Note: A previous version of this story failed to state that the offering was a shelf registration. MannKind Corp. could raise as much as $50 million through a secondary stock offering, according to a company filing Tuesday with the Securities and Exchange Commission. The Valencia biotech, in filing the shelf registration, said it would use the proceeds for operating expenses, including research and development of its primary pipeline product, an inhaled insulin drug called Afrezza. The company is conducting additional clinical trials of the drug after the Food and Drug Administration called for more research in 2011. The company plans to resubmit Afrezza for FDA approval later this year. MannKind said any future offerings under the registration would total no more than 25 mllion shares. The company went public in 2004 and has yet to report a profit. It has generated small amounts of revenue by licensing its intellectual property, but most income has come through secondary offerings and the backing of its founder, billionaire entrepreneur Alfred Mann. In December, Mann converted more than $107 million debt owed to him by MannKind into 40 million shares and warrants to purchase another 30 million. Shares lost 9 cents, or nearly 3 percent, to close at $3.31 in trading Tuesday on the Nasdaq.