Direct Detection of 8-Oxo-Deoxyguanosine Using UV Resonance Raman Spectroscopy

Toward a SERS Diagnostic Tool for Discrimination between Cancerous and Normal Bladder Tissues via Analysis of the Extracellular Fluid

Vibrational spectroscopy provides the possibility for sensitive and precise detection of chemical changes in biomolecules due to development of cancers. In this work, label-free near-infrared surface enhanced Raman spectroscopy (SERS) was applied for the differentiation between cancerous and normal human bladder tissues via analysis of the extracellular fluid of the tissue. Specific cancer-related SERS marker bands were identified by using a 1064 nm excitation wavelength. The prominent spectral marker band was found to be located near 1052 cm^-1 and was assigned to the C-C, C-O, and C-N stretching vibrations of lactic acid and/or cysteine molecules. The correct identification of 80% of samples is achieved with even limited data set and could be further improved. The further development of such a detection method could be implemented in clinical practice for the aid of surgeons in determining of boundaries of malignant tumors during the surgery.

Cationic Porphyrin-Mediated G-Quadruplex DNA Oxidative Damage: Regulated by the Initial Interplay between DNA and TMPyP4

G-quadruplex (G4) ligand-induced DNA damage has been involved in many physiological functions of cells. Herein, cationic porphyrin (TMPyP4)-mediated DNA oxidation damage was investigated aiming at mitochondrial G4 DNA (mt9438) and its structural analogue of the thrombin-binding aptamer (TBA). TMPyP4 is found to stabilize TBA G4 but destabilize mt9438. For two resulting DNA-TMPyP4 assemblies, the distinct light-induced singlet oxygen (¹O₂) generation and the subsequent DNA damage were found. For mt9438-TMPyP4, a slower ¹O₂-induced DNA damage takes place and results in the formation of DNA aggregation. In contrast, ¹O₂ tends to promote DNA unfolding in a relatively faster rate for TBA-TMPyP4. Despite of such distinct DNA damage behavior, UV resonance Raman spectra reveal that for both mt9438-TMPyP4 and TBA-TMPyP4 the DNA damage commonly stems from the guanine-specific oxidation. Our results clearly indicate that the ligand-mediated DNA damage is strongly dependent on the initial interplay between DNA and the ligand.

Initial Excited-State Structural Dynamics of dT and dA Oligonucleotide Homopentamers Using Resonance Raman Spectroscopy

Photochemical damage of DNA is initiated by absorption of ultraviolet light, and the photoproducts are formed as a result of excited-state structural and electronic dynamics. We have used UV resonance Raman spectroscopy to measure the initial excited-state structural dynamics of homopentamers of adenosine monophosphate (3'-dApdApdApdApdAp-5') and thymidine monophosphate (3'-dTpdTpdTpdTpdTp-5') and compare them to those of the monomeric nucleobases. The resonance Raman spectra of the homopentamers are similar to those of the corresponding monomers. Initial excited-state slopes, homogeneous and inhomogeneous broadening, and other excited-state parameters were extracted by self-consistent simulation of the resonance Raman excitation profiles and absorption spectra with a time-dependent formalism and are also similar to the initial excited-state slopes and broadening in the nucleotide monomers. The lack of differences between the initial excited-state structural dynamics of the nucleotides within the pentamer and the isolated nucleobases is consistent with a model in which the formation of photochemical products in oligonucleotides and DNA is dependent on the formation of the transition-state structure within these polymers, dictated by their large-scale dynamics. These results are discussed in light of the known photochemistry of DNA and the nucleobases.