The clinics offer futuristic-sounding treatments for everything from eye problems to osteoarthritis.

Listed on a government website, they present the opportunity to participate in clinical trials to test the potential of one of the most promising tools in medicine — the body’s own stem cells. It’s an attractive pitch for many patients, even though some of the clinics charge $6,000 and up to participate.

Now, with a national debate raging over the future of one of the hottest frontiers in 21st-century medicine, a University of Minnesota bioethicist has taken center stage in questioning whether many of these services are legitimate.

“You have these businesses that don’t have meaningful clinical research going on,” the U’s Leigh Turner said in an interview. “There is a risk for fraud, in that people may be charged thousands of dollars to get an intervention that has no chance” of working.

Turner has emerged as a major critic of the clinics, some of which he says have flawed procedures that allow bias to distort the results of treatment studies. He also says allowing clinics to list studies can imply government approval, lending false legitimacy to marketing pitches.

“My concern is that you basically take clinicaltrials.gov and transform it into a marketing platform,” Turner said.

In the past, Turner has moved beyond academic criticism, reporting several clinics he considered questionable to regulators at the U.S. Food and Drug Administration.

One of them, Celltex Therapeutics Corp., received a warning letter from the FDA for its practices in 2012. The company eventually moved its stem-cell infusion operations to Mexico, but it pushed back against Turner in a complaint lodged with U President Eric Kaler.

Clinics have also fired back at Turner’s latest critical article, which appeared last month in the medical journal Regenerative Medicine.

Research scientist Duncan Ross of Florida-based Kimera Labs, which was identified in Turner’s July 19 article as advertising an undisclosed pay-for-participation stem-cell study on clinicaltrials.gov, has threatened legal action.

“I encourage you to amend your publication or I am going to bring suit against the institution for defamation or slander,” Ross wrote to Turner. “I am going to lobby the journal for the retraction of this publication. I followed the letter of the FDA as it exists at this time and I am not going to have my name disparaged because of your lack of interest in due diligence.”

Turner said no litigation has materialized, and an editor at Regenerative Medicine said no request for a retraction has been made.

Beverly Hills cosmetic surgeon Dr. Mark Berman — who is co-medical director of the national Cell Surgical Network, another clinic group named in Turner’s article — said academic researchers like Turner are “misguided” and out of touch with real-world medical needs.

“We are not taking public funding and using it to our benefit while pursuing ‘scientific’ excellence — we’re actually trying to help our patients while learning about the treatments and the disease they have,” Berman said in an e-mail to the Star Tribune. “Frankly, I think this is much more ethical than a major university with billions of endowment dollars taking millions of dollars of taxpayer money so they can build new offices and laboratories to further the study of stem cells.”

Stem cells are the undifferentiated raw cells in the body that have the ability to quickly produce copies of themselves and also change into other kinds of cells like bone, muscle and blood cells.

Hospitals have safely used stem-cell transplant procedures to treat cancers for decades, but the FDA has approved just one commercial stem-cell product to date, which is made from infant cord blood and can only be used to produce more blood cells.

One of the most common sources of stem cells in pay-to-participate studies is body fat, often obtained via liposuction and known as “adipose-derived stem cells.” The fact that a byproduct of liposuction can be turned into a potentially therapeutic substance helps explain why smaller clinics are often affiliated with or run by plastic surgeons and cosmetic surgery centers.

Some critics have called for more oversight by the FDA. FDA officials, for their part, have said they share the “excitement” over the theoretical promise of stem cells to treat or cure disease by converting into cell types needed by the patient. But the agency has sounded a cautionary tone over the profusion of stem-cell clinics and studies popping up around the country.

Studies so far “have not reliably demonstrated the effectiveness of stem-cell treatments, even in some of the most systematically studied conditions,” FDA officials wrote in the New England Journal of Medicine in March. “This lack of evidence is worrisome.”

Turner said that many of the studies advertised on clinicaltrials.gov don’t seem geared to produce high-quality data that will be medically useful, especially when they involve “open-label” study designs, where doctors and patients know what treatments are given, and patients are paying out of their own pockets.

“In most clinical trials, study subjects are not charged fees to participate. In contrast, individuals enrolled in what are often called ‘pay-to-participate’ studies are charged thousands or tens of thousands of dollars,” Turner’s report says. “ ‘Pay-to-participate’ studies also risk amplifying placebo effects as a result of the sizable fees companies often charge research participants and the hyperbole used to promote such studies.”

Allowing participants to know what treatments are given departs from a typical randomized, blind study in which the intervention is kept secret for a period of time. That practice reduces the risk of a placebo effect, which can run high in medical studies.

A 2010 analysis of studies of irritable bowel syndrome treatments found that nearly 40 percent of 8,400 patients experienced an improvement in their symptoms even though they didn’t receive the drug being studied.

Tennessee resident Doug Oliver, a nationally known advocate for stem-cell research who says he was legally blind before his eyes were treated with stem cells, agreed that placebo-controlled trials are the best way to ensure that patients are really being helped by a treatment.

But he argues that the coming age of “cellular medicine” will also require a wider understanding of how medical evidence is generated.

Oliver said most stem-cell clinics are trying to do the right thing, and many people feel that it wasn’t even possible to get true FDA oversight of a stem-cell clinical trial before the signing of the 21st Century Cures Act last December. But even Oliver acknowledges that some clinics have exploited clinicaltrials.gov and disregarded any form of regulation thus far.

“You have a group of clinics, which I think is a minority, maybe 20 percent, who are ill-intended, unqualified, or there is a personal and cultural … aversion to doing anything that even smacks of following a regulation,” he said. “There are a number of clinics out there like that, and they are hurting people and they should be shut down.”