Gastric electrical stimulation for obesity: the need for a new device using wider pulses

Impact of adaptive gastric electrical stimulation on weight, food intake, and food intake rate in dogs

BACKGROUND

Gastric electrical stimulation (GES) has been studied for decades as a promising treatment for obesity. Stimulation pulses with fixed amplitude and pulse width are usually applied, but these have limitations with regard to overcoming habituation to GES and inter-subject variation. This study aims to analyze the efficacy of an adaptive GES protocol for reducing food intake and maintaining lean weight in dogs.

METHODS

Six beagle dogs were implanted with a remotely programmable gastric stimulator. An adaptive protocol was designed to increase the stimulation energy proportionally to the excess of food consumption, with respect to the dogs' maintenance energy requirements. After surgery and habituation to experimental conditions, the dogs went through both a control and a stimulation period of 4 weeks each, in a randomized order. The stimulation parameters were adapted daily. Body weight, food intake, food intake rate, and postprandial cutaneous electrogastrograms (EGG) were recorded to assess the effect of adaptive GES.

RESULTS

Adaptive GES decreased food intake and food intake rate (p < 0.05) resulting in weight maintenance. In the absence of GES, the dogs gained weight (p < 0.05). Postprandial EGG dominant frequency was accelerated by GES (p < 0.05). The strategy of adapting the stimulation energy was effective in causing significant mid-term changes.

CONCLUSION

Adaptive GES is effective for reducing food intake and maintaining lean weight. The proposed adaptive strategy may offer benefits to counter habituation and adapt to inter-subject variation in clinical use of GES for obesity.

Gastric neurons in the nucleus tractus solitarius are selective to the orientation of gastric electrical stimulation

Objective.Gastric electrical stimulation (GES) is a bioelectric intervention for gastroparesis, obesity, and other functional gastrointestinal disorders. In a potential mechanism of action, GES activates the nerve endings of vagal afferent neurons and induces the vago-vagal reflex through the nucleus tractus solitarius (NTS) in the brainstem. However, it is unclear where and how to stimulate in order to optimize the vagal afferent responses.Approach.To address this question with electrophysiology in rats, we applied mild electrical currents to two serosal targets on the distal forestomach with dense distributions of vagal intramuscular arrays (IMAs) that innervated the circular and longitudinal smooth muscle layers. During stimulation, we recorded single and multi-unit responses from gastric neurons in NTS and evaluated how the recorded responses depended on the stimulus orientation and amplitude.Main results.We found that NTS responses were highly selective to the stimulus orientation for a range of stimulus amplitudes. The strongest responses were observed when the applied current flowed in the same direction as the IMAs in parallel with the underlying smooth muscle fibers. Our results suggest that gastric neurons in NTS may encode the orientation-specific activity of gastric smooth muscles relayed by vagal afferent neurons.Significance.This finding suggests that the orientation of GES is critical to effective engagement of vagal afferents and should be considered in light of the structural phenotypes of vagal terminals in the stomach.

Stomach region stimulated determines effects on duodenal motility in rats

Gastric electrical stimulation (GES) is used clinically to promote proximal GI emptying and motility. In acute experiments, we measured duodenal motor responses elicited by GES applied at 141 randomly chosen electrode sites on the stomach serosal surface. Overnight-fasted (H2O available) anesthetized male rats (n = 81) received intermittent biphasic GES for 5 min (20-s-on/40-s-off cycles; I = 0.3 mA; pw = 0.2 ms; 10 Hz). A strain gauge on the serosal surface of the proximal duodenum of each animal was used to evaluate baseline motor activity and the effect of GES. Using ratios of time blocks compared with a 15-min prestimulation baseline, we evaluated the effects of the 5-min stimulation on concurrent activity, on the 10 min immediately after the stimulation, and on the 15-min period beginning with the onset of stimulation. We mapped the magnitude of the duodenal response (three different motility indices) elicited from the 141 stomach sites. Post hoc electrode site maps associated with duodenal responses suggested three zones similar to the classic regions of forestomach, corpus, and antrum. Maximal excitatory duodenal motor responses were elicited from forestomach sites, whereas inhibitory responses occurred with stimulation of the corpus. Moderate excitatory duodenal responses occurred with stimulation of the antrum. Complex, weak inhibitory/excitatory responses were produced by stimulation at boundaries between stomach regions. Patterns of GES efficacies coincided with distributions of previously mapped vagal afferents, suggesting that excitation of the duodenum is strongest when GES electrodes are situated over stomach concentrations of vagal intramuscular arrays, putative stretch receptors in the muscle wall.

Intestinal electrical stimulation attenuates hyperglycemia and prevents loss of pancreatic β cells in type 2 diabetic Goto-Kakizaki rats

BACKGROUND/OBJECTIVE

Recently, intestinal electrical stimulation (IES) has been reported to result in weight loss; however, it is unclear whether it has a therapeutic potential for diabetes. The aim of the present study was to explore the potential hypoglycemic effects of IES and its possible mechanisms involving β cells in diabetic rats.

SUBJECTS/METHODS

Diabetic Goto-Kakizaki (GK) rats were chronically implanted with one pair of electrodes in the duodenum. The oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were performed with or without IES, and plasma glucagon-like peptide-1 (GLP-1) and insulin level were measured. In the other two OGTT sessions, rats were treated with either Exendin (9-39) (GLP-1 antagonist) or Exendin (9-39) plus IES to investigate the underlying mechanism involving GLP-1. Gastric emptying and small intestinal transit were also measured with or without IES. In a chronic study, GK rats were treated with IES or Sham-IES for 8 weeks. Blood glucose, plasma GLP-1 and insulin level, body weight, and food intake were measured. Pancreas weight, islet β-cell apoptosis, and proliferation were also analyzed.

RESULTS

Acute IES reduced blood glucose level from 60 to 120 min during OGTT by 16-20% (all p < 0.05, vs. Sham-IES). GLP-1 antagonist significantly blocked the inhibitory effect of IES on hyperglycemia from 15 to 120 min (all p < 0.05). IES accelerated the small intestinal transit by 15% (p = 0.004). After 8 weeks of chronic stimulation, IES significantly reduced blood glucose (p < 0.05) and body weight (p = 0.02) and increased the plasma GLP-1 concentration (p < 0.05). Furthermore, we observed that chronic IES reduced pancreatic β-cell apoptosis (p = 0.045), but showed no effects on β-cell proliferation.

CONCLUSIONS

Our study firstly proved the hypoglycemic effect of IES in a rodent model of type 2 diabetes, possibly attributed to the increasing GLP-1 secretion and improvement in β-cell functions.

Gastric electrical stimulation improves enteric neuronal survival

Research and clinical experience with vagotomy have confirmed that damage to the central nervous system severely affects physiological movement in the gastrointestinal system. The aim of this study was to investigate the effects of synchronized dual-pulse gastric electrical stimulation (SGES) on the apoptosis of enteric neurons and the possible pathways involved in these effects in vagotomized rats. For this purpose, Male Sprague-Dawley (SD) rats were randomized into a control group, an early subdiaphragmatic vagotomized group (ESDV group), an early subdiaphragmatic vagotomized group with short-term SGES (ESDV + SSGES group), a terminal subdiaphragmatic vagotomized group (TSDV group) and a terminal subdiaphragmatic vagotomized group with long-term SGES (TSDV + LSGES group). The expression levels of connexin 43 (Cx43), glial cell line-derived neurotrophic factor (GDNF), p-Akt, pan-Akt and PGP9.5 were assessed by RT-qPCR, western blot analysis and immunofluorescence staining. Apoptosis was determined by terminal-deoxynucleoitidyl transferase-mediated nick-end labeling (TUNEL) assay. We found that Cx43 expression was decreased in the ESDV and TSDV groups, but was significantly upregulated in the SSGES and LSGES groups. In addition, the GDNF and PGP9.5 expression levels were significantly decreased in the ESDV group compared with the control and TSDV groups and were upregulated in both the SSGES and LSGES groups. The LSGES group exhibited a clear increase in p-Akt expression compared with the TSDV group. Fewer TUNEL-positive cells were observed in the SSGES and LSGES groups than in the ESDV and TSDV groups. More TUNEL-positive cells were found in the stomach of rats subjected to subdiaphragmatic vagotomy. On the whole, our data indicate that SGES improved enteric neuronal survival, possibly through GDNF and the phosphatidylinositol 3-kinase (PI3K)/Akt pathways.

Electrical therapies for gastrointestinal motility disorders

Gastrointestinal (GI) motility disorders are common in clinical settings, including esophageal motility disorders, gastroesophageal reflux disease, functional dyspepsia, gastroparesis, chronic intestinal pseudo-obstruction, post-operative ileus, irritable bowel syndrome, diarrhea and constipation. While a number of drugs have been developed for treating GI motility disorders, few are currently available. Emerging electrical stimulation methods may provide new treatment options for these GI motility disorders. Areas covered: This review gives an overview of electrical therapies that have been, and are being developed for GI motility disorders, including gastroesophageal reflux, functional dyspepsia, gastroparesis, intestinal motility disorders and constipation. Various methods of gastrointestinal electrical stimulation are introduced. A few methods of nerve stimulation have also been described, including spinal cord stimulation and sacral nerve stimulation. Potentials of electrical therapies for obesity are also discussed. PubMed was searched using keywords and their combinations: electrical stimulation, spinal cord stimulation, sacral nerve stimulation, gastrointestinal motility and functional gastrointestinal diseases. Expert commentary: Electrical stimulation is an area of great interest and has potential for treating GI motility disorders. However, further development in technologies (devices suitable for GI stimulation) and extensive clinical research are needed to advance the field and bring electrical therapies to bedside.

Parameter selection and stimulating effects of an adjustable gastric electrical stimulator in dogs

Background

Gastric electrical stimulation (GES) has been proposed as a promising therapeutic option in treating obesity for 20 years. Currently, the available device of GES cannot meet the clinical needs. The purpose of this study is to verify the effect of a new type of adjustable gastric electrical stimulator in reducing food intake and body weight.

Methods

Eight beagle dogs randomly followed GES and sham GES for 3 months in a crossover design. Parameters were adjusted and individualized during the experiment. Symptoms of GES were recorded, and the effective parameters were selected. Resistance to GES was assessed. Food intake and body weight were measured to evaluate the effect of GES.

Results

The effective parameters were varied among the dogs. Resistance to GES was observed in different periods in dogs. Parameters needed to be adjusted every 10.2 ± 2.1 days during the period of GES. Food intake during GES for 3 months was significantly reduced than that during sham GES of 3 months (P < 0.05). With the decreased food intake, body weight was significantly reduced by the end of GES of 3 months compared with that of sham GES of 3 months (P < 0.05).

Conclusions

Food intake and body weight of dogs are significantly reduced by adjustable GES. Individual parameters and resistance during GES are required to be considered. The new adjustable device may have good prospects of clinical application for obesity.

The effects of individualized gastric electrical stimulation on food craving and gastrointestinal peptides in dogs

BACKGROUND

Using an adjustable stimulator with a wide range of stimulation parameters, the aims of this study were 1) to investigate the effects of long-term gastric electrical stimulation (GES) on appetite and differential food cravings for three different foods and 2) to investigate the effects of GES on plasma gastrointestinal peptide concentrations.

METHODS

The study was performed in eight Beagle dogs implanted with one pair of serosal electrodes. They were followed during GES and sham GES sessions in a crossover design. GES was conducted using a series of individualized parameters. Food intake and food cravings were observed to evaluate the effects of long-term GES. Enzyme-linked immunosorbent assay was used to measure the plasma concentrations of gastrointestinal peptides.

RESULTS

Dogs on GES for three months ate significantly less food than those on sham GES for three months (p < 0.05). A significant change in food cravings was induced by GES. Dogs with GES ate significantly less high-fat food. However, there was no significant difference in consumption of high-carbohydrate food or balanced food between the periods of GES and sham GES. The plasma concentrations of ghrelin, peptide YY3-36, and glucagon-like peptide 1 did not differ significantly between the periods of GES and sham GES.

CONCLUSIONS

Food intake and food craving were changed significantly by adjustable GES. GES may be used for treating obesity by changing food preferences. Further clinical studies are necessary to highlight the effect of adjustable GES on eating behavior.

Advances in research of colonic electrical stimulation

In recent years great attention has been paid to the study of colonic electrical stimulation. Colonic electrical stimulation is expected to become a valuable option for treatment of gastrointestinal dysfunction. This article reviews the classification, mechanisms and clinical applications of colonic electrical stimulation.

Effects of ghrelin on gastric distention sensitive neurons in the arcuate nucleus of hypothalamus and gastric motility in diabetic rats

This study was performed to observe the effects of ghrelin on the activity of gastric distention (GD) sensitive neurons in the arcuate nucleus of hypothalamus (Arc) and on gastric motility in vivo in streptozocin (STZ) induced diabetes mellitus (DM) rats. Electrophysiological results showed that ghrelin could excite GD-excitatory (GD-E) neurons and inhibit GD-inhibitory (GD-I) neurons in the Arc. However, fewer GD-E neurons were excited by ghrelin and the excitatory effect of ghrelin on GD-E neurons was much weaker in DM rats. Gastric motility research in vivo showed that microinjection of ghrelin into the Arc could significantly promote gastric motility and it showed a dose-dependent manner. The effect of ghrelin promoting gastric motility in DM rats was weaker than that in normal rats. The effects induced by ghrelin could be blocked by growth hormone secretagogue receptor (GHSR) antagonist [d-Lys-3]-GHRP-6 or BIM28163. RIA and real-time PCR data showed that the levels of ghrelin in the plasma, stomach and ghrelin mRNA in the Arc increased at first but decreased later and the expression of GHSR-1a mRNA in the Arc maintained a low level in DM rats. The present findings indicate that ghrelin could regulate the activity of GD sensitive neurons and gastric motility via ghrelin receptors in the Arc. The reduced effects of promoting gastric motility induced by ghrelin could be connected with the decreased expression of ghrelin receptors in the Arc in diabetes. Our data provide new experimental evidence for the role of ghrelin in gastric motility disorder in diabetes.

Food intake and body weight responses to intermittent vs. continuous gastric electrical stimulation in diet-induced obese rats

BACKGROUND

Gastric electrical stimulation (GES) has recently been introduced as a potential therapy for the treatment of obesity. The main challenge for the new generation of devices is to achieve desired clinical outcomes at a suitably low level of energy consumption. The aim of this study is to compare the effectiveness of GES with continuous and intermittent duty cycles in reducing food intake and body weight in diet-induced obesity-prone rats.

METHODS

In macro duty cycle experiment, 40 rats were divided into groups to receive a sham GES, continuous GES, or intermittent GES (15 min On-45 min Off or 15 min On-15 min Off) for 28 days. In micro duty cycle experiment, 18 rats received cross-over treatment of continuous stimulation, 60 % time cycle or 40 % time cycle. Food intake, body weight, gastric emptying and ghrelin level were measured to evaluate the effect of different GES.

RESULTS

GES with macro duty cycle intensity-dependently reduced mean daily food intake increase by 18.6, 10.2 and -6.0 % compared to 42.7 % with sham GES and body weight gain by 6.1 %, 3.4 and -0.8 % compared to 5 % with sham GES. Daily food intake decreased with increasing micro duty cycle intensity, averaging 16.5, 15.6 and 13.7 g/day under 40 % cycle, 60 % cycle and continuous stimulation respectively. Gastric emptying was intensity-dependently delayed by GES. GES has no effect in modulating plasma ghrelin level.

CONCLUSIONS

GES energy-dependently reduces food intake, body weight and gastric emptying. Peripheral modulation of plasma ghrelin level is not related to the GES effects.

Gastric stimulation for weight loss

The prevalence of obesity is growing to epidemic proportions, and there is clearly a need for minimally invasive therapies with few adverse effects that allow for sustained weight loss. Behavior and lifestyle therapy are safe treatments for obesity in the short term, but the durability of the weight loss is limited. Although promising obesity drugs are in development, the currently available drugs lack efficacy or have unacceptable side effects. Surgery leads to long-term weight loss, but it is associated with morbidity and mortality. Gastric electrical stimulation (GES) has received increasing attention as a potential tool for treating obesity and gastrointestinal dysmotility disorders. GES is a promising, minimally invasive, safe, and effective method for treating obesity. External gastric pacing is aimed at alteration of the motility of the gastrointestinal tract in a way that will alter absorption due to alteration of transit time. In addition, data from animal models and preliminary data from human trials suggest a role for the gut-brain axis in the mechanism of GES. This may involve alteration of secretion of hormones associated with hunger or satiety. Patient selection for gastric stimulation therapy seems to be an important determinant of the treatment’s outcome. Here, we review the current status, potential mechanisms of action, and possible future applications of gastric stimulation for obesity.

Gastric electrical stimulation parameter dependently alters ventral medial hypothalamic activity and feeding in obese rats

Gastric electrical stimulation (GES) has been used to treat obesity with unclear mechanisms and limited parameter ranges. This study explores effects of GES parameters on ventral medial hypothalamic (VMH) activity, feeding, and body weight in diet-induced obese (DIO) rats. For experiment 1, discharge rates were recorded in 39 gastric distension-responsive (GD-R) neurons in 12 DIO rats. Basal rates were compared with rates under GES using varied pulse amplitudes, widths, frequencies, and train-on times. For experiment 2, a crossover experiment in 16 DIO rats measured food intake and weight effects of GES pulse width, the parameter with the steepest neuronal response gradient in experiment 1. Treatments were sham and 0.5-, 2.0-, and 5.0-ms pulse GES. In experiment 1, 11 of 13 GES parameter sets tested produced significantly (P < 0.05) altered discharge rates of GD-R neurons. Increases in pulse amplitude (P < 0.05) and width (P < 0.0001) produced significant upward linear trends in response over the range tested, with the trend being strongest for pulse width. In experiment 2, over 4 days of 0.5-, 2.0-, and 5.0-ms GES treatment, food intake was 9.6% (P < 0.05), 21.0% (P < 0.0001), and 47.3% (P < 0.0001) lower than under sham-GES, whereas body weight changes were 0.7 (P = 0.48), 2.2 (P < 0.05), and 3.5 (P < 0.002) percentage points lower, respectively. We concluded that GES pulse width increases had the largest effect on VMH neuronal activity, and these effects were paralleled by pulse width-dependent reductions in food intake and body weight. Lengthening pulse width beyond the range used in prior clinical studies may be critical to making GES a viable obesity treatment.

Short pulse gastric electrical stimulation for cisplatin-induced emesis in dogs

BACKGROUND

In a previous study, we investigated the ameliorating effect of gastric electrical stimulation (GES) with a single set of parameters on emesis and behaviors suggestive of nausea induced by cisplatin in dogs. The aim of this study was to investigate the effects of GES with different parameters on cisplatin-induced emesis in dogs.

METHODS

Seven dogs implanted with gastric serosal electrodes were studied in six randomized sessions: one control session with cisplatin (2 mg kg(-1)) and five sessions with cisplatin plus GES of different parameters: GES-A: 14 Hz, 5 mA, 0.3 ms, 0.1 s on and 5 s off; GES-B: increased frequency and on-time; GES-C: increased frequency; GES-D: increased frequency and pulse width; and GES-E: increased frequency and amplitude. Gastric slow waves and emetic responses were recorded in each session.

KEY RESULTS

(i) Cisplatin induced emetic responses and gastric dysrhythmia. The peak time of the emetic response was during the fourth hour after cisplatin. (ii) GES with appropriate parameters reduced cisplatin-induced emesis. The number of vomiting times during the 6 h after cisplatin was 7.0 ± 1.4 in the control, 4.7 ± 1.2 with GES-A (P = 0.179), 4.2 ± 1.2 with GES-B (P = 0.109), 7.0 ± 0.8 with GES-C (P = 0.928), 2.1 ± 0.3 with GES-D (P = 0.005) and 4.7 ± 1.5 with GES-E (P = 0.129). However, none of the GES parameters could improve gastric dysrhythmia.

CONCLUSIONS & INFERENCES

Gastric electrical stimulation with appropriate parameters reduces cisplatin-induced emetic responses and behaviors suggestive of nausea in dogs. Among the tested parameters, GES with increased pulse width seems to produce better relief of cisplatin-induced emesis.

Effects of electrical stimulation on isolated rodent gastric smooth muscle cells evaluated via a joint computational simulation and experimental approach

Gastric electrical stimulation (GES) involves the delivery of electrical impulses to the stomach for therapeutic purposes. New GES protocols are needed that are optimized for improved motility outcomes and energy efficiency. In this study, a biophysically based smooth muscle cell (SMC) model was modified on the basis of experimental data and employed in conjunction with experimental studies to define the effects of a large range of GES protocols on individual SMCs. For the validation studies, rat gastric SMCs were isolated and subjected to patch-clamp analysis during stimulation. Experimental results were in satisfactory agreement with simulation results. The results define the effects of a wide range of GES parameters (pulse width, amplitude, and pulse-train frequency) on isolated SMCs. The minimum pulse width required to invoke a supramechanical threshold response from SMCs (defined at -30 mV) was 65 ms (at 250-pA amplitude). The minimum amplitude required to invoke this threshold was 75 pA (at 1,000-ms pulse width). The amplitude of the invoked response beyond this threshold was proportional to the stimulation amplitude. A high-frequency train of stimuli (40 Hz; 10 ms, 150 pA) could invoke and maintain the SMC plateau phase while requiring 60% less power and accruing approximately 30% less intracellular Ca(2+) concentration during the plateau phase than a comparable single-pulse protocol could in a demonstrated example. Validated computational simulations are an effective strategy for efficiently identifying effective minimum-energy GES protocols, and pulse-train protocols may also help to reduce the power consumption of future GES devices.

Intestinal electric stimulation accelerates whole gut transit and promotes fat excrement in conscious rats

INTRODUCTION

Intestinal electric stimulation (IES) is proposed as a potential tool for the treatment of morbid obesity. Our earlier study showed that IES with one pair of electrodes accelerated intestinal transit and decreased fat absorption in a segment of the jejunum in anesthetized rats. The aims of this study were to assess the effects of IES on whole gut transit and fat absorption in conscious rats, to examine the effects of multi-pairs IES and to explore the cholinergic mechanism behind the effects of IES.

METHODS

Thirty-eight male rats implanted with serosal electrodes were randomized into five groups: control without IES, two- or three-pairs IES with short pulses, atropine and atropine plus IES. The whole gut transit and fat remained and emptied from the gut were analyzed after continuous 2-h IES.

RESULTS

Two- and three-pairs IES significantly accelerated phenol red (PR, marker used for transit) excretion (analysis of variance (ANOVA), P<0.001). No significant difference was found between two- and three-pairs IES. Two-pairs IES significantly increased the excretion of fat (P<0.05). Atropine significantly blocked the accelerated transit induced by IES (ANOVA, P<0.001). Correlation was found between the percentage of PR and fat retained in the whole gut (r=0.497, P<0.01).

CONCLUSIONS

IES accelerates whole gut transit and promotes fat excrement in conscious rats, and these effects are mediated through the cholinergic nerves. These findings are in support of the concept that IES may be a promising treatment option for obesity.