Diabetes researchers take aim at dangerous complication: kidney disease

By Whitney L.J. Howell
and OU-HCOM staff reports

Oct. 18, 2011
 

Take a moment to consider the largest health epidemic the United States faces today. Obesity may have flashed into your mind first. But America’s expanding waistline isn’t society’s lone health danger. It’s strongly linked to another crisis—diabetes. Nearly 24 million Americans live with the disease, and physicians will diagnose an additional 1.6 million cases this year, according to the American Diabetes Association (ADA).
 

What’s worse is that developing diabetes increases the likelihood that a patient will experience additional complications, such as kidney disease. In fact, diabetes is the No. 1 cause of kidney failure and, based on ADA statistics, accounts for 44 percent of all new cases diagnosed annually.
 

This problem―diabetes-induced kidney disease, or diabetic nephropathy― has brought Ohio University Heritage College of Osteopathic Medicine (OU-HCOM) researchers into the lab. The group studying this aspect of the disease includes Felicia Nowak, M.D., Ph.D., associate professor of molecular neuroendocrinology; Sharon Inman, Ph.D., associate professor of renal physiology; Ramiro Malgor, M.D., associate professor of pathology; and Karen Coschigano, Ph.D., associate professor of cellular and molecular biology. The team is looking at the issue from various angles in hopes of learning why it occurs, how to prevent it and how to treat it.

Testing the Impact of Diet
 

Type II diabetes, traditionally referred to as adult-onset, accounts for 90 to 95 percent of all cases of diabetes nationwide. A significant amount of oxidative stress—a process that produces free radicals in the body that can damage cells—is common with the disease, Nowak said, and can adversely affect the kidneys. This stress affects the nitric oxide system that controls the dilation of blood vessels in the kidney by inducing inflammation and causing constriction, which cuts down the perfusion of the kidney, leading to tissue damage and impaired function.
 

Together with Inman and Malgor, Nowak works with rats that are genetically bred for obesity and hypertension research to determine if introducing a diet rich in antioxidants—molecules known to protect cells from harm—can shield the kidneys in diabetic animals. A fourth member of the team, Yuriy Slyvka, M.D., Ph.D., came from the Ukraine to work for four years as a postdoctoral fellow on the project. The team’s results were published in the February 2009 issue of Endocrine and the January 2011 issue of Nitric Oxide: Biology and Chemistry.
 

“One would never treat diabetes with only an antioxidant diet, but it could have clinical relevance as a supplement to controlling blood glucose and insulin levels,” Nowak said. We are also extremely interested in its potential as a proactive preventive therapy. The importance of this is underscored by the recent rise in incidence of obesity and diabetes in children and adolescents.”
 

With funding from the National Institutes of Health (NIH) and the Diabetes Research Initiative of Ohio University, the team divided 115 four-week-old rats into two groups, giving one the antioxidant diet and one a standard rat diet. The antioxidant diet was composed of the regular diet containing moderately increased amounts of vitamins E and C, beta-carotene, zinc, selenium, copper, and manganese. At six weeks, 13 weeks, and 20 weeks, the team tested the rats’ blood glucose levels, blood pressure, and how well their kidneys filtered waste.
 

To determine the diet’s effect on the rat kidney tissues, the team removed and dissected the organs and examined the pieces under a microscope, Malgor said. They treated the kidney sections with stains that highlight scarring on the organ’s blood vessels that separate urine from blood as well as any damage to kidney tissue.
 

The team then compared the results from each test. While results at 20 weeks showed more damage than those at six weeks, they found the antioxidant diet did provide a protective effect for one group.

At 20 weeks, antioxidant diet females had better kidney filtration than either the females eating the regular diet or any of the male rats. In addition, those females exhibited lower blood glucose levels at 13
weeks than any other rats.
 

Although the antioxidant diet requires further study and clinical trials to determine its ultimate usefulness, Inman said that applying the diet in humans will likely have a beneficial impact.
 

“We know that oxidative stress is a big factor in diabetes, and it has a deleterious effect on the kidney,” she said. “We also know that a big problem is poor nutritional education. If we can introduce an antioxidant diet, perhaps we can help people control the disease before it becomes chronic.”
 

Diabetes at the Genetic Level
 

While outside stimuli can affect diabetic activity in the body, much of how the disease behaves depends on genetics. In a previous study, Coschigano used transgenic mice—mice genetically engineered to over-express a gene—to link the over-expression of growth hormone (GH) to the increased inflammation present with kidney damage. Her latest work, funded by the NIH, investigates how disturbing GH signaling impacts the same inflammation.
 

She is particularly interested in mesangial cells—specialized cells that help regulate blood flow through the capillaries in the kidneys.
 

“We’re focusing on inflammation genes and inflammation pathways to see if there’s any cross-talk between the growth hormone signal and the inflammatory paths,” said Coschigano, who published recent findings in an article in the October 2010 issue of Growth Hormone & IGF Research. “We want to see which path for growth hormone receptor signaling is responsible for kidney damage and protection.”
 

Based on her previous work, Coschigano hypothesized that mice with broken signaling below the growth hormone receptor would be protected from kidney damage. To test her theory, she used knockout  mice—genetically engineered mice that have one or more genes silenced—to specifically look at the growth hormone signaling pathway involving STAT5 proteins, members of a family of proteins that affects cell growth and differentiation. She injected mice that had both intact and disrupted STAT5 pathways with streptozotocin, a natural toxin in insulin-producing cells, inducing Type I diabetes in the animals.
 

Approximately 12 weeks after the injections, she measured blood sugar levels and kidney weight—both of which were elevated in mice receiving the streptozotocin injections. Surprisingly, urine protein levels were exceptionally high in the mice that had a dysfunctional STAT5 pathway. These results, she says, suggest that STAT5 plays a protective role in the kidney rather than a destructive one.

Clinical Implications
 

With diabetes currently ranked as the seventh leading cause of death in the United States, properly controlling it is a medical necessity. Patients with poorly monitored diabetes can develop additional medical conditions, including heart disease, high blood pressure and nerve damage. For some patients, the disease can progress so far that they lose a lower extremity. It’s also an extremely costly disease. The ADA reports that average medical expenditures for people diagnosed with diabetes are 2.3 times higher than those for healthy individuals.
 

But it’s the emotional price tag that often prompts patients to be proactive about the disease. 
 

“Diabetic nephropathy is, in part, familial, so many diabetic patients have witnessed the consequences of losing kidney function in their relatives. They’re motivated to prevent complications and would be agreeable to implementing this or other therapies,” said Alicia Parks, D.O. (’05).  “So, the possibility of ameliorating the effects of diabetic nephropathy with an antioxidant-rich diet is very exciting.”
 

Parks focused on diabetic nephropathy in her second fellowship. She investigated ways to identify diabetic patients at risk for progression to overt kidney disease.
 

“There’s still so much to learn about diabetes and its complications,” she said. “We need to keep investigating the mechanisms underlying kidney disease in diabetes, the prevention of diabetic nephropathy and the best approaches to treatments.”