Postprandial retinyl palmitate and squalene metabolism is age dependent

Lipoprotein removal mechanisms and aging: implications for the cardiovascular health of the elderly

PURPOSE OF REVIEW

The speed of removal from the plasma of apolipoprotein B-containing lipoproteins, for example, chylomicrons, VLDL and LDL is determinant of the plasma concentration of these lipoproteins, is influenced by genetic features and ambient factors, and has implications in atherogenesis. As aging increases the clinical complications of atherosclerosis, it is important to appraise the status of the removal mechanisms in elderly individuals.

RECENT FINDINGS

Removal of triglyceride-rich lipoproteins remnants is delayed but the triglyceride breakdown is unchanged in elderly individuals. The discovery of PCSK9, enzyme that degrades LDL receptors, and the recent observation that PCSK9 is elevated in the elderly raises another hypothesis to account for the increased LDL-cholesterol levels in the elderly. The removal of cholesterol from cells by HDL, the first step of cholesterol reverse transport is also less efficient in the elderly, which may compromise the body cholesterol homeostasis.

SUMMARY

Aging determines reduction of the efficiency of lipoprotein plasma removal mechanisms, which is implicated in increased incidence of cardia complications. Moreover, aging is frequently accompanied by physical activity reduction, weight gain, and metabolic disturbances that can further decrease the efficacy of the removal mechanisms. This knowledge is important for promoting cardiovascular health in the elderly and prolonging survival.

Comparison of the Acute Postprandial Circulating B-Vitamin and Vitamer Responses to Single Breakfast Meals in Young and Older Individuals: Preliminary Secondary Outcomes of a Randomized Controlled Trial

B-vitamin deficiency is common in ageing populations either due to altered dietary habits or altered digestive and metabolic functions. There is limited data on the acute circulating concentrations of B-vitamins and their various forms (vitamers), following ingestion of realistic meals. This study compared the acute circulating B-vitamin and vitamer responses to either an energy-dense (ED) or a nutrient-dense (ND) breakfast meal, consumed in a randomized cross-over sequence, in older and younger adults (n = 15 and 15, aged 67.3 ± 1.5 and 22.7 ± 0.5 years (mean ± SEM), respectively). Eleven differing B-vitamins and vitamers were determined in plasma samples by ultra-high-performance liquid chromatography-tandem mass spectrometry, in the fasting and postprandial state (hourly for 5 h). While postprandial thiamine concentration increased following both meals, riboflavin increased only following a ND meal in both age groups. Many vitamins including nicotinic acid, pantothenic acid, pyridoxal, pyridoxamine, pyridoxal-5'phosphate, and 4-pyridoxic acid remained unaltered, and flavin mononucleotide (FMN), nicotinamide and nicotinuric acid concentrations reduced following both meals. Biological age and food composition had minimal impact on postprandial B-vitamin concentrations, yet the differences between the ED and ND meals for riboflavin highlight the importance of riboflavin intake to achieve adequacy.

Removal of Chylomicron Remnants from the Bloodstream is Delayed in Aged Subjects

Dietary fats absorbed in the intestine are transported in the circulation as chylomicrons and remnants that have atherogenic potential. Although postprandial lipidemia is increased in older subjects, the specific chylomicron metabolism has not been explored in older subjects nor compared to young subjects, which is the focus of this study. After a 12 h fast, artificially-made emulsions similar to lymph chylomicrons and doubly labeled with radioactive cholesteryl esters and triglycerides were intravenously injected in 23 older (66±4 years) and 20 young (24±3 years) subjects. Sequential blood samples were collected to determine fractional clearance rates (FCR, in min^-1) by compartmental analysis. Older subjects had higher LDL-cholesterol (p<0.001) and triglycerides (p<0.0001) than young subjects; HDL-cholesterol presented no difference. The emulsion cholesteryl-ester FCR was lower in older subjects compared to the young (p=0.0001). The emulsion triglyceride FCR did not differ in the two groups. Tested in vitro, however, the lipolysis of the emulsion triglycerides was less intense in the older than in the young subjects. As delayed removal of remnants, indicated by the pronouncedly smaller cholesteryl ester FCR, is related to the presence of cardiovascular diseases, this can be a risk factor which could accelerate atherogenic complications occurring in aged subjects

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

Clinical considerations and mechanistic determinants of postprandial lipemia in older adults

The typical diet of individuals in Western societies results in metabolic responses associated with fed-state fat metabolism for most of the daily life of the individual. This fat metabolism is characterized specifically by an increase in the concentration of plasma lipids, primarily triglycerides. Increased postprandial lipemia, which is typically observed in older individuals (i.e., >65 y old), has now emerged as an important correlate of cardiovascular disease risk. An understanding of the mechanisms contributing to the increased postprandial lipemia in older individuals becomes, therefore, of particular clinical importance in any effort to explain and address the well-documented increase in cardiovascular disease risk as individuals age. Current evidence points to an increase in the accumulation of ingested lipid in lipoprotein particles of hepatic origin, together with an overall accumulation of lipid in these lipoproteins during the postprandial period, as primary contributors to the postprandial lipemia in older persons. When this evidence is considered together with the evidence suggesting large atherogenic potential of lipoproteins of hepatic origin, this can, at least in part, explain the increased risk of cardiovascular disease in older individuals. Understanding changes in the metabolism of ingested fat in the immediate postprandial period with advancing age, and how lifestyle interventions such as diet and physical exercise can ameliorate the increase in postprandial lipemia in older individuals, is important in order to address the increased cardiovascular disease risk in this particularly affected and growing segment of the population.

The effect of aging on the immunohistochemistry of apolipoprotein E in the liver

Apolipoprotein E (apoE) is involved in hepatic disposition of chylomicron remnants, which is impaired in old age. Isoforms of apoE have been implicated in age-related diseases and possibly the aging process itself. Because the effects of old age on expression and distribution of apoE in the liver have not been reported, we studied the effect of old age on the immunohistochemistry of apoE in the livers of humans and the non-human primate, Papio hamadryas. Overall, old age was not associated with marked changes in the expression of apoE between adult (48+/-19 years) and old (82+/-5 years) humans. However, there was a change in the distribution of apoE staining. The livers of older humans displayed increased hepatocyte cytoplasmic staining and reduced peri-sinusoidal staining. Similar trends were noted in the livers from the baboons. Such findings are suggestive of altered apoE recycling in old age and have implications for age-related dyslipidaemia.

Issues surrounding age: vascular disease in the elderly

One-fifth of all humans who have survived beyond the age of 65 are alive today, and in the industrialized world the elderly segment of the population is expanding most rapidly. In biological terms, these survivors are healthier than the elderly of previous generations. However 'there are no diseases peculiar to old age and very few from which it is exempt' (Alfred Worcester, 1855-1951), and so society will inevitably accumulate a significant share of degenerative diseases within the ranks of its senior citizens. In the last two decades, the prevalence of stroke, diabetes mellitus, arthritis and heart disease has increased significantly as a tangible index of ageing in the population, and these diseases have been accompanied by degenerating cognitive function and physical disability, both of which are adding increasing stress to community healthcare and social services. Policy-makers need to understand and monitor these trends in order to make informed and cogent decisions about the management of this growing problem. This review highlights some of the key health issues facing the elderly in regard to coronary artery disease, insulin resistance, redox status, and statin therapy, in the hope that enlightened debate will inform decision making on resource allocation for this important and growing segment of society.