###### Abstract  
Scaffolds can provide a healthy environment for cell attachment, differentiation, proliferation, and migration in vitro and in vivo. Lysophosphatidic acid (LPA) is a naturally occurring bioactive phospholipid that is present in the serum mainly bound to albumin. The present study aims to investigate the biocompatibility of LPA. It also aims to determine the effect of different LPA species on the proliferation and migration of human bone marrow-derived mesenchymal stem cells (hBM-dMSCs) for LPA and human serum albumin (HSA) containing bone scaffold development. The HSA-LPA complex formation was assessed using Fourier-transform infrared (FTIR) spectroscopy. The effect of 18:1, 18:2, or 16:0 LPA alone, or in combination with 4% HSA, on cell viability and proliferation was determined by XTT. The cell migration was examined in a wound healing assay. The changes in the FTIR spectra of LPA-HSA compositions, compared with HSA alone, indicate the complex formation between the components. Our study showed that 18:1, 18:2, and 16:0 LPA species had no cytotoxic effects up to 10 uM concentration. The different LPA species increased the proliferation of hBM-dMSCs in a dose-dependent manner when administered in the presence of HSA, without an effect on the migration of this cell type. These findings make the in vivo application of LPA-HSA complex promising for bone regeneration. Lysophosphatidic acid; albumin; mesenchymal stem cells; scaffold; FTIR; viability; migration +
Footnote †: journal: Medical Zrt., 1123 Budapest, Hungary
Our approach within regenerative medicine aims to replace and repair lost or damaged tissues by stimulating the natural regeneration process [3]. Mesenchymal stem cells are multi-lineage cells, capable of self-renewal and differentiation into a variety of cell types [4], which play key roles in tissue healing and regenerative medicine. Bone-marrow-derived mesenchymal stem cells are the most frequently used stem cells in cell therapy and tissue engineering [5]. Allogeneic bone substitutes, such as fresh-frozen, freeze-dried, or demineralized bone, are commonly used in bone replacement interventions [6]. According to previous studies, freeze-dried human serum albumin is able to improve the adherence and proliferation of mesenchymal stem cells on bone allografts [7], and the serum albumin coating of the bone matrix showed stronger bone formation in vivo [8,9]. Lysophosphatidic acid (LPA) is a naturally occurring bioactive glycerophospholipid that is present in the systemic circulation in high nanomolar to low micromolar concentrations [10]. All LPA molecules consist of a glycerol backbone connected to a phosphate head group and ester-linked to an acyl chain [11]. The acyl chain length and degree of saturation of the formed LPA species are different. There are 16:0 \(>\) 18:0 \(>\) 20:4 \(>\) 18:1 \(>\) 18:2 LPAs that have been identified in resting and activated platelets. By contrast, in plasma, the rank order is 18:2 \(>\) 18:1 \(\geq\) 18:0 \(>\) 16:0 \(>\) 20:4, whereas in serum the order is 20:4 \(>\) 18:2 \(>\) 16:0 \(\geq\) 18:1 \(>\) 18:0 [12,13, 14]. Extracellular LPA acts through at least six specific, G protein-coupled receptors (GPCRs), LPAR1-6, and regulates various cellular signaling pathways. LPA has a crucial role in numerous biological responses, including cell adhesion, migration, proliferation [15], differentiation [16], vascular development, wound healing, apoptosis regulation, and immunity [17,18]. In common with long-chain fatty acids, LPA binds with a high affinity to serum albumin, the main extracellular LPA binding protein, at a molar ratio of approximately 3:1 [19,20]. LPA binds to the primary high-affinity fatty acid-binding sites on albumin [19]. Albumin is necessary for the biological activity of LPA, and albumin concentration is critical for the activation of LPA receptors in a receptor-type-specific manner [21].