Effects of insulin and lipid emulsion on renal haemodynamics and renal sodium handling in IDDM patients

The influence of insulin and incretin-based therapies on renal tubular transport

The tubular function of the kidney is very complex and is finely regulated by many factors. These include a variety of hormonal signaling pathways which are involved in the expression, activation and regulation of renal transporters responsible for the handling of electrolytes. Glucose-lowering drugs such as insulin and incretin-based therapies, exert a well-known renal protective role in diabetic kidney disease, mainly acting at the glomerular level. In the literature, several studies have described the effect of insulin and the incretin hormones on tubular transport. Most of these studies focused on the variations in excretion and clearance of sodium but did not extensively and systematically investigate the possible variations that these hormones may induce in the tubular regulation of all the other electrolytes, urea metabolism, acid-base balance and urinary pH. While insulin action on the kidney is very well-described, the renal tubular impact of incretin-based therapies is less consistent and the results available are scarce. To our knowledge, this is the first review summarizing the effects induced on renal tubules by insulin, glucagon-like peptide-1 (GLP-1) receptor agonists and serine protease dipeptidyl peptidase-4 (DPP4) inhibitors in both healthy and diabetic human subjects. This is significant because it highlights the existence of a renal-gut and pancreas axis which also has a direct tubular effect and enables a deeper understanding of renal physiology.

AGE Content of a Protein Load Is Responsible for Renal Performances: A Pilot Study

OBJECTIVE

Chronic kidney disease is associated with higher morbidity and mortality in patients with diabetes. A low-protein diet is recommended to slow diabetic nephropathy progression because each protein load leads to renal hemodynamic variations. The aim of our study was to evaluate whether the advanced glycation end products (AGE) content of a protein load is responsible for the protein-induced renal hemodynamic variations in humans.

RESEARCH DESIGN AND METHODS

Ten healthy subjects were assigned to a high-protein (1 g/kg) low-AGE (3,000 kU AGE) versus high-AGE (30,000 kU AGE) meal. Renal perfusion, oxygen consumption, and oxygen content were measured before and 120 min after each meal.

RESULTS

Renal perfusion (3.2 ± 0.5 vs. 3.8 ± 0.4 mL/min/g; P = 0.0002) and oxygen consumption (0.3 ± 0.04 vs. 0.4 ± 0.08 min^-1; P = 0.005) increased significantly after the high-AGE meal compared with the low-AGE meal.

CONCLUSIONS

Our results suggest that the AGE content of a protein load is responsible for renal hemodynamic modifications. Therefore, prevention of diabetic nephropathy progression could aim predominantly at reducing food AGE content.

Combined intervention with pioglitazone and n-3 fatty acids in metformin-treated type 2 diabetic patients: improvement of lipid metabolism

Background

The marine n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) exert numerous beneficial effects on health, but their potency to improve treatment of type 2 diabetic (T2D) patients remains poorly characterized. We aimed to evaluate the effect of a combination intervention using EPA + DHA and the insulin-sensitizing drug pioglitazone in overweight/obese T2D patients already treated with metformin.

Methods

In a parallel-group, four-arm, randomized trial, 69 patients (66 % men) were assigned to 24-week-intervention using: (i) corn oil (5 g/day; Placebo), (ii) pioglitazone (15 mg/day; Pio), (iii) EPA + DHA concentrate (5 g/day, containing ~2.8 g EPA + DHA; Omega-3), or (iv) pioglitazone and EPA + DHA concentrate (Pio& Omega-3). Data from 60 patients were used for the final evaluation. At baseline and after intervention, various metabolic markers, adiponectin and cytokines were evaluated in serum using standard procedures, EPA + DHA content in serum phospholipids was evaluated using shotgun lipidomics and mass spectrometry, and hyperinsulinemic-euglycemic clamp and meal test were also performed. Indirect calorimetry was conducted after the intervention. Primary endpoints were changes from baseline in insulin sensitivity evaluated using hyperinsulinemic-euglycemic clamp and in serum triacylglycerol concentrations in fasting state. Secondary endpoints included changes in fasting glycemia and glycated hemoglobin (HbA_1c), changes in postprandial glucose, free fatty acid and triacylglycerol concentrations, metabolic flexibility assessed by indirect calorimetry, and inflammatory markers.

Results

Omega-3 and Pio& Omega-3 increased EPA + DHA content in serum phospholipids. Pio and Pio& Omega-3 increased body weight and adiponectin levels. Both fasting glycemia and HbA_1c were increased by Omega-3, but were unchanged by Pio& Omega-3. Insulin sensitivity was not affected by Omega-3, while it was improved by Pio& Omega-3. Fasting triacylglycerol concentrations and inflammatory markers were not significantly affected by any of the interventions. Lipid metabolism in the meal test and metabolic flexibility were additively improved by Pio& Omega-3.

Conclusion

Besides preventing a modest negative effect of n-3 fatty acids on glycemic control, the combination of pioglitazone and EPA + DHA can be used to improve lipid metabolism in T2D patients on stable metformin therapy.

Trial registration

EudraCT number 2009-011106-42.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-015-0047-9) contains supplementary material, which is available to authorized users.

Eating two larger meals a day (breakfast and lunch) is more effective than six smaller meals in a reduced-energy regimen for patients with type 2 diabetes: a randomised crossover study

AIMS/HYPOTHESIS

The aim of the study was to compare the effect of six (A6 regimen) vs two meals a day, breakfast and lunch (B2 regimen), on body weight, hepatic fat content (HFC), insulin resistance and beta cell function.

METHODS

In a randomised, open, crossover, single-centre study (conducted in Prague, Czech Republic), we assigned 54 patients with type 2 diabetes treated with oral hypoglycaemic agents, both men and women, age 30-70 years, BMI 27-50 kg/m(2) and HbA1c 6-11.8% (42-105 mmol/mol), to follow two regimens of a hypoenergetic diet, A6 and B2, each for 12 weeks. Randomisation and allocation to trial groups (n = 27 and n = 27) were carried out by a central computer system. Individual calculations of energy requirements for both regimens were based on the formula: (resting energy expenditure × 1.5) - 2,092 kJ. The diet in both regimens had the same macronutrient and energy content. HFC was measured by proton magnetic resonance spectroscopy. Insulin sensitivity was measured by isoglycaemic-hyperinsulinaemic clamp and calculated by mathematical modelling as oral glucose insulin sensitivity (OGIS). Beta cell function was assessed during standard meal tests by C-peptide deconvolution and was quantified with a mathematical model. For statistical analysis, 2 × 2 crossover ANOVA was used.

RESULTS

The intention-to-treat analysis included all participants (n = 54). Body weight decreased in both regimens (p < 0.001), more for B2 (-2.3 kg; 95% CI -2.7, -2.0 kg for A6 vs -3.7 kg; 95% CI -4.1, -3.4 kg for B2; p < 0.001). HFC decreased in response to both regimens (p < 0.001), more for B2 (-0.03%; 95% CI -0.033%, -0.027% for A6 vs -0.04%; 95% CI -0.041%, -0.035% for B2; p = 0.009). Fasting plasma glucose and C-peptide levels decreased in both regimens (p < 0.001), more for B2 (p = 0.004 and p = 0.04, respectively). Fasting plasma glucagon decreased with the B2 regimen (p < 0.001), whereas it increased (p = 0.04) for the A6 regimen (p < 0.001). OGIS increased in both regimens (p < 0.01), more for B2 (p = 0.01). No adverse events were observed for either regimen.

CONCLUSIONS/INTERPRETATION

Eating only breakfast and lunch reduced body weight, HFC, fasting plasma glucose, C-peptide and glucagon, and increased OGIS, more than the same caloric restriction split into six meals. These results suggest that, for type 2 diabetic patients on a hypoenergetic diet, eating larger breakfasts and lunches may be more beneficial than six smaller meals during the day. Trial registration ClinicalTrials.gov number, NCT01277471, completed. Funding Grant NT/11238-4 from Ministry of Health, Prague, Czech Republic and the Agency of Charles University - GAUK No 702312.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Improvement in β-cell function after diet-induced weight loss is associated with decrease in pancreatic polypeptide in subjects with type 2 diabetes

OBJECTIVE

The aim of our study was to evaluate the effect of a lifestyle intervention program on β-cell function and to explore the role of gastrointestinal peptides in subjects with T2D.

METHODS

Subjects with T2D (n=74) received 24 weeks of intervention: 12 weeks of slimming diet (-500 kcal/day) and the subsequent 12 weeks of diet were combined with aerobic exercise. All subjects were examined at weeks 0, 12 and 24. β-cell function was assessed during standard meal tests. Insulin secretory rate (ISR) was calculated by C-peptide deconvolution, and β-cell function was quantified with a mathematical model. Plasma concentrations of gastrointestinal peptides were measured in a fasting state and during hyperinsulinemia induced by hyperinsulinemic isoglycemic clamp.

RESULTS

Mean weight loss was 5.03±4.38 kg (p<0.001) in weeks 0-12. Weight did not change significantly in weeks 12-24. Both insulin secretion at the reference level and glucose sensitivity increased in weeks 0-12 (by 33%±54% and by 26%±53%, respectively, p<0.001) and remained unchanged in weeks 12-24. Both fasting and hyperinsulinemic plasma concentrations of pancreatic polypeptide (PP) decreased in weeks 0-12 (p<0.05 for both) and did not change significantly in weeks 12-24. Changes in insulin secretion at the reference level correlated negatively with plasma concentrations of PP during hyperinsulinemia (r=-0.36; p<0.001). Changes in glucose sensitivity correlated negatively with changes in plasma concentrations of PP, both in fasting and during hyperinsulinemia (r=-0.2; p=0.01 for both). The correlations remained significant after adjustment for changes in body-mass-index.

CONCLUSIONS

After diet-induced weight loss, β-cell function improved in T2D subjects and remained unchanged after the addition of exercise. We demonstrate for the first time that these changes are associated with a decrease in PP secretion.

Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes

AIMS

The aim of this study was to compare the effects of calorie-restricted vegetarian and conventional diabetic diets alone and in combination with exercise on insulin resistance, visceral fat and oxidative stress markers in subjects with Type 2 diabetes.

METHODS

A 24-week, randomized, open, parallel design was used. Seventy-four patients with Type 2 diabetes were randomly assigned to either the experimental group (n = 37), which received a vegetarian diet, or the control group (n = 37), which received a conventional diabetic diet. Both diets were isocaloric, calorie restricted (-500 kcal/day). All meals during the study were provided. The second 12 weeks of the diet were combined with aerobic exercise. Participants were examined at baseline, 12 weeks and 24 weeks. Primary outcomes were: insulin sensitivity measured by hyperinsulinaemic isoglycaemic clamp; volume of visceral and subcutaneous fat measured by magnetic resonance imaging; and oxidative stress measured by thiobarbituric acid reactive substances. Analyses were by intention to treat.

RESULTS

Forty-three per cent of participants in the experimental group and 5% of participants in the control group reduced diabetes medication (P < 0.001). Body weight decreased more in the experimental group than in the control group [-6.2 kg (95% CI -6.6 to -5.3) vs. -3.2 kg (95% CI -3.7 to -2.5); interaction group × time P = 0.001]. An increase in insulin sensitivity was significantly greater in the experimental group than in the control group [30% (95% CI 24.5-39) vs. 20% (95% CI 14-25), P = 0.04]. A reduction in both visceral and subcutaneous fat was greater in the experimental group than in the control group (P = 0.007 and P = 0.02, respectively). Plasma adiponectin increased (P = 0.02) and leptin decreased (P = 0.02) in the experimental group, with no change in the control group. Vitamin C, superoxide dismutase and reduced glutathione increased in the experimental group (P = 0.002, P < 0.001 and P = 0.02, respectively). Differences between groups were greater after the addition of exercise training. Changes in insulin sensitivity and enzymatic oxidative stress markers correlated with changes in visceral fat.

CONCLUSIONS

A calorie-restricted vegetarian diet had greater capacity to improve insulin sensitivity compared with a conventional diabetic diet over 24 weeks. The greater loss of visceral fat and improvements in plasma concentrations of adipokines and oxidative stress markers with this diet may be responsible for the reduction of insulin resistance. The addition of exercise training further augmented the improved outcomes with the vegetarian diet.

The metabolic syndrome and uric acid nephrolithiasis: novel features of renal manifestation of insulin resistance

BACKGROUND

Uric acid nephrolithiasis primarily results from low urinary pH, which increases the concentration of the insoluble undissociated uric acid, causing formation of both uric acid and mixed uric acid/calcium oxalate stones. These patients have recently been described as exhibiting features of insulin resistance. This study was designed to evaluate if insulin resistance is associated with excessively low urinary pH in overtly healthy volunteers (non-stone formers) and if insulin resistance may explain the excessively low urinary pH in patients with uric acid nephrolithiasis.

METHODS

Fifty-five healthy volunteers (non stone-formers) with a large range of body mass index and 13 patients with recurrent uric acid nephrolithiasis underwent hyperinsulinemic euglycemic clamp, 24-hour urinary studies, and anthropometric measurements of adiposity. A subgroup of 35 non-stone formers had 2-hour timed urinary collection before and during the hyperinsulinemic phase of the clamp studies.

RESULTS

For the non-stone former population, low insulin sensitivity measured as glucose disposal rate significantly correlated with low 24-hour urinary pH (r= 0. 35; P= 0.01). In addition to the previously described acidic urine pH and hypouricosuria, patients with recurrent uric acid nephrolithiasis were found to be severely insulin resistant (glucose disposal rate: uric acid stone-formers vs. normals; 4.1 +/- 1.3 vs. 6.9 +/- 2.1 mg/min/kg of lean body mass, P= 0.008). Acute hyperinsulinemia was associated with higher urinary pH (6.1 +/- 0.7 at baseline to 6.8 +/- 0.7 during hyperinsulinemia; P < 0.0001), urinary ammonia excretion (2.7 +/- 1.6 mEq/2 hr at baseline and 4.0 +/- 2.6 mEq/2 hr P= 0.002) and urinary citrate excretion (48 +/- 33 mg/2 hr at baseline and 113 +/- 68 mg/2 hr P < 0.0001).

CONCLUSION

We conclude that one renal manifestation of insulin resistance may be low urinary ammonium and pH. This defect can result in increased risk of uric acid precipitation despite normouricosuria.

Effect of acute hyperglycaemia on sodium handling and excretion of nitric oxide metabolites, bradykinin, and cGMP in Type 1 diabetes mellitus

AIMS

The aim of this study was to evaluate the effect of acutely induced hyperglycaemia on renal sodium handling and to explore the role of the bradykinin-nitric oxide-cGMP signalling pathway.

PATIENTS AND METHODS

We compared 20 Type 1 diabetic (DM1) patients without microalbuminuria with 15 weight-, age-, and sex-matched healthy controls (C). Clearances of para-aminohippuric acid (CPAH), inulin (Cin), lithium, sodium, and urinary nitrite/nitrate (NOx), cGMP and bradykinin excretion rates were measured in two 90-min periods: a glycaemic clamp-induced euglycaemia (5 mmol/l-period I) and hyperglycaemia (12 mmol/l-period II) (Study 1) and during time-controlled euglycaemia (5 mmol/l-period I and 5 mmol/l-period II) to avoid the effects of time and volume load (Study 2).

RESULTS

Cin and CPAH were not significantly different during euglycaemia (period I of Study 1) in DM1 and controls, whereas fractional excretion of sodium was decreased in DM1 (1.84 +/- 0.75 vs. 2.36 +/- 0.67%; P < 0.05) due to an increase in fractional distal tubular reabsorption of sodium (94.01 +/- 1.94 vs. 92.24 +/- 2.47%; P < 0.05). A comparison of changes during Study 1 and Study 2 revealed acute hyperglycaemia did not change renal haemodynamics significantly, while fractional distal tubular reabsorption of sodium increased (DM1: P < 0.05; C: P < 0.01) and fractional excretion of sodium decreased (P < 0.01) in both groups. The urinary excretion rates of NOx were comparable during euglycaemia in DM1 and C. While in C, they significantly increased during Study 1 (period I: 382 +/- 217 vs. period II: 515 +/- 254 nmol/min; P < 0.01) and Study 2 (period I: 202.9 +/- 176.8 vs. period II: 297.2 +/- 267.5 nmol/min; P < 0.05) as a consequence of the water load, no changes were found in DM1. The urinary excretion of bradykinin was lower in DM1 compared with C (0.84 +/- 0.68 vs. 1.20 +/- 0.85 micro g/min; P < 0.01) during euglycaemia; it was not affected by hyperglycaemia. There were no significant differences between DM1 and C and in cGMP urinary excretion rates following hyperglycaemia.

CONCLUSION

This study demonstrates that DM1 without renal haemodynamic alterations is associated with impaired renal sodium handling. Moreover, we did not find a relationship between the renal excretion rates of vasoactive mediators and sodium handling due to hyperglycaemia.

Effects of physiological hyperinsulinemia on systemic, renal, and hepatic substrate metabolism

To determine the effect of physiological hyperinsulinemia on renal and hepatic substrate metabolism, we assessed systemic and renal glucose release and uptake, systemic and renal gluconeogenesis from glutamine, and certain aspects of systemic and renal glutamine and free fatty acid (FFA) metabolism. These were assessed under basal postabsorptive conditions and during 4-h hyperinsulinemic euglycemic clamp experiments in nine normal volunteers using a combination of isotopic techniques and renal balance measurements. Hepatic glucose release (HGR) and glutamine gluconeogenesis were calculated as the difference between systemic and renal measurements. Infusion of insulin suppressed systemic glucose release and glutamine gluconeogenesis by approximately 50% during the last hour of the insulin infusion (P < 0.001). Renal glucose release and glutamine gluconeogenesis decreased from 2.3 +/- 0.4 to 0.9 +/- 0.2 (P < 0.002) and from 0.52 +/- 0.07 to 0.14 +/- 0.03 micromol. kg-1. min-1 (P < 0.001), respectively. HGR and glutamine gluconeogenesis decreased from 8.7 +/- 0.4 to 4.5 +/- 0.5 (P < 0.001) and from 0.35 +/- 0.02 to 0.27 +/- 0.03 micromol. kg-1. min-1 (P < 0.002), respectively. Renal glucose uptake (RGU) increased from 1.61 +/- 0.19 to 2.18 +/- 0.25 micromol. kg-1. min-1 (P = 0.029) but accounted for only approximately 5% of systemic glucose disposal (40.6 +/- 4.3 micromol. kg-1. min-1). Both systemic and renal FFA clearance increased approximately fourfold (P < 0.001 for both). Nevertheless, renal FFA uptake decreased (P = 0.024) and was inversely correlated with RGU (r = -0.582, P = 0.011). Finally, insulin increased systemic glutamine release (P = 0.007), uptake (P < 0.005), and clearance (P < 0.001) but left renal glutamine uptake and release unaffected (P > 0.4 for both).