Effect of Pb exposure on the cells and matrix of the intervertebral disc of rats

Abstract

Degenerative spine diseases are common throughout the world. There are many factors that lead to these diseases. One of these exogenous factors may be Pb exposure. Most of the fundamental investigations about the negative effects of the Pb exposure have investigated the impact of high doses of Pb, while Pb exposure in low concentrations has been insufficiently studied. The nutrition of the intervertebral disc is provided by the vessels that grow into the vertebral bodies and the paravertebral tissue. This suggests the possibility that Pb penetrates from the bone to the intervertebral disc together with nutrients. This article reports an experimental study which was performed in rats aged 1.5 months (n = 40). Rats in the experimental group received lead acetate solution (230 mg of Pb per1 literof distilled water) as drinking water and the animals in the control group received distilled water for 10 weeks. In the isolated intervertebral discs, the content of Pb was determined by X-ray fluorescence spectrometry. The effect of lead on the structural organization of the intervertebral disc was investigated by light microscopy. The ultrastructural features of cells and the matrix intervertebral disc were studied by transmission electron microscopy. In the young animals after Pb exposure, a significant increase was found in the content of Pb in the intervertebral disc tissue, of 4.6 times compared to the control group. The histological analysis showed degenerative changes in the annulus fibrosus (AF) of the intervertebral disc. In the outer region cracks and defibration of the lamellae were observed. Large isogenic groups were detected in the inner region of the intervertebral disc. A decrease in the height by 12.2% in the outer parts and by 10% in the central part of the intervertebral disc was recorded. Also a reduction in the width of the lamellae by 8% was shown. Cell density of the annulus fibrous decreased by 12% and in the gelatinous nucleus pulposus (NP) by 24.2%. Electron microscopic analysis of the inner region of the AF of the intervertebral disc showed chondrocytes with electron-dense mitochondria, vacuolization of the cytoplasm, fragmented nuclei and destructive cavities. The matrix of the lamellae of the AF had a diverse electron density, so areas with high electron density of various sizes were observed. Collagen fibrils of the AF had blurred outlines, sometimes the transverse striation disappeared or it was irregular, which can indicate the matrix mineralization and possibly the accumulation of Pb in these areas. In the NP, the most notochordal cells revealed the formation of myelin figures. The effect of Pb at low concentration results in its accumulation in the tissues of the intervertebral disc of rats and causes degenerative changes in the intervertebral disc structure, leading to the reduction in the height of the intervertebral disc, decrease in the width of the lamellae and in cell density, thereby violating both the structures of matrix and cells. Future investigations of the collagen content of intervertebral disc after Pb exposure are needed.