Effects of dietary essential fatty acid deficiency on the development of the rat thymus and immune system

Insulin-like growth factor-I stimulates erythropoiesis when administered enterally

BACKGROUND

Insulin-like growth factors I and II (IGF-I and IGF-II) are potent growth factors involved in development. IGF-I stimulates proliferation of erythropoietic progenitors and parenteral IGF-I administration stimulates in vivo erythropoiesis in animals. IGF-I and IGF-II are both present in mammalian milks and when milk-borne, are resistant to neonatal gastrointestinal degradation. Whether milk-borne IGF-I or IGF-II regulates neonatal erythropoiesis in not known. We hypothesized that physiological doses of enteral IGFs stimulate erythropoiesis in suckling rats.

METHODS

Eight day-old Sprague Dawley rats were artificially fed for 4 days with rat milk substitute (RMS) or RMS supplemented with physiological levels of IGF-I or IGF-II. Rats fed IGF-I and IGF-II were compared to control RMS. Blood and marrow were collected; measures of red cell mass, measures of erythropoietic stimulus, and indices of iron status were measured.

RESULTS

Rats fed IGF-I had higher hemoglobin (Hb) levels (100 +/- 10 g/l), compared to those fed RMS (94 +/- 9) or IGF-II (91 +/- 6), p < 0.001. After IGF-I supplementation, red blood cell counts (RBC) (p < 0.04) and hematocrits (p < 0.002) were also higher. Plasma erythropoietin (Epo) levels, reticulocytes, plasma iron and erythrocyte iron incorporation were similar.

CONCLUSION

Intact enteral IGF-I reaches distal erythropoietic tissue resulting in greater red cell mass, but not by increasing plasma Epo levels or by altering cellular iron transport.

Effects of essential fatty acid deficiency on periodontal tissue adaptation to spontaneous tooth migration

Essential fatty acids (EFAs) play a significant role in bone metabolism. Herein we studied the adaptation of alveolar bone to physiologic tooth drift in young rats deprived of essential fatty acids from birth. Reductions in femur size and trabecular bone volume reflected body growth impairment. Along the alveolar wall, osteoclastic resorption and bone formation were depressed, disrupting the adaptive deformation of the tooth socket to ongoing migration. As a result, the periodontal ligament narrowed considerably, and further adaptation was achieved through root resorption. Essential fatty acid deficiency (EFAD), did not affect precursor recruitment or differentiation in the periodontal ligament (PDL), but caused redistribution of nonspecific-esterase (NSE)-positive osteoclast precursors and tartrate-resistant acid phosphatase (TRAP)-positive pre-osteoclasts between the bone compartment (which was depleted) and the root compartment (which was enriched). EFAD had also a marked effect on the PDL vasculature; the number of vessels was reduced, whereas their size was markedly increased. As a whole, our results show that EFAD disturbs alveolar bone adaptation to drift, but that a reaction (detrimental to root integrity) prevents root collision with the bone surface, thereby preserving the PDL as a source of precursor cells for bone and cementum homeostasis. Moreover, our results confirm that although alveolar bone resorption is arachidonic acid-dependent, the factors activating root resorption are different.

Fatty acids, the immune response, and autoimmunity: a question of n-6 essentiality and the balance between n-6 and n-3

The essentiality of n-6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20:4n-6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (1 8:2n-6, LA) for membrane phospholipids. Low n-6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n-6 PUFA produced by gamma-linolenic acid (18:3n-6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n-6 PUFA, GLA, dihomo-gamma-linolenic acid (20:3n-6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (TGF)-beta-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha production. Low intakes of long-chain n-3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and Th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n-3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n-3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n-3 PUFA augment disease, whereas n-6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n-6 and n-3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n-6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.

Maternal milk reduces severity of necrotizing enterocolitis and increases intestinal IL-10 in a neonatal rat model

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of premature infants. Maternal milk has been suggested to be partially protective against NEC; however, the mechanisms of this protection are not defined. The aim of this study was to examine the effect(s) of artificial feeding of rat milk (RM)-versus cow milk-based rat milk substitute (RMS) on the development of NEC in a neonatal rat model and elucidate the role of inflammatory cytokines in NEC pathogenesis. Newborn rats were artificially fed with either collected RM or RMS. Experimental NEC was induced by exposure to asphyxia and cold stress and evaluated by histologic scoring of damage in ileum. Intestinal cytokine mRNA expression was determined by real-time PCR. Cytokine histologic localization was performed by confocal microscopy. Similar to human NEC, artificial feeding of RM reduces the incidence and severity of NEC injury in neonatal rats. Freezing and thawing of collected RM did not eliminate the protective effect of maternal milk. Ileal IL-10 expression was significantly increased in the RM group compared with RMS. Increased IL-10 peptide production was detected in the RM group with signal localized predominantly in the cytoplasm of villus epithelial cells. These results suggest that the protective effect of maternal milk is associated with increased production of anti-inflammatory IL-10 in the site of injury. Better understanding of the mechanisms underlying these protective effects could be beneficial either in the prevention of NEC or in the development of future therapeutic strategies to cure NEC.

Experimentally induced gluten enteropathy and protective effect of epidermal growth factor in artificially fed neonatal rats

BACKGROUND

A protective effect of breast-feeding against the development of celiac disease has been described, but the nature and effects of the actual milk components have not been established. Epidermal growth factor (EGF), a milk cytokine affecting the proliferation and differentiation of mucosal epithelial cells, was studied as to its potential protective effect on the damage of intestinal mucosa by gliadin in a model system.

METHODS

Enteropathy was induced by gliadin in inbred AVN strain rat pups delivered by cesarean section, breast-fed, or hand-fed a milk formula. All experimental groups were treated with interferon-gamma (1,000 U per animal, administered intraperitoneally) after birth. Gliadin (0.5 and 3 mg) was intragastrically administered to the pups on days 0 and 3, and a 30-mg challenge dose was given on day 20 (24 hours before the termination of the experiment). One group of artificially fed pups received EGF (100 ng/ml) continuously in the diet.

RESULTS

Gliadin- and interferon-gamma-treated formula-fed rat pups showed villus atrophy, increase of inflammatory cells, including CD4+ T lymphocytes in the lamina propria, and damage to epithelial tight junctions and the enterocyte brush border. Morphometrically, the villus height was significantly less than in other groups. Recombinant EGF was markedly increased in the epithelial cells of injured jejunum. The intestinal mucosa of gliadin- and interferon-gamma-treated pups kept on a EGF-supplemented artificial diet resembled that of breast-fed pups.

CONCLUSION

Pathologic changes in jejunal mucosa (villus atrophy and inflammation) resembling gliadin-induced atrophy appeared on administration of interferon-gamma and gliadin to rat pups fed an artificial milk diet immediately after birth. Addition of EGF to the diet protected the rats against pathologic mucosal changes.

IGF alters jejunal glucose transporter expression and serum glucose levels in immature rats

Milk-borne insulin-like growth factors (IGFs) enhance nutrient absorption in the immature intestine, which is characterized by low levels of glucose oxidation. We therefore hypothesized that feeding a rat milk substitute (RMS) devoid of growth factors to rat pups would lower serum glucose levels relative to dam-fed control rats and that supplementation of RMS with physiological doses of either IGF-I or IGF-II would normalize serum glucose levels via increased jejunal glucose transporter 2 (GLUT2) and high-affinity Na(+)-glucose cotransporter (SGLT1) expression. We found lower serum glucose concentrations in RMS-fed pups; in contrast, serum glucose levels in the IGF-supplemented pups were similar to those of dam-fed controls. RT-PCR and laser scanning confocal microscopy similarly demonstrated that IGF supplementation increased expression of jejunal glucose transporters. Further experiments demonstrated that IGF supplementation altered mRNA levels of key mitochondrial enzymes without altering jejunal lactase activity. We conclude that IGF-I and IGF-II supplementation increases serum glucose levels in the immature rat pup fed artificial formula and alters gene expression of the jejunal glucose transporters.

Maternal dietary intake of essential fatty acids affects adipose tissue growth and leptin mRNA expression in suckling rat pups

We have previously shown that maternal intake of essential fatty acids during late gestation and lactation affects the level of serum leptin in pups. The aim of the present study was to investigate the effect of dietary essential fatty acids on leptin content in the milk of rat dams and leptin expression in white adipose tissue of pups during the suckling period. During late gestation and throughout lactation, rats were fed a control or an essential fatty acid-deficient (EFAD) diet. Milk of the EFAD dams contained more saturated and less polyunsaturated fatty acids compared with the control dams. Milk leptin levels were higher in the EFAD dams than in the control dams at 3 wk of lactation. The weight of inguinal white adipose tissue depots and the serum leptin levels of the EFAD pups were significantly lower than in the control pups during the whole suckling period. In addition, semiquantitative reverse transcriptase-PCR analysis of leptin mRNA levels in inguinal white adipose tissue showed a reduction in the EFAD pups compared with the control pups at 3 wk of age. We conclude that maternal dietary essential fatty acid intake affects serum leptin levels in pups by regulating both the amount of adipose tissue and the leptin mRNA expression.

Dietary fatty acid modulation of mucosally-induced tolerogenic immune responses

Immunological unresponsiveness or hyporesponsiveness (tolerance) can be induced by feeding protein antigens to naive animals. Using a classical oral ovalbumin gut-induced tolerance protocol in BALB/c mice we investigated the effects of dietary n-6 and n-3 polyunsaturated fatty acids (PUFA) on high-and low-dose oral tolerance (and in non-tolerised animals, i.e. effects of antigen challenge alone) in relation to lymphoproliferative, cytokine and antibody responses. Fish oil rich in long-chain n-3 fatty acids decreased both T-helper (Th) 1- and Th2-like responses. In contrast, borage (Borago officinalis) oil rich in n-6 PUFA, of which gamma-linolenic acid is rapidly metabolised to longer-chain n-6 PUFA, increased Thl-like responses and decreased Th2-like responses, and possibly enhanced suppressor cell or Th3-like activity. These findings are in general agreement with other studies on the effects of long chain n-3 PUFA on immune system functions, and characterise important differences between long-chain n-3 and n-6 PUFA, defining more precisely and broadly the immunological regulatory mechanisms involved. They are also discussed in relation to autoimmune disease.

Enteral absorption of erythropoietin in the suckling rat

Milk contains biologically relevant concentrations of erythropoietin (Epo), the primary hormone responsible for erythrocyte production. In animals, milk-borne Epo stimulates erythropoiesis. Epo receptors have been found in nonerythropoietic tissues including gastrointestinal tract. We hypothesized that milk-borne Epo is distributed to local gastrointestinal tissues, absorbed intact, and then distributed peripherally via the systemic circulation. Rat milk protected recombinant human Epo (rhEpo) from degradation in the suckling rat gastrointestinal tract. Simulated digestion of (125)I-rhEpo in suckling rat gastrointestinal juices was performed. When measured by acid precipitation and immunoassay, rat milk protected rhEpo from gastrointestinal juices better than saline (p < 0.0001). The fate of enterally administered milk-borne (125)I-rhEpo was examined in 10-d-old rats. RhEpo fed in rat milk was better protected from in vivo proteolytic degradation than rhEpo in saline (p < 0.05). After enteral (125)I-rhEpo dosing, radiolabeled protein from gastric tissue comigrated on SDS-PAGE with intact rhEpo at 36.5 kD. To determine the local and systemic distribution of physiologic intakes of rhEpo, suckling rats were fed (125)I-rhEpo in rat milk, and tissues were harvested 1, 2, and 4 h later. Intact (125)I-rhEpo was found in gastric and small intestinal walls and lumens. Five percent of total administered dose was found intact in the plasma, whereas another 8 to 10% of total administered dose was localized to bone marrow, percentages comparable to those seen after parenteral administration. Radiolabel was also localized to liver and peripheral solid tissues. These patterns of localization and degradation of rhEpo after acute administration support both systemic absorption and gastrointestinal cellular processing.

Artificial formula induces precocious maturation of the small intestine of artificially reared suckling rats

BACKGROUND

The artificially reared rat model was used successfully to study the effect of nutrition during the early postnatal period on growth and development of the neonate. Overgrowth and morphologic changes of the gastrointestinal tract are known consequences of artificial rearing. The major goal of our study was to elucidate whether artificial rearing-enhanced gut development is caused by artificial diet or by gastrostomy and the artificial rearing technique itself.

METHODS

Suckling rats at day 8 of age underwent intragastric cannulation and were machine fed either a cow's milk-based artificial rat's milk substitute or pooled rat's milk for 4 days. Dam-fed littermates served as a control.

RESULTS

Body growth did not differ in the three experimental groups. In rats receiving rat's milk substitute, small intestinal wet weight was approximately 60% greater than in rats fed rat's milk or control rats. Additionally, the entire small intestine was approximately 20% longer in the rat's milk substitute group. Morphologically, rat's milk substitute-fed pups demonstrated significantly greater intestinal villus length and crypt depth compared with rat's milk-fed or control rats. Jejunum and midjejunum of the rat's milk and control groups did not differ in these parameters. Intestinal sucrase activity of rat's milk substitute-fed rats was significantly elevated compared with rat's milk-fed rats or control animals.

CONCLUSIONS

These results indicate that cow's milk-based formula, not gastrostomy or artificial feeding technique, is a principal cause of the small intestine overgrowth and precocious maturation of some intestinal functions observed in artificially reared sucklings.

Milk-borne epidermal growth factor modulates intestinal transforming growth factor-alpha levels in neonatal rats

Epidermal growth factor (EGF) is present in milk from various mammalian species, but its physiologic function in neonatal development remains unclear. Transforming growth factor-alpha (TGF-alpha) is a peptide structurally related to EGF, and its presence is detected in the developing small intestine of rats. The purpose of the present study was to examine the effect of milk-borne EGF on endogenous production of EGF and TGF-alpha in the small intestine of suckling rats. Neonatal rats were fed via gastrostomy either growth factor-free rat milk substitute (RMS) or RMS supplemented with EGF (100 ng/mL of RMS) from 8 to 12 d of age. Artificially reared rats were then compared with their dam-fed littermates. Animals fed the EGF-deficient diet RMS had markedly increased EGF and TGF-alpha mRNA levels in duodenum and ileum compared with dam-fed controls and significantly elevated total intestinal content of TGF-alpha peptide. Intestinal EGF content and EGF serum levels were significantly decreased in the RMS group compared with controls. The addition of EGF to the RMS diet normalized TGF-alpha mRNA levels in the duodenum and ileum, EGF mRNA levels in the ileum, and total intestinal TGF-alpha content and EGF serum levels to the levels measured in dam-fed littermates. Motility studies showed that enteral administration of EGF did not affect stomach emptying and intestinal transit. These studies indicate that exogenous milk-borne EGF modulates endogenous production of TGF-alpha in developing small intestine. It is likely that neither TGF-alpha nor EGF are solely responsible for small intestinal overgrowth of artificially reared neonatal rats.

Is allergy increasing?--early life influences

Data from epidemiological studies conducted in several countries worldwide have revealed that the prevalences of allergic conditions, including allergic rhinitis, asthma and eczema, have increased from the 1940s/50s to the 1990s. These allergic conditions involve specific IgE-mediated responses, and a few studies have demonstrated that IgE levels have increased in some communities over time in a manner similar to the incidences of allergic conditions. The predisposition for atopy appears to be determined in early life, and evidence indicates that events occurring in utero and in infancy can influence the future development of atopy. The intrauterine environment favours TH2 cell development and IgE production and could predispose to atopy. It can be hypothesized that dietary or other factors favouring TH2 proliferation might contribute to the development of atopic disease. Conversely, early infection has been found to have a negative association with the development of atopy, perhaps through promotion of a TH response; the reduction in infection in the very young as a consequence of modern healthcare may have contributed to the increase in atopic disease. Thus, it is a plausible hypothesis that changes in the conditions of the intrauterine environment and/or in infancy (for example, in nutrition and in rates of infection) may explain the observed increases in atopy and allergic conditions.

Chemical and epidemiological aspects of modified butter oil fractions

Butter lipids are an important traditional source of dietary energy intake in the form of fat. Butter lost a sizable portion of its market share due to controversies associated with its cholesterol content and high percentage of long-chain saturated fatty acids. Accordingly, the use of vegetable oils and their chemically manipulated counterparts such as those produced by partial hydrogenation or interestrification increased proportionally. However, beginning in 1940, researchers developed several procedures such as temperature-controlled crystallization, refractionation of crystallized butter oil solids, and supercritical carbon dioxide extraction to improve the acceptance of butter oil. Others proposed preparation of synthetic substitutes such as sucrose polyesters to reduce intestinal absorption of fatty acids, thus reducing caloric intake with concomitant reduction in serum cholesterol. The present review provides a summary of the efforts of several attempts to improve the acceptability of butter together with the anticipated epidemiological consequences of long-term consumption of altered butter oil to mammalian health.