James M Hempe

Louisiana State University Health Sciences Center Shreveport, Shreveport, Louisiana, United States

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Publications (56)212.44 Total impact

  • James M Hempe, Jeannine Ory-Ascani
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    ABSTRACT: This report describes modifications to a capillary zone electrophoresis method developed by Serru et al. (Clinical Chemistry 47:1321, 2001) for the simultaneous analysis of reduced glutathione (GSH) and glutathione disulfide (GSSG). Lowering the pH of the run buffer (75 mmol/l boric acid, 25 mmol/l bis-tris) from pH 8.4 to 7.8 markedly improved GSH peak area reproducibility and allowed multiple samples to be analyzed without changing run buffers due to ion depletion. Sample preparation using red blood cells (RBC) instead of whole blood, combined with glutathione extraction at a lower concentration of metaphosphoric acid (5%), increased assay sensitivity and decreased interference. CZE assay results for clinical samples containing 1000 to 3200 μmol GSH/l RBC and 100 to 400 μmol GSSG/l RBC were highly correlated (r(2) ≥0.95) with results obtained using a commercial dithionitrobenze-based glutathione assay. The modified CZE assay has proven useful for the analysis of glutathione in both mouse and human RBC. This article is protected by copyright. All rights reserved.
    Electrophoresis 12/2013; · 3.26 Impact Factor
  • Pediatric Diabetes 09/2013; 14(6):391-8. · 2.08 Impact Factor
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    ABSTRACT: To estimate skin content of advanced glycation endproducts (AGEs) by measurements of skin intrinsic fluorescence (SIF) from youth with diabetes in comparison with a population of youth and adults without diabetes. Using a specialized instrument, skin AGEs were estimated from skin auto-fluorescence induced at 420 nm and corrected for skin pigmentation (SIF420[kx0.5, km0.5]) in children with types 1 and 2 diabetes, as well as children and adults without diabetes. The effect of age, sex, ethnicity, and diabetes status on SIF420[kx0.5, km0.5] was analyzed. SIF420[kx0.5, km0.5] increased with chronologic age and was higher in children with diabetes compared with children without diabetes (P = .0001). SIF420[kx0.5, km0.5] from 43% of children with type 1 diabetes and 55% with type 2 diabetes overlapped the range of adults without diabetes. SIF420[kx0.5, km0.5] was higher in girls than boys in patients with diabetes patients. However, there was no effect of sex or race on SIF420[kx0.5, km0.5] in subjects without diabetes. After 4-6 years' exposure to diabetes, many children will have precociously high estimates of skin AGEs, comparable with levels that would naturally accumulate only after ∼25 years of chronologic aging. Potentially, this technology identifies children who are at increased risk for complications.
    The Journal of pediatrics 08/2013; · 4.02 Impact Factor
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    ABSTRACT: Inter-individual and ethnic variation in glycated hemoglobin levels, unrelated to blood glucose variation, complicates the clinical use of glycated hemoglobin assays for the diagnosis and management of diabetes. Assessing the types and amounts of glycated hemoglobins present in erythrocytes could provide insight into the mechanism. Blood samples and self-monitored mean blood glucose (MBG) levels were obtained from 85 pediatric type 1 diabetes patients. Glycated hemoglobin levels were measured using three primary assays (boronate affinity chromatography, capillary isoelectric focusing (CIEF), and standardized DCA2000+ immunoassay), and a two-dimensional (2D) analytical system consisting of boronate affinity chromatography followed by CIEF. The 2D system separated hemoglobin into five subfractions, four of which contained glycated hemoglobins. Glycated hemoglobin measurements were compared in patients with low, moderate or high hemoglobin glycation index (HGI), a measure of glycated hemoglobin controlled for blood glucose variation. MBG was not significantly different between HGI groups. Glycated hemoglobin levels measured by all three primary assays and in all four glycated 2D subfractions were significantly different between HGI groups and highest in high HGI patients. These results show that inter-individual variation in glycated hemoglobin levels was evident in diabetes patients with similar blood glucose levels regardless of which glycated hemoglobins were measured.
    Analytical Biochemistry 07/2013; · 2.58 Impact Factor
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    ABSTRACT: Glucose spontaneously reacts with hemoglobin amino groups to produce unstable Schiff base complexes that can dissociate or rearrange to form stable Amadori products. We used dynamic capillary isoelectric focusing and boronate affinity chromatography to assess the formation and dissociation of unstable hemoglobin complexes in vitro. Formation was studied by incubating erythrocytes at 37°C for up to 24h in phosphate-buffered saline (PBS) supplemented with 0 to 55.6 mmol/L glucose. Dissociation was studied by incubating glucose-loaded erythrocytes in PBS without glucose. Dynamic capillary isoelectric focusing separated hemoglobin A1c into two subfractions identified as A1c1 and A1c2. The A1c1 subfraction contained both stable and unstable hemoglobin complexes. The A1c2 subfraction contained only unstable hemoglobin complexes. Both subfractions quantitatively increased in the presence of glucose and decreased in its absence. Rates of increase and decrease were faster and time to equilibrium was shorter for A1c2 (~4 h) compared with A1c1 (~20 h). Unstable hemoglobin complexes did not bind to boronate affinity columns but instead eluted intact in A1c1 and A1c2 subfractions from nonglycated affinity fractions. Cyanoborohydride reduction confirmed the presence of Schiff base complexes. Evidence of multiple unstable hemoglobin complexes with different rates of glycation suggests that new models are needed to describe nonenzymatic hemoglobin glycation.
    Analytical Biochemistry 02/2012; 424(2):149-55. · 2.58 Impact Factor
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    ABSTRACT: Hypoglycemia is an acute complication of diabetes that increases morbidity, mortality and economic costs of diabetes. It presents major clinical problems for the management of Type 2 diabetes as this disease represents the great majority of all diabetes cases. Hypoglycemia makes it difficult for some individuals to achieve good glycemic control, reduces quality of life and increases the burden of diabetes to healthcare systems. Understanding hypoglycemia risk factors can help patients with Type 2 diabetes to correct and avoid hypoglycemia. Recently, an increased risk of hypoglycemia with intensive glycemic control has been identified as an important problem in optimally controlling blood glucose levels in patients with Type 2 diabetes.
    Expert Review of Pharmacoeconomics & Outcomes Research 02/2012; 12(1):47-51. · 1.67 Impact Factor
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    Diabetes care 11/2011; 34(11):e170; author's reply e171. · 7.74 Impact Factor
  • JAMA The Journal of the American Medical Association 06/2011; 305(24):2522; author reply 2522-3. · 29.98 Impact Factor
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    ABSTRACT: To evaluate the relationship between skin advanced glycation end products (sAGEs) with mean blood glucose (MBG), hemoglobin A(1c) (HbA(1c)), and MBG-independent, between-patient differences in HbA(1c) among children with type 1 diabetes. Children aged 5 to 20 years with type 1 diabetes of at least 1 year duration participated. At a clinic visit, sAGE was estimated noninvasively by measurement of skin intrinsic fluorescence (SIF). SIF data were adjusted to correct for variation in skin pigmentation. MBG-independent, between-patient differences in HbA(1c) were examined by statistically controlling HbA(1c) for MBG or alternatively by use of a hemoglobin glycation index (HGI). Results were similar whether HbA(1c), MBG, and HGI were analyzed as single values from the time of the SIF examination visit or as the mean values from all available visits of the patient. HbA(1c) was correlated with MBG (r = 0.5; P < 0.001; n = 110). HbA(1c) and HGI, but not MBG, were statistically associated with SIF after adjustment for age, duration of diabetes, race, sex, and BMI z-score. SIF increased with age and duration of diabetes and was higher in girls than boys. sAGE levels estimated by SIF increase with age, duration of diabetes, and female sex. sAGE is correlated with MBG-independent biological variation in HbA(1c), but not with MBG itself. These results suggest that factors besides MBG that influence HbA(1c) levels also contribute to accumulation of sAGE.
    Diabetes care 06/2011; 34(8):1816-20. · 7.74 Impact Factor
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    ABSTRACT: The hemoglobin glycation index (HGI) assesses biological variation in A1c after accounting for the effect of mean blood glucose (MBG). Previous studies minimized analytical variation that could mask biological variation and showed that HGI was consistent within individuals over time and positively associated with risk for microvascular complications. We tested the hypothesis that biological variation in A1c can be assessed by HGI calculated using routine MBG and A1c data obtained from a typical diabetes clinic. Self-monitored MBG and A1c were collected from charts of 202 pediatric type 1 diabetes patients attending 1612 clinic visits over 6 yr. Predicted A1c was calculated from the linear regression equation of A1c on MBG in the study population. HGI was calculated by subtracting predicted A1c from observed A1c. Patients were divided into low, moderate, and high HGI tertile groups. Patients used 12 models of glucose meters. Download protocols varied with clinical practice over time. A1c was measured by multiple assays and laboratories. Despite this analytical heterogeneity, HGI was significantly different between individuals and correlated within individuals. MBG (mean ± SD, mg/dL) was similar in the low (186 ± 31), moderate (195 ± 28), and high (199 ± 42) HGI groups. A1c (%) was significantly different (p < 0.0001) in the low (7.6 ± 0.7), moderate (8.4 ± 0.7), and high (9.6 ± 1.1) HGI groups. Biological variation in A1c is a robust quantitative trait that can be assessed using HGI calculated from routine clinic data. This suggests that HGI could be used clinically for more personalized assessment of complications risk.
    Pediatric Diabetes 11/2010; 11(7):455-61. · 2.08 Impact Factor
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    ABSTRACT: The A1C-Derived Average Glucose study recommended reporting A1C in estimated average glucose (eAG) equivalents. We compared eAG with self-monitored mean blood glucose (MBG) to determine whether eAG is systematically biased due to biological variation in the relationship between MBG and A1C. MBG and A1C were recorded from charts of 202 pediatric type 1 diabetic patients at 1,612 clinic visits. Patients were divided into groups with low, moderate, or high A1C bias based on a hemoglobin glycation index (HGI). The mean +/- SD values for MBG versus eAG were as follows: total population, 194 +/- 34 vs. 196 +/- 36 mg/dl; low-HGI group, 186 +/- 31 vs. 163 +/- 20 mg/dl; moderate-HGI group, 195 +/- 28 vs. 193 +/- 19 mg/dl; and high-HGI group, 199 +/- 42 vs. 230 +/- 31 mg/dl. eAG underestimated MBG in low HGI patients and overestimated MBG in high HGI patients. Disagreement between eAG and MBG downloaded from patient glucose meters will cause confusion if eAG is implemented for clinical use.
    Diabetes care 03/2010; 33(7):1449-51. · 7.74 Impact Factor
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    Jodi L Kamps, James M Hempe, Stuart A Chalew
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    ABSTRACT: Mean blood glucose (MBG) and MBG-independent factors both influence A1C levels. Race was related to A1C independent of MBG in adults. The goal of this study was to determine if racial disparity exists in A1C independent of MBG in children with diabetes. Participants included 276 children with type 1 diabetes. A1C and MBG were obtained from multiple clinic visits, and a hemoglobin glycation index (HGI) (an assessment of A1C levels independent of MBG) was calculated. A1C and HGI were analyzed controlling for age, diabetes duration, and MBG. RESULTS African Americans had statistically significantly higher A1C (9.1 +/- 0.1) and HGI (0.64 +/- 0.11) than Caucasians (A1C 8.3 +/- 0.1, HGI -0.15 +/- 0.07) independent of covariates. Because of racial disparity in A1C, which is independent of MBG, we recommend that A1C and MBG be used together to make therapeutic decisions for children with diabetes.
    Diabetes care 02/2010; 33(5):1025-7. · 7.74 Impact Factor
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    ABSTRACT: We hypothesized that labile A1C (LA1C) is directly correlated with stable A1C (SA1C) and between-patient differences in SA1C, which are independent of mean blood glucose (MBG). We measured SA1C, LA1C, MBG, and a single clinic capillary glucose (CCG) from 152 pediatric patients with type 1 diabetes. Patients were grouped as high, moderate, or low glycators by hemoglobin glycation index (HGI). LA1C and SA1C were correlated with CCG and MBG. LA1C was not correlated with SA1C (r = 0.06, P = 0.453). LA1C level was significantly associated with glycator group status (P < 0.0019) and CCG (P < 0.0001). Adjusted LA1C levels were highest in the low-HGI patients and lowest in the high-HGI group. A conventional model of SA1C being directly correlated with LA1C concentration was not confirmed. Between-patient differences in SA1C at the same MBG may be due to complex intracellular factors influencing formation of SA1C from LA1C.
    Diabetes care 11/2009; 33(2):273-4. · 7.74 Impact Factor
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    ABSTRACT: S-glutathionyl hemoglobin is a proposed biomarker of oxidative stress but has not been measured in sickle cell disease patients. Unlike the S-glutathionyl adduct of normal adult hemoglobin, S-glutathionyl sickle hemoglobin (HbSSG) cannot be directly measured by capillary isoelectric focusing, because it coelutes with fetal hemoglobin (HbF). This suggests that HbF, measured in sickle cell patients with or without hydroxyurea therapy, might contain endogenous HbSSG. As S-glutathionyl hemoglobin can form during sample storage, HbSSG could falsely elevate HbF levels in stored samples. We measured HbSSG based on the quantitative difference in the heterogeneous HbF/HbSSG peak before and after hemolysates were treated with dithiothreitol. Paired t tests showed that dithiothreitol reduced HbF/HbSSG in blood from pediatric sickle cell patients (n=25, mean decrease+/-SD=1.0%+/-0.6, P<0.05) but not in normal infants (n=25). Higher HbF levels in hydroxyurea-treated patients (n=5) were not attributable to HbSSG. HbSSG increased significantly within 1 day in samples stored at -20 degrees C but was unchanged in samples stored 60 days at-70 degrees C. We conclude that blood from sickle cell patients contained up to 2.2% HbSSG, and that endogenous HbSSG is a minor interferent in the measurement of HbF in fresh blood but a major interferent in improperly stored samples.
    Journal of Pediatric Hematology/Oncology 10/2009; 31(12):895-900. · 0.97 Impact Factor
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    ABSTRACT: Genetic variation in the number and reactivity of beta globin sulfhydryl groups causes variation in erythrocyte redox status in mouse populations. These experiments demonstrate the use of capillary isoelectric focusing for measuring endogenous S-glutathionyl hemoglobin and identifying mouse beta globin (Hbb) haplotype in inbred and outbred mouse strains with mono-cysteinyl or di-cysteinyl beta globins. Hbb haplotype can be readily determined in all strains based on characteristic differences in peak profiles or on peak mobility shift induced by thiol exchange with glutathione disulfide in vitro. This method could prove useful for in vivo study of factors that influence thiol protein modification.
    Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 07/2009; 877(28):3462-6. · 2.78 Impact Factor
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    ABSTRACT: Most hemoglobin separation techniques do not preserve the chemical structure or naturally-occurring abundance of unstable glycation products that are intermediates in the formation of stable HbA1c. Consequently, few studies have compared rates of non-enzymatic hemoglobin glycation among individuals in human populations. The present experiments used a rapid, high-resolution capillary isoelectric focusing (CIEF) technique to 1) validate procedures for assessing hemoglobin glycation in intact RBC in vitro, and 2) test the hypothesis that hemoglobin glycation rates vary in human populations and differ in RBC from non-diabetic and diabetic subjects. Blood samples were obtained from 25 non-diabetic children and 31 pediatric patients attending diabetes clinics. RBC were washed twice in PBS (pH 7.4) then incubated at 37°C in PBS supplemented with glucose (55 mmol/l). RBC were collected after 0, 1, 2, 3, 4, 5, 6 and 24 h of incubation for separation and quantification of stable and unstable hemoglobin isoforms. CIEF separated HbA1c into two peaks, A1c1 and A1c2, each of which contained unstable hemoglobin complexes with slightly different charge properties. Unlike A1c2, A1c1 also contained stable hemoglobin complexes. Both A1c1 and A1c2 proportionally increased when RBC were incubated in glucose-supplemented PBS and both decreased when glucose-loaded RBC were incubated in glucose-free PBS. Unstable hemoglobin complexes in the A1c2 peak initially formed more rapidly than those in the A1c1 peak. Although RBC from different subjects were exposed to the same glucose concentration, rates of A1c1 and A1c2 formation were highly variable between individuals and significantly higher in non-diabetic subjects compared to diabetic subjects. We conclude that 1) RBC contain at least two chemically-unstable hemoglobin complexes with different charge properties and different in vitro rates of formation, and 2) in vitro hemoglobin glycation rates are variable in human populations and markedly influenced by glycemic status. Similar between-individual variation in hemoglobin glycation in vivo could help explain why diabetes patients with similar blood glucose levels sometimes have different HbA1c levels.
    69th Scientific Sessions American Diabetes Association; 06/2009
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    ABSTRACT: Hemoglobin A1c (HbA1c) is highly correlated with mean blood glucose (MBG) levels and widely used in assessment of diabetes therapy. It has been proposed to report HbA1c in terms of an estimated average glucose (eAG) derived from the population regression of MBG on HbA1c. Pertinent to the clinical utility of eAG would be the degree of agreement between eAG and MBG estimated from multiple sampled glucose measurements over time. We examined agreement between eAG and MBG by Bland-Altman analysis from two different populations of type 1 diabetes patients: 150 children at our clinic in New Orleans and publicly available data from 1440 participants in the Diabetes Control and Complications Trial (DCCT). In New Orleans, MBG was derived from the mean of each patient's self-monitored glucose records over the 3 months before the HbA1c was obtained at the patient's clinic visit. Hemoglobin A1c was traceable to the DCCT. In DCCT participants, MBG was calculated from the patient's seven-sample glucose profile set submitted during each quarterly visit. Estimated average glucose was calculated from each individual's HbA1c using a previously reported regression equation of MBG versus HbA1c, eAG = (HbA1c * 28.7) - 47.7, derived from a continuous glucose monitoring protocol over a 12-week period. The analysis showed that there is frequent and clinically significant disagreement between MBG and eAG. Estimated average glucose over or under estimated MBG by 28.7 mg/dl or greater (HbA1c difference of 1% or greater) in approximately 33% of patients from both populations. The eAG overestimation of MBG was highest at lower MBG. The difference between eAG and MBG was skewed upward with increasing mean of eAG and MBG in the DCCT. Frequent discordance between eAG and MBG in clinical practice will likely be confusing to patients and clinicians. In patients where eAG overestimates MBG, intensive management based on eAG alone will likely lead to greater frequency of hypoglycemic episodes. To overcome these limitations of eAG, a customized assessment of HbA1c with respect to a patient's MBG should be performed using directly monitored patient glucose levels over time.
    Journal of diabetes science and technology 01/2009; 3(5):1128-35.
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    S Chalew, J M Hempe
    Diabetologia 06/2008; 51(5):903-4; author reply 905-6. · 6.49 Impact Factor
  • Diabetes 03/2008; 57(2):e4; author reply e5. · 7.90 Impact Factor
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    ABSTRACT: We studied tracking of BP and its impact on GFR in 44 PRTP followed for 56 months. Three months PT 77% had elevated SBP percentile. First year SBP and DBP correlated positively with final values (p < 0.0001, 0.0002, respectively). Pretransplant and three month PT SBP correlated positively (p = 0.02). At one yr, SBP and DBP were inversely associated with GFR (p = 0.002, p < 0.0001, respectively). SBP and BMI were positively associated at all time points. DBP was significantly higher in deceased recipients throughout the study period. Final DBP was higher (p = 0.03) and GFR lower (p = 0.04) in African-American patients. Patients with end-stage renal disease caused by glomerular disease had higher SBP (p = 0.03) and DBP (p = 0.04) than those with congenital malformations. GFR at one-yr PT (p = 0.02) and end of study (p = 0.003) was significantly lower in patients with high BP. Moreover, patients who maintained a normal systolic BP throughout the study had a significantly higher final GFR than those who were hypertensive at both time points [84 (normal BP throughout) vs. 52 mL/min/1.73 m(2) (high BP throughout), p = 0.02]. We conclude that PT hypertension is common in PRTP and predicts lower GFR.
    Pediatric Transplantation 12/2007; 11(8):860-7. · 1.50 Impact Factor

Publication Stats

558 Citations
212.44 Total Impact Points

Institutions

  • 2013
    • Louisiana State University Health Sciences Center Shreveport
      Shreveport, Louisiana, United States
  • 2002–2013
    • Research Institute for Children at Children's Hospital New Orleans
      New Orleans, Louisiana, United States
  • 1995–2013
    • Louisiana State University Health Sciences Center New Orleans
      • • Section of Pediatric Endocrinology
      • • Department of Pediatrics
      • • Research Institute For Children
      • • Department of Surgery
      New Orleans, LA, United States
  • 2010
    • Riley Hospital for Children
      Indianapolis, Indiana, United States
  • 2006
    • Children's National Medical Center
      Washington, Washington, D.C., United States
  • 1989–1994
    • University of Florida
      • • Department of Food Science and Human Nutrition
      • • Department of Nutritional Sciences
      Gainesville, FL, United States