Jejunal feeding is followed by a greater rise in plasma cholecystokinin, peptide YY, glucagon-like peptide 1, and glucagon-like peptide 2 concentrations compared with gastric feeding in vivo in humans: a randomized trial

The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell

The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.

Hypothesis: Bolus jejunal feeding via an enteral feeding tube simulates key features of gastric bypass to initiate similar clinical benefits

BACKGROUND

Therapy for obesity and related comorbidities should be clinically effective, widely available and acceptable, and used in conjunction with an optimized lifestyle. Dieting is widely available and acceptable but has poorly sustained clinical efficacy. By contrast, Roux-en-Y gastric bypass (GB) is highly effective but cost and safety concerns limit widespread use. In this article this we discuss the hypothesis that bolus jejunal feeding (BJ) via an enteral feeding tube simulates key features of GB with the potential for similar clinical benefits. We further hypothesize that a practical manner of providing BJ therapeutically is via an externally inapparent orojejunal feeding tube.

RATIONALE

The first hypothesis is underpinned by the outcomes of research in three fields: 1) investigations into the mechanisms underlying the benefit of GB, 2) studies investigating gastrointestinal physiology and pathophysiology using enteral feeding tubes, and3) investigations into the mechanism underlying involuntary anorexia and weight loss in clinical situations that entail rapid nutrient delivery to the jejunum. There is compelling evidence that a supraphysiologic rate of delivery of nutrient to the jejunum suppresses appetite and energy intake and improves glucose homeostasis, and that these effects can be achieved non-surgically using an enteral feeding tube. The second hypothesis is supported by clinical demonstration of the feasibility of administering intermittent cycles of bolus feeds via an intraorally anchored feeding tube in ambulatory obese adults.

CONCLUSION

The hypotheses are testable in clinical studies. If validated, BJ could be used to induce the clinical benefits of GB, but without its costs or safety concerns.

What Is an L-Cell and How Do We Study the Secretory Mechanisms of the L-Cell?

Synthetic glucagon-like peptide-1 (GLP-1) analogues are effective anti-obesity and anti-diabetes drugs. The beneficial actions of GLP-1 go far beyond insulin secretion and appetite, and include cardiovascular benefits and possibly also beneficial effects in neurodegenerative diseases. Considerable reserves of GLP-1 are stored in intestinal endocrine cells that potentially might be mobilized by pharmacological means to improve the body's metabolic state. In recognition of this, the interest in understanding basic L-cell physiology and the mechanisms controlling GLP-1 secretion, has increased considerably. With a view to home in on what an L-cell is, we here present an overview of available data on L-cell development, L-cell peptide expression profiles, peptide production and secretory patterns of L-cells from different parts of the gut. We conclude that L-cells differ markedly depending on their anatomical location, and that the traditional definition of L-cells as a homogeneous population of cells that only produce GLP-1, GLP-2, glicentin and oxyntomodulin is no longer tenable. We suggest to sub-classify L-cells based on their differential peptide contents as well as their differential expression of nutrient sensors, which ultimately determine the secretory responses to different stimuli. A second purpose of this review is to describe and discuss the most frequently used experimental models for functional L-cell studies, highlighting their benefits and limitations. We conclude that no experimental model is perfect and that a comprehensive understanding must be built on results from a combination of models.

Intermittent versus continuous enteral nutrition attenuates increases in insulin and leptin during short-term bed rest

PURPOSE

To compare endocrine responses to intermittent vs continuous enteral nutrition provision during short-term bed rest.

METHODS

Twenty healthy men underwent 7 days of bed rest, during which they were randomized to receive enteral nutrition (47%E as carbohydrate, 34%E as fat, 16%E as protein and 3%E as fibre) in a continuous (CONTINUOUS; n = 10; 24 h day-1 at a constant rate) or intermittent (INTERMITTENT; n = 10; as 4 meals per day separated by 5 h) pattern. Daily plasma samples were taken every morning to assess metabolite/hormone concentrations.

RESULTS

During bed rest, plasma leptin concentrations were elevated to a lesser extent with INTERMITTENT vs CONTINUOUS (iAUC: 0.42 ± 0.38 vs 0.95 ± 0.48 nmol L-1, respectively; P = 0.014) as were insulin concentrations (interaction effect, P < 0.001) which reached a peak of 369 ± 225 pmol L-1 in CONTINUOUS, compared to 94 ± 38 pmol L-1 in INTERMITTENT (P = 0.001). Changes in glucose infusion rate were positively correlated with changes in fasting plasma GLP-1 concentrations (r = 0.44, P = 0.049).

CONCLUSION

Intermittent enteral nutrition attenuates the progressive rise in plasma leptin and insulinemia seen with continuous feeding during bed rest, suggesting that continuous feeding increases insulin requirements to maintain euglycemia. This raises the possibility that hepatic insulin sensitivity is impaired to a greater extent with continuous versus intermittent feeding during bed rest. To attenuate endocrine and metabolic changes with enteral feeding, an intermittent feeding strategy may, therefore, be preferable to continuous provision of nutrition. This trial was registered on clinicaltrials.gov as NCT02521025.

Uptake of dietary amino acids into arterial blood during continuous enteral feeding in critically ill patients and healthy subjects

BACKGROUND

Amino acid availability is a regulatory factor of protein anabolism and is partly dependent on enteral amino acid uptake. During continuous enteral feeding, enteral amino acid uptake may vary considerably, but this has not been documented systematically.

METHODS

In this pragmatic study, we investigated patients in the intensive care unit (n = 10) and healthy adults (n = 10). The time course of essential amino acid concentrations in arterial plasma and the uptake of dietary phenylalanine were recorded during 12 hours of continuous enteral feeding, using a ¹³C-labeled phenylalanine tracer.

RESULTS

Plasma essential amino acid concentrations and ¹³C-phenylalanine enrichment reached a tentative steady state after no more than 4.5 h from start of tracer infusion. There was a large intra- and inter-individual variability in both cohorts. No periodicity could be detected in the temporal variation.

CONCLUSION

During continuous enteral feeding, uptake of amino acids shows large intra- and inter-individual variation. A tentative steady state of ¹³C-phenylalanine uptake is eventually reached.

TRIAL REGISTRATION

Registered at Australian New Zealand Clinical Trials Registry, trial ID ACTRN12616000593437.

Effect of bolus enteral tube feeding on body weight in ambulatory adults with obesity and type 2 diabetes: a feasibility pilot randomized trial

Background/objectives

To ascertain the effect on body weight of 14 days of bolus enteral feeding with mixed meal (MM) and electrolyte solution (ES) in ambulatory adults with type 2 diabetes and obesity, and also the safety and feasibility of using a modified, intraorally anchored enteral feeding tube for this purpose.

Subjects/methods

We conducted a randomized, crossover pilot trial with 16 participants. A 140 cm, 8-French feeding tube was placed in the jejunum under electromagnetic guidance and anchored intraorally. Participants were randomized to self-administer 120 mL 523 kJ (125 kcal) MM, or 50 kJ (12 kcal) ES four times/day for 14 days. After ≥14 days without the tube, participants crossed over to the other treatment. The primary outcome compared weight change between treatments. Thereafter, participants could elect to undergo additional MM cycles. Participants were encouraged to continue with all usual activities including eating ad lib throughout the study.

Results

Ten participants withdrew prior to completing two randomized 14-day cycles (4 social, 3 intolerant of anchor, and 3 intolerant of tube). Six participants were assessed for the primary outcome and showed no significant difference in weight loss between MM and ES (p = 0.082). For the secondary outcome of within-group weight loss, average weight loss from baseline was significant for MM but not for ES: −2.40 kg (95% CI: −3.78, −1.02; p = 0.008) vs. −0.64 kg (95% CI: −2.01, 0.74; p = 0.27). A total of 23 2-week cycles were completed (12 paired, 2 unpaired, and 9 additional), with no significant adverse events for 334 days of tube use.

Conclusions

Repeated bolus nutrient administration via enteral feeding tube is associated with weight loss in adults with obesity and type 2 diabetes, with no significant difference seen between MM and ES feeds. The prototype device was safe, but requires development for further investigation into the effect of bolus jejunal feeding on weight and to improve acceptability.

Amino Acid Availability of a Dairy and Vegetable Protein Blend Compared to Single Casein, Whey, Soy, and Pea Proteins: A Double-Blind, Cross-Over Trial

Protein quality is important for patients needing medical nutrition, especially those dependent on tube feeding. A blend of dairy and vegetable proteins (35% whey, 25% casein, 20% soy, 20% pea; P4) developed to obtain a more balanced amino acid profile with higher chemical scores, was compared to its constituent single proteins. Fourteen healthy elderly subjects received P4, whey, casein, soy, and pea (18 g/360 mL bolus) on five separate visits. Blood samples were collected at baseline until 240 min after intake. Amino acid availability was calculated using incremental maximal concentration (iCmax) and area under the curve (iAUC). Availability for P4 as a sum of all amino acids was similar to casein (iCmax and iAUC) and whey (iCmax) and higher vs. soy (iCmax and iAUC) and pea (iCmax). Individual amino acid availability (iCmax and iAUC) showed different profiles reflecting the composition of the protein sources: availability of leucine and methionine was higher for P4 vs. soy and pea; availability of arginine was higher for P4 vs. casein and whey. Conclusions: The P4 amino acid profile was reflected in post-prandial plasma levels and may be regarded as more balanced compared to the constituent single proteins.

Co-ingestion of whey protein hydrolysate with milk minerals rich in calcium potently stimulates glucagon-like peptide-1 secretion: an RCT in healthy adults

Purpose

To examine whether calcium type and co-ingestion with protein alter gut hormone availability.

Methods

Healthy adults aged 26 ± 7 years (mean ± SD) completed three randomized, double-blind, crossover studies. In all studies, arterialized blood was sampled postprandially over 120 min to determine GLP-1, GIP and PYY responses, alongside appetite ratings, energy expenditure and blood pressure. In study 1 (n = 20), three treatments matched for total calcium content (1058 mg) were compared: calcium citrate (CALCITR); milk minerals rich in calcium (MILK MINERALS); and milk minerals rich in calcium plus co-ingestion of 50 g whey protein hydrolysate (MILK MINERALS + PROTEIN). In study 2 (n = 6), 50 g whey protein hydrolysate (PROTEIN) was compared to MILK MINERALS + PROTEIN. In study 3 (n = 6), MILK MINERALS was compared to the vehicle of ingestion (water plus sucralose; CONTROL).

Results

MILK MINERALS + PROTEIN increased GLP-1 incremental area under the curve (iAUC) by ~ ninefold (43.7 ± 11.1 pmol L⁻¹ 120 min; p < 0.001) versus both CALCITR and MILK MINERALS, with no difference detected between CALCITR (6.6 ± 3.7 pmol L⁻¹ 120 min) and MILK MINERALS (5.3 ± 3.5 pmol L⁻¹ 120 min; p > 0.999). MILK MINERALS + PROTEIN produced a GLP-1 iAUC ~ 25% greater than PROTEIN (p = 0.024; mean difference: 9.1 ± 6.9 pmol L⁻¹ 120 min), whereas the difference between MILK MINERALS versus CONTROL was small and non-significant (p = 0.098; mean difference: 4.2 ± 5.1 pmol L⁻¹ 120 min).

Conclusions

When ingested alone, milk minerals rich in calcium do not increase GLP-1 secretion compared to calcium citrate. Co-ingesting high-dose whey protein hydrolysate with milk minerals rich in calcium increases postprandial GLP-1 concentrations to some of the highest physiological levels ever reported. Registered at ClinicalTrials.gov: NCT03232034, NCT03370484, NCT03370497.

Electronic supplementary material

The online version of this article (10.1007/s00394-019-02092-4) contains supplementary material, which is available to authorized users.

A Comparison of Gastric and Jejunal Feeding in Hypercatabolism Associated With Hypothalamic AMPK-Autophagy-POMC in Endotoxemic Rats

BACKGROUND

Hypercatabolism is associated with increased infectious rates and mortality in critically ill patients. Enteral nutrition (EN) is usually used to counteract hypercatabolism. However, the impact of different routes of EN on hypercatabolism remains unknown. Here, we compared the impact of gastric feeding (GF) and jejunal feeding (JF) on gastrointestinal hormones and hypercatabolism, which is associated with hypothalamic adenosine 5'-monophosphate-activated protein kinase (AMPK)-autophagy-proopiomelanocortin (POMC).

METHODS

Sixty adult male Sprague-Dawley rats were divided into 5 groups: Sham and lipopolysaccharide (LPS) groups fed a standard chow diet, a pair-fed group that was a subset of saline-treated rats pair-fed with the LPS group, and LPS + JF and LPS + GF groups (received EN via jejunal and gastric tube, respectively, for 3 days [100 kcal/kg/d]). Hypercatabolism was measured by insulin resistance, muscle protein synthesis, and atrophy. Serum gastrointestinal hormones, hypothalamic ghrelin, growth hormone secretagogue receptor-1α (GHS-R1α), and AMPK-autophagy-POMC markers were also detected.

RESULTS

GF increased serum total, acylated, desacylated, and hypothalamic ghrelin and decreased glucagon-like peptide-1 (GLP-1). But no effect on pancreatic polypeptide (PYY) and hypothalamic GHS-R1α was observed. JF showed no effect on hypothalamic ghrelin, GHS-R1α, and serum total, acylated, and desacylated ghrelin and even further aggravated GLP-1 and PYY. GF could effectively augment hypothalamic AMPK-autophagy-POMC and hypercatabolism. However, JF showed no effect on hypothalamic AMPK-autophagy-POMC and hypercatabolism.

CONCLUSIONS

GF could activate hypothalamic AMPK-autophagy and suppress POMC expression via gastrointestinal hormones to ameliorate hypercatabolism compared with JF, which suggested that GF may be the preferred route of EN in endotoxemic rats.

Hyperosmolar Duodenal Saline Infusion Lowers Circulating Ghrelin and Stimulates Intestinal Hormone Release in Young Men

CONTEXT

The mechanisms regulating the postprandial suppression of ghrelin secretion remain unclear, but recent observations in rats indicate that an increase in duodenal osmolarity is associated with a reduction in ghrelin levels. Several hormones have been implicated in the regulation of ghrelin.

OBJECTIVE

We hypothesized that intraduodenal infusion of a hyperosmolar solution would lower plasma ghrelin concentrations.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Eighteen healthy young men were studied after an overnight fast on two occasions in a randomized double-blinded fashion. A nasoduodenal catheter was positioned and isoosmolar (300 mOsm/L) or hyperosmolar (1500 mOsm/L) saline was infused intraduodenally (4 mL/min, t = 0 to 45 minutes). Venous blood was sampled at t = -45, -30, -15, 0, 15, 30, 45, 60, 75, 90, 120, and 180 minutes.

MAIN OUTCOME MEASURES

Plasma concentrations of ghrelin, glucagonlike peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), glucagon, pancreatic polypeptide (PP), neurotensin (NT), peptide YY (PYY), motilin, and glucose.

RESULTS

Ghrelin concentrations were suppressed with hyperosmolar when compared with isoosmolar saline, and remained lower until t = 180 minutes. CCK, NT, GLP-1, PYY, and glucagon all increased during hyperosmolar, but not isoosmolar, saline infusion (P < 0.01 for all), whereas GIP, PP, and motilin levels were not affected by either infusion.

CONCLUSIONS

Plasma ghrelin concentrations are lowered, whereas CCK, GLP-1, PYY, NT, and glucagon concentrations are augmented, by hyperosmolar duodenal content in healthy individuals. These observations have implications for the evaluation of studies comparing the effects of different types and loads of nutrients and chemicals on gut hormone secretion.

A new proposed mechanism of action for gastric bypass surgery: Air hypothesis

Roux-en-Y gastric bypass (RYGB) surgery is one of the most effective treatments for obesity and type II diabetes. RYGB was originally believed to work by mechanically restricting caloric intake or causing macronutrient malabsorption. However, such mechanical effects play no role in the remarkable efficacy of gastric bypass. Instead, mounting evidence shows that altered neuroendocrine signaling is responsible for the weight reducing effects of RYGB. The exact mechanism of this surgical response is still a mystery. Here, we propose that RYGB leads to weight loss primarily by inducing a functional shift in the gut microbiome, manifested by a relative expansion of aerobic bacteria numbers in the colon. We point to compelling evidence that gastric bypass changes the function of the microbiome by disrupting intestinal gas homeostasis, causing excessive transit of swallowed air (oxygen) into the colon.