Characterization of the binding of amyloid-beta peptide to cell culture-derived native apolipoprotein E2, E3, and E4 isoforms and to isoforms from human plasma

The epsilon 4 allele of apolipoprotein E (apoE, protein; APOE, gene) is a major risk factor for Alzheimer's disease (AD). Genetically, the frequency of the epsilon 4 allele is enriched in early-onset sporadic, late-onset familial, and common late-onset sporadic AD. ApoE is found in the extracellular amyloid-beta (A beta) deposits that are characteristic features of AD. In this study, we examined the interaction between A beta and apoE isoforms. The apoE isoforms used in this study were either produced by stably transfected Chinese hamster ovary cells (CHO) or were from human plasma. We report that when similar concentrations of the apoE isoforms were used, native nonpurified apoE3 from recombinant CHO-derived sources bound A beta, but apoE4 did not. In fact, in our system, binding of recombinant apoE4 to A beta was never detectable, even after incubation for 4 days. Furthermore, using the same assay conditions, native apoE2, like apoE3, binds A beta avidly. Furthermore, when human plasma apoE isoforms are tested in A beta binding experiments, apoE3 bound A beta more avidly than apoE4, and a major apoE/A beta complex (the 40-kDa form) was observed with plasma apoE3 but not apoE4. These data extend our understanding of apoE isoform-dependent binding of A beta by associating apoE2 with efficient apoE/A beta complex formation and demonstrate that native apoE3 (whether recombinant or derived from human plasma) forms sodium dodecyl sulfate-stable apoE/A beta complexes more readily than native apoE4. The different A beta-binding properties of native apoE4 versus native apoE3 provide insight into the molecular mechanisms by which the APOE epsilon 4 allele exerts its risk factor effects in AD.

The uncertain response in humans and animals

There has been no comparative psychological study of uncertainty processes. Accordingly, the present experiments asked whether animals, like humans, escape adaptively when they are uncertain. Human and animal observers were given two primary responses in a visual discrimination task, and the opportunity to escape from some trials into easier ones. In one psychophysical task (using a threshold paradigm), humans escaped selectively the difficult trials that left them uncertain of the stimulus. Two rhesus monkeys (Macaca mulatta) also showed this pattern. In a second psychophysical task (using the method of constant stimuli), some humans showed this pattern but one escaped infrequently and nonoptimally. Monkeys showed equivalent individual differences. The data suggest that escapes by humans and monkeys are interesting cognitive analogs and may reflect controlled decisional processes prompted by the perceptual ambiguity at threshold.

Allocation of attentional resources during habituation to food cues

Two experiments were designed to test the hypothesis that habituation to repeated food cues can be inhibited by allocating processing resources to nonfood cues. In two experiments, the salivary response to 10 presentations of lemon yogurt was assessed while subjects engaged in a controlled cognitive search task (demanding attentional resources), an automatic search task (needing fewer attentional resources), or no task. In Experiment 1, the controlled and automatic search tasks differed in the number of memory set items. In Experiment 2, the size of the memory sets was held constant, and individuals were provided practice to stabilize the different search strategies in the task. The automatic search and no task groups habituated to the repeated presentation of food cues in both experiments, but the controlled search group did not. These results support the hypothesis that allocation of attentional resources to external cues can influence the processing of food cues.

Cyclic AMP induces apolipoprotein E binding activity and promotes cholesterol efflux from a macrophage cell line to apolipoprotein acceptors

RAW 264 mouse macrophage cells were stably transfected with human apolipoprotein E (apoE) expression vectors. Clonal derivatives were characterized for expression of the human apoE2, apoE3, and apoE4 isoforms. An apoE4-expressing clonal cell line and a non-expressing clonal control cell line were loaded overnight with either [3H]cholesterol or [3H]choline. The cells were washed and incubated for 24 h in serum-free medium with or without the addition of 8-bromo-cyclic AMP (8-Br-cAMP). Only the apoE-secreting cells and only in the presence of 8-Br-cAMP released large amounts of labeled cholesterol or phosphatidylcholine into the medium. Mass analyses of cellular free and esterified cholesterol confirmed the results of the labeling studies; a decrease in cellular cholesterol content was observed in the 8-Br-cAMP-treated apoE-secreting cells, concurrent with an increase in cholesterol found in the medium. FPLC analysis of the medium demonstrated that 8-Br-cAMP treatment of the apoE-secreting cells led to an increased size fraction and amount of a peak of secreted cholesterol which comigrated with apoE. The 8-Br-cAMP-mediated increase in cholesterol efflux was also observed in non-apoE-secreting cells incubated with exogenous apoE or apoAI, and the effect of apoE was saturable. The apoE2, apoE3, and apoE4 isoforms were equally efficient in promoting 8-Br-cAMP-dependent cholesterol efflux. Reductive methylation of apoE abolished its ability to promote 8-Br-cAMP-dependent cholesterol efflux. Brefeldin A and monensin, inhibitors of protein processing through the Golgi, both blocked the 8-Br-cAMP stimulation of cholesterol efflux to exogenous apoE. 8-Br-cAMP induced specific apoE and apoAI binding, but not apoE degradation, by the RAW cells. We present a model wherein cAMP induces a membrane apolipoprotein receptor that does not lead to endocytosis and degradation, but instead promotes the transfer of lipids to apolipoproteins, which can then be released from the cell.

Differential modification of activities of the high-affinity and low-affinity insulin receptors of 3T3-L1 fibroblasts by phosphonolipids in vivo

The low-affinity and high-affinity forms of the insulin receptor respond differently to modifications of cellular phospholipid content in mouse 3T3-L1 fibroblasts in vivo. When cells are cultured with 2-aminoethylphosphonate the resulting phosphonolipid, which has previously been demonstrated to prevent the insulin-induced differentiation of the fibroblasts into adipocytes [J. D. Smith et al., Biochem. Arch. 8, 339-344 (1992)] results in alterations in both the affinity for insulin and receptor number of the low-affinity receptor while leaving the high-affinity receptor unaffected. That this phospholipid modification induces a specific change in the cellular insulin effect is demonstrated by the lack of alteration in the mobilization of GLUT-4 and glucose transport in the lipid modified cells. The results suggest that this specific cellular phospholipid modification will be useful in dissecting the specific functions of the two forms of the mammalian insulin receptor.

Indicators of postoperative pain in cats and correlation with clinical criteria

OBJECTIVE

To identify clinical indicators that may help identity postoperative pain in cats after ovariohysterectomy.

ANIMALS

Healthy, laboratory animal source cats.

PROCEDURE

Clinical indicators of pain were identified, and relief from pain in response to butorphanol was studied in 5 groups of cats. 10 cats had 1 hour of general anesthesia only, followed by recovery without additional medication. 10 cats had general anesthesia and ovariohysterectomy, followed by recovery without additional medication. 10 cats had general anesthesia, ovariohysterectomy, and postoperative administration of 0.1 mg of butorphanol/kg of body weight. Another 10 cats had general anesthesia, ovariohysterectomy, and postoperative administration of 0.3 mg butorphanol/kg. 10 cats received 0.1 mg of butorphanol/kg, IM, only. Samples and recorded data were obtained before, during, and after the anesthesia period. Clinical variables measured included heart rate, blood pressure, respiratory rate, rectal temperature, PCV, and blood glucose concentration. Results were compared with changes in norepinephrine, epinephrine, and cortisol concentrations.

RESULTS

Cats that did not receive analgesics had higher cortisol concentration than did cats without surgery and cats that received butorphanol after surgery. Systolic blood pressure measured by ultrasonic Doppler was found to be predictive of cortisol concentration, using a multiple linear regression model.

CONCLUSIONS

Cortisol concentration increased in response to surgical stress and pain, and this increase was diminished by use of butorphanol.

CLINICAL RELEVANCE

Systolic blood pressure was the best clinical predictor of postoperative pain.

Apolipoprotein E allele-specific antioxidant activity and effects on cytotoxicity by oxidative insults and beta-amyloid peptides

The apolipoprotein E (APOE) E4 allele is associated with Alzheimer's disease, cardiovascular disease, and decreased longevity. To probe the mechanism of these associations, cell lines were created which secrete each apoE isoform. ApoE conditioned media, purified apoE, and commercially obtained apoE protected B12 cells from hydrogen peroxide cytotoxicity with E2 > E3 > E4. Physiological levels of apoE protected cells from beta-amyloid peptides, while higher doses of apoE led to increased cytotoxicity. E2 > E3 > E4 possessed antioxidant activity, and apoE bound certain metal ions. The decreased antioxidant activity of E4 could contribute to its association with Alzheimer's disease, cardiovascular disease and decreased longevity.

Novel neuritic clusters with accumulations of amyloid precursor protein and amyloid precursor-like protein 2 immunoreactivity in brain regions damaged by thiamine deficiency

Experimental thiamine deficiency (TD) is a classical model of a nutritional deficit associated with a generalized impairment of oxidative metabolism and selective cell loss in the brain. In rats, TD-induced cell degeneration is accompanied by an accumulation of amyloid precursor protein (APP)/amyloid precursor-like protein 2 (APLP2) immunoreactivity in abnormal neurites and perikarya along the periphery of, or scattered within, the lesion. Prompted by these data and our previous findings of a genetic variation in the development of TD symptoms, we extended our studies to mice. C57BL/6, ApoE knockout, and APP YAC transgenic mice received thiamine-deficient diet and pyrithiamine injections. Unlike rats, APP/APLP2-immunoreactive neurites in all strains of mice were sparsely scattered within damaged areas and did not delimit the thalamic lesion. In addition, abnormal clusters of intensely immunoreactive neurites occurred only in areas of damage including the thalamus, mammillary body, and inferior colliculus. The clusters appeared as either irregular clumps or round or oval rosettes that strikingly resembled the neuritic component of Alzheimer amyloid plaques. However, immunostaining using various antisera to synthetic amyloid beta-protein (A beta 1-40) and thioflavine S histochemistry failed to show evidence of a component of A beta Neither APP/APLP2-immunoreactive clusters nor amyloid plaques were observed in the brain from patients with Wernicke-Korsakoff syndrome, the clinical manifestation of TD in man. Our results demonstrate species (i.e., genetic) differences in the response to TD-induced damage and support a role for APP and APLP2 in the response to brain injury. This is the first report that chronic oxidative deficits can lead to this novel pathology.

Combined hyperlipidemia in transgenic mice overexpressing human apolipoprotein Cl

We have generated transgenic mice over-expressing human apolipoprotein CI (apo CI) using the native gene joined to the downstream 154-bp liver-specific enhancer that we defined for apo E. Human apo CI (HuCI)-transgenic mice showed elevation of plasma triglycerides (mg/dl) compared to controls in both the fasted (211 +/- 81 vs 123 +/- 52, P = 0.0001) and fed (265 +/- 105 vs 146 +/- 68, P < 0.0001) states. Unlike the human apo CII (HuCII)- and apo CIII (HuCIII)-transgenic mouse models of hypertriglyceridemia, plasma cholesterol was disproportionately elevated (95 +/- 23 vs 73 +/- 23, P = 0.002, fasted and 90 +/- 24 vs 61 +/- 14, P < 0.0001, fed). Lipoprotein fractionation showed increased VLDL and IDL + LDL with an increased cholesterol/triglyceride ratio (0.114 vs 0.065, P = 0.02, in VLDL). The VLDL apo E/apo B ratio was decreased 3.4-fold (P = 0.05) and apo CII and apo CIII decreased in proportion to apo E. Triglyceride and apo B production rates were normal, but clearance rates of VLDL triglycerides and postlipolysis lipoprotein "remnants" were significantly slowed. Plasma apo B was significantly elevated. Unlike HuCII- and HuCIII-transgenic mice, VLDL from HuCI transgenic mice bound heparin-Sepharose, a model for cell-surface glycosaminoglycans, normally. In summary, apo CI overexpression is associated with decreased particulate uptake of apo B-containing lipoproteins, leading to increased levels of several potentially atherogenic species, including cholesterol-enriched VLDL, IDL, and LDL.

Further characterization of the metabolic properties of triglyceride-rich lipoproteins from human and mouse apoC-III transgenic mice

We previously showed that human apoC-III expression in transgenic mice causes hypertriglyceridemia due to the accumulation of enlarged very low density lipoprotein (VLDL)-like particles, with increased triglycerides and apoC-III and decreased apoE. In vivo turnover studies indicated the metabolic basis was decreased particle fractional catabolic rate. The presence of enlarged triglyceride-rich particles with prolonged residence time in plasma implied defective lipolysis, but in vitro these particles were good substrates for purified lipoprotein lipase (LPL). In the current study we further characterize the metabolic properties of these particles. We show that expression of a mouse apoC-III transgene can also cause hypertriglyceridemia with a similar accumulation of a VLDL-like particle with increased apoC-III and decreased apoE. A vitamin A fat tolerance test was used to show that MoCIIITg and HuCIIITg mice had similarly delayed clearance of triglyceride-rich postprandial particles. Thus, the previously observed hypertriglyceridemia caused by human apoC-III transgene expression was not due interspecies incompatibility but a property of apoC-III. In further experiments we showed VLDL from apoC-III transgenic mice interacted poorly with fibroblast lipoprotein receptors and this could be corrected by adding exogenous apoE. In addition, control VLDL interaction could be decreased by exogenous apoC-III. Moreover, the hypertriglyceridemia of HuCIIITg mice could be normalized by crossbreeding with HuETg mice. Thus, a functionally significant reciprocal relationship of apoC-III and apoE exists, presumably due to competition for space on the surface of triglyceride-rich lipoproteins. Finally, VLDL from HuCIITg and MoCIIITg mice showed decreased binding to heparin-Sepharose. This suggests and additional locus of the defect in these mice could potentially be in the binding of triglyceride-rich lipoproteins to heparan sulfate proteoglycan matrix on the surface of endothelial cells in which LPL is embedded. This could explain the predicted functional lipase deficiency in apoC-III transgenic mice based on the observation of a prolonged residence time of enlarged triglyceride-rich lipoproteins.

Competition and the canonical ensemble

Gibbs' canonical ensemble model from equilibrium statistical mechanics furnishes solutions to Eigen's phenomenological rate equations under constant total organization in cases with or without mutability. The evolution of species with mutation under constant total organization reduces to the evolution of substantial virtual species without mutation under the same constant total organization. Application of the canonical ensemble model provides an exact correspondence between thermodynamic and biological parameters. In particular, evolutionary time, as the analog of temperature, emerges as a statistical aggregate of the condition of the evolving system.

Alzheimer amyloid-beta peptide forms denaturant-resistant complex with type epsilon 3 but not type epsilon 4 isoform of native apolipoprotein E

BACKGROUND

The apolipoprotein E (apoE) type epsilon 4 isoform specifies increased cerebral and cerebrovascular accumulation of amyloid-beta protein (A beta) and contributes to the genetic susceptibility underlying a large proportion (approximately 60%) of typical, sporadic Alzheimer disease. Unfortunately, in vitro biochemical studies of direct apoE isoform-specific interactions with A beta have been inconsistent, perhaps due to the use by different research groups of apoE isoform preparations in different conformational states (purified denatured versus native).

MATERIALS AND METHODS

In the current study, we have investigated the possibility that synthetic A beta(1-40) preferentially associates with native apoE of either the type epsilon 3 or the type epsilon 4 isoform.

RESULTS

Here, we demonstrate the preferential association of synthetic A beta(1-40) with native apoE epsilon 3. The complex between apoE epsilon 3 and A beta(1-40) could not be disrupted by sodium dodecyl sulfate. In a parallel assay, no denaturant-resistant association of A beta(1-40) with apoE epsilon 4 was detectable.

CONCLUSIONS

These results support the notion that the apoE epsilon 4 isoform may foster beta-amyloidogenesis because apoE epsilon 4 is inefficient in forming complexes with A beta.

The uncertain response in the bottlenosed dolphin (Tursiops truncatus)

Humans respond adaptively to uncertainty by escaping or seeking additional information. To foster a comparative study of uncertainty processes, we asked whether humans and a bottlenosed dolphin (Tursiops truncatus) would use similarly a psychophysical uncertain response. Human observers and the dolphin were given 2 primary discrimination responses and a way to escape chosen trials into easier ones. Humans escaped sparingly from the most difficult trials near threshold that left them demonstrably uncertain of the stimulus. The dolphin performed nearly identically. The behavior of both species is considered from the perspectives of signal detection theory and optimality theory, and its appropriate interpretation is discussed. Human and dolphin uncertain responses seem to be interesting cognitive analogs and may depend on cognitive or controlled decisional mechanisms. The capacity to monitor ongoing cognition, and use uncertainty appropriately, would be a valuable adaptation for animal minds. This recommends uncertainty processes as an important but neglected area for future comparative research.

Tetrahymena thermophila: analysis of phospholipids and phosphonolipids by high-field 1H-NMR

The phospholipids of control and lipid-modified Tetrahymena thermophila were identified and quantified, using 1-D and 2-D COSY proton NMR spectroscopy on intact lipids, before and after HPLC separation. The results are comparable to those obtained using classical lipid analytical techniques. The results indicate that the study of enzyme pathways and other metabolic processes involving phospholipids in Tetrahymena and related protozoa can be carried out using proton NMR spectroscopy as the investigating technique.

Management and complications following trigonal-colonic anastomosis in a dog: five-year evaluation

Urinary diversion procedures in the dog have been described for both benign and malignant processes involving the bladder, urethra, or both. These procedures are performed rather infrequently, primarily because of the potential complications associated with urinary diversion into an intact gastrointestinal system. A case managed for five years following trigonal-colonic anastomosis for lymphocytic-plasmacytic urethritis is presented, along with a review of urinary diversion techniques. Postoperative management recommendations following urinary diversion are discussed.

Cytochrome P450 1A1 promoter as a genetic switch for the regulatable and physiological expression of a plasma protein in transgenic mice

Transgenic and gene knockout techniques allow for in vivo study of the consequences of adding or subtracting specific genes. However, in some instances, such as the study of lethal mutations or of the physiological consequences of changing gene expression, turning on and off an introduced gene at will would be advantageous. We have used cytochrome p450 1A1 promoter to drive expression of the human apolipoprotein E (apoE) gene in transgenic mice. In six independent lines, robust expression of the transgene depended upon injection of the inducer beta-naphthoflavone, whereas the seventh line had high basal expression that was augmented further by the inducer. The low level of basal expression in an inducer-dependent line was confirmed upon breeding the transgene onto the hypercholesterolemic apoE-deficient background. In the basal state transgene expression was physiologically insignificant, as these mice were as hypercholesterolemic as their nontransgenic apoE-deficient littermates. When injected with the inducer, plasma cholesterol levels of the transgenic mice decreased dramatically as apoE expression was induced to yield greater than physiological levels in plasma. The inducer could pass transplacentally from an injected mother to her fetuses with concomitant induction of fetal transgene mRNA. Inducer could also pass via breast milk from an injected mother to her suckling neonatal pups, giving rise to the induction of human apoE in neonate plasma. These finding suggest a strategy to temporarily ameliorate genetic deficiencies that would otherwise lead to fetal or neonatal lethality.

Common genetic variation in the promoter of the human apo CIII gene abolishes regulation by insulin and may contribute to hypertriglyceridemia

Overexpression of plasma apolipoprotein CIII (apo CIII) causes hypertriglyceridemia in transgenic mice. A genetically variant form of the human apo CIII promoter, containing five single base pair changes, has been shown to be associated with severe hypertriglyceridemia in a patient population. In animals and in cultured cells the apo CIII gene is transcriptionally downregulated by insulin. In this study we demonstrate that, unlike the wild-type promoter, the variant promoter was defective in its response to insulin treatment, remaining constitutively active at all concentrations of insulin. The loss of insulin regulation was mapped to polymorphic sites at -482 and -455, which fall within a previously identified insulin response element. Loss of insulin regulation could result in overexpression of the apo CIII gene and contribute to the development of hypertriglyceridemia. The variant apo CIII promoter is common in the human population and may represent a major contributing factor to the development of hypertriglyceridemia.

The uncertain response in the bottlenosed dolphin (Tursiops truncatus)

Humans respond adaptively to uncertainty by escaping or seeking additional information. To foster a comparative study of uncertainty processes, we asked whether humans and a bottlenosed dolphin (Tursiops truncatus) would use similarly a psychophysical uncertain response. Human observers and the dolphin were given 2 primary discrimination responses and a way to escape chosen trials into easier ones. Humans escaped sparingly from the most difficult trials near threshold that left them demonstrably uncertain of the stimulus. The dolphin performed nearly identically. The behavior of both species is considered from the perspectives of signal detection theory and optimality theory, and its appropriate interpretation is discussed. Human and dolphin uncertain responses seem to be interesting cognitive analogs and may depend on cognitive or controlled decisional mechanisms. The capacity to monitor ongoing cognition, and use uncertainty appropriately, would be a valuable adaptation for animal minds. This recommends uncertainty processes as an important but neglected area for future comparative research.

Reduction of cellular rejection and increase in longer-term survival after heart transplantation after HLA-DR matching

HLA matching in cardiac transplants is perceived as being logistically difficult. We studied 1135 consecutive primary cardiac allografts between 1980 and 1994 to assess the effect of HLA mismatching on long-term graft survival and cellular rejection episodes within 3 months of transplantation. We found a significant association between HLA-DR mismatching and the number of episodes of rejection (no mismatch 0.80 [SE 0.13], one mismatch 1.22 [0.06], two mismatches 1.42 [0.06], p < 0.05). We found a similar correlation between the total number of biopsy specimens showing evidence of cellular rejection and HLA-DR mismatch. The time between operation and the first rejection episode shortened with increasing HLA-DR mismatch (no mismatch 85.5 [37.3] days, one mismatch 43.1 [8.1], two mismatches 24.1 [2.9], p < 0.05). Furthermore, the proportion of patients with no evidence of rejection correlated with HLA-DR incompatibility. A significant association between improved graft survival and HLA-DR mismatching was found over 1, 5, and 10 years after transplantation (no mismatch 1 year 92%, 5 years 83%, 10 years 76%, one mismatch 1 year 81%, 5 years 73%, 10 years 59%, and two mismatches 78% 1 year, 5 years 70%, and 10 years 52%, p = 0.02). Increased efforts to prospectively HLA match patients has resulted in 25% of patients transplanted between January and May 1995 (n = 13/52) receiving grafts matched for HLA-DR. HLA matching reduces the frequency and severity of acute cardiac allograft rejection and improves graft survival for up to 10 years. Our preliminary results suggest that it is possible to use HLA matching prospectively for our selection of recipients.

The role of subvocalization in auditory imagery

Five experiments explored the utility of subvocal rehearsal, and of an inner-ear/inner-voice partnership, in tasks of auditory imagery. In three tasks (reinterpreting ambiguous auditory images, parsing meaningful letter strings, scanning familiar melodies) subjects relied on a partnership between the inner ear and inner voice, one similar to the phonological loop system described in the short-term memory literature. Apparently subjects subvocally rehearsed the imagery material, which placed the material in a phonological store that allowed the imagery judgement. In a fourth task (distinguishing voiced and unvoiced consonants in imagery), subjects still subvocally rehearsed, but seemed to need no additional phonological store to respond correctly. In this case they may have consulted articulatory or kinesthetic cues instead. In a fifth experiment (making homophone judgements), subjects hardly even needed to subvocally rehearse, a result suggesting that homophone judgements rely on some direct route from print to phonology. We consider the breadth of the partnership between the inner ear and inner voice, the level that subvocal rehearsal occupies in the cognitive system, and the functional neuroanatomy of the phonological loop system.

Decreased atherosclerosis in mice deficient in both macrophage colony-stimulating factor (op) and apolipoprotein E

To develop a murine model system to test the role of monocyte-derived macrophage in atherosclerosis, the osteopetrotic (op) mutation in the macrophage colony-stimulating factor gene was bred onto the apolipoprotein E (apoE)-deficient background. The doubly mutant (op/apoE-deficient) mice fed a low-fat chow diet had significantly smaller proximal aortic lesions at an earlier stage of progression than their apoE-deficient control littermates. These lesions in the doubly mutant mice were composed of macrophage foam cells. The op/apoE-deficient mice also had decreased body weights, decreased blood monocyte differentials, and increased mean cholesterol levels of approximately 1300 mg/dl. Statistical analysis determined that atherosclerosis lesion area was significantly affected by the op genotype and gender. The confounding variables of body weight, plasma cholesterol, and monocyte differential, which were all affected by op genotype, had no significant additional effect on lesion area once they were adjusted for the effects of op genotype and gender. Unexpectedly, there was a significant inverse correlation between plasma cholesterol and lesion area, implying that each may be the result of a common effect of macrophage colony-stimulating factor levels. The data support the hypothesis that macrophage colony-stimulating factor and its effects on macrophage development and function play a key role in atherogenesis.