Reduction of De Novo Lipogenesis Mediates Beneficial Effects of Isoenergetic Diets on Fatty Liver: Mechanistic Insights from the MEDEA Randomized Clinical Trial

Clusters of adipose tissue dysfunction in adults with type 2 diabetes identify those with worse lipidomic profile despite similar glycaemic control

AIMS

To investigate clusters of adipose tissue dysfunction, that is, with adipose tissue insulin resistance (ADIPO-IR) and large waist circumference (WC), identify a worse lipidomic profile characterised by a high proportion of lipids rich in saturated fatty acids (SFA).

MATERIALS AND METHODS

Hierarchical clustering based on WC and ADIPO-IR (calculated as fasting plasma non-esterified fatty acids times fasting plasma insulin, FFA×INS), was performed in 192 adults with overweight/obesity and type 2 diabetes (T2D) treated with metformin (HbA1c = 7.8%). Free fatty acid composition and lipidomic profile were measured by mass spectrometry (GC-MS and LC-MSQTOF). Indexes of fatty acid desaturation (stearoyl-coA desaturase-1 activity, SCD116 = palmitoleic acid/palmitic acid and SCD118 = oleic acid/stearic acid) and of insulin resistance (HOMA-IR) were also calculated.

RESULTS

Three clusters were identified: CL1 (ADIPO-IR = 4.9 ± 2.4 and WC = 96±7 cm, mean ± SD), CL2 (ADIPO-IR = 6.5 ± 2.5 and WC = 114 ± 7 cm), and CL3 (ADIPO-IR = 15.0 ± 4.7 and WC = 107 ± 8 cm). Insulin concentrations, ADIPO-IR, and HOMA-IR significantly increased from CL1 to CL3 (all p < 0.001), while fasting glucose concentrations, HbA1c, dietary lipids and caloric intake were similar. Moreover, CL3 showed significantly higher concentrations of monounsaturated free fatty acids, oleic and palmitoleic acids, triglycerides (TAG) rich in saturated FA and associated with de novo lipogenesis (i.e., TAG 46-50), higher SCD116, SCD118, ceramide (d18:0/18:0), and phosphatidylcholine aa(36:5) compared with CL1/CL2 (all p < 0.005).

CONCLUSIONS

High ADIPO-IR and large WC identify a worse lipid profile in T2D characterised by complex lipids rich in SFA, likely due to de novo synthesis given higher plasma monounsaturated FFA and increased desaturase activity indexes.

REGISTRATION NUMBER TRIAL

ID NCT00700856 https://clinicaltrials.gov.

Differential Effects of Two Isocaloric Healthy Diets on Postprandial Lipid Responses in Individuals with Type 2 Diabetes

BACKGROUND

High blood concentrations of triglycerides (TG) in the postprandial period have been shown to be more closely associated with the risk of cardiovascular disease (CVD) than fasting values in individuals with type 2 diabetes (T2D). Dietary changes are the primary determinants of postprandial lipid responses.

METHODS

We investigated the effects of an isocaloric multifactorial diet, rich in n-3 PUFA, MUFA, fiber, polyphenols, and vitamins, compared to an isocaloric diet, containing the same amount of MUFA, on the postprandial lipid response in T2D individuals. Following a randomized, controlled, parallel group design, 43 (25 male/18 female) T2D individuals were assigned to an isocaloric multifactorial (n = 21) or a MUFA-rich diet (n = 22). At the beginning and after the 8 weeks of dietary intervention, the concentrations of plasma triglycerides, total cholesterol, HDL cholesterol, and non-HDL cholesterol were detected at fasting and over a 4-h test meal with the same composition as the prescribed diet.

RESULTS

The concentrations of fasting plasma triglycerides, total cholesterol, HDL cholesterol, and non-HDL cholesterol did not change after both diets. Compared with the MUFA diet, the 8-week multifactorial diet significantly lowered the postprandial response, which was evaluated as the incremental area under the curve (iAUC), of triglycerides by 33% (64 ± 68 vs. 96 ± 50 mmol/L·240 min, mean ± SD, respectively, p = 0.018), total cholesterol by 105% (-51 ± 33 vs. -25 ± 29, p = 0.013), and non-HDL cholesterol by 206% (-39 ± 33 vs. -13 ± 23, p = 0.013).

CONCLUSIONS

In T2D individuals, a multifactorial diet, characterized by several beneficial components, improved the postprandial lipid response compared to a MUFA diet, generally considered a healthy diet being reduced in saturated fat, and probably contributed to the reduction of cardiovascular risk.

Intrapancreatic fat deposition and nutritional treatment: the role of various dietary approaches

Ectopic fat accumulation in various organs and tissues, such as the liver, muscle, kidney, heart, and pancreas, is related to impaired capacity of adipose tissue to accumulate triglycerides, as a consequence of overnutrition and an unhealthy lifestyle. Ectopic fat promotes organ dysfunction and is a key factor in the development and progression of cardiometabolic diseases. Interest in intrapancreatic fat deposition (IPFD) has developed in the last few years, particularly in relation to improvement in methodological techniques for detection of fat in the pancreas, and to growing evidence for the role that IPFD might have in glucose metabolism disorders and cardiometabolic disease. Body weight reduction represents the main option for reducing fat, and the evidence consistently shows that hypocaloric diets are effective in reducing IPFD. Changes in diet composition, independently of changes in energy intake, might offer a more feasible and safe alternative treatment to energy restriction. This current narrative review focused particularly on the possible beneficial role of the diet and its nutrient content, in hypocaloric and isocaloric conditions, in reducing IPFD in individuals with high cardiometabolic risk, highlighting the possible effects of differences in calorie quantity and calorie quality. This review also describes plausible mechanisms by which the various dietary approaches could modulate IPFD.

Pediococcus acidilactici (pA1c®) alleviates obesity-related dyslipidemia and inflammation in Wistar rats by activating beta-oxidation and modulating the gut microbiota

Due to the importance of the gut microbiota in the regulation of energy homeostasis, probiotics have emerged as an alternative therapy to ameliorate obesity-related disturbances, including cholesterol metabolism dysregulation, dyslipidemia and inflammation. Therefore, the objectives of this study were to evaluate the effect of the probiotic strain Pediococcus acidilactici (pA1c®) on the regulation of adiposity, cholesterol and lipid metabolism, inflammatory markers and gut microbiota composition in diet-induced obese rats. Twenty-nine four-week-old male Wistar rats were divided into three groups: rats fed a control diet (CNT group, n = 8), rats fed a high fat/high sucrose diet (HFS group, n = 11), and rats fed a HFS diet supplemented with pA1c® (pA1c®group, n = 10). Organs and fat depots were weighed, and different biochemical parameters were analysed in serum. Gene expression analyses in the adipose tissue were conducted using real-time quantitative-PCR. Faecal microbiota composition was evaluated using 16S metagenomics. Animals supplemented with pA1c® exhibited a lower proportion of visceral adiposity, a higher proportion of muscle, an improvement in the total-cholesterol/HDL-cholesterol ratio and a decrease in the total cholesterol, triglyceride and aspartate aminotransaminase (AST) serum levels, together with a decrease in several inflammation-related molecules. The expression of key genes related to adipose (Adipoq, Cebpa and Pparg) and glucose (Slc2a1 and Slc2a4) metabolism in the adipose tissue was normalized by pA1c®. Moreover, it was demonstrated that pA1c® supplementation activated fatty acid β-oxidation in the adipose tissue and the liver. Metagenomics demonstrated the presence of pA1c® in the faecal samples, an increase in alpha diversity, an increase in the abundance of beneficial bacteria, and a decrease in the abundance of harmful micro-organisms, including the Streptococcus genus. Thus, our data suggest the potential of pA1c® in the prevention of obesity-related disturbances including hypercholesterolemia, hypertriglyceridemia, inflammation and gut microbiota dysbiosis.

Gut liver brain axis in diseases: the implications for therapeutic interventions

Gut-liver-brain axis is a three-way highway of information interaction system among the gastrointestinal tract, liver, and nervous systems. In the past few decades, breakthrough progress has been made in the gut liver brain axis, mainly through understanding its formation mechanism and increasing treatment strategies. In this review, we discuss various complex networks including barrier permeability, gut hormones, gut microbial metabolites, vagus nerve, neurotransmitters, immunity, brain toxic metabolites, β-amyloid (Aβ) metabolism, and epigenetic regulation in the gut-liver-brain axis. Some therapies containing antibiotics, probiotics, prebiotics, synbiotics, fecal microbiota transplantation (FMT), polyphenols, low FODMAP diet and nanotechnology application regulate the gut liver brain axis. Besides, some special treatments targeting gut-liver axis include farnesoid X receptor (FXR) agonists, takeda G protein-coupled receptor 5 (TGR5) agonists, glucagon-like peptide-1 (GLP-1) receptor antagonists and fibroblast growth factor 19 (FGF19) analogs. Targeting gut-brain axis embraces cognitive behavioral therapy (CBT), antidepressants and tryptophan metabolism-related therapies. Targeting liver-brain axis contains epigenetic regulation and Aβ metabolism-related therapies. In the future, a better understanding of gut-liver-brain axis interactions will promote the development of novel preventative strategies and the discovery of precise therapeutic targets in multiple diseases.

Human skin stem cell-derived hepatic cells as in vitro drug discovery model for insulin-driven de novo lipogenesis

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is characterized by intrahepatic triglyceride accumulation and can progress to metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis. Hepatic de novo lipogenesis (DNL), activated by glucose and insulin, is a central pathway contributing to early-stage development of MASLD. The emerging global prevalence of MASLD highlights the urgent need for pharmaceutical intervention to combat this health threat. However, the identification of novel drugs that could inhibit hepatic DNL is hampered by a lack of reliable, insulin-sensitive, human, in vitro, hepatic models. Here, we report human skin stem cell-derived hepatic cells (hSKP-HPC) as a unique in vitro model to study insulin-driven DNL (iDNL), evidenced by both gene expression and lipid accumulation readouts. Insulin-sensitive hSKP-HPC showed increased sterol regulatory element-binding protein 1c (SREBP-1c) expression, a key transcription factor for DNL. Furthermore, this physiologically relevant in vitro human steatosis model allowed both inhibition and activation of the iDNL pathway using reference inhibitors and activators, respectively. Optimisation of the lipid accumulation assay to a high-throughput, 384-well format enabled the screening of a library of annotated compounds, delivering new insights on key players in the iDNL pathway and MASLD pathophysiology. Together, these results establish the value of the hSKP-HPC model in preclinical development of antisteatotic drugs to combat MASLD.

Precision nutrition for targeting pathophysiology of cardiometabolic phenotypes

Obesity is a heterogenous disease accompanied by a broad spectrum of cardiometabolic risk profiles. Traditional paradigms for dietary weight management do not address biological heterogeneity between individuals and have catastrophically failed to combat the global pandemic of obesity-related diseases. Nutritional strategies that extend beyond basic weight management to instead target patient-specific pathophysiology are warranted. In this narrative review, we provide an overview of the tissue-level pathophysiological processes that drive patient heterogeneity to shape distinct cardiometabolic phenotypes in obesity. Specifically, we discuss how divergent physiology and postprandial phenotypes can reveal key metabolic defects within adipose, liver, or skeletal muscle, as well as the integrative involvement of the gut microbiome and the innate immune system. Finally, we highlight potential precision nutritional approaches to target these pathways and discuss recent translational evidence concerning the efficacy of such tailored dietary interventions for different obesity phenotypes, to optimise cardiometabolic benefits.

Fatty acid composition of cholesterol esters reflects dietary fat intake after dietary interventions in a multinational population

BACKGROUND

The effects of different dietary fatty acids (FA) on cardiovascular risk still needs clarification. Plasma lipids composition may be a biomarker of FA dietary intake.

PURPOSE

To evaluate in a composite population the relationships between changes in dietary fat intake and changes in FA levels in serum cholesterol esters.

METHODS

In a multinational, parallel-design, dietary intervention (KANWU study), dietary intakes (3-day food record) and FA composition of serum cholesterol esters (gas-liquid chromatography) were evaluated at baseline and after 3 months in 162 healthy individuals, randomly assigned to a diet containing a high proportion of saturated (SFA) or monounsaturated (MUFA) fat, with a second random assignment to fish oil or placebo supplements.

RESULTS

Main differences in serum lipid composition after the two diets included saturated (especially myristic, C14:0, and pentadecanoic, C15:0) and monounsaturated (oleic acid, C18:1 n-9) FA. C14:0 and C15:0 were related to SFA intake, while C18:1 n-9 was associated with MUFA intake. Fish oil supplementation induced a marked increase in eicosapentaenoic (C20:5 n-3) and docosahexaenoic (C22:6 n-3) acids. After the 3-month intervention, Δ-9 desaturase activity, calculated as palmitoleic acid/palmitic acid (C16:1/C16:0) ratio, was more reduced after the MUFA (0.31±0.10 vs 0.25±0.09, p<0.0001) than SFA diet (0.31±0.09 vs 0.29±0.08, p=0.006), with a statistically significant difference between the two groups (p<0.0001).

CONCLUSIONS

This study shows that serum cholesterol ester FA composition can be used during randomized controlled trials as an objective indicator of adherence to experimental diets based on saturated and monounsaturated fat modifications, as well as fish oil supplementation.

Regulation of Autophagy via Carbohydrate and Lipid Metabolism in Cancer

Metabolic changes are an important component of tumor cell progression. Tumor cells adapt to environmental stresses via changes to carbohydrate and lipid metabolism. Autophagy, a physiological process in mammalian cells that digests damaged organelles and misfolded proteins via lysosomal degradation, is closely associated with metabolism in mammalian cells, acting as a meter of cellular ATP levels. In this review, we discuss the changes in glycolytic and lipid biosynthetic pathways in mammalian cells and their impact on carcinogenesis via the autophagy pathway. In addition, we discuss the impact of these metabolic pathways on autophagy in lung cancer.

Nutritional regulation of hepatic de novo lipogenesis in humans

PURPOSE OF REVIEW

De novo lipogenesis (DNL) is a metabolic process occurring mainly within the liver, in humans. Insulin is a primary signal for promoting DNL; thus, nutritional state is a key determinant for upregulation of the pathway. However, the effects of dietary macronutrient composition on hepatic DNL remain unclear. Nor is it clear if a nutrition-induced increase in DNL results in accumulation of intra-hepatic triglyceride (IHTG); a mechanism often proposed for pathological IHTG. Here, we review the latest evidence surrounding the nutritional regulation of hepatic DNL.

RECENT FINDINGS

The role of carbohydrate intake on hepatic DNL regulation has been well studied, with only limited data on the effects of fats and proteins. Overall, increasing carbohydrate intake typically results in an upregulation of DNL, with fructose being more lipogenic than glucose. For fat, it appears that an increased intake of n-3 polyunsaturated fatty acids downregulates DNL, whilst, in contrast, an increased dietary protein intake may upregulate DNL.

SUMMARY

Although DNL is upregulated with high-carbohydrate or mixed-macronutrient meal consumption, the effects of fat and protein remain unclear. Additionally, the effects of different phenotypes (including sex, age, ethnicity, and menopause status) in combination with different diets (enriched in different macronutrients) on hepatic DNL requires elucidation.

We are what we eat: The role of lipids in metabolic diseases

Lipids play a fundamental role, both structurally and functionally, for the correct functioning of the organism. In the last two decades, they have evolved from molecules involved only in energy storage to compounds that play an important role as components of cell membranes and signaling molecules that regulate cell homeostasis. For this reason, their interest as compounds involved in human health has been gaining weight. Indeed, lipids derived from dietary sources and endogenous biosynthesis are relevant for the pathophysiology of numerous diseases. There exist pathological conditions that are characterized by alterations in lipid metabolism. This is particularly true for metabolic diseases, such as liver steatosis, type 2 diabetes, cancer and cardiovascular diseases. The main issue to be considered is lipid homeostasis. A precise control of fat homeostasis is required for a correct regulation of metabolic pathways and safe and efficient energy storage in adipocytes. When this fails, a deregulation occurs in the maintenance of systemic metabolism. This happens because an increased concentrations of lipids impair cellular homeostasis and disrupt tissue function, giving rise to lipotoxicity. Fat accumulation results in many alterations in the physiology of the affected organs, mainly in metabolic tissues. These alterations include the activation of oxidative and endoplasmic reticulum stress, mitochondrial dysfunction, increased inflammation, accumulation of bioactive molecules and modification of gene expression. In this chapter, we review the main metabolic diseases in which alterations in lipid homeostasis are involved and discuss their pathogenic mechanisms.

An Isoenergetic Multifactorial Diet Reduces Pancreatic Fat and Increases Postprandial Insulin Response in Patients With Type 2 Diabetes: A Randomized Controlled Trial

OBJECTIVE

To compare the effect of an isocaloric multifactorial diet with a diet rich in monounsaturated fatty acids (MUFA) and similar macronutrient composition on pancreatic fat (PF) and postprandial insulin response in type 2 diabetes (T2D).

RESEARCH DESIGN AND METHODS

According to a randomized controlled parallel-group design, 39 individuals with T2D, 35-75 years old, in satisfactory blood glucose control, were assigned to an 8 week isocaloric intervention with a multifactorial diet rich in MUFA, polyunsaturated fatty acids, fiber, polyphenols, and vitamins (n = 18) or a MUFA-rich diet (n = 21). Before/after the intervention, PF content was measured by the proton-density fat fraction using a three-dimensional mDIXON MRI sequence, and plasma insulin and glucose concentrations were measured over a 4 h test meal with a similar composition as the assigned diet.

RESULTS

After 8 weeks, PF significantly decreased after the multifactorial diet (from 15.7 ± 6.5% to 14.1 ± 6.3%; P = 0.024), while it did not change after the MUFA diet (from 17.1 ± 10.1% to 18.6 ± 10.6%; P = 0.139) with a significant difference between diets (P = 0.014). Postprandial glucose response was similar in the two groups. Early postprandial insulin response (incremental postprandial areas under the curve [iAUC0-120]) significantly increased with the multifactorial diet (from 36,340 ± 34,954 to 44,138 ± 31,878 pmol/L/min; P = 0.037), while it did not change significantly in the MUFA diet (from 31,754 ± 18,446 to 26,976 ± 12,265 pmol/L/min; P = 0.178), with a significant difference between diets (P = 0.023). Changes in PF inversely correlated with changes in early postprandial insulin response (r = -0.383; P = 0.023).

CONCLUSIONS

In patients with T2D, an isocaloric multifactorial diet, including several beneficial dietary components, markedly reduced PF. This reduction was associated with an improved postprandial insulin response.