BiomarkerMEDICINE UNIT 1

Introduction

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Definition:

The US FDA (2001)defines a biomarker as a characteristic i.e. objectively measured & evaluated as an indicator of normal biologic, pathogenic or pharmacologic responses to therapeutic intervention.

WHO (2010) Biomarkers includes-

“Almost any measurement reflecting an interaction between a biological system and a potential hazard, which may be chemical, physical, or biological; The measured response may be functional and physiological, biochemical at the cellular level or a molecular interaction.”

Ex : Pulse and blood pressure through basic chemistries to more complex laboratory tests of blood and other tissues.

Ideal biomarker

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Ideal biomarker

Biomarker & Diagnosis

Ideal Marker for diagnosis•Should have great sensitivity (>0.9), specificity (>0.9), and accuracy in reflecting total disease burden.•A tumor marker should also be prognostic of outcome and treatment.

Samples for biomarker detection•Blood, urine, or other body fluids samples•Tissue samples.

Biomarker for ScreeningThe marker must be highly specific, minimize

false positive and negativeThe marker must be able to clearly reflect the

different stages of the disease (early)The marker must be easily detected without

complicated medical procedures. The disease markers released to serum and

urine are good targets for application of early screening.

The method for screening should be cost effective.

Biomarker

Detection of biomarker – diagnosisSelf properties, e.g enzymatic activities, Antibodies, IHC, ELISA.

Detection of biomarker• Quantitative a link between quantity of the marker and disease• Qualitative a link between exist of a marker and disease.

Quantitative ApproachesStable Isotope Labeling methods• adds heavy isotopes to one sample so chemically identical compounds are mass shifted• added to the peptides/proteins using reactive groups• added to the proteins in vivo using heavy amino acids• can be multiplexed

Label free methods• extracted ion chromatograms• spectral counting

Validation of BiomakerAccuracy (agreement with a reference)Precision (repeatability, reproducibility)Limit of Detection (sensitivity)Interference, Cross-reactivity (specificity)Sample preparation / conditionsPerformance around the cut-offPotential for carryover, cross-hybridization.

Biomarker Uses Diagnosis, in symptomatic patients Early detection (screening), enabling intervention

at an earlier and potentially more curable stage than under usual clinical diagnostic conditions

Monitoring of disease response during therapy, with potential for adjusting level of intervention (e.g. dose) on a dynamic and personal basis

Risk assessment, leading to preventive interventions for those at sufficient risk

Prognosis, allowing for more (less) aggressive therapy for patients with worse (better) prognosis

Prediction. E.g., predicts safety, efficacy (PK/PD) of a specific therapy, thereby providing guidance in selecting it for patients or tailoring its dose.

Last three are attempts to predict the future.

Advantages Disadvantages

Objective assessment Timing is critical

Precision of measurement Expensive (cost for analysis)

Reliable; validity can be established Storage (longevity of samples)

Less biased than questionnaires Laboratory errors

Disease mechanisms often studied Normal range difficult to establish

Homogeneity of risk or disease Ethical responsibility

Biomarker

Biomarkers in Sepsis

Ideal biomarker for sepsisSensitive and specific for bacterial infection

.Single reliable cut-off value.Unaffected by acute illness or chronic

disease.Level correlates with severity and

mortality.Short half-life.Inexpensive and timely result (<1hr).Ex . Procalcitonin ,CRP,aptt,TNF, IL

The potential role of biomarkers for diagnosis remains undefined.

RecomendationUse of low procalcitonin levels or similar

biomarkers to assist the clinician in the discontinuation of empiric antibiotics in patients who initially appeared septic, but have no subsequent evidence of infection (grade 2C).

International Guidelines for Management ofSevere Sepsis and Septic Shock: 2013

Biomarkers in malaria

Malaria diagnosisserological biomarker

Rapid detection tests (RDTs) - immunochromatography assay.Plasmodial lactate dehydrogenase (pLDH).Histidine-rich protein II (HRP II).

Published sensitivities of RDTs for P. falciparum range from comparable to those of good field microscopy (> 90% at 100–500 parasites/μl of blood) to very poor (40–50%) for some widely used products.

Priyamvada Jain et al; Potential Biomarkers and Their Applications for Rapid and Reliable Detection of Malaria. 852645, 2014, 1-20. The use of rapid diagnostic tests. Geneva, Roll Back Malaria, WHO Regional Office for theWestern Pacific and UNDP/World Bank/WHO/UNICEF Special Programme for Researchand Training in Tropical Diseases, 2004

WHO maintains a list of RDT manufacturers with ISO 13485:2003 certification.

Advantages Rapid diagnosis.Fewer requirement of trained and skilled

personal. Disadvantages Unpredictable sensitivity.Inability to differentiate between new infection

and recently treated infection as few antibodies (HRP2) persist for 2 to 3 weeks.

Biomarkers in TB

TB pleural effusion (ADA) Diagnosis of TB pleural effusion is a challenging

task. None of the diagnostic modalities available till date

are able to diagnose TB pleural effusion as So ADA is being used as a biomarker in diagnosing

TB pleural effusion . It is a quantitative biomarker produced from T

Lymphocytes .

LAMDetection of the Mycobacterium tuberculosis cell

wall antigen lipoarabinomannan (LAM) in urine permits diagnoses of tuberculosis (TB).

This can be achieved at the point-of-care within just 30 minutes using the Determine TB-LAM, which is a commercially available, lateral-flow urine ‘strip test’ assay.

Currently this test is validated in africa in HIV positive patients .

Sensitivity and specificity are low in compared to the Xpert MTB/RIF assay.

Advantagessimplicity of use, lack of instrumentation, speed of use with results available after 25 minutesLow cost (initially marketed at $3.50 per test) Implemented at the point-of-care.

This is currently used in patients enrolled for ART treatment as a rapid test to rule out dissemenated TB.

Biomarkers in Alzheimer DiseaseCSF (Cerebrospinal fluid) Total tau

T-tau – increase (sensitivity- 95% & specificity- 84%).CSF Phosphorylated tau

P-tau - increase (sensitivity- 95% & specificity- 83%).CSF Aβ

Aβ42 – decrease (sensitivity- 95% & specificity- 82%).Magnetic resonance imaging MRI (functional scan using

FDG 18 Glucose ) atrophy of Hippocampus (sensitivity 88% & specificity 91%).

SPECT scanning (63% sensitivity and an 87% specificity).

K. Blennow et al. Fluid Biomarkers in Alzheimer Disease, Cold Spring Harb Perspect Med, Apr 2012;2:006221.J Cummings et al. Biomarker-Driven Therapeutic Management of Alzheimer’s Disease: Establishing the Foundations, Nov 2014; 95:1.

BIOMARKERS IN PARKINSON’S DISEASE

CSF Amyloid β and tau. Neuromelanin antibodies.PET biomarkers include [18F]-DOPA for

estimating dopaminergic neurotransmission.Reduced brain regional N-acetyl-aspartate using

magnetic resonance spectroscopy.α-Synculein index & Charnoly body.