Diabetes blamed for brain neurochemical abnormalities in bipolar disorder

By Eleanor McDermid, Senior medwireNews Reporter

Diabetes may underlie some of the neurochemical abnormalities observed in the brains of patients with bipolar disorder, say researchers.

The team, led by Tomas Hajek (Dalhousie University, Halifax, Nova Scotia, Canada), found that neurochemical and metabolic changes worsened in line with patients’ glucose tolerance status, being larger in those with Type 2 diabetes than those with insulin resistance.

Notably, these brain changes correlated with patients’ functional status.

“These findings have important clinical implications and emphasize the need to improve diabetes care in [bipolar disorder],” Hajek et al write in Biological Psychiatry.

They say that the dose-response effect observed in their study “may indicate that similar to other diabetic end organ damage, the neuronal sequeallae of impaired glucose metabolism could be prevented or alleviated by early detection and treatment.”

There were 15 euglycemic patients with bipolar disorder in the study, and they had similar prefrontal cortex levels of the neuronal marker N-acetyl aspartate (NAA) and the metabolic marker total creatine (creatine plus phosphocreatine) to 11 euglycemic, mentally healthy controls.

Levels of both markers were significantly reduced in 19 patients with insulin resistance or glucose intolerance, and were even lower in 14 bipolar disorder patients with Type 2 diabetes, although not significantly.

NAA and total creatine levels correlated with each other, even after accounting for gray matter volume, which the researchers say is “in keeping with impaired mitochondrial energy metabolism in neurons.”

Both NAA and total creatine levels also correlated positively with patients’ Global Assessment of Functioning scores, so patients with reduced levels of these markers had the worst function.

Hajek et al suggest that their findings explain why only some studies have previously found metabolic changes in the brains of bipolar disorder patients, given that diabetes is underdiagnosed in these patients and their insulin sensitivity would probably not have been tested.

But the fact that brain changes in patients with insulin resistance were almost as marked as those in patients with manifest diabetes “is of clinical concern,” says the team.

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