotic) to initiate CYP3A4 production by causing PXR and RXR together to form heterodimer which promotes production of CYP3A4, which can metabolize warfarin, doxorubicin, atorvastatin and many other drugs.
Describe GSTs
Glutathione-S-transferases
7 cytosolic families (A, M, T, P, S, O and Z) that participate in xenobiotic biotransformation
Mitochondrion (K family)
Play a role in detoxification of highly reactive drug metabolites
Describe drug transporters in the human body
Membrane proteins throughout body working in a coordinated fashion for drug disposition, therapeutic efficacy, adverse drug reactions, and drug-drug interactions.
SLCs (passive and active that rely on gradients) and ABCs (are ATP dependent)_
What are biomarkers?
Can be a gene, protein, or other change that indicates a biochemical phenotype before that phenotype is clinically apparent.
Important for diagnosing disease or determining risk of disease, establishing and/or predicting drug response and toxicity
Describe the difference between bimodal and unimodal distribution of drug-related polymorphisms
Biomodal represents mutations that eliminate activity of drug-clearing enzymes, while unimodal represents polymorphisms that cause small (basically no) variation in drug-clearing enzyme activity
Ideal Marker for Diagnosis
Sensitivity, specificity, accuracy, prognostic or outcome and treatment
Describe the ideal biomarker for screening
Highly specific (minimize false positives and negatives), able to clearly reflect the different stages of the disease, easily detected without complicated medical procedures, and cost effective method for screening
Describe Warfarin
Most commonly prescribed anticoagulant (2M people start taking every year in US) and is the 2nd most common drug implicated in emergency room visits for ADRs next to insulin.
Synthetic derivative of coumarin, originally developed as rat poison, and belongs to a class of Vitamin K antagonists
Common indications include: atrial fibrillations, deep venous thrombosis, pulmonary embolism, etc.
Warfarin is metabolized primarily by ________ and inhibits _____________________________
CYP2C9
Vitamin K epoxide reductase complex subunit 1 (VKORC1)