bioassay ppt by dr sumit
TRANSCRIPT
BIOASSAYBy :Dr. Sumit Kumar Mahato Junior Resident( Academic)Guide: Dr. Uma Shanker Pd. Keshri Associate Professor Department of Pharmacology RIMS, Ranchi
An assay is an investigative (analytic) procedure in laboratory medicine, pharmacology, environmental biology, and molecular biology for qualitatively assessing or quantitatively measuring the presence or amount or the functional activity of a target entity (the analyte) which can be a drug or biochemical substance or organic sample
Assay
Chemical Assay Immunoassay Bioassay
Types Of Assay
Chemical Assay: It is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Immunoassay:A technique that makes use of the binding between an antigen and its homologous antibody in order to identify and quantify the specific antigen or antibody in a sample.
Comparative assessment of relative potency of a test compound to a standard compound on a living or biological tissue.
Quantitative measurement of the amount of active principle or substance in a pharmaceutical preparation or biological material using a suitable biological system
Introduced by Paul Ehrlich - biostandardization of Diphtheria antitoxin
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Bioassay
Comparison Of Chemical & Bioassay
BioassayBioassay
Chemical Assay Less Precise More time consuming More expensive Active constituent &
structure not known. More sensitive More men power
Required Difficult to handle
More Precise Less time consuming Less expensive Active constituent &
structure fully established.
Less sensitive Less men power
required Easy to handle
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Synonyms
Biological assay
Biometrics
Biological standadizatio
n
Bio-standadizati
on
To compare the test substance with the International Standard preparation of the same
To find out how much test substance is required to produce the same biological effect, as produced by the standard
Activity assayed should be the activity of interest
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Principles of bioassay
Standard & test sample - similar pharmacological effects & mode of action
Both should be compared for their established pharmacological effect using specified technique
Ex: *Ach – contractile response on frog rectus abdominis muscle
*Histamine – contractile response on guinea pig ileum
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Contd..
Problem of biological variation must be minimized
Experimental conditions - kept constant
Animals - same species, sex and weight
Number of animals - large enough to minimize error (individual variation)
Isolated preparations - sensitive
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Contd..
No chemical method has been developed
Chemical assay is too complex /not sensitive enough to measure (ex: insulin, Ach)
To measure the pharmacological activity of new or chemically undefined substances
For biological standardization of drugs obtained from
natural sources as these cannot be obtained in pure form. Eg: Oxytocin,Vasopressin,Insulin,Heparin..
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Indications of bioassay
To compare the strength of a drug obtained from various sources due to different compositions
Chemicals with similar structure, but different biological activity
Chemical structure of the active principle is unknown
Chemical structure known; cannot be actively purified. Eg: Peptide hormones
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Contd…
Sensitivity Specificity Repeatability Reproducibility Precision Accuracy Stability – tissue has to stay
“bioassay-fit
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Characteristics of a good assay method
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Bioassay can be performed on
• Intact animalsInvivo
• Isolated tissuesInvitr
o
WHOLE ANIMALS
Nor Adrenaline – Cat Cardiac Glycosides – Guinea Pig Insulin – Mice Estrogens – Ovariectamised Female Rat
ISOLATED TISSUE
Acetyl Choline – Frog Rectus Abdominus muscle Histamine – Guinea Pig ileum Adrenaline – Rat uterus Oxytocin – Rat uterus oestrogen primed
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Types of BioassayQualitative bioassayIs used for assessing the physical effects of a substance that may not be quantified, such as abnormal development or deformity.Eg: Arnold Adolph Berthold's famous experiment on castrated chickens. This analysis found that by removing the testes of a chicken, it would not develop into a rooster because the endocrine signals necessary for this process were not available.Quantitative bioassays involve estimation of concentration/potency of a substance by measurement of the biological response it produces. These bioassays are typically analyzed using the methods of biostatistics
1.Direct end point assay (DEPA)2.Quantal assay (all or none assay)3.Graded assay : a) Bracketting assay b) Matching assay c) Interpolation assay d) Multiple point assay ( 3-point, 4point, 6-
point, 8-point).
Bioassay Classification
Principle: is to measure direct response of dose of standard and test preparation. The threshold dose required for response is determined for each experimental unit. Ratio between these doses estimates the potency of the test preparation relative to the standard.
Concentration of test= TDS/TDT×CSD Where, TDS= Threshold dose of standard TDT= Threshold dose of test CSD= Concentration of standard drugThreshold dose of standard = Total period of infusion × rate
of drug administration
Direct End Point Assay:
Advantage: Drug effects appear rapidly and are easily
recognised Drug effect is directly proportional to drug dose Rapid end-point detection.
Disadvantages: Only toxicity study or high dose study is possible Dose ranging study cannot be done
Quantal response – the unknown is compared with the standard with respect to potency which produces the quantal affect, i.e change is easily recognised sign or often death.
In a quantal assay there is use of dose response relationship. quantal response to a drug is obtained and percentage of positive response
at each dose is calculated. The response in quantal assay is varying, i.e some responses are irreversible
and hence animal used is once and some responses have no permanent effect and animal can be used in next experiment
e.g – Determination of LD50 Hypoglycemic convulsion in mice in the assay of insulin
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Quantal assay( All or None assay):
Graded response - In these assays, as the dose increases there is an equivalent rise in response. The potency of a test agonist is determined by comparing its mean response to standard mean response.
This process is also known as “analytical dilution assay”
GRA is the simplest way of determining potency of a test drug because it does not require statistical analysis
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Graded assay
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Graded DRC
standard Test/unknown
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DRC & Log DRC
30%
70%
Sigmoid curveWide range of doses can plot
Rectangular hyperbola
• Potency• Efficacy• Slope of curve
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Used when test sample is too small. Comparison of potency between unknown and standard drug is done
by trial and error method. Response is matched at only one dose Does not need dose respone curve of test compound It require most sensitive tissue Concentration of test= (Dose of standard/ Dose of test)× conc. Of standard
Disadvantage: Experimental error is not excluded out There is no sign of parallelism as it lack dose response relationship.
MATCHING ASSAY:
Used when test sample is too small. Single or few responses is taken by using any test drug
concentration. This response is bracketed between two responses one
higher and one lower of the standard drug. The strength of the unknown can be found by simple
interpolation of this bracketted response on dose axis
Bracketing Assay
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Bracketing or Direct Matching
less accurate,time consuming, troublesome cannot get exact match of response quantitative difference b/w test & standard not obtained
Disadvantages
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standard Test/unknown
A log dose-response curve is plotted with the standard, Single or few responses of test drug are plotted. The dose of test drug which comes at the linear log dose-
response is interpolated from the dose respone plot
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Interpolation assay
100
50
0 x x1
Interpolation
standard%
RESPONSE
LOG DOSE
Sensitivity of tissue is 1st determined by prior plotting of a conc-response curve with known agonist
Dose can be plotted even if it varies over thousand fold range
Error is normally distributed
Advantages
Sensitivity of tissue changes with time
Timing of doses not taken into account
Variation in mode of application of drugs
Disadvantages
Responses are repeated several times and the mean of each is taken
Chances of error are minimized 3 point method - 2 doses of std+1 dose of test 4 point method - 2 doses of std+2 doses of test 6 point method - 3 doses of std+3 doses of test
Latin square method of randomization to avoid any bias
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Multiple point assays
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3 - point assay t s1 s2s1 s2 ts2 t s1
3 cycles
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3-POINT ASSAY
%RESPONSE
LOG DOSEs1
T
t
S2
s2
S1
s1 s2 t
t s1 s2
s2 s1 t
t s2 s1
Latin square design
• Mean responses of these 3 sets plotted• Log potency ratio (M) = (T-S1÷ S2-S1)× log d where, d – dose ratio = s2/s1• Strength of unknown = s1/t × antilog of M S1, S2- length of standard dose response selected
between 25-75% T-length of test dose response selected in between of
two standard responsess2/s1 -standard drug dose which came in contact with
tissueand given the response S1, S2. respectively
t = Test drug dose which came in contact with tissu and given the response T 39
CALCULATION
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4 - POINT ASSAY
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4-POINT ASSAY
%RESPONSE
LOG DOSEs1
T1
t1
S2
s2
S1
T2
t2
s2 t1 t2 s1
t1 t2 s1 s2
t2 s1 s2 t1
Latin square designs1 s2 t1 t2
• Mean responses of 4 sets plotted• Log potency ratio (M)
(T2-S2)+(T1-S1) × Log d (S2-S1)+(T2-T1) where, d-dose ratio = s2/s1
• Strength of unknown = s1/t1 × antilog of M
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Calculation
3+3 dose assay 3 conc each of std & test drug are used 6 sets of experiments using 6 doses in each
set More time consuming,lesser in use Reliability is excellent
Six point assay
to measure the pharmacological activity of new/ chemically undefined substances
to investigate the function of endogenous mediators
to measure drug toxicity and unwanted effects
to measure the conc of drugs and other active substances in the blood or other body fluids
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Uses of Bioassay
Determination of potency, ED50/LD50 of drugs
New drug development
Measure clinical effectiveness
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• Biological variation• Troublesome• Time consuming• Expensive• Less accurate than physico-chemical
methods
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Drawbacks
Successful tool in estimation & discovery of biologically active substances
Sensitivity & Specificity – important tool in pharmacology
Conclusion