Pathogenesis of atherosclerosis

Reassessing the Effects of Dietary Fat on Cardiovascular Disease in China: A Review of the Last Three Decades

Cardiovascular disease (CVD) is a leading cause of global mortality, and is considered one of diseases with the most rapid growth rate in China. Numerous studies have indicated a closed relationship between an increased incidence of CVD and dietary factors. Dietary fat is one of the three primary nutrients of consumption; however, high fat dietary in causing CVD has been neglected in some official dietary guidelines. Our present review has analyzed the relationship between dietary fat consumption and CVD in China over the past 30 years (from 1990 to 2019). There is a significant correlation between CVD incidence and mortality for consumption of both vegetable oils and animal fats, per capita consumption, and the relative weight of dietary fat exceeding that of other food ingredients (e.g., salt, fruit, and marine food). For fatty acid species, the proportion of ω6 fatty acid consumption increased, causing a significant increase in the ratios of ω6/ω3 fatty acids, whereas the proportion of monounsaturated fatty acid consumption decreased. Such changes have been considered a characteristic of dietary fat consumption in Chinese residents over the past 30 years, and are closely related to the incidence of CVD. Therefore, we suggest that the government should spread awareness regarding the consumption of dietary fat intake to prevent CVD and related health disorders. The public should be educated to avoid high fat diet and increase the intake of monounsaturated fatty acids and ω3 fatty acids.

Kidney involvement in a nongenetic rat model of type 2 diabetes

BACKGROUND

Rats fed a high fat diet and given a low dose of streptozotocin (STZ) (35 mg/kg) develop type 2 diabetes with insulin resistance, hyperinsulinemia, moderate hyperglycemia, hyperlipidemia, and salt-sensitive hypertension. We postulated that rats with noninsulinopenic (type 2) diabetes develop lesions of diabetic nephropathy significantly more prominent than those seen in classic insulinopenic (type 1) diabetic rats.

METHODS

Rats were fed regular chow or high fat diet (60% calories from fat and 70% animal fat). After 5 weeks, rats fed regular chow received vehicle (controls) or 55 mg/kg STZ (type 1 diabetes mellitus). Rats fed high fat diet received vehicle (high fat) or low dose STZ, 35 mg/kg (type 2 diabetes mellitus). Rats were sacrificed 14 weeks after STZ/vehicle injection.

RESULTS

Blood glucose, systolic blood pressure, and urinary protein excretion were significantly higher in both diabetes groups than in controls. Serum insulin levels (ng/mL) were higher in type 2 diabetes than in type 1 diabetes groups (0.49 +/- 0.12 vs. 0.07 +/- 0.07) (P= 0.01). Percentage of sclerosed glomeruli was significantly higher in type 2 diabetes group than in control and type 1 diabetes groups. Fibronectin expression was significantly increased in high fat, type 1 and type 2 diabetes groups compared to controls. The expression of type IV collagen, connective tissue growth factor (CTGF), and transforming growth factor-beta (TGF-beta) was significantly increased in high fat and type 2 diabetes groups compared to controls.

CONCLUSION

Rats fed a high fat diet and given a low dose of STZ developed diabetes (with normal/high insulin levels), hypertension, and proteinuria. Kidney lesions in this type 2 model appear to be more pronounced than in type 1 diabetic rats despite lower blood glucose levels and proteinuria. We present a nongenetic rat model of type 2 diabetes mellitus and nephropathy.

Secondary distal extension of infrainguinal bypass: long-term limb and patient survival

The potential benefits of secondary distal extension vein grafts required after failing or failed initial infrainguinal bypasses were evaluated. Outcomes of secondary distal extension bypass procedures (n = 58) performed between July 1983 and March 1993 were reviewed. Patients (n = 51) had critical ischemia or tissue loss, with an average of 2.8 previous vascular procedures. The 58 initial infrainguinal bypasses included 38 above-the-knee and 13 below-the-knee femoropopliteal, 5 femorodistal, and 2 popliteal-distal. Thirty-nine of the 58 femoropopliteal grafts were prosthetic. The extension bypasses included popliteal-tibial, graft-tibial, and peroneal-plantar. They were performed for recurrent or persistent ischemia after failed initial infrainguinal bypasses in limbs, and with still-patent bypasses. All extension bypasses were vein conduits. Mean follow-up was 59 (range: 6 to 164) months. The cumulative life-table 5-year survival rate for all patients was 95%. The 27-month limb-salvage rate was 70%. Our findings indicate that patients with advanced peripheral vascular disease may have prolonged survival, and extension bypasses contribute significantly to their limb salvage. Thus, aggressive application of extension bypass to save threatened limbs is supported.

Platelets and atherosclerosis

Despite the broad array of mechanisms designed to protect the endothelial lining of every blood vessel in the body and maintain the fluid state of blood, injury does occur. Chronic and recurrent damage result in development of lesions characteristic of atherosclerosis. The loss of vascular integrity associated with the pathological process of atherogenesis triggers the haemostatic mechanism. As a result, fibrin and platelets become a part of atherosclerotic lesions and play a role in their progression. Growth of the plaques and destruction of normal endothelium triggers further involvement of platelets leading to occlusion of arteries in the heart and brain, resulting in myocardial infarction and stroke. Understanding the role of platelets in atherosclerosis and limiting its contribution may reduce morbidity and mortality of this dread disease.

Distribution of glycosaminoglycans in the intima of human aortas: changes in atherosclerosis and diabetes mellitus

Arterial glycosaminoglycans are considered to be important in atherogenesis due to their ability to trap lipid inside the vessel wall and to influence cellular migration and proliferation. Atherosclerotic lesions have displayed an altered glycosaminoglycan content and distribution. Diabetes is a recognized risk factor for atherosclerosis, but no information is available on the arterial glycosaminoglycans in human diabetes. We examined glycosaminoglycans in normal and atherosclerotic intima of non-diabetic and Type 2 (non-insulin-dependent) diabetic patients. Intima was stripped from autopsy samples of thoracic aortas; normal and plaque areas were separated. Glycosaminoglycans were isolated by delipidation, proteolytic digestion, and precipitation and characterized by quantitation of total glycosaminoglycan and evaluation of glycosaminoglycan distribution by electrophoresis and densitometry. Results indicate a significant decrease in total glycosaminoglycan and significant changes in their distribution in atherosclerotic plaques: a relative decrease in heparan sulphate, a relative increase in dermatan sulphate and thus a decrease in the ratio of heparan sulphate to dermatan sulphate. A similar but less marked change in the ratio was found in normal intima of diabetic subjects, while in their plaques this change was more pronounced. This suggests that changes in arterial glycosaminoglycans (especially the ratio of heparan sulphate to dermatan sulphate) precede the development of lesions in diabetes and may be important in atherogenesis.

Intimal alterations in rabbit aortas during the first 6 months of alloxan-induced diabetes

Diabetes mellitus is a major risk factor for atherosclerosis. Since endothelial alteration is probably associated with the development of atherosclerosis, we questioned whether morphological evidence of endothelial injury could be observed during the first 6 months of diabetes induced by a single intravenous injection of alloxan in normally fed rabbits compared with age-matched controls. Diabetes (plasma glucose greater than 16 mM) was established by 5 days after alloxan injection. Endothelial alterations consistent with injury, including adhesion of white blood cells, platelets, and fibrin-like material to the endothelial surface, were seen in diabetic rabbit aortas by 2 weeks. These alterations became more severe during the next 6 months. Increased endothelial replication in diabetic vessels was shown by the uptake of tritium-labeled thymidine at 2 weeks and at 3 and 6 months. Hyperplasia of intimal smooth muscle cells progressed during 3 months after treatment. About one third of the diabetic rabbits also showed an elevated plasma cholesterol level, which correlated with increased intimal proliferation but not with endothelial injury or replication. The onset of alloxan-induced diabetes in rabbits is associated with nondenuding endothelial injury and subsequent intimal hypertrophy, changes that are consistent with atherogenesis.

High concentrations of low density lipoprotein decrease basement membrane-associated heparan sulfate proteoglycan in cultured endothelial cells

The effect of increasing low density lipoprotein (LDL) concentrations on the synthesis of basement membrane components was investigated in proliferating porcine aortic endothelial cells (PAEC) in culture. Basement membrane-associated heparan sulfate proteoglycan (HSPG) and fibronectin were determined by enzyme immunoassay. Low extracellular LDL-levels increase, high extracellular LDL-levels decrease the HSPG content of PAEC. Fibronectin synthesis was only slightly affected while proliferation and metabolic activity as assessed by lactate production were constant. Insulin or high extracellular glucose did not influence the effect of LDL on basement membrane components.

Renal injury of diet-induced hypercholesterolemia in rats

Abnormalities in lipid metabolism frequently accompany renal disease and may be important in the pathogenesis of progressive renal injury. In the present study, the effects of a high cholesterol diet on renal histology, cortical lipids, and glomerular hemodynamic function were examined in normal rats with and without reduced renal mass. Cholesterol feeding for 19 weeks increased serum cholesterol from 66 +/- 10 mg/dl to 256 +/- 93 mg/dl in two-kidney rats, and from 73 +/- 15 mg/dl to 407 +/- 274 mg/dl in nephrectomy rats (P less than 0.01). Both sham-operated and unilateral nephrectomy rats fed a high cholesterol diet had a greater amount of glomerulosclerosis and tubulointerstitial damage than rats fed standard chow. Cortical cholesteryl esters were increased by the cholesterol diet, and correlated with the amount of glomerulosclerosis (r = 0.90, P less than 0.01) and tubulointerstitial injury (r = 0.64, P less than 0.05). Cholesterol feeding and nephrectomy both caused alterations in tissue essential fatty acids, and a panel of specific monoclonal antibodies indicated that renal injury and cortical lipid alterations were associated with an increase in glomerular macrophages. Finally, micropuncture experiments carried out in a separate group of rats fed high cholesterol for 8 to 10 weeks demonstrated increases in glomerular capillary pressure. These results suggest that additional investigations may ultimately determine how cholesterol deposition, altered fatty acid metabolism, macrophages, and increased glomerular pressure might combine to cause chronic progressive renal injury.

Model system to study interaction of platelets with damaged arterial wall. II. Inhibition of smooth muscle cell proliferation by dipyridamole and AH-P719

A new in vivo model for the initial events in atherogenesis was employed to investigate drugs which may inhibit intimal muscle cell proliferation following repeated limited endothelial cell injury. An artery forceps was placed over the central artery of the ear of an anesthetized rabbit for 30 min. The forceps were removed, blood flow resumed in the vessel, and platelets contacted the damaged vessel wall. When a vessel was injured two or more times the smooth muscle cells of the media migrated into the intima and proliferated there between 1 and 3 weeks after the last injury despite restoration of an apparently intact endothelium. The intima of control undamaged vessels sometimes contained a few individual smooth muscle cells while vessels injured two, four, or six times showed correspondingly increasing numbers of layers of intimal smooth muscle cells covering increasing amounts of the intima. Arteries from thrombocytopenic rabbits showed, at most, a single layer of smooth muscle cells covering a small area. In rabbits pretreated with dipyridamole (1.5 mg/kg) for 3 days before each injury, proliferation was also limited to a small area. Neither aspirin (8 mg/kg) nor ticlopidine (40 mg/kg, 5X over 3 days), which inhibit platelet aggregation ex vivo, nor the continuous presence of heparin (800 U/kg, bid), reported to inhibit smooth muscle cell growth in vitro and in vivo, prevented smooth muscle cell proliferation in response to two injuries. However, a potent inhibitor of platelet cyclic-adenosine monophosphate (cAMP) phosphodiesterase, AH-P719 (1.5 or 2.1 mg/kg), was able to inhibit intimal smooth muscle cell proliferation in doses that inhibited platelet aggregation ex vivo.

Occurrence of lipid oxidation products in foods

Lipid oxidation products are ubiquitous in foods, although much variation exists in the levels present. Although these levels are generally low, the problem of lipid oxidation severely compromises the quality of some foods and limits the shelf-life of others. Lipid oxidation represents a key barrier in the development of new food products and processes, especially convenience items and processes required to manufacture them. Deleterious changes in foods caused by lipid oxidation include loss of flavour, development of off-flavours, loss of colour, nutrient value and functionally, and the accumulation of compounds which may be detrimental to the health of consumers. All foods that contain lipids are susceptible to oxidation but especially affected are foods which are dehydrated, subjected to high temperatures or cooked and subsequently stored, e.g. dehydrated eggs, cheeses and meats, foods fried in frying oils, and cooked (uncured) meats. Specific examples of compounds which are of health concern include lipid peroxides and the free radicals involved in their formation and propagation, malonaldehyde, and several cholesterol oxidation products. Coronary artery disease (CAD) may be in part caused by the consumption of lipid oxidation products.