Protein intake and blood glucose as modulators of GFR in hyperfiltering diabetic patients

SGLT2 inhibition increases serum copeptin in young adults with type 1 diabetes

AIMS

Copeptin, a surrogate of vasopressin, is elevated in type 1 diabetes (T1D) and predicts kidney disease and cardiovascular mortality. Given the cardiorenal protective effects of SGLT2 inhibition (SGLT2i), our aim was to examine: 1) the relationship between serum copeptin, metabolic, renal and systemic hemodynamic parameters in adults with T1D; and 2) serum copeptin after SGLT2i with empagliflozin.

MATERIALS AND METHODS

In this post-hoc, exploratory analysis, serum copeptin, glomerular filtration rate (GFR_Inulin), effective renal plasma flow (ERPF_PAH), plasma renin angiotensin aldosterone system markers, HbA_1c, 24-hour urine volume and sodium excretion were measured in 40 participants with T1D (24.3±5.1 years) during eu- and hyperglycaemia before and after 8 weeks of 25mg of daily empagliflozin.

RESULTS

Higher baseline copeptin correlated with higher HbA_1c, lower 24-hour urine volume and sodium excretion, after correcting for age, sex, systolic blood pressure, and HbA_1c. Copeptin concentrations increased in response to empagliflozin under euglycaemia (4.1±2.1 to 5.1±2.8pmol/L, P=0.0053) and hyperglycaemia (3.3±1.4 to 5.6±2.8pmol/L, P<0.0001). The rise in copeptin in response to empagliflozin correlated with change in 24-hour urine volume, but was independent of changes in fractional excretion of sodium and haematocrit.

CONCLUSIONS

Elevated serum copeptin was associated with worse glycaemic control and lower diuresis and natriuresis. SGLT2i increased serum copeptin in adults with T1D, and the rise correlated with change in diuresis, but not natriuresis and hemo-concentration. Further work is required to evaluate the clinical implications of elevated copeptin with SGLT2i, including whether it is simply a marker of diuresis or may contribute to cardiorenal disease long-term.

Association between uric acid, renal haemodynamics and arterial stiffness over the natural history of type 1 diabetes

AIMS

To examine the relationship between normal plasma uric acid (PUA) levels, renal haemodynamic function, arterial stiffness and plasma renin and aldosterone over a wide range of type 1 diabetes (T1D) durations in adolescents, young adults and older adults.

MATERIALS AND METHODS

PUA, glomerular filtration rate (GFR), effective renal plasma flow (ERPF), vascular stiffness parameters (aortic augmentation index [AIx], carotid AIx, carotid femoral pulse wave velocity [cfPWV]), and plasma renin and aldosterone were measured during a euglycaemic clamp in people with T1D: 27 adolescents (mean ± SD age 16.8 ± 1.9 years), 52 young adults (mean ± SD age 25.6 ± 5.5 years) and 66 older adults (mean ± SD age 65.7 ± 7.5 years).

RESULTS

PUA was highest in patients with the longest T1D duration: 197 ± 44 μmol/L in adolescents versus 264 ± 82 μmol/L in older adults (P < 0.001). Higher PUA correlated with lower GFR only in older adults, even after correcting for age, glycated haemoglobin and sex (β = -2.12 ± 0.56; P = 0.0003), but not in adolescents or young adults. Higher PUA correlated with lower carotid AIx (β = -1.90, P = 0.02) in adolescents. In contrast, PUA correlated with higher cfPWV (P = 0.02) and higher plasma renin (P = 0.01) in older adults with T1D.

CONCLUSIONS

The relationship between higher PUA with lower GFR, increased arterial stiffness and renin angiotensin aldosterone system (RAAS) activation was observed only in older adults with longstanding T1D. T1D duration may modify the association between PUA, renal haemodynamic function and RAAS activation, leading to renal vasoconstriction and ischaemia. Further work must determine whether pharmacological PUA-lowering prevents or reverses injurious haemodynamic and neurohormonal sequelae of longstanding T1D, thereby improving clinical outcomes.

Renal and Vascular Effects of Uric Acid Lowering in Normouricemic Patients With Uncomplicated Type 1 Diabetes

Higher plasma uric acid (PUA) levels are associated with lower glomerular filtration rate (GFR) and higher blood pressure (BP) in patients with type 1 diabetes (T1D). Our aim was to determine the impact of PUA lowering on renal and vascular function in patients with uncomplicated T1D. T1D patients (n = 49) were studied under euglycemic and hyperglycemic conditions at baseline and after PUA lowering with febuxostat (FBX) for 8 weeks. Healthy control subjects were studied under normoglycemic conditions (n = 24). PUA, GFR (inulin), effective renal plasma flow (para-aminohippurate), BP, and hemodynamic responses to an infusion of angiotensin II (assessment of intrarenal renin-angiotensin-aldosterone system [RAAS]) were measured before and after FBX treatment. Arterial stiffness, flow-mediated dilation (FMD), nitroglycerin-mediated dilation (GMD), urinary nitric oxide (NO), and inflammatory markers were measured before and after FBX treatment. Gomez equations were used to estimate arteriolar afferent resistance, efferent resistance (R_E), and glomerular hydrostatic pressure (P_GLO). FBX had a modest systolic BP-lowering effect in T1D patients (112 ± 10 to 109 ± 9 mmHg, P = 0.049) without impacting arterial stiffness, FMD, GMD, or NO. FBX enhanced the filtration fraction response to hyperglycemia in T1D patients through larger increases in R_E, P_GLO, and interleukin-18 but without impacting the RAAS. FBX lowered systolic BP and modulated the renal R_E responses to hyperglycemia but without impacting the RAAS or NO levels, suggesting that PUA may augment other hemodynamic or inflammatory mechanisms that control the renal response to hyperglycemia at the efferent arteriole. Ongoing outcome trials will determine cardiorenal outcomes of PUA lowering in patients with T1D.

Renal and Systemic Effects of Calorie Restriction in Patients With Type 2 Diabetes With Abdominal Obesity: A Randomized Controlled Trial

In individuals with type 2 diabetes with abdominal obesity, hyperfiltration is a risk factor for accelerated glomerular filtration rate (GFR) decline and nephropathy. In this academic, single-center, parallel-group, prospective, randomized, open-label, blinded end point trial, consenting patients with type 2 diabetes aged >18 years, with waist circumference >94 (males) or >80 (females) cm, serum creatinine <1.2 mg/dL, and normoalbuminuria were randomized (1:1) with permuted blocks to 6 months of a 25% calorie restricted (CR) or standard diet (SD). Primary outcome was measured GFR (iohexol plasma clearance). Analyses were by modified intention to treat. At 6 months, GFR significantly decreased in 34 patients on CR and did not change appreciably in 36 on SD. Changes were significantly different between the groups. GFR and body weight reduction were correlated. GFR reduction was larger in hyperfiltering (GFR >120 mL/min) than nonhyperfiltering patients and was associated with BMI, waist circumference, blood pressure, heart rate, HbA_1c, blood glucose, LDL-to-HDL cholesterol ratio, C-reactive protein, angiotensin II, and albuminuria reduction and with increased glucose disposal rate (measured by hyperinsulinemic-euglycemic clamps). Protein and sodium intake and concomitant treatments were similar between the groups. CR was tolerated well. In patients with type 2 diabetes with abdominal obesity, CR ameliorates glomerular hyperfiltration, insulin sensitivity, and other cardiovascular risk factors, effects that might translate into long-term nephro- and cardioprotection.

The effect of sex on humanin levels in healthy adults and patients with uncomplicated type 1 diabetes mellitus

Diabetes mellitus (DM) is associated with a loss of renal and vascular protection in women compared with men, but the responsible mechanisms are unclear. Recent experimental work implicated humanin (HN) as a novel cytoprotective hormone in DM. Our goal was to measure sex-related differences in HN levels in uncomplicated type 1 DM patients (T1D) and healthy controls (HC), as well as the interaction between HN, circulating neurohormones, and vascular function. Plasma HN, cGMP and aldosterone, blood pressure (BP), glomerular filtration rate, and effective renal plasma flow (inulin and para-aminohippurate) were measured in HC (11 men, 10 women) and T1D (23 men and 18 women) during clamped euglycemia (4-6 mmol·L(-1)). Plasma HN levels were generally lower in HC men by comparison with the women, but the differences were not statistically significant. In contrast, levels in the T1D men were higher compared with the T1D women (p = 0.026) and HC men (p < 0.0001). In the HC men, but not the women, HN correlated negatively with BP, but not with renal function, cGMP, or aldosterone. In the T1D men, HN negatively correlated with plasma cGMP. In the T1D women, HN did not correlate with neurohormones or vascular function. Future work should determine the role of HN in the pathogenesis of sex-related vascular function differences in DM.

Glycosuria-mediated urinary uric acid excretion in patients with uncomplicated type 1 diabetes mellitus

Plasma uric acid (PUA) is associated with metabolic, cardiovascular, and renal abnormalities in patients with type 2 diabetes but is less well understood in type 1 diabetes (T1D). Our aim was to compare PUA levels and fractional uric acid excretion (FEUA) in patients with T1D vs. healthy controls (HC) during euglycemia and hyperglycemia. PUA, FEUA, blood pressure (BP), glomerular filtration rate (GFR-inulin), and effective renal plasma flow (ERPF-paraaminohippurate) were evaluated in patients with T1D (n = 66) during clamped euglycemia (glucose 4-6 mmol/l) and hyperglycemia (9-11 mmol/l), and in HC (n = 41) during euglycemia. To separate the effects of hyperglycemia vs. increased glycosuria, parameters were evaluated during clamped euglycemia in a subset of T1D patients before and after sodium glucose cotransporter 2 (SGLT2) inhibition for 8 wk. PUA was lower in T1D vs. HC (228 ± 62 vs. 305 ± 75 μmol/l, P < 0.0001). In T1D, hyperglycemia further decreased PUA (228 ± 62 to 199 ± 65 μmol/l, P < 0.0001), which was accompanied by an increase in FEUA (7.3 ± 3.8 to 11.6 ± 6.7, P < 0.0001). In T1D, PUA levels correlated positively with SBP (P = 0.029) and negatively with ERPF (P = 0.031) and GFR (P = 0.028). After induction of glycosuria with SGLT2 inhibition while maintaining clamped euglycemia, PUA decreased (P < 0.0001) and FEUA increased (P < 0.0001). PUA is lower in T1D vs. HC and positively correlates with SBP and negatively with GFR and ERPF in T1D. Glycosuria rather than hyperglycemia increases uricosuria in T1D. Future studies examining the effect of uric acid-lowering therapies should account for the impact of ambient glycemia, which causes an important uricosuric effect.

A practical method to measure GFR in people with type 1 diabetes

AIMS

Improved early diagnostic methods are needed to identify risk for kidney disease in people with type 1 diabetes. We hypothesized that glomerular filtration rate (GFR) measured by iohexol clearance in dried blood spots (DBS) on filter paper would be comparable to plasma (gold-standard) and superior to estimated GFR (eGFR) and, second, that adjustment for ambient blood glucose would improve accuracy and precision of GFR measurement.

METHODS

GFR was measured by iohexol clearance in plasma, DBS, and as estimated by the CKD-Epidemiology Collaboration equations in 15 adults with type 1 diabetes at two visits, one euglycemic and one hyperglycemic.

RESULTS

GFR measured by DBS was more comparable and less biased than GFR cystatin C, serum creatinine, and both combined. GFR was higher during hyperglycemia. Correction for between visit glycemia statistically significantly reduced bias and mean squared error for GFR measured by DBS as compared to gold-standard during euglycemia.

CONCLUSIONS

Iohexol clearance measured with DBS performed better than eGFR methods. Correction for ambient blood glucose improved precision and accuracy of GFR measurement. This method is more convenient than the gold-standard GFR method and may improve screening and diagnostic capabilities in people with type 1 diabetes, especially when GFR is >60ml/min/1.73m(2).

Soy protein intake, cardiorenal indices, and C-reactive protein in type 2 diabetes with nephropathy: a longitudinal randomized clinical trial

OBJECTIVE

Several short-term trials on the effect of soy consumption on cardiovascular risks are available, but little evidence exists regarding the impact of long-term soy protein consumption among type 2 diabetic patients with nephropathy. To determine the effects of long-term soy consumption on cardiovascular risks, we measured C-reactive protein (CRP) and kidney function indexes among type 2 diabetic patients with nephropathy.

RESEARCH DESIGN AND METHODS

This longitudinal randomized clinical trial was conducted among 41 type 2 diabetic patients with nephropathy (18 men and 23 women). Twenty patients in the soy protein group consumed a diet containing 0.8 g protein/kg body weight (35% animal proteins, 35% textured soy protein, and 30% vegetable proteins) and 21 patients in the control group consumed a similar diet containing 70% animal proteins and 30% vegetable proteins for 4 years.

RESULTS

Soy protein consumption significantly affected cardiovascular risks such as fasting plasma glucose (mean change in the soy protein versus control groups: -18 +/- 3 vs. 11 +/- 2 mg/dl; P = 0.03), total cholesterol (-23 +/- 5 vs. 10 +/- 3 mg/dl; P = 0.01), LDL cholesterol (-20 +/- 5 vs. 6 +/- 2 mg/dl; P = 0.01), and serum triglyceride (-24 +/- 6 vs. -5 +/- 2 mg/dl; P = 0.01) concentrations. Serum CRP levels were significantly decreased by soy protein intake compared with those in the control group (1.31 +/- 0.6 vs. 0.33 +/- 0.1 mg/l; P = 0.02). Significant improvements were also seen in proteinuria (-0.15 +/- 0.03 vs. 0.02 +/- 0.01 g/day; P = 0.001) and urinary creatinine (-1.5 +/- 0.9 vs. 0.6 +/- 0.3 mg/dl, P = 0.01) by consumption of soy protein.

CONCLUSIONS

Longitudinal soy protein consumption significantly affected cardiovascular risk factors and kidney-related biomarkers among type 2 diabetic patients with nephropathy.

Renal functional reserve in patients with Type 1 diabetes mellitus

AIM

Decreased renal functional reserve might precede incipient diabetic nephropathy in patients with Type 1 diabetes. The aim of this study was to assess the relationship between renal functional reserve and easily assessable estimates of systemic endothelial dysfunction in normoalbuminuric patients with Type 1 diabetes and diabetic retinopathy.

METHODS

Renal functional reserve was calculated as the relative change in glomerular filtration rate after protein ingestion. Glomerular filtration rate was measured using pharmacokinetic compartmental analysis of single-shot plasma sinistrin clearance. We measured the activity of von Willebrand factor and concentrations of C-reactive protein and apolipoprotein B, as easily assessable estimates of systemic endothelial dysfunction.

RESULTS

Twenty-two patients were studied. Renal functional reserve was inversely associated with activity of von Willebrand factor (R=-0.431, p=0.045) and, in a multivariate model, with concentration of C-reactive protein (R=0.652, p=0.031).

CONCLUSION

Renal functional reserve is inversely associated with concentration of C-reactive protein in normoalbuminuric patients with Type 1 diabetes and diabetic retinopathy. This finding provides evidence that decreased renal functional reserve might reflect endothelial dysfunction. We speculate that decreased renal functional reserve might possibly show as an early marker of diabetic nephropathy.

Metabolic status in diabetes mellitus affects markers for glomerular filtration rate

The present study was performed in newly diagnosed diabetic children to evaluate the effect of metabolic derangement on routine tests for glomerular filtration rate (GFR). Children with ( n=16) and without ( n=10) ketonuria at diagnosis of diabetes followed a routine clinical treatment program. Serum creatinine, creatinine clearance, serum cystatin C, and iohexol clearance were analyzed at diagnosis and after 20 days of treatment. Iohexol clearance was used as the "true GFR". Serum creatinine and iohexol clearances were not affected by the acute metabolic status or ketonuria. In contrast, serum cystatin C was significantly influenced by ketonuria. Creatinine clearance was an unreliable marker for GFR both in the more deranged and in the balanced metabolic situation.

Effects of amino acids and glucagon on renal hemodynamics in type 1 diabetes

Increased dietary protein and circulating amino acids raise glomerular filtration rate (GFR) and pressure. In diabetes, this glomerular hyperfiltration response is augmented. The purpose of this study was to determine whether glucagon mediates the augmented GFR response to amino acids in diabetes and whether the responses to amino acids and glucagon depend on prostaglandins. Patients with type 1 diabetes mellitus (n = 12) and normal control subjects (n = 12) were studied in a series of six experiments, each on different occasions. Baseline GFR was not significantly increased, but filtration fraction was higher in diabetes. In response to amino acid infusion, GFR increased more and filtration fraction was greater among those with diabetes. Their augmented GFR response to amino acids was not inhibited by octreotide or indomethacin. Participants with diabetes also had enhanced GFR and renal plasma flow responses to glucagon infusion, both of which were inhibited by indomethacin. Glomerular hyperfiltration responses induced by amino acids or glucagon occur by divergent pathways in diabetes; only the response to glucagon is prostaglandin dependent.

Cardiovascular and renal benefits of dry bean and soybean intake

Dry beans and soybeans are nutrient-dense, fiber-rich, and are high-quality sources of protein. Protective and therapeutic effects of both dry bean and soybean intake have been documented. Studies show that dry bean intake has the potential to decrease serum cholesterol concentrations, improve many aspects of the diabetic state, and provide metabolic benefits that aid in weight control. Soybeans are a unique source of the isoflavones genistein and diadzein, which have numerous biological functions. Soybeans and soyfoods potentially have multifaceted health-promoting effects, including cholesterol reduction, improved vascular health, preserved bone mineral density, and reduction of menopausal symptoms. Soy appears to have salutary effects on renal function, although these effects are not well understood. Whereas populations consuming high intakes of soy have lower prevalences of certain cancers, definitive experimental data are insufficient to clarify a protective role of soy. The availability of legume products and resources is increasing, incorporating dry beans and soyfoods into the diet can be practical and enjoyable. With the shift toward a more plant-based diet, dry beans and soy will be potent tools in the treatment and prevention of chronic disease.