The significance of lowered jejunal disaccharidase levels

Mucosal Defense Against Giardia at the Intestinal Epithelial Cell Interface

Human giardiasis, caused by the protozoan parasite Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis, Lamblia intestinalis), is one of the most commonly-identified parasitic diseases worldwide. Chronic G. duodenalis infections cause a malabsorption syndrome that may lead to failure to thrive and/or stunted growth, especially in children in developing countries. Understanding the parasite/epithelial cell crosstalk at the mucosal surfaces of the small intestine during human giardiasis may provide novel insights into the mechanisms underlying the parasite-induced immunopathology and epithelial tissue damage, leading to malnutrition. Efforts to identify new targets for intervening in the development of intestinal immunopathology and the progression to malnutrition are critical. Translating these findings into a clinical setting will require analysis of these pathways in cells and tissues from humans and clinical trials could be devised to determine whether interfering with unwanted mucosal immune responses developed during human giardiasis provide better therapeutic benefits and clinical outcomes for G. duodenalis infections in humans.

Dietary lipids containing gangliosides reduceGiardia murisinfectionin vivoand survival ofGiardia lambliatrophozoitesin vitro

We examined whether a ganglioside supplemented diet affected the course ofGiardia murisinfection in mice and survival ofGiardia lambliatrophozoitesin vitro. Female CD-1 mice were fed 1 of 5 experimental diets: standard lab chow as a control diet; semi-synthetic diets containing 20% (w/w) triglyceride based on the fat composition of a conventional infant formula; triglyceride diet; triglyceride diet containing a low level of ganglioside (0·1% w/w); and triglyceride diet containing a high level of ganglioside (1·0% w/w of diet). After 2 weeks of feeding, mice were inoculated withG. murisby gastric intubation and fed the experimental diets during the course of the infection. Cysts released in the faeces and trophozoites present in the small intestine were enumerated at various times post-infection. The average cyst output and the number of trophozoites during the course of the infection in mice fed ganglioside-containing diet were found to be significantly lower (3-log10reduction) compared to animals fed control diets. The results ofin vitrogrowth studies indicated that gangliosides may be directly toxic to the parasites. Thus, gangliosides have a protective effect againstG. murisinfectionin vivoand affect the survival ofG. lambliatrophozoitesin vitro.

Disaccharidase activity in male and female C57BL/6 mice infected with Giardia muris

To elucidate the contribution of host and parasite factors in induction of small-intestinal disaccharidase deficiency in giardiasis, we determined the activity of four enzymes in male and female C57BL/6 mice infected with Giardia muris. Both male and female mice exhibited significant disaccharidase deficiency as shown by decreases in the activities of lactase, sucrase, trehalase and maltase on day 10 after infection. However, by 20 days after infection the females had normal enzyme activities, whereas those in males remained significantly reduced. Prolonged disaccharidase deficiency in the males was related to the course of the primary infection where males had higher parasite loads in the small intestine than did females on day 20 after infection. By day 40 after the primary infection the enzyme activities had returned to normal levels and were similar in male and female mice. Secondary exposure of mice to either the infective cysts or a crude extract of the trophozoites caused disaccharidase deficiency. The females had lower activities of sucrase and trehalase as compared with males after the challenge. Thus, during the primary infection, disaccharidase deficiency was strongly associated with parasite number, whereas after challenge infections the more resistant females had lower enzyme activities in the small intestine than did males.

Disaccharidase deficiencies in Mongolian gerbils (Meriones unguiculatus) protected against Giardia lamblia

The activities of the disaccharidases lactase, maltase, sucrase and trehalase were examined in gerbils during Giardia lamblia infections. In a primary infection with trophozoites, the activities of all four enzymes were reduced from day 10 post-infection (p.i.) and remained at low levels well past the elimination phase of the infection. However, during a challenge infection, the disaccharidase decreases were short-lived, with impairments being seen only on days 2 and/or 4 post-challenge (p.c.). Sucrase activity was not affected by a challenge infection. When 0.1 mg of a soluble extract of G. lamblia trophozoites was used to challenge gerbils previously exposed to the live parasite, the pattern and duration of enzyme deficiencies were comparable with those observed after the challenge with the live parasite. In addition, decreasing the extract dose used to challenge the gerbils led to smaller disaccharidase deficiencies. G. lamblia-infected gerbils were also challenged with a soluble extract of Entamoeba histolytica trophozoites, and this had no effect on the disaccharidase activities. Therefore, the presence of the intact parasite was not necessary to induce enzyme reductions in immune animals. In addition, the effects seen during the secondary infection were parasite-specific and may have involved the host's immune response to Giardia antigens. Immune gerbils were further challenged with the in vitro-released excretory/secretory products of G. lamblia. Under our experimental conditions, disaccharidase activities were found to be affected by these products in a manner that was inconsistent with the results of the live parasite challenge, and this merits further study.

A retrospective assessment of the clinical value of jejunal disaccharidase analysis

BACKGROUND

The measurement of jejunal disaccharidases is used by several gastroenterologists when investigating suspected small-bowel disease. The clinical value of this analysis is assessed.

METHOD

The histology and disaccharidase results in 1585 jejunal biopsy specimens were reviewed retrospectively.

RESULTS

Disaccharidase and histology results concurred in most cases (72%). However, disaccharidases were an insensitive indicator of small-bowel disease: low levels were found in only 65% of coeliac patients with villous atrophy, 15% of patients with giardiasis, and 6% of patients with villous atrophy associated with non-coeliac histology. Low disaccharidase levels were sometimes found in patients with normal histology (1.6%) and when biopsy specimens were unwittingly taken from non-jejunal sites (1.4%). Isolated low lactase activities were found in 3.2%. Usually this finding was not clinically relevant because patients had no symptoms of lactose intolerance (38%), had another diagnosis that responded to appropriate treatment (8%), or had no response to a low-lactose diet (14%). In 16 patients sucrase activities were markedly low, and this investigation proved central to the diagnosis of sucrase-alpha-dextrinase deficiency, which was subsequently confirmed in 9.

CONCLUSION

Jejunal disaccharidases are clinically useful only in the diagnosis of sucrase-alpha-dextrinase deficiency. We recommend that their measurement be reserved for the investigation of patients suspected of having this condition.

Activity of duodenal disaccharidases in relation to normal and abnormal mucosal morphology

Endoscopic duodenal biopsy specimens from 100 predominantly adult Caucasian patients under investigation for gastrointestinal symptoms were used to establish reference ranges for lactase, sucrase, and maltase in the duodenum. Duodenal and jejunal disaccharidase values were compared and the association between disaccharidase activity and morphology in the duodenum was examined. Mean lactase activities were about 40% lower in the duodenum compared with the jejunum; maltase was reduced to a lesser extent; and sucrase activities were much the same in the two sites. Lactase deficiency was found in 24 patients of whom 14 (58%) had duodenal disease. The presence of moderate to severe duodenal lesions was associated with a significant decrease in all disaccharidase activities, while only lactase was reduced in mild lesions. Twelve patients had normal lactase activity, despite the presence of duodenal disease. It is concluded that specific reference ranges for duodenal mucosal disaccharidase activity are required as this is less than that of jejunum. Reduced duodenal disaccharidase activity is usually but not invariably associated with morphological abnormality.

Disaccharidase activity in the small intestine of gerbils (Meriones unguiculatus) during primary and challenge infections with Giardia lamblia

The sequence of changes in the activity of six disaccharidases in the small intestine of gerbils during primary and secondary G lamblia infections was examined. The primary G lamblia infection induced a transient reduction in disaccharidase activity which was related to the highest trophozoite burden in the small intestine. During the primary exposure, a 30% to 85% decrease in the activity of enzymes was observed on days 10 and 20 after infection. Secondary exposure of gerbils to G lamblia caused a sharp decrease in disaccharidase activity as early as 24 h after challenge. The reduction in the enzyme activity was not influenced by the size of the challenge inoculum and occurred even when there were no live trophozoites in the small intestine. Disaccharidase deficiency could also be induced by challenge with the soluble extract of the trophozoites. Multiple challenge administrations of G lamblia trophozoites to gerbils induced a persistent disaccharidase deficiency. The results indicate that disaccharidase deficiency associated with the primary G lamblia infection probably represents a direct effect of the parasite on the brush border of the small intestine. On the other hand, the observed disaccharidase deficiency in the secondary G lamblia infection appears to be induced by the local immune responses of the host.

Iron malabsorption in giardiasis

Among 10 children with giardiasis, eight had iron deficiency; iron deficiency anemia was the main complaint in three. Evaluation of iron absorption by the oral iron load test demonstrated a subnormal response (i.e., increase in serum iron levels of less than 100 micrograms/dl) in all eight patients with iron deficiency. In contrast, in two iron-sufficient patients with giardiasis the response to an oral iron load was normal. Xylose absorption was abnormal in five of the 10 patients. After metronidazole dosing, iron absorption became normal in seven patients but remained abnormal in one patient, who also had IgA deficiency. Xylose absorption became normal in all five patients who underwent a second test, but remained abnormal in the patient with IgA deficiency. Concomitant morphologic-studies of jejunal biopsy material from these patients revealed moderate changes in the intestinal mucosa of two patients. We conclude that malabsorption of iron is a complication of giardiasis.

Clinical studies in adults presenting with giardiasis to a gastro-intestinal unit

Eight adults presenting with giardiasis to a gastrointestinal unit during a two year period were studied in detail. Symptoms were varied, diarrhoea occurring in only five patients. Four of the eight gave a history of travel to endemic zones, and three of those who gave no such history had possible predisposing conditions (gastric surgery (2), and borderline IgA deficiency (1]. Most patients exhibited mild malabsorption of fat and vitamin B12, and some abnormality of jejunal disaccharidases was usual. Jejunal histology varied from normal to partial villous atrophy, and the intraepithelial lymphocyte count was raised in those patients with the most marked histological abnormality. Treatment with metronidazole was uniformly successful, and most of the above abnormalities reverted to normal within a month of treatment.

Vestibular disorders caused by defective enzyme mechanisms in the small intestine

A group of patients suffering from long periods of unsteadiness and presenting hyperreflexia in response to torsion swing and/or caloric stimulations were found to have abnormal results in glucose and lactose tolerance tests, but normal or reduced insulin liberation. Biopsies of the jejunal mucosa have shown abnormal enzyme activity or deficiencies in transport mechanisms. The use of a diet suited to each specific deficiency resulted in a high percentage of relief from the vestibular symptoms of these patients.

Intestinal lactase, sucrase and alkaline phosphatase in relation to age, sex and site of intestinal biopsy in 477 Irish subjects

Small intestinal lactase, sucrase and alkaline phosphatase activities were measured in histologically normal peroral intestinal biopsies from 477 individuals. Enzyme activities varied with age, sex, site of biopsy, and were lowest in post-weaning children and highest in young adults. Lactase activity does not decrease with advancing age.

Features of small intestinal pathology (epithelial cell kinetics, intraepithelial lymphocytes, disaccharidases) in a primary Giardia muris infection

In an attempt to correlate host and parasite-related events occurring during the course of a primary Giardia infection in the mouse we have measured epithelial cell kinetics, enzymes, and intraepithelial lymphocytes at different stages of the infection. New methods were developed for the accurate measurement of parasite numbers and distribution within the gut. In jejunum a modest decrease in villus length and intraepithelial lymphocytes at week 1 preceded a pronounced disaccharidase deficiency at week 2, the time of maximum trophozoite numbers, whereas crypt lengthening and increased cell production became maximal at week 3. As trophozoite numbers fell the intraepithelial lymphocyte count and disaccharidase values rose. With the exception of the intraepithelial lymphocyte count, which followed the same pattern as in jejunum but two weeks later, the changes seen in the ileum were the opposite of those in jejunum, suggesting rapid ileal adaptation. The results indicate that the disaccharidase deficiency associated with giardiasis is likely to represent a direct effect of the parasite on the brush border rather than enterocyte immaturity, whereas the intraepithelial lymphocyte response reflects host immunity to the parasite. Profound adaptive changes occur throughout the small intestine in response to a relatively localised insult.