Ahmed Saad

Diurnal pattern of insulin action in type 1 diabetes: implications for a closed-loop system.

We recently demonstrated a diurnal pattern to insulin action (i.e., insulin sensitivity [SI]) in healthy individuals with higher SI at breakfast than at dinner. To determine whether such a pattern exists in type 1 diabetes, we studied 19 subjects with C-peptide–negative diabetes (HbA1c 7.1 ± 0.6%) on insulin pump therapy with normal gastric emptying. Identical mixed meals were ingested during breakfast, lunch, and dinner at 0700, 1300, and 1900 h in randomized Latin square of order on 3 consecutive days when measured daily physical activity was equal. The triple tracer technique enabled measurement of glucose fluxes. Insulin was administered according to the customary insulin:carbohydrate ratio for each participant. Although postprandial glucose excursions did not differ among meals, insulin concentration was higher (P < 0.01) and endogenous glucose production less suppressed (P < 0.049) at breakfast than at lunch. There were no differences in meal glucose appearance or in glucose disappearance between meals. Although there was no statistical difference (P = 0.34) in SI between meals in type 1 diabetic subjects, the diurnal pattern of SI taken across the three meals in its entirety differed (P = 0.016) from that of healthy subjects. Although the pattern in healthy subjects showed decreasing SI between breakfast and lunch, the reverse SI pattern was observed in type 1 diabetic subjects. The results suggest that in contrast to healthy subjects, SI diurnal pattern in type 1 diabetes is specific to the individual and cannot be extrapolated to the type 1 diabetic population as a whole, implying that artificial pancreas algorithms may need to be personalized.

Stent Revascularization Restores Cortical Blood Flow and Reverses Tissue Hypoxia in Atherosclerotic Renal Artery Stenosis but Fails to Reverse Inflammatory Pathways or Glomerular Filtration Rate

Background—Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury. Methods and Results—Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na+ intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R2*) were measured by blood oxygen level–dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R2*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase–associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-&agr;. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase–associated lipocalin, tumor necrosis factor-&agr;, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase–associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-&agr; remained unchanged. Conclusions—These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease.

The Effect of Walking on Postprandial Glycemic Excursion in Patients With Type 1 Diabetes and Healthy People

OBJECTIVE Physical activity (PA), even at low intensity, promotes health and improves hyperglycemia. However, the effect of low-intensity PA captured with accelerometery on glucose variability in healthy individuals and patients with type 1 diabetes has not been examined. Quantifying the effects of PA on glycemic variability would improve artificial endocrine pancreas (AEP) algorithms. RESEARCH DESIGN AND METHODS We studied 12 healthy control subjects (five males, 37.7 ± 13.7 years of age) and 12 patients with type 1 diabetes (five males, 37.4 ± 14.2 years of age) for 88 h. Participants performed PA approximating a threefold increase over their basal metabolic rate. PA was captured using a PA-monitoring system, and interstitial fluid glucose concentrations were captured with continuous glucose monitors. In random order, one meal per day was followed by inactivity, and the other meals were followed by walking. Glucose and PA data for a total of 216 meals were analyzed from 30 min prior to meal ingestion to 270 min postmeal. RESULTS In healthy subjects, the incremental glucose area under the curve was 4.5 mmol/L/270 min for meals followed by walking, whereas it was 9.6 mmol/L/270 min (P = 0.022) for meals followed by inactivity. The corresponding glucose excursions for those with type 1 diabetes were 7.5 mmol/L/270 min and 18.4 mmol/L/270 min, respectively (P < 0.001). CONCLUSIONS Walking significantly impacts postprandial glucose excursions in healthy populations and in those with type 1 diabetes. AEP algorithms incorporating PA may enhance tight glycemic control end points.

Human Renovascular Disease: Estimating Fractional Tissue Hypoxia to Analyze Blood Oxygen Level–dependent MR

PURPOSE To test the hypothesis that fractional kidney hypoxia, measured by using blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging, correlates with renal blood flow (RBF), tissue perfusion, and glomerular filtration rate (GFR) in patients with atherosclerotic renal artery stenosis (RAS) better than regionally selected region of interest-based methods. MATERIALS AND METHODS The study was approved by the institutional review board according to a HIPAA-compliant protocol, with written informed consent. BOLD MR imaging was performed in 40 patients with atherosclerotic RAS (age range, 51-83 years; 22 men, 18 women) and 32 patients with essential hypertension (EH) (age range, 26-85 years; 19 men, 13 women) during sodium intake and renin-angiotensin blockade. Fractional kidney hypoxia (percentage of entire axial image section with R2* above 30 sec(-1)) and conventional regional estimates of cortical and medullary R2* levels were measured. Stenotic and nonstenotic contralateral kidneys were compared for volume, tissue perfusion, and blood flow measured with multidetector computed tomography. Statistical analysis was performed (paired and nonpaired t tests, linear regression analysis). RESULTS Stenotic RBF was reduced compared with RBF of contralateral kidneys (225.2 mL/min vs 348 mL/min, P = .0003). Medullary perfusion in atherosclerotic RAS patients was lower than in EH patients (1.07 mL/min per milliliter of tissue vs 1.3 mL/min per milliliter of tissue, P = .009). While observer-selected cortical R2* (18.9 sec(-1) [stenosis] vs 18.5 sec(-1) [EH], P = .07) did not differ, fractional kidney hypoxia was higher in stenotic kidneys compared with kidneys with EH (17.4% vs 9.6%, P < .0001) and contralateral kidneys (7.2%, P < .0001). Fractional hypoxia correlated inversely with blood flow (r = -0.34), perfusion (r = -0.3), and GFR (r = -0.32). CONCLUSION Fractional tissue hypoxia rather than cortical or medullary R2* values used to assess renal BOLD MR imaging demonstrated a direct relationship to chronically reduced blood flow and GFR.

Management of atherosclerotic renovascular disease after Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL)

Many patients with occlusive atherosclerotic renovascular disease (ARVD) may be managed effectively with medical therapy for several years without endovascular stenting, as demonstrated by randomized, prospective trials including the Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial, the Angioplasty and Stenting for Renal Artery Lesions (ASTRAL) trial and the Stent Placement and Blood Pressure and Lipid-Lowering for the Prevention of Progression of Renal Dysfunction Caused by Atherosclerotic Ostial Stenosis of the Renal Artery (STAR) and ASTRAL. These trials share the limitation of excluding subsets of patients with high-risk clinical presentations, including episodic pulmonary edema and rapidly progressing renal failure and hypertension. Although hemodynamically significant, ARVD can reduce renal blood flow and glomerular filtration rate; adaptive mechanisms preserve both cortical and medullary oxygenation over a wide range of vascular occlusion. Progression of ARVD to severe vascular compromise eventually produces cortical hypoxia, however, associated with active inflammatory cytokine release and cellular infiltration of the renal parenchyma. In such cases ARVD produces a loss of glomerular filtration rate that no longer is reversible simply by restoring vessel patency with technically successful renal revascularization. Each of these trials reported adverse renal functional outcomes ranging between 16 and 22% over periods of 2-5 years of follow-up. Blood pressure control and medication adjustment may become more difficult with declining renal function and may prevent the use of angiotensin receptor blocker and angiotensin-converting enzyme inhibitors. The objective of this review is to evaluate the current management of ARVD for clinical nephrologists in the context of recent randomized clinical trials and experimental research.

Blood oxygen level-dependent (BOLD) MRI analysis in atherosclerotic renal artery stenosis.

Purpose of reviewBlood oxygen level-dependent MRI (BOLD MRI) is a noninvasive technique for evaluating kidney tissue oxygenation that requires no contrast exposure, with the potential to allow functional assessment in patients with atherosclerotic renal artery stenosis. Normal cortical-to-medulla oxygenation gradients are preserved in many patients treated for several years with medical antihypertensive therapy without restoring renal blood flow. The current review is of particular interest as new methods have been applied to the analyses of BOLD MRI, opening the perspective of its wider utilization in clinical practice. Recent findingsRecent findings show that more severe vascular compromise ultimately overwhelms renal adaptive changes, leading to overt cortical hypoxia and expansion of medullary hypoxic zones. ‘Fractional kidney hypoxia’ method of analysis, developed as an alternative method of BOLD MRI analysis, avoids the assumption of discrete cortical and medullary values and decreases the bias related to operator selection of regions of interests. SummaryWe believe that thoughtful application and analysis of BOLD MRI can provide critical insights into changes in renal function prior to the onset of irreversible renal injury and may identify patients most likely to gain from measures to reverse or repair disorders of tissue oxygenation.

Biomarkers of Kidney Injury and Klotho in Patients with Atherosclerotic Renovascular Disease

BACKGROUND AND OBJECTIVES Occlusive renovascular disease and hypertension may progress to CKD. Circulating levels of several biomarkers, including fibroblast growth factor (FGF)-23, Klotho, and soluble urokinase plasminogen activator receptor (suPAR), are altered in patients with CKD, but their role in essential hypertension (EH) and renovascular hypertension (RVH) remains unclear. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Levels of FGF-23, Klotho, suPAR, plasminogen activator inhibitor (PAI)-1, tissue factor, and tissue factor pathway inhibitor (TFI) were measured in the inferior vena cava and renal vein of hypertensive patients with atherosclerotic renal artery stenosis (n=12) or age-matched participants with EH (n=12) and relatively preserved renal function. Single-kidney blood flow was measured to calculate renal release of markers. For control, peripheral vein levels were measured in healthy volunteers (HVs; n=12). RESULTS FGF-23 levels did not differ among the groups, whereas Klotho levels were lower in participants with RVH and EH than in HVs, and suPAR levels were elevated in patients with RVH compared with HVs and patients with EH (6.1±1.5 versus 4.4±1.9 and 3.2±1.2 ng/ml, P<0.05). PAI-1 levels were higher in patients with RVH than in patients with EH, but tissue factor and TFI levels were not statistically significantly different. After adjustment for GFR, Klotho levels remained decreased in both RVH and EH, and suPAR and PAI-1 levels remained elevated in RVH. eGFR correlated inversely with systemic and renal vein suPAR levels, and directly with systemic Klotho levels. CONCLUSIONS Klotho levels are low in hypertensive patients, whereas suPAR and PAI-1 levels are specifically elevated in RVH, correlating with GFR. Klotho, PAI-1, and suPAR may be markers of kidney injury in hypertensive patients.

Increased Circulating Inflammatory Endothelial Cells in Blacks With Essential Hypertension

Morbidity and mortality attributable to hypertension are higher in black essential hypertensive (EH) compared with white EH patients, possibly related to differential effects on vascular injury and repair. Although circulating endothelial progenitor cells (EPCs) preserve endothelial integrity, inflammatory endothelial cells (IECs) detach from sites of injury and represent markers of vascular damage. We hypothesized that blood levels of IECs and inflammatory markers would be higher in black EH compared with white EH patients. Inferior vena cava and renal vein levels of CD34+/KDR+ (EPC) and VAP-1+ (IEC) cells were measured by fluorescence-activated cell sorting in white EH and black EH patients under fixed sodium intake and blockade of the renin–angiotensin system, and compared with systemic levels in normotensive control subjects (n=19 each). Renal vein and inferior vena cava levels of inflammatory cytokines and EPC homing factors were measured by Luminex. Blood pressure, serum creatinine, lipids, and antihypertensive medications did not differ between white and black EH patients, and EPC levels were decreased in both. Circulating IEC levels were elevated in black EH patients, and inversely correlated with EPC levels (R2=0.58; P=0.0001). Systemic levels of inflammatory cytokines and EPC homing factors were higher in black EH compared with white EH patients, and correlated directly with IECs. Renal vein inflammatory cytokines, EPCs, and IECs did not differ from their circulating levels. Most IECs expressed endothelial markers, fewer expressed progenitor cell markers, but none showed lymphocyte or phagocytic cell markers. Thus, increased release of cytokines and IECs in black EH patients may impair EPC reparative capacity and aggravate vascular damage, and accelerate hypertension-related complications.

Transaldolase exchange and its effects on measurements of gluconeogenesis in humans

The deuterated water method is used extensively to measure gluconeogenesis in humans. This method assumes negligible exchange of the lower three carbons of fructose 6-phsophate via transaldolase exchange since this exchange will result in enrichment of carbon 5 of glucose in the absence of net gluconeogenesis. The present studies tested this assumption. ²H₂O and acetaminophen were ingested and [1-¹³C]acetate infused in 11 nondiabetic subjects after a 16-h fast. Plasma and urinary glucuronide enrichments were measured using nuclear magnetic resonance spectroscopy before and during a 0.35 mU·kg FFM⁻¹·min⁻¹ insulin infusion. Rates of endogenous glucose production measured with [3-³H]- and [6,6-²H₂]glucose did not differ either before (14.0 ± 0.7 vs. 13.8 ± 0.7 μmol·kg⁻¹·min⁻¹) or during the clamp (10.4 ± 0.9 vs. 10.9 ± 0.7 μmol·kg⁻¹·min⁻¹), consistent with equilibration and quantitative removal of tritium during triose isomerase exchange. Plasma [3-¹³C] glucose-to-[4-¹³C]glucose and urinary [3-¹³C] glucuronide-to-[4-¹³C]glucuronide ratios were <1.0 (P < 0.001) in all subjects both before (0.66 ± 0.04 and 0.60 ± 0.04) and during (059 ± 0.05 and 0.56 ± 0.06) the insulin infusion, respectively, indicating that ∼35-45% of the labeling of the 5th carbon of glucose by deuterium was due to transaldolase exchange rather than gluconeogenesis. When corrected for transaldolase exchange, rates of gluconeogenesis were lower (P < 0.001) and glycogenolysis higher (P < 0.001) than uncorrected rates both before and during the insulin infusion. In conclusion, assuming negligible dilution by glycerol and near-complete triose isomerase equilibration, these data provide strong experimental evidence that transaldolase exchange occurs in humans, resulting in an overestimate of gluconeogenesis and an underestimate of glycogenolysis when measured with the ²H₂O method. Use of appropriate ¹³C tracers provides a means of correcting for transaldolase exchange.

Urinary Mitochondrial DNA Copy Number Identifies Chronic Renal Injury in Hypertensive Patients

Mitochondrial injury contributes to renal dysfunction in several models of renal disease, but its involvement in human hypertension remains unknown. Fragments of the mitochondrial genome released from dying cells are considered surrogate markers of mitochondrial injury. We hypothesized that hypertension would be associated with increased urine mitochondrial DNA (mtDNA) copy numbers. We prospectively measured systemic and urinary copy number of the mtDNA genes cytochrome-c oxidase-3 and NADH dehydrogenase subunit-1 by quantitative polymerase chain reaction in essential (n=25) and renovascular (RVH, n=34) hypertensive patients and compared them with healthy volunteers (n=22). Urinary kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin served as indices of renal injury. Renal blood flow and oxygenation were assessed by multidetector computed tomography and blood oxygen level–dependent magnetic resonance imaging. Blood pressure, urinary neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 were similarly elevated in essential hypertension and RVH, and estimated glomerular filtration rate was lower in RVH versus healthy volunteers and essential hypertension. Renal blood flow was lower in RVH compared with essential hypertension. Urinary mtDNA copy number was higher in hypertension compared with healthy volunteers, directly correlated with urinary neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 and inversely with estimated glomerular filtration rate. In RVH, urinary mtDNA copy number correlated directly with intrarenal hypoxia. Furthermore, in an additional validation cohort, urinary mtDNA copy number was higher in RVH compared with healthy volunteers (n=10 each). The change in serum creatinine levels and estimated glomerular filtration rate 3 months after medical therapy without or with revascularization correlated with the change in urinary mtDNA. Therefore, elevated urinary mtDNA copy numbers in hypertensive patients correlated with markers of renal injury and dysfunction, implicating mitochondrial injury in kidney damage in human hypertension.