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Mass spectrometry (MS) is increasingly being adopted by clinical laboratories for an expanding range of healthcare applications, from forensic toxicology to precision medicine. Faster, more precise and often more cost-effective MS-based workflows and laboratory-developed tests are enabling clinical researchers to obtain results with improved confidence using smaller sample volumes. Yet some healthcare testing labs are late to adopt this technology due to concerns over upfront equipment cost and the time and resources required to develop and validate protocols. To address these challenges, MS systems are becoming more intuitive, allowing operation by nonspecialists, and emerging technologies are set to eliminate sample preparation steps.
Benefits in precision, throughput and affordability
Early clinical MS applications were, for the most part, limited to drugs-of-abuse testing using gas chromatography/mass spectrometry (GC/MS). The use of MS in the clinical laboratory really took off with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Its adoption over the last 15 years has been driven by the need for greater immunoassay accuracy, faster results and a desire for cost reduction.
The high specificity and sensitivity of LC-MS/MS overcomes many of the limitations associated with traditional immunoassays, such as nonspecific antibody binding and cross-reactivity,1 giving clinical scientists increased confidence in results. Immunoassay-based analyses of thyroid cancer patients, for example, are often unable to differentiate disease progression biomarkers such as thyroglobin and autoantibodies produced in the body, resulting in false readings.2
LC-MS/MS also allows clinical research laboratories to develop or replicate tests for disease biomarkers more quickly than is possible with traditional immunoassays. For instance, many immunosuppressants have a narrow therapeutic index (a measure of the difference between therapeutic and toxic dose), necessitating post-treatment monitoring of drug distribution over extended periods. Therapeutic drug monitoring panels are capable of evaluating toxicokinetic response to dosing in addition to monitoring real-time biological response through antibody production. Advances in full-scan MS technology enable clinical research laboratories to screen for multiple analytes simultaneously, which is beneficial for monitoring individuals taking multiple therapies.
Affordability is another reason clinical laboratories are turning to LC-MS/MS. Conventional hospital diagnostic assays have largely been based on clinical chemistry and immunoassay techniques, which require analyte-specific reagents and antibodies. LC-MS/MS-based approaches are considered reagent-free, which means there is less waste and running costs are approximately one-fifth those of immunoassays.3 Combined with the expense associated with sending samples externally when specific immunoassays are unavailable in-house, the cost over equipment lifetime can be considerably less.
Trends in MS
LC/MS is the dominant technology for clinical research, ’omics and the discovery and targeted quantitation of protein-based and small-molecule biomarkers. Hybrid MS technology, such as quadrupole-Orbitrap systems (Thermo Fisher Scientific, Sunnyvale, Calif.), couple high-resolution ion-trap instruments with a front-end quadrupole component that allow analytes to be identified with high precision through analyte fragmentation in a more affordable benchtop design. These full-scan techniques enable clinical researchers to scan for highly mass-resolved structures more quickly. Such technology can be employed for “shotgun” proteomics, where proteins are digested to peptides and sequenced by their MS/MS spectra, and for metabolite screening.
Advances in clinical multi-’omics show promise to enable noninvasive liquid biopsies for early detection of diseases such as cancer in patients who otherwise present no symptoms. Researchers are leveraging highly sensitive LC-MS/MS for targeted analysis of protein biomarkers in donor samples, providing oncologists with information in minutes. Future approaches may allow greater patient stratification, leading to more targeted treatment, while potentially facilitating improved patient monitoring.
Other MS-based techniques, such as inductively coupled plasma/mass spectrometry (ICP/MS), have undergone intensive development in recent years. With detection limits for most elements about 100 times greater than those achieved by graphite furnace atomic analysis (GFAA) and its multielement capability, ICP/MS has become the standard technique for trace elemental analysis of donor samples. For heavy-metal forensic toxicology, for instance, ICP/MS not only offers more precise quantification, but also the ability to perform isotopic tracer, dilution and ratio measurements. Such isotopic fingerprinting can help identify the external metal source. Medical scientists are researching the application of this technique to understand an individual’s “personal” ability to absorb essential elements, as well as select therapeutics to enable more effective treatment programs in the future.
Advances in ionization techniques such as laser ablation (LA) are enabling clinical researchers to move beyond the ability to merely quantify the amount of metal in tissue and to employ proteomic approaches to elucidate metalloprotein structure and function. Metalloproteomic approaches are proving particularly useful in the study of neurodegenerative diseases, where abnormal accumulations of metals are found in the brain.4
The future of clinical MS
With the advent of increasingly sensitive technologies, the range of MS technologies and applications will continue to expand. Tissue imaging using MS techniques is a developing field that is set to enter the clinical mainstream. Metallomic tissue mapping using LA-ICP/MS is already helping researchers understand the effects of traumatic brain injury.5 Tissue mapping can be used to quantify neuroinflammation and disruption to the blood–brain barrier in specimens with variable elemental and isotopic composition. Such approaches may be used to provide clinical insights into the pathophysiological mechanisms of concussion.
Since improving sample-to-knowledge analysis time is critical for labs processing routine samples, continued progress toward simplified “pushbutton” MS processes is to be expected. While instruments can deliver results at exceptional speed, in some cases sample preparation steps are still tedious. Increased automation and seamless integration of sample preparation and analysis are helping to simplify processes and reduce times to results. Sample preparation techniques such as the Prosolia Velox 360 PaperSpray System (Thermo Fisher Scientific) allow liquid samples to be applied onto a porous paper matrix before being analyzed directly through electrospraying from the tip of the matrix into the instrument. These techniques eliminate steps most commonly associated with workflow down time and are being researched for drugs-of-abuse testing and other clinical utility areas. Additionally, the development of transportable or handheld mass spectrometers could open up a range of possibilities for point-of-care applications.
An additional challenge associated with high-throughput MS multi-’omics is the large amount of data produced. Recent advances in laboratory infrastructure are making data processing simpler and faster. LIMS are increasingly being used to manage entire workflows and integrate seamlessly with MS structure identification tools and cloud libraries to identify analytes based on fragmentation patterns. The ability to share information on biomarkers quickly between institutions will further draw MS into the clinical laboratory.
Conclusion
Researchers and clinicians are continuing to push the boundaries of MS, driven by advances in instrument precision and sensitivity and new techniques for integrated sample preparation, automation and data analysis.
References
- Soldin, S.J.; Soukhova, N. et al. The measurement of free thyroxine by isotope dilution mass spectrometry. Clin. Chim. Acta 2005; doi: 10.1016/j.cccn.2005.02.010.
- Tate, J. and Ward, G. Interferences in immunoassay, Clin. Biochem. Rev. 2004, 25(2), 105–20.
- www.nxtbook.com/nxtbooks/gen/clinical_ omics_vol3iss9/#/12
- Lothian, A.; Hare, D.J. et al. Metalloproteomics: principles, challenges, and applications to neurodegeneration. Frontiers in Aging Neuroscience 2013; doi: 10.3389/ fnagi.2013.00035.
- Hare, D.J.; George, J.L. et al. Three-dimensional elemental bio-imaging of Fe, Zn, Cu, Mn and P in a 6-hydroxydopamine lesioned mouse brain. Metallomics 2010; doi: 10.1039/C0MT00039F.
Lisa Thomas is senior director of marketing for the clinical and forensic markets in the Chromatography and Mass Spectrometry business ([email protected]), and Bradley Hart is market development director in the Life Sciences Mass Spectrometry business at Thermo Fisher Scientific, 490 Lakeside Dr., Sunnyvale, Calif. 94085, U.S.A.