Raman spectroscopy of the human nail: A potential tool for evaluating bone health?

Abstract

Dual X-ray absorptiometry (DEXA) is the current gold standard for the diagnosis of osteoporosis. However, patients can suffer osteoporotic fractures despite normal bone mineral density, partly because of unmeasured influences of both the protein and mineral phases of bone that are affected in osteoporosis. There is currently no clinically applicable method of evaluating the health of the protein phase. The proteins in human nail (keratin) and bone (collagen) require sulphation and disulphide bond (S-S) formation for structural integrity and disorders of either sulphur metabolism or cystathione beta-synthase can lead to structural abnormalities in these tissues. Raman protein spectra provide a method of non-invasive measurement of the degree of sulphation of structurally related proteins that may be indicative of bone health. Raman spectroscopy was used to evaluate the disulphide (S-S) content of fingernails. The nail samples came from from 169 women (84 pre- and 85 post-menopausal), of which 39 had a history of osteoporotic fracture. BMD was measured by DXA at the spine. Analyses included parametric and non-parametric tests, dependent on the distribution of the test variable. Mean disulphide content of the nail reduced with age and was slightly higher in pre-, compared to post-menopausal women (P = 0.187). Significantly lower disulphide content was observed in nails obtained from subjects with a history of fracture (P = 0.025). When either disulphide content or BMD was used as a predictor, the odds ratio of these two measures were found to be comparable predictors for fracture status. This suggests that measurements of change in the protein phase of structural proteins such as keratin in the human nail may be correlated with clinically relevant changes in bone proteins that are important in fracture risk.

Raman spectroscopy of fingernails: A novel tool for evaluation of bone quality?

“…In this study, the BQT performed comparably with DXA (Lumbar BMD, p = 0.009) which is the current gold standard for diagnosis of osteoporosis. This is in agreement with a previous study which suggests that BQT and BMD are equivalent predictors of fracture status (BQT odds ratio 0.188 vs. BMD 0.282, p < 0.0005) [26]. DXA evaluates the mineral phase of bone.…”

“…Two determinations were performed upon each of the two nails. In previous work the intensity of S-S bonding in the sample (Bone Quality Test; BQT) was evaluated manually [20,26]. However, manual determination of peak intensity may be influenced by the subjective assessment of the peak base, especially for spectra with varying background shapes.…”

“…Preliminary work by the authors has evaluated the use of Raman spectroscopy to investigate the link between fingernail protein structure (keratin) and bone protein structure (collagen) [20,24,26]. Both proteins require cysteine incorporation and sulphation for structural integrity.…”

“…Significantly lower disulphide content of fingernails have been observed in subjects with a history of low-impact fracture, using the Raman spectroscopy based Bone Quality Test (BQT) [20,26]. Therefore, the aim of this study is to further investigate the validity of Raman spectroscopy as a tool in the assessment of bone health and to compare its efficacy with the other techniques currently available in clinical practice.…”

Bone Quality Test (BQT) scores of fingernails in postmenopausal patients treated with adjuvant letrozole or tamoxifen for early breast cancer

“…Some preliminary studies have shown significantly lower disulphide content in nails obtained from patients with a history of fracture (3) and in patients with osteoporosis (4). A weak association was observed between Raman measurement of disulphide content and bone mineral density as measured by DXA (2).…”