Electrogenic glucose absorption in untreated and treated coeliac disease

Celiac Disease and Pregnancy Outcomes in Patients with Gestational Diabetes Mellitus

AIM

Gestational diabetes mellitus (GDM) and celiac disease, if not diagnosed and properly treated, are associated with adverse outcomes of pregnancy. The aim of our study was to examine pregnancies complicated by GDM in celiac and nonceliac women in terms of their metabolic parameters and maternal and fetal outcomes.

METHODS

The study involved 60 women with GDM, 20 with and 40 without celiac disease. Maternal clinical and metabolic parameters (glucose and insulin levels in the oral glucose tolerance test (OGTT), fasting plasma glucose, HbA1c, lipid profile, prepregnancy BMI, gestational weight gain, and chronic diseases), pregnancy outcomes (gestational hypertension, pre-eclampsia, eclampsia, time, and mode of delivery), and fetal parameters (weight and length at birth, and neonatal complications) were recorded.

RESULTS

The two groups did not differ significantly in maternal parameters other than blood glucose levels at 120' in the diagnostic OGTT (141.2 ± 35.2 vs 161.2 ± 35.4, mg/dl, p=0.047), prepartum cLDL (127.2 ± 43.5 vs 179.6 ± 31.7 mg/dl, p ≤ 0.001), and total cholesterol (229.0 ± 45.9 vs 292.5 ± 42.1 mg/dl, p ≤ 0.001), which were significantly lower in celiac women than in nonceliac controls. Children born from celiac women had a significantly higher birth weight (3458.1 ± 409.8 vs 3209.0 ± 432.7 g, p=0.044) and ponderal index (2.89 ± 0.32 vs 2.66 ± 0.25 g/cm3, p=0.006) and were more likely to be large for gestational age (27.8% vs 2.5%, p=0.012). Analyzing the composition of the celiac and nonceliac women's diet showed that, for the same amount of kilocalories, the gluten-free diet was associated with a slight increase in the amount of carbohydrates (49.75% vs 48.54%) and a reduction in the amount of protein (21.10% vs 23.31%) and especially of fiber (9.84% vs 12.71%).

CONCLUSIONS

Celiac women with GDM have much the same pregnancy outcomes as nonceliac women with GDM, except for fetal overgrowth. Gluten-free food, being richer in carbohydrates and less rich in fiber and protein, could have a role in fetal growth in celiac women.

Appetite and Gastrointestinal Hormone Response to a Gluten-Free Meal in Patients with Coeliac Disease

Coeliac disease (CeD) is an immune-mediated inflammatory enteropathy triggered by the ingestion of gluten in genetically susceptible individuals. Gastrointestinal (GI) hormone response related to appetite and glucose metabolism is still under-investigated in patients with CeD. This study aimed at shedding light on the appetite sensations, glycaemia and hormone response induced by a complex meal in patients with coeliac disease. Twenty-two women with CeD, nine at the diagnosis (CeDD) and thirteen under a gluten-free diet (CeDGF), and ten healthy subjects (HS) were enrolled in a single day intervention study. All subjects consumed a test meal, recorded their appetite sensations, and blood was collected over three hours after meal consumption. The study found a lower decrease in hunger in CeDD compared to CeDGF and HS after meal intake. Data showed no difference of fullness and satiety between the groups. CeDD had lower insulin and glucose-dependent insulinotropic polypeptide (GIP) than CeDGF and HS. Both CeDD and CeDGF experienced a lower post-prandial response of glucose than HS. Data suggested that patients with CeD have an impaired glucose absorption after more than 12 months of gluten-free diet. Postprandial GIP may play a significant role in appetite cues and insulin response to a complex meal.

Greater postprandial glucose excursions and inadequate nutrient intake in youth with type 1 diabetes and celiac disease

The gluten free diet (GFD) has a high glycemic index and low-fiber content, which potentially influences glycemic excursions in type 1 diabetes (T1D) and celiac disease (CD). Participants in this case-control study of youth with T1D+CD (n = 10) and T1D only (n = 7) wore blinded continuous glucose monitoring systems for six days. Blood glucose levels (BGLs) were compared between groups for each meal, including pre-meal, peak, 2-hour postprandial and time-to-peak. Participants consumed a test-breakfast of GF cereal and milk for three days and kept weighed food diaries; nutrient intake was analyzed and compared to national recommendations. Youth with T1D+CD had shorter time-to-peak BGL (77 vs 89 mins, P = 0.03), higher peak (9.3 vs 7.3 mmol/L, P = 0.001) and higher postprandial BGLs than T1D (8.4 vs 7.0 mmol/L, P = 0.01), despite similar pre-meal BGLs (9.2 vs 8.6 mmol/L, P = 0.28). Regarding test breakfast, greater pre and post-meal BGL difference correlated with longer CD duration (R = 0.53, P = 0.01). Total energy and macronutrient intake didn’t differ between groups; however the majority of participants collectively had inadequate intake of calcium (76%), folate (71%) and fiber (53%), with excessive saturated fat (12%) and sodium (>2,000 mg/day). The GFD is associated with greater glycemic excursions and inadequate nutritional intake in youth with T1D+CD. Clinical management should address both glycemic variability and dietary quality.

Solute transporters and aquaporins are impaired in celiac disease

BACKGROUND INFORMATION

Celiac disease is a chronic inflammatory disorder of the small bowel induced in genetically susceptible subjects by gluten ingestion. Diarrhoea, weight loss and malabsorption represent the major clinical presentation of the disease. Here we examined the possible alteration in the expression and localization of water channels [AQPs (aquaporins)] and some solute transporters in duodenal mucosa of celiac disease patients. Duodenal biopsies from untreated celiacs, treated celiacs, healthy controls and disease controls were considered in the present study. The expressions of some AQPs and transporter mRNAs in human duodenal biopsies were determined by semi-quantitative RT-PCR (reverse transcription PCR) and real-time RT-PCR. The localization of AQPs 3, 7 and 10 and of SGLT1 (Na+/glucose co-transporter 1), PEPT1 (H+/oligopeptide transporter 1) and NHE3 (Na+/H+ exchanger 3) was evaluated by immunohistochemistry.

RESULTS

AQPs 3, 7, 10 and 11, SGLT, PEPT and NHE, CFTR (cystic fibrosis transmembrane conductance regulator) and NKCC (Na-K-2Cl co-transporter) mRNAs were expressed in duodenal biopsies of healthy controls, treated celiac patients and disease controls. The expression of transcripts was virtually absent in duodenal biopsies of untreated celiac disease patients except for CFTR and NKCC. In healthy controls, immunohistochemistry revealed a labelling in the apical membrane of surface epithelial cells of the duodenum. The immunolabelling was heavily reduced or absent in untreated celiac patients, while it was normal in patients consuming a gluten-free diet for at least 12 months.

CONCLUSIONS

Our results indicate that the main routes for water and solute absorption are deficient in celiac disease and may play a role in the onset of malabsorption symptoms.

Abnormal jejunal potential difference in cystic fibrosis

Transmucosal potential difference (PD) and intraluminal pressure were recorded from the same jejunal site in 15 healthy adult controls and 4 adults with cystic fibrosis. In the controls, runs of contractions were associated with wave-like changes in PD with, during phase III-like activity, a mean peak amplitude of -9.7 mV. Although there were no obvious differences in motor patterns, wave-like changes in PD were absent in patients with cystic fibrosis. Intraluminal boluses of 4 mg pilocarpine, or 0.1 mg prostaglandin E2, caused changes of -4.6 mV and -4.5 mV, respectively, in controls; these responses were not seen in patients with cystic fibrosis. There were no significant differences in basal PD and PD changes caused by altered concentrations of infused saline or glucose between patients and controls.

Intestinal uptake of fatty acids and cholesterol in four animals species and man: role of unstirred water layer and bile salt micelle

The uptake (Jd) of fatty acids (FA), fatty alcohols (Alc) and cholesterol (C) into the jejunum of rats (R, Rattus norvegicus), rabbits (RAB, Oryctolagus cuniculus), guinea pigs (GB, Cavia porcellus), and hamsters (H, Mesocricetus auratus) was assessed in vitro. Using jejunal discs the Jd of Alc was H greater than R = GP greater than RAB, the Jd of FA was H-RAB greater than R greater than GP, but the Jd of C was R greater than H greater than RAB greater than GP. The Jd of FA was quantitatively and qualitatively different when using jejunal biopsies; in man the Jd of FA into biopsies was greater than in the other animal species, but there was no difference in Jd of FA into normal human jejunal biopsies and those showing severe abnormalities in villus architecture. There are marked species differences in the passive permeability properties of the jejunum and in the effective resistance of the overlying unstirred water layer, but these differences do not explain the species variations in the uptake of cholesterol.

Kinetic constants for intestinal transport of four monosaccharides determined under conditions of variable effective resistance of the unstirred water layer

Theoretical considerations have suggested that variations in the resistance of the unstirred water layer (UWL) have a profound effect on the kinetic constants of intestinal transport. In this study, a previously validated in vitro technique was employed to determine the unidirectional flux rate of glucose, galactose, 3-O-methyl glucose and fructose into the rabbit jejunum under carefully-defined conditions of stirring of the bulk phase known to yield different values for the effective resistance of the UWL. For each monosaccharide, uptake is much greater when the resistance of the UWL is low than when high. The maximal transport rate, Jd m, of glucose was half as large as the Jd m of galactose and 3-O-methyl glucose (3-O-MG), and was twice as great as the Jd m of fructose. The apparent affinity constant, Km * of glucose is less than that of fructose, which was lower than the Km * of galactose and 3-O-MG. The use of the Lineweaver-Burk double reciprocal plot is associated with an overestimation of both Jd m and Km *. This discrepancy between the true and apparent values of the kinetic constants is much greater for lower than for higher values of Jd m and Km *; variations in the resistance of the unstirred layer influences the magnitude and direction of the discrepancy. The apparent passive permeability coefficient is similar for each sugar, but because of the different values of Jd m, passive permeation contributes relatively more to the uptake of glucose and fructose than of galactose or 3-O-MG. Under conditions of high unstirred layer resistance, differences in uptake rates of the sugars are due to differences in their Jd m rather than their Km *. Kinetic analysis is compatible with the suggestion that the glucose carriers are predominantly near the tip of the villus, whereas those for galactose and 3-O-MG are located along the entire villus and the Km * of their carriers at the tip is lower than their Km * towards the base of the villus. It is proposed that there are multiple or heterogeneous intestinal carriers for glucose, galactose and 3-O-methyl glucose in the jejunum of the rabbit.

Transport kinetics of D-glucose in human small intestinal mucosa: rate constants in histologically normal and abnormal mucosal biopsies

Using D-glucose as the probe molecule, we analysed conditions which must be fulfilled in mucosal biopsy studies before the kinetic nature of the transport process can be established. Mucosal biopsies were obtained from the region of the ligament of Treitz from four healthy volunteers and from 47 patients: 29 of the 47 had histologically normal mucosa; seven had mild abnormalities; and 11 had moderate or severe ("flat") abnormalities in villus architecture. The rate of uptake of 40 mM glucose was constant only between 4 and 10 min, extrapolating through zero uptake at zero time with a constant adherent mucosal fluid volume. Incubation for shorter or longer periods was associated with over- or underestimation of the rate of uptake. Failure to use a nonabsorbable marker was also associated with overestimation of the rate of uptake. When biopsies were incubated for 6 min, a curvilinear relationship was observed between uptake rate and concentration. In biopsies with moderate and severe abnormalities, there was a marked reduction in the magnitude of the maximal transport rate and the apparent passive permeability coefficient, with little change in the magnitude of the apparent affinity constant. When human mucosal biopsies are used to study nutrient absorption, certain criteria must be fulfilled to establish valid rate constants and to make comparisons between normal and abnormal mucosa.

Unstirred water layer and age-dependent changes in rabbit jejunal D-glucose transport

The unidirectional flux of solutes into the intestinal mucosal cell is determined by passage through the microvillus membrane and the overlying unstirred water layer, UWL. An in vitro technique was employed to determine the effect of the UWL on glucose transport into the jejunum of suckling, mature, and old rabbits. When the resistance of UWL was high, the uptake from high concentrations of glucose increased as the animals grew older; this change with aging was not seen from low concentrations of glucose. When UWL resistance was minimized by stirring the bulk phase, similar amounts of glucose were absorbed from high doses, but uptake from low doses was greater in young than in old animals. Studies undertaken to determine the kinetic basis of these age-related changes showed that with increasing age i) the apparent passive permeability coefficient P of glucose fell, ii) the maximum transport rate Jdmax rose, and iii) the apparent affinity constant Km increased. These differences were not observed when the resistance of the UWL was high: P and Km were similar in suckling, mature, and old animals, and the increase in glucose uptake with age was due to the greater Jdmax. Thus the potential benefit of the high affinity, high permeability transport system of young animals may be obscured by high resistance of the UWL.

Limitations of the Eadie-Hofstee plot to estimate kinetic parameters of intestinal transport in the presence of an unstirred water layer

In the presence of an intestinal unstirred water layer, the relationship between substrate concentration (C1) and unidirectional flux (Jd) is not described by the equation for a rectangular hyperbole. Accordingly, transformations of the Michaelis-Menten equation may not necessarily be linear and may lead to serious errors in the estimation of the affinity constant (Km) and maximal transport rate (Jdm) of carrier-mediated processes. An equation has previously been derived which described Jd under conditions of varying effective thickness or surface area of the unstirred water layer, the free diffusion coefficient of the probe molecule, and the distribution of transport sites along the villus. These theoretical curves have been analyzed by using the Eadie-Hofstee transformation (Jd vs. Jd/C1) of the Michaelis-Menten equation. Use of this plot leads to serious discrepancies between the true and apparent affinity constants and between true and apparent maximal transport rates. These differences are further magnified by failure to correct for the contribution of passive permeation. The Eadie-Hofstee plot is of use, however, to infer certain qualitative characteristics of active transport processes, such as the variation in affinity constants and overlying resistance of the unstirred water layer at different sites along the villus and to predict the adequacy of the correction for the contribution of passive permeation.

The influence of gestational age and size on the absorption of D-xylose and D-glucose from the small intestine of the human neonate

D-Xylose absorption (using the one-hour blood levels) and active D-glucose absorption (calculated from changes in transmural electrical potential difference) have been measured after intraduodenal infusion of the appropriate sugar, in groups of neonates who were full-term or preterm, and who were in addition either appropriately sized for gestational age, or growth-retarded in utero. The one-hour D-xylose blood levels were significantly lower in preterm infants, and were even lower in the growth-retarded group. In follow-up studies D-xylose absorption rose in all groups of infants over the first three weeks of postnatal life but there was no sign of 'catch-up' in the results of the growth-retarded infants. In the studies of D-glucose absorption the theoretical kinetic parameters 'apparent P.D.max' (equivalent to Vmax) and 'apparent Km' were calculated. Normal full-term infants had values for both parameters that were approximately two-thirds of published adult values. Malnourished neonates had significantly lower P.D.max and apparent Km, and preterm infants had a lower P.D.max, than the values obtained in those infants who were full-term and appropriately grown.

Gut-hormone profile in coeliac disease

Patients with coeliac disease have a highly significant reduction in the release of secretin and gastric inhibitory polypeptide from the upper small intestine, but a greatly increased release of enteroglucagon, and also of neurotensin, from the lower part of the small intestine. The release of gastrin and pancreatic polypeptide, from the antrum and pancreas respectively, is, however, normal. Thus the pattern of hormone release reflects the location of the mucosal lesion. The gut-hormone profile may also help to characterise other gastrointestinal diseases.

Unstirred layer and kinetics of electrogenic glucose absorption in the human jejunum in situ

Using an electrical technique we estimated the thickness of the unstirred layer in the human jejunum during kinetic studies of electrogenic glucose absorption. The unstirred layer in seven healthy volunteers (632 +/- 24 mum: mean +/- SEM) was significantly thicker than in 10 patients with active coeliac disease (442 +/- 23 mum) but not significantly different in seven patients who had responded to treatment by gluten withdrawal (585 +/- 49 mum). There were similar differences in the values of ;Apparent Km' for electrogenic glucose absorption between healthy control subjects (36 +/- 6 mM) active coeliac patients (11 +/- 1 mM) and treated coeliac patients (31 +/- 5 mM). The changes in PDmax however, showed a different pattern. The PDmax in the active coeliac group (6.8 +/- 0.7 mV) was lower than in controls (7.6 +/- 0.6 mV) but not significantly so, while the PDmax in the treated coeliac group (10.6 +/- 0.9 mV) was significantly higher than in both the active coeliac and control groups. It should be noted that both operational kinetic parameters obtained in the present study are much lower than those obtained previously (Read et al., 1976b) because of the use of siphonage. Analysis of the results using a computer simulation indicates that the reduction in Apparent Km in active coeliac disease can be caused by the interaction of the decreased maximal absorption rate for glucose (Jmax) with the attenuated unstirred layer. In these circumstances it is not necessary to postulate any change in the affinity of the transport mechanism for glucose (;Real Km'). It is remarkable that the disease process produces an Apparent Km which is much closer to the Real Km than that found in health.

Electrical assessment of functional lactase activity in conscious man

Using an electrical technique for measuring transjejunal potential differences (PDs) in conscious man, we have estimated the electrogenic absorption of the hexoses liberated by hydrolysis of lactose which was infused into the jejunum of one normal control and 21 patients with diarrhoea. The results were compared with jejunal lactase levels determined from biopsy specimens taken from the recording site immediately after infusion. The PD evoked by 100 mM lactose was very significantly lower in patients with lactase levels below 4 units (lactase deficient) compared with subjects with normal lactase levels. There was also a significant correlation (r = 0.87, P less than 0.005) between the magnitude of the lactose potential (expressed as the ratio of the maximum glucose transfer potential) and the mucosal lactase level in the hypolactasic subjects but not in patients with normal lactase levels. Thus, in the subjects with lactase deficiency, the electrogenic transfer of hexose is clearly limited by the rate of lactose hydrolysis. Unlike other assessments of functional lactase activity, the electrical test provides a specific index of jejunal function and, moreover, can be adapted to investigate the possible disorders of small intestinal motility and secretion associated with hypolactasia.

Relationship between changes in intraluminal pressure and transmural potential difference in the human and canine jejunum in vivo

Recordings of transmural potential difference (PD) across the jejunum of conscious man in situ are characterised by spontaneous fluctuations of up to 10 mV. In 25 of 31 subjects (comprising seven normal controls and 24 patients under investigation for malabsorption, six of whom had coeliac disease) we observed a clear association between these fluctuations and changes in intraluminal pressure recorded at the same site. The most frequent PD changes were associated with type III pressure waves. These consisted predominantly of large waver (3-1 +/- 0-1 mV; mean +/- SEM, n = 317) which reached maximal amplitude approximately 45 seconds after the pressure peak and had a duration of 120 +/- 3 s, but also included less frequent spikes (0-5 +/- 0-1 mV; n = 110) concurrent with the pressure wave with a duration of 5 +/- 1 s. Although by recording at two sites in the jejunum 10 cm apart we were able to demonstrate that type III pressure waves appeared to be propagated aborally at a median rate of 60 cm per minute, the apparent rates of propagation of the corresponding PD waves were much more variable. The largest PD changes (7-8 +/- 0-4 mV; n = 19), lasting several minutes, were found in association with runs of type I waves (basic rhythm) superimposed on a type III wave. Both pressure and PD activities were suppressed by intramuscular propantheline bromide. Intraluminal pilocarpine caused a transient rise in PD not always accompanied by a change in pressure. Distention of the jejunum by rapid injection of a bolus of isotonic sodium chloride produced a delayed rise in the PD which could be prevented by prior administration of propantheline bromide. Experiments using Thirty-Vella loops of proximal jejunum in conscious dogs confirmed the effect of jejunal distension on the PD and also demonstrated that spontaneous retching is preceded by an increase in the PD. Consideration of these results in conjunction with data from other workers suggests the hypothesis that the larger spontaneous fluctuations in transmural PD in the jejunum of conscious man are caused by changes in electrogenic secretion associated with intestinal motility and mediated by cholinergic mechanisms. The possible association of increased secretory activity with motility may have functions of lubrication as well as diluting and mixing the chyme for easier digestion and absorption.