New insights into how the intestine can regulate lipid homeostasis and impact vascular disease: frontiers for new pharmaceutical therapies to lower cardiovascular disease risk

Efficacy of Polyphenols in the Management of Dyslipidemia: A Focus on Clinical Studies

Polyphenols (PLPs), phytochemicals found in a wide range of plant-based foods, have gained extensive attention in view of their antioxidant, anti-inflammatory, immunomodulatory and several additional beneficial activities. The health-promoting effects noted in animal models of various non-communicable diseases explain the growing interest in these molecules. In particular, in vitro and animal studies reported an attenuation of lipid disorders in response to PLPs. However, despite promising preclinical investigations, the effectiveness of PLPs in human dyslipidemia (DLP) is less clear and necessitates revision of available literature. Therefore, the present review analyzes the role of PLPs in managing clinical DLP, notably by dissecting their potential in ameliorating lipid/lipoprotein metabolism and alleviating hyperlipidemia, both postprandially and in long-term interventions. To this end, PubMed was used for article search. The search terms included polyphenols, lipids, triglycerides, cholesterol, LDL-cholesterol and /or HDL-cholesterol. The critical examination of the trials published to date illustrates certain benefits on blood lipids along with co-morbidities in participant’s health status. However, inconsistent results document significant research gaps, potentially owing to study heterogeneity and lack of rigor in establishing PLP bioavailability during supplementation. This underlines the need for further efforts in order to elucidate and support a potential role of PLPs in fighting DLP.

Metabolic and transcriptome responses of RNAi-mediated AMPKα knockdown in Tribolium castaneum

Background

The AMP-activated protein kinase (AMPK) is an intracellular fuel sensor for lipid and glucose metabolism. In addition to the short-term regulation of metabolic enzymes by phosphorylation, AMPK may also exert long-term effects on the transcription of downstream genes through the regulation of transcription factors and coactivators. In this study, RNA interference (RNAi) was conducted to investigate the effects of knockdown of TcAMPKα on lipid and carbohydrate metabolism in the red flour beetle, Tribolium castaneum, and the transcriptome profiles of dsTcAMPKα-injected and dsEGFP-injected beetles under normal conditions were compared by RNA-sequencing.

Results

RNAi-mediated suppression of TcAMPKα increased whole-body triglyceride (TG) level and the ratio between glucose and trehalose, as was confirmed by in vivo treatment with the AMPK-activating compound, 5-Aminoimidazole-4-carboxamide1-β-D-ribofuranoside (AICAR). A total of 1184 differentially expressed genes (DEGs) were identified between dsTcAMPKα-injected and dsEGFP-injected beetles. These include genes involved in lipid and carbohydrate metabolism as well as insulin/insulin-like growth factor signaling (IIS). Real-time quantitative polymerase chain reaction analysis confirmed the differential expression of selected genes. Interestingly, metabolism-related transcription factors such as sterol regulatory element-binding protein 1 (SREBP1) and carbohydrate response element-binding protein (ChREBP) were also significantly upregulated in dsTcAMPKα-injected beetles.

Conclusions

AMPK plays a critical role in the regulation of beetle metabolism. The findings of DEGs involved in lipid and carbohydrate metabolism provide valuable insight into the role of AMPK signaling in the transcriptional regulation of insect metabolism.

The Role of the Gut Microbiota in Lipid and Lipoprotein Metabolism

Both environmental and genetic factors contribute to relative species abundance and metabolic characteristics of the intestinal microbiota. The intestinal microbiota and accompanying microbial metabolites differ substantially in those who are obese or have other metabolic disorders. Accumulating evidence from germ-free mice and antibiotic-treated animal models suggests that altered intestinal gut microbiota contributes significantly to metabolic disorders involving impaired glucose and lipid metabolism. This review will summarize recent findings on potential mechanisms by which the microbiota affects intestinal lipid and lipoprotein metabolism including microbiota dependent changes in bile acid metabolism which affects bile acid signaling by bile acid receptors FXR and TGR5. Microbiota changes also involve altered short chain fatty acid signaling and influence enteroendocrine cell function including GLP-1/GLP-2-producing L-cells which regulate postprandial lipid metabolism.

Drosophila Gut-A Nexus Between Dietary Restriction and Lifespan

Aging is often defined as the accumulation of damage at the molecular and cellular levels which, over time, results in marked physiological impairments throughout the organism. Dietary restriction (DR) has been recognized as one of the strongest lifespan extending therapies observed in a wide array of organisms. Recent studies aimed at elucidating how DR promotes healthy aging have demonstrated a vital role of the digestive tract in mediating the beneficial effects of DR. Here, we review how dietary restriction influences gut metabolic homeostasis and immune function. Our discussion is focused on studies of the Drosophila digestive tract, where we describe in detail the potential mechanisms in which DR enhances maintenance of the intestinal epithelial barrier, up-regulates lipid metabolic processes, and improves the ability of the gut to deal with damage or stress. We also examine evidence of a tissue-tissue crosstalk between gut and neighboring organs including brain and fat body. Taken together, we argue that the Drosophila gut plays a critical role in DR-mediated lifespan extension.

Interaction of azadirachtin with the lipid-binding domain: Suppression of lipid transportation in the silkworm, Bombyx mori

This study investigates the effects of the insect growth regulator azadirachtin on lipid transportation to the ovary of the silkworm, Bombyx mori. Lipids are hydrophobic in nature and require a carrier for circulation in the blood. Protein-lipid interactions play a vital role in lipid transport, thereby keeping the system balanced. In general, lipids bind to lipoproteins in a specific region called the lipid-binding domain (LBD). In this study, B. mori apolipophorin amino acid sequences were retrieved from NCBI and the LBD was identified. The LBD structure was predicted by (PS)² and validated in ProSA. The LBD structure was docked with DMPC, POPC and sphingomyelin by SwissDock, each binding with GLN 171, ASN 162, and ASN 160 and 162, respectively. Interestingly, azadirachtin binds with ASN 160 and 162 and GLN 171, which shows that lipids and azadirachtin are binding with the same amino acid residues in the LBD. Later, this result was confirmed with wet lab work using a fluorescent phospholipid probe. Azadirachtin binding with the LBD was indirectly proportional to the fluorescent lipid binding. These results suggest that azadirachtin binds with the LBD instead of the lipids and interrupts the protein-lipid interaction, leading to the suppression of lipid transportation to the ovary.

The serum metabolomics signature of type 2 diabetes is obscured in Alzheimer's disease

There is evidence for systemic metabolic impairment in Alzheimer's disease (AD), and type 2 diabetes (T2D) increases AD risk. Although studies analyzing blood metabolomics signatures have shown differences between cognitively healthy (CH) and AD subjects, these signatures have not been compared with individuals with T2D. We utilized untargeted analysis platforms (primary metabolism and complex lipids) to characterize the serum metabolome of 126 overnight-fasted elderly subjects classified into four groups based upon AD status (CH or AD) and T2D status [nondiabetic (ND) or T2D]. Cognitive diagnosis groups were a priori weighted equally with T2D subjects. We hypothesized that AD subjects would display a metabolic profile similar to cognitively normal elderly individuals with T2D. However, partial least squares-discriminant analysis (PLS-DA) modeling resulted in poor classification across the four groups (<50% classification accuracy of test subjects). Binary classification of AD vs. CH was poor, but binary classification of T2D vs. ND was good, providing >79.5% and >76.9% classification accuracy for held-out samples using primary metabolism and complex lipids, respectively. When modeling was limited to CH subjects, T2D discrimination improved for the primary metabolism platform (>89.5%) and remained accurate for complex lipids (>73% accuracy). Greater abundances of glucose, fatty acids (C20:2), and phosphatidylcholines and lower abundances of glycine, maleimide, octanol, and tryptophan, cholesterol esters, phosphatidylcholines, and sphingomyelins were identified in CH subjects with T2D relative to those without T2D. In contrast, T2D was not accurately discriminated within AD subjects. Results herein suggest that AD may obscure the typical metabolic phenotype of T2D.

Relationship between hepatic ischemia-reperfusion injury and lipid peroxidation

Hepatic ischemia-reperfusion injury results in a mixture of apotosis or necrosis which are caused by various mechanisms such as mitochondrial injury, endoplasmic reticulum stress, burst of reactive oxygen species, calcium overload, and release of various cytokines that induce the change of intracellular or extracellular signal transduction pathways. Lipid peroxidation can be described generally as a process in which oxidants such as free radicals attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs) which manily form the plasma membrane system. Lipid peroxidation occurring throughout the entire biological reaction process during HIRI, especially the mitochondrial lipid peroxidation, may be the central molecular event that is worthy of further exploration and research.

Targeting fatty acid metabolism to improve glucose metabolism

Disturbances in fatty acid metabolism in adipose tissue, liver, skeletal muscle, gut and pancreas play an important role in the development of insulin resistance, impaired glucose metabolism and type 2 diabetes mellitus. Alterations in diet composition may contribute to prevent and/or reverse these disturbances through modulation of fatty acid metabolism. Besides an increased fat mass, adipose tissue dysfunction, characterized by an altered capacity to store lipids and an altered secretion of adipokines, may result in lipid overflow, systemic inflammation and excessive lipid accumulation in non-adipose tissues like liver, skeletal muscle and the pancreas. These impairments together promote the development of impaired glucose metabolism, insulin resistance and type 2 diabetes mellitus. Furthermore, intrinsic functional impairments in either of these organs may contribute to lipotoxicity and insulin resistance. The present review provides an overview of fatty acid metabolism-related pathways in adipose tissue, liver, skeletal muscle, pancreas and gut, which can be targeted by diet or food components, thereby improving glucose metabolism.

Characterization of the proteome of cytoplasmic lipid droplets in mouse enterocytes after a dietary fat challenge

Dietary fat absorption by the small intestine is a multistep process that regulates the uptake and delivery of essential nutrients and energy. One step of this process is the temporary storage of dietary fat in cytoplasmic lipid droplets (CLDs). The storage and mobilization of dietary fat is thought to be regulated by proteins that associate with the CLD; however, mechanistic details of this process are currently unknown. In this study we analyzed the proteome of CLDs isolated from enterocytes harvested from the small intestine of mice following a dietary fat challenge. In this analysis we identified 181 proteins associated with the CLD fraction, of which 37 are associated with known lipid related metabolic pathways. We confirmed the localization of several of these proteins on or around the CLD through confocal and electron microscopy, including perilipin 3, apolipoprotein A-IV, and acyl-CoA synthetase long-chain family member 5. The identification of the enterocyte CLD proteome provides new insight into potential regulators of CLD metabolism and the process of dietary fat absorption.

Role of the gut in modulating lipoprotein metabolism

The intestinal production of lipoproteins is one of the key processes by which the body prepares dietary lipid for dissemination to locations throughout the body where they are required. Paramount to this is the relationship between dietary lipid and the enterocytes that line the gut, along with the processes which prepare this lipid for efficient uptake by these cells. These include those which occur in the mouth and stomach along with those which occur within the intestinal lumen itself. Additionally, the interplay between digested lipid, dual avenues for lipid uptake by enterocytes (passive and lipid transporter proteins), a system of intercellular lipid resynthesis and transport, and a complex system of lipoprotein synthesis yield a system open to significant modulation. In this review, we will attempt to outline the processes of lipid digestion, lipoprotein synthesis and the exogenous and endogenous factors which exert their influence.

Genetic demonstration of intestinal NPC1L1 as a major determinant of hepatic cholesterol and blood atherogenic lipoprotein levels

OBJECTIVE

The correlation between intestinal cholesterol absorption values and plasma low-density lipoprotein-cholesterol (LDL-C) levels remains controversial. Niemann-Pick-C1-Like 1 (NPC1L1) is essential for intestinal cholesterol absorption, and is the target of ezetimibe, a cholesterol absorption inhibitor. However, studies with NPC1L1 knockout mice or ezetimibe cannot definitively clarify this correlation because NPC1L1 expression is not restricted to intestine in humans and mice. In this study we sought to genetically address this issue.

METHODS AND RESULTS

We developed a mouse model that lacks endogenous (NPC1L1) and LDL receptor (LDLR) (DKO), but transgenically expresses human NPC1L1 in gastrointestinal tract only (DKO/L1(IntOnly) mice). Our novel model eliminated potential effects of non-intestinal NPC1L1 on cholesterol homeostasis. We found that human NPC1L1 was localized at the intestinal brush border membrane of DKO/L1(IntOnly) mice. Cholesterol feeding induced formation of NPC1L1-positive vesicles beneath this membrane in an ezetimibe-sensitive manner. Compared to DKO mice, DKO/L1(IntOnly) mice showed significant increases in cholesterol absorption and blood/hepatic/biliary cholesterol. Increased blood cholesterol was restricted to very low-density lipoprotein (VLDL) and LDL fractions, which was associated with increased secretion and plasma levels of apolipoproteins B100 and B48. Additionally, DKO/L1(IntOnly) mice displayed decreased fecal cholesterol excretion and hepatic/intestinal expression of cholesterologenic genes. Ezetimibe treatment virtually reversed all of the transgene-related phenotypes in DKO/L1(IntOnly) mice.

CONCLUSION

Our findings from DKO/L1(IntOnly) mice clearly demonstrate that NPC1L1-mediated cholesterol absorption is a major determinant of blood levels of apolipoprotein B-containing atherogenic lipoproteins, at least in mice.

Control of lipid metabolism by tachykinin in Drosophila

The intestine is a key organ for lipid uptake and distribution, and abnormal intestinal lipid metabolism is associated with obesity and hyperlipidemia. Although multiple regulatory gut hormones secreted from enteroendocrine cells (EEs) regulate systemic lipid homeostasis, such as appetite control and energy balance in adipose tissue, their respective roles regarding lipid metabolism in the intestine are not well understood. We demonstrate that tachykinins (TKs), one of the most abundant secreted peptides expressed in midgut EEs, regulate intestinal lipid production and subsequently control systemic lipid homeostasis in Drosophila and that TKs repress lipogenesis in enterocytes (ECs) associated with TKR99D receptor and protein kinase A (PKA) signaling. Interestingly, nutrient deprivation enhances the production of TKs in the midgut. Finally, unlike the physiological roles of TKs produced from the brain, gut-derived TKs do not affect behavior, thus demonstrating that gut TK hormones specifically regulate intestinal lipid metabolism without affecting neuronal functions.

Elevated remnant lipoproteins may increase subclinical CVD risk in pre-pubertal children with obesity: a case-control study

OBJECTIVES

Current clinical guidelines to assess paediatric cardiovascular disease (CVD) risk heavily rely on cholesterol parameters that are generally normal for obese children. Remnant lipoproteins have emerged as a critical CVD risk factor particularly in adults with normolipidemia. We assessed remnant lipoprotein concentration (measured by apolipoprotein [apo] B48) and its relationship with other traditional CVD risk biomarkers in pre-pubertal children with obesity.

METHODS

Pre-pubertal children (n = 78) with obesity (n = 39, 9.9 ± 0.3 years old) as well as sex-matched normal-weight controls (n = 39, 9.8 ± 0.3 years) were assessed for anthropometry, blood pressure and fasting plasma biochemical parameters for remnant lipoprotein, lipid and glucose/insulin metabolism, and inflammatory status.

RESULTS

Children with obesity had striking 2-fold higher apoB48-containing remnant lipoproteins concentrations relative to normal-weight peers; the magnitude of elevation in the remnant lipoproteins is comparable to the levels previously reported for adults with established CVD and type-2 diabetes. Fasting apoB48 was positively correlated with fasting triglyceride concentration in children with obesity (r = 0.51, P < 0.001) and their normal-weight peers (r = 0.45, P < 0.01). Traditional CVD biomarkers including low-density lipoprotein cholesterol showed no difference between groups and remained within the normal range for a paediatric population.

CONCLUSION

Elevated apoB48-containing remnant lipoprotein is a stronger biomarker for paediatric CVD risk compared to traditional cholesterol parameters and may be associated with early adaptation of the intestine during obesity. Further investigation of abnormalities associated with the secretion and/or clearance of atherogenic remnant lipoproteins during the postprandial state may yield insight into our understanding of and therapeutic targets for managing risk for CVD in children with obesity.

Scavenger receptor BI and ABCG5/G8 differentially impact biliary sterol secretion and reverse cholesterol transport in mice

Biliary lipid secretion plays an important role in gallstone disease and reverse cholesterol transport (RCT). Using Sr-bI/Abcg5 double knockout mice (dko), the present study investigated the differential contribution of two of the most relevant transporters: adenosine triphosphate (ATP)-binding cassette subfamily G member 5 and 8 (ABCG5/G8) and scavenger receptor class B type I (SR-BI) to sterol metabolism and RCT. Plasma cholesterol levels increased in the following order, mainly due to differences in high density lipoprotein (HDL): Abcg5 ko < wild type < Sr-bI/Abcg5 dko < Sr-bI ko. Liver cholesterol content was elevated in Sr-bI ko only (P < 0.05). In Sr-bI/Abcg5 dko plasma plant sterols were highest, while hepatic plant sterols were lower compared with Abcg5 ko (P < 0.05). Under baseline conditions, biliary cholesterol secretion rates decreased in the following order: wild type > Sr-bI ko (-16%) > Abcg5 ko (-75%) > Sr-bI/Abcg5 dko (-94%), all at least P < 0.05, while biliary bile acid secretion did not differ between groups. However, under supraphysiological conditions, upon infusion with increasing amounts of the bile salt tauroursodeoxycholic acid, Abcg5 became fully rate-limiting for biliary cholesterol secretion. Additional in vivo macrophage-to-feces RCT studies demonstrated an almost 50% decrease in overall RCT in Sr-bI/Abcg5 dko compared with Abcg5 ko mice (P < 0.01).

CONCLUSION

These data demonstrate that (1) SR-BI contributes to ABCG5/G8-independent biliary cholesterol secretion under basal conditions; (2) biliary cholesterol mass secretion under maximal bile salt-stimulated conditions is fully dependent on ABCG5/G8; and (3) Sr-bI contributes to macrophage-to-feces RCT independent of Abcg5/g8.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Lipidomic and spatio-temporal imaging of fat by mass spectrometry in mice duodenum during lipid digestion

Intestinal absorption of dietary fat is a complex process mediated by enterocytes leading to lipid assembly and secretion of circulating lipoproteins as chylomicrons, vLDL and intestinal HDL (iHDL). Understanding lipid digestion is of importance knowing the correlation between excessive fat absorption and atherosclerosis. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we illustrated a spatio-temporal localization of fat in mice duodenum, at different times of digestion after a lipid gavage, for the first time. Fatty acids progressively increased in enterocytes as well as taurocholic acid, secreted by bile and engaged in the entero-hepatic re-absorption cycle. Cytosolic lipid droplets (CLD) from enterocytes were originally purified separating chylomicron-like, intermediate droplets and smaller HDL-like. A lipidomic quantification revealed their contents in triglycerides, free and esterified cholesterol, phosphatidylcholine, sphingomyelin and ceramides but also in free fatty acids, mono- and di-acylglycerols. An acyl-transferase activity was identified and the enzyme monoacylglycerol acyl transferase 2 (MGAT2) was immunodetected in all CLD. The largest droplets was also shown to contain the microsomal triglyceride transfer protein (MTTP), the acyl-coenzyme A-cholesterol acyltransferases (ACAT) 1 and 2, hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL). This highlights the fact that during the digestion of fats, enterocyte CLD contain some enzymes involved in the different stages of the metabolism of diet fatty acids and cholesterol, in anticipation of the crucial work of endoplasmic reticulum in the process. The data further underlines the dual role of chylomicrons and iHDL in fat digestion which should help to efficiently complement lipid-lowering therapy.

Novel LDL-oriented pharmacotherapeutical strategies

Elevated levels of low-density cholesterol (LDL-C) are highly correlated with increased risk of cardiovascular diseases (CVD). Thus, current guidelines have recommended progressively lower LDL-C for cholesterol treatment and CVD prevention as the primary goal of therapy. Even so, some patients in the high risk category fail to achieve recommended LDL-C targets with currently available medications. Thereby, additional pharmaceutical strategies are urgently required. In the review, we aim to provide an overview of both current and emerging LDL-C lowering drugs. As for current available LDL-C lowering agents, attentions are mainly focused on statins, niacin, bile acid sequestrants, ezetimibe, fibrates and omega-3 fatty acids. On the other hand, the emerging drugs differ from mechanisms are including: intervention of cholesterol biosynthesis downstream enzyme (squalene synthase inhibitors), inhibition of lipoprotein assembly (antisense mRNA inhibitors of apolipoprotein B and microsomal transfer protein inhibitors), enhanced lipoprotein clearance (proprotein convertase subtilisin kexin type 9, thyroid hormone analogues), inhibition of intestinal cholesterol absorption (Niemann-Pick C1-like 1 protein and acyl coenzyme A:cholesterol acyltransferase inhibitors) and interrupting enterohepatic circulation (apical sodium-dependent bile acid transporter inhibitors). Several ongoing agents are in their different stages of clinical trials, in expectation of promising antihyperlipidemic drugs. Therefore, alternative drugs monotherapy or in combination with statins will be sufficient to reduce LDL-C concentrations to optimal levels, and a new era for better LDL-C managements is plausible.