The effects of cyclic stretch on gene transfer in alveolar epithelial cells

Cyclic stretch has been shown to alter cell physiology, cytoskeletal structure, signal transduction, and gene expression in a variety of cell types. To determine the effects of stretch on the gene transfer process, we compared the transfection efficiencies of human A549 cells grown either statically or exposed to 10% cyclic stretch (Delta surface area) at 60 cycles/min (1 Hz) for 24 hours prior to, and/or after transfection with pEGFP-N1 and pCMV-lux-DTS using lipoplex or electroporation. Stretching the cells prior to transfection had no effect on gene transfer. By contrast, cyclic, but not continuous, stretch applied immediately after transfection for as little as 30 minutes resulted in a 10-fold increase in gene transfer and expression by either transfection technique. These stretch conditions did not result in rupture of the plasma membrane based on the fact that DNA was unable to enter stretched cells unless either an electric field was applied or the DNA was complexed with liposomes. Taken together with the timing of the stretch response and the known effects of stretch on transcription, these findings suggest that cyclic stretch may be altering the intracellular transport of plasmids to increase gene expression.

Regional variation in myocardial water content in the edematous pig heart

BACKGROUND

The purpose of this study was to examine regional variation in myocardial water content (%MWC) throughout the iatrogenically edematous pig heart.

METHODS

Edema was induced by hemodilution in domestic swine (n = 26). Hearts were arrested with potassium chloride. The left ventricular free wall (LVFW), interventricular septum (IVS), and right ventricular free wall (RVFW) were biopsied at the apex, base, and equator. Full-thickness biopsy (Full, 0.5-1 g) and subendocardial (Endo, 0.1-0.2 g) biopsies were removed from each region. %MWC was determined for each biopsy.

RESULTS

The %MWC for all hearts were as follows: Endo, 81.1 +/- 0.1, and Full, 80.6 +/- 0.1* (*P < 0.02); apex, 81.1 +/- 0.2*, equator, 80.7 +/- 0.2, and base, 80.4 +/- 0.2 (*P < 0.02); RVFW, 81.4 +/- 0.3*, IVS, 80.8 +/- 0.2*, and LVFW, 80.3 +/- 0.1* (*P < 0.02). For 18 hearts with LV samples with average %MWC >or= 80%, the percentages were apex, 81.4 +/- 0.2*, equator, 81.0 +/- 0.2*, and base, 80.6 +/- 0.2* (*P < 0.02) (repeated measures, ANOVA).

CONCLUSION

In the iatrogenically edematous porcine heart, a significant water gradient exists, with Endo > Full, apex > equator > base, and RVFW > IVS > LVFW. These results indicate that when examining edema, consistent biopsy results depend on a reproducible sampling site. Water content tends to be highest in thin-walled portions of the heart, suggesting that contractile force may be important in the distribution of edema.

Hyperoxia-induced apoptosis does not require mitochondrial reactive oxygen species and is regulated by Bcl-2 proteins

Exposure of animals to hyperoxia results in lung injury that is characterized by apoptosis and necrosis of the alveolar epithelium and endothelium. The mechanism by which hyperoxia results in cell death, however, remains unclear. We sought to test the hypothesis that exposure to hyperoxia causes mitochondria-dependent apoptosis that requires the generation of reactive oxygen species from mitochondrial electron transport. Rat1a cells exposed to hyperoxia underwent apoptosis characterized by the release of cytochrome c, activation of caspase-9, and nuclear fragmentation that was prevented by the overexpression of Bcl-X(L.) Murine embryonic fibroblasts from bax(-/-) bak(-/-) mice were resistant to hyperoxia-induced cell death. The administration of the antioxidants manganese (III) tetrakis (4-benzoic acid) porphyrin, ebselen, and N-acetylcysteine failed to prevent cell death following exposure to hyperoxia. Human fibrosarcoma cells (HT1080) lacking mitochondrial DNA (rho(0) cells) that failed to generate reactive oxygen species during exposure to hyperoxia were not protected against cell death following exposure to hyperoxia. We conclude that exposure to hyperoxia results in apoptosis that requires Bax or Bak and can be prevented by the overexpression of Bcl-X(L). The mitochondrial generation of reactive oxygen species is not required for cell death following exposure to hyperoxia.

Transforming growth factor-beta induction of smooth muscle cell phenotpye requires transcriptional and post-transcriptional control of serum response factor

Transforming growth factor-beta induces a smooth muscle cell phenotype in undifferentiated mesenchymal cells. To elucidate the mechanism(s) of this phenotypic induction, we focused on the molecular regulation of smooth muscle-gamma-actin, whose expression is induced at late stages of smooth muscle differentiation and developmentally restricted to this lineage. Transforming growth factor-beta induced smooth muscle-gamma-actin protein, cytoskeletal localization, and mRNA expression in mesenchymal cells. Smooth muscle-gamma-actin promoter-luciferase reporter activity was enhanced by transforming growth factor-beta, and deletion analysis revealed that CArG box 2 in the promoter was necessary for this transcriptional activation. CArG motifs bind transcriptional activator serum response factor; gel shift analyses revealed increased binding of serum response factor-containing complexes to this site in response to transforming growth factor-beta, paralleled by increased serum response factor protein expression. Serum response factor expression was found to be up-regulated by transforming growth factor-beta via transcriptional activation of the gene and post-transcriptional regulation. Using mesenchymal cells stably transfected with wild type or dominant-negative serum response factor, we demonstrated that its expression is sufficient for induction of a smooth muscle phenotype in mesenchymal cells and is necessary for transforming growth factor-beta-mediated smooth muscle induction.

Nonviral gene transfer strategies for the vasculature

Major attention has been focused on the development of gene therapy approaches for the treatment of vascular diseases. In this review, we focus on an alternative use of gene therapy: the use of genetic means to study vascular cell biology and physiology. Both viral and nonviral gene transfer strategies have limitations, but because of the overwhelming inflammatory responses associated with the use of viral vectors, nonviral gene transfer methods are likely to be used more abundantly for future applications in the vasculature. Researchers have made great strides in the advancement of gene delivery to the vasculature in vivo. However, the efficiency of gene transfer seen with most nonviral approaches has been exceedingly low. We discuss how to circumvent and take advantage of a number of the barriers that limit efficient gene delivery to the vasculature to achieve high-level gene expression in appropriate cell types within the vessel wall. With such levels of expression, gene transfer offers the ability to alter pathways at the molecular level by genetically modulating the activity of a gene product, thus obviating the need to rely on pharmacological agents and their foreseen and unforeseen side effects. This genetic ability to alter distinct gene products within a signaling or biosynthetic pathway or to alter structural interactions within and between cells is extremely useful and technologically possible today. Hopefully, with the availability of these tools, new advances in cardiovascular physiology will emerge.

High-level gene transfer to the cornea using electroporation

BACKGROUND

Methods for gene transfer to the cornea that yield high-level expression without inflammation or trauma are currently lacking. Because electroporation has proven effective for gene transfer in other tissues in terms of expression levels and safety, this study quantitatively evaluated its use in the cornea.

METHODS

To evaluate the use of electroporation in the mouse cornea, plasmids expressing either luciferase or green fluorescent protein were injected intracorneally or subconjunctivally and square-wave electric pulses were immediately applied to the eyes. Gene expression was quantified at later times and trauma and inflammation were monitored visually and by measuring interleukin-6 (IL-6) production.

RESULTS

The application of electric pulses to eyes injected with plasmid resulted in nanogram levels of gene product expression. At an optimal field strength of 200 V/cm, no trauma, corneal edema or inflammation was observed. However, at higher field strengths, corneal damage was detected. Compared with injection of DNA alone, up to 1000-fold more gene product was produced using electroporation. Expression was detected as early as 6 h post-electroporation, remained high for 3 days, and decreased by 7 days. Gene expression was detected over the entire surface of the cornea in both epithelial and stromal layers.

CONCLUSIONS

These results demonstrate that electroporation is an excellent method for delivering genes to multiple cell layers within the mouse cornea and that it results in extremely high levels of gene expression with little, if any, inflammatory response or tissue damage, making this a very useful technique for corneal gene transfer.

Serine/threonine protein phosphatase 5 (PP5) participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling

BACKGROUND

In most cells glucocorticoid receptors (GR) reside predominantly in the cytoplasm. Upon hormone binding, the GR translocates into the nucleus, where the hormone-activated GR-complex regulates the transcription of GR-responsive genes. Serine/threonine protein phosphatase type 5 (PP5) associates with the GR-heat-shock protein-90 complex, and the suppression of PP5 expression with ISIS 15534 stimulates the activity of GR-responsive reporter plasmids, without affecting the binding of hormone to the GR.

RESULTS

To further characterize the mechanism by which PP5 affects GR-induced gene expression, we employed immunofluorescence microscopy to track the movement of a GR-green fluorescent fusion protein (GR-GFP) that retained hormone binding, nuclear translocation activity and specific DNA binding activity, but is incapable of transactivation. In the absence of glucocorticoids, GR-GFP localized mainly in the cytoplasm. Treatment with dexamethasone results in the efficient translocation of GR-GFPs into the nucleus. The nuclear accumulation of GR-GFP, without the addition of glucocorticoids, was also observed when the expression of PP5 was suppressed by treatment with ISIS 15534. In contrast, ISIS 15534 treatment had no apparent effect on calcium induced nuclear translocation of NFAT-GFP.

CONCLUSION

These studies suggest that PP5 participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling, and that the GR-induced transcriptional activity observed when the expression of PP5 is suppressed by treatment with ISIS 15534 results from the nuclear accumulation of GR in a form that is capable of binding DNA yet still requires agonist to elicit maximal transcriptional activation.

Muscle-specific enhancement of gene expression by incorporation of SV40 enhancer in the expression plasmid

Skeletal muscle is established as an ideal tissue for gene delivery to treat systemic diseases. However, the relatively low levels of gene expression obtained from using naturally occurring promoters, including the strong cytomegalovirus (CMV) enhancer/promoter (E/P), have limited the use of muscle as a target tissue. The relatively weak simian virus 40 (SV40) enhancer is known to have dual functions promoting localization of DNA to the nucleus and activating transcription. An SV40 enhancer incorporated either at the 5' end of CMV E/P or the 3' end of the polyadenylation site gave as much as a 20-fold increase in the level of exogenous gene expression in muscle in vivo, compared with expression observed with CMV E/P alone. The minimum requirement for this enhancement is a single copy of a 72-bp element of the SV40 enhancer, in combination with either the CMV E/P or skeletal actin (SkA) promoter. Enhancement of gene expression in muscle by this SV40 enhancer was also observed by using the powerful electroporation delivery. However, the SV40 enhancer does not increase the level of CMV E/P driven reporter gene expression in dividing tumor cells in vivo and in the dividing myoblast cell C2C12 in vitro. The data suggest that including this enhancer in the plasmid will enhance the level of gene production for muscle-based gene therapy.

Peptide nucleic acids: versatile tools for gene therapy strategies

Peptide nucleic acids, or PNAs, are oligonucleotide analogs in which the phosphodiester backbone is replaced with a polyamide structure. First synthesized less than 10 years ago, they have received great attention due to their several favorable properties, including resistance to nuclease and protease digestion, stability in serum and cell extracts, and their high affinity for RNA and single and double-stranded DNA targets. Although initially designed and demonstrated to function as antisense and antigene reagents that inhibit both transcription and translation by steric hindrance, more recent applications have included gene activation by synthetic promoter formation and mutagenesis of chromosomal targets. Most notably for gene delivery, they have been used to specifically label plasmids and act as adapters to link synthetic peptides or ligands to the DNA. Thus, their great potential lies in the ability to attach specific targeting peptides to plasmids to circumvent such barriers to gene transfer as cell-targeting or nuclear localization, thereby increasing the efficacy of gene therapy.

Store-operated calcium entry and increased endothelial cell permeability

We hypothesized that myosin light chain kinase (MLCK) links calcium release to activation of store-operated calcium entry, which is important for control of the endothelial cell barrier. Acute inhibition of MLCK caused calcium release from inositol trisphosphate-sensitive calcium stores and prevented subsequent activation of store-operated calcium entry by thapsigargin, suggesting that MLCK serves as an important mechanism linking store depletion to activation of membrane calcium channels. Moreover, in voltage-clamped single rat pulmonary artery endothelial cells, thapsigargin activated an inward calcium current that was abolished by MLCK inhibition. F-actin disruption activated a calcium current, and F-actin stabilization eliminated the thapsigargin-induced current. Thapsigargin increased endothelial cell permeability in the presence, but not in the absence, of extracellular calcium, indicating the importance of calcium entry in decreasing barrier function. Although MLCK inhibition prevented thapsigargin from stimulating calcium entry, it did not prevent thapsigargin from increasing permeability. Rather, inhibition of MLCK activity increased permeability that was especially prominent in low extracellular calcium. In conclusion, MLCK links store depletion to activation of a store-operated calcium entry channel. However, inhibition of calcium entry by MLCK is not sufficient to prevent thapsigargin from increasing endothelial cell permeability.

Dendrimer-assisted patch-clamp sizing of nuclear pores

Macromolecular translocation (MMT) across the nuclear envelope (NE) occurs exclusively through the nuclear pore complex (NPC). Therefore, the diameter of the NPC aqueous/electrolytic channel (NPCC) is important for cellular structure and function. The NPCC diameter was previously determined to be approximately equal to 10 nm with electron microscopy (EM) using the translocation of colloidal gold particles. Here we present patch-clamp and fluorescence microscopy data from adult cardiomyocyte nuclei that demonstrate the use of patch-clamp for assessing NPCC diameter. Fluorescence microscopy with B-phycoerythrin (BPE, 240 kDa) conjugated to a nuclear localization signal (NLS) demonstrated that these nuclei were competent for NPC-mediated MMT (NPC-MMT). Furthermore, when exposed to an appropriate cell lysate, the nuclei expressed enhanced green fluorescence protein (EGFP) after 5-10 h of incubation with the plasmid for this protein (pEGFP, 3.1 MDa). Nucleus-attached patch-clamp showed that colloidal gold particles were not useful probes; they modified NPCC gating. As a result of this finding, we searched for an inert class of particles that could be used without irreversibly affecting NPCC gating and found that fluorescently labeled Starburst dendrimers, a distinct class of polymers, were useful. Our patch-clamp and fluorescence microscopy data with calibrated dendrimers indicate that the cardiomyocyte NPCC diameter varies between 8 and 9 nm. These studies open a new direction in the investigation of live, continuous NPC dynamics under physiological conditions.

Calcium, ATP and nuclear pore channel gating

Nuclear envelope (NE) cisternal Ca2+ and cytosolic ATP are required for nuclear-pore-complex-(NPC-) mediated transport of DNAs, RNAs, transcription factors and other large molecules. Isolated cardiomyocyte nuclei, capable of macromolecular transport (MMT), have intrinsic NPC ion channel behavior. The large ion conductance (gamma) activity of the NPC channel (NPCC) is blocked by the NPC monoclonal antibody mAb414, known to block MMT, and is also silenced during periods of MMT. In cardiomyocytes, neither cytosolic Ca2+ nor ATP alone directly affects NPCC gating. To test the role of Ca2+ and ATP in NPCC activity, we carried out the present patch-clamp study with the pipette attached to the outer NE membrane of nuclei isolated from cultured Dunning G prostate cancer cells. Our investigations demonstrate that in these isolated nuclei neither cytosolic Ca2+ nor ATP alone directly affects NPCC gating. However, when simultaneously applied to the bath and pipette, they transiently silence NPCC activity through stimulation of MMT by raising the Ca2+ concentration in the NE cisterna ([Ca2+]NE). Our fluorescence microscopy observations with nuclear-targeted macromolecular fluorochromes (B-phycoerythrin and plasmid for the enhanced green fluorescence protein EGFP, pEGFP-C1) and with FITC-labeled RNA support the view that channel silence accompanies MMT. Repeated Ca2+ loading of the NE with Ca2+ and ATP, after unloading with 1-5 microM inositol 1,4,5-trisphosphate (IP3), thapsigargin (TSG) or 5 mM BAPTA or EGTA, failed to affect channel gating. This result indicates that other factors are involved in this phenomenon and that they are exhausted during the first cycle of NE Ca2+ loading/unloading--in agreement with current theories of NPC-mediated MMT. The results explain how Ca2+ and IP3 waves may convert the NE into an effective Ca2+ barrier and, consequently, affect the regulation of gene activity and expression through their feedback on MMT and NPCC gating. Thus, [Ca2+]NE regulation by intracellular messengers is an effective mechanism for synchronizing gene activity and expression to the cellular rhythm.

Gene transfer to intact mesenteric arteries by electroporation

The purpose of the present study was to develop a rapid, reproducible method of nonviral gene transfer to the intact vasculature. Male Sprague-Dawley rats were anesthetized, a midline abdominal incision was made and segmental branches of the superior mesenteric artery were dissected free of surrounding mesentery. A specially designed electroporation probe was placed around the neurovascular bundle and the electroporation chamber filled with a solution containing the firefly luciferase expressing plasmid (pCMV-Lux-DTS) or the green fluorescent protein expressing plasmid (pEGFP-N1). Vessels were electroporated with eight 10-ms pulses of 200 V/cm. Sixty seconds after electroporation, the DNA solution was removed, the intestine returned to the abdomen and the abdominal wall closed with suture and metal wound clips. Six hours to 5 days later, rats were sacrificed and electroporated vessels were recovered. Luciferase activity of the blood vessels was monitored. Gene expression was detected as early as 6 h postelectroporation, peaked at 1-3 days with levels up to 1 ng of reporter gene product per vessel segment and returned towards baseline by day 5. Histological analysis of blood vessel segments revealed green fluorescent protein-positive cells throughout the thickness of the vessel wall (endothelial cells to adventitia). Responses of electroporated vessels to vasoconstricting stimuli were indistinguishable from those of control vessels at either 2 or 40 days posttreatment. The results of this study provide evidence that electroporation is an effective means for introducing naked DNA into the blood vessel wall and form the basis for future studies on targeted gene therapy to the intact vasculature.

Sequence requirements for plasmid nuclear import

The nuclear envelope is a major barrier for nuclear uptake of plasmids and represents one of the most significant unsolved problems of nonviral gene delivery. We have previously shown that the nuclear entry of plasmid DNA is sequence-specific, requiring a 366-bp fragment containing the SV40 origin of replication and early promoter. In this report, we show that, although fragments throughout this region can support varying degrees of nuclear import, the 72-bp repeats of the SV40 enhancer facilitate maximal transport. The functions of the promoter and the origin of replication are not needed for nuclear localization of plasmid DNA. In contrast to the import activity of the SV40 enhancer, two other strong promoter and enhancer sequences, the human cytomegalovirus (CMV) immediate-early promoter and the Rous sarcoma virus LTR, were unable to direct nuclear localization of plasmids. The inability of the CMV promoter to mediate plasmid nuclear import was confirmed by measurement of the CMV promoter-driven expression of green fluorescent protein (GFP) in microinjected cells. At times before cell division, as few as 3 to 10 copies per cell of cytoplasmically injected plasmids containing the SV40 enhancer gave significant GFP expression, while no expression was obtained with more than 1000 copies per cell of plasmids lacking the SV40 sequence. However, the levels of expression were the same for both plasmids after cell division in cytoplasmically injected cells and at all times in nuclear injected cells. Thus, the inclusion this SV40 sequence in nonviral vectors may greatly increase their ability to be transported into the nucleus, especially in nondividing cells.

Nuclear import of plasmid DNA in digitonin-permeabilized cells requires both cytoplasmic factors and specific DNA sequences

Although much is known about the mechanisms of signal-mediated protein and RNA nuclear import and export, little is understood concerning the nuclear import of plasmid DNA. Plasmids between 4.2 and 14.4 kilobases were specifically labeled using a fluorescein-conjugated peptide nucleic acid clamp. The resulting substrates were capable of gene expression and nuclear localization in microinjected cells in the absence of cell division. To elucidate the requirements for plasmid nuclear import, a digitonin-permeabilized cell system was adapted to follow the nuclear localization of plasmids. Nuclear import of labeled plasmid was time- and energy-dependent, was inhibited by the lectin wheat germ agglutinin, and showed an absolute requirement for cytoplasmic extract. Addition of nuclear extract alone did not support plasmid nuclear import but in combination with cytoplasm stimulated plasmid nuclear localization. Whereas addition of purified importin alpha, importin beta, and RAN was sufficient to support protein nuclear import, plasmid nuclear import also required the addition of nuclear extract. Finally, nuclear import of plasmid DNA was sequence-specific, requiring a region of the SV40 early promoter and enhancer. Taken together, these results confirm and extend our findings in microinjected cells and support a protein-mediated mechanism for plasmid nuclear import.

Peptide nucleic acid (PNA) binding-mediated induction of human gamma-globin gene expression

Peptide nucleic acids (PNAs) can bind to homopurine/homopyrimidine sequences of double-stranded DNA targets in a sequence-specific manner and form [PNA]2/DNA triplexes with single-stranded DNA D-loop structures at the PNA binding sites. These D-loop structures have been found to have a capacity to initiate transcription in vitro. If this strategy can be used to induce transcription of endogenous genes, it may provide a novel approach for gene therapy of many human diseases. Human [beta] globin disorders such as sickle cell anemia and beta-thalassemia are very common genetic diseases that are caused by mutations in the beta-globin gene. When gamma-globin genes are highly expressed in sickle cell patients, the presence of high levels of fetal hemoglobin (HbF, alpha2gamma2) can compensate for the defective beta-globin gene product and such patients have much improved symptoms or are free of disease. However, the gamma-globin genes are developmentally regulated and normally expressed at very low levels (>1%) in adult blood cells. We have investigated the possibility of inducing gamma-globin gene expression with PNAs. Using PNAs designed to bind to the 5' flanking region of the gamma-globin gene, induction of expression of a reporter gene construct was demonstrated both in vitro and in vivo. More importantly, PNA-mediated induction of endogenous gamma-globin gene expression was also demonstrated in K562 human erythroleukemia cells. This result suggests that induction of gamma-globin gene expression with PNAs might provide a new approach for the treatment of sickle cell disease. PNA-induced gene expression strategy also may have implications in gene therapy of other diseases such as genetic diseases, cancer and infectious diseases.

Nuclear targeting of plasmid DNA in human corneal cells

PURPOSE

To characterize the mechanisms of plasmid DNA nuclear localization in primary cultures of human corneal epithelial cells and keratocytes.

METHODS

Purified, supercoiled plasmid DNA was microinjected into the cytoplasm of human corneal epithelial cells and keratocytes that had been established from donor corneas two to three passages previously, and localized 8 hours later by in situ hybridization. To confirm the sequence-specificity of nuclear import observed in microinjected cells, liposome-mediated transient transfection experiments also were performed on human corneal epithelial cell and keratocyte cultures.

RESULTS

Primary cultures of human corneal epithelial cells and keratocytes have the capacity to transport plasmid DNA from the cytoplasm to the nucleus in the absence of cell division. This transport activity is sequence-dependent requiring portions of the simian virus 40 (SV40) early promoter and enhancer. The majority of this nuclear transport activity resides within the enhancer domain of the SV40 DNA, a region rich in transcription factor binding sites. This DNA nuclear import sequence also manifested itself in liposome-mediated transfection experiments, causing a greater than 2-fold increase in reporter gene expression in human corneal cells in a beta-galactosidase-expressing vector and up to a 1000-fold increase in a luciferase-expressing vector when compared to similar expression plasmids lacking the sequence.

CONCLUSION

These results demonstrate that primary, non-transformed human corneal epithelial cells and keratocytes display sequence-specific nuclear import of plasmid DNA in the absence of mitosis. The small sequence that mediates nuclear localization of plasmids is active both in microinjected and cationic liposome transfected cells, and leads to increased gene expression. Thus, inclusion of this DNA sequence into non-viral vectors should improve the efficiency of ocular gene transfer in vivo.

Cell-specific nuclear import of plasmid DNA

One factor limiting the success of non-viral gene therapy vectors is the relative inability to target genes specifically to a desired cell type. To address this limitation, we have begun to develop cell-specific vectors whose specificity is at the level of the nuclear import of the plasmid DNA. We have recently shown that nuclear import of plasmid DNA is a sequence-specific event, requiring the SV40 enhancer, a region known to bind to a number of general transcription factors (Dean DA, Exp Cell Res 1997; 230: 293). From these studies we developed a model whereby transcription factor(s) bind to the DNA in the cytoplasm to create a protein-DNA complex that can enter the nucleus using the protein import machinery. Our model predicts that by using DNA elements containing binding sites for transcription factors expressed in unique cell types, we should be able to create plasmids that target to the nucleus in a cell-specific manner. Using the promoter from the smooth muscle gamma actin (SMGA) gene whose expression is limited to smooth muscle cells, we have created a series of reporter plasmids that are expressed selectively in smooth muscle cells. Moreover, when injected into the cytoplasm, plasmids containing portions of the SMGA promoter localize to the nucleus of smooth muscle cells, but remain cytoplasmic in fibroblasts and CV1 cells. In contrast, a similar plasmid carrying the SV40 enhancer is transported into the nuclei of all cell types tested. Nuclear import of the SMGA promoter-containing plasmids could be achieved when the smooth muscle specific transcription factor SRF was expressed in stably transfected CV1 cells, supporting our model for the nuclear import of plasmids. Finally, these nuclear targeting sequences were also able to promote increased gene expression in liposome- and polycation-transfected non-dividing cells in a cell-specific manner, similar to their nuclear import activity. These results provide proof of principle for the development of cell-specific non-viral vectors for any desired cell type.

Conductance artifacts in a novel in vitro model of ventriculothoracic electrical coupling

The utility of open chest conductance (COND) ventriculography is limited by artifacts altering the relationship between COND and left ventricular (LV) volume. Pressure-COND loops often lean to the left during LV volume reduction by caval occlusion. Time varying alterations in the pericardial-LV contact area affect electrical coupling in the open chest during the cardiac cycle, producing COND artifacts. In this study, an open-mediastinum model was constructed. Components represented the LV, blood, pericardium, and thoracic contents. Varying ventriculothoracic coupling was simulated by changing the volume of pericardial saline (0, 30, 60 ml). Raw dual field COND was repeatedly (n = 20) compared with volumes of normal saline from 60 to 120 ml at 5 ml intervals. Groups were compared by linear regression and repeated measures ANOVA. Artifacts significantly (p < 0.01) altered parallel COND, indicated by the y-intercept, with the exception of 0 versus 30 ml. The slope constant also changed significantly, with the exception of 30 versus 60 ml. These results suggest that variable pericardial-LV contact can cause time varying artifacts in COND in the open chest. Therefore, posterior insulation may reduce artifacts in COND ventriculography and should be tested for this effect.

Reversal of iatrogenic myocardial edema and related abnormalities of diastolic properties in the pig left ventricle

OBJECTIVE

This study examines the resolution of iatrogenic edema and related changes in systolic and diastolic properties in the intact pig left ventricle.

METHODS

The coronary arteries were perfused for 50 to 60 seconds with diluted blood (hematocrit value 10% +/- 1%, edema group, n = 5) or whole blood (hematocrit value 28% +/- 1%, control group, n = 6) infused into the aortic root during aortic crossclamping in conditioned, anesthetized pigs. After whole blood reperfusion, preload reduction by vena caval occlusion was used to define systolic and diastolic properties at 15-minute intervals. Left ventricular pressure and conductance, aortic flow, and two-dimensional echocardiography were recorded.

RESULTS

Left ventricular mass (wall volume) in the edema group increased significantly compared with that in control pigs after crossclamp removal. Mass returned to preperfusion levels after 45 minutes. The ventricular stiffness constant (beta) increased significantly in the edema group versus the control group, returning to baseline by 30 minutes. The diastolic relaxation constant (tau) and base constant (alpha) did not differ between groups. There was no significant change in contractility.

CONCLUSION

Increases in left ventricular mass and diastolic stiffness induced by coronary perfusion with hemodiluted blood resolve after 45 minutes of whole blood perfusion in pigs. This study defines physiologic effects of edema in the normal heart while eliminating most common confounding experimental errors.

Membranes of herpes simplex virus type-1-infected human corneal epithelial cells are not permeabilized to macromolecules and therefore do not release IL-1alpha

Nanogram amounts of the proinflammatory cytokine interleukin-1alpha (IL-1alpha) were detected in uninfected cultures of human corneal epithelial cells (HCEC). Although HSV-1 replicated >10(4)-fold in these cells and caused extensive cytopathic effects, virus infection was not accompanied by significant extracellular release of IL-1alpha. Additional studies showed that release of radiolabeled cytosolic proteins from virus-infected HCEC was no greater than that released by mock-infected cells. These findings indicate that HSV-1 infection of HCEC does not result in IL-1alpha release because newly formed virus progeny can escape infected cells without disrupting cell membranes.

A method for detecting changes in left ventricular mass during variations in filling volume

Two-dimensional echocardiography has been useful for measuring changes in left ventricular mass (LVM) at constant left ventricular end-diastolic volume (LVEDV). Two-dimensional echocardiographic measurement of LVM changes during variations in LVEDV requires definition of the LVM/LVEDV relation because two-dimensional echocardiographic measurements could be affected by asymmetrical redistribution of LVM. Echocardiography data were recorded during caval occlusions in pigs (n = 6). Results confirm that A(M) (left ventricular [LV] short-axis cross-sectional [SACS] wall thickness area), was inversely related to AL (LV SACS lumen area), the average relation being A(M) = -0.33 AL + 20 (r = 0.82 +/- 0.05 [SE]). In addition, we developed a model that computes normal relation between LV SACS wall thickness area (AMc) and LV SACS lumen area (ALc) over a physiologic range of LVEDVs based on a single end-diastolic two-dimensional echocardiographic SACS image. Each computed relation corresponds uniquely to an LVM (LVMc). Theoretically, a difference between AMc/ALc relation before an intervention and the computed relation after the intervention would indicate a change in LVM. To test the utility of this model, edema was induced in a second group of pigs (n = 6) by coronary hemodilution. Two conditions were tested: pre-edema and edema. Serial AMc/ALc and LVMc were computed. Pre-edema and edema AMc were compared at matched LV SACS end-diastolic areas (ALc = 15 cm2). Results showed a significant increase in LVMc (two-tailed p value < 0.05), as observed by two-dimensional echocardiography. We conclude that the A(M) and AL are inversely related. This relation is useful for detecting alterations in LVM during variations in LVEDV.

Inhaled nitric oxide is not a myocardial depressant in a porcine model of heart failure

BACKGROUND

Inhaled nitric oxide has been shown to be a potent and selective pulmonary vasodilator. Reports of increases in left ventricular end-diastolic pressure and episodes of pulmonary edema during the clinical use of inhaled nitric oxide in patients with preexisting left ventricular dysfunction have raised concerns that this agent may have myocardial depressant effects. We therefore undertook a study of the effects of inhaled nitric oxide on myocardial contractility in a porcine model of ventricular failure and pulmonary hypertension.

METHODS

After inducing heart failure in 10 pigs by rapid ventricular pacing, hemodynamic measurements and pressure-volume diagrams (by the conductance method) were obtained in six animals at baseline and during administration of inhaled nitric oxide at concentrations of 20 and 40 ppm. Myocardial contractile state was assessed by the end-systolic pressure-volume relationship and preload-recruitable stroke work, whereas diastolic function was measured in terms of the end-diastolic pressure-volume relationship and the pressure decay time constant T.

RESULTS

Baseline hemodynamics reflected heart failure and pulmonary hypertension, and inhaled nitric oxide induced significant reductions in mean pulmonary artery pressure and pulmonary vascular resistance. Although left ventricular end-diastolic pressure increased during administration of inhaled nitric oxide, no changes were observed in measures of systolic or diastolic function.

CONCLUSIONS

Inhaled nitric oxide reduced pulmonary vascular resistance but did not alter myocardial contractility or diastolic function. Increases in left ventricular end-diastolic pressure during inhaled nitric oxide therapy are therefore not due to myocardial depression and may be related to increases in volume delivery to the left side of the heart resulting from reduced pulmonary vascular resistance.

Surgical perspective on invasive Candida infections

Invasive and disseminated Candida infections have become a major source of morbidity and mortality in the modern surgical intensive care unit. The most common risks for invasion and dissemination are the use of antibiotics, central venous lines, total parenteral nutrition, burns, immunosuppression, and other markers for severity of illness (APACHE > 10, ventilatory use for > 48 hours). Data suggest that colonization can be a late predictor of invasive disease in today's critically ill surgical patient and that prophylaxis or early treatment in high risk patients is warranted, particularly before invasive/disseminated disease becomes life-threatening. When advanced disease is present, the diagnosis of invasive or disseminated Candida infection is often prompted by clinical suspicion and supported by consistent clinical data; laboratory tests alone lack sufficient sensitivity and specificity to direct therapeutic decision-making. Once the diagnosis of invasive or disseminated Candida infection is ascertained, early systemic treatment, along with treatment of localized infection, is as fundamental as with any other serious infectious disease. Reported toxicity and efficacy supports the use of fluconazole for most patients with invasive/disseminated Candida infections. For the most critically ill surgical patient amphotericin B remains the treatment of choice. Prophylaxis and early treatment strategies with minimally toxic agents may diminish the need to use more toxic therapy in the most severely ill patients.