Instability of the amyloidogenic cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type

A cystatin C variant with L68Q substitution and a truncation of 10 NH2-terminal residues is the major constituent of the amyloid deposited in the cerebral vasculature of patients with the Icelandic form of hereditary cerebral hemorrhage with amyloidosis (HCHWA-I). Variant and wild type cystatin C production, processing, secretion, and clearance were studied in human cell lines stably overexpressing the cystatin C genes. Immunoblot and mass spectrometry analyses demonstrated monomeric cystatin C in cell homogenates and culture media. While cystatin C formed concentration-dependent dimers, the HCHWA-I variant dimerized at lower concentrations than the wild type protein. Amino-terminal sequence analysis revealed that the variant and normal proteins produced and secreted are the full-length cystatin C. Pulse-chase experiments demonstrated similar levels of normal and variant cystatin C production and secretion. However, the secreted variant cystatin C exhibited an increased susceptibility to a serine protease in conditioned media and in human cerebrospinal fluid, explaining its depletion from the cerebrospinal fluid of HCHWA-I patients. Thus, the amino acid substitution may induce unstable cystatin C with intact inhibitory activity and predisposition to self-aggregation and amyloid fibril formation.

Refined genetic mapping of the darier locus to a <1-cM region of chromosome 12q24.1, and construction of a complete, high-resolution P1 artificial chromosome/bacterial artificial chromosome contig of the critical region

Darier disease (DD) (MIM 124200) is an autosomal dominant skin disorder characterized by loss of adhesion between epidermal cells and by abnormal keratinization. We present linkage analysis showing, in four families, key recombination events that refine the location of the DD locus on chromosome 12q23-24.1 to a region of <1 cM. We have constructed a YAC/P1 artificial chromosome (PAC)/bacterial artificial chromosome (BAC)-based physical map that encompasses this refined DD region. The map consists of 35 YAC, 69 PAC, 16 BAC, and 2 cosmid clones that were ordered by mapping 54 anonymous sequence-tagged sites. The critical region is estimated to be 2.4 Mb in size, with an average marker resolution of 37.5 kb. The refinement of the critical interval excludes the ALDH2, RPL6, PTPN11, and OAS genes, as well as seven expressed sequence tags (ESTs) previously mapped in the DD region. The three known genes (ATP2A2, PPP1CC, and SCA2) and the 10 ESTs mapped within the critical region are not obvious candidates for the DD gene. Therefore, this detailed integrated physical, genetic, and partial transcript map provides an important resource for the isolation of the DD gene and, possibly, other disease genes.

The effects of cholesterol uptake from high-density lipoprotein subfractions on biliary sterol secretion in rats with essential fatty-acid deficiency

High-density lipoprotein (HDL) participates in the transfer of cholesterol to the liver, in which it is subsequently excreted into bile as bile acid and cholesterol. In this study, the effect of essential fatty-acid (EFA) deficiency on cholesterol contribution from HDL subfractions to bile was investigated. Rats that were rendered EFA-deficient over 4 weeks displayed changes in their plasma HDL subfractions and liver tissue fatty acids. Plasma linoleic (18:2n6), linolenic (18:3n3,) and arachidonic (20:4n6) acids decreased, whereas palmitoleic (16:1n7) and eicosatrienoic (20:3n9) acids increased. EFA deficiency was confirmed by an elevation of the 20:3(n-9)/20:4(n-6) index. To examine the hepatic handling of lipoprotein-derived cholesterol, HDL2 and HDL3 from donor rats were isolated, labeled with [14C]-cholesterol, and injected iv into EFA-deficient and normal rats with a bile fistula. In HDL subfractions from control rats, no significant variations were noted in the specific activity of cholesterol output in both groups of EFA recipient rats; however, the output of biliary bile acids was significantly decreased in EFA-deficient rats following the administration of labeled HDL3. In HDL2 and HDL3 originating from EFA-deficient rats, a decrease in the specific activity of both biliary cholesterol and bile acid output was recorded in EFA-deficient rats. Concomitant with the defective HDL2- and HDL3-[14C] cholesterol translocation into bile of EFA-deficient rats, increased hepatic very-low-density lipoprotein (VLDL)-[14C] cholesterol secretion was observed in vivo. HDL2 and HDL3 particles, derived from EFA-deficient rats, had an altered composition including a depletion in apo A-I and an enrichment in apo E isoforms, which are the the two major HDL apolipoproteins involved in the delivery of cholesterol to the liver. Taken together, these results show that normal EFA status is necessary for efficient HDL-cholesterol processing by the liver.

Tyrosine kinase and MAPK inhibition of TNF-alpha- and EGF-stimulated IEC-6 cell growth

The role of TNF-alpha in modulating intestinal crypt cell growth was examined, in comparison with EGF. Both significantly increased IEC-6 cell proliferation. Neither EGF nor TNF-alpha overcame the inhibitory effect on growth exerted by the tyrosine kinase inhibitor genistein. Immunoblots with phosphotyrosine antibodies showed increased tyrosine phosphorylation of IEC-6 cell proteins in response to EGF and TNF-alpha stimulation. TNF-alpha increased ERK1 and ERK2 MAPK phosphorylation. A MAPK assay confirmed the increased activity upon TNF-alpha stimulation. Selective inhibition of MAPK activation by PD98059 resulted in a dose dependent inhibition of TNF-alpha or EGF-induced IEC-6 cell growth. These findings suggest a role for TNF-alpha in the regulation of intestinal epithelial cell growth and that the mitogenic effect of TNF-alpha requires protein tyrosine phosphorylation and MAPK activation.

Radiotherapy in the management of epidemic Kaposi's sarcoma: a retrospective study of 643 cases

PURPOSE

To report to the literature the largest published series of epidemic Kaposi's sarcoma (EKS), treated with radiation therapy, to summarize and discuss our 10 years experience in the treatment of this malignancy.

METHODS AND MATERIALS

From June 1986 to December 1996, 643 patients with acquired immunodeficiency syndrome (AIDS)-related epidemic Kaposi's sarcoma were treated with radiation therapy (RT) at the Cancerology Department of Henri Mondor University Hospital. The patients, 640 men and 3 women had an average age of 38.5 years (range 20-68 years). Three hundred eighty-seven patients (60.1 %) had received previous treatment for their Kaposi's sarcoma (KS). In total, 6777 fields were irradiated, as follows: face 1342 (19.8%), eyelid and conjunctiva 362 (5.3%), trunk 1903 (28.1%), upper and lower limbs 2866 (42.3%), genitals 189 (2.8%). and oral cavity 115 fields (1.7%). Radiation therapy consisted of 4 MV or 45-70 kV X-rays, depending on tumor size and location. Doses ranged from 10 to 30 Gy, according to tumor response and toxicity.

RESULTS

Objective response (CR and PR) was observed in 92% (5947/6464) of all cases, treated for cutaneous form of EKS. All patients with irradiated oral lesions had an objective response. The overall tolerance was acceptable for the cutaneous lesions. By contrast, in oral lesions, mucosal reactions were often observed after relatively low doses of radiotherapy.

CONCLUSIONS

Doses of 15 Gy for oral lesions, 20 Gy for lesions involving eyelids, conjunctiva, and genitals, have been shown to be sufficient to produce shrinkage of the tumor and good palliation of the symptoms. For the cutaneous EKS, we propose 30 Gy given in a local field, using a fractionated scheme with small size applicators. Radiotherapy has its own place in the management of EKS, as an efficient treatment.

Efficacy of intravenous continuous infusion of fluorouracil compared with bolus administration in advanced colorectal cancer

PURPOSE

The administration of fluorouracil (5-FU) by continuous intravenous infusion (CI) is an alternative to the bolus administration of 5-FU in patients with advanced colorectal cancer. Although more than 1,200 patients have been enrolled onto randomized trials that compared these two treatment modalities, there is still no definitive evidence of an advantage of 5-FU CI, and the magnitude of this advantage, if any, is also controversial. A meta-analysis was performed to assess this benefit in terms of tumor response and survival, and to compare the toxicity profiles of these two modalities of administration of 5-FU.

DESIGN

Individual data of 1,219 patients included in six randomized trials served as the basis for this meta-analysis, which was conducted by an independent secretariat in close collaboration with the investigators.

RESULTS

Tumor response rate was significantly higher in patients assigned to 5-FU CI than in patients assigned to 5-FU bolus (22% v 14%; overall response odds ratio, 0.55; 95% confidence interval [95% CI], 0.41 to 0.75; P = .0002). Overall survival was also significantly higher in patients assigned to 5-FU CI (overall hazards ratio [HR], 0.88; 95% CI, 0.78 to 0.99; P = .04), although the median survival times were close. Multivariate analyses showed that randomized treatment and performance status were the only two significant predictors of tumor response, whereas the same plus primary tumor site were independent significant predictors of survival (patients with rectal cancer did somewhat better). Grade 3 or 4 hematologic toxicity was more frequent in patients assigned to 5-FU bolus (31% v 4%; P < 10(-16)), whereas hand-foot syndrome was more frequent in the 5-FU CI group (34% v 13%; P < 10(-7)).

CONCLUSION

5-FU CI is superior to 5-FU bolus in terms of tumor response and achieves a slight increase of overall survival. The hematologic toxicity is much less important in patients who receive 5-FU CI, but hand-foot syndrome is frequent in this group of patients.

Metabolism of 4,7,10,13,16,19-docosahexaenoic acid in isolated perfused adult and newborn pig eyes

We performed open-circuit perfusions of newborn and adult pig eyes to study the age-dependent metabolism of 4,7,10,13,16,19-docosahexaenoic acid (DHA) in this organ. DHA taken up by the perfused eyes was partitioned into glycerolipids, beta-oxidation, and the intracellular nonesterified fatty acid pool. In newborn eyes, DHA was incorporated into structural lipids to a greater extent than in adult eyes. Competition experiments suggest that the adult eye is more selective for DHA than the newborn eye. Finally, pulse-chase data indicate that DHA transport from the circulation across the retinal pigment epithelium and into the retina is more rapid in adult than in newborn eyes. The results are discussed with respect to the rapid accumulation of retinal DHA in early life and the avid retention of this fatty acid by the adult retina.

Postprandial lipaemia is exacerbated in fat-cholesterol-fed rabbits: relationship to atheroma deposition

The aim of the present study was to evaluate the links between chronic fat-cholesterol intake, postprandial lipaemia and atherogenesis in New Zealand White rabbits. Adult rabbits were fed on either a low-fat control diet (LF) or a high-fat, high-cholesterol diet (HF). Rabbits received a test meal containing [3H]cholesterol and [14C]triolein on days 0 and 63 for the LF group and days 14, 28, 42, 63 and 84 for the HF group. Blood was collected 24 h post-absorptively and 10, 24, 34 and 48 h after test-meal intake. Post-absorptive as well as postprandial lipoproteins and lipaemia were not modified in the LF rabbits, who did not show any atheroma deposition on day 119. In HF rabbits, postprandial plasma triacylglycerols peaked 24-34 h after meal intake. The 0-48 h areas under the curves of triacylglycerol and triacylglycerol-rich lipoproteins (TRL) steadily increased with time of chronic lipid feeding with values significantly higher than those in the LF rabbits. The postprandial plasma and TRL concentrations of dietary radiolabelled lipids were significantly higher in HF than LF rabbits. Post-heparin lipoprotein lipase (EC 3.1.1.34) and hepatic lipase (EC 3.1.1.3) activities were twofold higher in HF rabbits than in LF rabbits at day 105. In HF rabbits, a marked atheroma plaque deposition in the aorta was observed (30.9 (SE 3.9) % of total surface). The extent of atheroma deposition was positively correlated to the postprandial responses of plasma total triacylglycerols and dietary-derived lipids as well as total cholesterol and dietary-derived cholesterol in HF rabbits. In conclusion, chronic ingestion of a HF diet led to marked increases in postprandial lipaemia and TRL particles, and atheroma deposition.

Utilisation of prenatal services and birth outcomes: a community-based study in Israel

The purpose of this paper was to assess several measures of utilisation of prenatal care as predictors of birth outcome in a community where the availability and quality of services were equal for all pregnant women. A case-control study was conducted in a small community in Israel, comparing 189 women whose pregnancy resulted in an unfavourable outcome (perinatal mortality, preterm birth and low birthweight at term) with 384 women, matched by birth order, who had a live, full-term infant weighing 2500 g or more. In a multivariable analysis, adjusting for pregnancy complications, maternal age, parity and socio-economic disadvantage, gestational age at initiation of prenatal care was not an independent predictor of unfavourable outcome; neither was lower than the recommended number of visits for the period under care. However, a higher than expected number of visits was associated with unfavourable outcome [odds ratio (OR) = 6.10, 95% CI 2.09-17.78], as was non-compliance with medical recommendations [OR = 2.02, 95% CI 1.24-3.29. The context of prenatal care delivery, as well as the process of care and compliance with recommendations, should be assessed in order to determine the impact of prenatal care on birth outcomes.

Ontogeny and location of HMG-CoA reductase, ACAT, and MGAT in human small intestine

Because a few enzymes are in most tissues, enabling them to produce lipids necessary for growth and differentiation, the development of their activity in the intestine, an important organ of fat transport and metabolism, is of great interest. In this investigation, the ontogeny and location of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase (the key regulatory enzyme in the cholesterol pathway), acyl-CoA:cholesterol acyltransferase (ACAT; responsible for cholesterol esterification), and monoacylglycerol acyltransferase (MGAT; the more representative enzyme of the neutral lipid pathway) were examined in the human fetal small intestine. The developing gut exhibited high levels (pmol.mg-1.min-1) of HMG-CoA reductase (7.65 +/- 0.35), ACAT (16.98 +/- 1.12), and MGAT (689.74 +/- 37.54). Significant positive correlations were recorded between fetal age (8-22 wk) and the enzyme activities of HMG-CoA reductase in the proximal (P < 0.005) and middle (P < 0.01) segments, ACAT in the distal segment (P < 0.03), and MGAT in the proximal segment (P < 0.03) of the gut. Age-specific changes were found in the location of the three enzymes in the contiguous intestinal segments that were investigated. We concluded that the fetal small intestine has substantial HMG-CoA reductase, ACAT, and MGAT activity, which displays specific patterns during development.

Carboxyl-terminal fragments of beta-amyloid precursor protein bind to microtubules and the associated protein tau

Alzheimer's disease is a neurodegenerative disorder characterized by protein depositions in intracellular and extracellular spaces in the brain. The intraneuronal deposits are formed by neurofibrillary tangles composed mainly of abnormally phosphorylated tau, a microtubule-associated protein, whereas the major constituent of the amyloid deposited extracellularly in the brain parenchyma and vessel walls is amyloid beta-protein (A beta). The proteolytic processing of the beta-amyloid precursor protein (beta PP) results in the generation of a complex set of carboxyl-terminal peptides that contain A beta. In this study, we have used fusion proteins containing carboxyl-terminal fragments of beta PP to investigate the association of beta PP with cellular components. We demonstrate that specific domains within the carboxyl end of beta PP contain binding sites for cytoskeletal components; one, within residues 1 to 28 of A beta, binds directly to tubulin, and the second one, within sequences carboxyl-terminal to A beta, binds tau and tubulin. We propose that the two neuropathological hallmarks of Alzheimer's disease, A beta deposition and neurofibrillary tangles, represent the residual of a disrupted beta PP-tubulin-tau complex.

Selective effects of hydrocortisone on intestinal lipoprotein and apolipoprotein synthesis in the human fetus

Studies employing human fetal intestine have yielded much interesting information on the role of polarized enterocytes in fat absorption and transport. Using the organ culture model, we examined the influence of hydrocortisone on the synthesis and secretion of lipids and lipoproteins. Human jejunal explants were cultured for 5 days at 37 degrees C in serum-free medium containing either [14C]-oleic acid or [14C]-acetate, alone or supplemented with hydrocortisone (25 or 50 ng/ml). The uptake of [14C]-oleic acid was associated with the production of triglycerides, phospholipids, and cholesteryl esters, which were all affected by hydrocortisone. This hormonal agent (50 micrograms) led to the marked reduction of secreted triglycerides (43%, P < 0.01), phospholipids (39%, P < 0.01), and cholesteryl esters (36%, P < 0.05) without altering the characteristic distribution of tissue and medium lipid classes. Similarly, hydrocortisone significantly (P < 0.01) decreased (approximately 60%) the incorporation of [14C]-acetate into secreted free and esterified cholesterol in the medium. With [14C]-oleic acid as a precursor, hydrocortisone significantly diminished the delivery of chylomicrons and very low density lipoproteins to the medium while consistently enhancing the secretion of high density lipoproteins. In parallel, [35S]-methionine pulse-labeling of jejunal explants revealed the concomitant inhibitory effect of hydrocortisone on apo B-100 synthesis and hydrocortisone's stimulatory effect on apo B-48 and apo A-1. These studies suggest that glucocorticoids play a critical role in lipoprotein processing during intestinal development.

Chronic heat improves mechanical and metabolic response of trained rat heart on ischemia and reperfusion

Cardiac mechanics and metabolic performance were studied in isolated perfused hearts of rats subjected to a combined chronic stress of heat acclimation and swimming training (EXAC) or swimming training alone (EX). Diastolic (DP) and systolic pressures (SP), coronary flow (CF), and oxygen consumption were measured during normoperfusion (80 mmHg), and the appearance of ischemic contracture (IC), DP, and SP were measured during progressive graded ischemia, total ischemia (TI), and reperfusion insults. ATP, phosphocreatine, and intracellular pH were measured during TI and reperfusion with 31P nuclear magnetic resonance spectroscopy. During normoperfusion, SP and cardiac efficiency (derived from rate-pressure product-oxygen consumption relationships) were the highest in the 2-mo EXAC hearts (P < 0.0001). During progressive graded ischemia, the development of IC (percentage of total hearts) was similar in both EXAC and EX hearts; the only significant difference was confined to the 1- vs. 2-mo groups. The onset of IC was delayed in the EXAC hearts and, on reperfusion, recovery, particularly of DP, was significantly improved in the latter. After TI, EXAC hearts retained 30% of the ATP pool and there was a delayed decline in intracellular pH. On reperfusion, these hearts also displayed improved ATP and phosphocreatine recovery, the 2-mo EXAC heart demonstrating significantly faster high-energy phosphate salvage, improved diastolic function, and pulse pressure recovery. The data attest to the beneficial effects of heat acclimation on cardiac mechanics of trained rats during normoperfusion and cardiac protection on ischemia and reperfusion. Possibly, energy sparing, lesser acidosis, and shorter duration of IC on ischemia and improved energy salvage on reperfusion contribute synergistically to this potent beneficial effect.

Oxidative tyrosylation of high density lipoprotein impairs biliary sterol secretion in rats

The oxidation of low density lipoprotein plays a central role in the pathogenesis of atherosclerosis. Oxidative modification could also occur in high density lipoprotein (HDL), which may alter reverse cholesterol transport. It has recently been proposed that myeloperoxidase-generated tyrosyl radical may modify HDL. In the present study we have examined whether the oxidative tyrosylation of HDL by peroxidase may alter biliary cholesterol secretion and bile acid transformation. HDL was modified by exposure to L-tyrosine, H2O2 and peroxidase labelled with [14C]cholesterol and injected i.v. into rats with bile diversion. A reduced excretion of radioactivity (14-20%) was recovered in the bile of animals administered with tyrosylated HDL at the different periods of collection. Both labelled cholesterol (14.3%, P < 0.05) and bile acids (18.9%, P < 0.05) were decreased in these rats, similarly to results obtained from malondialdehyde-modified HDL. Consequently, this kind of oxidative modification resulted in a loss of the hepatobiliary systems capacity to normally process HDL.

Iron-salicylate complex induces peroxidation, alters hepatic lipid profile and affects plasma lipoprotein composition

Iron overload, with its associated toxic effects, has serious health consequences and results in damage to the liver, heart and other organs. Salicylate may be used as the lipophilic carrier, transporting more iron into hepatocytes. In this study, we examined the effect of the combined administration of these compounds on plasma lipid profile and lipoprotein composition, as well as on hepatic lipid concentration. Male Spraque-Dawley rats were injected i.p. with Fe (15 mg/kg weight). This injection was repeated 24 h later with a gavage of sodium salicylate (700 mg/kg). Control rats received 0.9% NaCl only. The peroxidation indices TBARS (P < 0.001) and conjugated dienes (P < 0.05) significantly increased in the blood (50 and 122%, respectively) and liver (333 and 101%, respectively) of Fe salicylate-treated rats. Concomitantly, blood and liver arachidonic acid content was diminished by iron treatment. In parallel, the plasma lipid profile was markedly affected in Fe-salicylate treated-rats. Lower plasma concentrations of total cholesterol (25%, P < 0.0001) cholesteryl ester, (34%, P < 0.001) and high-density lipoprotein-cholesterol (50%, P < 0.001) were observed. Lipoprotein composition analysis revealed enrichment of free cholesterol and depletion of cholesterol ester in very low-density, intermediate-density, low-density and high-density (HDL2, HDL3) lipoproteins. Furthermore, SDS-polyacrylamide gel electrophoresis revealed several alterations in the apolipoprotein distribution of these lipoproteins. The activity of lecithin:cholesterol acyltransferase was unchanged and could not account for the reduction of cholesterol esterification. As for the plasma, the liver exhibited a significant (P < 0.001) decrease in total cholesterol (2.42 +/- 0.07 versus 1.89 +/- 0.06 mg/g liver), essentially due to a reduction in cholesteryl ester (0.93 +/- 0.07 versus 0.51 +/- 0.03 mg/g, P < 0.001). Again, the activity of ACAT (dpm/mg microsomal protein) was not lower (12,700 +/- 1250) than that of controls (9650 +/- 1080). Thus, the iron-salicylate was able to induce peroxidation and to profoundly affect the intravascular and intrahepatic lipid, and plasma lipoprotein metabolism. Additional work is needed to elucidate the mechanisms involved in the underlying lipid and lipoprotein abnormalities.

Paradoxical cerebral air embolism from a hemodialysis catheter

Air embolism is a rare complication of the use of central venous catheters as vascular access for hemodialysis. We report a patient with an intracardiac shunt who had a paradoxical air embolism following manipulation of her hemodialysis catheter that resulted in transient hemiplegia. This case illustrates the potentially devastating consequences of even a small air leak into the circulation if it gains access to the arterial system.

Association of an exon 3 mutation (Trp66-->Gly) of the LDL receptor with variable expression of familial hypercholesterolemia in a French Canadian family

The ligand-binding domain of low-density lipo-protein (LDL) is composed of seven 40-amino-acid repeats encoded by exons 2-6. Previous studies identified a missense mutation in codon 66 of exon 3, which resulted in the production of LDL receptor protein that is not processed to its mature form. In the current investigation, we documented the presence of two identical mutant LDL receptor alleles (Trp66-->Gly) in two familial hypercholesterolemia (FH) probands, II-1 and II-2, associated with markedly elevated plasma LDL cholesterol (17.22 +/- 0.78 and 11.95 +/- 0.24 mmol/liter, respectively). Functional assays of their fibroblast LDL receptor showed inefficient binding (39 and 50%), internalization (33 and 37%), and degradation (32 and 37%) compared with controls. The contribution of the apo B gene to variation in LDL levels was virtually eliminated given the normal ligand interaction with cell surface receptors and the absence of the mutation occurring in codon 3500 of the apo B gene. Similarly, the homozygous apo E3/E3 wildtype phenotype excluded any genetic contribution of apo E to the lipoprotein abnormalities. Furthermore, the LPL mutations commonly observed in French Canadians could not account for the observed lipid alterations. Several alterations in lipoprotein composition characterized VLDL, IDL, LDL, HDL2, and HDL3 fractions. Moreover, defective intestinal fat transport was observed in both probands (II-1 and II-2). Thus, the disturbance of lipoprotein concentration, composition, size, and metabolism may in part be related to the exon 3 mutation (Trp66-->Gly) of the LDL receptor gene. The biochemical phenotype was more severe in the father (I-1) than in the mother (I-2), and in the younger homozygous proband (II-1) than in the older (II-2). The greater severity was associated with a higher LDL cholesterol/HDL cholesterol ratio. Whether the differences between the two probands are due to polygenic factors or to a metabolic consequence of a major nonallelic trait is unknown. Nevertheless, the present biochemical findings stress the extent of the lipid abnormalities associated with homozygous FH and the importance of the phenotypic variability encountered even among subjects carrying the same mutation.

Lipid, apolipoprotein, and lipoprotein synthesis and secretion during cellular differentiation in Caco-2 cells

Although Caco-2 cells are frequently employed for the study of enterocyte lipid metabolism, variable results have been reported regarding their ability to synthesize and secrete lipids and apolipoproteins. The major goal of this investigation is to examine the capacity of Caco-2 cells to elaborate and secrete lipids, lipoproteins, and apolipoproteins at different degrees of morphological and functional differentiation. Cells were cultured in medium with 5% fetal bovine serum (FBS), on permeable polycarbonate filters from 2 to 30 d in the presence of 14C-oleate or 35S-methionine. Cellular differentiation, as assessed by morphology (light and electron microscopy), transepithelial resistance, free fatty acid flux, and sucrase activity, progressed steadily up to 20 d of culture. Caco-2 cells esterified oleic acid mainly into phospholipids, triglycerides (TG), and smaller amounts of cholesterol esters. Lipid synthesis began as early as 2 d, and TG secretion was enhanced with increased duration of culture. However, very low efficiency of lipid export was observed at all levels of differentiation, reaching a maximum of only 6% of intracellular lipids. VLDL and LDL were the dominant lipoproteins secreted, with HDL comprising < 20% of the total. VLDL secretion increased, while LDL decreased, whereas the lipid composition of lipoproteins varied little with increasing duration of culture. Apoprotein B and A-I synthesis and secretion increased markedly from 11 to 20 d of culture. The ratio of apo B-100/B-48 decreased between 11 and 30 d, consistent with enhanced apo B editing of more mature enterocytes. Taken together, our data suggest that from 20 d of culture, Caco-2 cells are morphologically and functionally mature, capable of lipid esterification, and lipoprotein and apolipoprotein synthesis. However, despite their functional and morphological similarities to mature enterocytes, Caco-2 cells have a very limited lipid export capacity.

Developmental expression of calcitriol receptors, 9-kilodalton calcium-binding protein, and calcidiol 24-hydroxylase in human intestine

Human intestinal mucosa consists of highly active epithelial cells in continual renewal and differentiation processes located at different portions of the villi. The crypt contains abundant replicating cells which, upon reaching the villus tip, acquire their fully differentiated state. Besides its well recognized role in bone cell homeostasis, calcitriol has been attributed a role in cellular differentiation and proliferation in normal leukocytes and myeloid leukemia cells. We have previously documented the presence and the distribution of specific calcitriol receptors in the cells of the small and large intestine from 13-20-wk-old human fetuses and that calcitriol was able to promote human intestinal epithelium proliferation or differentiation, in organ culture, depending upon fetal age. We now show that, whereas transcripts for calcitriol receptors are abundant from duodenum to colon, those for the 9-kD calcium-binding protein are present mainly in the duodenum and the jejunum and to a lesser extent in the ileum and the colon. Transcripts for 25-hydroxycholecalciferol-24-hydroxylase could not be detected in any of the intestine segments despite a prolonged exposition of the gels. Immunofluorescence staining for the 9-kD calcium-binding protein was exclusively observed in the epithelial cells of the small intestine and colon, the subepithelial layers being always negative. The 9-kD calcium-binding protein distribution along the crypt-villus axis appeared as a gradient, increasing from the developing crypt to the tip of the villus in the duodenum, jejunum, and ileum. Based on the present observations and on the fact that calcitriol promotes human fetal proliferation and differentiation, the presence of transcripts for calcitriol receptors and 9-kD calcium-binding protein in the intestinal cell opens interesting possibilities as of their role in the in utero human gut development and the control of colorectal cancers.

The phosphotyrosine interaction domains of X11 and FE65 bind to distinct sites on the YENPTY motif of amyloid precursor protein

The phosphotyrosine interaction (PI) domains (also known as the PTB, or phosphotyrosine binding, domains) of Shc and IRS-1 are recently described domains that bind peptides phosphorylated on tyrosine residues. The PI/PTB domains differ from Src homology 2 (SH2) domains in that their binding specificity is determined by residues that lie amino terminal and not carboxy terminal to the phosphotyrosine. Recently, it has been appreciated that other cytoplasmic proteins also contain PI domains. We now show that the PI domain of X11 and one of the PI domains of FE65, two neuronal proteins, bind to the cytoplasmic domain of the amyloid precursor protein ((beta)APP). (beta)APP is an integral transmembrane glycoprotein whose cellular function is unknown. One of the processing pathways of (beta)APP leads to the secretion of A(beta), the major constituent of the amyloid deposited in the brain parenchyma and vessel walls of Alzheimer's disease patients. We have found that the X11 PI domain binds a YENPTY motif in the intracellular domain of (beta)APP that is strikingly similar to the NPXY motifs that bind the Shc and IRS-1 PI/PTB domains. However, unlike the case for binding of the Shc PI/PTB domain, tyrosine phosphorylation of the YENPTY motif is not required for the binding of (beta)APP to X11 or FE65. The binding site of the FE65 PI domain appears to be different from that of X11, as mutations within the YENPTY motif differentially affect the binding of X11 and FE65. Using site-directed mutagenesis, we have identified a crucial residue within the PI domain involved in X11 and FE65 binding to (beta)APP. The binding of X11 or FE65 PI domains to residues of the YENPTY motif of (beta)APP identifies PI domains as general protein interaction domains and may have important implications for the processing of (beta)APP.

Cystatin C. Icelandic-like mutation in an animal model of cerebrovascular beta-amyloidosis

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy (CAA) occurs as a sporadic disorder in aged humans, as a frequent component of Alzheimer's disease, or in hereditary cerebral hemorrhage with amyloidosis (HCHWA). The primary histological locus of cerebral amyloid deposition varies in aged humans and in different species of nonhuman primates. In aged rhesus monkeys, amyloid deposition occurs most frequently in senile plaques, whereas in aged squirrel monkeys CAA is more common. We hypothesized that the preponderance of CAA in squirrel monkeys is related to a species-specific amino acid change in cystatin C, a cysteine protease inhibitor, similar to the Leu68Gln substitution found in the amyloid protein of Icelandic patients with HCHWA-I, also termed hereditary cystatin C amyloid angiopathy.

METHODS

We performed immunohistochemical analyses of brain sections of aged squirrel and rhesus monkeys with anti-amyloid-beta and anti-cystatin C antibodies and sequenced the cystatin C cDNA of these monkeys.

RESULTS

Cerebral amyloid in aged squirrel and rhesus monkeys, previously shown to be immunoreactive with anti-amyloid-beta anti-bodies, reacts also with antibodies to cystatin C. While the predicted amino acid sequence in rhesus monkeys differs from the human sequence by four residues, that of the squirrel monkeys has seven additional amino acid substitutions, one of which is Leu68Met.

CONCLUSIONS

The presence of a mutation in squirrel monkeys similar to the one found in HCHWA-I suggests that alterations in cystatin C may influence the likelihood that amyloid will be deposited in the walls of cerebral blood vessels. These observations support the utilization of the monkeys as models to study CAA.

The genetic basis of primary disorders of intestinal fat transport

For decades, research interest has focused on hypertriglyceridemia and hypercholesterolemia, because of their association with atherosclerosis. Recently, however, increasing attention has been paid to rare hypolipidemic states that can cause adverse consequences in young patients. Studies of genetic disorders of fat transport have afforded new insights into the mechanisms involved in intestinal lipid handling and lipoprotein metabolism. This article reviews briefly the current state of knowledge about inherited lipoprotein deficiencies, including abetalipoproteinemia, hypobetalipoproteinemia and chylomicron retention disease. These disorders share many common characteristics: they all cause fat malabsorption, low levels of circulating lipids and fat-soluble vitamins, failure to thrive in early childhood, ataxic neuropathy and visual impairment. However, their etiology is genetically different. Abetalipoproteinemia is caused by the absence of microsomal transfer protein, whereas hypobetalipoproteinemia is due to defects in the apolipoprotein B gene. The etiopathogenesis of chylomicron retention disease is as yet unexplained. Research on these rare, inherited fat disorders of absorption will continue to provide significant advances in our understanding of human physiology and may yield novel therapeutic approaches to atherosclerosis.