Researchers may have uncovered a molecular mechanism that sets into motion dangerous infection in the feet and hands often occurring with uncontrolled diabetes, according to a recent study in PLOS One. It appears that high blood sugar unleashes destructive molecules that interfere with the body’s natural infectioncontrol defenses.
A team led by Janna Kiselar, PhD, of Case Western Reserve University School of Medicine, in Cleveland, Ohio, discovered how two dicarbonyls — methylglyoxal (MGO) and glyoxal (GO) — alter the structure of human beta-defensin-2 (hBD- 2) peptides, hobbling their ability to fight inflammation and infection.
“Our in vitro findings alone could have a significant impact on development of more effective antimicrobial treatment strategies for patients with uncontrolled diabetes,” Kiselar says. “The findings also emphasize the importance of lowering high blood sugar and keeping it under control.”
Kiselar and senior author Wesley M. Williams, PhD, collaborated on experiments that compared the mass spectra, the bacterial-killing potential, and the immune cell-attracting ability of dicarbonyl-treated hBD-2 with untreated hBD-2. This beta-defensin was initially exposed to the activities of two key dicarbonyls — MGO and GO, both of which are known to increase in humans with high blood sugar. Mass spectral analysis showed that MGO was the more reactive of the two dicarbonyls, so subsequent bacteria-killing and chemotactic experiments were performed by exposing hBD-2 to MGO.
First, the investigators compared the mass spectra for the dicarbonyl-exposed hBD-2 with untreated hBD-2. In the dicarbonyl-exposed hBD-2, they found that in addition to binding to several other amino acid residues, the dicarbonyl irreversibly binds to two positively charged arginine amino acids located near the surface of the hBD-2 peptide. Then the investigators compared dicarbonyl-treated hBD-2 to untreated hBD-2 in their ability to kill gram-negative bacteria. The untreated hBD-2 is quite effective in killing gram-negative bacteria, while dicarbonyl-exposed hBD- 2 greatly impaired this defensin’s ability to stop the onslaught of bacteria.
“In the petri dish of hBD-2 treated with dicarbonyl, we saw a roughly 50% reduction in the ability of hBD-2 to inhibit growth or kill the bacteria,” Williams says. “It was a significant loss of function, and we saw this effect quite visually. Experiments were repeated multiple times using several bacterial strains, and we found a loss of function in all cases. It establishes that the antimicrobial function was being significantly impeded by the MGO dicarbonyl.”
Finally, investigators examined the effects of MGO on hBD-2’s critical role in an early-stage immune system response. Defensins such as hBD-2 not only inhibit entry into the body of microbes, such as bacteria and viruses, but they also post an alert to the immune system about the invader. The adaptive and innate features of the immune system can then identify the microbe for destruction now and into the future. Defensins work, in part, through chemoattraction of specific immune cells in order to activate the next stage of the immune response, called adaptive immunity.
To test the chemoattraction effect, Kiselar and Williams, in collaboration with George Dubyak, PhD, examined the effects of dicarbonyl on the chemoattraction capabilities of hBD-2.
Usually, specific human immune cells are responsive and attracted by hBD-2. In the cells exposed to the MGO-treated hBD-2, the beta-defensin lost much of its ability to initiate chemoattraction.
Studies in animal models or human tissues will be needed to verify the in vitro findings about the harmful effects of dicarbonyl on the beta-defensin family of antimicrobial peptides, particularly among people with diabetes who have uncontrolled hyperglycemia. Additionally, human antimicrobial peptides other than the beta-defensins may also be affected negatively by a dicarbonyl attack, thus reducing both their antimicrobial and chemoattractive functions.
“The body does have defense mechanisms against molecules such as dicarbonyl, but with a chronic disease such as diabetes, the effectiveness of these defense mechanisms responsible for keeping dicarbonyl levels under control may be overwhelmed,” Williams says. “The result may be dicarbonyl accumulation that could eventually overwhelm the ability of beta-defensins to effectively control inflammation and infection.” For now, control of blood sugar through diet and medicine can hold the dicarbonylbeta defensins dynamic at bay. The need is great for the development of effective antimicrobial peptides and antihyperglycemia drugs and medications with fewer or more tolerable side effects that would help to neutralize the dicarbonyl pathway.
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