# PC12 and THP-1 Cell Lines as Neuronal and Microglia Model in Neurobiological Research
## 3 Results and Discussion
### THP-1 Cells and Lipopolysaccharide  
MTT assay performed on undifferentiated THP-1 cells showed no decrease of metabolic activity after incubation with bacterial lipopolysaccharide in any of the tested concentrations, while in cells differentiated with PMA significant decrease was noted (Figure 9A). The differences depending on the differentiation were significant and ranged from 18.9% to 23.1%.  
In the DCF-DA assay, a significant increase in the ROS level was observed (by 7.1-18.4%), except for the concentration of 1 \(\upmu\)M LPS. The oxidant response was LPS dose-dependent (Figure 9B). The free radicals level was slightly higher in cells differentiated with PMA, but these were not statistically significant differences.  
In THP-1 cells differentiated to microglia, each applied concentration of LPS (1-100 \(\upmu\)M) caused a significant increase of DSBs (40.9-80.8%), while in undifferentiated cells, at 5-100 \(\upmu\)M LPS concentrations (22.4-61.6%) (Figures 8 and 9C). Significant differences depending on cell differentiation were observed at LPS concentrations of 1 and 5 \(\upmu\)M--29.2-29.9% more DNA damage in differentiated THP-1 cells.  
Figure 7: Effect of A\(\beta_{25\text{-}35}\) on undifferentiated and differentiated THP-1 cells: (**A**) metabolic activity (MTT assay); (**B**) level of reactive oxygen species (DCF-DA assay); (**C**) double-stranded DNA damage (FHA assay); Control—cell culture incubated without A\(\beta_{25\text{-}35}\); * \(p<0.05\)—significant difference compared to control; # \(p<0.05\)—significant difference between undifferentiated and differentiated THP-1 cells.  
Figure 8: Exemplary micrographs of nuclear halo in undifferentiated (**A–C**) and differentiated (**D–F**) THP-1 cells taken in the FHA assay: (**A**) control culture of undifferentiated cells; (**B**) undifferentiated cells incubated with 5 \(\upmu\)M \(\Delta\beta_{25,35}\); (**C**) undifferentiated cells incubated with 100 \(\upmu\)M LPS; (**D**) control culture of differentiated cells; (**E**) differentiated cells incubated with 5 \(\upmu\)M \(\Delta\beta_{25,35}\); (**F**) differentiated cells incubated with 100 \(\upmu\)M LPS.  
Figure 9: Effect of lipopolysaccharideaccharide (LPS) on undifferentiated and differentiated THP-1 cells: (**A**) metabolic activity (MTT assay); (**B**) level of reactive oxygen species (DCF-DA assay); (**C**) double-stranded DNA damage (FHA assay); Control—cell culture incubated without LPS; * \(p<0.05\)—significant difference compared to control; # \(p<0.05\)—significant difference between undifferentiated and differentiated THP-1 cells.  
Microglia serve as innate immunity agents in the immune-privileged brain by producing pro-inflammatory cytokines, removing microbes, their parts or cellular debris via phagocytosis. Both bacterial LPS and amyloid \(\beta\) interact with microglia through Toll-like receptors (TLRs), triggering the inflammatory response, stimulating upregulated production of reactive oxygen species and cytokines and making the phagocytosis of these harmful compounds ineffective, leading to cellular death [40; 41].