Postprandial dyslipidemia in insulin resistance: Mechanisms and role of intestinal insulin sensitivity

Revisiting the concepts of de novo lipogenesis to understand the conversion of carbohydrates into fats: Stop overvaluing and extrapolating the renowned phrase "fat burns in the flame of carbohydrate"

Carbohydrates can be converted into fatty acids via de novo lipogenesis (DNL). Although DNL is considered inefficient, these endogenous fatty acids contribute substantially to the esterification pathway in adipose tissue, together with fatty acids of feeding. This article revisited the concepts of DNL and aimed to discuss the clinical magnitude of carbohydrate overfeeding and fat mass accumulation. Although fat storage resulting from fat intake is more favorable for fat mass accrual than carbohydrates due to molecule structure and metabolism (e.g., oxidation and thermic effect), carbohydrates can substantially participate in lipogenesis and esterification under excess carbohydrate intake over time. Regarding only monosaccharide overfeeding, glucose and fructose favor the subcutaneous and visceral adipose tissue, respectively. While fructose and sucrose are considered villains in nonalcoholic fatty liver disease, energy surplus from carbohydrates, regardless of sources, can be considered an underlying cause of obesity. Interestingly, some degree of DNL in adipocytes may be favorable to mitigate a high deposition of fatty acids in the liver, conferring a physiological role. Although "fat burns in the flame of carbohydrate" is a praiseworthy phrase that has helped describe basic concepts in biochemistry for many decades, it appears to be overvalued and extrapolated even nowadays. DNL cannot be neglected. It is time to consider DNL an efficient biochemical process in health and disease.

The chylomicron saga: time to focus on postprandial metabolism

Since statins have had such tremendous therapeutic success over the last three decades, the field of atherosclerosis has become somewhat LDL-centric, dismissing the relevance of triglycerides (TG), particularly chylomicrons, in atherogenesis. Nonetheless, 50% of patients who take statins are at risk of developing atherosclerotic cardiovascular disease (ASCVD) and are unable to achieve their goal LDL-C levels. This residual risk is mediated, in part by triglyceride rich lipoproteins (TRL) and their remnants. Following his seminal investigation on the subject, Zilversmit proposed that atherosclerosis is a postprandial event in 1979 (1-4). In essence, the concept suggests that remnant cholesterol-rich chylomicron (CM) and very-low density lipoprotein (VLDL) particles play a role in atherogenesis. Given the foregoing, this narrative review addresses the most recent improvements in our understanding of postprandial dyslipidemia. The primary metabolic pathways of chylomicrons are discussed, emphasizing the critical physiological role of lipoprotein lipase and apoCIII, the importance of these particles' fluxes in the postprandial period, their catabolic rate, the complexities of testing postprandial metabolism, and the role of angiopoietin-like proteins in the partition of CM during the fed cycle. The narrative is rounded out by the dysregulation of postprandial lipid metabolism in insulin resistance states and consequent CVD risk, the clinical evaluation of postprandial dyslipidemia, current research limits, and potential future study directions.

Postprandial Dysmetabolism and Its Medical Implications

An unbalanced diet increases the risk of developing a variety of chronic diseases and cancers, leading to higher morbidity and mortality rates worldwide. Low-grade systemic chronic inflammation mediated by the activation of the innate immune system is common to all these pathologies. Inflammation is a biological response of the body and a normal part of host defense to combat the effects of bacteria, viruses, toxins and macronutrients. However, when the innate immune system is constantly activated, it can promote the development of low-grade systemic chronic inflammation, which could play an important role in the development of chronic diseases and cancer. Since most chronic inflammatory diseases are associated with diet, a balanced healthy diet high in anti-inflammatory food components could prevent chronic diseases and cancer. The cells of the body's immune system produce chemokines and cytokines which can have pro-inflammatory and tumor-promoting as well as anti-inflammatory and tumor-fighting functions. A challenge in the future will be to assess whether polymorphisms in immune-related genes may play a role in promoting pro-inflammatory activity. Thanks to this duality, future research on immune regulation could focus on how innate immune cells can be modified to convert a pro-inflammatory and tumor-friendly microenvironment into an anti-inflammatory and anti-tumor one. This review describes inflammatory responses mediated by the innate immune system in various diseases such as hyperglycemia and/or hyperlipemia, obesity, type II diabetes, cardiovascular disease and cancer.

Sugar and Dyslipidemia: A Double-Hit, Perfect Storm

The availability of sugar has expanded over the past 50 years, due to improved industrial processes and corn subsidies, particularly in the form of sweetened beverages. This correlates with a surge in the prevalence of cardiometabolic disorders, which has brought this issue back into the spotlight for public health. In this narrative review, we focus on the role of fructose in the genesis of cardiometabolic dyslipidemia (an increase in serum triglyceride-rich lipoproteins (TRL): VLDL, chylomicrons (CM), and their remnants) bringing together the most recent data on humans, which demonstrates the crucial interaction between glucose and fructose, increasing the synthesis while decreasing the catabolism of these particles in a synergistic downward spiral. After reviewing TRL metabolism, we discuss the fundamental principles governing the metabolism of fructose in the intestine and liver and the effects of dysregulated fructolysis, in conjunction with the activation of carbohydrate-responsive element-binding protein (ChREBP) by glucose and the resulting crosstalk. The first byproduct of fructose catabolism, fructose-1-P, is highlighted for its function as a signaling molecule that promotes fat synthesis. We emphasize the role of fructose/glucose interaction in the liver, which enhances de novo lipogenesis, triglyceride (TG) synthesis, and VLDL production. In addition, we draw attention to current research that demonstrates how fructose affects the activity of lipoprotein lipase by increasing the concentration of inhibitors such as apolipoprotein CIII (apoCIII) and angiopoietin-like protein 3 (ANGPTL3), which reduce the catabolism of VLDL and chylomicrons and cause the building up of their atherogenic remnants. The end outcome is a dual, synergistic, and harmful action that encourages atherogenesis. Thus, considering the growing concerns regarding the connection between sugar consumption and cardiometabolic disease, current research strongly supports the actions of public health organizations aimed at reducing sugar intake, including dietary guidance addressing "safe" limits for sugar consumption.

Solanum aethiopicum L. from the Basilicata Region Prevents Lipid Absorption, Fat Accumulation, Oxidative Stress, and Inflammation in OA-Treated HepG2 and Caco-2 Cell Lines

Obesity is widely associated with intestine barrier impairment, nonalcoholic fatty liver disease (NAFLD) outbreaks, oxidative stress, and inflammation. In a previous investigation, the Solanum aethiopicum L. growing in Basilicata Region has demonstrated to have antioxidant activity; hence this investigation was aimed to evaluate for the first time the antilipidemic and anti-inflammatory activity of the Lucanian S. aethiopicum L. peel extract in vitro on OA-treated HepG2 and Caco-2 cell lines. It was shown that the extract could reduce lipogenesis by down-regulating SREBP-1c and HMGCR expression and fatty acid β-oxidation by up-regulating PPARα, CPT1A, and UCP2 expression. In addition, the S. aethiopicum L. peel extract might also improve oxidative stress by reducing endoplasmic reticulum stress and regulating the Nrf2 and Nf-κB molecular pathways. Altogether, these results demonstrated for the first time the possible application of the Lucanian S. aethiopicum peel extract for preventing obesity and managing NAFLD.

The roles of dietary lipids and lipidomics in gut-brain axis in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM), one of the main types of Noncommunicable diseases (NCDs), is a systemic inflammatory disease characterized by dysfunctional pancreatic β-cells and/or peripheral insulin resistance, resulting in impaired glucose and lipid metabolism. Genetic, metabolic, multiple lifestyle, and sociodemographic factors are known as related to high T2DM risk. Dietary lipids and lipid metabolism are significant metabolic modulators in T2DM and T2DM-related complications. Besides, accumulated evidence suggests that altered gut microbiota which plays an important role in the metabolic health of the host contributes significantly to T2DM involving impaired or improved glucose and lipid metabolism. At this point, dietary lipids may affect host physiology and health via interaction with the gut microbiota. Besides, increasing evidence in the literature suggests that lipidomics as novel parameters detected with holistic analytical techniques have important roles in the pathogenesis and progression of T2DM, through various mechanisms of action including gut-brain axis modulation. A better understanding of the roles of some nutrients and lipidomics in T2DM through gut microbiota interactions will help develop new strategies for the prevention and treatment of T2DM. However, this issue has not yet been entirely discussed in the literature. The present review provides up-to-date knowledge on the roles of dietary lipids and lipidomics in gut-brain axis in T2DM and some nutritional strategies in T2DM considering lipids- lipidomics and gut microbiota interactions are given.

From worms to humans: Understanding intestinal lipid metabolism via model organisms

The intestine is responsible for efficient absorption and packaging of dietary lipids before they enter the circulatory system. This review provides a comprehensive overview of how intestinal enterocytes from diverse model organisms absorb dietary lipid and subsequently secrete the largest class of lipoproteins (chylomicrons) to meet the unique needs of each animal. We discuss the putative relationship between diet and metabolic disease progression, specifically Type 2 Diabetes Mellitus. Understanding the molecular response of intestinal cells to dietary lipid has the potential to undercover novel therapies to combat metabolic syndrome.

Effects of time-restricted feeding (16/8) combined with a low-sugar diet on the management of non-alcoholic fatty liver disease: A randomized controlled trial

OBJECTIVES

Emerging studies have employed time-restricted feeding (TRF) and a low-sugar diet alone in the management of non-alcoholic fatty liver disease (NAFLD), but their combination has not been tested. The aim of this study was to investigate the effects of TRF combined with a low-sugar diet on NAFLD parameters, cardiometabolic and inflammatory biomarkers, and body composition in patients with NAFLD.

METHODS

A 12-wk randomized controlled trial was performed to compare the effects of TRF (16 h fasting/8 h feeding daily [16/8]) plus a low-sugar diet versus a control diet based on traditional meal distribution in patients with NAFLD. Changes in body composition, anthropometric indices, and liver and cardiometabolic markers were investigated.

RESULTS

TRF 16/8 with a low-sugar diet reduced body fat (26.7 ± 5.4 to 24.2 ± 4.9 kg), body weight (83.8 ± 12.7 to 80.5 ± 12.1 kg), waist circumference (104.59 ± 10.47 to 101.91 ± 7.42 cm), and body mass index (29.1 ± 2.6 to 28 ± 2.7 kg/m2), as well as circulating levels of fasting blood glucose and liver (alanine aminotransferase, 34 ± 13.9 to 21.2 ± 5.4 U/L; aspartate aminotransferase, 26.3 ± 6.2 to 20.50 ± 4 U/L; γ-glutamyl transpeptidase, 33 ± 15 to 23.2 ± 11.1 U/L; fibrosis score, 6.3 ± 1 to 5.2 ± 1.2 kPa; and controlled attenuation parameter, 322.9 ± 34.9 to 270.9 ± 36.2 dB/m), lipids (triacylglycerols, 201.5 ± 35.3 to 133.3 ± 48.7 mg/dL; total cholesterol, 190 ± 36.6 to 157.8 ± 33.6 mg/dL; and low-density lipoprotein cholesterol, 104.6 ± 27.3 to 84 ± 26.3 mg/dL), and inflammatory markers (high-sensitivity C-reactive protein, 3.1 ± 1.1 to 2 ± 0.9 mg/L; and cytokeratin-18, 1.35 ± 0.03 to 1.16 ± 0.03 ng/mL). These results were statistically significant (P < 0.05) compared with the control group.

CONCLUSIONS

TRF plus a low-sugar diet can reduce adiposity and improve liver, lipid, and inflammatory markers in patients with NAFLD.

Interorgan Metabolism of Ganglioside Is Altered in Type 2 Diabetes

GM3 is implicated in cell signaling, inflammation and insulin resistance. The intestinal mucosa metabolizes ganglioside and provides gangliosides for uptake by peripheral tissues. Gangliosides downregulate acute and chronic inflammatory signals. It is likely that transport of intestinal derived gangliosides to other tissues impact the same signals characteristic of inflammatory change in other chronic conditions such as Type 2 Diabetes (T2DM). The postprandial ceramide composition of GM3 and other gangliosides in plasma and chylomicrons has not been examined in T2DM. The present study assessed if diet or T2DM alters ganglioside components in plasma and chylomicrons secreted from the intestinal mucosa after a meal. GD1, GD3, and GM3 content of chylomicrons and plasma was determined by LC/triple quad MS in non-diabetic (control) and T2DM individuals in the fasting and postprandial state after 2 days of consuming a low or high fat diet in a randomized blinded crossover design. Diet fat level did not alter baseline plasma or chylomicron ganglioside levels. Four hours after the test meal, plasma monounsaturated GD3 was 75% higher, plasma saturated GD3 was 140% higher and plasma polyunsaturated GM3 30% lower in diabetic subjects compared to control subjects. At 4 h, chylomicron GD1 was 50% lower in T2DM compared to controls. The proportion of d34:1 in GD3 was more abundant and d36:1 in GD1 less abundant in T2DM compared to control subjects at 4 h. The present study indicates that T2DM alters ceramide composition of ganglioside available for uptake by peripheral tissues.

Molecular Biological and Clinical Understanding of the Statin Residual Cardiovascular Disease Risk and Peroxisome Proliferator-Activated Receptor Alpha Agonists and Ezetimibe for Its Treatment

Several randomized, double blind, placebo-controlled trials (RCTs) have demonstrated that low-density lipoprotein cholesterol (LDL-C) lowering by using statins, including high-doses of strong statins, reduced the development of cardiovascular disease (CVD). However, among the eight RCTs which investigated the effect of statins vs. placebos on the development of CVD, 56-79% of patients had the residual CVD risk after the trials. In three RCTs which investigated the effect of a high dose vs. a usual dose of statins on the development of CVD, 78-87% of patients in the high-dose statin arms still had the CVD residual risk after the trials. An analysis of the characteristics of patients in the RCTs suggests that elevated triglyceride (TG) and reduced high-density lipoprotein cholesterol (HDL-C), the existence of obesity/insulin resistance, and diabetes may be important metabolic factors which determine the statin residual CVD risk. To understand the association between lipid abnormalities and the development of atherosclerosis, we show the profile of lipoproteins and their normal metabolism, and the molecular and biological mechanisms for the development of atherosclerosis by high TG and/or low HDL-C in insulin resistance. The molecular biological mechanisms for the statin residual CVD risk include an increase of atherogenic lipoproteins such as small dense LDL and remnants, vascular injury and remodeling by inflammatory cytokines, and disturbed reverse cholesterol transport. Peroxisome proliferator-activated receptor alpha (PPARα) agonists improve atherogenic lipoproteins, reverse the cholesterol transport system, and also have vascular protective effects, such as an anti-inflammatory effect and the reduction of the oxidative state. Ezetimibe, an inhibitor of intestinal cholesterol absorption, also improves TG and HDL-C, and reduces intestinal cholesterol absorption and serum plant sterols, which are increased by statins and are atherogenic, possibly contributing to reduce the statin residual CVD risk.

Efficacy of artemisinin and its derivatives in animal models of type 2 diabetes mellitus: A systematic review and meta-analysis

Although current evidence suggests that artemisinin and its derivatives play a multitarget therapeutic role in type 2 diabetes mellitus (T2DM), their efficacy and safety remain under debate. This meta-analysis aimed to evaluate the effects and safety of artemisinin and its derivatives in T2DM animal models. Preclinical studies that met the inclusion criteria were retrieved from PubMed, Embase, Web of Science, Scopus, CINAHL, OpenGrey, Google Scholar, Psyclnfo, British Library Ethos, ProQuest Dissertations & Theses, China National Knowledge Internet, VIP Information Chinese Periodical Service Platform, Chinese Biomedicine Literature Database, and Wanfang Data Knowledge Service Platform. Twenty-two studies involving 526 animals were included in the meta-analysis. The RevMan 5.3 and Stata 15.0, were used to perform the statistical analyses. The overall results showed that artemisinin or its derivatives could significantly reduce fasting plasma glucose, 2-h plasma glucose (2hPG) in the intraperitoneal glucose tolerance test (IPGTT), 2hPG in the intraperitoneal insulin tolerance test (IPITT), glycated hemoglobin A1c, under the curve in the IPGTT/IPITT, total cholesterol, triglyceride, low-density lipoprotein cholesterol, free fatty acid, and urine volume. Although increase in body weight was observed due to administration of the compounds, no significant effect was observed regarding serum insulin. In terms of adverse reactions, only two of the included studies reported that high-dose artemether may cause digestive inhibition in mice. Our results suggest that artemisinins could improve several parameters related to glycolipid metabolism in T2DM animal models. However, to evaluate the antidiabetic effects and safety of artemisinins in a more accurate manner, additional preclinical studies are necessary.

Obesity-Related Metabolic Dysfunction in Dairy Cows and Horses: Comparison to Human Metabolic Syndrome

Obesity has become a serious health problem with frequent occurrence both in human and animal populations. It is estimated that it may affect over 85% of the human population and 70–80% of horses and cows by 2030. Fat cow syndrome (FCS) is a combination of metabolic, digestive, infectious, and reproductive disorders that affects obese periparturient dairy cows, and occurs most frequently in loose-housing systems, where periparturient and dry cows are fed and managed in one group disregarding the lactation stages. Equine metabolic syndrome (EMS) was named after human metabolic syndrome (MetS) and has insulin dysregulation as a central and consistent feature. It is often associated with obesity, although EMS may occur in a lean phenotype as well. Other inconsistent features of EMS are cardiovascular changes and adipose dysregulation. Laminitis is the main clinical consequence of EMS. MetS holds a 30-years old lead in research and represents a clustering of risk factors that comprise abdominal obesity, dyslipidemia, hypertension, and hyperglycemia (impaired fasting glucose or type 2 diabetes mellitus—T2DM), which are associated with doubled atherosclerotic cardiovascular disease risk, and a 5-fold increased risk for T2DM. The main aim of this review is to provide critical information for better understanding of the underlying mechanisms of obesity-related metabolic dysfunction in animals, especially in cows and horses, in comparison with MetS. Human medicine studies can offer suitable candidate mechanisms to fill the existing gap in the literature, which might be indispensable for owners to tackle FCS, EMS, and their consequences.

ApoB-lipoprotein remnant dyslipidemia and high-fat meal intolerance is associated with markers of cardiometabolic risk in youth with obesity

INTRODUCTION

Cardiovascular disease (CVD) originates in childhood and risk is exacerbated in obesity. Mechanisms of the etiologic link between early adiposity and CVD-risk remain unclear. Postprandial or non-fasting dyslipidemia is characterized by elevated plasma triglycerides (TG) and intestinal-apolipoprotein(apo)B48-remnants following a high-fat meal and is a known CVD-risk factor in adults. The aim of this study was to determine (a) whether the fasting concentration of apoB48-remnants can predict impaired non-fasting apoB48-lipoprotein metabolism (fat intolerance) and (b) the relationship of these biomarkers with cardiometabolic risk factors in youth with or without obesity.

METHODS

We assessed fasting and non-fasting lipids in youth without obesity (n = 22, 10 males, 12 females) and youth with obesity (n = 13, 5 males, 8 females) with a mean BMI Z-score of 0.19 ± 0.70 and 2.25 ± 0.31 (P = .04), respectively.

RESULTS

Fasting and non-fasting apoB48-remnants were elevated in youth with obesity compared to youth without obesity (apoB48: 18.04 ± 1.96 vs 8.09 ± 0.59, P < .0001, and apoB48_AUC : 173.0 ± 20.86 vs 61.99 ± 3.44, P < .001). Furthermore, fasting plasma apoB48-remnants were positively correlated with the non-fasting response in apoB48_AUC (r = 0.84, P < .0001) as well as other cardiometabolic risk factors including HOMA-IR (r = 0.61, P < .001) and leptin (r = 0.56, P < .0001).

CONCLUSION

Fasting apoB48-remnants are elevated in youth with obesity and predict apoB48 postprandial dyslipidemia. ApoB48-remnants are associated with the extent of fat intolerance and appear to be potential biomarker of CVD-risk in youth.

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.

Bitter Melon Extract Yields Multiple Effects on Intestinal Epithelial Cells and Likely Contributes to Anti-diabetic Functions

The intestines have been recognized as important tissues for metabolic regulation, including glycemic control, but their vital role in promoting the anti-diabetic effects of bitter melon, the fruit of Momordica charantia L, has seldom been characterized, nor acknowledged. Evidence suggests that bitter melon constituents can have substantial interactions with the intestinal epithelial cells before circulating to other tissues. We therefore characterized the effects of bitter melon extract (BME) on intestinal epithelial cells. BME was found to contain substantial amounts of carbohydrates, proteins, and triterpenoids. TNF-α induced insulin resistance in an enterocyte cell line of IEC-18 cells, and BME promoted glucose utilization of the insulin-resistant cells. Further analysis suggested that the increased glucose consumption was a result of the combined effects of insulin sensitizing and insulin substitution functions of BME. The functions of insulin substitution were likely generated due to the activation of AMP-activated protein kinase. Meanwhile, BME acted as a glucagon-like peptide 1 (GLP-1) secretagogue on enteroendocrine cells, which may be mediated by the activation of bitter-taste receptors. Therefore, BME possesses insulin sensitizing, insulin substitution, and GLP-1 secretagogue functions upon intestinal cells. These effects of BME on intestinal cells likely play a significant part in the anti-diabetic action of bitter melon.

Postprandial NMR-Based Metabolic Exchanges Reflect Impaired Phenotypic Flexibility across Splanchnic Organs in the Obese Yucatan Mini-Pig

The postprandial period represents one of the most challenging phenomena in whole-body metabolism, and it can be used as a unique window to evaluate the phenotypic flexibility of an individual in response to a given meal, which can be done by measuring the resilience of the metabolome. However, this exploration of the metabolism has never been applied to the arteriovenous (AV) exploration of organs metabolism. Here, we applied an AV metabolomics strategy to evaluate the postprandial flexibility across the liver and the intestine of mini-pigs subjected to a high fat–high sucrose (HFHS) diet for 2 months. We identified for the first time a postprandial signature associated to the insulin resistance and obesity outcomes, and we showed that the splanchnic postprandial metabolome was considerably affected by the meal and the obesity condition. Most of the changes induced by obesity were observed in the exchanges across the liver, where the metabolism was reorganized to maintain whole body glucose homeostasis by routing glucose formed de novo from a large variety of substrates into glycogen. Furthermore, metabolites related to lipid handling and energy metabolism showed a blunted postprandial response in the obese animals across organs. Finally, some of our results reflect a loss of flexibility in response to the HFHS meal challenge in unsuspected metabolic pathways that must be further explored as potential new events involved in early obesity and the onset of insulin resistance.

Role of the Gut in Diabetic Dyslipidemia

Type 2 diabetes (T2D) is associated with increased risk of cardiovascular disease (CVD). In insulin resistant states such as the metabolic syndrome, overproduction and impaired clearance of liver-derived very-low-density lipoproteins and gut-derived chylomicrons (CMs) contribute to hypertriglyceridemia and elevated atherogenic remnant lipoproteins. Although ingested fat is the major stimulus of CM secretion, intestinal lipid handling and ultimately CM secretory rate is determined by numerous additional regulatory inputs including nutrients, hormones and neural signals that fine tune CM secretion during fasted and fed states. Insulin resistance and T2D represent perturbed metabolic states in which intestinal sensitivity to key regulatory hormones such as insulin, leptin and glucagon-like peptide-1 (GLP-1) may be altered, contributing to increased CM secretion. In this review, we describe the evidence from human and animal models demonstrating increased CM secretion in insulin resistance and T2D and discuss the molecular mechanisms underlying these effects. Several novel compounds are in various stages of preclinical and clinical investigation to modulate intestinal CM synthesis and secretion. Their efficacy, safety and therapeutic utility are discussed. Similarly, the effects of currently approved lipid modulating therapies such as statins, ezetimibe, fibrates, and PCSK9 inhibitors on intestinal CM production are discussed. The intricacies of intestinal CM production are an active area of research that may yield novel therapies to prevent atherosclerotic CVD in insulin resistance and T2D.

Relationship between plasma Atherogenic index and final pathology of Bosniak III-IV renal masses: a retrospective, single-center study

Background

There is an increased incidence of renal cell carcinoma (RCC) in patients with metabolic syndrome who usually have high levels of serum triglyceride (TG) and low high-density lipoprotein-cholesterol (HDL-C). Plasma atherogenic index (PAI) is the logarithmic ratio of serum TG level to HDL-C and related to cardiovascular diseases. In this study, we aimed to determine the accuracy of PAI in determining renal malignancy in localized renal masses preoperatively.

Methods

Totally 169 patients who were diagnosed with Bosniak III-IV lesions by imaging modalities and treated in our hospital with partial or radical nephrectomy were retrospectively analyzed using institutional renal cancer database between 2013 and 2018. Preoperative images were evaluated by two experienced radiologists. The patients were divided into two groups according to their postoperative pathological diagnosis as malignant or benign tumors. The PAI of each patient was calculated and the statistical significance of PAI in predicting malignancy for renal masses was analyzed using uni- and multivariable analyses.

Results

Of patients, 109 (64.5%) were males and 60 (35.5%) were females with a median age of 61 (33–84) years. Median tumor size was 6.5 (2–18) cm. Pathological diagnosis was malignant in 145 (85.8%) and benign in 24 (14.2%) patients. There was no statistically significant difference in serum TG levels between malignant and benign cases (p > 0.05). The HDL-C levels were significantly lower in malignant cases (p = 0.001). Median PAI value was 0.63 (0.34–1.58) and significantly higher in malignant cases (p = 0.003). The PAI cut-off value for malignancy was ≥0.34. The sensitivity was calculated as 88.2% and specificity as 45.8%, the positive predictive value as 90.8, negative predictive value as 39.3, and odds ratio as 6.37 (95% CI: 2.466–16.458). In multivariable analysis, gender, smoking status, and hypertension had no effect on malignancy, whereas PAI and HDL-C were independent risk factors (p = 0.003 and p = 0.003, respectively). The risk of malignancy was 5.019 times higher, when PAI was > 0.34 (95% CI: 1.744–14.445) in multivariable logistic regression analysis.

Conclusions

The PAI can be used as a predictive tool in suspicion of malignant renal masses. In case of a benign pathology, PAI levels may be encouraging for surgeons for nephron-sparing surgery.

Effects of short-term sprint interval and moderate-intensity continuous training on liver fat content, lipoprotein profile, and substrate uptake: a randomized trial

Type 2 diabetes (T2D) and increased liver fat content (LFC) alter lipoprotein profile and composition and impair liver substrate uptake. Exercise training mitigates T2D and reduces LFC, but the benefits of different training intensities in terms of lipoprotein classes and liver substrate uptake are unclear. The aim of this study was to evaluate the effects of moderate-intensity continuous training (MICT) or sprint interval training (SIT) on LFC, liver substrate uptake, and lipoprotein profile in subjects with normoglycemia or prediabetes/T2D. We randomized 54 subjects (normoglycemic group, n = 28; group with prediabetes/T2D, n = 26; age = 40-55 yr) to perform either MICT or SIT for 2 wk and measured LFC with magnetic resonance spectroscopy, lipoprotein composition with NMR, and liver glucose uptake (GU) and fatty acid uptake (FAU) using PET. At baseline, the group with prediabetes/T2D had higher LFC, impaired lipoprotein profile, and lower whole body insulin sensitivity and aerobic capacity compared with the normoglycemic group. Both training modes improved aerobic capacity (P < 0.001) and lipoprotein profile (reduced LDL and increased large HDL subclasses; all P < 0.05) with no training regimen (SIT vs. MICT) or group effect (normoglycemia vs. prediabetes/T2D). LFC tended to be reduced in the group with prediabetes/T2D compared with the normoglycemic group posttraining (P = 0.051). When subjects were divided according to LFC (high LFC, >5.6%; low LFC, <5.6%), training reduced LFC in subjects with high LFC (P = 0.009), and only MICT increased insulin-stimulated liver GU (P = 0.03). Short-term SIT and MICT are effective in reducing LFC in subjects with fatty liver and in improving lipoprotein profile regardless of baseline glucose tolerance. Short-term MICT is more efficient in improving liver insulin sensitivity compared with SIT. NEW & NOTEWORTHY In the short term, both sprint interval training and moderate-intensity continuous training (MICT) reduce liver fat content and improve lipoprotein profile; however, MICT seems to be preferable in improving liver insulin sensitivity.

A Newly Integrated Model for Intestinal Cholesterol Absorption and Efflux Reappraises How Plant Sterol Intake Reduces Circulating Cholesterol Levels

Cholesterol homeostasis is maintained through a balance of de novo synthesis, intestinal absorption, and excretion from the gut. The small intestine contributes to cholesterol homeostasis by absorbing and excreting it, the latter of which is referred to as trans-intestinal cholesterol efflux (TICE). Because the excretion efficiency of endogenous cholesterol is inversely associated with the development of atherosclerosis, TICE provides an attractive therapeutic target. Thus, elucidation of the mechanism is warranted. We have shown that intestinal cholesterol absorption and TICE are inversely correlated in intestinal perfusion experiments in mice. In this review, we summarized 28 paired data sets for absorption efficiency and fecal neutral sterol excretion, a surrogate marker of TICE, obtained from 13 available publications in a figure, demonstrating the inverse correlation were nearly consistent with the assumption. We then offer a bidirectional flux model that accommodates absorption and TICE occurring in the same segment. In this model, the brush border membrane (BBM) of intestinal epithelial cells stands as the dividing ridge for cholesterol fluxes, making the opposite fluxes competitive and being coordinated by shared BBM-localized transporters, ATP-binding cassette G5/G8 and Niemann-Pick C1-like 1. Furthermore, the idea is applied to address how excess plant sterol/stanol (PS) intake reduces circulating cholesterol level, because the mechanism is still unclear. We propose that unabsorbable PS repeatedly shuttles between the BBM and lumen and promotes concomitant cholesterol efflux. Additionally, PSs, which are chemically analogous to cholesterol, may disturb the trafficking machineries that transport cholesterol to the cell interior.

Associations of vitamin D status and metabolic dyslipidemia and hypertriglyceridemic waist phenotype in apparently healthy adults

BACKGROUND

Recent studies have shown that Vitamin D deficiency is very common globally. Vitamin D deficiency is associated with lipid metabolism. A relationship between vitamin D levels and waist circumference (WC) has been observed. The purpose of this study is to evaluate the relationship between vitamin D status and metabolic dyslipidemia and the hypertriglyceridemic waist phenotype.

METHODS

This cross-sectional study was conducted on 265 healthy Tehran adults. Hypertriglyceridemic waist phenotype (HTGWP) was described as serum triacylglycerol concentrations >150 mg/dL and concurrent WC > 88 cm (women) and >102 cm (men). Dyslipidemia was defined as: 1) TG level of >150 mg/dL 2) HDL > 40 mg/dL for men or >50 mg/dL for women, as has been previously described.

RESULTS

Current study's results demonstrated that HTGWP was significantly associated with weight, age, WC, hip, fat percent, TG, lipid profile, ALT and BMI. We found 77% reduction in the chances of developing metabolic dyslipidemia in suficient satus of vitamin D in compare to deficiency, although the significancy was mariginal, OR: 0.33, 95% CI of 0.09 to 1.21, P = 0.09. However, our results revealed that vitamin D deficiency, compared with normal status, can increase the risk of phenotype 1 (high TG/high WC); OR: 3.86 and 95% CI from 0.86 to 0.99, p for trend = 0.05.

CONCLUSIONS

Significant associations were found between vitamin D status and HTGWP. In addition, there was a relationship between vitamin D and lipid profiles. There is a direct correlation between TG and waist circumference in insulin resistance in healthy Tehran adults.

The adaptor protein PID1 regulates receptor-dependent endocytosis of postprandial triglyceride-rich lipoproteins

Objective

Insulin resistance is associated with impaired receptor dependent hepatic uptake of triglyceride-rich lipoproteins (TRL), promoting hypertriglyceridemia and atherosclerosis. Next to low-density lipoprotein (LDL) receptor (LDLR) and syndecan-1, the LDLR-related protein 1 (LRP1) stimulated by insulin action contributes to the rapid clearance of TRL in the postprandial state. Here, we investigated the hypothesis that the adaptor protein phosphotyrosine interacting domain-containing protein 1 (PID1) regulates LRP1 function, thereby controlling hepatic endocytosis of postprandial lipoproteins.

Methods

Localization and interaction of PID1 and LRP1 in cultured hepatocytes was studied by confocal microscopy of fluorescent tagged proteins, by indirect immunohistochemistry of endogenous proteins, by GST-based pull down and by immunoprecipitation experiments. The in vivo relevance of PID1 was assessed using whole body as well as liver-specific Pid1-deficient mice on a wild type or Ldlr-deficient (Ldlr^−/−) background. Intravital microscopy was used to study LRP1 translocation in the liver. Lipoprotein metabolism was investigated by lipoprotein profiling, gene and protein expression as well as organ-specific uptake of radiolabelled TRL.

Results

PID1 co-localized in perinuclear endosomes and was found associated with LRP1 under fasting conditions. We identified the distal NPxY motif of the intracellular C-terminal domain (ICD) of LRP1 as the site critical for the interaction with PID1. Insulin-mediated NPxY-phosphorylation caused the dissociation of PID1 from the ICD, causing LRP1 translocation to the plasma membrane. PID1 deletion resulted in higher LRP1 abundance at the cell surface, higher LDLR protein levels and, paradoxically, reduced total LRP1. The latter can be explained by higher receptor shedding, which we observed in cultured Pid1-deficient hepatocytes. Consistently, PID1 deficiency alone led to increased LDLR-dependent endocytosis of postprandial lipoproteins and lower plasma triglycerides. In contrast, hepatic PID1 deletion on an Ldlr^−/− background reduced lipoprotein uptake into liver and caused plasma TRL accumulation.

Conclusions

By acting as an insulin-dependent retention adaptor, PID1 serves as a regulator of LRP1 function controlling the disposal of postprandial lipoproteins. PID1 inhibition provides a novel approach to lower plasma levels of pro-atherogenic TRL remnants by stimulating endocytic function of both LRP1 and LDLR in the liver.

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PID1 is a retention adaptor protein that regulates activity of the endocytic receptor LDL receptor-related protein 1 (LRP1).

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PID1 regulates the insulin-dependent LRP1-mediated endocytosis of lipoproteins in vivo.

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PID1 deficiency in liver reduces LRP1 levels via cell surface shedding, and paradoxically increases LDL receptor activity.

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PID1 antagonism has therapeutic potential to reduce pro-atherogenic lipoproteins in hyperlipidemic and diabetic patients.

GLP-1 Elicits an Intrinsic Gut-Liver Metabolic Signal to Ameliorate Diet-Induced VLDL Overproduction and Insulin Resistance

OBJECTIVE

Perturbations in hepatic lipid and very-low-density lipoprotein (VLDL) metabolism are involved in the pathogenesis of obesity and hepatic insulin resistance. The objective of this study is to delineate the mechanism of subdiaphragmatic vagotomy in preventing obesity, hyperlipidemia, and insulin resistance.

APPROACH AND RESULTS

By subjecting the complete subdiaphragmatic vagotomized mice to various nutritional conditions and investigating hepatic de novo lipogenesis pathway, we found that complete disruption of subdiaphragmatic vagal signaling resulted in a significant decrease of circulating VLDL-triglyceride compared with the mice obtained sham procedure. Vagotomy further prevented overproduction of VLDL-triglyceride induced by an acute fat load and a high-fat diet-induced obesity, hyperlipidemia, hepatic steatosis, and glucose intolerance. Mechanistic studies revealed that plasma glucagon-like peptide-1 was significantly raised in the vagotomized mice, which was associated with significant reductions in mRNA and protein expression of SREBP-1c (sterol regulatory element-binding protein 1c), SCD-1 (stearoyl-CoA desaturase-1), and FASN (fatty acid synthase), as well as enhanced hepatic insulin sensitivity. In vitro, treating mouse primary hepatocytes with a glucagon-like peptide-1 receptor agonist, exendin-4, for 48 hours inhibited free fatty acid, palmitic acid treatment induced de novo lipid synthesis, and VLDL secretion from hepatocytes.

CONCLUSIONS

Elevation of glucagon-like peptide-1 in vagotomized mice may prevent VLDL overproduction and insulin resistance induced by high-fat diet. These novel findings, for the first time, delineate an intrinsic gut-liver regulatory circuit that is mediated by glucagon-like peptide-1 in regulating hepatic energy metabolism.

Influence of endogenous glucagon-like peptide-2 on lipid disorders in mice fed a high-fat diet

AIM

The purpose of the present study was to investigate the influence of endogenous glucagon-like peptide-2 (GLP-2) on lipid profile in mice fed a standard diet (STD) or a high-fat diet (HFD).

MATERIALS AND METHODS

HFD- and age-matched STD mice were injected once a day with GLP-2 (3-33), a GLP-2 receptor (GLP-2R) antagonist, or vehicle for 4 weeks.

RESULTS

HFD mice displayed increased intrahepatic lipid concentration and hepatic steatosis and higher plasma concentrations of cholesterol, LDL, AST, and ALT than STD mice. No difference was observed in lipid fecal elimination. In STD mice, the chronic treatment with GLP-2 (3-33) did not affect any parameter, while in HFD mice, it enhanced plasma triglycerides, cholesterol, ALT, and AST and reduced HDL, it increased intrahepatic lipid concentration, and it worsened the hepatic steatosis degree, without affecting lipid fecal elimination.

CONCLUSIONS

The present results suggest that GLP-2R antagonism worsens lipid disorders in HFD mice, and endogenous GLP-2 might even exert a defensive role against lipid imbalance.

Effects of exercise training on intrahepatic lipid content in humans

Non-alcoholic fatty liver (NAFL) is the most common liver disorder in western society. Various factors may play a role in determining hepatic fat content, such as delivery of lipids to the liver, de novo lipogenesis, hepatic lipid oxidation, secretion of intrahepatic lipids to the circulation or a combination of these. If delivery of lipids to the liver outweighs the sum of hepatic lipid oxidation and secretion, the intrahepatic lipid (IHL) content starts to increase and NAFL may develop. NAFL is closely related to obesity and insulin resistance and a fatty liver increases the vulnerability to type 2 diabetes development. Exercise training is a cornerstone in the treatment and prevention of type 2 diabetes. There is a large body of literature describing the beneficial metabolic consequences of exercise training on skeletal muscle metabolism. Recent studies have started to investigate the effects of exercise training on liver metabolism but data is still limited. Here, first, we briefly discuss the routes by which IHL content is modulated. Second, we review whether and how these contributing routes might be modulated by long-term exercise training. Third, we focus on the effects of acute exercise on IHL metabolism, since exercise also might affect hepatic metabolism in the physically active state. This will give insight into whether the effect of exercise training on IHL could be explained by the accumulated effect of acute bouts of exercise, or whether adaptations might occur only after long-term exercise training. The primary focus of this review will be on observations made in humans. Where human data is missing, data obtained from well-accepted animal models will be used.

Short Term Palmitate Supply Impairs Intestinal Insulin Signaling via Ceramide Production

The worldwide prevalence of metabolic diseases is increasing, and there are global recommendations to limit consumption of certain nutrients, especially saturated lipids. Insulin resistance, a common trait occurring in obesity and type 2 diabetes, is associated with intestinal lipoprotein overproduction. However, the mechanisms by which the intestine develops insulin resistance in response to lipid overload remain unknown. Here, we show that insulin inhibits triglyceride secretion and intestinal microsomal triglyceride transfer protein expression in vivo in healthy mice force-fed monounsaturated fatty acid-rich olive oil but not in mice force-fed saturated fatty acid-rich palm oil. Moreover, when mouse intestine and human Caco-2/TC7 enterocytes were treated with the saturated fatty acid, palmitic acid, the insulin-signaling pathway was impaired. We show that palmitic acid or palm oil increases ceramide production in intestinal cells and that treatment with a ceramide analogue partially reproduces the effects of palmitic acid on insulin signaling. In Caco-2/TC7 enterocytes, ceramide effects on insulin-dependent AKT phosphorylation are mediated by protein kinase C but not by protein phosphatase 2A. Finally, inhibiting de novo ceramide synthesis improves the response of palmitic acid-treated Caco-2/TC7 enterocytes to insulin. These results demonstrate that a palmitic acid-ceramide pathway accounts for impaired intestinal insulin sensitivity, which occurs within several hours following initial lipid exposure.

Association of faecal elastase 1 with non-fasting triglycerides in type 2 diabetes

AIMS

Intestinal absorption of esterified fatty acids depends on exocrine pancreatic function and influences plasma triglycerides levels. The aim was to investigate the association of reduced exocrine pancreatic function (low fecal elastase-1; FE1) with plasma triglycerides in type 2 diabetes and controls without diabetes.

METHODS

FE1 (μg/g stool) and non-fasting plasma triglyceride measurements were undertaken in 544 type 2 diabetes patients (age: 63 ± 8 years) randomly selected from diabetes registers in Cambridgeshire (UK), and 544 matched controls (age, sex, practice) without diabetes. Linear regression models were fitted using FE1 as dependent and log-triglycerides as independent variable adjusting for sex, age, body mass index, alcohol consumption, serum lipase, HbA1c, and smoking.

RESULTS

FE1 concentrations were lower (mean ± SD: 337 ± 204 vs. 437 ± 216 μg/g, p < 0.05) and plasma triglycerides were higher (geometric mean */: standard deviation factor: 2.2*/:1.9 vs. 1.6*/:1.8 mmol/l, p < 0.05) in type 2 diabetes compared to controls, respectively. Within the category of type 2 diabetes and controls separately, a 10% increase in plasma triglycerides was associated with 4.5 μg/g higher FE1 concentrations (p < 0.01) after adjusting for confounders. In contrast, in diabetes patients and controls with pathological FE1 (<100 μg/g), low FE1 levels were associated with high plasma triglycerides (significant only in controls).

CONCLUSIONS

Non-fasting triglycerides were positively related to FE1 in both type 2 diabetes and controls suggesting that impairment of exocrine pancreas function is influencing plasma triglycerides. Marked loss of exocrine pancreatic function had the opposite effect, resulting in higher levels of plasma triglycerides.

The Ingestion of a Fructose-Containing Beverage Combined with Fat Cream Exacerbates Postprandial Lipidemia in Young Healthy Women

AIM

To investigate the acute effects of the ingestion of a fructose-containing beverage combinedwith fat on postprandial lipoprotein metabolism.

METHODS

Twelve young healthy Japanese women with apolipoprotein E phenotype 3/3 were enrolled in this study. At each of four sessions, the subjects ingested one of four sugar beverages containing fructose and/or glucose (total: 0.5g/kg body weight) combined with OFTT cream (1g/kg, 0.35g/kg as fat) in a randomized crossover design. The four sugar beverages were as follows: 100% (w/w) fructose (F100), 90% fructose+10% glucose (F90G10), 55% fructose+45% glucose (F55G45) and 100% glucose (G100). Venous blood samples were obtained at baseline and 0.5, one, two, four and six hours after ingestion.

RESULTS

The serum concentrations of TG in the F100, F90G10 and F55G45 trials were significantlyhigher than each fasting value at two and four hours, and returned to baseline at six hours, except inthe F100 trial. The concentrations at four hours and the incremental areas under the curve for thehepatic triglyceride-rich lipoprotein-triglyceride (VLDL-TG(TM)) levels in the F100 and F90G10 trialswere significantly higher and larger, respectively, than those observed in the G100 trial. Meanwhile,the concentrations of RLP-TG and apolipoprotein B-48 peaked at two hours in the G100 trial, versusfour hours in the other trials, and did not return to baseline at six hours, except in the G100 trial.At four hours, the ⊿apoB48 tended to be higher in the F100 trial than in the G100 trial.

CONCLUSIONS

The ingestion of a high-fructose-containing beverage with fat cream delays the clearance of chylomicron and its remnant derived from the intestine and enhances the secretion of triglyceride-rich lipoprotein particles from the liver, thereby inducing postprandial lipidemia, even in young healthy women.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

High-fructose feeding promotes accelerated degradation of hepatic LDL receptor and hypercholesterolemia in hamsters via elevated circulating PCSK9 levels

BACKGROUND

High fructose diet (HFD) induces dyslipidemia and insulin resistance in experimental animals and humans with incomplete mechanistic understanding. By utilizing mice and hamsters as in vivo models, we investigated whether high fructose consumption affects serum PCSK9 and liver LDL receptor (LDLR) protein levels.

RESULTS

Feeding mice with an HFD increased serum cholesterol and reduced serum PCSK9 levels as compared with the mice fed a normal chow diet (NCD). In contrast to the inverse relationship in mice, serum PCSK9 and cholesterol levels were co-elevated in HFD-fed hamsters. Liver tissue analysis revealed that PCSK9 mRNA and protein levels were both reduced in mice and hamsters by HFD feeding, however, liver LDLR protein levels were markedly reduced by HFD in hamsters but not in mice. We further showed that circulating PCSK9 clearance rates were significantly lower in hamsters fed an HFD as compared with the hamsters fed NCD, providing additional evidence for the reduced hepatic LDLR function by HFD consumption. The majority of PCSK9 in hamster serum was detected as a 53 kDa N-terminus cleaved protein. By conducting in vitro studies, we demonstrate that this 53 kDa truncated hamster PCSK9 is functionally active in promoting hepatic LDLR degradation.

CONCLUSION

Our studies for the first time demonstrate that high fructose consumption increases serum PCSK9 concentrations and reduces liver LDLR protein levels in hyperlipidemic hamsters. The positive correlation between circulating cholesterol and PCSK9 and the reduction of liver LDLR protein in HFD-fed hamsters suggest that hamster is a better animal model than mouse to study the modulation of PCSK9/LDLR pathway by atherogenic diets.

The pathophysiology of intestinal lipoprotein production

Intestinal lipoprotein production is a multistep process, essential for the absorption of dietary fats and fat-soluble vitamins. Chylomicron assembly begins in the endoplasmic reticulum with the formation of primordial, phospholipids-rich particles that are then transported to the Golgi for secretion. Several classes of transporters play a role in the selective uptake and/or export of lipids through the villus enterocytes. Once secreted in the lymph stream, triglyceride-rich lipoproteins (TRLs) are metabolized by Lipoprotein lipase (LPL), which catalyzes the hydrolysis of triacylglycerols of very low density lipoproteins (VLDLs) and chylomicrons, thereby delivering free fatty acids to various tissues. Genetic mutations in the genes codifying for these proteins are responsible of different inherited disorders affecting chylomicron metabolism. This review focuses on the molecular pathways that modulate the uptake and the transport of lipoproteins of intestinal origin and it will highlight recent findings on TRLs assembly.

Cardiometabolic risk factors and insulin resistance in obese children and adolescents: relation to puberty

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The prevalence of obesity with concomitant increasing risk for having cardiometabolic diseases is rising in the childhood population. Insulin resistance has a key role in metabolic changes in these children. Insulin levels elevate as puberty commences in every individual.

WHAT THIS STUDY ADDS

Children with increased risk for cardiometabolic diseases show significant differences in insulin levels even before the onset of puberty compared with those without risks. The pattern of appearance of dyslipidaemia also varies in children with risk factors even in the pre-pubertal group from those without risk. Children with metabolic syndrome display considerably pronounced changes in their metabolic parameters before the onset of puberty, which become more pronounced as puberty passes.

BACKGROUND

Insulin resistance (IR) has a key role in the metabolic changes in obese children. In commencing puberty, the insulin levels elevate. It is not clear, however, how insulin levels develop if the metabolic syndrome appears.

OBJECTIVES

Metabolic changes were assessed in obese children before, during and after puberty to analyse the relationship between IR and puberty in subjects with and without metabolic syndrome.

METHODS

Three hundred thirty-four obese children (5-19 years) attended the study. The criteria of the International Diabetes Federation were used to assess the presence of cardiometabolic risks (CMRs). Subjects with increased CMR were compared with those without risk (nCMR). Pubertal staging, lipid levels, plasma glucose and insulin levels during oral glucose tolerance test were determined in each participant. IR was expressed by homeostasis model assessment (HOMA-IR) and the ratio of glucose and insulin areas under the curve (AUC-IR).

RESULTS

Significantly higher AUC-IR were found in pre-pubertal CMR children compared with nCMR subjects (11.84 ± 1.03 vs. 8.00 ± 0.69; P < 0.01), but no difference was discovered during and after puberty. HOMA-IR differs between CMR and nCMR only in post-puberty (6.03 ± 1.26 vs. 2.54 ± 0.23; P < 0.01). CMR children have dyslipidaemia before the onset of puberty.

CONCLUSIONS

CMR is associated with increased postprandial IR in pre-pubertal and increased fasting IR in post-pubertal obese children. Dyslipidaemia appeared already in pre-puberty in CMR children.

Postprandial lipemia as a cardiometabolic risk factor

High levels of fasting circulating triglycerides (TG) represent an independent risk factor for cardiovascular disease. In western countries, however, people spend most time in postprandial conditions, with continuous fluctuation of lipemia due to increased levels of TG-rich lipoproteins (TRLs), including chylomicrons (CM), very low density lipoproteins (VLDL), and their remnants. Several factors contribute to postprandial lipid metabolism, including dietary, physiological, pathological and genetic factors. The presence of coronary heart disease, type 2 diabetes, insulin resistance and obesity is associated with higher postprandial TG levels compared with healthy conditions; this association is present also in subjects with normal fasting TG levels. Increasing evidence indicates that impaired metabolism of postprandial lipoproteins contributes to the pathogenesis of coronary artery disease, suggesting that lifestyle modifications as well as pharmacological approaches aimed at reducing postprandial TG levels might help to decrease the cardiovascular risk.

AMPK in the small intestine in normal and pathophysiological conditions

The role of AMPK in regulating energy storage and depletion remains unexplored in the intestine. This study will to define its status, composition, regulation and lipid function, as well as to examine the impact of insulin resistance and type 2 diabetes on intestinal AMPK activation, insulin sensitivity, and lipid metabolism. Caco-2/15 cells and Psammomys obesus (P. obesus) animal models were experimented. We showed the predominance of AMPKα1 and the prevalence of α1/β2/γ1 heterotrimer in Caco-2/15 cells. The activation of AMPK by 5-aminoimidazole-4-carboxamide ribonucleoside and metformin resulted in increased phospho(p)-ACC. However, the down-regulation of p-AMPK by compound C and high glucose lowered p-ACC without affecting 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Administration of metformin to P. obesus with insulin resistance and type 2 diabetes led to 1) an up-regulation of intestinal AMPK signaling pathway typified by ascending p-AMPKα(-Thr172); 2) a reduction in ACC activity; 3) an elevation of carnitine palmitoyltransferase 1; 4) a trend of increase in insulin sensitivity portrayed by augmentation of p-Akt and phospho-glycogen synthetase kinase 3β; 5) a reduced phosphorylation of p38-MAPK and ERK1/2; and 6) a decrease in diabetic dyslipidemia following lowering of intracellular events that govern lipoprotein assembly. These data suggest that AMPK fulfills key functions in metabolic processes in the small intestine.

The real role of prediagnostic high-density lipoprotein cholesterol and the cancer risk: a concise review

BACKGROUND

In several observational and clinical studies, the association between serum cholesterol levels and cancer is still unsettled although serum total cholesterol has been associated with increased mortality from cancer. Moreover, the importance of abnormal levels of serum lipid components as the main features of dyslipidemia and the risk of individual cancers is unclear. The prevalence of dyslipidemia is increasing worldwide but, the precise aetiology of the link between risk of cancer and the behaviour of lipid profile, prior diagnosis, has yet to be determinated. Low levels of high-density lipoprotein cholesterol (HDL) at baseline of many of the studies analyzed has to be taken into account, and continued low levels of HDL without explanation should be considered by clinicians.

AIMS

The main aim of this review was to undertake the assessment of the most recent studies implying the lipid profile and cancer risk, and focused on low HDL levels at baseline and follow up, and also analyzing this behaviour on the different cancer types.

MATERIAL AND METHODS

A literature search was performed to identify publications. The most recent prospective and case-control studies with multivariate Cox models were analyzed and also were considered some recent meta-analyses.

RESULTS AND CONCLUSIONS

The findings exposed in this review suggest that the association with low HDL levels at baseline of different studies of cancer risk is shared among many types of cancer, and it is mainly linked to obesity and inflammation, suggesting a common pathway.

Ezetimibe prevents hepatic steatosis induced by a high-fat but not a high-fructose diet

Nonalcoholic fatty liver disease is the most frequent liver disease. Ezetimibe, an inhibitor of intestinal cholesterol absorption, has been reported to ameliorate hepatic steatosis in human and animal models. To explore how ezetimibe reduces hepatic steatosis, we investigated the effects of ezetimibe on the expression of lipogenic enzymes and intestinal lipid metabolism in mice fed a high-fat or a high-fructose diet. CBA/JN mice were fed a high-fat diet or a high-fructose diet for 8 wk with or without ezetimibe. High-fat diet induced hepatic steatosis accompanied by hyperinsulinemia. Treatment with ezetimibe reduced hepatic steatosis, insulin levels, and glucose production from pyruvate in mice fed the high-fat diet, suggesting a reduction of insulin resistance in the liver. In the intestinal analysis, ezetimibe reduced the expression of fatty acid transfer protein-4 and apoB-48 in mice fed the high-fat diet. However, treatment with ezetimibe did not prevent hepatic steatosis, hyperinsulinemia, and intestinal apoB-48 expression in mice fed the high-fructose diet. Ezetimibe decreased liver X receptor-α binding to the sterol regulatory element-binding protein-1c promoter but not expression of carbohydrate response element-binding protein and fatty acid synthase in mice fed the high-fructose diet, suggesting that ezetimibe did not reduce hepatic lipogenesis induced by the high-fructose diet. Elevation of hepatic and intestinal lipogenesis in mice fed a high-fructose diet may partly explain the differences in the effect of ezetimibe.

Hepatic triacylglycerol synthesis and secretion: DGAT2 as the link between glycaemia and triglyceridaemia

lThe liver regulates both glycaemia and triglyceridaemia. Hyperglycaemia and hypertriglyceridaemia are both characteristic of (pre)diabetes. Recent observations on the specialised role of DGAT2 (diacylglycerol acyltransferase 2) in catalysing the de novo synthesis of triacylglycerols from newly synthesized fatty acids and nascent diacylglycerols identifies this enzyme as the link between the two. This places DGAT2 at the centre of carbohydrate-induced hypertriglyceridaemia and hepatic steatosis. This function is complemented, but not substituted for, by the ability of DGAT1 to rescue partial glycerides from complete hydrolysis. In peripheral tissues not normally considered to be lipogenic, synthesis of triacylglycerols may largely bypass DGAT2 except in hyperglycaemic/hyperinsulinaemic conditions, when induction of de novo fatty acid synthesis in these tissues may contribute towards increased triacylglycerol secretion (intestine) or insulin resistance (adipose tissue, and cardiac and skeletal muscle).

Simultaneous ingestion of fructose and fat exacerbates postprandial exogenous lipidemia in young healthy Japanese women

AIM

To investigate the acute effects of the simultaneous ingestion of fructose and fat on postprandial lipoprotein metabolism in healthy young women.

METHODS

Nine young healthy Japanese women with a normal weight (body mass index: 18.5≤-< 25 kg/m(2)), a normal ovarian cycle and an apolipoprotein E 3/3 phenotype were enrolled as participants and studied on four occasions. At each session, the subjects ingested one of four beverages containing either glucose or fructose (0.5 g/kg body weight each) with or without OFTT cream (1 g/kg, 0.35 g/ kg as fat) in a randomized crossover design. Blood samples were collected at baseline and at 0.5, 1, 2, 4 and 6 hours after ingestion.

RESULTS

The ingestion of fructose combined with fat led to significantly higher rises in the serum triglyceride (TG), remnant-like particle (RLP)-TG, remnant lipoprotein-cholesterol (RemL-C) and apolipoprotein B-48 (apoB48) concentrations with delayed peaks compared with that observed following ingestion of the other three types of beverages. The incremental area under the curve (ΔAUC)-TG and ΔAUC-apoB48 were larger than those observed for the ingestion of fat only. The serum RLP-TG and apoB48 concentrations returned to the fasting levels (0 hours) at the end of the test (6 hours) following the ingestion of fat only; however, these concentrations did not return to the fasting levels following the intake of fructose combined with fat.

CONCLUSIONS

These findings suggest a delay in the clearance of intestinal TG-rich lipoproteins, namely chylomicron and its remnant, following the ingestion of fructose combined with fat. The simultaneous ingestion of fructose and fat markedly enhances postprandial exogenous lipidemia in young healthy Japanese women.

Arterial retention of remnant lipoproteins ex vivo is increased in insulin resistance because of increased arterial biglycan and production of cholesterol-rich atherogenic particles that can be improved by ezetimibe in the JCR:LA-cp rat

BACKGROUND

Literature supports the "response-to-retention" hypothesis-that during insulin resistance, impaired metabolism of remnant lipoproteins can contribute to accelerated cardiovascular disease progression. We used the JCR:LA-cp rat model of metabolic syndrome (MetS) to determine the extent of arterial accumulation of intestinal-derived remnants ex vivo and potential mechanisms that contribute to exacerbated cholesterol deposition in insulin resistance.

METHODS AND RESULTS

Arteries from control and MetS (insulin-resistant) JCR:LA-cp rats were perfused ex vivo with Cy5-labeled remnant lipoproteins, and their arterial retention was quantified by confocal microscopy. Arterial proteoglycans were isolated from control and MetS rats at 6, 12, and 32 weeks of age. There was a significant increase in the arterial retention of remnants and in associated cholesterol accumulation in MetS rats as compared to control rats. Mechanistic studies reveal that increased cholesterol deposition is a result of greater arterial biglycan content; longer glycosaminoglycans and increased production of cholesterol-rich intestinal-derived remnants, as compared to controls. Additionally, perfusion of vessels treated with ezetimibe, alone or in combination with simvastatin, with remnants isolated from the respective treatment group reduced ex vivo arterial retention of remnant-derived cholesterol ex vivo as compared to untreated controls.

CONCLUSIONS

Increased progression of atherosclerotic cardiovascular disease in MetS and type 2 diabetes mellitus might be explained in part by an increase in the arterial retention of cholesterol-rich remnants. Furthermore, ezetimibe alone or in combination treatment with simvastatin could be beneficial in ameliorating atherosclerotic cardiovascular disease in insulin resistance and MetS.

Serum Lipids and the Risk of Gastrointestinal Malignancies in the Swedish AMORIS Study

Background. Metabolic syndrome has been linked to an increased cancer risk, but the role of dyslipidaemia in gastrointestinal malignancies is unclear. We aimed to assess the risk of oesophageal, stomach, colon, and rectal cancers using serum levels of lipid components. Methods. From the Swedish Apolipoprotein Mortality Risk (AMORIS) study, we selected 540,309 participants (> 20 years old) with baseline measurements of total cholesterol (TC), triglycerides (TG), and glucose of whom 84,774 had baseline LDL cholesterol (LDL), HDL cholesterol (HDL), apolipoprotein B (apoB), and apolipoprotein A-I (apoA-I). Multivariate Cox proportional hazards regression was used to assess glucose and lipid components in relation to oesophageal, stomach, colon, and rectal cancer risk. Results. An increased risk of oesophageal cancer was observed in persons with high TG (e.g. HR: 2.29 (95% CI: 1.42–3.68) for the 4th quartile compared to the 1st) and low LDL, LDL/HDL ratio, TC/HDL ratio, log (TG/HDL), and apoB/apoA-I ratio. High glucose and TG were linked with an increased colon cancer risk, while high TC levels were associated with an increased rectal cancer risk. Conclusion. The persistent link between TC and rectal cancer risk as well as between TG and oesophageal and colon cancer risk in normoglycaemic individuals may imply their substantiality in gastrointestinal carcinogenesis.

Lipoproteins in Drosophila melanogaster--assembly, function, and influence on tissue lipid composition

Interorgan lipid transport occurs via lipoproteins, and altered lipoprotein levels correlate with metabolic disease. However, precisely how lipoproteins affect tissue lipid composition has not been comprehensively analyzed. Here, we identify the major lipoproteins of Drosophila melanogaster and use genetics and mass spectrometry to study their assembly, interorgan trafficking, and influence on tissue lipids. The apoB-family lipoprotein Lipophorin (Lpp) is the major hemolymph lipid carrier. It is produced as a phospholipid-rich particle by the fat body, and its secretion requires Microsomal Triglyceride Transfer Protein (MTP). Lpp acquires sterols and most diacylglycerol (DAG) at the gut via Lipid Transfer Particle (LTP), another fat body-derived apoB-family lipoprotein. The gut, like the fat body, is a lipogenic organ, incorporating both de novo-synthesized and dietary fatty acids into DAG for export. We identify distinct requirements for LTP and Lpp-dependent lipid mobilization in contributing to the neutral and polar lipid composition of the brain and wing imaginal disc. These studies define major routes of interorgan lipid transport in Drosophila and uncover surprising tissue-specific differences in lipoprotein lipid utilization.

Mechanism of hypertriglyceridemia in CTP:phosphoethanolamine cytidylyltransferase-deficient mice

Phosphatidylethanolamine is an important inner-leaflet phospholipid, and CTP:phosphoethanolamine cytidylyltransferase-Pcyt2 acts as the main regulator of the de novo phosphatidylethanolamine synthesis from ethanolamine and diacylglycerol. Complete deletion of the mouse Pcyt2 gene is embryonic lethal, and the single-allele deficiency leads to development of the metabolic syndrome phenotype, including liver steatosis, hypertriglyceridemia, obesity, and insulin resistance. This study aimed to specifically elucidate the mechanisms of hypertriglyceridemia in Pcyt2 heterozygous mice (Pcyt2(+/-)). Evidence here shows that unlike 8 week-old mice, 32 week- and 42 week-old Pcyt2(+/-) mice experience increased VLDL secretion and liver microsomal triglyceride transfer protein activity. Older Pcyt2(+/-) mice also demonstrate increased levels of postprandial plasma TAGs, increased stimulation of genes responsible for intestinal lipid absorption, transport and chylomicron secretion, and dramatically elevated plasma Angptl4, apoB-100, and apoB-48 content. In addition, plasma HL and LPL activities and TAG clearance following a lipid challenge were significantly reduced in Pcyt2(+/-) mice relative to control littermates. Collectively, these results establish that the hypertriglyceridemia that accompanies Pcyt2 deficiency is the result of multiple metabolic adaptations, including elevated hepatic and intestinal lipoprotein secretion and stimulated expression and/or activity of genes involved in lipid absorption and transport and lipoprotein assembly, together with reduced plasma TAG clearance and utilization with peripheral tissues.