S. E. Anderson

Na/H exchange inhibition protects newborn heart from ischemia/reperfusion injury by limiting Na+-dependent Ca2+ overload

The results of the Guardian/Expedition trials demonstrate the need for more precisely controlled studies to inhibit Na/H exchange (NHE1) during ischemia/reperfusion. This is because overwhelming evidence is consistent with the hypothesis that myocardial ischemic injury results in part from increases in intracellular Na (Nai) mediated by NHE1 that in turn promote Na/Ca exchanger-mediated increases in intracellular Ca ([Ca]i) and Ca-dependent cell damage. We used a more potent and specific NHE1 inhibitor HOE 694 (HOE) to test whether inhibition of NHE1 during ischemia limits increases in Nai and [Ca]i in newborns. NMR was used to measure pHi, Nai, [Ca]i, and ATP in isolated newborn rabbit hearts. Perfusion pressure, left ventricular developed pressure, and creatine kinase were measured. HOE was added before global ischemia. Results are reported as mean ± SE. Nai (mEq/kg dry weight) rose from 11.6 ± 0.9 before ischemia to 114.0 ± 16.1 at the end of ischemia and recovered to 55.2 ± 11.8 in the control group. During ischemia and reperfusion, the corresponding values for Nai in the HOE group (63.1 ± 8.4 and 15.9 ± 2.5, respectively, P < 0.05) were lower than control. In the control group [Ca]i (nM/L) rose from 331 ± 41 to 1069 ± 71 and recovered to 814 ± 51, whereas in the HOE group [Ca]i rose less (P < 0.05): 359 ± 50, 607 ± 85, and 413 ± 40, respectively. Total creatine kinase release was significantly reduced in the HOE group. Perfusion pressure and left ventricular developed pressure also recovered significantly better in the HOE group than in the control. In conclusion, NHE1 inhibition diminishes ischemia-induced increases in Nai and therefore [Ca], and thus diminishes myocardial injury in neonatal hearts.

Cognitive dysfunction associated with diabetic ketoacidosis in rats

BACKGROUND Type 1 diabetes mellitus in children may be associated with neurocognitive deficits of unclear cause. A recent retrospective study in children suggested possible associations between diabetic ketoacidosis (DKA) and decreased memory. The current investigation was undertaken to determine whether cognitive deficits could be detected after a single episode of DKA in an animal model. METHODS Streptozotocin was used to induce diabetes in juvenile rats, and rats were then treated with subcutaneous insulin injections. In one group, insulin was subsequently withdrawn to allow development of DKA, which was then treated with insulin and saline. After recovery from DKA, subcutaneous insulin injections were re-started. In the diabetes control group, rats continued to receive subcutaneous insulin and underwent sham procedures identical to the DKA group. One week after recovery, cognitive function was tested using the Morris Water Maze, a procedure that requires rats to locate a hidden platform in a water pool using visual cues. During a 10 day period, mean time to locate the platform (latency) during 4 trials per day was recorded. RESULTS Comparison of latency curves demonstrated longer mean latency times on days 7 and 8 in the DKA group indicating delayed learning compared to diabetic controls. CONCLUSIONS These data demonstrate that a single DKA episode results in measurable deficits in learning in rats, consistent with findings that DKA may contribute to neurocognitive deficits in children with type 1 diabetes.

Hyponatremia in Pediatric Diabetic Ketoacidosis: Reevaluating the Correction Factor for Hyperglycemia

H yperglycemia osmotically draws water into the vascular space, decreasing serum sodium concentration. In 1973, Katz theorized that sodium concentration should decrease by 1.6 mmol/L for every 100-mg/dL increase in serum glucose concentration (to convert serum glucose to millimoles per liter, multiply by 0.0555). More recent calculations suggest coefficients ranging from 1.35 to 2.0. A study in adults found empirical values ranging from 2.4 to 4.0, contrasting with theoretical estimates. We empirically determined the sodium correction factor for hyperglycemia using data from children with diabetic ketoacidosis.

Brain cell swelling during hypocapnia increases with hyperglycemia or ketosis

Severe hypocapnia reduces cerebral blood flow (CBF) and is known to be a risk factor for diabetic ketoacidosis (DKA)‐related cerebral edema and cerebral injury in children. Reductions in CBF resulting from hypocapnia alone, however, would not be expected to cause substantial cerebral injury. We hypothesized that either hyperglycemia or ketosis might alter the effects of hypocapnia on CBF and/or cerebral edema associated with CBF reduction.

Characterizing blood–brain barrier perturbations after exposure to human triglyceride-rich lipoprotein lipolysis products using MRI in a rat model

Previous studies indicated hyperlipidemia may be a risk factor for Alzheimers disease, but the contributions of postprandial triglyceride‐rich lipoprotein (TGRL) are not known. In this study, changes in blood–brain barrier diffusional transport following exposure to human TGRL lipolysis products were studied using MRI in a rat model.

Glucose Uptake and Intracellular pH in a Mouse Model of Ductal Carcinoma In situ (DCIS) Suggests Metabolic Heterogeneity

Mechanisms for the progression of ductal carcinoma in situ (DCIS) to invasive breast carcinoma remain unclear. Previously we showed that the transition to invasiveness in the mammary intraepithelial neoplastic outgrowth (MINO) model of DCIS does not correlate with its serial acquisition of genetic mutations. We hypothesized instead that progression to invasiveness depends on a change in the microenvironment and that precancer cells might create a more tumor-permissive microenvironment secondary to changes in glucose uptake and metabolism. Immunostaining for glucose transporter 1 (GLUT1) and the hypoxia marker carbonic anhydrase 9 (CAIX) in tumor, normal mammary gland and MINO (precancer) tissue showed differences in expression. The uptake of the fluorescent glucose analog dye, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG), reflected differences in the cellular distributions of glucose uptake in normal mammary epithelial cells (nMEC), MINO, and Met1 cancer cells, with a broad distribution in the MINO population. The intracellular pH (pHi) measured using the fluorescent ratio dye 2′,7′-bis(2-carboxyethyl)-5(6)-155 carboxyfluorescein (BCECF) revealed expected differences between normal and cancer cells (low and high, respectively), and a mixed distribution in the MINO cells, with a subset of cells in the MINO having an increased rate of acidification when proton efflux was inhibited. Invasive tumor cells had a more alkaline baseline pHi with high rates of proton production coupled with higher rates of proton export, compared with nMEC. MINO cells displayed considerable variation in baseline pHi that separated into two distinct populations: MINO high and MINO low. MINO high had a noticeably higher mean acidification rate compared with nMEC, but relatively high baseline pHi similar to tumor cells. MINO low cells also had an increased acidification rate compared with nMEC, but with a more acidic pHi similar to nMEC. These findings demonstrate that MINO is heterogeneous with respect to intracellular pH regulation which may be associated with an acidified regional microenvironment. A change in the pH of the microenvironment might contribute to a tumor-permissive or tumor-promoting progression. We are not aware of any previous work showing that a sub-population of cells in in situ precancer exhibits a higher than normal proton production and export rate.

Response to: Effect of inhibition of Na+/Ca+ exchanger at the time of myocardial reperfusion on hypercontracture and cell death

See article by Inserte et al. [12] (pages 739–748) in this issue. The functional and biochemical characterization of the sarcolemmal Na/Ca exchanger (NCX) testifies to the success of novel approaches by numerous investigators [1,2] and, in particular, development of new techniques for measuring sarcolemmal ion fluxes and cytosolic Na and Ca concentrations ([Na]i and [Ca]i) [3,4]. Our current understanding of the role NCX plays in ischemia-induced changes in cytosolic calcium concentration ([Ca]i) is, to a great extent, derived from studies which used recently developed technology to measure intracellular Na and Ca in the intact heart [5,6]. Much of this work supports the general hypothesis that ischemia-induced myocardial injury is largely the result of the following chain of events: (1) increased anerobic metabolism increases cytosolic proton concentration ([H]i); (2) protons stimulate Na-dependent pH regulatory transporters such as Na/H exchange and Na-HCO3 cotransport; (3) increased Na uptake increases [Na]i; (4) decreased driving force for Ca extrusion via NCX increases [Ca]i; (5) a cascade of Ca-dependent events leads to cell injury and/or death [7–9]. Although this series of events has been articulated by numerous investigators and supported by numerous studies, … * Tel.: +1-530-752-7621; fax: +1-530-752-5423 seanderson{at}ucdavis.edu