Energy intake, gastrointestinal transit, and gut hormone release in response to oral triglycerides and fatty acids in men with and without severe obesity

A guide to developing population files for physiologically-based pharmacokinetic modeling in the Simcyp Simulator

The Simcyp Simulator is a software platform widely used in the pharmaceutical industry to conduct stochastic physiologically-based pharmacokinetic (PBPK) modeling. This approach has the advantage of combining routinely generated in vitro data on drugs and drug products with knowledge of biology and physiology parameters to predict a priori potential pharmacokinetic changes in absorption, distribution, metabolism, and excretion for populations of interest. Combining such information with pharmacodynamic knowledge of drugs enables planning for potential dosage adjustment when clinical studies are feasible. Although the conduct of dedicated clinical studies in some patient groups (e.g., with hepatic or renal diseases) is part of the regulatory path for drug development, clinical studies for all permutations of covariates potentially affecting pharmacokinetics are impossible to perform. The role of PBPK in filling the latter gap is becoming more appreciated. This tutorial describes the different input parameters required for the creation of a virtual population giving robust predictions of likely changes in pharmacokinetics. It also highlights the considerations needed to qualify the models for such contexts of use. Two case studies showing the step-by-step development and application of population files for obese or morbidly obese patients and individuals with Crohn's disease are provided as the backbone of our tutorial to give some hands-on and real-world examples.

Understanding the gastrointestinal tract in obesity: From gut motility patterns to enzyme secretion

BACKGROUND AND PURPOSE

The pathophysiology of obesity has been the product of extensive research, revealing multiple interconnected mechanisms contributing to body weight regulation. The regulation of energy balance involves an intricate network, including the gut-neuroendocrine interplay. As a consequence, research on the gut-brain-microbiota axis in obesity has grown extensively. The physiology of the gastrointestinal tract, far from being underexplored, has significant implications for the development of specific complications in people living with obesity across the fields of gastroenterology, nutrition, and pharmacology. Clinical research indicates higher fasting bile acids serum levels, and blunted postprandial increases in bilious secretions in people living with obesity. Findings are less straightforward for the impact of obesity on gastric emptying with various studies reporting accelerated, normal, or delayed gastric emptying rates. Conversely, the effect of obesity on gastrointestinal pH, gastrointestinal transit, and gastric and pancreatic enzyme secretion is largely unknown. In this review, we explore the current evidence on the gastrointestinal physiology of obesity.

Inflammatory crosstalk between saturated fatty acids and gut microbiota-white adipose tissue axis

PURPOSE

High-fat diets have different metabolic responses via gut dysbiosis. In this review, we discuss the complex interaction between the intake of long- and medium-chain saturated fatty acids (SFAs), gut microbiota, and white adipose tissue (WAT) dysfunction, particularly focusing on the type of fat.

RESULTS

The evidence for the impact of dietary SFAs on the gut microbiota-WAT axis has been mostly derived from in vitro and animal models, but there is now also evidence emerging from human studies. Most current reports show that, in response to high long- and medium-chain SFA diets, WAT functions are altered and can be modulated from microbial metabolites in several manners; and it appears to be also modified under conditions of obesity. SFAs overconsumption can reduce bacterial content and disrupt the gut environment. Both long- and medium-chain SFAs may contribute to proinflammatory cytokines release and TLR4 cascade signaling, either by regulation of endotoxemia markers or myristoylated protein. Palmitic and stearic acids have pathological effects on the intestinal epithelium, microbes, and inflammatory and lipogenic WAT profiles. While myristic and lauric acids display somewhat controversial outcomes, from probiotic effects and contribution to weight loss to cardiometabolic alterations from WAT inflammation.

CONCLUSION

Identifying an interference of distinct types of SFA in the binomial gut microbiota-WAT may elucidate essential mechanisms of metabolic endotoxemia, which may be the key to triggering obesity, innovating the therapeutic tools for this disease.

Differences in gastrointestinal hormones and appetite ratings between individuals with and without obesity-A systematic review and meta-analysis

Determining if gastrointestinal (GI) hormone response to food intake differs between individuals with, and without, obesity may improve our understanding of obesity pathophysiology. A systematic review and meta-analysis of studies assessing the concentrations of GI hormones, as well as appetite ratings, following a test meal, in individuals with and without obesity was undertaken. Systematic searches were conducted in the databases MEDLINE, Embase, Cochrane Library, PsycINFO, Web of Science, and ClinicalTrials.gov. A total of 7514 unique articles were retrieved, 115 included in the systematic review, and 70 in the meta-analysis. The meta-analysis compared estimated standardized mean difference in GI hormones' concentration, as well as appetite ratings, between individuals with and without obesity. Basal and postprandial total ghrelin concentrations were lower in individuals with obesity compared with controls, and this was reflected by lower postprandial hunger ratings in the former. Individuals with obesity had a lower postprandial concentration of total peptide YY compared with controls, but no significant differences were found for glucagon-like peptide 1, cholecystokinin, or other appetite ratings. A large methodological and statistical heterogeneity among studies was found. More comprehensive studies are needed to understand if the differences observed are a cause or a consequence of obesity.

Early effects of Roux-en-Y gastric bypass on dietary fatty acid absorption and metabolism in people with obesity and normal glucose tolerance

INTRODUCTION

Roux-en-Y gastric bypass (RYGB) surgery markedly increases the rate of intestinal nutrient exposure after food intake, accelerates intestinal absorption of dietary glucose and protein, and alters the postprandial gut hormone response. However, our understanding of postprandial fat absorption and metabolism after RYGB is incomplete.

METHODS

Stable palmitate tracers were administered intravenously (K-[2,2-²H₂]palmitate) and orally with a mixed meal ([U-¹³C₁₆]palmitate) to study fatty acid absorption and metabolism before and 3 months after RYGB in 10 participants with obesity and normal glucose tolerance.

RESULTS

There was a tendency toward reduced fasting plasma nonesterified palmitate concentrations after RYGB, but neither fasting palmitate kinetics nor fasting triacylglycerol (TAG) concentrations changed compared with before surgery. Postprandial TAG concentrations were numerically, but nonsignificantly, reduced 3-4 h after meal intake after compared with before RYGB. However, the postprandial appearance of the oral palmitate tracer in the plasma TAG pool and overflow into the nonesterified palmitate pool were initially faster but overall reduced after RYGB by 50% (median, IQR: [47;64], P = 0.004) and 46% (median, IQR: [33;70], P = 0.041), respectively. The maximal postprandial suppression of plasma nonesterified palmitate concentrations was slightly greater but shorter lasting after RYGB ('time × visit' interaction: P < 0.001), without detectable effects of surgery on the rate of appearance and disappearance of plasma palmitate.

CONCLUSION

RYGB resulted in an initially accelerated but overall ~50% reduced 4-h postprandial systemic appearance of dietary palmitate in participants with obesity and normal glucose tolerance. This is likely a result of faster but incomplete intestinal fat absorption combined with enhanced chylomicron-TAG clearance, but it needs further investigation in studies specifically designed to investigate these mechanisms.

Diet-induced obesity enhances postprandial glucagon-like peptide-1 secretion in Wistar rats, but not in diabetic Goto-Kakizaki rats

Glucagon-like peptide-1 (GLP-1) is postprandially secreted from enteroendocrine L-cells and enhances insulin secretion. Currently, it is still controversial whether postprandial GLP-1 responses are altered in obesity and diabetes. To address the issue and to find out possible factors related, we compared postprandial GLP-1 responses in normal rats and in diabetic rats chronically fed an obesogenic diet. Male Wistar rats and diabetic Goto-Kakizaki (GK) rats were fed either a control diet or a high-fat/high-sucrose (HFS, 30 % fat and 40 % sucrose) diet for 26 weeks. Meal tolerance tests were performed for monitoring postprandial responses after a liquid diet administration (62·76 kJ/kg body weight) every 4 or 8 weeks. Postprandial glucose, GLP-1 and insulin responses in Wistar rats fed the HFS diet (WH) were higher than Wistar rats fed the control diet (WC). Although GK rats fed the HFS diet (GH) had higher glycaemic responses than GK rats fed the control diet (GC), these groups had similar postprandial GLP-1 and insulin responses throughout the study. Jejunal and ileal GLP-1 contents were increased by the HFS diet only in Wistar rats. Furthermore, mRNA expression levels of fatty acid receptors (Ffar1) in the jejunum were mildly (P = 0·053) increased by the HFS diet in Wistar rats, but not in GK rats. These results demonstrate that postprandial GLP-1 responses are enhanced under an obesogenic status in normal rats, but not in diabetic rats. Failure of adaptive enhancement of GLP-1 response in GK rats could be partly responsible for the development of glucose intolerance.

Enteroendocrine Hormone Secretion and Metabolic Control: Importance of the Region of the Gut Stimulation

It is now widely appreciated that gastrointestinal function is central to the regulation of metabolic homeostasis. Following meal ingestion, the delivery of nutrients from the stomach into the small intestine (i.e., gastric emptying) is tightly controlled to optimise their subsequent digestion and absorption. The complex interaction of intraluminal nutrients (and other bioactive compounds, such as bile acids) with the small and large intestine induces the release of an array of gastrointestinal hormones from specialised enteroendocrine cells (EECs) distributed in various regions of the gut, which in turn to regulate gastric emptying, appetite and postprandial glucose metabolism. Stimulation of gastrointestinal hormone secretion, therefore, represents a promising strategy for the management of metabolic disorders, particularly obesity and type 2 diabetes mellitus (T2DM). That EECs are distributed distinctively between the proximal and distal gut suggests that the region of the gut exposed to intraluminal stimuli is of major relevance to the secretion profile of gastrointestinal hormones and associated metabolic responses. This review discusses the process of intestinal digestion and absorption and their impacts on the release of gastrointestinal hormones and the regulation of postprandial metabolism, with an emphasis on the differences between the proximal and distal gut, and implications for the management of obesity and T2DM.

What Is GLP-1 Really Doing in Obesity?

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released in response to meal ingestion and enhances insulin secretion from pancreatic β cells. In several human studies, GLP-1 secretory responses to oral glucose load or a meal were decreased in subjects with obesity, glucose intolerance, or diabetes compared with those in healthy subjects. However, the results of meta-analysis and cohort studies do not necessarily support this concept. Results from animal studies are also inconsistent; in multiple studies, GLP-1 secretory responses to a meal were repeatedly higher in diet-induced obese rats than in control rats. Thus, the postprandial GLP-1 response is not necessarily decreased but rather enhanced during obesity development, which is likely to play a protective role against glucose intolerance.

Intestinal sensing and handling of dietary lipids in gastric bypass-operated patients and matched controls

BACKGROUND

Altered meal-related gut hormone secretion seems important for weight loss and diabetes remission after Roux-en-Y gastric bypass (RYGB). Elucidating the responsible meal components and receptors could aid discovery of new treatments of obesity and diabetes. Enteroendocrine cells respond to digestion products of dietary triacylglycerol, especially long-chain fatty acids (LCFAs) and 2-oleoyl-glycerol (2-OG), but not medium-chain fatty acids (MCFAs).

OBJECTIVE

We examined the impact of olive oil (20 mL) and its derivates, LCFAs and 2-OG, on enteroendocrine secretions [glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), peptide YY (PYY), and neurotensin (NT)] and on glucose, lipid, and bile acid metabolism in RYGB-operated and unoperated individuals.

METHODS

In an exploratory randomized crossover design, 10 RYGB-operated patients and 10 matched controls ingested 3 equimolar triacylglycerol formulations on separate days: olive oil (digested to 2-OG + LCFAs), C8-dietary oil (2-OG + MCFAs), and tricaprylin (MCFAs; negative control). Hormone responses were calculated as area under the curve (AUC).

RESULTS

Independent of group status, olive oil had greater effects than C8-dietary oil on AUCs of plasma GLP-1 (+32%; 95% CI: 23%, 43%; P < 0.01), CCK (+53%, P < 0.01), and NT (+71%, P < 0.01), whereas the effect on GIP differed between groups (+90% in controls, P < 0.01; +24% in RYGB, P = 0.10). Independent of group status, C8-dietary oil had greater effects than tricaprylin on AUCs of plasma CCK (+40%, P < 0.01) and NT (+32%, P < 0.01), but not GLP-1 (+5%; 95% CI: -2.9%, 13%; P = 0.22), whereas the effect on GIP again differed between groups (+78% in controls, P < 0.01; +39% in RYGB, P = 0.01). Distal (GLP-1/PYY/NT), but not proximal (CCK/GIP), enteroendocrine responses were generally greater in RYGB patients than in controls.

CONCLUSIONS

The combination of LCFAs plus 2-OG was substantially more effective than 2-OG plus MCFAs in stimulating enteroendocrine secretion in RYGB-operated and matched control individuals. Distal lipid-induced gut hormone release was greater after RYGB.This trial was registered at clinicaltrials.gov as NCT03223389.