Insulin resistance in uremia: in vitro model in the rat liver using human serum to study mechanisms

n-3 PUFA dietary lipid replacement normalizes muscle mitochondrial function and oxidative stress through enhanced tissue mitophagy and protects from muscle wasting in experimental kidney disease

INTRODUCTION AND METHODS

Skeletal muscle mitochondrial dysfunction may cause tissue oxidative stress and consequent catabolism in chronic kidney disease (CKD), contributing to patient mortality. We investigated in 5/6-nephrectomized (Nx) rats the impact of n3-polyunsaturated fatty-acids (n3-PUFA) isocaloric partial dietary replacement on gastrocnemius muscle (Gm) mitochondrial master-regulators, ATP production, ROS generation and related muscle-catabolic derangements.

RESULTS

Nx had low Gm mitochondrial nuclear respiratory factor-2 and peroxisome proliferator-activated receptor gamma coactivator-1alpha, low ATP production and higher mitochondrial fission-fusion protein ratio with ROS overproduction. n3-PUFA normalized all mitochondrial derangements and pro-oxidative tissue redox state (oxydized to total glutathione ratio). n3-PUFA also normalized Nx-induced muscle-catabolic proinflammatory cytokines, insulin resistance and low muscle weight. Human uremic serum reproduced mitochondrial derangements in C2C12 myotubes, while n3-PUFA coincubation prevented all effects. n3-PUFA also enhanced muscle mitophagy in-vivo and siRNA-mediated autophagy inhibition selectively blocked n3-PUFA-induced normalization of C2C12 mitochondrial ROS production.

CONCLUSIONS

In conclusion, dietary n3-PUFA normalize mitochondrial master-regulators, ATP production and dynamics in experimental CKD. These effects occur directly in muscle cells and they normalize ROS production through enhanced mitophagy. Dietary n3-PUFA mitochondrial effects result in normalized catabolic derangements and protection from muscle wasting, with potential positive impact on patient survival.

Continuous glucose monitoring in patients with type 2 diabetes on hemodialysis

Diabetic kidney disease is the leading cause of end-stage kidney disease in high-income countries. The strict control of glycemic oscillations is the principal therapeutic target, but this could be hard to achieve in uremic patients due to their unpredictable insulin sensitivity. Currently, the evaluation of the glycemic profile relies on serum markers (glycated hemoglobin HbA1c, glycated albumin, and fructosamine), capillary glucose blood control (self-monitoring of blood glucose), and interstitial glucose control (continue glucose monitoring). We conducted a systematic review of published articles on continue glucose monitoring in hemodialysis patients with type 2 diabetes, which included 12 major articles. Four studies found significant fluctuations in glucose levels during hemodialysis sessions. All studies reported a higher mean amplitude of glucose variations on the hemodialysis day. Three studies agreed that continue glucose monitoring is better than glycated hemoglobin in detecting these abnormalities. Moreover, continue glucose monitoring was more accurate and perceived as easier to use by patients and their caregivers. In patients with type 2 diabetes on hemodialysis, glucose levels show different variation patterns than the patients on hemodialysis without diabetes. Considering manageability, accuracy, and cost-effectiveness, continue glucose monitoring could be the ideal diagnostic tool for the patient with diabetes on hemodialysis.

Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease

Unacylated ghrelin (UnAG) may lower skeletal muscle oxidative stress, inflammation, and insulin resistance in lean and obese rodents. UnAG-induced autophagy activation may contribute to these effects, likely involving removal of dysfunctional mitochondria (mitophagy) and redox state maintenance. In chronic kidney disease (CKD) oxidative stress, inflammation and insulin resistance may negatively influence patient outcome by worsening nutritional state through muscle mass loss. Here we show in a 5/6 nephrectomy (Nx) CKD rat model that 4 d s.c. UnAG administration (200 µg twice a day) normalizes CKD-induced loss of gastrocnemius muscle mass and a cluster of high tissue mitochondrial reactive oxygen species generation, high proinflammatory cytokines, and low insulin signaling activation. Consistent with these results, human uremic serum enhanced mitochondrial reactive oxygen species generation and lowered insulin signaling activation in C2C12 myotubes while concomitant UnAG incubation completely prevented these effects. Importantly, UnAG enhanced muscle mitophagy in vivo and silencing RNA-mediated autophagy protein 5 silencing blocked UnAG activities in myotubes. UnAG therefore normalizes CKD-induced skeletal muscle oxidative stress, inflammation, and low insulin signaling as well as muscle loss. UnAG effects are mediated by autophagy activation at the mitochondrial level. UnAG administration and mitophagy activation are novel potential therapeutic strategies for skeletal muscle metabolic abnormalities and their negative clinical impact in CKD.-Gortan Cappellari, G., Semolic, A., Ruozi, G., Vinci, P., Guarnieri, G., Bortolotti, F., Barbetta, D., Zanetti, M., Giacca, M., Barazzoni, R. Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease.

Gold nanoparticle sensors for detecting chronic kidney disease and disease progression

AIM

To study the feasibility of a novel nanomedical method that utilizes breath testing for identifying chronic kidney disease (CKD) and disease progression.

MATERIALS & METHODS

Exhaled breath samples were collected from 62 volunteers. The breath samples were analyzed using sensors based on organically functionalized gold nanoparticles, combined with support vector machine analysis. Sensitivity and specificity with reference to CKD patient classification according to estimated glomerular filtration rate were determined using cross-validation. The chemical composition of the breath samples was studied using gas chromatography linked with mass spectrometry.

RESULTS

A combination of two to three gold nanoparticles sensors provided good distinction between early-stage CKD and healthy states (accuracy of 79%) and between stage 4 and 5 CKD states (accuracy of 85%). A single sensor provided a distinction between early and advanced CKD (accuracy of 76%). Several substances in the breath were identified and could be associated with CKD-related biochemical processes or with the accumulation of toxins through kidney function loss.

CONCLUSION

Breath testing using gold nanoparticle sensors holds future potential as a cost-effective, fast and reliable diagnostic test for early detection of CKD and monitoring of disease progression.

Morphological and functional differences in haemostatic axis between kidney transplanted and end-stage renal disease patients

End-stage renal disease (ESRD) is characterized by several atherothrombotic abnormalities, and kidney transplant seems to improve most of them. However, because it is not clear which mechanism is responsible for such improvement, our purpose was to clarify that point.We conducted a cross sectional study involving 30 ESRD patients, 30 ESRD kidney-transplanted patients (Ktx) and 30 healthy controls (C) to evaluate platelet morphology and function, atherothrombotic profile, endothelial abnormalities and cytokine levels involved in the insulin resistance/endothelial dysfunction. (i) Platelet morphology: The ESRD group showed platelet size similar to the other two groups (ESRD=3518x10(3)+/-549x10(3) nm2, C=3075x10(3)+/-197x10(3) nm2, Ktx=2862x10(3)+/-205x10(3) nm2) with similar platelet granules and number. (ii) Platelet surface glycoprotein: The CD41 and P-Selectin were similar between groups. (iii) Platelet intracellular calcium: Resting intracellular calcium was statistically higher in ESRD compared to the C group (ESRD=182.1+/-34.5, Ktx=126.7+/-14.1, C=72.0+/-11.0 nM, P<0.01). (iv) Hypercoagulability markers and natural anticoagulants: The Ktx and ESRD groups showed higher levels of hypercoagulability markers compared to the C group. A reduction in antithrombin activity was evident in ESRD compared to the Ktx group (P=0.03). (v) Endothelial morphology: The ESRD group showed a thickened vessel basal membrane compared to the Ktx and C groups with more endothelial sufference. (vi) Insulin resistance and pro-inflammatory cytokine profile: The ESRD showed a higher homeostasis model assessment provided equations for estimating insulin resistance (HOMA-IR) compared to the Ktx and C groups (ESRD=2.6+/-0.3, Ktx=1.8+/-0.2, C=1.1+/-0.1, P=0.005) and increased soluble tumor neurosis factor alpha (sTNFalpha) (P<0.05) and soluble vascular cell adhesion molecule (sVCAM) levels (P<0.01). Positive correlations were evident among HOMA-IR and sTNFalpha (P<0.001) and sVCAM (P=0.01), respectively. In a small subgroup of ESRD who underwent Ktx (five pts), our findings were confirmed at 1 year of follow-up, suggesting an improvement of almost haemostatic abnormalities. Kidney transplant is associated with a better atherothrombotic profile in ESRD, platelet intracellular calcium and cytokines seem to be most influenced by the transplant, while most morphological abnormalities are retained.

Splanchnic tissues play a crucial role in uremic glucose intolerance

OBJECTIVE

Determine the mechanism of glucose intolerance in chronically uremic subjects.

DESIGN

Comparison of doubly labeled oral glucose tolerance tests.

SUBJECTS

Seven nondialyzed chronically uremic subjects (creatinine, 420 +/- 104 micromol/L) and 7 healthy subjects, matched for age and body mass index.

INTERVENTION

Plasma glucose was labeled by an infusion of dideuterated glucose started 120 minutes before ingestion of 1 g/kg of naturally 13C-enriched corn starch glucose. Glucose levels and oxidation were monitored for 330 minutes after glucose ingestion.

RESULTS

Uremic subjects had normal fasting plasma glucose levels and impaired glucose tolerance with high plasma insulin (P <.001 versus controls). Glucose tolerance was impaired because of an increased total rate of appearance of glucose (cumulated on 330 minutes: uremic, 1,231 +/- 42 mg/kg/330 min, controls, 1,031 +/- 64; P <.05). Peripheral glucose uptake was increased (P <.05) because of an increased nonoxidative disposal (P =.051).

CONCLUSIONS

Although peripheral glucose uptake resisted the stimulatory effect of the high insulin levels, glucose tolerance was impaired through splanchnic metabolic disturbances: reduced splanchnic glucose uptake and increased endogenous glucose production. The respective contribution of these abnormalities remains to be determined.

Effect of insulin on urinary phosphate excretion in type II diabetes mellitus with or without renal insufficiency

We investigated the effect of insulin on urinary excretion of phosphate in type II diabetes mellitus (DM) with respect to the absence or presence of renal insufficiency. A euglycemic-hyperinsulinemic clamp was performed in 37 type II DM patients. Subjects were divided into two groups: group A consisted of patients with serum creatinine levels less than 1.5 mg/dL (n = 22), and group B consisted of patients with serum creatinine levels of 1.5 mg/dL or greater (n = 15). Blood and urine samples were collected at the beginning and end of the clamp, and urinary excretion of phosphate was evaluated by calculating fractional excretion (FE-P). Tissue sensitivity to insulin in the whole body was expressed as the glucose infusion rate (M value) and that divided by steady-state plasma insulin levels (M/I ratio) during the last 30 minutes of the clamp. FE-P in group A patients significantly decreased during the clamp (from 9.46 +/- 0.67% before the clamp to 7.12 +/- 0.73% after the clamp, P < .004), whereas FE-P in group B patients did not change significantly during the clamp. The percent decrease of FE-P (decrease of FE-P during the clamp divided by FE-P before the clamp) in group A patients was significantly higher than in group B patients (22.5 +/- 7.0% and 2.5 +/- 5.1 %, respectively, P < .04). In all 37 patients, the percent decrease of FE-P was negatively correlated with blood urea nitrogen ([BUN] r = -.36, P < .05), serum creatinine (r = -.34, P < .05), and serum beta2-microglobulin (r = -.44, P < .01) and positively correlated with creatinine clearance (r = .570, P < .004), but it was not correlated with the M value or M/I ratio. These results showed that the kidneys of diabetic patients with renal insufficiency are insulin-insensitive in terms of phosphate transport, and the insulin insensitivity is related to the glomerular filtration rate but not to systemic insulin insensitivity. The percent decrease of FE-P on clamp study could be useful for assessing the insulin insensitivity of the kidney, which probably occurs primarily in the renal tubules.

Oral glucose tolerance test after high-dose i.v. biotin administration in normoglucemic hemodialysis patients

Abnormal glucose metabolism in uremia may result from a complex interplay between decreased insulin secretion and insulin resistance. Recent studies report beneficial effect of biotin administration in glucose metabolism in diabetic animals and in a small number of patients with diabetes mellitus. The aim of the present study was to evaluate the response of oral glucose tolerance test (OGTT) to the i.v. administration of large doses of biotin in hemodialysis patients. Eleven hemodialysis patients aged 56.90 +/- 11.20 (32-76) years on regular hemodialysis thrice a week for 2.72 +/- 1.79 (1-7) years were studied. Fasting venous plasma glucose, glucosylated hemoglobin (%GH), and plasma glucose concentration 2 h after the administration of a 75-g glucose load were measured before, and 2 weeks and 2 months after administration of 50 mg of biotin i.v. postdialysis, and after a 2-month washout period. During the study, dialysis schedule and patients' medication, diet, and dry weight were kept unchanged. OGTT was abnormal in 4 patients before biotin administration and became normal in 3 patients (75%). Our results offer support to the findings of other studies about the beneficial effect of biotin in experimental or clinical diabetes mellitus, and argue for the involvement of biotin in glucose metabolism.

Insulin induces a similar reduction in the concentrations of its own receptor and of an insulin-sensitive glycosyl-phosphatidylinositol in isolated rat hepatocytes

We have used isolated rat hepatocytes to study whether the insulin-induced reduction of its own receptors may modify the transduction of hormone signals by changes in the content of a glycosyl-phosphatidylinositol. Both subsequent insulin binding and glycosyl-phosphatidylinositol concentrations markedly decreased as a function of time and insulin concentration during preincubation of hepatocytes with insulin. The modifications observed in insulin binding were due to changes in receptor concentration. These results show that insulin regulates both the number of its own receptors and glycosyl-phosphatidylinositol concentrations in target cells, which may be of interest in many pathophysiological situations.

Insulin resistance of uremia

Glucose intolerance is a nearly universal finding in patients with chronic renal failure and in animal models of uremia. The glucose intolerance results from impaired insulin-mediated glucose disposal by muscle, adipose, and liver tissue. Insulin binding by these tissues is not reduced. Rather, several defects exist in the postreceptor cascade of insulin action. Although impaired insulin-mediated glucose uptake and metabolism occur, the primary defect and causative agent are not established. The purpose of the present article is to review recent literature on the potential mechanisms underlying the insulin resistance of chronic renal failure.

Glyburide but not ciglitazone enhances insulin action in the liver independent of insulin receptor kinase activation

To test the hypothesis that sulfonylureas enhance insulin action by activating the insulin receptor tyrosine kinase, the effects of glyburide, a second generation sulfonylurea, and ciglitazone, a nonsulfonylurea hypoglycemic agent, were determined in primary cultures of rat hepatocytes on insulin action and insulin receptor structure and function. Twenty hours of preincubation with glyburide (1 microgram/mL) resulted in increased insulin (1 X 10(-7) mol/L) stimulation of [14C] acetate incorporation into lipids and [14C] alpha-aminoisobutyric acid uptake without any change in basal activity. Ciglitazone (1 microgram/mL) was without any effect. Glyburide's actions were mediated without altering the following: (1) 125I-insulin binding; (2) the electrophoretic mobility of the affinity labeled alpha-subunit or the autophosphorylated beta-subunit of the insulin receptor; and (3) the insulin-stimulated insulin receptor kinase activity using histone or the beta-subunit of the insulin receptor as phosphoacceptors. These data suggest that the action of sulfonylureas is distal to the insulin receptor tyrosine kinase. Ciglitazone in vitro is ineffective in the liver, which suggests the peripheral tissues as the possible site of action.

Effect of chronic renal failure on the level of albumin messenger RNA

The effects of chronic renal failure on the level of albumin mRNA and the transcription rate of the albumin gene were studied in seven of eight nephrectomized rats. A paired feeding procedure was employed to eliminate a nutritional difference between sham-operated control and uremic rats. Total RNA was isolated from the livers of control and uremic rats fasted for 24 or 48 hours. The mRNA level was measured by RNA-cDNA dot blot hybridization, and the transcription rate was measured by the "run-on" transcription assay in isolated nuclei. The albumin mRNA levels in uremic rat livers were reduced to 75% at the 24-hour fasted state, and to 45% at 48-hour fasted state compared with those in the respective control groups. There was no difference in the level of beta-actin mRNA between these groups. However, there was no difference in the transcription rate of the albumin gene between control and uremic rats. Northern analysis showed that albumin mRNA isolated from uremic rat liver was identical in size with that from the control. These results suggested that a posttranscriptional process, involving the destabilization of cytoplasmic mRNA, is responsible for the uremia-induced repression of albumin synthesis.

Insulin binding and insulin receptor tyrosine kinase activity are not altered in the liver of rats with non-insulin-dependent diabetes

Using the insulin-glucose clamp technique, we have previously shown that an increased sensitivity to insulin in vivo is a characteristic of the liver in rats with non-insulin-dependent diabetes induced by neonatal streptozotocin administration. We have thus studied the properties of liver insulin receptor in that model. 125I-porcine insulin binding was found normal both in isolated plasma membranes and in solubilized, wheat germ agglutinin purified receptors prepared from livers of rats with non-insulin-dependent diabetes, when compared to controls. Basal and insulin-stimulated insulin receptor kinase activities were also found normal for both the autophosphorylation of the beta subunit of the insulin receptor and the phosphorylation of the artificial substrate poly (Glu-Tyr) 4:1. Thus, in that model of chronic insulin deficiency and mild hyperglycemia: 1) liver insulin receptors are not up-regulated; 2) tyrosine kinase activity remains unaffected. This last observation supports the hypothesis that the increased insulin effect in the liver of rats with non-insulin-dependent diabetes is probably distal to the insulin receptor kinase.

Insulin resistance in uremia: insulin receptor kinase activity in liver and muscle from chronic uremic rats

We have studied the structure and function of the partially purified insulin receptors from liver and skeletal muscle in a rat model of severe chronic uremia. 125I-insulin binding was higher in the liver from uremic rats when compared with ad libitum- and pair-fed controls. Furthermore, the ability of insulin to stimulate the autophosphorylation of the beta-subunit and insulin receptor kinase activity using Glu80, Tyr20 as exogenous phosphoacceptor was increased in the liver of the uremic animals. The structural characteristic of the receptors, as determined by electrophoretic mobilities of affinity labeled alpha-subunit and the phosphorylated beta-subunit, were normal in uremia. 125I-insulin binding and insulin receptor kinase activity were similar in the skeletal muscle from uremic and pair- and ad libitum-fed animals. Thus our data are supportive of the hypothesis that in liver and muscle of chronic uremic rats, insulin resistance is due to a defect(s) distal to the insulin receptor kinase.