Role of fatty acids and eicosanoids in modulating proteoglycan metabolism in endothelial cells

Endothelial cell dysfunction is considered to be a critical event in the etiology of atherosclerosis. Thus, the preservation of endothelial structure and function are a prerequisite for normal control of vascular permeability properties, mediation of both inflammatory and immunologic responses and the general 'communication' between blood-borne cells and abluminal tissues. Many of these properties can be influenced by proteoglycans present in vascular tissues. There is evidence that selected lipids can be atherogenic by altering endothelial proteoglycan metabolism. Little is known about the role of fatty acids in modulating proteoglycan composition in endothelial cells. Data suggest, however, that linoleic acid in particular can adversely alter proteoglycan metabolism, which may be related to an imbalance in eicosanoid synthesis patterns. These events could be sufficient to disrupt normal endothelial barrier function, initiate smooth muscle migration and proliferation, and result in other metabolic dysfunctions associated with the etiology of vascular diseases such as atherosclerosis. Thus, the focus of this review is on fatty acids and eicosanoids as they may alter proteoglycan metabolism of vascular tissues and in particular of the endothelium.

Fumonisin B1 alters sphingolipid metabolism and disrupts the barrier function of endothelial cells in culture

Fumonisins are responsible for at least two diseases of veterinary importance (equine leukoencephalomalacia and porcine pulmonary edema) and are carcinogenic for experimental animals and, perhaps, humans. They have been found to disrupt sphingolipid metabolism in many types of cells, including hepatocytes, neurons, and renal cells. In this study, endothelial cells form porcine pulmonary arteries were cultured on micropore filters as a model for the endothelial barrier, and barrier function was quantitated as the movement of albumin across the endothelial monolayers. Fumonisin B1 increased the amount of free sphinganine by 20- to 30-fold within 3 hr, as expected for inhibition of sphinganine (sphingosine) N-acyltransferase by this mycotoxin. At 30 to 50 microM, fumonisin B1 doubled the rate of albumin transfer across endothelial monolayers; however, there was no loss of cell viability based on morphology or trypan blue exclusion. When 15 microM D-erythro-sphinganine was added to the cells, the rate of albumin transfer also doubled (after 24 hr incubation) without a loss of viability; however, this treatment increased the cellular level of sphinganine by > 100-fold. Addition of 25 microM sphinganine caused even greater albumin transfer, but also resulted in significant cell death. These results establish that fumonisin B1 and D-erythro-sphinganine allow accelerated passage of macromolecules across the endothelium. Fumonisin B1 alters sphingolipid biosynthesis with an elevation of sphinganine in the cells which may, at least in part, explain the observed disruption of endothelial barrier function.

Tumor necrosis factor reduces proteoglycan synthesis in cultured endothelial cells

Tumor necrosis factor (TNF)-induced disruption of vascular endothelial barrier function may be due in part to alterations in proteoglycan metabolism. To test this hypothesis, confluent endothelial cell monolayers were exposed for 24 h to 500 or 1,000 U of TNF per milliliter of culture medium together with 20 microCi Na2 35SO4. HPLC anion-exchange separation of proteoglycans secreted into media of control as well as TNF-treated cultures revealed one major peak (representing 95% of total radioactivity) and one minor peak (representing 5% of total radioactivity), which eluted at 0.6 and 0.9 M NaCl, respectively. One single peak was obtained from control as well as TNF-treated endothelial cell monolayers and eluted at 1.2 M NaCl. TNF treatment did not change the total quantity of radioactive proteoglycans secreted into the media but significantly decreased the amount of proteoglycans in endothelial cell monolayers. However, TNF treatment did not alter the size or glycosaminoglycan (GAG) composition of the proteoglycans either in the media or in the cell monolayers. In addition, mRNA levels of specific proteoglycans, perlecan and biglycan, were measured upon TNF treatment, using Northern analysis. TNF treatment caused a dose-dependent decrease in mRNA levels for the core proteins of perlecan, a major heparan sulfate proteoglycan (HSPG), and biglycan in endothelial cultures. These results suggest that TNF decreases production of proteoglycans and alters normal endothelial cell proteoglycan metabolism which may be sufficient to impair endothelial barrier function.

Prevalence of sickle cells in Irula, Kurumba, Paniya & Mullukurumba tribes of Nilgiris (Tamil Nadu, India)

A total of 1377 tribals, comprising Irulas (536), Paniyas (196), Kurumbas (87), Mullukrurumbas (156) and Soligas (402), living in the Nilgiris, Tamil Nadu, India were studied for sickle cell trait between 1981-85. Patients attending various tribal clinics at Arayure, Kozhikarai, Kothagiri and Biligiri Rengan hills for various ailments were screened at random by solubility test and by acetate paper electrophoresis, if required. HbAS carrier frequency was 30-37.8 per cent in all the tribals studied except Kurumbas (19.5%). The frequency of carriers were more (37.8%) on the western part of Nilgiris (Nedungode, Kappala and adjoining regions) than the eastern part (30%). Further, the prevalence of carriers was higher (47-49%) in the 10-19 yr age group amongst Paniyas and Mullukurumbas living in the western part of Nilgiris. An episodic, epidemic of malaria so rampant during the early part of this century in the western parts of Nilgiris might have eliminated many children with HbAA and hence the higher frequency of HbAS in this particular age group.

Proteoglycans and endothelial barrier function: effect of linoleic acid exposure to porcine pulmonary artery endothelial cells

Certain fatty acids induce changes in endothelial barrier function which may be mediated by alterations in normal proteoglycan synthesis/metabolism. To test this hypothesis, pulmonary artery derived endothelial cells were treated with media supplemented with linoleic acid (18:2), and/or a known proteoglycan synthesis inhibitor, beta-D-xyloside. Independent exposure to 1 mM beta-D-xyloside or 90 microM 18:2 increased albumin transfer, i.e., decreased barrier function, when compared with control cultures. 18:2 and beta-D-xyloside increased albumin transfer additively, suggesting that the mechanisms by which 18:2 and beta-D-xyloside alter the proteoglycan metabolism are different. Compared with the control group, treatment with 18:2 inhibited proteoglycan synthesis, decreased anionic properties of heparan sulfate proteoglycans in the cell monolayers and caused the release of a unique chondroitin sulfate proteoglycan into the culture media. Treatment with beta-D-xyloside caused an increased incorporation of radioactive sulfate into glycosaminoglycans but inhibited proteoglycan synthesis. These results suggest that the fatty acid- and beta-D-xyloside-induced impairment in endothelial barrier function may involve changes in the synthesis, release and physicochemical properties of proteoglycans.

Selective disruption of endothelial barrier function in culture by pure fatty acids and fatty acids derived from animal and plant fats

Endothelial cell integrity has been suggested to play a role in the development of atherosclerosis. The effects of fatty acids on endothelial barrier function were tested by measuring albumin transport across endothelial monolayers cultured on polycarbonate filters. Compared with control cultures, a 24-h exposure to 90 mumol/L lauric (12:0) and linoleic acid (18:2) but not to butyric (4:0), hexanoic (6:0), octanoic (8:0), decanoic (10:0), myristic (14:0), palmitic (16:0) or stearic acid (18:0) caused an increase in albumin transfer across endothelial monolayers. Selective enrichment of a "physiological" serum fatty acid mixture (FA-Mix; 90 mumol/L) with 90 mumol/L of 12:0 or 18:2 significantly increased albumin transfer, whereas enrichment with 90 mumol/L of 4:0, 16:0 or 18:0 significantly decreased albumin transfer relative to 180 mumol/L FA-Mix. Only 12:0- or 18:2-treated cultures showed increased Ca(++)-ATPase activity and the presence of lipid droplets. Fatty acids (60 mumol/L) extracted from butter fat and beef tallow had no effect on albumin transfer, whereas fatty acids extracted from chicken fat and corn oil consistently disrupted endothelial barrier function. This fat-induced disruption of endothelial barrier function seems to be related to the amount of 18:2 present in each fat source. These data indicate that unsaturated fats cause cellular perturbations that result in a decrease in endothelial barrier function in this model system, and that high dietary levels of unsaturated fats may be detrimental to cell integrity.

Zinc protects against tumor necrosis factor-induced disruption of porcine endothelial cell monolayer integrity

Some nutrients influence the metabolic response of cytokines such as tumor necrosis factor. Inadequate levels of the essential trace element zinc may play a role in tumor necrosis factor-induced disruption of the vascular endothelial barrier function. To test this hypothesis, endothelial cells cultured on polycarbonate filters or culture plates were exposed to six different treatments for 3 d: medium 199 enriched with 5% fetal bovine serum (control), control+two levels of supplemental zinc (7.7 and 12.3 mumol/L medium), tumor necrosis factor (5 x 10(5) U/L) and tumor necrosis factor+the two levels of Zn as noted previously. Endothelial barrier function, expressed as albumin transfer across cultured endothelial monolayers, was not affected by Zn enrichment alone. Tumor necrosis factor treatment significantly increased albumin transfer compared with control cultures. The lower concentration of Zn partially and the higher concentration totally prevented the tumor necrosis factor-induced increase in albumin transfer. The increase in cytosolic release of [3H]adenine (marker of cell injury) induced by tumor necrosis factor was prevented by added Zn. Tumor necrosis factor treatment significantly decreased angiotensin-converting enzyme activity, and tumor necrosis factor also decreased activities of two other membrane-bound enzymes, total ATPase and Ca(2+)-ATPase. These activities all were restored by Zn enrichment. Tumor necrosis factor treatment caused a decrease in cellular Zn concentration, which was prevented when the culture media were enriched with Zn. These data suggest that an important relationship exists between Zn status and tumor necrosis factor-induced endothelial cell dysfunction.

Risk factors for fatal pneumonia: a case control study

We conducted a case control study to identify the risk factors for death among hospitalized children with acute pneumonia at the Institute of Child Health, Madras. All the 70 patients who died of pneumonia constituted the case--patients and 140 children recovered from pneumonia, selected by systematic sampling, during the same period served as controls. By univariate analysis, the risk factors for death in pneumonia observed were associated illnesses--Odds Ratio (OR) 22.2. (95% confidence interval [CI] 9.8-51.4; p = < 0.001); congenital anomalies--OR 10.4 (2.9-37.8; p = < 0.001); severe pneumonia--OR 4.2 (1.2-14.4; p = 0.09); marasmic status--OR 2.9 (1.5-5.7; p = 0.001); age under 6 months--OR 2.8 (1.3-5.7; p = 0.004); and severity of the pneumonia (lobar versus segmental)--OR 2.0 (0.9-4.5; p = 0.09). By logistic regression analysis the following risk factors were significant--associated illnesses. (51.6; 18-146.9; p = < 0.001); age under 6 months (6.5; 2-20.6; p = < 0.001), marasmic status (5.8; 2.2-15.6; p = < 0.001); and congenital anomalies (3.8; 2.0-7.1; p = < 0.001). These risk factors should be kept in mind by the clinicians for appropriate intervention at an earlier stage to minimize death.

Oxysterol-induced endothelial cell dysfunction in culture

Cholesterol oxidation products (oxysterols), such as cholestan-3 beta,5 alpha,6 beta-triol (Triol), may be atherogenic by altering the barrier function of the vascular endothelium. We have shown that incubation of endothelial cell monolayers with Triol increased transendothelial albumin transfer (i.e., decreased barrier function) in a concentration- and time-dependent manner. Such dysfunction of endothelium could result from alterations in membrane characteristics, including changes in membrane-associated enzyme activities. To test this hypothesis, endothelial monolayers were treated with 20 microM Triol and the activities of selected membrane enzymes were measured at 0, 2, 4, 6, 12 and 24 hours. Calcium-adenosine triphosphatase (Ca(++)-ATPase) and sodium, potassium, magnesium-adenosine triphosphatase (Na+, K+, Mg(++)-ATPase) activities were significantly increased after 4 or 2 hours incubation with 20 microM Triol, respectively. 5'-nucleotidase activity was significantly elevated only after a 24-hour exposure to Triol, whereas there was no change in angiotensin-converting enzyme (ACE) activity in response to 20 microM Triol treatment at any time studied. Compared with all concentrations tested 40 microM Triol increased Ca(++)-ATPase activity most markedly, with a significant increase already after a 2-hour exposure. No major morphological changes were noted until 12 hours of exposure to 20 microM Triol; obvious cellular damage was observed by 24 hours. Cultures treated with Triol for 24 hours showed significant signs of toxicity, measured by an elevated [3H]adenine release, compared with control cultures. These data demonstrate that Triol alters the activity of certain membrane-bound enzymes, particularly Na+, K+, Mg(++)-ATPase and Ca(++)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

Zinc deficiency alters barrier function of cultured porcine endothelial cells

Zinc is necessary for normal membrane function and stability. We postulated that Zn deficiency may disrupt the integrity of the vascular endothelium by decreasing its barrier function. To test this hypothesis, endothelial cells were cultured on polycarbonate filters and exposed to media enriched with either 1% fetal bovine serum (FBS) (low FBS; total Zn, 1.07 mumols/L medium) or 5% FBS (control; total Zn, 2.29 mumols/L) or low FBS plus two supplemental levels of Zn, 3.36 and 5.66 mumols total zinc/L. Endothelial cell barrier function, expressed as albumin transfer across cultured endothelial monolayers, was significantly lower in cultures exposed to low FBS compared with control medium. Supplementation with 5.66 mumols total Zn/L completely restored endothelial barrier function. A divalent cation chelator, 1,10-orthophenanthroline, was used to induce Zn deficiency in vitro. Compared with control cultures, the presence of 1,10-orthophenanthroline in the culture medium resulted in markedly lower endothelial barrier function that was increased by the addition of Zn but not calcium or magnesium. Activity of the membrane-bound zinc-dependent angiotensin-converting enzyme (ACE) was depressed by low zinc medium, whereas membrane-bound Ca(2+)-ATPase and total ATPase were not depressed. Furthermore, cells cultivated in low zinc medium did not have greater cytosolic release of adenine, indicating no increase in cell injury or death. These data suggest that Zn is vital to endothelial cell integrity and that Zn may play an important role in vascular endothelial barrier function.

Linoleic acid-induced endothelial cell injury: role of membrane-bound enzyme activities and lipid oxidation

High plasma levels of linoleic acid (18:2) may injure endothelial cells, resulting in decreased barrier function of the vascular endothelium. The effects of linoleic acid on endothelial barrier function (transendothelial movement of albumin), membrane-bound enzyme activities, and possible autooxidation of linoleic acid under experimental conditions were studied. The exposure of endothelial monolayers to 18:2 for 24 hr at 60, 90, and 120 microM fatty acid concentrations caused a significant increase in transendothelial movement of albumin, with maximum albumin transfer at 90 microM. Fatty acid treatment resulted in the increased appearance of cytosolic lipid droplets. Activities of the membrane-bound enzymes, angiotensin-converting enzyme (ACE), and Ca(2+)-ATPase increased steadily with increasing time of cell exposure to 90 microM 18:2, reaching significance at 24 hr. Treatment of endothelial cultures with up to 120 microM 18:2 did not cause cytotoxicity, as evidenced by a nonsignificant change in cellular release of [3H]-adenine. Incubation of 18:2-supplemented serum-containing culture media with 1000 microM 18:2 at 37 degrees C for up to 48 hr did not result in formation of autooxidation products. These results suggest that 18:2 itself, and not its oxidation products, plays a major role in disrupting endothelial barrier function.