One potential issue I see with that is if the content contains Shortcodes.
You can strip Shortcodes before passing it to wp_trim_words if you want them removed, or alternately, if you want to maintain them you can apply the Shortcodes beforehand.
You may also want to check that $news_item["post_excerpt"] is not empty, in case a custom excerpt has been entered in place of your auto-trimmed version.