COL4A1 and Myocardial fibrosis: The expression of different genes related to myocardial fibrosis was assessed in the rat hearts, revealing that at the 3rd week TiO2-NPs instillation the expression of different collagen isoform genes (namely COL1A2, COL3A1, COL4A1) were definitively upregulated in treated animals compared to CTRL (Fig. 9b-d).