Some gutted by the truth’s serious nature (8)
I believe the answer is:
severity
'serious nature' is the definition.
'severity' can be an answer for 'nature' (severity is a kind of nature). I am not sure about the 'serious' bit.
'some gutted by the truth's' is the wordplay.
'some gutted' suggests removing the centre (to gut something is to remove its insides).
'by' becomes 'side' ('side' can be a synonym of 'by').
'the truth' becomes 'verity' (verity is a kind of truth).
'side' with its centre taken out is 'se'.
'se'+'verity'='SEVERITY'
Can you help me to learn more?
(Other definitions for severity that I've seen before include "Sternness" , "Intensity; harshness" , "Harshness, asperity" .)