Total intestinal lactase and sucrase activities are reduced in aged rats

Identification of prospective aging drug targets via Mendelian randomization analysis

Aging represents a multifaceted process culminating in the deterioration of biological functions. Despite the introduction of numerous anti-aging strategies, their therapeutic outcomes have often been less than optimal. Consequently, discovering new targets to mitigate aging effects is of critical importance. We applied Mendelian randomization (MR) to identify potential pharmacological targets against aging, drawing upon summary statistics from both the Decode and FinnGen cohorts, with further validation in an additional cohort. To address potential reverse causality, bidirectional MR analysis with Steiger filtering was utilized. Additionally, Bayesian co-localization and phenotype scanning were implemented to investigate previous associations between genetic variants and traits. Summary-data-based Mendelian randomization (SMR) analysis was conducted to assess the impact of genetic variants on aging via their effects on protein expression. Additionally, mediation analysis was orchestrated to uncover potential intermediaries in these associations. Finally, we probed the systemic implications of drug-target protein expression across diverse indications by MR-PheWas analysis. Utilizing a Bonferroni-corrected threshold, our MR examination identified 10 protein-aging associations. Within this cohort of proteins, MST1, LCT, GMPR2, PSMB4, ECM1, EFEMP1, and ISLR2 appear to exacerbate aging risks, while MAX, B3GNT8, and USP8 may exert protective influences. None of these proteins displayed reverse causality except EFEMP1. Bayesian co-localization inferred shared variants between aging and proteins such as B3GNT8 (rs11670143), ECM1 (rs61819393), and others listed. Mediator analysis pinpointed 1,5-anhydroglucitol as a partial intermediary in the influence LCT exhibits on telomere length. Circulating proteins play a pivotal role in influencing the aging process, making them promising candidates for therapeutic intervention. The implications of these proteins in aging warrant further investigation in future clinical research.

Maternal acrylamide exposure changes intestinal epithelium, immunolocalization of leptin and ghrelin and their receptors, and gut barrier in weaned offspring

Acrylamide (ACR) is an amide formed as a byproduct in many heat-processed starchy-rich foods. In utero ACR exposure has been associated with restricted fetal growth, but its effects of postnatal functional development of small intestine is completely unknown. The current study investigated the time- and segment-dependent effects of prenatal ACR exposure on morphological and functional development of small intestine in weaned rat offspring. Four groups of pregnant female Wistar rats were exposed to ACR (3 mg/kg b.w./day) for 0, 5, 10 and 15 days during pregnancy. Basal intestinal morphology, immunolocalization of gut hormones responsible for food intake and proteins of intestinal barrier, activity of the intestinal brush border disaccharidases, apoptosis and proliferation in intestinal mucosa were analyzed in offspring at weaning (postnatal day 21). The results showed that in utero ACR exposure disturbs offspring gut structural and functional postnatal development in a time- and segment-depended manner and even a short prenatal exposure to ACR resulted in changes in intestinal morphology, immunolocalization of leptin and ghrelin and their receptors, barrier function, activity of gut enzymes and upregulation of apoptosis and proliferation. In conclusion, prenatal ACR exposure disturbed the proper postnatal development of small intestine.

Ultrasonication of Milk Decreases the Content of Exosomes and MicroRNAs in an Exosome-Defined Rodent Diet

BACKGROUND

Bovine milk exosomes (BMEs) harbor regulatory proteins, lipids, and microRNAs. Consumption of an exosome- and RNA-depleted (ERD) diet elicited phenotypes compared with controls fed an exosome- and RNA-sufficient (ERS) diet in mice. All other ingredients were identical in the diets. ERD and ERS diets were prepared by substituting ultrasonicated and nonultrasonicated milk, respectively, for casein in the AIN-93G formulation.

OBJECTIVES

The objective of this study was to assess the effect of ultrasonication of milk on exosome content and bioavailability, and cargo content.

METHODS

Bovine milk was ultrasonicated and exosomes were isolated by ultracentrifugation [ultrasonicated exosomes (USEs)]; controls were not ultrasonicated [nonultrasonicated exosomes (NSEs)]. Exosome count, size, and morphology were assessed using a nanoparticle tracker and electron microscopy. RNAs, lipids, and proteins were analyzed by RNA sequencing and MS. Intestinal transport, bioavailability, and distribution were measured by using fluorophore-labeled USEs and NSEs in Caco-2 cells, FHs 74 Int cells, and C57BL/6J mice (n = 3; age: 6-8 wk).

RESULTS

The exosome count was 76% ± 22% lower in USEs than in NSEs (P < 0.05). Ultrasonication caused a degradation of ≤100% of microRNAs. USEs and NSEs contained 145 and 332 unique lipid signatures, respectively (P < 0.05). We detected a total of 525 and 484 proteins in USEs and NSEs, respectively. The uptake of USEs decreased by 46% ± 30% and 40% ± 27% compared with NSEs in Caco-2 and FHs 74 Int cells, respectively (P < 0.05). The hepatic accumulation of USEs was 48% ± 28% lower than the accumulation of NSEs in mice (P < 0.05).

CONCLUSIONS

Ultrasonication of milk depletes bioavailable BMEs in studies of Caco-2 cells, FHs 74 Int cells, and C57BL/6J mice and causes a near-complete degradation of microRNA cargos.

The pleiotropic effects of prebiotic galacto-oligosaccharides on the aging gut

BACKGROUND

Prebiotic galacto-oligosaccharides (GOS) have an extensively demonstrated beneficial impact on intestinal health. In this study, we determined the impact of GOS diets on hallmarks of gut aging: microbiome dysbiosis, inflammation, and intestinal barrier defects ("leaky gut"). We also evaluated if short-term GOS feeding influenced how the aging gut responded to antibiotic challenges in a mouse model of Clostridioides difficile infection. Finally, we assessed if colonic organoids could reproduce the GOS responder-non-responder phenotypes observed in vivo.

RESULTS

Old animals had a distinct microbiome characterized by increased ratios of non-saccharolytic versus saccharolytic bacteria and, correspondingly, a lower abundance of β-galactosidases compared to young animals. GOS reduced the overall diversity, increased the abundance of specific saccharolytic bacteria (species of Bacteroides and Lactobacillus), increased the abundance of β-galactosidases in young and old animals, and increased the non-saccharolytic organisms; however, a robust, homogeneous bifidogenic effect was not observed. GOS reduced age-associated increased intestinal permeability and increased MUC2 expression and mucus thickness in old mice. Clyndamicin reduced the abundance Bifidobacterium while increasing Akkermansia, Clostridium, Coprococcus, Bacillus, Bacteroides, and Ruminococcus in old mice. The antibiotics were more impactful than GOS on modulating serum markers of inflammation. Higher serum levels of IL-17 and IL-6 were observed in control and GOS diets in the antibiotic groups, and within those groups, levels of IL-6 were higher in the GOS groups, regardless of age, and higher in the old compared to young animals in the control diet groups. RTqPCR revealed significantly increased gene expression of TNFα in distal colon tissue of old mice, which was decreased by the GOS diet. Colon transcriptomics analysis of mice fed GOS showed increased expression of genes involved in small-molecule metabolic processes and specifically the respirasome in old animals, which could indicate an increased oxidative metabolism and energetic efficiency. In young mice, GOS induced the expression of binding-related genes. The galectin gene Lgals1, a β-galactosyl-binding lectin that bridges molecules by their sugar moieties and is an important modulator of the immune response, and the PI3K-Akt and ECM-receptor interaction pathways were also induced in young mice. Stools from mice exhibiting variable bifidogenic response to GOS injected into colon organoids in the presence of prebiotics reproduced the response and non-response phenotypes observed in vivo suggesting that the composition and functionality of the microbiota are the main contributors to the phenotype.

CONCLUSIONS

Dietary GOS modulated homeostasis of the aging gut by promoting changes in microbiome composition and host gene expression, which was translated into decreased intestinal permeability and increased mucus production. Age was a determining factor on how prebiotics impacted the microbiome and expression of intestinal epithelial cells, especially apparent from the induction of galectin-1 in young but not old mice. Video abstract.

Transcriptional heterogeneity in the lactase gene within cell-type is linked to the epigenome

Transcriptional variation in histologically- and genetically- identical cells is a widespread phenomenon in tissues, yet the processes conferring this heterogeneity are not well understood. To identify contributing factors, we analyzed epigenetic profiles associated with the in vivo transcriptional gradient of the mouse lactase gene (Lct), which occurs in enterocytes along the proximal-to-distal axis of the small intestine. We found that epigenetic signatures at enhancer and promoter elements aligns with transcriptional variation of Lct in enterocytes. Age and phenotype-specific environmental cues (lactose exposure after weaning) induced changes to epigenetic modifications and CTCF binding at select regulatory elements, which corresponded to the alterations in the intestinal Lct mRNA gradient. Thus, epigenetic modifications in combination with CTCF binding at regulatory elements account for the transcriptional gradient in Lct in cells of the same type. Epigenetic divergence within enterocytes may contribute to the functional specialization of intestinal subregions.

Microbial shifts in the aging mouse gut

BACKGROUND

The changes that occur in the microbiome of aging individuals are unclear, especially in light of the imperfect correlation of frailty with age. Studies in older human subjects have reported subtle effects, but these results may be confounded by other variables that often change with age such as diet and place of residence. To test these associations in a more controlled model system, we examined the relationship between age, frailty, and the gut microbiome of female C57BL/6 J mice.

RESULTS

The frailty index, which is based on the evaluation of 31 clinical signs of deterioration in mice, showed a near-perfect correlation with age. We observed a statistically significant relationship between age and the taxonomic composition of the corresponding microbiome. Consistent with previous human studies, the Rikenellaceae family, which includes the Alistipes genus, was the most significantly overrepresented taxon within middle-aged and older mice. The functional profile of the mouse gut microbiome also varied with host age and frailty. Bacterial-encoded functions that were underrepresented in older mice included cobalamin (B12) and biotin (B7) biosynthesis, and bacterial SOS genes associated with DNA repair. Conversely, creatine degradation, associated with muscle wasting, was overrepresented within the gut microbiomes of the older mice, as were bacterial-encoded β-glucuronidases, which can influence drug-induced epithelial cell toxicity. Older mice also showed an overabundance of monosaccharide utilization genes relative to di-, oligo-, and polysaccharide utilization genes, which may have a substantial impact on gut homeostasis.

CONCLUSION

We have identified taxonomic and functional patterns that correlate with age and frailty in the mouse microbiome. Differences in functions related to host nutrition and drug pharmacology vary in an age-dependent manner, suggesting that the availability and timing of essential functions may differ significantly with age and frailty. Future work with larger cohorts of mice will aim to separate the effects of age and frailty, and other factors.

Aging of the mammalian gastrointestinal tract: a complex organ system

Gastrointestinal disorders are a major cause of morbidity in the elderly population. The gastrointestinal tract is the most complex organ system; its diverse cells perform a range of functions essential to life, not only secretion, digestion, absorption and excretion, but also, very importantly, defence. The gastrointestinal tract acts not only as a barrier to harmful materials and pathogens but also contains the vast number of beneficial bacterial populations that make up the microbiota. Communication between the cells of the gastrointestinal tract and the central nervous and endocrine systems modifies behaviour; the organisms of the microbiota also contribute to this brain-gut-enteric microbiota axis. Age-related physiological changes in the gut are not only common, but also variable, and likely to be influenced by external factors as well as intrinsic aging of the cells involved. The cellular and molecular changes exhibited by the aging gut cells also vary. Aging intestinal smooth muscle cells exhibit a number of changes in the signalling pathways that regulate contraction. There is some evidence for age-associated degeneration of neurons and glia of the enteric nervous system, although enteric neuronal losses are likely not to be nearly as extensive as previously believed. Aging enteric neurons have been shown to exhibit a senescence-associated phenotype. Epithelial stem cells exhibit increased mitochondrial mutation in aging that affects their progeny in the mucosal epithelium. Changes to the microbiota and intestinal immune system during aging are likely to contribute to wider aging of the organism and are increasingly important areas of analysis. How changes of the different cell types of the gut during aging affect the numerous cellular interactions that are essential for normal gut functions will be important areas for future aging research.

Role of intestinal hydrolase in the absorption of prenylated flavonoids present in Yinyanghuo

PURPOSE

Yinyanghuo (Herba Epimdii) is a traditional Chinese herb containing prenylated flavonoids as its active constituents. The aim of this study was to examine the significance of the intestinal hydrolysis of prenylated flavonoids by lactase phlorizin hydrolase (LPH), an enzyme at the brush border membrane of intestinal cells.

METHODS

A four-site perfused rat intestinal model was used. The concentration of the flavonoids of interest and their metabolites in different intestinal segements were analyzed by HPLC, and the apparent permeabilities were calculated. A lactase phlorizin hydrolase inhibitor (gluconolactone) was employed to investigate the mechanism of the intestinal absorption, and the metabolites of the four flavonoids were identified using LC/MS/MS.

RESULTS

Diglycosides (icariin) or triglycosides (epimedin A, epimedin B, and epimedin C) were hydrolyzed rapidly in duodenum and jejunum producing one or two metabolites, while a monoglycoside (baohuoside I) was absorbed directly. When co-perfused with glucono-lactone, both the hydrolysis of diglycosides and triglycosides were significantly inhibited, with inhibition rates for icariin (62%, 50%, 40%, 46%), epimedin A, (55%, 26%, 21%, 14%); epimedin B (42%, 40%, 74%, 22%), and epimedin C (42%, 40%, 52%, 35%) in duodenum, jejunum, ileum, and colon, respectively. Also the metabolites of icariin, epimedin A, epimedin B, and epimedin C were identified as baohuoside I (one of two), sagittatoside A, sagittatoside B, and 2"-O-rhamnosylicariside II, respectively.

CONCLUSIONS

The results showed that lactase phlorizin hydrolase was a major determinant of the intestinal absorption of prenylated flavonoids present in Yinyanghuo.

Ingestion of potato starch containing esterified phosphorus increases alkaline phosphatase activity in the small intestine in rats

Alkaline phosphatase (ALP) hydrolyzes a variety of monophosphate esters and plays an important role in phosphorus (P) metabolism. Several nutrients in food have been reported to affect intestinal ALP activity in animal models. Previous reports indicated that high levels of P or phosphate in diets decreased intestinal ALP activity in rats. Because potato starch contains considerable amounts of esterified P, unlike other starch-derived plants, we hypothesized that the feeding of potato starch would decrease ALP activity in the intestinal tract. Male Sprague-Dawley rats (7 weeks old) were fed 3 different types of diet containing 60% corn starch or 1 of 2 types of potato starch with different esterified P content for 1 or 5 weeks. Body weight and food intake of each rat were measured every day throughout the experimental periods. At the end of the feeding periods, the small intestine was removed to determine ALP activity in the mucosal tissues. Significant differences were observed in ALP activity in the small intestine between the 2 feeding periods, among the 4 segments of the small intestine, and among the 3 diet groups. Significant positive linear correlations between the amount of P derived from the starch and mucosal ALP activity were obtained in the jejunum and jejunoileum in rats after feeding for 5 weeks. We concluded, contrary to our hypotheses, that the ingestion of potato starch adaptively increases ALP activity in the upper part of the small intestine of growing rats in an esterified P content-dependent manner.

Lactose intolerance and African Americans: implications for the consumption of appropriate intake levels of key nutrients

Lactose intolerance is a complex condition that is complicated by cultural beliefs and perceptions about the consumption of dairy products. These attitudes about dairy may contribute to inadequate intake of key nutrients that may impact conditions that contribute to health disparities in African Americans. While a complex health problem, lactose intolerance is easy to treat. However, no treatment can improve the body's ability to produce lactase. Yet, symptoms can be controlled through dietary strategies. This position paper emphasizes the importance of using patient and provider-level strategies in order to reduce the risks to the health of African Americans that may accrue as a result of dairy nutrient deficiency. Evaluation and assessment of interventions tested is critical so that evidence-based approaches to addressing dairy nutrient deficiency and lactose Intolerance can be created. Lastly, it is essential for physicians to communicate key messages to their patients. Since dairy nutrients address important health concerns, the amelioration of lactose intolerance is an investment in health. Lactose intolerance is common, is easy to treat, and can be managed. It is possible to consume dairy even in the face of a history of maldigestion or lactose intolerant issues. Gradually increasing lactose in the diet--drinking small milk portions with food, eating yogurt, and consuming cheese--are effective strategies for managing lactose intolerance and meeting optimal dairy needs.

Genetic test for lactase non-persistence and hydrogen breath test: is genotype better than phenotype to diagnose lactose malabsorption?

BACKGROUND

Adult-type hypolactasia is a widespread condition throughout the world, causing lactose malabsorption. The lactose breath test is a simple tool for diagnosis but the need for prolonged monitoring of hydrogen excretion has led to a genetic test proposal. The aim of this study was to compare the genetic test with the lactose breath test in order to give some insights into the clinical value of genetic testing.

METHODS

Thirty-two consecutive functional patients underwent lactose breath test and lactase genetic polymorphism analysis (C/T 13910 and G/A 22018). Intolerance symptoms after lactose load were also monitored.

RESULTS

All patients with positive lactose breath test showed homozygosis for both polymorphisms. Among the nine patients with a negative breath test result, six showed heterozygosis while three showed homozygosis. Intolerance symptoms were present in 16 homozygotic patients but also in one heterozygotic patient. The k value for the agreement between the genetic test and the lactose breath test was 0.74.

CONCLUSION

A positive genetic test for lactase non-persistence indicates whether lactase activity decline may represent a clinical problem for the patient, but does not give information on actual patient symptoms. On the contrary, this information is already available by combining the lactose breath test with intolerance symptom evaluation. Lactose absorption phenotype may be not yet evident until young adult age.

Gastrointestinal pathology in a mouse model of mucopolysaccharidosis type IIIA

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by a deficiency in sulphamidase (NS), a lysosomal enzyme required for the degradation of heparan sulphate glycosaminoglycans (gags). The MPS IIIA mouse is a naturally occurring model that accurately reflects the human pathology and disease course. It displays primarily central nervous system pathology accompanied by widespread accumulation of gag in somatic tissues. MPS IIIA mice exhibit greater bodyweight gain than normal littermates and attain a higher mature bodyweight. In this study, gastrointestinal morphology and function was characterised in the IIIA mouse. Stomach and duodenum weight increased in MPS IIIA mice and duodenum length also increased. An increased submucosal thickness was observed in MPS IIIA intestine compared to normal mice and lysosomal storage of gag was observed in this region. Storage was also observed in the lamina propria of the villus tip. All other morphometric measurements including villus height and crypt depth fell within the normal range. The gastric emptying half-life of solid and liquid meals decreased with age in normal mice whereas the T(1/2) of solid meals did not alter with age in MPS IIA mice such that they were elevated above normal by 38 weeks of age. Sucrase activity was higher than normal in MPS IIIA at all ages tested. These abnormalities in GI structure and function observed in MPS IIIA may contribute to weight gain in this disorder.

Yoghurts containing probiotics reduce disruption of the small intestinal barrier in methotrexate-treated rats

Small intestinal permeability was employed to assess the efficacy of commercially available yoghurts containing probiotics in a rat model of methotrexate (MTX)-induced mucositis. Male Sprague-Dawley rats were allocated to four groups (n = 8): MTX + water, MTX + cow's milk yoghurt (CY; fermented with Lactobacillus johnsonii), MTX + sheep's milk yoghurt (SY; containing Lactobacillus bulgaricus and Streptococcus thermophilus), and saline. Treatment gavage occurred twice daily for 7 days pre-MTX and 5 days post-MTX. Intestinal permeability was assessed on days -7, -1, 2, and 5 of the trial. Intestinal sections were collected at sacrifice for histological and biochemical analyses. Histology revealed that rats receiving CY and SY did not have a significantly damaged duodenum compared to controls. However, an improved small intestinal barrier function was evident, determined by a decreased lactulose/mannitol ratio. Probiotics containing SY and CY may be useful in preventing disruption to intestinal barrier function in MTX-induced mucositis.

Lactose malabsorption in the elderly: role of small intestinal bacterial overgrowth

OBJECTIVE

The prevalence of lactose malabsorption (LM) is increased in the elderly, although the mechanisms responsible are still a matter of speculation. The objective of this study was to investigate the possible roles of reduced functional small intestinal absorptive area, lactase deficiency and small intestinal bacterial overgrowth (SIBO).

MATERIAL AND METHODS

Twenty Caucasian (Anglo-Celtic), asymptomatic, well-nourished, elderly volunteers (median age 79 years, range 70-94 years) with no clinically apparent predisposition to SIBO underwent a 50 g lactose breath hydrogen test (LBHT) and mannitol absorption test, the latter as an index of functional small intestinal absorptive area. Those with LM additionally underwent bacteriological assessment of small intestinal secretions and mucosal biopsy, to assess the contribution of SIBO and lactase deficiency, respectively, to the pathogenesis of LM in individual cases. The prevalence of SIBO was also determined in elderly subjects without LM. Twenty asymptomatic younger subjects (median age 29 years, age range 18-35 years) served as controls. All subjects were "hydrogen producers" in response to lactulose.

RESULTS

LM was evident in 10/20 (50%) elderly subjects and 1/20 (5%) younger subjects (p=0.003). Mannitol absorption did not differ significantly in elderly and younger subjects or in elderly subjects with and without LM. SIBO was documented in 9/10 (90%) elderly subjects with LM; eradication was associated with resolution of LM. Lactase deficiency was evident in only one elderly subject with LM. SIBO was evident in 2/10 (20%) elderly subjects without LM (p=0.005 compared to those with LM). Lactulose breath hydrogen test identified only 2/11 (18%) elderly subjects with SIBO.

CONCLUSIONS

Increased prevalence of LM in the elderly is mostly due to clinically non-apparent SIBO, rather than mucosal factors. The lactulose breath hydrogen test cannot be relied upon to identify elderly subjects with SIBO, even in those without an anatomical predisposition.

Aging and the intestine

Over the lifetime of the animal, there are many changes in the function of the body’s organ systems. In the gastrointestinal tract there is a general modest decline in the function of the esophagus, stomach, colon, pancreas and liver. In the small intestine, there may be subtle alterations in the intestinal morphology, as well as a decline in the uptake of fatty acids and sugars. The malabsorption may be partially reversed by aging glucagon-like peptide 2 (GLP2) or dexamethasone. Modifications in the type of lipids in the diet will influence the intestinal absorption of nutrients: for example, in mature rats a diet enriched with saturated as compared with polysaturated fatty acids will enhance lipid and sugar uptake, whereas in older animals the opposite effect is observed. Thus, the results of studies of the intestinal adaptation performed in mature rats does not necessarily apply in older animals. The age-associated malabsorption of nutrients that occurs with aging may be one of the several factors which contribute to the malnutrition that occurs with aging.

In vitro translation of RNA to lactase during postnatal development of rat intestine

mRNA levels encoding lactase were detected by Northern blot analysis using two different probes in developing rat intestine. Probe I and probe II corresponding to second half of prolactase gene showed a 6.8 kb mRNA transcript in 7, 14, 21 and 30 day old rat intestine. There was no change in quantity of lactase mRNA detected using probe II, but hybridization with probe I showed a progressive decrease in mRNA transcript encoding lactase with age. At day 7 and 14 of postnatal development, the lactase mRNA was quite high, but it reduced upon weaning. The in vitro translation products of RNA detected by Western blot analysis using brush border lactase antibodies showed several isoforms of lactase antigen with molecular weight ranging from 100-220 kDa. Analysed at days 7 and 30 of postnatal development, lactase isoforms of molecular weight 130 kDa and 220 kDa were similar to those found in purified brush border membranes. The translation of RNA to 220 kDa lactase protein was high in 7 and 14 day old pups, but it was markedly reduced in 30 day old animals. These findings support the contention that translation of mRNA to lactase is impaired in weaned animals, which may also be responsible for the maturational decline in lactase activity in adult rat intestine.

Comparison of triglycerides and phospholipids as supplemental sources of dietary long-chain polyunsaturated fatty acids in piglets

Addition of arachidonic acid (AA) and docosahexaenoic acid (DHA) to infant formula promotes visual and neural development. This study was designed to determine whether the source of dietary long-chain polyunsaturated fatty acids (LCPUFA) affected overall animal health and safety. Piglets consumed ad libitum from 1 to 16 d of age a skim milk-based formula with different fat sources added to provide 50% of the metabolizable energy. Treatment groups were as follows: control (CNTL; no added LCPUFA), egg phospholipid (PL), algal/fungal triglyceride (TG) oils, TG plus PL (soy lecithin source) added to match phospholipid treatment (TG + PL) and essential fatty acid deficient (EFAD). Formulas with LCPUFA provided 0.6 and 0.3 g/100 g total fatty acids as AA and DHA, respectively. CNTL piglets had 40% longer ileal villi than PL piglets (P < 0.03), but the TG group was not different from the CNTL group. Gross liver histology did not differ among any of the formula-fed groups (P > 0.1). Apparent dry matter digestibility was 10% greater in CNTL, TG and TG + PL groups compared with PL piglets (P < 0.002). No differences in alanine aminotransferase were detected among treatments, but aspartate aminotransferase was elevated (P < 0.03) in PL piglets compared with TG + PL piglets. Total plasma AA concentration was greater in the TG group compared with CNTL piglets (P < 0.05). Total plasma DHA concentrations were greater in TG piglets compared with PL (P < 0.06) or CNTL (P < 0.02) piglets. These data demonstrate that the algal/fungal TG sources of DHA and AA may be a more appropriate supplement for infant formulas than the egg PL source based on piglet plasma fatty acid profiles and apparent dry matter digestibilities.

Intestinal brush border membrane catalyzes hydrolysis of pyridoxine-5'-beta-D-glucoside and exhibits parallel developmental changes of hydrolytic activities toward pyridoxine-5'-beta-D-glucoside and lactose in rats

Pyridoxine-5'-beta-D-glucoside (PNG) is a major form of vitamin B-6 in plant foods that exhibits partial bioavailability as vitamin B-6 in humans. We previously identified an intestinal mucosal cytosolic PNG hydrolase that catalyzes the partial hydrolysis of PNG absorbed without prior deglycosylation. Recent observations that the brush border membrane also catalyzes PNG hydrolysis led to the hypothesis that PNG hydrolysis may be another function of the beta-glucosidase lactase-phlorizin hydrolase (LPH) and, thus, brush border PNG hydrolysis would undergo a developmental decline similar to that of lactose hydrolysis. In this study, the relationships among hydrolytic activities in small intestinal cytosolic and brush border fractions in rats (n = 9 per group) of various ages (1-2 d and 2, 4, 8, 12 and 24 wk) were examined. In vitro specific activities toward PNG and lactose were greater in brush border than cytosol, and these were greater in newborn rats than in all other age groups (P < 0.01). Brush border activities toward PNG and lactose and were closely correlated (r = 0.84; P < 0.0001). These findings suggest that the hydrolysis of PNG is catalyzed at least partially at the brush border and that the bioavailability of PNG may be influenced by the residual LPH activity in children and adults.

Small bowel disease in the elderly: diarrhoea and malabsorption

Diarrhoea and malabsorption are common problems in elderly persons. Worldwide, diarrhoea is the second leading cause of mortality. In the developed world, 85% of its mortality affects the elderly. The diagnostic work up for diarrhoea and malabsorption is more complex for the elderly than for the young patient. If diarrhoea persists for more than 24 h, oral rehydration solutions or intravenous fluids must be administered promptly in order to prevent hypotension and organ failure in the often multi-morbid patient. Both the immunocompromised patient and the severely affected out-patient should have stool culture performed. Malabsorption usually presents with weight loss, osteoporosis, anaemia, skin and neurological symptoms. The careful diagnostic work-up must aim at the identification of treatable disorders such as coeliac disease, Crohn's disease and bacterial overgrowth. Often, a detailed drug history is of help in identifying a readily treatable cause.

Bacterial dissemination and metabolic changes in rats induced by endotoxemia following intestinal E. coli overgrowth are reduced by ornithine alpha-ketoglutarate administration

The efficacy of ornithine alpha-ketoglutarate (OKG) in preventing bacterial translocation and dissemination, metabolic disorders and changes in mucosal enzyme activities was assessed in a model of bacterial translocation in rats. Antibiotic decontamination was performed 4 d before intragastric inoculation with an Escherichia coli strain (10(10) bacteria/kg body). Two days later, the rats were given either a lipopolysaccharide (LPS) 0127:B8 or a saline injection and were deprived of food for 24 h. Enteral nutrition, [Osmolite, 880 kJ/(kg. d)] supplemented with either OKG (LPS + OKG) or glycine (Saline + Gly or LPS + Gly), was then given for 2 d. Urinary total nitrogen losses and 3-methylhistidine excretion were determined daily. On killing at d 3, bacterial translocation to the mesenteric lymph nodes (MLN) and dissemination to the spleen and liver were evaluated, jejunal mucosa enzyme activities were assayed and tissue free amino acids in muscles were measured. Endotoxin induced translocation from the gut lumen to the MLN in all groups, whereas dissemination occurred only in LPS-treated rats. OKG significantly reduced dissemination of the bacteria in the spleen. 3-Methylhistidine excretion was greater in the LPS + Gly group (+25%, P: < 0.05) than in either the LPS + OKG or Saline + Gly group. The group fed the OKG-enriched diet had higher muscular glutamine, ornithine and arginine concentrations than did the Gly-supplemented groups (P: < 0.05). Intestinal sucrase and aminopeptidase activities were higher in the LPS + OKG group than in the LPS + Gly group (-30%, P: < 0.05). OKG supplementation limits bacterial dissemination and metabolic changes after injury in rats and thus may be useful in the prevention of gut-derived sepsis in critically ill patients.

Influence of age on duodenal brush border membrane and specific activities of brush border membrane enzymes in Wistar rats

To examine age-related changes in the morphology of intestinal brush border membrane (BBM; microvilli) and specific activities of intestinal BBM enzymes including alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (gamma-GT), and disacchridase, four groups of Wistar rats were sacrificed at 2.5 wk, 5 wk, 5 mon and 23 mon. In an electron microscopic examination, morphologically a less dense BBM structure in the duodenum of rats aged 23 mon was observed than that of rats aged 5 mon. Specific activity of ALP in the duodenum from 5-mon-old rats was significantly higher than from rats aged 2.5 wk and 23 mon. The mucosal tissues from 5-wk-old rats had significantly higher specific activity of gamma-GT than did tissues from the other ages. In sucrase and maltase specific activities, 5-mon-old rats had higher activities of these enzymes than other age groups, especially 2.5-wk- and 23-mon-old rats. There was also a significant effect of site on intestinal BBM enzyme activities in post-weanling rats. Regional gradients of ALP and gamma-GT along the entire small intestine (duodenum > jejunum > ileum) were remarkable. Disaccharidase activities peaked in the jejunum and declined toward both the duodenum and ileum. Taken together the result obtained here suggested that 5-mon-old rats had the most elevated intestinal function. This result also strongly indicated that the structure of the intestinal BBM and development of intestinal BBM enzymes in Wistar rate were markedly influenced by age during the postnatal period.

Human adult-onset lactase decline: an update

Human adult-onset lactase decline is a biologic feature characteristic of the maturing intestine in the majority of the world's population. The digestion and absorption of lactose, the major carbohydrate in milk and also the main substrate for lactase, is often variable, a consequence of lactase levels, gastric emptying rate, and colonic salvage. Although commercially available "lactase" products alleviate symptoms in many lactose-intolerant people, a greater understanding of this variability in lactose tolerance could lead to interventions that reduce the rate of gastric emptying and/or increase the proliferation of lactose-metabolizing bacteria in the colon, leading to more efficient lactose utilization. Adult-onset lactase decline appears to be a risk factor for developing osteoporosis, owing to avoidance of dairy products or interference of undigested lactose with calcium absorption. Elderly with both adult-onset lactase decline and atrophic gastritis or those undergoing anti-ulcer treatment may have an increased risk of low calcium absorption owing to the lack of gastric acid that facilitates calcium uptake. Thus, lactose-intolerant elders should monitor their calcium nutrition status carefully.