High density lipoprotein subpopulations in chronic liver disease

Adrenal insufficiency in cirrhosis

Hypothalamus-pituitary-adrenal axis assessment in patients with cirrhosis is challenging. The phenotype of fatigue, hypotension, electrolyte disarray, and abdominal pain characterizing primary adrenal insufficiency (AI) overlaps significantly with decompensated liver disease. Reliance on total cortisol assays in hypoproteinemic states is problematic, yet abnormal stimulated levels in cirrhosis are associated with poor clinical outcomes. Alternative measures including free plasma or salivary cortisol levels have theoretical merit but are limited by unclear prognostic significance and undefined cirrhosis-specific reference ranges. Further complicating matters is that AI in cirrhosis represents a spectrum of impairment. Although absolute cortisol deficiency can occur, this represents a minority of cases. Instead, there is an emerging concept that cirrhosis, with or without critical illness, may induce a “relative” cortisol deficiency during times of stress. In addition, the limitations posed by decreased synthesis of binding globulins in cirrhosis necessitate re-evaluation of traditional AI diagnostic thresholds.

Abnormal cholesterol metabolism underlies relative adrenal insufficiency in decompensated cirrhosis

BACKGROUND AND AIMS

Relative adrenal insufficiency (RAI) in patients with cirrhosis is associated with increased mortality. Although the pathogenesis of RAI remains unclear, disordered cholesterol metabolism may contribute.

METHODS

We performed a prospective cohort study of 96 non-critically ill subjects with decompensated cirrhosis at a tertiary care centre. Subjects were administered 250 µcg cosyntropin, with RAI defined as an increase in total cortisol <9 µg/dL. High-density lipoprotein (HDL) levels and serum cholesterol esterification percentage (%CE), a validated surrogate marker of lecithin-cholesterol acyltransferase (LCAT) activity, were measured to assess the relationship between disordered cholesterol metabolism and the presence of RAI. Subjects were followed until death, liver transplantation or a maximum of 6 months.

RESULTS

Subjects with RAI had decreased levels of HDL (18 vs 29 mg/dL, P < .01) and %CE (64% vs 66%, P = .03). Correlation was seen between HDL and %CE (r = 0.7, R²  = 0.49; P < .01) and each integer decrease in %CE predicted an approximately 2% increase in the probability of RAI. Transplant-free survival was reduced in subjects with RAI at both 6 months (43% vs 71%, P = .01) and 90 days (54% vs 81%, P < .01).

CONCLUSIONS

Disruption in cholesterol metabolism contributes to the development of RAI in cirrhosis, as decreased LCAT activity leads to reduced HDL trafficking to the adrenal gland.

Naphthenic Acid Mixtures from Oil Sands Process-Affected Water Enhance Differentiation of Mouse Embryonic Stem Cells and Affect Development of the Heart

Extraction of petrochemicals from the surface mining of oil sand deposits results in generation of large volumes of oil sands process-affected water (OSPW). Naphthenic acids (NA) are generally considered to be among the most toxic components of OSPW. Previous studies have shown that NAs are toxic to aquatic organisms, however knowledge of their effects on mammalian health and development is limited. In the present study, we evaluated the developmental effects of an NA extract prepared from fresh OSPW on differentiating mouse embryonic stem cells (ESC). We found that treatment of differentiating cells with the NA extract at noncytotoxic concentrations alters expression of various lineage specification markers and development of the heart. Notably, expression of cardiac specific markers such as Nkx2.5, Gata4, and Mef2c were significantly up-regulated. Moreover, exposure to the NA extract enhanced differentiation of embryoid bodies and resulted in the early appearance of spontaneously beating clusters. Interestingly, exposure of undifferentiated mouse ESCs to the NA extract did not change the expression level of pluripotency markers (i.e., Oct4, Nanog, and Sox2). Altogether, these data identify some of the molecular pathways affected by components within this NA extract during differentiation of mammalian cells.

An update on alcohol and atherosclerosis

PURPOSE OF REVIEW

Epidemiological studies consistently link moderate alcohol use with a lower risk of cardiovascular disease, but a number of important issues remain controversial. These include the putative impact of non-alcoholic constituents of some alcoholic beverages, the role of genetic factors, potential mechanisms for this association, and confirmation of the relationship in experimental models.

RECENT FINDINGS

Although high-density lipoprotein cholesterol (HDL-C) is considered the primary mediator of the cardiovascular effects of moderate drinking, recent evidence has shown the alcohol-HDL-C relation is not linear beyond the range of moderate drinking. Moderate alcohol use also has important inverse relations with inflammatory factors. Some, but not all, animal models confirm the anti-atherogenic effects of ethanol and highlight inflammatory factors as one possible mechanism. The non-alcoholic constituents of red wine also have anti-atherogenic and perhaps even life-extending properties in vitro, but their relevance to humans remains uncertain. Genetic variants of the apolipoprotein E and interleukin 6 genes in humans may modify how alcohol influences atherosclerosis, further emphasizing the importance of HDL-C and inflammatory factors as mediators.

SUMMARY

The robust relationship between moderate drinking and lower risk of cardiovascular disease remains an intriguing area of investigation. Clarifying potential gene-environment interactions and translational research into uses for non-alcoholic components will be important areas for future investigation.

A new liquid homogeneous assay for HDL cholesterol determination evaluated in seven laboratories in Europe and the United States

We evaluated a new liquid homogeneous assay for the direct measurement of high density lipoprotein cholesterol (HDL-C Plus) in seven laboratories. The assay includes two reagents which can be readily used in most available clinical chemistry analyzers. The total CVs of the new method were below 4.6% and the bias in relation to the designated comparison method was below 3.9%. The total error ranged between 4 to 7%. HDL-C values determined by this method were in good agreement with those obtained by the old homogeneous assay using lyophilized reagents, and other homogeneous and precipitation assays (0.944 < r < 0.996). The assay was linear up to at least 3.89 mmol/l HDL-C. Hemoglobin did not interfere, whereas in icteric samples slight deviations were observed. Lipemia up to 11.3 to 22.6 mmol/l triglycerides did not interfere with this homogeneous HDL-C assay. In samples of patients with paraproteinemia, discrepant results were seen. This liquid homogeneous HDL-C assay was easy to handle and produced similar results in all laboratories participating in this study. This method will enable clinical laboratories to reliably measure HDL-C for risk assessment of coronary heart disease.

Dyslipoproteinaemia of liver disease

Hepatic diseases differ from most other causes of secondary dyslipidaemia in that the circulating lipoproteins are not only present in abnormal amounts but they frequently also have abnormal composition, electrophoretic mobility and appearance. Pre-beta and alpha bands can be absent on electrophoresis in all types of liver disease although material in the VLDL and HDL ranges can be isolated in the ultracentrifuge. Cholestatic liver disease has been the most extensively studied and the hyperlipidaemia can be extreme with marked elevations of free cholesterol and phospholipids. This results largely from the presence of LP-X, an abnormal LDL, with a vesicular structure that appears in rouleaux formation under the electron microscope. It is virtually specific for cholestasis and familial LCAT deficiency. The LDL, however, is heterogeneous and may also contain a large triglyceride-rich particle (LP-Y) as well as more normal-looking particles, which are none the less depleted in cholesteryl esters and rich in triglycerides. Indeed, when patients with cholestasis are hypertriglyceridaemic the excess triglyceride is to be found predominantly in these two LDL fractions rather than in VLDL. HDL in cholestasis may contain disc-like particles, similar to those newly secreted by the liver and intestine, as well as more normal-looking spherical particles. In extrahepatic obstruction concentrations of HDL and its major apolipoproteins, apoAI and apoAII, are frequently reduced, although a subfraction rich in apoE is often found. In all but the latest stages of chronic intrahepatic cholestasis due to primary biliary cirrhosis, however, HDL, especially HDL2, concentrations are increased, probably due to the presence of a circulating inhibitor of HL. Many of these lipoprotein changes found in cholestasis resemble those of familial LCAT deficiency, although the hyperlipidaemia is not usually so severe in the latter condition. Indeed, in patients with cholestasis but well-preserved LCAT activity many of the characteristic lipoprotein changes, such as LP-X, LP-Y and discoidal HDL, may not be seen. In acute hepatocellular disease, such as alcoholic or viral hepatitis, it is not unusual for the patient to go through a cholestatic phase and many of the same lipoprotein changes may be seen. In cirrhosis without cholestasis the patients are not usually significantly hyperlipidaemic and in advanced cases cholesterol and apoB levels may be reduced. Although LCAT activity and the proportion of plasma cholesterol esterified may also be markedly reduced, LP-X is not usually seen, possibly because the flux of free cholesterol and phospholipid (lecithin), the LCAT substrates, is relatively low. Discoidal HDLs are often present.(ABSTRACT TRUNCATED AT 400 WORDS)

Bile salt shift from albumin to high-density lipoprotein in cholestasis

The distribution of [3H]taurocholate between albumin and the lipoproteins of serum of patients with various diseases in which lipoprotein metabolism and/or bile salt concentrations were altered and of healthy control subjects was investigated by means of the density gradient centrifugation method. 1. In control sera, bile salts distribute mainly between albumin and high-density lipoprotein. An amount of 19.7 +/- 3.6% (mean +/- S.D., n = 6) of the total serum bile salts was found in the high-density lipoprotein fraction of the density gradient. 2. In sera of nonicteric patients, the distribution pattern of [3H]taurocholate in the fractions of the density gradient showed no essential differences to normal serum. The relative amounts of taurocholate in the albumin-containing fractions and the high-density lipoprotein fractions were dependent on the concentrations of albumin and high-density lipoprotein. 3. In sera of deeply jaundiced patients, the distribution pattern of [3H]taurocholate showed two distinct peaks in the high-density lipoprotein density range, one of which codistributed with high-density lipoprotein2 and the other with a high-density fraction of high-density lipoprotein3 in the density range of 1.19 to 1.23 gm per ml. The distribution of [3H]taurocholate between albumin and high-density lipoprotein was markedly shifted toward high-density lipoprotein. No [3H]taurocholate association with lipoprotein X was observed. 4. Bilirubin was found to cause a shift of taurocholate from albumin to high-density lipoprotein in vitro. It is proposed that bilirubin is responsible, at least in part, for the observed shift in icteric sera.