The Los Angeles Business Journal’s index of largest local public companies was down for the week, after investor optimism over better U.S. economic data was tempered by renewed concerns over Europe’s debt crisis.

The weighted LABJ Stock Index closed down 1.3 percent to 115.06 for the week ended Dec. 16. Decliners outpaced gainers 89 to 76, with eight companies unchanged.

Among the biggest decliners was Virco Manufacturing Corp., dropping 19.5 percent to $1.32. The Torrance maker of business and school furniture reported disappointing fiscal third quarter earnings.

Arrowhead Research Corp. fell more than 16 percent to $4.10. Shares have been volatile since the Pasadena nanomedicine company completed a 1-for-10 reverse stock split last month.

THQ Inc. lost 15 percent to 76 cents. The Agoura Hills video-game maker lowered its earnings outlook for the year based on worse-than-expected sales.

Among the largest gainers was Manhattan Bancorp, which gained 17 percent to close at $3.40 after falling 25 percent the previous week. Shares of the El Segundo bank holding company have been volatile since it announced a merger with Pasadena’s Professional Business Bank last month.

Cadiz Inc. gained nearly 17 percent to $10.53. The Los Angeles water resources company has raised $11 million in working capital through private placements and other investments over the last two weeks.