LOS ANGELES – As obese, nondiabetic individuals become more insulin resistant, a decrease in insulin clearance is the first change to occur, according to Sun H. Kim, MD.
Dr. Sun H. Kim
“You will often hear about how insulin resistance enhances demand on beta cells to increase insulin secretion, which leads to hyperinsulinemia,” Dr. Kim said at the World Congress on Insulin Resistance, Diabetes & Cardiovascular Disease. “While well accepted, this model ignores the role of insulin clearance rate in maintaining hyperinsulinemia in insulin resistance states.”
In an effort to understand the physiologic adaptation to insulin resistance prior to the development of type 2 diabetes mellitus, Dr. Kim, an associate professor of endocrinology at Stanford (Calif) University, Stanford, and her colleagues enrolled 91 adults who had a body mass index of at least 30 kg/m2. The study was published in the March 2018 issue of Diabetologia. Each subject underwent a 75-g oral glucose tolerance test as well as the insulin suppression test to measure insulin resistance and the graded glucose infusion test to determine each subject’s insulin secretion rate and insulin clearance rate. For the graded glucose infusion test, the researchers increased the glucose infusion rate every 40 minutes, from 1 mg/kg per minute up to 8 mg/kg per minute. Next, they divided the cohort of obese individuals into tertiles of insulin resistance as quantified by the steady-state plasma glucose (SSPG): less than 9.7 mmol/L (tertile 1), 9.7-12.7 mmol/L (tertile 2), and 12.8 mmol/L or greater (tertile 3).
The mean age of subjects was 54 years. The mean SSPG level was 7.2 mmol/L among subjects in tertile 1, 11.3 mmol/L among those in tertile 2, and 14.3 mmol/L among those in tertile 3. The remainder of the demographics was similar. “Most importantly, body mass index among tertiles was nearly identical,” Dr. Kim said. “The only biomarker that was different was ALT, which increased with increasing tertiles. The individuals who were more insulin resistant likely had more fatty liver. We didn’t do imaging in this particular study.”
When the researchers evaluated oral glucose tolerance test data, they observed that subjects who were most insulin resistant had slightly higher glucose levels, “which we often see,” she said. “The body does try to keep glucose in a narrow range. What was dramatic were the insulin levels. The most insulin-resistant subjects had insulin levels that were double those of the least insulin-resistant subjects in tertile 1 during the oral glucose tolerance test.”
During the intravenous glucose infusion test, glucose levels rose similarly in the three groups, but those in tertile 3 had slightly higher glucose levels (P = .04). The insulin secretion rate, meanwhile, was similar among subjects in tertiles 1 and 2 but was increased significantly among subjects in tertile 3 (P less than .001). In contrast, the researchers observed a stepwise decline in insulin clearance rate from tertiles 1 to 3. Thus the insulin clearance rate was significantly different between subjects in tertile 1 and tertile 2 (P = .04) as well as between subjects in tertile 2 and those in tertile 3 (P less than .001).
“We propose that insulin resistance leads to an increase in intrahepatic fat, which decreases the insulin clearance rate and helps maintain euglycemia,” Dr. Kim concluded. “In the most insulin-resistant tertile, a decrease in insulin clearance rate is not sufficient, and an increase in the insulin secretion rate is also required. If you look at the relationship between insulin resistance and insulin clearance rate, there is a negative correlation, so the more insulin resistant you are, the lower your insulin clearance rate. However, there are insulin-resistant individuals who perhaps have higher insulin clearance rates than we think they should have. Could those individuals be at the highest risk to develop diabetes? That’s the story to which I don’t yet have an ending.” She reported having no financial disclosures.
SOURCE: Jung SH et al. Diabetologia. 2018;61(3):681-7.