Cells in middle of disc that are low in glucose at risk of dying

Disc cells at the edge consumed more oxygen and glucose, starving those in the middle.

Disc cells need lots of glucose to survive, according to results of a study conducted by researchers in the physiology laboratory at Oxford University, England.

The investigators also studied the roles that oxygen and proper pH played in disc cell viability and found them to be less important to overall cell survival.

"Not surprising to us, if we removed the glucose, the cells began to die," said Jill P.G. Urban. Sometimes cell death occurred as soon as within 24 hours, she added.

These findings came from a study Urban and Susan R.S. Bibby conducted where they analyzed bovine disc cells in different environments. During the 2005 Annual Congress of the Spine Society of Europe (EuroSpine 2005) in Barcelona, they received the Grammer Award for their research, which provided new information about the key nutrients involved in maintaining disc cells.

Cells provide disc structure, function

Cells determine disc function and volume. "The cells actually have a vital role because they are responsible for making and maintaining the structural matrix of the disc. And, of course, it's the matrix of the disc that governs its biomechanical behavior," said Urban, who presented the results.

"It is essential that these cells remain alive and are able to function and produce a structural matrix."

Previous studies have shown that reduced levels of disc nutrients may lead to disc degeneration. "We all know that cell viability is really low in degenerate discs," Urban noted.

The researchers focused their award-winning study on identifying those conditions that might be too adverse for disc cell survival. To do that, they removed specimens of bovine disc tissue and isolated the disc cells using enzyme digestion and then placed the cells in a medium where the exact environment was known. That included specific amounts of glucose, oxygen or their absence, and known values of pH.

After incubating the cells in those environments for up to seven days, they checked cell viability.

Close-up look at glucose

The researchers analyzed the effects that glucose had by looking at cells incubated with either no glucose, or 0.5 or 5.0 mM glucose concentrations. They also studied how pH levels of 7.4 and 6.2 affected the cells.

Urban described a pH 7.4 level as close to that found in the normal disc during sitting or standing, and a level of pH 6.4 as "that level of pH that has been measured inside degenerative discs," first by Alf Nachemson, MD, 40 years ago, and confirmed in later studies. "So, you actually see the pH levels as low as pH 6.2 and lower in degenerative discs," she said.

The researchers were surprised by the effect pH had on cell survival. "Disc acid pH also kills the cells," Urban said.

Oxygen: lesser nutrient

They also studied cell oxygen levels of 21% and 0%. "The oxygen has very little effect on the viability of cells, so the cells stayed alive with no oxygen present at all, if there is plenty of glucose and the pH level is adequate," she said.

Because of how disc cells normally function, with the ones at the outer edge consuming most of the nutrients, the cells at the center of the disc appeared to be most at risk, based on these findings. "Therefore, conditions in the center of degenerative discs are generally unsafe for cell survival," Urban said.

These results might have implications for some new approaches to treating disc problems, such as inserting special cells into the disc to help improve the function and status of the cells already present. "If the pH is low and there is not enough glucose, I think the chances of achieving a biological solution to disc degeneration are low," Urban said.

Bibby recently graduated with a medical degree from Otago School of Medicine in Wellington, New Zealand.

For more information:
Bibby SRS, Urban JPG. Effect of nutrient deprivation on the viability of intervertebral disc cells. Presented at EuroSpine 2005. Sept. 21-24, 2005. Barcelona.