\[- 8a^{5} + 8a^{3} - 2a =\]
\[= - 2a\left( 4a^{4} - 4a^{2} + 1 \right) =\]
\[= - 2a\left( 2a^{2} - 1 \right)^{2} =\]
\[= - 2a\left( 2a^{2} - 1 \right)\left( 2a^{2} + 1 \right)\]