Comparison of the human's and camel's red blood cell deformability by optical tweezers and Raman spectroscopy

Abstract

Red blood cells of vertebrates have undergone evolutionary changes over time, leading to the diversification of morphological and mechanical properties of red blood cells (RBCs). Among the vertebrates, camelids have the most different RBC characteristics. As a result of adaptation to the desert environment, camelid RBCs can expand twice as much of their total volume in the case of rapid hydration yet are almost undeformable under mechanical stress. In this work, the mechanical and chemical differences in the RBC properties of the human and camelid species were examined using optical tweezers and Raman spectroscopy. We measured the deformability of camel and human RBCs at the single-cell level using optical tweezers. We found that the deformability index (DI) of the camel and the human RBCs were 0.024 ± 0.019 and 0.215 ± 0.061, respectively. To investigate the chemical properties of these cells, we measured the Raman spectra of the whole blood samples. The result of our study indicated that some of the Raman peaks observed on the camel's blood spectrum were absent in the human blood's spectrum, which further points to the difference in chemical contents of these two species' RBCs.

Keywords: Cell mechanics; Optical tweezers; Raman spectroscopy; Red blood cells.

Fig. 1

(a) The single-cell stretching process by the optical tweezers, (b) Demonstration of whole blood sample measurement on the Raman spectroscopy setup. The red beam shows the laser light whereas, the orange beam indicates the Raman signal from the sample. Abbreviations: DM (Dichroic Mirror), REF (Raman Edge Filter). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

(a1–4) Top view of stretching and relaxation processes of a human (top row) and, (b1–4) a camel (bottom row) RBCs. Stretching speed was set to 1 $\mathrm{\mu }\mathrm{m/s}$ and the experiment duration was 10 s. The calculated Feret diameters were labeled on the RBCs in each frame. (c) The unmarked cells were suspended camel RBCs in the solution, and the marked cell was the camel RBC in the optical trap.

Fig. 3

Normal kernel distribution of initial ($L_i$) and maximum ($L_{max}$) stretched RBC cell sizes with the corresponding bandwidths were: (a) for the camel group 0.2964 and 0.3130 and, (b) for the human group 0.2304 and 0.2496 c) The violin graph of the DI with the mean values and the standard deviations for camel and human groups were calculated as 0.024±0.019 and 0.215$\pm$0.061, respectively. The result of the t-test was $p<0.001$.

Fig. 4

The Raman spectra of the two groups indicated dramatic differences in intensities at three wavenumbers: 540 cm⁻¹, 714 cm⁻¹ and 1080 cm⁻¹. The bands, 838 cm⁻¹ and 945 cm⁻¹, were found as absent on the human spectrum, while these bands were present on the camel spectrum.

Fig. 5

The bar graph shows the selected peak Raman intensities after the band component analysis. These peak intensities were correlated to the amount of lipid and protein compositions; 714 cm⁻¹ and 1080 cm⁻¹ phospholipids, 1220 cm⁻¹ amide III, 1305 cm⁻¹ and 1443 cm⁻¹ lipids, and 1650 cm⁻¹ amide I.