Lipoproteins from normolipidemic and dyslipidemic subjects modify the thromboxane A2 generation by platelets in clotting human blood

Outdoor temperature is associated with serum HDL and LDL

BACKGROUND

While exposures to high and low air temperatures are associated with cardiovascular mortality, the underlying mechanisms are poorly understood. The risk factors for cardiovascular disease include high levels of total cholesterol and low-density lipoprotein (LDL), and low levels of high-density lipoprotein (HDL). We investigated whether temperature was associated with changes in circulating lipid levels, and whether this might explain part of the association with increased cardiovascular events.

METHODS

The study cohort consisted of 478 men in the greater Boston area with a mean age of 74.2 years. They visited the clinic every 3-5 years between 1995 and 2008 for physical examination and to complete questionnaires. We excluded from analyses all men taking statin medication and all days with missing data, resulting in a total of 862 visits. Associations between three temperature variables (ambient, apparent, and dew point temperature) and serum lipid levels (total cholesterol, HDL, LDL, and triglycerides) were studied with linear mixed models that included possible confounders such as air pollution and a random intercept for each subject.

RESULTS

We found that HDL decreased -1.76% (95% CI: from -3.17 to -0.32, lag 2 days), and -5.58% (95% CI: from -8.87 to -2.16, moving average of 4 weeks) for each 5°C increase in mean ambient temperature. For the same increase in mean ambient temperature, LDL increased by 1.74% (95% CI: 0.07-3.44, lag 1 day) and 1.87% (95% CI: 0.14-3.63, lag 2 days). These results were also similar for apparent and dew point temperatures. No changes were found in total cholesterol or triglycerides in relation to temperature increase.

CONCLUSIONS

Changes in HDL and LDL levels associated with an increase in ambient temperature may be among the underlying mechanisms of temperature-related cardiovascular mortality.

A novel role for CD36 in VLDL-enhanced platelet activation

Type 2 diabetes is characterized by increased plasma triglyceride levels and a fourfold increase in ischemic heart disease, but the mechanism is unclear. CD36 is a receptor/transporter that binds fatty acids of lipoproteins. CD36 deficiency has been linked with insulin resistance. There is strong evidence of in vivo interaction between platelets and atherogenic lipoproteins suggesting that atherogenic triglyceride-rich lipoproteins, such as VLDL, that are increased in diabetic dyslipidemia are important in this process. This study demonstrates that VLDL binds to the platelet receptor CD36, enhances platelet thromboxane A2 production, and causes increased collagen-mediated platelet aggregation. VLDL enhanced collagen-induced platelet aggregation by 1) shortening the time taken for aggregation to begin (lag time) to 70% of control (P = 0.001); 2) increasing maximum aggregation to 170% of control (P = 0.008); and 3) increasing thromboxane production to 3,318% of control (P = 0.004), where control represents platelets stimulated with collagen (100%). A monoclonal antibody against CD36 attenuated VLDL-enhanced collagen-induced platelet aggregation by 1) inhibiting binding of VLDL to platelets by 75% (P = 0.041); 2) lengthening lag time to 190% (P < 0.001); and 3) decreasing thromboxane production to 8% of control (P < 0.001). In support of this finding, platelets from Cd36-deficient rats showed no increase in aggregation, thromboxane production, and VLDL binding in contrast to platelets from rats expressing CD36. These data suggest that platelet Cd36 has a key role in VLDL-induced collagen-mediated platelet aggregation, possibly contributing to atherothrombosis associated with increased VLDL levels.

Influence of diet-modified lipoprotein fractions from rabbits on eicosanoid production and on proliferation of rabbit skin fibroblasts

Three groups of rabbits received for 8 weeks either ordinary pellets, fish oil-enriched pellets or a cholesterol-rich (0.5%) diet for modification of lipoprotein composition. At the end of the dietary period, low density lipoproteins (LDL) and high density lipoproteins (HDL) were prepared from plasma of these rabbits. Rabbit skin fibroblasts (RSF) in culture were exposed to these isolated LDL and HDL fractions or to human serum albumin (HSA), respectively. Eicosanoid release was estimated after stimulation of cells with the Ca ionophore A 23187. Exogenous added HDL from the pellet group and HDL from the cholesterol-fed group as well as HSA stimulated PGI2 production by rabbit skin fibroblasts (P < 0.05, respectively) as compared to controls. All LDL preparations investigated inhibited PGI2 release from RSF (P < 0.05, respectively). The TXA2 release from RSF was increased only by HDL from cholesterol-fed rabbits and by HSA (P < 0.05, respectively). Pretreatment of RSF with cholesterol significantly decreased the number of detectable cells. Subsequent addition of HDL from the pellet or from the fish oil group completely restored the ability of cholesterol-enriched RSF to proliferate (P < 0.05, respectively).

Antiatherosclerotic potency of high density lipoprotein of different origins: a review and some new findings

The antiatherosclerotic potency of isolated high density lipoproteins (HDL) of different origins was investigated in three experimental models: (1) isolated HDL were injected into cholesterol-rich fed rabbits; (2) the effect of HDL on the intracellular level of free and esterified cholesterol as well as on proliferation of smooth muscle cells and fibroblasts was investigated in cell cultures; and (3) we studied the influence of isolated HDL fractions on thromboxane (TXB2) formation in clotting whole blood with different cholesterol content.

Effects of daphnodorin A, B and C, new flavans isolated from traditional Chinese medicine, on the 12-lipoxygenase and cyclooxygenase metabolism of arachidonic acid in rabbit platelets

The effects of daphnodorin A, B and C, isolated from the root and bark of Daphne odora THUNB, on the activities of 12-lipoxygenase and cyclooxygenase in rabbit platelets were examined. Daphnodorin A and C were inhibitors of platelet 12-lipoxygenase and cyclooxygenase activities. Daphnodorin B had no effect on the two enzymatic pathways. The present data raise the possibility that daphnodorin A and C can be anti-thrombotic and anti-atherosclerotic drugs through the suppressive influence on the platelet 12-lipoxygenase and cyclooxygenase.