Except as to the rights of a member or retirant or beneficiary, no trustee and no officer or employee of the board shall have any interest direct or indirect in the gains or profits of any investment made by the board; nor shall any of them directly or indirectly for himself or as an agent in any manner use the assets of the system except to make such current and necessary payments as are authorized by the board; nor shall any of them become an endorser or surety or become in any manner an obligor for moneys loaned by or borrowed from the board.
§ 70.750, RSMo