Abstract 164: The Chaperone Holdase Bag6 Modulates the Intracellular Fate of Newly Synthesized ApoB100

Apolipoprotein B-100 (apoB) is the central protein component of very low density lipoproteins (VLDL) and is subject to endoplasmic reticulum-associated degradation (ERAD). Hepatic assembly of VLDL particles is monitored by the cellular quality control machinery, which determines whether a properly formed lipoprotein is secreted or the inadequately lipidated apoB protein is degraded. Changes in lipid supply, ER folding capacity or ERAD pathway function can alter VLDL output from HepG2 cells. Bag6 is a cytosolic protein that has a role in the bilayer integration of proteins and is also implicated in maintaining the solubility of proteasome substrates that contain exposed hydrophobic regions. Notably, Bag6 has been observed to interact with the ERAD components gp78 and p97, which are known to facilitate apoB degradation. The goal of this study was to evaluate the role of cytosolic Bag6 in apoB metabolism in HepG2 cells. When MG132 was used to inhibit proteasomal degradation of apoB, Bag6 was co-immunoprecipitated with apoB as determined by functional proteomics and immunoblot analysis. Conversely, if VLDL assembly was enhanced by treatment of the cells with the MEK/ERK inhibitor U0126, both the Bag6-apoB and p97-apoB associations were no longer detectable. Metabolic labelling studies indicated that siRNA knockdown of Bag6 did not alter the initial rate of apoB biosynthesis, but decreased the secretion of newly synthesized apoB. The decrease in apoB secretion with Bag6 knockdown could not be reversed by U0126. In addition, Bag6 knockdown decreased the effectiveness of MG132 as an inhibitor of cellular apoB degradation even though ubiquitination of apoB appeared to be unaffected. These observations suggest that Bag6 may be a component of the ERAD pathway that modulates VLDL assembly. Reduction of Bag6 partially decreases both secretion and MG132-inhibitable degradation of apoB, suggesting that another mechanism is also involved in apoB degradation. We hypothesize that the “holdase” function of Bag6 may temporarily stabilize exposed hydrophobic domains of apoB prior to its progression to assembly or degradation.

Drosophila female precopulatory behavior is modulated by ecdysteroids

The effect of ecdysteroid signaling on Drosophila female precopulatory behavior was investigated using two types of mutants with either globally reduced ecdysteroid availability or reduced expression of ecdysone receptors in fruitless neurons, known to control sexual behavior. While being courted by males, mutant females performed significantly less full ovipositor extrusion behavior to reject male copulation attempts. Ecdysteroid depleted females (ecdysoneless(1)) performed male-like courtship behaviors, including unilateral wing extension and song production with patterns very similar to male courtship song. These results support the hypothesis that ecdysteroids modulate female sexual behavior, perhaps acting as a regulator of sexual motivation, and as a component affecting the performance of sex specific behavior patterns.

Drosophila male courtship behavior is modulated by ecdysteroids

Temperature-dependent induction of ecdysteroid deficiency in the ecdysoneless mutant ecd(1) adult Drosophila melanogaster results in altered courtship behavior in males. Ecdysteroid deficiency brings about significantly elevated male-male courtship behavior including song production resembling that directed toward females. Supplementation with dietary 20-hydroxyecdysone reduces male-male attraction, but does not change motor activity, courtship patterns or attraction to females. These observations support the hypothesis that reduced levels of ecdysteroids increase the probability that male fruit flies will display courtship behaviors to male stimuli.

Ubiquitination regulates the assembly of VLDL in HepG2 cells and is the committing step of the apoB-100 ERAD pathway

Apolipoprotein B-100 (apoB-100) is degraded by endoplasmic reticulum-associated degradation (ERAD) when lipid availability limits assembly of VLDLs. The ubiquitin ligase gp78 and the AAA-ATPase p97 have been implicated in the proteasomal degradation of apoB-100. To study the relationship between ERAD and VLDL assembly, we used small interfering RNA (siRNA) to reduce gp78 expression in HepG2 cells. Reduction of gp78 decreased apoB-100 ubiquitination and cytosolic apoB-ubiquitin conjugates. Radiolabeling studies revealed that gp78 knockdown increased secretion of newly synthesized apoB-100 and, unexpectedly, enhanced VLDL assembly, as the shift in apoB-100 density in gp78-reduced cells was accompanied by increased triacylglycerol (TG) secretion. To explore the mechanisms by which gp78 reduction might enhance VLDL assembly, we compared the effects of gp78 knockdown with those of U0126, a mitogen-activated protein kinase/ERK kinase1/2 inhibitor that enhances apoB-100 secretion in HepG2 cells. U0126 treatment increased secretion of both apoB100 and TG and decreased the ubiquitination and cellular accumu-lation of apoB-100. Furthermore, p97 knockdown caused apoB-100 to accumulate in the cell, but if gp78 was concomitantly reduced or assembly was enhanced by U0126 treatment, cellular apoB-100 returned toward baseline. This indicates that ubiquitination commits apoB-100 to p97-mediated retrotranslocation during ERAD. Thus, decreasing ubiquitination of apoB-100 enhances VLDL assembly, whereas improving apoB-100 lipidation decreases its ubiquitination, suggesting that ubiquitination has a regulatory role in VLDL assembly.

Missense mutations in APOB within the betaalpha1 domain of human APOB-100 result in impaired secretion of ApoB and ApoB-containing lipoproteins in familial hypobetalipoproteinemia

Familial hypobetalipoproteinemia (FHBL) is associated with mutations in the APOB gene. We reported the first missense APOB mutation, R463W, in an FHBL kindred (Burnett, J. R., Shan, J., Miskie, B. A., Whitfield, A. J., Yuan, J., Tran, K., Mc-Knight, C. J., Hegele, R. A., and Yao, Z. (2003) J. Biol. Chem. 278, 13442-13452). Here we identified a second nonsynonymous APOB mutation, L343V, in another FHBL kindred. Heterozygotes for L343V (n = 10) had a mean plasma apoB at 0.31 g/liter as compared with 0.80 g/liter in unaffected family members (n = 22). The L343V mutation impaired secretion of apoB-100 and very low density lipoproteins. The secretion efficiency was 20% for B100wt and 10% for B100LV and B100RW. Decreased secretion of mutant apoB-100 was associated with increased endoplasmic reticulum retention and increased binding to microsomal triglyceride transfer protein and BiP. Reduced secretion efficiency was also observed with B48LV and B17LV. Biochemical and biophysical analyses of apoB domain constructs showed that L343V and R463W altered folding of the alpha-helical domain within the N terminus of apoB. Thus, proper folding of the alpha-helical domain of apoB-100 is essential for efficient secretion.

Characterization of aortic root atherosclerosis in ApoE knockout mice: high-resolution in vivo and ex vivo MRM with histological correlation

In vivo, cardiac-gated, black-blood, and ex vivo magnetic resonance microscopy (MRM) images of the aortic root, and histopathology data were obtained from 12 transgenic and wild-type (WT) mice. MRM was performed using a black-blood imaging spin-echo sequence with upstream and downstream in-flow saturation pulses to obtain aortic root images in three contrast techniques: proton density-weighted (PDW), T(1)- (T(1)W), and T(2)-weighted (T(2)W). Aortic wall thickness and area were measured and correlated with histopathology data (R > 0.90). Ex vivo lesion components (lipid core, fibrous tissue, and cell tissue) were identified and characterized by differing image contrast in PDW, T(1)W, and T(2)W MRM, and by histopathology. The differences between WT and transgenic mice for maximal wall thickness and area were statistically significant (P < 0.05). This study demonstrates the feasibility of in vivo murine aortic root lesion assessment and ex vivo plaque characterization by MRM.

The level and species of plasma non-esterified fatty acids are not related to elevated plasma apolipoprotein B levels in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL), the leading cause of familial hyperlipidemia with premature coronary artery disease, has been associated with insulin resistance and elevated plasma levels of apolipoproten B (apoB) and non-esterified fatty acids (NEFA). Becaus dietary fats affect plasma cholesterol levels, and specific saturated fatty acids (FA) are particularly potent stimulators in vitro of apoB secretio from hepatocytes, we hypothesized that FCHL patients would exhibit elevations in plasma levels of total FA or specific saturated species. Five families containing 12 FCHL subjects (5 adults, 7 children and 8 normals (5 adults, 3 children) were assessed by dietary, anthropometric, and plasma measurements (glucose, insulin, lipoproteins, total NEFA, and specific FA types). After adjustment of the data for age, gender, and family affiliation, multivariate ANOVA indicated that FCHL was significantly associated with elevated plasma levels of apoB (p = 0.001) and insulin (p< 0.001) and increased body weight (p=0.043). Nevertheless, dietary intakes of total and saturated fat were comparable in the two groups, as were plasma levels of total NEFA and the major saturated species. In a study population possessing the salient features of FCHL, circulating total NEFA were not elevated, nor were specific saturated NEFA that had been associated with apoB oversecretion in vitro. Despite the speculated link between plasma FA and apoB overproduction in FCHL, our data suggest that other metabolic factors underlie this disease.

Elevating high-density lipoprotein cholesterol in apolipoprotein E-deficient mice remodels advanced atherosclerotic lesions by decreasing macrophage and increasing smooth muscle cell content

BACKGROUND

HDL cholesterol levels are inversely correlated with coronary heart disease risk in humans, and in animal studies, HDL elevation decreases formation and progression of foam-cell lesions. The potential for HDL to affect preexisting advanced atherosclerotic lesions is not known. To approach this issue, we used a novel mouse aortic transplantation model.

METHODS AND RESULTS

ApoE-deficient (EKO) mice were fed a Western-type diet for 6 months, and thoracic aortic segments containing advanced lesions replaced segments of the abdominal aorta of 4-month-old EKO syngeneic mice not expressing (plasma HDL cholesterol approximately 26 mg/dL) or expressing (HDL approximately 64 mg/dL) a human apoAI (hAI) transgene. Both types of recipients had comparable non-HDL cholesterol levels. Five months after transplantation, mice were killed and grafts analyzed. Compared with lesion area in pretransplant mice (0.14+/-0.04 mm(2), mean+/-SEM), there was progression in the EKO recipients (0.39+/-0.06 mm(2), P<0.01). Compared with EKO recipients, hAI/EKO recipients had retarded progression (0.24+/-0.04 mm(2), P<0.05). Immunostaining for CD68 and other macrophage-associated proteins, monocyte chemoattractant protein-1, acyl coenzyme A:cholesterol acyltransferase, and tissue factor, in lesions of pretransplant and EKO recipient mice showed abundant macrophages. In contrast, compared with any other group, lesional macrophage area in hAI/EKO mice decreased >80% (P<0.003), and smooth muscle cell content (alpha-actin staining) increased >300% (P<0.006). The decrease in macrophages and increase in smooth muscle cells was primarily in the superficial subendothelial layer.

CONCLUSIONS

Increasing HDL cholesterol levels in EKO mice retards progression of advanced atherosclerotic lesions and remodels them to a more stable-appearing phenotype.

Dramatic remodeling of advanced atherosclerotic plaques of the apolipoprotein E-deficient mouse in a novel transplantation model

OBJECTIVE

Regression of atherosclerotic lesions is an important goal. No extensive experimental evidence shows that it can be achieved for advanced lesions. To study this, we developed a model to maintain a long-term change in the plasma lipoprotein environment of advanced arterial lesions of hyperlipidemic (apolipoprotein E [apoE]-deficient) mice.

METHODS

The apoE-deficient mice (plasma total cholesterol of 1334 +/- 219 [+/- SEM] mg/dL) on a typical Western diet for 38 weeks had advanced atherosclerotic lesions (ie, beyond the macrophage foam cell stage) throughout the arterial tree. Lesion-containing thoracic aortas were transplanted (replacing a segment of abdominal aorta) into either apoE-deficient or wild-type (WT) (total cholesterol of 86 +/- 10 mg/dL) recipients. Grafts were harvested after 9 weeks.

RESULTS

Compared with pretransplant lesions (area = 0.0892 +/- 0.0179 mm(2)), lesion size tended to increase in apoE-deficient to apoE-deficient grafts (0.2411 +/- 0.0636 mm(2); P =.06), whereas a significant reduction was seen in apoE-deficient to WT grafts (0.0214 +/- 0.0049 mm(2); P <.001). Also, foam cells were absent in apoE-deficient to WT grafts, but abundant in pretransplant lesions and apoE-deficient to apoE-deficient grafts. Grafts were evaluated noninvasively in vivo with magnetic resonance imaging, and wall thickening was detected in the apoE-deficient to apoE-deficient group.

CONCLUSIONS

Nearly complete regression of advanced atherosclerotic lesions can be achieved with sustained normalization of the plasma lipoprotein profile. Syngeneic arterial transplantation in mice is a novel and valuable model system for atherosclerosis research; and magnetic resonance imaging can detect differences in characteristics in lesions undergoing regression.

The triple threat to nascent apolipoprotein B. Evidence for multiple, distinct degradative pathways

We previously showed that Omega-3 fatty acids reduce secretion of apolipoprotein B (apoB) from cultured hepatocytes by stimulating post-translational degradation. In this report, we now characterize this process, particularly in regard to the two known processes that degrade newly synthesized apoB, endoplasmic reticulum (ER)-associated degradation and re-uptake from the cell surface. First, we found that Omega-3-induced degradation preferentially reduces the secretion of large, assembled apoB-lipoprotein particles, and apoB polypeptide length is not a determinant. Second, based on several experimental approaches, ER-associated degradation is not involved. Third, re-uptake, the only process known to destroy fully assembled nascent lipoproteins, was clearly active in primary hepatocytes, but Omega-3-induced degradation of apoB continued even when re-uptake was blocked. Cell fractionation showed that Omega-3 fatty acids induced a striking loss of apoB100 from the Golgi, while sparing apoB100 in the ER, indicating a post-ER process. To determine the signaling involved, we used wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, which blocked most, if not all, of the Omega-3 fatty acid effect. Therefore, nascent apoB is subject to ER-associated degradation, re-uptake, and a third distinct degradative pathway that appears to target lipoproteins after considerable assembly and involves a post-ER compartment and PI3K signaling. Physiologic, pathophysiologic, and pharmacologic regulation of net apoB secretion may involve alterations in any of these three degradative steps.

Apoprotein B degradation is promoted by the molecular chaperones hsp90 and hsp70

Apoprotein B (apoB) is the major protein of liver-derived atherogenic lipoproteins. The net production of apoB can be regulated by presecretory degradation mediated by the ubiquitin-proteasome pathway and cytosolic hsp70. To further explore the mechanisms of apoB degradation, we have established a cell-free system in which degradation can be faithfully recapitulated. Human apoB48 synthesized in vitro was translocated into microsomes, glycosylated, and ubiquitinylated. Subsequent incubation with rat hepatic cytosol led to proteasome-mediated degradation. To explore whether hsp90 is required for apoB degradation, geldanamycin (GA) was added during the degradation assay. GA increased the recovery of microsomal apoB48 approximately 3-fold and disrupted the interaction between hsp90 and apoB48. Confirming the hsp90 effect in the cell-free system, we also found that transfection of hsp90 cDNA into rat hepatoma cells enhanced apoB48 degradation. Finally, apoB48 degradation was reconstituted in vitro using cytosol prepared from wild type yeast. Notably, degradation was attenuated when apoB48-containing microsomes were incubated with cytosol supplemented with GA or with cytosol prepared from yeast strains with mutations in the homologues of mammalian hsp70 and hsp90. Overall, our data suggest that hsp90 facilitates the interaction between endoplasmic reticulum-associated apoB and components of the proteasomal pathway, perhaps in cooperation with hsp70.

Acyl-CoA:cholesterol acyltransferase inhibition reduces atherosclerosis in apolipoprotein E-deficient mice

BACKGROUND

Acyl-COA:cholesterol acyltransferase (ACAT) converts cholesterol to cholesteryl esters. The form of ACAT in macrophages, ACAT1, contributes to foam cell formation in the arterial wall and the development of atherosclerosis. Recent studies in a mouse model of atherosclerosis (the apolipoprotein E [apoE]-deficient mouse), however, have suggested that complete deficiency of ACAT1 activity is not antiatherogenic, in part because of toxicity resulting from adverse effects on tissue cholesterol homeostasis. We have tested whether partial inhibition of ACAT1 and ACAT2 (expressed in liver and intestine) activities reduces atherosclerosis development in apoE-deficient mice and avoids toxicity.

METHODS AND RESULTS

ApoE-deficient mice were maintained for 17 weeks on a Western-type diet without (control) or with the ACAT inhibitor F-1394 (effective against ACAT1 and ACAT2) at doses of either 300 (low) or 900 (high) mg/kg. Intimal lesion area at the aortic sinus in controls was 0.69+/-0.06 mm(2). F-1394 treatment significantly decreased lesional area by 39% (low) or 45% (high). F-1394 treatment also reduced lesional immunostaining for macrophages by 61% (low) or 83% (high). En face analysis showed that surface lipid staining in control aortas was 20.0+/-2.8%; F-1394 treatment reduced this by 46% (low) or 62% (high). There were no obvious signs of systemic or vessel wall toxicity associated with F-1394 treatment.

CONCLUSIONS

Partial ACAT inhibition by F-1394 had antiatherogenic effects in apoE-deficient mice that were achieved without obvious toxicity. Partial ACAT inhibition may have therapeutic potential in the clinical treatment of atherosclerosis.

Co-translational interactions of apoprotein B with the ribosome and translocon during lipoprotein assembly or targeting to the proteasome

Hepatic lipoprotein assembly and secretion can be regulated by proteasomal degradation of newly synthesized apoB, especially if lipid synthesis or lipid transfer is low. Our previous studies in HepG2 cells showed that, under these conditions, newly synthesized apoB remains stably associated with the endoplasmic reticulum (ER) membrane (Mitchell, D. M., Zhou, M., Pariyarath, R., Wang, H., Aitchison, J. D., Ginsberg, H. N., and Fisher, E. A. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 14733-14738). We now show that independent of lipid synthesis, apoB chains that appear full-length are, in fact, incompletely translated polypeptides still engaged by the ribosome and associated with the ER translocon. In the presence of active lipid synthesis and transfer, translation and lipoprotein assembly are completed, and the complexes exit the ER. Upon omitting fatty acids from, or adding a microsomal triglyceride transfer protein inhibitor to, culture media to reduce lipid synthesis or transfer, respectively, apoB was degraded while it remained associated with the ER and complexed with cytosolic hsp70 and proteasomes. Thus, unlike other ER substrates of the proteasome, such as major histocompatibility complex class I molecules, apoB does not fully retrotranslocate to the cytosol before entering the ubiquitin-proteasome pathway. Although, upon immunofluorescence, apoB in proteasome-inhibited cells accumulated in punctate structures similar in appearance to aggresomes (cytosolic structures containing molecules irreversibly lost from the secretory pathway), these apoB molecules could be secreted when lipid synthesis was stimulated. The results suggest a model in which 1) apoB translation does not complete until lipoprotein assembly terminates, and 2) assembly with lipids or entry into the ubiquitin-proteasome pathway occurs while apoB polypeptides remain associated with the translocon and attached to the ribosome.

High-density lipoprotein: gene-based approaches to the prevention of atherosclerosis

Although the atheroprotective role of high-density lipoprotein (HDL) has been well documented in epidemiological and animal studies, highly effective therapeutic approaches for the selective increase of plasma HDL levels or function are not yet available. Several mechanisms by which HDL exerts an atheroprotective effect have been proposed on the basis of experiments in vitro and in vivo. These mechanisms include directing excess cellular cholesterol from the peripheral tissues to the liver in 'reverse cholesterol transport', inhibiting oxidative modification or aggregation of LDL, and modulating inflammatory responses to favour vasoprotection. This review gives an overview of the genes regulating these mechanisms, such as those encoding apolipoprotein AI, lecithin:cholesterol acyltransferase (LCAT), scavenger receptor B1 (SR-BI), and the ATP-binding cassette transporter 1 (ABC1), and the potential to exploit them to develop gene-based therapeutic approaches to increase the level or function of HDL.

Sulindac inhibits neointimal formation after arterial injury in wild-type and apolipoprotein E-deficient mice

Neointimal hyperplasia is a critical component of restenosis, a major complication of angioplasty and related therapeutic procedures. We studied the effects of hyperlipidemia and the nonsteroidal anti-inflammatory drugs, aspirin (acetyl-salicylic acid; ASA), and sulindac, on neointimal formation in a mouse femoral arterial injury model. At 2 months of age, normolipidemic, wild-type (WT), and hyperlipidemic, apolipoprotein E-deficient (apoE-/-) mice were divided into three treatment groups: Western-type diet (WD), WD + ASA (200 mg/kg food), and WD + sulindac (300 mg/kg food). After 1 week, mice underwent arterial injury and treatments were maintained for 4 weeks. Histomorphometry of the injured arteries showed striking effects of plasma cholesterol levels and drug treatment on neointimal hyperplasia. In the WD or WD + ASA groups, apoE-/- mice had twice the neointimal area than WT mice ( approximately 30,000 vs. 13,000 microm(2) per section; P < 0.0001). Compared with ASA or WD alone, sulindac treatment resulted in approximately 70% (P = 0.0001) and 50% (P = 0.01) reductions in the neointimal area in apoE-/- and WT mice, respectively. ASA, at a dose sufficient to inhibit platelet aggregation, did not affect neointimal formation in mice of either genotype. Evidence of macrophages was noted in the lesions of apoE-/- mice in the WD and WD + ASA groups, but remarkably, none was detectable with sulindac treatment, despite hyperlipidemia, suggesting early steps in the response to injury were abrogated. These results demonstrate sulindac reduces neointimal formation in both normolipidemic and hyperlipidemic settings and raise the possibility that similar benefits may be obtained in patients undergoing angioplasty and related procedures.

The amino-terminal domain of apolipoprotein B does not undergo retrograde translocation from the endoplasmic reticulum to the cytosol. Proteasomal degradation of nascent apolipoprotein B begins at the carboxyl terminus of the protein, while apolipoprotein B is still in its original translocon

We studied the sequential topology of the NH(2) and COOH termini of apoB during translocation by expressing, in Chinese hamster ovary (CHO) and HepG2 cells, an apoB42 construct with c-Myc and hemagglutinin (HA) tags at 2 and 41% (relative to apoB100) of its amino acid sequence. We conducted similar studies using monoclonal antibodies against the NH(2) and COOH termini of apoB100 in HepG2 cells. After radiolabeling, microsomes were immunoisolated from transfected CHO cells using anti-c-Myc or anti-HA antibodies. Throughout a 60-min chase in the presence of N-acetyl-leucyl-norleucinal, more than 90% of microsomes were isolated by anti-HA antibodies, whereas less than 10% were isolated by anti-c-Myc antibodies. Proteinase K digestion of total microsomes consistently generated two fragments ( approximately 70 and approximately 120 kDa) of apoB42 containing the NH(2) terminus throughout the chase; no fragments containing the COOH terminus were detected. Immunofluorescent studies of transfected CHO cells were consistent with results from the labeling studies. Essentially identical results were obtained from pulse-chase studies in both native and apoB42-transfected HepG2 cells. The present studies support a model in which, in the absence of adequate core lipid synthesis, there is partial translocation of apoB leading to cytosolic exposure, ubiquitination, and proteasomal degradation directly from the original translocation channel.

Inhibition of translocation of nascent apolipoprotein B across the endoplasmic reticulum membrane is associated with selective inhibition of the synthesis of apolipoprotein B

In HepG2 cells, inhibition of apolipoprotein B100 (apoB) translocation across the endoplasmic reticulum by an microsomal triglyceride transfer protein (MTP) inhibitor (CP-10447) in the presence of N-acetyl-leucinyl-norleucinal, a proteasomal inhibitor, results in accumulation of newly synthesized apoB in the translocation channel. Here we demonstrated that such accumulation led to a specific reduction of apoB synthesis. ApoB mRNA levels remained unchanged, but we observed reduced rates of elongation of nascent apoB in puromycin-synchronized cells pretreated with MTP inhibitor. This observation was consistent with a longer half-ribosome transit time for the synthesis of apoB in MTP-inhibited cells. Initiation of translation of apoB mRNA was not impaired by MTP inhibition. Overall, these findings suggest that translocation arrest of apoB in the endoplasmic reticulum channel can exert a selective and negative effect on the synthesis of apoB at the stage of elongation.

Release of active tissue factor by human arterial smooth muscle cells

Tissue factor (TF), the initiator of coagulation, is thought to function predominantly at the cell surface. Recent data have suggested that active TF is present extracellularly in atherosclerotic plaques, the arterial wall, and the blood. This study was conducted to determine whether smooth muscle cells (SMCs), a major source of arterial TF, could generate extracellular TF. Active TF accumulated in the medium of cultured human SMCs, representing approximately 10% of that measured in the underlying cells at 24 hours. Platelet-derived growth factor, phorbol ester, and tumor necrosis factor-alpha caused approximately 3-fold increases in TF activity in the medium. Release of TF into the medium was dependent on the presence of the TF transmembrane domain but not the cytoplasmic domain. Antibodies to TF precipitated most of the activity from the culture medium, whereas antibodies to the beta(1)-integrin subunit precipitated approximately 33% of the activity. Treatment with detergent or phosphatidylserine:phosphatidylcholine did not increase activity, suggesting that all TF released by SMCs was in the appropriate lipid milieu and not encrypted. Western blotting showed that the medium contained full-length TF protein. Fluorescent cytometry showed that extracellular TF was present largely in particles < or =200 nm, which had a density of 1.10 g/mL. We hypothesize that active extracellular TF found in the injured arterial wall and atherosclerotic plaques derives, in part, from SMC microparticles.

Hydrolysis of retinyl esters by pancreatic triglyceride lipase

Previously [van Bennekum, A. M., et al. (1999) Biochemistry 38, 4150-4156] we showed that carboxyl ester lipase (CEL)-deficient (CELKO) mice have normal levels of pancreatic, bile salt-dependent retinyl ester hydrolase (REH) activity. In the present study, we further investigated this non-CEL REH activity in pancreas homogenates of CELKO and wild-type (WT) mice, and rats. REH activity was detected in both the presence and absence of tri- and dihydroxy bile salts in rats, WT mice, and CELKO mice. In contrast, pancreatic cholesteryl ester hydrolase (CEH) activity was only detected in the presence of trihydroxy bile salts and only in rats and WT mice, consistent with CEL-mediated cholesteryl ester hydrolysis. Enzyme assays of pancreatic triglyceride lipase (PTL) showed that there was a colipase-stimulated REH activity in rat and mouse (WT and CELKO) pancreas, consistent with hydrolysis of retinyl ester (RE) by PTL. Pancreatic enzyme activities related to either CEL or PTL were separated using DEAE-chromatography. In both rats and mice (WT and CELKO), REH activity could be attributed mainly to PTL, and to a much smaller extent to CEL. Finally, purified human PTL exhibited similar enzymatic characteristics for triglyceride hydrolysis as well as for retinyl ester hydrolysis, indicating that RE is a substrate for PTL in vivo. Altogether, these studies clearly show that PTL is the major pancreatic REH activity in mice, as well as in rats.

Dietary therapy for children with hypercholesterolemia

Accumulating evidence clearly shows that atherosclerosis begins in youth. The National Cholesterol Education Program (NCEP) has recommended that children at high risk of developing coronary artery disease as adults be screened so that those with elevated low-density lipoprotein (LDL) cholesterol levels can be treated, primarily by modification of diet. The initial approach to these youthful patients is to use the NCEP step I diet. This diet provides calories and nutrients that support normal growth and development, but limits saturated fat and total fat intake to no more than 10 and 30 percent of total calories, respectively, and cholesterol intake to no more than 100 mg per 1,000 kcal per day, to a maximum of 300 mg. If the goal of reducing the LDL cholesterol level to below 130 mg per dL (3.35 mmol per L) is not achieved, the more restrictive step II diet should be initiated. However, the step II diet may not provide sufficient calories and nutrients to support normal growth and development; therefore, trained nutritionists may be required to effectively manage a child on this diet.

Intraatrial mitral valve insertion with native valve preservation in children

Two patients underwent intraatrial mitral valve insertion for an unsuccessful valvotomy for severe mitral stenosis and left-sided atrioventricular valve insufficiency associated with corrected transposition utilizing a porcine valve from a valved conduit with preservation of the native valve. The valves were inserted using continuous suture distally at the mitral annulus and proximally at the pulled atrial wall distal to the pulmonary veins. Both patients had uneventful hospital course and are doing well at up to 6 months postoperatively. This approach provides a viable option for congenital mitral stenosis or insufficiency in children.

Intestinal absorption of dietary cholesteryl ester is decreased but retinyl ester absorption is normal in carboxyl ester lipase knockout mice

Carboxyl ester lipase (CEL; EC 3.1.1.13) hydrolyzes cholesteryl esters and retinyl esters in vitro. In vivo, pancreatic CEL is thought to liberate cholesterol and retinol from their esters prior to absorption in the intestine. CEL is also a major lipase in the breast milk of many mammals, including humans and mice, and is thought to participate in the processing of triglycerides to provide energy for growth and development while the pancreas of the neonate matures. Other suggested roles for CEL include the direct facilitation of the intestinal absorption of free cholesterol and the modification of plasma lipoproteins. Mice with different CEL genotypes [wild type (WT), knockout (CELKO), heterozygote] were generated to study the functions of CEL in a physiological system. Mice grew and developed normally, independent of the CEL genotype of the pup or nursing mother. Consistent with this was the normal absorption of triglyceride in CELKO mice. The absorption of free cholesterol was also not significantly different between CELKO (87 +/- 26%, mean +/- SD) and WT littermates (76 +/- 10%). Compared to WT mice, however, CELKO mice absorbed only about 50% of the cholesterol provided as cholesteryl ester (CE). There was no evidence for the direct intestinal uptake of CE or for intestinal bacterial enzymes that hydrolyze it, suggesting that another enzyme besides CEL can hydrolyze dietary CE in mice. Surprisingly, CELKO and WT mice absorbed similar amounts of retinol provided as retinyl ester (RE). RE hydrolysis, however, was required for absorption, implying that CEL was not the responsible enzyme. The changes in plasma lipid and lipoprotein levels to diets with increasing lipid content were similar in mice of all three CEL genotypes. Overall, the data indicate that in the mouse, other enzymes besides CEL participate in the hydrolysis of dietary cholesteryl esters, retinyl esters, and triglycerides.

Carboxyl ester lipase overexpression in rat hepatoma cells and CEL deficiency in mice have no impact on hepatic uptake or metabolism of chylomicron-retinyl ester

To study the role of carboxyl ester lipase (CEL) in hepatic retinoid (vitamin A) metabolism, we investigated uptake and hydrolysis of chylomicron (CM)-retinyl esters (RE) by rat hepatoma (McArdle-RH7777) cells stably transfected with a rat CEL cDNA. We also studied tissue uptake of CM-RE in CEL-deficient mice generated by targeted disruption of the CEL gene. CEL-transfected cells secreted active enzyme into the medium. However, both control and CEL-transfected cells accumulated exogenously added CM-RE or CM remnant (CMR)-derived RE in equal amounts. Serum clearance of intravenously injected CM-RE and cholesteryl ester were not different between wild-type and CEL-deficient mice. Also, the uptake of the two compounds by the liver and other tissues did not differ. These data indicate that the lack of CEL expression does not affect the uptake of dietary CM-RE by the liver or other tissues. Moreover, the percentage of retinol formed in the liver after CM-RE uptake, the levels of retinol and retinol-binding protein in serum, and retinoid levels in various tissues did not differ, indicating that CEL deficiency does not affect hepatic retinoid metabolism and retinoid distribution throughout the body. Surprisingly, in both pancreas and liver of wild-type, heterozygous, and homozygous CEL-deficient mice, the levels of bile salt-dependent retinyl ester hydrolase (REH) activity were similar. This indicates that in the mouse pancreas and liver an REH enzyme activity, active in the presence of bile salt and distinct from CEL, is present, compatible with the results from our accompanying paper that the intestinal processing and absorption of RE were unimpaired in CEL-deficient mice.

Apoprotein B100 has a prolonged interaction with the translocon during which its lipidation and translocation change from dependence on the microsomal triglyceride transfer protein to independence

When lipid synthesis is limited in HepG2 cells, apoprotein B100 (apoB100) is not secreted but rapidly degraded by the ubiquitin-proteasome pathway. To investigate apoB100 biosynthesis and secretion further, the physical and functional states of apoB100 destined for either degradation or lipoprotein assembly were studied under conditions in which lipid synthesis, proteasomal activity, and microsomal triglyceride transfer protein (MTP) lipid-transfer activity were varied. Cells were pretreated with a proteasomal inhibitor (which remained with the cells throughout the experiment) and radiolabeled for 15 min. During the chase period, labeled apoB100 remained associated with the microsomes. Furthermore, by crosslinking sec61beta to apoB100, we showed that apoB100 remained close to the translocon at the same time apoB100-ubiquitin conjugates could be detected. When lipid synthesis and lipoprotein assembly/secretion were stimulated by adding oleic acid (OA) to the chase medium, apoB100 was deubiquitinated, and its interaction with sec61beta was disrupted, signifying completion of translocation concomitant with the formation of lipoprotein particles. MTP participates in apoB100 translocation and lipoprotein assembly. In the presence of OA, when MTP lipid-transfer activity was inhibited at the end of pulse labeling, apoB100 secretion was abolished. In contrast, when the labeled apoB100 was allowed to accumulate in the cell for 60 min before adding OA and the inhibitor, apoB100 lipidation and secretion were no longer impaired. Overall, the data imply that during most of its association with the endoplasmic reticulum, apoB100 is close to or within the translocon and is accessible to both the ubiquitin-proteasome and lipoprotein-assembly pathways. Furthermore, MTP lipid-transfer activity seems to be necessary only for early translocation and lipidation events.

Anomalous right coronary artery from the pulmonary artery in Taussig-Bing anomaly

The presence of associated anomalies in patients with double-outlet right ventricle can significantly alter surgical intervention. Preoperative delineation of these anomalies can facilitate surgical planning and improve outcome. We describe a case in which the right coronary artery and anterior descending coronary artery arose from the pulmonary artery in a patient with double-outlet right ventricle with subpulmonary ventricular septal defect (Taussig-Bing anomaly). Recognition of this important anomaly prevented significant intraoperative myocardial damage by altering techniques of cardioplegia administration for myocardial preservation.

Noninvasive In vivo high-resolution magnetic resonance imaging of atherosclerotic lesions in genetically engineered mice

BACKGROUND

The pathogenesis of atherosclerosis is currently being investigated in genetically engineered small animals. Methods to follow the time course of the developing pathology and/or the responses to therapy in vivo are limited.

METHODS AND RESULTS

To address this problem, we developed a noninvasive MR microscopy technique to study in vivo atherosclerotic lesions (without a priori knowledge of the lesion location or lesion type) in live apolipoprotein E knockout (apoE-KO) mice. The spatial resolution was 0.0012 to 0.005 mm3. The lumen and wall of the abdominal aorta and iliac arteries were identified on all images in apoE-KO (n=8) and wild-type (n=5) mice on chow diet. Images obtained with MR were compared with corresponding cross-sectional histopathology (n=58). MR accurately determined wall area in comparison to histopathology (slope=1.0, r=0.86). In addition, atherosclerotic lesions were characterized in terms of lesion shape and type. Lesion type was graded by MR according to morphological appearance/severity and by histopathology according to the AHA classification. There was excellent agreement between MR and histopathology in grading of lesion shape and type (slope=0.97, r=0.91 for lesion shape; slope=0. 64, r=0.90 for lesion type).

CONCLUSIONS

The combination of high-resolution MR microscopy and genetically engineered animals is a powerful tool to investigate serially and noninvasively the progression and regression of atherosclerotic lesions in an intact animal model and should greatly enhance basic studies of atherosclerotic disease.

Regulated Co-translational ubiquitination of apolipoprotein B100. A new paradigm for proteasomal degradation of a secretory protein

Presentation of a wild-type secretory protein, apolipoprotein B100 (apoB), to the cytosol for ubiquitin-proteasome proteolysis has been observed in HepG2 cells. A currently accepted model for proteasomal degradation of secretory proteins is retrograde translocation of the substrate polypeptides from the lumen of endoplasmic reticulum (ER) back to the cytosol. In this report, we present evidence that newly synthesized apoB becomes exposed to the cytosol and targeted to the proteasomes in a co-translational manner. Thus, after protein translation was synchronized with puromycin, partially synthesized apoB polypeptides were found to be conjugated to ubiquitin. The magnitude of co-translational ubiquitination and subsequent degradation of apoB was increased when cells were pretreated with either herbimycin A to induce cytosolic Hsp70 or with an inhibitor of microsomal triglyceride transfer protein; both treatments impede translocation of nascent apoB across the ER membrane. These treatments also decreased secretion of apoB and increased its degradation via the ubiquitin-proteasome pathway. We suggest that translocation arrest with subsequent co-translational exposure to the cytosol provides an alternative model to explain how mammalian secretory proteins can overcome topological segregation by the ER membrane and undergo degradation by the ubiquitin-proteasome pathway.

Modified Konno-Rastan procedure for subaortic stenosis: indications, operative techniques, and results

BACKGROUND

Diffuse or unresectable subaortic stenosis (SAS) necessitates an aggressive surgical approach for the elimination of left ventricular outflow tract obstruction. In this article we report our experience with the modified Konno-Rastan procedure, with inherent preservation of the native aortic valve and annulus, in the treatment of diffuse or unresectable SAS.

METHODS

Sixteen children (age range, 21 months to 18 years) underwent the modified Konno-Rastan procedure through either a transventricular (n = 12) or a transatrial approach (n = 4) to the conal septum. Indications for operation were recurrent SAS (n = 3), hypertrophic obstructive cardiomyopathy (n = 3), tunnel stenosis (n = 2), SAS related to a canal (n = 3), and SAS after ventricular septal defect closure (n = 5). Eleven patients had undergone previous procedures and 5 underwent the modified Konno-Rastan procedure as their primary operation.

RESULTS

The mean preoperative left ventricular outflow tract gradient of 50 +/- 17 mm Hg was reduced to 3 +/- 7 mm Hg (p < 0.001) after surgical repair. Postoperative complications included sternal infection (n = 1), heart block (n = 2), mediastinal bleeding (n = 1), and renal and cerebral ischemia (n = 1). There was 1 late postoperative death caused by pneumonia 2 years after operation (6.2% mortality rate). The mean follow-up period was 62 +/- 39 months and all patients had complete relief of preoperative symptoms and were in New York Heart Association class I. One patient underwent a successful redo modified Konno-Rastan procedure 7 years after the first operation for residual left ventricular outflow tract obstruction immediately below the aortic valve. One patient is awaiting reoperation for aortic incompetence unrelated to conal enlargement 1.5 years after the first procedure.

CONCLUSIONS

The modified Konno-Rastan procedure represents an excellent therapy for diffuse or unresectable SAS in patients with a normal aortic valve. In addition, it produces excellent results in a limited number of patients with hypertrophic obstructive cardiomyopathy, in whom the Morrow procedure traditionally has been performed. Although it usually is performed through a transventricular approach, the modified Konno-Rastan procedure also can be performed through a transatrial approach; this is particularly useful in patients who have had previous ventricular septal defect closure associated with SAS occurring proximal to the prosthetic patch.

The full induction of human apoprotein A-I gene expression by the experimental nephrotic syndrome in transgenic mice depends on cis-acting elements in the proximal 256 base-pair promoter region and the trans-acting factor early growth response factor 1

To identify molecular factors regulating apo A-I production in vivo, we induced in transgenic mice the experimental nephrotic syndrome, which results in elevated levels of HDL cholesterol (HDL-C), plasma apo A-I, and hepatic apo A-I mRNA. Human (h) apo A-I transgenic mice with different length 5' flanking sequences (5.5 or 0.256 kb, the core promoter for hepatic-specific basal expression) were injected with nephrotoxic (NTS) or control serum. With nephrosis, there were comparable (greater than twofold) increases in both lines of HDL-C, h-apo A-I, and hepatic h-apo A-I mRNA, suggesting that cis-acting elements regulating induced apo A-I gene expression were within its core promoter. Hepatic nuclear extracts from control and nephrotic mice footprinted the core promoter similarly, implying that the same elements regulated basal and induced expression. Hepatic mRNA levels for hepatocyte nuclear factor (HNF) 4 and early growth response factor (EGR) 1, trans-acting factors that bind to the core promoter, were measured: HNF4 mRNA was not affected, but that of EGR-1 was elevated approximately fivefold in the nephrotic group. EGR-1 knockout (EGR1-KO) mice or mice expressing EGR-1 were injected with either NTS or control serum. Levels of HDL-C, apo A-I, and hepatic apo A-I mRNA were lowest in nonnephrotic EGR1-KO mice and highest in nephrotic mice expressing EGR-1. Although in EGR1-KO mice HDL-C, apo A-I, and apo A-I mRNA levels also increased after NTS injection, they were approximately half of those in the nephrotic EGR-1-expressing mice. We conclude that in this model, basal and induced apo A-I gene expression in vivo are regulated by the trans-acting factor EGR-1 and require the same cis-acting elements in the core promoter.

O-Glycosylation of C-terminal tandem-repeated sequences regulates the secretion of rat pancreatic bile salt-dependent lipase

Amino acid sequences rich in Pro, Glu, Ser, and Thr (PEST) are common to rapidly degraded proteins (Rogers, S., Wells, R. & Rechsteiner, M. (1986) Science 234, 364-368). On pancreatic bile salt-dependent lipase (BSDL), PEST sequences are present in the C-terminal region of the enzyme to which is associated the O-glycosylation. We have postulated that the O-glycosylation of BSDL may contribute to mask PEST sequences and to trigger the secretion of this enzyme instead of its delivery into a degradative pathway (Bruneau, N., and Lombardo, D. (1995) J. Biol. Chem. 270, 13524-13523). To further examine the role of the O-linked glycosylation on BSDL metabolism, rat pancreatic BSDL cDNA was stably transfected into two Chinese hamster ovary (CHO) cell lines, the CHO K1 wild-type line and the O-glycosylation defective CHO ldlD line. In these latter cells, O-glycosylation can be reversibly modulated by culture conditions. Results indicate that the rate of BSDL synthesis by transfected CHO K1 or CHO ldlD cells reflects, independently of culture conditions, the amount of mRNA specific for BSDL present in these transfected cells. Nevertheless, the rate of secretion of the enzyme depends upon cell culture conditions and increases with the cell capability to O-glycosylate C-terminal tandem-repeated sequences. Immunoprecipitation experiments performed on cell lysates suggested that a rapid degradation of BSDL occurred particularly when transfected CHO ldlD cells were cultured under non-permissive conditions. We further showed that BSDL secreted by CHO ldlD cells grown under non-permissive conditions that normally prevent O-glycosylation incorporated galactose and was reactive with peanut agglutinin, which recognizes the core structure of O-linked glycans. We concluded that the BSDL expressed by CHO ldlD cells grown under non-permissive conditions was rapidly degraded but a fraction of the enzyme was allowed to O-glycosylate and consequently was secreted.

The syndecan family of proteoglycans. Novel receptors mediating internalization of atherogenic lipoproteins in vitro

Cell-surface heparan sulfate proteoglycans have been shown to participate in lipoprotein catabolism, but the roles of specific proteoglycan classes have not been examined previously. Here, we studied the involvement of the syndecan proteoglycan family. First, transfection of CHO cells with expression vectors for several syndecan core proteins produced parallel increases in the cell association and degradation of lipoproteins enriched in lipoprotein lipase, a heparan-binding protein. Second, a chimeric construct, FcR-Synd1, that consists of the ectodomain of the IgG Fc receptor Ia linked to the highly conserved transmembrane and cytoplasmic domains of syndecan-1 directly mediated efficient internalization, in a process triggered by ligand clustering. Third, internalization of lipase-enriched lipoproteins via syndecan-1 and of clustered IgGs via the chimera showed identical kinetics (t1/2 = 1 h) and identical dose-response sensitivities to cytochalasin B, which disrupts microfilaments, and to genistein, which inhibits tyrosine kinases. In contrast, internalization of the receptor-associated protein, which proceeds via coated pits, showed a t1/2 < 15 min, limited sensitivity to cytochalasin B, and complete insensitivity to genistein. Thus, syndecan proteoglycans can directly mediate ligand catabolism through a pathway with characteristics distinct from coated pits, and might act as receptors for atherogenic lipoproteins and other ligands in vivo.

The degradation of apolipoprotein B100 is mediated by the ubiquitin-proteasome pathway and involves heat shock protein 70

Apolipoprotein B (apoB) is the major protein component of atherogenic lipoproteins of hepatic origin. In HepG2 cells, the standard cell culture model of human hepatic lipoprotein metabolism, there is a limited availability of core lipids in the endoplasmic reticulum for association with nascent apoB. Under these conditions, apoB is partially translocated, interacts with cytosolic Hsp70, and undergoes rapid degradation. We show that increasing the expression of Hsp70 in HepG2 cells promotes apoB degradation. In addition, apoB is polyubiquitinated and its degradation both normally and after Hsp70 induction is blocked by inhibitors of the proteasome. The apoB that accumulates after proteasome inhibition is endoplasmic reticulum-associated and can be assembled into lipoproteins and secreted if new lipid synthesis is stimulated. Thus, apoB is the first example of a wild-type mammalian protein whose secretion is regulated by degradation in the cytosol via the ubiquitin-proteasome pathway. Furthermore, targeting of this secretory protein to the proteasome is regulated by the molecular chaperone Hsp70 and the availability of apoB's lipid-ligands.

Molecular cloning of the cDNA for rat hepatic, bile salt-dependent cholesteryl ester/retinyl ester hydrolase demonstrates identity with pancreatic carboxylester lipase

Rat liver homogenates contain a neutral lipid ester hydrolase that requires millimolar concentrations of bile salts for maximal activity in catalyzing the hydrolysis of cholesteryl esters and retinyl esters in vitro. Previous studies have demonstrated that this hepatic hydrolase resembles rat pancreatic carboxylester lipase because it reacts with a specific pancreatic carboxylester lipase antibody and the eight N-terminal amino acids of the hepatic protein are identical to those of the pancreatic enzyme. Nonetheless, the exact molecular relationship between the hepatic and pancreatic enzymes is unclear. In the present study, a rat hepatic cDNA encoding the enzyme was cloned. Sequence analysis demonstrated that this cDNA corresponds to the full-length mature pancreatic carboxylester lipase (EC# 3.1.1.13). In individual animals the hepatic and pancreatic cDNA sequences were identical. However, among rats there were sequence variations, suggesting a polymorphic nature for this rat gene.

Cost-effectiveness of transaxillary muscle-sparing same-day operative closure of patent ductus arteriosus

Transaxillary muscle-sparing patent ductus arteriosus closure performed as same-day surgery is described in 10 patients. This approach provides a superb cosmetic result while obviating the need for thoracostomy tube placement.

Fenestrated fontan procedure: evolution of technique and occurrence of paradoxical embolism

The Fenestrated Fontan procedure (FFP) has improved outcome in high risk patients. The technique is evolving, however, and complications are not fully known. Over a 3-year period 13 patients (mean age 35 +/- 29 months) underwent an FFP in our institution. In the first two patients the fenestration had to be created because of high right atrial pressure and low cardiac output; in 11 patients the FFP was planned. In three patients the sutures for the adjustable fenestration were crossing the defect. In 10 patients, purse-string sutures were placed around but not across the defect. Because large fenestrations were created in 11 patients (8-12 mm) Glenn shunts were performed to improve arterial saturation. The postoperative course was relatively uneventful, with chest tubes being removed 1-8 days (mean 4 +/- 3 days) postoperatively and the hospital stay ranging from 7 to 27 days (mean 14 +/- 6 days). One patient had bleeding and another had a mediastinal abscess. The first patient died (7.6%) because of hemodynamic instability due to prolonged cardiopulmonary bypass from the creation and enlargement of the fenestration. One patient had a paradoxical cerebral embolism from clots that formed on the sutures crossing the fenestration. Because of this problem the remaining patients were placed on salicylates while awaiting closure of their fenestration. All 12 patients had their fenestrations closed, performed under local anesthesia in 9, at mediastinal abscess drainage in 1, and spontaneously in 2. We conclude that creation of large fenestrations in combination with Glenn shunts and the use of adjustable fenestrations are viable modifications of the FFP. The use of purse-string sutures around the fenestration and antiplatelet drugs can probably minimize the occurrence of paradoxical embolism.

Management of arch hypoplasia after successful coarctation repair

BACKGROUND

Pronounced arch obstruction can be seen after a well-repaired coarctation, and this probably results from the failure of a somewhat hypoplastic arch to grow or from clamp injury at the time of the initial repair, or from both causes. Because of mediastinal adhesions and minimal collateral circulation, use of extraanatomic bypass grafts appears to be the preferred approach.

METHODS

Six children or young adults presented with arch obstruction over a 3-year period. Their mean age was 13.5 +/- 4 years, and the mean interval from the time of the initial repair was 10 +/- 4 years. The mean age of the patients at the time of the initial repair was 3.2 +/- 5 years. Symptoms included exertional headache and chest pain. The mean systolic gradients, as shown by echocardiography and cardiac catheterization, were 34 +/- 7 mm Hg and 33 +/- 6 mm Hg, respectively. Repair was accomplished through a midsternotomy using a polytetrafluoroethylene patch placed in the concavity of the arch, which extended from the ascending to the descending aorta. Dissection was kept close to the aorta and arch to minimize injury to the phrenic and recurrent laryngeal nerves. Cardiopulmonary bypass and moderate hypothermia (25 degrees to 27 degrees C bladder temperature) without circulatory arrest were used.

RESULTS

All patients were discharged home 4 to 20 days postoperatively (mean, 7 +/- 6 days). All patients were found to be normotensive at a mean follow-up of 1.3 +/- 1 years. Postoperative echocardiograms, which were obtained in all patients, revealed no residual gradients. Exercise blood pressure was evaluated in 2 patients and found to be normal.

CONCLUSIONS

Transsternal arch enlargement using cardiopulmonary bypass and moderate hypothermia without circulatory arrest is an attractive and safe approach for the treatment of arch obstruction after coarctation repair. Unlike the use of extraanatomic bypass grafts, it allows complete relief of the obstruction, unhampered aortic growth, the minimal use of foreign material, and a repair that is protected deep within the mediastinal space.

UVB irradiation alters cellular responses to cytokines: role in extracellular matrix gene expression

Solar radiation causes cutaneous photodamage characterized by alterations in the quantity and structure of the extracellular matrix. We determined the direct and cytokine-mediated effects of UV irradiation on mRNA levels for two matrix elements, tropoelastin and fibrillin 1. (i) Comparison of normal versus end-stage photodamaged skin failed to reveal differences in these message levels. (ii) Acutely irradiated skin showed suppression of both tropoelastin and fibrillin mRNAs. (iii) UVB irradiation (50 mJ) of cultured skin fibroblasts suppressed fibrillin mRNA by 50%, consistent with a direct effect of radiation. Addition to the cultured fibroblasts of several cytokines upregulated by UVB showed that IL-1alpha had no effect on fibrillin mRNA in unirradiated cells, but in irradiated cells, this cytokine enhanced the suppression of fibrillin mRNA. There were no changes in the message stability, suggesting altered gene transcription. In contrast, UVB had no effect on tropoelastin mRNA levels in cultured fibroblasts, indicating the absence of a direct effect of radiation. IL-1alpha stimulated tropoelastin mRNA 2.8-fold in unirradiated cells, and this stimulation was entirely blocked by UVB. Overall, our results indicate acute suppression of matrix genes by UVB in vivo. The suppression of fibrillin message was a direct effect of UVB on fibroblasts and was augmented by IL-1alpha. Suppression of tropoelastin message by UVB occurred in vitro only in IL-1alpha-stimulated cells. We conclude that UVB substantially alters the pattern of cellular response to cytokines. The interplay between UVB and cytokines is essential to explain the acute responses of matrix genes to UVB in vivo.

Recognition and management of obstructed pulmonary veins draining to the coronary sinus

BACKGROUND

Obstruction of the pulmonary veins in total anomalous pulmonary venous drainage to the coronary sinus is generally considered rare. However, if it is present, the usual treatment of unroofing the coronary sinus will lead to a poor result.

METHODS

Four patients with total anomalous pulmonary venous drainage to the coronary sinus with obstruction were identified over a 14-month period. Three patients in whom the diagnosis of obstruction was not made underwent coronary sinus unroofing. Retrospective review of the preoperative echocardiograms and Doppler studies showed the presence of obstruction in the vertical vein in 2 patients and in the branches in the other. In the fourth patient, obstruction in the vertical vein was recognized preoperatively with echocardiography and Doppler study. This patient underwent direct common pulmonary vein-left atrial anastomosis.

RESULTS

All 3 patients who had coronary unroofing were seen with obstructed pulmonary veins 2 to 7 months postoperatively. After reoperation, 1 died, and the other 2 have done relatively well 3 1/2 and 15 months postoperatively. The patient who had an anastomosis between the common pulmonary vein and the left atrium is doing well 18 months postoperatively.

CONCLUSIONS

Obstruction in total anomalous pulmonary venous drainage to the coronary sinus is not as rare as previously reported. To improve outcome, its presence should be sought using complete echocardiography including Doppler studies. When obstruction is present, transection of the vertical vein and common pulmonary vein-left atrial anastomosis through the superior approach is an attractive technique that also eliminates the right-to-left shunting associated with coronary sinus unroofing and simplifies closure of the atrial septal defect.

Clinical improvement after revision in Fontan patients

BACKGROUND

Arrhythmias, decreased exercise tolerance, or malabsorption will develop in a significant number of Fontan patients. Fontan revision consisting of creation of lateral atrial tunnel, reconnection of the Glenn shunt when present, or both appears to improve these patients.

METHODS

Over a 34-month period, 9 patients underwent Fontan revision. The mean age was 11 +/- 5 years and the mean interval from Fontan operation to revision was 3 +/- 2 years. The reason for revision included marked impairment in exercise capacity, inability to go to school consistently, and chronic fatigue in 6 patients, 3 of whom also had serious atrial arrhythmias. Five of the 6 patients had a classic Glenn shunt. The mean right atrial pressure was greater than the pressure of the Glenn shunt (20 +/- 1.6 versus 17 +/- 0.8 mm Hg). Three of the 6 patients also showed a significant gradient between the right or left pulmonary artery wedge and ventricular end-diastolic pressure, indicating pulmonary vein obstruction from the bulging atrial septum or partitioning patch (13 +/- 3 versus 6.8 +/- 1 mm Hg). The remaining 3 patients had revision because of malabsorption (1), hepatomegaly and obstructed right pulmonary veins from bulging atrial septum (1), and tricuspid insufficiency (1). Fontan revision was accomplished with creation of a lateral atrial tunnel and Glenn reconnection in 6 patients, Glenn reconnection in 2, and creation of a lateral atrial tunnel in 1. Four patients had additional procedures.

RESULTS

One patient died of Pseudomonas pneumonia. Early extubation, chest tube removal, and postoperative hospital discharge were accomplished in 8 patients (mean = 1.4 +/- 1, 2.8 +/- 1, and 8 +/- 3 days, respectively). One patient died 8 months postoperatively of brain damage after ventricular fibrillation from attempted cardioversion for atrial flutter. The remaining patients had marked improvement in exercise capacity with ability to consistently go to school, improvement in duration and tolerance to arrhythmias on less medication, and resolution of malabsorption up to 37 months postoperatively (mean, 20 +/- 12 months).

CONCLUSIONS

We conclude that creation of lateral atrial tunnel with excision of a bulging atrial septum or atrial partitioning patch that causes pulmonary venous obstruction, reconnection of the Glenn shunt, which allows better distribution of flow based on the pulmonary vascular bed and resistance of each lung, or a combination of these procedures will improve Fontan patients.