Higher prevalence of coronary microvascular dysfunction in asymptomatic individuals with high levels of lipoprotein(a) with and without heterozygous familial hypercholesterolaemia

BACKGROUND AND AIMS

Microvascular dysfunction underlies many cardiovascular disease conditions; little is known regarding its presence in individuals with high levels of lipoprotein(a) [Lp(a)]. The aim of the present study was to determine the frequency of microvascular dysfunction among such subjects with and without concomitant familial hypercholesterolemia (FH).

METHODS

Four groups of asymptomatic individuals aged 30-59 years, without manifest cardiovascular disease, were recruited (n = 30 per group): controls with Lp(a) < 30 nmol/L, mutation-confirmed FH with Lp(a) < 30 nmol/L, or >125 nmol/L, and individuals with isolated Lp(a) > 125 nmol/L. Participants underwent evaluation of myocardial microvascular function by measuring coronary flow reserve (CFR) using transthoracic Doppler echocardiography, and of peripheral microvascular endothelial function by peripheral arterial tonometry.

RESULTS

The groups were balanced in age, sex, and body mass index. Each of the three dyslipoproteinaemic groups had a greater proportion of individuals with impaired coronary flow reserve, 30%, compared to 6.7% of controls (p = 0.014). The median CFR levels did not differ significantly between the four groups, however. Cholesterol-lowering treatment time was longer in the individuals with normal than in those with impaired CFR in the FH + Lp(a) > 125 group (p = 0.023), but not in the group with FH + Lp(a) < 30 (p = 0.468). There was no difference in peripheral endothelial function between the groups.

CONCLUSIONS

Coronary microvascular dysfunction is more prevalent in asymptomatic individuals with isolated Lp(a) elevation and in heterozygous FH both with and without high Lp(a) compared to healthy controls. Cholesterol-lowering treatment could potentially prevent the development of microvascular dysfunction.

Neurobiology of eating behavior, nutrition, and health

Eating behavior and food-related decision making are among the most complex of the motivated behaviors, and understanding the neurobiology of eating behavior, and its developmental dynamics, is critical to advancing the nutritional sciences and public health. Recent advances from both human and animal studies are revealing that individual capacity to make health-promoting food decisions varies based on biological and physiological variation in the signaling pathways that regulate the homeostatic, hedonic, and executive functions; past developmental exposures and current life-stage; the food environment; and complications of chronic disease that reinforce the obese state. Eating rate drives increased calorie intake and represents an important opportunity to lower rates of food consumption and energy intake through product reformulation. Understanding human eating behaviors and nutrition in the context of neuroscience can strengthen the evidence base from which dietary guidelines are derived and can inform policies, practices, and educational programs in a way that increases the likelihood they are adopted and effective for reducing rates of obesity and other diet-related chronic disease.

A3907, a systemic ASBT inhibitor, improves cholestasis in mice by multiorgan activity and shows translational relevance to humans

BACKGROUND AND AIMS

Cholestasis is characterized by intrahepatic accumulation of bile constituents, including bile acids (BAs), which promote liver damage. The apical sodium-dependent BA transporter (ASBT) plays an important role in BA reabsorption and signaling in ileum, bile ducts, and kidneys. Our aim was to investigate the pharmacokinetics and pharmacological activity of A3907, an oral and systemically available ASBT inhibitor in experimental mouse models of cholestasis. In addition, the tolerability, pharmacokinetics, and pharmacodynamics of A3907 were examined in healthy humans.

APPROACH AND RESULTS

A3907 was a potent and selective ASBT inhibitor in vitro. In rodents, orally administered A3907 distributed to the ASBT-expressing organs, that is, ileum, liver, and kidneys, and dose dependently increased fecal BA excretion. A3907 improved biochemical, histological, and molecular markers of liver and bile duct injury in Mdr2-/- mice and also had direct protective effects on rat cholangiocytes exposed to cytotoxic BA concentrations in vitro . In bile duct ligated mice, A3907 increased urinary BA elimination, reduced serum BA levels, and prevented body weight loss, while improving markers of liver injury. A3907 was well tolerated and demonstrated target engagement in healthy volunteers. Plasma exposure of A3907 in humans was within the range of systemic concentrations that achieved therapeutic efficacy in mouse.

CONCLUSIONS

The systemic ASBT inhibitor A3907 improved experimental cholestatic disease by targeting ASBT function at the intestinal, liver, and kidney levels, resulting in marked clearance of circulating BAs and liver protection. A3907 is well tolerated in humans, supporting further clinical development for the treatment of cholestatic liver diseases.

Molecular programming modulates hepatic lipid metabolism and adult metabolic risk in the offspring of obese mothers in a sex-specific manner

Male and female offspring of obese mothers are known to differ extensively in their metabolic adaptation and later development of complications. We investigate the sex-dependent responses in obese offspring mice with maternal obesity, focusing on changes in liver glucose and lipid metabolism. Here we show that maternal obesity prior to and during gestation leads to hepatic steatosis and inflammation in male offspring, while female offspring are protected. Females from obese mothers display important changes in hepatic transcriptional activity and triglycerides profile which may prevent the damaging effects of maternal obesity compared to males. These differences are sustained later in life, resulting in a better metabolic balance in female offspring. In conclusion, sex and maternal obesity drive differently transcriptional and posttranscriptional regulation of major metabolic processes in offspring liver, explaining the sexual dimorphism in obesity-associated metabolic risk.

Sex and maternal obesity drive differently transcriptional and posttranscriptional regulation of major metabolic processes in the livers of female and male offspring, contributing to the sexual dimorphism in obesity-associated metabolic risk.

Nutrition and stem cell integrity in aging

Adult stem cells (SCs) represent the regenerative capacity of organisms throughout their lifespan. The maintenance of robust SC populations capable of renewing organs and physiological systems is one hallmark of healthy aging. The local environment of SCs, referred to as the niche, includes the nutritional milieu, which is essential to maintain the quantity and quality of SCs available for renewal and regeneration. There is increased recognition that SCs have unique metabolism and conditional nutrient needs compared to fully differentiated cells. However, the contribution of SC nutrition to overall human nutritional requirements is an understudied and underappreciated area of investigation. Nutrient needs vary across the lifespan and are modified by many factors including individual health, disease, physiological states including pregnancy, age, sex, and during recovery from injury. Although current nutrition guidance is generally derived for apparently healthy populations and to prevent nutritional deficiency diseases, there are increased efforts to establish nutrient-based and food-based recommendations based on reducing chronic disease. Understanding the dynamics of SC nutritional needs throughout the life span, including the role of nutrition in extending biological age by blunting biological systems decay, is fundamental to establishing food and nutrient guidance for chronic disease reduction and health maintenance. This review summarizes a 3-day symposium of the Marabou Foundation (www.marabousymposium.org) held to examine the metabolic properties and unique nutritional needs of adult SCs and their role in healthy aging and age-related chronic disease.

Founder effects facilitate the use of a genotyping-based approach to molecular diagnosis in Swedish patients with familial hypercholesterolaemia

AIM

To investigate whether genotyping could be used as a cost-effective screening step, preceding next-generation sequencing (NGS), in molecular diagnosis of familial hypercholesterolaemia (FH) in Swedish patients.

METHODS AND RESULTS

Three hundred patients of Swedish origin with clinical suspicion of heterozygous FH were analysed using a specific array genotyping panel embedding 112 FH-causing mutations in the LDLR, APOB and PCSK9 genes. The mutations had been selected from previous reports on FH patients in Scandinavia and Finland. Mutation-negative cases were further analysed by NGS. In 181 patients with probable or definite FH using the Dutch lipid clinics network (DLCN) criteria (score ≥ 6), a causative mutation was identified in 116 (64%). Of these, 94 (81%) were detected by genotyping. Ten mutations accounted for more than 50% of the positive cases, with APOB c.10580G>A being the most common. Mutations in LDLR predominated, with (c.2311+1_2312-1)(2514)del (FH Helsinki) and c.259T>G having the highest frequency. Two novel LDLR mutations were identified. In patients with DLCN score < 6, mutation detection rate was significantly higher at younger age.

CONCLUSION

A limited number of mutations explain a major fraction of FH cases in Sweden. Combination of selective genotyping and NGS facilitates the clinical challenge of cost-effective genetic screening in suspected FH. The frequency of APOB c.10580G>A was higher than previously reported in Sweden. The lack of demonstrable mutations in the LDLR, APOB and PCSK9 genes in ~1/3 of patients with probable FH strongly suggests that additional genetic mechanisms are to be found in phenotypic FH.

Obese mother offspring have hepatic lipidic modulation that contributes to sex-dependent metabolic adaptation later in life

With the increasing prevalence of obesity in women of reproductive age, there is an urgent need to understand the metabolic impact on the fetus. Sex-related susceptibility to liver diseases has been demonstrated but the underlying mechanism remains unclear. Here we report that maternal obesity impacts lipid metabolism differently in female and male offspring. Males, but not females, gained more weight and had impaired insulin sensitivity when born from obese mothers compared to control. Although lipid mass was similar in the livers of female and male offspring, sex-specific modifications in the composition of fatty acids, triglycerides and phospholipids was observed. These overall changes could be linked to sex-specific regulation of genes controlling metabolic pathways. Our findings revised the current assumption that sex-dependent susceptibility to metabolic disorders is caused by sex-specific postnatal regulation and instead we provide molecular evidence supporting in utero metabolic adaptations in the offspring of obese mothers.

Regulation of bile acid metabolism in biliary atresia: reduction of FGF19 by Kasai portoenterostomy and possible relation to early outcome

BACKGROUND

Fibroblast growth factor 19 (FGF19) is produced in the small intestine and is involved in suppression of hepatic bile acid (BA) synthesis. FGF19 is also expressed in the liver and serum levels are elevated in adults with cholestatic liver disease. This may reflect a rescue mechanism to dampen liver injury caused by increased intrahepatic BAs.

OBJECTIVES

To examine circulating FGF19 at early stages of biliary atresia and at short-term follow-up post-Kasai portoenterostomy (KPE) in relation to noncholestatic infants. The relationship between FGF19, BAs and markers for BA synthesis and hepatic gene expression of factors involved in BA metabolism were also evaluated.

METHODS

Liver tissue, portal and peripheral blood samples were obtained from fifteen patients at KPE; additional blood was collected 4-6 months after surgery. Two control groups were included; to examine possible changes related to surgery and to compare FGF19 in biliary atresia to noncholestatic infants.

RESULTS

Circulating FGF19 levels correlated to its hepatic gene expression at time of KPE in biliary atresia and levels were elevated compared to noncholestatic infants. At follow-up, FGF19 levels were markedly reduced, and the decline coincided with reductions in bilirubin and conjugated chenodeoxycholic acid and with increased levels of the BA synthesis marker C4.

CONCLUSION

Elevated circulating FGF19 in biliary atresia is of hepatic origin and reduced following KPE. Changes in serum FGF19 may reflect the level of restoration of the enterohepatic circulation, and this warrants further long-term studies on the role of FGF19 in the cholestatic liver.

A Physiology-Based Model of Bile Acid Distribution and Metabolism Under Healthy and Pathologic Conditions in Human Beings

BACKGROUND & AIMS

Disturbances of the enterohepatic circulation of bile acids (BAs) are seen in a number of clinically important conditions, including metabolic disorders, hepatic impairment, diarrhea, and gallstone disease. To facilitate the exploration of underlying pathogenic mechanisms, we developed a mathematical model built on quantitative physiological observations across different organs.

METHODS

The model consists of a set of kinetic equations describing the syntheses of cholic, chenodeoxycholic, and deoxycholic acids, as well as time-related changes of their respective free and conjugated forms in the systemic circulation, the hepatoportal region, and the gastrointestinal tract. The core structure of the model was adapted from previous modeling research and updated based on recent mechanistic insights, including farnesoid X receptor-mediated autoregulation of BA synthesis and selective transport mechanisms. The model was calibrated against existing data on BA distribution and feedback regulation.

RESULTS

According to model-based predictions, changes in intestinal motility, BA absorption, and biotransformation rates affected BA composition and distribution differently, as follows: (1) inhibition of transintestinal BA flux (eg, in patients with BA malabsorption) or acceleration of intestinal motility, followed by farnesoid X receptor down-regulation, was associated with colonic BA accumulation; (2) in contrast, modulation of the colonic absorption process was predicted to not affect the BA pool significantly; and (3) activation of ileal deconjugation (eg, in patents with small intestinal bacterial overgrowth) was associated with an increase in the BA pool, owing to higher ileal permeability of unconjugated BA species.

CONCLUSIONS

This model will be useful in further studying how BA enterohepatic circulation modulation may be exploited for therapeutic benefits.

Of mice and men: murine bile acids explain species differences in the regulation of bile acid and cholesterol metabolism

Compared with humans, rodents have higher synthesis of cholesterol and bile acids (BAs) and faster clearance and lower levels of serum LDL-cholesterol. Paradoxically, they increase BA synthesis in response to bile duct ligation (BDL). Another difference is the production of hydrophilic 6-hydroxylated muricholic acids (MCAs), which may antagonize the activation of FXRs, in rodents versus humans. We hypothesized that the presence of MCAs is key for many of these metabolic differences between mice and humans. We thus studied the effects of genetic deletion of the Cyp2c70 gene, previously proposed to control MCA formation. Compared with WT animals, KO mice created using the CRISPR/Cas9 system completely lacked MCAs, and displayed >50% reductions in BA and cholesterol synthesis and hepatic LDL receptors, leading to a marked increase in serum LDL-cholesterol. The doubling of BA synthesis following BDL in WT animals was abolished in KO mice, despite extinguished intestinal fibroblast growth factor (Fgf)15 expression in both groups. Accumulation of cholesterol-enriched particles ("Lp-X") in serum was almost eliminated in KO mice. Livers of KO mice were increased 18% in weight, and serum markers of liver function indicated liver damage. The human-like phenotype of BA metabolism in KO mice could not be fully explained by the activation of FXR-mediated changes. In conclusion, the presence of MCAs is critical for many of the known metabolic differences between mice and humans. The Cyp2c70-KO mouse should be useful in studies exploring potential therapeutic targets for human disease.

Selective estrogen receptor (ER)β activation provokes a redistribution of fat mass and modifies hepatic triglyceride composition in obese male mice

Estrogen exerts its action through the binding to two major receptors, estrogen receptor (ER)α and β. Recently, the beneficial role of selective ERβ activation in the regulation of metabolic homeostasis in obesity has been demonstrated, but its importance is still controversial. However, no data are available regarding possible gender differences in response to pharmaceutical activation of ERβ. Male mice were fed a control diet (CD) or a high fat diet (HFD) before being treated with the ERβ selective ligand, 4-(2-(3-5-dimethylisoxazol-4-yl)-1H-indol-3yl)phenol (DIP) in the same conditions as in our recently published paper in female mice. Magnetic resonance imaging and spectroscopy were performed repeatedly in vivo after 6 weeks of diet and after 2 weeks of DIP. Adipose tissue distribution and hepatic triglycerides composition were quantified. HFD-treated males showed a feminization of their fat distribution towards more subcutaneous fat depots and increase total fat content and visceral adipose tissue showed clear browning sites after DIP. Hepatic lipid composition was modified by DIP, with less saturated and more unsaturated lipids and an improved insulin sensitivity. Finally, brown adipose tissue size expended after DIP, due to an increase of the size of the lipid droplets. Our data demonstrate that selective activation of ERβ exerts a tissue-specific and sex-dependent response to metabolic adaptation to overfeeding. Most importantly, together with our previously published results in females, the current findings support the concept that sex should be considered in the future development of obesity-moderating drugs.

MON-163 Lowering of Circulating FGF21 by Modulation of Bile Acid Metabolism in Healthy Males

FGF21 is a circulating protein of hepatic origin proposed to be involved in the regulation of lipid and glucose metabolism. Increased levels have been reported in conditions of metabolic overload. Recent animal studies have also suggested that FGF21 levels may be influenced by modulation of bile acid metabolism, but knowledge about the human situation is sparse. In this study we aimed to evaluate the response of circulating FGF21 to perturbations of bile acid metabolism in healthy humans. We studied samples obtained from two clinical studies characterizing bile acid metabolism: (i) Eight healthy males underwent repeated blood sampling during 32 hr in three experiments: under basal conditions, following initiation of treatment with cholestyramine (CME), and following initiation of CME when under treatment with atorvastatin (CME+STAT). (ii) 54 healthy males were randomized into 8 groups that were treated orally with a single dose of placebo or the nonsteroidal FXR agonist, Px-102 (0.15mg/kg, 0.3mg/kg, 0.6mg/kg, 1.12mg/kg, 2.25mg/kg, 3.38mg/kg, or 4.5mg/kg) and monitored for 24 hr. Serum levels of FGF21 were related to previously reported levels of markers of cholesterol and bile acid metabolism. (iii) In a third previously conducted study based on a survival training program for healthy volunteers, FGF21 serum levels were investigated during 50 hrs of sleep and 66 hrs of food deprivations. In the untreated normal subjects, serum FGF21 levels displayed a distinct diurnal rhythm, characterized by an early morning peak. Following CME and CME+STAT treatment, circulating FGF21 was lowered and the early morning peak was abolished. Intake of Px-102 strongly and rapidly reduced FGF21 levels which remained lowered for the 24 hr-period. There was no obvious correlation of FGF21 levels to the diurnal variation patterns of the enterohepatic circulation of BAs, nor to those of cholesterol and bile acid syntheses or serum FGF19. Our data also failed to show any clear effects of sleep deprivation or 66 hrs of starvation on circulating FGF21. Both during marked stimulation and pronounced reduction of bile acid synthesis, serum FGF21 levels were reduced. The results do not support the proposal that FXR activation is an important regulator of hepatic FGF21 secretion in humans, which has been suggested from animal experiments. Instead, we would propose that our findings reflect the response to depletion of intracellular bile acid levels, both when caused by interruption of their normal enterohepatic circulation and by suppression of their de novo synthesis from cholesterol.

Asynchronous rhythms of circulating conjugated and unconjugated bile acids in the modulation of human metabolism

BACKGROUND AND OBJECTIVES

Bile acids (BAs) traversing the enterohepatic circulation (EHC) influence important metabolic pathways. By determining individual serum BAs in relation to markers of metabolic activity, we explored how diurnal variations in their EHC relate to hepatic metabolism in normal humans.

METHODS

Serum BAs, fibroblast growth factor 19 (FGF19), lipoproteins, glucose/insulin and markers of cholesterol and BA syntheses were monitored for 32 h in 8 healthy males. Studies were conducted at basal state and during initiation of cholestyramine treatment, with and without atorvastatin pretreatment. Time series cross-correlation analysis, Bayesian structural model and Granger causality test were applied.

RESULTS

Bile acids synthesis dominated daytime, and cholesterol production at night. Conjugated BAs peaked after food intake, with subsequent FGF19 elevations. BA synthesis was reduced following conjugated BA and FGF19 peaks. Cholestyramine reduced conjugated BAs and FGF19, and increased BA and cholesterol production; the latter effects attenuated by atorvastatin. The relative importance of FGF19 vs. conjugated BAs in this feedback inhibition could not be discriminated. Unconjugated BAs displayed one major peak late at night/early morning that was unrelated to FGF19 and BA synthesis, and abolished by cholestyramine. The normal suppression of serum triglycerides, glucose and insulin observed at night was attenuated by cholestyramine.

CONCLUSIONS

Conjugated and unconjugated BAs have asynchronous rhythms of EHC in humans. Postprandial transintestinal flux of conjugated BAs increases circulating FGF19 levels and suppresses BA synthesis. Unconjugated BAs peak late at night, indicating a non-postprandial diurnal change in human gut microflora, the physiological implications of which warrants further study.

An FXR Agonist Reduces Bile Acid Synthesis Independently of Increases in FGF19 in Healthy Volunteers

Bile acid (BA) synthesis is regulated through suppression of hepatic cholesterol 7α-hydroxylase via farnesoid X receptor (FXR) activation in hepatocytes and/or enterocytes; in enterocytes, this process requires FGF19 signaling. To study these pathways, we quantified markers of BA synthesis (7α-hydroxy-4-cholesten-3-one [C4]) and cholesterol production (lathosterol), fibroblast growth factor (FGF)19, and BAs in serum from healthy male volunteers given 1 oral dose of the nonsteroidal FXR agonist Px-102 (0.15 mg/kg, 0.3 mg/kg, 0.6 mg/kg, 1.12 mg/kg, 2.25 mg/kg, 3.38 mg/kg, or 4.5 mg/kg). After 8 hours, serum levels of C4 decreased by 80% in volunteers given 0.15 mg/kg, whereas serum levels of FGF19 were unchanged. Serum levels of FGF19 increased significantly, in a dose-dependent manner, in volunteers given >0.3 mg/kg Px-102, up to as much as 1600%, whereas C4 levels remained significantly reduced (by >80%). For all doses, FGF19 levels returned to normal 24 hours after administration of Px-102. Serum levels of C4 decreased before levels of FGF19 levels increased, and were still reduced by 95% 24 hours after the highest dose (4.5 mg/kg) of Px-102, even though levels of FGF19 had returned to baseline. Our findings indicate that activation of hepatic FXR is able to suppress BA synthesis, independent of FGF19.

Gemfibrozil Reduces Thrombin Generation in Patients with Combined Hyperlipidaemia, without Influencing Plasma Fibrinogen, Fibrin Gel Structure or Coagulation Factor VII

A double-blind, placebo-controlled, cross-over study was conducted in 21 men with combined hyperlipoproteinaemia to examine if lipid-lowering treatment with gemfibrozil (10-12 weeks) affects blood coagulation and fibrin gel structure at rest or during mental stress. Gemfibrozil lowered plasma triglycerides by 57 ± 4%, whereas high density lipoprotein (HDL) cholesterol increased by 22 ± 5%. Gemfibrozil lowered the triglyceride content of low density lipoprotein (LDL). Gemfibrozil reduced the plasma concentrations of thrombin-antithrombin complex (TAT) and prothrombin fragment F1+2 (F1+2), both at rest and during mental stress. However, there were no effects of gemfibrozil treatment on the plasma concentrations of fibrinogen, factor VII antigen, activated factor VII (Vila) or activated factor XII (XIIa), or on fibrin gel structure. Acute mental stress per se did not influence coagulation factors, reaction products or fibrin gel structure, or their responses to the study drug. Thus, gemfibrozil reduces thrombin generation in men with combined hyperlipoproteinaemia, without influencing the plasma levels of fibrinogen, Vila and XIIa, or fibrin gel structure. Attenuation of thrombin generation may contribute to the primary-preventive effects of gemfibrozil on coronary heart disease.

Influence of Metoprolol Treatment on Sympatho-Adrenal Activation of Fibrinolysis

The effects of mental stress (a colour word conflict test, CWT) and adrenaline infusions (0.1 and 0.4 nmol kg−1 min−1) on t-PA activity, t-PA antigen, PAI-1 activity and PAI-1 antigen were studied in 18 healthy male volunteers. Furthermore, the effects of metoprolol (200 mg/day during 1 week) or placebo (double-blind cross-over study) on fibrinolytic responses to sympatho-adrenal activation, and relationships between fibrinolysis and blood lipids were investigated.

Low and high dose adrenaline infusions yielding plasma adrenaline levels of 0.9 ± 0.1 and 3.4 ± 0.4 nmol/1, respectively, dose-dependently increased t-PA levels with a concomitant decrease in PAI-1 levels. A similar, but weaker, fibrinolytic response seemed to occur during CWT when plasma adrenaline levels were only moderately increased (to 0.4 ± 0.1 nmol/1). Metoprolol treatment did not influence the resting levels of the fibrinolytic variables studied, but tended to enhance the t-PA response to CWT and further reduce PAI-1 during adrenaline infusion. Metoprolol treatment was not accompanied by any rise in PAI-1 levels despite drug induced elevations of triglyceride levels. Thus, the present study shows that sympatho-adrenal activation increases fibrinolytic activity in vivo and that meto prolol treatment may have a favourable influence on this activity.

Platelet Activity In Vivo in Hyperlipoproteinemia – Importance of Combined Hyperlipidemia

Platelet hyperactivity in vitro is found in patients with isolated hypercholesterolemia. It is, however, less well established if platelet activity in vivo is enhanced, and if there are differences between various types of hyperlipoproteinemia.

Platelet function in vivo was studied at rest and during mental stress in men with isolated hypercholesterolemia (phenotype IIa; n = 21) or combined hyperlipidemia (phenotype IIb; n = 29), and age-matched normolipidemic controls (n = 41). The urinary excretion of 11-dehydrothromboxane B2 was elevated in patients compared to controls (IIa, p <0.05; IIb, p <0.001), and higher in type IIb than in IIa patients (p <0.05). Platelet secretion, assessed as plasma β-thromboglobulin levels, was higher in type IIb patients compared to controls (p <0.01) and type IIa patients (p <0.05) during mental stress. The urinary excretion of β-thromboglobulin was also elevated in type IIb patients compared to controls (p <0.05). Platelet aggregability at rest, as measured by filtragometry ex vivo was, however, reduced in both patient groups compared to controls (p <0.05). No correlations were found between plasma lipoprotein levels and markers of platelet function in vivo. Type IIb patients had higher plasma fibrinogen levels and higher leukocyte counts than controls (p <0.05 and p <0.001) and type IIa patients (p <0.05 and p = 0.06). Thromboxane excretion was positively related to fibrinogen levels and leukocyte counts (p <0.01 for both). Preliminary data regarding serum TNF-α also indicated an elevation of this inflammatory cytokine in type IIb patients (p <0.05 vs controls).

In conclusion, thromboxane generation and platelet secretion in vivo are enhanced in patients with hypercholesterolemia, and particularly so among patients with concomitant elevation of plasma triglycerides. The mechanism is unknown, but inflammatory mediators may be involved. The present findings are of interest in relation to the role of triglycerides in coronary artery disease.

Cholestyramine treatment of healthy humans rapidly induces transient hypertriglyceridemia when treatment is initiated

Bile acid (BA) production in mice is regulated by hepatic farnesoid X receptors and by intestinal fibroblast growth factor (FGF)-15 (in humans, FGF-19), a suppressor of BA synthesis that also reduces serum triglycerides and glucose. Cholestyramine treatment reduces FGF-19 and induces BA synthesis, whereas plasma triglycerides may increase from unclear reasons. We explored whether FGF-19 may suppress BA synthesis and plasma triglycerides in humans by modulation of FGF-19 levels through long-term cholestyramine treatment at increasing doses. In a second acute experiment, metabolic responses from 1 day of cholestyramine treatment were monitored. Long-term treatment reduced serum FGF-19 by >90%; BA synthesis increased up to 17-fold, whereas serum BAs, triglycerides, glucose, and insulin were stable. After long-term treatment, serum BAs and FGF-19 displayed rebound increases above baseline levels, and BA and cholesterol syntheses normalized after 1 wk without rebound reductions. Acute cholestyramine treatment decreased FGF-19 by 95% overnight and serum BAs by 60%, while BA synthesis increased fourfold and triglycerides doubled. The results support that FGF-19 represses BA synthesis but not serum triglycerides. However, after cessation of both long-term and 1-day cholestyramine treatment, circulating FGF-19 levels were normalized within 2 days, whereas BA synthesis remained significantly induced in both situations, indicating that also other mechanisms than the FGF-19 pathway are responsible for stimulation of BA synthesis elicited by cholestyramine. Several of the responses during cholestyramine treatment persisted at least 6 days after treatment, highlighting the importance of removing such treatment well before evaluating dynamics of the enterohepatic circulation in humans.

Can LDL cholesterol be too low? Possible risks of extremely low levels

Following the continuous accumulation of evidence supporting the beneficial role of reducing low-density lipoprotein cholesterol (LDL-C) levels in the treatment and prevention of atherosclerotic cardiovascular disease and its complications, therapeutic possibilities now exist to lower LDL-C to very low levels, similar to or even lower than those seen in newborns and nonhuman species. In addition to the important task of evaluating potential side effects of such treatments, the question arises whether extremely low LDL-C levels per se may provoke adverse effects in humans. In this review, we summarize information from studies of human cellular and organ physiology, phenotypic characterization of rare genetic diseases of lipid metabolism, and experience from clinical trials. Specifically, we emphasize the importance of the robustness of the regulatory systems that maintain balanced fluxes and levels of cholesterol at both cellular and organismal levels. Even at extremely low LDL-C levels, critical capacities of steroid hormone and bile acid production are preserved, and the presence of a cholesterol blood-brain barrier protects cells in the central nervous system. Apparent relationships sometimes reported between less pronounced low LDL-C levels and disease states such as cancer, depression, infectious disease and others can generally be explained as secondary phenomena. Drug-related side effects including an increased propensity for development of type 2 diabetes occur during statin treatment, whilst further evaluation of more potent LDL-lowering treatments such as PCSK9 inhibitors is needed. Experience from the recently reported and ongoing large event-driven trials are of great interest, and further evaluation including careful analysis of cognitive functions will be important.

Treatment with the natural FXR agonist chenodeoxycholic acid reduces clearance of plasma LDL whilst decreasing circulating PCSK9, lipoprotein(a) and apolipoprotein C-III

BACKGROUND

The natural farnesoid X receptor (FXR) agonist chenodeoxycholic acid (CDCA) suppresses hepatic cholesterol and bile acid synthesis and reduces biliary cholesterol secretion and triglyceride production. Animal studies have shown that bile acids downregulate hepatic LDL receptors (LDLRs); however, information on LDL metabolism in humans is limited.

METHODS

Kinetics of autologous ¹²⁵ I-LDL were determined in 12 male subjects at baseline and during treatment with CDCA (15 mg kg^-1 day^-1 ). In seven patients with gallstones treated with CDCA for 3 weeks before cholecystectomy, liver biopsies were collected and analysed for enzyme activities and for specific LDLR binding. Serum samples obtained before treatment and at surgery were analysed for markers of lipid metabolism, lipoproteins and the LDLR modulator proprotein convertase subtilisin/kexin type 9 (PCSK9).

RESULTS

Chenodeoxycholic acid treatment increased plasma LDL cholesterol by ~10% as a result of reduced clearance of plasma LDL-apolipoprotein (apo)B; LDL production was somewhat reduced. The reduction in LDL clearance occurred within 1 day after initiation of treatment. In CDCA-treated patients with gallstones, hepatic microsomal cholesterol 7α-hydroxylase and HMG-CoA reductase activities were reduced by 83% and 54%, respectively, and specific LDLR binding was reduced by 20%. During treatment, serum levels of fibroblast growth factor 19 and total and LDL cholesterol increased, whereas levels of 7α-hydroxy-4-cholesten-3-one, lathosterol, PCSK9, apoA-I, apoC-III, lipoprotein(a), triglycerides and insulin were reduced.

CONCLUSIONS

Chenodeoxycholic acid has a broad influence on lipid metabolism, including reducing plasma clearance of LDL. The reduction in circulating PCSK9 may dampen its effect on hepatic LDLRs and plasma LDL cholesterol. Further studies of the effects of other FXR agonists on cholesterol metabolism in humans seem warranted, considering the renewed interest for such therapy in liver disease and diabetes.

Mental distress in treatment seeking young adults (18-25 years) with severe obesity compared with population controls of different body mass index levels: cohort study

Young adults (18-25) with severe obesity constitute a challenging patient group, and there is limited evidence about their mental health status compared to population controls. Mental distress in treatment seeking young adults with severe obesity (n = 121, mean body mass index [BMI] = 39.8 kg m^-2 ) was compared with matched (1:3 for age, gender and socioeconomic status) population controls of normal weight (n = 363, mean BMI = 22.4 kg m^-2 ), as well as unmatched population controls with class I obesity (n = 105, mean BMI = 32.1 kg m^-2 ) or severe obesity (n = 41, mean BMI = 39.7 kg m^-2 ). Mental distress was measured by the General Health Questionnaire-12 (GHQ-12), and we quantified physician-diagnosed depression, present anxiety and suicide attempts. Poisson regression and linear regression analysis were used for analysing differences in mental distress between groups. Treatment seekers experienced more mental distress than normal weight controls as measured by continuous (adjusted mean: 3.9 vs. 2.2 points, P <0.001) and categorical (cut-off for mental distress ≥3 points, RR: 1.76, P <0.001) GHQ-12 scores, depression (RR: 2.18, P < 0.001), anxiety (RR: 1.97, P < 0.001) and suicide attempts (RR: 2.04; P = 0.034). Treatment seekers also experienced more mental distress as measured by continuous GHQ-12 than controls with class I obesity (adjusted mean: 2.3 points) or severe obesity (adjusted mean: 2.1; both, P < 0.001). Young adult treatment seekers with severe obesity constitute a risk group for mental distress compared to population controls of different BMI levels.

Metabolic Syndrome: One Speckled Stone Kills a Flock of Birds?

Effectively treating metabolic syndrome and its progression to type 2 diabetes, steatohepatitis and cardiovascular disease remain a major clinical challenge. The use of a novel engineered molecule that combines thyroid hormone and glucagon to target liver and adipose tissue might provide a new 'magic bullet' with exciting future prospects.

High-density lipoprotein-associated sphingosine-1-phosphate activity in heterozygous familial hypercholesterolaemia

BACKGROUND

Patients with heterozygous familial hypercholesterolaemia (FH) suffer from high plasma cholesterol and an environment of increased oxidative stress. We examined its potential effects on high-density lipoprotein (HDL)-associated sphingosine-1-phosphate (S1P) content (HDL-S1P) and HDL-mediated protection against oxidative stress, both with and without statin treatment.

MATERIALS AND METHODS

In a case-control study, HDL was isolated from 12 FH patients with and without statin treatment and from 12 healthy controls. The HDL-S1P content and the capacity of HDL to protect cardiomyocytes against oxidative stress in vitro were measured.

RESULTS

HDL-associated S1P was significantly correlated with cell protection, but not with HDL-cholesterol or apolipoprotein AI. The latter did not correlate with HDL-mediated cell protection. Neither the HDL-S1P content nor HDL protective capacity differed between nontreated FH patients and controls. The relative amounts of apolipoprotein AI and apolipoprotein M were similar between controls and FH patients. Statin treatment had no effect on any of these measures.

CONCLUSIONS

The FH environment is not detrimental to HDL-S1P content or HDL-S1P-mediated cell protection. Statin treatment does not modulate HDL function in this regard.

Arginase inhibition improves endothelial function in patients with familial hypercholesterolaemia irrespective of their cholesterol levels

BACKGROUND

Elevated LDL cholesterol is an important risk factor for atherosclerosis. Endothelial dysfunction, an early event in the development of atherosclerosis, is characterized by a reduction in nitric oxide (NO) bioavailability. Arginase has emerged as a key regulator of endothelial function through competition with NO synthase for the common substrate l-arginine. Arginase in endothelial cells is activated by oxidized LDL. The study aim was to investigate the importance of arginase for endothelial dysfunction in patients with familial hypercholesterolaemia (FH).

METHODS AND RESULTS

Endothelial function was evaluated in 12 patients with heterozygous FH and 12 age-matched healthy normocholesterolaemic subjects using forearm venous occlusion plethysmography. The evaluations in FH patients occurred when they were on lipid-lowering therapy and 4 weeks after withdrawal of treatment. Endothelium-dependent vasodilatation (EDV) was assessed by intrabrachial artery infusion of serotonin, and endothelium-independent dilatation was assessed by infusion of nitroprusside before and after 120 min administration of the arginase inhibitor N (ω) -hydroxy-nor-l-arginine (nor-NOHA; 0.1 mg min(-1)). In FH patients LDL cholesterol increased from 4.3 ± 0.9 mmol L(-1) at baseline to 7.6 ± 1.9 mmol L(-1) at follow-up (P < 0.001). Arginase inhibition enhanced EDV in FH patients by a similar degree independent of lipid-lowering therapy. The improvement in EDV by arginase inhibition was significantly greater in FH patients than in the control group.

CONCLUSION

Arginase inhibition results in greater improvement in endothelial function in patients with FH compared to healthy controls irrespective of their cholesterol levels. Arginase may be a promising therapeutic target for improving endothelial function in patients with hypercholesterolaemia.

Impaired Cholesterol Efflux Capacity of High-Density Lipoprotein Isolated From Interstitial Fluid in Type 2 Diabetes Mellitus-Brief Report

Supplemental Digital Content is available in the text.

Objective—

Patients with type 2 diabetes mellitus (T2D) have an increased risk of cardiovascular disease, the mechanism of which is incompletely understood. Their high-density lipoprotein (HDL) particles in plasma have been reported to have impaired cholesterol efflux capacity. However, the efflux capacity of HDL from interstitial fluid (IF), the starting point for reverse cholesterol transport, has not been studied. We here investigated the cholesterol efflux capacity of HDL from IF and plasma from T2D patients and healthy controls.

Approach and Results—

HDL was isolated from IF and peripheral plasma from 35 T2D patients and 35 age- and sex-matched healthy controls. Cholesterol efflux to HDL was determined in vitro, normalized for HDL cholesterol, using cholesterol-loaded macrophages. Efflux capacity of plasma HDL was 10% lower in T2D patients than in healthy controls, in line with previous observations. This difference was much more pronounced for HDL from IF, where efflux capacity was reduced by 28% in T2D. Somewhat surprisingly, the efflux capacity of HDL from IF was lower than that of plasma HDL, by 15% and 32% in controls and T2D patients, respectively.

Conclusion—

These data demonstrate that (1) HDL from IF has a lower cholesterol efflux capacity than plasma HDL and (2) the efflux capacity of HDL from IF is severely impaired in T2D when compared with controls. Because IF comprises the compartment where reverse cholesterol transport is initiated, the marked reduction in cholesterol efflux capacity of IF-HDL from T2D patients may play an important role for their increased risk to develop atherosclerosis.

Circulating Hepcidin-25 Is Reduced by Endogenous Estrogen in Humans

OBJECTIVE

Hepcidin reduces iron absorption by binding to the intestinal iron transporter ferroportin, thereby causing its degradation. Although short-term administration of testosterone or growth hormone (GH) has been reported to decrease circulating hepcidin levels, little is known about how hepcidin is influenced in human endocrine conditions associated with anemia.

RESEARCH DESIGN AND METHODS

We used a sensitive and specific dual-monoclonal antibody sandwich immunoassay to measure hepcidin-25 in patients (a) during initiation of in vitro fertilization when endogenous estrogens were elevated vs. suppressed, (b) with GH deficiency before and after 12 months substitution treatment, (c) with hyperthyroidism before and after normalization, and (d) with hyperprolactinemia before and after six months of treatment with a dopamine agonist.

RESULTS

In response to a marked stimulation of endogenous estrogen production, median hepcidin levels decreased from 4.85 to 1.43 ng/mL (p < 0.01). Hyperthyroidism, hyperprolactinemia, or GH substitution to GH-deficient patients did not influence serum hepcidin-25 levels.

CONCLUSIONS

In humans, gonadotropin-stimulated endogenous estrogen markedly decreases circulating hepcidin-25 levels. No clear and stable correlation between iron biomarkers and hepcidin-25 was seen before or after treatment of hyperthyroidism, hyperprolactinemia or growth hormone deficiency.

Who is the Treatment-Seeking Young Adult with Severe Obesity: A Comprehensive Characterization with Emphasis on Mental Health

OBJECTIVE

To characterize treatment-seeking young adults (16-25 years) with severe obesity, particularly mental health problems.

STUDY DESIGN AND PARTICIPANTS

Cross-sectional study of 165 participants (132 women, 33 men) with BMI ≥35 kg/m2 or ≥30 kg/m2 with comorbidities, enrolling in a multidisciplinary obesity treatment program.

METHOD

Data collection at admission of present and life-time health issues including symptomatology of anxiety, depression (Hospital Anxiety and Depression Scale) and attention-deficit/hyperactivity disorder (Adult ADHD Self-Report scale); self-esteem (Rosenberg Self-Esteem Scale), suicide attempts, health-related quality of life (Short Form-36 Health Survey), psychosocial functioning related to obesity (Obesity-related Problems Scale), cardiorespiratory fitness (Astrand's bicycle ergometer test), somatic and psychiatric co-morbidities, cardiometabolic risk factors, and micronutritional status. We used multiple regression analysis to identify variables independently associated with present anxiety and depressive symptomatology.

RESULTS

Mean body mass index was 39.2 kg/m2 (SD = 5.2). We found evidence of poor mental health, including present psychiatric diagnoses (29%), symptomatology of anxiety (47%), depression (27%) and attention-deficit/hyperactivity disorder (37%); low self-esteem (42%), attempted suicide (12%), and low quality of life (physical component score = 46, SD = 11.2; mental component score = 36, SD = 13.9, P<0.001 for difference). Variables independently associated with present anxiety symptomatology (R2 = 0.33, P<0.001) included low self-esteem (P<0.001) and pain (P = 0.003), whereas present depressive symptomatology (R2 = 0.38, P<0.001) was independently associated with low self-esteem (P<0.001), low cardiorespiratory fitness (P = 0.009) and obesity-related problems (P = 0.018). The prevalence of type 2 diabetes was 3%, and hypertension 2%. Insulin resistance was present in 82%, lipid abnormality in 62%, and poor cardiorespiratory fitness in 92%. Forty-eight percent had at least one micronutritional deficiency, vitamin D being the most common (35%).

CONCLUSION

A wide range of health issues, including quite severe mental health problems, was prevalent in treatment-seeking young adults with severe obesity. These are likely to constitute a major treatment challenge, including options relating to bariatric surgery.

Levels of atherogenic lipoproteins are unexpectedly reduced in interstitial fluid from type 2 diabetes patients

At a given level of serum cholesterol, patients with T2D have an increased risk of developing atherosclerosis compared with nondiabetic subjects. We hypothesized that T2D patients have an increased interstitial fluid (IF)-to-serum gradient ratio for LDL, due to leakage over the vascular wall. Therefore, lipoprotein profiles in serum and IF from 35 T2D patients and 35 healthy controls were assayed using fast performance liquid chromatography. The IF-to-serum gradients for VLDL and LDL cholesterol, as well as for apoB, were clearly reduced in T2D patients compared with healthy controls. No such differences were observed for HDL cholesterol. Contrary to our hypothesis, the atherogenic VLDL and LDL particles were not increased in IF from diabetic patients. Instead, they were relatively sparser than in healthy controls. The most probable explanation to our unexpected finding is that these lipoproteins are more susceptible to retainment in the extravascular space of these patients, reflecting a more active uptake by, or adhesion to, tissue cells, including macrophages in the vascular wall. Further studies are warranted to further characterize the mechanisms underlying these observations, which may be highly relevant for the understanding of why the propensity to develop atherosclerosis is increased in T2D.

Influence of dietary sugar on cholesterol and bile acid metabolism in the rat: Marked reduction of hepatic Abcg5/8 expression following sucrose ingestion

Previous studies have indicated that dietary intake of sugar may lower bile acid production, and may promote cholesterol gallstone formation in humans. We studied the influence of dietary sucrose on cholesterol and bile acid metabolism in the rat. In two different experiments, rats received high-sucrose diets. In the first, 60% of the weight of standard rat chow was replaced with sucrose (high-sucrose diet). In the second, rats received a diet either containing 65% sucrose (controlled high-sucrose diet) or 65% complex carbohydrates, in order to keep other dietary components constant. Bile acid synthesis, evaluated by measurements of the serum marker 7-alpha-hydroxy-4-cholesten-3-one (C4) and of the hepatic mRNA expression of Cyp7a1, was markedly reduced by the high-sucrose diet, but not by the controlled high-sucrose diet. Both diets strongly reduced the hepatic - but not the intestinal - mRNA levels of Abcg5 and Abcg8. The differential patterns of regulation of bile acid synthesis induced by the two sucrose-enriched diets indicate that it is not sugar per se in the high-sucrose diet that reduces bile acid synthesis, but rather the reduced content of fiber or fat. In contrast, the marked reduction of hepatic Abcg5/8 observed is an effect of the high sugar content of the diets.

Reductions in serum levels of LDL cholesterol, apolipoprotein B, triglycerides and lipoprotein(a) in hypercholesterolaemic patients treated with the liver-selective thyroid hormone receptor agonist eprotirome

BACKGROUND

Liver-selective thyromimetic agents could provide a new approach for treating dyslipidaemia.

METHODS

We performed a multicentre, randomized, placebo-controlled, double-blind study to evaluate the efficacy and safety of eprotirome, a liver-selective thyroid hormone receptor agonist, in 98 patients with primary hypercholesterolaemia. After previous drug wash-out and dietary run-in, patients received 100 or 200 μg day(-1) eprotirome or placebo for 12 weeks. The primary end-point was change in serum LDL cholesterol; secondary end-points included changes in other lipid parameters and safety measures.

RESULTS

Eprotirome treatment at 100 and 200 μg daily reduced serum LDL cholesterol levels by 23 ± 5% and 31 ± 4%, respectively, compared with 2 ± 6% for placebo (P < 0.0001). Similar reductions were seen in non-HDL cholesterol and apolipoprotein (apo) B, whereas serum levels of HDL cholesterol and apo A-I were unchanged. There were also considerable reductions in serum triglycerides and lipoprotein(a), in particular in patients with elevated levels at baseline. There was no evidence of adverse effects on heart or bone and no changes in serum thyrotropin or triiodothyronine, although the thyroxine level decreased. Low-grade increases in liver enzymes were evident in most patients.

CONCLUSION

In hypercholesterolaemic patients, the liver-selective thyromimetic eprotirome decreased serum levels of atherogenic lipoproteins without signs of extra-hepatic side effects. Selective stimulation of hepatic thyroid hormone receptors may be an attractive way to modulate lipid metabolism in hyperlipidaemia.

Influence of physiological changes in endogenous estrogen on circulating PCSK9 and LDL cholesterol

Pharmacologically increased estrogen levels have been shown to lower hepatic and plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) levels in animals and humans. We hypothesized that physiological changes in estrogen levels influence circulating PCSK9, thereby contributing to the known wide inter-individual variation in its plasma levels, as well as to the established increase in LDL cholesterol (LDL-C) with normal aging. Circulating PCSK9, estradiol, and other metabolic factors were determined in fasting samples from 206 female and 189 male healthy volunteers (age 20-85 years), The mean levels of PCSK9 were 10% higher in females than in males (P < 0.05). PCSK9 levels were 22% higher in postmenopausal than in premenopausal (P < 0.001) females. Within the group of premenopausal females, circulating PCSK9 correlated inversely to estrogen levels, and PCSK9 was higher (305 ng/ml) in the follicular phase than in the ovulatory (234 ng/ml) or the luteal (252 ng/ml) phases (P < 0.05). Changes in endogenous estrogen levels during the menstrual cycle likely contribute to the broad inter-individual variation in PCSK9 and LDL-C in normal females. PCSK9 levels increase in females after menopause but not in men during this phase in life. This likely contributes to why LDL-C in women increases in this period.

Thyroid hormone reduces PCSK9 and stimulates bile acid synthesis in humans

Reduced plasma LDL-cholesterol is a hallmark of hyperthyroidism and is caused by transcriptional stimulation of LDL receptors in the liver. Here, we investigated whether thyroid hormone (TH) actions involve other mechanisms that may also account for the reduction in LDL-cholesterol, including effects on proprotein convertase subtilisin/kexin type 9 (PCSK9) and bile acid synthesis. Twenty hyperthyroid patients were studied before and after clinical normalization, and the responses to hyperthyroidism were compared with those in 14 healthy individuals after 14 days of treatment with the liver-selective TH analog eprotirome. Both hyperthyroidism and eprotirome treatment reduced circulating PCSK9, lipoprotein cholesterol, apoB and AI, and lipoprotein(a), while cholesterol synthesis was stable. Hyperthyroidism, but not eprotirome treatment, markedly increased bile acid synthesis and reduced fibroblast growth factor (FGF) 19 and dietary cholesterol absorption. Eprotirome treatment, but not hyperthyroidism, reduced plasma triglycerides. Neither hyperthyroidism nor eprotirome treatment altered insulin, glucose, or FGF21 levels. TH reduces circulating PSCK9, thereby likely contributing to lower plasma LDL-cholesterol in hyperthyroidism. TH also stimulates bile acid synthesis, although this response is not critical for its LDL-lowering effect.

Influence of growth hormone on circulating fibroblast growth factor 21 levels in humans

OBJECTIVE

Findings from animal studies indicate that growth hormone (GH) may stimulate the production of the putative metabolic regulator fibroblast growth factor 21 (FGF21). We investigated whether circulating FGF21 levels are altered in patients with GH deficiency and characterized how levels of this growth factor are influenced by acute and long-term administration of GH, and the potential relationship between FGF21 and nonesterified fatty acids (NEFAs).

DESIGN AND SETTING

GH-deficient patients (n = 9) were studied prior to and during 1 year of replacement with GH. Healthy subjects (n = 8) received an intravenous bolus of GH with or without concomitant oral glucose. Healthy subjects and patients with heterozygous familial hypercholesterolaemia (n = 23) were monitored following increasing doses of GH for 3 weeks. The main outcome measures were serum FGF21 and NEFA levels. Studies were performed at two academic centres.

RESULTS

GH-deficient patients had FGF21 levels within the normal range, and GH replacement did not influence circulating FGF21 or NEFA concentrations. Acute GH administration to healthy control subjects did not change FGF21 levels, whereas an oral glucose load increased serum FGF21 by 25% and reduced NEFA levels by 48%. Similar effects were seen on administration of glucose together with GH. However, FGF21 levels increased dose dependently up to 3.7-fold in control subjects treated with GH for 3 weeks; simultaneously NEFA levels were increased by 47%.

CONCLUSIONS

GH is not critical for the maintenance of basal serum FGF21 levels in humans, but circulating FGF21 levels increase following administration of GH to healthy individuals. There is no correlation between plasma NEFA and circulating FGF21 levels.

Interstitial fluid lipoproteins

PURPOSE OF REVIEW

The interstitium represents the fluid, proteins, solutes, and extracellular matrix comprising the microenvironment of tissues. We here review attempts to characterize the levels and composition of lipoproteins in human interstitial fluid, and identify potentially important questions for future research.

RECENT FINDINGS

Despite the high relevance of understanding how lipoproteins enter and exit the interstitial compartment, and how they interact with extracellular and cellular molecules, scientific progress in this field has been rather slow. This is partly due to methodological difficulties, both regarding how to obtain representative samples and how to perform appropriate measurements to compare patient cohorts and to evaluate responses to treatment. Predominant techniques include peripheral lymph cannulation and suction blister creation, both of which have inherent advantages and disadvantages. Detailed studies comparing the effects of long-term incubation of serum and lymph lipoproteins are compatible with the view that HDL in interstitial fluid takes up free cholesterol from cells and transfers it into the circulation.

SUMMARY

Studies of the concentration, composition, functionality, and turnover of interstitial fluid lipoproteins will be of great future interest for understanding how tissue cholesterol metabolism is regulated, and how different diseases link to increased risk for development of atherosclerosis.

Gut microbiota regulates bile acid metabolism by reducing the levels of tauro-beta-muricholic acid, a naturally occurring FXR antagonist

Bile acids are synthesized from cholesterol in the liver and further metabolized by the gut microbiota into secondary bile acids. Bile acid synthesis is under negative feedback control through activation of the nuclear receptor farnesoid X receptor (FXR) in the ileum and liver. Here we profiled the bile acid composition throughout the enterohepatic system in germ-free (GF) and conventionally raised (CONV-R) mice. We confirmed a dramatic reduction in muricholic acid, but not cholic acid, levels in CONV-R mice. Rederivation of Fxr-deficient mice as GF demonstrated that the gut microbiota regulated expression of fibroblast growth factor 15 in the ileum and cholesterol 7α-hydroxylase (CYP7A1) in the liver by FXR-dependent mechanisms. Importantly, we identified tauro-conjugated beta- and alpha-muricholic acids as FXR antagonists. These studies suggest that the gut microbiota not only regulates secondary bile acid metabolism but also inhibits bile acid synthesis in the liver by alleviating FXR inhibition in the ileum.

Stimulation of murine biliary cholesterol secretion by thyroid hormone is dependent on a functional ABCG5/G8 complex

Secretion of cholesterol into bile is important for the elimination of cholesterol from the body. Thyroid hormone (TH) increases biliary cholesterol secretion and hepatic gene expression of adenosine triphosphate (ATP)-binding cassette, subfamily G (WHITE), member 5 (ABCG5) and ATP-binding cassette, subfamily G (WHITE), member 8 (ABCG8), two half-transporters that act as a heterodimeric complex promoting sterol secretion. In addition, nuclear liver x receptor-alpha (LXRa), also regulated by TH, induces gene expression of ABCG5/G8. We here investigated if the TH-induced stimulation of biliary cholesterol secretion is mediated by the ABCG5/G8 complex in vivo, and if so, whether LXRa is involved. Mice homozygous for disruption of Abcg5 (Abcg5(-/-) ) or Lxra (Lxra(-/-) ) and their wild-type counterparts were treated with triiodothyronine (T3) for 14 days and compared to untreated mice of corresponding genetic backgrounds. Bile was collected by gallbladder cannulation, and liver samples were analyzed for gene expression levels. Basal biliary cholesterol secretion in Abcg5(-/-) mice was 72% lower than in Abcg5(+/+) mice. T3 treatment increased cholesterol secretion 3.1-fold in Abcg5(+/+) mice, whereas this response was severely blunted in Abcg5(-/-) mice. In contrast, biliary cholesterol secretion in T3-treated Lxra(+/+) and Lxra(-/-) mice was increased 3.5- and 2.6-fold, respectively, and did not differ significantly.

CONCLUSIONS

TH-induced secretion of cholesterol into bile is largely dependent on an intact ABCG5/G8 transporter complex, whereas LXRa is not critical for this effect.

Circulating human hepcidin-25 concentrations display a diurnal rhythm, increase with prolonged fasting, and are reduced by growth hormone administration

BACKGROUND

Hepcidin-25 reduces iron absorption by binding to the intestinal iron transporter ferroportin and causing its degradation. Currently, little is known about the basal regulation of circulating hepcidin-25. In addition, although erythropoietin administration has been reported to decrease the circulating hepcidin concentration, information is limited regarding how other stimulators of erythropoiesis, such as growth hormone (GH), might alter hepcidin-25 concentrations.

METHODS

We used a sensitive and specific hepcidin-25 dual-monoclonal antibody sandwich immunoassay to measure hepcidin-25 in healthy human volunteers at various time points throughout the day and during 3 days of fasting and subsequent refeeding. We also measured hepcidin-25 concentrations in healthy volunteers after GH administration.

RESULTS

In healthy individuals, hepcidin-25 concentrations displayed a diurnal variation, with concentrations being lowest in the early morning and steadily increasing throughout the day before declining during the evening hours, a pattern that was not influenced by food intake. Prolonged fasting produced statistically significant increases in hepcidin-25 concentrations. Refeeding reversed this process, and GH administration markedly decreased hepcidin-25 concentrations.

CONCLUSIONS

Our results indicate that in humans, hepcidin-25 exhibits diurnal changes that can be altered by prolonged fasting, which increases hepcidin-25 concentrations approximately 3-fold after 3 days of fasting, possibly owing to a suppression of erythropoiesis that may occur during the fasting state to preserve tissue iron concentrations. In contrast, GH administration decreased hepcidin-25 concentrations by approximately 65%, presumably by stimulating erythropoiesis. These results indicate that circulating hepcidin-25 concentrations display much more dynamic and rapid variation than might have been anticipated previously.

Endogenous estrogens lower plasma PCSK9 and LDL cholesterol but not Lp(a) or bile acid synthesis in women

OBJECTIVE

Cholesterol and lipoprotein metabolism display pronounced gender differences. Premenopausal women have lower LDL and higher HDL cholesterol, whereas men display higher synthetic rates of bile acids and cholesterol. The effects of the administration of exogenous hormones to humans and animals indicate that these gender differences can often be explained by estrogens. We evaluated how increased levels of endogenous estrogens modulate cholesterol and lipoprotein metabolism in women.

METHODS AND RESULTS

We studied healthy women during initiation of in vitro fertilization using blood samples obtained when endogenous estrogens were low and high. Cholesterol in VLDL and LDL, but not in HDL, was reduced 20% when estrogens were high. Apolipoprotein B levels decreased 13%. Apolipoprotein A-I and triglyceride levels increased 8% and 37%, respectively, whereas lipoprotein(a) levels were unchanged. Circulating PCSK9, a suppressor of LDL receptors, was reduced 14% when estrogens were high. Serum markers of bile acid and cholesterol synthesis were unaltered. Growth hormone levels increased 3-fold when estrogens were high, whereas insulin-like growth factor-1 and fibroblast growth factor-21 concentrations were unaltered.

CONCLUSION

In women, Apolipoprotein B-containing particles and circulating PCSK9 are reduced when endogenous estrogens are high, indicating that endogenous estrogens induce hepatic LDL receptors partly through a posttranscriptional mechanism. However, estrogens do not stimulate bile acid or cholesterol synthesis.

Pronounced variation in bile acid synthesis in humans is related to gender, hypertriglyceridaemia and circulating levels of fibroblast growth factor 19

BACKGROUND

Bile acid (BA) synthesis is essential in cholesterol and lipid homoeostasis.

METHODS

Serum samples from 435 normal and 23 cholecystectomized subjects were obtained after overnight fasting and assayed for markers of BA and cholesterol synthesis, as well as cholesterol absorption. We determined whether BA synthesis was related to fibroblast growth factor 19 (FGF19; a circulating metabolic regulator that is thought to inhibit BA synthesis), gender, age and serum lipids.

RESULTS

Bile acid synthesis varied more than 9-fold in normal individuals and was 29% higher in men than in women. Whilst low-density lipoprotein cholesterol increased with age, BA and cholesterol synthesis were stable. BA production was positively correlated with serum triglycerides (TGs), and 35% of individuals with a high level (>95th percentile) of BA synthesis had hypertriglyceridaemia (HTG) (>95th percentile). Serum FGF19 levels varied by 7-fold in normal individuals and were related inversely to BA synthesis but were not related to gender, plasma lipids or history of cholecystectomy.

CONCLUSIONS

Bile acid synthesis has a wide inter-individual variation, is lower in women than in men and is correlated positively with serum TGs. High BA production is frequently linked to HTG. Age-related hypercholesterolaemia is not associated with changes in BA or cholesterol production, nor to an increase in cholesterol absorption. In humans, the circulating level of FGF19 may regulate hepatic BA production under fasting conditions.