Preservation of 5300 year old red blood cells in the Iceman

Abstract

Changes in elasticity and structures of red blood cells (RBCs) are important indicators of disease, and this makes them interesting for medical studies. In forensics, blood analyses represent a crucial part of crime scene investigations. For these reasons, the recovery and analysis of blood cells from ancient tissues is of major interest. In this study, we show that RBCs were preserved in Iceman tissue samples for more than 5000 years. The morphological and molecular composition of the blood corpuscle is verified by atomic force microscope and Raman spectroscopy measurements. The cell size and shape approximated those of healthy, dried, recent RBCs. Raman spectra of the ancient corpuscle revealed bands that are characteristic of haemoglobin. Additional vibrational modes typical for other proteinaceous fragments, possibly fibrin, suggested the formation of a blood clot. The band intensities, however, were approximately an order of magnitude weaker than those of recent RBCs. This fact points to a decrease in the RBC-specific metalloprotein haemoglobin and, thus, to a degradation of the cells. Together, the results show the preservation of RBCs in the 5000 year old mummy tissue and give the first insights into their degradation.

Figure 1.

AFM images of RBCs. (a,b) Single RBCs from recent human tissue. (c) An assembly of RBCs. (d,e) Single corpuscles found in Iceman sample A and sample B are shown. An assembly of several randomly distributed corpuscles, similar to those found within the recent sample (c), are displayed in image (f). The imaged corpuscles (d–f) feature the characteristic discoid and concave surface of RBCs.

Figure 2.

Raman spectra of air-dried whole blood (a), a single red blood cell (b), and the corpuscle found in the Iceman tissue sample A (c). All spectra show peaks at 1586, 1395, 1308 and 747 cm⁻¹, which are characteristic of porphyrin. Apart from some bands, the spectra show considerable similarities.

Figure 3.

Raman spectra of the corpuscle in Iceman sample A (a), a fibrin meshwork (b), and the corpuscles found in the Iceman tissue sample B (c). The spectrum obtained from sample B strongly differs from that of sample A. It has features with considerable similarities to the spectrum of fibrin.

Figure 4.

Raman scan and AFM image (30 × 30 µm) of the agglomerated corpuscle in Iceman sample B. The scan in (a) represents the intensity distribution of the Rayleigh scattered light. For comparison the corresponding AFM topography image is shown. (b–g) The datasets of the Raman scan filtered for porphyrin or protein-specific Raman bands around 1656, 1586, 1449, 1395, 1308 and 1125 cm⁻¹ wavenumbers. Red indicates regions with strong Raman intensity, and blue indicates low Raman intensities. The examined molecule vibrations largely occurred at the positions of the ancient particles.

Figure 5.

The distribution of Young's moduli from the corpuscle of Iceman sample B and contemporary single RBCs. Young's modulus for the mummy particles (grey) is significantly lower than Young's modulus for the recent RBCs (black).