Suppressive effect of insulin on the synthesis of sucrase-isomaltase complex in small intestinal epithelial cells, and abnormal increase in the complex under diabetic conditions

Diagnostic and Research Aspects of Small Intestinal Disaccharidases in Coeliac Disease

Disaccharidases (DS) are brush border enzymes embedded in the microvillous membrane of small intestinal enterocytes. In untreated coeliac disease (CD), a general decrease of DS activities is seen. This manuscript reviews different aspects of DS activities in CD: their utility in the diagnosis and their application to in vitro toxicity testing. The latter has never been established in CD research. However, with the recent advances in small intestinal organoid techniques, DS might be employed as a biomarker for in vitro studies. This includes establishment of self-renewing epithelial cells raised from tissue, which express differentiation markers, including the brush border enzymes. Determining duodenal DS activities may provide additional information during the diagnostic workup of CD: (i) quantify the severity of the observed histological lesions, (ii) provide predictive values for the grade of mucosal villous atrophy, and (iii) aid diagnosing CD where minor histological changes are seen. DS can also provide additional information to assess the response to a gluten-free diet as marked increase of their activities occurs four weeks after commencing it. Various endogenous and exogenous factors affecting DS might also be relevant when considering investigating the role of DS in other conditions including noncoeliac gluten sensitivity and DS deficiencies.

Anti-hyperglycemic effects and mechanism of traditional Chinese medicine Huanglian Wan in streptozocin-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Huanglian Wan (HLW) is a prescription of traditional Chinese medicine (TCM), which has been used to treat diabetes mellitus for thousands of years in China. In this study we provide experimental evidence for the clinical use of HLW in the treatment of diabetes mellitus.

MATERIALS AND METHODS

HLW extract was prepared and the main components (namely berberine and catalpol) contained in the extract were assayed with high performance liquid chromatography (HPLC), and diabetic model rats were induced by intraperitoneal injection of streptozotocin (STZ). After grouped randomly, diabetic rats were administered low or high dose of HLW extract, acarbose and vehicle for 33 days, respectively. Body weight, food intake, urine volume, urine sugars, fasting plasma glucose and fasting plasma insulin were monitored to evaluate its antidiabetic effects in diabetic rats. Intestinal mucosa homogenate was prepared and the activities of intestinal disaccharidases were assayed. Moreover, oral sucrose tolerance test (OSTT) was performed and the inhibitory effect of HLW extract on the maltase and sucrase in vitro was evaluated.

RESULTS

After the treatment of HLW extract, the body weight and the fasting plasma insulin level were found to be increased while food intake, urine volume, urine sugars and fasting plasma were decreased. OSTT showed that HLW extract could lower the postprandial plasma glucose level of diabetic rats. Furthermore, HLW extract could inhibit the activities of sucrase and maltase in vitro.

CONCLUSIONS

According to our present findings, the TCM prescription HLW possessed potent anti-hyperglycemic effect on STZ-induced diabetic rats. And HLW extract exerted anti-hyperglycemic effect partly via inhibiting the increased activities of intestinal disaccharidases and elevating the level of plasma insulin in diabetic rats induced by streptozotocin.

Gestational diabetes affects postnatal development of transport and enzyme functions in rat intestine

The effect of alloxan-induced gestational diabetes on the postnatal development of brush border disaccharidases and D-glucose transport in rat intestine was studied. Pups born to diabetic mothers showed 92-22% increase in blood sugar levels compared with the controls. Western blot and RT-PCR analyses revealed that the activities of brush border sucrase, lactase and Sodium Glucose Co-transporter 1 (SGLT1) correlates with protein and mRNA levels in intestine of pups born to diabetic rat mothers after 5-45 days of birth. Intestinal histology in pups born to diabetic mothers at day 10 and 45 after birth showed distorted cellular organization of mucosa with a decrease in the number of secretary goblet cells and regression of tubular mass. These findings suggest that the genetic switch in utero regulates the postnatal expression of enzyme and transport functions in intestine of pups born to diabetic rat mothers. This may influence the growth and development of offsprings later in life.

Berberine suppresses intestinal disaccharidases with beneficial metabolic effects in diabetic states, evidences from in vivo and in vitro study

Clinical reports have demonstrated that berberine is a potential antidiabetic agent, but the underlying mechanism is unclear. The purpose of this study was to investigate if berberine exerts its hypoglycemic action via inhibiting intestinal disaccharidases using in vivo and in vitro experiments. Streptozotocin-induced diabetic rats received berberine (100 or 200 mg/kg) orally once daily or acarbose (40 mg/kg) orally twice daily for 5 weeks. Disaccharidase activities and sucrase-isomaltase (SI) complex messenger RNA (mRNA) expression in intestinal regions were assessed. The same treatment was operated in normal rats. Sucrose and maltose loading tests were also documented. In addition, Caco-2 cells were cultured in medium containing berberine or berberine plus chelerythrine. Compound C or H-89 for 5 days, disaccharidase activities, and SI complex mRNA levels were measured. The animal experiments showed that berberine significantly decreased the disaccharidase activities and SI complex mRNA expression both in diabetic rats and normal rats. Berberine can also significantly lower postprandial blood glucose levels induced by sucrose or maltose loading in normal rats. The cellular results showed that berberine may suppress disaccharidase activities and downregulate SI complex mRNA expression in a concentration-dependent manner. Only H-89, an inhibitor of protein kinase A (PKA), may reverse the decrease in disaccharidase activities and SI complex mRNA expression induced by berberine. In conclusion, berberine suppresses disaccharidase activities and SI complex mRNA expression with beneficial metabolic effects in diabetic states. The inhibitory effect, at least partly, involves the PKA-dependent pathway.

A comparative study on hypoglycemic and hypocholesterolemic effects of high and low molecular weight chitosan in streptozotocin-induced diabetic rats

The hypoglycemic and hypocholesterolemic effects of high and low molecular weight chitosan were evaluated in streptozotocin (STZ)-induced diabetic rats. Rats were divided into three groups of normal rats (Experiment I) and three groups of diabetic rats (Experiment II). The first group received a cellulose (control) diet, the second group received a low MW (1.4 x 10(4)Da) chitosan diet and the third group received a high MW (1.0 x 10(6)Da) chitosan diet. All three diets were containing 0.5% cholesterol. Experiment I: rats fed with high MW or low MW chitosan diet had increased high density lipoprotein (HDL) cholesterol. However, chitosan did not affect plasma glucose in normal rats. Experiment II: significantly decreased plasma glucose and total cholesterol and increased HDL cholesterol and fecal cholesterol excretion were observed in diabetic rats fed with high MW chitosan diet than animals fed with cellulose diet. However, no statistical significant difference in plasma glucose and total cholesterol was observed in diabetic rats fed with low MW chitosan. The total content of SCFAs in cecum was significantly increased and the ratio of acetate to propionate was slight but significantly decreased in diabetic rats after consuming high MW chitosan diet. The activities of hepatic hexokinase were significantly increased and the intestinal disaccharidases including sucrase and maltase were significantly decreased in normal and diabetic rats fed with high MW chitosan diet. Results obtained from the present study demonstrated the potential of high MW chitosan in reducing hyperglycemia and hypercholesterolemia in STZ-induced diabetic rats.

Eucalyptus leaf extract inhibits intestinal fructose absorption, and suppresses adiposity due to dietary sucrose in rats

Sucrose is more lipogenic than starch, and the extreme ingestion of sucrose induces adiposity and obesity. The aim of this study was to examine the effect of the eucalyptus (Eucalyptus globulus) leaf extract (ELE) on adiposity due to dietary sucrose in rats. In addition, in this study, the effect of ELE on intestinal fructose absorption was also examined. Rats were fed a high-sucrose diet (75 % in calorie base) with or without ELE (10 g/kg diet) for 5 weeks. Body weight was lower in the rats receiving ELE than in the controls (342 (sd 37·9)v. 392 (sd 26·0) g (n7);P<0·05). Furthermore, ELE resulted in decreases in the triacylglycerol concentrations in the plasma (1·44 (sd 0·448)v.2·79 (sd 0·677) mmol/l (n7);P<0·05) and liver (19·1 (sd 5·07)v.44·1 (sd 16·28) μmol/g (n7);P<0·05). In contrast, ELE did not show any significant effects in the rats fed a starch diet. When rats were orally given ELE 10 min before fructose administration, the intestinal fructose absorption, which was examined by measuring the elevated concentration of fructose in the portal vein at 30 min after the fructose administration, was significantly inhibited in a dose-dependent manner. Furthermore, in rats fed a high-fructose diet, the plasma and hepatic triacylglycerol concentrations were significantly decreased by ELE. These results indicate that ELE, which inhibits the intestinal fructose absorption, can suppress adiposity in rats that ingest large amounts of sucrose or fructose.

Quercetin alleviates activities of intestinal and renal disaccharidases in streptozotocin-induced diabetic rats

Specific activities of both intestinal and renal dissacharidases, such as sucrase, maltase, and lactase, were altered in diabetic rats. Our study was focused to evaluate the effect of feeding quercetin - a bioflavanoid on intestinal and renal dissacharidases in streptozotocin-induced diabetic rats. The rats were fed with 0.1% quercetin in diet. A reduction in intestinal maltase and sucrase, activities in quercetin-fed diabetic rats was observed in contrast to the increased activities in the starch-fed diabetic rats. A significant amelioration in renal dissacharidase activities in quercetin-fed diabetic rats was observed when compared to decreased activity in starch-fed diabetic rats.

Enhancement of sucrase-isomaltase gene expression induced by luminally administered fructose in rat jejunum

We have previously shown that feeding a diet containing sucrose to rats causes an elevation of sucrase-isomaltase (SI) mRNA level in the jejunum. In this study, we examined whether the SI mRNA level could be directly elevated by administration of one of the constituting monosaccharides (i.e., glucose and/or fructose). Gastric intubation of a sucrose solution caused increases in both sucrase activity and SI mRNA level in the jejunum. Intrajejunal intubation of fructose, but not glucose, led to an elevation of sucrase activity and SI mRNA level. To examine whether fructose directly affects the gene expression of SI at the segment where the absorption of this sugar takes place or the sugar-induced increase in the gene expression of SI is secondary to any possible changes in the level(s) of certain hormonal factor(s) in the blood stream, a solution containing either fructose or glucose was simultaneously perfused into two consecutive cannulated and irrigated loops of jejunum that were not isolated from blood circulation. Compared with the loop perfused with glucose, the loop perfused with fructose exhibited significantly greater sucrase activity and SI mRNA level as well as the elevated GLUT5 mRNA level. These results suggest that fructose is capable of directly increasing the gene expression of SI and GLUT5 in the confined segment where fructose is absorbed.

Effect of mutations in HNF-1α and HNF-1β on the transcriptional regulation of human sucrase–isomaltase in Caco-2 cells

Mutations in transcription factors hepatocyte nuclear factors (HNF)-1alpha and HNF-1beta cause maturity-onset diabetes of the young (MODY) types 3 and 5, respectively. HNF-1alpha and HNF-1beta mutations are well studied in some tissues, but the mechanism by which HNF-1alpha and HNF-1beta mutations affect sucrase-isomaltase (SI) transcription in the small intestine is unclear. We studied the effects of 13 HNF-1alpha mutants and 2 HNF-1beta mutants on human SI gene transcription, which were identified in subjects with MODY3 and MODY5, respectively. Transactivation activity of 11 HNF-1alpha and 2 HNF-1beta mutants was significantly lower than that of wild (wt)-HNF-1alpha and wt-HNF-1beta. Furthermore, in co-expression studies with mutant (mu)-HNF-1alpha/ wt-HNF-1beta and wt-HNF-1alpha/mu-HNF-1beta, the combination of mu-HNF-1alpha (P379fsdelCT and T539fsdelC)/wt-HNF-1beta impaired SI transcription, but the others were not remarkably different from wt-HNF-1alpha/wt-HNF-1beta. Although wt-HNF-1beta inhibited the transactivation activity of wt-HNF-1alpha on SI transcription, the inhibitory effect was reduced by 2 HNF-1beta mutants. These results suggest that SI transcription might tend to be unchanged or lower in MODY3, while occurring more in MODY5.

Effects of dietary L-arginine supplementation on serum lipids and intestinal enzyme activities in diabetic rats

We investigated whether dietary supplementation with L-arginine, the endogenous precursor of nitric oxide, might affect serum lipid levels and activities of intestinal mucosa enzymes in animals, in which diabetes was induced by administration of streptozotocin. Control and diabetic rats were fed diets with or without 2% L-arginine supplementation for 4 weeks. Diabetic rats had significantly higher concentrations of serum triglycerides and LDL-cholesterol than control rats. These alterations were partially reduced by L-arginine supplementation. Experimental diabetes did not influence the lactase and leucine aminopeptidase activity in the intestine, but the activity of alkaline phosphatase was increased. Furthermore, activities of maltase and sucrase in the intestinal mucosa were elevated in streptozotocin-induced diabetic rats and were restored to control levels after dietary L-arginine supplementation. On the basis of the present experimental evidence, dietary L-arginine supplementation appears to affect the metabolism of lipoproteins and might alleviate some gastrointestinal dysfunctions, commonly seen in diabetes mellitus.

Small bowel review: normal physiology part 1

In the past year there have been many advances in the area of small bowel physiology and pathology and therapy. In preparation for this review, over 1500 papers were assessed. The focus is on presenting clinically useful information for the practising gastroenterologist. Selected important clinical learning points include the following: (1) glucose absorption mediated by SGLT1 is controlled by mRNA abundance, as well as by posttranscriptional processes including protein trafficking; (2) inducers of cytochrome P-450 decrease glucose and fructose absorption and increase glucose consumption in the intestine; (3) the regulated release of nutrients from the stomach into the upper intestine ensures that the modest intestinal transport reserve capacity is not exceeded; (4) hepatocyte growth factor and short-chain fatty acids may enhance intestinal adaptation and prevent the atrophy seen when total parenteral nutrition is infused; (5) inhibitors of pancreatic lipase and phospholipase H2 may be useful clinically to reduce absorption as part of a treatment program for obesity and hyperlipidemia; (6) several membrane-bound and cytosolic proteins have been identified in the enterocyte as well as in the hepatocyte and may be the target for the future therapeutic manipulation of bile acid metabolism and control of hyperlipidemia; (7) suspect bile acid malabsorption in the patient with otherwise unexplained chronic diarrhea; (8) a proportion of lipid absorption is protein-mediated, and this opens the way to targeting these proteins and thereby therapeutically modifying lipid absorption; (9) a high protein diet may be useful to increase the intestinal absorption of drugs transported by the H+/dipeptide cotransporter; (10) a metal transporter DCT1 has been identified, and this may open the way to a better understanding of disorders of, for example, iron and zinc metabolism; (11) the nutrient transporters such as SGLT1 are responsible for a portion of the intestinal absorption of water; (12) the influence of nitric oxide on intestinal water absorption and secretion depends on its concentration; (13) a trial of bile acid-sequestering agent may prove useful in the treatment of the patient who experiences diarrhea while taking an enteral diet; (14) a proteolytic extract from pineapple stems may prove to be useful to treat diarrhea, although the mechanism of this effect remains to be established; and (15) the antisecretory effect of the new peptide, sorbin, needs to be tested in a clinical situation on patients with diarrhea. Other new and promising antidiarrheal agents include bromelain, an extract from pineapple stems, and igmesine, a final sigma ligand.

High prevalence of lactose absorbers in Northern Sardinian patients with type 1 and type 2 diabetes mellitus

BACKGROUND

Increased intestinal lactase activity has been shown to occur in alloxan and streptozotocin diabetic rats.

OBJECTIVE

The objective of this study was to determine whether increased intestinal lactase activity is present in humans with diabetes mellitus.

DESIGN

We assessed the capacity to digest lactose by measuring breath-hydrogen production after oral administration of lactose in 50 patients with type 1 diabetes, 50 patients with type 2 diabetes, and 50 healthy control subjects from Sassari, Sardinia, Italy, a population characterized by a low prevalence of lactase persistence (lactose absorbers).

RESULTS

Fourteen percent of control subjects were lactose absorbers, compared with 48% of patients with type 1 diabetes and 52% of patients with type 2 diabetes (P < 0.005). The odds ratio of lactase persistence in patients with type 1 diabetes was 5.3 (95% CI: 2.0, 14.0) and in patients with type 2 diabetes was 5.5 (95% CI: 2.1, 14.5).

CONCLUSIONS

Diabetes is associated with increased intestinal lactase activity in humans. Consequently, there is a greater exposure to glucose and galactose in diabetic patients with high lactose consumption. This may explain the association between diabetes and the risk of cataract.

Dietary regulation of intestinal gene expression

We are becoming increasingly aware of inherited genetic abnormalities as causes of disease. However, alterations in gene expression can also contribute to other disease processes. Recently it has been suggested that our environment may alter such genes and thus be a direct influence on disease. Diet is a potent mechanism for altering the environment of cells of most organs, particularly the gastrointestinal tract. This review addresses the influence of nutritional factors on intestinal gene regulation. These influences include insulin, which is not a dietary component but responds to dietary changes, and butyrate, a short chain fatty acid produced by normal intestinal flora. Manipulation of diet may be a means of treating intestinal disorders. Nutritional treatment therefore is also discussed in the light of its effect on gene expression.

Luminal amino acids acutely decrease intestinal mucosal protein synthesis and protease mRNA in piglets

Because parenteral feeding is associated with negative N balance and reduced rates of protein synthesis in intestinal mucosa, we hypothesized that luminal exposure to specific amino acids or energy fuels would stimulate intestinal protein synthesis. We studied the acute effects of luminal nutrients on mucosal protein synthesis in the absence of systemic influences. Multiple jejunal segments constructed in piglets deprived of food overnight (n = 6) were randomly assigned to luminal perfusion with saline, 30 mmol/L amino acid mixture with or without 50 mmol/L glucose, or 30 mmol/L glutamine for 90 min. Protein synthesis was then measured by luminal perfusion with L-[2,6-(3)H]-phenylalanine. Energy substrates (glucose, short-chain fatty acids or beta-hydroxybutyrate) had no effect on mucosal protein synthesis. Relative to saline, a 30 mmol/L amino acid mixture or 30 mmol/L glutamine suppressed mucosal protein synthesis by 20-25% (P < 0.05). On the basis of these surprising results, we speculated that a coordinate reduction of proteolytic processes would be required to maintain positive intestinal N balance. Although intestinal protein catabolism cannot be assessed directly, the 30 mmol/L amino acid mixture acutely suppressed mucosal levels of mRNA encoding ubiquitin, 14-kDa ubiquitin conjugating enzyme and the C9 subunit of the proteasome by 20-30% (P < 0.05), demonstrating the sensitivity of components of the ATP-ubiquitin proteolytic pathway to acute regulation by nutrients. The suppression of protein synthesis by luminal amino acids in the absorptive state might lower intestinal utilization of amino acids to ensure efficient allocation of absorbed nutrients to nonintestinal tissues.

Nutrient regulation of intestinal gene expression

This review examines recent advances in the dietary modulation of gene expression in the gastrointestinal tract. We have chosen to concentrate on individual genes and examine what is known about their regulation, attempting to link different studies together.

Disordered expression of the sucrase-isomaltase complex in the small intestine in Otsuka Long-Evans tokushima fatty rats, a model of non-insulin-dependent diabetes mellitus with insulin resistance

To clarify the relationship between diabetes mellitus and carbohydrate digestion, the activities of sucrase and isomaltase, which form a complex enzyme (SI complex) on the brush border membranes, were compared in the progression of diabetes mellitus in Otsuka Long-Evans Tokushima fatty (OLETF) rats, a model of human non-insulin-dependent diabetes mellitus with insulin resistance, and Long-Evans Tokushima Otsuka (LETO) rats as non-diabetic controls. Until 40 weeks of age, OLETF rats were obese and had a high plasma glucose level, compared to age-matched LETO rats, but the sucrase and isomaltase activities showed no significant differences between the two strains. Oral glucose tolerance test revealed that during 40-48 weeks of age, NIDDM became very severe with advancing insulin resistance in OLETF rats. In OLETF rats, in contrast to LETO rats, at 48 weeks of age, abnormal increases in the sucrase and isomaltase activities occurred, along with a remarkable decrease in body weight and a further great increase in the plasma glucose level in the non-fasting state. Hyperinsulinemia occurred in 20-week-old OLETF rats; however, at 40 and 48 weeks of age, the plasma insulin level in the non-fasting state in OLETF rats was not significantly different from that in LETO rats. The level of mRNA encoding the SI complex increased abnormally in 48-week-old OLETF rats. These results suggest that the advance of insulin resistance leads to an increase in the expression of the SI complex on the transcriptional level.