Effects of postgastric 13C-acetate processing on measurement of gastric emptying: a systematic investigation in health

Abstract Uniform postgastric processing of the gastric emptying (GE) marker ¹³C‐acetate (Ac) is an unverified assumption behind its widespread application to measure GE. This study assessed the postgastric processing of Ac administered by intraduodenal (i.d.) infusion simulating different physiological conditions. ¹³CO₂ in breath was assessed in three groups of six volunteers after i.d. administration of A: Different caloric densities (0.75/1.5/3 kcal min^?1) in a 200 mL meal at constant 1 mg Ac min^?1 simulating a physiological range of nutrient delivery rates; B: different tracer delivery rates (0.5/1.0/2.5 mg Ac min^?1) simulating delayed, normal and increased GE; C1: a 500 mL meal resulting in same marker and caloric delivery compared to protocol A; C2: 50 mL water bolus injections of 12.5/25/50/100 mg Ac and C3 bolus injections of 50 mg Ac in 50/100/200 mL water in randomized order. A: ¹³CO₂ excretion was independent of caloric load (P = 0.59). B: The dynamic of ¹³CO₂ excretion was modulated by tracer elimination which was in turn dependent on the speed of tracer delivery, i.e. with faster deliveries resulting in lower ¹³CO₂ recovery during infusion (P < 0.001). C: Increasing Ac doses resulted in decreased ¹³CO₂ recovery (P < 0.001) over the first hour. ¹³CO₂ recovery kinetics was independent of the volume delivered. This study shows ¹³C‐acetate absorption and metabolism is independent of the volume and caloric delivery of test meals. The ‘lag’ in estimates of GE derived from ¹³CO₂ breath tests is due to a postgastric, dose‐dependent delay to ¹³CO₂ elimination. This can be corrected for in analytical derivations of GE parameters based on ¹³C‐acetate breath test measurements.     

The 13C-octanoic acid breath test: validation of a new noninvasive method of measuring gastric emptying in rats

Abstract Currently available rat models for measuring gastric emptying are hampered by the necessity to kill the animals at the end of each experiment, which makes repetitive testing impossible. We have developed and validated a noninvasive test model, adapted from the¹³C‐octanoic breath test in humans, for repetitive measurements of gastric emptying in rats. Male Wistar rats were trained on a fixed protocol to eat a piece of pancake doped with 1 μg¹³C‐octanoic acid after 12 h fasting, and to stay thereafter in cylindrical glass cages. Breath tests were performed by a fully automated system of computer‐guided switching valves, which collected consecutive breath samples. All breath samples were analysed by gas chromatography and isotope mass spectrometry. The area under the curve (AUC) from the cumulative¹³CO₂excretion from 0 to 6 h was determined by the trapezium method to calculate the gastric half‐emptying times (t½). Inter‐day variability was determined. The effect of subcutaneous or intraperitoneal injection of saline was studied. The test was further validated for pharmacological interventions by oral administration of cisapride and parenteral administration of atropine, to induce, respectively. acceleration and delay of gastric emptying. Mean gastric emptying times ± SD of 24 rats were 119.3 ± 28.2 min, 138.7 ± 26.0 min, and 124.5 ± 30.9 min on three different test days. The mean coefficient of variation of three repeated measurements in the same 24 rats was 17.5%. No significant differences were observed after subcutaneous or intraperitoneal injection of saline. In a second test series of eight rats, cisapride significantly accelerated gastric emptying (mean t½ 112.7 ± 33.1 min, P < 0.05), while atropine caused a significant delay (mean t½ 205.9 ± 24.9 min, P < 0.05) when compared to control test results (mean t½ 140.7 ± 16.7 min) in the same rats. We validated the¹³C‐octanoic breath test to study gastric emptying in rats. This test method obviates the necessity to kill laboratory animals and allows repetitive measurements of gastric emptying to study its physiology or pathophysiology as well as the effect of pharmacological agents.     

Indirect vs direct assessment of gastric emptying: A randomized crossover trial comparing C‐isotope breath analysis and MRI

Background

Indirect methods to assess gastric emptying (GE), such as ¹³C breath tests (BT), are commonly used. However, BT usually use a sampling time of 4+ hours. The current study aims to assess the validity of BT for four liquid meals differing in physicochemical properties. To this aim, we compared them to MRI GE‐measurements.

Methods

Fifteen healthy males (age 22.6 ± 2.4 years, BMI 22.6 ± 1.8 kg/m²) participated in a randomized 2 × 2 crossover experiment. Test foods were liquid meals, which were either thin/thick and 100/500 kcal, labeled with 100 mg of ¹³C‐octanoate. GE was measured with MRI and assessed by ¹³C recovery from breath. Participants were scanned every 10 minutes and at six time points breath samples were collected up to t = 90 minutes. Two curves were fitted to the data to estimate emptying halftime (t_{50 Ghoos} and t_{50 Bluck}). T₅₀ times were ranked per participant and compared between methods.

Key Results

On average, MRI and BT showed similar t₅₀ rankings for the four liquid meals. In comparison to MRI, t_{50 Ghoos} overestimated, while t_{50 Bluck} underestimated GE time_. Moreover, more viscous foods were overestimated. In most participants individual t₅₀ time rankings differed significantly between methods.

Conclusions & Inferences

BT can assess relative emptying differences on group level and collecting breath data for 90 minutes constitutes a lower burden for participants and the research facility. However, BT has severe shortcomings compared to MRI for individual GE assessment. Notably, food matrix effects should be considered when interpreting the results of BT.     

Two novel laboratory tests facilitating diagnosis of glycine encephalopathy (nonketotic hyperglycinemia)

Glycine encephalopathy (GE), also known as non-ketotic hyperglycinemia, is a life-threatening metabolic disease caused by inherited deficiency of the glycine cleavage system (GCS). GE is characterized by accumulation of a large amount of glycine in serum and cerebrospinal fluids. In typical cases with GE, coma, profound hypotonia, and intractable seizures develop within several days of life. Patients with atypical symptoms may have delayed or missed diagnosis because of non-specific symptoms. It is sometimes problematic to confirm the diagnosis of GE since it requires either invasive liver biopsy for measurement of GCS activity or exhaustive mutational screening of three GCS genes, GLDC, AMT, and GCSH. We herein describe two novel laboratory tests for diagnosis of GE, [1-¹³C]glycine breath test and the multiplex ligation-dependent probe amplification (MLPA) for detection of large deletions in GLDC. The [1-¹³C]glycine breath test has been developed for noninvasive enzymatic diagnosis of GE. Because the GCS generates CO₂ by degradation of glycine, the GCS activity could be evaluated in vivo by measurement of exhaled ¹³CO₂ after administration of a stable isotope, [1-¹³C]glycine. The MLPA has been developed for improvement in mutation detection rate in GE: Deletions involving multiple GDLC exons are prevalent among GE patients, but cannot be detected by the exon-sequencing analysis. Two novel diagnosis methods would facilitate diagnosis of hyperglycinemic patients as having GE.     

Characterization of gastric volume responses and liquid emptying in functional dyspepsia and health by MRI or barostat and simultaneous 13C-acetate breath test

Abstract The assessment of gastric accommodation and emptying by different methodologies provides inconsistent results. We aimed to compare magnetic resonance imaging (MRI), barostat and ¹³C‐acetate breath test (BT) for the assessment of gastric volume responses and emptying in healthy controls (HC) and patients with functional dyspepsia (FD). Eight HC and eight FD patients underwent: (i) continuous BT with simultaneous MRI in the upright position after ingestion of isocaloric, 300 kcal, 200 and 800 mL meals, both labelled with 100 mg of ¹³C‐acetate; and (ii) BT with gastric barostat after ingestion of the 200 mL meal. MRI measured total gastric volume and gastric content volume (GCV) at baseline, after filling and during emptying. Meal emptying half‐times (T½) for MRI and BT were calculated (mean ± SD). We found: (i) Initial GCV was lower in FD than in HC (762 ± 22 vs 810 ± 52 mL, P < 0.04) after the 800 mL meal but not the 200 mL meal. T½_MRI was shorter for the 800 mL than the 200 mL meal (P < 0.001), but similar in HC and FD (200 mL: HC 117 ± 30 min vs FD 138 ± 42 min, ns; 800 mL: HC 71 ± 16 min vs FD 78 ± 27 min, ns). In contrast, T½_BT was similar between meals and groups (200 mL: HC 111 ± 11 min vs FD 116 ± 19 min; 800 mL: HC 114 ± 14 min vs FD: 113 ± 17 min). (ii) Barostat measurements showed similar postprandial volume increases between groups. We conclude that direct measurements by MRI provide a sensitive, non‐invasive assessment of gastric accommodation and emptying after a meal. In contrast to MRI, BT did not detect faster emptying of high‐volume compared to low‐volume liquid nutrient meals in HC or FD.     

Is there a difference in gastric emptying between Parkinson’s disease patients under long-term <Emphasis Type="SmallCaps">l</Emphasis>-dopa therapy with and without motor fluctuations? An analysis using the <Superscript>13</Superscript>C-acetate breath test

The mechanism underlying the motor fluctuations that develop after long-term l-dopa therapy is not fully known. It has been speculated that malabsorption of l-dopa from the small intestine occurs. It was reported that gastric retention in Parkinson’s disease (PD) patients with motor fluctuations is increased as compared with that in PD without fluctuations. Because l-dopa therapy may worsen the symptoms of delayed gastric emptying (GE), it was not clear whether the delayed GE of PD patients with motor fluctuation was affected by l-dopa therapy. We assessed GE in PD patients with and without motor fluctuations. We investigated GE in 40 patients with PD under long-term l-dopa therapy, 20 fluctuators with “delayed-on” and “no-on” phenomena, 20 nonfluctuators, and 20 healthy volunteers. GE was examined by the ¹³C-acetate breath test (¹³C-ABT) [the half emptying time (HET), the peak time of the ¹³C-%-dose-excess curve (T _max)], with expirations collected for 4 h after a test meal and analyzed for ¹³CO₂ using an infrared (IR) spectrophotometer. The T _max of GE as assessed using the ¹³C-ABT was significantly delayed in all PD patients as compared with controls (P = 0.002). The HET was significantly delayed in all PD patients as compared with controls (P < 0.001). The T _max and HET were not significantly delayed in PD patients with motor fluctuations as compared with PD patients without motor fluctuations. These results demonstrated that GE is commonly delayed in PD patients with long-term l-dopa therapy. Delayed GE does not differ between PD patients with and without motor fluctuations. This finding demonstrated that the motor fluctuation in PD may not be influenced by GE.     

Gastric secretion does not affect the reliability of the 13C‐acetate breath test: A validation of the 13C‐acetate breath test by magnetic resonance imaging

Background ¹³C‐Acetate labeled meals are widely used to determine meal emptying by means of analyzing resulting ¹³CO₂ exhalation dynamics. In contrast to the underlying metabolic processes, only few ¹³C breath test meal emptying studies have focused on intragastric processes that may alter ¹³CO₂ exhalation. This work assessed the effect of enhanced gastric secretion on the reliability of half emptying time (t50) measurements by ¹³C‐acetate breath test. Methods ¹³CO₂ exhalation data were acquired in a double‐blind, randomized, cross‐over gastric emptying study in 12 healthy volunteers receiving either pentagastrin or placebo intravenously. The standard method proposed by Ghoos et al. was applied to calculate t50 (t50_Ghoos) from ¹³CO₂ exhalation data, which were compared and tested for agreement to meal half emptying times (t50_MV) from concurrent recorded MRI (magnetic resonance imaging) volume data. In addition, the accumulated gastric secretion volumes during infusion as detected by MRI (AUC_SV₆₀) were correlated with the corresponding cumulative percent ¹³C doses recovered (cPDR₆₀). Key Results t50_Ghoos and t50_MV showed a linear correlation with a slope of 1.1 ± 0.3 (r² = 0.67), however, a positive offset of 136 min for t50_Ghoos. No correlation was detected between AUC_SV₆₀ and cPDR₆₀ (r² = 0.11). Both, breath test and MRI, revealed a prolonged t50 under pentagastrin infusion with median differences in t50_Ghoos of 45[28–84] min (P = 0.002) and t50_MV of 39[28–52] min (P = 0.002). Conclusions & Inferences This study suggests that ¹³CO₂ exhalation after ingestion of a ¹³C‐labeled liquid test meal is not affected by stimulated gastric secretion, but is rather reflecting the dynamics of meal or caloric emptying from the stomach.     

Comprehensive assessment of gastric emptying with a stable isotope breath test

Background The [¹³C]‐Spirulina platensis gastric emptying breath test (GEBT) with five samples is accurate relative to scintigraphy. This study was primarily designed to further validate this GEBT using a slightly different process for incorporating [¹³C] in Spirulina and to evaluate the utility of additional samples for assessing early gastric emptying. Methods After a 223 kcal, test meal labeled with ^99mTc and [¹³C]‐S. platensis, scintigraphic images, and five breath samples (45, 90, 120, 180, and 240 min, GEBT5) were collected in 14 controls (Part A). In Part B, nine breath samples were collected at 15, 30, 45, 60, 90, 120, 150, 180, and 240 min (GEBT9) in 30 subjects (15 controls, 15 dyspepsia). Using correlation between [¹³C] breath excretion and scintigraphic emptying, lag time (t₁₀, time for 10% emptying), emptying at 30 min (GE₃₀), and half time (t₅₀) were estimated for GEBT5 (Parts A and B) and GEBT9 (Part B). Key Results Half time values for scintigraphy, GEBT5, and GEBT9 were highly concordant. t₁₀ by GEBT9 (90%CI, 6–15 min) was more strongly correlated [CCC 0.80 (95% CI, 0.63–0.90)] with scintigraphy (90% CI, 5–12 min), than GEBT5 [10–19 min, CCC 0.73 (95% CI, 0.54–0.85)]. The correlation between estimated values (GEBT9) and linearly interpolated values (GEBT5) was closer at 60 [CCC 0.95 (95% CI, 0.91–0.97)] than 30 min [CCC 0.81 (95% CI, 0.71–0.89)]. Conclusions & Inferences The [¹³C]‐S. platensis GEBT can accurately measure GE. While 5‐ and 9‐samples are equally accurate for measuring t₅₀, GEBT9 provides a more comprehensive assessment of early GE (t₁₀ and GE₃₀).     

Performance characteristics of scintigraphic measurement of gastric emptying of solids in healthy participants

Background Gastric emptying (GE) is measured in pharmacodynamic and diagnostic studies. Our aim was to assess inter‐ and intra‐subject coefficients of variation (COV) of scintigraphic GE measurements in healthy subjects, and associations of GE with gender and body mass index (BMI). Methods Data from participants with scintigraphic measurements of gastric emptying of solids were analyzed. Primary endpoints were gastric emptying T_1/2 (GE T_1/2) and GE at 1, 2, 3, and 4 h. Key Results The patient cohort consisted of 105 males and 214 females; at least two studies were performed in 47 subjects [16 males (M), 32 females (F)]. Inter‐subject COV (COV_inter) for GE T_1/2 were similar in M and F: overall 24.5% (M 26.0%, F 22.5%); COV are predictably lowest for GE at 4 h (COV_inter 9.6%). COV_intra for T_1/2 and GE at 4 h were overall 23.8% and 12.6%, and were similar to COV_inter values. Gender (but not age or BMI) was significantly associated with GE T1/2 [P < 0.001, F 127.6 ± 28.7 (SD) min; M 109.9 ± 28.6 min] and with GE at 1 h and 2 h. Repeat GE T_1/2 values in 47 participants were significantly correlated (r = 0.459, P < 0.001) with median difference of ?6 min (mean ?1.6, range ?56 to 72 min). Bland–Altman plots showed Δ GE T_1/2 similarly distributed across mean GE T_1/2 100–155 min, and across studies conducted 90–600 days apart. Conclusions & Inferences Inter‐subject variations in scintigraphic GE results are only slightly higher than the intra‐subject measurements, which are also reproducible over time in healthy volunteers. Gender, but not BMI, is significantly associated with GE results.     

Comparison of calculations to estimate gastric emptying half‐time of solids in humans

Background Measuring solid gastric emptying (GE) at 4 h is used to identify gastroparesis. GE half‐time (GE T_1/2) is useful to assess overall and early GE. Aim To examine the validity of hourly imaging as a measurement of GE T_1/2 compared with estimates from more detailed imaging. Methods 155 human subjects (99 female, 56 male) underwent scintigraphic GE of a solid–liquid meal. We calculated the GE T_1/2 using linear interpolation based on a full set of abdominal images obtained over 4 h, and the GE T_1/2 based on images at 1, 2, 3, and 4 h after the meal with interpolation of data. Key Results Differences in GE T_1/2 values (entire set of scan times compared with just the hourly scans) were small [overall median (5th, 95th percentiles) = ?0.2[?7.5, 4.6] min] with slightly greater differences in males compared with females. The agreement between the two methods was very high [concordance correlation coefficient (CCC) (95% CI) = 0.993 (0.990, 0.995)] and a Bland–Altman plot indicated the variation in the results between the two methods did not change appreciably across the range of GE studied (within ±10 min for all but four subjects). Calculated GE T_1/2 values, omitting the 3‐h data from the hourly measurements, were associated with similar high accuracy overall and for fast GE, but were less accurate with slow GE. Conclusions & Inferences Results of GE T_1/2 solids, using hourly imaging over 4 h, are accurate in the range 75–235 min which reflects the typical range of GE of solids in health and disease.     

Is there a difference in gastric emptying between myotonic dystrophy type 1 patients with and without gastrointestinal symptoms?

Gastrointestinal symptoms are frequent complaints in patients with myotonic dystrophy type 1 (MyD1) and may be associated with reduced gastrointestinal motility caused by smooth muscle dysfunction. Although previous studies have found delayed gastric emptying (GE) in MyD1 patients, the relationship between GE and symptoms has been unclear. We investigated GE in 23 MyD1 patients and 20 healthy volunteers using the ¹³C-acetate breath test. The MyD1 patients were divided into two groups: those with gastrointestinal symptoms (n = 9) and those without gastrointestinal symptoms (n = 14). The GE function was estimated using the ¹³C-acetate breath test as half-emptying time (HET) and peak time of the ¹³C-%-dose-excess curve (T _max). GE (HET and T _max) was more significantly delayed in patients with MyD1 than in the controls. The GE in MyD1 patients with gastrointestinal symptoms was significantly delayed compared to those without gastrointestinal symptoms. The GE in MyD1 patients with gastrointestinal symptoms was more significantly delayed than in the controls. The GE was significantly delayed in MyD1 patients with gastrointestinal symptoms for >5 years as compared to those with the disease for <5 years, while GE of MyD1 patients without gastrointestinal symptoms did not correlate with the duration of the disease. The GE in MyD1 patients did not correlate with the muscular disability rating scale. These findings suggest that impairment of GE evolves over time and that the progression of delayed GE and skeletal muscle impairment are independent. Smooth muscle impairment may be affected at an earlier stage in MyD1.     

The effect of gastric secretion on gastric physiology and emptying in the fasted and fed state assessed by magnetic resonance imaging

Abstract Conventional measurement of gastric secretion is invasive and cannot assess the intra‐gastric distribution of gastric contents or the effects of secretion on gastric function. This study assessed the effect of gastric secretion on gastric volume responses and emptying (GE) using a validated fast T₁ mapping magnetic resonance imaging (MRI) technique. Twelve healthy participants were studied in the fasted state and after 200 kcal Gadolinium‐DOTA labelled glucose meal during intravenous infusion of pentagastrin or placebo in double‐blind, randomized order. Total gastric volume (TGV) and gastric content volume (GCV) was assessed by MRI volume scans and secretion by fast T₁ mapping. Data was described by the κ‐coefficient (volume change after meal ingestion), by GE half time (T₅₀) and maximal GE rate (GER_max) derived all from a GE model. Pentagastrin increased GCV and TGV compared to placebo [κ(GCV):1.6 ± 0.1 vs 0.6 ± 0.1; κ(TGV): 1.6 ± 0.1 vs 0.7 ± 0.1; P < 0.001]. T₁ maps revealed a secretion layer above the meal, the volume of which was associated with κ (R² = 83%, P < 0.001). TGV and GCV change were similar in both conditions (κ; P = ns). T₅₀ was higher for pentagastrin than for placebo (84 ± 7 vs 56 ± 4min, P < 0.001); however, GER_max was similar (5.9 ± 0.6 vs 4.9 ± 0.4 mL min^?1, P = ns). This study shows volume and distribution of gastric secretion can be quantified in‐vivo by non‐invasive MRI T₁ mapping. Increased GCV drove TGV accommodation without evidence of a direct effect of pentagastrin or excess acid on gastric function. Secretion increases GCV thus prolongs GE as assessed by T₅₀; however, GE rate is unchanged.     

A new gastric‐emptying mouse model based on in vivo non‐invasive bioluminescence imaging

Background Different techniques were used to assess gastric emptying (GE) in small animals; most of them require sophisticated equipment, animal sacrifice and are expensive. In the present investigation a simple, non‐invasive method based on bioluminescence imaging (BLI) is reported to study GE, using light‐emitting Escherichia coli cells as a marker of the gastric content. Methods A new thermostable red‐emitting luciferase was chosen as reporter gene to transform E. coli cells. Bioluminescent (BL) bacteria were administered to fasting mice, after a solid meal, and in response to different doses of metoclopramide (MET) and hyoscine butylbromide (HY). Bioluminescence imaging allowed to evaluate the real time 2D spatial and temporal distribution of bacteria along the gastrointestinal tract in animals and to calculate GE rate in basal conditions and following pharmacological stimulation. Key Results The administered BL bacteria were easily imaged and localized in the stomach and subsequently followed in the duodenum and upper intestine allowing to accurately calculate GE. Gastric emptying after the test meal was significantly slower (T_1/2 16 ± 3 min) than that obtained in fasting conditions (T_1/2 2 ± 1 min); administration of HY (1 mg kg⁻¹ b.w.) significantly (P < 0.05) increased T_1/2 that was delayed up to 25 ± 4 min; MET (1 mg kg⁻¹ b.w.) significantly (P < 0.05) accelerated T_1/2, that was achieved within 8 ± 2 min. Conclusion & Inferences The reported model is simple, inexpensive, reliable, sensitive and accurate; it can detect both acceleration and slowdown of GE. The model is useful in the investigation of new drug‐induced alterations of gastric motility allowing to reduce the number of experimental animals.     

Gastric emptying of hexose sugars: role of osmolality,molecular structure and the CCK1 receptor

Background It is widely reported that hexose sugars slow gastric emptying (GE) via osmoreceptor stimulation but this remains uncertain. We evaluated the effects of a panel of hexoses of differing molecular structure, assessing the effects of osmolality, intra‐individual reproducibility and the role of the CCK₁ receptor, in the regulation of GE by hexoses. Methods Thirty one healthy non‐obese male and female subjects were studied in a series of protocols, using a ¹³C‐acetate breath test to evaluate GE of varying concentrations of glucose, galactose, fructose and tagatose, with water, NaCl and lactulose as controls. GE was further evaluated following the administration of a CCK₁ receptor antagonist. Three subjects underwent repeated studies to evaluate intra‐individual reproducibility. Key Results At 250 mOsmol, a hexose‐specific effect was apparent: tagatose slowed GE more potently than water, glucose and fructose (P < 0.05). Fructose (P < 0.05) also slowed GE, but with substantial inter‐, but not intra‐, individual differences. As osmolality increased further the hexose‐specific differences were lost. At 500 mOsmol, all hexoses slowed GE compared with water (P < 0.05), whereas lactulose and saline did not. The slowing of GE by hexose sugars appeared to be CCK₁ receptor‐dependent. Conclusions & Inferences The effects of hexose sugars on GE appear related to their molecular structure rather than osmolality per se, and are, at least in part, CCK₁ receptor‐dependent.     

A phase 2a,randomized, double‐blind 28‐day study of TZP‐102 a ghrelin receptor agonist for diabetic gastroparesis

Background Gastroparesis causes significant morbidity and treatment options are limited. TZP‐102 a novel, macrocyclic, selective, oral ghrelin receptor agonist, was evaluated in a randomized, double‐blind, placebo‐controlled trial in patients with diabetic gastroparesis. Methods A total of 92 outpatients were randomized to once‐daily administrations of 10‐mg (n = 22), 20‐mg (n = 21), 40‐mg (n = 23) TZP‐102 or placebo (n = 26). The primary endpoint was the change from baseline in gastric half‐emptying time (T_½) utilizing ¹³C‐breath test methodology and secondary endpoints included symptom improvement using patient‐reported gastroparesis symptom scores (PAGI‐SYM questionnaire) and patient and physician overall treatment evaluations (OTE). Key Results Gastric T½ changes were not statistically significant between TZP‐102 and placebo after 28 days of treatment at any dose. Clinical improvements (?1.0 to ?1.4 point mean decrease in symptom severity) occurred in the Gastroparesis Cardinal Symptom Index (GCSI) component of the PAGI‐SYM, which was significant vs placebo for all TZP‐102 doses combined. Improvements became evident after 1 week of treatment. Significantly, more patients given TZP‐102 (any dose) had a 50% reduction in baseline GCSI score (28.8%vs 7.7% placebo). Safety profiles were similar across groups. All TZP‐102 doses were well‐tolerated with no adverse cardiac, weight, or glucose control outcomes. Conclusions & Inferences TZP‐102 for 28 days, at doses of 10–40 mg once daily, was well‐tolerated and resulted in a reduction in symptoms of gastroparesis. The lack of correlation between symptom improvement and gastric emptying change is consistent with previous studies in diabetic gastroparesis, and emphasizes the value of patient‐defined outcomes in determining therapeutic benefit.     

Gastric emptying of enterally administered liquid meal in conscious rats and during sustained anaesthesia

Background Gastric motility studies are frequently conducted with anaesthetized animal models. Some studies on the same animal species have reported differences in vagal control of the stomach that could not be explained solely by slightly different experimental conditions. A possible limitation in the comparison between similar studies relates to the use of different anaesthetic agents. Furthermore, anaesthetic effects may also limit generalizations between mechanistic studies of gastric function and the gastric function of conscious animals. In the present study, we used the [¹³C]‐breath test following a liquid mixed‐nutrient test meal (Ensure^®, 1 ml) with the aim to investigate the rate of gastric emptying in animals that were either conscious or anaesthetized with either Inactin^® or urethane. Methods One week after determining the maximum ¹³CO₂ concentration, time to peak [¹³C] recovery and gastric half emptying time in control, conscious rats, we repeated the experiment in the same rats anaesthetized with Inactin^® or urethane. Key Results Our data show that Inactin^® anaesthesia prolonged the time to peak [¹³C] recovery but did not significantly reduce the maximum ¹³CO₂ concentration nor delay gastric half emptying time. Conversely, urethane anaesthesia resulted in a significant slowing of all parameters of gastric emptying as measured by the maximum ¹³CO₂ concentration, time to peak [¹³C] recovery and half emptying time. Conclusions & Inferences Our data indicate that Inactin® anaesthesia does not significantly affect gastric emptying while urethane anaesthesia profoundly impairs gastric emptying. We suggest that Inactin®, not urethane, is the more suitable anaesthetic for gastrointestinal research.     

Evaluation of dopamine D₂/₃ specific binding in the cerebellum for the positron emission tomography radiotracer [¹¹C]FLB 457: implications for measuring cortical dopamine release

In a recent positron emission tomography (PET) study, we demonstrated the ability to measure amphetamine‐induced dopamine (DA) release in the human cortex with the DA D_2/3 radioligand [¹¹C]FLB 457. As previous studies in animals have shown that a relatively high fraction of the [¹¹C]FLB 457 signal in the cerebellum represents specific binding to D_2/3 receptors, there was concern that the use of the cerebellum as a measure of nonspecific binding (i.e., reference region) to derive [¹¹C]FLB 457 binding potential (BP) (BP_ND) would bias cortical DA release measurements. Thus, we evaluated the fractional contribution of specific binding to D_2/3 receptors in the human cerebellum for [¹¹C]FLB 457. Six healthy human subjects (5M/1F) were studied twice with [¹¹C]FLB 457, once at baseline and again following a single oral dose of 15 mg of aripiprazole, a D_2/3 partial agonist. [¹¹C]FLB 457 distribution volume (V_T) was estimated using kinetic analysis in the cortical regions of interest and potential reference regions. The change in [¹¹C]FLB 457 V_T following aripiprazole ranged from ?33 to ?42% in the cortical regions of interest (ROIs). The aripiprazole‐induced change in [¹¹C]FLB 457 V_T in three potential reference regions suggests significant specific binding the cerebellum (CER, –17 ± 12%), but not pons (PON, –10 ± 10%) and centrum semiovale (CESVL, –3 ± 12%). Nevertheless, a reanalysis of the published [¹¹C]FLB 457 test–retest and amphetamine studies suggests that the use of the PON V_T and CESVL V_T as an estimate of nonspecific binding to derive [¹¹C]FLB 457 BP_ND in DA release studies is unlikely to be successful because it leads to less reproducible outcome measures, which in turn diminishes the ability to measure DA release in the cortex. D_2/3 blocking studies with aripiprazole and [¹¹C]FLB 457 suggest specific binding to D_2/3 receptors in the cerebellum. These data also suggest that the contribution of specific binding to D_2/3 receptors in the cerebellum is lower than that in the cortical ROIs and that CER V_T is mostly representative of nonspecific binding. Nevertheless, caution is advised when using reference tissue methods that rely solely on the cerebellum signal as an input function to quantify [¹¹C]FLB 457 BP_ND. Synapse, 2011. © 2011 Wiley‐Liss, Inc.     

Effect of lateral positioning on gastroesophageal reflux (GER) and underlying mechanisms in GER disease (GERD) patients and healthy controls

Background Posture has been shown to influence the number of transient lower esophageal sphincter relaxation (TLESRs) and gastroesophageal reflux (GER), however, the physiology explaining the influence of right lateral position (RLP), and left lateral position (LLP) is not clear. The aim of this study was to determine the influence of RLP and LLP on TLESRs and GERD after a meal in GER disease (GERD) patients and healthy controls (HC) while monitoring gastric distension and emptying. Methods Ten GERD patients and 10 HC were studied for 90 min (30 min test meal infusion, 30 min postprandial in either RLP or LLP (randomly assigned) and 30 min in alternate position). The study was repeated on a separate day in reverse position order. TLESRs, GER, and gastric emptying rate were recorded using manometry, multichannel intraluminal impedance, and ¹³C‐octanoate breath tests. Gastric distension was visualized by five serial gastric volume scintigraphy scans during the first 30 min. Key Results Gastroesophageal reflux, (GER) disease patients had increased numbers of TLESRs in RLP compared to LLP in the first postprandial hour [5 (4–14) and 4.5 (2–6), respectively, P = 0.046] whereas the number of TLESRs was not different in RLP and LLP [4 (2–4) and 4 (3–6), respectively, P = 0.7] in HC. Numbers of GER increased similar to TLESRs in GERD patients. In GERD patients, gastric emptying reached peak ¹³CO₂ excretion faster and proximal gastric distension was more pronounced. Conclusions & Inferences In GERD patients, TLESRs, GER, distension of proximal stomach, and gastric emptying are increased in RLP compared to LLP. This effect is not seen in HC.     

Optimizing analysis of stable isotope breath tests to estimate gastric emptying of solids

Abstract  Breath tests (BT) using ¹³C–substrates have been proposed for the measurement of gastric emptying (GE). The mathematical analysis of the breath ¹³CO₂ excretion that most accurately predicts GE t _1/2 from simultaneous scintigraphy is unresolved. To compare five mathematical methods to estimate GE t _1/2 by BT with t _1/2 from simultaneous scintigraphy. Data acquired from a dual-labelled solid–liquid meal containing ^99mTc sulphur colloid and ¹³C- Spirulina platensis from 57 healthy volunteers were used to compare four mathematical methods reported in the literature [Ghoos method; generalized linear regression (Viramontes); linear regression (Szarka); Wagner–Nelson method] and the total cumulative breath ¹³CO₂ excretion with ≥12 breath samples collected over at least 4 h. The concordance correlation coefficient (CCC) for the t _1/2 results obtained with each method using BT data was compared with the results obtained with scintigraphy. The linear regression and generalized linear regression methods used five samples at 45, 90, 120, 150 and 180 min. All methods, except for the Wagner–Nelson method, resulted in mean GE t _1/2 that approximated t _1/2 obtained with scintigraphy. The highest CCC was observed with the linear regression method. Simple cumulative excretion of breath ¹³CO₂ provides a better CCC than the Ghoos method. The linear regression and generalized linear regression methods (which also require relatively few breath samples) provide the most accurate analyses of breath ¹³CO₂ excretion in stable isotope GEBT.     

Evaluation of (‐)‐[18F]Flubatine‐specific binding: Implications for reference region approaches

We aimed to characterize changes in binding of (‐)‐[¹⁸F]Flubatine to α₄β₂*‐nicotinic acetylcholine receptors (α₄β₂*‐nAChRs) during a tobacco cigarette smoking challenge. Displacement of (‐)‐[¹⁸F]Flubatine throughout the brain was quantified as change in (‐)‐[¹⁸F]Flubatine distribution volume (V_T), with particular emphasis on regions with low V_T. Three tobacco smokers were imaged with positron emission tomography (PET) during a 210 min bolus‐plus‐constant infusion of (‐)‐[¹⁸F]Flubatine. A tobacco cigarette was smoked in the PET scanner ～125 min after the start of (‐)‐[¹⁸F]Flubatine injection. Equilibrium analysis was used to estimate V_T at baseline (90‐120 min) and after cigarette challenge (180‐210 min), at the time of greatest receptor occupancy by nicotine. Smoking reduced V_T by 21 ± 9% (average ±SD) in corpus callosum, 17 ± 9% in frontal cortex, 36 ± 11% in cerebellum, and 22 ± 10% in putamen. The finding of displaceable (‐)‐[¹⁸F]Flubatine binding throughout the brain is an important consideration for reference region‐based quantification approaches with this tracer. We observed displacement of (‐)‐[¹⁸F]Flubatine binding to α₄β₂*‐nicotinic acetylcholine receptors in corpus callosum by a tobacco cigarette challenge. We conclude that reference region approaches utilizing corpus callosum should first perform careful characterization of displaceable (‐)‐[¹⁸F]Flubatine binding and nondisplaceable kinetics in this putative reference region.