The proposed takeover by Highmark of West Penn Allegheny Health System got the U.S. Department of Justice's approval Tuesday, clearing one of the major obstacles to the proposed insurer/provider merger. The Justice Department's Antitrust Division gave its thumbs up a week before a hearing at which the state Department of Insurance will hear testimony on the merger. The insurance department's review is considered the highest hurdle to Highmark's takeover of West Penn, which will include a $475 million infusion.