Regression of atherosclerosis by the intravenous infusion of specific biochemical nutrient substrates in animals and humans

Homocysteine stimulates MAP kinase in bovine aortic smooth muscle cells

BACKGROUND

Hyperhomocysteinemia is recognized as a risk factor for atherosclerotic disease. However, the mechanism of homocysteine effects on smooth muscle cell proliferation, which is a hallmark of atherosclerosis, is unknown. The object of this study was to test the effects of homocysteine on smooth muscle cell proliferation, and to examine the mitogen-activated protein (MAP) kinases, extracellular signal-regulated protein kinase 1 and 2, that are known to be involved in cell proliferation.

METHODS

For the proliferation study, bovine aortic smooth muscle cells (BASMC, 10, 000/well) were allowed to grow for 2 days before 2 mmol/L D,L -homocysteine was added for 2, 4, 6, and 8 days to simulate the clinical hyperhomocysteinemic condition. For the MAP kinase study, quiescent BASMC were exposed to 2 mmol/L D,L -homocysteine for 1.5, 5, 10, 20, 30, and 60 minutes, and the active forms of MAP kinase were detected with Western immunoblotting. The degree of phosphorylation of MAP kinase was determined by densitometry.

RESULTS

D,L -homocysteine stimulated BASMC proliferation by 20% by day 8. MAP kinase phosphorylation was activated as much as six fold by D,L -homocysteine, with a peak at 30 minutes. PD98059, an inhibitor of MAP kinase phosphorylation, inhibited the homocysteine-induced MAP kinase phosphorylation and attenuated the increase in BASMC proliferation.

CONCLUSIONS

These data are consistent with the hypothesis that D,L -homocysteine stimulation of BASMC proliferation involves MAP kinase activation.

Surgery, drugs, lifestyle, and hyperlipidemia

Heart disease is the number-one cause of death in the United States, and more money is spent on its treatment each year than for any other condition. Both epidemiologic and experimental data clearly show that elevated plasma cholesterol levels increase the risk of death from coronary heart disease. Genetic insufficiencies can cause high blood cholesterol, but most people with high cholesterol do not have genetic abnormalities; rather, they have lifestyles that include high-fat diets and little exercise. Cholesterol can be managed aggressively with coronary artery bypass surgery, percutaneous transluminal coronary angioplasty, partial ileal bypass, and even liver transplant. Antihyperlipidemic drugs include bile-acid-binding resins, nicotinic acid, fibric acid derivatives, hydroxymethyglutaryl coenzyme A-reductase inhibitors, and the antioxidant probucol. Strict programs of low-fat diets and exercise are also effective for reducing cholesterol, lowering blood pressure, and preventing heart disease without the side effects associated with surgery and drug therapy. Such lifestyle changes are critical to reducing the incidence of heart disease in this country.

Short-term cholesterol lowering decreases size and severity of perfusion abnormalities by positron emission tomography after dipyridamole in patients with coronary artery disease. A potential noninvasive marker of healing coronary endothelium

BACKGROUND

Cholesterol lowering over 1- to 3-year trials is associated with modest regression or no progression of focal coronary artery stenoses compared with progression in controls, a decrease in cardiac events proportionately more than the modest improvement in percent stenosis, and in experimental animals improved endothelial-mediated coronary vasodilation.

METHODS AND RESULTS

Accordingly, we hypothesized that there would be improvement in size and severity of perfusion abnormalities by rest-dipyridamole positron emission tomography (PET) imaging in a randomized intensive cholesterol-lowering trial with each patient studied after a baseline control period, a 90-day intensive cholesterol-lowering treatment, and a final control period off cholesterol-lowering regimens. Completely automated, objective measures of size and severity of perfusion abnormalities on rest-dipyridamole PET images were made by computer algorithm in 12 patients with coronary artery disease. There were statistically significant decreases (improvement) in size and severity of perfusion abnormalities by rest-dipyridamole PET on comparison of baseline control with perfusion abnormalities after intensive 90-day cholesterol lowering and significant increases (worsening) in size and severity after the final control period, respectively, as follows. (1) The percent of left ventricle outside 2.5 SD of normal values on the dipyridamole-to-rest ratio image of normalized counts was 22 +/- 20% after the initial control period, 13 +/- 14% after the treatment period, and 26 +/- 22% after the final control period with a significant decrease (improvement) occurring between the initial control and treatment periods (P = .02) and an increase (worsening) occurring between the treatment and final control periods (P = .009). (2) The percent of left ventricle with a ratio of < or = 0.66 in the dipyridamole-to-rest ratio image of normalized counts was 11 +/- 13% after the initial control period, 5.8 +/- 10% after the treatment period, and 14 +/- 19% after the final control period with a significant decrease (improvement) occurring between the initial control and treatment periods (P = .04) and an increase (worsening) occurring between the treatment and final control periods (P = .02). (3) The myocardial quadrant on the polar display with the lowest average activity expressed as a percent of maximal activity was 0.81 +/- 0.18 after the initial control period, 0.87 +/- 0.014 after the treatment period, and 0.77 +/- 0.23 after the final control period with significant improvement occurring between the initial control and treatment periods (P = .05) and worsening occurring between the treatment and final control periods (P = .05).

CONCLUSIONS

These results suggest that relatively short-term, intensive cholesterol lowering over 90 days improves myocardial perfusion capacity before anatomic regression of stenoses occurs and that such improvement, or deterioration after withdrawal of lipid-lowering treatment, can be followed noninvasively by dipyridamole PET, reflecting the integrated flow capacity of the entire coronary arterial/arteriolar vascular system affected by diffuse atherosclerosis.

Homocysteine metabolism and the oxidative modification of proteins and lipids

Altered homocysteine metabolism is implicated as a pathogenic factor in atherogenesis, neoplasia, and aging. Hereditary enzymatic deficiencies and nutritional deficiencies of folate, pyridoxine, or cobalamin are associated with elevated blood homocysteine, accelerated atherosclerosis, and manifestations of aging. The failure of malignant cells to metabolize homocysteine thiolactone to sulfate is attributed to deficiency of thioretinaco, a complex containing cobalamin, homocysteine thiolactone, and retinoic acid. The sulfhydryl group of homocysteine is believed to act catalytically with ferric or cupric ions in a mixed function oxidation system to generate hydrogen peroxide, oxygen radicals, and homocysteinyl radicals. These reactive species may interact with the active site of enzyme protein to cause inactivation of catalytic activity. Homocysteine thiolactone is oxidized to sulfate by a process involving ascorbate, thioretinamide, and superoxide, under the control of thyroxine and growth hormone. Thioretinaco is believed to be the active site of adenosine triphosphate (ATP) binding in oxidative phosphorylation with the participation of oxygen, ascorbate, proton gradient, and electron transport. Depletion of thioretinaco from mitochondrial and microsomal membranes may be associated with increased formation and release of radical oxygen species within neoplastic and senescent cells. Specific proposals are made for investigating the importance of homocysteine metabolism in the oxidative modification of proteins and lipids.

Endocytosis of oxidized LDL and reversibility of migration inhibition in macrophage-derived foam cells in vitro. A mechanism for atherosclerosis regression?

The ability of macrophage-derived foam cells to migrate from atherosclerotic lesions represents one potential mechanism for the regression of atherosclerosis. It is, however, generally recognized that the transformation of macrophages into foam cells results in greatly reduced migrational ability. In the present study, we set out to investigate the factors affecting migratory capability in foam cell-like cells with the use of an in vitro assay. Foam cell-like cells were prepared by incubating macrophages in the presence of oxidized low density lipoprotein (LDL). The transformation to a typical foam cell morphology was demonstrated by Nile red staining (light microscopy), and the mechanisms of binding, uptake, and intracellular processing of oxidized LDL were established by colloidal gold labeling on the ultrastructural level. With the in vitro assay, the migration of these foam cell-like cells was found to be markedly inhibited compared with untreated, control macrophages. However, zymosan-activated mouse serum restored migration in oxidized LDL-treated cells to levels similar to those of control cells. Restoration of migratory capacity was accompanied by alterations in the cytoskeleton system, especially in actin arrangement.

Arrest and reversal of atherosclerosis with parenteral nutrition

In a large subset of patients with atherosclerotic cardiovascular disease, all medical and surgical treatment alternatives have been exhausted or have proved to be ineffective. Intravenous infusion of specially formulated amino acid solutions, developed in the animal laboratory, has been efficacious in arresting and reversing atherosclerosis in humans for the first time. It is anticipated that the principles derived from these precise parenteral studies will eventually permit development of oral and enteral dietary formulations effective for the systemic control and management of atherosclerosis.

Practicalities of lipids: ICU patient, autoimmune disease, and vascular disease

Although the use of lipids should be individualized, certain generalizations are appropriate. 1. Lipid infusion should be limited in the fulminately septic patient to 10% of total calories in an effort to reduce immunosuppression. 2. The stressed, nonseptic patient with difficulties in ventilator weaning or TPN-induced hepatic dysfunction may reap benefit from a reduction in dextrose calories and the provision of daily lipids. 3. Patients with severe autoimmune disease have had mild amelioration of symptoms with PUFA supplementation. The relative benefits of omega-6 vs omega-3 continue to be examined. 4. Dietary immunomodulation in transplant and burns remains an area of active investigation. 5. Patients with fat-free TPN show transient declines in serum lipids. The development of a "fat-solubilizer" remains in the experimental realm. 6. The provision of fish oil, high in W-3 EPA, has shown promise in atherosclerosis and immunomodulation. The changes in the relative amounts of each prostaglandin class depend on precursor prevalence.