Linoleic acid esterified in low density lipoprotein serves as substrate for increased arachidonic acid synthesis in differentiating monocytic cells

Linoleic acid increases monocyte deformation and adhesion to endothelium

Fatty acids have been implicated in having both anti- or pro-inflammatory actions, which may contribute to the progression and severity of atherosclerosis. Linoleic acid has been shown by others to decrease CD18 expression and leukocyte adhesion under static conditions. We investigated the effect of steric acid (18:0), oleic acid (18:1), and linoleic acid (18:2) on the cortical tension (a measure of cell membrane deformability) and adhesion characteristics of the monocytic cell line Mono Mac 6 (MM6) cells to TNF-alpha activated HUVEC under fluid flow. Linoleic acid concentrations up to 23 microM decreased cortical tension and increased adhesion frequencies. Increased adhesion was not due to altered cell morphology or adhesion kinetics and occurred despite decreases in receptor expression (CD18 and CD11a). At higher levels of linoleic acid (> or = 46 microM), cell dissociation constants significantly increased. Results show that decreasing cortical tension increased the probability that contact between MM6 cells and endothelium would produce an adhesive interaction, possibly due to increased deformation of the microvilli and the cell membrane cortex. However, more deformable cells rolled more erratically at low shear rates. The different behavior during initial contact and rolling suggest that adhesion is influenced by two force-dependent mechanisms, deformation of microvilli and a steric barrier. Incubation of MM6 with 23 microM steric or oleic acid did not significantly affect cortical tension. However, cells incubated with steric acid greatly increased their adherence to HUVEC and cells incubated with oleic acid showed no significant effect, indicating factors other than deformability may dominate.

Lipids in vascular function

Physiological and pathological vascular responses depend on the action of numerous intercellular mediators, ranging from hormones to gases like nitric oxide, proteins, and lipids. The last group consists not only of the different types of lipoproteins, but also includes a broad array of other lipophilic signaling molecules such as fatty acids, eicosanoids, phospholipids and their derivatives, sphingolipids and isoprenoids. Due to space limitations, it is impossible to discuss all the vascular effects of lipophilic mediators or compounds. Therefore, we will focus on one of the most important lipid-mediated diseases, atherosclerosis. Lipoproteins and especially their native or oxidized lipid compounds affect vascular function in many different ways, and these effects do not only modulate atherogenesis but are of paramount physiological and pathophysiological importance in other diseases, such as inflammation, tumor metastasis, or normal wound healing.

Effects of low density and high density lipoproteins isolated from non-insulin dependent diabetic patients on prostaglandin secretion by mouse macrophage cell line P388D1

We have previously shown that low-density (LDL) and high-density (HDL) lipoprotein from healthy subjects can promote in vitro prostaglandin (PG) release by murine macrophages. In this pilot study, we have measured PG production induced by lipoproteins of six diabetic patients with poor metabolic control, compared to five healthy controls. Plasma lipoprotein levels were similar in both groups. Lipoprotein fractions were purified by sequential ultracentrifugation. After lipoprotein incubation with cells, supernatants were extracted and PG quantified by HPLC. In presence of LDL, in control subjects, there was an increase in total PG production, mainly due to thromboxane B2 (TxB2). In diabetic patients, the secretion pattern was similar. In presence of HDL, in control subjects, total PG secretion was also increased, but it was balanced between TxB2 and prostacyclin. In diabetic patients, at low HDL concentration (10 mg/l) the secretion was mainly due to TxB2, while at higher HDL concentrations (100 mg/l). the secretion was balanced between TxB2 and prostacyclin. Comparison of means of areas under curve for the two groups studied showed that LDL increased all PG secretion in diabetic patients compared to controls (P < 0.05 for PGF2alpha), while HDL increased all PG secretion in controls compared to diabetic patients, except PGF2alpha. Our work suggests a key role of LDL in TxB2 secretion in diabetic patients, which is a major proaggregant and vasoconstrictive agent. There was also an increased secretion of all PG in diabetic patients.