Minimal Model-Derived Insulin Sensitivity Index Underestimates Insulin Sensitivity in Black Americans.

OBJECTIVE: To examine the ethnic differences in insulin sensitivity (SI) as measured by the minimal model approach (SI-MM) and the reference method, the euglycemic-hyperinsulinemic clamp (EHC). RESEARCH DESIGN AND METHODS: In a prospective study design, thirty Black Americans (BA) were age, sex, and BMI matched with non-Hispanic Whites (NHW). Participants underwent frequently sampled intravenous tolerance test (FSIVGTT) and EHC on 2 separate days during a single visit. RESULTS: SI-MM values were significantly lower in BA when compared with NHW (0.035 ± 0.025 vs. 0.058 ± 0.036 [dL/min]/[µU/mL]; P = 0.003). However, there were no ethnic differences in SI measured by EHC (0.028 ± 0.012 vs. 0.035 ± 0.019 [dL/min]/[µU/mL]; P = 0.18). CONCLUSIONS: SI-MM systematically underestimates SI in BA when compared with NHW. These findings suggest that studies inferring lower SI in BA based on FSIVGTT and SI-MM should be interpreted cautiously.

The proteome of sickle cell disease: insights from exploratory proteomic profiling.

The expanding realm of exploratory proteomics has added a unique dimension to the study of the complex pathophysiology involved in sickle cell disease. A review of proteomic studies published on sickle cell erythrocytes and plasma shows trends of upregulation of antioxidant proteins, an increase in cytoskeletal defects, an increase in protein repair and turnover components, a decrease in lipid raft proteins and apolipoprotein dysregulation. Many of these findings are consistent with the pathophysiology of sickle cell disease, including high oxidant burden, resulting in damage to cytoskeletal and other proteins, and erythrocyte rigidity. More unexpected findings, such as a decrease in lipid raft components and apolipoprotein dysregulation, offer previously unexplored targets for future investigation and potential therapeutic intervention. Exploratory proteomic profiling is a valuable source of hypothesis generation for the cellular and molecular pathophysiology of sickle cell disease.

Proteomic identification of altered apolipoprotein patterns in pulmonary hypertension and vasculopathy of sickle cell disease.

Pulmonary arterial hypertension (PAH) is emerging as a major complication and independent risk factor for death among adults with sickle cell disease (SCD). Using surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF MS), we searched for biomarkers of PAH in plasma specimens from 27 homozygous sickle cell anemia (HbSS) patients with PAH and 28 without PAH. In PAH patients, analysis consistently showed lower abundance of a 28.1-kDa peak (P < .001), identified by high-resolution mass spectrometry as the oxidant-scavenging protein apolipoprotein A-I (apoA-I), which correlated with clinical assays of apoA-I (r = .58, P < .001) and high-density lipoprotein (HDL) levels (r = .50, P = .001). Consistent with endothelial dysfunction that may mediate this effect in PAH, HbSS patients with lower apoA-I levels also displayed impaired vasodilatory responses to acetylcholine (mean +/- SEM, 189% +/- 34% [n = 13] vs 339% +/- 51% [n = 13], P < .001). As a group, patients with SCD demonstrated significantly lower apoA-I levels than African-American control subjects. The PAH cohort was further characterized by high levels of apolipoproteins A-II and B and serum amyloid A, and low levels of haptoglobin dimers and plasminogen. These results imply a relationship of apolipoproteins to the development of PAH vasculopathy in SCD, potentially involving an unexpected mechanistic parallel to atherosclerosis, another proliferative vasculopathy.

Ceruloplasmin is a NO oxidase and nitrite synthase that determines endocrine NO homeostasis.

Nitrite represents a bioactive reservoir of nitric oxide (NO) that may modulate vasodilation, respiration and cytoprotection after ischemia-reperfusion injury. Although nitrite formation is thought to occur via reaction of NO with oxygen, this third-order reaction cannot compete kinetically with the reaction of NO with hemoglobin to form nitrate. Indeed, the formation of nitrite from NO in the blood is limited when plasma is substituted with physiological buffers, which suggests that plasma contains metal-based enzymatic pathways for nitrite synthesis. We therefore hypothesized that the multicopper oxidase, ceruloplasmin, could oxidize NO to NO+, with subsequent hydration to nitrite. Accordingly, plasma NO oxidase activity was decreased after ceruloplasmin immunodepletion, in ceruloplasmin knockout mice and in people with congenital aceruloplasminemia. Compared to controls, plasma nitrite concentrations were substantially reduced in ceruloplasmin knockout mice, which were more susceptible to liver infarction after ischemia and reperfusion. The extent of hepatocellular infarction normalized after nitrite repletion. These data suggest new functions for the multicopper oxidases in endocrine NO homeostasis and nitrite synthesis, and they support the hypothesis that physiological concentrations of nitrite contribute to hypoxic signaling and cytoprotection.