The debt-burdened parent of the largest wealth management firm in the region is shaking up the Santa Barbara company’s leadership ranks.

Michael Mayfield, CEO and co-chief investment officer of Santa Barbara Asset Management, is retiring from the firm effective March 1, after 18 years with the company. James Boothe, a portfolio manager at the Santa Barbara office, has been promoted to chief investment officer.

Nuveen Investments, the Chicago-based firm that purchased Santa Barbara Asset Management for $50 million in cash in 2005, confirmed the leadership changes.

Executives at SBAM did not return requests for comment for this story.

In a possible sign that the firm is cutting staff or downsizing, Santa Barbara Asset Management’s 8,474-square-foot offices on the fifth floor of the El Paseo building at 820 State St. have also been put back on the leasing market, according to Hayes Commercial Group broker Greg Bartholomew, who is listing the space. SBAM moved into the prominent downtown location, which features ocean and mountain views, in early 2011 from a smaller space on Carrillo Street.

Nuveen spokeswoman Kristyna Muñoz declined to comment about the possible relocation of Santa Barbara Asset Management. She also declined  to offer further details on the changes at the firm.

Santa Barbara Asset Management has $5.3 billion in assets under management and handles about 3,000 accounts, making it by far the largest wealth management firm based in the Tri-Counties.

Muñoz did confirm that some of SBAM’s business are being moved to another affiliate, Nuveen Asset Management, which big-name portfolio manager Bob Doll stepped up to lead last year. Doll left Wall Street giant BlackRock to join Nuveen last November. She declined to say how many employees are at the Santa Barbara firm or if any of them would be affected by the “transition.”

When Nuveen purchased Santa Barbara Asset Management in 2005, the South Coast firm had $2.8 million in assets under management, according to a statement from the firm at the time. Nuveen noted then that SBAM had already doubled its assets under management in the two years before the buyout.

SBAM, which operates as an independent subsidiary of Nuveen, has gone on to almost double that amount again.

Mayfield joined SBAM in 1995 from NatWest Markets in New York. He was a recipient of a prominent South Coast Business & Technology Award in 2011, which recognized him as Executive of the Year for his role in building the wealth management firm into a regional heavyweight.

Boothe, SBAM’s new chief investment officer, joined the firm in 2002 from USAA Investment Management, according to the Santa Barbara firm’s website. Before that, he was a portfolio manager and analyst at San Juan Asset Management. He holds a bachelor’s degree in business administration from Kent State University and an MBA in finance from Loyola Marymount University.

Mounting debt at Nuveen

Two years after it purchased Santa Barbara Asset Management, Nuveen was in turn purchased by Chicago private equity firm Madison Dearborn Partners in a leveraged buyout deal. In such a  transaction, a company is taken over using borrowed funds, typically with the target company’s assets serving as security for the debt taken out by the buyer.

In Nuveen’s case, the $5.4 billion buyout by Madison Dearborn resulted in it being saddled with more than $3.1 billion in high-interest debt.

Nuveen last month announced the terms of a $2.6 billion term loan, marking the third time in three years that the company has sought to refinance its billions of dollars of debt. The firm had $4.5 billion in total liabilities as of Sept. 30, 2012, according to its regulatory filings with the U.S. Securities & Exchange Commission.

Its liability levels have also raised the alarm among some major investors. Nuveen is “trapped in a debt service cycle it cannot escape,” the International Brotherhood of Teamsters, whose pension and benefit funds has more than $100 billion in assets, said in a statement last month.

“We are concerned that Nuveen’s strategy to annually ask lenders for relief on massive loans may signal potential for trouble ahead,” Ken Hall, general secretary-treasurer of the Teamsters union, said in a statement. “Nuveen’s debt burden could ultimately result in higher fees for clients, a sale of assets or possibly liquidation.”

In 2011, Nuveen was fined $3 million by the Financial Industry Regulatory Authority for misleading customers on the safety of auction-rate securities before the market for those investments collapsed in February 2008.