Non-contact micro-cantilevers detect photothermally induced vibrations that can segregate different categories of exfoliative cervical cytology

Vibrational spectroscopic mapping and imaging of tissues and cells

Vibrational spectroscopic mapping (point-by-point measurement) and imaging of biological samples (cells and tissues) covering Fourier-transform infrared (FTIR) and Raman spectroscopies has opened up many exciting new avenues to explore biochemical architecture and processes within healthy and diseased cells and tissues, including medical diagnostics and drug design.

FTIR Microspectroscopy Coupled with Two-Class Discrimination Segregates Markers Responsible for Inter- and Intra-Category Variance in Exfoliative Cervical Cytology

Infrared (IR) absorbance of cellular biomolecules generates a vibrational spectrum, which can be exploited as a “biochemical fingerprint” of a particular cell type. Biomolecules absorb in the mid-IR (2–20 μm) and Fourier-transform infrared (FTIR) microspectroscopy applied to discriminate different cell types (exfoliative cervical cytology collected into buffered fixative solution) was evaluated. This consisted of cervical cytology free of atypia (i.e. normal; n = 60), specimens categorised as containing low-grade changes (i.e. CIN1 or LSIL; n = 60) and a further cohort designated as high-grade (CIN2/3 or HSIL; n = 60). IR spectral analysis was coupled with principal component analysis (PCA), with or without subsequent linear discriminant analysis (LDA), to determine if normal versus low-grade versus high-grade exfoliative cytology could be segregated. With increasing severity of atypia, decreases in absorbance intensity were observable throughout the 1,500 cm⁻¹ to 1,100 cm⁻¹ spectral region; this included proteins (1,460 cm⁻¹), glycoproteins (1,380 cm⁻¹), amide III (1,260 cm⁻¹), asymmetric (ν_as) PO₂⁻ (1,225 cm⁻¹) and carbohydrates (1,155 cm⁻¹). In contrast, symmetric (ν_s) PO₂⁻ (1,080 cm⁻¹) appeared to have an elevated intensity in high-grade cytology. Inter-category variance was associated with protein and DNA conformational changes whereas glycogen status strongly influenced intra-category. Multivariate data reduction of IR spectra using PCA with LDA maximises inter-category variance whilst reducing the influence of intra-class variation towards an objective approach to class cervical cytology based on a biochemical profile.

Complex mixtures that may contain mutagenic and/or genotoxic components: a need to assess in vivo target-site effect(s) associated with in vitro-positive(s)

A battery of short-term in vitro assays and/or in vivo protocols to evaluate single-agent mutagenicity and/or genotoxicity is available. However, a protocol to assess the effect(s) of complex mixtures in vivo following a positive test finding in vitro remains difficult. Complex interactions may occur in vivo because component pharmacokinetics increases the unpredictability of pharmacodynamic outcomes. The question arises as to whether in vitro mutagenic component(s) of a complex mixture, probably unidentified, reach target organ(s) in vivo at a sufficient concentration. To address the issue of an in vitro positive, standard in vivo chromosome damage assays to test both mixtures and fractions could be conducted but, to assess site-of-contact effects, the alkaline single cell-gel electrophoresis ("comet") assay or DNA reactivity (e.g., (32)P-postlabelling of DNA adducts) might be employed. A newer approach may be the derivation of a "biochemical-cell fingerprint" of potential target sites using infrared microspectroscopy. There is interest in platforms such as gene expression, proteomics, epigenomics or metabolomics as biomarkers of signature genotoxic or non-genotoxic mechanisms. One still needs to address whether a mutagenic and/or genotoxic component reaches a target organ. An approach to track levels of target-organ exposure may be to radio-label components with a short-lived positron-emitting radionuclide. The parent compound retains its physicochemical properties whilst allowing non-invasive in vivo tissue-specific imaging. However, determining target-organ concentration(s) and effect(s) in vivo remains a difficult challenge.