Sequence of cellular events in pancreatic islets leading to impaired insulin secretion in chronic kidney disease

Improving Glucose Homeostasis after Parathyroidectomy for Normocalcemic Primary Hyperparathyroidism with Co-Existing Prediabetes

We have previously described increased fasting plasma glucose levels in patients with normocalcemic primary hyperparathyroidism (NPHPT) and co-existing prediabetes, compared to prediabetes per se. This study evaluated the effect of parathyroidectomy (PTx) (Group A), versus conservative follow-up (Group B), in a small cohort of patients with co-existing NPHPT and prediabetes. Sixteen patients were categorized in each group. Glycemic parameters (levels of fasting glucose (fGlu), glycosylated hemoglobin (HbA1c), and fasting insulin (fIns)), the homeostasis model assessment for estimating insulin secretion (HOMA-B) and resistance (HOMA-IR), and a 75-g oral glucose tolerance test were evaluated at baseline and after 32 weeks for both groups. Measurements at baseline were not significantly different between Groups A and B, respectively: fGlu (119.4 ± 2.8 vs. 118.2 ± 1.8 mg/dL, p = 0.451), HbA_1c (5.84 ± 0.3 %vs. 5.86 ± 0.4%, p = 0.411), HOMA-IR (3.1 ± 1.2 vs. 2.9 ± 0.2, p = 0.213), HOMA-B (112.9 ± 31.8 vs. 116.9 ± 21.0%, p = 0.312), fIns (11.0 ± 2.3 vs. 12.8 ± 1.4 μIU/mL, p = 0.731), and 2-h post-load glucose concentrations (163.2 ± 3.2 vs. 167.2 ± 3.2 mg/dL, p = 0.371). fGlu levels demonstrated a positive correlation with PTH concentrations for both groups (Group A, rho = 0.374, p = 0.005, and Group B, rho = 0.359, p = 0.008). At the end of follow-up, Group A demonstrated significant improvements after PTx compared to the baseline: fGlu ((119.4 ± 2.8 vs. 111.2 ± 1.9 mg/dL, p = 0.021) (−8.2 ± 0.6 mg/dL)), and 2-h post-load glucose concentrations ((163.2 ± 3.2 vs. 144.4 ± 3.2 mg/dL, p = 0.041), (−18.8 ± 0.3 mg/dL)). For Group B, results demonstrated non-significant differences: fGlu ((118.2 ± 1.8 vs. 117.6 ± 2.3 mg/dL, p = 0.031), (−0.6 ± 0.2 mg/dL)), and 2-h post-load glucose concentrations ((167.2 ± 2.7 vs. 176.2 ± 3.2 mg/dL, p = 0.781), (+9.0 ± 0.8 mg/dL)). We conclude that PTx for individuals with NPHPT and prediabetes may improve their glucose homeostasis when compared with conservative follow-up, after 8 months of follow-up.

Increased parathyroid hormone is associated with higher fasting glucose in individuals with normocalcemic primary hyperparathyroidism and prediabetes: A pilot study

AIMS

This pilot study aimed to evaluate differences in glycemic parameters between patients with prediabetes and normocalcemic primary hyperparathyroidism (NPHPT) and controls with prediabetes and normal parathyroid hormone (PTH) and calcium concentrations.

METHODS

20 patients with NPHPT and prediabetes and 42 age-, gender-, and body mass index-matched controls with prediabetes were included. Glycemic parameters [fasting glucose (fGlu), glycosylated hemoglobin (HbA1c), fasting insulin (fIns)] were evaluated. Homeostasis Model Assessment was used for estimating insulin secretion (HOMA-B) and resistance (HOMA-IR). Participants underwent a 75-g oral glucose tolerance test.

RESULTS

HbA_1c (5.9 ± 0.0 vs 5.9 ± 0.0%, p = 0.44), HOMA-IR (3.7 ± 1.2 vs 2.9 ± 0.2, p = 0.48), HOMA-B (117.8 ± 31.8 vs 146.9 ± 22.0%, p = 0.14), fIns (14.0 ± 4.3 vs 12.2 ± 1.1 μIU/ml, p = 0.53) and 2-hour post-load glucose concentrations (157.2 ± 2.2 vs 152.2 ± 2.0 mg/dl, p = 0.07), were nondifferent in the two groups. Higher fGlu levels were evident in the NPHPT, compared to the control group (105.6 ± 2.8 vs 98.2 ± 1.8 mg/dl, p = 0.01). fGlu demonstrated a positive correlation with PTH concentrations (rho = 0.374, p = 0.005).

CONCLUSIONS

Individuals with NPHPT and prediabetes present an unfavorable glycemic profile compared to age-matched people with prediabetes, suggesting a direct adverse effect of elevated PTH on glucose homeostasis.

Theoretical overview of clinical and pharmacological aspects of the use of etelcalcetide in diabetic patients undergoing hemodialysis

Etelcalcetide is the first intravenous calcimimetic agent authorized for the treatment of secondary hyperparathyroidism (sHPT) in patients undergoing hemodialysis in Europe, the US, and Japan. The relationship between sHPT and diabetes resides on complex, bidirectional effects and largely unknown homeostatic mechanisms. Although 30% or more patients with end-stage renal disease are diabetics and about the same percentage of those patients suffer from sHPT associated with hemodialysis, no data on the specificities of the use of etelcalcetide in such patients are available yet. Regarding pharmacokinetic interactions, etelcalcetide may compete with oral hypoglycemics recommended for use in patients undergoing hemodialysis and insulins detemir and degludec, causing unexpected hypocalcemia or hypoglycemia. More importantly, hypocalcemia, a common side effect of etelcalcetide, may cause decompensation of preexisting cardiac insufficiency in diabetic patients or worsen dialysis-related hypotension and lead to hypotension-related cardiac events, such as myocardial ischemia. In diabetic patients, hypocalcemia may lead to dangerous ventricular arrhythmias, as both insulin-related hypoglycemia and hemodialysis prolong QT interval. Patients with diabetes, therefore, should be strictly monitored for hypocalcemia and associated effects. Due to an altered parathormone activity in this patient group, plasma calcium should be the preferred indicator of etelcalcetide effects. Until more clinical experience with etelcalcetide is available, the clinicians should be cautious when using this calcimimetic in patients with diabetes.

Mechanism of insulin resistance in a rat model of kidney disease and the risk of developing type 2 diabetes

Chronic kidney disease is associated with homeostatic imbalances such as insulin resistance. However, the underlying mechanisms leading to these imbalances and whether they promote the development of type 2 diabetes is unknown. The effect of chronic kidney disease on insulin resistance was studied on two different rat strains. First, in a 5/6^th nephrectomised Sprague-Dawley rat model of chronic kidney disease, we observed a correlation between the severity of chronic kidney disease and hyperglycemia as evaluated by serum fructosamine levels (p<0.0001). Further, glucose tolerance tests indicated an increase of 25% in glycemia in chronic kidney disease rats (p<0.0001) as compared to controls whereas insulin levels remained unchanged. We also observed modulation of glucose transporters expression in several tissues such as the liver (decrease of ≈40%, p≤0.01) and muscles (decrease of ≈29%, p≤0.05). Despite a significant reduction of ≈37% in insulin-dependent glucose uptake in the muscles of chronic kidney disease rats (p<0.0001), the development of type 2 diabetes was never observed. Second, in a rat model of metabolic syndrome (Zucker Lepr^fa/fa), chronic kidney disease caused a 50% increased fasting hyperglycemia (p<0.0001) and an exacerbated glycemic response (p<0.0001) during glucose challenge. Similar modulations of glucose transporters expression and glucose uptake were observed in the two models. However, 30% (p<0.05) of chronic kidney disease Zucker rats developed characteristics of type 2 diabetes. Thus, our results suggest that downregulation of GLUT4 in skeletal muscle may be associated with insulin resistance in chronic kidney disease and could lead to type 2 diabetes in predisposed animals.

Current therapeutic approaches in the management of hyperglycemia in chronic renal disease

Diabetes mellitus (DM) and chronic kidney disease (CKD) are intricately intertwined. DM is the most common cause of CKD. Adequate control of DM is necessary for prevention of progression of CKD, while careful management of the metabolic abnormalities in CKD will assist in achieving better control of DM. Two of the key organs involved in glucose production are the kidney and the liver. Furthermore, the kidney also plays a role in glucose filtration and reabsorption. In CKD, monitoring of glycemic control using traditional methods such as Hemoglobin A1c (Hba1c) must be done with caution secondary to associated hematological abnormalities in CKD. With regard to medication management in the care of patients with DM, CKD has significant effects. For example, the dosages of oral and non-insulin anti-hyperglycemic agents often need to be modified according to renal function. Insulin metabolism is altered in CKD, and a reduction in insulin dose is almost always needed. Dialysis also affects various aspects of glucose homeostasis, necessitating appropriate changes in therapy. Due to the aforementioned factors glycemic management in patients with DM and CKD can be quiet challenging.

Mitochondrial oxidative stress mediates high-phosphate-induced secretory defects and apoptosis in insulin-secreting cells

Inorganic phosphate (Pi) plays an important role in cell signaling and energy metabolism. In insulin-releasing cells, Pi transport into mitochondria is essential for the generation of ATP, a signaling factor in metabolism-secretion coupling. Elevated Pi concentrations, however, can have toxic effects in various cell types. The underlying molecular mechanisms are poorly understood. Here, we have investigated the effect of Pi on secretory function and apoptosis in INS-1E clonal β-cells and rat pancreatic islets. Elevated extracellular Pi (1~5 mM) increased the mitochondrial membrane potential (ΔΨm), superoxide generation, caspase activation, and cell death. Depolarization of the ΔΨm abolished Pi-induced superoxide generation. Butylmalonate, a nonselective blocker of mitochondrial phosphate transporters, prevented ΔΨm hyperpolarization, superoxide generation, and cytotoxicity caused by Pi. High Pi also promoted the opening of the mitochondrial permeability transition (PT) pore, leading to apoptosis, which was also prevented by butylmalonate. The mitochondrial antioxidants mitoTEMPO or MnTBAP prevented Pi-triggered PT pore opening and cytotoxicity. Elevated extracellular Pi diminished ATP synthesis, cytosolic Ca(2+) oscillations, and insulin content and secretion in INS-1E cells as well as in dispersed islet cells. These parameters were restored following preincubation with mitochondrial antioxidants. This treatment also prevented high-Pi-induced phosphorylation of ER stress proteins. We propose that elevated extracellular Pi causes mitochondrial oxidative stress linked to mitochondrial hyperpolarization. Such stress results in reduced insulin content and defective insulin secretion and cytotoxicity. Our data explain the decreased insulin content and secretion observed under hyperphosphatemic states.