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Volume 7, Issue 1, March – April 2011; Article-010ISSN 0976 – 044XReview ArticleA REVIEW ON ‘BIOMARKERS’ AS DIAGNOSTIC TOOL*Kuldeep Kinja , Gupta NKuldeep Kinja, Dept. of Pharmacology, NIMS Institute of Pharmacy, Shobha Nagar, Jaipur-303121, Rajastan, India.Accepted on: 01-01-2011; Finalized on: 23-02-2011.ABSTRACTBiomarker is a biochemical feature or facet that can be used to measure the progress of disease or the effects of treatment. Abiomarker can be a substance that is introduced into an organism as a means to examine organ function or other aspects of health.Biomarkers provide a dynamic and powerful approach to understanding the spectrum of neurological disease with applications inobservational and analytic epidemiology, randomized clinical trials, screening and diagnosis and prognosis. These markers offer themeans for homogeneous classification of a disease and risk factors, and the can extend our base information about the underlyingpathogenesis of disease. Biomarkers can also reflect the entire spectrum of disease from the earliest manifestations to the terminalstages. This brief review describes the major uses of biomarkers in clinical investigation. Issues that affect the analysis of biomarkersare discussed along with recommendations on how to deal with bias and confounding.Keywords: Antecedent biomarkers, diagnostic biomarkers, cardiac biomarkers, cancer biomarkers.INTRODUCTIONTYPES OF BIOMARKERSBiological markers (biomarkers) have been defined by‘Hulka and colleagues1’as “cellular, biochemical ormolecular alterations that are measurable in biologicalmedia such as human tissues, cells, or fluids.” Morerecently, the definition has been broadened to includebiological characteristics that can be objectivelymeasured and evaluated as an indicator of normalbiological processes, pathogenic processes, on. In practice, biomarkers include tools andtechnologies that can aid in understanding the prediction,cause, diagnosis, progression, regression, or outcome oftreatment of disease.Biomarkers have been classified by Perera andWeinsteinbased3 on the sequence of events fromexposure to disease. Schulte9 has outlined the capabilitiesof biomarkers. Biomarkers have the potential to identifythe earliest events in the natural history, reducing thedegree of misclassification of both disease and exposure,opening a window to potential mechanisms related to thedisease pathogenesis, accounting for some of thevariability and effect modification of risk prediction, thesecan also provide insight into disease progression,prognosis, and response to therapy. There are two majortypes of biomarkers:Biomarkers of all types have been used by generations ofepidemiologists, physicians, and scientists to studyhuman disease. The application of biomarkers in thediagnosis and management of cardiovascular disease,infections, immunological and genetic disorders, andcancer are well known1,2,3. Their use in research hasgrown out of the need to have a more directmeasurement of exposures in the causal pathway ofdisease that is free from recall bias, and that can alsohave the potential of providing information on the4absorption and metabolism of the exposures .The rapid growth of molecular biology and laboratorytechnology has expanded to the point at which theapplication of technically advanced biomarkers will soonbecome even more feasible. Molecular biomarkers will, inthe hands of clinical investigators, provide a dynamic andpowerful approach to understanding the spectrum ofneurological disease with obvious applications in analyticepidemiology, clinical trials and disease prevention,diagnosis, and disease management.5,6,7,81.Biomarkers of exposure, which are used in riskprediction, and2.Biomarkers of disease; for screening, diagnosis,monitoring of disease progression.In epidemiological (or quasi-experimental) investigations,biomarkers improve validity while reducing bias in themeasurement of exposures (or risk factors) forneurological disease. Rather than relying on a history ofexposure to a putative risk factor, direct measurement ofthe level of exposure or the chromosomal alterationresulting from the exposure lessens the possibility ofmisclassification of exposure.Molecular biomarkers have the additional potential toidentify individuals susceptible to disease. Moleculargenetics have already had an impact on neurologicalpractice, leading to improved diagnosis. Classification ofpopulations in terms of the degree of susceptibility on thebasis of such biomarkers produces greater accuracy thanrelying on historical definitions of susceptibility. Forexample, a biomarker will allow the stratification of apopulation on the basis of a specific “genotype”International Journal of Pharmaceutical Sciences Review and ResearchAvailable online at www.globalresearchonline.netPage 54

Volume 7, Issue 1, March – April 2011; Article-010associated with a disease rather than relying on a reportof the “family history” of the EDENTEnvironmental exposures, effect modifiers, or riskfactorsExternal exposure is the measured concentration of thetoxin in an individual’s immediate environment. Whilequestionnaires offer an historical account of theexposure, direct measurement of the alleged toxin in theair, water, soil, or food can provide accurate informationregarding the “dose” of the exposure.When the toxin is identified in tissues or body fluids itbecomes a biomarker for the internal dose. A biomarkerthat measures a “biologically effective dose” generallyindicates the amount of toxin or chemical measured inthe target organ or its surrogate. The pharmacokineticproperties of the toxin or chemical become important toconsider in measurement of the internal dose because anumber of body fluids could be used based on thepharmacologic properties of the agent. Some chemicalssuch as halogenated hydrocarbons are stored in adiposetissue but others, such as organophosphate pesticides,are better measured in blood or urine.Genetic susceptibilityEpidemiologic analyses can examine familial aggregationand assess genetic and environmental contributions to adisease by using life table methods and recurrence risk.Mutations in genes that result in Mendelian forms ofdisease are typically deterministic. Variant alleles in genesor polymorphisms may be related to susceptibility but arenot deterministic. Most adult-onset degenerativediseases of the nervous system are likely to be acomposite of related characteristics, heritable andenvironmental. The correlated combinations of thesefeatures constitute the trait or disease.For neurological disorders, biomarkers of geneticsusceptibility are rapidly becoming more available.Identification of the variant allele in a gene, such as APOE(apolipoprotein E), is quite useful in assessing risk and inproviding information regarding the pathogenesis of theAlzheimer’s disease. With this information investigatorscan examine other genes or environmental risk factors todetermine whether they modified (increase or decrease)the risk of Alzheimer’s disease or not. Similarly, variationsin several genes appear to influence susceptibility toParkinson’s disease, which has also been related toenvironmental risk factors. Once established, a specificgenotype might be used to predict an association with a12particular environmental toxin .Intermediate biomarkersSome biomarkers represent direct steps in the causalpathway of a disease and are therefore strongly relatedto disease, others are related in some indirect way. Thereare numerous possibilities to consider. A biomarker couldISSN 0976 – 044Xbe dependent on another known or unknown factor tocause disease. Thus, it is not the only determinant but it isin the causal pathway and remains strongly related to thedisease. The biomarker could also be related to anexposure that has already been identified or representsan alteration caused by the exposure that results in thedisease. The most precarious situation is one in which thebiomarker is related to some unknown factor that is alsorelated to the exposure. This type of confounder, ifunidentified, can decrease the validity of the associationbetween the biomarker and the disease.BIOMARKERS OF DISEASEBiomarkers depicting prodromal signs enable earlierdiagnosis or allow for the outcome of interest to bedetermined at a more primitive stage of disease. Blood,urine, and cerebrospinal fluid provide the necessarybiological information for the diagnosis. In theseconditions, biomarkers are used as an indicator of abiological factor that represents either a subclinicalmanifestation, stage of the disorder, or a surrogatemanifestation of the disease. Biomarkers used forscreening or diagnosis also often represent surrogatemanifestations of the disease. The potential uses of thisclass of biomarkers include:1.Identification of individuals destined to becomeaffected or who are in the “preclinical” stages of theillness,2.Reduction in disease heterogeneity in clinical trialsor epidemiologic studies,3.Reflection of the natural history of diseaseencompassing the phases of induction, latency anddetection, and4.Target for a clinical trial.Cardiac BiomarkersCardiac biomarkers are substances that are released intothe blood when the heart is damaged. Measurement ofthese biomarkers is used to help diagnose, evaluate, andmonitor patients with suspected acute coronarysyndrome (ACS)13. The symptoms of ACS are associatedwith heart attacks and angina, but they may also be seenwith non-heart-related conditions. Increases in one ormore cardiac biomarkers can identify patients with ACS,allowing rapid diagnosis and appropriate treatment oftheir condition.Cardiac biomarker tests are ordered to help detect thepresence of ACS and to evaluate its severity as soon aspossible so that appropriate therapy can be initiated. It isimportant to distinguish heart attack from angina, heartfailure, or another condition because the treatments andmonitoring requirements are different. For heart attacks,prompt medical intervention is crucial to minimize heart14damage and future complications . Cardiac biomarkertests must be available to the doctor 24 hours a day, 7days a week with a rapid turn-around-time15. Some of theInternational Journal of Pharmaceutical Sciences Review and ResearchAvailable online at www.globalresearchonline.netPage 55

Volume 7, Issue 1, March – April 2011; Article-010ISSN 0976 – 044Xtests may be performed at the point of care (POC) – in theEmergency Room or at the patient’s bedside. Serialtesting of one or more cardiac biomarkers is often doneto ensure that a rise in their blood levels is not missed16,17and to estimate the severity of a heart attack .The current biomarker test of choice for detecting heartdamage is troponin. Other cardiac biomarkers are lessspecific for the heart and may be elevated in skeletalmuscle injury, liver disease, or kidney disease. Many otherpotential cardiac biomarkers are being researched, buttheir clinical utility has yet to be established18,19.Cancer BiomarkersCancer biomarkers are employed across the entirehealthcare spectrum from the cancer biological researchlaboratory to patient monitoring in the clinic. Cancerbiomarker’s applications include the identification ofnovel therapeutic targets in cancer drug discovery anduses of cancer biomarkers as surrogate markers for drugefficacy in clinical trials. This report describes a number offactors providing the driving forces behind cancerbiomarker growth and commercialization20,21. Emergingcancer biomarker types and the increasing interest incirculating tumour cells, as well as data on potential DNA,RNA, and protein biomarkers under study, includesOncogenes, Germline inheritance, Mutations in drugtargets, Epigenetic changes.Biomarkers in Drug DevelopmentWith the increasing cost and complexity of drugdevelopment, biomarkers play an increasing role in theearly phases of drug development. Biomarkers can beclassified into target, mechanistic, or outcome withvarying degrees of linkage to disease or treatment effect.They can be used to determine proof of concept bycharacterizing the efficacy or safety profiles, ordetermining differentiation from any competitordrugs. Clinical validation of the biomarker has a directinfluence on the clinical utility and therefore on the labelof the co-developed product. As shown in Figure 1.Table 1: COMMONLY USED CARDIAC BIOMARKER TESTSMarkerWhat it isTissuesourceReason forincreaseTime toincreaseTime back tonormalWhen/howusedCKEnzyme- 3differentisoenzyme existHeart, brain,and skeletalmuscleInjury to muscleand/or heartcells4 to 6 hoursafter injury,peaks in 18 to24 hours48 to 72 hours,unless due tocontinuing injuryPerformed incombinationwith CK-MBCK-MBHeart-relatedisoenzymes ofCKHeartprimarily,but also inskeletalmuscleInjury to heartand/or musclecells4 to 6 hoursafter heartattack, peaksin 12 to 20hours24 to 48 hours,unless new orcontinuingdamageLess specificthan troponin,used whentroponin is notavailableMyoglobinOxygen-storingproteinHeart andother musclecellsInjury to muscleand/or heartcells2 to 3 hoursafter injury,peaks in 8 to12 hoursWithin one dayafter injuryPerformed withtroponin toprovide earlydiagnosisDiagnose heartattack, accessHeartInjury to heart4 to 8 hoursdegree ofdamageThese tests are used to help diagnose, evaluate, and monitor patients suspected of having Acute Coronary Syndrome(ACS).CardiactroponinRemainselevated for 7 to14 daysRegulatoryprotein complex.Table 2: Biomarker Tests User for PrognosisBIOMARKERWHAT IT ISREASON FOR INCREASEWHEN/HOW USEDhs-CRPProteinInflammationMay help determine risk of future cardiac events inpatients who have had a heart attackBNP and NT-proBNPHormoneHeart failureHelp diagnose and evaluate heart failure, prognosisand to monitor therapyThese tests may be used to evaluate risk of future cardiac events.International Journal of Pharmaceutical Sciences Review and ResearchAvailable online at www.globalresearchonline.netPage 56

Volume 7, Issue 1, March – April 2011; Article-010ISSN 0976 – 044XFigure 1: Flow chart showing the importance of biomarkers in drug development processVARIABILITYAlthough biomarkers have numerous advantages,variability is a major concern. Variability appliesregardless of whether the biomarker represents anexposure or effect modifier, a surrogate of the disease, oran indication of susceptibility. Inter-individual variabilitycan result from the amount of an external exposure orfrom the way a putative toxin is metabolized. Forexample, individuals exposed to the same chemical mightdiffer in their ability (or inability) to metabolize the agent,or they may have experienced different types ofexposures (in the field as compared with in the office).Intra-individual variability is usually related to laboratoryerrors or other conditions, or exposures unique to theindividual. Group variability is also encountered, but thisis often the desired outcome of a study. Whilemeasurement error is always a concern with biomarkers,other important factors may explain individual or groupvariability. Some workers may always wear protectiveequipment whereas others may not. Interaction withother exposures, drugs, or effect modifiers can increaseor decrease the effect of the biomarker underconsideration as an exposure or as a measure ofsusceptibility. Variability can also be attributed to theeffects of factors such as individual diet or other personalcharacteristics. Amount of dietary fat can influence thebiological measurement of lipid-soluble vitamins as wellas toxic chemicals.VALIDITYReliability or repeatability is crucial. Laboratory errors canlead to misclassification of exposures or disease if thebiomarker is not reliable. Pilot studies should beperformed to establish a reasonable degree of reliability.Changes in laboratory personnel, laboratory methods,storage, and transport procedures may all affect thereliability of the biomarkers used in any investigation.Kappa statistics for binary or dichotomous data and intraclass correlation coefficients should be used to assesstest-retest agreement and consistency.The evaluation of the validity of a biomarker is complex.Schulte and Perera22suggest three aspects ofmeasurement validity:1) Content validity, shows degree to which biomarkerreflects bio-phenomenon studied,2) Construct validity, which pertains to other relevantcharacteristics of disease or trait, and3) Criterion validity, which shows the extent to which thebiomarker correlates with the specific disease and isusually measured by sensitivity, specificity, and predictivepower.23,24As with other diagnostic methods, sensitivity andspecificity tell us the accuracy of the test but not theprobability of disease. For that we need to estimate thepredictive values (positive and negative). Positivepredictive value (PPV) is the percentage of people with apositive test who actually have the disease. This providesus with information about the likelihood of the diseasebeing present if the test is positive. Negative predictivevalue (NPV) is the percentage of people with a negativetest who do not have the disease. Increasing the priorprobability will increase the PPV but decrease the NPV,assuming that the sensitivity and specificity remainunchanged.CONCLUSIONMany studies using biomarkers never achieve their fullpotential because of the failure to adhere to the samerules that would apply for the use of variables that arenot biological. The development of any biomarker shouldprecede or go in parallel with the standard design of anyepidemiological project or clinical trial. In forming thelaboratory component, pilot studies must be completedto determine accuracy, reliability, interpretability, andfeasibility. The investigator must establish “normal”distributions by important variables such as age andgender. The investigator will also want to establish theextent of intra-individual variation, tissue localization, andpersistence of the biomarker. Moreover, he or she willInternational Journal of Pharmaceutical Sciences Review and ResearchAvailable online at www.globalresearchonline.netPage 57

Volume 7, Issue 1, March – April 2011; Article-010need to determine the extent of inter-individual variationattributable to acquired or genetic susceptibility. Most, ifnot all of these issues can be resolved in pilot studiespreceding the formal investigation.ISSN 0976 – 044XAACC/ members/nacb/LMPG/OnlineGuide/ PublishedGuidelines/ACSHeart14.Weinrauch, L. (2007 March 30, Updated). Heart Attack.MedlinePlus Medical Encyclopedia. Available online 000195.htm .15.(2007 May). What is a Heart Attack. National Heart tAttack.html.16.Schreiber, D. and Miller, S. (2006 June 26, Updated). Useof Cardiac Markers in the Emergency medicine.com/emerg/TOPIC932.HTM.17.Clinical Laboratory News: New NACB GuidelinesEmphasize Cardiac Troponin for ACS. Clinical LaboratoryNews April 2007: V33 (4).18.Pagana, Kathleen D. & Pagana, Timothy J. Mosby’sDiagnostic and Laboratory Test Reference; 8th Edition:Mosby, Inc., Saint Louis, MO.2007; 319, 321, 668-670.19.Clarke, W. and Dufour, D. R., Editors. ContemporaryPractice in Clinical Chemistry, AACC Press, Washington,DC.2006; 306-315.20.Bouras, T., Southey, M. C, and Venter, D. J.Overexpression of the steroid receptor coactivator AIB 1in breast cancer correlates with the absence of estrogenand progesterone receptors and positivity for p53 andHER2/neu. Cancer Res,2001; 61: 903-907.21.Cloven, N. G., Kyshtoobayeva, A., Burger, R. A., Yu, I. R.,and Fruehauf, J. P. In vitro chemoresistance andbiomarker profiles are unique for histologic subtypes ofepithelial ovarian cancer. GynecolOncol, 2004; 92: 160166.REFERENCES1.Hulka BS. Overview of biological markers. Biologicalmarkers in epidemiolo

uses of cancer biomarkers as surrogate markers for drug ... Emerging cancer biomarker types and the increasing interest in circulating tumour cells, as well as data on potential DNA, RNA, and protein biomarkers under study, includes Oncogenes, Germline inheritance, Mutations in drug targets, Epigenetic changes. ...