Chylomicron-sized lipid particles are formed in the setting of apolipoprotein B deficiency

The mechanisms for packaging large quantities of neutral lipids into apolipoprotein (apo) B-containing lipoproteins (chylomicrons or VLDL) are incompletely understood. However, several lines of evidence have suggested that the addition of core lipids to apoB to form a lipoprotein particle within the endoplasmic reticulum (ER) may involve two steps: first, the addition of small amounts of core lipids to membrane-bound apoB, generating a lipid-poor, small apoB-containing particle, and second, the fusion of that particle with a larger, independently formed triglyceride-rich and apoB-free "lipid particle." We sought to test this two-step hypothesis of apoB core lipidation by using electron microscopy to compare chylomicron assembly in mice that are genetically deficient in the ability to synthesize apoB in the intestine to control mice. In 19-day gestational mice (fasting setting) that were deficient in intestinal apoB synthesis, chylomicron-sized lipid particles in the lumen of the enterocyte ER were even more abundant and were 2- to 3-fold larger than those in the enterocytes of normal control mice. However, there were fewer lipid-staining particles in the Golgi apparatus, and many fewer particles in the extracellular space, compared with normal control mice. In both types of newborn suckling mice, much larger lipid particles were assembled within the lumen of the ER. They were however, less abundant and rarely reached the Golgi apparatus in fatty enterocytes of intestines deficient in apoB synthesis. These observations provide in vivo evidence that chylomicron formation could involve the synthesis of apoB-free triglyceride-rich particles within the endoplasmic reticulum (ER) lumen, and that the transport of these lipid particles out of the ER to Golgi apparatus and interstitium is facilitated by the acquisition of apoB.

A real-time algorithm to improve the response time of a clinical multigas analyser

OBJECTIVE

An algorithm to improve the response time of a clinical respiratory multigas analyser is presented.

METHODS

The algorithm involves the application of a second order differential equation to the analyser gas output signals in real-time. The adjusted analyser output signals are compared with those of a quadrupole respiratory mass spectrometer sampling and analysing simultaneously.

RESULTS

Our results show a close correlation between the adjusted clinical gas analyser and the mass spectrometer signals. Lung volumes derived from a non-invasive sinusoidal inert gas forcing technique, in a model test lung, using the adjusted clinical gas analyser and the mass spectrometer signals demonstrated comparable results.

CONCLUSIONS

The algorithm provides an improvement on the relatively slow response times of the clinical gas analyser for breath-by-breath time-dependent applications. The same algorithm can also be applied to other instruments which have slow response times.

Knockout of the abetalipoproteinemia gene in mice: reduced lipoprotein secretion in heterozygotes and embryonic lethality in homozygotes

Abetalipoproteinemia, an inherited human disease characterized by a near-complete absence of the apolipoprotein (apo) B-containing lipoproteins in the plasma, is caused by mutations in the gene for microsomal triglyceride transfer protein (MTP). We used gene targeting to knock out the mouse MTP gene (Mttp). In heterozygous knockout mice (Mttp+/- ), the MTP mRNA, protein, and activity levels were reduced by 50%, in both liver and intestine. Compared with control mice (Mttp+/+), chow-fed Mttp+/- mice had reduced plasma levels of low-density lipoprotein cholesterol and had a 28% reduction in plasma apoB100 levels. On a high-fat diet, the Mttp+/- mice exhibited a marked reduction in total plasma cholesterol levels, compared with those in Mttp+/+ mice. Both the livers of adult Mttp+/- mice and the visceral endoderm of the yolk sacs from Mttp+/- embryos manifested an accumulation of cytosolic fat. All homozygous embryos (Mttp-/-) died during embryonic development. In the visceral endoderm of Mttp-/- yolk sacs, lipoprotein synthesis was virtually absent, and there was a marked accumulation of cytosolic fat droplets. In summary, half-normal MTP levels do not support normal levels of lipoprotein synthesis and secretion, and a complete deficiency of MTP causes lethal developmental abnormalities, perhaps because of an impaired capacity of the yolk sac to export lipids to the developing embryo.

Genes for apolipoprotein B and microsomal triglyceride transfer protein are expressed in the heart: evidence that the heart has the capacity to synthesize and secrete lipoproteins

BACKGROUND

Expression of both the apolipoprotein B (apoB) gene and the microsomal triglyceride transfer protein (MTP) gene is required for the assembly and secretion of triglyceride-rich lipoproteins in the liver and intestine. Both genes have been assumed to be silent in the heart.

METHODS AND RESULTS

Northern blot and RNase protection analyses showed that the apoB and MTP genes were expressed in the hearts of mice and humans. In situ hybridization studies revealed that the apoB mRNA was produced in cardiac myocytes. Electron microscopy of human cardiac myocytes revealed lipid-staining particles of relatively small diameter (approximately 250 A) within the Golgi apparatus.

CONCLUSIONS

These studies strongly suggest that the heart synthesizes and secretes apoB-containing lipoproteins.

Synthesis and proteinase inhibitory properties of diphenyl phosphonate analogues of aspartic and glutamic acids

The synthesis of diphenyl phosphonate analogues of aspartic and glutamic acid, and their inhibitory activity against S. aureus V8 protease and granzyme B, is described. The study has revealed difficulties with protecting group compatibility in the synthesis of these analogues. Two analogues, Acetyl. AspP (OPh)2 and Acetyl.GluP (OPh)2 were found to function as irreversible inactivators of V8 proteinase, yet exhibit no activity against granzyme B.

Case of the month: February 1998--82 year old man with progressive visual defects

An 82 year old man with a recurrent prolactin-secreting pituitary adenoma had clinically asymptomaptic fungal growth in necrotic tissue adjacent to the tumor. This fungus was characterized by clumps of basophilic hyphae with pigment production. Ascus formation containing nucleated conidiopores was present. The asci had tapered and cylindrical beaks making Microascus sp. the most likely diagnosis, however, without cultures, Pseudoallesheria boydii could not eliminated. The patient was treated with Amphotericin B and there was no evidence of intracranial extension 4 months later.

A reproducible model of circulatory arrest and remote resuscitation in rats for NMR investigation

BACKGROUND AND PURPOSE

Because noninvasive physiological monitoring of cerebral blood flow, metabolic integrity, and brain ion and water homeostasis can now be accomplished with new, state-of-the-art MR spectroscopy and imaging techniques, it is appropriate to develop controllable and reproducible animal models that permit prolonged circulatory arrest and resuscitation in the magnet and also allow for studies of long-term survival and outcome. We have developed such a model in rats that involves minimal surgical preparations and can achieve resuscitation remotely within precisely controlled time.

METHODS

Cardiac arrest was induced by asphyxiation, the duration of which ranged from 8 to 24 minutes. Resuscitation was achieved remotely by a slow, intra-aortic infusion of oxygenated blood (withdrawn either from the same rat before asphyxia or from a healthy donor rat) along with a resuscitation cocktail containing heparin (50 U/100 g), sodium bicarbonate (0.1 mEq/100 g), and epinephrine (4 micrograms/100 g). The body temperature was measured by a tympanic thermocouple probe and was controlled either by a heating pad (constant tympanic temperature = 37 degrees C) or by warm ambient air (constant air temperature = 37 degrees C). Interleaved 31P/1H nuclear magnetic resonance (NMR) spectroscopy was used in a selected group of rats to measure the cerebral metabolism before and during approximately 20 minutes of circulatory arrest and after resuscitation.

RESULTS

The overall success rate of resuscitation, irrespective of the duration of cardiac arrest, was 82% (51 of 62). With a programmed infusion pump, the success rate was even higher (95%). The survival time for rats subjected to 15 and 19 minutes of asphyxia with core temperature tightly controlled was significantly lower than that with ambient temperature control (P < 0.001 and P < 0.04, respectively). High-quality NMR spectra can be obtained continuously without interference from the resuscitation effort. Final histological examinations taken 5 days after resuscitation showed typical neuronal damages, similar to those found in other global ischemia models.

CONCLUSIONS

Because the no-flow time and resuscitation time can be precisely controlled, this outcome model is ideally suited for studies of ischemic and reperfusion injuries in the brain and possibly in other critical organs, permitting continuous assessment of long-term recovery and follow-up in the same animals.

Neurodevelopmental anomalies in children with neuroblastoma

BACKGROUND

Case reports have associated neuroblastoma, a cancer derived from the embryonal neural crest, with aganglionosis coli and neurofibromatosis type I. The aim of the current study was to test the hypothesis that neuroblastoma is part of a global defect in neurodevelopment.

METHODS

Neuropathologic findings from autopsies of children who died of neuroblastoma during the period 1980-1995 at the Children's Hospital of Pittsburgh were reviewed for macroscopic and microscopic abnormalities. As controls, autopsies of children who had died of other primary extracranial cancers over the same time period also were studied. Medical records of neuroblastoma patients for whom autopsies were available were reviewed for clinical evidence of preexisting nonmalignant neurologic disease.

RESULTS

Of 145 children diagnosed with neuroblastoma, 49 had died, and autopsies not restricting examination of the brain had been performed on 13. Macroscopic anatomic abnormalities (a small cerebellum and the absence of the corpus callosum) were noted in one patient who was known to have been mentally retarded without having a defined syndrome. Microscopic abnormalities of cytoarchitecture were noted in that patient as well as 3 of the 12 other patients (focal cortical dysplasia [fcd], n = 3; leptomeningeal heterotopia, n = 1; abortive sulcation or flattened gyri, n = 2). None of 3 patients with only microscopic abnormalities had clinical evidence of problems with neurodevelopment. Of the 26 children with nonneuroblastoma cancers for whom complete autopsies were available, 1 infant had major macroscopic structural abnormalities of the brain. None of these patients had microscopic abnormalities (P < 0.01).

CONCLUSIONS

Children with neuroblastoma have an increased incidence of abnormalities of brain cytoarchitecture, particularly fcd. These abnormalities are generally asymptomatic and are diagnosed by histologic examination. Such abnormalities cannot be attributed to chemotherapy and are not observed in other children with non-central nervous system tumors. These findings are consistent with the concept that neuroblastoma may occur in the setting of a more global defect in neurodevelopment. A blinded review of larger numbers of cases will be needed to verify these data.

Case of the month: September 1997--a 26 year old woman with new onset seizures

A twenty-six year old, previously healthy nurse presented with new onset of seizures and was given a clinical diagnosis of herpes simplex encephalitis. After treatment with acyclovir there was incomplete resolution of the lesions by MRI scans and within a few months the patient's neurologic symptoms worsened, prompting a stereotactic biopsy. A diagnosis of progressive multifocal leukoencephalopathy (PML) was made using electron microscopy, and in situ hybridization studies. Subsequent to this biopsy, she was shown to be infected with human immunodeficiency virus (HIV) and had a CD4 T-cell count of 63. She had no known risk factors for HIV infections and had been tested as recently as eighteen months previously during her pregnancy. Neither the husband nor the child were positive for HIV. PML as a presenting sign of HIV infection is rare.

Primary parafalcine chondrosarcoma in a child

Intracranial cartilaginous tumors are rare lesions, usually arising from the skull base in older individuals. We report the case of a 12-year-old girl with a low-grade type chondrosarcoma arising from the falx cerebri. To our knowledge this is the first such case reported in a child. She was treated with gross total surgical resection followed by external beam radiation because there was evidence of dural infiltration by tumor in and around the superior sagittal sinus. The patient remains progression free 9 months after surgery.

Complication of ventricular demand pacing after orthotopic heart transplantation: unusual case of pacemaker syndrome in an infant

BACKGROUND

Sinus node dysfunction is the most common indication for antibradycardiac permanent pacing after heart transplantation. Lack of atrioventricular synchrony during pacing can result in symptoms ranging from mild chest discomfort to severe manifestations such as dyspnea, hypotension, and cardiovascular collapse, all of which are ascribed to pacemaker syndrome. In infants pacemaker syndrome is often only recognized in the face of marked hemodynamic compromise.

RESULTS

This report details an unusual account of pacemaker syndrome in an infant after orthotopic heart transplantation.

CONCLUSIONS

Careful assessment of atrioventricular synchrony is important after infant transplantation.

Basic fibroblast growth factor expression as a predictor of prognosis in pediatric high-grade gliomas

Clinical and histopathological factors fail to adequately predict outcomes in children with high-grade gliomas, indicating a need to identify relevant biological markers of tumor behavior to guide therapeutic decision-making. Basic fibroblast growth factor (bFGF) is a mitogenic and angiogenic factor that has been observed to be overexpressed in a significant percentage of malignant gliomas, although the prognostic significance of this expression is unknown. To address this issue, the expression status of bFGF was examined immunohistochemically in a series of 27 archival pediatric malignant non-brainstem gliomas treated consecutively at our institution between 1975 and 1992. Tumors were categorized based on expression levels, and the association between expression status and outcome was examined. Sixteen cases showed high levels of expression of bFGF, and 11 showed low levels. There was no correlation between expression status and either tumor histology, patient age, or tumor location. However, there was a significant difference in outcome between patients with high levels of bFGF immunoreactivity and those with low expression. Median progression-free survival was >66 months in the low bFGF group as compared to 6 months in the high bFGF group (P = 0.006). Median overall survival was >66 months in the low bFGF group as compared to 18 months in the high bFGF group (P = 0.03). Tumor bFGF expression seems to be strongly associated with outcome in children with high-grade gliomas and, consequently, may serve as a biological correlate of patient prognosis in conjunction with other prognostic variables.

Immunohistochemical study of GABA(A) receptor beta2/3 subunits in the hippocampal formation of aged brains with Alzheimer-related neuropathologic changes

In AD, it is hypothesized that one factor contributing to the vulnerability of neurons is a delicate balance of excitatory and inhibitory inputs. To examine this hypothesis we have initiated a number of studies examining the role of the excitatory neurotransmitter glutamate and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the neurodegeneration of AD. As an initial investigation into the GABAergic system in AD, we employed immunocytochemical techniques and examined the distribution and density of the GABAA receptor subunits beta2/3 within the hippocampus of 13 subjects with a clinical diagnosis of AD and 6 nondemented elderly subjects. Collectively, these 19 subjects presented with a broad range of pathologic severity (i.e., Braak stages I-VI). Density measurements of nine hippocampal regions demonstrated highest levels of beta2/3 immunolabeling in the inner molecular layer of the dentate gyrus > CA1 > CA2, while the lowest levels were found in the granular layer of the dentate gyrus < or = CA4 < CA3 field. Despite these regional variations no significant difference in the mean density of beta2/3 immunolabeling was observed when comparing the pathologically mild (stages I and II), moderate (stages III and IV), and severe (stages V and VI) groups. These data suggest that in the hippocampus receptor subunits associated with GABAergic neurotransmission are relatively maintained even until the terminal stages of the disease.

Efficient gene transfer into primary and immortalized human fetal glial cells using adeno-associated virus vectors: establishment of a glial cell line with a functional CD4 receptor

Adeno associated virus (AAV) is a non-pathogenic dependent parvovirus with a broad host range, capable of high levels of transduction and stable integration into the host cell genome. We have investigated the potential for using AAV as a vector for gene transfer into glial cells of the human fetal nervous system. Recombinant AAV vectors expression either the reporter gene beta-galactosidase or a human CD4 receptor were able to transduce both primary glial cells of the human fetal nervous system and an SV40 immortalized human fetal glial cell line (SVG). No difference in transduction efficiency was observed between the primary cells and the cell line which in both cases was as high as 95%. Stable transfectants of the glial cell line expressing the CD4 receptor were selected. An SVG/CD4 expressing line was then established. The presence of the CD4 receptor was confirmed by immunohistochemistry, Westerm immuno-blotting and flow cytometric analysis. The CD4 receptor was shown to be functional by infection of the SVG/CD4 cell line with the human immunodeficiency virus (HIV). Upon infection, the SVG/CD4 cells produced 20-fold higher levels of the HIV intracellular core antigen P24 than the CD4 negative parental cells and in addition formed syncytia. The use of AAV vectors should prove useful in biological investigations of human glial cells and offers promise as a means of ex vivo and in vivo gene delivery.

Nasal provocation with allergen induces a secondary serum IgE antibody response

The study of the IgE response to seasonal antigen exposure is limited by its occurrence once a year and by the variability of patient exposure to pollens. To overcome these problems, we investigated whether nasal challenge with antigen causes an increase in serum anti-ragweed IgE levels. We challenged individuals with ragweed allergy intranasally with nanogram quantities of ragweed antigen extract and measured their serum anti-ragweed IgE levels before and at weekly intervals after challenge. In a series of studies we found that there was a reproducible rise in antigen-specific serum IgE levels beginning the first week after challenge that plateaued at about 180% of baseline levels during the fourth week and remained elevated for 8 weeks. Not all individuals showed this response. The magnitude of the allergen-specific IgE response to nasal challenge appeared to be greater than the response to seasonal exposure. Treatment with intranasal beclomethasone before challenge did not affect the response. The results demonstrate a human in vivo model for the study of the antigen-specific secondary IgE response to allergen.

Cutaneous injection of RANTES causes eosinophil recruitment: comparison of nonallergic and allergic human subjects

RANTES, a member of the C-C chemokine family, is a potent chemoattractant for T lymphocytes and eosinophils, but not neutrophils. To determine the effect of RANTES on cell recruitment in vivo, we injected up to 4 microg of RANTES intradermally into both allergic and nonallergic subjects and obtained biopsies 30 min, 6 h, and 24 h later. A dose- and time-dependent recruitment of eosinophils, CD45RO+ cells, and CD3+ cells was observed, with no effect seen on polymononuclear, cutaneous lymphocyte Ag+, CD68+, or tryptase+ cells. Eosinophil recruitment occurred more rapidly in allergic subjects than in nonallergic subjects. No eosinophil infiltrate was observed in nonallergic biopsies at 30 min and 6 h, whereas significant eosinophil recruitment was observed in allergic subjects by 30 min, reaching near-maximum levels by 6 h. The peak responses at 24 h were similar in both groups (nonallergic, 110 +/- 24 eosinophils/mm2; allergic, 113 +/- 38 eosinophils/mm2). The two groups had comparable numbers of circulating eosinophils. Major basic protein staining demonstrated eosinophil degranulation in both allergic and nonallergic groups. RANTES injection resulted in activation of endothelial E-selectin expression at 24 h. Incubation of cultured HUVECs with RANTES had no effect on adhesion molecule expression, suggesting that the in vivo effect may have been indirect. Our studies demonstrate that RANTES is a potent chemoattractant for eosinophils, CD3+ cells, and CD45RO+ cells in human skin. The accelerated eosinophil recruitment in allergic subjects provides support for the hypothesis that eosinophils from these subjects are primed in vivo.

Cutaneous injection of RANTES causes eosinophil recruitment: comparison of nonallergic and allergic human subjects

RANTES, a member of the C-C chemokine family, is a potent chemoattractant for T lymphocytes and eosinophils, but not neutrophils. To determine the effect of RANTES on cell recruitment in vivo, we injected up to 4 microg of RANTES intradermally into both allergic and nonallergic subjects and obtained biopsies 30 min, 6 h, and 24 h later. A dose- and time-dependent recruitment of eosinophils, CD45RO+ cells, and CD3+ cells was observed, with no effect seen on polymononuclear, cutaneous lymphocyte Ag+, CD68+, or tryptase+ cells. Eosinophil recruitment occurred more rapidly in allergic subjects than in nonallergic subjects. No eosinophil infiltrate was observed in nonallergic biopsies at 30 min and 6 h, whereas significant eosinophil recruitment was observed in allergic subjects by 30 min, reaching near-maximum levels by 6 h. The peak responses at 24 h were similar in both groups (nonallergic, 110 +/- 24 eosinophils/mm2; allergic, 113 +/- 38 eosinophils/mm2). The two groups had comparable numbers of circulating eosinophils. Major basic protein staining demonstrated eosinophil degranulation in both allergic and nonallergic groups. RANTES injection resulted in activation of endothelial E-selectin expression at 24 h. Incubation of cultured HUVECs with RANTES had no effect on adhesion molecule expression, suggesting that the in vivo effect may have been indirect. Our studies demonstrate that RANTES is a potent chemoattractant for eosinophils, CD3+ cells, and CD45RO+ cells in human skin. The accelerated eosinophil recruitment in allergic subjects provides support for the hypothesis that eosinophils from these subjects are primed in vivo.