Peter G. Lunn

Intestinal permeability mucosal injury and growth faltering in Gambian infants.

There is controversy over whether children in developing countries can catch up on their growth rates after bouts of diarrhoea. A factor influencing catch-up growth is the extent and duration of mucosal injury. To explore the relation between intestinal disease and growth performance, a non-invasive test of intestinal integrity, the lactulose:mannitol permeability test, was done regularly on children aged 2-15 months, whose growth was monitored over a mean of 7.5 months. The study revealed persistent abnormalities in the small bowel mucosa of 2-15 month old Gambian infants and a negative correlation between these abnormalities and growth. Up to 43% of observed growth faltering can be explained on the basis of these long-term intestinal lesions.

The impact of infection and nutrition on gut function and growth in childhood

Poor growth performance during infancy and early childhood is a frequent fact of life in most developing countries. Work in The Gambia has demonstrated that more than 43 % of observed growth faltering during the first 15 months of life can be explained by the presence of a mucosal enteropathy in the small intestine. Within communities the illness is very common: in the area investigated more than 95 % of infants above 8 months of age were affected, and on average they suffered a growth-limiting enteropathy for more than 75 % of their first year of life. Two mechanisms of weight loss have been defined. First, partial villus atrophy reduces absorption and digestion of lactose and probably other nutrients. Second, and more importantly, damage to the mucosal barrier allows translocation of macromolecules into the mucosa and blood, triggering both local and systemic immune and inflammatory mechanisms. Given the severity of the enteropathy it is not surprising that infants fail to grow at a normal rate. Recent findings suggest that these lesions continue throughout childhood and into adulthood. Thus, a persistence of chronic, local and systemic inflammation throughout childhood may be responsible for continued poor growth during this period. Although the nature of the enteropathy and the mechanisms of growth failure have been defined, the factors involved in the initiation and persistence of the intestinal lesion remain uncertain, making clinical management difficult. More work is clearly required to elucidate these factors and to define interventions to prevent or treat the enteropathy.

Chronic T Cell-Mediated Enteropathy in Rural West African Children: Relationship with Nutritional Status and Small Bowel Function

Previous studies from The Gambia have shown that poor childhood growth is resistant to all but the most intense nutritional intervention and highly dependent on small bowel permeability related to enteropathy. We thus aimed to characterize the mucosal inflammatory response in rural Gambian children in relation to intestinal permeability and nutritional status. Small bowel biopsies were taken from 38 rural Gambian children (age, 0.5-3 y) with a range of nutritional and clinical states (median weight z score, −4.6; range, 0.5 to −6.4), 75% of whom had diarrhea. Morphometry was performed with immunohistochemical analysis for a range of lineage and activation markers, including proinflammatory and regulatory cytokines, and related to current clinical status and gut permeability. Comparison was made with 19 age-matched U.K. controls. All Gambian children, regardless of nutritional status, had evidence of chronic cell-mediated enteropathy with crypt hyperplasia, villous stunting, and high numbers of intraepithelial lymphocytes. CD25+ cells were 20-fold higher than in U.K. controls. Although small bowel architecture was independent of nutritional status, T cell numbers rose and B cell numbers fell with worsening nutrition, and mucosal cytokine production became biased toward a proinflammatory response, with progressive decrease of transforming growth factor-β expression. Tropical enteropathy predates the onset of marasmus and is characterized by a cell-mediated TH1 response. Protein-energy malnutrition is associated with reduction of regulatory immune responses in the mucosal microenvironment, potentially impairing the mechanisms of oral tolerance.

INFLUENCE OF MATERNAL DIET ON PLASMA-PROLACTIN LEVELS DURING LACTATION

An improvement in maternal diet produced significant reductions in plasma-prolactin concentration at all stages of lactation. The prolonged high prolactin concentrations found in undernourished mothers may ensure milk synthesis when food intake is limited, by preferentially channelling nutrients towards the breast. The lower hormonal levels associated with improved maternal nutrition may shorten the period of post-partum infertility despite prolonged breast-feeding.

Progressive changes in serum cortisol, insulin and growth hormone concentrations and their relationship to the distorted amino acid pattern during the development of kwashiorkor.

1. During the initial stages of the development of hypoalbuminaemia, with concentrations between 25 and 30 g/l, fasting serum cortisol and growth hormone values remained normal. Corresponding fasting serum insulin concentrations were, however, significantly above normal. During the same period, called phase B, valine concentrations were moderately low but alanine concentrations were raised. 2. In more severe hypoalbuminaemia, culminating in kwashiorkor, a marked switch in hormonal balance occurred. Insulin concentrations fell to subnormal levels whereas cortisol became raised. Eventually growth hormone concentrations also increased rapidly to values similar to those found in acromegaly. By this time, phase C, alanine concentrations as well as those of valine were falling to very low levels. 3. The possible causes of these changes in hormonal balance, their role in the development of the distorted fasting serum amino acid pattern and their consequent effect on serum albumin synthesis and the appearance of clinical kwashiorkor are discussed. 4. Information is also presented on the differences between these components in kwashiorkor and marasmus. Attempts have been made to rationalize apparent inconsistencies in the literature.

Intestinal inflammation measured by fecal neopterin in Gambian children with enteropathy: Association with growth failure, Giardia lamblia, and intestinal permeability

Objectives: Investigate whether fecal neopterin concentration (a potential marker of gut inflammation) in Gambian children with enteropathy was associated with growth failure. Secondary outcome measures tested the associations between Giardia lamblia infestation, fecal neopterin and lactulose mannitol absorption ratio(L:M), a measure of intestinal permeability. Methods: Seventy-two children had height and weight measured every 6 to 8 weeks until 15 months of age in a rural Gambian village. L:M ratio, a measure of small intestinal permeability and fecal neopterin were measured at these times. Stool was examined by immunoflorescence and light microscope for Giardia cysts. Results: Long-term height and weight gains were negatively associated with mean subject fecal neopterin concentration (r = −0.29 and −0.36, respectively; P < 0.001). There was no correlation between fecal neopterin and intestinal permeability or history of diarrhea. Of 72 children studied, 19 had Giardia cysts in stool and 38 had negative stool examinations. Infected children had a mean of 0.7 days of diarrhea/week (95% confidence interval [CI], 0.31–1.03) versus 0.8 days/week (95% CI, 0.71–0.85) in uninfected children. No difference in growth was detected between those with positive or negative fecal smears. Mean L:M ratio was the same in both groups (0.31; 95% CI, 0.26–0.34). Conclusions: Consistent with the theory that intestinal inflammation in tropical infants may impair growth, fecal neopterin concentrations were inversely associated with growth. Factors other than Giardia are causing enteropathy and growth failure in Gambian infants.

Age-related association of small intestinal mucosal enteropathy with nutritional status in rural Gambian children.

Small bowel enteropathy (assessed by the lactulose (L) : mannitol (M) permeability test) is a major factor in infant growth faltering and malnutrition in The Gambia. However, little is known about its persistence and nutritional effect beyond 2 years of age. This was addressed by two cross-sectional studies of intestinal permeability and nutritional status in 162 residents, aged 2-60 years, living in three villages in rural Gambia. L:M ratio was found to be highest in the youngest children and although there was a significant improvement with age (P<0.0001), values were always greater than the range found in UK counterparts. M recovery (mean value 5.68 (se 0.12) %) was at all times between one-third and one-half of expected UK values and showed no improvement with age. Gut barrier function, assessed by L uptake, improved with age (P<0.001) and fell within the UK normal range beyond age 10 years. Both the L:M permeability ratio and L recovery were significantly associated with height-for-age z-scores and -0.22 respectively, P<0.001), a relationship that persisted throughout childhood and into adulthood. Change in height-for-age z-score between the two visits was also related to the L:M ratio P=0.018). The close within-subject correlation of permeability variabilities between the two visits suggests a long-term persistence of enteropathy within individuals. It appears that the small bowel enteropathy previously described in Gambian infants persists through to adulthood. Although the lesion improves with age, the relationship between attained height and L:M permeability raises the possibility that enteropathy may continue to limit growth throughout childhood and puberty.

The relative effects of a low-protein-high-carbohydrate diet on the free amino acid composition of liver and muscle.

1. Free amino acid concentrations in the plasma have been compared with those in liver and quadriceps muscle, in rats fed on diets containing 209 (control) and 31 (low-protein) g protein/kg. The effects of the low-protein diet on diurnal variations in these values were also measured. 2. In the plasma, the total amino acid concentration was significantly lower in animals given the low-protein diet, at all times of day except 12.00 hours. In the liver, and to a lesser extent the muscle, total amino acid concentration was maintained. 3. In the control animals, diurnal variation in the concentrations of both essential and nonessential amino acids was very similar in plasma, liver and muscle. In animals given the low-protein diet, although the same diurnal pattern was maintained for non-essential amino acids, that occurring among the essential amino acids had virtually disappeared 4. In plasma, the mean 24 h concentration of essential amino acids decreased from 2-43 mmol/l in control animals to only 1-29 mmol/l in the low-protein-fed animals. Concentrations in muscle and liver were reduced by a similar proportion (from 8-60 to 5-56 mumol/g and from 8-67 to 5-05 mumol/g respectively). Conversely the concentrations of non-essential amino acids in animals given the low-protein diet were increased in plasma (from 1-53 to 2-00 mmol/l), muscle (from 12-5 to 14-3 mumol/g), and liver (from 16-8 to 20-5 mumol/g), muscle showing the lowest increase. 5. With the exceptions of lysine, threonine, cystine and tyrosine, the concentrations of all other essential amino acids were reduced more in liver than in muscle. The relationship between this and the failure to maintain plasma albumin concentations is discussed.

Reasons why hypoalbuminaemia may or may not appear in protein-energy malnutrition

1. Investigations have been carried out in experimentally-malnourished rats in an attempt to explain the reasons for the development of the two main forms of protein-energy malnutrition in children, kwashiorkor and marasmus. 2. Isoenergetic diets with values for protein: energy (P:E) of 0.21 (control diet; C) 0.032 (low-protein diet; LP) and 0.005 (very-low-protein diet; VLP) were fed to groups of twenty-six rats either ad lib. or in restricted amounts from 5 weeks of age. Rats were killed at the start of the experiment and 1, 2 and 3 or 4 weeks later. Estimations were made of plasma albumin, insulin, corticosterone and amino acid concentrations and of the total protein content of the gastrocnemius muscles and liver. 3. Rats given diet LP ad lib. gained weight slowly and by week 1 plasma albumin concentration was slightly reduced. Rats given diet VLP ad lib. gradually lost weight and plasma albumin concentrations decreased continuously. 4. In contrast the major effect of dietary restriction during the first 2 weeks of the experiment was to maintain plasma albumin concentrations at normal values, irrespective of the diet given. 5. At later stages, however, when the ‘restricted’ animals had become very severely wasted, albumin concentrations decreased rapidly to values approaching those found in rats given diet VLP ad lib. 6. When diets LP and VLP were given ad lib. body protein was proportionally distributed in favour of muscle rather than liver. For ‘restricted’ rats the reverse was true, at least up to the time when plasma albumin concentration began to decrease. 7. Plasma corticosterone concentrations increased and insulin concentrations decreased when diets LP and VLP were fed in both an ad lib. and a ‘restricted’ regimen but the effects were significantly greater in the latter situation. 8. Ad lib. feeding of diets LP and VLP produced a distorted plasma amino acid pattern resembling that of kwashiorkor, but although dietary restriction resulted in a decrease in total amino acid concentration, the plasma concentration ratio, non-essential amino acids:essential amino acids was virtually unaffected. 9. It was concluded that whilst the lower the protein concentration in the diet the greater is the extent of hypoalbuminaemia which develops, dietary restriction with an increase in plasma glucocorticoid concentration and body-wasting can initially delay the development of the hypoalbuminaemia. However, in the final stages of wasting which ensue, low plasma albumin concentrations can appear because of a failure of the mechanisms which had earlier been able to preserve them at normal levels. It is possible that these two separate and distinct routes to hypoalbuminaemia observed in this study may have parallels in human situations in developing countries.

2. Chronic diarrhoea and malnutrition in The Gambia: studies on intestinal permeability

Chronic diarrhoea and malnutrition in Gambian children is associated with persisting damage to the mucosa of the small intestine. Intestinal permeability tests suggest that mucosal status gradually deteriorates with age throughout the first year of life in tandem with increasingly severe growth faltering. The ability of the dual sugar permeability test to assess intestinal mucosal status frequently in a non-invasive way makes the technique a valuable tool for future studies into the aetiology of this syndrome.