The Nikkei stock index ended Wednesday slightly higher in tepid trading ahead of the U.S. Federal Reserve’s policy decision due later in the day, while most early gains were erased amid continuing concerns over tensions in Ukraine, according to Nikkei Asian Review.The 225-issue Nikkei Stock Average ended up 51.25 points, or 0.36 percent, from Tuesday at 14,462.52. However, the broader Topix index of all First Section issues on the Tokyo Stock Exchange finished 1.61 points, or 0.14 percent, lower at 1,164.33.Gainers were led by pharmaceutical, food and retail issues while mining, nonferrous metal and utility shares skidded lower.