Autofluorescence spectroscopy and multispectral autofluorescence microscopy for characterization of lupus nephritis...

The study investigates lupus nephritis in label-free mode using simultaneous autofluorescence spectroscopy and multispectral autofluorescence microscopy. Lupus nephritis (LN) is an autoimmune disease with proteinuria as the most typical symptom and indicator of renal damage and disease activity. This study includes the development and application of a micro-spectro-endoscope on the renal tissues of murine LN, covering three stages, advanced end-stage (proteinuric), early onset disease (antibody-positive), and healthy with no disease manifestations (young). The micro-spectro-endoscope exploits the autofluorescence (AF) at two excitation wavelengths, 365 and 405 nm, to probe endogenous autofluorescence activity. Multispectral autofluorescence microscopy performed using a 365 nm light emitting diode (LED) collected information from three spectral bands, 440-490 nm, 500-560 nm, and 600-650 nm, respectively. Three regions, medulla, medulla-cortex, and cortex, were investigated using autofluorescence microscopy, and the maximum autofluorescence was recorded in the cortex region. Acquiring simultaneous AF spectroscopy and AF microscopy provided molecular and morphological information from the same tissue location. Simultaneous autofluorescence microscopy and spectra of kidney tissues from proteinuric, antibody-positive, and young mice were recorded with a micro-spectro-endoscope by exciting at 405 nm LED. A significant change in the peak of the autofluorescence spectrum for proteinuric, antibody-positive, and young mice was observed, with peaks around ~ 480 nm, ~ 493 nm, and ~ 532 nm, respectively. The alternation in the autofluorescence peak is likely due to the variations of nicotinamide adenine dinucleotide and flavin adenine nucleotide fluorophores during the progression of the disease. An additional peak around ~ 616 nm is also observed in antibody-positive tissue, showing the presence of lipofuscin, which is absent in young and proteinuric tissues, indicating the possibility of increasing lysosomal activity and oxidative stress.