Insulin treatment restores islet microvascular vasomotion function in diabetic mice

Role of insulin in pancreatic microcirculatory oxygen profile and bioenergetics

BACKGROUND

The pancreatic islet microcirculation adapts its metabolism to cope with limited oxygen availability and nutrient delivery. In diabetes, the balance between oxygen delivery and consumption is impaired. Insulin has been proven to exert complex actions promoting the maintenance of homeostasis of the pancreas under glucotoxicity.

AIM

To test the hypothesis that insulin administration can improve the integrated pancreatic microcirculatory oxygen profile and bioenergetics.

METHODS

The pancreatic microcirculatory partial oxygen pressure (PO₂), relative hemoglobin (rHb) and hemoglobin oxygen saturation (SO₂) were evaluated in nondiabetic, type 1 diabetes mellitus (T1DM), and insulin-treated mice. A three-dimensional framework was generated to visualize the microcirculatory oxygen profile. Ultrastructural changes in the microvasculature were examined using transmission electron microscopy. An Extracellular Flux Analyzer was used to detect the real-time changes in bioenergetics by measuring the oxygen consumption rate and extracellular acidification rate in islet microvascular endothelial cells (IMECs).

RESULTS

Significantly lower PO₂, rHb, and SO₂ values were observed in T1DM mice than in nondiabetic controls. Insulin administration ameliorated the streptozotocin-induced decreases in these microcirculatory oxygen parameters and improved the mitochondrial ultrastructural abnormalities in IMECs. Bioenergetic profiling revealed that the IMECs did not have spare respiratory capacity. Insulin-treated IMECs exhibited significantly greater basal respiration than glucotoxicity-exposed IMECs (P < 0.05). An energy map revealed increased energetic metabolism in insulin-treated IMECs, with significantly increased ATP production, non-mitochondrial respiration, and oxidative metabolism (all P < 0.05). Significant negative correlations were revealed between microcirculatory SO₂ and bioenergetic parameters.

CONCLUSION

Glucotoxicity deteriorates the integrated pancreatic microcirculatory oxygen profile and bioenergetics, but this deterioration can be reversed by insulin administration.

Insulin protects against type 1 diabetes mellitus-induced ultrastructural abnormalities of pancreatic islet microcirculation

Pancreatic islet microcirculation, consisting of pancreatic islet microvascular endothelial cells (IMECs) and pericytes (IMPCs), provides crucial support for the physiological function of pancreatic islet. Emerging evidence suggests that pancreatic islet microcirculation is impaired in type 1 diabetes mellitus (T1DM). Here, we investigated the potential ultrastructural protective effects of insulin against streptozotocin (STZ)-induced ultrastructural abnormalities of the pancreatic islet microcirculation in T1DM mouse model. For this purpose, pancreatic tissues were collected from control, STZ-induced T1DM and insulin-treated mice, and a pancreatic IMECs cell line (MS1) was cultured under control, 35 mM glucose with or without 10⁻⁸ M insulin conditions. Transmission and scanning electron microscopies were employed to evaluate the ultrastructure of the pancreatic islet microcirculation. We observed ultrastructural damage to IMECs and IMPCs in the type 1 diabetic group, as demonstrated by destruction of the cytoplasmic membrane and organelles (mainly mitochondria), and this damage was substantially reversed by insulin treatment. Furthermore, insulin inhibited collagenous fiber proliferation and alleviated edema of the widened pancreatic islet exocrine interface in T1DM mice. We conclude that insulin protects against T1DM-induced ultrastructural abnormalities of the pancreatic islet microcirculation.

Integrated pancreatic microcirculatory profiles of streptozotocin-induced and insulin-administrated type 1 diabetes mellitus

OBJECTIVE

As an integrated system, pancreatic microcirculatory disturbance plays a vital role in the pathogenesis of type 1 diabetes mellitus (T1DM), which involves changes in microcirculatory oxygen and microhemodynamics. Therefore, we aimed to release type 1 diabetic and insulin-administrated microcirculatory profiles of the pancreas.

METHODS

BALB/c mice were assigned to control, T1DM, and insulin-administrated groups randomly. T1DM was induced by intraperitoneal injection of streptozotocin (STZ). 1.5 IU insulin was administrated subcutaneously to keep the blood glucose within the normal range. After anesthetizing by isoflurane, the raw data set of pancreatic microcirculation was collected by the multimodal device- and computer algorithm-based microcirculatory evaluating system. After adjusting outliers and normalization, pancreatic microcirculatory oxygen and microhemodynamic data sets were imported into the three-dimensional module and compared.

RESULTS

Microcirculatory profiles of the pancreas in T1DM exhibited a loss of microhemodynamic coherence (significantly decreased microvascular blood perfusion) accompanied by an impaired oxygen balance (significantly decreased PO₂ , SO₂ , and rHb). More importantly, with insulin administration, the pathological microcirculatory profiles were partially restored. Meanwhile, there were correlations between pancreatic microcirculatory blood perfusion and PO₂ levels.

CONCLUSIONS

Our findings establish the first integrated three-dimensional pancreatic microcirculatory profiles of STZ-induced and insulin-administrated T1DM.

Comparison of pancreatic microcirculation profiles in spontaneously hypertensive rats and Wistar-kyoto rats by laser doppler and wavelet transform analysis

Pancreatic microcirculatory dysfunction emerged as a novel mechanism in the development of hypertension. However, the changes of pancreatic microcirculation profiles in hypertension remain unknown. Pancreatic microcirculatory blood distribution pattern and microvascular vasomotion of spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKYs) were determined by laser Doppler. Wavelet transform analysis was performed to convert micro-hemodynamic signals into time-frequency domains, based on which amplitude spectral scalograms were constructed. The amplitudes of characteristic oscillators were compared between SHRs and WKYs. The expression of eNOS was determined by immunohistochemistry, and plasma nitrite/nitrate levels were measured by Griess reaction. Additionally, endothelin-1, malondialdehyde, superoxide dismutase and interleukin-6 were determined by enzyme-linked immunosorbent assay. SHRs exhibited a lower scale blood distribution pattern with decreased average blood perfusion, frequency and amplitude. Wavelet transform spectral analysis revealed significantly reduced amplitudes of endothelial oscillators. Besides reduced expression of eNOS, the blood microcirculatory chemistry complements micro-hemodynamic profiles as demonstrated by an increase in plasma nitrite/nitrate, endothelin-1, malondialdehyde, interleukin-6 and a decrease of superoxide dismutase in SHRs. Here, we described abnormal pancreatic microcirculation profiles in SHRs, including disarranged blood distribution pattern, impaired microvascular vasomotion and reduced amplitudes of endothelial oscillators.

Multimodal Device and Computer Algorithm-Based Monitoring of Pancreatic Microcirculation Profiles In Vivo

OBJECTIVES

Pancreatic microcirculation has an essential role in orchestrating pancreatic homeostasis. Inherent complexity and technological limitation lead to interobserver variability and 1-sided microcirculatory data. Here, we introduce a multimodal device and computer algorithm-based platform for monitoring and visualizing integrated pancreatic microcirculation profiles.

METHODS

After anesthetizing and exposing pancreas tissue of BALB/c mice, probes of Oxygen to See, Microx TX3, and MoorVMS-LDF2 were positioned at pancreas in situ to capture the pancreatic microcirculatory oxygen (hemoglobin oxygen saturation, relative amount of hemoglobin, and partial oxygen pressure) and microhemodynamic data (microvascular blood perfusion and velocity). To assess and visualize pancreatic microcirculation profiles, raw data of pancreatic microcirculation profiles were processed and transformed using interquartile range and min-max normalization by Python and Apache ECharts.

RESULTS

The multimodal device-based platform was established and 3-dimensional microcirculatory modules were constructed. Raw data sets of pancreatic microcirculatory oxygen and microhemodynamic were collected. The outlier of data set was adjusted to the boundary value and raw data set was preprocessed. Normalized pancreatic microcirculation profiles were integrated into the 3-dimensional histogram and scatter modules, respectively. The 3-dimensional modules of pancreatic microcirculation profiles were then generated.

CONCLUSIONS

We established a multimodal device and computer algorithm-based monitoring platform for visualizing integrated pancreatic microcirculation profiles.

Angiotensin-(1-7) Treatment Restores Pancreatic Microcirculation Profiles: A New Story in Acute Pancreatitis

OBJECTIVES

The aim of this study was to investigate the changes of pancreatic microvascular vasomotion and blood distribution pattern in acute pancreatitis (AP), and whether Angiotensin (Ang)-(1-7) treatment could restore pancreatic microcirculation profiles.

METHODS

Mice were randomly separated into control, AP, and Ang-(1-7)-treated AP (A-AP) group. Acute pancreatitis was induced in mice by intraperitoneal injection of cerulein and lipopolysaccharide. Pancreatitis was confirmed by histopathology, serum amylase, and high-sensitive C-reactive protein. Pancreatic microvascular vasomotion and blood distribution pattern in AP progression were assessed by laser Doppler. Meanwhile, ultrastructural changes of pancreatic microcirculation, including microvascular cavity and wall and endothelial mitochondria, were evaluated by transmission electron microscopy.

RESULTS

Acute pancreatitis mice exhibited pathological pancreatic injuries with lower blood distribution pattern and decreased average blood perfusion, relative velocity, effective frequency, and amplitude of microvascular vasomotion. The pancreatic pathological injuries in Ang-(1-7)-treated mice were significantly alleviated. Consistently, Ang-(1-7) treatment led to a restoration in pancreatic microcirculation profiles. Furthermore, non-Ang-(1-7)-treated mice showed an irregular microvascular wall, narrow cavity, and swelling mitochondria, and these ultrastructural impairments were reversed by Ang-(1-7) administration.

CONCLUSIONS

Pancreatic microcirculation profiles are abnormal in the progression of AP. Angiotensin-(1-7) administration could restore functional status of pancreatic microcirculation.

The browning of white adipose tissue and body weight loss in primary hyperparathyroidism

Background

Parathyroid hormone related protein (PTHrP) triggers white adipose tissue (WAT) browning and cachexia in lung cancer mouse models. It remains unknown whether excessive PTH secretion affects WAT browning and to what extent it contributes to body weight change in primary hyperparathyroidism (PHPT).

Methods

Using the adeno-associated virus injection, Pth gene over-expressed mice mimicking PHPT were firstly established to observe their WAT browning and body weight alteration. The association between PTH and body weight was investigated in 496 PHPT patients. The adipose browning activities of 20 PHPT and 60 control subjects were measured with PET/CT scanning.

Findings

Elevated plasma PTH triggered adipose tissue browning, leading to increased energy expenditure, reduced fat content, and finally decreased body weight in PHPT mice. Higher circulating PTH levels were associated with lower body weight (β = −0.048, P = .0003) independent of renal function, serum calcium, phosphorus,and albumin levels in PHPT patients. PHPT patients exhibited both higher prevalence of detectable brown/beige adipose tissue (20% vs 3.3%, P = .03) and increased browning activities (SUV in cervical adipose was 0.77 vs 0.49,P = .02) compared with control subjects.

Interpretation

Elevated serum PTH drove WAT browning program, which contributed in part to body weight loss in both PHPT mice and patients. These results give insights into the novel pathological effect of PTH and are of importance in understanding the metabolic changes of PHPT.

Fund

This research is supported by the National Key Research and Development Program of China and National Natural Science Foundation of China.

Pancreatic-islet microvascular vasomotion dysfunction in mice with spinal cord injury

Patients with spinal cord injury (SCI) have an increased risk for developing type 2 diabetes. It is unknown whether the pancreatic-islet microvascular vasomotion is involved. We used female C57BL/6 mice and a 100-kilodyne T10 Infinite Horizons contusion SCI (or T10 laminectomy) to detect blood glucose and pancreatic-islet microvascular vasomotion. Blood glucose obtained from tail vein was detected using one Touch UltraEasy glucometer. Glucose tolerance test was performed by d-glucose administration intraperitoneally. Functional status of pancreatic-islet microvascular vasomotion was determined by laser Doppler monitoring. Expressions of insulin and glucagon were determined by immunohistochemistry. Expression of VEGF-A was determined by immunohistochemistry and Western blotting. Our result demonstrated that blood glucose was significantly increased at 4 h postinjury compared to that in sham group, with continuous higher blood glucose until 4 days postinjury (p < 0.05). SCI mice at day 7 and day 14 had significantly impaired glucose tolerance following glucose administration (p < 0.01). Average blood perfusion, amplitude, frequency, and relative velocity of vasomotion were significantly lower at 6 h postinjury than those in the sham group (p < 0.05), which were gradually upregulated over time. The expression of insulin was decreased, while the expression of glucagon was increased at 6 h postinjury. Similarly, the expression of VEGF-A was significantly decreased at 6 h postinjury, compared to that in sham group (p < 0.05), with slight increases by 14 days postinjury. Our study suggests that the functional status of pancreatic-islet microvascular vasomotion is impaired after injury, which may have implications for developing effective therapeutic interventions for SCI.

Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory alterations of the spinal cord. In this article, our goal was to use both Laser Doppler imaging and monitoring to analyze the change of BF after spinal cord injury. Both the laser Doppler image scanner and the probe/monitor were being employed to obtain each readout. The data of LDPI provided a local distribution of BF, which gave an overview of perfusion around the injury site and made it accessible for comparative analysis of BF among different locations. By intensely measuring the probing area over a period of time, a combined probe was used to simultaneously measure the BF and oxygen saturation of the spinal cord, showing overall spinal cord perfusion and oxygen supply. LDF itself has a few limitations, such as relative flux, sensitivity to movement, and biological zero signal. However, the technology has been applied in clinical and experimental study due to its simple setup and rapid measurement of BF.

Gene expression profiles of glucose toxicity-exposed islet microvascular endothelial cells

OBJECTIVE

Islet microcirculation is mainly composed by IMECs. The aim of the study was to investigate the differences in gene expression profiles of IMECs upon glucose toxicity exposure and insulin treatment.

METHODS

IMECs were treated with 5.6 mmol L^-1 glucose, 35 mmol L^-1 glucose, and 35 mmol L^-1 glucose plus 10^-8  mol L^-1 insulin, respectively. Gene expression profiles were determined by microarray and verified by qPCR. GO terms and KEGG analysis were performed to assess the potential roles of differentially expressed genes. The interaction and expression tendency of differentially expressed genes were analyzed by Path-Net algorithm.

RESULTS

Compared with glucose toxicity-exposed IMECs, 1574 mRNAs in control group and 2870 mRNAs in insulin-treated IMECs were identified with differential expression, respectively. GO and KEGG pathway analysis revealed that these genes conferred roles in regulation of apoptosis, proliferation, migration, adhesion, and metabolic process etc. Additionally, MAPK signaling pathway and apoptosis were the dominant nodes in Path-Net. IMECs survival and function pathways were significantly changed, and the expression tendency of genes from euglycemia and glucose toxicity exposure to insulin treatment was revealed and enriched in 7 patterns.

CONCLUSIONS

Our study provides a microcirculatory framework for gene expression profiles of glucose toxicity-exposed IMECs.

Functional status of microvascular vasomotion is impaired in spontaneously hypertensive rat

Accumulating evidence demonstrates that microcirculation plays a role in the pathogenesis of hypertension. In the current study, we demonstrated that pancreatic islet microvascular vasomotion of spontaneously hypertensive rats (SHRs) lost the ability to regulate blood flow perfusion and exhibited a lower microvascular blood perfusion pattern which was negative correlated with blood glucose level. SHRs administrated with insulin revealed an improvement of pancreatic islet microvascular vasomotion and blood perfusion pattern. In vitro, the expressions of endothelial nitric oxide synthase (eNOS) and phospho-eNOS^ser1177 (p-eNOS^ser1177) were significantly decreased in high glucose exposed islet endothelial cells (iECs), accompanied with a higher ratio of eNOS monomer to eNOS dimer and a significantly increased malondialdehyde and nitrite levels. Meanwhile, barrier function, tube formation and migration capacities of high glucose exposed iECs were significantly inhibited. In contrast, iECs dysfunction induced by glucose toxicity and oxidative stress was attenuated or improved by supplement with insulin, L-arginine and β-mercaptoethanol. In summary, our findings suggest that functional status of pancreatic islet microvascular vasomotion is impaired in SHRs and provide evidence that treatment with insulin, L-arginine and β-mercaptoethanol improves endothelium-dependent microvascular vasomotion and meliorates iECs function due to anti-hyperglycemic and anti-oxidative effects, partly through mechanism involving regulation of eNOS and p-eNOS^ser1177.