Extreme Hyperglycemia and Insulin Secretion
Katherine Gerber, Nicholas Whitticar, Daniel Rochester, Kathryn Corbin, Criag Nunemaker
Contributers
Scientific Minds
Katherine Gerber
Undergraduate Researcher
Dr. Craig Nunemaker
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Principal Investigator
Nick Whitticar
PhD Student
Daniel Rochester
Summer Research Fellow
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Kathryn Corbin
Lab Manager
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Overview of Our Research
Maximum glucose stimulation creating insulin secretory response is thought to be 16-20 mmol/L glucose in mice and human cells [1,2].
The world blood glucose level is 147.6 mmol/L! Other cases have reported levels >100mmol/L! [3,4,5].
What happens to insulin secretion in B-cells in cases of extreme hyperglycemia seen in these cases?
Research
Extreme Hyperglycemic Response
Mouse Islet Insulin Secretion
Pancreatic islets were isolated from outbred CD-1 mice
Incubated in either low, medium, and high glucose solutions
Mouse islet insulin secretion significantly increases between low and medium (p<0.01), low and high (p<0.001) and extreme (p<0.05) treatment groups
Average Human Islet Insulin Secretion
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Figure Pancreatic human islets were isolated from outbred CD-1 mice and incubated in either low, medium, or high glucose solutions
Average insulin secretion in human islets significantly increases from the low to medium group (0.05), low to high group (p<0.001), medium and high glucose group (p<0.05), and the low to extreme group (0.001).
Calcium Response to High Glucose
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By measuring intracellular calcium at 4-second intervals with the fluorescent probe fura-2AM, we can capture the calcium influx following exposure to 3mmol/L, 24mmol/L, and 144 mmol/L of glucose.
As demonstrated in the graph, increasing the glucose concentration from 24 mmol/L to 144 mmol/L does not cause an additional influx of calcium into the beta cells.
Extreme Hyperglycemia and apoptosis and cell death
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After 24-hour exposure, islets showed significantly increased cell death in 144mM glucose compared to RPMI and glucose + mannitol (p<0.001, p<0.05, respectively).After 24-hour exposure, apoptosis measurements revealed glucose + mannitol treatment led to significantly lower levels of apoptosis than both RPMI control (p<0.05) and high mannitol (p<0.05) (Fig 1b). After 48-hour exposure, no significant differences in cell death (Fig 1c) or apoptosis (Fig 1d) were found between treatment groups.
Effect of Osmolarity on Insulin Secretion
The general trend shows, each 84mM glucose group secreted significantly more insulin than the glucose free treatments (p<0.01).
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Findings!​
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Mannitol can effectively balance osmolarity in custom glucose solutions
Exposure to extremely high glucose is not toxic to mouse islets for at least 48 hours
Increased osmolarity due to mannitol does not alter insulin secretion
Intracellular calcium is maximally stimulated in 24mM glucose
Insulin secretion continues well beyond normal physiological glucose levels in human islets
EC50 values for insulin secretion are much higher than previously reported