Biomarkers in health and diseases

Biomarkers are measurable characteristics in the body that indicate health status, disease presence, or response to treatment. These indicators can be various proteins, lipids, chemicals, molecules, genes, pathogen-derived fingerprints, or even the cellular components of body fluids. The most common source of these measurable markers is whole blood or its components, other bodily fluids, including the excretions, or body tissues. These are used for determining the health of the individual or for disease diagnosis, predicting disease prognosis, and monitoring the effectiveness of the given treatment. Biomarkers can be used to provide valuable insights into diseases where clinical signs and symptoms are not very specific, and laboratory investigations become crucial to arrive at a specific diagnosis. The spectrum of biomarkers is becoming wider with every passing year, and this is because of the thrust of research in the field of biomarker discovery, especially for diseases such as cancer, neurological conditions, cardiovascular diseases, immunology, and infectious disease diagnosis.

The biomarkers market size was exhibited at USD 91.65 billion in 2024 and is projected to hit around USD 321.45 billion by 2034.^[1] Cancer remains the dominant disease segment, accounting for the largest (40%) biomarker use in diagnostics, therapeutics, and clinical trials. Biomarkers such as human epidermal growth factor receptor 2, cancer antigen-125, programmed death-ligand 1, and breast cancer gene mutations have revolutionized cancer detection, subtype classification, and, most importantly, personalized treatment. Liquid biopsies using circulating tumor DNA are further expanding cancer biomarker applications, allowing for non-invasive monitoring and recurrence tracking. With the rising number of cancer patients globally and precision oncology becoming standard practice, this segment continues to thrive and has a great future.

The market for cardiovascular disease biomarkers is closely second (25%) to the cancer segment. It is followed by neurological disorders (15%). The neurological disorder area is a rapidly emerging opportunity that lies in the expansion of biomarker applications in neurological diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. Unfortunately, immunological disorders and infectious diseases combinedly share only 20% market share, but hopefully pave the way for future expansion.

In this issue of the Journal of Laboratory Physicians, Mathew et al.,^[2] have shown that the mycolic acid (MA), a cell wall component of all mycobacterial species, can be detected in the body fluids of the patient by Raman spectroscopy.

MAs are a hallmark feature of the cell wall in Mycobacterium species, including the causative agent of tuberculosis, Mycobacterium tuberculosis. While their general structure as long-chain a-alkyl b-hydroxy fatty acids is conserved across the genus, variations in chain length, the degree of unsaturation (double bonds or cyclopropane rings), and the presence of functional groups such as methoxy and keto groups account for differences observed between species and even within strains of the same species.^[3]

Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is a mycobacterial species used primarily as a vaccine against tuberculosis, but recently it has also been used as a model for mycobacterial infection, for enhancing immunogenicity, and for host-pathogen interaction studies. Its immunogenic effect has been exploited by scientists to use it as immunotherapy for the treatment of non-muscle invasive bladder cancer and in skin diseases such as common warts and melanoma. The identification of BCG and its therapeutic dose monitoring is currently dependent on microscopy, culture, or nucleic acid amplification methods such as polymerase chain reaction. As these methods are cumbersome or require human skill, there exists a need for methods for rapid detection that are not operator dependent, easy to perform, and cost-effective. As such, Mycobacterial infections are chronic in nature and pose a diagnostic challenge to the treating physician.^[4] Technologies such as Raman spectroscopy, which is an optical and non-contact technology to identify large biological molecules such as lipids, peptides, and proteins in biological fluids in a non-invasive manner, have the potential to detect several of these biomarkers.

Here, in a preliminary study, Mathew et al.,^[2] have studied freeze-dried BCG power routinely used for immunotherapy and marketed by Ms Cipla India (Onco BCG), reconstituted and the suspension was utilized in the Raman spectroscopy instrument setup (IndiRAM-CTR 300^®, Technos Instruments) which consisted of a 532 nm laser with a spectral range of 97–4097 cm⁻¹. A ×20 magnification lens was used to focus the laser onto the sample and to collect the scattered Raman signal. The authors have claimed that they found a characteristic peak in the 2849–2882 cm⁻¹ region. These peaks are considered to correspond to carbon–hydrogen stretching vibrations in long-chain MAs. After obtaining the results, the authors conclude that detection of MA by Raman spectroscopy is a promising technology that can be applied to biological specimens such as slit-skin smears, sputum, synovial fluid, fine-needle aspiration specimens, ascitic fluid, and other biofluids for rapid bedside diagnostics.

Although these conclusions and optimism of authors are based on the experiments they did only on the BCG strain, it would be worthwhile to expand this study to a larger number of clinical samples. Earlier, Raman spectroscopic studies have shown finer differences in the arrangement of two closely related mycobacterial strains, such as Mycobacterium indicus pranii and Mycobacterium intracellulare.^[5] Such differences are found mainly in the functional groups, such as the methoxy and keto groups of MA, as mentioned above.^[3] Therefore, care should be taken to include a larger sample size and a representative number of various species and even lineages of Mycobacterium to validate these claims that Ram spectroscopy can be used for the diagnosis of human tuberculosis.