Variations in the fatty acid composition of lipid classes from lipoproteins in elderly women

Why is elevation of serum cholesterol associated with exposure to perfluoroalkyl substances (PFAS) in humans? A workshop report on potential mechanisms

Serum concentrations of cholesterol are positively correlated with exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in humans. The associated change in cholesterol is small across a broad range of exposure to PFOA and PFOS. Animal studies generally have not indicated a mechanism that would account for the association in humans. The extent to which the relationship is causal is an open question. Nonetheless, the association is of particular importance because increased serum cholesterol has been considered as an endpoint to derive a point of departure in at least one recent risk assessment. To gain insight into potential mechanisms for the association, both causal and non-causal, an expert workshop was held Oct 31 and Nov 1, 2019 to discuss relevant data and propose new studies. In this report, we summarize the relevant background data, the discussion among the attendees, and their recommendations for further research.

Fatty acid and cholesterol composition of the uterine artery intima in relation to menopausal status, age, and serum cholesterol

OBJECTIVES

Estrogens modulate lipid metabolism and the increased risk of atherosclerosis in postmenopausal women is at least partly due to the reduction of estrogen production after menopause. We studied the effect of menopause on the contents of long-chain fatty acids, free cholesterol (FC) and cholesterol ester (CE) in uterine artery wall.

METHODS

The uterine artery intima samples were obtained in connection with surgery of 21 postmenopausal and 51 premenopausal women. The amount of FC, CE and phospholipid fatty acids were measured by gas chromatography after extraction and fractionation and these lipid values were related to menopausal status, age and serum total and low-density lipoprotein (LDL) cholesterol levels.

RESULTS

Premenopausal females had significantly less intimal FC (161 +/- 50 vs. 407 +/- 276 microg/100 mg wet weight, P = 0.003) and CE (19 +/- 34 vs. 305 +/- 348 microg/100 mg wet weight, P = 0.050) and smaller proportion of linoleic acid out of all phospholipid fatty acids (4.2 vs. 7.2%, P = 0.002) than postmenopausal women after adjustment with age. The content of CE (r = 0.34, P = 0.025) and the FC-to-CE ratio (r = -0.45, P = 0.002) correlated with age in premenopausal but not in postmenopausal women. Moreover, the intimal content of CE correlated with the percentage of intimal phospholipid linoleic acid in postmenopausal women (r = 0.79, P = 0.020). The same was true for FC (r = 0.73, P < 0.001).

CONCLUSIONS

These results indicate that CE and FC accumulation into the wall of uterine artery depends on menopausal status, independently of age, and that the phospholipid long-chain fatty acid composition differs significantly between premenopausal and postmenopausal women. This suggests that estrogens may be involved in the regulation of artery wall lipid composition.

Lipoprotein modification and atherosclerosis in aging

The development of extensive atherosclerosis of major arteries of the heart, brain, and lower extremities is a particularly frequent problem in elderly individuals and is responsible for the majority of the cardiovascular morbidity and mortality in this population. Although the frequency and severity of this problem is well recognized, there has been relatively little investigation of the effects of aging on the development of atherosclerosis. Work by a number of investigators over the last 10-15 years has demonstrated that modifications of lipoproteins, resulting from oxidative stress, glycoxidation, formation of AGE, or other processes may play an important role in atherosclerosis. As described in this review, the aging process may enhance lipoprotein modification and atherosclerosis in several ways. Conditions such as hypertension, diabetes, and menopause all increase in frequency with advancing age and may contribute both directly and indirectly to lipoprotein modification and vascular injury.Additionally, in some studies of older animals and humans, there seems to be evidence for greater in vivo oxidative stress. Whether this is a specific consequence of aging and associated medical conditions, or related to differences in dietary fatty acid or antioxidant content or other lifestyle differences is currently unknown. One important consequence of this may be enhanced susceptibility of lipoproteins to oxidation. Additional study of lipoprotein modifications associated with aging is clearly needed, and may provide new insight and solutions to the common problem of atherosclerosis in the elderly.

Properties of low density lipoproteins relevant to oxidative modifications change paradoxically during aging

Atherosclerosis is a common problem among the elderly. Because lipid peroxidation is considered a contributor to the development of atherosclerosis, we compared oxidative properties of lipoproteins in an otherwise healthy (SENIEUR-classified) aged population (65-74 years) with young controls (18-30 years). Relative amounts of oxidatively altered low density lipoprotein (LDL), estimated by means of an antibody against LDL modified by 4-hydroxynonenal, a product of lipid peroxidation, were increased marginally in serum from the elderly (9.8 vs. 7.4%, P = 0.07). In contrast, isolated LDL from the elderly revealed a decreased susceptibility to in vitro oxidation: the lag time was increased (2.34 vs. 2.10 h, P < 0.01), and the maximal rate of LDL oxidation decreased (0.88 vs. 1.01 O.D./h, P = 0.001). However, there were no age-related changes in lipid composition of native LDL and consumption of fatty acids during in vitro oxidation. The serum concentrations of ascorbic acid and most lipophilic anti-oxidants (the latter expressed per g serum lipids) were significantly decreased in the elderly except tocopherols which tended to be higher. In conclusion, our data reveal paradox age-related alterations of LDL as to its behaviour in oxidation in vivo vs. in vitro.

Fatty acid composition of lipoprotein lipids in hepatobiliary diseases

Liver damage and alterations in the exocrine function of the gland lead to a profound alteration of the plasma lipoprotein profile. To determine whether hepatic disease results in changes in the lipoprotein fatty acid composition, i.e. to determine whether liver function influences the homeostasis of complex lipids in plasma, we studied the fatty acid profile of lipids from VLDL, LDL and HDL, as well as from total plasma, in thirty-one patients of both sexes with hepatobiliary pathology (compensated liver cirrhosis, uncompensated liver cirrhosis, primary biliary cirrhosis, other intrahepatic cholestasis, and acute viral hepatitis). We also studied a group of healthy adults as controls. We present the lipoprotein profile and the fatty acid composition (myristic C14, palmitic C16, palmitoleic C16: 1, stearic C18, oleic C18: 1, linoleic C18: 2, eicosatrienoic C20: 3 omega 6 and arachidonic C20: 4) of lipoprotein and total plasma triacylglycerols, cholesteryl esters and phospholipids. The main observation of this study is that, despite the profound changes in the lipoprotein profile and the lower abundance of polyunsaturated fatty acids in complex lipids, the composition of all triacylglycerols, cholesteryl esters and phospholipids is very similar for the corresponding lipoproteins of patients with hepatobiliary disease and of control subjects. This indicates that in the controls as in the studied patients, the exchange of lipids between plasmatic lipoproteins is very rapid and demonstrates the possible importance of the extrahepatic synthesis of cholesteryl ester transfer protein.

Cholesteryl ester transfer activity in liver disease and cholestasis, and its relation with fatty acid composition of lipoprotein lipids

Liver disease is accompanied by major qualitative and quantitative disturbances in plasma lipoprotein metabolism, the extent and intensity of which depend on the degree of parenchymal damage, cholestasis, or both. The main objective of this study was to determine the cholesteryl ester transfer CETP activity and its association with the lipoprotein neutral lipid composition in patients with either liver cirrhosis or cholestasis, as compared to normal controls. Lipoproteins were isolated by ultracentrifugation, lipids and apolipoproteins were measured by conventional methods, and the fatty acid composition was established by gas chromatography; CETP activity in lipoprotein-deficient plasma was measured by determining the transfer of [3H]cholesteryl esters from HDL to VLDL. Lipoprotein lipase and hepatic lipase activities were measured in post-heparin plasma by radiochemical methods. In patients with liver cirrhosis, low levels of VLDL, HDL, apo B, and Lp(a) were observed, as well as a change in the composition of HDL particles, with increases in the relative proportion of triglyceride and free cholesterol. Respectively, the last two changes could be attributed in part to the low hepatic lipase activity observed in this study, and to the low lecithin:cholesterol acyltransferase activity previously observed by others. In patients with cholestasis, a moderate hyperlipidemia due to the elevation of LDL was found. In contrast, HDL and apo A-I levels were very low reflecting a low number of HDL particles, which also had altered compositions with increases in the triglyceride and free cholesterol contents relative to apo A-I and esterified cholesterol, respectively. As regards the fatty acid composition of lipoprotein lipids, the two groups of patients showed, in general, a lower proportion of linoleic acid and a compensating higher proportion of oleic acid as compared to the controls, changes that were observed in both cholesteryl esters and triglycerides. In contrast, the proportions of oleic and palmitoleic acids in phospholipids were increased, whereas that of stearic acid was decreased in patients as compared to controls. In patients with liver cirrhosis, as well as in controls, no changes were observed in the fatty acid compositions of cholesteryl ester, triglycerides, or phospholipids among the different lipoproteins, which probably reflects the equilibration reached by the action of CETP. In patients with cholestasis, no differences were observed in fatty acid composition among the lipoprotein phospholipids but, interestingly, cholesteryl esters from VLDL had a significantly lower linoleic acid content than those from HDL, whereas triglycerides from VLDL had significantly higher oleic acid and lower linoleic acid contents than those from HDL. This distinct fatty acid composition of the neutral lipids between lipoproteins was associated with a significant decrease (25%) in the cholesteryl ester transfer activity in patients with cholestasis. We suggest that fat malabsorption due to the biliary defect may induce a decrease in cholesteryl ester transfer protein synthesis or section, which in turn would slow the equilibration of the neutral lipids among plasma lipoproteins.

Postmenopausal changes of lipid and glucose metabolism: a review of their main aspects

In postmenopausal women, partly in relation to advancing age and partly due to oestrogen deficiency, there is a frequent increase in body weight, and more specifically, in android fat distribution. In addition, loss of ovarian function is associated with the development of a more atherogenic profile with increased triglycerides, LDL-cholesterol and its smaller dense subfractions, decreased HDL- and HDL2-cholesterol and, potentially, an irregular increase in Lp(a). Not only does oestrogen therapy counteract all these changes towards a definitely less atherogenic profile but oestrogens seem also implicated in reducing LDL oxidative products, in favouring a higher ratio of prostacyclin to thromboxane and, potentially, of endothelium derived relaxing factor to endothelin, and also in acting as a calcium antagonist in the vessel wall. All of these favourable vascular effects are not solely attributable to lipid-related oestrogen effects. Excess weight and central obesity, diet changes and lack of exercise, more frequent with advancing age, all concur to alter glucose tolerance and increase insulin resistance during the postmenopause. Impaired glucose tolerance and diabetes mellitus may be found in nearly 20% of women aged 55 to 65 years. In addition, oestrogen deficiency may be further responsible for decreased pancreatic insulin secretion and alteration of its metabolic clearance rate-changes that can be reversed toward improved insulin secretion and sensitivity by oestrogen treatment in small dosages. By contrast, synthetic androgenic progestins can counteract these effects of oestrogens more than progesterone derivatives do, and they may partly help to promote insulin resistance and hyperinsulinism.(ABSTRACT TRUNCATED AT 250 WORDS)