Calcium crystal deposition diseases: lessons from histochemistry

Biochemical and molecular aspects of spectral diagnosis in calcinosis cutis

Calcinosis cutis (CC) is a type of calcinosis wherein insoluble compounds or salts deposited on the skin. Clinical diagnosis of CC is usually achieved through time consuming histopathological or immunohistochemical procedures, but it can only be empirically identified by experienced practitioners. The use of advanced vibrational spectroscopy has been recently shown to have great potential as a diagnostic technique for various diseased tissues because it analyses the chemical composition of diseased tissue rather than its anatomy and predicts disease progression. This review article includes a summary of the application of Fourier transform infrared (FT-IR) and Raman spectroscopic or microspectroscopic analysis for the rapid diagnosis and identification of the chemical composition of skin calcified deposits in patients with various CC symptoms. Both advanced techniques not only can detect the types of insoluble salts such as calcium phosphate, calcium carbonate, and monosodium urate, and β-carotene in the calcified deposits of human skin tissue but also can directly differentiate the carbonate substitution in the apatite structure of the skin calcified deposits. In particular, the combination of both vibrational techniques may provide complementary information to simultaneously assess the intact components of the calcified deposits. In the future, both FT-IR and Raman vibrational microspectroscopic techniques will become available tools to support the standard test techniques currently used in some clinical diagnoses. Molecular spectroscopy technique is rapidly changing disease diagnosis and management.

Calcification of senile cataractous lens determined by Fourier transform infrared (FTIR) and Raman microspectroscopies

A calcified plaque on the surface of a senile cataractous lens (CL) isolated from a 79-year-old male patient was identified and its chemical composition quantified using Fourier transform infrared (FTIR) and confocal Raman microspectroscopies. The noncalcified area of the same CL and hydroxyapatite (HA) were selected as a control. Several unique absorption bands, at 960, 1034 and 1090 cm(-1) assigned to the nu(1) and nu(3) stretching modes of phosphate and at 875 cm(-1) attributed to carbonate, were clearly displayed in the infrared (IR) spectra of calcified plaque and HA. A peak at 961 cm(-1) due to the nu(1) stretching mode of phosphate was also evidenced in the Raman spectra of calcified plaque and HA. The calcified plaque formed within the lens protein was found to mainly consist of a mature HA, in which type-A carbonate apatites (11.4%), type-B carbonate apatites (55.6%) and liable surface carbonate ions (33.0%) were presented. A higher content of the liable carbonate implies that the calcification or mineralization in this calcified lens was incomplete and still in progress. Moreover, calcification seems not to influence the secondary structure of lens protein because both IR and Raman spectra for the lens protein in the noncalcified area and calcified plaque were similar. The result suggests that both microscopic FTIR and Raman spectroscopies were easy to perform and capable of determination of the chemical composition of a calcified CL.