A32 EMPAGLIFOZIN IMPROVES GASTROINTESTINAL INFLAMMATION IN A MOUSE MODEL OF COLITIS

Background

Empagliflozin (EMPA) is a highly selective sodium glucose cotransporter-2 (SGLT2) inhibitor and is increasingly being utilized as an antihyperglycemic agent in the management of type 2 diabetes. Interestingly, it has been demonstrated in human trials that EMPA treatment exerts potent cardioprotective effects by reducing cardiac inflammation independently of glycemic control. Further, EMPA has also been shown to suppress LPS-induced renal and systemic inflammation in an animal model. Based on these findings, we hypothesized that EMPA treatment may also be effective in reducing gut inflammation.

Aims

The aim of this study was to examine the effects of treatment with EMPA on gastrointestinal inflammation in an animal model of inflammatory bowel disease and to determine mechanistic insights regarding its direct effects on gut cytokine secretion.

Methods

Adult male and female IL-10-/- mice with established colitis were treated with a daily gavage of EMPA (10mg/kg; n=10) or vehicle (n=10) for 14 days. Disease activity was assessed by measurement of mouse weight, colonic weight and length, histological score, cytokine levels in colonic homogenate and lipocalin-2 levels in stool. To examine for possible direct effects of EMPA, colonic explants from wild-type (n=8) and IL-10-/- (n=8) mice were incubated with increasing doses of EMPA (0.1–5 µM) ± LPS (10µg/ml) for 2 hours and tissue levels of IL-1β and TNFα protein measured by ELISA.

Results

After 14 days EMPA treated IL-10-/- mice had a significant improvement in colonic inflammation as evidenced by decreased colonic weight to length ratio (p=0.019), decreased fecal lipocalin-2 (p=0.03), as well as decreased enterocyte injury (p=0.01), decreased lamina propria neutrophils (p=0.01) and decreased total histological score (p=0.006). EMPA treated mice also maintained their weight over the 14 days while untreated mice continued to lose weight (p=0.04). There were no significant differences in colonic homogenate levels of TNFα, IL-1β, or IL-6 or in blood glucose levels between EMPA-treated mice and controls. In addition, EMPA did not suppress levels of basal or LPS-induced TNFα and IL-1β in colonic explants from either wild-type or IL-10-/- mice suggesting that the beneficial effects in IL-10-/- mice were not due to direct effects of EMPA on colonic TNFα or IL-1β cytokine levels.

Conclusions

EMPA treatment dramatically improved histologic and fecal inflammatory markers and maintained body weight in adult IL-10-/- mice with established colitis. These findings suggest further investigations into the effects of EMPA in treating gut inflammation are warranted.

Funding Agencies

CAG, CIHR

Abstract P1-03-07: Breast cancer diagnosis is associated with relative left ventricular hypertrophy

Background: Cardiac dysfunction is a major concern for patients with breast cancer (BC) receiving adjuvant therapy. Retrospective, cross-sectional echocardiographic data suggests that patients with cancer have reduced myocardial strain prior to cancer therapy exposure. Cardiac magnetic resonance (CMR) is the gold standard imaging modality for cardiac structure and function and can also evaluate myocardial micro-architecture with T1 mapping. We hypothesized that treatment naïve patients with early-stage BC (ESBC) have abnormal myocardial tissue characteristics on CMR.

Methods: Women with newly diagnosed ESBC were prospectively recruited for CMR prior to cancer drug treatment. Those with hypertension, diabetes mellitus or prior cancer treatments were excluded. Age and sex matched healthy controls were identified from a prior prospective study. All participants underwent a non-contrast CMR scan on a 1.5T magnet. Image acquisition included cines for cardiac structure and function as well as T1 mapping using saturation recovery single-shot acquisitions. Global longitudinal strain (GLS) was derived from cine images. Demographics and imaging metrics for healthy controls and patients were compared using two-sample t-test.

Results: 106 patients with ESBC, mean age 51±9, were included along with 55 matched healthy controls. Body mass index and systolic blood pressure were similar between groups, however resting heart rate was elevated in patients compared to controls, 77±11 vs 67±11 /min respectively, p<0.001 (Table 1). On CMR there was no difference in left ventricular volume or ejection fraction however global longitudinal strain was higher in patients compared to controls, -20.9±2.3 vs -19.9±3.7%, p=0.04 (Table 2). Left ventricular mass was higher compared to controls, 52±6 and 47±6 g/m2 respectively, p<0.001. However myocardial T1 was similar between groups, T1=1198±27ms for controls vs 1206±46ms for patients, p=0.42.

Conclusions: The cardiac phenotype of patients with ESBC is characterized by relative left ventricular hypertrophy with normal myocardial tissue. Further understanding of the mechanisms involved may provide insight into the cardiovascular risk associated with BC diagnosis.

Table 1.Demographics Healthy Controls (n=55)Breast Cancer (n=106)P valueAge, years (SD)52(14)51(9)0.49Body mass index, kg/m2 (SD)26(5)27(6)0.38Hypertension, number00NADiabetes Mellitus, number00NAReceptor status, number (%)  NAER/PRNA92(87%) HER2NA74(70%) Triple negativeNA2(2%) Stage, number (%)  NA1NA43(42%) 2NA41(38%) 3NA23(20%) Systolic blood pressure, mmHg (SD)127(15)124(13)0.19Heart rate, /min (SD)67(11)77(11)<0.001SD=standard deviation, NA=not applicable

Table 2.Cardiac Magnetic Resonance Healthy Controls (n=55)Breast Cancer (n=106)P valueLVEF, % (SD)62(4)62(5)0.91Indexed LVEDV, ml/m2 (SD)69(9)72(14)0.18Indexed LV mass, g/m2 (SD)47(6)52(6)<0.001LV mass/LVEDV (SD)0.69(0.08)0.74(0.13)0.002Indexed left atrial volume, ml/m2 (SD)40(9)37(10)0.21Global longitudinal strain, % (SD)-19.9(3.7)-20.9(2.3)0.04Myocardial T1, ms (SD)1198(27)1206(46)0.42SD=standard deviation, LVEF=left ventricular ejection fraction, LVEDV=left ventricular end-diastolic volume, LV=left ventricular

Citation Format: Kirkham A, Xu L, Wang H, Chow K, Pagano JJ, White J, Haykowsky MJ, Dyck JR, Ezekowitz JA, Oudit GY, Mackey JR, Thompson RB, Pituskin E, Paterson I. Breast cancer diagnosis is associated with relative left ventricular hypertrophy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-03-07.

Successful Semi-Ambulatory Veno-Arterial Extracorporeal Membrane Oxygenation Bridge to Heart-Lung Transplantation in a Very Small Child

Lung transplantation (LTx) may be denied for children on extracorporeal membrane oxygenation (ECMO) due to high risk of cerebral hemorrhage. Rarely has successful LTx been reported in children over 10 years of age receiving awake or ambulatory veno-venous ECMO. LTx following support with ambulatory veno-arterial ECMO (VA ECMO) in children has never been reported to our knowledge. We present the case of a 4-year-old, 12-kg child with heritable pulmonary artery hypertension and refractory right ventricular failure. She was successfully bridged to heart-lung transplantation (HLTx) using ambulatory VA ECMO. Initial resuscitation with standard VA ECMO was converted to an ambulatory circuit using Berlin heart cannulae. She was extubated and ambulating around her bed while on VA ECMO for 40 days. She received an HLTx from an oversized marginal lung donor. Despite a cardiac arrest and Grade 3 primary graft dysfunction, she made a full recovery without neurological deficits. She achieved 104% force expiratory volume in 1 s 33 months post-HLTx. Ambulatory VA ECMO may be a useful strategy to bridge very young children to LTx or HLTx. Patient tailored ECMO cannulation, minimization of hemorrhage, and thrombosis risks while on ECMO contributed to a successful HLTx in our patient.

Regional distribution of putative rhythm-generating and pattern-forming components of the mammalian locomotor CPG

The ventromedial spinal cord of mammals contains a neural network known as the locomotor central pattern generator (CPG) which underlies the basic generation and coordination of muscle activity during walking. To understand how this neural network operates, it is necessary to identify, characterize, and map connectivity among its constituent cells. Recently, a series of studies have analyzed the activity pattern of interneurons that are rhythmically active during locomotion and suggested that they belong to one of two functional levels; one responsible for rhythm generation and the other for pattern formation. Here we use electrophysiological techniques to identify locomotor-related interneurons in the lumbar spinal cord of the neonatal mouse. By analyzing their activity during spontaneous deletions that occur during fictive locomotion we are able to distinguish between those likely to belong to the rhythm-generating and pattern-forming levels, and determine the regional distribution of each. Anatomical tracing techniques are also employed to investigate the morphological characteristics of cells belonging to each level. Results demonstrate that putative rhythm-generating cells are medially located and extend locally projecting axons, while those with activity consistent with pattern formation are located more laterally and send axonal projections to the lateral edge of the spinal cord, in the direction of the motoneuron pools. Results of this study provide insight into the detailed anatomical organization of the locomotor CPG.

Phase II feasibility study of concurrent radiotherapy and gemcitabine in chemonaive patients with squamous cell carcinoma of the head and neck: long-term follow up data

BACKGROUND

Radiotherapy (RT) with concurrent chemotherapy is the current standard of care for patients with unresectable locally advanced squamous cell carcinoma of the head and neck (SCCHN). Gemcitabine (GEM) is a potent radiosensitizer and in addition has activity as an anticancer agent in SCCHN.

PATIENTS AND METHODS

Twenty-six patients with locally far advanced SCCHN were enrolled in a chemoradiation feasibility study between November 1998 and September 2003. Use was made of conventionally fractionated RT and GEM 100 mg/m(2), which was given within 2 h prior to radiotherapy on a weekly basis starting on day 1 of RT. Response was assessed according to WHO criteria, toxicity according to NCI-CTC version 2.

RESULTS

The patients received a median of 7 (2-8) weekly cycles of gemcitabine and a median cumulative RT dose of 70 Gy (66-84.75). Hematologic toxicity was mild, but non-hematologic toxicity was severe: grade 3-4 stomatitis occurred in 85% of patients, dermatitis in 69%, pharyngitis/esophagitis in 81% and 80% of the patients needed a feeding tube during treatment. All 22 evaluable patients responded (50% complete, 50% partial). Median follow up of the surviving patients is 46 months. Median disease-free and overall survival is 13 months and 19 months, respectively; 27% of the patients are alive without evidence of recurrence beyond 3 years.

CONCLUSIONS

Conventionally fractionated RT in combination with GEM 100 mg/m(2) weekly is feasible and highly active in the treatment of locally advanced SCCHN. In particular, long-term local control rate is promising. Acute mucosal toxicities are significant but manageable. Long-term toxicity interferes with normal food intake.

A phase I study of bendamustine hydrochloride administered day 1+2 every 3 weeks in patients with solid tumours

The aim of the study was to determine the maximum tolerated dose (MTD), the dose limiting toxicity (DLT), and the pharmacokinetic profile (Pk) of bendamustine (BM) on a day 1 and 2 every 3 weeks schedule and to recommend a safe phase II dose for further testing. Patients with solid tumours beyond standard therapy were eligible. A 30-min intravenous infusion of BM was administered d1+d2 q 3 weeks. The starting dose was 120 mg m(-2) per day and dose increments of 20 mg m(-2) were used. Plasma and urine samples were analysed using validated high-performance liquid chromatography/fluorescence assays. Fifteen patients were enrolled. They received a median of two cycles (range 1-8). The MTD was reached at the fourth dose level. Thrombocytopaenia (grade 4) was dose limiting in two of three patients at 180 mg m(-2). One patient also experienced febrile neutropaenia. Lymphocytopaenia (grade 4) was present in every patient. Nonhaematologic toxicity including cardiac toxicity was not dose limiting with this schedule. Mean plasma Pk values of BM were tmax 35 min, t(1/2) 49.1 min, Vd 18.3 l m(-2), and clearance 265 ml min(-1) m(-2). The mean total amount of BM and its metabolites recovered in the first micturition was 8.3% (range 2.7-26%). The MTD of BM in the present dose schedule was 180 mg m(-2) on day 1+2. Thrombocytopaenia was dose limiting. The recommended dose for future phase II trials with this schedule is 160 mg m(-2) per day.

Gene transfer and metabolic modulators as new therapies for pulmonary hypertension. Increasing expression and activity of potassium channels in rat and human models

Chronic Hypoxic Pulmonary Hypertension (CH-PHT) is characterized by pulmonary artery (PA) vasoconstriction and cell proliferation/hypertrophy. PA smooth muscle cell (PASMC) contractility and proliferation are controlled by cytosolic Ca++ levels, which are largely determined by membrane potential (E(M)). E(M) is depolarized in CH-PHT due to decreased expression and functional inhibition of several redox-regulated, 4-aminopyridine (4-AP) sensitive, voltage-gated K+ channels (Kv1.5 and Kv2.1). Humans with Pulmonary Arterial Hypertension (PAH) also have decreased PASMC expression of Kv1.5 and Kv2.1. We speculate this "K+-channelopathy" contributes to PASMC depolarization and Ca++ overload thus promoting vasoconstriction and PASMC proliferation. We hypothesized that restoration of Kv channel expression in PHT and might eventually be beneficial.

METHODS

Two strategies were used to increase Kv channel expression in PASMCs: oral administration of a metabolic modulator drug (Dichloroacetate, DCA) and direct Kv gene transfer using an adenovirus (Ad5-Kv2.1). DCA a pyruvate dehydrogenase kinase inhibitor, promotes a more oxidized redox state mimicking normoxia and previously has been noted to increase K+ current in myocytes. Rats were given DCA in the drinking water after the development of CH-PHT and hemodynamics were measured approximately 5 days later. We also tested the ability of Ad5-Kv2.1 to increase Kv2.1 channel expression and function in human PAs ex vivo.

RESULTS

The DCA-treated rats had decreased PVR, RVH and PA remodeling compared to the control CH-PHT rats (n=5/group, p<0.05). DCA restored Kv2.1 expression and PASMC Kv current density to near normoxic levels. Adenoviral gene transfer increased expression of Kv2.1 channels and enhanced 4-AP constriction in human PAs.

CONCLUSION

Increasing Kv channel function in PAs is feasible and might be beneficial.

Phase I study of MEN-10755, a new anthracycline in patients with solid tumours: a report from the European Organization for Research and Treatment of Cancer, Early Clinical Studies Group

A phase I study was performed with MEN-10755, a novel anthracycline with promising preclinical antitumour activity, in patients with solid tumours to determine the maximum tolerated dose (MTD); the dose-limiting toxicities (DLTs); to document antitumour activity; and to propose a safe dose for phase II evaluation. MEN-10755 at a starting dose of 15 mg/m2/week was given by short intravenous infusion weekly for 3 weeks and cycles were repeated every 28 days. Twenty-four patients received 55 cycles. Doses of MEN-10755 were 15, 30, 40 and 45 mg/m2. At a dose of MEN-10755 45 mg/m2, treatment could not be given as planned due to neutropenia and one patient developed a decrease in cardiac function. This dose level was considered to be the MTD. Chemotherapy-naive patients could be treated with 40 mg/m2/week, and only one DLT (grade 4 neutropenia) was observed. At that dose, three of six chemotherapy pretreated patients developed a DLT during their first treatment cycle: one patient developed a grade 4 thrombocytopenia, one patient a grade 4 neutropenia and one patient developed a grade 3 acute hypersensitivity reaction resulting in discontinuation of treatment. At this dose level, one other patient did not receive treatment on day 15 as planned due to grade 3 neutropenia. No responses were observed. MEN-107555 at a dose of 30 mg/m2/week in pretreated patients and 40 mg/m2/week in chemotherapy-naive patients for three consecutive weeks followed by 1 week rest is recommended for phase II testing.

Characterization of rat liver malonyl-CoA decarboxylase and the study of its role in regulating fatty acid metabolism

In the liver, malonyl-CoA is central to many cellular processes, including both fatty acid biosynthesis and oxidation. Malonyl-CoA decarboxylase (MCD) is involved in the control of cellular malonyl-CoA levels, and functions to decarboxylate malonyl-CoA to acetyl-CoA. MCD may play an essential role in regulating energy utilization in the liver by regulating malonyl-CoA levels in response to various nutritional or pathological states. The purpose of the present study was to investigate the role of liver MCD in the regulation of fatty acid oxidation in situations where lipid metabolism is altered. A single MCD enzyme of molecular mass 50.7 kDa was purified from rat liver using a sequential column chromatography procedure and the cDNA was subsequently cloned and sequenced. The liver MCD cDNA was identical to rat pancreatic beta-cell MCD cDNA, and contained two potential translational start sites, producing proteins of 50.7 kDa and 54.7 kDa. Western blot analysis using polyclonal antibodies generated against rat liver MCD showed that the 50.7 kDa isoform of MCD is most abundant in heart and liver, and of relatively low abundance in skeletal muscle (despite elevated MCD transcript levels in skeletal muscle). Tissue distribution experiments demonstrated that the pancreas is the only rat tissue so far identified that contains both the 50.7 kDa and 54. 7 kDa isoforms of MCD. In addition, transfection of the full-length rat liver MCD cDNA into COS cells produced two isoforms of MCD. This indicated either that both initiating methionines are functionally active, generating two proteins, or that the 54.7 kDa isoform is the only MCD protein translated and removal of the putative mitochondrial targeting pre-sequence generates a protein of approx. 50.7 kDa in size. To address this, we transiently transfected a mutated MCD expression plasmid (second ATG to GCG) into COS-7 cells and performed Western blot analysis using our anti-MCD antibody. Western blot analysis revealed that two isoforms of MCD were still present, demonstrating that the second ATG may not be responsible for translation of the 50.7 kDa isoform of MCD. These data also suggest that the smaller isoform of MCD may originate from intracellular processing. To ascertain the functional role of the 50. 7 kDa isoform of rat liver MCD, we measured liver MCD activity and expression in rats subjected to conditions which are known to alter fatty acid metabolism. The activity of MCD was significantly elevated under conditions in which hepatic fatty acid oxidation is known to increase, such as streptozotocin-induced diabetes or following a 48 h fast. A 2-fold increase in expression was observed in the streptozotocin-diabetic rats compared with control rats. In addition, MCD activity was shown to be enhanced by alkaline phosphatase treatment, suggesting phosphorylation-related control of the enzyme. Taken together, our data demonstrate that rat liver expresses a 50.7 kDa form of MCD which does not originate from the second methionine of the cDNA sequence. This MCD is regulated by at least two mechanisms (only one of which is phosphorylation), and its activity and expression are increased under conditions where fatty acid oxidation increases.

Silkiness in brown mink pelts characterized with optical methods

In mink production, silkiness refers to a silky fur surface. The sensory evaluation of silkiness may be based on information perceived by the eyes and the hands. Silkiness is assumed to depend on hair fiber properties such as guard hair straightness, glossiness, and smoothness. Our objective was to characterize the dorsal surface of brown mink pelts by means of optical variables and relate these to the visual grades of silkiness, thereby forming some objective criteria of silkiness. Two groups of brown male mink pelts (winter coat) that originated from a selection trial with a focus on silkiness were used. The pelts came from a basic (Group 1992) population and a selected (Group 1994) generation. Group 1992 was graded visually on a scale from 1 to 6 (most silky); Group 1994 was graded on a scale from 1 to 8 (most silky). With goniophotometric, nondestructive methods, the reflectance from each pelt surface was measured describing the angle-dependent distribution of reflection in the shape of angular reflectance curves. The measurements were performed along (w-reflectance curve) and across (c-reflectance curve) the guard hairs. The w-curve included a maximum assumed to be related to silkiness. Specular gloss, indicated by the maximum reflectance (s) in the direction of mirror reflection, was positively correlated with silkiness. For Group 1994, s = 72.94 + .49 x silkiness; r2 = .33, P = .0003. Correspondingly, an area representing specular (S) plus diffuse (D) reflectance (S + D) under the curve was positively correlated with silkiness. A decreasing band width of the w-curve at 90% of maximum specular reflectance (w90) was related to an increase of silkiness (Group 1992: r = -.50, P < .01). Furthermore, both s/w90 and (S + D)/w90 were positively correlated with silkiness (Group 1992: r = .49, P < .01 and r = .51, P < .01, respectively). Measures of contrast gloss involving relations or differences between specular and diffuse reflectance were not suitable. From our results, a high degree of specular gloss, indicated by s, explained and was related to an essential part of silkiness and general sensory quality of the pelts investigated. Also, s was relatively easy to measure. Thus, even if the objective variables did not correlate perfectly with visual judgments, s was considered to be the most usable objective variable in characterizing silkiness.

Identification of genes regulated during mechanical load-induced cardiac hypertrophy

Cardiac hypertrophy is associated with both adaptive and adverse changes in gene expression. To identify genes regulated by pressure overload, we performed suppressive subtractive hybridization between cDNA from the hearts of aortic-banded (7-day) and sham-operated mice. In parallel, we performed a subtraction between an adult and a neonatal heart, for the purpose of comparing different forms of cardiac hypertrophy. Sequencing more than 100 clones led to the identification of an array of functionally known (70%) and unknown genes (30%) that are upregulated during cardiac growth. At least nine of those genes were preferentially expressed in both the neonatal and pressure over-load hearts alike. Using Northern blot analysis to investigate whether some of the identified genes were upregulated in the load-independent calcineurin-induced cardiac hypertrophy mouse model, revealed its incomplete similarity with the former models of cardiac growth.

Fatty acid oxidation in the reperfused ischemic heart

Myocardial ATP production is dependent chiefly on the oxidative decarboxylation of glucose and fatty acids. The co-utilization of these and other substrates is determined by both the amount of any given substrate supplied to the heart as well as by complex intracellular regulatory mechanisms. This regulated balance is altered during and after ischemia. During aerobic reperfusion of ischemic myocardium, a rapid recovery of energy production is desirable for the complete recovery of muscle contractile function. It is now clear that the type of energy substrate used by the heart during reperfusion will directly influence this contractile recovery. By increasing the relative proportion of glucose oxidized to that of fatty acids, the mechanical function of the reperfused heart can be improved. However, fatty acid oxidation recovers quickly during reperfusion and dominates as a source of oxygen consumption. These high rates of fatty acid oxidation occur at the expense of glucose oxidation, resulting in a decreased recovery of both cardiac function and efficiency during reperfusion. One contributory factor to these high rates of fatty acid oxidation is a decrease in myocardial malonyl-coenzyme A (CoA) levels. Malonyl-CoA, which is synthesized by acetyl-CoA carboxylase, is an essential metabolic intermediary in the regulation of fatty acid oxidation. A decrease in malonyl-CoA level results in an increase of carnitine palmitoyl transferase-1 mediated fatty acid uptake into the mitochondria. This mechanism seems important in the regulation of fatty acid oxidation in the postischemic heart and is discussed in detail in this review, with reference to specific clinical scenarios of ischemia and reperfusion and options for modulating cardiac energy metabolism.

Cloning and expression of rat pancreatic beta-cell malonyl-CoA decarboxylase

To gain insight into the function and regulation of malonyl-CoA decarboxylase (MCD) we have cloned rat MCD cDNA from a differentiated insulin-secreting pancreatic beta-cell-line cDNA library. The full-length cDNA sequence shows 69% identity with the cDNA cloned previously from the goose uropygial gland, and predicts a 492 amino acid protein of 54.7 kDa. The open reading frame contains an N-terminal mitochondrial targeting sequence and the C-terminal part of the enzyme ends with a peroxisomal (Ser-Lys-Leu) targeting motif. Since the sequence does not reveal hydrophobic domains, MCD is most likely expressed in the mitochondrial matrix and inside the peroxisomes. A second methionine residue, located 3' of the mitochondrial presequence, might be the first amino acid of a putative cytosolic MCD, since the nucleotide sequence around it fits fairly well with a consensus Kozak site for translation initiation. However, primer extension detects the presence of only one transcript initiating upstream of the first ATG, indicating that the major, if not exclusive, transcript expressed in the pancreatic beta-cell encodes MCD with its mitochondrial presequence. The sequence also shows multiple possible sites of phosphorylation by casein kinase II and protein kinase C. mRNA tissue-distribution analysis indicates a transcript of 2.2 kb, and that the MCD gene is expressed over a wide range of rat tissues. The distribution of the enzyme shows a broad range of activities from very low in the brain to elevated in the liver and heart. The results provide the foundations for further studies of the role of MCD in lipid metabolism and metabolic signalling in various tissues.

Phosphorylation control of cardiac acetyl-CoA carboxylase by cAMP-dependent protein kinase and 5'-AMP activated protein kinase

Acetyl-CoA carboxylase (ACC) is regarded in liver and adipose tissue to be the rate-limiting enzyme for fatty acid biosynthesis; however, in heart tissue it functions as a regulator of fatty acid oxidation. Because the control of fatty acid oxidation is important to the functioning myocardium, the regulation of ACC is a key issue. Two cardiac isoforms of ACC exist, with molecular masses of 265 kDa and 280 kDa (ACC265 and ACC280). In this study, these proteins were purified from rat heart and used in subsequent phosphorylation and immunoprecipitation experiments. Our results demonstrate that 5' AMP-activated protein kinase (AMPK) is able to phosphorylate both ACC265 and ACC280, resulting in an almost complete loss of ACC activity. Although cAMP-dependent protein kinase phosphorylated only ACC280, a dramatic loss of ACC activity was still observed, suggesting that ACC280 contributes most, if not all, of the total heart ACC activity. ACC280 and ACC265 copurified under all experimental conditions, and purification of heart ACC also resulted in the specific copurification of the alpha2 isoform of the catalytic subunit of AMPK. Although both catalytic subunits of AMPK were expressed in crude heart homogenates, our results suggest that alpha2, and not alpha1, is the dominant isoform of AMPK catalytic subunit regulating ACC in the heart. Immunoprecipitation studies demonstrated that specific antibodies for both ACC265 and ACC280 were able to coimmunoprecipitate the alternate isoform along with the alpha2 isoform of AMPK. Taken together, the immunoprecipitation and the purification studies suggest that the two isoforms of ACC in the heart exist in a heterodimeric structure, and that this structure is tightly associated with the alpha2 subunit of AMPK.

Characterization of cardiac malonyl-CoA decarboxylase and its putative role in regulating fatty acid oxidation

Malonyl-CoA is a potent inhibitor of fatty acid uptake into the mitochondria. Although the synthesis of malonyl-CoA in the heart by acetyl-CoA carboxylase (ACC) has been well characterized, no information is available as to how malonyl-CoA is degraded. We demonstrate that malonyl-CoA decarboxylase (MCD) activity is present in the heart. Partial purification revealed a protein of approximately 50 kDa. The role of MCD in regulating fatty acid oxidation was also studied using isolated, perfused hearts from newborn rabbits and adult rats. Fatty acid oxidation in rabbit hearts increased dramatically between 1 day and 7 days after birth, which was accompanied by a decrease in both ACC activity and malonyl-CoA levels and a parallel increase in MCD activity. When adult rat hearts were aerobically reperfused after a 30-min period of no-flow ischemia, levels of malonyl-CoA decreased dramatically, which was accompanied by a decrease in ACC activity, a maintained MCD activity, and an increase in fatty acid oxidation rates. Taken together, our data suggest that the heart has an active MCD that has an important role in regulating fatty acid oxidation rates.

Glucose metabolism, H+ production and Na+/H+-exchanger mRNA levels in ischemic hearts from diabetic rats

Glycolysis uncoupled from glucose oxidation is a major reason for the intracellular acidosis that occurs during severe myocardial ischemia. The imbalance between glycolysis and glucose oxidation, and the resultant H+ produced from glycolytically derived ATP hydrolysis in the diabetic rat heart is the focus of this study. Isolated working hearts from 6 week streptozotocin diabetic rat hearts were perfused with 11 mM glucose and 1.2 mM palmitate and subjected to a 25 min period of global ischemia. A second series of experiments were also performed in which hearts from control, diabetic, and islet-transplanted diabetic rats were subjected to a 30 min aerobic perfusion, followed by a 60 min period of low-flow ischemia (coronary flow = 0.5 ml/min) and 30 min of aerobic reperfusion. H+ production from glucose metabolism was measured throughout the two protocols by simultaneous measurement of glycolysis and glucose oxidation using perfusate labelled with [5-3H/U-14C]-glucose. Rates of H+ production were calculated by measuring the difference between glycolysis and glucose oxidation. The H+ production throughout the perfusion was generally lower in diabetic rat hearts compared to control hearts, while islet-transplantation of diabetic rats increased H+ production to rates similar to those seen in control hearts. This occurred primarily due to a dramatic increase in the rates of glycolysis. Despite the difference in H+ production between control, diabetic and islet-transplanted diabetic rat hearts, no difference in mRNA levels of the cardiac Na+/H+-exchanger (NHE-1) was seen. This suggests that alterations in the source of protons (i.e. glucose metabolism) are as important as alterations in the fate of protons, when considering diabetes-induced changes in cellular pH. Furthermore, our data suggests that alterations in Na+/H+-exchange activity in the diabetic rat heart occur at a post-translational level, possibly due to direct alterations in the sarcolemmal membranes.

Posttranslational modifications of the 5'-AMP-activated protein kinase beta1 subunit

The AMP-activated protein kinase (AMPK) consists of catalytic alpha and noncatalytic beta and gamma subunits and is responsible for acting as a metabolic sensor for AMP levels. There are multiple genes for each subunit and the rat liver AMPK alpha1 and alpha2 catalytic subunits are associated with beta1 and gamma1 noncatalytic subunits. We find that the isolated gamma1 subunit is N-terminally acetylated with no other posttranslational modification. The isolated beta1 subunit is N-terminally myristoylated. Transfection of COS cells with AMPK subunit cDNAs containing a nonmyristoylatable beta1 reduces, but does not eliminate, membrane binding of AMPK heterotrimer. The isolated beta1 subunit is partially phosphorylated at three sites, Ser24/25, Ser182, and Ser108. The Ser24/25 and Ser108 sites are substoichiometrically phosphorylated and can be autophosphorylated in vitro. The Ser-Pro site in the sequence LSSS182PPGP is stoichiometrically phosphorylated, and no additional phosphate is incorporated into this site with autophosphorylation. Based on labeling studies in transfected cells, we conclude that alpha1 Thr172 is a major, although not exclusive, site of both basal and stimulated alpha1 phosphorylation by an upstream AMPK kinase.

Idiopathic dilation of the right atrium: case report and survey of the literature

Idiopathic dilation of the right atrium (IDRA) is a rare cardiac anomaly of unknown etiology. Whether it is an acquired or congenital lesion is controversial. A case of IDRA detected in utero and confirmed postnatally is reported. The postnatal course was complicated by the development of atrial flutter successfully treated with sotalol. A review of the literature concerning IDRA is presented.

Structure and analysis of the mouse Na+/H+ exchanger (NHE1) gene: homology and conservation of splice sites

The Na+/H+ exchanger is a widely distributed integral membrane protein that is responsible for pH regulation in mammalian tissues. We have cloned and analyzed the NHE1 isoform of the mouse genomic Na+/H+ exchanger. A clone from a mouse genomic library contained the NHE1 promoter region and the 5'-untranslated region. It also contained the first 121 amino acids of the coding region of the Na+/H+ exchanger. A splice site occurred after amino acid 121, at the same region as in the human NHE1 gene. The deduced amino terminal coding sequence was 76 and 88% identical to the human and rat NHE1 sequences respectively. The 5'-untranslated region was highly homologous to that of other species and two minicistrons contained in the human Na+/H+ exchanger were present in the mouse sequence. The results show that the deduced protein sequence of the mouse NHE1 gene has a high level of homology with other species and that the splice site of the first intron is conserved. These results suggest that the first large intron may play an important role in the NHE1 gene expression.

A novel method to create atrial septal defect using a cutting balloon in piglets

A new method of creating atrial septal defect, using a 3- or 4-blade cutting balloon catheter combined with conventional static balloon dilation, is discussed. Radially directed surgical cuts made in the atrial septum were enlarged by balloon angioplasty, producing defects measuring 3 to 8 mm, with a mean Qp/Qs of 1.96/L.

Regulation of 5'-AMP-activated protein kinase activity by the noncatalytic beta and gamma subunits

The mammalian 5'-AMP-activated protein kinase is a heterotrimer consisting of an alpha catalytic subunit and beta and gamma noncatalytic subunits, each of which is represented in a larger isoprotein family, related to the SNF1 kinase and its interacting proteins in yeast. In this study, we have used mammalian cell transfection to compare the activities of the two alpha subunit isoforms, alpha-1 and alpha-2, and to study the influence of the noncatalytic subunits on enzyme subunit association and activity. Expression of epitope-tagged protein subunits in COS7 cells indicates detectable but low level kinase activity for each of the two catalytic alpha subunits. Co-expression of alpha subunits with the beta or gamma subunits modestly increases kinase activity accompanied by the formation of alpha/beta or alpha/gamma heterodimers. Co-expression of all three subunits, however, is accompanied by a 50-110-fold increase in kinase activity with the formation of a heterotrimeric complex. In addition to binding of each noncatalytic subunit to the alpha subunit, the beta and gamma subunits bind to each other, likely resulting in a more stable heterotrimeric complex. The increase in kinase activity associated with expression of this heterotrimer is due both to an increase in enzyme-specific activity (units/enzyme mass) and to an apparent enhanced alpha subunit expression. Co-expression of a catalytically defective alpha subunit or the beta/gamma-binding COOH-terminal domain of the alpha subunit results in reduced heterotrimeric kinase activity. The synergistic positive regulatory roles for both the noncatalytic beta and gamma subunits of 5'-AMP-activated protein kinase contrasts with the Snf1p kinase, where only heterodimers of Snf1p and Snf4p seem to be required for maximum kinase activity.

Transaortic balloon valvoplasty of the pulmonary valve

An unconventional transaortic to transductal approach was performed to perforate and dilate the pulmonary valve in pulmonary atresia. Ductal arteriosus patency was maintained by prostaglandin.

Non-catalytic beta- and gamma-subunit isoforms of the 5'-AMP-activated protein kinase

The mammalian 5'-AMP-activated protein kinase (AMPK) is a heterotrimeric protein consisting of alpha-, beta-, and gamma-subunits. The alpha-subunit is the catalytic subunit and is related to the yeast Snf1p kinase. In this study, we report the cloning of full-length cDNAs for the non-catalytic beta- and gamma-subunits. The rat liver AMPK beta-subunit clone predicts a protein of 30,464 Da, which is related to the Sip1p, Sip2p, and Gal83p subfamily of yeast proteins that interact with Snf1p and are involved in glucose regulation of gene expression. The AMPK beta-subunit, when expressed in bacteria and in mammalian cells, migrates anomalously on SDS gels at an apparent molecular mass of 40 kDa. Rat and human liver AMPK gamma-subunit clones predict a protein of 37,577 Da (AMPK-gamma1), which is related to the yeast Snf4p protein that copurifies with Snf1p and to a larger family of other human AMPK gamma-isoforms. The mRNAs for both AMPK- beta and AMPK-gamma1 are widely expressed in rat tissues, consistent with a broad role for AMPK in cellular regulation. These data reveal a mammalian multisubunit protein kinase strikingly similar to the multisubunit glucose-sensing Snf1 kinase complex. The identification of isoform families for the AMPK subunits indicates the potential diversity of the roles of this highly conserved signaling system in nutrient regulation and utilization in mammalian cells.

Regulation of NHE1 expression in L6 muscle cells

We examined regulation of expression of the NHE1 promoter on rat L6 cells. Transient transfection of these cells showed that there are two regions critical for basal expression in this cell type. One is from bp -155 to -171 and second more proximal region is between bp -92 and -125. When cells were induced to differentiate by serum withdrawal, mRNA levels rose 2-3-fold. To investigate the mechanisms of this phenomenon a series of stable transfectants were made of the NHE1 promoter in L6 cells. Muscle differentiation caused a significant stimulation of transcriptional activity in the stable cells containing the more distal regions of the promoter. The results show that basal expression of the NHE1 promoter is mediated largely by two proximal regions of the gene. However, during the process of differentiation more distal regions of the gene are involved in elevation of the level of expression.

Regulation of NHE-1 promoter in mammalian myocardium

The Na+/H exchanger (NHE-1) is an integral membrane protein responsible for intracellular pH regulation in the myocardium and other tissues. The NHE-1 isoform is universally distributed in mammalian cells. We examined regulation of a 1.1-kb fragment of the NHE-1 promoter in neonatal rat cardiomyocytes. Deletion of most of the promoter up to an AP-2 site reduced activity 75%. Further deletion of the promoter or mutation of the AP-2 site reduced or eliminated activity almost completely. Gel mobility shift assay showed that purified AP-2 protein or AP-2-like protein from nuclear extracts of isolated myocytes can bind to DNA of the NHE-1 protein. External acidosis did not cause increased transcription from the promoter. Removal of serum from the medium reduced activity of the NHE-1 promoter. The elements responsible for activation of the promoter by serum were contained within both the 1.1-kb and AP-2-containing region. The results show that the cis-acting putative AP-2 site and the presence of serum are important in NHE-1 expression, whereas external acidosis had no direct effect on the promoter.

Specific activation of the Na+/H+ exchanger gene during neuronal differentiation of embryonal carcinoma cells

We examined the regulation of the Na+/H+ exchanger gene during differentiation of the P19 mouse embryonal carcinoma cells. Treatment of P19 cells with retinoic acid induces the development of neurons, astroglia, and microglia cells. Upon retinoic acid-induced differentiation of P19 cells, there was an early and rapid 10-fold increase in NHE1 transcription. A proximal cis-acting AP-2 site of the NHE1 promoter was sufficient for stimulation of transcription of the gene by differentiation. Bandshift experiments demonstrated that in retinoic acid-treated cells there was an elevated level of AP-2 transcription factor binding to the AP-2 consensus site of the Na+/H+ exchanger gene. In the differentiation defective mutant RAC65, the effect of differentiation on Na+/H+ exchanger gene expression was reduced by 60%. Examination of Na+/H+ exchanger activity showed that retinoic acid-treated P19 cells recovered from an acid load at a rate approximately three times greater than untreated cells. The increases in gene expression and protein activity preceded major changes in cell morphology, suggesting that the initiation of differentiation is linked to NHE1 gene expression. Our findings show for the first time that the NHE1 gene is activated early in cell differentiation and that this activation may play an important role in the process of neuronal cell differentiation.

Induction of expression of the sodium-hydrogen exchanger in rat myocardium

OBJECTIVE

The aim was to examine the regulation of the cardiac Na+/H+ exchanger NHE-1 isoform mRNA in response to ischaemia and acidosis in the mammalian myocardium.

METHODS

Male Sprague Dawley rat hearts were perfused in a non-circulated retrograde fashion according to the Langendorff method. Hearts were perfused for 3 h at flow rates of either 10 ml.min-1 (control), or 3, 1, or 0 ml.min-1 (ischaemia) followed by 5 min of reperfusion. Hearts were immediately frozen in liquid N2, and stored at -80 degrees C until ready for RNA isolation. Northern blot analysis was used to examine expression of the NHE-1 isoform of the Na+/H+ exchanger message in these isolated perfused hearts. Activity of the Na+/H+ exchanger was assessed in primary cultures of neonatal rat myocytes under either control conditions or after treatment with chronic, low external pH.

RESULTS

A decrease in developed tension and an increase in resting tension was observed which was dependent upon the severity of the ischaemic episode. Low flow ischaemia of 3 ml.min-1 caused increased Na+/H+ exchanger message levels, while perfusion at more reduced flow rates eliminated the increase. Treatment of primary cultures of isolated myocytes with low external pH resulted in increased ability to recover from an acute acid load.

CONCLUSIONS

Low flow ischaemia can increase the Na+/H+ exchanger message in the intact mammalian myocardium. More severe ischaemia prevents the increase, suggesting that severely damaged tissue may not be capable of the ischaemic response. Primary cultures of isolated myocytes can respond to chronic low external pH by increasing Na+/H+ exchanger activity.

Activation of the Na+/H+ exchanger gene by the transcription factor AP-2

We have isolated and characterized regions important for expression of the mouse Na+/H+ exchanger gene. A 1.1-kilobase fragment upstream of the 5'-untranslated region contains specific DNA motifs characteristic of promoter and enhancer elements including a TATA box, two CAAT boxes, an SP-1 site, a cyclic AMP response element-binding site, and an AP-2-like site. This 1.1-kilobase fragment directs transcription of a luciferase reporter gene in mouse fibroblasts (NIH 3T3) and human Hep G2 cells. Deletion or mutation of an AP-2-like site 100 base pairs from the start site of transcription resulted in loss of most of the reporter plasmid activity. In addition, cotransfection of an AP-2 expression plasmid and the mouse promoter/luciferase plasmid increased the amount of Na+/H+ exchanger-directed transcription in AP-2-deficient Hep G2 cells. Moreover, mobility shift analysis indicated that a putative AP-2-binding site is capable of binding purified AP-2 protein and a specific protein from nuclear extracts of NIH 3T3 cells. The results show that the transcription factor AP-2 may play an important role in regulation of transcription of the mouse Na+/H+ exchanger gene.

Cardiac dysfunction late after cardiotoxic therapy for childhood cancer

Despite a wealth of data documenting acute cardiac injury from anthracycline therapy and/or mediastinal radiotherapy used for childhood cancer, little information is available on the long-term consequence of these insults. Twenty-nine patients (mean age 15 +/- 4.3 years) from The Late Effects Follow-Up Clinic For Childhood Cancer study, who had been in continuous, complete remission and off chemotherapy for a minimum of 2 years (mean follow-up 7.2 +/- 3.2) were studied. All patients had normal ejection fractions before and during cancer therapy and all were in New York Heart Association class I at the time of study. Systolic and diastolic functions were assessed by 2-dimensional echocardiography, Doppler flow velocity, and radionuclide angiography, and results were compared with normal control subjects. Left ventricular mass and mass index were significantly reduced in the patient population. Fractional shortening was decreased overall and end-systolic wall stress was much higher in patients than in controls. However, contractility, as assessed by the relation of wall stress to rate-corrected velocity of shortening, was decreased by > or = 2 SDs in only 6 of 28 patients, and the force-mass relation was actually increased in the patient group as a whole. Mitral valve inflow velocities were significantly increased but the pattern was abnormal. These results suggest a pattern consistent with a thin-walled, complaint left ventricle with reduced muscle mass performing under above-normal levels of wall stress. Contractility measurements were normal or increased in the group, but some patients clearly demonstrated development of reduced contractile function.(ABSTRACT TRUNCATED AT 250 WORDS)

Pediatric transesophageal echocardiography in the evaluation of acute disruption of the mitral valve following blunt thoracic trauma: case report

Disruption of the mitral valve following blunt thoracic trauma has been only occasionally reported. A case of a pediatric patient with this complication is presented and the value of transesophageal echocardiography in diagnosis and management is documented.

Cloning and analysis of the human myocardial Na+/H+ exchanger

The Na+/H+ exchanger is an integral membrane protein that is universally distribute in mammalian tissues and is responsible for intracellular pH regulation. Several isoforms of the Na+/H+ exchanger exist (NHE-1-NHE-4). The first that was cloned is the amiloride sensitive isoform (NHE-1). Using a fragment of the rabbit cardiac Na+/H+ exchanger cDNA clone we isolated and sequenced Na+/H+ exchanger cDNA from a human heart coding for the complete human Na+/H+ exchanger (NHE-1 isoform). Two overlapping cDNA clones were obtained, giving a combined sequence that contained both 3' and 5' untranslated regions. The 5' and 3' untranslated regions proved to be highly homologous to human sequences described earlier but contained some variations that could affect the mRNA stability and/or the efficiency of translation of the Na+/H+ exchanger. Northern blot analysis and reverse transcriptase polymerase chain reaction confirmed the presence of the 5 kb NHE-1 message in primary cultures of isolated myocytes.

Characterization of the placental brush border membrane Na+/H+ exchanger: identification of thiol-dependent transitions in apparent molecular size

We examined the protein and mRNA encoding the amiloride-sensitive Na+/H+ exchanger from human placenta. Reverse transcriptase PCR of human placental RNA and a human choriocarcinoma cell line showed that the message for the amiloride-sensitive Na+/H+ exchanger from human placenta. Reverse transcriptase PCR of human placental RNA and a human choriocarcinoma cell line showed that the message for the amiloride-sensitive Na+/H+ exchanger is present in the placenta and its derived cell line. Northern blot analysis showed only one species of Na+/H+ exchanger mRNA, of about 5 kb in size. To examine the Na+/H+ exchanger protein two different affinity-purified antibodies were produced against the C-terminal cytoplasmic region of the Na+/H+ exchanger. The antibodies both identified a 105 kDa protein in human placental brush border membrane vesicles. Under non-reducing conditions the amount of 105 kDa protein was greatly decreased, while a 205 kDa protein became apparent. This is probably a dimer of the 105 kDa protein. The monomer-to-dimer transition was dependent on the concentration of beta-mercaptoethanol. The results show that the amiloride-sensitive Na+/H+ exchanger is relatively abundant in human placenta and that it can exist as a larger 205 kDa protein linked by disulphide bonds.

Identification of a small Na+/H+ exchanger-like message in the rabbit myocardium

We examined the Na+/H+ exchanger message in isolated perfused rabbit hearts using Northern blot analysis with cDNA encoding for the rabbit cardiac Na+/H+ exchanger. A cDNA probe from the coding region of the rabbit myocardial Na+/H+ exchanger hybridized to mRNA of 5 kb under high stringency, and to a second 3.8 kb mRNA species under low stringency. When Northern blots were re-probed with a section of the 3'-untranslated region of the cDNA, the 5 kb message was apparent while the smaller 3.8 kb message was not. If isolated working rabbit hearts were subjected to ischemia we observed increases in the 3.8 kb message. Overall, the results show that a 3.8 kb mRNA product, which is homologous to the amiloride sensitive Na+/H+ exchanger, exists in the myocardium and increases during ischemia in the myocardium.

Balloon atrial septostomy under transesophageal echocardiographic guidance

Balloon atrial septostomy is an established method of palliation for several forms of congenital heart disease. Previously performed under fluoroscopic x-ray control, recent reports have demonstrated the utility of transthoracic echocardiographic monitoring. We report the first application of uniplane transesophageal echocardiography (TEE) (6.7-mm probe) as an alternative imaging modality for control of balloon atrial septostomy on neonates in the intensive care unit.

Results of the Fontan procedure for patients with univentricular heart

One hundred twenty-four consecutive patients with univentricular heart undergoing the Fontan operation were reviewed. Patients with tricuspid atresia or biventricular heart with hypoplasia of one ventricle were excluded. Eighty-four patients had left ventricular morphology. Atrioventricular connection was double-inlet (n = 76), common (n = 29), absent left atrioventricular connection (n = 14), and absent right atrioventricular connection (n = 5). Actuarial survival was 77% (70% confidence limits, 73% to 81%) at 1 year, 66% (70% confidence limits, 60% to 72%) at 5 years, and 49% (70% confidence limits, 36% to 61%) at 10 years, indicating a continuing risk for premature death. Multivariate analysis identified preoperative ventricular function and hypertrophy as risk factors for survival. High postrepair right atrial pressure (greater than 15 mm Hg) emerged as a strong intraoperative predictor of survival. Logistic regression analysis of these factors predicts high probability of death for certain subgroups of patients after the Fontan operation. Forty-four percent (n = 53) of these original 124 patients are alive and in New York Heart Association class I at follow-up. Thirty-eight percent (n = 33) of survivors have worse ventricular function than preoperative. Long-term survival is disappointing. Certain identifiable subgroups of patients with univentricular heart have unacceptable risks for the Fontan operation and should have alternate management. High postrepair right atrial pressure is an ominous sign, and if it persists the Fontan should be fenestrated or taken down.