Adipocytes May Act as Reservoir for Pro-Inflammatory Activity in Cushing’s Disease

In patients with Cushing’s disease, possible long-term exposure to glucocorticoids may lead to an altered adipose structure increasing systemic inflammation, which may be behind the development of insulin resistance, obesity, and cardiovascular disease.

With Eliza Geer, MD, and Derek LeRoith, MD, PhD

Cushing’s Disease, caused by a tumor in the pituitary gland, is characterized by a chronic production of glucocorticoids (GCs). Although GCs are known for their anti-inflammatory properties, patients with Cushing’s disease commonly develop pro-inflammatory conditions such as insulin resistance, obesity, and cardiovascular disease.1-3

A team of researchers sought to explore the impact of long-term exposure to GCs in contributing to systemic inflammation in patients with Cushing’s disease.4 Eliza B. Geer, MD, associate professor and medical director of the Multidisciplinary Pituitary and Skull Base Tumor Center at Memorial Sloan Kettering Cancer Center New York City, and colleagues investigated whether chronic, elevated levels of glucocorticoids in patients with Cushing’s disease may promote pro-inflammatory activity in adipocytes, resulting in the inflammation-related constellation of chronic diseases that arise in these patients.4

Fat cells appear to function as an inflammation factory raises disease risks.

Analysis of Adipose Tissue for Macrophage Infiltration 

Using immunohistochemistry, the researchers reported a higher mean infiltration of macrophages in adipose tissue of patients with Cushing’s disease;4 the results were published in the Journal of Clinical Endocrinology & Metabolism.

Noting that the increased systemic inflammation in patients with Cushing’s disease has not been explained,4 these researchers drew from another condition with chronic low-grade inflammation—obesity—in which adipose tissue activity was believed to contribute to systemic insulin resistance and systemic inflammation.4

Building on this pattern, Dr. Geer and her team examined the adipose tissue of patients with Cushing’s disease in comparison to healthy controls (n = 10) who were matched for body mass index (BMI), age, and sex, using immunohistochemistry and analysis of mRNA expression to determine whether there was a measurable increase in pro-inflammatory cells.

The lateral lower abdominal subcutaneous adipose tissue was biopsied and analyzed for markers of macrophages, particularly pro-inflammatory M1 macrophages over anti-inflammatory M2 macrophages. In addition, RNA was isolated and several inflammatory genes, macrophage surface markers, and anti-inflammatory genes were tested for transcript levels using PCR.4

Four markers: CD68+ (total macrophages), CD4+ (CD4+ helper T cells), CD11c (pro-inflammatory M1 total macrophages), and CD11c+ were clustered around “crown-like structures” (CLS). All of these markers had a higher mean percent of infiltration in adipose tissue of patients with Cushing’s disease than the controls (P = 0.001, 0.04, 0.004, 0.02, respectively).

Sixty and 90% of the adipose tissue samples in Cushing’s patients showed at least one M1/metabolically activated macrophage forming CLS, as assessed by the markers CD11c and CD68. In contrast, only 20% and 50% of the adipose tissue samples in the control group presented with at least one CLS staining by CD68 and CD11c.4

Several other markers, including CD3 (a general marker for T cells), CD8 (CD8+ cytotoxic T cells), CD31 (endothelial marker), and CD163 (anti-inflammatory M2 macrophages), showed no difference in activity between patients with Cushing’s disease and the control group. Additionally, caspase (apoptosis marker), CD20 (B cell marker), and CD56 (natural killer cell marker) were not expressed in any of the samples.4

Structural Differences Found in Adipose Tissue in Cushing’s Disease

The researchers also looked at vimentin, an intermediate filament, which they used to assess the architectural phenotypes of the adipose tissue. Patients with Cushing’s disease had less mean vimentin than controls (P = 0.04).4

The findings of decreased vimentin, increased presence of CD4+ lymphocytes, CD68+ macrophages, CD11c+ pro-inflammatory M1/metabolically activated macrophages, and CLS in the adipose tissue “suggested that this site may be the source of systemic inflammation. And that the increased inflammation in adipose tissue may have arisen as a result of chronic exposure to glucocorticoids,” said Dr. Geer.

“This whole issue of inflamed adipose tissue that has all these infiltrates of macrophages, which give off cytokines some of which may come from the adipocytes and some may come from the inflammatory cells, may be the cause all of the abnormalities that we see,” said Derek LeRoith, MD, PhD, who was not associated with the study but reviewed the findings for EndocrineWeb. "These findingmay help provide a clearer understanding of the prevalence of obesity, cardiovascular disease, and diabetes in patients with Cushing's disease."

“So if the pathway is steroids (ie, glucocorticoids) affecting the inflammatory process in the adipose tissue, which in turn initiated all of these cardiometabolic disorders, as is believed today, I think the researchers have offered evidence that this whole process—as is common in general—may also be common to Cushing’s disease,” Dr. LeRoith said.

Interestingly, mRNA expression of CD11b, CD68, EMR-1, IL-6, IL-10, MCP-1, and TNF-a expression did not differ in the adipose tissue of those with Cushing’s disease and the control group (P > 0.05). Although some of these genes are pro-inflammatory cytokines (IL-6, MCP-1 and TNF-a), their expression was not increased in the adipose tissue samples despite an increased presence of pro-inflammatory macrophages and T-cells.4

“We were surprised that we did not find increased adipose tissue expression of pro-inflammatory cytokines from Cushing’s patients, despite the elevated macrophage content. This suggests that recruitment of macrophages in glucocorticoid-exposed adipose tissue may occur by mechanisms other than altered expression of these cytokines,” Dr. Geer told EndocrineWeb.

To Address Inflammation,  Start Intervention with Lifestyle Management

As for the future of this research, and how it relates to treating patients with Cushing’s disease, “prospective studies of patients with Cushing’s disease are needed in order to understand the effect of their treatment on adipose tissue inflammation over time,” said Dr. Geer.

“These patients suffer from long-term increased cardiovascular and mortality risks, even after achieving remission. Whether adipose tissue inflammation persists after treatment as the contributory factor in this risk is not yet known. We also need to understand the mechanisms by which glucocorticoids induce adipose tissue inflammation in order to understand the probable causes of increased mortality in these patients.,

Dr. LeRoith agreed, saying, “in an ideal situation, take away the steroids, treat the disease, and then show that there’s a regression of these changes. Therefore, the next stage of research would be to look at the adipose tissue in those same cured Cushing’s disease patients and show that this process has disappeared. This would give strength to the idea that it is the steroids driving the systemic inflammation," she said.

Both clinicians concurred that patients with Cushing’s disease needed to be managed not only for pituitary hormone overproduction but for the potential cardiometabolic disorders that are associated with this disease.

“Lifestyle changes, involving diet and exercise, are of course not the whole answer but certainly remain the one key aspect that we can always introduce in trying to reduce this inflammatory process,” said Dr. LeRoith. “On the other hand, patients with Cushing’s disease need to be treated for their Cushing's disease, and that should change a lot of this but it might not change all of it.”

“Our findings reinforce the need for careful management of metabolic and cardiovascular risk markers in patients with Cushing’s disease. It’s evident that these patients are at high risk for developing systemic inflammation, which may originate from their fat depots, and increases the likelihood of insulin resistance and cardiovascular disease,” Dr. Geer said.

 

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Anti-Inflammatory Therapy for CVD, Diabetes Risk Reduction
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