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J J Alexander

Publications and source records attributed to J J Alexander.

At least 55 records · Page 3Linked to original sources
PubMed1993

Second messenger regulation of lipoprotein uptake by an arterial wall model.

Second messenger signaling has been shown to regulate a variety of cellular functions in response to external stimuli. The following study was performed to determine the potential role of second messengers on influencing lipoprotein uptake by the arterial wall. An aortic endothelial cell (EC)-smooth muscle cell (SMC) bilayer was preexposed to various mediators of the cyclic AMP and inositol phosphate pathways for 30 min. The permeability, binding, and cellular uptake of 125I-labeled low-density lipoprotein (LDL) (10 micrograms/ml) added to the upper well media of the bilayer were then measured for each cell type after a 3-h incubation period. Forskolin (100 microM), an activator of adenylate cyclase, resulted in an increase in all measured parameters. 8-Br-cAMP (30 microM), a cAMP analogue, showed a similar effect on EC permeability (P < 0.00005) while galanin (0.1 mg/ml), an adenylate cyclase inhibitor, had no effect. GTP-binding protein inhibition with pertussis toxin (10 mg/ml) led to a marked reduction in SMC uptake (P < 10(-7)) without affecting membrane binding. Protein kinase C activation with phorbol myristate acetate (0.1 mg/ml) also increased EC permeability to LDL but, unlike forskolin, had no effect on LDL binding. This effect was further potentiated by calcium ionophore A23187 (5 x 10(-6) M), indicating a contributing role of intracellular calcium. These results would suggest that LDL uptake can be influenced by several second messenger systems, and that EC and SMC may respond differently to these intracellular signals. Second messenger regulation may allow changes in lipoprotein uptake by the arterial wall in response to external stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

The effect of nifedipine on lipid and monocyte infiltration of the subendothelial space.

PURPOSE: Calcium channel blockade has been shown to inhibit experimental atherosclerosis in cholesterol-fed animals, and early clinical trials suggest its benefit in human subjects as well. METHODS: To determine the effect of the calcium channel blocker nifedipine on lipid and monocyte infiltration of the subendothelial space, an endothelial cell (EC)-smooth muscle cell (SMC) bilayer model of the arterial wall was incubated for 18 hours with nifedipine (0.1 micrograms/ml). Iodine 125-labeled low-density lipoprotein (125I-LDL) (10 micrograms protein/ml) was then added to the upper-well medium. RESULTS: After a 3-hour incubation period, nifedipine-treated bilayers showed an increased permeability to LDL (p < 10(-7). Nifedipine had no effect on the membrane binding or cellular uptake of LDL by the EC but did increase SMC binding and uptake (p < 0.0005). U937 monocytes were found to incorporate 125I-LDL in a concentration-dependent fashion, without saturation to 25 micrograms/ml, the highest concentration studied. Nifedipine increased monocyte uptake of LDL (10 micrograms/ml; p < 0.003 but reduced monocyte movement through the EC barrier (p < 10(-7). A study of the selective preincubation of each cell type (EC, SMC, and monocyte) with nifedipine indicated that this reduction was likely the result of a direct effect on the monocyte. CONCLUSIONS: Given the potential cytotoxic effects of the monocyte within the subendothelial space, nifedipine-induced inhibition of monocyte infiltration and enhancement of lipoprotein uptake by the SMC may be protective.

Animals↗
PubMed1992

Origins of HIV.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Further characterisation of human rotaviruses isolated from asymptomatically infected neonates in South Africa.

Stool specimens were collected from healthy neonates at Ga-Rankuwa Hospital in the winters of 1984 and 1986 and tested for the presence of rotavirus infection. Asymptomatic excretion was found to occur in 25% of the newborn babies analysed. Gel electrophoresis of the rotavirus RNA genome revealed that a genomically stable strain of rotavirus was endemic in the ward at the time intervals examined. Hybridisation analysis of the VP4 and VP7 rotavirus genes, which encode the outer capsid neutralization proteins of the virus, was conducted. These results showed the presence of a serotype 4 rotavirus strain with an M37-like VP4 gene allele, which remained conserved in the nursery over the time period examined. Partial nucleotide sequences were obtained for a variable region of the VP7 gene and for the hyperdivergent region of the VP4 gene from 8 of these viruses and showed that remarkable conservation of these regions in the genes of the viruses occurred over time.

Base Sequence↗
PubMed1992

The effect of thrombin on low-density lipoprotein permeability and uptake by an arterial endothelial smooth muscle cell bilayer.

Thrombin, a mediator of thrombosis, has been shown to directly alter the function of vascular cells. We studied the effect of thrombin on low-density lipoprotein permeability and uptake by an arterial endothelial cell-smooth muscle cell bilayer to determine its potential role in atherogenesis. Confluent cell bilayers were incubated in media containing thrombin (10 or 50 units/ml) for a period of 24 hours to 9 days. Iodine 125 (125I)-LDL (10 micrograms protein/ml) was then added to the media, and after a 3-hour incubation, 125I-LDL transit through the endothelial cell layer as well as membrane binding and uptake by each cell type were measured. The lower concentration of thrombin caused a delayed increase in both the permeability (p less than 0.0001) and uptake (p less than 0.05) of LDL, but had no effect on membrane binding of the lipoprotein. The higher thrombin concentration led to an immediate increase in endothelial cell permeability to LDL (p less than 10(-7)) and a significant reduction in both cellular uptake (p less than 10(-7)) and membrane binding (p less than 0.0005). In contrast, smooth muscle cell binding and uptake were unaffected at the lower concentration of thrombin. At the higher concentration, smooth muscle cell uptake of LDL was increased (p less than 10(-7)) disproportionately to a more limited increase in membrane binding (p less than 0.05). Endothelial DNA content, reflecting cell number, was increased at 10 units/ml thrombin (p less than 0.001) but markedly reduced at 50 units/ml thrombin (p less than 0.0005), whereas smooth muscle cell DNA content remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The molecular epidemiology of rotavirus-associated gastro-enteritis in the Transkei, southern Africa.

Rotaviruses were detected in 32.8% (71/216) of stool specimens collected from young children with gastro-enteritis attending the Rehydration Unit at Umtata General Hospital between April 1988 and March 1989. A seasonal distribution was observed with an increase in numbers shedding the virus during the colder months of the year. Based on variations in the migration pattern of the RNA genome segments when passed through polyacrylamide gels, 14 different electrophoretypes were identified: 69% were long patterns and 27% were short patterns. A single dominant long electrophoretype persisted throughout the 12-month study period, whereas 13 other minor types co-circulated at varying intervals. Mixed infections were observed in three cases, including one infant who was infected with both a long (Wa-like) virus and a short (DS-1-like) virus.

Child, Preschool↗
PubMed1991

Outcome of complex vascular and orthopedic injuries of the lower extremity.

Thirty-two patients undergoing limb salvage procedures for complex vascular and orthopedic injuries of the lower extremity were studied in order to identify prognostic indicators for delayed amputation in this select group. A high incidence of nerve (38%), soft tissue (66%), and remote injury (47%) was noted. A comprehensive and integrated approach to vascular, orthopedic, and plastic reconstruction was utilized. Of the 32 patients studied, 1 (3.1%) died as a result of remote injury and sepsis. Amputation was required in 9 patients (28%), while 13 (56%) of the patients with limb salvage showed persistent functional or neurologic deficits. Infection was the most significant factor associated with amputation (p less than 0.0005) and was not avoided by the perioperative use of antibiotics. Delayed amputation resulted in a significant extension of total hospitalization (p less than 0.005). The authors favor an aggressive approach to limb salvage with IIIC injury but recommend early amputation in the presence of significant nerve disruption. An attentive use of tissue debridement, intravenous antibiotics, and early wound coverage is needed to limit infection.

Adolescent↗
PubMed1991

Oxygen radicals alter LDL permeability and uptake by an endothelial-smooth muscle cell bilayer.

There is evidence to suggest that the deposition of lipid within the arterial wall, which is characteristic of atherosclerosis, involves a break in the integrity of the endothelial barrier. Oxidative modification of low density lipoproteins by reactive oxygen species may enhance this process. In this study, an aortic endothelial (EC) smooth muscle cell (SMC) bilayer was briefly exposed to a free-radical generating system to determine the effect of superoxides on lipid permeability and uptake. 125I-LDL (10 micrograms/ml) was added to the EC medium at various time intervals (3, 24, and 48 hr and 9 days). The amount of lipid reaching the subendothelial space was measured. Measurements of EC and SMC binding and uptake of LDL were also obtained and compared with those of untreated cells. The results demonstrate a significant increase in the permeability of the treated EC layer to LDL (P less than 10(-6)), which was sustained over time. Superoxide exposure led to a limited initial increase in EC binding and uptake of LDL, which later returned to control values. In contrast, SMC uptake of LDL was significantly (P less than 10(-3)) and persistently increased over control values and disproportionately increased over cellular binding. Such results suggest that superoxides can increase LDL permeability of the EC barrier. Because this was not associated with a comparable increase in EC binding and uptake, it is unlikely to be due to changes in receptor-mediated, transcellular transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Low density lipoprotein uptake by an endothelial-smooth muscle cell bilayer.

To study the interaction of endothelial and smooth muscle cells, and the means by which such interaction may affect lipid permeability of the arterial wall, cell bilayers were established by use of a transwell culture system. After confluent growth of both cell types had been achieved, iodine 125 bound to low-density lipoprotein (10 ng protein/ml) was added to the media of the upper well. After a 3-hour incubation period, the iodine 125-bound low-density lipoprotein content of the upper and lower media demonstrated an impedance to lipoprotein movement across the endothelial cell monolayer as compared to the bare porous polycarbonate filter of the transwell (p less than 10(-6)). The presence of smooth muscle cells in the bottom well significantly enhanced the permeability of the endothelial cell layer (p less than 10(-60). This effect remained unchanged over a 9-day time course. Membrane binding and cellular uptake of low-density lipoprotein by endothelial cells was not altered by smooth muscle cells, indicating that this change in permeability could not be easily attributed to changes in receptor-mediated transport or transcytosis. Membrane binding (p less than 0.02) and cellular uptake (p less than 10(-6)) of low-density lipoprotein by smooth muscle cells in the bilayer, when adjusted for counts available in the smooth muscle cell media, were both reduced in the early incubation period as compared to isolated smooth muscle cells. The disproportionate reduction in uptake as compared to binding would suggest that this was not entirely a receptor-dependent process.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Aortic endothelial and smooth muscle cell co-culture: an in vitro model of the arterial wall.

Interactions between vascular endothelial (EC) and smooth muscle cells (SMC) contribute both to the normal function of the vascular wall and to the pathogenesis of lesions such as atherosclerosis and fibrointimal hyperplasia. However, study of these interactions has been hampered by the difficulty in growing these two cell types in simultaneous culture. Methods using conditioned media, shared media, and bilayer culture have been described, but none is well suited to the study of vascular cell interactions. We report a method for EC-SMC co-culture that preserves bilayer morphology, allows independent study of the cells and their matrices after intervention, remains stable over long periods in culture, and permits study of changes in cell-cell interaction with growth of the cells to confluence. This simple bilayer co-culture system simulates the in vivo situation and may enhance our understanding of EC-SMC interactions.

Animals↗
PubMed1991

Expansion of the venous outflow tract in arteriovenous grafts of the forearm using antebrachial venoplasty.

The use of venoplasty to widen the antecubital venous outflow during the placement of arterio-venous grafts in the forearm for angioaccess is described. This has allowed an increased use of grafts for the forearm for angioaccess in instances in which antecubital veins were otherwise believed to be inadequate in size. Expansion of the venous outflow tract may also increase the long term patency of these grafts.

Arteriovenous Shunt, Surgical↗
PubMed1990

Competitive inhibition of LDL binding and uptake by HDL in aortic endothelial cells.

High-density lipoprotein (HDL) may inhibit the binding and cellular uptake of low-density lipoprotein (LDL) as one means of regulating the delivery of exogenous cholesterol to nonhepatic tissues. This may play an important role in atherogenesis, by altering lipid metabolism in cells of the arterial wall. To verify and better characterize this effect, endothelial cells were harvested from bovine aorta and maintained in tissue culture. Following initial preincubation in lipid-deficient culture media, these cells were incubated for 2 hr at 4 degrees C in media containing 125I-LDL (10 micrograms protein/ml) and varying concentrations of either HDL (0-400 micrograms protein/ml) or comparable amounts of Apoprotein A (Apo A), the major protein component of HDL. Intracellular and trypsin-released counts were assayed separately, as a measurement of cellular uptake and membrane bound LDL, respectively. Results of this study indicated an inhibition of LDL binding and uptake by HDL (P less than 0.005, ANOVA). A similar inhibition was found with Apo A alone (P less than 0.005). When identical studies were performed using 125I-Apoprotein B, the protein component of LDL, and Apo A, the latter was found to inhibit the binding of Apo B to the same extent (P less than 0.0006). These results indicate that HDL does inhibit LDL binding and uptake by bovine aortic endothelial cells and that, because this effect is seen equally with only the protein component of these lipoprotein particles, it is most likely due to competitive binding at the receptor level rather than to stearic hindrance or an alteration of the cell membrane.

Animals↗
PubMed1990

The effects of thrombin on bovine aortic endothelial and smooth muscle cells.

Recent evidence suggests that thrombin interacts with various cell types, stimulating cellular proliferation and protein and prostanoid production. To further delineate its role in vascular healing, we have studied the effects of thrombin on proliferation and matrix production by the cells of the vessel wall. The addition of thrombin (1 unit/ml) to cultures of bovine aortic smooth muscle cells resulted in an increase in cell proliferation (p less than 0.01) and number (p less than 0.03), whereas in cultures of bovine aortic endothelial cells thrombin produced a decrease in cell proliferation (p less than 0.01) and number (p less than 0.02). Thrombin also altered matrix composition in cultures of these cells. In both bovine aortic endothelial cells and bovine aortic smooth muscle cell cultures grown in the presence of thrombin, total protein content was significantly increased when compared to controls (p less than 0.03). In bovine aortic endothelial cell cultures the addition of thrombin resulted in a decrease in collagen content (p less than 0.01) and an increase in sulfated glycosaminoglycan content (p less than 0.02). In contrast, in bovine aortic smooth muscle cell cultures thrombin resulted in an increase in collagen content (p less than 0.03), whereas glycosaminoglycan content was unaffected. These findings suggest that thrombin may significantly influence vascular healing and function by altering cell number and matrix composition.

Animals↗
PubMed1990

High density lipoprotein inhibits low density lipoprotein binding and uptake by bovine aortic endothelial cells.

The antiatherogenic effect of high density lipoprotein (HDL) has been attributed to either an inhibition of cholesterol uptake or to reversed cholesterol transport from peripheral cells. In order to determine whether HDL competitively blocks receptor-mediated low density lipoprotein (LDL) binding and uptake, bovine aortic endothelial cells (BAECs) were cultured in Dulbecco's modified Eagles Medium (DMEM) containing 10% LDL-free fetal bovine serum, and incubated with 125I-LDL in concentrations of either 10 or 25 micrograms protein/mL. Varying amounts of HDL (0-200 micrograms/mL) were added to the media. Following a twenty-four hour incubation period at 37 degrees C, 125I-LDL binding and uptake were measured. At the lower concentration of 125I-LDL, which represents high-affinity receptor binding, there was no significant difference in either binding or uptake within the range of HDL concentrations studied. At the higher concentration of LDL, however, there was a marked inhibition of 125I-LDL binding (p less than .006) and uptake (p less than, 001; ANOVA), which did not saturate at the highest HDL concentrations used. These data suggest that HDL does not influence high-affinity, receptor-mediated binding and uptake of LDL but that its effect is seen at a concentration of LDL representing nonspecific binding. The lack of saturation at increasing concentrations of HDL also indicates that HDL-receptor interaction is not essential for the effect.

Animals↗
PubMed1989

Effect of estradiol on low density lipoprotein uptake by bovine aortic endothelial cells.

The means by which estrogen retards atherosclerosis cannot be explained solely by changes in circulating lipoprotein levels. We studied the effects of 17 beta-estradiol on the binding, incorporation, and degradation of low density lipoprotein (LDL) by cultured bovine aortic endothelial cells (BAEC). Estrogen receptors in the cytoplasm and nucleus of BAEC could be demonstrated by immunofluorescent staining. Estradiol was found not to affect surface binding of LDL to BAEC. However, at physiologic concentrations (50 pg/ml), estradiol did enhance LDL uptake by the BAEC (P less than 0.005). This enhancement was present but somewhat reduced at higher concentrations of estrogen (P less than 0.05). Only approximately 10% of incorporated LDL was trichloroacetic acid soluble, indicating a low rate of LDL degradation. The relative rate of LDL breakdown within the BAEC was not altered by estrogen. These results, showing estrogen stimulation of LDL uptake by the BAEC, do not clarify the protective effect of this hormone. It is speculated that estrogen may augment the cellular clearance of LDL.

Animals↗
PubMed1989

Effects of argon laser radiation on aortic endothelial cells: early membrane changes and proliferative response.

Membrane fluidity, transmembrane signaling responses, and proliferative characteristics of endothelial cells were studied to characterize biochemical and molecular changes after treatment with argon laser energy. Bovine aortic endothelial cells grown in monolayers were irradiated at 50, 100, and 200 J with an argon laser (wavelength, 488 and 514 nm). Proliferation, assayed by [3H]thymidine incorporation, was measured daily for 6 days. An initial lag phase was observed for irradiated cells when compared to nonirradiated controls (P less than 0.03), with eventual recovery by the third day. Membrane fluidity, determined by fluorescence anisotropy, was measured 1 hr after irradiation. A decrease in static rotational motion of 1,6-diphenyl-1,3,5-hexatriene (DPH) was noted in irradiated versus nonirradiated cells indicating a decrease in membrane fluidity (P less than 0.02). Dynamic studies of intracellular calcium and pH flux utilizing fluorescent probes demonstrated a preserved response to mitogenic stimulation. An increase in intracellular Ca2+ with a concomitant alkalinization of the intracellular milieu was observed in irradiated and non-irradiated cells in response to stimulation with endothelial cell growth factor (ECGF). These responses resemble those characterized for other mitogens. Argon laser energy applied to aortic endothelial cells decreases membrane fluidity early after irradiation. These alterations probably cause the initial lag observed in their proliferative response; however, the capacity to respond to exogenous mitogenic stimulation is maintained.

Animals↗